Abstract – Extensive use of the Non-linear elements like power electronic devices, circuits with inductor and capacitor are effecting the quality of power.
All non-linear loads induces harmonics into the system. Shunt active power filters (SAPF) are used to improve the power quality by reducing the harmonics under specified levels along with improving the power factor. This paper deals with the development of different control methods for power quality improvement in shunt active power filter. Apart from other familiar existence techniques, four different methods are developed, first constant instantaneous power control by using the Instantaneous active reactive power theory, second sinusoidal current control method by using phase locked loop control, third Fryze current control with a positive sequence detector, and fourth Synchronous Reference Frame theory (DQ). Bridge rectifier with RL load is considered. SAPF controlled by mentioned controlling techniques were implemented by using MATLAB/Simulink environment. Simulation results are obtained with wave forms for different controlling techniques for SAPF. Total harmonic distortion (THD) data of all four cases are tabulated and discussed.
By analyzing all the simulation results, it comes out that Synchronous Reference Frame method gives good results. Keywords – Shunt Active Power Filter (SAPF), Constant Instantaneous Power Method (CIP), Sinusoidal Current Control Strategy with Phase Locked Loop (SCC), Synchronous Reference Frame (DQ), Positive Sequence Detector (PSD).I. IntroductionThe utilization of power electronic devices has been enormously increased now a days, major industries with different equipment, loads in the distribution system creates lot of disturbances to the current waveforms, causing distortion in the waveform. Non-linear loads causes disturbances to the other users and causes interference in Telecommunication networks. Compensation control scheme was developed to limit the effect of non-linear loads 1.
Rapid technical advances in power electronics and micro-electronics such as uninterrupted power supplies, personal computers, and various other consumer electronics draw highly distorted current from the grid. A large harmonic currents flows in phases in case three phase loads, and flows through neutral wire in case of single phase loads. A constant-hysteresis, tolerance-band controller is developed to protect the other users from the adverse effects of these loads 2. Shunt active power filter is designed to achieve reactive power compensation to bring the power factor near to the unity. Feedback control law with analytically tuned PI controller is used in APF 3. Various controlling techniques are developed for APF, mathematical modelling of synchronous reference frame approach is proposed to eliminate harmonics and to compensate reactive power of non-linear load in three phase systems 4.
Measuring the all variables for power quality analysis at each every point is not economical. Therefore, an efficient algorithm has been prepared to make the system observable. So that the overview of the power quality can be observed by managers of utility companies. Algorithm evaluate the power in distribution network and make available for the power quality process 5. Harmonics caused by the non-linear loads has an effect on the other users, efficiency of the transmission lines and responsible for malfunctioning of the protective relays.
Kalman filter and the artificial neural network algorithm was developed for the protection of the transmission line 6.There are various control algorithms for shunt active power filter to reduce the harmonics in non-linear loads. Synchronous source current detection method, instantaneous active reactive power theory, I cos Ø theory and power balance theories are discussed and analysed the results of all the four methodologies 7. PQ theory was developed for APF for reactive power compensation and current harmonic reduction. It improves the efficiency of the system and brings the power factor nearer to the unity. APF with PQ theory will also eliminates the oscillations in active power. Thereby, end user will get constant instantaneous active power 8.
Shunt active power filter with sinusoidal source current control strategy has been discussed. This method balances the voltage fluctuations and voltage imbalances in the power supply 9. Fryze current control method for active power filter is one of the efficient method of control. A positive sequence detector was introduced in this method. The reference currents are generated by using the Fryze current minimization algorithm and hysteresis current controller generates the switching signal for voltage source inverter 10.
A comparative study of three control methods for APF was discussed. From the obtained results, it has been observed that the current harmonics are reduced considerably to bring the value down to meet the IEEE standards. Now, in this paper, one more technique ‘synchronous reference frame’ (DQ) is introduced. Results shows that this method is effectively reduces the harmonic level in the given distribution system.II