Система керування силовими активними фільтрами за наявності коливань напруги в розподільних електричних мережах

Abstract

Lebed D. Yu. Control system for power active filters in the presence of voltage fluctuations in distribution electrical networks. – Qualification scientific work in the form of a manuscript. The dissertation is submitted for the degree of Doctor of Philosophy in specialty 141 – Electric Power Engineering, Electrical Engineering and Electromechanics. – Vinnytsia National Technical University, Vinnytsia, 2025. The dissertation work sets and solves the urgent task of improving the control system for power active filters to improve the quality of filtering higher harmonics and reduce voltage fluctuations in distribution electrical networks in the presence of rapidly changing and nonlinear loads. The scientific novelty of the obtained results and the provisions submitted for defense consists in improving the control system for power active filters in the presence of rapidly changing nonlinear loads by forming control signals for the current of the power active filter and the voltage of the storage capacitor. The work yielded the following scientific results: 1. For the first time, the control laws of a parallel power active filter and a unified power quality regulator during voltage fluctuations have been established, taking into account their power limitations and requirements for voltage fluctuations, which ensures the ion of parameters for their control system. 2. The control system of the parallel power active filter has been improved using adaptive adjustment of the integration time interval of the active and reactive components of the control current and the delay time of the control signals, which ensures high performance of the parallel power active filter. 3. The control system of the unified power quality regulator has been further developed using a digital filter with a finite impulse response in the storage 9 capacitor voltage control system, which ensures increased stability of the capacitor voltage under external disturbances. The practical significance of the obtained results is: improvement and implementation of a control system for power active filters to reduce nonsinusoidality in the presence of voltage fluctuations in distribution electrical networks. Its application will contribute to improving the quality of electricity, in particular, reducing voltage fluctuations and non-sinusoidality in distribution electrical networks. The first section considers the methodology for calculating short-term and long-term flicker intensity. The impact of voltage fluctuations on the operation of distribution networks and measures to reduce them are analyzed. Based on the analysis of literary sources, modern means and devices for improving the quality of electric energy in distribution electrical networks are analyzed. The principles of operation of control systems for parallel and series power active filters (PAF) are presented. The application of parallel and series PAF in distribution electrical networks is analyzed. The characteristics of the unified power quality conditioner (UPQC) are given. The second section investigates the control processes of a parallel PAF and a unified power quality conditioner (UPQC) under conditions of rapid voltage changes. The main attention is paid to improving voltage stability. The modes of passive and active reactive power compensation are considered, mathematical models are presented that describe the dependence of the voltage in the load node on the parameters of the SAF and the power source. The active compensation mode provides directional control of reactive power, which allows to achieve greater voltage stability in the network node. The optimal dependence of the compensator`s reactive power has been determined, which allows to ensure voltage stability during rapid changes in the power source parameters. The results of the research confirm that the introduction of the PAF in distribution networks 10 improves the stability of the supply voltage of consumers. The choice of compromise compensator operating modes allows to ensure sufficient voltage stability at the load with limited PAF power. Proposed PAF control models can be used as the basis for a disturbance control system for reducing voltage fluctuations. The analysis of parallel-serial and series-parallel UPQC schemes for stabilizing the load voltage with minimal consumption of active and reactive power is carried out. Special attention is paid to adaptive regulation, studied within the framework of a mathematical model that provides stabilization of the load voltage. The dependences of UPQC parameters that ensure voltage stability under variable network operating modes are determined. Mathematical modeling has shown that the parallel UPQC compensator effectively reduces the consumption of reactive power the network, while the serial UPQC compensator stabilizes the load voltage. The results obtained demonstrate the change in the load voltage depending on the fluctuations in the power source voltage, as well as the influence of active regulation of UPQC parameters on the stability of the network voltage. The proposed regulation methods allow adapting the UPQC operation to the conditions of the variable mode of the electrical network. Analysis of the mathematical model confirmed that the application of the considered approaches ensures voltage stability. The results obtained can be the basis for further research in the field of power quality management. The third section presents a control system for a parallel PAF based on the dq theory, which includes an automatic voltage stabilization unit on the capacitor. The system provides fast voltage stabilization, which justified using the root hodograph method. The automatic voltage stabilization unit contains an adaptive delay control system and a low-pass filter that is adjusted according to the ed sliding integration interval. Adaptive adjustment of the integration interval of the active and reactive current components T/2 or T/6 together with the corresponding delays of the control signals T/6 or T/12 allows you to optimize the compensation 11 processes. A system with an averaging interval T/6 is characterized as a high-speed control system (HSCS), while traditional integration with an interval T/2 is characterized as a medium-speed control system (MSCS). To increase the compensation capability for asymmetrical loads, integration with an interval T/2 is used. Reducing the interval to T/6 speeds up the system, but worsens the load balancing and the quality of compensation of higher harmonics for network voltage asymmetries. The results obtained confirm the effectiveness of the proposed control methods that ensure voltage stability and compliance with standards for the content of higher harmonics. A digital capacitor voltage regulator has been developed for a parallel PAF control circuit, which includes a delay unit, a first-order digital low-pass filter (FIR or IIR, depending on the circuit variant) and a linearization unit that takes into account the sign of the output signal to stabilize the voltage. The circuit is implemented completely digitally, which allows replacing the analog PI regulator and ensuring the system`s adaptation to variable load modes. When using IIR filters, an additional coefficient is introduced to adjust the group delay, which determines the duration of the signal delay at a certain frequency, while FIR filters usually do not create phase distortion. This regulator is aimed at reducing the charge and discharge time of storage capacitors and providing additional filtering of higher harmonics due to nonlinear signal processing of the linearization unit and a delay of 300 clock cycles of the digital signal, which allows reducing the amplitudes of the 5th, 7th harmonics, etc. In the fourth section, a comparative analysis of PAF control systems using an FIR filter, a delay regulator and a PI regulator in the presence of voltage fluctuations in electrical networks is carried out. The voltage fluctuation indicators, in particular the indicator of rapid voltage changes (δUt) and flicker intensity (Pt), are quantitatively evaluated. The effectiveness of the capacitor voltage control 12 scheme with an FIR filter and a delay regulator for reducing current harmonic distortion (THDI) in comparison with the classical scheme based on a PI regulator. The operation of the unified power quality conditioner (UPQC) under voltage fluctuations is analyzed, paying special attention to the assessment of consumption and generation of active and reactive power, as well as the stability of the voltage level. The operation of the series-parallel UPQC circuit at stable voltage and when it changes by 10% is studied. The results of the analysis demonstrate the influence of compensator operating modes on voltage stability and power balance in the electrical network. Modeling of the series-parallel UPQC has shown high efficiency in reducing harmonic distortions, compensating for rapid voltage changes, and reducing the intensity of voltage flicker. The fifth section considers practical aspects of implementing a control system for single-phase power active filters, which provide correction of current harmonics and compensation of voltage fluctuations. Particular attention is paid to recommendations for measures aimed at ensuring high system response speed in response to changes in the parameters of the electrical network. The analysis shows that the introduction of such devices contributes to improving the quality of electrical energy in conditions of voltage instability. It is shown that the introduction of such devices in distribution networks ensures compliance with modern requirements for the quality of electricity.