Phase lock loop–based algorithms for DSTATCOM to mitigate load created power quality problems

Abstract

Summary This paper describes about implementation of phase‐locked loop (PLL)–based control algorithms for distribution static compensator (DSTATCOM) used to mitigate power quality issues due to unbalanced and non‐linear load. Three control algorithms based on moving average filter PLL (MAF‐PLL), double second order generalized integrator PLL (DSOGI‐PLL), and adaptive filter with frequency estimation loop PLL (AFFEL‐PLL) are used in this paper. These are more suitable to mitigate the power quality problems created by non‐linear and unbalanced loads in distribution system. The reason behind selection in this application is explained as follows. The MAF‐PLL has great filtering quality with less computational burden on processor which is verified using total harmonic distortion (THD) performance. AFFEL‐PLL has variable integral gain that prevents large phase jump during frequency drift and load transient condition, this gives fast response. DSOGI‐PLL uses both orthogonal components and prevents oscillatory error and gives more stable operation. The MAF‐PLL and AFFEL‐PLL uses only quadrature axis “q” component for reduction of phase error and detection of theta. To mitigate power quality issues, continuous monitoring of AC grid system is required, which provide information in terms of frequency, phase, and fundamental voltage magnitude. Out of all, the phase detecting methods using PLL is standard method to extract such information. All the PLLs mentioned here extract the required grid information. Further, DSOGI‐PLL converts the distorted three‐phase load current into respective orthogonal components. All the control algorithms mentioned are implemented using MATLAB and performance of most effect algorithm is recorded in laboratory environments.

A New Quasi Open Loop Synchronization Technique for Grid-Connected Applications

“…3, the frequency response is asymmetrical around zero, which allows distinguishing the negative polarities from the positive ones for the same frequency. The transfer function for obtaining the positive sequence is given in (8) and the negative sequence is as follows:…”

“…In recent years, the increased energy demand and technological advances in semiconductor technology and signal processing have made power converters more efficient and less expensive, and are now widely used for interfacing renewable energy such as wind turbines and photovoltaic for the connection to the main grid and/or local loads [1]- [8]. These energies have high levels of penetration and can affect power quality.…”

“…Besides, from January 2011 the FRT of photovoltaic (PV) installations had full participation in the dynamic support of grid in faulty conditions: to stay connected and provide voltage support by injecting a reactive current into the grid. These requirements have made the synchronization task more challenging than before [7], [8].…”

A Non-Adaptive Single-Phase PLL Based on Discrete Half-Band Filtering to Suppress Severe Frequency Disturbances

“…Discrete implementation of SRF-PLLs is now dominated by MAFs, regarded as ideal low-pass filters (LPF) as they notch their cut-off frequencies and their harmonics [9]. Nevertheless, the MAF interacts with non-harmonic frequencies, just as a first-order LPF [6], making frequency disturbances particularly harmful for the PLL performance.…”

An Adaptive Controller for DSTATCOM for Power Quality Improvement in Distribution System

“…For harmonics elimination the commonly used adaptive control techniques like digital frequency control, time effective adaptive control and notch filter-based control has been presented in [13][14][15][16][17]. Three different adaptive control technique for DSTATCOM in distribution system has been implemented for power qualities issues mitigation [18]. For computation of essential load current without using the Voltage Controlled Oscillator (VCO) less PLL for three phases to two phases transformation has been implemented [19].…”