Three-winding LLC Resonant Converter with Integrated Voltage Balancing

When the power is unbalanced between the positive and negative buss, the bipolar DC distribution system faces the challenge of voltage imbalance, and a voltage balancer is required for voltage equalization. However, the introduction of additional voltage balancing components increases the size and cost of the device, and reduces the conversion efficiency of the converter. A three-winding LLC resonant converter for centralized voltage balancing in two-pole DC distribution system is proposed. The proposed converter uses frequency and phase shift modulation to transmit power. Importantly, it automatically equalizes the voltage at the two poles and redistributes the unbalanced current on the load side. For the proposed converter, the operating characteristics are analyzed, including the voltage equalization principle, the unbalanced current distribution process, soft switching, losses, and device stresses. In addition, a magnetic flux balance control strategy is proposed to prevent transformer saturation. Finally, the pressure equalization capacity of the converter and the effectiveness of the magnetic flux balance control are verified by simulation.