Xing Hu

A Novel Hybrid Five-Level Voltage Source Converter Based on T-Type Topology for High-Efficiency Applications

A novel hybrid five-level voltage-source converter for high-efficiency applications is investigated in this paper. Compared with traditional multilevel converters, this hybrid multilevel converter generates desired staircase voltage levels with a reduced number of power devices and isolated drivers at higher voltage levels. It has redundant switching state combinations in hybrid multilevel converter, which makes it easy to balance flying capacitor voltages and realize fault-tolerant operation. A voltage-balancing control strategy based on switching state redundancies is presented for the hybrid multilevel converter to generate desired levels and also keep voltage balance of flying capacitors at the same time. The performance of the hybrid multilevel converter under various operating conditions is investigated in MATLAB/Simulink. The effectiveness of the proposed hybrid multilevel converter is validated by experiment results.

Fault diagnosis of modular multilevel converters based on extended state observer

A fault diagnosis strategy for open-circuit failure of semiconductor switching device in modular multilevel converters is proposed in this paper. Fault detection and location are both included in this strategy. An extended state observer based on arm current equation is put forward and designed. The inputs of the observer are the arm current, ac voltage, and the dc link voltage. The observer is used to track the arm current and output the observed value of the extended state. The theoretical calculated value of the extended state can be acquired by the sub-module operation states and the capacitor voltages. The deviation between the observed and calculated value can be used to detect and locate the fault switching device. The effectiveness of the proposed strategy is verified in Matlab/Simulink.

A novel hybrid five-level voltage source converter based on T-type topology for high-efficiency applications

A novel hybrid five-level voltage source converter for high-efficiency applications is presented and investigated in this paper, and the topology configuration is based on the upgrade of three-level T-type converter and two-level converter. Compared with traditional stacked multilevel converter and flying capacitor multilevel converter, this hybrid multilevel converter generates desired staircase voltage levels with a reduced number of power devices and isolated drivers. It has nine redundant switching state combinations in hybrid five-level converter, which makes it easy to balance the flying capacitor voltage and realize fault-tolerant operation. A simple control strategy based on phase disposition PWM method is presented for the proposed hybrid converter, in order to generate desired levels while control the flying capacitor voltage. The performance of the hybrid multilevel converter is investigated in MATLAB/Simulink under various operating conditions. The effectiveness of the proposed hybrid multilevel converter is validated by experimental platform.

Extended state observer based fault detection and location method for modular multilevel converters

Modular multilevel converter (MMC) is a promising converter in medium and high voltage applications due to its modularity and easiness to meet any voltage level by cascading the sub-modules. However, large amount of modules not only increase the failure probability of the devices, but also increase the difficulty of the fault diagnosis, which have brought a challenging for popularization and application of the MMC. Therefore, an extended state observer based fault diagnosis strategy for MMC is proposed in this paper. The extended state observer is designed based on the circulating current equation. The output of the extended state observer is compared with the theoretical value calculated by the modified switching models to locate the fault. The simulation is modeled and carried out in Matlab/Simulink. The effectiveness of the proposed strategy is verified by the simulation results.

Investigation of a new modular multilevel converter with DC fault blocking capability

This paper proposes a new modular multilevel converter with symmetric bidirectional DC fault blocking capability for high voltage direct current transmission systems. The new modular multilevel converter is composed of novel submodules, which is developed from a three-level T-type converter combined with some clamp circuits. The proposed novel submodule can output three voltage levels with six IGBTs, two diodes and two capacitors. The two capacitors can be separately controlled in the novel submodule, which improves the balancing of the two capacitors voltages. Compared with full-bridge submodules, the proposed topology has not only the symmetric bidirectional dc fault blocking capability but also the features of lower conduction losses, fewer submodules and semiconductor switching devices. The operation principle and DC fault blocking capability of the proposed topology are presented. Simulation models are established in Matlab/Simulink and the effectiveness of the proposed modular multilevel converter is validated by simulation results.

Modeling and voltage balancing control for a hybrid stacked five-level converter

A capacitor voltage-balancing control strategy based on switching state redundancies is proposed for the hybrid stacked five-level converter. In order to obtain the balancing properties for flying capacitors, a hybrid model in state-space representation is established by considering the continuous and discrete variables. The proposed balancing strategy can control the flying capacitor voltages to track the reference value, and simultaneously ensure the desired voltage levels. The attractive characteristic of the proposed strategy is that no additional balancing circuit is required but simple measurements and logical judgments are needed. Moreover, the desired voltage levels can be generated by many different PWM schemes. A three-phase hybrid stacked five-level converter system is modeled in MATLAB/Simulink. Both steady-state and transient operation conditions are investigated to evaluate the effectiveness and robustness of the proposed control strategy.

A brushless doubly-fed generator based on permanent magnet field modulation for wind power generation

A new brushless doubly-fed double stator double rotor (DSDR) generator based on permanent magnet field modulation for the wind power application is proposed in this paper. This generator adopted double stator to achieve the decoupling of the control winding and power winding. To improve the power density, a freely rotating rotor is introduced. To achieve the variable-speed constant-frequency operation and cancel the brush and slip ring, rotating field modulation ring is adopted to link with the wind turbine directly. In this paper, the operation principle of DSDR generator is detailed described. To verify the correctness of the principle, the performance of the DSDR generator is analyzed by the means of finite element analysis (FEA). The proposed DSDR generator owns the advantages such as low cost, low maintenance, high power density, high reliability, low speed direct driven, and good performance on grid fault ride-through. It has the potential on application of future large-scale wind power generation systems.

Optimal control for shunt active power filter based on adaptive-hysteresis controller and droop controller

This paper proposes an optimal control method with adaptive-hysteresis controller (AHCC) and droop controller for shunt active power filter (SAPF). The voltage source inverter (VSI) gate switching signals are generated by adaptive-hysteresis current controller, in which the bandwidth is modulated with the system parameters to maintain the modulation frequency nearly constant. The droop controller is used to optimize the dc-side reference voltage for PI control under different grid or load conditions. A three-phase three-wire SAPF system is simulated in MATLAB/Simulink to validate the optimal control method and evaluate the effect of the harmonic compensation. Simulation results verify that SAPF with this control method has better dynamic compensation characteristic.

Anti-slip control of electric vehicles based on disturbance observer and PID controller

If an electric vehicle has slip phenomenon in a longitude motion, the output torque of the motor must be limited to anti the slip. This paper proposes an anti-slip control strategy composed with a torque limiter and PID controller. The PID controller is used to improve the performance of drive and antislip system. The relationships between the adhesion coefficient and slip ratio are discussed by magic formula. Simulation models are constructed in Matlab/Simulink surrounding. Simulations are carried out and simulation results verify the effectiveness of this anti slip control for the electric vehicle.