고속 발전기를 장착한 마이크로터빈의 전력 변환 시스템에 관한 연구
Power Conditioning System for the Microturbine with High Speed Generator
고속 발전기 마이크로터빈 전력 변환 시스템 동기 전동기 모델링 공간 벡터 PWM 컨버터;
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This thesis presents Power Conditioning System(PCS) design for the microturbine with High Speed Generator(HSG). Microtubine is classified split-shaft structure with gear-box and single-shaft structure with HSG. In mechanical structure, a single shaft microturbine has HSG and PCS while a split-shaft microturbine has gear-box, DC motor and low speed conventional motor for generation. Because of this mechanical structure, each microturbine has many difference in operation. First, in gas turbine engine starting sequence, gas turbine engine makes proper air fuel ratio and ignite at high speed. After ignition, for perfect start-up, starting system give external power to gas turbine to reach to self-sustain speed. Self-sustain speed is a speed of gas turbine engine has self sustain rotational energy without any external power. In start-up operation, split-shaft microturbine makes high speed with proper air fuel ratio using DC motor speed increased through gear-box and after ignition, DC motor give rotational energy to engine reach to stable speed. Single shaft microturbine makes high speed with HSG is driven by PCS and after ignition, inverter in PCS control high speed of engine for engine stat-up. In generation mode, split-shaft microturbine generates AC power by conventional generator of which speed is decreased by gear-box give a conventional generator and DC power by DC motor rotation. Single-shaft microturbine generate AC power by inverting DC high voltage is made by rectification high speed AC power from HSG and DC power by a DC-DC converter. Compared with single shaft microturbine, split-shaft microturbine has mechanical loss, system complexity, weight, and high capacity lubrication system because of gear-box. But single shaft microturbine has difficulty of PCS design instead of mechanical complexity. This thesis presents result of the PCS design for single shaft microturbine. In this thesis, for start-up system, following is considered on PCS design. Rated speed of the single shaft microturbine has 30,000 to 100,000 rpm. For stable start-up , single shaft microturbine requires motoring speed up to 40% of the rated speed. Microturbine developed in this thesis have rated speed of 57,000 rpm and is motorized to 27,000 rpm at start-up. And for controlling a high frequency current to be injected to a motor winding with a low leakage inductance, the inverter with a high precision and a high speed operation was designed and for a stable ignition, the starting algorithm of microturbine was proposed. Because a known current control method can't generate stable alternating current of 450 Hz, special current control method which can control high speed current with Digital Signal Processor(DSP) is used. And sensorless vector control is adopted in this thesis, because of mechanical difficulty of the installation speed sensor to HSG and the weak control performance by delayed output signal from speed sensor. In this thesis, for generation, following is considered on PCS design. In this thesis, HSG rotate synchronous speed same as engine speed, have rated speed of 57,000rpm and generate AC power of 950 Hz directly. For power conditioning, high speed rectifier is needed for rectification and convert AC power to DC power. And buck converter with high capacity is designed for system rated output, ie. 28 Vdc and 8 kW. Also in this thesis, boost converter with DC output of 235 Vdc and 6 kW is designed for supplying high DC_Link voltage to inverter operate high speed to HSG. And in this thesis, system with compact size and light weight is needed for appling to microturbine of mobile vehicle. Therefore, bi-directional system for buck-boost converter with sharing hardware and logic sequence is adopted and had extremely high space and hardware availability ratio. Also, for precise calculation at buck-boost parallel operation, fast current response, stable high capacity DC output and DSP(TMS320LF2406) for buck-boost voltage controller is adopted. In this thesis, microturbine was operated by the designed PCS to verify the performances.