Aiming at overcoming the problem that the auxiliary commutation circuit (ACC) of auxiliary resonant commutated pole (ARCP) inverters has a high loss in commutation processes, this paper presents a novel modulation strategy based on an improved ARCP inverter. In comparison with the original modulation strategy, this modulation strategy can not only realize soft-switching for all switches, but also avoid the superposition of resonance current and load current at commutation moments in ACCs and make the maximum current through ACCs approximately equal to load current in commutation processes. So the circulating current loss in ACCs and the current peak stress of auxiliary switches can be effectively reduced. According to the equivalent circuit in different operation modes under this modulation strategy, this paper analyses the operation principle, soft-switching implementation condition, and optimal parameter design procedure of the improved ARCP inverter. Finally, the novel modulation strategy is applied to a 10 kW 16 kHz improved ARCP inverter prototype with insulated gate bipolar transistor-based switches. Experimental results are given to demonstrate the validity and features of the inverter under the novel modulation strategy.

Research on a Novel Modulation Strategy for Auxiliary Resonant Commutated Pole Inverter With the Smallest Loss in Auxiliary Commutation Circuits

In order to overcome the complexity of the double auxiliary commutation circuit (DACC) and the coupling of the resonance process of the double auxiliary resonant commutated pole (DARCP) inverter, a modified DARCP inverter topology and its modulation strategy are proposed. The modified topology not only retains the advantage of reliable zero voltage switching (ZVS) turn-off of auxiliary switches and so on, but also realizes the simplification of the DACC and the decoupling of the resonance process. The cost of the inverter and the system oscillation caused by coupling resonance are reduced, and the performance and practicability of the inverter are improved. According to the equivalent circuits of different operation modes under the proposed modulation strategy, the operation principle, the soft-switching implementation condition, and the parameter design method are analyzed. Finally, a 10-kW, 16-kHz soft-switching inverter prototype is built. Experimental results are given to demonstrate the validity of the proposed inverter.

Modified Double Auxiliary Resonant Commutated Pole Inverter and its Modulation Strategy

The multizonal medium voltage dc architecture of all-electric ship shipboard power systems (SPSs) includes a variety of distributed energy resources, energy storage devices, and power electronic voltage source converters. Due to the limited fuel supply and tight space, control of the converters should be aimed at increasing their efficiency and compactness. In this paper, a novel approach to voltage control in all-electric ship power systems is proposed to fulfill these goals. In contrast to the traditional SPSs that emulate the land-based electricity grid, maintaining a steady bus voltage is no longer an objective here. On the contrary, the voltage is compelled to fluctuate in order to minimize switching losses in the converters. A method for calculation of the minimum required dc voltage level is described, and results of computer simulations of an SPS with a flexible-voltage dc bus are presented. The minimum-voltage operation of the system results in a significant efficiency increase.

Flexible-Voltage DC-Bus Operation for Reduction of Switching Losses in All-Electric Ship Power Systems

A novel single-stage high-frequency link three-phase ( $3\phi$ ) inverter along with a modulation strategy is presented in this paper. The topology is targeted for grid integration of utility scale renewable and alternative energy sources like solar, fuel cell, and wind, where the power flow is unidirectional (from dc to ac). The primary side converter has a $3\phi$ voltage source inverter (VSI) structure along with an additional half-bridge leg. Sinusoidal pulsewidth modulation is implemented in the primary side converter. The three legs of the primary side VSI are zero voltage switched (ZVS) for most part of the line cycle. The additional half bridge leg is ZVS over the complete line cycle. The active switches in secondary side converter are line frequency switched and thus results in negligible switching loss. The converter switching process is described in detail to show the soft-switching of the primary side converter using the device capacitances and leakage inductances of the high-frequency transformers (HFTs). The HFT galvanic isolation results in high power density. A 4-kW laboratory scale hardware prototype is built and tested with the proposed modulation strategy. The experimental results are presented to verify the converter operation.

A Soft-Switched High-Frequency Link Single-Stage Three-Phase Inverter for Grid Integration of Utility Scale Renewables

In this article, a concept of separation of an inverter-fed induction motor drive from its mains supply by two transistor switches inserted in the dc-link circuit is re-examined based on the proposed parallel quasi-resonant dc-link inverter (PQRDCLI). The objective of the article is to show an advantage of the proposed topology in limiting high-frequency common-mode voltage and bearing currents. In the laboratory setup, an induction machine was equipped with hybrid ceramic bearings and an insulated clutch to measure the shaft-to-frame bearing voltage and the shaft-grounding current. Experimental tests of the PQRDCLI confirm significant reduction of common-mode voltage and shaft-to-frame bearing voltage at dc-link zero voltage notches. By controlling the output voltage slopes, the shaft-grounding brush current and the ground leakage current are also reduced. The efficiency measurement and evaluation of the proposed topology, as compared with a two-level hard switched inverter, reveal comparable efficiency of around 95% and indicate loss distributions in both inverters.

Reducing Common-Mode Voltage and Bearing Currents in Quasi-Resonant DC-Link Inverter

Two quasi-resonant dc-link (QRDCL) inverter topologies are discussed for motor-friendly application. For the control of an inverter, a modified space-vector pulsewidth modulation is implemented, which requires only two resonant cycles per switching period and helps in better utilization of dc-link voltage. The first topology is tested experimentally with a 34-m-long cable connected between inverter and induction machine for reduced voltage overshoot at motor-side cable end and common-mode (CM) voltage. Even though results are satisfying, a freewheeling interval of this topology produces high losses. So a new motor-friendly QRDCL inverter with lossless variable zero-voltage duration is proposed. In this topology, during a zero-voltage interval, energy is stored in a capacitor rather than an inductor. No current is freewheeling through inverter switches, and it clearly helps in reducing the losses under a low-modulation index region. Simulation results are presented to verify the validity of the proposed inverter and its motor-friendly characteristics.

J. Kedarisetti

Papers

A Motor-Friendly Quasi-Resonant DC-Link Inverter With Lossless Variable Zero-Voltage Duration