Brushless Wound Rotor Synchronous Machine using Thyristor-generated Third Harmonic Current

Abstract

권선형 동기전동기는 영구자석형 동기전동기와 비교했을 때, 발전, 높은 출력 및 휴대용 전기기기에서 고효율적이고, 융통성 있는 자기장 제어, 약자속 능력이 강한 장점이 있다. 그러나 중소형 기기의 경우 부피 및 브러시를 사용한 여자 시스템이 문제가 되고 다른 적합한 기기가 없기에 고가의 PMSM이 사용된다. 결과적으로 가격과 기기의 성능간의 절충으로 형상이 선택된다. 하지만, WRSM에 대한 연구가 많아짐에 따라 브러시리스 WRSM 토폴로지가 연구되어 브러시를 사용한 여자 문제가 해결 되였다. 특히 고조파 여자 WRSM에 초점을 맞춘 브러시리스 여자에 관한 문헌에서 많은 해결책이 제공되고 있다.

본 논문은 회전자 자기장 여자를 위한 3차 고조파 전류 생성 토폴로지를 제안한다. 제안 된 토폴로지는 3상 전기자 권선에 각각 사이리스터 스위치를 병렬로 연결한다. 스위치는 전류의 제로 크로싱에 근접할 때 짧은 시간 동안 켜진다. 스위칭을 통해 기본 주파 전류를 포함하는 전기자 권선에서 제로 시퀀스 제3 고조파 전류를 생성한다. 이 토폴로지의 주요 이점은 스위치를 끄는데 정류 회로가 필요하지 않다는 것입니다. 그리고 스위치 온 기간을 조정하여 기기의 고조파 전류 및 여자 레벨을 제어 할 수 있습니다.

이러한 이유로, 기기의 회전자는 공극 자기장에서 고조파 전력을 적출하기 위해 3차 고조파 권선을 특별히 설계하였다. 4극 12슬롯 동기 전동기의 기본 모델로부터 정류기와 함께 회전자에 12극 고조파 권선을 통합하도록 수정하였다. 출력 단자는 계자 권선에 연결되어 여자를 위한 직류 전류를 공급한다. 유한 요소 해석(FEA)을 수행하여 토플로지 및 기기의 구조를 검증한다. 해석한 결과는 제안된 토폴로지를 사용하여 상당한 양의 토크를 생성했음을 나타낸다.

응용 분야의 기기 채용에는 실제 요구 사항이 있으므로 기기 구조는 토크 리플을 줄이기 위해 2상 고조파 권선으로 설계 되었다. 동시에 영구자석은 기기의 기동을 보조하기 위해 설계 되였다.

또한, 제로 시퀀스 전류가 정류기를 흘러 고정자의 고조파 권선으로 흐르는 개선 된 토폴로지도 분석하였다. 이 토폴로지는 모터 및 발전기에 모두 사용할수 있다. 이 토폴로지로부터 4극 18슬롯 기기는 추가 고조파 권선이 있는 12극 구조 대신 6극 구조로 분석 되었다. 동일한 구조의 기기는 전동기 및 발전기의 구동에 사용된다.

개선 된 토폴로지는 2D FEA 시뮬레이션 소프트웨어로 분석되었으며, 전동기 및 발전기 작업 모두에 대한 실험 분석도 수행하였다. 실험 결과는 시뮬레이션 결과와 일치한 것으로 확인 하였다.

|Compared to permanent magnet synchronous machines (PMSMs) Wound rotor synchronous machines (WRSMs) are preferred in power generating, high-power drives and portable electrical machine applications due to their high efficiency, flexible field control and high flux weakening ability. However, for small-medium size machines the volume and brushed excitation system becomes a problem and expensive PMSM is used due to lack of other suitable machines. Consequently, a trade-off between price machine performance is referred traditionally. However, trends in research on WRSM have led researchers to brushless WRSM topologies to address brushed-excitation problems. Many solutions are available in literature on brushless excitation specially focused on the harmonic-excited WRSM.

This thesis proposes a third harmonic current generation topology for rotor field excitation. The proposed topology employs thyristor switches in parallel with each of the three-phase armature winding. The switches are turned on for short duration of time near zero crossing of current. The switching creates a zero-sequence third harmonic current in the same armature winding which contains the fundamental frequency current. The main benefit of this topology is that no commutation circuit is needed to turn off the switches. The harmonic current and consequently the excitation level in the machine can be flexibly controlled by adjusting the switch-on duration of the thyristors.

In this regards, the machine’s rotor is specially designed to incorporate third harmonic winding to extract the harmonic power form the air gap field. A basic 12-slot 4-pole synchronous machine structure was used to modify to incorporate a 12-pole harmonic winding on the rotor along with a rectifier. The output terminals are connected to the field winding to feed direct current for excitation. Finite-element analysis (FEA) was performed to validate the topology and machine structure. The analysis results indicate a significant amount of torque produced using the proposed topology.

Since the machine employment in an application has practical requirements, the machine structure was designed with two-phase harmonic winding for reducing the torque ripple. Similarly, a permanent magnet (PM) structure was designed to assist the machine with starting.

Furthermore, an improved topology was also analyzed in which the zero-sequence currents flow through a rectifier to an additional harmonic winding mounted on the stator. This topology has the benefit that it can be used for both motor and generator operation. With this topology, an 18-slot 4-pole machine was analyzed using the additional harmonic winding with 6-pole configuration instead of 12-pole. Moreover. The same machine structure was used for both motoring and generating operation.

The improved topology was analyzed in 2D FEA simulation software and experimental analysis was also performed for both motoring and generating operation. The experiment results are in good agreement with the simulation results.; Compared to permanent magnet synchronous machines (PMSMs) Wound rotor synchronous machines (WRSMs) are preferred in power generating, high-power drives and portable electrical machine applications due to their high efficiency, flexible field control and high flux weakening ability. However, for small-medium size machines the volume and brushed excitation system becomes a problem and expensive PMSM is used due to lack of other suitable machines. Consequently, a trade-off between price machine performance is referred traditionally. However, trends in research on WRSM have led researchers to brushless WRSM topologies to address brushed-excitation problems. Many solutions are available in literature on brushless excitation specially focused on the harmonic-excited WRSM.

This thesis proposes a third harmonic current generation topology for rotor field excitation. The proposed topology employs thyristor switches in parallel with each of the three-phase armature winding. The switches are turned on for short duration of time near zero crossing of current. The switching creates a zero-sequence third harmonic current in the same armature winding which contains the fundamental frequency current. The main benefit of this topology is that no commutation circuit is needed to turn off the switches. The harmonic current and consequently the excitation level in the machine can be flexibly controlled by adjusting the switch-on duration of the thyristors.

In this regards, the machine’s rotor is specially designed to incorporate third harmonic winding to extract the harmonic power form the air gap field. A basic 12-slot 4-pole synchronous machine structure was used to modify to incorporate a 12-pole harmonic winding on the rotor along with a rectifier. The output terminals are connected to the field winding to feed direct current for excitation. Finite-element analysis (FEA) was performed to validate the topology and machine structure. The analysis results indicate a significant amount of torque produced using the proposed topology.

Since the machine employment in an application has practical requirements, the machine structure was designed with two-phase harmonic winding for reducing the torque ripple. Similarly, a permanent magnet (PM) structure was designed to assist the machine with starting.

Furthermore, an improved topology was also analyzed in which the zero-sequence currents flow through a rectifier to an additional harmonic winding mounted on the stator. This topology has the benefit that it can be used for both motor and generator operation. With this topology, an 18-slot 4-pole machine was analyzed using the additional harmonic winding with 6-pole configuration instead of 12-pole. Moreover. The same machine structure was used for both motoring and generating operation.

The improved topology was analyzed in 2D FEA simulation software and experimental analysis was also performed for both motoring and generating operation. The experiment results are in good agreement with the simulation results.