Power regulation system (PRS) is necessary to mitigate the power fluctuation and stabilize the voltage for smart grid. This paper proposes a method to balance the DC link voltage of H-bridge cascade PRS. The unbalance of the PRS is mainly due to the different input/output currents in each battery bank units. The balancing control is based on the negative sequence voltage injection concept. The control algorithm is analyzed and the experimental results verify the effectiveness of the method.