Jiaqiang Yang

Strategies for the fault-tolerant current control of a multiphase machine under open phase conditions

Multiphase machines have higher reliability than 3-phase machines. In order to produce smooth torque after one or more phases are open circuit, the stator Magnetic Motive Force (MMF) is kept unchanged. This paper presents fault-tolerant current control strategies of a concentrated winding multiphase machine under open-circuited fault conditions. In a concentrated winding multiphase machine, other current harmonics can be injected to improve the flux distribution as well as torque density. Both phase currents and winding configurations are taken into consideration to keep the harmonics of stator MMF unchanged after the fault occurrence. In the high phase order machine, with Lagrange Method, the remaining phase currents commands are solved when the copper losses are minimized by neglecting some higher-order harmonics of MMF. A detailed discussion and simulation of the strategies are included. FEA Simulation results of torque ripple and power loss are presented for the verification of the control methods.

A direct torque control strategy of five-phase induction motor with duty cycle optimization

The conventional direct torque control has some disadvantages, such as large torque ripple and high harmonic components. In order to make the best use of five-phase motors more freedom and flexibility for direct torque control, the concept of a direct torque control strategy with duty cycle optimization is introduced in this paper. It adds a medium vector in each sampling period to reduce the influence of harmonic current. Not only the torque ripple is decreased, but also the third harmonic current appeared in the motor is suppressed. Simulation results verify the proposed strategy can achieve a good torque and current performance.

A Cost-Effective Regenerative Braking System for Electric Vehicles Driven by Induction Machine

In this paper, a cost-effective regenerative braking system for Electric Vehicles (EV) driven by induction machine (IM) is proposed. The structure of the system is simple because the extra demands are only the capacitor bank and resistor bank. A five- phase IM is chosen in this paper to adapt the high- power trend of EV and lower the device size. The required reactive power for the braking system is supplied by means of a parallel connected capacitor bank and a voltage source PWM converter. The capacitor bank is used as a bulk uncontrolled source to transfer reactive power to minimize the converter current and filter voltage harmonic. An instantaneous power based control algorithm is also implemented to regulate the AC output voltage and DC link voltage. The proposed scheme can be used efficiently for the electric vehicle (EV) to provide good voltage regulation charging the battery, and auxiliary effective brake torque during a wide speed range. Simulations are performed in Matlab/Simulink and the result verified the feasibility of the proposed approach.

Exponential response electrical pole-changing method for a five-phase induction machine with a current sliding mode control strategy

Electrical pole-changing technology leads to torque ripple and speed fluctuation despite broadening the constant power speed range of the multiphase induction machine (IM) system. To reduce the torque ripple and speed fluctuation of the machine, we investigate an exponential response electrical pole-changing method for five-phase IM with a current sliding-mode control strategy. This control strategy employs the dual-plane (d1–q1 and d2–q2) vector control method, which allows the IM to operate under different pole modes. Current sliding-mode controllers are applied instead of conventional proportional integral (PI) controllers to adjust the current vectors, and exponential current response achieves a smooth transition between the d1–q1 and d2–q2 planes. Compared with the step response pole-changing with PI control method, the proposed pole-changing method greatly reduces the torque ripple and speed fluctuation of the IM during the pole-changing process. Experimental results verify the exceptional performance of the proposed electrical pole-changing strategy.

An improved discharge control strategy with load current and rotor speed compensation for High-Speed Flywheel Energy Storage System

This paper proposes an improved discharge control strategy with load current and rotor speed compensation to suppress the fluctuation of DC bus voltage in High-speed Flywheel Energy Storage System (FESS). Mathematical model of FESS is built at first and conventional discharge control strategy with pure PI controller is analyzed. Then a load current and rotor speed compensation module is added to the outer DC bus voltage loop to recalculate the reference value of q-axis current with the DC bus voltage, load current, rotor speed and motor flux considered. In addition, feedforward decoupling strategy is utilized in the inner-current-loop to realize the independent control of the d-axis and q-axis currents. Simulation results with MATLAB/Simulink verify the proposed strategy improves the tracking capability of the d-q axis current, accelerates the DC bus voltage recovery speed and eliminates the fluctuation of the DC bus voltage caused by abrupt change of load current.

Voltage balancing strategy based on reference vector angle prediction for three-level shunt APF

In order to maintain the neutral-point voltage balance of neutral-point-clamped (NPC) shunt active power filter(APF), a neutral-point voltage balance strategy based on reference vector angle prediction is proposed in this paper. The proposed approach considers the effect of every vector on neutral-point voltage and corresponding switching sequences for the reference vector in each sector. By modifying the reference vector angle to select optimized switching sequences, the approach maintains dc-bus capacitor voltage balance and reduces neutral-point voltage ripples. Simulation is performed in Matlab to verify the validity and effectiveness of the proposed approach.

Research on a Novel AC Variable-Frequency Dynamic Power Dynamometer

Traditional dynamometers, such as hysteretic dynamometers, eddy current dynamometers, mechanic dynamometers and waterpower dynamometers, may consume lots of fuels and electrical energy while working, which causes the energy waste. Also, these dynamometers should be equipped with additional radiators to keep the dynamometers cool. A type of novel dynamic power dynamometer scheme is presented based on PWM rectifier and direct torque control (DTC) technology for induction motor in this paper. The proposed dynamometer can operate in both motoring and generating states by DTC of induction motor, which ensures the swift torque response of the dynamometers. Three-phase PWM technology enables the bidirectional flow of the energy. PWM rectifier can not only provide DC link voltage for the induction motor, but also feed back the energy generated by the dynamometer to AC mains, which guarantees both current sinusoid and unit power factor. This scheme decreases the harmonic disturbance to the AC mains, saves the energy sources, and cut the cost of purchasing radiator. In order to validate the feasibility of the scheme, an experimental device based on the DSP and intelligent power module IPM is designed. Experimental results indicate that the novel dynamometer has an outstanding dynamic and static performance