A HIGH FREQUENCY LINK SINGLE STAGE PWM INVERTER FOR HIGH FREQUENCY AC VOLTAGE USING CYCLOCONVERTER
This paper presents a single-stage bidirectional high frequency transformer (HFT) link DC/AC converter topology for a three-phase adjustable magnitude and frequency PWM AC drive. This type of converters find wide range of applications including UPS systems, drives involving renewable energy sources (Solar, Fuel cell) and energy storage systems (typically low voltage DC to high voltage PWM AC). HFT results in reduction in cost and weight along with a considerable increase in power density.
... ower density. Adverse effects of common-mode voltage are well known in this kind of applications. The proposed topology along with a modulation technique reduces common-mode voltage to practically zero and generates high quality output voltage waveform comparable to Conventional Space Vector PWM (CSVPWM). A source based commutation method, presented in this paper, to commute the energy stored in the leakage inductance of the HFT resulting in the following advantages. No need for any auxiliary circuits with passive components Almost complete recovery of the leakage energy Soft switching of the output side converter for all load conditionsn Minimization of common-mode voltage switching due to commutation Keywords: Common-mode voltage, High-frequency transformer, leakage commutation, PWM inverter. 1. INTRODUCTION Transformers are typically used to connect systems at different voltage levels and to provide galvanic isolation often necessary for safety. Replacement of a line frequency transformer with a high frequency transformer leads to a large reduction in weight and cost. Due to high power density, high frequency link inverters may find a wide range of applications including un-interruptible power sources (UPS), distributed power generation from renewable energy sources like solar and wind (connecting HVDC grid to offshore wind generators), energy storage systems (battery interfaced grid tied inverters), vehicle to grid applications, fuel cell powered electric motor drives and also in space and naval applications where a compact solution is necessary. A conventional system involves a three stage power conversion (DC-high frequency AC-DC-adjustable frequency AC) and requires intermediate passive elements leading to reduced reliability, efficiency and power density. A single phase version of this topology can be found in. In this topology, additional SNUBBER circuits involving passive components are required for the proper commutation of leakage energy. In a new topology has been proposed where the secondary side H-bridge rectifier is replaced with a three-phase diode bridge and the primary side converter is modified to incorporate a bank of three HFTs. In this topology, along with a novel hybrid modulation strategy, proper commutation of leakage energy has been achieved without any additional