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A MOSFET-based series-resonant indirect-matrix-type power electronic transformer (PET) consists of line-frequency-switching folding–unfolding bridges and series-resonant dc–dc converters (SRCs), which is an attractive choice to achieve ac–ac conversion due to its high efficiency and high power density. However, the conduction losses, switching losses, and core losses in each of the high-frequency switching cycles Ts are different due to the pulsating dc voltage |ac|, which introduces difficulties in the calculation of losses. In addition, the small dc capacitors also participate in the resonance, and the resonant current shape deviates from a pure sine. Therefore, the conventional loss model is not suitable for PETs. In this paper, the time-domain analysis of SRC resonant current considering the dc capacitor is developed. Then, the analytical expression of the resonant current RMS value in grid cycle Tg is derived, which is more accurate in calculating conduction loss than the conventional model. In addition, it avoids the calculating losses in each Ts. Next, an analytical switching loss model is developed based on the curve fitting of the capacitance–voltage relationship. A simplified analytical core loss model is provided. Each part of the loss of the PET is verified by thermal simulations, and the total losses are verified by efficiency tests on an experiment prototype.

This paper introduces a single-phase five-branch direct ac–ac modular multilevel converter (MMC) with the capability of equal frequency conversion for railway power conditioning applications. By analyzing the branch energy balance mechanism, the basic operating principle of the proposed MMC is clarified and the control strategy is also proposed. Comparisons between the proposed MMC and the traditional modular multilevel matrix converter (MMMC) on branch voltage and current ratings as well as capacitor dimension requirements are also presented. The effectiveness of the proposed topology and the control strategy is validated on a down-scaled prototype. Both the theoretical analyses and the experimental results reveal that for compensating low power factor traction loads in Scott transformer-based railway power systems, the proposed MMC has decreased branch current stresses and capacitor voltage fluctuations compared to the traditional MMMC, and the required total submodule numbers of these two MMCs are comparable.

The voltage balancing of the floating capacitors in modular multilevel converter (MMC) is of great importance for the safe operation. However, the existing voltage-balancing algorithms usually suffer from high switching frequency, leading to unnecessary switching losses and device costs. This paper proposes an adaptive capacitor voltage-balancing method for high-power MMCs with reduced switching frequency. The operational characteristics and switching process of the submodules (SMs) are analyzed in detail. And then the relationship between the switching frequency and the capacitor voltage deviation is derived. Based on the analysis, an adaptive method is proposed to make a trade-off between the switching losses and the balancing effect through a closed-loop control of the alternating number of the SMs. The calculation formulas of the switching frequency are also presented. PSCAD/EMTDC simulation and RT-LAB-based real-time control hardware in the loop (HIL) test results demonstrate the effectiveness of the proposed method under different operating conditions.

Modular multilevel converter (MMC) is a well-proved circuit topology in voltage-source converter-based high voltage direct current (VSC-HVdc) transmission systems. As is known, the conventional half-bridge submodule (HBSM)-based MMC-HVdc is not suitable for overhead line transmission applications. In addition, high energy storage requirements, i.e., large capacitance is inevitable. The conventional design of the full-bridge submodule (FBSM)-based MMC usually does not utilize the negative voltage state of FBSM in normal operation. Considering the same dc voltage as with the HBSM case and utilizing the negative voltage state of the FBSM, this paper presents the design method of the power transmission capability of a single FBSM. Meanwhile, an optimized energy storage capacitance design method of the FBSM is proposed. With this method, the capacitance of FBSM can be reduced significantly. The correctness and effectiveness of the proposed method is verified by the simulation of a ±160 kV VSC-HVdc MMC and the comparison results of the dc short fault blocking and ride through capability are also provided.

The cascaded H bridge-power electronic transformer (CHB-PET) has potential application in traction and smart grid, however, it is a great challenge to achieve fast electromagnetic transit because of numerous nodes and nonlinear devices and high switching frequency. The equivalent model of the submodule and three-phases CHB-PET with the detailed feature of the high-frequency circuit, which can reduce the size of the admittance matrix, eliminate the affection of switching state to admittance matrix, and alleviate the impact of the increasing number of submodules per arm on computing time, are proposed to speed up simulation of CHB-PET. The accuracy and computing performance are verified by comparison of reference and proposed models in Matlab Simulink. Simulation results show that the proposed model has good performance of accuracy under blocked mode and unlock mode, and has excellent performance of computing time with the increasing of the number of submodules per arm. It can significantly speed up the offline simulation of CHB-PET. Moreover, the proposed model has great potential for real-time simulation by CPU and FPGA hardware platform.

The pulse width modulation current source converter (PWM-CSC) has been regarded as one of many interesting circuit topologies in high-power systems. This paper analyzes the influence of system parameters on the power operating range of PWM-CSC, and designs the parameters for PWM-CSC applied to HVDC transmission system. A 250 kV/500 MW PWM-CSC based HVDC transmission system is built using PSCAD/EMTDC software, and the experimental platform was built to verify the correctness of the analysis and the feasibility of the design.

Compared with three-level neutral point clamped (NPC) converter, three level active neutral point clamped (ANPC) converter provides more flow paths which can improve the balance of power loss distribution. Fault diagnosis in power electronic converters is necessary to prevent further damage, the open circuit switch fault of every device in three level ANPC converter is analyzed in this paper. An optimized open circuit switch faults diagnostic strategy for three level ANPC is proposed. This strategy can diagnose any faulty switch and diode based on the phase voltages. A low cost and fast phase voltage detection circuit based on linear photoelectric isolation is presented in this paper. Compared with the existing open circuit switch faults diagnostic strategies, this strategy has the advantages of simplicity, cost-effectiveness and faster detection speed. Simulation results verified the effectiveness of the introduced fault diagnosis method.

In this paper, a novel three-stage power electronic transformer (PET) is proposed for AC/DC conversion. Compared with the existing PET topologies, the feature of the proposed PET is the decreased number of the power conversion stages. The mixed-frequency synchronous control strategy is also presented, which fulfills unity power factor (UPF) at the AC input stage and zero current switching (ZCS) in H-bridge (HB) convertors. Simulation results verify the validity of the proposed PET topology with its control strategy.

This letter focuses on the power module (PM) capacitor voltage balancing of a $\pm 350$ -kV/1000-MW modular multilevel converter (MMC). For this MMC, the current flowing through the IGBTs will exceed the nominal current of the adopted commercial high-voltage (3.3 kV or higher) IGBT products, i.e., 1500 A. As for the PM voltage balancing of this MMC, the switching frequency must be kept low to reduce the losses and the accurate calculation of the PM switching frequency is of great importance to the design of the cooling system. This letter presented a low-switching frequency PM balancing method by introducing the balancing adjusting number (BAN). The PM switching frequency calculation method is also presented with different BANs. Computer simulation and the real-time control hardware in the loop test results based on RT-LAB show the effectiveness of the proposed PM balancing method and the accuracy of the switching frequency calculation method under the rated power.

In order to reduce the cost of the high voltage direct current (HVDC) transmission system, a hybrid HVDC transmission system adopting line commutated converter (LCC) on the rectifier side and dual phase shift pulse width modulated current source converters (PWM -CSCs) on the inverter side is proposed in this paper. The mathematical model and the output ac current harmonic characteristics of the PWM -CSC are analyzed in detail. A maximum power factor control method is proposed. Finally, a 400 kV/1250 MW PWM-CSC based unipolar HVDC transmission system is built using PSCAD/EMTDC software. The simulation results verify that the proposed control method realizes the maximum power factor operation under normal state and that the proposed hybrid HVDC transmission system can ride through both ac and dc faults smoothly.

Modular multilevel converter (MMC) has been proved a prospective topology in high voltage and high power occasions. Hybrid MMC mixed with half-bridge (HB) and full-bridge submodules (FBSMs), which achieves a good tradeoff between power devices quantity and dc short circuit fault handling capability, attracts extensive attention. In this paper, the characteristics of SM capacitor voltage ripples are analyzed in detail when FBSM negative voltage state is utilized. The optimal operation point is derived which minimizes the SM voltage fundamental frequency ripples. Under the equivalent ripples with the hybrid MMC without negative voltage state, the analytical expression of SM capacitance design principle is also derived. However, the SM voltage ripples of the hybrid MMC increases dramatically with reactive power increasing. Based on this, a circulating current injection (CCI) method is proposed, which can suppress the ripples caused by reactive power. With this method, the SM capacitance achieves a significant reduction. Comparative simulation results on a ±200 kV hybrid MMC verified the correctness of the theoretical analyses and the proposed CCI method.

The great number of power modules (PMs) imposes great computational challenge on the voltage balancing of modular multilevel converter (MMC) as the sorting of the PM capacitor voltages is usually adopted. This paper presents a distributed control method for PM capacitor voltage balancing in MMC. With this method, all PMs in one arm are grouped and the sorting algorithm of the voltage balancing in each group is implemented in decentralized control unit. To keep the voltage balancing among different groups, a close-loop control system is proposed, using the average capacitor voltage of each group as the feedback. With this method, the computational load is reduced compared to the conventional method while the voltage balancing effect and the switching frequency are almost the same. Real-time experimental results on a ±350 kV/1000 MW MMC based on RT-LAB (OP7020 and OP5607) verify the feasibility and effectiveness of the proposed method.

Turn-off delay time is temperature sensitive and can be used to estimate the junction temperature of insulated-gate bipolar transistors (IGBTs). In this paper, a high-resolution measurement circuit is designed to detect the turn-off delay time and estimate the corresponding junction temperature. Details of the circuit are demonstrated. Turn-off delay time at different junction temperature, different switching current and different switching voltage is investigated using the measurement circuit. Based on the experimental results, the junction temperature estimation method is tested on IGBT device IKW40N120T2. Compared with the on-state collector-emitter voltage-based method and short current-based method, turn-off delay time-based method shows the feature of high accuracy and feasible online estimation.

Improved from the conventional analytical thermal model, a fast compact model based on finite differential method wtih PSPICE is presented in this paper. The paper presents the physical basis and the practical consideration. Based on the model, a cooling system example was introduced and verified for high power density converter systems design.

It is a key issue for inductively coupled power transfer system that the output power is regulated with high efficiency especially over a wide load range. In this paper, a novel harmonic-based phase-shifted control method is proposed. With this method, the harmonic component other than the fundamental component of the resonant inverter output voltage is employed to regulate the transferred power. The output power is controlled by changing the phase-shifted angle of the inverter. Different from the conventional approaches, the switching frequency in this method is much lower than the resonant frequency, meaning much reduced switching losses. The operation principle, switching strategy, and dead-time effect have all been presented. Experimental results demonstrate that the proposed power control method can achieve significant performance improvement at the light-load condition.

In this paper, a novel voltage balancing method of modular multilevel converters (MMCs) is proposed. This method divides the voltages of sub-module capacitors in each arm into several groups and the voltage balancing is based on these groups. The proposed method can save sorting time greatly compared with the conventional method. Simulation results on a MMC based three-phase inverter show validity of the proposed method.

The high-capacity modular multilevel converter (MMC) is becoming the most popular type of voltage-source converters for high voltage direct current (HVDC) transmission. However, the nonlinearity of the loss characteristics of the switching devices and the complexity of the switching patterns impose great challenge on the loss modeling of MMC. The present methods still have some flaws in modulation methods and switching loss calculation. This paper proposes a simplified MMC loss mathematical model based on the RMS and average value of the arm current. The analytical expressions of this simplified model are also presented. Simulation results of a ±350 kV/1000 MW MMC using PSCAD/EMTDC verify the correctness and the accuracy of the proposed model.

Modular Multilevel Converter (MMC) is considered a promising circuit topology for high voltage and high power applications. There is a trade-off between submodule (SM) capacitor voltage balancing and switching frequency. In this paper, an adaptive SM capacitor voltage balancing method is proposed based on that different arm currents have different charging or discharging capabilities. The algorithm can reduce switching frequency without affecting capacitor voltage balancing. The threshold current selection and average switching frequency calculation of power device are presented which provide theoretical basis to system design. Finally, the simulation results validate the effectiveness of the proposed method.

This paper focuses on the distributed control method of the power module (PM) capacitor voltage balancing in modular multilevel converters (MMCs). The large number of PMs imposes great computational challenge on the capacitor voltage balancing in MMC based high voltage direct current (HVDC) transmission system. In this paper, a distributed voltage balancing method is proposed to reduce the computational load of control strategy of MMCs with hundreds of PMs per arm. With this method, all PMs in one arm of MMC are grouped first. The PMs in each group is balanced independently by voltage sorting and arm current polarity. The sorting all the PM voltages in this arm is avoided. Meanwhile, a close-loop control strategy is also introduced to balance the average PM voltage of each group dynamically. Simulation results on a ±350 kV/ 1000 MW MMC based HVDC system show the effectiveness of the proposed distributed control method.

Modular multilevel converter (MMC) is a promising circuit topology in the field of high-voltage direct current transmission (HVDC) systems. To enhance the reliability of the MMC in this field, the popular method is the addition of redundant submodules (SMs). However, the MMC will become unbalanced when some SMs fails and the performance will be deteriorated, especially when the number of the failed SMs is high. This paper analyzes the impact of the SM fault on the performance of the MMC. Theoretical analyses show that fundamental frequency component appears in the dc side current when some SMs fails. Furthermore, the approximate expression of the fundamental frequency component is derived. Based on the analyses, the number of the redundant SM design criterion is proposed. In addition, a rebalancing method is proposed to eliminate the harmonic component in the dc side and arm currents under SM faults scenario. Simulation results verified the theoretical analyses and the proposed rebalancing method.

The three-phase Power Electronic Load (PEL) simulation of the asynchronous motor operation can be the divided into AC sine wave drive mode, the inverter open-loop drive mode and the inverter closed-loop drive mode. The control strategy of these three kinds of working conditions is simple to complex, and has certain inheritance and progressive relations. In the AC sine wave drive condition, the discrete solution method of the motormathematical model is studied and a current tracking control strategy based on the deadbeat controller is proposed. In the inverter open-loop drive mode, a new method of PWM pulse voltage detection based on FPGA is proposed to improve the accuracy of the motor model. In the inverter closed-loop drive mode, a simulation method based on antielectromotive force is proposed to solve the coupling problem of two converters. Simulation and experiments verify the effectiveness of these methods.

The layout of power modules is one of the key points in power module design. In this paper, along with design examples, an improved automatic layout method for planar power module is presented. Some practical considerations and implementations are introduced in the optimization procedure.

In this paper, a novel single-phase five-level inverter is proposed using coupled inductors. This inverter can output five-level voltage with only one dc source. No split of the dc voltage capacitor is needed, totally avoiding the voltage balancing problem in conventional multilevel inverters. The level of the output voltage is only half of the dc-link voltage in all conditions, leading to much reduced dv/dt . This inverter is based on the widely used three-arm power module and the voltage stresses on all the power switches are the same, making it very easy to construct. Operation mechanism of this inverter is analyzed and the possible switching patterns are investigated. Based on these analyses, a novel optimized modulation scheme is presented. With this modulation method, no dc components exist in the inductor currents, which is very helpful for minimization of the inductors. Simulation and experimental results show the validity of the proposed inverter together with the optimized modulation scheme.

In this paper, the influence of one-sample delay for sampling and computation in digital control on the bandwidth of the inner current loop of a 400-Hz ground power unit (GPU) is analyzed first. The results show that it is difficult and even impossible for high-power 400-Hz GPUs to maintain low total harmonic distortion content in the output voltage with the conventional proportional-integral-based double-loop control. To improve the performance, resonant controllers with parallel structure which are widely used in active power filters are applied to the single-loop control of the 400-Hz GPU. The parameter design criterion for the parallel resonant controllers is discussed in the discrete time domain. Meanwhile, adoption of proportional gain in the single-loop control is investigated. The results show that it can improve the performance little and may cause instability problems. Comparisons between different control methods for the 400-Hz GPU are also made, and the single-loop control method in this paper seems to be the most suitable one in terms of simplicity and performance. Experiments on a 16-b fixed-point DSP-controlled 90-kVA 400-Hz GPU prototype show satisfactory results of the single-loop method feeding linear/nonlinear and balanced/unbalanced loads.

This paper presents power angle characteristics of single-sided ironless linear synchronous motor (LSM) based on permanent magnet Halbach array. Sinusoidal magnetic field of air gap is established by magnet Halbach array and normal attraction can be decreased by ironless coil. The problem is pole pitches of primary and secondary are different, that effects power angle characteristics. Besides, normal attraction is produced when magnet Halbach array above the steel sleepers. So linear analytic method and finite element method is adopted to analysis these complications, a method of static scanning point is presented to calculate power angle characteristics when pole pitches are unequal, some important conclusions of this type motor are obtained. Experimental results on a 200KW type motor verify the conclusions and accuracy of calculation.

In this paper, a power module capacitor voltage balancing method is presented for a ±350 kV/ 1000 MW modular multilevel converter (MMC) oriented for a back-to-back grid interconnecting project. In this method, a Balancing Adjusting Number (BAN) is proposed to adjust the voltage balancing effect and the switching frequency of the power modules. An accurate switching frequency calculation method is also presented. Verification results show the effectiveness of the proposed voltage balancing method and the correctness of the switching frequency calculation method.

Smart energy router (SER), also called as power electronics transformer (PET) or solid state transformer (SST), will serve as a critical component in the next-generation electric power system. Taking advantage of modular multilevel converter (MMC) and input series output parallel (ISOP) topologies, new type of smart energy router has been developed. Presented architecture using two stages with AC/DC conversion in the medium-voltage (MV) side, and ISOP type DC/DC conversion in the low-voltage (LV) side, thus allows interaction with DC grid and local renewable sources, etc. Compared to existing topologies, proposed SER uses less power switches and high-frequency transformers. The details related to the 2-MVA SER prototype, including the electrical design of the circuits and control system is presented in this paper. Simulation and experimental results on this prototype with distribution DC grid show validity of this SER.

In order to improve the parameter precision of induction motor in identification at standstill, a novel method by adaptive compensation of dead-time effect in inverter control is proposed. Proportional resonant controller, phase locked loop and the feature of dead-time effect are implemented to adaptively compensate the dead-time effect of current and to relieve the voltage wave distortion. The nonlinear influence of dead-time effect in direct current measurement is also relieved. The experimental results show the proposed method can reduce the harmonics of current and voltage 8.92% and 7.65% separately. The amplitude and phase of voltage are also compensated. The fluctuation of voltage amplitude is less than uncompensated one. It is validated that the proposed method can improve the measurement precision of resistance and inductance.

Because Single-phase PWM rectifier usually runs unity power factor condition; the phase between grids input voltage and current are the same. In this paper, a novel dead time compensation method of single-phase PWM rectifier is proposed by the observation of grid input voltage based on resonant controller phase-looked loop. The new method avoids the noise of the current detection, so that zero-crossing detection is more accurate, and does not cause the phase delay. Comparative analysis with traditional dead time compensation method based on the current. The simulation and experiment results show that the grid input current total harmonic distortion with grid input voltage observation are lower and compensation effect is better.

In this paper, modeling and control strategy study of a modular multilevel converter based high voltage direct current transmission system are carried out. The modulation methods and control strategies are discussed. A ±10kV/15MVA back-to-back MMC based HVDC experimental system is built up. A sorting algorithm and capacity voltage balance control method are used in the experimental system. The control method are validated with experimental results.

Dual active bridge dc/dc converter with high frequency isolation is gaining more attentions due to its small size and high-power density. In this paper, the principle of series resonant dual active bridge(SRC-DAB) DC-DC converter is discussed based on the fundamental analysis. The control method and principle of soft switching are also presented. Finally, the analysis is verified by computer simulation and experiment results.

In this paper, a novel voltage balancing method of modular multilevel converters (MMCs) based on phase shifted carrier pulse width modulation is proposed. The proposed method is using redundant sub-modules to balance voltages between sub-modules in the arm. This method bypass several selected sub-modules every carrier cycle based on arm current and voltage sorting result. When the arm current is charging sub-modules, the sub-modules with higher voltage are selected to bypass. Otherwise, the sub-modules with lower voltage are chose to bypass. Simulation results on a MMC based on three-phase inverter show validity of the proposed method.

In this paper, an improved voltage balancing method of modular multilevel converters (MMCs) is proposed. This method divides sub-modules in same arm into several groups which voltage balancing is based on. The voltage balancing between groups is based on the sorting result of group sub-module average voltage and the voltage balancing within group is based on the sorting result of sub-module voltages in group. The proposed method can save sorting time greatly compared with the conventional method. Simulation results on a MMC based three-phase inverter show validity of the proposed method.

In order to analyze and calculate the switching frequency of power switches in modular multilevel converter (MMC) quantitatively, a mathematical model for sinusoidal pulse width modulation (SPWM) and nearest level modulation (NLM) is proposed in this paper. The factors influencing the switching frequency are summarized, and the superior and inferior limits in extreme cases of operation are analyzed which infer the range of switching frequency. And then, the theoretical formulae for calculating the switching frequency are presented, which is helpful for designing the parameters of the power switches and the control system. Finally, the correctness of the calculation formulae and the feasibility of the analysis are well validated by simulation results.

The dc-link pole to pole short circuit is one of the most serious fault of a modular multilevel converter. Because of this, it is also one of the most important research objects for institutes and companies. However, there are not so many papers about this experiment published yet. Actually, the short circuit current before blocking the sub modules is the combination of the ac injection current and the capacitor discharge current. This paper analyzes the model of the capacitor discharging circuit and demonstrates the results of the experiment done with a ±10 kV prototype MMC.

In this paper, a novel simple algorithm of nonlinear load simulation is proposed. The characteristic of load simulation is very important for power electronic load (PEL). About this content, there are few articles mentioned, especially the study of nonlinear load simulation algorithm is less. So on the basis of linear load simulation algorithm introduced, this paper summarizes a kind of algorithm that is easy to be realized in engineering focusing on the implementation of nonlinear load simulation. Through software simulation and experiment, the feasibility and accuracy of the algorithm is verified.

By now the modular multilevel converter (MMC) is mainly applied to high frequency applications (50 or 60Hz) especially in the field of HVDC systems. This paper presents a control scheme for modular multilevel converter, which allows the converter to operate at continuous coverage in the 0Hz to 50Hz frequency band.

A novel resonant current control method especially the fast sampling method for contactless power transfer system is proposed. Within this method, the amplitude of primary resonant current is obtained by sampling at the maximum of the resonant current only one time during a resonant period, which doesn't need extra peak detecting circuit. The resonant period is well measured, and the delay time is accurately set to ensure the sampling point of ADC at the crest or the trough of the resonant current. The resonant current is controlled by PI controller with phase-shifted control. Simulation and experiment verify the effectiveness of proposed sampling and control method.

The paper is talked about a high power active power filter. The main circuit topology adopts a three-phase three-line voltage source converter,which is constituted by three H-bridges. The delta connection H-bridge topology has a good ability to compensate unbalanced load and fulfills the requirements of energy compensation device for use in high power applications. This paper presents a compound control methods, which can achieve the ideal control effect of the harmonic current and reactive current of grid.

The Modular Multilevel Converter (MMC) has become a very important topology in many applications for its unique advantages. Modulation strategy is very important to MMC converter because it will affect the output characteristics and switching loss. In this paper, two widely applied modulation strategies, submodule unified pulse width modulated (SUPWM) and carrier-phase-shifted PWM (CPSPWM), are analyzed and compared. Simulations are conducted in different number of submodules and different frequencies. The results will provide a useful consultation for selecting the appropriate modulation strategy in different applications.

Recently modular multilevel converters are highly attractive for medium, high-voltage power transition and electrical machine drive. Capacitor voltage sorting is very important for capacitor voltage-balancing control. This paper describes a novel sorting algorithm for capacitor voltage of modular multilevel converters (MMC).

A novel single-phase five-level rectifier with coupled inductor has been proposed. Detailed analysis of this new circuit structure and working principle has been made. Modulation strategy and control strategy of this circuit topology have been given. This new topology has unity power factor operation, low input current total harmonic distortion, stable output DC bus voltage, and no voltage balancing problem. The simulation and experimental results show that this new topology has better performance, less IGBT devices, a set of secondary windings, simple control strategy, which is suitable for applications in high-power rectifier.

Analyzing and measuring power losses of power electronics and motor system are of great importance. This paper compares several methods for power loss calculation and measurement. A general scheme for modeling losses of power semiconductors is given. As for the harmonic losses of converter-fed motors, an effective FEM process is described. The constraint of conventional calorimeter is discussed and a simplified calorimetric method is introduced.