Three-phase Three-wire Power System Research Articles

Parallel active power filter based on single-phase independent control

With the rapid development of high-voltage power grids and power electronics technology, the integration of numerous power electronic devices has led to a significant increase in harmonic pollution in power grids. Consequently, the demand for high-voltage and large-capacity active power filters has become increasingly urgent. This article introduces a novel approach using single-phase independent control and proposes a parallel active power filter based on magnetic flux compensation. This filter not only enhances power quality but also achieves three-phase decoupling control. It is specifically designed for medium and high-voltage three-phase three-wire power systems. Simulation experiments were conducted to validate the efficacy of the proposed active power filter, demonstrating its ability to effectively reduce the total harmonic distortion rate at the grid connection point and subsequently improve power quality.

Power factor correction and power quality improvement of supply grid with self-supported transformer-less DSTATCOM for different control strategies

This paper investigates the performance of transformer-less distribution static compensator (DSTATCOM) integrated at the side of the utility distribution system for four different control strategies, viz., unit template (UT) theory, synchronous reference frame (SRF) theory, instantaneous reactive power theory (IRPT) and power balance theory (PBT). The simulation models for the three-phase three-wire power system have been designed to achieve unity power factor with different loading conditions (balanced and unbalanced linear and nonlinear loads). The DC-link is self-supported, i.e., no energy storage element is used but a DC-link capacitor is used only. DSTATCOM fulfils almost all the objectives related to the current related power quality problems created by different types of load. Here, it eliminates the harmonics, compensates reactive power which reduces the burden on the grid, makes the grid power factor unity and eliminates the load unbalances. Here, steady-state and dynamic state analysis has been discussed and comparative results have been presented.

Power factor correction and power quality improvement of supply grid with self-supported transformer-less DSTATCOM for different control strategies

This paper investigates the performance of transformer-less distribution static compensator (DSTATCOM) integrated at the side of the utility distribution system for four different control strategies, viz., unit template (UT) theory, synchronous reference frame (SRF) theory, instantaneous reactive power theory (IRPT) and power balance theory (PBT). The simulation models for the three-phase three-wire power system have been designed to achieve unity power factor with different loading conditions (balanced and unbalanced linear and nonlinear loads). The DC-link is self-supported, i.e., no energy storage element is used but a DC-link capacitor is used only. DSTATCOM fulfils almost all the objectives related to the current related power quality problems created by different types of load. Here, it eliminates the harmonics, compensates reactive power which reduces the burden on the grid, makes the grid power factor unity and eliminates the load unbalances. Here, steady-state and dynamic state analysis has been discussed and comparative results have been presented.

Methodology for Calculating the Parameters of a Reactive Compensator of a Linear Asymmetric Load of a Three-Phase Three-Wire Network

The article describes the method of calculating the parameters of a reactive compensator of a linear asymmetric load of a three-phase three-wire network, which allows to increase the power factor of an asymmetric load to a unit value. It is shown that as a result of the use of a reactive compensator, the power loss in the transmission line can be reduced to two times. In this paper the main equation for the calculation of the parameters of the reactive compensator is derived. The reactive compensator of the circuit with asymmetrical two-arm active load is synthesized. The method is illustrated by an example of a scheme with asymmetric single-cell active load. As known, the unbalanced load of three-phase three-wire power systems leads to a deterioration in the quality of electricity, which manifests itself in the emergence of reciprocal currents and pulsations of instantaneous power, which cause additional losses on the active supports of the transmission line and asymmetry of supply voltages in the nodes of the overall connection of loads. In order to balance the asymmetric stationary linear load, passive filters on reactive elements are effectively used, the calculation of which is based on two approaches: the removal of the pulsating component of instantaneous power and the compensation of the inactive components of the input currents. Among various possible methods, the inductive-capacitive systems are of particular importance. When the limit values of unbalance factor, specified in standards are exceeded, the use of symmetrization systems is required. A symmetrizator should not cause significant active power losses during operation; it implies that the symmetrization process shall be carried out by means of reactive elements (LC) or using active methods (power electronic systems).The purpose of a compensator is to measure adequate electric quantities of the load and generate in the compensator such currents, that the resultant load: compensator-compensated load, as seen from the supply network, was symmetrical, and the fundamental harmonic reactive current drawn from the network did not exceed the value permitted in the supply conditions. In the work vector diagrams of currents and voltages are constructed, power loss is calculated.As a result of the work done, it was established:1) Increasing the power factor of the three-phase system to the maximum unit value leads to a gain in power loss.2) Losses in the wires unbalanced system in 2 times more loss symmetric system, and power factor for unbalanced system in square root of two times less than a coefficient symmetrical.Ref. 3, fig. 8.

СURRENT FILTERING IN A THREE-PHASE THREE-WIRE POWER SYSTEM AT ASYMMETRIC SINUSOIDAL VOLTAGES

Purpose. Investigation of the optimal current distribution between source, shunt active filter and reactive compensator of a three-phase three-wire system that provides consumption of a sinusoidal symmetric current under asymmetric source voltages with minimal power losses was provided. Methodology. The tasks were solved by conducting theoretical and experimental studies. The main provisions of the theory of electrical circuits, the apparatus of mathematical analysis, methods for solving linear differential and algebraic equations, elements of matrix and complex calculus and vector algebra are used. During the development, modern methods and software of computer simulation of electrical engineering complexes and dynamic systems were applied: Matlab-Simulink, MATHCAD. Originality. The principle of compensating current distribution between PAF and reactive compensator of a three-phase three-wire power system with asymmetric sinusoidal voltage was proposed at which the input current is equal to the positive-sequence active current and rms value of PAF current is minimal. The feasibility to compensate the inactive sinusoidal Fryze current by reactive elements under arbitrary combination of load and source parameters was proved and expression for direct calculation of the reactive compensator parameters for generation of inactive Fryze current in the source unbalanced mode was obtained. Practical value. The simulative example for transmission line load showed that combined application of PAF and reactive compensator with the specified distribution of compensating currents ensured a reduction of power losses in 3.273 times and rms value of the SAF current is 12.9 % of rms value total compensation current.

Generalized Design of High Performance Shunt Active Power Filter With Output LCL Filter

This paper concentrates on the design, control, and implementation of an LCL-filter-based shunt active power filter (SAPF), which can effectively compensate for harmonic currents produced by nonlinear loads in a three-phase three-wire power system. With an LCL filter added at its output, the proposed SAPF offers superior switching harmonic suppression using much reduced passive filtering elements. Its output currents thus have high slew rate for tracking the targeted reference closely. Smaller inductance of the LCL filter also means smaller harmonic voltage drop across the passive output filter, which in turn minimizes the possibility of overmodulation, particularly for cases where high modulation index is desired. These advantages, together with overall system stability, are guaranteed only through proper consideration of critical design and control issues, like the selection of LCL parameters, interactions between resonance damping and harmonic compensation, bandwidth design of the closed-loop system, and active damping implementation with fewer current sensors. These described design concerns, together with their generalized design procedure, are applied to an analytical example, and eventually verified by both simulation and experimental results.

Novel Bridge-Type FCL Based on Self-Turnoff Devices for Three-Phase Power Systems

In this paper, a novel bridge-type fault current limiter (FCL) based on self-turnoff devices for three-phase power systems is proposed. Compared with the SCR-based bridge type FCL, the new one is smaller in size, better in dynamic performance, and simpler in control method and control circuitry. The novel FCL is composed of a rectifier bridge-a dc-limiting reactor and one/three bypass reactor/reactors-for a single-phase/three-phase structure. The increasing speed of the fault current just after the occurrence of a fault is limited by a dc-limiting reactor, whose inductance is designed according to the response speed of the control circuit. The bypass reactors are designed in terms of the requirements of the coordination of protective relays. The source currents during limiting events are sinusoidal and do not have any harmful effects on the overall protection schemes, impedance relays, and conventional current and voltage transformers. The topologies of the proposed FCL for three-phase four-wire and three-phase three-wire power systems are investigated, respectively, in detail. Parameter design and optimization are presented. The fault and fault-mode judgment method is described briefly. Simulations and experimental results prove the feasibility of the new FCL.

Accurate and Computationally Efficient Implementation of the IEEE 1459-2000 Standard in Three-Phase Three-Wire Power Systems

The definitions for the measurement of electrical power quantities under sinusoidal, nonsinusoidal, balanced, or unbalanced conditions are established in IEEE Standard 1459-2000. Measured magnitudes, such as apparent powers or effective quantities, are evaluated considering the frequency spectrum of voltage and current signals (fundamental, nonfundamental, and combined magnitudes). Previous papers implement these definitions in the frequency domain (DFT) and in the time domain (Clarke-Park Transformations). In the time domain, low-pass filters (LPFs) must be applied to obtain the fundamental magnitudes but, in this case, the quality of the measurements depends on the LPFs orders and their cutoff frequencies. This paper proposes a time-domain implementation of the standard definitions without LPFs and employs a recursive averaging algorithm which improves the measurements precision and reduces the computational burden. Simulation and experimental tests showing the proposed method performance are included