Power System Voltage Research Articles

Assessment of the voltage stability index of electric networks supplying charging stations using a multilayer perceptron

Ensuring power system voltage stability is one of the key challenges in power system planning and operation. At the moment, as a result of a number of technological incidents in the form of a violation of the stability of the voltage of the power system, multilayer perceptrons were tested on the territory of various countries.PURPOSE. Development of an intelligent approach to assessing the Load Stability Index (LSI) in the power system using computational intelligence methods (neural networks).METHODS. In the course of these studies, a method for estimating the ISI was used, which is used to monitor the stability of voltage in the power system using the "Smart Park" calculation method.RESULTS. The results of providing the development stage are obtained, which substantiate the possibility of using the Multilayer Perceptron (MLP) for estimating the IEL with a high degree of accuracy.CONCLUSION. In the course of these studies, the authors of the article put forward the following conclusions: an approach based on a multilayer perceptron (MPP) neural network with feed-forward is presented; an assessment of the ISI was carried out on the example of a power system using the calculation method "Smart Park"; the presented neural network approach does not depend on the open-circuit voltage on a particular load bus; the presence of indicators of active power, reactive power and voltage on the load bus is sufficient to assess the IPL; The MSP approach allows for an accurate assessment of the ISI even when the topology and operating conditions change. The obtained indicators can be applied in changing the methodology for assessing the stability of voltage in electrical systems and complexes and calculating their operating modes.

Analisis Pengaruh Penambahan Gardu Induk Terhadap Aliran Daya dan Profil Tegangan

Addition of the Guluk-Guluk Substation, it will affect the flow of power and voltage in the electric power system. Based on the analysis of normal conditions before and after the Guluk-Guluk Substation in terms of the voltage value on each connected bus, it is still within the permitted limits, while the contingency ranking calculation using the Voltage Performance Index (PIv) method can determine contingency conditions N-1 to N -3 before and after the Guluk-Guluk Substation. In this case, it was found that during the contingency conditions N-1 to N-3 before the Guluk-Guluk Substation there was a decrease in the value of the voltage which was still within the permissible limits, but in the N-3 contingency there was also an overload on the line due to the release of two generator units and one channel. After the existence of the Guluk-Guluk Substation, during the N-1 to N-2 contingency conditions the voltage value was still within the permissible limits, but the voltage drop that occurred was bigger than the condition before the Guluk-Guluk Substation. For the N-3 contingency condition the voltage value does not meet the standard due to overload on the Ujung Substation - Bangkalan Substation line and the lack of power flow.

Identification of the Harmonic Composition of Currents and Voltages in an Autonomous Power System with Unstable Current Frequency

Identification of the Harmonic Composition of Currents and Voltages in an Autonomous Power System with Unstable Current Frequency

Research on Influence of Battery Energy Storage System on Voltage Transient Stability

In view of the current transient stability of the grid voltage, this paper studies the reactive power support of the access point when the energy storage system is connected to the power grid by studying the four-quadrant working mode of the energy storage system. Using the energy storage system built in the Power System Analysis Software Package PSASP and the CEPRI36 node example, the transient stability changes of the power system voltage before and after the energy storage connection are simulated and compared. The results show that the energy storage has a restraining effect on the voltage fluctuation.

Evaluation of the VLSS-LMS Method Parameters’ Influence on the Effective Estimation of Power System Current and Voltage Harmonics Content

Nowadays, power quality is considered as a major concern that is faced by electrical energy producer, consumers, industries and researchers. Whereas one among the main issues in such concern is the current and voltage harmonics detection, mitigation and compensation. Indeed, the proliferation of harmonics in power system can create serious problems within all levels and their impacts along the whole power system from the production to the end users can lead to critical technical and economic situations. Therefore, their accurate detection in real time is of great importance and interest where many techniques have been proposed for solving such major problem. The work presented in this paper deals with the evaluation of a technique that has been proposed for the estimation of harmonic content in a signal based on iterative computing technique. This technique is based on several keystone parameters, which have major influences on the accuracy of the identification of the different harmonics without the need of a costly computation, and that can be easily implemented and performed in real-time. It is worthy to clarify that the technique under investigation in this paper is the based on the idea of adaptive filtering process called the Variable length Step Size- Least mean squares method (VLSS-LMS), it is basically very sensitive to three main parameters such as the sampling frequency, the step size value and the measurement window. The evaluation of the effects of these parameters have been assessed based on simulation testes of a specific original signal containing harmonics components. The obtained simulation results clearly prove the optimal choices of the aforementioned parameters in ensuring precise estimation of the harmonics content and the reconstruction of the estimated signal with high precision and minimized average error.

Dynamic Phasor Model of Grid-Connected Photovoltaic System in MATLAB/Simulink Considering Low Voltage Ride through Characteristics for Voltage Stability Analysis of Power System

This paper proposes a model of grid-connected photovoltaic (PV) system with low voltage ride through (LVRT) characteristic in MATLAB/Simulink based on dynamic phasor approach. Unlike all PV system models available in MATLAB/Simulink using detailed model with small capacity, the proposed model focuses on control loops of PV system to simulate a large capacity system that is appropriate for voltage stability analysis of power system installing high penetration level of PV generation. An intuitive and convenient tool for adjusting the LVRT characteristics of the PV system is also developed. The effectiveness of dynamic phasor model and the impact of the LVRT characteristic of the PV system on voltage stability are examined through MATLAB/Simulink simulations conducted on IEEE 9-bus test system. The simulation results provide an insight of how the system integrated with a large PV generation behaves under the disturbances. It also points out that the LVRT of the PV system is very important to the power system voltage stability.

Probabilistic Load Shedding Scheme for Power System Voltage Stability Enhancement Using Discrete Group Search Optimization Algorithm

This paper presents a discrete heuristic algorithm to improve voltage stability margins of the power system, during under frequency conditions. Discrete group search optimization algorithm is proposed for the first time in this work and applied to a load shedding problem. Sometimes, after initial frequency drop following severe disturbances, the system frequency might return to its acceptable value, however, the system might become unstable due to voltage problems. This paper proposes discrete group search optimization algorithm to solve the load shedding problem as well as returning system frequency to the acceptable range. The objective of proposed method is to enhance voltage stability margins of the power system. Furthermore, in the paper the load uncertainty as the most critical source of uncertainty in power system is handled using point estimation approach. The proposed method is implemented on the modified IEEE 14-Bus test system as well as 39 bus New England Network to demonstrate its applicability and effectiveness. The performance of discrete group search optimization method is also compared with several methods in terms of enhancing voltage stability margins. The results confirm that the proposed method provides a considerable enhancement in the power system voltage stability margin.

Deep learning-driven evolutionary algorithm for power system voltage stability control

The voltage stability problem has strong nonlinearity and sensitive to dimensionality, which makes it hard to balance accuracy and efficiency in its control. To enhance voltage stability margin (VSM) precisely and rapidly, a surrogate control algorithm with back propagation neural network (BPNN) embedded is carried out. Firstly, BPNN is adopted to parameterize a nonlinear voltage stability boundary mapped by operational variables. Further, benefited from the speed and precision ability of BPNN calculation, BPNN is embedded into preventive control model to replace the time-consuming calculation process of VSM. In doing so, an efficient and nonlinear simplified control model oriented to voltage stability can be constructed to enable efficiency for load margin enhancement. Besides, non-dominated sorting genetic algorithm (NSGA-II) is proposed to solve the VSM control model with the advantages of fast running speed and good convergence of solution set. At last, numerical studies on 118-bus systems testify that BPNN can achieve VSM evaluation with high accuracy and rapidly assist in NSGA-II improving the static voltage stability margin.

2모선 Voltage-Power Formula를 이용한 배전선로 두 P-Q 부하점의 전압계산

For a distribution power system, the load connected to a load point is represented by kVA or P+jQ form in general. Existing methods for calculation of bus voltages in a power system include power flow computation, Ohmic method, PU method, Equivalent resistance method and etc. The Equivalent resistance method yields a fairly reliable solution and has been widely used for calculation of voltages in distribution power systems, however, the method requires the loads to be represented by constant current form. Calculation by Equivalent resistance method is very simple when the loads are given current form, however, it becomes much complicated when the loads are given kVA or P+jQ form, This paper presents a new voltage calculation using two-bus Voltage-Power formula and illustrates an example calculation for a distribution line with two P-Q load points, to compare with existing methods.

Impact of Probabilistic Modelling of Wind Speed on Power System Voltage Profile and Voltage Stability Analysis

Wind speed characteristics may have a significant impact on the power system operation, stability and dynamics. Hence, appropriate modelling and quantification of wind probability distribution function (PDF) are critical for probabilistic power system analysis. Weibull distribution is the most widely used PDF for power system (particularly power system stability) studies, which might not be a valid PDF for different wind regimes having high, average, and low wind speed data. In this study, twenty different wind speed datasets (each dataset is different based on the location, duration, and resolution) have been collected and analysed with eight PDFs to model the wind speed to replicate different wind speed characteristics. The PDFs include Rayleigh, Weibull, Gamma, Lognormal, Normal, Inverse Gaussian, Generalized Extreme Value, and Exponential distributions. Root mean square error (RMSE) and the coefficient of determination (R2) are applied as the measure of accuracy. The obtained results show that the locations, duration, and resolution have a notable impact on the selection of suitable PDFs. It was found that the Gamma distribution is the best-suited PDF for representing low wind speed data. In comparison, the Weibull distribution represents the best PDF for high wind speed data. Also, the selection of the Gamma PDF for low wind speed data and Weibull distribution for high wind speed data is further validated by presenting voltage profile and voltage stability analysis. Study outcomes would assist power system planners to select the appropriate PDF for power system stability studies based on the characteristics of the available wind speed dataset.

Norton’s current theorem based online voltage stability analysis for wind connected power grid

The impact of wind power integration on power system voltage stability has received extensive attention recently. A new voltage stability H-index based on the Norton’s current distribution law is established, which could be quickly calculated by phasor measurement unit (PMU) data. For steady-state analysis, the voltage stability margin could be directly assessed by computing the difference between H-index and 1. Applicability of the proposed H-index is validated in the case of reverse power flow, i.e. the active power is transmitted from wind farms to the point of common coupling (PCC). Then, the characteristics of H-index with increased wind power are analyzed. Based on the relationship between H-index and wind farm current injection, an online voltage stability monitoring method is presented. In this monitoring process, three important currents are proposed to be mainly monitored along with the H-index, namely the ‘worry current’, ‘transition current’ and ‘limit current’. Therefore, the voltage stability analysis and control strategies can be implemented according to the monitored currents and H-index. Effectiveness of the proposed online voltage stability analysis method is further verified by simulation results performed in an improved 39-bus system.

Development of Broadband Resistive–Capacitive Parallel–Connection Voltage Divider for Transient Voltage Monitoring

The on-site measurement of transient voltages is of great significance in analyzing the fault cause of power systems and optimizing the insulation coordination of power equipment. Conventional voltage transformers normally have a narrow bandwidth and are unable to accurately measure various transient voltages in power systems. In this paper, a wideband parallel resistive–capacitive voltage divider is developed, which can be used for online monitoring of transient voltages in a 220 kV power grid. The structures of the high-voltage and low-voltage arms were designed. The internal electric field distribution of the high-voltage arm was analyzed. The influence factors and improvement techniques of the upper frequency limit were studied. The parameters of the elements of the divider were determined. The voltage withstand performances and scale factors under lightning impulses and AC and DC voltages, the temperature stabilities of scale factors and the step response and bandwidth of the developed voltage divider were tested. The results show that the deviations of the scale factors under various voltage waveforms and different temperatures ranging from −20 to 40 °C are within 3%. The withstand voltage meets the relevant requirements specified in IEC60071-1-2011. The step response 10~90% rise time is approximately 29 ns, and the 3 dB bandwidth covers the range of DC to 10 MHz.

Impact of energy storage and flexible alternating current transmission devices in combined voltage and frequency regulation of multiarea multisource interconnected power system

AbstractThis article emphasizes the impact of coordinated energy storage (ES) and flexible alternating current transmission (FACTS) devices in the combined voltage and frequency control of multi‐area systems having hydro, thermal, geothermal, and solar thermal power plants. Appropriate realistic constraints are equipped with both hydro and thermal units. A novel fuzzy logic controller‐based cascade PI and PID with filter coefficient (N), FCPI‐PIDN controller is proposed and optimized various controller parameters using artificial flora algorithm. Comparative analysis of FCPI‐PIDN, Cascade PI and PIDN (CPI‐PIDN), and PIDN controllers show the superiority of the FCPI‐PIDN controller to others. Integration of ES devices (ESDs), such as redox flow battery (RFB), capacitive energy storage (CES), and superconducting magnetic energy storage (SMES) indicates that the incorporation of ESDs enhance the system performance and RFB is superior to SMES and CES. Moreover, integration of FACTS devices, such as interline power flow controller (IPFC), thyristor control series capacitor (TCSC), and unified power flow controller (UPFC) indicates the incorporation of FACTS devices improve the system dynamic and coordination of IPFC‐RFB provide better response than TCSC‐RFB and UPFC‐RFB. Investigation reveals that the optimal location of RFB is Area 1 and IPFC is in between Areas 1 and 3. Sensitivity analysis validated the robustness of the FCPI‐PIDN controller.

Consensus Admm-Based Distributed Mpc Applied to Voltage and Frequency Control in Power Systems

Consensus Admm-Based Distributed Mpc Applied to Voltage and Frequency Control in Power Systems

On Ensuring Dynamic Stability of Voltage in Electric Power Systems under Critical Loads

On Ensuring Dynamic Stability of Voltage in Electric Power Systems under Critical Loads

Theory and Experimental Validation of Two Techniques for Compensating VT Nonlinearities

Inductive instrument transformers (ITs) are still the most used voltage and current sensors in power systems. Among the numerous applications that require their use, one of the most important is surely represented by harmonics measurement. In this case, the recent literature shows that, since they suffer from both a filtering behavior due to their dynamics and from nonlinear effects produced by their iron core, they can introduce errors up to some percent. This article wants to deeply investigate, in the very same experimental conditions, about the performance of two digital signal processing techniques, recently introduced for the improvement of harmonics measurements performed through ITs, namely, SINusoidal characterization for DIstortion COMPensation (SINDICOMP) and compensation of harmonic distortion through polynomial modeling in the frequency domain (PHD). These methods have been applied to two different voltage transformers, having different specifications, by using two measurement setups based on different architectures. The impact of the voltage generator employed during the identification on the achieved accuracy is theoretically and experimentally evaluated. Modified versions of SINDICOMP and PHD compensation, which are more robust against nonidealities of the measurement setup, are presented. The performances of the techniques are evaluated by adopting voltage waveforms similar to those that can be encountered during the normal operation in a real distribution grid.

Accelerated Derivative-Free Deep Reinforcement Learning for Large-Scale Grid Emergency Voltage Control

Load shedding has been one of the most widely used and effective emergency control approaches against voltage instability. With increased uncertainties and rapidly changing operational conditions in power systems, existing methods have outstanding issues in terms of either speed, adaptiveness, or scalability. Deep reinforcement learning (DRL) was regarded and adopted as a promising approach for fast and adaptive grid stability control in recent years. However, existing DRL algorithms show two outstanding issues when being applied to power system control problems: 1) computational inefficiency that requires extensive training and tuning time; and 2) poor scalability making it difficult to scale to high dimensional control problems. To overcome these issues, an novel derivative-free DRL algorithm named PARS was developed and tailored for power system voltage stability control via load shedding. The method was tested on both the IEEE 39-bus and IEEE 300-bus systems, and the latter is by far the largest scale for such a study. Test results show that, compared to other methods including model-predictive control (MPC) and proximal policy optimization(PPO) methods, PARS shows better computational efficiency (faster convergence), more robustness in learning, excellent scalability and generalization capability.

Frequency Optimization of PZT-FBG Voltage Sensor Based on Temperature-Independent Demodulation Method

Fiber grating sensors have been widely used in industry and has been an important research topic in power systems due to their small size, satisfactory electric shielding ability, and high compatibility with optical fibers. Voltage is a crucial parameter that must be monitored in the power system. Existing PZT-FBG voltage sensors are small, inexpensive, and present acceptable linearity in the range of 50 Hz-20 kHz. However, voltages in power systems cover signals with a frequency from DC to MHz and the existing frequency range is insufficient. Finite element method is adopted to improve frequency characteristics of the PZT-FBG sensor and choose the optimal basic structure by initially calculating resonant frequencies. Structural parameters are then selected via dielectric spectrum analysis. The test platform is established to verify amplitude response, frequency response, three-wave response, temperature characteristics, and impulse voltage response of the frequency-optimized PZT-FBG sensor. Test results showed that the sensor presents satisfactory linearity and the temperature-independent demodulation method improves its stability with temperature changes. Impulse voltage tests indicated that the sensor can respond to impulse waveforms with a wave front time of 250 and 10 μs. Hence, the sensor can respond to a voltage signal of 100 kHz with acceptable consistency. The optimization achieved in this study can provide a reference for further improvement of this sensor and other similar sensors with PZTs.

Reverse Osmosis Desalination Plants Energy Consumption Management and Optimization for Improving Power Systems Voltage Stability with PV Generation Resources

This paper studies energy consumption management of seawater Reverse Osmosis (RO) desalination plants to maintain and enhance the Voltage Stability (VS) of Power Systems (PS) with Photovoltaic (PV) plant integration. We proposed a voltage-based management algorithm to determine the maximum power consumption for RO plants. The algorithm uses power flow study to determine the RO plant power consumption allowed within the voltage-permissible limits, considering the RO process constraints in order to maintain the desired fresh water supply. Three cases were studied for the proposed RO plant: typical operation with constant power consumption, controlled operation using ON/OFF scheduling of the High-Pressure Pumps (HPPs) and controlled operation using Variable Frequency Drive (VFD) control. A modified IEEE 30-bus system with a variable load was used as a case study with integration of three PV plants of 75 MWp total power capacity. The adopted 33.33 MW RO plant has a maximum capacity of 200,000 m3/day of fresh water production. The results reveal that while typical operation of RO plants can lead to voltage violation, applying the proposed load management algorithm can maintain the vs. of the PS. The total transmission power loss and power lines loading were also reduced. However, the study shows that applying VFD control is better than using ON/OFF control because the latter involves frequent starting up/shutting down the RO trains, which consequently requires flushing and cleaning procedures. Moreover, the specific energy consumption (SEC) and RO plant recover ratio decreases proportionally to the VFD output. Furthermore, the power consumption of the RO plant was optimized using the PSO technique to avoid unnecessary restriction of RO plant operation and water shortage likelihood.

Power Quality Enhancement in Four-Wire Systems under different distributed Energy Resource Penetrations

Reactive and harmonic currents that are being injected into the power supply by nonlinear loads, cause an increasing deterioration of the power system voltages and currents, whereas active power filter (APF) has been widely used to overcome this problem and to improve the power quality delivered by the power supply. In this paper, a three-level four-legged active power filter based on a neutral-point-clamped (NPC) inverter is presented. To fulfil the requirement of the active power filtering function under balanced, unbalanced, and distorted (including 3rd and 5th harmonics) power supply voltages, a control method based on the instantaneous power theory has been used and discussed. On the other side, the inverter switching state control has been achieved based on PWM current controller. The performance of the proposed topology under the control approach has been finally discussed through the obtained simulation results.