선박 추진용 저압 전동기에 대한 2레벨 및 3레벨 인버터의 직접토크제어 비교
Comparison of DTC between two-level and three-level inverters for LV propulsion electric motor in ship
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초록
해상 환경 규제와 무인 자율 선박의 도입됨에 따라 전기 추진 선박이 많은 주목을 받고 있다. 추진 전동기로 사용되는 유도기는 유지 관리 측면에서는 장점이 있으나 속도 제어가 매우 복잡하고 어렵다. 일반적으로 사용되는 속도 제어 기술 중 하나가 DTC(Direct Torque Control)이다. DTC는 좌표 변환과 고정자 자속 계산이 간단하다. 한편, 2레벨 및 3레벨 전압형 인버터가 주로 사용된다. 3레벨 인버터는 2레벨 인버터보다 전압 공간 벡터 선택에 더 많은 유연성을 제공한다. 본 논문에서는 추진 전동기의 사양을 기반으로 DTC 방식으로 속도를 제어한다. 속도 제어기는 와인드업이 적용된 PI 제어기를 사용한다. 또한, 동일한 조건에서 2레벨 인버터와 3레벨 인버터의 특성을 비교한다. 시뮬레이션을 통해 속도와 토크가 적절하게 제어되는 것을 확인하였다. 특히 3레벨 인버터에서는 토크 리플이 작고 저속에서 낮은 직류 전압으로 제어가 가능하였다. 본 연구를 통해, 3레벨 인버터를 이용한 DTC 기법이 시스템 응답 성능 개선에 기여함을 확인하였다.
Abstract
In compliance with environmental regulations at sea and the introduction of unmanned autonomous ships, electric propulsion ships are garnering significant attention. Induction machines used as propulsion electric motor (PEM) have maintenance advantages, but speed control is very complicated and difficult. One of the most commonly used techniques for speed control is DTC (direct torque control). DTC is simple in the reference frame transformation and the stator flux calculation. Meanwhile, two-level and three-level voltage source inverters (VSI) are predominantly used. The three-level VSI has more flexibility in voltage space vector selection compared to the two-level VSI. In this paper, speed is controlled using the DTC method based on the specifications of the PEM. The speed controller employs a PI controller with anti-windup functionality. In addition, the characteristics of the two-level VSI and three-level VSI are compared under identical conditions. It was confirmed through simulation that proper control of speed and torque has been achieved. In particular, the torque ripple was small and control was possible with a low DC voltage at low speed in the three-level VSI. The study confirmed that the application of DTC, using a three-level VSI, contributes to enhancing the system's response performance.
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