To achieve miniaturization and high step-up in resonant converters, high resonant frequencies and high transformer turns ratios are required, resulting in small primary magnetizing inductance and large secondary winding capacitance. This leads to the transition from mainstream three-element resonant topologies (e.g., LLC, LCC) to more complex four element resonant modes, for which existing analytical methods become inadequate. This paper proposes a generalized precise modeling framework for such high-resonant-frequency high step-up (HRF-HSU) converters. The framework abstracts the resonant behavior of four elements into sequences of two fixed operational stages, standardizing the modeling process across the entire switching frequency range. Models derived from this framework accurately describe resonant dynamics in any frequency band and precisely plot full-range gain-frequency characteristics. The accuracy of the proposed modeling framework is assessed against experimental data and compared with that of mainstream modeling methods, demonstrating its advantage in reducing error. Finally, using the calculated gain frequency curves and resonant tank state trajectories, a case study on switching frequency range selection and resonant parameter optimization is presented.

To solve the problem that the auxiliary resonant pole (ARP) inverter cannot realize the soft switching of all switches, an improved ARP inverter is proposed in this article. This inverter ensures that the main switches as well as the auxiliary switches can realize soft switching by adding a symmetrical auxiliary buffer circuit, which solves the hard-switching turn-off problem of the traditional ARP inverter, and thus greatly reduces the turn-off loss of the inverter and improves the system efficiency. Second, this inverter further improves the topology of the auxiliary circuit (AC), and the use of a single resonant inductor can greatly reduce the size and cost of the AC. Finally, this inverter improves the turn-on environment of the auxiliary switch and reduces the turn-on loss of the auxiliary switch. The working principle of this inverter is given in this article, the inverter working mode is analyzed and compared, and finally, the feasibility of this inverter is experimentally verified.

In order to fulfill the requirements of high step-up, wide gain, and high efficiency in photovoltaic (PV) microconverter, an LCC resonant converter using a hybrid modulation strategy that combines variable-frequency and secondary-side phase-shift (VF-SSPSM LCC) is proposed in this article. By proposing a precise theoretical model, the most appropriate switching frequency (SF) and secondary-side phase-shift angle (SSPSA) that match the steady-state gain under the maximum power point (MPP) of the PV panel are determined, thereby enhancing efficiency while keeping MPP. First, in order to achieve the optimal matching of SF and SSPSA, the working principle of VF-SSPSM LCC with PV panel is analyzed, and three operating states are defined according to the difference of resonant tank state. Second, the time-domain state trajectory model is built for three operating states, and the boundary conditions of each state are calculated. Third, the proposed model is employed to conduct loss analysis and derive the theoretical optimal efficiency curve, from which the corresponding SF and SSPSA are determined. Then, a simple efficiency optimization strategy for an MPP steady state of a PV panel is designed. Finally, a prototype is built to verify the accuracy and validity of the proposed theoretical model and optimization strategy.

The resonant capacitor of the auxiliary circuit (ac) of the resonant dc-link inverter (RDCLI) increases the size of the main circuit, increases the amplitude of the resonant current, and reduces the stability of the system. To address these problems, this article proposes a new RDCLI to reduce the influence of resonant capacitors. First, this inverter does not need to connect resonant capacitors in parallel with the main switches, thus reducing the size of the main circuit. Second, this inverter avoids the series connection of large-capacity capacitors on the dc side as the auxiliary power supply, thus avoiding the influence of large capacitors on the system stability. Finally, this inverter reduces the energy required for the precharge mode by changing the topology of the ac, thus effectively reducing the amplitude of the resonant current, reducing the losses of the ac, and improving the system efficiency. The operation principle of this inverter and the detailed design procedure are given in this article. Finally, the feasibility and stability of this RDCLI are experimentally verified.

Since high power energy transmission is required for a grid-level energy storage system, a high-power energy storage system based on modular multilevel converter (MMC) is very promising at present. However, in order to produce desired high power, an MMC-based energy storage system needs to be constructed by cascading a large number of energy storage units, which will make it difficult to balance state of charge (SOC) of these units. To solve SOC unbalancing of these units, special modeling and control methods are employed and an SOC balancing controller is designed. First, a high-power energy storage system is modeled as a multi-agent model. Then, an event-trigger control method is used to control information transmission and operation period of the energy storage agent, which further reduces the amount of communication and computation. Moreover, observers are designed to estimate battery current, which can reduce in half the amount of status information that needs to be collected. Finally, the simulation platform of the MMC-based storage system is established with MATLAB, the proposed SOC balancing control method is simulated and its validity is verified.

To eliminate the circulation current loss in resonant dc-link inverters, an efficient parallel resonant dc-link inverter without circulation current loss is proposed in this article. When the commutation of the auxiliary circuit ends, there is no constant current circulating freely through either the auxiliary circuit or the main circuit. Besides, when the bus voltage is zero, it is not necessary to set the threshold value of the resonant elements according to the load current, which reduces the control difficulty and improves the reliability of the inverter. At the same time, the peak current of the resonant inductor is suppressed, which reflects that the current stress of the switches is reduced. Thus, the loss caused by the auxiliary circuit is further reduced. In this article, all switches of the proposed parallel resonant dc-link inverter realize soft switching, main switches realize zero-voltage-switching (ZVS) turn-on and ZVS turn-off, and auxiliary switches realize zero-current-switching (ZCS) turn-on and ZCS turn-off. Finally, the effectiveness of the proposed topology and the modulation strategy is verified by an experimental prototype.

To solve the problem of large circulation current loss in a parallel resonant dc link inverter, the no-circulation current commutation modulation strategy based on SVPWM method is proposed. In this modulation strategy, the main switches still maintain the sequence generated by the original modulation strategy, and the auxiliary commutation circuit still operates once in every pulsewidth modulation cycle. Besides, the switching time of the auxiliary switches can be adjusted dynamically according to the load current. When the commutation process of the auxiliary commutation circuit ends, no constant current is circulating freely through the switches of the inverter. It effectively eliminates the circulation current loss and improves the efficiency. At the same time, the time of the zero-voltage notch is not fixed, and it can also change with the load current changes. In the full load range, the duration of zero-voltage notch is shortened, which improves the utilization rate of the bus voltage. This modulation strategy is suitable for any resonant dc link inverter with circulation current. In this article, the operation principle and circuit characteristics are analyzed based on the equivalent circuits in different operation modes. Finally, the validity of the modulation strategy is verified on a 10 kW/16 kHz prototype.

During the resonant process, the resonant element of the resonant dc-link inverter (RDCLI) auxiliary resonant circuit (ARC) resonates with the shunt capacitors of the main switch, which will increase the current stress of the main switch and affect the waveform quality of the output waveform. To address this problem, this article proposes an improved RDCLI. Compared with the original RDCLI, this inverter simplifies the topological complexity of the ARC by reducing the switching devices. In the meanwhile, the main switch does not require shunt capacitors, so there is no resonant current in the main switch. In addition, during the zero-voltage notch, the resonant current also does not flow through the main circuit. So, this proposed inverter lowers the current stress in the main switch, which further improves the waveform quality. The working principle of the improved RDCLI and the design method are given in detail in this article, and the corresponding experimental results are also given at the end of this article.

The modulation strategy of the auxiliary resonant commutation circuit (ARCC) of the original auxiliary resonant pole three-level T-type inverter (ARPT-TNPC) is complicated and the main switch of the ARPT-TNPC cannot realize soft switching. To address the issues, this paper proposes an improved ARPT-TNPC inverter and gives a suitable modulation strategy for the improved ARCC. Compared with the original ARPT-TNPC inverter, this inverter can firstly ensure the soft-switching of all switches, avoiding the problem that the main switch cannot realize the soft-switching, which can further improve the inverter efficiency. Secondly, the ARCC operates only during the dead time, thus reducing the auxiliary switch operation time. Meanwhile, the modulation strategy of this ARCC is not affected by the phase commutation process. Finally, this ARCC does not participate in the control of the main circuit, the control of the ARCC and the main circuit are independent of each other, which helps to reduce the overall control complexity of the inverter. The topology, operating principle and corresponding design principles are given in the paper, and finally the effectiveness of the ARPT-TNPC is experimentally verified.

The auxiliary circuit of the resonant dc link (RDCL) inverter is likely to cause soft-switching failure and voltage loss problems when it operates frequently under small pulses. To solve those problems, this article proposes an FPGA-based sine pulsewidth modulation method (SPWM) with an auxiliary triangular carrier. This method can solve the operation problem of the auxiliary circuit under small pulses, and the method does not need to acquire the load current, but only judges the width of the small pulse based on the magnitude of the modulating waveforms, so as to restructure the driving signals inside the FPGA and avoid the soft switching failure problem. Compared with existing SPWM method, this method compensates the output voltage and improves the waveform quality. The method is experimentally verified to reduce the output current harmonics by 0.89% at 16 kHz switching frequency. When the switching frequency was increased to 40 kHz, the output current harmonics decreased by 1.44%.

Secondary-side phase-shift-control (SSPSC) is an effective method to widen the gain range of resonant converter with pulse frequency modulation (PFM). However, SSPSC not only induces a large circulating current through MOSFETs in secondary side semiactive bridge but also makes these MOSFETs operate under hard switching, thereby diminishing efficiency. To address these issues in this article, a semisynchronous rectification (S-SR) scheme is proposed, and it is realized on LCC resonant converter with SSPSC and PFM (SSPS-PFM LCC). This scheme will not conflict with SSPSC, can avoid circulating current flowing through body diodes of secondary side MOSFETs, and realize ZVS turn- on of these MOSFETs, thus improving efficiency. First, the concept of S-SR is proposed. Second, a time-domain state trajectory model of SSPS-PFM LCC is built. According to this model, the mathematical relation of S-SR conduction angle with switching frequency (SF) and secondary-side phase shift angle (SSPSA) is derived, and a simple calculation method of S-SR conduction angle is designed. This enables the realization of S-SR scheme with no additional sensors and almost no additional controller computational burden. Finally, a SSPS-PFM LCC prototype is built to verify the effectiveness of the proposed S-SR scheme.

The precharging process of the auxiliary circuit of the auxiliary resonant pole inverter increases the current stress of the switch and the loss of the inverter. To overcome these problems, this article proposes an auxiliary resonant pole soft-switching inverter with low precharging current. In contrast to the existing auxiliary resonant pole soft-switching inverter, this inverter can effectively decrease the precharging current of the auxiliary circuit, thus reducing the current stress of the switch, lowering the conduction loss of the switch, and improving the inverter efficiency. Moreover, the main switch and auxiliary switch of this inverter share a common resonant capacitor, which reduces the loss resulting from reactive energy conversion of the auxiliary commutation circuit so that the inverter achieves the purpose of simplicity and efficiency. On the basis of the equivalent circuit diagram in each operating mode, the operating mechanism of this inverter is analyzed. In addition, the soft switching conditions and the parameter optimization design method of this inverter are provided. Finally, the validity of this inverter is experimentally verified.

The resonant current of the resonant dc link inverter is superimposed on the main switch in periods of the zero-voltage notch creation, which increases the current stress as well as the conduction loss of the main switch, and inevitably escalates the selection cost of the main circuit. To solve these problems, a parallel resonant dc link inverter with low current stress on main switch is proposed in this article. The main switch of this inverter does not need parallel resonant capacitors, and it also ensures that the current of the main switch remains at the load current value during the whole resonance process or the zero-voltage notch, thus effectively reduces the current stress of the main switch, and thereby the hardware cost of the main circuit can be further diminished. At the same time, the conduction loss of the main switch is significantly decreased since the resonant current is no longer considered, thus improving the efficiency of the inverter. The operation principle of this circuit is analyzed and compared with existing literatures and the design method is also given in the article. Finally, the effectiveness of this resonant dc link inverter is experimentally verified.

In order to decrease the switching loss of the auxiliary circuit of the resonant dc-link (RDCL) inverter and improve the voltage utilization and system efficiency, this article presents a new space vector pulsewidth modulation (SVPWM) method based on the zero-voltage notch of the RDCL inverter. This RDCL inverter reduces the current stress in the main circuit by paralleling auxiliary switch. And this method makes the operation of the auxiliary resonant circuit (ARC) less frequent, thus reducing the losses of the ARC and, therefore, improving the system efficiency. At the same time, this method analyzes and compensates for the missing voltage vectors based on the ideal output voltage so that the inverter output voltage vector under this modulation is the same as the ideal SVPWM output voltage vector. Compared with the original modulation of RDCL inverter, this method does not change the switching sequence, the switching times, and the action time of the vector while reducing the switching ripple. The effectiveness and feasibility of the modulation strategy is verified in this article through theoretical analysis as well as experiments.

针对辅助谐振极逆变器存在的辅助换流回路结构复杂,逆变器总体效率不高的问题,提出一种简洁高效的辅助谐振极逆变器,所提逆变器的主开关管和辅助开关管公用一套谐振元件完成软开关动作,简化辅助换流回路的结构,降低主开关管的电流应力,减小辅助换流回路中无功能量转化造成的损耗和主开关管的导通损耗,使逆变器达到了简洁高效的目的.根据不同工作模式下的等效电路图,分析逆变器的工作原理,提供该逆变器的软开关实现条件以及最佳参数设计方法.最后,使用IGBT作为开关器件制作一台10kW/16kHz实验样机,实验结果验证所提逆变器具有简洁高效的特点.

In order to solve the output voltage loss problem caused by the zero-voltage notch of resonant dc-link (RDCL) inverter and improve system efficiency, this article proposes an RDCL inverter and its voltage compensation method. The topology of this auxiliary circuit is simpler, and the resonant current is separated from the load current by parallel auxiliary switch, which reduces the current stress of the main switches. At the same time, the method is based on the conventional sinusoidal pulsewidth modulation (SPWM); this method first calculates the operation time of the auxiliary circuit based on the magnitude of the phase current, second adjusts the position of the triangular carrier according to the calculation results, and finally generates the driving signals for early turn-on and delayed turn-off, which solves the voltage loss problem and improves the voltage utilization, the output voltage is the same as that of the ideal SPWM. The working principle, parameter design conditions, and voltage compensation method are analyzed in detail in the article. Finally, a 5-kW/16 kHz prototype is created with insulated gate bipolar transistor (IGBT) as switching device, which verifies the novel resonant dc-link inverter and its modulation strategy is effective.

为降低并联谐振直流环节逆变器辅助换相电路的动作频率和损耗,以及辅助开关管的电流应力,该文提出一种新型空间矢量脉宽调制(space vector pulse width modulation,SVPWM)方法.新型SVPWM方法在实现所有开关管的软开关动作的基础上,在1个脉宽调制(pulse width modulation,PWM)周期内辅助换相电路只动作1次,从而降低辅助换相电路的动作频率和损耗;所提新型SVPWM方法通过增加分流死区时间,可避免谐振电流与负载电流相叠加,从而最大化地抑制辅助开关管的电流应力.新型SVPWM方法可适用于任何可调整零电压凹槽时间的并联谐振直流环节逆变器.在新型SVPWM方法下,根据不同工作模式的等效电路图,分析该逆变器的工作原理、软开关实现条件以及参数设计方法.最后使用绝缘栅双极型晶体管作为开关器件制作一台10kW、16kHz样机,通过实验验证所提调制策略的有效性.

To realize a three-phase soft-switching inverter with a simple structure, low cost, and easy modularization, this paper proposes a novel three-phase passive soft-switching inverter, which realizes soft-switching of the switches in the inverter through energy consumption of the auxiliary snubber circuit. When compared with the traditional passive soft-switching inverter, it avoids the use of transformers, coupled inductors, and bulk electrolyte capacitors. Thus, it has a small size, a high power density, and is suitable for integration. Its three single phases are independent of each other, which makes it easy for the inverter to apply various control strategies. This study chooses a single-phase circuit, and investigates the operating principle, soft-switching implementation characteristics, and parameter design methods of the novel passive soft-switching inverter under various operation modes. Finally, a 10 kW/16 kHz prototype is made using an IGBT as a switch, and experiments are conducted to confirm the validity of the inverter.

In order to reduce the operating frequency and loss of the auxiliary commutation circuit (ACC) and current stress of auxiliary switches of a parallel resonant dc-link inverter (PRDCLI), this article proposes a novel space vector pulsewidth modulation (SVPWM) method. The novel SVPWM method can reduce the number of operations of the ACC to once in every PWM cycle on the premise of realizing soft switching of all switches, thereby reducing the operating frequency and loss of the ACC. At the same time, by adding the shunt dead time, the novel SVPWM method can avoid the superposition of the resonant current and load current, thereby minimizing the current stress of auxiliary switches. In addition, the novel SVPWM method can apply to any PRDCLI with the ability of variable zero voltage durations. Under the novel SVPWM method, according to the equivalent circuits of different operation modes, the operation principle, soft switching realization conditions and parameter design methods of the inverter are analyzed. Finally, a 10-kW/16-kHz prototype is built using insulated gate bipolar transistors to verify the validity of the novel SVPWM method.

To address the complex topology of auxiliary resonant commutated pole inverters and the large current stress of auxiliary switches, this paper proposes an auxiliary resonant commutated pole soft-switching inverter with a simple topology. The proposed inverter not only reduces the current stress of the auxiliary switches and the loss caused by the reactive energy conversion in the circuit but also simplifies the topology of the auxiliary commutated circuit, reduces the cost of the inverter, and improves the reliability of the inverter. The inverter is suitable for small and medium power applications. Under the proposed modulation strategy, the operation principle of the inverter, the conditions of soft-switching realization, and the optimal parameter design method are analyzed in detail according to the equivalent circuit diagrams in different operating modes. Finally, a 10-kW, 16-kHz prototype is fabricated using insulated gate bipolar transistors (IGBT) as switches, and the effectiveness of this inverter is verified through experiments.