Inertial support for hybrid AC/DC microgrid systems is provided by the virtual synchronous generator (VSG). However, the fast performance of the system is neglected while enhancing the stability of the system. To address this problem, an adaptive virtual inertia control strategy based on VSG technology is proposed. This control approach adaptively adjusts the system virtual inertia when the system operation deviates from the nominal value, by slowing down the rate of change of AC frequency and DC voltage and improving the deviation of AC frequency and DC voltage. Meanwhile, when the AC frequency and DC voltage restore back to the rated value, the rate of change of AC frequency is accelerated and the DC voltage fluctuation is reduced by dynamically adjusting the virtual inertia of the system. The proposed adaptive virtual inertia control method combines the advantages of large and small inertia to effectively improve the dynamic response of the system voltage and frequency in both rectifier and inverter modes. Finally, the simulation and experimental results verify the effectiveness of the proposed control algorithm.

This paper proposes an accurate mathematical model of three-level neutral-point-clamped (NPC) converters that can accurately represent the midpoint potential drift of the DC link with parameter perturbation. The mathematical relationships between the fluctuation in neutral-point voltage, the parametric perturbation, and the capacitance error are obtained as mathematical expressions in this model. The expressions can be used to quantitatively analyze the reason for the neutral-point voltage imbalance and balancing effect based on a zero-sequence voltage injection. The injected zero-sequence voltage, which can be used to balance the DC-side voltages with the combined action of active current, can be easily obtained from the proposed model. A balancing control under four-quadrant operation modes is proposed by considering the active current to verify the effectiveness of this model. Both the simulation and experiment results validate the excellent performance of the proposed model compared to the conventional model.Energies 2019, 12, 3367 2 of 22 pulse width modulation (SVPWM) strategies were proposed to adjust the dwell time between small vector switching states by judging the direction of the neutral point current and the deviation of the neutral point potential. However, the calculation methods are complex and difficult to implement. In [24], a pulse width modulation (PWM) strategy was proposed where the both DC-side voltages can be adjusted independently through zero-sequence voltage injections and compensation for the unbalance in neutral point voltages, but the process of calculating the injected zero-sequence voltages is complicated.However, these control strategies, above all, ignore the quantitative analysis of the potential drift and balancing effect based on zero-sequence voltage injection. Meanwhile, if the converter is used in renewable energy generation and energy storage with four-quadrant operation modes, the DC voltage balancing control is very difficult to realize in existing literature because the active current of the converter is not taken into consideration.This paper proposes an accurate mathematical model of the neutral-point potential in three-level NPC converters based on the SPWM strategy with parametric perturbation and zero-sequence voltage injection. The model is simple and direct, but very interesting and valuable. To the best of our knowledge, it is novel and has not been previously reported in the literature. From this model, the relationship between the drift potential value and all the AC-side and DC-side variables can be deduced by quantitative analyses. The calculated drift potential value shows that the basic reason for the neutral-point potential drift is the uneven shunt loss caused by the parametric perturbation, and the capacitance error has no influence on it. The balancing control can be directly obtained based on the combined action of the injected zero-sequence voltage and active current. The required zero-sequence voltage for balancing control can be easily calculated b...

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Abstract. Due to the low damping in a central driven electric vehicle and lack of passive damping mechanisms as compared with a conventional vehicle, the vehicle may endure torsional vibrations which may deteriorates the vehicle's drivability. Thus active damping control strategy is required to reduce the undesirable oscillations in an EV. In this paper, the origin of the vibration and the design of a damping control method to suppress such oscillations to improve the drivability of an EV are studied. The traction motor torque that is given by the vehicle controller is adjusted according to the acceleration rate of the motor speed to attenuate the resonant frequency. Simulations and experiments are performed to validate the system. The results show that the proposed control system can effectively suppress oscillations and hence improve drivability.

A novel Line-start Permanent Magnet Synchronous Motor (LS-PMSM) with arc straight inserted permanent magnet is presented in this paper. The Simulink model is established according to voltage equation and motion equation, starting performance with rated voltage is calculated, performance on different voltages is also calculated, and the lowest voltage is obtained. Experimental facility is established. Influence of voltage on starting performance, such as electromagnetic torque, armature current, speed and slip ratio is analyzed by simulation and experimentation respectively. Results verify that good matching attributes are got. The foundation for widely industrial application of this LS-PMSM with novel rotor structure is found with performance research done above.