본 논문은 단위 인버터를 병렬로 연결하여 대용량 계통연계형 인버터 구성 시에 인버터 모듈 간에 발생하는 순환 전류를 저감하기 위한 PWM 위상 동기화 기법을 제안한다. 제안된 방법은 DSP에 내장된 CAN 통신 모듈의 메시지 수신과 송신 시점을 기록할 수 있는 Time Stamp 기능을 이용하므로 직렬 통신 방법으로 구성된 대용량 계통연계형 인버터의 제어 플랫폼에 적용이 가능하다.
본 논문에서는 병렬 연결된 계통연계형 인버터 동작 시에 단위 인버터 사이로 흐르는 순환전류의 특성을 분석하고, 기존에 연구된 순환전류 저감 기법의 효과를 기술하며 제어기 간의 PWM 출력 신호에 위상 차이에 따른 순환전류 특성을 모의하기 위한 인버터 모델링과 시뮬레이션 결과를 제시한다. 병렬 인버터 모듈의 공통 연결 조건에 따른 실험 결과를 통해 제안된 방법을 검증한다.
Alternative Abstract
In this paper, a large-capacity grid-connected inverter composed of unit inverter modules in parallel can be increased to various capacities according to the number of parallel units of the unit inverter module. There is a possible advantage, but there is a disadvantage in that a circulating current flows between the unit inverter modules due to the common input and the common output, so that 100% of the total capacity of the configured system cannot be used, and main elements may be burned.
In order to solve this problem, the cause of the circulating current was briefly examined, and the previous circulating current reduction study was also examined.
Circulating current is classified into low-frequency circulating current and highfrequency circulating current according to its cause. Among them, considering the limited DSP (Digital Signal Processor) performance among methods for reducing high frequency circulating current, a PWM phase synchronization method between controllers of parallel connected unit inverter modules was proposed using the CAN Time Stamp function of TI's TMS320F28335. A 250kW grid-connected inverter connected in parallel with two 125kW class inverters was constructed by remodeling the transformer less grid-connected inverter product for photovoltaic power generation.
As the test conditions, 1) the input individual and output common connection conditions, and 2) the input and output common connection conditions, respectively, constituted a test set, and the proposed PWM phase synchronization technique was verified through experiments.
Even if the DSP manufacturers are different, the proposed technique in this paper will be applicable if there is a Time Stamp function that can store the time with an internal timer when transmitting and receiving CAN communication modules and CAN messages inside the DSP.