Zhou Jinghua

Research on hybrid modulation strategies based on general hybrid topology of multilevel inverter

Based on the research on several multilevel basic topologies, this paper presents a general type of multilevel hybrid topology and introduces several selectable degrees of freedom. No matter what change in the hybrid topology it can be resulted in the combination and selection of the degrees of freedom, which expands the topology collection of the multilevel inverter. According to the degrees of freedom, all the cascaded topologies have been unified and several new types of hybrid topologies have been constructed. Based on the research on the hybrid topologies and multi-carrier SPWM (Sinusoidal Pulse Width Modulation) used for the multilevel inverter, this paper presents the hybrid modulation strategies for hybrid topologies. Simulation results prove that hybrid topologies and corresponding modulation strategies are effective, which lay the foundation for practical application of hybrid multilevel inverter topologies.

Research on the fault characteristics and fault diagnosis methods of three-level high-power inverter

As one kind of multilevel inverters, three-level inverter is widely used in the high-power and high-voltage applications. However, the increasing of the power devices improves the systems fault rate. How to ensure stable operation of the system has become an important research question. Through theoretical analysis and simulation on three-level high-power inverter, the paper analyses the working situation of the power devices of main circuit under the open-circuit fault, the specific fault characteristics and the typical waveform in detail, and sums up the rules of fault diagnosis. Finally, based on the three-level high-power inverter, the open-circuit fault experiment of power devices is carried out .The experimental results further validate the fault analysis and simulation results of the power devices.

Research on the control strategy of PV grid-connected inverter upon grid fault

To stabilize the PV-connected grid with high penetration factor, the State formulates strict provisions on connecting the PV power stations into the power grid to ensure the safety of power system. On the basis of high-power PV power station LVRT technology, this paper elaborates the research on solving the inverter protection upon low-voltage operation by means of the control strategy under conditions of not adding other hardware to fulfill the safe ride through in the low-voltage zone, and to provide the power grid with reactive support, so as to help the recovery of grid system.

A new interleaved three-level Boost converter and neutral-point potential balancing

Due to a voltage imbalance of the divided capacitors in the output side of three-level Boost photovoltaic grid-connected inverter, a new topology of interleaved three-level Boost converters is presented. The proposed topology can balance the voltage of the divided capacitors through adjusting the duty cycle of the power switches. The operational principle is detailed and the work modes are analyzed. The neutral point drift problem of the inverter has been solved within the first level three-level Boost converter. The prototype has been verified both by a PSPICE simulation and a new topology inverter platform. Simulation and experimental results show that the current ripple of the converter equals to 1/8 of the traditional Boost converter current ripple, and the converter can well solve the neutral point drift problem of the inverter with voltage divided capacitors to obtain good dynamic and steady-state performance.

A neutral-point potential control method for three-level inverters by injecting zero-sequence voltage

The imbalance of neutral-point potential is an internal problem with three-level inverters. To solve this problem, this paper proposes a novel neutral-point potential control method by injecting zero-sequence voltage, and gives the valid criteria for selecting which zero-sequence voltage to use. Simulations and experiments validate that the imbalance of neutral-point potential could be controlled effectively at various states of the inverter by using this method, and this control method is simple and easy and is robust.

Reducing voltage energy-saving control method of induction motor

The paper starts from the angle of the induction motor energy loss, antis light-load energy conservation issues for induction motor, proposes a closed-loop control method of the motor power factor which is the amount of system feedback, and gives the constraint condition of the reducing voltage energy-saving. Different loads have different values of the optimal motor power factor, real-time adjusting the motor power factor to make the motor always run at the optimal power factor, and when running at light load, reducing the output voltage of the inverter, to reduce the motor copper loss and iron loss, to improve motor efficiency and power factor, to achieve reducing voltage energy-saving purposes, and to achieve the function of induction motor load following energy-saving. The experimental results show that the motor is able to maintain a high power factor operation in light load conditions, and has a good energy-saving effect.

Development of digital experiment system for multi-module-cascaded multilevel high-power inverter

Based on a multi-module-cascaded multilevel inverter structure for the optimization of harmonics, this paper introduces a horizontal phase-shifting sinusoidal pulse width modulation (SPWM) strategy applied to multi-module-cascaded inverter, and at the same time, based on Digital Signal Processor (DSP) and Complex Programmable Logic Device (CPLD), this paper also presents a digital algorithm for horizontal phase-shifting SPWM modulation, which has solved the problem of the exactly lock of each triangular carrier phase in the multi-module-cascaded system. The simulation and experimental results have proven the method proposed correct.

Research on control method of three-level NPC voltage source rectifier

In this paper, the mathematical model of three-phase four-wire three-level neutral-point-clamped (NPC) voltage source rectifier (VSR) using switching functions is founded and its operating principle analyzed. Then a new nonlinear control law based on Lyapunovpsilas stability theory for the PWM rectifier is presented. With this control law, the converter can be stabilized globally for handling large-signal disturbances, and exhibit good transient response. Also, by designing new three-level sinusoidal PWM method, this paper solves effectively the problem that the neutral point potential of DC-link has triple-harmonic fluctuation resulting from existing three-level SPWM method. Computer simulations of the system confirm the validity of the mathematical model and the effectiveness of the proposed control strategy.

Optimization design and analysis of permanent magnet synchronous motor based on VC

In This paper, an improved adaptive genetic algorithm is presented for the design optimization on Permanent magnet synchronous motor(PMSM), which can availably reduce the iterative time and simplify the magnetic circuit calculation during optimization designing. To obtain higher computation speed, C++ language is applied to develop both the basic electromagnetic calculation program and optimization algorithm based on the Microsoft Visual studio 2010 development tools. According to the developed program, the optimal solution of motor designing can be quickly and accurately gotten, thus shortening the development cycle and improving the optimization design efficiency. In addition, the finite element analysis (FEA)is used in the motor design scheme before and after the optimization with static and transient ways, and the optimization design validity is confirmed through the simulated results.

Control Strategy for MMC-HVDC Under Unbalanced Grid Conditions

Modular multilevel converters have become a new choice of high voltage direct current transfer (HVDC) due to the advantages of lower switching loss and unnecessary of switch devices series. This paper researches the control strategy Of MMC-HVDC system according to the unbalanced grid conditions. In order to restrain the negative sequence current caused by the faulted grid, a mathematical model is build, and a dual current controller is designed. An MMC-HVDC of 11 levels model is established in Matlab, and the simulation result confirms the correctness of the control strategy.