應用於雙饋式感應發電機之虛功率控制策略及轉子側電流控制器設計

Abstract

本論文主要的研究在雙饋式感應發電機上分析轉子電流激磁對虛功率控制策略之影響及轉子側電流控制器之設計。 本研究為了說明直軸轉子電流對定子側虛功率及轉子側虛功率的影響，利用三種等效電路模型(1.最簡單模型A、 2.簡單模型B、3.完整模型)及六種不同操作模式(1.最大定子虛功率吸收模式、2.轉子側單位功因模式、3.整流器損失最小化模式、4.實功率損失最小化模式、5.定子側單位功因模式及6.最大定子虛功率輸出模式)來敘述。在簡單模型A及簡單模型B求得直軸轉子電流的解析解，另外在完整模型C中利用有效率功率疊代演算法去求得直軸轉子電流的精確解。 本研究另外提出標準型滑動模式控制器應用於轉子側電流控制設計，在風速變動下都能達到最大機械功率輸出。滑動模式控制器除了可以使得發電機在不同的風速下都能達到最大功率輸出目標外，也對發電機的內部參數變動有著低敏感度的特性。 最後以一台大型容量2.5MW雙饋式感應風力發電機為例，說明在六種不同的操作模式下利用有效功率疊代演算法去求得轉子電流、定子電流、實功率及虛功率等數值。再者，針對標準型滑動模式控制器的控制效能與固定增益比例積分控制器比較，也證明標準型滑動模式控制器有較好的控制效能及對發電機參數變動有低敏感度的能力，另外也提出積分型滑動模式控制器來減少標準型滑差模式控制器所產生的抖動現象。

Reactive power control strategy and rotor current regulator design for a wind farm with a doubly fed induction generator (DFIG) are investigated. To examine the effect of Idr on stator reactive power Qs and rotor reactive power Qr, the DFIG is operated under six different operating modes, i.e, the maximum Qs absorption mode, the rotor unity power factor mode, the minimum converter loss mode, the minimum copper loss mode, the stator unity power factor mode, and the maximum Qs generation mode with three models. The analytical results can be solved by the simplified model A and the simplified model B. The exact results can be solved by the complete model C. Maximum power tracking of a DFIG can be achieved through the control of rotor currents. A sliding mode regulator (SMR) is presented to regulate the rotor currents of a DFIG. The robustness to parameter variations can be accomplished by the proposed SMR when the wind turbine is subject to changing wind speed. Simulation results of a DFIG system with a 2.5MW generator are provided. To demonstrate the effectiveness of the proposed iterative algorithm, the rotor current, rotor voltage, stator current, real power and reactive power of a DFIG operated under the six different operating modes are computed. It is observed from the simulation results that the dynamic responses achieved by the proposed SMR are more robust than those by the fixed-gain PI regulator. The chattering effect caused by the switching function of the SMR can be reduced by an integral type sliding mode regulator (ISMR).