The main battery voltage of electric vehicles (EVs) has been suggested to increase to an 800-V system, which improves driving distance and charging speed. However, the design of an 800-V dc/dc ...converter is challenging because of the high voltage and current stress of the switching devices. Therefore, this article proposes a novel double-inductor rectifier with separated resonant circuits (SRCs) based on a phase-shift full-bridge (PSFB) converter for 800-V on- board charger (OBC) applications, which overcomes the drawbacks of the frequency stress of the diodes in a single-series resonant circuit (SSRC). Moreover, the configuration of input-series–output-parallel (ISOP) improves the voltage safety margin, and the use of 650-V switching devices reduces the system cost. In addition, the SRC achieves more effective energy transfer, which greatly reduces the switching loss and the thermal effects of high-power transmission by achieving a wide range of zero-voltage switching (ZVS) in the leading-leg switches and zero-current switching (ZCS) in the lagging-leg switches. Finally, the effectiveness of the proposed converter is validated on a 760-V/20-kW experimental prototype with 98.3% maximum efficiency.
This article proposes a novel single-stage isolated cascade photovoltaic (PV) inverter topology based on a multibus dc collection. The PV power plant can be divided into many arrays, each of which ...supplies power to three cascaded isolated inverter units through a dc bus. This isolated inverter unit is composed of cascade isolated bridge cells (I-BCs) connected in input-parallel output-series (IPOS). Compared with a conventional two-stage isolated cascade PV converter, the proposed PV topology can totally eliminate the individual dc-link capacitors at the high-voltage (HV) side, which leads to extremely reduced system volume and eliminated the voltage-balancing control between the dc-link capacitors. This article, first, describes the basic principle and the carrier phase shift pulse-width modulation (CPS-PWM) applied to this topology and, then, analyzes the power balance constraints between the cascade three-phase units for the PV grid-connected system. Finally, the effectiveness of the novel topology is verified by the simulation and experimental results.
In the medium-voltage AC/DC distribution networks with distributed renewable sources on islands, a multi-port receiver is the key factor for hybrid power conversion. However, the most used modular ...multilevel converter (MMC)-based multi-port converters (MCs) face the coordination and complexity challenges due to their double-stage control system and voltage-balancing control of capacitors. In particular, the control system is more unstable and complicated when the control of circulating currents is considered. In this paper, an isolated modular multilevel converter (I-MMC) is used as a receiver, and a unified coordinated control scheme based on the multiple modulation freedoms is proposed. Due to the voltage clamping of high-frequency transformers, there is no concern of the capacitors' voltage-balancing control. Based on the proposed single-stage control system, the unified coordinated control scheme solves the coordination problem of the MMC-based MCs. The multiple modulation freedoms corresponding to an AC port, two DC ports, and three-phase circulating currents can independently control respective targets. The control structure is simplified, while the control freedoms are ensured. Experimental results confirming the performance of the designed control system is shown.
In the three-phase photovoltaic (PV) cascaded inverter, the output power of PV arrays is not equal due to the difference of solar radiation, temperature and other factors, which leads to the over ...modulation of PV cascaded inverter. In order to solve the above problems, the carrier phase-shifted PWM (CPS-PWM) control strategy based on third harmonic injection is proposed in this paper, taking a single-stage high-frequency-link isolated cascaded PV inverter topology with clamping circuits as an example. It can not only improve the utilization of DC voltage, but also enlarge the power balance constraint range between the units in the phase of cascaded PV inverter, so as to ensure that all units can avoid over modulation under some serious power imbalance cases, and will not increase the third harmonic component injection of grid current. Firstly, the topology and working principle of the proposed inverter based on CPS-PWM control strategy are introduced. Then, the improved CPS-PWM control strategy which can improve the DC voltage utilization of the PV cascaded inverter is analyzed, and the control strategy of intra-phase power balance is emphatically analyzed in the overall control strategy of PV cascaded inverter system, and it is discussed that the proposed control strategy can also enlarge the power balance constraint range between the units of the cascaded inverter. Finally, the effectiveness of the proposed PV cascaded inverter based on the improved CPS-PWM control strategy is verified by the simulation and experimental results.
This paper introduces the high-frequency link concept into the modular multilevel converter (MMC) topology, which can totally reduce the individual dc-link capacitors at the high-voltage side. The ...proposed converter, called isolated MMC, has basic triple ports of medium-voltage ac, medium-voltage dc, and low-voltage dc. Thus, it is especially suitable for hybrid dc and ac applications in power generation and transmission, such as solid-state transformer. The fundamental principle and applied control scheme of phase-shift pulsewidth modulation are presented in detail. The design of the voltage clamping circuit and analysis of duty loss are carried out. The experimental results are given to illustrate the efficient operation characteristics.
Based on partial power conversion concept, this article proposes a hybrid silicon carbide (SiC)-silicon (Si) dc-ac topology to improve performance in high power application. First, master unit (MU) ...uses Si-IGBT working in low frequency to handle main high power because of its high rated current capacity and high switching loss, whereas the low power quality of MU is induced by the low switching frequency. And SiC-MOSFET suffers from high cost and high conduction loss at high power level. To solve these problems, the partial-power slave unit (SU) based on SiC-MOSFET is connected with MU in series through line-frequency transformer, whereas SU works in high frequency to compensate the harmonic of MU and adjusts the total output voltage. In this new topology, the corresponding hybrid modulation strategy and multiple quasi-proportional-resonance control for single-phase system are introduced in detail to ensure the reliable operation. In the end, a 4.5-kW converter prototype was implemented and tested. Simulation and experiment results are given to verify the performance of the proposed hybrid dc-ac topology.
This paper proposes a novel solid-state transformer (SST) having a low-frequency medium-voltage AC (LF-MVAC) port distinctively, which can be as the key equipment for smart distribution networks ...based on LF-MVAC interconnection. The proposed SST has four ports of power-frequency medium-voltage AC (MVAC), LF-MVAC, low-voltage DC (LVDC), and lowvoltage AC (LVAC). In addition to the two-level low-voltage DC/AC converter, the proposed SST is mainly composed of an isolated modular multilevel matrix converter (I-M3C), which can achieve single-stage three-port power conversion. First, the topology of the I-M3C is introduced. Then, a simple modulation scheme is provided to achieve single-stage three-port power conversion, and the operating principles of the I-M3C are given in detail. Additionally, a control strategy based on dual-dq coordinate system is designed, which can achieve stable operation without the complex multi-stage coordinated control and voltagebalancing control strategies. Finally, the effectiveness of the proposed control strategy is verified through a 10-kV/2-MW full power simulation platform, and a 100-V/1-kW scaled-down experimental prototype is built to further demonstrate the correctness of the proposed I-M3C.
This paper proposes a novel triple-port solid-state transformer (SST) topology based on a hybrid isolated modular multilevel converter (HI-MMC), which overcomes the limitation of voltage ratio R(pu) ...in the conventional MMC-based SST. By integrating a high-frequency link into the MMC structure and applying various types of isolated submodule (ISM), the proposed SST can function as a step-down rectifier, where UMVDC < UMVAC(p-p). In this case, the power electronics converters used to connect downstream MVDC-Link and distributed energy resources (DER) or battery storage require fewer active devices and may minimize the cost of protection equipment. In addition, the proposed SST retains the significant advantages of single-stage SSTs, such as single-stage power conversion, saving capacitor, and a simple control system. First, the topology and modulation strategy of two types of ISMs are discussed. In addition, this article provides a detailed analysis of operation principles, power flow, grid-tied control, and system reliability. Moreover, the proposed converter is compared to other SST topologies in terms of key performance indicators, such as peak efficiency, system volume, and number of active semiconductor devices. Finally, a 300 V/20 kW scaled-down prototype is developed, and the experimental results demonstrate the performance and verify the correctness of the proposed converter.
This article introduces a novel bidirectional high-frequency isolated direct ac/ac converter with unipolar phase-shifted modulation strategy based on double dc modulation indexes. The main idea of ...topological construction is that the non-isolated two-level nondifferential bipolar direct ac/ac converter is combined to the bidirectional phase-shifted full-bridge converter, which inherits the advantages of no commutation problem, zero voltage switching, simple control, bipolar output voltage gains, et al. The operating principles of this converter and the design considerations for the key parameters are given in detail. Moreover, the application in voltage sag/swell compensation is simply analyzed. Thanks to the high-frequency isolation capability, it satisfies needs of distribution networks in terms of sensitive loads protection, voltage resilience control without applying the bulky line frequency transformers. Finally, the feasibility of this proposed topology is verified by the various experimental results of the prototype.
This paper proposes a single-phase bipolar pulse-width modulation (PWM) direct ac-ac converter with unipolar modulation strategy. The converter is composed of two odd symmetrical two-level ...no-differential ac chopper legs, which can work in non-inverting and inverting modes for the utility voltage sag or swell compensation. The number switches working at high frequency in each operating mode are minimized thanks to the proposed unipolar modulation strategy, so the total switching losses can be effectively reduced in theory, and the efficiency of the converter is improved. In addition, capacitor symmetry can be realized in the positive and negative half cycle of the input voltage, and the converter has no commutation problems. Finally, on the basis of theoretical analysis, the experimental results under different working conditions are also provided to verify the correctness of the theoretical analysis and the superiority of the proposed topology and modulation strategy.
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