三相無刷直流風扇馬達高效率無感測控制方法之研究

Abstract

本論文提出三相無刷直流風扇馬達的高效率無感測控制方法，發展可應用於微小型風扇馬達無感測控制IC之控制架構。本文提出一種新型的無感測控制方法，利用電壓偵測與遮蔽機制估測反抗電動勢的零交越點(zero-crossing point, ZCP)，配合數位相位移器產生對應的換相訊號可達成無感測驅動。無感測驅動在靜止或低轉速下訊雜比(signal-to-noise ratio, SNR)較低不易啟動，因此本文結合開迴路啟動以及電流限制架構提出一種電流限制軟啟動控制，使電流逐漸增加以獲得更穩定的啟動，同時也改善了開迴路啟動下電流過大的問題。在效率提升方面，為了改善傳統120o導通控制下換相時產生的劇烈轉矩變化，本文提出軟換相控制減緩換相電流變化以降低轉矩漣波，並經由分析取得各操作點所需的軟換相角度；馬達屬於電感性負載，電壓與電流間存在相位落後使得效率低落，此部份可加入相位超前控制進行相位補償，將軟換相控制與相位超前控制做結合可達到在速控範圍內的高效率運轉。本文使用數位訊號處理器(TMS320LF2407A)驗證所提出控制方法的可行性與性能，將實驗結果與市售IC Sanyo LV8805進行比較，也可在三顆不同的風扇馬達上得到相等或較佳的效率。

This paper proposes a high efficiency sensorless control strategy for three-phase brushless dc (BLDC) fan motors and develops a control structure using on small fan motor sensorless control IC. This paper proposes a novel sensorless control strategy. Zero-crossing point (ZCP) estimation accomplished by specific voltage sampling and mask schemes. ZCP signal shifts for 30 degrees by digital phase shifter for corresponding commutation signals to maintain sensorless commutation. It’s hard to start-up due to low signal-to-noise ratio (SNR) when motor at low speed operation or in standstill. Therefore, this paper proposes a current limit soft-start control which combined open-loop starting and current limit strategies. Start-up current increases gradually to make start-up more robust and maximum start-up current reduced under this start-up strategy. 120 degrees conduction control results large torque variation during commutation interval and caused low efficiency. This paper proposes a soft-commutation control to decrease the torque ripple by slowing down the changing rate of commutation current. Soft-commutation angles at each operation point are analyzed by simulation. Motor current exists phase delay with voltage and it results in low efficiency. To solve this problem, phase advance control adopted to compensate the phase delay. The combination of soft-commutation control and phase advance control achieves high efficiency within speed control range. This paper uses a single chip DSP controller (TMS320LF2407A) to verify the performance and feasibility of proposed control strategies. According to experimental results, high efficiency control strategy has same or better efficiency than commercial IC Sanyo LV8805 with different three fan motors.