Fundamental Reactive Power Research Articles

Voltage Independent Reactive Current Based Sensor for Static VAr Control Applications

The use of renewable energy-based converters is continuously increasing in modern power systems which inject voltage harmonics in the line. In this work, a novel, simple technique based on a binary (on/off) control of an analog switch is proposed to measure reactive current and reactive power. This method eliminates the requirement of finding <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sin</i> (ϕ) and its multiplication with the current signal in reactive power computation. The proposed transducer gives a dc signal proportional to the reactive current of a power system, i.e., <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Isin</i> (ϕ), which is suitable for static VAr compensator (SVC) applications. This transducer output is sufficient as the terminal voltage is common for the measurement as well as for the compensation current. Thus, the required current of SVC for compensation is equal to or proportional to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Isin</i> (ϕ). Moreover, voltage harmonics are common in a power system. These harmonics affect the measurement of fundamental reactive power. This method eliminates the need of voltage measurement and hence the measurement is independent of harmonics of the voltage, which reduces the measurement error. The proposed method is proved mathematically, and its performance is successfully validated through simulation analysis and hardware implementation. The advantages of the proposed technique are linearity of the transducer output, simple working, inexpensive hardware realization, fast response, and online measurement capability. The response time of the transducer is one cycle of supply voltage which is suitable for SVC applications.

Hybrid VAR compensator operating study under conditions of a three-wire network

The approaches to the control of the hybrid VAR compensator are considered. A hybrid VAR compensator is a passive and active compensator connected in series. The passive part is represented by a thyristor-switched capacitor bank. The power part of the active part is implemented on the basis of an autonomous voltage inverter, connected through a voltage transformer in series with a passive part. Most of the reactive power is compensated by means of the compensator’s passive part. The hybrid compensator combines the advantages of passive (low price, reliability) and active compensators (possibility of smooth control of reactive power, operation in networks with non-sinusoidal currents). This configuration allows to significantly reduce the rated power of the active part, while maintaining the possibility of smooth control of the reactive power. Mathematical modeling of the hybrid system operation in a three-wire network is carried out. Two operating modes are checked: the reactive power compensation mode and the mode of providing the sinusoidal waveform of the network current. The first mode provides fundamental reactive power compensation only (the compensator current is sinusoidal, therefore, provides «insulation» of capacitor bank from higher harmonics) and the second mode provides limitedly non-active power compensation, including distortion power (overvoltages and exceeding the permissible currents of the capacitor bank are not allowed). When choosing a control strategy, the network configuration and the real requirements of power consumers for power quality indicators are taken into account. The efficiency of the proposed model under conditions of non-sinusoidal load current and unbalance of the main’s voltage is provided

Passive Power Filter Optimization Problem Based on Adaptive Multipopulation NSGA-II and CRITIC-TOPSIS

The best configuration of passive filters in extra-high voltage systems is investigated in this study using a two-stage multiobjective decision-making (MODM) framework. A collection of Pareto solutions is found using an adaptive multipopulation-modified nondominated ranking genetic algorithm (AMP NSGA-II) in the first stage. The goals taken into account include the least fundamental reactive power compensation losses, overall cost and maintenance cost, and simultaneous minimum harmonic current distortion rate. The objective weights are determined and the optimum solution is chosen in the second stage using the criteria importance interrelationship (CRITIC) and similarity ranking preference technique (TOPSIS). A number of examples show how the suggested method performs more effectively than the conventional and well-known algorithm and can identify the relationship between the objective functions, indicating that the suggested scheme has better superiority in filters and has a promising future in the solution of multiobjective problems.

Multi-Objective Teaching–Learning-Based Optimization with Pareto Front for Optimal Design of Passive Power Filters

This paper proposes an optimal design method to suppress critical harmonics and improve the power factor by using passive power filters (PPFs). The main objectives include (1) minimizing the total harmonic distortion of voltage and current, (2) minimizing the initial investment cost, and (3) maximizing the total fundamental reactive power compensation. A methodology based on teaching–learning-based optimization (TLBO) and Pareto optimality is proposed and used to solve this multi-objective PPF design problem. The proposed method is integrated with both external archive and fuzzy decision making. The sub-group search strategy and teacher selection strategy are used to improve the diversity of non-dominated solutions (NDSs). In addition, a selection mechanism for topology combinations for PPFs is proposed. A series of case studies are also conducted to demonstrate the performance and effectiveness of the proposed method. With the proposed selection mechanisms for the topology combinations and parameters for PPFs, the best compromise solution for a complete PPF design is achieved.

Optimal modulation strategy based on fundamental reactive power for dual-active-bridge converters

Optimal modulation strategy based on fundamental reactive power for dual-active-bridge converters

Design an Accurate Power Control Strategy of Parallel Connected Inverters in Islanded Microgrids

When the overall loads change periodically, the accurate real power and reactive power sharing considered is essential for the operation of an islanded microgrid. In this work, an accurate power control strategy of parallel-connected inverters in an AC microgrid in islanded mode has been designed. The examined microgrid involves four inverters linked to the load via different system impedance conditions is performed. Also, the control strategy for islanded microgrid operation with detailed switching models is simulated by using PSCAD/EMTDC software, and all dynamic and steady-state real and reactive power sharing is explained. Moreover, the real power sharing is achieved using only the decentralized control (droop control), while the reactive power sharing control approach is proposed as a central controller (secondary controller) in order to improve the precision of fundamental reactive power sharing, gives an efficient dynamic performance, and reduce the circulating current. The central controller in the microgrid requires communications. It is used as an external loop to accomplish identical reactive power sharing according to reactive power load especially when the mismatch in voltage drops through the feeders is occurred. The control approach will still work with traditional droop control when the central controller is a failure. The obtained results show that the proposed approach is immune to the time delay in the central controller. Additionally, the active power and the reactive power is shared accurately.

Optimal Placement and Sizing of Inverter-Based Distributed Generation Units and Shunt Capacitors in Distorted Distribution Systems Using a Hybrid Phasor Particle Swarm Optimization and Gravitational Search Algorithm

In this paper, a novel hybrid population-based meta-heuristic algorithm, called the hybrid Phasor Particle Swarm Optimization and Gravitational Search Algorithm (PPSOGSA), is proposed to solve the problem of optimal placement and sizing of inverter-based distributed generation (DG) units and shunt capacitors in radial distribution systems with linear and non-linear loads. The objective of the problem is reduction of active power losses considering constraints of the fundamental frequency active and reactive power balance, RMS voltage, and total harmonic distortion of voltage (THDV) at each bus of the network, as well as the branch flow constraints. The performance of the PPSOGSA-based approach is evaluated on the standard IEEE 33- and 69-bus test systems under sinusoidal and non-sinusoidal operating conditions. Compared to the original PPSO and GSA and other algorithms commonly used in the optimal sitting and sizing problem of DG units and shunt capacitors, it is found that the proposed algorithm has yielded better results.

Control Strategy of Reactive Power Sharing in an Islanded Microgrids

Precise power sharing considered is necessary for the effective operation of an Autonomous microgrid with droop controller especially when the total loads change periodically. In this paper, reactive power sharing control strategy that employs central controller is proposed to enhance the accuracy of fundamental reactive power sharing in an islanded microgrid. Microgrid central controller is used as external loop requiring communications to facilitate the tuning of the output voltage of the inverter to achieve equal reactive power sharing dependent on reactive power load to control when the mismatch in voltage drops through the feeders. Even if central controller is disrupted the control strategy will still operate with conventional droop control method. additionally, based on the proposed strategy the reactive power sharing accuracy is immune to the time delay in the central controller. The developed of the proposed strategy are validated using simulation with detailed switching models in PSCAD/EMTDC.

Uncertainty of the Energy Measurement Function deriving from Distortion Power Terms for a 16.7 Hz Railway

&lt;p class="Abstract"&gt;In electrified railways, harmonic active power terms can be significant in the order of the uncertainty required by the EN 50463-2 standard for power and energy measurements in railways. Nonactive power terms (encompassing reactive and distortion harmonic terms) are much more significant than the sole fundamental reactive power. This work considers the implementation of the EN 50463-2 energy measurement function, including the criteria for the significance of the measured and calculated terms, and it carries out a Monte Carlo analysis to assess the impact of harmonic power terms on the measured energy and its uncertainty.&lt;/p&gt;

Optimal design method for LLCL filters based on NSGA-III

The LLCL filter is usually used as a switching ripple suppressor since it can attenuate switching-frequency current harmonics much better than an LCL filter using lower total inductance and capacitance. However, it is more difficult to design LLCL parameters. In addition, it has a number of initial design constraints: the fundamental reactive power, the resonant frequency fres, etc. are coupled and always contradictory, which means that designing the parameters is a Many-objective optimization problem (MaOP). The non-dominated sorting genetic algorithm-III (NSGA-III) does well in solving this kind of problem. In recent studies, the proposed methods only provide a range of parameters. Thus, obtaining certain parameters relies on experience, and using the boundary value cannot be proved optimal. However, using original NSGA-III is somewhat time-consuming for achieving specific parameters. To deal with this problem, this paper proposes a novel optimal design method for an LLCL filter based on NSGA-III with the handling of constraints. The proposed method gives a set of specific parameters and achieves a high computing efficiency. The proposed method is verified through simulations and a grid-connected inverter system based on a virtual instrument to show the effectiveness of the proposed method.

Control-Winding Direct Power Control Strategy for Five-Phase Dual-Stator Winding Induction Generator DC Generating System

A control-winding direct power control (CWDPC) strategy for a dc generating system based on the five-phase dual-stator winding induction generator is proposed and investigated in this article. For this generator, the flux-oriented control is usually employed in the previous work mainly for the sake of good static performance. However, the present control strategy has the limitation of the further enhancement of the dynamic properties. This article explores a CWDPC strategy to upgrade the dynamic performance of this generating system. The fundamental active power of the five-phase control winding (CW) relates to its dc bus voltage while the dc bus voltage on the five-phase power-winding (PW) side is related to the control of five-phase CW fundamental reactive power. By replacing inner current loops to power control loops, the CW instantaneous fundamental active and reactive powers are calculated through the power observer and regulated directly through two power-control loops. In the transient process, the CW fundamental active power changes slightly while the reactive power can be quickly controlled for fast recovery of the dc bus voltage on the five-phase PW side. As the system has an additional control degree of freedom, the third harmonic is also considered in the proposed strategy, and the corresponding implementation is given as well. The simulation and experimental results demonstrate that using the proposed CWDPC strategy, the system has shorter transient time and lower voltage change in the dynamic response than the flux-oriented control strategy, which means the dynamic performance is further improved.

Optimal Sizing, Siting and Operation of Custom Power Devices With STATCOM and APLC Functions for Real-Time Reactive Power and Network Voltage Quality Control of Smart Grid

A new custom power device (CPD) is introduced for real-time control of reactive power and improving the overall network voltage quality of smart grid (SG) at fundamental and harmonic frequencies, respectively. The idea is to take advantage of the online smart meter data transmitted from each bus to the SG central control to concurrently perform the static synchronous compensator and the active power line conditioner operations by optimal compensations of fundamental reactive power and harmonic currents at selected optimal buses. The proposed strategy involves two particle swarm optimization algorithms. The first algorithm is implemented for the worse operating condition to determine the optimal locations and sizes of CPDs while the second algorithm relies on smart meter information to continuously compute fundamental and harmonic reference currents for real-time operation and control of the allocated CPDs. The objective functions are cost minimizations associated with bus voltage regulations, network total harmonic distortions voltage and custom device sizing while the constraints include upper limits for CPD sizes, fundamental, and harmonic bus voltages. Detailed simulations are performed in MATLAB/Simulink to evaluate the performances of allocated CPDs in controlling the reactive power and voltage quality of a distorted 15-bus SG with six nonlinear loads according to the IEEE-519 standard.

Novel four‐quadrant variable impedance and its application

The variable impedance can be applied in many fields of power system. A novel four-quadrant variable impedance based on voltage-sourced inverter control is proposed in the study. The schematic diagram of the novel variable impedance is presented, and its principle and transient characteristic are addressed. The system stability of the variable impedance when it is connected in series with a resistive and inductive load is described. Based on the developed variable impedance, a novel shunt power quality controller (SPQC) is proposed. In the SPQC, the fundamental equivalent impedance of the primary winding is a variable impedance, which can be used to compensate the fundamental reactive power. The equivalent impedance of the primary winding for nth order harmonics is short-circuit impedance, which is very low impedance and the harmonics produced by loads will be short-circuited in primary winding. The control strategy is also analysed. Two sets of single-phase prototypes have been constructed. One is for the demonstration of the variable impedance, the other is for the demonstration of the SPQC. The validity of the novel variable impedance and the SPQC has also been verified through experimental results.

Simulation and real time implementation of predictive direct power control for three phase shunt active power filter using robust phase-locked loop

This paper proposes a predictive direct power control for shunt active power filters. The main goal of the proposed active filtering system is to eliminate the unwanted harmonics and compensate fundamental reactive power drawn from the non-linear loads. The proposed control is characterized by a high transient dynamic, which makes it an interesting alternative for classic direct power control. In order to improve the efficiency of the proposed control, different simulation and experimental tests were carried out with real time implementation on dSPACE 1104 card in steady and transient states. The obtained results indicate closeness between simulation and experimental tests, which prove and verify the effectiveness of the proposed control strategy.

Reactive Power Billing Under Nonsinusoidal Conditions for Low-Voltage Systems

This paper analyzes reactive power definitions for billing purposes in low-voltage installations with high harmonic distortion levels. First, the theoretical definitions of power under nonsinusoidal conditions and their outcomes are presented and two of them are chosen as the focus to determine which one is the most appropriate for billing: nonactive power and fundamental reactive power. The regulatory framework of different countries is then analyzed and compared with the theoretical definitions. Subsequently, different reactive power measurement methods are analyzed and their outputs are again compared with the definitions. Simulations performed with typical nonsinusoidal voltage and current signals show that several measurement techniques can easily be used for fundamental reactive power measurement, whereas the measurement of nonactive power requires more effort. Finally, a regulatory comparison of the pros and cons of each reactive power quantity is conducted. It is concluded that the surplus of reactive power in electricity grids should be controlled via fundamental reactive power (or displacement power factor), since it is independent of the harmonic distortion, the responsibility for it can be easily assigned, and it is easy to be measured with the use of several simple electronic measurement techniques.

Load Sharing in Ship Microgrids Under Nonsinusoidal Conditions—Case Study

The paper is focused on the problem of load sharing between generators running in parallel in ship microgrids loaded by variable-speed drives with power converters. It is based on an experimental study of a number of real cases recorded on three ships. Chosen power quantities defined in the IEEE 1459-2010 standard are calculated, and their sharing between generators working in parallel in ship systems are assessed. Particularly, sharing of active, nonactive, and apparent power as well as active, reactive, and apparent power of voltage and current fundamental components is determined for various loads. The levels of voltage and current distortions as well as harmonic power flow are also assessed. The results are commented on in the wake of related provisions of ship classification societies rules. Finally, it has been determined that there are differences between sharing of various power components, which must not be neglected, particularly in the case of nonactive power and fundamental reactive power. Therefore, amendments to related ship classification societies rules are necessary.

Simple method of fundamental reactive power measurement for ASIC application

This study presents a simple method for measuring the fundamental reactive power concurrently with the other basic power components defined in IEEE Standard 1459-2010. The method has low hardware requirements and is suitable for implementation in low cost devices, e.g. application-specific integrated circuits (ASICs). The algorithm is based on voltage samples that are shifted by a constant number that represents one-quarter of the rated period. The impact of instantaneous frequency variations on the measurement is mitigated by a sine function Taylor expansion. The algorithm is described in detail and the results of an experimental investigation are presented, which consisted of simulations and laboratory research into known testing signals. Next, the method was applied to an actual microgrid with fluctuating load and a high level of distortion, and the results were compared to those of the reference methods. The results confirm the usefulness of the proposed solution for the measurement of power flows in power systems, including highly disturbed ones.

Enhanced Power Generation From Two-Winding Single-Phase SEIG Using LMDT-Based Decoupled Voltage and Frequency Control

This paper proposes a leaky minimal disturbance theory (LMDT)-based decoupled control of voltage and frequency for two-winding single-phase self-excited induction generators (SEIGs) for enhanced power generation and power quality improvement. Single-phase two-winding SEIGs are normally designed with 33% derated capacity in comparison to three-phase SEIGs of the same frame size. Using single-point operation performed by the proposed decoupled voltage and frequency controller (DVFC), the two-winding single-phase machine can generate enhanced power output, nearly 33% higher than its normal capacity. It is equal to the power generated by a three-phase machine with the same frame size. The DVFC consists of a voltage source converter (VSC) and a closed-loop controlled dump load. A single-phase VSC is used for harmonics and fundamental reactive power compensation for system voltage control and harmonics mitigation. The control of VSC is achieved using an LMDT-based control algorithm. The minimal disturbance theory-based control algorithm is used for potentially fast convergence and fast dynamic response, whereas the leakage factor is added for improving the steady-state performance of the system. The LMDT control-based VSC-battery energy storage system scheme is also implemented for the voltage and frequency control of a single-phase SEIG. Both schemes are implemented in real time using a digital signal processor.

Reviews on MATLAB DSTATCOM Simulation Models in Mitigating Power Quality Problems

This paper reviews the performance of detailed and average model for distribution static compensator (DSTATCOM) in order to remove voltage flicker, regulate the voltage at point of common coupling (PCC), power factor correction and harmonics elimination. In these models, d-q theory is used to extract fundamental active and reactive power components of the load currents which will be required to estimate the reference source currents. Both models are evaluated and compared in MATLAB/Simulink based simulation platform.

Development of optimal shunt hybrid compensator based on improving the measurement of various signals

Voltage and current harmonics generated by nonlinear loads in power systems cause a reduction in electric power quality (EPQ) which has recently become a serious preoccupation in electrical networks due to the increasing number of perturbing loads such as electric arc furnaces and nonlinear loads. Various devices such as static Var compensator (SVC) and static synchronous compensator (STATCOM) can be used to improve EPQ. Due to economic issues, using a STATCOM with high-rated power is not cost-effective. So, development of hybrid compensator based on STATCOM and SVC, type of TCR-BPF, is proposed in this paper by improving the measurement of various signals in their control systems. Hence, the SVC will compensate the fundamental reactive power and balancing of nonlinear load and STATCOM can be used with lower-rated power as an active filter to eliminate the harmonics generated by set of TCR and load. Also, STATCOM compensates the reactive power, voltage flicker, and the unbalancing load which SVC has not been able to compensate them. To use all of the capabilities of TCR-BFP, its control system is improved by new TCR reactive power measurement and predicted reactive power (PRP). Also, the STATCOM control strategy is optimized by FPSO method. Then, the proposed hybrid compensator is implemented in one of the largest steel industries in Iran, Mobarakeh Steel Company (MSC).