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This paper presents a new maximum torque per ampere (MTPA) control strategy for sensorless V/f controlled PMSM drives. The proposed theoretical basis can be applied to both surface permanent magnet synchronous motor (SPMSM) and interior permanent magnet synchronous motor (IPMSM) drives to obtain high efficiency. Two closed loops are required in the proposed drive. First, by using the oscillatory active power information, a load angle compensation component is generated to adjust the load angle to stabilize the system. Second, the drive imaginary power is regulated to follow the imaginary power of MTPA performance such that the drive can operate under the minimum copper loss condition in the steady state. The imaginary power controller can generate a voltage compensation component to properly adjust the drive voltage. Hence, the demanded MTPA performance is obtained. The provided simulation results show the performance and validity of the proposed strategy. The hardware implementation of the proposed control is now undertaking and the experimental results will soon be shown in the near publication. Index Terms-interior permanent magnet synchronous motor (IPMSM), maximum torque per ampere (MTPA), surface permanent magnet synchronous motor (SPMSM), V/f control

In this study, an exact circuit model for the class E inverter is proposed to analyse the circuit behaviour in frequency domain without mathematical assumptions. Through this model, a close form formula is proposed to solve the load current and drain-source end voltage of metal oxide semiconductor field effect transistor at switching instants in steady-state instead of complicated numerical iteration. With these current and voltage at switching instants, the load current can be expressed with exact function and evaluated. By means of the proposed formula and current expression, the optimal and suboptimal conditions for the zero voltage switching (ZVS) operation have been expressed in terms of the shifting angle of load current with respect to drain-source voltage. Further, the ZVS and non-ZVS operation regions can be marked via calculating the shifting angle and optimal shifting angle, which are proposed in the study. To demonstrate the proposed formulas and ZVS conditions, some examples are given to examine the analysis and ZVS drifting behaviour with comparing of calculation, simulation and experiment. Good agreements from the illustrated examples have given the verification of the analysis and design for the class E inverter.

Class E resonant power amplifier (or inverter) is often applied to design a high frequency switching power converter. The zero voltage switching (ZVS) or zero current switching (ZCS) operation leads the converter to high converting efficiency even the converter works at high frequency. Theoretically, with a high speed power transistor, the class E amplifier can work from several megahertzes to dozen of megahertzes. While the resonant components of class E inverter are varying, the ZVS operation will be shifting around the dominant operating point. In this paper, an exact circuit model is proposed to analyze the circuit behavior for the class E inverter. Unnecessarily mathematical assumption and complicated numerical iteration, the proposed model is easy to analyze the class E circuits in frequency domain. Through this model, a close form formula is proposed to solve the load current and drain-source end voltage of MOSFET at switching instants for steady state without a complicated numerical iterating. By this formula, the optimal and suboptimal conditions for the ZVS operation are expressed in terms of the shifting angle of load current with respect to drain-source voltage. Also, some practical design examples are given to demonstrate the formula calculating results that are good agreement with the numerical iterating results.

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