Based on current research into the mathematical model of the permanent magnet synchronous motor (PMSM) and the feedback linearization theory, a control strategy established upon feedback linearization is proposed. The Lie differential operation is performed on the output variable to obtain the state feedback of the nonlinear system, and the dynamic characteristics of the original system are transformed into linear dynamic characteristics. A current controller based on the input–output feedback linearization algorithm is designed to realize the input–output linearization control of the PMSM. The current controller decouples the d–q axis current from the flux linkage information of the motor and outputs a control voltage. When the motor speed reaches above the base speed, the field-forward and straight-axis current components are newly distributed to achieve field weakening control, which can realize the smooth transition between the constant torque region and weak magnetic region. Simulation and experimental results show the feasibility and viability of the strategy.

During the power transmission of doubly-fed induction generator (DFIG), due to the influence of series compensating capacitance and long-distance transmission, DFIG is prone to sub-synchronous oscillation, which damages the stability of the system. By establishing the mathematical model of DFIG system, the cause of sub-synchronous oscillation and its influence on the control strategy of DFIG system are discussed. In order to solve the problem of performance degradation of traditional phase-locked loop (PLL) under sub-synchronous oscillation, an improved PLL is proposed to replace the traditional PLL. Aiming at the problem that the control of rotor side converter(RSC) and grid side converter(GSC) in doubly-fed wind power generation system under sub-synchronous oscillation is disturbed by harmonic signals, a control method of adding a quasi resonant controller in the control link of RSC and GSC to suppress sub-synchronous oscillation is proposed, and the feasibility of the method is verified by simulation and experiment. Finally, based on the research process of RSC direct resonance control, the sub-synchronous oscillation suppression strategy based on harmonic current extraction is proposed for the frequency adaptability of the quasi resonant controller. The actual performance of the sub-synchronous oscillation suppression strategy is verified through simulation and experiment. The experimental results show that the strategy is effective.

A harmonic excitation brushless synchronous machine has higher power density compared with the traditional aerial three-stage generator due to removing the axial exciter and is suitable for use as an integrated starting-generator (ISG). However, the field current cannot always be generated in the field windings at different rotor positions in the starting mode. A new excitation scheme employing double three-phase phase orthogonal zero-sequence armature currents is proposed in this article. Harmonic electromotive forces and field current can be produced by the zero-sequence rotating excitation magnetic field and almost has no relationship with the rotor positions. In addition, in order to obtain a constant field current during the starting process, a control method of the generated field current is also presented. The rotating speed and field intensity of the zero-sequence excitation magnetomotive forces are both feedback controlled by the zero-sequence current in the whole starting process. Comparing with the original harmonic excitation machine, a higher and more stable field current can be generated in the proposed ISG whenever the rotor is at any position or at a low speed. The prototype machine is manufactured and experiments are carried out together with the excitation control method to verify the effectiveness of the theoretical and finite element analysis results.

Owing to low voltage stresses, wide range of input voltage and the same polarity of output voltage and input voltage, double-switch buck-boost converter (DSBBC) is a popular choice to achieve dc/dc conversion in photovoltaic generations (PV), power factor correction (PFC), portable devices and so on. Combined control (CC) makes DSBBC operate efficiently, but large ripples of output voltage are unavoidable during mode transition. With two equal duties, interleaved modulation (IM) makes the inductor ripple current decrease remarkably compared with synchronous modulation (SM) while inductor average current is still high. By introducing duty offset, inductor average current declines and efficiency is enhanced obviously under interleaved modulation with duty cycle offset (IMDO). However, with 180-degree phase-shifted angle, the ripple current is not low enough in some cases. Thus, to make further improvement on ripple current, an interleaved modulation scheme with optimized phase shifting (IMOPS) is proposed for DSBBC in this paper. Current features, optimal phase-shifted angle (OPSA) and operating region under IMOPS are described meticulously. Besides, theoretical and quantitative comparisons of different modulation schemes are presented, including inductor average current, inductor ripple current and ratio of direct power transfer (DPT). Based on a 150W prototype, the feasibility and effectiveness of IMOPS are demonstrated by experimental results.

This paper focuses on the power grid oscillation of grid-side converter (GSC) in doubly-fed induction generator (DFIG) caused by grid sub-synchronous oscillation (SSO), and designs a measure to improve the output power quality of GSC. Firstly, the influence mechanism of multipath disturbance of GSC under SSO is sorted out, and the disturbance factors and action modes are clarified. Secondly, the influence of SSO on the output estimation of phase-locked loop (PLL) in the control strategy and power calculation process is analyzed. Furthermore, the mathematical model of GSC output power considering the influence of PLL is established. At the same time, the key factors of SSO for GSC power oscillation suppression strategy are determined by analyzing the oscillation suppression effect of quasi-resonant controller when SSO amplitude, frequency and phase change. Based on the above theoretical analysis and research, the resonant controller is used to eliminate the estimation error of the PLL; according to the mechanism analysis of SSO characteristic change, an adaptive quasi-resonant controller for DFIG-GSC sub-synchronous power oscillation suppression strategy is designed, which eliminates the influence of SSO on GSC multipath disturbance and improves its output power quality. Finally, the effectiveness of the proposed suppression strategy is verified by simulation and experimental results.

The doubly fed induction generator with super capacitor is helpful to enhance the system inertia. At the same time, its structural characteristics are more suitable for the power grid topology without communication lines. However, the change of its topology also brings some problems. In this article, when SCESS-DFIG is participating in frequency regulation, DC bus voltage fluctuation caused by power imbalance of multiple converters is studied. The dynamic power response of super capacitor with DC-DC converter is a step load for grid side converter. The load of DC bus is nonlinear and random, so the balance and stability of the original system will change accordingly. Because of the complex topology and system composition of the doubly fed induction generator with super capacitor, the conventional feed-forward compensation control strategy can not be used to improve its dynamic response speed. Therefore, this article designs a control strategy which is applied for DC bus voltage fluctuation of the doubly fed induction generator with super capacitor. The theory proposed in this article is verified by simulation model and experiment.