Ming-yan Wang

A New Topology of Capacitor-Clamp Cascade Multilevel Converters

Use of multilevel converter has become popular in recent years. This paper will present a new topology of capacitor-clamp cascade multilevel converter that is derived from two popular topologies. The new concept of the novel capacitor-clamp cascade converter is based on the connection of multiple three-level capacitor-clamp converter modules. Nine level waveform of the proposed multilevel converter is synthesized by adding of each converter output voltage. Sub-harmonic PWM method is employed in the new topology. The proposed converter is also verified by computer simulation using MATLAB-Simulink. Simulation results are also presented in this paper

Spectral Analysis of Hybrid Capacitor-Clamp Cascade 13-Level Inverter

This paper presents a novel hybrid capacitor-clamp cascade 13-level inverter. The inverter is based on the series connection between two inverter modules with different dc bus voltage. It is the fact of a hybrid control scheme that higher voltage devices and faster devices operate in synergism. Subharmonic PWM method is employed in lower voltage module. In the case of three carrier dispositions, mathematic models of the modulation process are constructed. The rigorous analytic solution is derived, which facilitates the evaluation of spectra accurately. Spectral characteristics of output waveforms including all operation conditions were studied. The proposed inverter is also verified by simulation to confirm the feasibility of the proposed approach.

A Novel Hybrid Flying-Capacitor-Half-Bridge Cascade 13-Level Inverter for High Power Applications

A novel hybrid flying-capacitor-half-bridge cascade inverter is developed in this paper. The novel inverter is based on connection of multiple single-phase flying-capacitor-half-bridge (FCH) 5-level inverter modules per phase. With the dc bus voltage ratio V1:V2=1 :2, the phase voltage of the novel inverter with two modules per phase will output 13 voltage levels. A new hybrid FCH modulation control technique for the inverter is proposed. Spectral analysis of the phase output voltage is carried out. According to the spectral analysis, there is no real power exchange between modules in a phase leg. A two-module three-phase inverter was verified by simulation. Simulation results are presented as well as comparison with hybrid capacitor-clamp cascade multilevel converter is given.

Simulation analysis of a new electric dynamic load simulator based on double-stator permanent-magnet synchronous motor

In order to increase the bandwidth of a electric dynamic load simulator and restrain redundancy torque acting on rudder, parallel double stator permanent magnet synchronous motor is used as the execution device of the electric dynamic load simulator. In this method, one stator is used to track the position of the rudder and keep the relative position to the rudder consistent within expectation, by means of position closed-loop control; the other stator is used to track load torque by means of torque closed-loop control. Two stators independently implement position tracking and torque servo control. Based on the method of current decoupling, the load torque bandwidth achieved by the system and the rejection ratio of redundancy torque are theoretically obtained in synchronous rotating reference coordinate. Simulation results verify the validity of the theoretical analysis and the feasibility of the method.

An Evaluation of Spectral Characteristics of Hybrid Flying-Capacitor-Half-Bridge 5-Level Inverter

In this paper, a novel flying-capacitor-half-bridge 5-level inverter is studied which is composed of a half-bridge capacitor-clamp inverter and a conventional half-bridge inverter connected to a common split-capacitor power supply. Analysis of a modulation technique for the inverter, which incorporates square-wave synthesis in conjunction with the PWM subharmonic method, is illustrated. According to the proposed control technique, new configuration permits faster devices and higher voltage devices operating together. In order to estimate spectra accurately, the mathematic models of the modulation process with three carrier dispositions will be built, at the same time rigorous analytic solution of spectra is derived from an extension of Bennets method. We illustrate and sum up spectral feature of output waveform covering all operation conditions. In order to verify the proposed approach simulation validation is carried out.

Novel Hybrid Flying-Capacitor-Half-Bridge 9-Level Inverter

This paper proposed a novel hybrid flying-capacitor-half-bridge 9-level inverter in which flying-capacitor-half-bridge 5-level inverter and an H-bridge inverter with equal dc bus voltage are series connected to form an inverter phase leg. A new hybrid FCH control technique for the novel inverter is proposed. Spectral analysis of output waveform is carried out. The proposed converter is also verified by simulation using MATLAB-Simulink. Simulation results are also presented in this paper

Control stratories for grid-connected and island dualmode operated inverter under unbalanced grid voltage conditions

The grid-connected inverter works as a controlled current source in grid-connected mode, while operates as a controlled voltage source in island mode. The grid-connected inverter should continue to operate normally under unbalanced grid voltage. In case of utility serious faults or intentional islanding, the inverter should be able to seamlessly transfer from grid-connected mode to island mode. In order to achieve these aims, this paper proposed a new feedback multi-loop control strategy with capacitor current, capacitor voltage and grid-side current in αβ reference frame, in which a proportional resonant (PR) regulator is adopted. Compared with the dual-PI control scheme in dq reference frame, the PR controller does not require decomposition of positive-and negative-sequence grid side currents, the transient performance will be improved and low voltage ride through (LVRT) capability of the grid-connected inverters during unbalanced grid voltage condition. The proposed scheme can realize the adjustable power factor, and produce symmetrical and balanced currents in case of unbalanced voltage dips. With this control method, seamless transfer can be achieved between island and grid-connected mode, and load voltage quality during the transition is improved with the proposed control method. Simulations are carried out to verify the proposed controllers and algorithms.

A neutral-point potential balancing technique implemented at the front end in back-to-back-connected three-level converter

This paper presents a neutral-point potential balancing (NPB) technique which is implemented only at the front end in back-to-back-connected three-level converter. The converter is a three-level inverter fed by a front end with a three-level rectifier. Hysteresis current control and optimized SVPWM algorithm are used for the rectifier and the inverter respectively. The proposed NPB technique is implemented only in the rectifier by injecting compensation currents into input currents according to the neutral-point potential deviation. This control scheme can achieve unity power factor, balanced and sinusoidal input currents and output voltages, and balanced neutral-point potential. Compared with the conventional NPB technique which is implemented in inverter, the proposed NPB technique does not modify the inverter modulation algorithm, and optimized modulation algorithm can be adopted for inverter, then output voltage harmonics are lower. The basic principles of the control scheme and NPB technique are introduced and verified by simulation in this paper. The proposed NPB technique is also compared with a conventional NPB technique which implements NPB in inverter. Simulation results show that the proposed control scheme and NPB technique are correct and effective.

A novel voltage regulation strategy for micro-inverters with a low-capacitance dc-link

The micro-inverter has become more and more attractive due to the inherent advantages compared to traditional photovoltaic inverters. In order to prolong the lifetime of micro-inverters, the film capacitor is usually used instead of the electrolytic capacitor in the dc-link. However, due to the small capacitance of the film capacitor, the voltage regulation of the dc-link capacitor is much more difficult than the traditional inverters with electrolytic capacitors. In this paper, a new dc-link voltage regulation strategy for the micro-inverter is proposed. Based on the hysteresis methodology, two kinds of control scheme is adopted, which can keep the dc-link voltage stable both in steady state and dynamic state, and export smooth current with low oscillation to the grid. Simulation results verify the validity of the theoretical analysis and the feasibility of the strategy.