Instantaneous Active Power Research Articles

COMPONENTS OF TOTAL ELECTRIC ENERGY LOSSES POWER IN PQR SPATIAL COORDINATES

Purpose. To obtain relations determining the components of the total losses power with p-q-r power theory for three-phase four-wire energy supply systems, uniquely linking four components: the lowest possible losses power, losses power caused by the reactive power, losses power caused by the instantaneous active power pulsations, losses power caused by current flowing in the neutral wire. Methodology. We have applied concepts of p-q-r power theory, the theory of electrical circuits and mathematical simulation in Matlab package. Results. We have obtained the exact relation, which allows to calculate the total losses power in the three-phase four-wire energy supply system using three components corresponding to the projections of the generalized vectors of voltage and current along the pqr axis coordinates. Originality. For the first time, we have established a mathematical relationship between spatial representation of instantaneous values of the vector components and the total losses power in the three-phase four-wire energy supply systems. Practical value. We have elucidated an issue that using the proposed methodology would create a measuring device for determining the current value of the components of total losses power in three-phase systems. The device operates with measuring information about instantaneous values of currents and voltages.

Voltage sensorless predictive direct power control of three‐phase PWM converters

This study develops a voltage sensorless predictive direct power control (PDPC) strategy for three-phase pulsewidth modulation (PWM) converters using accurate virtual flux (VF) estimation. This proposed PDPC can realise simultaneous control of the instantaneous active and reactive power, and achieve a constant switching frequency operation by adopting an on-line corrective space vector modulation modulator. AC voltage sensors are removed by using the following two techniques. One is that an accurate VF observer is employed to compensate the magnitude and phase errors introduced by the first-order low pass filter. The other is that grid voltages are estimated using the VF based estimation of instantaneous active and reactive power as intermediate variables. In addition, the time delay existing in a real system is taken into account in the proposed control model. Comparative results demonstrate the excellent performance of the proposed approach compared with the conventional look-up-table DPC and the conventional PDPC.

Performance and High Robustness DPC for PWM Rectifier under Unstable Direct Voltage Bus

This paper proposes a strategy de controlling a static AC/DC converter based on direct power control (DPC). The instantaneous active and reactive power is controlled in such a way to ensure the PWM rectifier with a sinusoidal current absorption. This control has proven effective in terms of reduction of total harmonic distortion (THD) of current absorbed. Offers a good control of active and reactive power with an operation at unitary power factor. The test of robustness carried out and the results have proven DPC good performance with strong possibility of de integrate it into the field of high voltage and high power as electric traction.

Optimal control strategy of voltage source converter‐based high‐voltage direct current under unbalanced grid voltage conditions

This study presents an optimisation control strategy for the power control of voltage source converter-based high-voltage direct current transmission under unbalanced grid voltage conditions. To facilitate simple implementation and flexible operation, the current references are derived and synthesised into one generalised equation that introduces two individually adaptable parameters. The two parameters can be adapted to eliminate the oscillations of instantaneous active and reactive power, as well as the currents at the grid side under unbalanced grid voltage conditions. The optimisation method based on particle swarm optimisation algorithm is presented to determine the two parameters. The simulation is conducted with PSCAD/EMTDC. The results show that the proposed strategy is effective and feasible.

Classification of short-circuit faults in high-voltage energy transmission line using energy of instantaneous active power components-based common vector approach

The majority of power system faults occur in transmission lines. The classication of these faults in power systems is an important issue. In this paper, the real parameters of a 28 km, 154 kV transmission line between Simav and Demirci in Turkey's electricity transmission network is simulated in MATLAB/Simulink. Wavelet packet transform (WPT) is applied to instantaneous voltage signals. Instantaneous active power components are obtained by multiplying instantaneous currents obtained from a voltage source side with these WPT-based voltage signal components. A new feature vector extraction scheme is employed by calculating the energies of instantaneous active power components. Constructed feature vectors are treated with a classier for short-circuit faults that occurred in high-voltage energy transmission lines; this is known as the common vector approach (CV A). This is therst implementation of CV A in the classication of short-circuit faults that occurred in high-voltage energy transmission lines. Furthermore, the same feature vector is applied to a support vector machine and articial neural network for a comparison with the CV A method regarding classication performance and testing duration issues. Additionally, a graphical user interface is designed in MATLAB/GUI. Various noise levels, source frequencies, fault distances, fault inception angles, and fault exposure durations can be investigated with this interface. Classication of short-circuit faults in high-voltage transmission line is achieved by using an offline monitoring methodology. It is concluded that a combination of the proposed feature extraction scheme with the CV A classier gives substantially high performance for the classication of short circuit faults in transmission line.

Complete mathematical model derivation for modular multilevel converter based on successive approximation approach

Considering the voltage difference between the neutral points of the DC side and the AC side, this study first establishes the differential mathematical model of the modular multilevel converter (MMC). Then, through the proposed successive approximation approach, the analytical expressions of the electrical quantities are derived, including the arm voltage and current, the output voltage and current, the capacitor voltage and current, the voltage difference between two neutral points, the instantaneous active and reactive power, the arm reactance voltage and the current of switching devices. The proposed successive approximation approach contains three main steps. In step 1, the preliminary analytical expressions of the MMC's electrical quantities based on the ideal step wave of the arm voltage with constant SM's capacitor voltage is deduced; step 2 is to derive the final analytical expressions of the MMC's electrical quantities according to the time-varying SM's capacitor voltage expression which is derived in the first step; and the convergence is analysed in step 3. A simulation model of the MMC is realised in PSCAD/EMTDC and the results show that the complete analytical model coincides well with the simulation results and has a higher accuracy than the traditional model.

PHYSICAL MEANING OF THE «REACTIVE POWER» CONCEPT APPLIED TO THREE-PHASE ENERGY SUPPLY SYSTEMS WITH NON-LINEAR LOAD

Purpose. The contradictions in the use of the term «reactive power» require justification by clarifying its physical meaning. The aim of the paper is to reveal the physical meaning of the term «reactive power» applied to three-phase three-wire and four-wire energy supply systems. Methodology. We have applied the modern theory of instantaneous active and reactive power, the graphical filling complex branched energy supply system of simplified design scheme, the theory of electrical circuits, computer Matlab-simulation. Results. We have provided answers to six basic questions that reveal the physical meaning and definition of the concept of «reactive power». We have justified the assumptions suggesting a universal calculation formula to determine the relative total power loss in the three-phase energy supply system as the sum of four components caused by: a minimal losses, reactive power, active power pulsations and instantaneous current flow in the neutral wire. Originality. We have developed the definition that reveals the physical meaning of the term «reactive power» for three-phase energy supply systems corresponding to modern theories of instantaneous active and reactive power. Practical value. We have proposed energy efficiency method ideas of energy supply systems with non-linear load based on the additional components of the power losses calculation. The further development of the method will allow to amend the design, selection and operation of the power active filters practices.

Performance improvement of a three‐phase phase‐locked‐loop algorithm under utility voltage disturbances using non‐autonomous adaptive filters

This study proposes phase-locked-loop (PLL) algorithms, which are employed to improve the performance related to the estimation of the phase angle, as well as the frequency, in three-phase systems under utility voltage disturbances. The proposed PLL schemes are based on the three-phase instantaneous active power (3pPLL), which is composed of non-autonomous adaptive filters (AFs) operating in conjunction with a positive-sequence detectors (PSDs), yielding the AF-PSD-3pPLL algorithms operating in both three-phase (abc-axis) and two-phase (αβ-axis) stationary reference frames. The AFs are used to extract the fundamental components of the utility voltages, allowing an adequate rejection of harmonic disturbances, whereas the PSDs at fundamental utility frequency are employed for rejecting the power quality problem related to the utility unbalances. A complete stability analysis of the PLL systems is carried out. In addition, to validate the theoretical development, the dynamic response and the robustness of the proposed AF-PSD-3pPLL schemes are evaluated by means of simulation and experimental tests, taking into account utility disturbances, such as voltage harmonics and unbalances, voltage sags, phase-angle jumps and frequency variations. The effectiveness of the proposed PLL schemes are emphasised by means of a comparative analysis with the conventional 3pPLL algorithm.

Improve the Power Quality of Wind Power Plant by Modifying the Theory of Instantaneous Active and Reactive Power

One of the most important issues in the clean energy topics is related to the clean electricity generation with desired quality. Low quality electricity causes increasing the losses, mis-operation of the protection relays, saturation of iron core transformer and etc. Hence, it seems necessary to supply electricity with acceptable quality satisfying related standards such as IEEE-519. Quality of the power generated by wind turbines should be investigated and in order to improve its performance, some strategies should be taken if needed. A wind turbine is connected to the grid through a converter. Traditional converters are fixed-speed and the advanced systems are variable-speed. The most important advantage of the advanced systems is related to the mitigated mechanical stress and increasing of the energy capacity. Rectifier and inverter are involved in the topology of variable-speed machines. In this paper, a mathematical model of this system i.e. variable speed machine which is defined in the rotating reference frame of rotor is presented. Rectifiers and inverters contains some power electronic elements which are the major causes of harmonic generation because of their nonlinear characteristics. Harmonics are the one of the most important phenomena decreasing the power quality. Therefore, it seems that mitigation of the harmonic will be necessary. Shunt active filter is used to reduce the current harmonics. This filter has three components namely identification, modulation and inverter. Some of the identification methods are sensitive with respect to the input voltage harmonics. So, an algorithm which shows the better performances, has been used in the identification part. Finally, performance of the mentioned filter has been proved through the simulation

Multilevel Inverter Compensation System of the Single-phase Based on Instantaneous P-instantaneous Real Power and Q-instantaneous Virtual Power Theory

This paper gives an introduction to the single-phase instantaneous PQ (P-instantaneous real power and Q-instantaneous virtual power) theory and carries out the calculation and simulation analysis on reactive power, active power, instantaneous reactive power and instantaneous active power for the single system before and after the compensation of the multilevel inverter. By analyzing the experimental results, it can be seen that harmonic current of the single phase system decreased significantly after using multilevel inverter, while the power factor improved obviously.

COMPONENTS OF THE TOTAL POWER LOSSES IN THREE-PHASE ENERGY SUPPLY SYSTEMS WITH SYMMETRIC SINUSOIDAL VOLTAGE SOURCE

Purpose. Three-phase energy supply system with a symmetrical resistive load operates in mode with the highest possible efficiency in a case of zero instantaneous reactive power and the absence of pulsations instantaneous active power. When load parameters are changed, three-phase energy supply system starts to operate in a mode with additional energy losses. The goal of the paper is to determinate the relations between the components of additional losses and their rezone. Methodology. We have applied the modern theory of instantaneous active and reactive power, the graphical filling complex branched energy supply system of simplified design scheme, the theory of electrical circuits, computer Matlab-simulation. Results. We have developed an universal relation to determine the components of total power loss in the three-phase supply systems with symmetrical three-phase sinusoidal voltage source and any possible load. Further verification of this relation in the Matlab-model of three-phase energy supply system shows its high accuracy. Originality. For the first time, we have carried out relation between RMS reactive and RMS active power instantaneous pulsation and the corresponding components of additional losses. Consequently it becomes possible to offer a unique method of weighting evaluation. Practical value. We have developed position for detecting the causes of additional losses in three-phase supply systems with symmetrical sinusoidal voltage source, as well as to substantiate the correctness of the choice of filter-compensating device. We have developed a Matlab-model which allows to investigate the energy efficiency of three-phase energy supply system and to calculate the components of additional power losses of any possible reasons for their occurrence.

Adaptive terminal sliding mode power control of DFIG based wind energy conversion system for stability enhancement

Summary A novel adaptive terminal sliding mode instantaneous active and reactive power control for both the rotor-side as well as grid-side converters of the doubly fed induction generator (DFIG) based wind power extraction system is proposed in this paper using the abc frame of reference. This approach is independent of unmodeled dynamics of the phase-locked loops that reduces the nonlinearities in computing the control objective. The adaptive nature of the terminal sliding mode controller design offers a better and enhanced transient response as compared with some of the conventional methods for a wide range of disturbances such as switching faults, reference tracking and wind speed variation for both the sub-synchronous and synchronous modes of operation of the doubly fed induction generator subjected to lower and higher wind speeds. Moreover, a maximum power point tracking algorithm has been incorporated to compute the reference power of the stator of the DFIG, which is utilized in designing the control system for the rotor-side converter. Further extensive computer simulations have been carried out with the DFIG operating in a single machine or multimachine environment to validate the effectiveness of the proposed control. Also the robustness and stability of the proposed adaptive terminal sliding mode control is verified using the MATLAB/SIMULINK based DFIG model. Copyright © 2015 John Wiley & Sons, Ltd.

MPPT strategy based on speed control for AWS-based wave energy conversion system

One of the attractive direct-drive wave energy conversion systems is the Archimedes Wave Swing (AWS) coupled to a Linear Permanent Magnet Synchronous Generator (LPMSG). This paper presents an integrated control strategy for the back-to-back converter interfacing the LPMSG not only to extract the maximum power from the wave, but also to ride-through the fault. The proposed maximum power tracking technique is based on speed sensorless control of the LPMSG. The unscented Kalman filter is adapted to estimate the translator velocity. The optimal velocity is obtained from the instantaneous active power at the generator terminals. Moreover, a low-voltage ride-through control is integrated to satisfy the grid-code requirements by injecting reactive current during grid disturbances. The generated active power at the fault instant is considered in determining the dynamic reactive power injection to not exceed the ratings of the grid-side converter. The superiority of the proposed strategy is the result of its ability to regulate the translator velocity that generates optimum power. Numerical simulations are conducted to evaluate the dynamic performance of the proposed integrated optimal strategy. Besides, it has been shown that the proposed methodology outdoes others by the decreased power fluctuations which leads to a reduction of the converter size.

An Aggregate Model of Plug-In Electric Vehicles for Primary Frequency Control

The penetration level of plug-in electric vehicles (PEVs) has the potential to be notably increased in the near future, and as a consequence, power systems face new challenges and opportunities. In particular, PEVs are able to provide different types of power system ancillary services. The capability of storing energy and the instantaneous active power control of the fast-switching converters of PEVs are two attractive features that enable PEVs to provide various ancillary services, e.g., primary frequency control (PFC). However, concurrently, PEVs are obliged to be operated and controlled within limits, which curbs the grid support from PEVs. This paper proposes a new model for PEV using a participation factor, which facilitates the incorporation of several PEV fleets characteristics such as minimum desired state of charge (SOC) of the PEV owners, drive train power limitations, constant current and constant voltage charging modes of PEVs. In order to reduce computational complexity, an aggregate model of PEVs is provided using statistical data. In the end, the performance of PEVs for the provision of PFC is evaluated in a power system. Results show that PEV fleets can successfully improve frequency response, once all the operating constraints are respected.

Analysis and Design of New Switching Lookup Table for Virtual Flux Direct Power Control of Grid-Connected Three-Phase PWM AC–DC Converter

This paper proposes a comprehensive and systematic approach in developing a new switching lookup table for direct power control (DPC) based on grid virtual flux estimation, implemented in a grid-connected three-phase ac-to-dc converter. The approach provides detailed information regarding the effects of a particular converter voltage space vector to the instantaneous input active and reactive power distributions in the converter system. Thus, the optimal converter switching states are able to be selected by the switching table, allowing the smooth control of the active and the reactive power for each sector. The usage of input ac voltage sensors for synchronization and input power calculation is avoided by applying a virtual flux concept in the control scheme. The grid virtual flux estimation technique is used to extract the grid voltage information from the converter switching states, line currents, and dc-link output voltage. Detailed explanation and analysis regarding the development of virtual flux DPC utilizing the proposed switching lookup table is given in this paper. Finally, the steady-state as well as dynamic performances of the proposed controller is tested both in simulations and laboratory experiments. There exist close agreements between the simulation and experimental results.

A New Multilevel Active Power Filter Using Switches Meticulously Controlled

Shunt active power filter based on multilevel inverter is used to compensate the power factor and to delete the harmonics. This one permits to reduce the inverse voltages applied to the filter switches and their switching frequencies. Nevertheless, the high number of used switches requires a complicated controller and increases the switching losses; where the necessity of finding another resolution system. In this work a new topology of multilevel inverter is proposed as a shunt active power filter using two IGBT transistors in series of opposite sense meticulously controlled by a parallel control algorithm, with the concept of reduced number of six switches which are able to create five levels of the output voltage. This system substute the classical system of eight switches. The harmonic currents identification is carried out using the instantaneous active and reactive power method. The simulation is performed using Matlab/Simulink. The obtained results show that the filtering performances are well enhanced.

Active Power Filtering Using the ZDPC Method under Unbalanced and Distorted Grid Voltage Conditions

In this paper, we propose a new Zero Direct Power Control (ZDPC) technique for active compensation of harmonics and reactive power, using shunt active power filter (SAPF), based on cancellation of instantaneous active and reactive power disturbances by comparison with their zero references. To separate harmonic and fundamental components of the line voltage and current a highly selective filter (HSF) has been used. Depending on the power errors and line voltage vector position, a switching table produces the appropriate control vectors leading to the active and reactive power variation required to reach the zero power references, even under grid voltage unbalanced and distorted conditions. The experimental validation of the proposed ZDPC has been performed. The results are compared to other recent techniques to demonstrate the superiority and feasibility of the proposed strategy.

계통 불평형시 과도 응답 특성이 개선된 고압 이중여자 유도형 풍력발전 시스템의 제어 전략

【This paper investigates control algorithms for a doubly fed induction generator with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage wind power system under unbalanced grid conditions. Negative sequence control algorithms to compensate for unbalanced conditions have been investigated with respect to four performance factors: fault ride-through capability, instantaneous active power pulsation, harmonic distortions, and torque pulsation. The control algorithm having zero amplitude of torque ripple indicates the most cost-effective performance in terms of torque pulsation. The least active power pulsation is produced by a control algorithm that nullifies the oscillating component of the instantaneous stator active and reactive power. A combination of these two control algorithms depending on operating requirements and depth of grid unbalance presents the most optimized performance factors under generalized unbalanced operating conditions, leading to a high-performance DFIG wind turbine system with unbalanced grid adaptive features.】

해상풍력단지에서의 PMSG 풍력발전기를 활용한 계통연계점 불평형 전원 보상

This paper proposes a control algorithm for permanent magnet synchronous generators with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage off-shore wind power system under unbalanced grid conditions. Specifically, the proposed control algorithm compensates for unbalanced grid voltage at the PCC (Point of Common Coupling) in a collector bus of an off-shore wind power system. This control algorithm has been formulated based on symmetrical components in positive and negative synchronous rotating reference frames under generalized unbalanced operating conditions. Instantaneous active and reactive power is described in terms of symmetrical components of measured grid input voltages and currents. Negative sequential component of AC input current is injected into the PCC in the proposed control strategy. The amplitude of negative sequential component is calculated to minimize the negative sequential component of grid voltage under the limitation of current capability in a voltage source converter. The proposed control algorithm enables the provision of balanced voltage at the PCC resulting in the high quality generated power from off-shore wind power systems under unbalanced network conditions.

Enhanced control scheme for grid-integrated photovoltaic inverter with wind-driven induction generator feeding unbalanced non-linear load

In this paper a composite power control design comprising of both voltage oriented control and direct power control (DPC) is developed for the grid-combined scheme based on photovoltaic array excited wind driven induction generator with unbalanced non-linear load (UNL) at the point of common coupling (PCC). The control and design strategy of the developed controller aims at control of instantaneous active and reactive power exchanged with the grid and suppression of the power oscillating terms that appear due to interaction between the different voltage and current sequences. When an induction generator feeds a non-linear load, de-rating of machine occurs and an attempt is made to reduce induction machine de-rating factor due to UNL with proposed control. Exhaustive simulations have been carried out with UNL at the PCC with varying wind speed and irradiation in grid-connected mode. The results are compared with existing DPC scheme. The proposed controller is also tested in islanding mode with line to line fault and load rejection at the PCC. The feasibility of incorporating the new developed control algorithm for grid-connected hybrid scheme is indicated in this work.