Full-bridge current source high frequency link inverter

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Full-bridge current source high frequency link inverter [Copy link]

Abstract: The full-bridge current source high-frequency link inverter is based on the Flyback converter and consists of three parts: a full-bridge high-frequency inverter, a high-frequency transformer and a cycloconverter. Its high-frequency transformer can not only realize the electrical isolation and voltage gain adjustment functions, but also store energy. This inverter solves the inherent voltage overshoot problem of the voltage source high-frequency link inverter, reduces the switching loss of the cycloconverter, simplifies the structure of the high-frequency transformer, and reduces the switching voltage stress of the inverter. This paper introduces its topology, working principle, control scheme and brief design. The simulation results and the experimental results of the prototype show that the inverter has the following advantages: compact topology, simple control scheme and high-frequency transformer structure, good dynamic response, nonlinear load capacity and low switching voltage stress.

Keywords: high frequency link inverter topology simulation

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1 Introduction Recently, high-frequency link inverter technology has aroused more and more research interest. High-frequency link inverter technology uses high-frequency transformers to replace the bulky industrial frequency transformers in traditional inverters, which greatly reduces the volume and weight of the inverter. In this paper, the existing high-frequency link inverters are divided into two categories according to the function of the high-frequency transformer: voltage source and current source. Different from the voltage source high-frequency link inverter, the high-frequency transformer in the current source high-frequency link inverter can not only realize electrical isolation and voltage gain adjustment, but also has the function of storing energy. However, this scheme can only transmit power in one direction, and requires three-stage power conversion DC-HFAC-DC-AC, resulting in higher conduction losses.

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Bidirectional voltage source high frequency link inverter is a common solution for realizing bidirectional power transmission at present [1,2,3]. This solution omits the DC link in the solution shown in Figure 1 and only requires three power conversion stages (DC-HFAC-AC), which reduces the conduction loss of the inverter. However, this solution has an inherent voltage overshoot problem: when the continuous current in the high frequency transformer is interrupted by the commutation of the device of the cycloconverter, the energy stored in the leakage inductance of the high frequency transformer will lose its release loop, resulting in voltage overshoot between the high frequency transformer and the cycloconverter. Therefore, a buffer loop or active clamping circuit must be used to absorb this part of the energy [3]. In order to solve this inherent problem, the literature [1] adopts a phase angle control scheme based on natural commutation in the cycloconverter to release the energy in the leakage inductance or feed it back to the input power supply through the commutation overlap phenomenon. However, this scheme can only be applied to instantaneous current control systems.

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The current source high frequency link inverter is based on the topology of the Flyback converter [4-6] and is also composed of three parts: a high frequency inverter, a high frequency transformer and a cycloconverter. Its high frequency transformer can not only realize electrical isolation and voltage gain adjustment functions, but also store energy. Therefore, the output filter inductor can be omitted and the voltage overshoot problem of the voltage source high frequency link inverter is solved. Therefore, the current source high frequency link inverter has a compact topology, a simple control scheme and good dynamic performance. However, in the inverter topology proposed in reference [4], the transformer structure is complex and requires two secondary windings, and each secondary winding only works for half of the power frequency cycle, resulting in low winding utilization. In addition, the current source high frequency link inverter works in the current discontinuous mode, resulting in higher current, voltage stress and conduction loss. The full-bridge current source high frequency link inverter is composed of three parts: a full-bridge high frequency inverter, a high frequency transformer and a cycloconverter. This scheme has a simpler high frequency transformer structure and lower switching voltage stress than the circuit topology in reference [4]. This paper explains its basic working principle, control scheme and brief design. The simulation results and prototype experimental results verify the conclusions of this paper. 　

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2 Main circuit description 2.1 Working principle Circuit waveform of full-bridge current source high-frequency link inverter, where the load is inductive load (power factor is cosφ), and the inverter works in current discontinuous mode. The inverter is based on the Flyback converter topology. Its high-frequency transformer can not only realize electrical isolation and voltage gain adjustment functions, but also store energy. Switches S5 and S6 in the cycloconverter usually work at the industrial frequency, and only work at high frequency when the load feeds energy back to the power supply. However, the switching devices in the voltage source high-frequency link inverter always work at high frequency. Therefore, this solution can solve the voltage overshoot problem inherent in the voltage source high-frequency link inverter and reduce the switching loss of the cycloconverter. Its high-frequency transformer has only one secondary winding, and its structure is simpler than that in the literature [4], which improves the utilization rate of the winding.

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The inverter has four-quadrant working capability, and each quadrant is a Flyback converter. When the output voltage and current are in the same direction, the inverter works in quadrants I and III, and the corresponding circuit topology is shown in Figure 5 (a) and (c). The power flow of the inverter is from input to output. When the output voltage and current are in opposite directions, the inverter works in quadrants II and IV, and the load feeds back energy to the power supply. Therefore, the current source high-frequency link inverter can transmit power in both directions and can be used in many applications.