A hybrid cascade static var generator (HC-SVG) composed of neutral-point clamped (NPC) and cascade H-bridge (CHB) power units produces phase-to-phase voltage imbalance when compensating for unbalanced loads. To address this, a phase-to-phase voltage balance control method for the CHB power unit is established based on zero sequence voltage feedforward. The DC side voltage value of HC-SVG after zero sequence voltage injection is analyzed. First, the relationship between the fundamental voltage component of the CHB power unit and the output fundamental voltage of the HC-SVG is analyzed. The zero-sequence voltage required by the phase-to-phase voltage balance of the CHB power unit when the HC-SVG compensates for unbalanced loads is deduced and zero sequence voltage feedforward control is established. Secondly, the constraint relationship between the degree of compensation current imbalance and the HC-SVG DC side voltage is discussed based on the analytical relationship between zero sequence voltage and compensation current. Taking a 6 kV/3 Mvar device as an example, the value of the DC side voltage is analyzed and compared with the star CHB-SVG. It reveals the characteristics of low DC voltage required by the HC-SVG when compensating unbalanced loads. Simulation results show the effectiveness of clustered voltage balance control and DC side voltage value analysis.