## 1 Introduction
The LMC enables the drivetrain to operate safely at the maximum attainable performance limits. In Ref. [24], the Bertotti iron loss formula is used to analyze the stator iron loss, and iron loss is verified by the FEM model. Based on the loss model, the proposed control method fully considers the cross effect and iron loss, and can maximize the efficiency of PMSMs. However, these recent optimized motor efficiency control strategies only focus on the optimization of the motor loss, and neglect the coupling relationship between motor loss and inverter loss. Therefore, as the inverter loss is an important part of system loss in the PMSM system for transportation, these motor control strategies will not achieve the maximum system efficiency. There are also many control strategies for three-phase half-bridge inverters in the PMSM drive system [25]. Modern methods about three-phase inverters such as selected harmonic elimination pulse width modulation (SHEPWM) [26], current harmonic distortion minimization PWM (CHMPWM) [27], harmonic injection PWM (HIPWM) [28], space vector pulse width modulation (SVPWM) [29], etc., always focus on the modulation optimization to decrease the harmonic components of the output voltage in the three-phase inverter. In Ref. [26], a method of smooth transition between different SHEPWMs is proposed to adapt to the SPMSMs and IPMSMs, by which smooth transition of current is guaranteed and the harmonic current is reduced. In Ref. [27], considering the saliency ratio and load angle constraints, a new current harmonic evaluation index is proposed, and based on it, the improved CHMPWM guarantees good performance of both current THD and the specific order current harmonics. All these control strategies ignore the coupling relationship between motor loss and inverter loss. As the inverter loss is an important part of the efficient performance in the PMSM drive system, the efficiency optimization of the three-phase inverter will directly improve the power loss of a PMSM system. Therefore, to acquire a higher system efficiency of a PMSM drive system, The PWM control strategy must take consideration both harmonic components of output voltage and the power loss of power devices in the three-phase bridge inverter. This paper proposes a novel efficiency control strategy to improve the power loss of PMSM drive systems, which can optimize both motor and inverter losses. An accurate nonlinear loss model of a three-phase half-bridge inverter is built to predict the conduction loss and switch loss exactly in the sine-wave PMSM system. This paper applies the double Fourier integral analysis to analytically calculate the fundamental component and harmonics of the inverter output voltage, by which a global motor loss model of the PMSM is established. The global motor loss model can take consideration of both the fundamental motor loss and harmonic motor loss, which shows the coupling relationship between motor loss and inverter loss. Based on the nonlinear inverter loss and global motor loss model, the proposed efficiency optimization control strategy can optimize the motor current and PWM frequency together, by which the PMSM drive system can achieve higher system efficiency compared with traditional control strategies. The loss reduction effect is tested and verified by experiments.