LCL 필터를 갖는 계통 연계형 인버터의 Interleaved PWM을 통한 병렬운전

Abstract

In this paper, an inverter parallel operation method that improves system performance by reducing harmonics injected into the grid connected inverter with an LCL filter was proposed. If an LCL filter is used to reduce harmonics in the grid connected inverters, there is a problem that the system is liable to become unstable due to its resonance characteristics, but it can be stabilized by adding damping to the system. This damping may be obtained simply by inserting a damping resistor, but most of the filtered harmonic noise current flows toward the damping resistor and a large power loss occurs, thereby degrading the performance of the system. In order to solve this problem, active damping that generates damping with a controller is attracting attention, but techniques using a digital filter are sensitive to circuit parameters and are complicated in design, and their operating range is limited by the bandwidth of the controller or additional sensors are required. The proposed system has two inverters paralleled and operated with interleaved PWM for powering up and performance improvement. Two LCL filters have two separate filter inductors and one set of filter capacitor and grid inductor in common. The differential mode current circulates through two inverters and two filter inductors. The differential mode current are got rid of from the filter capacitor and the power grid. Accordingly, performance improvement can be achieved due to the reduced currents in the filter capacitor and the reduced harmonics into a grid. A single phase prototype has been made and tested, and the proposal has been verified. Additionally, the system, which has four inverters paralleled and operates with PWM using 4-phase carrier, has also been verified. Harmonic reduction property of the proposed interleaved PWM will remain as long as stability is ensured whether passive damping is used or active damping is used.