This paper presents two new pulse-width modulation (PWM) methods for a high frequency ac-link (HF-link) inverter commutation which uses a form of four-step switching scheme for safe commutation. A HF-link inverter topology enables galvanic isolation and voltage step-up, with a reduced-size transformer, but eliminates the secondary-side rectification so it has less power conversion stages than other inverter topologies. However, converting the HF-link voltage to the desirable inverter output voltage adds complexity to the control of the circuits because it is a form of ac-ac converter with both the inverter bridge input and output voltages time-varying. The voltage-reference four-step switching technique was previously presented as a safe commutation technique for the ac-ac converter with bidirectional switches. The method provided safe commutation without detailed information of the exact output current zero-cross and without needing lossy snubber circuits. However, it assumed that the input voltage polarity remained constant during the current commutation interval. This paper proposes methods to overcome the limitation of the previous method to ensure so call safe-commutation even when the HF-link voltage is changing polarity and that can be implemented by modification of conventional triangular carrier PWM methods. Therefore, the four-step switching scheme can be safely applied to the HF-link inverter. Simulations of the proposed new PWM methods are conducted using Simulink and Plexim software to demonstrate the concepts. The proposed PWM methods were experimentally verified using the dSpace 1007 HIL platform.
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