Soft-switching Three-phase Research Articles

Review of Three-Phase Soft Switching Inverters and Challenges for Motor Drives

Review of Three-Phase Soft Switching Inverters and Challenges for Motor Drives

A Soft-Switched Three-Phase Inductor Coupling Quasi-Z-Source Integrated Charger with Reduced Output Current Ripple for Electric Vehicles

A Soft-Switched Three-Phase Inductor Coupling Quasi-Z-Source Integrated Charger with Reduced Output Current Ripple for Electric Vehicles

A Low Q Three-Phase Series Resonant Converter for PV Applications

In this paper, a soft-switched three-phase resonant converter with a low quality factor (Q) design is proposed for Photovoltaic (PV) energy harvesting systems with a very wide range of operating conditions. Due to the low quality factor (Q ≤ 1), the voltage stress across the capacitors is drastically reduced. However, a major challenge of using a low Q design is the wide switching frequency range required for operation over a wide range of load and input conditions. In order to reduce the switching frequency range, this paper introduces a hybrid modulation technique employing asymmetric pulse width modulation (APWM) along with variable frequency modulation. The proposed modulation scheme also substantially extends the soft-switching range of the converter from full-load upto 10–35% load condition over a wide range of line voltages. To sustain soft-switching in the entire operating region of the converter, the converter is operated in a hybrid structure with single-phase and burst modes at light load conditions. A comprehensive time-domain analysis of the proposed converter is presented, which greatly improves accuracy over conventional frequency-domain modeling. Experimental results from a 1 kW prototype are presented to verify the performance of the converter and validate the theoretical analysis.

Novel Soft-Switched Three-Phase Inverter With Output Current Ripple Cancellation

A novel three-phase dc–ac full-bridge soft-switched inverter topology is proposed in this article that provides an ultralow ripple output current. The proposed circuit utilizes a passive filter that comprises a transformer, an inductor, and a capacitor for achieving soft switching and output current ripple cancellation. Zero-voltage switching (ZVS) is achieved at turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> time instant for all the switches in the proposed circuit. The magnitude of ZVS current is optimized throughout the line cycle by the application of the variable frequency modulation technique. In addition to soft switching, an ultralow ripple output current is achieved due to the current ripple cancellation property of the proposed circuit. The output current ripple cancellation is achieved by combining the inverter current with an additional high-frequency ripple current generated by the passive filter. The soft-switched inverter operation and inherent current ripple cancellation achieved by the proposed circuit, result in a high power conversion efficiency. Theoretical analysis and the improvements in inverter performance presented in this article are validated through the experimental verification of the proposed converter topology using a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf{600\text{-}W}$</tex-math></inline-formula> lab prototype.

PCB Winding Coupled Inductor Design and Common-Mode EMI Noise Reduction for SiC-Based Soft-Switching Three-Phase AC–DC Converter

This article presents a PCB winding coupled inductor design for both high efficiency and effective common-mode (CM) noise reduction in a silicon carbide (SiC)-based soft-switching three-phase ac–dc converter. A balance technique is applied to reduce the CM noise, creating a return path with additional inductors. The inductors in the main circuit and return path are coupled in one core and implemented with PCB windings. A winding interleaving structure with strong coupling between the main inductors is selected to minimize the winding loss and to improve the converter efficiency; however, the interwinding capacitance brought on by the winding interleaving worsens the CM noise. An inductor model including the capacitance is introduced, and its impact on the CM noise is analyzed. A novel inductor structure is proposed to scale back the interwinding capacitance and to enhance the CM noise reduction capability. Experiments with a SiC-based 25-kW soft-switching three-phase ac–dc converter prototype validates the performances of the proposed PCB winding coupled inductors.

Light Load Efficiency Improvement for Two-Channel Paralleled Soft-Switching Three-Phase Inverter Using Phase Shedding Control

This article explores how to improve the light load efficiency of a critical conduction mode (CRM)-based two-channel paralleled soft-switching three-phase inverter. Although the CRM-based soft-switching scheme achieves high efficiency at heavy load, the efficiency drops rapidly as the output power decreases. Its CRM-based operation makes the switching frequency soar because of the small inductor currents at light load giving rise to the high switching-related loss. To enlarge the inductor current handled by the first channel of the inverter, a phase shedding control is proposed to not excite gate signals for the second channel, thus bringing the first channel's frequency down. The phase shedding is put into effect to only two phases in the second channel running at high frequency to circumvent the undesired circulating current in the two-channel paralleled inverter structure. In addition, for very light load conditions (below 10%), frequency limiting methods are introduced in conjunction with the phase shedding to further improve the efficiency. Experimental results with a 25-kW SiC-based inverter prototype verify that the phase shedding control improves the light load efficiency by 0.5 to 3.9%. It is further improved by 0.3 to 1.3% with the frequency limiting under very light load conditions.

Balance Techniques and PCB Winding Magnetics for Common-Mode EMI Noise Reduction in Three-Phase AC–DC Converters

In this article, balance technique is applied into two-channel interleaved three-phase ac–dc converters with critical conduction mode based soft switching modulation. By adding additional inductors and coupling them with the original ones, the realization of the balance becomes possible with proper design; thus reducing the common-mode (CM) EMI noise. The balance condition is derived, and the impact of balance technique on the circuit operation especially on the switching frequency variation is quantified in order to provide the design guideline. Based on the application of balance technique, instead of the commonly used litz-wire-based inductors, PCB winding coupled inductors are adopted and designed to effectively achieve the reduction of CM EMI noise. The design methodology and process are presented, and the design tradeoff is made between the inductor loss and the inductor footprint. Finally, the effect of CM EMI noise reduction and the system efficiency with balance techniques and PCB winding magnetics are tested on a 25-kW silicon-carbide-based soft-switching three-phase ac–dc converter prototype.

The DC side soft switching three-phase voltage inverters

The DC side soft switching three-phase voltage inverters

Isolated ZVS High-Frequency-Link AC-AC Converter With a Reduced Switch Count

This paper introduces an isolated soft-switched three-phase ac–ac converter with a high-frequency link and reduced switch count for low- and medium-power applications. A small air-gapped high-frequency transformer acts as the key component by providing galvanic isolation as well as transferring power using its magnetizing inductance. Two small ac capacitors are placed on both sides of the transformer to realize zero-voltage switching for the semiconductor devices in addition to passive clamping. Therefore, the proposed topology is expected to be highly efficient and reliable due to soft-switching operation and exclusion of limited-lifetime electrolytic capacitors. Furthermore, the proposed converter has a high input power factor, step-up/down ability, and bidirectional power flow with arbitrary output voltage amplitude and frequency. The basic operation of the converter includes eight modes and is described in detail. Theoretical analysis and design are also given to illustrate its operation at various operating points. Simulation and experimental results are provided to verify the performance of the proposed power converter.

Modified Soft-Switched Three-Phase Three-Level DC–DC Converter for High-Power Applications Having Extended Duty Cycle Range

A three-phase three-level dc-to-dc phase-shifted pulsewidth-modulation (PSPWM) converter which is reported in the literature for high-power and high-input-voltage applications is based on a three-phase three-wire configuration. However, the controllable duty cycle range of the aforementioned converter is 0-2π/3. Therefore, to obtain the rated voltage, the converter needs to be overrated by 33%. In order to overcome this problem, a modified topology of the three-level dc-to-dc PSPWM converter based on a three-phase four-wire configuration is proposed. The soft switching of devices is achieved by using a tapped filter inductor. The output voltage is controlled by incorporating PSPWM. The clocked gate signals of each leg are phase shifted by 2π/3 from each other. Major features of the converter include the following: 1) The outer two switches of each leg are operating as zero-voltage switch; 2) the inner two switches of each leg are operating as zero-current switch; and 3) this is achieved without involving any extra passive or active components. Realization of the secondary output filter by having a tapped inductor leads to considerable reduction in circulating current flow during a freewheeling period and results in appreciable mitigation in conduction losses. In order to obtain the behavioral and performance characteristics of the converter topology, analytical and simulation studies are carried out, and the viability of the scheme is ascertained through detailed experimental studies.

A Soft Switching Three-phase Current-fed Bidirectional DC-DC Converter With High Efficiency Over a Wide Input Voltage Range

In this paper, a three-phase current-fed dual-active-bridge (DAB) bidirectional DC-DC converter is presented. Compared to the voltage source DAB converter, the proposed converter allows low RMS current and maintains zero voltage switching (ZVS) in the whole operating range by keeping the ratio between primary side and secondary side DC-link voltage constant, leading to high efficient energy conversion over a wide input voltage range. In addition, the ZVS conditions can be maintained using small DC inductors and the input current ripple still remains small because of high DC inductor current ripples being alleviated by three-phase interleaving structure. Furthermore, the proposed topology with Y-Y connected transformers is proven to have better current sharing capability compared with other three-phase topologies with different transformer connections. The operation mode analysis, soft switching conditions, and hardware design guidelines are derived in this paper. A 6-kW hardware prototype with input voltage range of 24~48 V and rated 288 V output voltage is developed and tested in the laboratory. The experimental results verified that the proposed converter could maintain high efficiency over a wide input voltage and power range.

Harmonic distortion in three-phase inverters controlled by synchronous sigma-delta-modulation

Several soft switching three-phase inverters have been proposed in the literature, using a resonant AC or DC voltage link in order to reduce switching losses. This allows operation with higher switching frequencies. In these inverters, the switching instances have to be synchronized with the periodic zero crossings of the link voltage. Thus synchronous pulse modulation strategies like Sigma-Delta-Modulation have to be used for control. The benefit of high switching frequency has to be considered in the light of performance of the modulation scheme, which can be measured by determining the r.m.s. value of the distortion current. In this paper, this magnitude is calculated analytically for three-phase inverters controlled by synchronous Sigma-Delta Modulation. The derivation is based on the assumptions of constant link frequency and large ratio of link- to output frequency. The solutions allow to calculate the r.m.s. distortion current for any periodic shape of the link voltage including DC. Simulations show that the results hold for link- to output frequency ratios down to 100. The spectral performance of synchronous Sigma-Delta-Modulation is compared with conventional pulse width modulation.

A Novel Prototype of Auxiliary Edge Resonant Bridge Leg-Link Snubber-Assisted Soft-Switching Sinewave PWM Inverter

This paper proposes a new circuit topology of the three-phase soft switching PWM inverter and PFC converter using IGBT power modules, which has the improved active auxiliary switch and edge resonant bridge leg-commutation-link soft-switching snubber circuit with pulse current regenerative feedback loop as compared with the typical auxiliary resonant pole snubber discussed previously. This three-phase soft switching PWM double converter is more suitable and acceptable for a large capacity uninterruptible power supply, PFC converter, utility-interactive bi-directional converter and so forth. In this paper, the soft switching operation and optimum circuit design of the novel type active auxiliary edge resonant bridge leg commutation link snubber treated here are described for high power applications. Both the main active power switches and the auxiliary active power switches achieve soft switching under the principles of ZVS or ZCS in this three-phase inverter switching. This three-phase soft switching commutation scheme can effectively minimize the switching surge related electromagnetic noise and the switching power losses of the power semiconductor devices; IGBTs and modules used here. This three-phase inverter and rectifier coupled double converter system does not need any sensing circuit and its peripheral logic control circuits to detect the voltage or the current and does not require any unwanted chemical electrolytic capacitor to make the neutral point of the DC power supply voltage source. The performances of this power conditioner are proved on the basis of the experimental and simulation results. Because the power semiconductor switches (IGBT module packages) have the relation of the trade-off in the switching fall time and tail current interval characteristics as well as the conductive saturation voltage characteristics, this three-phase soft-switching PWM double converter can perform to improve actual efficiency in the output power ranges with a trench gate controlled MOS power semiconductor devices which is much more improved to the low saturation voltage. The effectiveness of this is verified from a practical point of view.

Elimination of low-frequency harmonics caused by PWM in a three-phase soft-switched boost rectifier

This paper presents three major causes of low-frequency harmonics in a high-frequency soft-switched three-phase pulsewidth modulation (PWM) boost rectifier: pulsewidth limits; an improper space-vector modulation scheme; and dead time. Among these, the pulsewidth limits are related to soft-switching techniques. To eliminate undesirable low-frequency harmonics, each cause is illustrated and a solution is provided. Both simulation and experimental results prove the effectiveness of the proposed solutions. Due to the similarities between boost rectifiers and voltage-source inverters, the conclusions of this paper are also applicable to high-frequency PWM voltage-source inverters.