This article proposes a cascade proportional-integral second-order sliding mode control (PI-SMC) method for matrix converter-fed brushless doubly fed induction machine (BDFIM). The PI-SMC method consists of a PI speed controller with an inner-loop second-order sliding mode control (SMC). The PI controller provides a reference to the inner-loop second-order SMC with constraints according to the system requirements in terms of maximum current and speed. As the discontinuous sign function in the traditional SMC is replaced by the continuous supertwisting function, the chattering problem is eliminated for inner-loop second-order SMC. Moreover, the inner-loop second-order SMC has robustness and interference immunity against nonlinear disturbances of the BDFIM. Simulation and experimental results demonstrate the excellent robust tracking performance of the proposed PI-SMC method.