Research On Harmonic Detection And Control Strategy Of Active Power Filter For Low Voltage Distribution Network

With the rapid development of national economy, more and more industrial and civilelectric equipment have been placed in the low voltage distribution network with thecharacteristics of low power factor, nonlinear, asymmetry, etc. these load decline thedynamic power quality of distribution network. Therefore, it is necessary to do theharmonic reduction and reactive power compensation for the effective power quality.Active power filter (APF) is an effective equipment to improve the quality of the grid byharmonic elimination, reactive power compensation, and current symmetry, Because ofconvenient installation and maintenance, the shunt active power filter is popular in practicalapplication. However, there are many technical problems to be solved for the application ofAPF in low-voltage distribution network. The harmonic detection and control strategy ofthe shunt APF in the grid has to be studied deeply.The energy exchange principle is discussed between the APF, nonlinear load and thesource, and limitations of the traditional instantaneous reactive power theory are alsomentioned in the paper. So a new adaptive method for harmonic current detection ofnonlinear load is proposed, that is, an adaptive linear neural filter (ADALINE) based onsynchronous rotating coordinate transformation are combined. The harmonic detectionscheme is designed in the power supply voltage balance and unbalance system. It ispossible to separate the positive (negative) current component or fundamental positiveactive current component from asymmetric and harmonic components to generate referencecurrent under different conditions. It is a real-time and accurate method which can adapt to thegrid voltage and load change.Three phase three leg APF, three phase three leg split-capacitor APF, and three phasefour leg APF are frequently used in distribution network. The mathematical models of maincircuit topology of shunt active power filter are established in abc stationary coordinate anddq0Synchronous rotating coordinate. The AC/DC-side voltage-current relationship andinfluence factors of DC capacitor voltage are analyzed which can provide a theoreticalbasis for voltage and current controller design. Comparison of the mathematical modelsbetween the three leg split-capacitor and the four leg APF is provided, on the basis of it thegeneral current controller design of is achieved. The compensation current of the APF is controlled to track the given reference signalaccurately and keep the DC side voltage stable. So the voltage and current controllers aredesigned for the three kinds of APF. According to the different characteristics of the currentcontroller and voltage controller, a compound controller is used in the inner-loop currentcontrol in dq0coordinate, which is based on the pseudo linear system constructed byinverse system method, and optimal linear quadratic control and space vector pulse widthmodulation (SVPWM) are used, while a basic PI controller is used in the outer-loopvoltage control. And the parameters are designed by its effect of controller performance.Therefore, a shunt three phase three leg APF prototype is built for experiment, and thedevice parameters of the main circuit are determined by the condition. Simulation andexperimental results prove the rationality of parameter selection and the feasibility of thecontrol scheme.