A new modulation scheme for the active clamping zero-voltage switching (ZVS) inverter is proposed. With the proposed modulation scheme, the inverter can realize ZVS operation in all switching devices and can remarkably suppress the reverse recovery current in insulated-gate bipolar transistor's antiparallel diodes as well. All the switches can operate at a fixed frequency in the new modulation scheme. Also, with the new modulation scheme, the ZVS inverter has some voltage boost capability, which is suitable for renewable energy generation. The inverter can achieve ZVS in all the switches under the grid current power factor angle from zero to ±π/6. The soft-switching condition of this inverter is analyzed. The operation principal and design guideline are described in detail. The previous theory is verified in a 30-kW inverter prototype.

A Zero-Voltage Switching Three-Phase Inverter

Three-phase voltage source converters (VSCs) are commonly used to convert ac power from a three-phase grid to a regulated dc voltage with unity input power factor. The control of the VSC is normally achieved by an outer voltage feedback loop and a sinusoidal pulsewidth-modulated inner current loop. However, the nonideal power grid and the presence of other interacting loads give rise to nonlinear operation and drive the VSC to enter an irreversible instability region. In this paper, an irreversible bifurcation phenomenon in a three-phase VSC connected to a power grid with an interacting load is reported. The converter can also be regarded as exhibiting a catastrophic bifurcation in which the input current expands to impose undesirable component stress. A large-signal analysis is adopted to identify the physical origin of the phenomenon and to locate the boundary of the instability. Experimental results on a 4-kVA ac/dc converter prototype provide verification of the instability phenomenon.

Nonlinear Behavior and Instability in a Three-Phase Boost Rectifier Connected to a Nonideal Power Grid With an Interacting Load

Three-port three-phase rectifiers (TPTPRs) are proposed by introducing a new low-voltage (LV) dc power port into the three-phase six-switch boost rectifier. An ac input port, an LV dc load port, and a high-voltage (HV) dc bus port are provided simultaneously by TPTPRs. A dc load, whose voltage is lower than the peak amplitude of the ac line voltage and varies over a wide range, can be connected to the LV dc load port of the TPTPR directly. A modified space vector pulse width modulation (SVPWM) strategy is proposed for the TPTPR to accomplish voltage and current regulations, based on which part of the ac input power can be directly fed to the LV dc load within single power conversion stage. As a result, the power rating and losses of the downstream dc–dc converter, which is connected to the HV dc bus port of the TPTPR, are reduced significantly. The conversion efficiency of the TPTPR-based ac–dc converter benefits not only from the reduced power conversion stages, but also from the reduced switching losses due to the multilevel characteristics of the TPTPR. Operation principles and characteristics of the proposed TPTPRs and modified SVPWM strategies are analyzed in detail and verified with experimental results.

Modified SVPWM-Controlled Three-Port Three-Phase AC–DC Converters With Reduced Power Conversion Stages for Wide Voltage Range Applications

This paper presents a control strategy using optimized switching sequences which results in capacitor voltage balancing of a three-phase neutral-point-clamped rectifier. In front end rectifiers, magnitude and lag angle of reference current vector (w.r.t supply voltage vector) varies depending upon amount of reactive power compensation and load current. Accordingly, the effectiveness of small and medium vectors (using SVPWM) for same switching state varies in each sector and its regions. This observation along with detailed analysis of current pattern for both the capacitors and their effect on neutral point voltage forms the basis of the proposed approach, which is to modify the reference vector for changing the number of sampling periods within each sector and its regions. The rectifier exhibits excellent performance in terms of other critical parameters like unity input power factor, low input current THD, minimum possible switching losses, reduced-rippled, and well-regulated dc-bus voltage, particularly, the capacitor voltage balancing. The proposed control algorithm is tested through exhaustive simulations and validated through experimental results obtained from a laboratory prototype of the rectifier.

Capacitor Voltage Balancing of Three-Phase Neutral-Point-Clamped Rectifier Using Modified Reference Vector

In this paper, a switching loss-free (SLF) concept for the first six-switches H-bridge inverter (H6-I) topology is proposed. SLF means that its switches are able to operate with soft turn-on and turn-off transitions. In order to implement the SLF goal, a new resonance-trajectory is proposed. Compared with the zero-current-transition H6-I (ZCT-H6-I) topology published in previous literature, the proposed resonance-trajectory can precisely compensate for losses of resonant tanks every switching period. With this intention, an implementing circuit is structured based on the H6-I topology, and its detailed operation principle and performance characteristics are analyzed. As a result, all active switches of the new circuit are switched under zero-current turn-on and zero-current turn-off conditions. Also, the reverse recovery problem of freewheeling diodes is alleviated owing to the zero-current turn-off property of diodes. The SLF target is realized in theory. Finally, experimental results from a 1 kW prototype at 50 kHz switching frequency are provided to verify the effectiveness of the proposed SLF concept in practice. Specifically, the conversion efficiency of the new circuit is over 95% in a wide load range, and there is roughly a 1.5% efficiency improvement compared with the hard-switching H6-I topology.

An Improved Zero-Current-Switching Single-Phase Transformerless PV H6 Inverter With Switching Loss-Free

A novel active clamping zero-voltage switching three-phase boost pulsewidth modulation (PWM) rectifier is analyzed and a modified minimum-loss space vector modulation (SVM) strategy suitable for the novel zero-voltage switching (ZVS) rectifier is proposed in this paper. The topology of the novel ZVS rectifier only adds one auxiliary active switch, one resonant inductor, and one clamping capacitor to the traditional hard-switched three-phase boost PWM rectifier. With the proposed SVM strategy, the novel ZVS rectifier can achieve ZVS for all the main and auxiliary switches. In addition, the antiparallel diodes can be turned OFF softly, so the reverse recovery current is eliminated. Besides, the voltage stress of all the switches is equal to the dc-link voltage. The operation principle and soft-switching condition of the novel ZVS rectifier are analyzed. The design guidelines of the soft switched circuit parameters are described in detail. A DSP controlled 30 kW prototype is implemented to verify the theory.

A Novel DC-Side Zero-Voltage Switching (ZVS) Three-Phase Boost PWM Rectifier Controlled by an Improved SVM Method

An active clamping soft-switching three-phase grid-connected inverter is introduced in this paper. With adding a simple auxiliary branch, all of the switches in the inverter can realize zero voltage switching (ZVS). No additional voltage stress will be caused. A modulation scheme to realize high efficiency power conversion is presented in this paper. Especially when the grid side power factor is not unity, modulation scheme is discussed. The proposed modulation scheme is verified in a 30kW prototype.

Xu Zhang

Papers

A Novel DC-Side Zero-Voltage Switching (ZVS) Three-Phase Boost PWM Rectifier Controlled by an Improved SVM Method

Study on an active clamping soft switching grid-connected inverter