負載切換實作波形

負載切換造成無感測控制進入暫態，因此必須考慮讓電路能在最短的時間內由不穩 定的暫態回復到穩態中。根據圖 5.8，當切載開始時負載R 從空載切換至_g 40，由於電 流增大，負載由輕載切入重載，估算換相時間降至約 2.18ms，馬達轉速瞬間降至約 2300rpm，但約在 1 秒內即能回復到穩定的狀態。根據無感測控制實作，其不論是在穩 態實作或者是暫態實作，系統均能維持穩定。

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圖 5.8 負載切換暫態實作波形

第六章 結論

本文呈現直流無刷馬達無位置感測之換相時間控制，以及無感測速度估測的設計與 分析結果，並以模擬與實驗的方式，驗證控制架構的可行性。所採用的架構主要使用由 電阻、電容以及三個電壓比較器組成的反應電動勢偵測電路，以 FPGA 為實現平台，提 出利用反應電動勢零交會點檢測轉子位置以計算出換相時間，進而達成馬達的速度回授 控制。整個系統的優點為利用偵測反應電動勢，取代霍爾位置感測元件。

無感測速度回授控制系統 FPGA 電路設計，其實現採用階層式、模組化的設計方 式，速度控制系統主要包含利用三位置訊號之零交會點估測電路、換相點產生電路、無 感測換相時間估測電路、PI 回授控制電路以及 PWM 產生電路。而透過 PSIM，整合馬 達模型以及速度控制系統進行系統層次模擬，驗證電路功能的正確性。

由實驗結果觀察可知在穩態時，不同負載情況下，換相時間與時間命令之誤差穩定 在一定的範圍內。當命令變化暫態的情況下，馬達也能夠很快的回復到所下達的轉速命 令。

本文所提出的方法尚有未臻完善之處。首先在啟動時，未考慮避免馬達反轉啟動。

使用同步加速的概念同時調整 PWM 責任周期與換相頻率，以達到馬達反應電動勢與相 電流同相。此一同步調整斜率需經過設計，當馬達不一樣時，此斜率需做重新調整。如 能搭配更好的啟動方式，將會使無感測啟動更加容易。由於馬達在低轉速時，反應電動 勢較不明顯，零交會點就更難準確偵測，使得馬達在低轉速時穩態誤差增大，雖然已經 使用平均法減少因零交會點不穩定所造成的換相時間估測誤差，卻仍無法完全消除，加 入一補償機制消除估測誤差是未來可進一步研究的方向，如此將能使此無感測控制換相 更為精準。

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