Buck-boost thyristor-based PWM current-source inverter

The traditional thyristor-based current-source inverter (CSI) has been reported for use in synchronous motor drives and utility-grid-interfacing systems, where its inherent output short-circuit protection and direct-current control have been added advantages. Despite these advantages, the thyristor-based CSI is known to suffer from poor waveform quality owing to its low-frequency six-step switching and only step-up (boost) operation. Both disadvantages severely constrain the use of thyristor-based CSI for utility interfacing, especially when the inverter input is fed from renewable-energy sources whose outputs vary continuously. To address the above limitations, the paper proposes the design of a buck-boost thyristor-based CSI with pulse-width-modulated (PWM) control. This CSI uses a unique X-shaped LC impedance network connected to its DC link for current-boosting and a controlled switch for actively commutating its main thyristor devices using an appropriately designed digital PWM scheme. The inverter is tested experimentally using a laboratory prototype, and is shown to perform smooth DC-AC current conversion, making it a competitive solution for both utility and industry applications.