DC electric springs with DC/DC converters

The concept of DC electric spring (DCES) was recently proposed to solve the stability issue caused by integrating intermittent renewable energy sources (RESs) to DC microgrids. In this paper, a new topology of DCES is proposed based on DC/DC converters. The proposed DCES consists of a bi-directional paralleled buck-boost converters (BBCs), a bi-directional phase-shift full-bridge converter (PSFBC) and an H-bridge circuit. Three basic operating modes of the proposed DCES can be achieved, and namely voltage boosting mode, voltage balancing mode and voltage suppression mode. Strategy of constant charging and/or constant discharging for batteries is adopted and four operating modes are analyzed as charging-positive, charging-negative, discharging-positive and discharging-negative modes. An additional mechanism for fast charging or fast discharging is also designed to secure normal operation of batteries. With the proposed DCES, the power fluctuations due to intermittent RESs can be passed to non-critical loads (NCLs) and batteries while power on critical loads (CLs) is kept stable. This is possibly the first attempt to design a DCES with only DC/DC converters. The performances of the proposed DCES are simulated, which validate the effectiveness of the proposed DCES and its control.