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Benthic microbial fuel cells (BMFCs) are important energy-harvesting devices for underwater sensors and electronic devices. However, it is a challenging problem to ensure the robustness of BMFCs in harsh ocean environment. In particular, the anode buried in sediment is subject to burrowing organisms tunneling, which breaks the anaerobic condition, and the electrons generated by the anode will be consumed locally. This eliminates the difference in electric potential between the anode and the cathode. The system then becomes short-circuited and ceases to function. This is a serious problem in the underwater environment due to the likelihood of bioturbation. Using a multianode BMFC can effectively address this problem due to the distributed structure of multiple anodes. This, however, requires a new power management system (PMS) to automatically detect and remove the effect of impaired anodes. This paper presents a new PMS for multianode BMFCs. The proposed PMS automatically disconnects the impaired anodes from the rest of the system for bioturbation resilience and better efficiency. The proposed PMS is self-starting, i.e., no need of extra power sources other than the BMFC. The PMS has been tested through a prototype BFMC. Experimental results demonstrate the effectiveness of this design for multianode BMFCs. [ABSTRACT FROM AUTHOR]

Cascaded converters are generally used for medium-voltage (MV) grid-connected applications due to the limitation in the voltage rating of available silicon (Si) power devices. These converters find application in active power filters, STATCOM or as the active front end converters for solid state transformers at the distribution voltage levels. The high voltage wide bandgap semiconductor devices have enabled the grid connected operation of noncascaded converters. This results in high power density, less number of switching devices, and high efficiency for three-phase MV grid interface. This also results in control simplicity without the need for complex dc bus balancing algorithms otherwise needed for cascaded converters. However, such noncascaded, grid-connected converters introduce challenges in maintaining power quality at low currents. This paper investigates the harmonic performance and current distortion of the grid-connected, three-level neutral point clamped converter using 15 kV silicon carbide Insulated Gate Bipolar Transistor (IGBTs). A suitable control scheme for stable harmonic compensation is proposed. The challenges and control performance are explained through frequency domain analysis, simulations, and experimental validation on a developed prototype of the three-phase converter up to 4.16 kV, three-phase MV grid-connected operation. [ABSTRACT FROM AUTHOR]

The growing installation of distributed generation (DG) units in low-voltage distribution systems has popularized the concept of nonlinear load harmonic current compensation using multifunctional DG interfacing converters. It is analyzed in this paper that the compensation of local load harmonic current using a single DG interfacing converter may cause the amplification of supply voltage harmonics to sensitive loads, particularly when the main grid voltage is highly distorted. To address this limitation, unlike the operation of conventional unified power quality conditioners with series converter, a new simultaneous supply voltage and grid current harmonic compensation strategy is proposed using coordinated control of two shunt interfacing converters. Specifically, the first converter is responsible for local load supply voltage harmonic suppression. The second converter is used to mitigate the harmonic current produced by the interaction between the first interfacing converter and the local nonlinear load. To realize a simple control of parallel converters, a modified hybrid voltage and current controller is also developed in the paper. By using this proposed controller, the grid voltage phase-locked loop and the detection of the load current and the supply voltage harmonics are unnecessary for both interfacing converters. Thus, the computational load of interfacing converters can be significantly reduced. Simulated and experimental results are captured to validate the performance of the proposed topology and the control strategy. [ABSTRACT FROM AUTHOR]

This paper introduces a cascaded H-bridge multilevel converter (CHB-MC)-based StatCom system that is able to operate with extremely low dc capacitance values. The theoretical limit is calculated for the maximum capacitor voltage ripple, and hence minimum dc capacitance values that can be used in the converter. The proposed low-capacitance StatCom (LC-StatCom) is able to operate with large capacitor voltage ripples, which are very close to the calculated theoretical maximum voltage ripple. The maximum voltage stress on the semiconductors in the LC -StatCom is lower than in a conventional StatCom system. The variable cluster voltage magnitude in the LC-StatCom system drops well below the maximum grid voltage, which allows a fixed maximum voltage on the individual capacitors. It is demonstrated that the proposed LC-StatCom has an asymmetric V–I characteristic, which is especially suited for operation as a reactive power source within the capacitive region. A high-bandwidth control system is designed for the proposed StatCom to provide control of the capacitor voltages during highly dynamic transient events. The proposed LC-StatCom system is experimentally verified on a low-voltage seven-level CHB-MC prototype. The experimental results show successful operation of the system with ripples as high as 90% of the nominal dc voltage. The required energy storage for the LC-StatCom system shows significant reduction compared to a conventional StatCom design. [ABSTRACT FROM PUBLISHER]

A family of bidirectional switched-capacitor (SC) converters with high-gain ratio of any positive integer is proposed in this paper for distributed energy resources applications. As compared with other existing SC converters achieving a same conversion gain, the main advantages of the proposed converters are that they require a relatively lower number of switches and capacitors, have a relatively lower switch's and capacitor's stress, and that their associated driver circuits are simpler to realize. Importantly, with the achievable conversion ratio being flexible and that the input and output of the proposed converters are of common ground, the proposed converters are widely suitable for many applications. Moreover, as the proposed converters do not possess magnetic component or any component that can severely degrade the converters’ performance at high temperature, they are especially useful for high-temperature applications. Besides, the proposed converters are capable of delivering bidirectional power, which is a key requirement for emerging applications with battery storages. Different aspects of the proposed converters, including a simple auxiliary power supply circuit for the MOSFETs’ drivers, will be discussed in this paper. A nine-time SC converter prototype that operates with 20-V input voltage, 100-W output, and at 75 kHz, is constructed and tested. Experiment results show that the maximum efficiency achievable with this prototype is over 98% (without driver's loss) and the efficiency over the entire load range between 25 and 100 W is over 95.5% including the driver's loss. The output voltage ripple of the SC converter is less than 1%. When the SC converter is open-loop controlled, the load voltage regulation is relatively well kept at less than 5% between full load and no load conditions. [ABSTRACT FROM PUBLISHER]

In this paper, average modeling and analysis of a dual-supercapacitor bank, actively balanced by a bidirectional buck–boost converter, is presented. In such a system, natural balancing is achieved when the converter is operated in open loop with 50% duty cycle, eliminating the need for measuring the voltage of each storage device. Nevertheless, excessive currents arise even for slight voltage misbalance because of the highly underdamped nature of the system. In order to remedy this drawback, bidirectional pulse-by-pulse inductor current limitation is introduced, which is equivalent to adding a peak-current-mode-like control loop to the system. Since the duty cycle never exceeds 50%, compensation ramp is not required to maintain stability. On the other hand, while the uncontrolled system dynamics is linear, introducing the current limit mechanism turns the closed-loop dynamics into a nonlinear one, burdening the analysis task and thus calling for suitable average model to perform fast simulations for system analysis. Therefore, dynamical equations of the system are developed in order to derive the switching-cycle-averaged model and reveal the tradeoff between current limit level, balancing time and efficiency for the worst case of imbalance. Simulations and experiments support the presented findings. [ABSTRACT FROM PUBLISHER]

A novel voltage-doubling circuit with parallel-resonant dc–dc converter is proposed. The converter consists of full-bridge inverter, resonant tank, high-frequency high-voltage transformer, and voltage-doubling circuit. In the high-voltage applications, low-output voltage ripple has been given much attention. The output voltage step-up ratio is increased by two parts. One is a high-frequency high-voltage transformer and the other is a voltage-doubling circuit. The novel voltage-doubling circuit can not only reach a higher output voltage but also reduce output ripple to a lower level than the conventional one. Therefore, while maintaining the same output voltage, the transformer's turn ratio can be reduced compared with the conventional voltage-doubling circuit. The output power can be adjusted by the phase-shift control technique. In addition, combining this technique with the parallel resonant tank can make all the switches achieve zero voltage turn on (ZVS). The operating principles, steady-state analysis, and the parameter designs are discussed in this paper. Finally, a prototype circuit with 400-V input voltage, 40-kV output voltage, and 300-W output power is developed in the laboratory to verify the performance of the proposed converter. [ABSTRACT FROM PUBLISHER]

Fast switching and large capacity in modern power converters generate large-voltage peak during the diode's reverse-recovery process. Being different from the steady-state reverse recovery, short-time freewheeling of diodes at higher speed switching may generate higher reverse-recovery voltage peak. In this paper, the reverse recovery of p-i-n diodes under short-time freewheeling in a typical power converter circuit is studied with considerations of different initial current of the related IGBTs. By establishing the boundary connections between the turn-on and the turn-off transient stages, a mixed model of the diode's reverse-recovery voltage peak under short-time freewheeling is finally obtained, which combines the physics-based model with the behavior model. Model parameters were then extracted through measurements and circuit extraction methods to relax the complexity. Experiments were performed in a half-bridge inverter unit with 1200-V/50-A IGBTs and p-i-n freewheeling diodes at different short freewheeling time. The accuracy of the proposed model is verified by comparing the simulated waveforms with the measured data. The influence of different initial current on the voltage peak at short-time freewheeling was also evaluated using the proposed model. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-space vector control scheme for the open-end winding permanent magnet synchronous motor (OEW-PMSM) drive fed by the dual inverter with a single dc supply. Potential zero-sequence current in the open-end winding drive system has to be considered since it causes circulating current in the winding and leads to high current stress of power semiconductor devices and high losses. Zero-sequence current in open-end winding ac motor drives is usually caused by the zero-sequence voltage, and therefore switching combinations which do not produce zero-sequence voltage are used to synthesize the reference voltage in existing methods. But even so, the zero-sequence voltage can also be produced by the dead time of the inverter. In order to suppress zero-sequence current in the OEW-PMSM drive, a dual-space vector control scheme is proposed and a novel dual-inverter space vector pulse width modulation (PWM) with the zero-sequence voltage reference is employed to regulate system zero-sequence voltage in this paper. Compared with existing dual inverter PWM strategies, the novel algorithm build a regulation mechanism for the zero-sequence voltage. The proposed method is compared with the conventional vector control by simulations and experiments, and the results shown that the proposed scheme can suppress zero-sequence current effectively. [ABSTRACT FROM AUTHOR]

Typical algorithms of multidimensional space-vector pulsewidth modulation (SVPWM) divide (n –1) dimensional space into (n–1)/2 subplanes with decoupling matrix or symmetrical component approach. However, the determination of effective sectors and appropriate space voltage vectors takes a heavy computing burden. Taking the five-phase inverter as example, the relationship between the operation time of branch switches and the dwell times of active space vectors in the SVPWM method is analyzed in this paper. Then, the branch space voltage vector (BSVV) corresponding to the individual active branch voltage is defined and the synthesis of other active space voltage vectors using BSVVs is given. Furthermore, only the BSVVs are chosen as the base vectors to synthesize the reference voltage vector, and a novel SVPWM algorithm is present. The operation time of branch switch is deduced, and the equivalence of the normalized load-phase voltages and operation times of branch switches is emphasized and used to analyze the simulation results. The zero-sequence voltage vector is also included in the algorithm as a parameter and its effects on the dwell time of the BSVVs, the modulation index and the common-mode voltage are explicated. Finally, the extension to an n-phase system is discussed. The algorithm eliminates the selection of sectors and proper active space vectors, and can effectively control the dwell time of switches of multiphase inverter. Experimental results proved the feasibility and effectiveness of the algorithm. [ABSTRACT FROM AUTHOR]

In this paper, the Z-source converter is introduced to power factor correction (PFC) applications. The concept is demonstrated through a wireless power transfer (WPT) system for electric vehicle battery charging, namely Z-source resonant converter (ZSRC). Due to the Z-source network (ZSN), the ZSRC inherently performs PFC and regulate the system output voltage simultaneously, without adding extra semiconductor devices and control circuitry to the conventional WPT system such as conventional PFC converters do. In other words, the ZSN can be categorized as a family of the single-stage PFC converters. In addition, the ZSN is suitable for high-power applications since it is immune to shoot-through states, which increases reliability and adds a boost feature to the system. The ZSRC-based WPT system operating principle is described and analyzed in this paper. Simulations and experimental results based on a 1-kW prototype with 20-cm air gap between the system primary and secondary sides are presented to validate the analysis and demonstrate the effectiveness of the ZSN in the PFC of the WPT system. [ABSTRACT FROM PUBLISHER]

Through coupling the impedance network between the grid and the conventional indirect matrix converter (IMC), the LC-filter-integrated quasi-Z-source (qZS) IMC overcomes the 0.866 voltage gain limitation of the conventional IMC and also avoids the input filter that is required to mitigate current harmonics of the conventional qZS matrix converters. This paper further investigates the voltage boosting and LC filtering function of the LC-filter-integrated qZS IMC. The voltage gain, the filtering function, and qZS network parameters design are presented using a small-signal model and circuit analysis. Simulation and experimental results validate the built model, the voltage gain analysis, and the parameters design of this type of qZS IMC. The input current of the LC-filter-integrated qZS network is compared to the conventional Z-source and qZS IMCs to investigate the integrated LC filtering capability. The experimental results verify that the LC-filter-integrated qZS network provides the necessary filtering function. Thus, the traditional input filter can be eliminated, which reduces the cost, power loss, volume, and weight for the overall system, when compared with the other conventional topologies that require the input filter, even those with impedance-source networks. [ABSTRACT FROM PUBLISHER]

Among the main control targets in a modular multilevel converter (MMC) is the control of the circulating currents within the phase legs of the topology. This paper presents a controller for the circulating current of the MMC that utilizes the available redundancies of the multilevel waveform in $2N+1$ modulated MMCs in order to regulate the circulating current to its reference. The main advantages of the approach are the elimination of control loops that generate the reference voltages for the control of the circulating current, simple implementation and very fast dynamic performance. The controller is implemented at the modulation stage and its operation is independent of the circulating current reference. An extension of the controller to track large deviations in the circulating current is also demonstrated. The simplicity and effectiveness of the proposed controller is illustrated through detailed simulations and experimental results from a single-phase laboratory prototype. [ABSTRACT FROM PUBLISHER]

Various magnetically coupled impedance source (MCIS) networks have been proposed in the literature for increasing voltage gain and modulation index simultaneously while reducing the number of passive components used in the converter. However, applications of such networks have been limited by their discontinuous currents drawn from the sources and/or high stresses experienced by their components. This paper thus proposes three new MCIS networks named, respectively, as quasi-Y-source, quasi-Γ-Z-source, and quasi-T-source or quasi-trans-Z-source networks. These new networks inherit all advantages of the existing MCIS networks. In addition, they demonstrate advantages like continuous input currents, reduced source stresses, and lower component ratings that are not achievable by other existing networks. Further, dc-current-blocking capacitors used in the networks help to avoid saturation of magnetic core. Derivations of all two-winding MCIS networks, including existing and new networks, from the generalized three-winding MCIS networks are then systematically illustrated, before comparing them. Operational principles, mathematical derivations, simulation, and experimental results of all studied networks have been presented in the paper. [ABSTRACT FROM PUBLISHER]

Modular multilevel converter (MMC) is considered to be one of the most promising multilevel topologies from the medium- to high-voltage power applications. However, by reason of energy exchange between the dc side and ac side, the fluctuation of sub-module (SM) capacitor voltage for the MMC system is inevitable. Moreover, this fluctuation would deteriorate the total harmonic distortion (THD) of the output voltage. The influence of the fluctuation of the SM capacitor voltage on the output voltage is analyzed mathematically in detail. In this paper, an improved phase-shifted carrier (PSC) pulse width modulation (PWM) for the MMC is presented to suppress the influence of the fluctuation of SM capacitor voltage. This improved modulation can be regarded as a nonlinear compensation applied in the traditional PSC-PWM method. The THD of the output voltage is improved with this modulation method noticeably. Simulation and experiment results verify the effectiveness of the proposed modulation. [ABSTRACT FROM AUTHOR]

This paper considers torque regulation of a variable-speed synchronous machine fed by a line-commutated rectifier and a load-commutated inverter. The proposed control approach is model-predictive control where both the rectifier and inverter firing angles are considered as control inputs. Conventional controllers assign different tasks to the rectifier and inverter firing angle. In contrast, the model-predictive controller coordinates the firing angles and this improves the dynamic performance and disturbance rejection. In particular, the proposed controller handles line side under voltage conditions better than a conventional PI controller. The nonlinear model-predictive torque controller has been implemented on an embedded system and applied in an experimental test bed. The experiments confirm that the controller is able to successfully ride through line side under voltage conditions. [ABSTRACT FROM AUTHOR]

This paper is a continuation of part I, which presented interturn fault (ITF) models for interior permanent magnet synchronous motors (IPMSMs). ITFs are defined by two ITF parameters: the healthy turn ratio and the fault contact resistance. First, this paper presents a proof that the two fault parameters defining a given ITF condition cannot be individually estimated from motor information and drive information (applied voltage, phase current, rotor speed, etc.) because they have multiple solutions. However, it is also shown that the additional Ohmic loss, which is the most important factor in heat generation and deterioration due to ITFs, is not dependent on these solutions. Thus, after arbitrarily setting one fault parameter, the other can be estimated for a given ITF condition; this model can be used to represent the effect of an ITF, particularly its Ohmic power loss. In this paper, an online fault parameter estimation method for IPMSMs is proposed after presenting one of the two fault parameters. The proposed method utilizes a searching algorithm that finds the fault parameter that has the minimum negative-sequence voltage error between the applied voltage and the ITF models (presented in part I). An experiment was performed to verify the proposed fault parameter estimation method. [ABSTRACT FROM AUTHOR]

A dominant-pole substitution (DPS) technique for low-dropout regulator (LDO) is proposed in this paper. The DPS technique involves signal-current feedforward and amplification such that an ultralow-frequency zero is generated to cancel the dominant pole of LDO, while a higher frequency pole substitutes in and becomes the new dominant pole. With DPS, the loop bandwidth of the proposed LDO can be significantly extended, while a standard value and large output capacitor for transient purpose can still be used. The resultant LDO benefits from both the fast response time due to the wide loop bandwidth and the large charge reservoir from the output capacitor to achieve the significant enhancement in the dynamic performances. Implemented with a commercial 0.18-μm CMOS technology, the proposed LDO with DPS is validated to be capable of delivering 100 mA at 1.0-V output from a 1.2-V supply, with current efficiency of 99.86%. Experimental results also show that the error voltage at the output undergoing 100 mA of load transient in 10-ns edge time is about 25 mV. Line transient responses reveal that no more than 20-mV instantaneous changes at the output when the supply voltage swings between 1.2 and 1.8 V in 100 ns. The power-supply rejection ratio at 3 MHz is −47 dB. [ABSTRACT FROM AUTHOR]

Three-phase four-leg inverters are commonly employed to supply unbalanced loads avoiding the use of a transformer. A suitable output filter is necessary to improve the harmonic content of the output voltage and current waveforms. To this aim, different kind of filters, presenting both symmetrical and asymmetrical phase-to-phase and phase-to-neutral behavior, can be used. The paper discusses and analyzes the effects of different carrier-based modulation techniques, based on the independent control of the fourth leg from that of the other phases, with reference to the different filter topologies. The comparison, performed through extensive simulations and experimental tests, have demonstrated that in case of the asymmetrical filter utilization, such as the active split dc-bus (also known as split-link), the conventional continuous and discontinuous space-vector modulations produce a significant harmonic content in the output voltages even at no-load condition. Moreover, the analysis is extended considering the interaction between the modulation strategy and load characteristics as linear, nonlinear, balanced and unbalanced loads. The problem is discussed in detail and a specific design procedure for the active split dc-bus is presented. [ABSTRACT FROM AUTHOR]

This paper proposes novel pulsewidth modulation (PWM) schemes for multi-space-vector pulsewidth modulation (MSVPWM), which is used in position sensorless control of interior permanent-magnet synchronous motor drives. The estimation of the rotor position is based on magnetic saliency and employs high-frequency components of voltage and current, which are excited by MSVPWM. The difference between the instantaneously applied voltage vector and the reference voltage vector causes current ripple. Since six or four voltage vectors are generated during a PWM period, the sequences of the error voltage vectors lead to different types of current ripples. In this paper, the proposed MSVPWM schemes employ six sequences for zero-/low-speed operation and 24 sequences for high-speed operation to reduce line current ripple. Experimental results confirm that the proposed MSVPWM schemes lead to significant reduction in harmonic current while maintaining high performance of sensorless estimation. [ABSTRACT FROM AUTHOR]

This paper proposes a digital phase leading filter current compensation (PLFCC) technique for a continuous conduction mode boost power factor correction to improve PF in high line voltage and light load conditions. The proposed technique provides a corrected average inductor current reference and utilizes an enhanced duty ratio feed-forward technique which can cancel the adverse effect of the phase leading currents caused by filter capacitors. Moreover, the proposed PLFCC technique also provides the switching dead-zone in nature so the switching loss can be reduced. Therefore, the proposed PLFCC can significantly improve power quality and can achieve a high efficiency in high line voltage and light load conditions. The principle and analysis of the proposed PLFCC are presented, and performance and feasibility are verified by experimental results from the universal input (90–260 VAC) and 750 W–400 V output laboratory prototype. [ABSTRACT FROM AUTHOR]

The three-phase buck rectifier (3ph-BR) is suitable for applications where a voltage step-down function is required. In this paper, an improved 3ph-BR topology is proposed to reduce the voltage stress on the transistors. The freewheeling diode in the conventional topology is split into two diodes in series and the input neutral point is connected to the common point of the two diodes. With the proposed topology and the corresponding modified modulation scheme, the transistors only need to withstand the input phase voltage instead of the line-to-line voltage, bringing about the significant reduction of voltage stress. The proposed topology enables a more cost-efficient and flexible selection of the transistors. Experimental results have verified the validity of the modified topology and associated modulation scheme. [ABSTRACT FROM AUTHOR]

An isolated bidirectional dc–dc converter, which combines parallel-connected two-level converters (TLCs) on the medium-voltage side and a modular multilevel converter (MMC) on the high-voltage side, namely a TLC-MMC converter, is a promising candidate for the interconnection of medium-voltage direct current (MVDC) and HVdc grids. Different from typical phase-shift controlled isolated bidirectional dc–dc converters, transformer currents of a TLC-MMC converter are regulated by the MMC in a closed-loop manner in order to achieve extremely low switching losses and low total device rating of power-semiconductor devices in TLCs. This paper addresses the dedicated operation technique and the voltage-balancing control of the TLC-MMC converter. The MMC in the TLC-MMC converter operates with six-step phase voltages and sinusoidal phase currents. Such an operation makes the MMC present remarkable differences to ac–dc applications. The direct-modulation technique, which is the most-used technique performed to MMCs in line-frequency ac–dc power conversion, has been concluded not applicable to the MMC in a TLC-MMC converter due to the significant sixth-order oscillation resulted in the dc-link voltage. Thus, the indirect-modulation technique is employed, and consequently a closed-loop voltage-balancing control is mandatory for the MMC. Possible measures for voltage balancing have been explored, and effective voltage-balancing control with a simplified implementation is proposed. Validity and effectiveness of the proposed control strategy have been verified by both simulations and experiment using a downscale prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage difference residual-based fault diagnosis approach for three-level converters in electric traction systems. Compared to the existing open-circuit fault diagnosis approaches, the proposed approach cannot only detect and identify the faulty devices among the transistors and clamp diodes in both of rectifier and inverter, but also hierarchically diagnose the leg-level and device-level faults. Furthermore, no additional sensors are required and all of specified parameters can be directly identified. Specifically, the current related term in the dc-link voltage difference equations are analyzed and modeled under the normal case and open-circuit fault cases in the transistors and clamp diodes, respectively. Subsequently, the estimation models of the dc-link voltage difference are developed, and then, the residuals and their evaluation functions between estimation and actual are generated. Furthermore, by analyzing the residual evaluation functions for various cases and building the current similarity functions, the hierarchical diagnosis algorithms are proposed to identify the leg-level and device-level faults. Finally, hardware-in-the-loop experiments are performed. The results show the effectiveness and robustness of the proposed approach. [ABSTRACT FROM AUTHOR]

Health monitoring and fault detection are becoming more and more important in electrical machine systems due to the increasing demand for reliability. Winding turn fault is a common fault in permanent magnet (PM) machines, which can cause severe damages and requires prompt detection and mitigation. High resistance connection fault, which results in phase asymmetry may also occur but does not require immediate shutdown. Thus, apart from the fault detection, the classification between the two faults is also required. In this paper, a new technique for detecting and classifying turn fault and HRC fault by utilizing both the high and low frequency components of the zero sequence voltage is proposed with the enhanced sensitivity. The dependence on the operating conditions is minimized with the proposed fault indicators. The effectiveness of fault detection and classification has been verified by extensive experimental tests on a triple redundant fault tolerant PM assisted synchronous reluctance machine. The robustness of the turn fault detection in transient states and under no load conditions has also been demonstrated. [ABSTRACT FROM AUTHOR]

Load-independent output characteristics of inductive power transfer (IPT) systems are increasingly popular in battery charging. This paper proposes a novel variable-parameter T-circuit (VT) for an IPT system charging a battery with constant current (CC) or constant voltage (CV) output. The VT can transfer a CC/CV input to a CC or CV output by using an ac switch and a passive component (inductor or capacitor). An IPT system with a VT for CC–CV charging can reduce the number of passive components and ac switches. Besides, the proposed VT merits more design freedom of charge current/voltage with the constraints imposed by the loosely coupled transformer parameters compared to that of the traditional one. In addition, there are three kinds of VTs for various IPT charging systems with different requirements. A 400 W laboratory-scale prototype with a 150 mm air gap was built to verify the theoretical analyses. Both electronic load and lead-acid battery are utilized to verify the charging profile of the proposed method. The experimental results of the IPT system indicate that the fluctuation of the charging current in CC mode is less than 2%, and the change rate of charging voltage in CV mode is within 2.9%. The maximum overall efficiency 93.93% of the charging system is achieved from a dc 110 V input to a dc 100 V output. [ABSTRACT FROM AUTHOR]

A fast output voltage equalization control strategy applied to 10-kV/100-kW high power density photovoltaic dc–dc converter system is proposed in this paper. The converter modules in the system have two dynamic priority factor loops for fast response with an inconsistent voltage between modules and a soft start-up circuit to precharge output capacitance for solving inrush current problem in boost circuit. The proposed strategy can realize fast voltage equalization control under inconsistent leakage inductance and parasitic resistance parameters condition between modules compared to the traditional unified duty cycle control strategy. The fast equalization performance is verified by 10-kV/100-kW photovoltaic dc–dc converter system. The converter system adopts an isolated boost full-bridge topology and input parallel output series structure, which meets high conversion ratio and high-power density requirements. [ABSTRACT FROM AUTHOR]

This paper proposes an interleaved active-clamp forward (IACF) converter modified for high efficiency without any additional component. To employ high input voltage, the components on one active-clamp forward module are re-arranged from the conventional IACF converter. The proposed converter can significantly reduce the primary conduction loss with large turns-ratio of the transformer due to the higher input voltage of the modified module and the expanded duty ratio at the nominal input voltage. In addition, unlike the existing approaches, the power density is not affected because there is no additional component. Finally, the proposed converter is validated experimentally using a prototype converter with 36–72 Vdc input and 480 W (12 Vdc/40 A) output. [ABSTRACT FROM AUTHOR]

In photovoltaic applications, many previous research works have focused on pulsewidth modulation (PWM) resonant converters in order to achieve a high efficiency with a wide input voltage range. Conventional approaches utilized symmetric boosting modulation at the secondary side rectifier to obtain a symmetric operation, and they utilized two boosting modes in a switching period. Among various rectifier structures, the voltage doubler structure has a strong advantage due to a small number of components. However, it suffers from serious hard switching losses in the secondary side rectifier. In this paper, a new converter with a novel asymmetrical modulation is proposed and verified. The strong point of the proposed converter is that it eliminates hard switching turn-on losses from the rectifier, while maintaining the minimized number of components. Although the proposed converter adopts an asymmetric modulation, the offset current on the transformer becomes zero inherently. Furthermore, a “forced half resonance” operation of the proposed converter keeps rms current stresses at the same level as conventional converter although it has a higher peak current. Accordingly, the proposed converter achieves a superior efficiency with the minimum number of components at 35–25 V input and 380 V/300 W output specification. [ABSTRACT FROM AUTHOR]

A systematic method for developing ultra-wide output voltage range power supply based on modular switched-converter principle is proposed in this paper. The basic symmetric switched-converter (SSC) module is composed of two dc–dc modules, two diodes, and one active switch. Multi-stage SSC modules are generated by symmetric cascaded connection method. By controlling the active switches in multi-stage SSC modules, the connections of all the dc–dc modules’ output ports can be changed flexibly among series, parallel, and partial–parallel–partial-series connections. Then segmented regulation can be realized and system output voltage range can be widely extended. Meanwhile, the voltage range of each dc–dc module can be narrowed and the voltage/current stress can be reduced to simplify the design, increase device utilization ratio, and improve overall efficiency. A full-bridge isolated buck–boost converter with a semiactive rectifier, which features soft-switching and wide voltage adjustment range, is adopted as the dc–dc module to realize the proposed system. Input current sharing control strategy is adopted to ensure proper power balancing in all possible operating modes. The stability of the proposed system is also explored. Simulation and experimental results are provided to verify the effectiveness and advantages of the proposed system configuration, the switched-converter principle, and the control strategies. [ABSTRACT FROM AUTHOR]

Voltage model observer is a simple and economical technique for flux estimation in induction motor sensorless drives. However, it shows poor performance in low-speed regions. Therefore, in most cases, the use of this observer is limited. On the other hand, using a simple but accurate estimator is important when the control method is sophisticated and requires heavy computation. This issue will be important in predictive control more than the other methods because the accuracy of the prediction is dependent on the flux estimation. In this paper, a modified closed-loop technique based on voltage model observer is proposed for flux estimation. The feedback loop is supported by the proposed model reference adaptive system direct flux magnitude estimation technique. The dependence of the feedback loop on the stator resistance is eliminated. Therefore, the drift error will be avoided. This will allow the method to withstand the high stator resistance error even at low speeds. Also, a new Lyapunov-based technique for the stator resistance estimation via reduced-order model is proposed. By using the proposed observer, the predictive direct voltage control technique is used as the control method in order to achieve a control method that requires low computation. The proposed method is validated through the experimental results. [ABSTRACT FROM AUTHOR]

A conventional asymmetrical half-bridge (AHB) converter is one of the most promising topologies in low-power applications because of the zero-voltage switching (ZVS) of all switches and the small number of components. However, when it operates with an asymmetrical duty ratio, it has a large dc-offset current in the transformer, which increases the size and core loss of the transformer. Moreover, because the dc-offset current decreases ZVS energy for one of the half-bridge switches, it has low efficiency in a light load condition. In addition, because most of the output current is concentrated in high-voltage-rating diodes that have large forward voltage drops, large conduction loss occurs in the secondary rectifier. To solve these problems, a new AHB converter with a coupled inductor rectifier (CIR) is proposed in this paper. By adopting the CIR structure in the AHB converter, the proposed converter not only eliminates the dc-offset current in the transformer, but it also has equalized current stress in the rectifier diodes. As a result, the proposed converter achieves high efficiency in entire load condition, compared to an AHB converter with a full-bridge rectifier. The effectiveness and feasibility are verified with a 250–400 V input and 100 V/200 W output prototype. [ABSTRACT FROM AUTHOR]

Synchronous rectification (SR) for LLC resonant converters has been developed to enhance the power conversion efficiency and achieve high-power-density design. Conventional SR driving strategies can be categorized as current-driven methods, $v_{\text{DS-ON}}$ sensing methods, and alternative approaches. The current-driven methods widely adopt current transformers (CTs) to sense the rectifier current and generate the SR driving signals. The CTs are lossy and bulky, which is unfavorable to high-power-density design. The $v_{\text{DS-ON}}$ sensing methods remove the current sensors by sensing the voltage across the on-state resistor of the SR mosfet, yet the sensed signal is small and prone to be offset by the inductive voltage induced from parasitic components. Most alternative approaches avoid sensing noise-sensitive signals; however, the operating range is narrow due to the limited information from the converter. This paper proposes an SR driving strategy based on the resonant capacitor voltage (RCV) to address those issues. The RCV SR driving strategy does not require current sensors. The sensed RCV is insensitive to the parasitic effects. In addition, the RCV strategy controls the SR on-time effectively over a wide range of operating frequency and loading conditions. Simulation and experimental results of a 650-W/24-V LLC converter are presented to validate the effectiveness of the proposed RCV strategy. Compared with the conventional $v_{\text{DS-ON}}$ sensing method, the on-time error caused by the parasitic effect is greatly reduced, which improves the power conversion efficiency and reduces the SR mosfet temperature. [ABSTRACT FROM AUTHOR]

A hybrid modular multilevel converter (MMC) consists of both half-bridge submodule (HBSM) and full-bridge submodule (FBSM) in each arm. It has several advantages over other MMC topologies, such as low system loss, reduced cost of the system, but still maintains fault ride-through capability against a solid dc-side fault. However, the hybrid MMC may have a difficulty of submodule (SM) voltage balancing under variation of its dc-bus voltage. Since the voltage unbalance of SMs results in SM capacitor overvoltage and low reliability of the system, the voltage of SMs, which can be also represented as energy of SMs, should be balanced at all time. In this paper, to extend the narrow adjustable range of dc-bus voltage due to the voltage/energy unbalance, new feedback and feedforward energy balancing controllers with revised sorting algorithm are proposed. The feedback control ensures the zero steady-state error, while the feedforward control provides fast dynamic response in the energy balancing control. By applying the proposed control scheme, the hybrid MMC can keep the voltage balance between HBSMs and FBSMs in wider range of dc-bus voltage. The full-scale computer simulation results and down-scale experimental results demonstrate the validity of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Linear droop faces the design tradeoff between voltage regulation and load sharing due to cable resistances and sensing errors. Using a larger droop resistance improves load sharing, but requires a wider droop voltage range. In the nonlinear droop, droop resistance is a function of the converter's output current, and its value increases when the output current increases. As a result, the impacts from sensors and cables are reduced. In this paper, the design of nonlinear droop in dc power distribution systems is studied with special emphasis on load sharing, voltage regulation, system efficiency, and stability. After discussing the piecewise linear and nonlinear droop control, a generic polynomial expression is presented to unify different droop equations. The impact of droop on dc system efficiency is analyzed by evaluating cable and power converter losses. The converter's output impedance using nonlinear droop is modeled to analyze the system stability with constant power loads. The selection and design guidelines of nonlinear droop are summarized, considering both the static performance and interaction with load systems. The analysis is verified in 400-V multi-source dc systems. The nonlinear droop is fully distributed as it only needs local information. [ABSTRACT FROM AUTHOR]

Generating dense multilevel voltage space structure using polygons of higher sides is one of the novel and elegant method to suppress low-order harmonics and to obtain refined sinusoidal voltages using voltage source inverters for variable frequency drive application without passive filters. Apart from the advantages of conventional multilevel inverter topologies, schemes generating polygonal voltage space vector structure can equip full dc-bus utilization, low switching frequency strategies to eliminate low-order harmonics, and increased linear modulation range. In this paper, an induction motor drive scheme generating a highly dense multilevel 24-sided polygonal voltage space vector structure using a single dc source, which can eliminate harmonics till 23rd order from phase voltages, is presented. Cascaded power circuit topology with a flying capacitor inverter fed with a dc source and two low voltage floating capacitor fed H-bridge inverters is used. Detailed experimentally validated results, under scalar as well as indirect rotor field oriented control of induction motor are provided. Studies on voltage ripple and reactive energy in various floating capacitors, harmonic performance of output voltage for wide range of speed operation, are also included. [ABSTRACT FROM AUTHOR]

In order to provide high and extendable power levels for inductive power transfer (IPT) system, a parallel multi-inverter system based on modular inverter is presented. Various power requirements can be implemented by an adjustment of the number of paralleled inverters, which provides a high modularity. A master−slave scheme is employed for the switching-driver signals of parallel inverters, where one acts as a leader while others act as followers. Despite the master−slave scheme, the proposed circuit topology has natural robustness because of the equality in terms of the hardware configuration of each modular inverter. For proper parameters, the output phase (current lagging corresponding voltage) of an inverter is lower than the average of output phase of all inverters, when its output voltage lags behind others, and vice versa. Based on this approach, PI controllers are designed to implement phase synchronization for output voltages of all inverters. An IPT prototype supplied by the proposed parallel multi-inverter with three inverters was designed, built, and tested. Experiments show that the proposed parallel multi-inverter system has not only good circulating current suppression capacity but also excellent performance of phase synchronization. The maximum dc−dc efficiency was 94% at a 35.1 kW receiving power. This paper is accompanied by a Matlab/Simulink file demonstrating phase synchronization control. [ABSTRACT FROM AUTHOR]

When providing ac output, modular multilevel converters (MMCs) experience power fluctuation in the phase arms. The power fluctuation causes voltage ripple on the module capacitors, which grows with the output power and inversely to the output frequency. Thus, low-frequency operations of MMCs, e.g., for motor drives, require injecting common-mode voltages and circulating currents, and strict dc voltage output relative to ground is impossible. To address this problem, this paper introduces a novel module topology that allows parallel module connectivity in addition to the series and bypass states. The parallel state directly transfers power across the modules and arms to cancel the power fluctuations and hence suppresses the capacitor voltage ripple. The proposed series/parallel converter can operate at a wide frequency range down to dc without common-mode voltages or circulating currents; it also allows sensorless operation and full utilization of the components at higher output frequencies. We present detailed simulation and experiment results to characterize the advantages and limitations of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper proposes a method for fault-tolerant operation of medium voltage modular multilevel converters (MMCs) with phase-shifted carrier (PSC) modulation. The existing methods need to recalculate and reconfigure all the carriers every time a submodule (SM) fails. However, the proposed method combines the sorting voltage balancing control and the PSC modulation to avoid breaking the symmetry and balance of the carriers. Therefore, the modulation stage in the proposed method can be kept the same and the output voltage of the MMC can remain unchanged without causing voltage mismatch. Moreover, considering the modulation margin and the physical redundancy configuration, two fault SM replacing strategies, i.e., optimal dynamic performance and optimal electrical stress are proposed as well as their respective control structures. Compared with the normal operation of the MMC, the proposed fault-tolerant operation method has only slightly changed the control system and thus the added calculation burden and control complexity can be ignored, which is extremely beneficial for the practical implementation. The effectiveness and performance of the proposed operation method are carefully verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a generalized design framework for three-phase Vienna rectifiers to handle the neutral point voltage balance issue. On the basis of the design framework, it is convenient to construct various neutral point voltage balancing methods with the guarantee of stability. As demonstration, three representative neutral point voltage balance approaches are presented by choosing different zero-sequence voltages. A comprehensive comparison among the three approaches is given in the aspects of input current quality, capacitor voltage fluctuation, and system efficiency. The comparison results provide guidance for constructing the most appropriate approach based on the specific requirement. Finally, simulation and experimental results verify the correctness and effectiveness of the presented approaches and the related performance analysis. [ABSTRACT FROM AUTHOR]

A conventional phase-shifted full-bridge (PSFB) converter is one of the most promising topologies in high-efficiency and high-power applications because of its small RMS current, inherent zero-voltage switching capability, and clamped voltage stress of the primary switches. However, when the PSFB converter operates with a small duty ratio, a large freewheeling current of an output inductor flows in the primary side, and it causes a large circulating current. In addition, it has a large voltage stress in the rectifier diodes due to a voltage ringing between parasitic components. To solve these problems, a new PSFB converter with a coupled inductor rectifier (CIR) is proposed in this paper. By adopting the CIR structure in the PSFB converter instead of the full-bridge rectifier, the proposed converter eliminates the freewheeling current in the primary side, which significantly reduces the primary circulating current. In addition, the two rectifier diodes of the CIR do not have voltage ringing. As a result, the proposed converter not only reduces the conduction loss in the primary side, but can also use two diodes in the rectifier with a low voltage rating. The effectiveness and feasibility were verified with a 320–400 V input and 56-V/12.8-A output prototype. [ABSTRACT FROM AUTHOR]

In this paper, a voltage harmonic injection method at the dc-link is proposed to reduce input current harmonics of the series-connected 12-pulse rectifier. The proposed method uses an auxiliary circuit to generate the voltage harmonics and injects the voltage harmonics into the dc link of the series-connected 12-pulse rectifier so that the input voltages of the 12-pulse rectifier can be shaped as 24 steps. The formation processes of the input voltage are analyzed based on the switching functions; and the turn ratio of injection transformer is optimally designed from the perspective of minimizing the total harmonic distortion (THD) of the input voltage. After using this method, experimental results show that the input voltages of the isolated transformer are 24-step waves with an experimental THD of around 3.34%; the input line currents of the proposed rectifier are close to sinusoidal waveforms with an experimental THD of around 2.65%. More importantly, the kVA rating of the injection transformer is only about 2.3% of the load power, which means that the cost of harmonic reduction is very low. [ABSTRACT FROM AUTHOR]

The efficiency improvement of the on–off controlled Class E dc–dc converter operated at 20 MHz switching frequency is investigated in this paper. It is found that with the on–off control, the input power of the converter during the on mode increases with the increase of the input voltage, and it can be reduced by increasing the switching frequency. With this discovery, a variable switching frequency (VSF) on–off control is proposed, which slightly increases the switching frequency when the input voltage increases, maintaining the input power during the on mode slightly higher than the rated output power over the entire input voltage range, and thus highly improving the efficiency of Class E dc–dc converter at high input voltage. A prototype of 9-V–18-V input, 10-W Class E dc–dc converter has been fabricated and tested in the lab. The experimental results show that the proposed VSF on–off control improves the conversion efficiency of the Class E dc–dc converter by 4%–10% compared to the constant switching frequency on–off control. [ABSTRACT FROM AUTHOR]

Three-level inverter has an outstanding performance and is more advantageous in the switching vector selection than two-level inverter. In particular, the neutral-point voltage unbalance and common-mode voltage (CMV) reduction of three-level inverter should be carefully regulated for the appropriate operation, both of which, however, are mutually coupled resulting that the conventional space vector modulation (SVM) scheme cannot deal with them properly. To overcome this limitation, this paper proposes an improved space vector modulation (ISVM) technique to reduce the CMV and neutral-point voltage imbalance simultaneously. The generating mechanism of neutral-point voltage oscillation is derived. Based on the analysis, the proposed ISVM method adopts four voltage vectors (large, medium, small, and zero vectors) with adjusted dwell times to eliminate the ac unbalance of the neutral-point voltage. Considering the occurrence of neutral-point voltage disturbances, the dc neutral-point unbalance voltage is controlled by selecting the P-type or N-type small vector and adjusting the dwell times of small vectors for neutral-point voltage recovery. In addition, a novel switching sequence arrangement method with the minimal number of switches transition in one switching cycles and between switching cycles is proposed to reduce the total switching loss. Theoretical analysis and verification results show that the proposed ISVM scheme can reduce the magnitude of CMV to half of value using the conventional SVM, and an accurate control of ac and dc unbalanced neutral-point voltage can be obtained. [ABSTRACT FROM AUTHOR]

This paper proposes a quasi-resonant boost half-bridge dc–dc converter with high power conversion efficiency and a wide input voltage range for a photovoltaic micro-inverter. The proposed converter has a combined structure of a boost-integrated half-bridge converter on the primary side of the transformer and a voltage doubler with a snubber capacitor on the secondary side. By using the quasi-resonance techniques, it achieves zero-voltage switching (ZVS) turn-on and low turn-off losses for the switches, as well as ZVS turn-on for the diodes. In addition, the proposed converter has no dc-magnetizing current for the transformer due to the dc-blocking capacitor, and it doubles the voltage gain with half the voltage stress of diodes through the voltage doubler. The effectiveness of the converter was verified with a 300-W prototype with an input voltage range of 13–50 V, an output voltage of 400 V, and a switching frequency of 50 kHz. The experimental results show that the converter had more than 90.0% power conversion efficiency for the output power range of ∼300 W, and its maximum power conversion efficiency was 97.5% for an output power of 160 W. [ABSTRACT FROM AUTHOR]

Energy harvesting (EH) technologies provide a promising solution for the self-power supply of wearable devices. However, it is challenging due to strict constraints of wearable systems in terms of size, weight, and cost. Additionally, a suitable method is required to transport the harvested energy from the environment or body to wearable devices. This letter proposes a cable-type packaging that embeds a converter into the connection wire to simultaneously regulate the voltage and transport the energy. A distributed inductor is implemented by winding the conductor in a helix around a flexible magnetic-sheet core to increase the inductance. This packaging method can aid the design of wearable EH systems and significantly reduce the size of the system. A prototype was fabricated based on the proposed packaging and compared with other two converters based on traditional packaging in terms of size, weight, and efficiency. The experimental results verify that the proposed packaging can reduce the system size by 75% and system weight by 35% under the same efficiency condition. [ABSTRACT FROM AUTHOR]

The degradation of submodule (SM) insulated gate bipolar transistors (IGBTs) in a modular multilevel converter (MMC) can be monitored through their on-state voltages. This paper proposes a scheme to calculate the IGBT on-state voltages at rated current and normal junction temperature. The equations of on-state resistances are established based on Kirchhoff voltage laws (KVL) in one MMC arm for positive and negative current directions separately. The arm current, arm voltage, capacitor voltages, gate signals, and junction temperatures are utilized in the equations, and most of the signals are known for the control system. The dimension of the equation set is reduced to make it solvable based on an assumption that all the on-state resistances of diodes remain equal. In addition, the Kalman filter (KF) is used to improve the stability and accuracy of the calculation results. The calculated results are converted to the normal condition based on the current-voltage (I–V) and resistance-temperature (R–T) characteristics of SM IGBTs and diodes. The scheme is verified by using the simulation of a five-level three-phase MMC model. The errors of the calculated VCE are within 0.3%, and the calculation accuracy is good enough for the estimation of IGBT degradation. Furthermore, the influences of the measurement accuracy and the equal diode voltage assumption on the calculation accuracy are analyzed. The proposed scheme is expected to be applicable in online condition monitoring of SM IGBTs. [ABSTRACT FROM AUTHOR]

In the context of reducing total CO $_2$ emissions as well as reducing the total copper cable length and weight on cars, automotive manufacturers propose to derive all the supply voltages from a single $\text{48 V}$ bus through high step-down ratio dc–dc converters. The series capacitor tapped inductor (SCTI) converter is a promising topology for efficient single-stage step-down conversion from the $\text{48 V}$ bus. In the synchronous version of the SCTI, however, turn-off of the synchronous rectifier at positive drain-to-source current leads to a voltage spike and to a potential catastrophic failure of the converter. In this paper, a simple control technique is proposed, which prevents the foregoing condition to occur. The approach enables a reliable operation of the synchronous SCTI topology without disrupting its main features and advantages, and eliminating the need for additional snubbers, voltage clamps or auxiliary windings. The approach is validated via computer simulations and experimental tests on a $\text{48}$ -to- $\text{1.5}\;\text{V}$ , $\text{4 A}$ SCTI converter prototype. [ABSTRACT FROM AUTHOR]

In this paper, a novel discontinuous pulsewidth modulation (DPWM) modulation strategy for a neutral-point-clamped (NPC) three-level converter (TLC) is proposed to reduce the switching loss, reduce common-mode voltage (CMV), and remove dc offset from the neutral-point (NP) voltage simultaneously, which is named as RCMV_DPWM. Based on the space vector diagram with reduced CMV, all clamping modes under RCMV_DPWM are revealed. Then, the NP voltage is controlled by selecting proper clamping mode. The realization of RCMV_DPWM is also discussed. Moreover, the performances of RCMV_DPWM are analyzed and compared with other PWM strategies in term of the NP voltage ripple, switching loss, and waveform quality. Finally, the feasibility and superiority of RCMV_DPWM are verified by experiments. [ABSTRACT FROM AUTHOR]

In recent years, dc distribution grids have become increasingly popular because of the interest in the diffusion of distributed renewable energy. In this scenario, dc distribution grids are also favored because of the increased use of batteries and power electronic loads. The main limit to the spread of dc grids is their protection devices, which still present several problems. At present, protection devices are represented by traditional mechanical breakers or static electronic components. The first, which interrupt dc currents, have good reliability but need maintenance and have long intervention periods. In contrast, electronic switches are fast and reliable, but they reduce the efficiency because of their voltage drop. In this scenario, some hybrid breakers have been proposed to obtain the advantages of both devices. The previous solutions of hybrid breakers still suffer several critical issues and, usually, are not capable of protecting a system from short circuits without significantly reducing their lifetime. In this paper, a new low-voltage hybrid circuit breaker topology is proposed. The procedure to dimension all of the active and passive components in the device is analyzed, and the effectiveness of the proposed solution is proven by means of experimental results obtained using a prototype. [ABSTRACT FROM AUTHOR]