Analysis of voltage modulation based active damping techniques for small DC-link drive system

Small DC-link drive system, built with film capacitor in the DC link, may have the advantages of longer lifetime and the possibility to achieve a more compact design of capacitor bank at medium and high power rates. However, it exhibits instability problem, especially when it is fed by a soft grid. Therefore, active damping techniques are usually needed in order to stabilize the system. This paper firstly describes the essential idea of active damping methods from energy flow point of view. Then a new method named as “virtual positive impedance” method is introduced to ensure the dc-link stability without the requirements of the information of system parameters and operating conditions. Finally, active damping techniques with minimized current magnitude and total duty cycle are discussed, in order to fit various operating conditions. Simulation and experimental results are presented to verify the proposed ideas.