目前家電產品常見之馬達驅動器直流端是以大容值電解電容為主，因為具備較佳之儲能特性，透過功率補償亦能滿足系統劇烈變動性負載。然而，大容值設計之功率因數校正電路體積較為龐大，且直流端電解電容容易損壞。為了追求縮小體積以及產品可靠度，無電解電容驅動器有逐漸取代傳統大容值驅動器之發展趨勢。
無電解電容驅動系統之直流端電容當選用低容值之薄膜電容，可延長驅動器壽命並縮小整體體積。但也導致直流端電壓產生漣波，進而影響馬達轉矩及轉速之輸出，因此應用領域受限。本研究應用場合為壓縮機，其離心式負載將可穩定轉速輸出，使其符合產品需求。
當直流端電壓大於市電輸入電壓將導致整流器截止，整流器導通角縮小會造成電源端功率因數下降，且截止區內之電流為不可控，造成系統的不穩定性。為了降低反電動勢對直流端電壓之影響，本研究利用直交軸電流控制，根據電壓關係式及轉矩關係式，在浮動電壓下，適當調整直軸電流命令，可有效提昇電源端功率因數。

Nowadays, the large DC-link capacitors are usually utilized at motor drive system for home appliances. Which possess outstanding energy-storage characteristic, can meet the system’s severely variable load through the power compensation. However, the large-capacitance design of power factor correction circuit is bulky, and the DC-link capacitor is easily damaged. In pursuit of shrinking volume and product reliability, electrolytic capacitor-less systems have gradually replaced the traditional large-capacitance drivers.
The low-capacitance film capacitor at electrolytic capacitor-less systems DC-link can not only extend the lifetime but reduce the volume. On the other hand, it also causes the ripple of DC bus voltage which effects the output of the motor torque and speed. Therefore, the application area is limited. In this study, the application focus on a compressor, and its centrifugal load makes the system torque ripple decrease the influence on the output speed.
When the DC bus voltage is greater than the electric supply input voltage, a cut-off region of the rectifier will be generated. The reduced conduction angle of the rectifier will decrease the power terminal power factor. As a result of the uncontrolled current in cut-off region, the system may become instable. This study uses the d-q axis current control to reduce the influence of back EMF on the DC bus voltage. According to the constant torque equation and voltage limit equation under the floating voltage, the proper adjustment of the d-q axis current command can effectively improve the power factor of the power supply terminal.

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