This paper proposes a new power control strategy of three phase voltage source PWM rectifiers to solve the coupling between instantaneous active power and instantaneous reactive power. This strategy is obtained based on the power control math model of three phase voltage source PWM rectifiers in synchronous dq coordinates. A new power control switching table is set up according to new dividing of input voltage space and resultant voltage space vectors for improving the properties of system and saving complicated PWM modulation module. The switching functions is selected in new power control switching table according to the position of source voltage space vector and input voltage space vector of rectifier required. This paper gives a design method of system controller. The control strategy is proved feasible by simulink simulation with different loads.

Study on Power Decoupling Control of Three Phase Voltage Source PWM Rectifiers

In order to regulate the instantaneous active and reactive powers of the rectifier in an optimized approach, a novel fuzzy-based and voltage-oriented direct power control strategy (FVO-DPC) is proposed in this study. The proposed strategy is based on the principle of the direct power control (DPC) strategy in three-phase voltage source pulse width modulations (PWM) rectifier. In the proposed FVO-DPC system, the active and reactive powers are controlled by a fuzzy logic controller and a fuzzy-based switching table. The fuzzy logic controller is run through introducing the errors between command and estimate values of the instantaneous active and reactive power. The switching loss, the control precision and the dynamic characteristics are taken into consideration simultaneously in the process of setting the switching states of the fuzzy-based switching table. The simulation model established under matlab/simulink environment is validated by comparing with the classical control scheme. The comparisons show that a near unit power factor and better transient and steady performance can be achieved with the proposed FVO-DPC.

A novel fuzzy-based and voltage-oriented direct power control strategy for rectifier

In order to alleviate the problems, such as the periodic fluctuations of reactive power, the poor quality of ac current and the long steady-state response time, caused by the traditional direct power control(DPC) in three-phase voltage source (Pulse Width Modulation)PWM rectifier, a novel DPC strategy of double hysteresis comparator bands and multiple switching tables (DM-DPC) is put forward in this paper According to the instantaneous errors between the commanded and estimated active and reactive power, the different switching table and hysteresis comparator band are selected in the new strategy The effect intensity table, which is used to increase/decrease active and reactive powers through switching state vectors in different sector, is summarized Based on the effect intensity table, four switching tables are provided The simulation model is constructed to compare the results obtained from both the proposed and the traditional direct power control strategy The simulation results show that, by using the novel scheme, not only the reactive power becomes more stable, but the ac current harmonic total distortion rate (THD) and the time that the system takes to reach the steady-state are also reduced to 335%, 625% of the classical one respectively

A novel direct power control strategy of double hysteresis and multiple switching tables for rectifiers

Developing a high performance control strategy for grid side PWM converter of DFIG wind power generation system is a significant point. In this paper, first, deriving and analyzing the mathematical model of grid side PWM converter, a vector control strategy is proposed. Second, the voltage vectors influence on the active power change and the reactive power change was analyzed, a direct power control based on a new switching table was proposed. At last, comparative experiments were tested for vector control and direct power control strategy. The feasibility and correctness, advantage and disadvantage of the control strategy are verified by experimental results.

Comparative study of vector control with direct power control for grid side converter of DFIG wind power generation system

HVDC Light system based on voltage source converter connecting large-scale offshore wind farm is illustrated in the paper. The simulation system is built on the basis of power control algorithm, implementing the independent control on bilateral-side converters. On wind turbine side, there are multiple wind generators with respective converter, adopting the power control method based on hysteresis comparison and the converter on system side adopts the virtual flux direct power control. The results of the simulation prove that the HVDC Light system connecting the large-scale offshore wind farm and power system can operate under a normal and stable situation. Every wind generator can be controlled to work under the optimal state. And this system is able to control the active power and reactive power coordinately to satisfy different reactive power demands of the power system.

Offshore wind farm with dispersed wind turbines control and HVDC grid-connected control

This paper analysies the principle and properties of the direct power control (DPC) system for present three phase boost type PWM rectifiers based on its mathematical model. Switching table in power loop of DPC system controls instantaneous active power and reactive power ,leading to the fluctuation of power and DC voltage in temporary state and DC dynamic voltage drop during load current disturbance. This paper presents a new direct power control strategy based on alternate use of instantaneous active power and reactive power switching tables. Good control properties are achieved by the new control strategy. Meanwhile, DC dynamic voltage drop during load current disturbance is decreased and stable voltage drop is eliminated by the duty cycle of square wave to control double switching table based on load current feedback. The new control strategy is proved feasible by simulink and experiment.

Wang Jiu-he

Papers

A new direct power control strategy of three phase boost type pwm rectifiers