This paper presents gain-scheduling control strategy for Z-source inverter used in traction motors. An iterative reduction-based heuristic algorithms (IRHA) is introduced for optimization of controller parameters. Since it is difficult to implement a stabilizable optimization with the conventional heuristic algorithm, optimum design can be achieved via creating stable sets by employing IRHA. In this optimization method, a new reduced subset is created at the end of each iteration, thereby reducing computation complexity. The proposed scheme adjusts proportional, integral, differential and derivative kick coefficients (K-p, K-i, K-d and T-d). In this study, various PID controllers are designed using IRHA and H-infinity norm-based optimization methods. Furthermore, in order to overcome non-linearity which exists in the nature of ZSI, gain scheduling is resorted to. The effectiveness of the proposed gain-scheduled controller structure is demonstrated over different input values and voltage fluctuations.