Three-phase Power Grid Research Articles

Low-frequency oscillation of train–network system considering traction power supply mode

The low-frequency oscillation (LFO) has occurred in the train–network system due to the introduction of the power electronics of the trains. The modeling and analyzing method in current researches based on electrified railway unilateral power supply system are not suitable for the LFO analysis in a bilateral power supply system, where the trains are supplied by two traction substations. In this work, based on the single-input and single-output impedance model of China CRH5 trains, the node admittance matrices of the train–network system both in unilateral and bilateral power supply modes are established, including three-phase power grid, traction transformers and traction network. Then the modal analysis is used to study the oscillation modes and propagation characteristics of the unilateral and bilateral power supply systems. Moreover, the influence of the equivalent inductance of the power grid, the length of the transmission line, and the length of the traction network are analyzed on the critical oscillation mode of the bilateral power supply system. Finally, the theoretical analysis results are verified by the time-domain simulation model in MATLAB/Simulink.

Modeling and Low-Frequency Oscillation Analysis of an Asymmetrical Traction Power System Connected to Power Grid

The traction power system is supplied by three-phase power grids in China, forming an asymmetrical system. However, current research on wideband-oscillation analysis of the traction power supply system assumes that vehicles in a feeding section are supplied by a single-phase ideal voltage source. Meanwhile, the existing vehicle impedance models are inapplicable for the stability analysis of this asymmetrical system. In this article, a single-input and single-output impedance of the vehicle is derived and the corresponding admittance can be directly used to form the system node admittance matrix and to analyze system stability by the modal analysis. The node admittance matrix of this asymmetrical system is established by putting the derived vehicles’ admittance into the node admittance matrix of two feeding section traction networks, the traction transformer and the equivalent circuit of power grids. Then, the modal analysis method is used to obtain the low-frequency oscillation modes of this asymmetrical system and to analyze the sensitivities of different parameters to the oscillation mode. The interaction between the two feeding sections and their interaction with power grids is studied. Finally, the correctness of theoretical findings is verified by simulation in MATLAB/Simulink and experiment in Starsim/HIL.

Cooperation of a Non-Linear Receiver with a Three-Phase Power Grid

This article presents an analysis of electrical parameters in a three-phase circuit characterized by the generation of harmonics. The Currents Physical Components (CPC) power theory for three-phase circuits were used. Relationships for three-wire circuits were used, and mathematical relationships were determined to enable decomposition into those components that depend on the direction of energy flow and the reasons for their creation. A calculation example using the previously determined dependencies was presented, and the results of the calculations were discussed. When mathematical analyses are required in circuits with non-linear receivers, and in particular, when there is a cooperation of several such receivers with a common power grid, the calculation concept presented is important. The generation of identical harmonic orders by several receivers causes a disturbance in the direction of energy flow in the power grid. For this reason, the case of a non-linear receiver generating harmonics of orders that has existed before in the power grid seems very interesting. Determining the value of individual powers can be used to estimate the impact of individual receivers on the quality of electricity.

Three-Level SOC Equalization Control Strategy for MMC-BESS Based on Feedforward Sliding Window Integral Method

The modular multilevel converter of the battery energy storage system (MMC-BESS) not only is suitable for the large-scale energy storage and dispatching of AC and DC grids, but also has a strong ability to suppress power fluctuations caused by the new energy output or grid failures. When an asymmetric voltage or a sudden change in DC load occurs in the AC grid, in order to compensate for the power difference between AC and DC sides, the energy storage submodule of the MMC-BESS will have a large unbalanced charging and discharging current, destroying the equalization state of SOC and seriously affecting energy storage capacity utilization and battery service life. In order to deal with the above problems, in this paper, the characteristics of the power difference between the MMC-BESS phase unit and the upper and lower bridge arms are analyzed. It is found that when considering the fluctuation of the submodule capacitor voltage, the phase unit power has the fundamental frequency AC circulating current component, and the power difference between the upper and lower bridge arms has the DC circulating current component. Therefore, the three-level SOC equalization correction control strategy is proposed based on interphase, upper and lower bridge arms, and submodules, and the feedforward sliding window integral method is introduced into the SOC equalization correction control layer of upper and lower bridge arms, so as to achieve the purpose of more balanced and accurate power distribution among phases and among upper and lower bridge arms of each phase. The simulation results show that the MMC-BESS has effective compensation ability when there is a large power difference in the AC and DC power grid. Under the unbalanced working conditions of the three-phase power grid, the three-phase AC current can quickly reach equalization, and the total harmonic content is 1.38%, and the unbalance degree is 2.4%. Under the same operating conditions, compared with the traditional optimal one-third average method, the SOC equalization correction control strategy proposed in this paper has smaller submodule capacitor voltage fluctuation rate, harmonic distortion rate, and three-phase system circulating current. And the SOC of each phase has a faster equalization convergence speed.

A Cascaded Controller for a Grid-Tied Photovoltaic System With Three-Phase Half-Bridge Interleaved Buck Shunt Active Power Filter: Hybrid Control Strategy and Fuzzy Logic Approach

This paper focuses on the control development of a grid-tied photovoltaic system coupled with a shunt active power filter. The considered power system includes a PV panel, a single-capacitor three half-bridge interleaved buck converter connected to a three-phase power grid and a nonlinear load. This study aims to accomplish simultaneously three objectives: i) to ensure a high compensation level of current harmonics and reactive power consumed by the nonlinear load in order to perform power factor correction at the grid side; ii) to extract the maximum power from the PV panel regardless the climatic conditions; iii) to regulate the dc bus capacitor voltage to its reference provided by the MPPT controller. To this end, a controller using a two-loop cascade strategy is designed. First, the inner loop is developed with the hybrid automaton approach to formulate the switching control signals with the aim of guaranteeing a unitary power factor. Second, the outer loop is designed using fuzzy logic control to ensure the regulation of the photovoltaic voltage, while the perturb and observe algorithm is employed to perform maximum power point tracking. Finally, the system with the developed control scheme is simulated using MATLAB/SimPowerSystems environment. The obtained results confirm that the proposed controller is able to achieve the previous objectives under varying environmental conditions.

Harmonic Power-Flow Study of Polyphase Grids With Converter-Interfaced Distributed Energy Resources—Part II: Model Library and Validation

In Part I, a method for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Harmonic Power-Flow</i> (HPF) study of three-phase power grids with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Converter-Interfaced Distributed Energy Resources</i> (CIDERs) is proposed. The method is based on generic and modular representations of the grid and the CIDERs, and explicitly accounts for coupling between harmonics. In Part II, the HPF method is validated. First, the applicability of the modeling framework is demonstrated on typical grid-forming and grid-following CIDERs. Then, the HPF method is implemented in MATLAB and compared against time-domain simulations with Simulink. The accuracy of the models and the performance of the solution algorithm are assessed for individual resources and a modified version of the CIGRÉ low-voltage benchmark microgrid (i.e., with additional unbalanced components). The observed maximum errors are 6.3E-5 p.u. w.r.t. voltage magnitude, 1.3E-3 p.u. w.r.t. current magnitude, and 0.9 deg w.r.t. phase. Moreover, the scalability of the method is assessed w.r.t. the number of CIDERs and the maximum harmonic order (≤25). For the maximum problem size, the execution time of the HPF method is 6.52 sec, which is 5 times faster than the time-domain simulation. The convergence of the method is robust w.r.t. the choice of the initial point, and multiplicity of solutions has not been observed.

Improved Genetic Algorithm for Phase-Balancing in Three-Phase Distribution Networks: A Master-Slave Optimization Approach

This paper addresses the phase-balancing problem in three-phase power grids with the radial configuration from the perspective of master–slave optimization. The master stage corresponds to an improved version of the Chu and Beasley genetic algorithm, which is based on the multi-point mutation operator and the generation of solutions using a Gaussian normal distribution based on the exploration and exploitation schemes of the vortex search algorithm. The master stage is entrusted with determining the configuration of the phases by using an integer codification. In the slave stage, a power flow for imbalanced distribution grids based on the three-phase version of the successive approximation method was used to determine the costs of daily energy losses. The objective of the optimization model is to minimize the annual operative costs of the network by considering the daily active and reactive power curves. Numerical results from a modified version of the IEEE 37-node test feeder demonstrate that it is possible to reduce the annual operative costs of the network by approximately 20% by using optimal load balancing. In addition, numerical results demonstrated that the improved version of the CBGA is at least three times faster than the classical CBGA, this was obtained in the peak load case for a test feeder composed of 15 nodes; also, the improved version of the CBGA was nineteen times faster than the vortex search algorithm. Other comparisons with the sine–cosine algorithm and the black hole optimizer confirmed the efficiency of the proposed optimization method regarding running time and objective function values.

Analysis of the negative sequence interactive impact of traction power supply system on the urban power grid

The high-speed railway adopts single-phase power supply, which is asymmetric load for the three-phase power grid. Its high power and fluctuation characteristics will cause the negative sequence voltage problem of urban power grid. With the rapid development of high-speed railway in recent years, this problem is becoming more and more serious. Therefore, it is urgent to analyse the negative sequence of the urban power grid caused by TPSS (Traction Power Supply System). Usually, the mathematical and simulation model of TPSS is established to analyse the power quality of TPSS. However, the modelling process is usually simplified, and the load of TPSS has randomness and volatility, which makes the simulation results deviate from the actual results. Therefore, based on the measured data of TPSS loads and the method of dynamic power flow calculation, considering the factors of station number, common phase of traction transformer and train marshal, the negative sequence influence of TPSS on the whole urban power grid under different conditions is analysed in this paper. Finally, the feasibility of alternation commutation phase to weaken negative sequence voltage is verified.

Topologies and Operation Modes of Rail Power Conditioners in AC Traction Grids: Review and Comprehensive Comparison

Electric locomotives in AC traction power systems represent a huge single-phase non-linear load and, detrimentally, affect the power quality and the efficiency of the three-phase power grid. Nevertheless, along the last decades, power electronics are being used to mitigate power quality problems in the three-phase power grid. In particular, Rail Power Conditioner (RPC) helps to increase the loading capacity of traction substations and improve the power quality of three-phase power grids. As the main characteristics, an RPC can supply reactive power, suppress current harmonics and overcome currents imbalance of the three-phase power grid. On the other hand, the traction substations may be constituted by different types of power transformers. For instance, single-phase power transformers and open-delta (V/V) power transformers are widely used, while Scott power transformers are less frequently used, since they are more complex and expensive. In this framework, this work presents a review study of RPC topologies, including their operation modes, and a comprehensive comparison between the characteristics of the RPC topologies when using different types of AC traction substations and power transformers. This helps to ensure the correct selection of the RPC topology for a specific application, according to the main structure of the traction substation. Consequently, and based on the established review, it is possible to sort and allocate each RPC topology for limited or wider applications.

A Three-Phase Power Grid Regulator with Different Structures of Output Filters

This paper is devoted to the study of a regulator based on a power electronic dc/ac converter that can carry out different functions on the improvement of electric power quality in the three-phase low-voltage grid. The algorithm of the control system is based on the Park–Gorev transform and the use of pulse-width modulation of converter voltage has been suggested. The effect of structure of an output passive converter filter on the operation of the grid regulator has been analyzed. A technique to calculate L- and LCL-filters of a regulator have been considered, as well as mathematical models of a regulator for analysis of its dynamic characteristics and determining the parameters of a control unit in the current feedback circuit, has been presented. Computer simulations that demonstrate the effect of the characteristics of an output filter and parameters of a control system on the dynamic characteristics of a device and level of current modulation distortion of the regulator have been carried out.

Deadbeat Predictive Current Control for Circulating Currents Reduction in a Modular Multilevel Converter Based Rail Power Conditioner

This paper presents a deadbeat predictive current control methodology to reduce the circulating currents in a modular multilevel converter (MMC) when it operates as a rail power conditioner (RPC) in a conventional railway system-based V/V connection. For this purpose, a half-bridge MMC based on half-bridge submodules, operating as an RPC is explained, and the total system is denominated as a simplified rail power conditioner (SRPC). The SRPC in this study is used to compensate harmonics, reactive power, and the negative sequence component of currents. This paper explains the SRPC system architecture, the key control algorithms, and the deadbeat predictive current control methodology. Mathematical analysis, based on the MMC equivalent circuit, is described and the reference equations are presented. Moreover, simulation results of the deadbeat predictive current control methodology are compared with the results of the conventional proportional-integral (PI) controller. This comparison is to verify the effectiveness of the proposed control strategy. Simulation results of the SRPC show reduced circulating currents in the MMC phases when using the predictive control approach, besides accomplishing power quality improvement at the three-phase power grid side.

SINKRONISASI GENERATOR DENGAN PENGENDALI BERBASIS ARDUINO MEGA 2560

&#x0D; Generators that enter the grid system must be synchronized. The synchronization requirements are the phase sequence, voltage magnitude of each phase, and the frequency between the generator and the system grid must be the same. Automatic control is required on the prime mover and generator excitation system to meet these requirements. This study proposes automatic adjustment of prime movers and excitation systems using a controlled rectifier from a constant AC voltage source to a variable DC voltage. Arduino Mega based settings for processing the measurement results of voltage sensors and frequency sensors from generators and grids. The difference in the measurement results of these sensors as a basis for control of the prime mover and excitation system. Arduino Mega sends the firing angle for setting the prime mover and excitation system to the Arduino Pro Mini in the controlled rectifier module for the prime mover and excitation system. The results showed the prime mover speed regulation resulted in a change in generator frequency with an increase of 1 rpm resulting in an increase of 0.0352 Hz. Setting the excitation voltage produces a change in the voltage of the generator Vrms with an increase in 1 volt of the excitation voltage resulting in an increase in the generator voltage of 4.0427 volts. The synchronous condition shown by the synchronronoscope, the difference in voltage and frequency of the generator with the three-phase power grid displayed by the synchronization module LCD is 0.13% for the voltage difference and 0.12% for the frequency difference, respectively.

A double closed-loop control of VIENNA rectifier based on sliding-mode of fuzzy approaching law

A novel double closed-loop control of VIENNA rectifier based on sliding-mode of fuzzy approaching law is proposed in this paper. This new control strategy improves dynamic response and steady accuracy of system, chattering phenomenon of the sliding-mode is eliminated. Combined with sliding-mode and fuzzy approaching law, a new type of inner loop power control is proposed to replace traditional current inner ring. Without coordinate transformation and phase-locked-loops(PLL), control algorithm is simple. Under unbalanced three-phase power grid, output voltage still maintains small voltage ripple, network side harmonic suppression and dynamic response perform well. Sliding-mode based on fuzzy approaching law can eliminate the chattering phenomenon of the system, the overshoot produced by load transition can be reduced. The outer ring adopts voltage PI control with real time current compensation, dynamic response performs good and the control algorithm is simple.

Allocation of Capacitors and Voltage Regulators in Three-Phase Distribution Networks

The development of electricity distribution networks has affected their planning and operation, requiring more specialized studies such as three-phase analyses that allow the inclusion of unbalanced loads and the mutual impedances of power cables. These more detailed modeling approaches allow a better understanding and control of the factors related to power quality such as losses and maintenance of the voltage profile and power factor. These quality issues can often be addressed using the appropriate allocation of capacitor banks and voltage regulators. This paper proposes an optimization approach for allocating these devices using a metaheuristic technique to improve the quality of the power supply in the context of unbalanced three-phase power grids. The optimization problem is solved via binary particle swarm optimization. The load flow analysis is carried out using OpenDSS software, which allows the modeling of unbalanced three-phase topologies. The mathematical formulation proposed is tested using an IEEE-34 and IEEE-123 system bus.

A new model predictive control algorithm by reducing the computing time of cost function minimization for NPC inverter in three-phase power grids

This paper presents a new control strategy based on finite-control-set model-predictive control (FCS-MPC) for Neutral-point-clamped (NPC) three-level converters. Containing some advantages like fast dynamic response, easy inclusion of constraints and simple control loop, makes the FCS-MPC method attractive to use as a switching strategy for converters. However, the large amount of required calculations is a problem in the widespread of this method. In this way, to resolve this problem this paper presents a modified method that effectively reduces the computation load compare with conventional FCS-MPC method and at the same time does not affect on control performance. The proposed method can be used for exchanging power between electrical grid and DC resources by providing active and reactive power compensations. Experiments on three-level converter for three Power Factor Correction (PFC), inductive and capacitive compensation modes verify the good and comparable performance. The results have been simulated using MATLAB/SIMULINK software.

Multicell Three-Phase AC–DC Driver for HB-LED Lighting Applications

High-brightness light-emitting diodes (HB-LEDs) are becoming omnipresent across all aspects of illumination products, due to their incredible characteristics such as efficiency, reliability, long lifetime, controllability, etc. This paper proposes power conversion topologies to drive medium to high power HB-LEDs in three-phase power grids when these connections are available. For that reason, an evaluation of several drivers for medium to high power HB-LEDs in three-phase power grids is done. Moreover, a new topology is proposed, which complies with IEC 1000-3-2 Class C requirements, achieves high power factor, low total harmonic distortion, and the capability to have a flicker free behavior while disposing of the bulk capacitor and having galvanic isolation. The HB-LED driver is based on a modular approach with several cells working together with their inputs connected to the three-phase network and their outputs connected in parallel generating a dc output. Each one of these cells is a dc–dc converter operating as a loss free resistor. In order to validate the concept, a prototype has been built by the use of flyback converters operating in discontinuous conduction mode. Furthermore, it operates in the full range of the European three-phase line voltage, which varies between 380 and 420 V, and it supplies an output voltage of 48 V with maximum power of 90 W.

Harmonic analysis and detection of power system based on double moment wavelet transform

The influence of unbalanced installation of single-phase DG unit with harmonic compensation function in three-phase and three-wire public power grid shows that there will be risk for the unbalanced installation to increase the three-phase current of the power grid. In order to overcome this problem, balanced triple-frequency harmonic function is proposed for the purpose of avoiding the increase in three-phase power grid current. In addition, compared with the traditional method, such method is also capable of reducing the rated power of harmonic current compensation. In order to verify the effectiveness of the method proposed, the balance and unbalanced conditions are verified in experiment and the experimental circuit is a simplified system based on actual three-phase three-wire system. In order to avoid the increase in the harmonic current, a balanced third harmonic suppression method is proposed. Finally, performance of the algorithm proposed has been verified through experiment.

Harmonic analysis and detection of power system based on double moment wavelet transform

The influence of unbalanced installation of single-phase DG unit with harmonic compensation function in three-phase and three-wire public power grid shows that there will be risk for the unbalanced installation to increase the three-phase current of the power grid. In order to overcome this problem, balanced triple-frequency harmonic function is proposed for the purpose of avoiding the increase in three-phase power grid current. In addition, compared with the traditional method, such method is also capable of reducing the rated power of harmonic current compensation. In order to verify the effectiveness of the method proposed, the balance and unbalanced conditions are verified in experiment and the experimental circuit is a simplified system based on actual three-phase three-wire system. In order to avoid the increase in the harmonic current, a balanced third harmonic suppression method is proposed. Finally, performance of the algorithm proposed has been verified through experiment.

Direct Power Control Strategy of PWM Rectifier Based on Improved Virtual Flux-Linkage Observer

In order to achieve the low cost and high performance control of three-phase PWM rectifier, a direct power control (DPC) strategy based on a new-style virtual flux-linkage observer is proposed. The model of three-phase PWM rectifier and the principle of virtual flux-linkage vector control are introduced firstly. Then, in order to avoid the effect of integral initial value and cumulative deviation, three first-order low-pass filters are cascaded to replace the pure integral link; an improved virtual flux-linkage observer of three-phase power grid is presented. From the observed virtual flux-linkage, the voltage and instantaneous power of three-phase power grid are online estimated. On this basis, the power grid voltage sensorless direct power control system of three-phase PWM rectifier is designed. Simulation results have shown that, both in the rectifying state and in the inverting state, the power grid side current and the DC side voltage of three-phase PWM rectifier all can be effectively controlled; the high power factor operation of three-phase PWM rectifier is realized.

Multilevel Power Conditioner and its Model Predictive Control for Railway Traction System

In the rapid development process of a high-speed electrified railway, power quality problems in traction power grid have become increasingly deteriorative. In order to ensure a three-phase balanced traction power grid, a modular multilevel converter based railway traction power conditioner (RTPC) is presented. The RTPC consists of four H-Bridge clusters and filter inductors, and it can be directly connected to traction feeders in a co-phase traction system without insulation transformers. According to the equivalent circuit analysis of RTPC system, it can be considered as four single-phase inversion systems. Based on the equivalent control model of each single-phase cluster, the relationship between the multilevel output voltage and current slopes in a control period is analyzed, and an improved model predictive control is proposed. Moreover, a linear combination of two different output levels is proposed to improve tracking performance of cluster current control, and enhance the waveform quality of ac current. Finally, both simulation and experiment results are presented to verify the effectiveness of the structure and its control method.