Thevenin Equivalent Research Articles

Harmonic Issues Assessment on PWM VSC-Based Controlled Microgrids Using Newton Methods

This paper presents the application of Newton-based methods in the time-domain for the computation of the periodic steady state solutions of microgrids with multiple distributed generation units, harmonic stability, and power quality analysis. Explicit representation of the commutation process of the power electronic converters and closed-loop power management strategies are fully considered. Case studies under different operating scenarios are presented: grid-connected mode, islanded mode, variations in the Thevenin equivalent of the grid and the loads. Besides, the close relation between the harmonic distortion, steady state performance of the control systems, asymptotic stability, and power quality is analyzed in order to evaluate the importance and necessity of using full models in stressed and harmonic distorted scenarios.

Thévenin Equivalent of Voltage-Source Converters for DC Fault Studies

This paper presents a simple modulation index-dependent Thevenin equivalent circuit model of the voltage-source converters (VSCs) and the associated anti-parallel diode rectifier. The model derivation uses orthogonal transformation and a transformer analogy to transfer impedances to the dc side of the converter. The paper proposes a switched equivalent representation of a three-phase diode rectifier formed due to the antiparallel diodes when VSC switching is inhibited. The proposed model is implemented in Alternate Transients Program–Electromagnetic Transients Program and simulation results are compared with the switched model. The proposed model is shown to under predict the fault currents for pole-ground (PG) faults and to provide a nearly exact match for pole-pole faults. The rectifier equivalent provides increased accuracy in the transient region with the inclusion of the source inductance. A multiterminal dc (MTDC) system model is used to study effects of aggregation which gives increased accuracy of the equivalent circuit. It is shown that the MTDC system simulation with the proposed Thevenin equivalent is about 3 times faster than full-switched circuit simulation for a time step of 5 $\mu$ s. The MTDC system simulation with the Thevenin equivalent circuit is still accurate and 126 times faster when the time step is increased to 750 $\mu$ s.

Application of Electromagnetic Transient-Transient Stability Hybrid Simulation to FIDVR Study

This paper deals with the development of a new electromagnetic transient (EMT)-transient stability (TS) hybrid simulation platform and its application to a detailed fault-induced delayed voltage recovery (FIDVR) study on the WECC system. A new EMT-TS hybrid simulation platform, which integrates PSCAD/EMTDC and the open source power system simulation software InterPSS has been developed. A combined interaction protocol with an automatic protocol switching control scheme is proposed. A multi-port three-phase Thevenin equivalent is developed for representing an external network in an EMT simulator. Correspondingly, the external network is represented in three-sequence, and a three-sequence TS simulation algorithm is developed. These techniques allow simulation of unsymmetrical faults within the internal network without the constraint of phase balance at the boundary. The effectiveness of the proposed techniques is first tested on the IEEE 9-bus system. Subsequently, the proposed hybrid simulation approach is applied to a detailed FIDVR study on a large WECC system. The study shows that a normally cleared single-line-to-ground (SLG) fault in the transmission system could lead to an FIDVR event, with compressor motors of the air conditioning units on the faulted phases stalling first, followed by a propagation of motor stalling to the unfaulted phase. Moreover, similar events are observed in simulations with a wide range of load compositions. Lastly, the effect of the point-on-wave (POW) at which a fault is applied on the occurrence of an FIVDR event is also analyzed.

Utilization of Events Measured by WAMS-BIOZE-Detector for System Voltage Stability Evaluation

Abstract: The paper summarizes results of research work focused on development of the voltage stability assessment method and its software implementation. Developed voltage stability detection algorithm is based on local synchronous phasor measurement. The Thevenin equivalence based assessment method, the identification algorithm as well as the developed WAMS-BIOZE-Detektor software are presented. The proposed voltage stability indices have different sensitivity to events in power systems. Sensitivity of the indices was tested by using records of various disturbances and failures in a HV grid. Test results validate applicability of the indices in practice. Finally, the index with the highest applicability for online detection is recommended.

Solar Irradiance Estimation of Photovoltaic Module based on Thevenin Equivalent circuit Model

Abstract— This Paper presents an accurate method for estimation of solar irradiance of a PV module. The solar irradiance estimation method is derived using the efficient approximation of a PV model based on Thevenin equivalent circuit . The short linear combination of exponential function is used for constructing a mathematical function that is used to express the Thevenin voltage source of a PV panel. The proposed algorithm for estimation of solar irradiance use Newton Raphson method based on extensively analysis of a photovoltaic mathematical model and it is applied for a wide range of operating point variations . The proposed method has the ability to estimate the parameters, which are required for constructing the mathematical model of a PV in addition to estimate the solar irradiance . The accuracy and effectiveness of the proposed algorithm is demonstrated in MATLAB for a photovoltaic panel by using experimental data which is obtained from data sheet under different operating conditions. Index Terms— photovoltaic modeling; pyranometer; solar irradiance Photovoltaic Model; Thevenin equivalent circuit System; Exponential sum models.

A Robust Approach for the Analysis of EMI/EMC Problems With Nonlinear Circuit Loads

The analysis of electromagnetic coupling in nonlinear circuit simulations requires a bidirectional, fully consistent approach. Nonlinear responses of semiconductor devices in electronic circuit components can change the impedances seen at circuit nodes, changing the boundary conditions encountered by impressed electromagnetic fields and, thus, changing the characteristics of the energy coupled from these external fields into that circuit. It is important to include the coupling in the circuit simulation self-consistently because this allows us to accurately predict the responses to various EMI/EMC problems of interest. It is also important to predict circuit responses efficiently because that opens the door to statistical applications for the technique being used. In this paper, we review a technique that we have developed called A Thevenin Equivalent Network Approach. This approach is shown to be quite robust in that it is computationally efficient; it can be implemented in a variety of commonly available circuit solving codes; it already includes a few additional techniques required to enhance its implementation in those codes; and it is quite accurate.

Impact of current controller dynamics in small signal stability analysis of two terminal VSC-HVDC system employing grid voltage vector orientation control

Summary Small signal stability model of two terminal voltage source converter based high voltage direct current link connected to the thevenin equivalent of the power system is presented in this paper. The dynamic equations of the thevinised alternating current system, direct current link, and the controllers are integrated to form the state space model. The impact of current controller dynamics and short circuit capacity of the power system on the controller gains are analyzed. The loci of the eigenvalues are traced to determine the optimal set of gain parameters. The most critical modes are identified and depending upon the sensitivity of the controller parameters to various modes, a sequential tuning methodology is proposed. The analysis reveals that d-axis current controller of inverter side needs to be fast when compared with the rest of the current controllers. The results obtained are validated using optimization technique and time-domain analysis. Copyright © 2015 John Wiley & Sons, Ltd.

Hybrid voltage stability assessment (VSA) for N − 1 contingency

With the growing deployment of phasor measurement units (PMUs), measurement-based voltage stability assessment (VSA) that estimates the system Thevenin equivalent has been widely discussed in recent years. This approach attracts favorable attentions mainly for its simplicity and great potential in real-time applications, as opposed to the continuation power flow (CPF) method which is model-based VSA. However, the existing measurement-based VSA deals with the normal case, but not any contingency case because there is no measurement data for a contingency case which is hypothetical. With this motivation, a hybrid VSA method is proposed based on both model-based and measurement-based techniques. First, an enhanced model-based sensitivity analysis estimating the post-contingency status is proposed, and then it is combined with the measurement-based Thevenin equivalent approach. The proposed sensitivity analysis has the feature of simplicity, which is aligned with the measurement-based Thevenin equivalent. Test results with the IEEE 14, 39, and 118-bus systems show that the proposed sensitivity is highly accurate in estimating N−1 contingency system variables and the proposed hybrid VSA method for N−1 contingency captures the insecure contingencies successfully. The proposed method greatly broadens the practical application of PMUs for VSA under N−1 contingency.

Solar Irradiance Estimation of Photovoltaic Module based on Thevenin Equivalent circuit Model

Solar Irradiance Estimation of Photovoltaic Module based on Thevenin Equivalent circuit Model

A Fully Adaptive PMU-Based Fault Location Algorithm for Series-Compensated Lines

This paper presents a fully adaptive fault location algorithm for series-compensated lines (SCLs) based on synchronized phasor measurements obtained by phasor measurement units (PMUs). The proposed algorithm does not require any knowledge on the exact model of the series-compensation device and, therefore, can be applied to transmission lines with any type of series compensation. In addition, the proposed algorithm utilizes only PMU synchronized measurements and does not require any data to be provided by the electric utility. The SCL parameters and Thevenin's equivalent (TE) of the system at SCL terminals are determined online, utilizing three independent sets of pre-fault PMU measurements, to ensure considering the actual operating conditions of the system. Fault-location accuracy evaluation of the proposed algorithm is performed with respect to various factors such as fault position, fault type, fault resistance, fault inception angle, pre-fault loading and line compensation degree. The proposed algorithm is simulated using both PSCAD/EMTDC and MATLAB and tested on a 400-kV system. Simulation results revealed that the developed algorithm is capable of producing reliable and highly accurate solutions.

EMI Behavioral Models of DC-Fed Three-Phase Motor Drive Systems

Behavioral electromagnetic interference (EMI) models based on Thevenin equivalents are proposed for a dc-fed three-phase motor drive system. Both common-mode (CM) and differential-mode (DM) noise models are developed to accurately predict the total EMI noise in accordance with the DO-160 standards for aerospace applications. Beyond the switching frequency of the drive, the CM noise model is found to behave like a two-port linear network and is shown to predict changes in the input-side EMI due to any changes in the load-side parameters or vice versa. Simplified one-port behavioral models for DM noise are then used to predict the total noise at both input and output side of the motor drive. Such models can be very useful in system level EMI analysis and also in understanding how EMI filters and harnesses affect the overall EMI in a motor drive system. The models run in the frequency domain and are validated with experiments up to 30 MHz.

Thevenin Equivalents of Some Interesting Networks with Dependent Sources

ABSTRACTThis paper presents two classes of networks whose Thevenin equivalents are interesting. One class of networks is without any independent source. The other class has loop or node method-based delta 0. If proper care is not taken, then their Thevenin equivalent resistances may result in indeterminate forms. A method, which not only leads the correct value instead of such indeterminate forms but also is efficient, is proposed. It is illustrated with two examples.

An adaptive fault location algorithm for power system networks based on synchrophasor measurements

This paper presents an adaptive fault location algorithm for power system networks based on synchronized phasor measurements obtained by Phasor Measurement Units (PMUs). To enhance its accuracy, the proposed algorithm is made to be independent of any data that shall be provided by the electric utility. The proposed algorithm requires three different sets of pre-fault voltage and current phasor measurements at both terminals of the faulty line to be obtained through PMUs. The three sets of local PMU measurements at each terminal are used for online calculation of the respective Thevenin's equivalent (TE). Using the method of multiple measurements with linear regression (MMLR), the three sets of PMU measurements are also employed for online calculation of the transmission line parameters. Online determination of the TEs and line parameters ensures avoiding any possible mismatch with the actual parameters due to system loading and other environmental conditions. The proposed method is applied to a 115kV system selected from the Saudi Electricity Company (SEC) network. The simulation results obtained using PSCAD/EMTDC and MATLABreveal that the proposed algorithm is highly accurate and independent of fault type, fault location, fault resistance, fault inception angle and pre-fault loading.

Simulación del compensador estático de VAR de la subestación Culiacán Tres para el análisis de transitorios

Since its emergence in the late 60's the FACTS (Flexible AC Transmission Systems) have been and continue to be studied and implemented in all electrical networks around the world, becoming an essential element for stability, control and maximum exploitation of thereof. One of the most used FACTS devices is the Static VAR Compensator or SVC. In this work, the modeling in Simulink of the Static VAR Compensator installed at the substation Culiacán Tres (CUT) belonging to CFE is presented. The SVC is the ability of ±100 MVAR and ABB brand. The modeling was performed to visually program in detail the different subsystems in Simulink such as the timing unit, the TSC (thyristor switched capacitor), TCR (thyristor controlled reactors), filters of the 5th and the 7th harmonic, the transformer bank, the control unit, distribution unit and the measurement unit. Data for major components were taken from data sheet and equipment manuals. ASPEN software was used in order to obtain Thevenin equivalent of the EPS to connect to them the SVC model to test the step and three-phase short circuit. The results of these tests were compared with test results of commissioning of the SVC.

A New Method for Monitoring Local Voltage Stability using the Saddle Node Bifurcation Set in Two Dimensional Power Parameter Space

This paper proposes a new method for monitoring local voltage stability using the saddle node bifurcation set or loadability boundary in two dimensional power parameter space. The method includes three main steps. First step is to determine the critical buses and the second step is building the static voltage stability boundary or the saddle node bifurcation set. Final step is monitoring the voltage stability through the distance from current operating point to the boundary. Critical buses are defined through the right eigenvector by direct method. The boundary of the static voltage stability region is a quadratic curve that can be obtained by the proposed method that is combining a variation of standard direct method and Thevenin equivalent model of electric power system. And finally the distance is computed through the Euclid norm of normal vector of the boundary at the closest saddle node bifurcation point. The advantage of the proposed method is that it gets the advantages of both methods, the accuracy of the direct method and simple of Thevenin Equivalent model. Thus, the proposed method holds some promises in terms of performing the real-time voltage stability monitoring of power system. Test results of New England 39 bus system are presented to show the effectiveness of the proposed method.

Online Overvoltage Prevention Control of Photovoltaic Generators in Microgrids

For grid-connected microgrids with high penetration of photovoltaic (PV) generation, overvoltage caused by reverse power flow is a major factor that limits PV power output. To tackle the challenge, this paper proposes a new online overvoltage prevention (OOP) control strategy to maintain PV terminal voltages within specified range while maximizing the PV energy yields. The proposed method is based on a precise active power limit prediction using the dynamic Thevenin equivalent. The active power output of PV array can be modulated in real time such that the voltage at a point of interconnection (POI) is always maintained within a specified range without triggering overvoltage protection. Simulation results using the IEEE 33-bus single-phase test system and IEEE 34-bus three-phase system have validated the effectiveness and accuracy of the proposed control method.

A New Method for Static Voltage Stability Assessment based on The Local Loadability Boundary

Abstract This paper proposes a new method for assessing static voltage stability based on the local loadability boundary or P- Q curve in two dimensional power parameter space. The proposed method includes three main steps. The first step is to determine the critical buses and the second step is building the local loadability boundary or the saddle node bifurcation set for those critical buses. The final step is assessing the static voltage stability through the distance from current operating point to the boundary. The critical buses are defined through the right eigenvector by direct method. The boundary obtained by the proposed method that is combining a variation of standard direct method and Thevenin equivalent model of electric power system is a quadratic curve. And finally the distance is computed through the Euclid norm of normal vector of the boundary at the closest saddle node bifurcation point. The advantage of the proposed method is that it keeps the advantages of both efficient methods, the accuracy of the direct method and simple of Thevenin Equivalent based method. Thus, the proposed method holds some promise in terms of performing the real time voltage stability assessment of power system. Test results of New England 39 bus system are presented to show the effectiveness of the proposed method.

Real-time electromagnetic transient simulation algorithm for integrated power systems based on network level and component level parallelism

The analysis and simulation of power system are becoming more and more challenging as the complexity of system topology and components has been increased. In this paper, a hybrid parallel algorithm is proposed for the real-time electromagnetic transient simulation (EMTS) of integrated power systems containing multiphase machines. The proposed algorithm is composed of a novel network partition method called component level parallelization and the Multi-Area Thevenin Equivalent (MATE) method, which extends the flexibility of the network partition in parallel simulation. Moreover, several methods are developed to enhance the efficiency of the communication and computation. Power systems with up to 410 single-phase electrical nodes and 336 switches are simulated in a time step of 50 μs to validate the proposed algorithm.

Improvement of Thevenin Equivalent Parameters and Computations

In this paper, the conventional method to acquire Thevenin equivalent parameters is described. The method is based on features of power systems and utilizes the base-case system information. Considering the impact of loads on Thevenin equivalent potential and impedance, this paper makes improvements and brings it closer to the actual situation. The necessary condition about limit power transmission is derived, and the impedance modulus margin can be used to determine voltage stability of power system. Finally, the results of IEEE-14 bus system calculations show effectiveness of the method.

Application of an impedance matching transformer to a plasma focus

A plasma focus was constructed using an impedance matching transformer to improve power transfer between the pulse power and the dynamic plasma load. The system relied on two switches and twelve transformer cores to produce a 100 kA pulse in short circuit on the secondary at 27 kV on the primary with 110 J stored. With the two transformer systems in parallel, the Thevenin equivalent circuit parameters on the secondary side of the driver are: C = 10.9 μF, V(0) = 4.5 kV, L = 17 nH, and R = 5 mΩ. An equivalent direct drive circuit would require a large number of switches in parallel, to achieve the same Thevenin equivalent. The benefits of this approach are replacement of consumable switches with non-consumable transformer cores, reduction of the driver inductance and resistance as viewed by the dynamic load, and reduction of the stored energy to produce a given peak current. The system is designed to operate at 100 Hz, so minimizing the stored energy results in less load on the thermal management system. When operated at 1 Hz, the neutron yield from the transformer matched plasma focus was similar to the neutron yield from a conventional (directly driven) plasma focus at the same peak current.