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This paper describes a dc-link voltage control method of a single-phase back-to-back cascaded H-bridge inverter (SBCI) for a medium-voltage motor drive system. The main advantage of the SBCI topology over the conventional regenerative cascaded H-bridge topology with a three-phase active front-end (AFE) is a simple system structure, which is composed of an input transformer, a power cell, a current sensor, etc. However, the challenging points of the SBCI are larger voltage ripple in the dc-link capacitor and imbalance of dc-link voltages of each phase. The asymmetric dc-link voltage of each power cells could cause unstable operation such as over-modulation due to the lack of the dc-link voltage of a particular phase and result in over-voltage or under-voltage faults. In this paper, the control strategy of the dc-link voltage for the SBCI that uses the negative-sequence voltage of the converter is described. The proposed control method is verified with a computer simulation whose target is a 6.6-kV–1.25-MW medium-voltage drive system. Also, through the experimental setup with the prototype SBCI whose power rating is 16.2 kVA, the dc-link voltage of each AFE has been controlled within a 0.5% error of its reference value at the full load. [ABSTRACT FROM AUTHOR]

This paper proposes a capacitor voltage regulation method for the dual converter with a floating bridge for aerospace applications. This topology has previously been reported, but with a constrained voltage utilization factor due to the need for capacitor voltage regulations. In this paper, the effect of switching states on the voltage variation of capacitor is quantitatively modeled and an enhanced space vector modulation scheme with current feedback is proposed to achieve an active control of the floating capacitor voltages. This proposed method also allows further exploitation and utilization of converter voltage. The relationship between the allowed modulation index of dual converter and load power factor is obtained and expressed using a fitted polynomial equation. The advantages of the proposed method include boosted voltage utilization and superior performance in term of capacitor voltage balance. These advantages have been proven through simulation and experimental results on RL loads as well as with an open-end winding induction motor. The proposed modulation scheme can boost the converter voltage utilization by at least 10% while achieving full four-level operation. More importantly, the higher available voltage allows extending the constant torque region of the motor, the further beginning of field weakening operation could be postponed. [ABSTRACT FROM AUTHOR]

A trinary multilevel converter uses a few heterogeneous H-bridge submodules (SMs) to synthesize an output voltage with multiple levels. Two major limitations of this converter are that it needs multiple dc sources and it cannot operate under pulsewidth modulation (PWM). This paper addresses these limitations by adding a low-voltage H-bridge SM to this converter and proposing a new switching algorithm. The resulting PWM-based asymmetric cascaded H-bridge converter uses only one dc source and synthesizes a high-quality output voltage. This improved converter can be a potential choice for real and reactive power support in power system applications. This paper also proposes methods for stability analysis and design of this converter. Experimental case studies evaluate the performance of the proposed converter for both standalone and grid-connected modes of operation. [ABSTRACT FROM AUTHOR]

Achieving high efficiency and high power density features of intermediate bus converter (IBC) in data center application is very critical. This paper proposes a nonisolated switched-tank dc–dc converter (STC) to meet the high requirement of IBC. The proposed STC has fixed voltage conversion ratio. Theoretical analysis provides the guideline for designing resonant tank and nonresonant tank as well as selecting proper deadtime for the proposed circuit. With resonant operation feature of the proposed circuit, zero current switching is realized on all switching devices to help the high-efficiency operation of the proposed converter. Through the proposed design methodology in this paper, power loss on switching devices and planar inductors can be minimized. In addition, detailed power loss analysis and breakdown provide hints for further efficiency improvement. Simulation has been performed to validate the operating principle of the proposed STC. A designed 6x STC (450 W nominal/600 W maximum) based on eGaNFETs is demonstrated. With 54 V typical input voltage, the output of the 6x STC is 9 V. The GaN-based prototype achieves a peak efficiency of 98.55%. Also, it achieves 97.18% efficiency and 750 W/in3 power density at 450 W. [ABSTRACT FROM AUTHOR]

This paper presents a study of the losses in the integrated buck–flyback converter (IBFC) used as high-power-factor LED driver. The aim of the study is to investigate the possibilities of increasing the efficiency of the IBFC converter. The procedure of the improvement is done by obtaining the equations of the current through each component in terms of converter parameters. The current is found in an average value or rms value, depending on the type of the parasitic component, whether it is modeled by a parasitic forward voltage source or by a parasitic resistance, respectively. Using these equations and the parasitic model, the losses of each element of the converter are estimated. This paper proposes a technique to increase the efficiency of the IBFC by redesigning the converter parameters. Furthermore, this paper presents a case of study with a step-by-step efficiency enhancement process of an existing driver. The driver is operating under universal input conditions, and 38 V output, supplying an LED luminary of 26.5 W. The new design shows an improvement of the efficiency from 82% in the old design to 89% in the proposed one. Moreover, the new design shows an improvement in the power factor and the THD and a 50% reduction in the output current ripple. Furthermore, a reduction in the number of components has been achieved, as it is found by the analysis that by adjusting the converter parameters, one diode can be removed. Finally, the presented methodology is explained in detail so that it can easily be applied to other dc–dc converters. [ABSTRACT FROM AUTHOR]

Dual active bridge (DAB) based converters offer the benefit of smaller volume due to high-frequency isolation and controllability of active power flow, making them attractive for various applications, such as renewable energy generation, plug-in hybrid vehicles, and distribution systems. This paper presents a novel converter topology along with a modulation strategy for a DAB-based three-phase ac to dc converter. The major benefits are single-stage conversion, no unreliable intermediate dc-link capacitor, reduced number of switches, i.e., only two active switches on the ac side, simple control scheme, open-loop unity power factor operation, bidirectional power flow, and partial soft-switching. This paper presents the analysis of all the operating modes of the converter, resulting in the analytical estimation of power transfer and rms winding current and investigation of soft-switching conditions for the power devices. Simulation and experimental results have been presented to demonstrate the advantages of the proposed technique and accuracy of the analysis.1 [ABSTRACT FROM AUTHOR]

This paper discusses dynamic behavior of a dual-active-bridge (DAB) dc–dc converter. Conventional phase-shift control methods for the DAB converter may cause dc offsets in both inductor current and transformer magnetizing current in transient states. The dc offset in the inductor current would introduce an excessive peak current through the switching devices. The dc offset in the magnetizing current may induce magnetic-flux saturation. Conventional methods simultaneously turn on and off the diagonal switches in each H-bridge converter and produce a square-wave voltage with a 50% duty ratio. In contrast, the proposed method in this paper independently controls each switch to modify the duty ratio in transient states. This paper clearly derives the requirements of each switch to eliminate the dc offsets in both currents with a settling time shorter than half the switching period. Experimental results using a 5-kW 20-kHz system verify the validity of the proposed control method, which is effective not only in a single step change, but also in a continuous change in the phase-shift reference. [ABSTRACT FROM AUTHOR]

This paper proposes a new bidirectional resonant dc–dc converter suitable for wide voltage gain range applications (e.g., energy storage systems). The proposed converter overcomes the narrow voltage gain range of conventional resonant dc–dc converters, and meanwhile achieves high efficiency throughout the wide range of operation voltage. It is achieved by configuring a full-bridge mode and a half-bridge mode operation during each switching cycle. A fixed-frequency phase-shift control scheme is proposed and the normalized voltage gain can be always from 0.5 to 1, regardless of the load. The transformer root-mean-square (rms) currents in both the forward and reverse power flow directions have a small variation with respect to the voltage gain, which is beneficial to the conduction losses reduction throughout a wide voltage range. Moreover, the power devices are soft-switched for minimum switching losses. The operation principles and characteristics of the proposed converter are firstly analyzed in this paper. Then the analytical solutions for the voltage gain, soft-switching, and rms currents are derived, which facilitates the parameters design and optimization. Finally, the proposed topology and analysis are verified with experimental results obtained from a 1-kW converter prototype. [ABSTRACT FROM PUBLISHER]

An extended-duty-ratio (EDR) boost converter is studied extensively in this paper for high voltage gain applications with a wide input (and/or output) voltage range. The EDR is a unique combination of an interleaved, multiphase boost converter and switched capacitor configuration that achieves high voltage gain with significantly lower switch voltage stress and switching losses compared to conventional high-gain solutions. Most of the switches in the multiphase EDR experience only a fixed fraction of the output voltage ($1/M, 2/M$ , etc., where $M$ is the number of phases). Through extensive analysis over a wide operating range, it is shown here that the EDR boost converter has inherent current sharing among the phases only in a limited range of duty ratio— $(M-1)/M \leq D \leq 1$. As the duty ratio reduces beyond this range as required in wide input voltage applications, inherent current sharing property is lost. In this paper, techniques to ensure current sharing under all operating zones without requiring current sensors are presented. Instead of having equal duty ratio for each phase, it is adjusted for each phase according to the operating region of the converter. Extensive analysis is presented to derive the required duty ratio changes for the different phases. The proposed concept is validated with experimental results from a 250 W, 3-phase EDR boost, and GaN-based hardware prototype. [ABSTRACT FROM AUTHOR]

A new static synchronous compensator (STATCOM) based on the diode-clamped modular multilevel converter (DCM2 C) is proposed in this paper. In this converter topology, the capacitor voltage is clamped by using a low power rating diode in each submodule. The quantity of voltage sensors is significantly reduced and is free from the number of voltage levels. Furthermore, the voltage balancing control method becomes very simple and the capacitor voltage balance speed is fast. Based on the structure of modular multilevel converter, the DCM2C-STATCOM has the capability of Var compensation and negative-sequence current compensation. The topology characteristics and compensation control method of DCM2C-STATCOM are investigated in this paper. Experimental results obtained from a laboratory prototype validate that the capacitor voltage of the proposed DCM2C-STATCOM can be well balanced and the Var and negative-sequence current compensations are effective. [ABSTRACT FROM AUTHOR]

In the no-load condition, LLC converter usually fails to regulate its output voltage although it operates at a high switching frequency. Till now, it is hard to obtain the exact relationship between design parameters and the maximum switching frequency for no-load regulation capability. In this paper, a specific criterion for no-load regulation of LLC converter is provided, without using active components or other modulation schemes. By analyzing the macroscopic switching period and microscopic switching transition in the no-load condition, it is shown that not only the peaking resonant current during the switching transition, but also the resonant tank design affect the no-load regulation of the LLC converter, which affects the no-load regulation capability. Furthermore, the relationship among design parameters is analyzed and the design guideline is also provided to achieve no-load regulation at the specified maximum switching frequency. To verify the effectiveness of the proposed design, 400 V input and 50 V/200 W output prototype is built and tested. [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]

In this paper, a systematic and analytical study of non-isolated topologies belonging to the family of reduced redundant power processing (R2P2) converters is presented. Based on this study, all the non-isolated R2P2 topologies that can be implemented in reality are derived. Detailed examples clarify all possible cases of this analysis. In addition to this, the voltage ratio and the efficiency for each one of the R2P2 configurations are calculated, being further illustrated with examples. A comparison among configurations is also discussed with criteria the high step-up voltage gain and efficiency, aiming for high-power applications. One of these R2P2 converters is selected for further examination, as the most suitable for such applications. The theoretical analysis, as well as the calculations of the step-up voltage ratio and efficiency of the selected converter, is compared to experimental results conducted on a 2-kW laboratory prototype designed to operate in various step-up voltage ratios and in a high-power range, proving the effectiveness of the proposed investigation. [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]

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, a new structure for symmetric and cascade multilevel converter is presented. This structure requires the least power electronic components, gate driver circuits, power diode, and dc voltage source. The number of output levels is high. Reduction of the number of power electronic switches against voltage levels is an important factor in multilevel converters due to safety in switches, circuit size, cost, installation area, and complexity in control. To maximize the number of output level in the proposed optimized structure in order to attain different goals, such as reduction of stress on switches, the result of comparing the proposed structure and other structures present. The proposed method is robust against the switching faults in multilevel converter for dc source and the equipment. The simulation and experimental results presented in this paper show the performance of the proposed method. [ABSTRACT FROM AUTHOR]

The large number of semiconductors typically implemented in multilevel converters generates large stray inductances in their commutation loops. As a consequence, high-voltage overshoots appear in the semiconductors during commutation which may limit the operation of the converter. The paper analyzes these overvoltages in the five-level active neutral-point-clamped (5L­ANPC) converter, one of the most popular five level converters and employed by ABB in its ACS­2000 drive. Experimental results show overvoltages almost three times higher than those corresponding to a two-level converter. In order to overcome this problem, the paper presents a new 5L­ANPC with the same characteristics (number of semiconductors, output waveform, switching frequency, efficiency, etc.), but with smaller overvoltages. This is achieved by adding some small capacitors to the busbar that behave like lossless snubbers but with a much simpler implementation. The experimental results illustrate the working principle of these capacitors and demonstrate the reduction of the overvoltages. As a result, the new converter can reach a higher output current or speed-up the commutations reducing, therefore, the losses and increasing the efficiency compared with the previous 5L­ANPC. [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]

Magnetically coupled impedance-source (MCIS) networks are recently introduced impedance networks intended for various high-boost applications. It employs coupled magnetic in the circuit to achieve higher voltage gain. Various MCIS networks have been proposed in the literature for myriad applications; however, due to effective role of system modeling in the closed-loop controller design, this paper is allocated to small-signal modeling and analysis of MCIS converters. The modeling is performed by means of the circuit averaging and averaged switch technique. A generalized small-signal derivation is demonstrated for pulse width modulation (PWM) MCIS converters and it is shown that the derived transfer functions can simply be applied to Y-source, Γ-source, and T-source impedance networks. Various transfer functions for capacitor voltage, output voltage, magnetizing current, input and output impedance are derived and have been validated through frequency and dynamic responses of computer simulation results. In addition, a comprehensive analysis has been done for all mentioned PWM MCIS converters regarding their circuit parameters. Furthermore, the effect of considering the equivalent series resistances of capacitor and inductor on the stability margin of MCIS converters is revealed in this paper. Finally, in order to validate the derived transfer functions and to consolidate the perfumed analysis, experimental results are presented for all mentioned MCIS converters. [ABSTRACT FROM PUBLISHER]

In this paper, a new multi-input multi-output (MIMO) dc–dc converter with high step-up capability is proposed for wide power ranges. Also, in order to increase each output voltage, diode–capacitor voltage multiplier (VM) stages are utilized in the proposed converter. The number of input stages, output stages, and VM stages are arbitrary and dependent on design conditions. At first, the general structure of proposed MIMO converter is presented. Then, in order to explain the converter operation, we walk through the design of a 1-kW four-input two-output example, including loss and efficiency calculations. We validate the design with a prototype that matches efficiency calculations. [ABSTRACT FROM AUTHOR]

When fast voltage control is used in a power factor control, the ripple of the dc link causes current harmonics. This paper proposes a method to reduce the harmonic content of a fast voltage loop in a power factor correction, which can both produce low distortion during steady-state operation and fast recovery from a load transient. The performance is achieved by using a Takagi–Sugeno-type nonlinear controller for dc-link voltage control. The proposed nonlinear control is compared with linear proportional–integral (PI) control, which is tuned to meet the standardized regulations for the harmonic content in a 3-kW single phase power supply. The results show that the presented nonlinear voltage controller can maintain the dynamic performance of the linear control with reduced current harmonics. It is also shown that the used nonlinear control method requires only marginally more complex control algorithm compared to commonly used linear PI control. [ABSTRACT FROM AUTHOR]

This paper presents a new reconfiguration module for asymmetrical multilevel inverters in which the capacitors are used as the dc links to create the levels for staircase waveforms. This configuration of the multilevel converter makes a reduction in dc sources. On the other hand, it is possible to generate 13 levels with lower dc sources. The proposed module of the multilevel inverter generates 13 levels with two unequal dc sources (2VDC and 1VDC). It also involves two chargeable capacitors and 14 semiconductor switches. The capacitors are self-charging without any extra circuit. The lower number of components makes it desirable to be used in wide range of applications. The module is schematized as two back-to-back T-type inverters and some other switches around it. Also, it can be connected as a cascade modular which leads to a modular topology with more voltage levels at higher voltages. The proposed module makes the inherent creation of the negative voltage levels without any additional circuit (such as H-bridge circuit). Nearest level control switching modulation scheme is applied to achieve high-quality sinusoidal output voltage. Simulations are executed in MATLAB/Simulink and a prototype is implemented in the power electronics laboratory in which the simulation and experimental results show a good performance. [ABSTRACT FROM AUTHOR]

The strive to increase the energy yield of photovoltaic (PV) power systems has made PV module integrated dc–dc converters (dc-MICs) a reality of modern PV plants. These converters regulate their input voltage, and their dynamic behavior is heavily influenced by the non-linear characteristic of the PV module. The regulation of the PV module voltage and average inductor current by means of a linear cascaded controller is a popular control technique, simplifying the converter dynamics, and providing inherent current limiting; however, it is prone to instability depending on the interaction between the PV source and the interfacing converter, as well as the value of the controller parameters. These factors present a clear challenge for control design; moreover, the converter transient response undesirably depends on the PV module operating point. In order to solve these issues, while maintaining regulation of PV module voltage and average inductor current, this paper proposes to adopt a non-linear controller designed with the feedback linearization control (FLC) technique. The control laws are derived and implemented in a non-inverting buck–boost dc module integrated converter, as this is a favorite topology for the PV interfacing application. A digitally controlled converter prototype is built and used to obtain experimental results, where the FLC technique is compared with a linear cascaded control technique. The results confirm the superior performance of the presented FLC technique, which is robust and able to regulate the converter input voltage with fast and consistent dynamics, regardless of the PV module or load operating conditions. [ABSTRACT FROM AUTHOR]

In this paper, an input-series flyback converter with the coupled-inductor-based passive snubber is proposed, where the input-series converter is based on transformer integration, and the passive snubber is composed of inductors, capacitors, and diodes. The inductors of the snubber in various series modules are made on a common magnetic core, and the coupled-inductor scheme is adopted. With the help of the coupled inductor, active input voltage sharing of the input-series converter can also be achieved after the switches are turned off, and voltage sharing of the switch in each series module can be ensured, which overcome the shortcomings of the existing input-series flyback converter. Active voltage sharing processes caused by the coupled inductor are analyzed in detail. Furthermore, the design guideline of the passive snubber is discussed. Finally, the experimental study has been done on a 1500 Vdc/60 W laboratory-made prototype composed of three flyback series modules, and the feasibility of the proposed method and the theoretical analysis is verified by the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, an expandable single-input three-output high step-up dc–dc boost converter is proposed. The voltage conversion ratio of the output ports of the converter can be increased by inductor-diode-capacitor and diode-capacitor cells. The proposed converter can be applied in renewable energy conversion systems, such as in photovoltaic and fuel cells. Also, due to the three output ports of the converter, it can be utilized in portable devices which require high voltage conversions. The main advantage of the proposed converter is supplying loads with different voltages and current ranges due to the expandable structure of the converter. Besides, the proposed converter has the merit of achieving high voltage gains at high frequencies without preselecting wide duty cycles. Furthermore, the proposed converter is able to achieve higher voltage ranges without having any transformer or coupled inductors in its structure; consequently, the related drawbacks are avoided. The switching pattern of the converter is simple and both switches are on and off simultaneously. In this study, a single switching period of the proposed converter, the voltage conversion ratios of the output ports and the expanded form of the structure are analyzed theoretically. Finally, to verify the theoretical results, the experimental results for 40-V input/200-V, 100-V and 360-V outputs with total 600-W output power are extracted and compared with each other. [ABSTRACT FROM AUTHOR]

This paper presents a sinusoidal pulsewidth modulation (SPWM) based direct digital control with average-voltage model (AVM) and division–summation process for paralleled three-phase three-wire (3φ3W) grid-connected converters to reduce circulating currents. With the direct digital control, plant of each single-phase converter can be derived directly, and a controller is then designed to cover the variation effects of filter inductance and grid voltage. Based on SPWM and AVM over a switching cycle, each 3φ3W converter can be decomposed into three single-phase converters and each converter is controlled individually to track its sinusoidal reference current tightly, reducing circulating currents significantly. Equal current sharing is therefore also achieved. The control laws for achieving grid connection are derived in detail. In the design and implementation, the inductances corresponding to various inductor currents are measured offline and stored in the controller for scheduling loop gain cycle by cycle. Experimental and simulated results from a three-converter system confirm the analysis and discussion of the proposed control approaches. [ABSTRACT FROM AUTHOR]

The ultra-high voltage gain dc–dc converters are extremely required because of the low voltage level of many nonpolluting power resources. This paper proposes an ultra-high voltage gain converter based on an interleave technique and using three-winding coupled inductor and voltage multiplier cell. The interleave technique is useful for reducing the size of the filter components. In the proposed converter, high voltage gain is achieved without extreme duty cycle of solid-state switches. The voltage stress across the semiconductor devices can be reduced by increasing the turn ratio of the secondary of the coupled inductors. In addition, because of the implementation of the interleave structure, peak-to-peak variation of the main input current and switching losses are substantially reduced. The steady-state principles of the proposed converter in continuous conduction mode operation are given. Also, design equations are presented. Validity and performance of the proposed converter are surveyed by simulation and experimental results of a 120 W prototype. [ABSTRACT FROM AUTHOR]

Direct power control (DPC) has gained much attention for medium-voltage applications due to its fast power control capability. However, a conventional static switching table based DPC can lead to unsatisfactory response when the converter is connected to an electric grid because it is commonly designed assuming ideal and constant voltages of the grid and the dc link. Therefore, the actual grid voltage and the actual converter dc-link voltage should be considered while designing the switching table. This paper proposes a novel dynamic switching table for the DPC, considering actual grid and dc-link voltages variation. The proposed dynamic switching table incorporates a new definition of power influence crossover angles of each converter space vector. The proposed scheme dynamically adapts the switching table by feeding forward the actual grid and dc-link voltages, and hence the converter's power is precisely controlled. The proposed technique is verified for the three-level neutral point clamped converters connected to a standard IEEE 9-bus test system. Moreover, the real-time simulations are performed in a real-time digital simulator, OPAL-RT. The obtained results verified the effectiveness of the proposed DPC strategy under different grid fault scenarios. [ABSTRACT FROM AUTHOR]

This paper proposes a novel modified LLC converter with two split resonant branches for wide input-range applications. It can operate in low-gain (LG) mode or medium-gain (MG) mode. The voltage gain of MG mode is 1.5 times that of LG mode, while they have same range of voltage gain $M_{{\rm{tank\_range}}}$ , i.e., the ratio of maximum voltage gain to minimum one. Therefore, the input voltage can be regulated in a wide range by operating the converter in different modes. To achieve the transition between modes, the required $M_{{\rm{tank\_range}}}$ of the proposed converter is as low as 1.5, resulting in lower magnetizing current and higher efficiency within the entire operation range. Smooth transition can be achieved by adjusting the duty cycles of switches gradually. The proposed LLC converter with primary dual-bridge is analyzed in detail as an example. To verify the theoretical analysis and performance of proposed solution, a 1-kW 400-V output prototype with input voltage ranging from 80 to 200 V is built, tested, and compared with two existing full-bridge LLC converters. Analysis and experimental results indicate that smaller volume of transformers, reduced rectifying diodes, and higher overall efficiency are achieved with the proposed converter. [ABSTRACT FROM AUTHOR]

In this paper, a new single-stage half-bridge (HB) resonant $LLC$ converter additionally employing one resonant capacitor and two relays with one package is proposed, compared with a single-stage HB $LLC$ converter. Moreover, a center-tapped transformer is replaced with a coupled transformer. Since the proposed converter changes the turns ratio of the coupled transformer using a relay according to low- or high-input-voltage range, it can decrease the range of its needed voltage gain. It means that the proposed converter can be designed with large transformer magnetizing inductance compared with the conventional single-stage HB $LLC$ converter. As a result, the primary conduction and turn-off losses are reduced. Moreover, in low input voltage range, it has smaller total primary wire resistance of the transformer due to parallel connection of the coupled transformer, which decreases its conduction loss. In addition, additionally employed small-sized components can be inserted to the conventional system. To confirm the operation, features, and validity of the proposed converter, universal input with low line and high line and 16.5 V/60 W output laboratory prototype targeting laptop adapters with wide-input-voltage range is built and tested. [ABSTRACT FROM AUTHOR]

This paper proposes a circuit structure that can improve the power-conversion efficiency \eta e of an AC–DC boost converter. The circuit uses a 1:1 transformer and a voltage boost circuit composed of an inductor, a capacitor, and a diode. The transformer forces the converter to operate in continuous conduction mode for input current, and thereby reduces input ripple. The voltage boost circuit enables the switch to operate in critical conduction mode, so the power loss due to turn-on of switch and reverse recovery of diode is minimized. The proposed converter has high \eta e over a wide range of AC input voltage $V_{{\rm{ac}}}:\,\eta _{e}= 92.9\% $ at $V_{{\rm{ac}}}= {\text{85}}\,{\text{V}} and \eta e= 97.4\% at V{\rm{ac}}= {\text{265}}\,{\text{V}}, when the converter was operated at DC output voltage of 400 V and output power of 500 W. The temperature of the switch stabilized at ∼84 °C for $V_{{\rm{ac}}}= {\text{85}}\,{\text{V}}$ , at ∼70 °C for $V_{{\rm{ac}}}= {\text{110}}\,{\text{V}}$, and at ∼42 °C for $V_{{\rm{ac}}}= {\text{220}}\,{\text{V}}$, whereas that in other AC–DC converters either failed or stabilized at much higher levels. The proposed converter is well suited to systems that require an input voltage range of 85–265 V in root-mean-square value. [ABSTRACT FROM AUTHOR]

This paper presents the active capacitor voltage-balancing (ACVB) methods based on the dynamic model for a five-level nested neutral-point piloted (NNPP) converter using hybrid carrier modulation. The traditional hybrid carrier modulation provides natural voltage balancing of floating capacitors and dc-link capacitors. First, the natural voltage-balancing ability under steady-state and ideal conditions is theoretically proved. However, there are accumulated errors and deviations of capacitor voltages in practical applications, especially under dynamic conditions. In order to address the accumulated errors and deviations of capacitor voltages, the dynamic models of floating-capacitor voltages and neutral-point voltage are established. Moreover, the ACVB method based on the dynamic model of the neutral-point voltage is proposed by injecting the zero-sequence voltage. And the ACVB method based on the dynamic model of floating-capacitor voltages is proposed by introducing the adjustment variables. The proposed ACVB methods have the advantages of simple formula, definite physical meaning, and high accuracy. Furthermore, the output voltage quality and current quality are evaluated in term of total harmonic distortion and the effect of model parameter mismatch on the proposed ACVB methods is presented. Finally, the comparative simulation and experimental results verify the correctness of the proposed ACVB methods based on the dynamic model under different conditions. [ABSTRACT FROM AUTHOR]

In this paper, a novel platform for the single phase switched-capacitor multilevel inverters (SCMLIs) is presented. It has several advantages over the classical topologies, such as an appropriate boosting property, higher efficiency, lower number of required dc voltage sources, and other accompanying components with less complexity and lower cost. The basic structure of the proposed converter is capable of making nine-level of the output voltage under different kinds of loading conditions. Hereby, by using the same two capacitors paralleled to a single dc source, a switched-capacitor (SC) cell is made that contributes to boosting the value of the input voltage. In this case, the balanced voltage of the capacitors can be precisely provided on the basis of the series–parallel technique and the redundant switching states. Afterward, to reach the higher number of output voltage levels, two suggested SC cells are connected to each other with a new extended configuration. Therefore, by the use of a reasonable number of required power electronic devices, and also by utilizing only two isolated dc voltage sources, which their magnitudes can be designed based on either symmetric or asymmetric types, a 17- and 49-level of the output voltage are obtained. Based on the proposed extended configuration, a new generalized version of SCMLIs is also derived. To confirm the precise performance of the proposed topologies, apart from the theoretical analysis and a complete comparison, several simulation and experimental results are also given. [ABSTRACT FROM AUTHOR]

This paper presents a new multilevel cascaded-type dynamic voltage restorer (MCDVR) with a fault current-limiting function. This topology can operate in two operational modes: 1) a compensation mode for voltage fluctuations and unbalances and 2) short-circuit current-limiting mode. The current-limiting function of the MCDVR is performed by activating antiparallel thyristors during the short-circuit fault, and deactivating them during normal operation. The mathematical model of the MCDVR system is also established in this paper. The control scheme design and optimal parameter selection are outlined based on the detailed theoretical analysis of the converter. The transient states of the MCDVR in the compensation mode and current-limiting mode are also analyzed. Simulation results based on the PSCAD/EMTDC software, and experimental results on a laboratory setup help to validate the proposed topology and the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, we introduced an improved transformer-based parallel-resonant converter, suitable for high voltage, high power dc loads. The resonant capacitors are connected in parallel with diodes of the high voltage rectifier, thus restraining dv/dt stress in high voltage circuits. The LC tank resonant frequency is well beyond the switching frequency, reducing in this way the VA rating of LC components. With rated load, the output current of the IGBT bridge is equal to zero at switching instants, and the switching losses are very low. Proposed subresonant circuit requires lower primary current for the given output power and it has reduced IGBT losses. Experimental setup delivers 79 kW with an efficiency of 96.78%. The paper explains the switching states of the devised topology, and provides the guidelines for designing the power transformer, the LC tank and controls. Analytical prediction of the performance curves is verified both in laboratory and by the field tests with an electrostatic precipitator plant. [ABSTRACT FROM AUTHOR]

Many publications have been presented on the modulation and control of the modular multilevel converter, some of which are based on phase-shifted carrier modulation. This paper presents an analysis of how the switching frequency affects the capacitor voltages, circulating currents, and alternating voltages using phase-shifted carrier modulation. It is found that switching frequencies that are integer multiples of the fundamental frequency should be avoided as they can cause the capacitor voltages to diverge. Suitable switching frequencies are derived for which the arm and line quantities will be periodic with symmetric operating conditions in the upper and lower arms. Thus, the practical outcome of this paper is a detailed description of how the switching frequency should be chosen in order to achieve advantageous operating conditions. The theoretical results from the analysis are validated by both simulations and experimental results. [ABSTRACT FROM AUTHOR]

Filters for switching ripple attenuation are essential at the input, and sometimes at the output for certain applications, for the deployment of matrix converters (MCs). Due to the absence of inertial elements in the MC structure and the consequent tight input–output coupling, the filter parameters significantly affect its dynamic behavior. This paper presents an exhaustive filter design method for synchronous applications of the MC in power systems. Apart from the usual considerations of ripple attenuation, voltage regulation, reactive current loading, and internal losses, this paper also addresses additional constraints which may be imposed by requirements of dynamic performance and reliable commutation. Rigorous analytical justification of each design step is provided and the sequential design process is summarized. Relevant experimental results are presented to validate the proposed design tool. [ABSTRACT FROM PUBLISHER]

This paper presents a generalized multilevel direct power control (ML-DPC) scheme for grid-connected multilevel power converters. The proposed method extends the original DPC operating principle by considering only the closest subset of two-level voltage vectors to the present switching state. The implementation of this principle requires the power derivatives for feedback, which can present numerical problems when applied experimentally, mainly due to high measurement noise sensitivity. Therefore, a derivative estimator is proposed based on the converter-grid model in the synchronous reference frame. In addition, a virtual flux observer is developed to achieve synchronization and improve robustness in the presence of grid voltage harmonics. The proposed method is applicable to any multilevel converter topology of any number of levels. In this paper, simulations and experimental results are presented for a seven-level cascaded H-bridge converter. [ABSTRACT FROM AUTHOR]

Due to the relatively low output voltage of photovoltaic (PV) source, a high step-up converter with high efficiency is needed when the PV source is connected to the power grid. A novel high step-up converter based on two switched capacitors and a coupled inductor is proposed in this paper. The operating principle is analyzed and the voltage gain is derived. A 100-W prototype is fabricated in the laboratory to verify the theoretical analysis, and the highest efficiency is 96.4%. [ABSTRACT FROM PUBLISHER]

The model of a modular multilevel converter (MMC) determines the extent of critical circuit information that electromagnetic transient simulations can reveal. In this paper, two MMC models are proposed for efficient real-time hardware-in-the-loop (HIL) emulation on the field-programmable-gate-arrays (FPGA). The nonlinear switch-based model employing the insulated-gate bipolar transistor (IGBT) dynamic curve-fitting model considers factors affecting its transient performance so that device-level behavior such as power loss and junction temperature can be reproduced accurately in the electro-magnetic-thermal simulation of a power converter for its design evaluation. Meanwhile, regarding the MMC submodule as a transmission line stub achieves faster computation speed and enables the formation of a hybrid arm to save FPGA hardware resources. As the large network that the MMC presents is burdensome for real-time execution with a small time-step, circuit simplification based on partitioning and merging is conducted. Hardware implementation of a three-terminal high-voltage direct-current system containing an MMC-based dc–dc converter is carried out and the efficacy of proposed models is validated by comparing HIL emulation results with the offline simulation tool PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

This paper presents a breaker arrangement concept, the multiline breaker (MLB), for the protection of multiterminal high voltage dc (MTdc) networks. Based on the design of a hybrid breaker, the MLB is an economically attractive solution for the protection of multiple dc lines in nodal connection using a single main breaker path. By using commutation units, the MLB directs the fault current through the main breaker in a unidirectional way, irrespective of the fault location. Hence, this study presents the design requirements for the MLB, regarding both hardware and control, and evaluates its operation within a grid. For this reason, a four-terminal half-bridge multilevel modular converters-based MTdc grid in radial configuration was used and pole-to-ground dc fault conditions were investigated. The dc fault response of the grid with one MLB at the central node is compared to the respective response of the grid when one hybrid breaker is employed at each dc line. The simulations show that the MLB is feasible and that the overall MTdc grid fault response for the two protection systems is very similar. As a result, the design advantages of the MLB make it a promising solution for the dc fault isolation in MTdc grids. [ABSTRACT FROM AUTHOR]

Power systems for exploration rovers tend to be complex as three separate converters are necessary; in addition to a main dc–dc converter and cell equalizer for rechargeable energy storage cells, an equalizer for photovoltaic (PV) modules is desirably equipped in order to preclude negative impacts of partial shading. This paper proposes the pulse width modulation (PWM) converter integrating voltage equalizers for PV modules and energy storage cells. The proposed integrated converter comprises a switched capacitor converter, PWM buck converter, and series-resonant voltage multiplier that perform PV equalization, power conversion from the PV modules to the load, and cell equalization, respectively. Three converters can be integrated into a single unit with reducing the total switch counts, achieving not only system-level but also circuit-level simplifications. The derivation procedure of the integrated converter is explained, followed by the operation analysis. Experimental tests were performed using series-connected supercapacitor (SC) modules and solar array simulators to emulate a partial shading condition. With the integrated converter, the extractable maximum power from the PV modules significantly increased while voltage imbalance of SC modules was adequately eliminated, demonstrating the integrated performance of the proposed converter. [ABSTRACT FROM AUTHOR]

Dead time significantly affects the reliability, power quality, and efficiency of voltage-source converters. For silicon carbide (SiC) devices, considering the high sensitivity of turn-off time to the operating conditions (> 5× difference between light load and full load) and characteristics of inductive loads (> 2× difference between motor load and inductor), as well as large additional energy loss induced by the freewheeling diode conduction during the superfluous dead time (∼15% of the switching loss), then the traditional fixed dead time setting becomes inappropriate. This paper introduces an approach to adaptively regulate the dead time considering the current operating condition and load characteristics via synthesizing online monitored turn-off switching parameters in the microcontroller with an embedded preset optimization model. Based on a buck converter built with 1200-V SiC MOSFETs, the experimental results show that the proposed method is able to ensure reliability and reduce power loss by 12% at full load and 18.2% at light load (8% of the full load in this case study). [ABSTRACT FROM AUTHOR]

Dynamic voltage restorer (DVR) technology has become a mature power quality product. In high-power applications, DVR using a multilevel converter is commonly used. However, DVR using a multilevel direct pulse width modulation (PWM) ac–ac converter has not been well studied. This paper presents a new DVR topology using a cascaded multilevel direct PWM ac–ac converter. In the proposed scheme, the unit cell of the multilevel converter consists of a single-phase PWM ac-ac converter using switching cell structure with coupled inductors. Therefore, the multilevel converter can be short- and open-circuited without damaging the switching devices. Neither lossy RC snubber nor a dedicated soft commutation strategy is required in the proposed DVR. This improves the reliability of the DVR system. The output voltage levels of the multilevel converter increase with the number of cascaded unit cells, and a high ac output voltage is obtained by using low-voltage-rating switching devices. Furthermore, a phase-shifted PWM technique is applied to significantly reduce the size of the output filter inductor. A 1-kW prototype of single-phase DVR is developed, and its performance is experimentally verified. Finally, the simulation results are shown for a three-phase DVR system. [ABSTRACT FROM AUTHOR]

Traditional load regulation methods for a resonant converter mainly rely on frequency modulation. It is always a tradeoff between the design of the resonant network and the range of load. Especially for wireless power transfer (WPT) systems, the resonant network usually has a high quality factor. Small variation on frequency leads to huge drop in gain and efficiency. Due to this problem, many WPT systems are unregulated and they need one or two more front-end stages to regulate the dc bus voltage and perform power factor correction (PFC). In order to lower the cost and complexity of two- or three-stages structure, a single-stage solution with a silicon carbide (SiC) based Z-source resonant converter (ZSRC) was recently proposed. The Z-source network provides high reliability as being immune to shoot-through problems. Additionally, a ZSRC can boost the dc bus voltage while the traditional voltage-source inverter can only produce a lower voltage. However, the load regulation of this new topology has not been addressed. Two effective load regulation methods with constant frequency are presented for this SiC-based ZSRC specifically. Operation principle of the two load regulation methods are described in this paper. Experimental results based on a 200-W scale-down prototype with a full-bridge series resonant dc–dc converter are presented to illustrate the mechanism of these two methods. [ABSTRACT FROM AUTHOR]

Distributed energy resources (DERs) are expected to provide ancillary functions including reactive power generation and harmonics compensation. Meanwhile, multilevel inverters and two-level converters with optimal pulsewidth modulation (OPWM) will be commonly used for DERs at high power levels. The challenge is to realize harmonic compensation with limited switching angles. This paper presents an online solution to realize the selective harmonics compensation (SHC), and power generation with DERs. For harmonics compensation, the selective harmonic components in the load current are detected. Then, the harmonic voltages are provided with DERs to cancel out these detected components. Since the power converter is requested to realize both harmonics filtering and power generation, limitations on harmonics compensation at the given power are discussed. Power hardware-in-the-loop-based online verifications are shown at the end of the paper. [ABSTRACT FROM AUTHOR]

Multilevel inverters are receiving more attentions nowadays as one of preferred solutions for medium- and high-power applications. As one of the most popular hybrid multilevel inverter topologies, the five-level active-neutral-point-clamped inverter (5L-ANPC) combines the features of the conventional flying-capacitor type and neutral-point-clamped (NPC) type inverter and was commercially used for industrial applications. In order to further decrease the number of active switches, this paper proposes a seven-switch 5L-ANPC (7S-5L-ANPC) topology, which employs only seven active switches and two discrete diodes. The analysis has shown a lower current rating can be selected for the seventh switch under high power factor condition, which is verified by simulation results. The modulation strategy for 7S-5L-ANPC inverter is discussed. A 1 kVA single-phase experimental prototype is built to verify the validity and flexibility of the proposed topology and modulation method. [ABSTRACT FROM AUTHOR]

Different power electronic converter topologies have been investigated to integrate renewable energy systems to the grid. Cascaded multilevel converters with a high-frequency link have emerged as a viable candidate for such applications. Electrical isolation can be provided using a compact high-frequency transformer connected in the link thus avoiding a bulky line frequency transformer. The use of cascaded modules allows the generation of a multilevel voltage having low total harmonic distortion but increases the overall system size. In this paper, a 15-level high-frequency ac-link single-stage asymmetrical multilevel converter for grid integration is proposed. The single-stage conversion approach eliminates the dc-link capacitors, resulting in a reduced footprint. The asymmetrical module voltages are generated by the multiwinding transformer having unequal turns on each of the secondaries. This allows the generation of 15 output voltage levels, using only three modules in each phase. A modulation strategy is proposed to generate multilevel output voltage. The effect of switch nonidealities on the output voltage is analyzed and two compensation techniques are developed to improve the voltage profile. A multiwinding high-frequency transformer is designed and characterized for the proposed converter. The presented concepts are verified by simulation and further validated experimentally on a three-phase 15-level converter prototype. [ABSTRACT FROM AUTHOR]

A variable-on-time (VOT) control scheme for a critical conduction mode (CRM) integrated buck–flyback power factor correction (PFC) converter with high power factor (PF) and low total harmonic distortion (THD) is proposed in this paper. By utilizing the input and output voltage to modulate the on-time of both buck and flyback switches, the input current harmonics can be eliminated and high PF will be obtained. The operating principles of both the conventional constant-on-time (COT) control and VOT control for the CRM buck–flyback PFC converter are analyzed. A 100-W prototype has been built and tested in the lab. The experimental results demonstrate that the THD and PF of the converter with VOT control are greatly improved compared to those with COT control. [ABSTRACT FROM AUTHOR]