Search

Grid-connected current control plays an important role in the renewable grid-connected system. This paper investigates the grid-connected current hysteresis control of the asymmetry three-level inverter. In order to effectively utilize asymmetry three-level inverter and conquer the disadvantages of traditional hysteresis control, the multistage hysteresis control and current predict hysteresis control are developed. In the multistage hysteresis control method, the switching times of main switches can be declined by regularly adjusting the bus voltage without altering the inductor and bandwidth. In addition, the current predict hysteresis control is developed, which adapts to proper bus voltage without dividing bus switching time. In order to overcome the invalidation issue of the bandwidth in hysteresis control, virtual sample technology is used without increasing real sample frequency. Both simulation and experimental tests have been conducted to verify the efficacy of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper proposes an enhanced sensorless vector control strategy using the predictive deadbeat algorithm for a direct-driven permanent magnet synchronous generator (PMSG). To derive favorable sensorless control performances, an enhanced predictive deadbeat algorithm is proposed. First, the estimated back electromotive force (EMF), corrected by a cascade compensator, was put into a deadbeat controller in order to improve the system stability, while realize the null-error tracking of the stator current at the same time. Subsequently, an advance prediction of the stator current based on the Luenberger algorithm was used to compensate the one-step-delay caused by digital control. Maintaining the system stability, parameters of the controller were optimized based on discrete models in order to improve the dynamic responses and robustness against changes in generator parameters. In such cases, the proposed methodology of synchronous rotating frame phase lock loop (SRF-PLL), which applies the estimated back EMF, can observe the rotor position angle and speed without encoders, realizing the flux orientation and speed feedback regulation. Finally, the simulation and experimental results, based on a 10-kW PMSG-based direct-driven power generation system, are both shown to verify the effectiveness and feasibility of the proposed sensorless vector control strategy. [ABSTRACT FROM AUTHOR]

In the literature, both photovoltaic voltage and PV current need to be sensed to perform maximum power point tracking (MPPT) control. For three-level boost converter, both capacitor voltages need to be sensed and an additional voltage balancing control loop is required to balance the capacitor voltages. In this paper, the MPPT control and the voltage balancing control with sensing only inductor current is proposed. The provided simulation and experimental results demonstrate the proposed method. [ABSTRACT FROM AUTHOR]

In order to obtain sufficient luminance and achieve high reliability, light-emitting diodes (LEDs) are usually arranged in parallel strings in many high-power applications. Since current imbalance should be avoided among the parallel LED strings, a multichannel constant current LED driver with dynamic high-frequency sinusoidal voltage regulation is proposed in this paper. The proposed driver is composed of one resonant inverter and several LCL-T resonant rectifiers. The number of the rectifiers equals to that of the LED strings. The rectifier whose output current is sensed and closed-loop controlled is called master rectifier and all the others slave rectifiers. The resonant inverter is used to convert dc voltage into high-frequency sinusoidal bus voltage and the LCL-T resonant rectifiers are included to drive LED strings with constant current. The amplitude of the high-frequency sinusoidal bus voltage is dynamically regulated to ensure the output current of the master resonant rectifier to be constant by a closed-loop controller. Since the output current of the slave rectifier is linear with the amplitude of the bus voltage as the master rectifier, there are not any auxiliary circuits included in the slave rectifier while the output current balancing is achieved. Finally, a 200-W prototype with one master and fifteen slave rectifiers is built to verify the performance of the proposed driver. [ABSTRACT FROM AUTHOR]

The advantages arising from dc distribution networks are related to the possibilities of achieving higher quality supply and easier reconfigurability of the system. This paper presents the concept of introducing some dc islands interconnected with the ac distribution network. This will make it easier to connect storage systems, electrical drives, power converters, and renewable sources (i.e., photovoltaic panels). In order to realize the aforementioned goals, a methodology for designing the control strategy of different power converters connected to a dc bus without a centralized system management control unit is proposed. In this way, a plug-and-play functionality for connecting new power converter interfaced elements in the dc network able to stabilize the voltage under different working conditions is realized. In order to prove the advantages obtainable with such a network, a 100-kW dc test facility has been realized at the laboratories of RSE. Different working conditions were tested by means both of numerical and experimental results, proving the effectiveness of the proposed strategy for voltage regulation, continuity of service, and the smart use of storage devices. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is attractive for medium- or high-power applications because of the advantages of its high modularity, availability, and high power quality. The voltage balancing of the floating capacitors in the cascaded submodules of the MMC is a key issue. In this paper, a voltage-balancing control method is proposed. This method uses the phase-shifted carrier-based pulsewidth modulation scheme to control high-frequency current components for capacitor voltage balancing in the MMC without measuring the arm currents. Simulations and experimental studies of the MMC were conducted, and the results confirm the effectiveness of the proposed capacitor voltage-balancing control method. [ABSTRACT FROM AUTHOR]

This paper deals with the influence produced by the solar array parasitic capacitance and its solving methods in the sequential switching shunt regulator (S3R). Nowadays, the usage of triple-junction Ga/As solar cells with larger parasitic capacitance has prompted new problems about power losses, steady state, and dynamic response in the S3R, especially for high section current, voltage applications. Effects of parasitic capacitance on voltage ripple, “double sectioning,” phase margin, and output impedance are represented and analyzed, and turn-off delay caused by parasitic capacitance is mathematically modeled. A novel shunt regulator topology passive and active shunt regulator (PASR) with low switching losses, low mass, and short turn-off time delay is proposed. To further reduce the impact of delay, nonlinear control is added in the control loop, achieving better performances in the stability margin, output impedance, and dynamic performance. Simulation and experimental results are provided to validate the proposed PASR together with nonlinear control scheme. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) is an emerging technology that may create new possibilities for wireless power charging and transfer applications. However, the rather complex control method and low efficiency remain the key obstructing factors for general deployment. In a regularly compensated IPT circuit, high efficiency and controllability of the voltage transfer function are always conflicting requirements under varying load conditions. In this paper, the relationships among compensation parameters, circuit efficiency, voltage transfer function, and conduction angle of the input current relative to the input voltage are studied. A design and optimization method is proposed to achieve a better overall efficiency as well as good output voltage controllability. An IPT system design procedure is illustrated with design curves to achieve a desirable voltage transfer ratio, optimizing between efficiency enhancement and current rating of the switches. The analysis is supported with experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a new technique in voltage balancing for single-phase railway substations. Using the concept of chopper-controlled impedance, the authors study the feasibility of an active Steinmetz circuit based on ac choppers. The low power losses in semiconductor devices make the proposed topology an interesting alternative to classical solutions such as those based on voltage source inverters. Design criteria are presented using information obtained from measurements carried out on a substation of the French National Railways. Finally, the study is validated by means of simulations and experimental results carried out on a 1.5 kVA prototype. [ABSTRACT FROM AUTHOR]

This paper presents a control strategy for input-series-output-series (ISOS) modular inverters. Each module is a bidirectional high-frequency ac-link (HFACL) inverter composed of an HF inverter, an HF transformer followed by a cycloconverter. The relationship between input voltage sharing (IVS) and output voltage sharing (OVS) is revealed with a general load based on bidirectional ISOS inverter systems. To achieve IVS and OVS, a stable power sharing control strategy eliminating mandatory IVS loops is proposed. For individual modules, the common output voltage regulation loop output multiplies its magnitude compensator loop output to work as its pulse width modulation signal. The loop gain design is also presented. With the proposed control strategy, excellent IVS and OVS can be obtained not only during steady state but also during transients. The effectiveness of the proposed control strategy is verified by simulation and experimental results of a 2420-VA ISOS two HFACL inverters. [ABSTRACT FROM AUTHOR]

This paper presents the analysis and design of a three-phase high power factor rectifier, based on the dc–dc single-ended primary-inductance converter (SEPIC) operating in discontinuous conduction mode, with output voltage regulation and high frequency isolation. The input high power factor is naturally attained through the operational mode without the use of current sensors and a current control loop. To validate the theoretical analysis, a design example and experimental results for a 4-kW, 380-V line-to-line input voltage, 400-V output voltage, 0.998 power factor, 40-kHz switching frequency, and 4% input current total harmonic distortion laboratory prototype are presented, considering two distinct modulators. In addition, experimental results for the output voltage closed-loop control are presented. [ABSTRACT FROM AUTHOR]

Voltage sags are one of the main problems in transmission and distribution grids with high penetration of distributed generation. This paper proposes a voltage support control scheme for grid-connected power sources under voltage sags. The control is based on the injection of reactive current with a variable ratio between positive and negative sequences. The controller determines, also, the amount of reactive power needed to restore the dropped voltage magnitudes to new reference values confined within the continuous operation limits required in grid codes. These reference values are chosen in order to guarantee low current injection when fulfilling the voltage support objective. Selected experimental results are reported in order to validate the effectiveness of the proposed control. [ABSTRACT FROM AUTHOR]

This paper proposed an improved phase disposition pulse width modulation (PDPWM) for a modular multilevel inverter which is used for Photovoltaic grid connection. This new modulation method is based on selective virtual loop mapping, to achieve dynamic capacitor voltage balance without the help of an extra compensation signal. The concept of virtual submodule (VSM) is first established, and by changing the loop mapping relationships between the VSMs and the real submodules, the voltages of the upper/lower arm's capacitors can be well balanced. This method does not requiring sorting voltages from highest to lowest, and just identifies the MIN and MAX capacitor voltage's index which makes it suitable for a modular multilevel converter with a large number of submodules in one arm. Compared to carrier phase-shifted PWM (CPSPWM), this method is more easily to be realized in field-programmable gate array and has much stronger dynamic regulation ability, and is conducive to the control of circulating current. Its feasibility and validity have been verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

In this paper, a soft-switching dc/dc converter with secondary-side phase-shift control strategy is proposed to improve the conversion efficiency and minimize the primary switch voltage stress in the high input voltage applications. Zero-voltage-switching performance is achieved for both the primary- and secondary-side power devices in a wide load range to reduce the switching losses due to the secondary-side phase-shift control scheme. Furthermore, compared with the conventional phase-shift control mechanism, the circulating current at the freewheeling stage is effectively suppressed as well to minimize the conduction losses. Moreover, the voltage stress of the primary switches is only half of the input voltage by employing the improved three-level structure, which makes the low-voltage rated power devices available to improve the circuit performance. In addition, the converter can work in the buck, balance, and boost modes to achieve a relatively wide input voltage range, which is an expected advantage for the communication power system to minimize the electrolytic capacitors with an acceptable hold-up time. The operation principle is analyzed and experimental results of a 1-kW 100-kHz prototype are provided to verify the effectiveness and the advantages of the proposed converter. [ABSTRACT FROM AUTHOR]

Ideally, the inner (the upper or lower arm) current of a modular multilevel converter (MMC) is ideally assumed to be the sum of a dc component and an ac component of the fundamental frequency. However, as ac current flows through the submodule (SM) capacitors, the capacitor voltages fluctuate with time. Consequently, the inner current is usually distorted and the peak/RMS value of it is increased compared with the theoretical value. The increased currents will increase power losses and may threaten the safe operation of the power devices and capacitors. This paper proposes a closed-loop method for suppression of the inner current in an MMC. This method is very simple and is implemented in a stationary frame, and no harmonic extraction algorithm is needed. Hence, it can be applied to single-phase or three-phase MMCs. Besides, this method does not influence the balancing of the SM capacitor voltages. Simulation and experimental results show that the proposed method can suppress the peak and RMS values of the inner currents dramatically. [ABSTRACT FROM AUTHOR]

The use of control theory in power electronics applications is aimed toward several objectives, which include, obtaining a good dynamic response, stabilizing in an operation point, regulation of state variable, reference tracking, rejecting of disturbances and robustness against parametric variations. It is also possible to eliminate stages that represent computational effort via control theory without loss of the main desirable characteristics. However, it should be considered the physical limitations of the topology given that even with sophisticated controllers they cannot achieve the established objectives if these limitations are exceeded. This paper aims at highlighting the importance of physical limitations of a single-phase multilevel rectifier (SPMR) using a nonlinear controller, an aspect not considered in previous works published by the authors. Thus, the design here presented is based on input–output linearization via feedback combined with a generalized PI controller. These controllers are used because they allow avoiding a voltage sag detection stage without changing the main characteristics of the topology. The procedure to reproduce these results is shown and the feasibility of the method is demonstrated by simulation and experimental results in a 1 kVA SPMR prototype. [ABSTRACT FROM AUTHOR]

This paper introduces a seamless grid interconnection control strategy for distributed generations (DG) with renewable energy. Based on the performance analysis of conventional voltage and current control loops, sophisticated control strategies, which can overcome the limited capability of the DG inverter control under mode transition conditions for unknown power plants, are needed in order to protect critical loads and operate the DG inverter without grid fault trip. The proposed control strategy consists of a current controller and a feedforward voltage controller to minimize the grid overvoltage. The feedforward voltage control loop is added to the d–q axis current control loop. The proposed control strategy reduces the overvoltage stress of the renewable energy and the critical load under the grid fault. In addition, the seamless operation of the DG inverter will also enhance the stability and reliability of the grid. Real-time digital simulator-based hardware-in-the-loop experimental results and simulation results show that the DG inverter achieves the seamless mode transition under grid overvoltage conditions. [ABSTRACT FROM AUTHOR]

The PowerChip research program is developing technologies to radically improve the size, integration, and performance of power electronics operating at up to grid-scale voltages (e.g., up to 200 V) and low-to-moderate power levels (e.g., up to 50 W) and demonstrating the technologies in a high-efficiency light-emitting diode driver, as an example application. This paper presents an overview of the program and of the progress toward meeting the program goals. Key program aspects and progress in advanced nitride power devices and device reliability, integrated high-frequency magnetics and magnetic materials, and high-frequency converter architectures are summarized. [ABSTRACT FROM AUTHOR]

This paper provides a perspective on progress toward realization of efficient, fully integrated dc–dc conversion and regulation functionality in CMOS platforms. In providing a comparative assessment between the inductor-based and switched-capacitor approaches, the presentation reviews the salient features in effectiveness in utilization of switch technology and in use and implementation of passives. The analytical conclusions point toward the strong advantages of the switched-capacitor (SC) approach with respect to both switch utilization and much higher energy densities of capacitors versus inductors. The analysis is substantiated with a review of recently developed and published integrated dc–dc converters of both the inductor-based and SC types. [ABSTRACT FROM AUTHOR]

This paper presents a high-efficiency positive buck–boost converter with mode-select circuits and feed-forward techniques. Four power transistors produce more conduction and more switching losses when the positive buck–boost converter operates in buck–boost mode. Utilizing the mode-select circuit, the proposed converter can decrease the loss of switches and let the positive buck–boost converter operate in buck, buck–boost, or boost mode. By adding feed-forward techniques, the proposed converter can improve transient response when the supply voltages are changed. The proposed converter has been fabricated with TSMC 0.35-μm CMOS 2P4M processes. The total chip area is 2.59 × 2.74 mm^2 (with PADs), the output voltage is 3.3 V, and the regulated supply voltage range is from 2.5–5 V. Its switching frequency is 500 kHz and the maximum power efficiency is 91.6% as the load current equals 150 mA. [ABSTRACT FROM AUTHOR]

It is important to improve the overall efficiency of a photovoltaic (PV) inverter when it is connected to the grid. Fundamentally, the conversion efficiency from dc to ac power of an inverter is important. However, in the presence of partial shading, maximum power point tracking (MPPT) on PV modules is more important than the conversion efficiency. In this paper, a new control method for a three-level inverter is proposed. With the proposed method, each dc-link voltage of the three-level inverter can be asymmetrically regulated. When PV modules are split into two and each split module is connected to the respective dc-link capacitors of the inverter, the asymmetric control can be helpful because separate MPPTs are possible. The effectiveness of the proposed method was examined through experiments with a T-type three-level inverter, where each dc-link capacitor was supplied by a PV simulator emulating two separate PV modules under different shading conditions. [ABSTRACT FROM AUTHOR]

An auxiliary capacitor-based balancing approach is adopted in this paper to equalize the dc-link capacitor voltages of a diode-clamped multilevel converter (DCMC). Four balancing circuits, including the generalized, one-level-capacitor, one-capacitor, and simplified one-capacitor-based configurations are discussed for a five-level DCMC system. These configurations are different in connection of the auxiliary circuits and numbers of the capacitors and switches, but they work on the same principle called ping-pong operation by utilizing the auxiliary capacitor as an equalizer between the capacitors of different voltages. The unbalance phenomenon, ping-pong principle, circuit configurations, and their switching schemes are analyzed, respectively. The superiorities of the proposed approach include balancing operation regardless of load power factor and modulation index, control simplicity, and independence from main circuits when compared to the traditional approaches. Simulations and experimental results verified the performances using the proposed balancing circuits and control strategies. [ABSTRACT FROM AUTHOR]

This paper investigates the use of adaptive repetitive and resonant control approaches for the control of a single-phase hybrid cascaded multilevel converter designed to interface with power grids of highly distorted voltage waveform. The proposed repetitive/resonant control (RPC/RSC) is used for the extraction of clean phase angle, frequency, and magnitude information of the fundamental grid voltage together with the control of the converter current and mitigation of current harmonics under distorted grid voltage and variable frequency. The RPC time period and the RSC resonant frequency are updated adaptively using the estimated grid frequency while interpolation is used to preserve the RPC rejection capability under noninteger number of time steps per period. Detailed modeling and experimental investigation of the proposed control scheme are carried out. [ABSTRACT FROM AUTHOR]

This paper proposes a new family of three-switch three-state single-phase Z-source inverters (TSTS-ZSIs) that can be classified into two groups, boost-based TSTS-ZSI and buck-boost-based TSTS-ZSI, according to the step-up circuit. All of the topologies have the merits of buck-boost capability and low voltage stress, and some of them have the feature of dual grounding. In addition, the step-up in dc side and inversion in ac side is completely decoupled in the proposed topologies. In terms of a linear voltage gain, the conventional linear control methods can be used, which makes the control system very simple. The operating principles of the two types of topologies are described, respectively, and the comprehensive comparison between them is provided. Finally, the theoretical analysis and comparison of the proposed topologies are verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a sensorless control scheme for a surface-mounted permanent-magnet synchronous machine (PMSM) based on the back-electromotive force voltage. It is a direct estimation method, meaning the rotor position is directly calculated based on stator-current measurements and the stator voltage commands as well as on the knowledge of stator resistance and stator inductance, but without the use of an asymptotic observer or integration of speed, respectively, flux. The estimated angle is filtered and used directly for sensorless field-oriented current and torque control. Analogously, the rotor speed is also directly calculated and used for sensorless speed control. A polar stator-current coordinate representation is chosen for the stator currents such that the scheme is easily extendable with filters to cope with measurement noise. A comparison to a reduced-order observer highlights the robustness advantage. Experimental results confirm good dynamical performance, even at low speeds. [ABSTRACT FROM AUTHOR]

Single-phase three-level neutral point clamped (NPC) converters are widely applied in high-speed railway electrical traction drive systems. A significant problem related to the single-phase three-level NPC converters is the fluctuation of the neutral-point voltage. In this paper, a capacitor voltage balancing technique is proposed that injects an offset voltage into the sinusoidal modulating signals of the conventional carrier-based pulsewidth modulation (CBPWM) method. Furthermore, when the injected offset voltage is maximized, it cannot only balance the dc-link capacitors voltages, but also reduce switching losses. Theoretical analysis has shown that both methods can control the neutral point voltage effectively, but the neutral point voltage controller in the CBPWM with maximum offset voltage injection (CBPWM-MOVI) has a faster dynamic response. It was observed that the high-order harmonics frequencies of the line current are centered around the twice switching frequency in the CBPWM with the offset voltage injection (CBPWM-OVI) but are centered around the switching frequency in the CBPWM-MOVI. And also, the CBPWM-MOVI has switching commutations number at least 25% below that of the CBPWM-OVI in one modulating signal period. The performances of the two strategies were verified by simulation and experimental tests. [ABSTRACT FROM AUTHOR]

A current source inverter (CSI) requires a capacitor filter for the commutation of switching device as well as for attenuating switching harmonics. Hence, the CSI-fed ac machine has a second-order system in the continuous time domain. This paper presents a design methodology for the closed-loop current controller of the CSI-fed ac machine drive system. A multiloop current controller design using a pole/zero cancellation method is employed with a transfer function matrix. To decouple the cross-coupling terms which cause mutual interferences between the d- and q-axes in the synchronous reference frame, two types of controller are proposed and implemented using different decoupling method. Additionally, active damping methods are incorporated to enhance the stability of the system. A stability analysis in discrete-time domain is investigated to verify the feasibility of the proposed closed-loop current controller. To evaluate the effectiveness of the proposed current controller, computer simulations and experimental tests were performed and the results are discussed. [ABSTRACT FROM AUTHOR]

In this paper, a beatless control that enables unity input power factor for the single-pulse operation in the matrix converter is proposed. The proposed method controls the output voltage to synchronize with the output current in terms of voltage–time product during the high output frequency operation. Following the proposed synchronous control method, the beat current is suppressed by approximately 1% at output frequency 1432 Hz. The experimental results also demonstrate that the input current waveform achieves sinusoidal waveform with unity power factor. In addition, the voltage transfer ratio of the matrix converter is improved from 0.866 to 0.955 in the high output frequency region. The maximum efficiency 96.4% is achieved at a 1.34-kW RL load. [ABSTRACT FROM AUTHOR]

Low system voltage in traction networks, mainly caused by active power absorption of locomotives, adversely affects the performance of the locomotives and also the power transmission capability of the catenary line. This paper introduces a voltage support scheme to compensate for the adverse effects of low system voltage. The proposed method is based on the injection of reactive power through the current-controlled line-side converter of locomotives. Comparing the catenary voltage with its reference value, the error is fed to a high-order controller. The controller generates the quadrature (q)-axis reference value of a current control strategy, which is responsible for the reactive power injection. To design the high-order controller, adopting the nonparametric models of the system at various locations, an optimization-based loop-shaping approach is used. The loop shaping guarantees the stability and the acceptable performance of the closed-loop system for various locomotive positions in the network. The performance of the proposed control strategy is evaluated based on simulation results in MATLAB/PLECS environment. Moreover, implementing a scaled-down laboratory setup, the performance of the proposed scheme is experimentally evaluated. [ABSTRACT FROM AUTHOR]

An essential requirement for a high-performance dual active bridge (DAB) dc-dc converter is to rapidly and accurately maintain its DC output voltage under all operating conditions. This paper uses a novel harmonic modeling strategy to create a linearized dynamic model of a DAB that accurately identifies its transient response to both a reference voltage change and an output load-current change. Using this model, a feedforward compensation strategy is presented that significantly improves the DAB's transient response to an output load change. The transient performance is then further enhanced by analytically compensating for the nonlinear dead-time distortion that is caused by the converter switching processes. The resultant control system achieves rapid and precise output voltage regulation for both reference voltage and output load changes. The theoretical analysis is confirmed by both matching simulation and experimental investigations. [ABSTRACT FROM AUTHOR]

This paper presents an improved full-bridge three-level (IFBTL) dc/dc converter for a wind turbine in a dc grid by inserting a passive filter into the dc/dc converter to improve the performance of the converter. The passive filter can effectively reduce the voltage stress of the medium frequency transformer in the IFBTL dc/dc converter. A modulation strategy, including two operation modes, is proposed for the IFBTL dc/dc converter. Then, a voltage balancing control strategy is proposed for the IFBTL dc/dc converter. Furthermore, the control of the wind turbine based on the IFBTL dc/dc converter in a dc-grid system is presented. Finally, a small-scale IFBTL dc/dc converter prototype was built and tested in the laboratory, and the results verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents an improved variable-band hysteresis current controller for a two-level three-phase voltage source inverter (VSI). The controller takes the average voltages of the phase-leg switched outputs as an approximation to the load back-EMF voltages, and uses these results to vary the hysteresis bands so as to maintain constant phase-leg switching frequencies. The switching frequency control process is then further refined by fine tuning the hysteresis band variations to synchronize the zero crossings of the phase-leg current errors with a fixed reference clock so as to achieve a nearest space vector switching sequence, which further ensures that the switched output spectrum has been optimized. Finally, a technique is proposed to replace the third phase-leg current regulator with a fixed-frequency open-loop pulse-width modulator, where its commanded reference is generated from the average switched output voltages of the other two phase legs. This avoids the hazard of the three independent hysteresis current regulators adversely interacting with each other in a conventional system, resulting from an overconstrained control problem with only two degrees of freedom. Additionally, this approach allows the linear modulation range to be increased by adding a common-mode third-harmonic component to the third phase-leg reference command signal. [ABSTRACT FROM AUTHOR]

The deployment of a single-phase, multilevel flying capacitor converter as a 1.5-kW active rectifier is discussed in this paper. The challenges associated with this approach include providing unity power factor, regulating the dc output voltage, and maintaining balanced voltages across the flying capacitors. In such applications, the input current is usually controlled via a reference-frame-based control approach. Here, a different approach, which is based on the hysteresis current-mode control scheme, is applied. The simulation and experimental results for both reference-frame-based and hysteresis-based controllers are presented and compared. The results show that the hysteresis-based method exhibits a tighter regulation of the input current and offers easier hardware implementation. [ABSTRACT FROM AUTHOR]

This paper presents a dead-beat predictive direct power control (DPC) strategy and its improved voltage-vector sequences for reversible three-phase grid-connected voltage-source converters (VSCs). The instantaneous variation rates of active and reactive powers, by applying each converter voltage vector in 12 different sectors, are deduced and analyzed. Based on the power variation rates, it is found that the values of the predicted duration times for the two conventional active converter voltage vectors are less than zero when the grid-connected VSC operates as either a rectifier or an inverter. In order to solve this issue, two new alternative vector sequences are proposed and compared. Experimental results on a 1.5 kW reversible grid-connected VSC system are presented to validate the feasibility of the proposed voltage-vector sequences on the dead-beat predictive DPC strategy. [ABSTRACT FROM AUTHOR]

Nowadays, the majority of the photovoltaic (PV) power sources are connected to the public grid. One of the main connection problems occurs when voltage sags appear in the grid due to short circuits, lightning, etc. International standards regulate the grid connection of PV systems, forcing the source to remain connected during short-time grid-voltage faults. As a consequence, during the voltage sag, the source should operate with increasing converter currents to maintain the injection of the generated power. This abnormal operation may result in nondesired system disconnections due to overcurrents. This paper proposes a controller for a PV three-phase inverter that ensures minimum peak values in the grid-injected currents, as compared with conventional controllers. From the system analysis, a design method is presented in order to set the parameters of the control scheme. Selected experimental results are reported in order to validate the effectiveness of the proposed control. [ABSTRACT FROM PUBLISHER]

A new type of Class E rectifier that can regulate the output voltage or power is proposed. The proposed rectifier is composed of a conventional Class E zero-voltage-switching rectifier and the controlled shunt capacitor whose capacitance is variable according to the state of the active switches. With turning the active switches ON or OFF, the shunt capacitance of the rectifier can be changed, which enables the rectifier to vary the output voltage or power. This paper presents an analysis, experimental results, and simulation results in the steady state. [ABSTRACT FROM AUTHOR]

The burst-mode control is generally used to regulate the output voltage of the ac/dc adapter under either lighter no-load condition. Although the burst-mode control reduces the switching loss, the control-IC and the feedback circuit at the output side still consume a large amount of power. In order to further reduce the power consumption at no-load condition, a no-load power reduction technique for ac/dc adapters is proposed in this paper. At first, the proposed technique employs a control-IC ON/OFF scheme to reduce the power consumption of the control-IC while the gate signal of primary power switch is idle. In addition, an out-put voltage drop scheme is adopted to cut down on the loss of the feedback circuit because the output voltage of the ac/dc adapter is not required to be regulated when the ac/dc adapter is disconnected from the load system. Thus, the proposed technique can greatly reduce the no-load power consumption below 30 mW. To verify the validity of the proposed technique, loss analysis and experimental results of 65 W/17.5 V ac/dc adapter are presented. [ABSTRACT FROM AUTHOR]

Conventional hysteresis current controllers have the disadvantage of a variable switching frequency. This paper presents a novel hysteresis current control method which uses the adjacent current error zero-crossing time to calculate the upper/lower hysteresis bandwidth after the measured half current error period. This strategy makes the algorithm independent of load parameters and thus it can achieve a stable switching frequency. An improved switching scheme has been successfully applied to a single-phase three-level H-bridge voltage source inverter driving a vibration test bench based on the novel hysteresis current. It can select appropriate switching states to overcome dead-time effects without dead-time compensation according to the relation of the current switching state, the current error, and the upper/lower hysteresis bandwidth. Field-programmable gate array has enough computational power to allow multiple sampling within a current error period and logic control power to implement state machine transitions. The simulation and experimental results are given to demonstrate the validity and features of the novel hysteresis current controller with the improved switching scheme. [ABSTRACT FROM AUTHOR]

This paper presents the positive feed-forward control (PFFC) scheme associated with the average current-mode control (ACMC) scheme for the distributed power conversion system with the multiple voltage sources of different power ratings to protect individual voltage sources from the chain reaction of the undervoltage lockout in order not to cause system voltage collapse. The ACMC scheme has the inherent function of the negative feed-forward control (NFFC) to increase the input current of the converter by increasing the control duty cycle of the converter while the source voltage decreases. However, the undervoltage lockout protection of the employed source or converter can be activated if the source voltage drops below the set threshold value. Therefore, the PFFC+ACMC scheme is proposed to reduce the control duty cycle of the employed converter once the source voltage is less than the set threshold value to avoid system voltage collapse. The input current of the individual converter module is regulated by the proposed PFFC+ACMC mechanism in correspondence with the level of the sensed input terminal voltage. Finally, the prototype circuit of a simple interleaved buck-type converter system is built to validate the proposed PFFC+ACMC function. [ABSTRACT FROM AUTHOR]

In this paper, a digital adaptive slope control technique is presented to improve the dynamic response of a current-programmed mode (CPM) buck converter employing a low-cost auxiliary phase. The advantages and drawbacks of the existing analog and digital nonlinear control techniques are discussed in detail. The benefits of the proposed control scheme include superior voltage drop and settling time, adaptive slope control to accommodate a range of auxiliary phase inductor values, and on-line calibration to compensate for tolerance in the main phase and auxiliary phase inductance. The proposed technique is experimentally verified on a 500-kHz, 10-2.5 V CPM buck converter prototype. Charge balancing and optimal transient response are achieved for a range of positive and negative load steps. Operating the auxiliary phase under light-load condition is also demonstrated to further justify the use of the auxiliary phase. Compared to a representative single-phase converter, the proposed system not only has over two times improvement on the voltage drop and three times lower steady-state voltage ripple but also achieves approximately 2% heavy-load and 10% light-load efficiency improvement. The impact of the auxiliary phase operation on the converter's dynamic efficiency is also evaluated at different load step amplitudes and frequencies. [ABSTRACT FROM AUTHOR]

Inverter-fed motor drive systems are widely used in industrial applications because of their energy efficiency and flexible control of machinery using maintenance-free induction motors. As switching inverters generate fast-switching voltage pulses, the transmission-line effects of the motor cable and motor stator windings become significant, and may lead to a doubling of the supply voltage to the motor and cable, overvoltage inside the motor windings, and an increase in the common-mode current. Such phenomena cause premature failure of the motor and cable insulation. A typical protective measure is the use of a passive filter to reduce the voltage surges and alter the rise time of the voltage pulses at the motor terminals. However, most passive filters have the drawbacks of bulky size and high power loss. This paper presents an active terminal filter that can perform the same functions as the passive filters with low power dissipation. An experimental filter has been built and evaluated on a 1-hp three-phase motor drive system with different motor cable lengths. A comparative study into the performance among the commonly used RLC filter and RC filter, and the proposed filter is provided. [ABSTRACT FROM AUTHOR]

An energy system powered by a low-voltage fuel cell (FC) is conditioned to generate higher--voltage regulated ac voltage. The power conditioning system typically requires two power stages: a boost stage and an inversion stage. In this paper, the buck--boost inverter topology that achieves both boosting and inversion functions in a single stage is used as a building block to develop a single-phase FC-based energy system that offers high conversion efficiency, low-cost and compactness. The proposed system incorporates a backup energy storage unit to support the slow dynamics of the FC. The single-phase buck--boost inverter is voltage-mode controlled and the backup unit is current-mode controlled. The low-frequency current ripple is supplied by the backup unit that minimizes the detrimental effects of such ripple being drawn directly from the FC itself. Experimental results from a 1-kW prototype operating at 20 kHz are presented to validate the analysis and performance of the proposed system. [ABSTRACT FROM AUTHOR]

Australian Grid Code has recently enforced stringent regulations on the transient response of large wind power plants (WPPs). The new grid code requires wind generators to ride-through severe low- and high-voltage conditions, provides reactive power support during the fault period, and exhibits fast power recovery after the supply voltage restoration. This paper proposes a new control scheme for doubly fed induction generator (DFIG)-based WPPs to fulfill these requirements in one inclusive approach. New design strategies for the outer power control loops of DFIG are suggested and their corresponding P-Q capability curves are rigorously studied. It is shown that safely overloaded converters can enhance the reactive power capability of DFIGs during the fault periods. Moreover, for the inner current control loops, the conventional PI current regulators are replaced with enhanced hysteresis-based current regulators. This current regulator, with very fast transient response, increases low- and high-voltage ride-through capabilities of the DFIG, as requested by the Australian Grid Code. Finally, time-domain simulation studies are conducted to evaluate the capability of the proposed control scheme to fulfill the Australian regulations and examine its positive impacts on the transient response of the adjacent fixed-speed WPP. [ABSTRACT FROM AUTHOR]

This paper deals with a cascaded multilevel converter which has multiple dc voltage values (multivoltage cascade converter or hybrid multilevel converter) for a 6.6-kV transformerless distribution static synchronous compensator (D-STATCOM). A control method is proposed to realize dc voltage regulation of series-connected multiple cells in the STATCOM operation, making it possible to remove dc sources from all H-bridge cells. The simplified configuration without the dc sources makes the STATCOM small and lightweight. A downscaled STATCOM model rated at 220 V and 10 kVA is built and a series of verification tests is executed. Theoretical analysis and experimental results prove the stable operating performance of the proposed method in steady states and transient states. [ABSTRACT FROM AUTHOR]

In this paper, the concept of the adaptive current source drivers (CSDs) is proposed for the high-frequency synchronous buck converters. Compared to the previous CSD circuits, the adaptive CSD can achieve adjustable drive current and drive voltage according to different load condition. The benefit is that higher drive current and voltage lead to lower switching loss and conduction loss when the load current increases. Therefore, the adaptive CSD is able to realize optimal design to reduce the switching loss, the gate drive loss, and the conduction loss in a wide load range. It should be noted that the adaptive concept is suitable for both the continuous and discontinuous CSDs regardless the drive circuit topologies. Through investigating the CSD circuits, one simple method to achieve the adaptive drive current based on the adaptive voltage is proposed. A 12 V input, 1.3 V output, and 1-MHz synchronous buck converter with the continuous and discontinuous CSDs was built, respectively, to verify the advantages of the proposed adaptive concept and efficiency improvement. [ABSTRACT FROM AUTHOR]

This paper presents enhanced control strategies for doubly fed induction generator (DFIG)-based wind power generation systems under distorted grid voltage conditions. The mathematical model of DFIG, in view of the fifth- and seventh-order components of grid voltage harmonics, is proposed and analyzed in detail. Based on the analytical model, further studies are conducted on the distortions of stator/rotor currents and the oscillations in the stator active/reactive powers as well as the electromagnetic torque, where the impact of DFIG's load conditions is considered. Meanwhile, alternative rotor current references are calculated to enhance the uninterruptable operation capability of the wind-turbine-driven DFIG systems under distorted grid conditions. An improved software PLL is designed, which is capable of accurately and rapidly tracking the frequency and phase angle of the fundamental grid voltage under distorted grid conditions. A proportional integral plus resonant (PI-R) current controller in the synchronously rotating (dq) reference frame is employed to simultaneously regulate the fundamental and harmonic components of rotor currents without any sequential component decomposition. Experiment results on a 3-kW DFIG prototype demonstrate the correctness of the analytical results and the effectiveness of the software PLL and PI-R current controller when the grid voltage is distorted. [ABSTRACT FROM AUTHOR]

This paper proposes an active technique to reconstruct and balance the phase currents in multiphase dc-dc converters implementing both of voltage- and current-mode controls. Only one current sensor at the dc link is required to measure and reconstruct the phase currents. Multiple current samples in the pulsewidth modulation switching period are synchronized with the carrier waveforms to actively reconstruct the phase currents using a simple active balancing algorithm that is implemented in a digital controller. The proposed technique improves system performance, stability, and efficiency, and prevents inductor saturation. A 5-kW four-phase dc-dc converter prototype for battery charging application is built to experimentally verify the proposed algorithm. [ABSTRACT FROM AUTHOR]

Renewable power systems as distributed generation units often experience big changes in the inverter input voltage due to fluctuations of energy resources. Often, a front-end boost converter is added to step up the dc voltage when the energy resources are at a weak point. However, when a very high boost gain is demanded, the duty cycle may come to its extreme, and large duty cycles causes serious reverse-recovery problems. This paper proposes a novel single-stage boost-type inverter with coupled inductor. By introducing impedance network, including coupled inductor, into the three-phase bridge inverter, and adjusting the previously forbidden shoot-through zero state, the converter can realize a high boost gain and output a stable ac voltage. The single-stage operation of the converter may lead to improved reliability and higher efficiency. Theoretical analysis, simulation, and experimental results are presented to verify good performance. [ABSTRACT FROM AUTHOR]

Conventional dynamic voltage restorers (DVRs) are connected to the power grid through power-frequency transformers. These bulky and costly transformers cause voltage drop and power losses. In this paper, a high-frequency-link dynamic voltage restorer (HFL-DVR) is proposed based on transformer-isolated topologies. This topology facilitates independent operation conditions for each phase in a three-phase system. It enjoys relatively low cost, low losses, and small size. Also, it is free from transformer inrush currents. Small-signal ac equivalent circuit for the power stage including HFL-DVR is derived based on an averaged modeling approach. Transfer functions are obtained to study the effect of inputs such as dc-link voltage, grid voltage, and the load current on the output of HFL-DVR. In order to obtain acceptable properties such as transient overshoot, setting time, and steady-state error, a PID controller is added to the system. This shows that the effect of disturbances on the output of HFL-DVR can be reduced. The experimental results are obtained from a 220V/50Hz HFL-DVR setup. The simulation and experimental results have been compared to verify theoretical aspect of the proposed DVR for both symmetrical and asymmetrical voltage sag conditions. [ABSTRACT FROM AUTHOR]

A multilevel H-bridge StatCom inherently contains redundancy in the available switching states. This paper develops a variation on the typical model predictive control scheme which is able to exploit this redundancy to simultaneously balance the H-bridge capacitor voltages, provide excellent current reference tracking, and minimize converter switching losses. The scheme consists of a dead-beat current controller that has been integrated with heuristic models of the voltage balancing and switching loss characteristics. The integration of a pulsewidth modulation scheme is also described. Simulation and experimental results are presented that confirm the correct operation of the control and modulation strategies. Comparison with traditional control and modulation schemes is provided in terms of the key performance indicators associated with multilevel H-bridge StatComs. [ABSTRACT FROM AUTHOR]