A comparative study of methods for estimating virtual flux at the point of common coupling in grid connected voltage source converters with LCL filter

Grid connected Voltage Source Converters (VSCs) with LCL filters usually have voltage measurements at the filter capacitors, while it can be important to control the active or reactive power injection at the grid-side of the LCL filter, for instance at a Point of Common Coupling (PCC). Synchronization to the PCC voltage can be obtained by Virtual Flux (VF) estimation, which can also allow for voltage sensor-less operation of VSCs. This paper is presenting a comparative evaluation of methods for estimating the VF at the PCC, considering a VSC connected to the grid through an LCL filter with a Proportional Resonant (PR) controller as the inner current control loop. The VF estimation is achieved by using frequency adaptive dual SOGI-QSGs (DSOGI-VF). The Frequency Locked Loop (FLL) is used in order to keep the positive and negative sequence (PNS) VF estimation inherently frequency adaptive. Three different methods are considered for obtaining the capacitor current needed for estimating the VF at the grid side of the LCL filter which are based on fully estimation by using the voltage sensor-less method, by estimating the capacitor current from the measured voltage or by using additional capacitor current sensors. The results have been compared and validated by simulation studies.Peer ReviewedPostprint (author's final draft

AMELIORATE DIRECT POWER CONTROL OF STANDALONE WIND ENERGY GENERATION SYSTEM BASED ON PERMANENT MAGNET SYNCHRONOUS GENERATOR BY USING FUZZY LOGIC CONTROL

Purpose. Electricity is a basic energy for life and its consumption increased so we need the discovery of new sources of energy such as wind energy .for this ameliorate the quality of generated wind energy by using the intelligent artificial control, this control is made to optimize the performance of three-phase PWM rectifier working. Methodology. These strategies are based on the direct control of the instantaneous power, namely: the control direct power control (DPC) with classic PI regulator and direct power control with fuzzy logic regulator. The fuzzy characterized by its ability to deal with the imprecise, the uncertain has been exploited to construct a fuzzy voltage regulator. The simulation of these methods was implemented using Matlab/Simulink. Results. A comparison with the results obtained by the classic PI showed the improvement in dynamic performance. This makes the fuzzy controller an acceptable choice for systems requiring quick, precise adjustments and less sensitive to outside disturbances. Originality. The proposed this control strategy using for to obtain a performance adjustment of the DC bus voltage and sinusoidal currents on the network side. Practical value. Fuzzy logic is proven to be effective in terms of reducing the harmonic distortion rate of the currents absorbed, correct adjustment of the active and reactive power and DC voltage and unit power factor operation.Мета. Електроенергія є основною енергією для життя, і її споживання збільшується, тому нам необхідно відкриття нових джерел енергії, таких як енергія вітру. Для поліпшення якості енергії вітру, що генерується за допомогою управління на основі штучного інтелекту, таке управління призначене для оптимізації продуктивності роботи трифазного ШІМ випрямляча. Методологія. Дані стратегії засновані на прямому управлінні миттєвою потужністю, а саме: пряме управління потужністю з класичним ПІ-регулятором і пряме управління потужністю регулятором з нечіткою логікою. Нечіткість, що характеризується її здатністю справлятися з неточністю, невизначеністю, була використана для створення нечіткого регулятора напруги. Моделювання цих методів було реалізовано за допомогою Matlab/Simulink. Отримані результати. Порівняння з результатами, отриманими за допомогою класичного ПІ-регулятора, показало поліпшення динамічних характеристик. Це робить нечіткий контролер прийнятним вибором для систем, що вимагають швидкої і точної настройки і менш чутливих до зовнішніх перешкод. Оригінальність. Запропоновано стратегію управління, що використовує для отримання регулювання продуктивності напруги шини постійного струму і синусоїдальні струми на стороні мережі. Практична цінність. Доведено, що нечітка логіка ефективна з точки зору зниження коефіцієнта гармонійних спотворень поглинаються струмів, коректного регулювання активної і реактивної потужності і постійної напруги, а також коефіцієнта потужності роботи блоку.

Combined voltage oriented control and direct power control based on backstepping control for four-leg PWM rectifier under unbalanced conditions

The present paper proposes a combined voltage-oriented control and direct power control (VOC-DPC) method associated with the backstepping control technique for a three-phase four-wire grid-connected four-leg rectifier in the synchronous rotating frame without using phase locked loop (PLL) and Parks transformation under balanced and unbalanced load and grid conditions. This control method is proposed in order to remove the drawbacks of the conventional VOC based on the PLL technique .The proposed control method is able to enhance the control performance and dynamic responses of the system when considering slow dynamics and instability issues of the PLL in several cases and can decrease the computational burden due to the absence of PLL and Park transformation. In addition, the performance of the proposed VOC-DPC method is enhanced by using backstepping control (BSC) based on Lyabonov theory for both the input currents and DC-bus voltage loops. As a consequence, constant DC-bus voltage, unit power factor, sinusoidal input currents, and neutral current minimization can be accurately carried out under both DC-bus voltage and load variations. Furthermore, robustness against filter inductance variations can also be achieved. The effectiveness, superiority, and performance of the proposed control method for a four-leg rectifier based on BSC in the dq0-frame are validated by several processor-in-the-loop (PIL) co-simulation tests sing the STM32F407 discovery development board

A Single-Input Single-Output Approach by using Minor-Loop Voltage Feedback Compensation with Modified SPWM Technique for Three-Phase AC–DC Buck Converter

The modified sinusoidal pulse-width modulation (SPWM) is one of the PWM techniques used in three-phase AC–DC buck converters. The modified SPWM works without the current sensor (the converter is current sensorless), improves production of sinusoidal AC current, enables obtainment of near-unity power factor, and controls output voltage through modulation gain (ranging from 0 to 1). The main problem of the modified SPWM is the huge starting current and voltage (during transient) that results from a large step change from the reference voltage. When the load changes, the output voltage significantly drops (through switching losses and non-ideal converter elements). The single-input single-output (SISO) approach with minor-loop voltage feedback controller presented here overcomes this problem. This approach is created on a theoretical linear model and verified by discrete-model simulation on MATLAB/Simulink. The capability and effectiveness of the SISO approach in compensating start-up current/voltage and in achieving zero steady-state error were tested for transient cases with step-changed load and step-changed reference voltage for linear and non-linear loads. Tests were done to analyze the transient performance against various controller gains. An experiment prototype was also developed for verification

Frequency-adaptive virtual flux estimation for grid synchronization under unbalanced conditions

This paper proposes a new and explicitly frequencyadaptive method for Virtual Flux estimation and voltage sensorless grid synchronization under unbalanced conditions. The proposed system is based on using Second Order Generalized Integrators, arranged to simultaneously fulfill the purposes of frequency-adaptive band-pass filtering, integration and quadrature signal generation. This results in a simple and efficient structure for combined Virtual Flux estimation and separation into positive and negative sequence components. The properties of the proposed Virtual Flux model is analyzed theoretically, first as an integrator for implementing generic Virtual Flux estimation, and then with respect to sequence separation. The dynamic performance of the proposed estimation method is tested by simulations for the case of an unbalanced voltage drop in the grid and for a step in grid frequency. The simulations verify the performance to be as expected, with similar dynamics as synchronization based on voltage measurements.Peer ReviewedPostprint (published version