A 3-phase Z-source inverter driven by a novel hybrid switching algorithm

Master Thesis


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University of Cape Town

A 3-phase Z-source inverter has been researched, designed, simulated, builtand tested. The purpose of the inverter is to deliver 3-phase 400 VAC from aDC supply that can vary over a range of 20 to 70 Vdc. This is done with a Zsourceinverter topology which is a single conversion method with no additionalDC to DC boost converter. A novel DSP control algorithm allows the inverter toachieve the following:· Run Space Vector Pulse Width Modulation (SV-PWM) for maximum DCbus voltage utilization while boosting the DC bus during zero space vectorstates using shoot through.· Seamless transition between modulation control and modulation / shootthrough control.· Optimised efficiency and DC bus utilisation using Hybrid Space VectorBoost Pulse Width Modulation (HSVB PWM) which is unique to thisdissertation.Such a system is particularly suited to fuel cell and particularly wind turbineapplications where the DC bus voltage is varies over a wide range resulting inthe need for a DC to DC buck/boost to regulate the DC bus to maintain a steady3-phase sinusoidal output. A further application could be for general purpose 3-phase inverter capable of operating on different DC standard bus voltages ( e.g.24, 36, 48 VDC).The benefits of a Z-source topology for the above purposes are a reduction inhigh power semi-conductor components (e.g. power MOSFET). There is also areduction in switching losses and inherent shoot through protection.Furthermore, the inverter is more robust in the sense that it is not vulnerable to spurious shoot through, which could be disastrous in the case of a traditionalvoltage fed inverter.