Three-level non-inverting buck–boost converters are promising for electric vehicle charging stations due to their wide voltage regulation capability and bidirectional power flow. However, the number of three-level operating states is four times that of two-level operating states, and the lack of a unified switching state selection mechanism leads to serious challenges in its application. To address these issues, a finite control set model predictive control (FCS-MPC) strategy is proposed, which can determine the optimal set and select the best switching state from the excessive number of states. Not only does the proposed method achieve fast regulation over a wide voltage range, but it also maintains the input- and output-side capacitor voltage balance simultaneously. A further key advantage is that the number of switching actions in adjacent cycles is minimized. Finally, a hardware-in-the-loop experimental platform is built, and the proposed control method can realize smooth transitions between multiple operation modes without the need for detecting modes. In addition, the state polling range and the number of switching actions are superior to conventional predictive control, which provides an effective solution for high-performance multilevel converter control in energy systems.

This article focuses on reactive power compensation and impedance matching of square-wave voltages. Square-wave voltage is the operating voltage in electromagnetic method (EM) exploration. The characteristics of a square-wave voltage are very different from those of a sinusoidal voltage in the power grid. Although some papers proposed impedance matching converters for square-wave voltages, they solved the high dc voltage requirement problem. The problem is caused by square-wave voltage having multiple and variable spectral components. An impedance-matching converter with an injection circuit (IMFR) for square-wave voltage is proposed. IMFR is composed of a thyristor-controlled inductor and capacitor (TCLC) part and injection circuit coupling active H-bridge part. TCLC can be controlled to resonate at the highest energy fundamental frequency for damping the largest part of the dc voltage requirement. The use of TCLC offsets the varying fundamental frequency demand on the dc voltage. First, this article gives a joint design and optimization approach for the lowest dc voltage requirement. Second, a synergistic control method of proposed IMFR is provided implementing IMFR. Third, two groups of comparative experiments show that the proposed IMFR can enlarge the current by 11.8%-38.5%. The effect on the current increase is 4.4%-7.9% higher than using only the H-bridge of the previous method when they are operated with the same dc voltage.

Submodule (SM) failures are a common fault type in modular multilevel converters (MMCs), and SM symmetrical bypass guarantees the uninterrupted operation of the system. However, the number of SMs between the phase legs is not equal after bypass, which results in a deviation in the capacitor voltage. In this condition, the SM loss difference between phase legs is large, and the reliable operation of the MMC is highly threatened. To address this problem, a loss-balancing control strategy is proposed in this article based on an asymmetric phase leg structure. Specifically, the currents of two-phase legs are improved by injecting fundamental frequency components in the proposed control strategy. In addition, the voltage stress of the device is relieved by adjusting the number of equivalent SMs. On this basis, the minimization of the average SM loss deviation between phase legs is taken as the objective function, where the solution for injecting the fundamental frequency components and the number of equivalent SMs is obtained by iterative optimization. Finally, simulation analysis and experimental results are provided to verify the effectiveness of the proposed control strategy.

The rapid and large-scale renewable energy development poses new challenges for the traditional power grid, particularly with the increasing utilization of high-power electronic interfaces. To address this, a novel grid simulator topology and its control strategy are proposed, which can generate various required waveforms with high performance. The grid simulator adopts a modular multilevel structure, a three-phase PWM module, and an H-bridge module with a shared DC bus. Model predictive control (MPC) outputs high-quality, fast voltage waveforms for accurate voltage tracking. Additionally, the model reference adaptive control (MRAC) is integrated into the PWM converter in the pre-stage to estimate the network side inductance value, which is used to improve the system’s robustness. Moreover, a switching distribution method is proposed for feedforward control to enhance reliability. Through simulation and experiment, it is verified that the proposed power grid simulator and its control strategy can effectively and accurately generate various fault waveforms such as voltage drop, voltage abrupt change, and abrupt frequency change. As a result, it can be used as test equipment for renewable energy or power electronic equipment.

To achieve a more economical and stable operation, the power output operation strategy of the electrochemical energy storage plant is studied because of the characteristics of the fluctuation of the operation efficiency in the long time scale. Second, an optimized operation strategy for an electrochemical energy storage station is presented based on the proposed efficiency transformation model. The energy storage station's economic efficiency and load-smoothing effect are studied. Finally, the proposed optimization strategy and operation indexes are verified by calculation and simulation comparison with an example of an energy storage station in Guangdong. The results show that the proposed operation strategy of electrochemical energy storage station has an excellent technical economy.

With the development of high-speed electrified railways, many serious power quality problems have arisen and caused widespread concern. In order to achieve comprehensive management of power quality, a modular railway power conditioner (MRPC) has been applied to traction systems. Because of the presence of multiple submodules (SMs), the reliability of the equipment is, however, threatened as the number of SMs increases. In medium-voltage applications, system reliability can be improved by adding redundant SMs; however, when the redundant SMs run out, the reliability of the whole system cannot be guaranteed. Therefore, a fault-tolerant method based on dc bus voltage regulation is proposed to improve the reliability of MRPC by modulation signal reconstruction. The proposed method not only achieves fault ride-through to maintain normal operation and improves the SMs voltage stress on the opposite converter but also effectively improves the overmodulation. The effectiveness of the proposed method is verified by down-scale experiments.

The inner winding of the power transformer is subjected to uniform compressive stress in the radial direction during the short circuit, which makes circular radial stability a crucial component of reliability. The radial stability evaluation system currently needs more state characteristic judgment quantity considering the manufacturing deviations(MD) and assembly gaps. Thus, there is a significant deviation in the transformer design, which seriously endangers the operation safety of the power system. This article proposes an improved radial buckling analysis method (IRBAM) to investigate the circular radial stability of inner winding. The IRBAM is implemented by defining two characteristic parameters: equivalent flexibility and MD. Besides, the relative change ratio of impedance (RCRI) is proposed as the buckling judgment for ending each short-circuit test. The destructive short-circuit tested transformer is designed with the rated power of 50 MVA and the high-voltage (HV) rated voltage of 110 kV. Then, 73 cumulative short-circuit tests are performed until impedance exceeds the permissible value based on the judgment. Finally, it is verified that IRBAM can effectively match the winding failure modes by comparing the buckling phenomena and calculation results. Further, the IRBAM can provide a reference for similar designs and verification with more minor deviations.

Currently, Z-source networks are widely employed to extend the output-voltage range of inverters operating at a low voltage DC source. However, these inverters are troubled by low power-conversion efficiency and an obvious current distortion due to the copper losses and core losses of the inductors. In addition, they have limited voltage levels. In this paper, a novel boost network composed of two power switches, two capacitors, and two diodes is proposed to overcome these shortcomings. Meanwhile, a corresponding modulation strategy is also set forth to achieve capacitor voltage self-balancing and to regulate the output AC voltage. Moreover, by adding more switched-capacitor cells, the range of the output voltage can be further improved, and the max DC/AC-voltage conversion ratio of the inverter with n cells is √3( n + 1)/3. At last, an inverter prototype with a 1 kW power rating is built, and the obtained results demonstrate that this inverter possesses the following superiorities: a wider range of output voltage, automatic balancing of the capacitor voltage, less current distortion, and high-efficiency power conversion.

The reliability of semiconductor devices directly determines the safe operation of the system. However, temperature is one of the key factors that affect the reliability of semiconductors. Since the dc component of arm current in modular multilevel converter results in the unbalanced thermal stress between the top and bottom devices in the submodule (SM), which causes the discrepancy in the lifetime of four devices inside the SM, and seriously threatens the reliability of the system. To solve this problem, an internal thermal distribution balance control between top and bottom devices is proposed in this article. The proposed control method has the advantage of reducing the junction temperature deviation between the top and bottom devices without affecting the electrical characteristics of the ac and dc ports. Moreover, the voltage stress of all devices is reduced especially for active power transfer, which alleviates the risk of overvoltage failure. The SM lifetime under the proposed control is increased by 14.2% based on full-scale simulation. Finally, a downscale experimental platform is built to verify the effectiveness of the proposed control method.

Modular input-parallel output-serial (IPOS) DC-DC converter is becoming a crucial solution for high-voltage applications due to its flexible combination form without switching device pressure limitation. It requires high efficiency, fast response, and wide-range output for broader applications. However, the existing solutions cannot simultaneously meet all these requirements. This paper proposes a new hybrid structure with interleaved LLC converters and a DAB converter. The interleaved LLC converters provide the most output voltage with fixed switching frequency and duty cycle, while the DAB converter regulates the output voltage. The wide range output is achieved by switching the LLC converter module and continuously adjusting the output voltage of the DAB converter. Furthermore, a switching control method based on the sliding-mode variable structure is proposed to achieve a smooth and fast output voltage response during the switching process. Finally, a 0.3/0.9-1.8kV, 2kW experimental platform is established to verify the proposed converter's effectiveness and advantages.

Modular railway power conditioner (MRPC) is excellent in high-speed railways power quality harnessed synthetically. However, the MRPC is composed of masses of sub-modules (SMs), which brings severe challenges to safe and reliable operation. In addition, since IGBT open-circuit is the most common fault, the diagnosis and location of the open-circuit fault are significant. In the steady-state operation of MRPC, the converters on both sides operate in the mutual rectification and inversion states, respectively. However, most of the existing open-circuit fault location strategies cannot satisfy the demand of two kinds of operation modes at the same time. To address this situation, a novel diagnosis method based on switching actions counting for IGBT open-circuit fault is proposed in this paper, which satisfies the fault location both in the rectification and inverter states. Finally, the effectiveness of the proposed control strategy is verified by simulation.

High-efficiency high voltage dc power supply is the core equipment for magnetron in the microwave industry. This article presents an input-parallel output-serial modular high isolated resonant converter for the magnetron. However, the high stray capacitance of the high isolation transformer brings some challenges, such as high turn- off current, longer dead time, increasing gain, and transformer optimization. A simplified model including the stray capacitances is built to deal with these problems, and the minimum turn- off current is derived after the detailed time-domain analysis. The appropriate deadtime and the maximum magnetic inductance needed for the proposed converter are obtained with the minimum turn- off current. Then, a 15 kW, 60 kV isolation multiple-windings output transformer is designed and optimized for the converter. The insulation design, core shape, losses, and parasitic parameters are calculated thoroughly. The Pareto optimization process optimizes the switching frequency and the transformer's turns to obtain higher efficiency and a more stable gain. The finite element method and time-domain simulation verified the optimized design results. Finally, a 0.8/2.5 kV, 15 kW all-SiC dc–dc converter module is developed to validate the proposed design. The results indicate that the module efficiency is as high as 98.6%.

The power modules become one of the most fragile and vulnerable components. To address this problem, the thermal performance of silicon carbide metal-oxide-semiconductor field-effect transistor (SiC-MOSFET) and silicon insulated gate bipolar transistor (Si-IGBT) is compared and evaluated in this paper. Firstly, the loss calculations and distribution of SiC-MOSFET and Si-IGBT are analyzed. Next, the junction temperature swing of SiC-MOSFET and Si-IGBT is calculated by the thermal resistance network method, and the analysis of the junction temperature swing at different influencing factors is elaborated. Then, a thermal platform based on optical fiber thermometer is built and experimental results are provided to validate the claims. Finally, the thermal properties of SiC-MOSFET and Si-IGBT are summarized to provide the theoretical reference for engineering applications.

The modular multilevel railway power conditioner (MM-RPC) can effectively improve the power quality of the railway power grid. However, since the operating conditions of MM-RPC frequently vary with the traction load, the junction temperatures of semiconductor devices fluctuate very drastically. Severe junction temperature swings can easily affect the service lifetime and reliability of the MM-RPC. In this article, a power hysteresis based on incomplete compensation control strategy is proposed. The proposed control can effectively reduce junction temperature fluctuations under complex mission profiles and increase the overall life of the system while meeting the power quality requirements. Furthermore, the effectiveness of the proposed control is verified in MATLAB/PLECS electrothermal cosimulation under a section of the load curve of the Beijing–Shanghai high-speed railway traction substation. Finally, the experimental thermal platform is built to validate the effectiveness of the proposed control strategy.

There are many sub-modules(SMs) in the modular multilevel converter(MMC), and the voltage balance among the SMs is a prerequisite for the normal operation of the converter. Thus, in order to maintain the balance of the capacitor voltage of the SMs, a general sorting algorithm based on the capacitor voltage of the SMs is adopted. However, due to the mismatch of the parameters among the SMs, there is a deviation in the consistency of the junction temperature among them in fact. Once a general sequencing method is adopted, the reliable operation of the equipment is seriously threatened. For this reason, the mechanism of the thermal balance control method is revealed. Moreover, a new control strategy of the capacitance embedded in the voltage sorting (CEVS) is proposed considering the difficulty of collecting the junction temperature of the device. Finally, the feasibility of the proposed control strategy is verified through thermoelectric co-simulation.

Modular input-parallel output-serial (IPOS) DC-DC converter is becoming significantly crucial for high-voltage and high-power applications. However, it requires high efficiency and high power density for further development. For this purpose, an LLC resonant converter with a 1:1 turns ratio transformer is adopted as the basic module in this paper. It utilizes soft switching to realize high efficiency. Besides, the converter uses one module cascaded an input buck converter to achieve output voltage regulation. Moreover, a hybrid interleaved structure design is proposed to reduce the capacitance value significantly. Based on these, an 80kW, 800V (input), 3-3.6kV (output) IPOS converter is designed, which is validated the high efficiency through simulation.

In the extremely low-frequency electromagnetic wave communication system (ELFEWC), the power amplifier is required to output extremely low-frequency voltages, which makes the junction temperature swing of the power device significantly large. It brings great challenges to the overall reliability of the system. In this article, an active thermal control strategy based on modulated model predictive control (M2PC) is proposed for the extremely low-frequency power amplifier (ELFPA) in ELFEWC to reduce the junction temperature swing of the power device and extend the life of ELFPA. Specifically, the proposed M2PC can guarantee the output accuracy of the power amplifier with the fixed switching frequency. Furthermore, the appropriate switching frequency is selected by considering the tradeoff between junction temperature swing and total harmonic distortion to improve the reliability. The proposed control strategy has the advantages of reducing the junction temperature swing of the power device while meeting the output accuracy. Finally, simulation and experimental results of a 10kW ELFPA demonstrate the effectiveness of the proposed control strategy on the junction temperature swing reduction of the power switch.

开关功率放大器在民用和军事中都有着广泛的应用,如电动振动试验台、通信系统和声纳探测等重要领域.文中针对应用于极低频电磁波通信的开关功率放大器,提出基于改进粒子群算法的最优开关频率控制策略,通过该方法可以在满足一定输出电压畸变率的同时,降低极低频工况的功率器件热摆幅,延长开关功率放大器的寿命.首先分析开关功率放大器的热应力控制自由度.然后对影响设备寿命长短的重要因素——热摆幅和表征输出效果的指标——谐波畸变率(total harmonic distortion,THD),这2个变量的影响因素进行研究.在此基础上,综合考虑热摆幅和THD,提出基于改进型粒子群优化算法的最优开关频率控制策略.最后,通过仿真和实验对所提控制方法进行验证.

模块化多电平换流器(MMC)因具备模块化、调度灵活等优势得到广泛应用.然而,逆变工况下,MMC子模块上下管绝缘栅双极型晶体管(IGBT)的损耗分布不一致,导致子模块内各器件的寿命差异大,而系统可靠性取决于寿命最低的器件,因此,子模块器件的可靠性将严重威胁到换流器的安全可靠运行.为此,文中提出了一种MMC子模块IGBT损耗优化控制策略.所提策略可以在不影响输出外特性的同时,改善子模块内部器件的损耗分布,提高系统的可靠性.具体而言,分析了模块内部损耗不平衡产生的机理,并通过在调制信号中叠加修正量的方式,减小子模块上下管IGBT的损耗偏差,实现了结温均衡.最后,通过损耗优化的数学证明及热-电联合仿真和器件寿命计算,验证了损耗分析的正确性及所提损耗优化控制策略的可行性.

开关功率放大器在民用和军事中,如电动振动试验台和电声发射系统等重要领域都有着广泛的应用.首先研究了一种模块化多电平结构的大功率开关功率放大器,介绍了其工作原理,并着重分析了模块化多电平开关功率放大器的热损耗,讨论了其损耗与负载功率大小以及功率因数的关系.然后根据理论分析结果,对模块化多电平开关功率放大器的散热系统进行了设计,并通过热仿真软件PLECS和有限元分析软件ANSYS对所设计的热系统进行了仿真验证.最后研制了30 kW的模块化多电平功率放大器样机,对理论分析和仿真分析结果进行了实验验证.