A Single-Stage Single-Phase Buck-Boost Inverter without Electrolytic Capacitor

The existing single-stage, single-phase non-isolated inverters need to solve the following problems: buck and boost voltage capability, electrolytic capacitors, single-supply inputs, the number of topology devices, device multiplexing rate, and the overall simplicity of topology and control, while most of the existing solutions can not take into account all problems. This paper proposes a simple and compact inverter. Its topology can meet the requirements of the Buck-Boost voltage without electrolytic capacitors. It only needs a low-value inductor as an energy storage component, and fewer power and passive devices. The proposed inverter is lightweight, has a high device reuse rate, and has simple working and control modes, suitable for small and medium-power photovoltaic power generation systems. The circuit consists of 6 IGBT switches (S1～S6, S3, and S4 with inverse resistance IGBT, the others are bidirectional IGBTs), 1 DC inductor, 1 AC filter capacitor, 1 AC filter inductor, and a single DC input power supply (photovoltaic panel). The output side is connected to the load or merged into the grid. After consulting a large number of domestic and foreign literature, it is found that the inverter proposed in this paper has superiority in structure. This paper provides a theoretical analysis of the circuit. The circuit has six operating modes when the energy storage inductor Ldc current is interrupted. The operating modes I, II, and V are positive half-cycles, and III, IV, and VI are negative half-cycles. Due to the special structure of the H-bridge front on the input power side, unipolar SPWM modulation is used, in which S3, S4, S5, and S6 power frequencies work, and S1 and S2 semi-high frequencies work. In this paper, the inverter has a good Buck-Boost capability, and the voltage gain is related to the duty cycle, DC inductance, and switching frequency. The maximum voltage stress of switches S1, S2, S5, and S6 is Uin+Uo, the maximum voltage stress of switches S3 and S4 is Uo, and the maximum current stress of all switches is Im. The parameters of the energy storage inductor and the filter in the circuit are designed separately, the energy storage inductor Ldc=0.25 mH, the filter capacitor is 2.2 μF, and the filter inductor is 3 mH. According to the theoretical, simulation, and experimental results, it can be concluded that the overall structure of the inverter proposed in this paper is simple, the power devices and passive devices are used less, and only one DC inductor works in positive and negative half weeks for energy storage and release, and the utilization rate is high. In the overall principle and cost of the switch selection, full use of the IGBT reverse diode reduces the device waste rate and loss rate. Compared with multi-stage and isolated inverters, the proposed inverter can improve efficiency, and is flexibly controlled by changing the modulation ratio to achieve a balanced Buck-Boost inverter, which can be well adapted to the wide range of DC input changes. Under the front-facing H-bridge structure, a simple control mode can make the inverter output sinusoidal degree good for low DC inductance, control volume, and cost while improving the power density. Clever power frequency breaking, high-frequency working mode makes the control not need a high-frequency dead zone to distort the output, which has excellent anti-disturbance ability. © 2023 Chinese Machine Press. All rights reserved.