在二階變頻器應用上，研究人員一直致力於提高脈衝寬度調變之頻率，因其可降低馬達電流漣波，亦可進而提高馬達變頻器的電流迴路之頻寬，以提高動態響應。但隨著功率元件的切換頻率變高，在馬達纜線較長時，可能導致馬達端電壓的過電壓。典型的解法為在馬達與變頻器間加裝LC濾波器。
本研究利用LC濾波器使二階變頻器變為弦波變頻器，但LC濾波器的寄生電阻很小，因此寄生電阻帶來的阻尼效果微乎其微，無法有效抑制LC濾波器的共振(Resonance)問題，進而導致系統的不穩定性。若要使變頻器能高效率運行，無法使用基於阻尼電阻的被動共振抑制，而必須實現主動共振抑制。為減少控制架構所需的感測器數量，本論文提出D-Module Observer，估測馬達電流與電容電流，以實現電流回路控制與主動共振抑制。D-Module Observer可使用低解析度的編碼器得到的速度資訊，避免坐標轉換的偏差，進而使估測電容電流與馬達電流足夠準確，因而應用於電容電流回授法實現主動共振抑制。本研究使用微控制器與硬體在環迴路系統(Hardware In the Loop, HIL)驗證架構。實驗結果中，基於D-Module Observer的電容電流回授法，能大幅度抑制馬達電流在共振頻率的成分，進而使總諧波失真(Total Harmonic Distortion, THD)降低。

A long cable between the inverter and the motor may result in overvoltage. To prevent overvoltage, an LC filter can be installed on the output side of the inverter because it effectively filters out the high frequency pulses ( ), resulting in an output voltage that resembles a sine wave. However, it's important to note that an efficient LC filter typically has almost zero resistance, which could potentially lead to an LC resonance issue if no measures are taken to address it. To effectively dampen this resonance, grid-connected inverters commonly employ either notch filters or the capacitor current feedback method. In the context of this thesis, a comparison is made between these two methods for motor inverter applications. Following the comparison, the capacitor current feedback method is selected as the preferred option. It's worth mentioning that this method necessitates the use of additional current sensors. In an effort to minimize the number of sensors and the need for anti-aliasing analog filters, this thesis proposes the use of a D-Module Observer. The D-Module Observer serves a dual purpose: it provides an estimation of capacitor current for implementing active damping in the capacitor current feedback method and also offers an estimation of motor current for the control loop. Remarkably, even with a low-resolution encoder, the D-Module Observer is capable of providing accurate estimations of both capacitor current and motor current. The estimated capacitor current is subsequently utilized to mitigate LC resonance during experiments, resulting in a reduced total harmonic distortion (THD) in the motor current, when active damping is employed alongside the D-Module Observer and the appropriate gain is set for the capacitor feedback method. Furthermore, the calculation of the D-Module Observer is straightforward due to the first-order nature of both the controller and observer models. Consequently, it can be implemented efficiently in low to medium-cost digital signal processor (DSP) applications.

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