PSCAD Simulation Research Articles

Induced Voltages on a Gas Pipeline due to Lightning Strikes on Nearby Overhead Transmission Line

<span lang="EN-US">The purpose of this paper is to investigate the severity of lightning induced voltages on a gas pipeline installed in parallel with overhead transmission line using two different simulation packages. The results from this study using CDEGS, which solves a given problem based on electromagnetic computations, reveal that the induced voltages on the pipeline are more accurate compared to that obtained by PSCAD simulation, which is based on the circuit approach. Unlike PSCAD, CDEGS considers many salient factors such as soil model, inductive, capacitive and conductive couplings, and multiple soil structures. Models of a double circuit 132kV transmission line, gas pipelines, soil with different resistivities and variable lightning surges were developed. The effects of pipelines located at various heights above ground and distance of pipeline from the power lines were also studied. Compared to previously published work using PSCAD, it is found that CDEGS has given more accurate results. Several findings which were not possible using PSCAD were observed such as the effect of soil structure on induced voltage and multiple layers soil. This also led to better understanding of the conductive coupling from lightning strikes and fault conditions. The modeling work using CDEGS not only useful for providing more reliable data for further protection and mitigation techniques, but is also very versatile to study the effects of various other important factors affecting the induced voltage on the pipelines. </span>

Performance analysis study on state estimation in power distribution network

Online state estimation is becoming one of the key functions in deregulated distribution control centres. The bus voltages in the system are estimated from the measured values of feeder real and reactive power flows, etc. To reduce the metre cost, few actual measurements are carried out on the system through meter placement and the rest of the measurement need is satisfied by using pseudo-measurements, where estimation accuracy is often affected. To improve the estimation accuracy, the swarm tuned artificial neural network approach for bus voltage estimation in radial distribution systems is presented, which does not require pseudo-measurements. The back propagation neural network is trained by minimising the error function in a search space based on weights, tuned using particle swarm. The training data for the ANN is collected from real time monitoring of the test system through PSCAD simulation. The algorithm is tested to IEEE and TNEB network systems.

海底电缆–架空线B型混合线路行波故障测距新方法

分析了海底电缆–架空线混合线路发生故障以后行波的传播特性，并提出了一种针对海底电缆–架空线B型混合输电线路的行波测距方法。首先把原有的B型三段混合输电线路分解组合成两段A型混合输电线路，先利用每段A型混合线路两端监测装置监测到的故障初始行波浪涌到达监测点的时间差与整定时间进行比较，对故障区段初步判断，依据监测点接收行波的时间再根据单端原理得出准确的测距结果。此方法不但可以消除单端测距方法故障区段判别中对第二个波头性质的识别的难题，并且可消除双端测距方法计算故障距离时两端间不能精确同步和线路长度对测距结果的影响。PSCAD仿真实验表明，本文所提出的关于海底电缆–架空线混合输电线路故障行波测距方法是可靠的，且测距精度得到了有效提高。 After analyzing the propagation characteristics of the traveling wave after the failure of the sub-marine cable-overhead line hybrid line, a fault location method through traveling wave for the hybrid transmission line is proposed. First, the original B type hybrid transmission line is decom-posed into two hybrid transmission lines of type A. Then the time difference between the two monitoring device located in the endpoints of each A type hybrid line is used to make a preliminary judgment of the fault section. Finally an accurate fault location result is made according to the principle of single-end method. This method eliminates the difficult problem of the identification of the second wave heads in the single-end fault location method, and it also eliminates the influence of the out-sync of time and the influence of the line length which is given of the two double-end fault location method. PSCAD simulation experiments show that the presented the Fault Location Method through Traveling Wave for the Submarine Cable-Overhead Line Hybrid Line is reliable, and the accuracy of fault location has been effectively improved.

Short-circuit current calculation method for partial coupling transmission lines under different voltage levels

Abstract In power system, there are partial coupling lines under different voltage level because of the development of power system. When faults occur on these lines, zero-sequence mutual impedances bring difficulty to short-circuit calculation. To solve the problem, a new method is proposed in this paper. First, the three phase components are transformed to independent positive-sequence, negative-sequence and coupling zero-sequence components. Then the coupling zero-sequence is decoupled using the idea of six-sequence component method, namely recirculating current method. Finally, the system impedances and impedance of the non-coupling part are modified by comparing the relationship between sequence voltages and sequence currents of the newly defined decoupling method and symmetrical component method. According to the boundary condition, the composite sequence networks are obtained and the short-circuit current can be calculated easily. The PSCAD simulation result of short circuit analysis and calculation indicate that the proposed decoupling method for partial coupling line is appropriate. The short circuit calculation based on the decoupling method is easy to implement. The calculation method is practical and the calculation accuracy is not affected by fault type, different voltage grade and fault resistance.

Simple method of fast discharge of capacitor banks using delta connected transformers: modelling and experimental testing

The discharge of capacitor banks at substations is necessary before their connection to the grid can occur. This study investigates the use of delta-connected transformers for capacitor discharge. The energy from the capacitor banks is discharged by driving the transformers into saturation after disconnection from the grid. To investigate this, simulations were conducted in PSCAD to identify the relationship between the size of the transformer, the size of discharge resistor and the time taken for the capacitor bank to discharge. To confirm the accuracy of the PSCAD simulations, a scaled physical model was constructed in the laboratory and discharge results were recorded. A PSCAD simulation of the scaled model was also created to directly compare the accuracy of PSCAD. It was found that PSCAD produced accurate representations of the laboratory model, resulting in a greater confidence in the full-scale results.

Control of High-Frequency Isolated Modular Converter

Recently, voltage-source converter (VSC)-based high-voltage dc (HVDC) transmission systems have gained more attention. In this paper, a control method for a modular VSC-based HVDC transmission system with high-frequency isolation referred to as high-frequency isolated modular converter is proposed. In the high-frequency isolated modular converter configuration, several floating dc capacitors in all three phases are connected in series, and voltage balancing control of these floating dc capacitors is required. In this paper, an appropriate control structure with the capacitor voltage balancing controller is proposed. The proposed control scheme consists of three layers to control terminal dc bus voltage and balance dc capacitor voltages of each building block. Detailed PSCAD simulation results are presented to evaluate the performance of high-frequency isolated modular converter. Controller hardware-in-the-loop simulation of the high-frequency isolated modular converter is also performed by real-time digital simulator (RTDS), and RTDS results are presented to verify the control structure. Finally, laboratory-scale experimental results are presented to validate the proposed control method.

Efficient model for modular multi-level converter simulation

Detailed models of modular multi-level converters (MMCs) are cumbersome for electromagnetic transient simulation programs because of their high number of components which involve large simulation times. In this work, the modeling of an MMC is addressed with the objective of reducing the simulation time. First, the MMC structure is presented, including the modulation technique, the voltage balancing algorithm and the circulating current control used to validate the model. Next, an efficient simplified model is proposed. This is formed by just one variable voltage source, one variable capacitor and one variable resistor per arm, regardless of the number of submodules. This simplified model allows the simulation time to be reduced while keeping the dynamics of the MMC. The comparison through several PSCAD simulations with a detailed 5-level MMC model proves its validity during both steady-state and transient conditions (ac and dc short-circuits).

Three-Phase Steady-State Models for a Distributed Generator Interfaced via a Current-Controlled Voltage-Source Converter

This paper proposes three-phase steady-state models for a distributed generator (DG) interfaced to a main system via a three-wire current-controlled voltage-source converter. In order to represent the DG in a realistic manner, the three major factors that determine the steady-state phase outputs under unbalanced operating conditions are considered: 1) the power control strategy; 2) output filter; and 3) voltage and current sensor positions. Based on these factors, the DGs are classified into various types. According to the position of the voltage sensor, two equivalent circuit models including an equivalent three-phase current source (ETCS) are proposed. For each type of DG, the output current of the ETCS is formulated as a function of the voltage of the ETCS-connected node, the filter impedances, and the active and reactive power references. To verify the accuracy of the proposed models, the results of the power flow incorporating them are compared with those obtained from the PSCAD simulation using detailed dynamic models of the DG.

Power Loss and Junction Temperature Analysis in the Modular Multilevel Converters for HVDC Transmission Systems

The power loss of the controllable switches in modular multilevel converter (MMC) HVDC transmission systems is an important factor, which can determine the design of the operating junction temperatures. Due to the dc current component, the approximate calculation tool provided by the manufacturer of the switches cannot be used for the losses of the switches in the MMC. Based on the enabled probabilities of each SM in an arm, the current analytical models of the switches can be determined. The average and RMS currents can be obtained from the corresponding current analytical model. Then, the conduction losses can be calculated, and the switching losses of the switches can be estimated according to the upper limit of the switching frequency. Finally, the thermal resistance model of the switches can be utilized, and the junction temperatures can be estimated. A comparison between the calculation and PSCAD simulation results shows that the proposed method is effective for estimating the junction temperatures of the switches in the MMC.

Analytic Approximation of Fault Current Contribution From AC Networks to MTDC Networks During Pole-to-Ground Faults

HVDC short-circuit calculation standards will be required to simplify the dimensioning and selection of circuit breakers (CBs) in future HVDC networks. This paper proposes new analytical formulas for the calculation of the ac-side contribution through the blocked half-bridge-based converters during pole-to-ground faults in multiterminal HVDC cable networks. Analytic approximations are derived for the steady-state short-circuit currents and the peak of the transient response for point-to-point HVDC links and extended to multiterminal HVDC cable networks with arbitrary grid topology. The results of the proposed expressions are compared with simulations in PSCAD and provide accurate calculations for the transient peak and steady-state values of the ac-side fault current contribution to the prospective CB current.

Ultra-High-Speed Travelling Wave Protection of Transmission Line Using Polarity Comparison Principle Based on Empirical Mode Decomposition

The traditional polarity comparison based travelling wave protection, using the initial wave information, is affected by initial fault angle, bus structure, and external fault. And the relationship between the magnitude and polarity of travelling wave is ignored. Because of the protection tripping and malfunction, the further application of this protection principle is affected. Therefore, this paper presents an ultra-high-speed travelling wave protection using integral based polarity comparison principle. After empirical mode decomposition of the original travelling wave, the first-order intrinsic mode function is used as protection object. Based on the relationship between the magnitude and polarity of travelling wave, this paper demonstrates the feasibility of using travelling wave magnitude which contains polar information as direction criterion. And the paper integrates the direction criterion in a period after fault to avoid wave head detection failure. Through PSCAD simulation with the typical 500 kV transmission system, the reliability and sensitivity of travelling wave protection were verified under different factors’ affection.

Development of a Self-Healing Strategy to Enhance the Overloading Resilience of Islanded Microgrids

This paper proposes a self-healing strategy for two neighboring islanded microgrids (MGs) that are connected together through a normally open interconnecting static switch (ISS). Each MG is expected to support the other during power deficiencies, which is facilitated by the developed self-healing agent. This agent operates based on either a centralized approach, when data communication system is available, or a decentralized approach, when data communication system does not exist or is temporarily unavailable. The necessity and possibility of the MGs interconnection or isolation is determined based on instantaneous power generation of the distributed energy resources in both MGs (in the centralized approach) and local frequency measurements at either side of ISS (in the decentralized approach). The dynamic performance of the MGs with the proposed strategies is evaluated by PSCAD simulation studies. Furthermore, the stability of the system of coupled MGs is investigated through small-signal stability and modal analyses in MATLAB.

Research on the Voltage Interaction of Multi-Infeed HVDC System and Interaction Factor

In multi-infeed HVDC system, the interactions and influences between DC systems AC systems are complex as the electrical distances among DC converter stations which are relatively short. Multi-infeed interaction factor (MIIF) can effectively reflect the interaction among DC systems. The paper theoretically analyzes the impact factors of MIIF like the electrical distances between two DC converter stations and the equivalent impedance of the receiving end AC system. By applying the Kirchhoff’s current law on the inverter AC bus, the paper deduces the analytical expressions for MIIF. From the expression, it is clear how the equivalent impedance of AC system and coupling impedance can affect MIIF. PSCAD simulations validate the effectiveness and the correctness of the proposed expression and some useful conclusions are drawn.

Optimal IPFC damping controller design based on simplex method and self-tuned fuzzy damping scheme in a two-area multimachine power system

This paper develops a novel self-tuned fuzzy damping control scheme for an interline power flow controller (IPFC) to suppress the interarea mode of oscillations in a multimachine power system. The nonlinear adaptive damping controller is based on coordinated operation of two fuzzy inference systems. The first one produces the required $q$-axis voltage reference of the quasi multipulse series converter in response to generator angle oscillations, while the second one is used to tune the output of the first one online for further reducing the error signal using a given set of fuzzy rules. The simplex method is employed to search for optimal gains of the damping controller by minimizing the objective function in which speed deviations between generators are formulated. The feasibility of the proposed technique is validated using time-domain simulation cases in the PSCAD simulation program. It is also shown that the proposed damping scheme for IPFC works better than the static synchronous series compensator, which utilizes the same damping scheme in reducing the interarea mode of oscillations.

Battery Energy Storage System for PV Output Power Leveling

Fluctuating photovoltaic (PV) output power reduces the reliability in power system when there is a massive penetration of PV generators. Energy storage systems that are connected to the PV generators using bidirectional isolated dc-dc converter can be utilized for compensating the fluctuating PV power. This paper presents a grid connected energy storage system based on a 2 kW full-bridge bidirectional isolated dc-dc converter and a PWM converter for PV output power leveling. This paper proposes two controllers: a current controller using the d-q synchronous reference and a phase-shift controller. The main function of the current controller is to regulate the voltage at the high-side dc, so that the voltage ratio of the high-voltage side (HVS) with low-voltage side (LVS) is equal to the transformer turns ratio. The phase-shift controller is employed to manage the charging and discharging modes of the battery based on PV output power and battery voltage. With the proposed system, unity power factor and efficient active power injection are achieved. The feasibility of the proposed control system is investigated using PSCAD simulation.

Modular Transformer Converter-Based Convertible Static Transmission Controller for Transmission Grid Management

This paper investigates the concept of convertible static transmission controller (CSTC) using modular transformer converter (MTC) as the building block. The MTC is a bidirectional back-to-back ac/ac power conversion unit and the CSTC is a versatile transmission controller asset for dynamic power flow control and contingency management of the transmission grid. The proposed CSTC with new functions has several advantages compared to existing flexible ac transmission system controllers. System modularity for manufacturers and utilities/system operators using standard high power electronic systems is one of the advantages of this structure. In this paper, algebraic models of the CSTC are derived in two different operation modes (series-shunt and shunt-shunt connecting configurations). The proposed algebraic models are used to define the reference values for the CSTC converters based on the desired operating points for the meshed power system, the power transformers in particular. The dynamic performance of the CSTC with the proposed control structures and algebraic models will be investigated based on the PSCAD simulation. To prove the CSTC as a transmission asset and to verify the control structure and algorithm, ultrahigh fidelity controller hardware-in-the-loop testing has been conducted and comparative results will be presented. Finally, lab-scale experimental results are reported on the dynamic performance of the MTC-based CSTC.

LCL and L-VSC Converters With DC Fault Current-Limiting Property and Minimal Power Losses

This paper studies the methodologies for developing dc fault-tolerant and highly efficient voltage-source converters (VSCs). Building on a recently proposed LCL-VSC converter, which suffers from low efficiency at partial load, an operating strategy of switchable capacitor banks instead of a fixed central capacitor is proposed to improve the efficiency. A theoretical framework is presented to enable LCL-VSC to achieve fault current limiting and avoid the blocking of insulated-gate bipolar transistors during dc faults. A design of traditional L-VSC (either two level or multilevel) that can limit fault current is also mathematically deduced as a comparison. The L-VSC can be designed to limit the fault current close to rated value, but this comes at an increase of around 40% in semiconductor costs and operating losses. The results show that the efficiency of LCL-VSC is similar to the conventional L-VSC. LCL-VSC cannot isolate dc faults, but their reduced fault current enables the converter to ride through dc faults and this significantly reduces the requirements on operating speed and capacity of dc circuit breakers. The LCL-VSC is especially suitable to replace conventional L-VSC at the grid points where a strong ac grid will feed significant dc fault current to the dc grid. Detailed PSCAD simulations confirm theoretical findings.

Research on Chain SVG Direct Current Control Simulation Based on PSCAD

SVG is a device parallel on the power grid for dynamic reactive power compensation, is a product of best performance and mature technology in the third generation dynamic reactive compensation technology so far. Thanks to power unit module series structure and PWM technology, compared with multiple SVG, chain SVG has high capacity, low loss, simple maintenance. But more complicated in control, indirect current control technology and direct current control technology are adopted. This paper utilizes PSCAD simulation software to build a chain SVG direct current controller model according to mathematical model of the chain SVG, simulates SVG compensation with inductive load and capacitive load, so as to verify advantages of fast tracking speed and stable control of direct current controller.

Simulation Realization of LV SVG Control Algorithm Based on EMTDC and C Language Mixed Programming

EMTDC is grid simulation analysis software that is capable of modeling for complex electrical and electronic devices, controllers and non-linear network. PSCAD is a user graphical interface of EMTDC. In PSCAD environment, functional modules can be taken from the element library conveniently to set up a complete set of LV SVG control system for simulation study of operation performances under various work conditions. However, the control program of LV SVG in actual application is written in C language, which has great differences from some functional modules in PSCAD simulation module in terms of data processing approach and calculation precision, so there is a huge gap from the simulation result and the actual result.In this paper, Fortran language is used to write interface function. Control program written in C language is embedded into the simulation module set up by EMTDC. An experiment shows that the simulation model built by EMTDC and C language mixed programming has higher precision than ordinary simulation module, and can be transplanted among LV SVG controllers, so it’s more practical.

PIR Regulator Using DTC for DFIG during Unbalanced Grid Voltage Conditions

This paper presents a PIR regulator using direct torque control strategy of grid connected wind turbine driven doubly fed induction generators (DFIGs) when the grid voltage is unbalanced. Under the unbalanced grid voltage condition, the stator voltage and current quality is strongly affected due to the negative and distorted components. It will be reducing the performance of other normal loads connected to the DFIG. That control scheme consisting of indirect matrix converter using DTC. To verify the value of the proposed control strategy, simulation results with 500 MVA DFIG topology are presented and discussed in the paper. Finally,the simulation studies are carried out on a 500 MVA wind-turbine driven DFIG system under unbalanced grid voltage conditions. All the results are validated by using PSCAD simulation.