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In the unfolding‐type interleaved two‐switch flyback inverter (ILTFI) operating in discontinuous conduction mode (DCM), the hybrid control strategy combining the one‐phase DCM and the two‐phase DCM has a significant impact on improving the efficiency under all load conditions. In the situation where the marginal power of this control strategy is increased, the converter may enter CCM. Consequently, the converter cannot track the reference current and the output current quality is notably decreased. To tackle this issue, a novel hybrid control method is proposed which varies the switching frequency based on the output power. The proposed approach is immune to the loss analysis and power losses of the components. Hence, it is independent of components selection and their characteristics. In this case, the smooth transition between the one‐phase and the two‐phase operation modes is guaranteed without affecting the output power quality and the stability of the converter in DCM. The control complexity of the proposed scheme is low and the converter can be easily controlled in DCM. The performance of the flyback microinverter with the proposed hybrid control scheme is verified by the simulation and the experimental results together with the loss analysis. [ABSTRACT FROM AUTHOR]

Two‐stage power conversion system (PCS) for energy storage systems has been considered in islanded operation mode. A three‐level T‐type three‐leg three‐phase four‐wire topology (3LT2 3L3P4W) is employed as AC/DC part and a three‐level buck/boost converter is used as DC/DC interface. This study is mainly focused on balancing the neutral‐point potential (NPP) of the PCS with asymmetrical load connection. An NPP low‐frequency ripple model of 3LT2 3L3P4 inverter is proposed considering various load conditions firstly, which includes detailed expression of low‐frequency ripple components at fundamental frequency and fundamental frequency multipliers. Then, a novel NPP balancing method based on front‐end three‐level buck/boost converter under proportional resonant control is presented, in which the resonance points are set at fundamental frequency and triple fundamental frequency to suppress the dominant components of NPP ripple. Furthermore, a small‐signal model of three‐level buck/boost NPP control system is established and stability analysis is carried out. Simulation and experimental results have been provided to verify the accuracy of the NPP low‐frequency ripple model and the effectiveness of the NPP balancing method. [ABSTRACT FROM AUTHOR]

This paper develops a new field weakening method for an integrated permanent magnet synchronous machine vehicle drive. This method adopts both the DC-link and the rotor speed as a feedback signals to generate the demagnetising current reference. This eliminates the effect of the rotor speed on the FW controller dynamics and ensures stable operation across the whole range of speeds. Mathematical analysis of the system is used to design the controller gains to achieve the desired dynamic response. A maximum torque per ampere (MTPA) strategy is included in the control design, with a linearised function to reduce the computational demand. Experimental results show stable and satisfactory operation at different speeds and load conditions. They also illustrate smooth transition between the MTPA operation and the FW operation when the rotor speed crosses base speed.

This paper develops a new field weakening method for an integrated permanent magnet synchronous machine vehicle drive. This method adopts both the DC-link and the rotor speed as a feedback signals to generate the demagnetising current reference. This eliminates the effect of the rotor speed on the FW controller dynamics and ensures stable operation across the whole range of speeds. Mathematical analysis of the system is used to design the controller gains to achieve the desired dynamic response. A maximum torque per ampere (MTPA) strategy is included in the control design, with a linearised function to reduce the computational demand. Experimental results show stable and satisfactory operation at different speeds and load conditions. They also illustrate smooth transition between the MTPA operation and the FW operation when the rotor speed crosses base speed. [ABSTRACT FROM AUTHOR]

Back-EMF-based sensorless control of permanent magnet synchronous machines (PMSMs) is preferred in many industrial applications due to its control simplicity and high machine efficiency. Position estimation based on the back-EMF is most reliable in the medium-to high-speed range. For applications where low-speed operation is not required, a simple-structure back-EMF-based sensorless controller coupled with a simple startup procedure offers an attractive low-cost solution. This paper proposes a new startup procedure based on closed-loop current regulation. Compared to the existing methods, the new starting method can work under different load conditions and allows smooth transition from the startup procedure to the back-EMF-based sensorless control mode. In order to determine the successful use of the proposed method in various applications, it stability under different load conditions is discussed in detail. The proposed method is robust when it comes to the motor parameter variation and can be used for both surface-mounted PMSMs (SPMSMs) and interior PMSMs. The method presented in this paper is validated using the experimental results on an SPMSM. A general design guideline is also given. [ABSTRACT FROM AUTHOR]