翻译：高频软开关PWM功率变换技术的发展与现状.doc

Development and Present Status of High FrequencySoft Switching PWM Power Converting TechniquesChen Daolian Yan Yangguang(Nanjing University of Aeronautics & Astronautics)Key words: Soft Switch PWM, Zero Voltage Switching, Zero Current SwitchingAbstract: Recently, power electronics researchers have proposed many soft switchingPWM power converting techniques, which combined advantages of both conventional PWM and resonant converters while avoided their respective limitations. In this paper, the features and operating principles of three classes of zero voltage soft switching PWM converters ( zero voltage switching quasi square wave converters, zero voltage switching PWM converters, and zero voltage transition PWM converters) and two classes of zero current soft switching PWM converters ( zero currents witching PWM converters and zero current transition PWM converters) are introduced.1. INTRODUCTIONIn order to meet the needs of small size, light weight, high efficiency power supply, and the switch type power conversion technology has from the traditional PWM converter development to resonant converter, quasi resonant converter, multi resonant converter. Recently, there has been soft switching PWM converter. The PWM converter is used to force the switching mode to interrupt the power flux to transform power. The result is that the pulse current and voltage are formed, and the power semiconductor device is subjected to large voltage and large current stress. The resonant converter comprises a conventional series and parallel resonant converter, an E converter, a quasi-resonant converter and a multi resonant converter. Power switch with zero voltage switching (ZVS) or zero current switching (ZCS) commutation, switching losses and switching transient stress than the PWM converter is low. But resonant converters are circulation circuit with high energy and steady-state voltage and current stress and device loss, ZVS or ZCS conditions on the variation range of the supply voltage or load sensitive, frequency of mode faults, and circuit design difficult to optimize.Recently, power electronics researchers propose all kinds between PWM and resonant technology of soft switching PWM technique (Soft-Switching techniques), its purpose lies in does not need too much energy cycle can achieve soft switching. Generally speaking, soft switching technology uses some resonance technology to soften the switching, switching converter to complete the converter to restore its similar PWM mode, making the circuit of the minimum cycle energy. Thus, the switching loss is greatly reduced in the case that the conduction loss is minimized.2. Zero voltage soft switching PWM transform technologyMany studies have shown that using power MOSFET as the power switch of the high frequency power conversion, ZVS is the preferred mode of operation.2.1 ZVS quasi square wave converter (ZVS-QSC)1ZVS-QSC switch as shown in Figure 1, S based switches, S1 for the auxiliary switch, Cr for the absorption of the S and S1 output capacitors, L both filtering and harmonic dual function. In order to obtain S1, ZVS can be a passive switch diode or an active switch. If the S1 is implemented by the diode, then the ZVS-QSC will work in the critical conduction mode PWM converter, in order to obtain the ZVS need to fix the input and output conditions. When the input voltage or load current is changed, the duty cycle and the switching frequency are adjusted in order to maintain the output stability and the ZVS condition. However, if S1 by the active switch to achieve, then ZVS-QSC can work in the constant frequency mode, and in the power supply and load variation range to obtain ZVS.Figure 1 ZVS-QSC switchWith ZVS-QSC switch to replace the basic PWM converter PWM switching can be derived as an example of a family of ZVS-QSC, Buck ZVS-QSC converter and the principle of waveform as shown in Figure 2, the circuit with bidirectional power flow and application in bi-directional power conversion applications such as battery charge / discharge occasions.ZVS-QSC realize the 2 transistors ZVS, switching voltage stress is minimum, to achieve two-way power flow. But it has disadvantages such as large transistor peak current, large input and output current ripple, and transformer leakage inductance, which is not suitable for IGBT, BJT, GTO and other small power devices.Figure 2 ZVS-QSC Buck circuit and its principle waveform2.2 Zero voltage switching PWM converterZVS-PWM converter can be as ZVS-QRC (zero voltage switching quasi resonant converter and the PWM converter, hybrid circuit in ZVS-QRC switch in both ends of the resonant inductor add an auxiliary switch can be obtained ZVS-PWM switch, as shown in Figure 3 (a) shows. The auxiliary switch S1 by short circuit resonant inductance Lr periodically eliminate circuit resonance, each cycle is only a short time resonance phenomenon, this is only used to create conditions for ZVS power switch. Pass the time by controlling the S1 guide can be obtained working frequency.Figure 3 Zero voltage and zero current switching PWMReplace PWM switch PWM converter with the ZVS-PWM switch, it is derived from a family of ZVS-PWM converters. Figure 4 shows the ZVS-PWM Buck converter circuit and the principle of waveform. The power switch to achieve the ZVS, the current stress is small, but the voltage stress (load range proportional), rectifier diode does not work in the soft switching condition, ZVS condition of input voltage and load variation sensitivity.Figure 4 ZVS-PWM Buck converter and its principle of waveform2.3 Zero voltage switching PWM converterResonant converter (including ZVS-PWM and ZCS-PWM) are common features of shaping the voltage and current waveforms using the resonant inductor, the resonance between the resonant inductor and resonant capacitor to achieve soft switching. Because the resonant elements are located in the main power channel, so it has the following problems:Resonant inductance under bidirectional voltage, inevitably produce additional voltage stress applied in semiconductor devices; all the power flow to produce high circulating energy through the resonant inductor, greatly increased the conduction losses; resonant inductance stored energy and the power supply voltage and load flow is closely related to, so soft switching conditions of supply voltage and load current is sensitive to the change of the, which is why most resonant converter in a wide power supply voltage and load range is difficult to maintain the fundamental cause of the soft switch.In order to overcome these shortcomings, it is necessary to resonant sensor is removed from the main channel, the power switch is connected in parallel with a resonant network is replaced series resonant element, switching during parallel resonant network resonant ZVS or ZCS and switch after the end of the circuit and to restore the similar to PWM mode. This approach makes the converter to obtain both PWM converter has the advantages of soft switching. ZVS-PWM and zero current switching PWM converter (ZCT-PWM) is the use of the concept of the parallel resonant network.The parallel resonant network in PWM switch is the derivation of ZVT -PWM switch, as shown in Figure 5 (a) shows. This is the resonant network by the resonant inductance Lr, auxiliary switch S1 and the diode D1, Cr is absorbed by the resonant capacitor switching power output capacitor and diode junction capacitance. Replacing the PWM switch with ZVT-PWM switches can be derived from the gens ZVT-PWM converter due to resonant network and the power switch are connected in parallel, the ZVT-PWM can make the transistor and diode voltage and current should be minimal force obtained under soft switching. This is the PWM converter with soft switching stress condition is put forward for the first time in no additional switching voltage and current technology.Figure 5 Zero voltage switching and zero current switchZVT-PWM Boost converter circuit and its principle of waveform as shown in Figure 6. Crystal triode and diode rectifier are soft switching, switching voltage, current should be minimum force, the power supply voltage and load range can achieve soft switching; but ZVT-PWM technology difficult to absorb transformer leakage inductance (similar to the ZVS-QSC) assisted switch is hard switch.Figure 6 ZVT-PWM Boost converter and the principle of waveformThe switch loss of auxiliary resonant circuit than PWM converter switching loss is much lower. First, ZVT-PWM converter, the switching loss is the capacitance of the auxiliary switch S1 turn-on loss, it is necessary to than capacitive PWM converter main switch turn-on loss is much lower, because S1 only with much lower effective current value, so you can use the low output capacitance of small capacity MOSFET devices as S1. If S1 is used to achieve MOSFET, because of its gate drive impedance is very low, so the S1 turn off loss is negligible. Secondly, ZVT-PWM converter auxiliary diode always working in ZCS, thus eliminating the problem of serious reverse recovery. However, PWM converter rectifier diode reverse recovery loss accounted for the total loss of the switch, so the ZVT-PWM technology is especially suitable for high output applications.3. Zero current soft switching PWM converterDue to the IGBT switching characteristics of continuous improvement, low conduction loss and price, it has been applied in the converter and inverter switching power converter is widely used in the. Because IGBT is less load device, turn off the performance of the current tailing phenomenon has resulted in a considerable loss off. In order to make IGBT work in a relatively high switching frequency, ZVS or ZCS technology can be used to reduce the switching loss. In general, ZVS eliminates the capacitive turn-on loss, by slowing the rate of voltage rise rate and reduce the overlap time of switch voltage and current to reduce the turn off loss, this technique for small tail current fast IGBT speaking is effective. If the application of ZCS technology in the switch before the voltage rise forced switch current to zero, it can eliminate the voltage and current overlap. In the aspect of ZCS is more effective than ZVS IGBT to reduce switching losses, especially for the slow component is even more so, this part introduces the zero current switching PWM converter.Figure 7 ZCS-PWM Buck converter and its principle of waveform3.1 Zero current switching PWM converterIn the zero current quasi resonant switch in ZCS-QRC, add a series with the resonant capacitor Cr auxiliary switch S1 ZCS-PWM switch can be obtained, as shown in Figure 3 (B). Auxiliary switch S1 is by disconnecting the Cr eliminating periodically between Lr and Cr resonant, ZCS-PWM switch and ZVS-PWM switching mutually dual relationship, ZVS-PWM converters can be as ZCS-QRC and PWM converter for hybrid circuit. Figure 7 ZCS-PWM Buck converter circuit and the principle of waveform. Power switch S and auxiliary switch S1 to achieve ZCS, diode rectifier ZVS and converter belongs to the constant frequency mode; but the power switch parasitic oscillation ZCS of supply voltage and load sensitive to changes, voltage rectifier diode should stress (is 2 times of the PWM converter).Figure 7 ZCT-PWM Boost converter and its principle of waveform3.2 Zero current switching PWM converterSimilar to the ZVT-PWM technology, the application of parallel resonant network concepts can be derived from a family of ZCT-PWM converters. Figure 5 (b) is the ZCT-PWM switch, which is composed of parallel resonant network (composed of resonant inductance Lr, resonant capacitor Cr, auxiliary switch S1, auxiliary diode D1) added in PWM switch. Only in a short period resonant branch switch of the positive role, as the main power switch to create conditions ZCS.Figure 8 ZCT-PWM Boost converter and its principle of waveform. ZCT-PWM technology to achieve the power switch ZCS, powe