# Minimization of the Decoupling Circuit (DC-Link) in Induction Motors
###### Abstract  
There is currently a growing interest in replacing the internal combustion engine with electric motors in transportation applications. However, there are different problems related to electric motors for this application. One of them is the oversizing of the energy decoupling system since to ensure that the decoupling capacitor can store the power fluctuations, the capacitance required by the system is usually oversized. This leads to preference for the use of capacitors with construction technologies that have a lower lifetime than the remaining elements of the propulsion system, directly affecting the reliability of the system. In this article, the energy flow handled by the decoupling capacitor is analyzed considering the critical case of operation of an induction motor to minimize the capacitance required by the propulsion system; emphasizing the conditions that generate a higher energy return, from the motor mode of the electric machine to the decoupling capacitor. From the energy analysis, an equation for the capacitor calculation is obtained, involving proportionality factors that relate to the different operating powers, reducing up to 62.2% of the capacitance value required by the decoupling system, under conditions of maximum energy return in motor mode, compared to existing equations in the literature. DC-link; electric vehicle; coupling capacitor; energy analysis Article Minimization of the Decoupling Circuit (DC-Link) in Induction Motors  
[PERSON], L.M. and [18] strategies that contribute to the improvement of the reliability of the battery element belonging to the propulsion system are presented. Another weak point of the propulsion system, due to its short lifetime, is the decoupling element. The decoupling element has the function of storing energy to damp the fluctuation between the constant power of the DC source and the power present in the load (Figure 2). However, this fluctuation can cause a variation of the DC voltage and a reduction in the system performance [19; 1; 20], which represents an affectation to the optimal system performance. Because of the negative impact of the aforementioned fluctuation, the importance of the decoupling system addressed in this paper is emphasized, as constant power demand is required to improve system performance [21; 22]. The decoupling element is usually oversized by selecting high capacitances to ensure its correct operation in various working scenarios. This leads to the use of electrolytic capacitors due to their high-power density and low cost. However, this capacitor construction technology has a low lifetime compared to the other elements of the propulsion system [19; 23; 24; 25; 26; 27]. Therefore, several studies have been carried out with alternatives to reduce the size of the decoupling element to select a different construction technology for the capacitor that has a longer lifetime and at the same time has a positive impact on the reliability of the system [28; 29]. However, most strategies to minimize the decoupling capacitance require adding additional topology to the system, such as passive filters and active filters [30; 31; 32; 33]. Passive filters include an electrolytic capacitor connected to the DC supply, a series inductance, or coupled filters [34; 35; 36]. As performed in [30], which adds two notch filter design techniques, the first modulated by triangular and sawtooth carriers and the second passive filter that reduces the current in the nominal operating region. As well as, in some works, a three-port ripple topology is added which allows the capacitor to be reduced [31]. Adding an extra topology or element to the system to perform the function of reducing the capacitance of the decoupling system can negatively affect the robustness, cost, and reliability of the system. Therefore, it is important to explore alternatives that allow the capacitance to be reduced without negatively affecting the system as a whole, which emphasizes the importance of the analysis developed in this article.