Active filters with synchronous detection methodologies are vividly employed in distribution system to make sure that the harmonics generated by non-linear loads is reduced and results in less voltage distortion and leads to lesser power superiority problems. The three physical characteristics that mostly underline the power quality and a power quality issues are Voltage, Current and Frequency.
Harmonics is defined as a disturbance demonstrated in current or voltage or frequency waveforms which result in devastation, or failure of final equipment. The greater switching frequency as well as the non-linearity in the characteristics of the power electronics equipments is mostly creditworthy for the power quality issue.
So significance is being given to the procurement of Active Power Filters to equate these problems to improvise power quality and of all these, shunt active power filter is used to take care of harmonics of voltage and load currents and for reactive power compensating.
The shunt active power filters have been built up on the basis of on control strategies like compensation scheme (p-q control) and instantaneous active and reactive current control scheme (control). Taking into consideration its superior quality, an analysis on the control scheme based shunt active filter presented in this project. The compensation is given by the usage of PI based controllers.
A theory based study on both the compensation schemes is carried out in the project and then control scheme is implemented in simulation using MATLAB/SIMULINK® work and its harmonic compensation results are analyzed. Then synchronous detection scheme algorithms are worked out for unbalanced three phase systems and simulation is done.
Mathematical Analysis of P – Q Method:
The expression instantaneous reactive power is a distinctive value for random three phase current waveforms and voltage waveforms along with all vague waveforms. By means of instantaneous imaginary power, a compensator eliminates the harmonics having the frequencies (f + 6f0).
Mathematical Analysis of ID–IQ Method:
Here the currents are got the components and of the non-linear load. Similarly, α-β components are to be deliberated as done previously. Though, the d-q load current parts are derivatives of a synchronously reference dframe on the basis of Parks Transformation, where θ denotes the instantaneous angle of space vectors.
DESIGN OF CONTROL CIRCUIT BASED ON IQ–IQ METHOD
Providing for the compensation to the lines, a 3 phase IGBT based on VSI is utilized. This makes a simple as well as robust design mechanism and proving for good dynamics even when well-known faults are present. The current controller is put to use that is composed of three self-regulating two-leveled comparators for hysteresis functioning on a three leg Inverter (VSI). This gives the compensated harmonic to be provided that consists of two parts namely–1-Harmonic Current Generator and 2-DC Voltage Regulator.
Harmonic Current Generator:
The currents are calculated with the algorithms of Park Transformation and injection circuit of disturbance current and using the dc voltage regulator. At first a-b-c to d-q axis conversion takes place by the Park Transformation model that is according to equation 16.
From there the load currents are calculated. The foremost harmonic current(carrying +ve sequence load) is converted in to dc parts. Then the first harmonics of -ve sequence and remaining distortions are converted into alternating parts that undergo a swing in frequency within the band. As a result , dc parts that should be preserved in the mains relate to the positive sequence of the first harmonic currents.
SIMULATION RESULTS AND DISCUSSION
3-φ 3 Winding Balance D Main Voltage Current Harmonic Compensation With Pi Controller:
HARMONIC CURRENT COMPENSATION FOR UNBALANCED SYSTEMS WITH SYNCHRONOUS DETECTION SCHEME
In instantaneous power theory, there is a requirement of a source that is balanced. But, in pragmatic distributions, it becomes hard to provide balanced voltages across the circuit. Hence, taking care of unbalanced sources with respect to harmonics becomes a challenge.,
The synchronous detection method is a scheme that works on phase by phase basis i.e. on every phase and calculations are done to obtain required compensating parts. Three different kind of approaches that use same power, similar current, and using equal resistance conceptions in the synchronous detection scheme are discoursed.
A synchronous detection scheme and a filter based on the principle of id–iq compensation scheme has been projected in this work. Also synchronous detection scheme is put to application in SIMULINK. A mathematical study of p-q method as well as id–iq compensation method has been done to assimilate the control schemes. As the id–iq compensation mechanism is dependent on a rotating frame resulting from mains voltages that does not incorporate phase locked loop and carries better-quality compensation results , simulation was done based on this control method.
When we consider balanced conditions the id–iq control scheme is found to have satisfactory harmonic compensation performance. Here the harmonics were produced by three–leg VSC and by the application of the Hysteresis controller. The control scheme depicted vows for the operation of the Active Filter in changing frequency circumstances sans any adaptation.
But the above method deals with only a balanced system, therefore synchronous detection method is used to take care of unbalanced three phase systems. With regard to synchronous detection method, from the results and simulation findings, the projected synchronous detection scheme is aptly fit for harmonic compensation in a system that is unbalanced.
Source: National Institute of Technology
Author: Preetam Kumar Nanda