Unbalanced voltage in the power grid can cause fluctuations in the active power of voltage source PWM rectifiers, leading to the generation of a large number of harmonic components in the AC and DC voltages, thereby deteriorating system performance. Due to the fact that Model Predictive Control (MPC) can achieve fast and accurate tracking of benchmarks, with small computational complexity and ease of implementation, this paper proposes an improved MPC control strategy to address the issue of voltage imbalance in the power grid. This strategy first uses the positive/negative sequence component separation method to decompose the unbalanced grid voltage, and provides a reference current in the two-phase stationary coordinates. In addition, the current inner loop adopts an improved MPC algorithm, which can achieve fast and accurate tracking of the reference current. The proposed control method avoids the coupling of reference currents and the problem of complex solutions, simplifies the control structure, and requires less computation. The simulation results show that this strategy can effectively suppress harmonics, stabilize output power, and improve system performance.