LTCL-Filter active-damping design considerations for low-switching-frequency grid-tied VSCs

Most electronic devices are connected to the grid by using power electronics converters and, in order to reduce the filter size and cost, novel filter topologies are being proposed in the literature. For high-power applications, LTCL filters are an attractive solution since the size of inductors can be reduced while maintaining a low switching frequency. However, this type of filter requires additional passive damping elements unless an active damping strategy is included in its control system. In this paper, the hardware and control system design of a VSC connected to the grid via a LTCL filter is addressed, with emphasis on the damping problem. It is shown that adequate damping can be provided by applying two different strategies. The first one is by changing the hardware of the converter (without additional passive elements), while the second one is by adding a compensator in series with the current controller. The proposed design methodology and control system improvements were tested in a simulation of a 15 kW VSC connected to the grid via a LTCL filter.