Journal of the Korea Academia-Industrial cooperation Society (한국산학기술학회논문지)

The Korea Academia-Industrial cooperation Society (한국산학기술학회)
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Eliminating Method of Estimated Magnetic Flux Offset in Flux based Sensorless Control of PM Synchronous Motor using High Pass filter with Variable Cutoff Frequency

모터 운전 주파수에 동기화된 차단주파수를 갖는 HPF(High pass filter)를 적용한 영구자석 동기전동기의 자속기반 센서리스 제어의 추정 자속 DC offset 제거 기법

  • Kang, Ji-Hun (Dept. of Control & Instrumentation Engineering, Korea National University of Transportation) ;
  • Cho, Kwan-Yuhl (Dept. of Electronic Engineering, Korea National University of Transportation) ;
  • Kim, Hag-Wone (Dept. of Electronic Engineering, Korea National University of Transportation)
  • 강지훈 (한국교통대학교 제어계측공학과) ;
  • 조관열 (한국교통대학교 전자공학과) ;
  • 김학원 (한국교통대학교 전자공학과)
  • Received : 2018.11.28
  • Accepted : 2019.03.08
  • Published : 2019.03.31
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Abstract

The sensorless control based on the flux linkage of PM synchronous motors has excellent position estimation characteristics at low speeds. However, a limitation arises because the integrator of flux estimator is saturated by the DC offset generated during the analog to digital conversion(ADC) process of the measured current. In order to overcome this limitation, HPF with a low cutoff frequency is used. However, the estimation performance is deteriorated (Ed- the verb deteriorate already includes the meaning of 'problem') at high speed due to the low cutoff frequency, and increasing the cutoff frequency of the HPF induces further problems of phase leading and initial starting failure at low speeds. In this paper, the cutoff frequency of HPF was synchronized to the operation frequency of the motor: at low speeds the cutoff frequency was set to low in order to reduce the phase leading of the estimated flux, and at high speeds it was set to high to raise the DC offset removal performance. As a result, the operating range was increased by 200%. Furthermore, a phase compensation algorithm is proposed to reduce the phase leading of the HPF to less than 1.5 degrees over the full operating range. The proposed sensorless control algorithm was verified by experiment with a PM synchronous motor for a washing machine.

영구자석동기전동기의 쇄교자속 기반 센서리스 제어는 저속에서 위치추정 특성이 우수 하지만 계측된 전류가 ADC를 통해 변환되는 과정에서 발생한 DC offset에 의하여 쇄교자속 추정기의 적분기가 포화되는 문제점을 가지고 있습니다. 이러한 현상을 방지하기 위해 낮은 차단주파수를 갖는 HPF를 사용하여 DC offset 성분을 제거하는 방법이 사용되나, HPF의 낮은 차단주파수로 인해 고속에서 추정 성능이 저하되는 문제점이 있다. 반면 HPF의 차단 주파수를 높이게 되면, 저속에서 위상 앞섬 및 초기기동 실패의 문제가 발생한다. 본 논문에서는 HPF의 차단주파수를 영구자석동기전동기의 운전주파수에 동기화함으로써 낮은 속도에서는 HPF의 차단주파수를 낮게 하여 HPF에 의한 위상 앞섬을 줄이고, 높은 속도에서는 HPF의 차단주파수를 높게 함으로써 높은 DC offset 제거 성능을 통해 운전영역을 200% 확대한다. 또한, 추가적인 위상 보상 알고리즘을 통해 전 운전영역에서 HPF의 위상 앞섬이 1.5도 미만으로 감소되는 방법을 제안한다. 제안된 센서리스 제어 알고리즘은 세탁기용 영구자석동기전동기를 이용한 실험을 통해 검증한다.

Keywords

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Fig. 1. Rotor position estimator

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Fig. 2. Conventional rotor position estimator

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Fig. 3. Block diagram for time constant analysis

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Fig. 4. Time constant by the operation frequency (a) Time constant (b) Enlarged waveform

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Fig. 5. Proposed rotor position estimator

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Fig. 6. HPF bode plot analysis (a) HPF with fixed cutoff frequency (b) HPF with variable cutoff frequency

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Fig. 7. Applying method

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Fig. 8. Vector diagram of estimated flux

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Fig. 9. Phase lead compensator block diagram

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Fig. 10. Proposed flux based sensorless control

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Fig. 11. Experiment set (a) Control board (b) Stator (c) Rotor

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Fig. 12. Vector diagram of estimated flux

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Fig. 13. Flux estimation performance at 50 rpm (a) Conventional method (b) Proposed method

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Fig. 14. Flux estimation performance at 200 rpm (a) Conventional method (b) Proposed method

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Fig. 15. Flux estimation performance at 600 rpm (a) Conventional method (b) Proposed method

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Fig. 16. Flux estimation of proposed method (a) 600rpm (b) 1200rpm

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Fig. 18. Phase error at 50rpm (a) Conventional method (b) Proposed method

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Fig. 17. Phase compensation by rotor speed (a) 50rpm (b) 200rpm (c) 600rpm (d) 1200rpm

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Fig. 19. Phase error at 200rpm (a) Conventional method (b) Proposed method

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Fig. 20. Phase error of proposed method (a) 600rpm (b) 1200rpm

Table 1. Experiment parameter

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Table 2. Cutoff frequency of HPF in experiment

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