of kHz. Since switching loss is proportional to switching frequency, switching loss of the power semiconductor in a high speed drive is so high that the power devices have to operate at its derating state for the safety. Thus the power rating of power device is unable to be fully utilized. An auxiliary resonance circuit is introduced to the DC side of the inverter as shown in Figure 1.26. The switch loss of the inverter is significantly reduced due to soft‐switching of the power devices in the inverter.
1.3.6 Fast EV Chargers
To reduce charging time of EV, power rating of EV chargers is becoming large and large. The EV charger shown in Figure 1.27 is composed of two power conversion stages. To increase power density of the charger, soft‐switching technique is used. The first stage is three‐phase rectifier where an auxiliary resonant circuit is introduced to realize soft‐switching for the rectifier. For the second stage, double inductors and one capacitor (LLC) resonant DC/DC converter is used. It can realize soft‐switching for all switches in the DC/DC converter. All switches in EV charger can realize soft‐switching so that its power density is enhanced.
Figure 1.26 High speed drives with auxiliary resonance circuit.
Figure 1.27 Soft‐switching EV charger.
1.3.7 Power Supply
With development of big data, cloud computing, etc., it is more stringent than ever to require the data centers to have higher computing speed and density with less energy consumption. Compared with super junction Metal‐oxide‐semiconductor field effect transistors (MOSFETS), Gallium nitride high Electron mobility Transistor (GaN HEMT) shows significant improvement on the switching performance, but its switching frequency is still limited when hard switching is used. A ZVS totem‐pole PFC circuit with fixed switching frequency is investigated for server power supply [34]. In Figure 1.28, the right leg with switch S2H and S2L operates at utility frequency and silicon MOSFET is used. The left leg with S1H and S1L operates at 500 kHz and GaN HEMT is chosen. With the auxiliary circuit, the GaN device can operate at ZVS condition. The turn‐on loss of the GaN is eliminated and its turn‐off loss is reduced.
1.4 The Topics of This Book
This book will focus on the soft‐switching technology for three‐phase converters or inverters and their applications. Aiming to reduce or even eliminate the voltage and current overlapping during the switching transient process, soft‐switching techniques provide a solution for power converters to achieve high conversion efficiency with dramatic reduction of the switching losses. This book is divided into four parts:
Part 1(Chapters 1–3) will provide an introduction to fundamentals of soft‐switching technology for three‐phase conversion. Impacts of the soft‐switching technique on three‐phase converter performance such as conversion efficiency, power density, and EMI noise is explained. Applications of three‐phase power converters in renewable energy, industry drives, power supplies, etc. are introduced. Development of soft‐switching technology for three‐phase converters is reviewed. A general soft‐switching PWM method for three‐phase converters, edge‐aligned PWM (EA‐PWM), is introduced.
Figure 1.28 ZVS totem power‐factor‐correction circuit.
Part 2(Chapters 4 and 5) will investigate applying soft‐switching technology to three‐phase rectifiers. Two types of soft‐switching circuits are investigated. It includes circuit analysis, soft‐switching condition derivation, and circuit parameters design. Then experimental result of the soft‐switching rectifier prototypes are provided.
Part 3(Chapters 6–9) will aim at applying soft‐switching technology to three‐phase grid inverters. Two types of soft‐switching circuits are investigated. It includes circuit analysis, soft‐switching condition derivation, and circuit parameters design. Then experimental result of the soft‐switching grid inverter prototypes are provided. Since the resonant inductor is a critical component with respect to its loss, size, and thermal design, design of the resonant inductor is introduced. In addition, optimization method for the grid inverter based on the loss model is provided.
Part 4(Chapters 10–12) will introduce the impact of SiC devices on soft‐switching converters. Improvement of efficiency and power density by introducing SiC to soft‐switching three‐phase converter will be investigated. Converter circuit layout design and its effect are explained. Designs of single‐phase grid inverter, a three‐phase grid inverter, and a BTB converter with soft‐switching technique are provided.
References
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2 2 P. T. Krein, Elements of Power Electronics, Oxford: Oxford University Press, 2015
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7 7 D. M. Divan and G. Skibinski, “Zero‐switching‐loss inverters for high‐power applications,” IEEE Transactions on Industry Applications, vol. 25, no. 4, pp. 634–643, 1989.
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