多相多位準電壓源反相器之切換控制策略與分析

Abstract

由於切換式功率放大器的功率效益較傳統類比功率放大器(A類、B類、AB類)高，因此常被廣泛應用於驅動馬達或喇叭等致動器元件，然而對於多數個致動元件之系統，若仍採用一對一之功率放大器，將使驅動系統的成本提高且體積龐大，本論文提出一個創新的電路架構，用以驅動致動器陣列系統，此電路架構以切換式功率放大電路為基礎，並且允許致動器之間互相共用切換元件，因此達到體積減小、降低成本的效果。由於元件互相共用，因此驅動各別致動器之切換訊號互相相關，因此本論文提出一個廣式閘級訊號產生策略，是一個多輸入多輸出系統，可以產生最佳化之閘級訊號，同時將本論文所提出之架構應用於多相多位準電壓源反相器之切換策略控制。 此策之ㄧ優點為可將有限載波寬度精準度所產生之量化誤差降到最低，經由線性分析可以發現此策略於實現上只需要加法器以及比較器，架構簡易且運算複雜度並不會隨系統的相數/位準數增加而增加，此為與傳統驅動策略之最大不同處，而另外一個特點為可將雜訊重新分佈於不同之頻帶，因此可以分離輸入以及雜訊所分佈的頻率範圍，除了可以降低雜訊干擾，經由實驗驗證可知，此特性讓系統以更有效率的方式產生切換策略，因此在達到一樣的諧波失真下，本策略所需要的切換次數較傳統方法少。 將本論文之架構應用於多相電壓源反相器的主要原因是希望改善目前現有之閘級訊號產生器，對於三相電壓源反相器系統，已經有許多相關文獻探討空間向量脈波寬度調變方法(space vector pulse-width modulation: SVPWM )，然而對於多相電壓源反相器系統卻沒有一個嚴謹的數學分析以及通用的閘級訊號產生器。經由特定參數的選取，傳統之三相SVPWM為本架構之ㄧ特例，因此本論文之分析同時將SVPWM延伸應用於多相系統，而創新之處在於本論文證明此方式所得到之電壓源使用率為最高，且基於平均電壓之概念，此策略之切換次數為最少。 為了驗證本論文所提之策略，實驗中將五相弦波訊號輸入本架構用以驅動五相電壓源反相器，由負載之電壓/電流訊號可知，本策略可以將期望的訊號波形於負載重現。另一實驗設定本策略之脈波解析度為無限大以及零(兩個極限值)，並改變系統工作頻率作為比較，由諧坡失真度以及切換次數可知，零位元之脈波解析度之系統在適當的工作頻率下，可以以更少的切換次數達到相同的響應效果(諧波失真)。本論文的最後一個實驗為將此策略配合Field-Oriented Control做馬達速度控制，在此實驗中可知開關之溫度與切換次數為正相關，因此採用本策略除了提高功率效益外所需之散熱系統體積可以減小。

Because of its high power efficiency, switch-mode power stage is commonly used to drive actuators such as electrical motors and loudspeakers. For an actuator array formed by a large number of actuators, the associated power amplifier becomes costly and bulky when each actuator is controlled by an independent amplifier. In this thesis, a general actuation circuit that allows sharing of power amplifiers and a general gating signal generation (GSG) system that produces optimal gating decision is introduced and applied to actuating the multi-level multi-phase voltage source inverters (VSI) by considering individual winding in a multi-phase system as an actuator. An immediate advantage is the filtered error induced by finite pulse-width resolution is minimized. Algebraic analyses show that only comparators and adders are needed to obtain gating signals, yielding a simple implementation. Further, different from the conventional strategies, mathematical (implementation) complexity of the proposed GSG is independent of the level/phase number. Another intrinsic characteristic of GSG is the noise shaping effect that relocates the frequency components of quantization error. This enhances the effectiveness of gating decision, yielding a decreased switching number without sacrificing harmonics performance. As a result, the operational life time of switches increase and the switching power loss reduces. Applying the proposed method to multi-phase VSI is aimed at improving the performance of the existing switching strategies. For 3-phase VSI, extensive research results using space vector PWM (SVPWM) have been reported. However, a general switching strategy under a fixed duty cycle period for multi-phase systems, supported by rigorous mathematical analyses, is still lacking. By setting particular parameters in GSG, the proposed GSG is equivalent to SVPWM for 3-phase VSIs. Therefore, the extension of 3-phase SVPWM to multi-phase one is obtained in this thesis. The novel finding is the method leads to the switching strategy for minimum number of switching and minimum conduction time considering equivalent mean voltage within each input period. In experiments, five-phase sinusoidal waves with/without third harmonic injection are applied as references for five-phase VSI. Current/voltage signals measured show that the GSG reproduces desired waves on the load precisely. Another experiment comparing two GSGs with different pulse-width resolutions, 0-bit and infinity-bit resolutions, is done. Switching number and harmonic distortion of current/voltage signals tell that with a proper oversampling ratio, GSG with 0-bit pulse-width resolution produces gating signals smartly, i.e., reduced switching number (compared with infinity-bit resolution one) with comparable harmonic distortion. Lastly, aforementioned GSGs are applied to the Field-Oriented Control (FOC) for controlling the motor speed. The temperature of MOSFETs is measured to confirm the characteristic of the proposed gating decision scheme.