Abstract: In the electrical primary equipment of hydropower plants, due to the limited use of three-phase stationary coordinate system equivalent circuits, control accuracy is relatively poor. To address this issue, a nonlinear harmonic current control method for the electrical primary equipment of hydropower plants is proposed. Based on the three-phase stationary coordinate system equivalent circuit, the three-phase voltage equations are first derived. Through coordinate transformation, a nonlinear mathematical model of the electrical primary equipment under the dq coordinate system is obtained. Assuming the average value of a certain counter electromotive force is 0, the average expression of the current harmonic components is derived by analyzing the probability of control variable values, leading to the calculation of nonlinear harmonic inductance. An improved quasi-harmonic inductance control method is proposed, using its transfer function, feedforward decoupling control strategy, and PI regulator to derive the control equation. By reasonably setting these parameters, the harmonic current can be precisely regulated, achieving zero steady-state error. Experimental results show that the total harmonic distortion rate of the harmonic current significantly decreases to 3.3%, and at 1000 Hz, the disturbance rejection function reaches 0.65, far exceeding other methods, demonstrating its superiority in control accuracy.