Based on the passive damping method of capacitor in parallel with resistor, the active damping method of virtual resistor in parallel with capacitor can complete the virtualization of shunt resistor using the control algorithm and realize the active damping of the resonant peak from the output filter through the capacitor current feedback. However, the existing method of virtual resistor in parallel with capacitor cannot achieve a strict equivalence of shunt resistance, which leads to the problem of poor dynamic performance. To solve this problem, through the transformation of the control block diagram, an active damping control method of fully equivalent shunt resistor based on capacitor voltage and capacitor current feedback is proposed, thus realizing the strict equivalence of passive damping method of capacitor in parallel with resistor. At the same time, the active damping control method of fully equivalent shunt resistor is obtained through the analysis of dominant poles of the system. Compared with the method of virtual resistor in parallel with capacitor based on the current loop, this method can effectively improve the damping ratio and response speed of the system while reducing the overshoot. Finally, simulation and experimental results verified the effectiveness of the proposed method.

Owing to its advantages such as simple structure, strong robustness and good dynamic and static performances, model predictive control (MPC) has been widely applied to three-phase voltage source PWM rectifier systems. However, the PI linear regulator adopted in the voltage outer loop of MPC affects the dynamic performance of DC-side voltage. Aimed at this problem, a virtual torque impulse balance control strategy is proposed to achieve a rapid convergence of DC-side voltage through only one time of regulation. To realize this strategy, the expression of virtual torque is derived based on the mathematical model at first. Second, the virtual torque impulse balance control equation under load mutation is analyzed and established according to the fact that the DC-side output voltage will remain unchanged before and after load mutation while combining the principle of power conservation. Afterwards, the acting time of zero and forward vectors can be obtained. Finally, the virtual torque impulse balance control of the three-phase voltage source PWM rectifier system under load mutation is realized through simulations and experiments, which verifies the correctness and effectiveness of the proposed algorithm.

The triple active bridge(TAB) DC-DC converter based on the phase-shifting plus duty cycle control strategy has advantages such as a high efficiency and an expandable soft switching range. However, its small signal modeling process is complex, and the parameter setting of closed-loop control loop is difficult. To solve these problems, a full-orer continuous generalized state space average modeling and PI controller design method for TAB converter under phase-shifting plus duty cycle control is proposed. First, the operation principle and Y-type equivalent structure of the TAB converter are analyzed. Second, combined with the characteristics of phase-shifting plus duty cycle control and the equivalent method of AC square wave source, the generalized state space average model of the TAB converter is derived. Third, based on the derived model, the transfer function from input to output is obtained, and the parameters of PI controller are designed. Finally, the correctness and effectiveness of the proposed method were verified by digital simulations and prototype tests.

In view of the serious current harmonics in a doubly-fed induction generator (DFIG)-DC connection system and the large loss of a dual-voltage source inverter (VSI) connection system, a novel dual-converter connection system which connects a three-phase DFIG to DC microgrid is designed. First, the topology, pulse-width modulation (PWM) measurement and DFIG model of the dual-converter connection system are described in detail. Different from the traditional connection systems, the proposed connection system adopts an open-end winding structure and uses a three-bridge arm rectifier on each side of the stator winding. Considering that these arms are usually composed of insulated gate bipolar transistors (IGBTs), a diode is used instead of the IGBT in the rectifier to decrease the number of control switches and reduce the cost. Second, the control strategies for a stator-side converter (SSC) and a rotor-side converter(RSC) under the new topology are given. Third, a comparison with the DFIG-DC connection system and the dual-VSI connection system is performed through simulations, and results show the advantages of the proposed method in terms of current harmonic distortion, torque ripple and semiconductor loss. Finally, experimental verification was carried out on a 0.56 kW DFIG, and results also verified the advantages of this method in terms of loss, harmonics and torque ripple.

With the rapid development of power generation by renewable energy and the grid-connection technology, the microgrid dominated by power electronic converters has attracted more and more attention in recent years. Owing to the low inertia and high nonlinearity of power electronic converters, an islanded microgrid under large disturbances is more likely to lose its transient stability. Considering the interactions between grid-forming and grid-following converters in the microgrid, a transient stability criterion based on the equal area criterion(EAC) and an improved control strategy for transient stability are proposed. First, the simplified second-order dynamic model of the islanded microgrid is established, which contains a nonlinear damping term relying on the power angle. Then, the impact of the nonlinear damping term on the acceleration and deceleration areas is revealed from the energy perspective. Considering the distribution characteristics of nonlinear damping, a transient stability criterion is formulated for the positive damping region. In addition, according to the stable boundary conditions, an improved control strategy for transient stability based on voltage feedforward is also put forward. Finally, simulations are carried out with MATLAB/Simulink to verify the effectiveness of the proposed stability criteria and the improved control strategy. The results show that the microgrid transient stability criterion and the improved control strategy proposed can provide a theoretical basis for the parameter optimization design of power electronic converters and the improvement of the stable operation capability of microgrid.

The inconsistency of line parameters at the outlet of distributed generator(DG) and its random output disturbance lead to a decrease in load power distribution accuracy of DC microgrid and grid-side voltage fluctuation. Aimed at these problems, a double-factor droop control strategy based on adaptive characteristics is proposed with the consideration of the transient-and steady-state of DG operation. First, the influence of line impedance is taken into account during the steady-state operation, a voltage regulation coefficient is introduced, and the steady-state component of double-factor droop coefficient is established. The exact distribution of load power can be realized when the impedance value is unknown, and the grid-side voltage can be raised to reduce the difference with the rated voltage. Second, the influence of random disturbance of DG output is considered in the transient process, and the distributed consistency iterative algorithm is introduced to establish the double-factor droop coefficient free component, which can quickly suppress the power disturbance and grid-side voltage fluctuation while maintaining the balanced output from DG, thus improving the system stability. Finally, a DC microgrid model is built in PSCAD, and simulation results show the effectiveness of the proposed strategy.

With the increasing attention to environmental issues, more and more distributed energy systems represented by microgrids are appearing in the power system, which also poses some challenges to the traditional power systems. For example, the delay in digital control system, variations in grid impedance of weak grid and the interaction between parallel converters in microgrids will cause adverse effects on the stable operation of microgrids. On this basis, a novel type of grid-forming control method for microgrid considering control delay and variation in grid impedance is put forward to enhance the stability of microgrids under uncertainties. First, the above problems are modeled, and a delay compensation method is proposed to improve the robustness of the control system with respect to the variation in grid impedance. Then, a feedforward loop is introduced into the control system to protect it from the interference of parallel inverters in microgrids. Finally, experimental results demonstrate the effectiveness and superiority of the proposed control method.

To ensure the safe, reliable and economic operation of high-speed railway, a multi-dimensional control method for the power supply operation energy of high-speed railway cophase power supply system is proposed. The composition structure and power supply process of the power supply system are analyzed, and a power flow controller is used to compensate the power of the system, thus ensuring its stable operation. Combined with indicators such as three-phase imbalance degree and distortion of voltage and current waveforms, the optimal load model of operation energy is constructed to minimize the loss of transmission energy. Through the active and reactive power compensation for current in two power supply arms, the negative-sequence current is eliminated. A control strategy for the railway power conditioner is formulated, and the changes in the step-down transformer are obtained to ensure a stable DC-side voltage. Afterwards, a proportional integral controller is used to obtain the ideal value of current and get the control signal, thus realizing the multi-dimensional control of power supply operation energy. Simulation results show that the proposed multi-dimensional control method can improve the three-phase current balance degree and achieve an effect of voltage sharing stability.

A frequency regulation method for a large number of electric vehicles (EVs) in an isolated grid with high permeability renewable energy sources is proposed. First, a disturbance observer is designed for the system's order reduction model to generate additional frequency control signals for clustered EVs. This order reduction model is obtained by combining the changes in load, wind power, photovoltaic system and clustered EVs, thus generating a lumped disturbance estimated by the disturbance observer. Second, a robust model predictive control method based on the Tube model is proposed to provide effective control signals to improve the responsiveness of clustered EVs. The control signals are generated to obtain the minimum frequency deviation error by means of the minimum control actions while considering various physical constraints on the system operation. Third, the influence of time delay on communication link is studied through the stability analysis, and the time delay margin is obtained. Finally, through simulation analysis, the effectiveness of the proposed method is verified, and the advantages of the proposed method over traditional model predictive control, fuzzy proportional integral control and linear quadratic regulator control are also verified.

The traditional coupling mechanism of multi-directional wireless power transfer (WPT) often adopts an xyz orthogonal circular coil structure, which requires three power supplies and has a charging area limited by the coil structure. To solve this problem, a novel multi-directional WPT coupling mechanism composed of two groups of 8-shaped coils and one group of circular coils is proposed. It presents five circular rings in different directions as a whole and only needs one single power supply. Based on the S-S type transmitter topology, the magnetic field distribution in the coil is changed by controlling the circuit, thus realizing power transfer inside and outside the coil and broadening the charging area. Based on the coil structure, a mathematical model of the proposed coupling mechanism is established, and the calculation formulas for mutual inductance and efficiency at any spatial position are derived. The best working area of the coupling mechanism is determined according to simulation and experimental results.