Voltage Sensitive Loads Research Articles

Optimal economic dispatching strategy for power systems considering distributed controllable load clusters

The day-ahead dispatching of power system depends on the predicted renewable energy output and load power, which brings great challenges to the real-time power balance. This paper focuses on voltage sensitive loads (VSLs) that are widely distributed in space, thus exploring the real-time dispatching potential for VSLs. Firstly, based on the P-V relationship of VSLs clusters, a ZIP model is adopted to establish VSLs’ power controllable model. Meanwhile, considering the potential voltage instability risk during the process of voltage regulation, a linear relationship between voltage safety margin (VSM) index and node power variation was derived. Then, a two-stage linear dispatching model for controllable VSLs clusters was established to meet the needs of online application. In detail, the first stage mainly focuses on evaluating the scheduling potential of VSLs clusters and the second stage determines the optimal real-time response strategy for VSLs clusters. Finally, the effectiveness and feasibility of the proposed method are verified through an improved IEEE-30 node system.

ANFIS controlled fuel cell powered series active filter for voltage waveform augmentation in the distribution grid

The high penetration of nonlinear and unstable loads into the grid network severely impacts the quality of power delivered by the grid system. Furthermore, it leads to a disruptive situation of maintaining good quality power in the distribution sectors. Consequently, maintaining a good quality of power is very difficult on the power distribution grid. In this proposed work, the Proton exchange membrane Fuel Cell sustained by a three-phase Series Active Filter (PFC-SAF) is employed to enhance the quality of sensitive load voltage in the distribution grid. The generalized bell-shaped membership function based on the Adaptive Neuro-Fuzzy Inference System (ANFIS) is used to generate the reference voltage signals of the PFC-SAF. The proposed system is modelled and analyzed in a Matlab/Simulink environment. The performance of the PFC-SAF is investigated based on various fault conditions and voltage harmonics. From the obtained results, it has been found that the PFC-SAF effectively regulates the voltage in the distribution grid. Also, the total harmonic distortion of the sensitive load voltage is reduced from 20.86 % to 0.55 %.

Three-Phase Second-Order Analytic Probabilistic Load Flow With Voltage-Dependent Load

This paper proposes a fully analytic second-order probabilistic load flow (PLF) method to realize an accurate and fast three-phase load flow analysis considering unbalanced uncertainties from voltage-sensitive loads and photovoltaic (PV) generation in distribution systems. The load flow equations are modelled by an accurate quadratic expression based on the bus injection model (BIM). To work at the distribution level, the voltage dependence of the load is considered based on the constant impedance, constant current, and constant power (ZIP) model, with the ZIP parameters acting as more realistic random variables. The PV generation is also considered as a constant power model. The uncertainties are modelled in time series as conditional probabilities, reducing the complexity of their probability distribution functions (PDFs). The PLF is modelled in a fully analytic second-order stochastic formulation, which can accurately and easily handle the PDFs of voltage and current by computing the first two moments. The computation is accelerated by an analytical calculation of the quadratic coefficients over the ZIP parameters. Case studies on a practical distribution network show the significance of considering the voltage-dependent load model and the high accuracy of the proposed method.

Optimizing Adaptive Disturbance Rejection Control Models Using the Chimp Optimization Algorithm for Ships' Hybrid Renewable Energy Systems.

Hybrid renewable energy systems are becoming widely prevalent in warships due to their reliability and acceptability. However, the uncertainty caused by using renewable energy resources is one of the primary challenges. Therefore, this paper investigates the implementation of a dynamic voltage restorer (DVR) with a new control strategy in a hybrid solar power generation system, including photovoltaic (PV) panels, diesel generators, battery storage, and conventional and sensitive loads. Furthermore, a new metaheuristic-based active disturbance rejection control (ADRC) strategy for fast and accurate DVR control is proposed. In this regard, a novel chimp optimization algorithm (ChOA)-based (i.e., ChOA-ADRC) strategy is suggested to increase the stability and robustness of the aforementioned hybrid system. The ADRC controller's parameters are updated in real-time using the ChOA approach as an automatic tuning mechanism. In order to evaluate the performance of the proposed control strategy, the model is evaluated under two and three-phase fault case scenarios. Also, a comparison with the conventional PI controller has been performed to further evaluate the proposed method. Simulation findings reveal the suggested control strategy's remarkable effectiveness in correcting fault-caused voltage drop and maintaining sensitive load voltage. Additionally, the results show that ChOA-ADRC presents a better dynamic response compared to conventional control strategies and increases the reliability of the hybrid power generation system.

Transmission distribution coordination for DER fault ride through support

Rapid renewable energy sources (RESs) deployments in transmission and distribution networks have changed power systems’ operation and control mechanisms. This fundamental shift makes the interaction between transmission and distribution systems more sensitive and requires robust TSO–DSO coordination to ensure system stability and ancillary services for the entire network. This paper uses an electromagnetic transient (EMT) simulation tool using a real-time digital simulator (RTDS) to investigate the dynamic transmission–distribution coordination with a high share of RESs in fault ride-through (FRT) capability of distributed energy resources (DERs). Then, the paper implements fault current injection (FCI), incorporating inverter-based resources (IBRs) in the transmission system to support dynamic voltage responses for the distribution system. Different reactive current control schemes are examined to evaluate the FRT performance of DERs under different fault locations. Additionally, hardware in the loop simulation for the under-voltage protection relay is implemented to validate the low-voltage ride-through capability of DERs. The comparison results show that the transmission system can provide dynamic voltage support for the distribution system through FCI from IBRs to help DER ride through. The FCI from the transmission system also significantly enhances fault-induced delayed voltage recovery of voltage-sensitive load in the distribution system.

Least Mean Fourth Theory-based Dynamic Voltage Restorer for the Mitigation of Voltage Sag and Harmonics

In the present paper, Dynamic Voltage Restorer (DVR) controller using the Least Mean Fourth (LMF) algorithm is presented. The proposed DVR is used for protecting various voltage-sensitive loads from voltage-related power quality issues (i.e. balanced voltage sag, unbalanced voltage sag and voltage harmonic distortion, balanced and unbalanced swell, etc.) in a distribution system. The active and reactive power components of distorted source voltage are extracted using an adaptive LMF-based control algorithm for the calculation of reference load voltage for the voltage source converter (VSC) of DVR. The control algorithm doesn’t require a phase-locked loop (PLL) and thus is less complex, robust and easy to implement. The adopted control algorithm for DVR is verified in MATLAB by simulation studies. The adaptive LMF-controlled DVR produces excellent dynamics response as compared to conventional adaptive Least Mean Square (LMS) and Synchronous reference frame theory (SRFT)-controlled DVR. The convergence rate of the source voltage fundamental active weight component is higher for the proposed adaptive LMF-controlled DVR. Various power quality issues such as balanced sag, unbalanced sag, balanced and unbalanced swell and a combination of these power quality issues are mitigated with the help of the LMF-controlled DVR. The simulation results are verified through real-time experimentation using an OPAL-RT under an RT lab environment.

Power Quality Improvement using Dynamic Voltage Restorer (DVR)

Abstract: This paper discusses the mitigation of power quality disturbance in low voltage distribution system due to voltage swells using one of the powerful power custom devices namely Dynamic Voltage Restorer (DVR). The DVR normally installed between the source voltage and critical or sensitive load. The new configuration of DVR has been proposed using improved d-q-o controller technique. The simulations are performed using MATLAB/Simulink’s SimPower Toolbox. The simulation and experimental results demonstrate the effective dynamic performance of the proposed configuration. Keywords: Dynamic Voltage Restorer, d-q-o controller, voltage swells, distribution system, sensitive load.

Energy Balance Control for Improving Transient Performance of DC Bus Voltage in Power Electronic Transformer for the Voltage-Sensitive Loads

The power electronic transformer (PET), as a main topology for the energy router in the energy internet, consists of the rectifiers, the dual active bridge (DAB), and the inverter, and these three parts are connected by two dc buses. So, the performance of the dc bus voltages is very important because it can totally affect the output waveforms of the dc and ac voltage, especially for the voltage-sensitive loads. Compared with the proportion integration (PI) control scheme, the energy control method utilizes the energy as the control variable, and the control strategy derived from the energy relationship, including the passive elements and all the interfaces, is more direct and explicit. In this paper, considering the energy between the dc bus capacitors and the input inductor and the load and the source in the PET topology, the energy balance control (EBC) strategy is proposed. For the two dc bus voltages, the energy balance relationship of the different time scales is used to decouple the interaction in the control scheme. The EBC strategy can obviously reduce the fluctuation and the transient time of the two dc bus voltages when the load power or voltage reference is changed. Thus, under the limited voltage fluctuation, the EBC strategy can reduce the dc bus capacitance in order to reduce the volume and weight of the converter and enhance the reliability. The simulation and experimental results verify the effectiveness of the proposed control strategy.

A Stochastic Economic Dispatch Method Considering a Voltage-Sensitive Load as a Reserve

The volatility and uncertainty of renewable energy seriously affect the stability of power systems. To overcome this challenge and improve the ability of power systems to deal with disturbances, an optimized dispatch method for a high-permeability renewable energy-integrated power system with a voltage-sensitive load (VSL) as the reserve is proposed. To fully utilize the flexibility of the VSL and the reactive power control capability of the transmission grid, this paper first establishes a voltage control model based on coordinated sensitivity-based transmission and distribution and quantifies the active power adjustment boundary considering voltage stability. Then, based on the corresponding risk, a stochastic reserve decision model of a power system considering the regulation capacity of a VSL is established. A case study of a modified IEEE RTS-79 system shows that the method can fully consider the influence of the voltage at the access point on the load power, change the power of the VSL, and provide an active power reserve for the power system. This approach can reduce the risk of wind curtailment and load shedding in the system and improve the economy and flexibility of system operation.

Multistage Coordination Volt/VAR Control With CVR in Active Distribution Network in Presence of Inverter-Based DG Units and Soft Open Points

The conservation voltage reduction (CVR) technique is a well-established technique for peak demand reduction and energy savings in the presence of voltage-sensitive loads. However, intermittent and uncertain nature of renewable energy sources such as photovoltaic generation may produce some operational issues under real-time CVR operation, which results in major problems such as undervoltage as well as increase in power losses in an active distribution network. Advanced power-electronics-based devices such as inverter-based distributed generators (IDGs) and soft open point (SOP) devices emerge as potential solutions for the aforementioned issues by providing the volt-ampere reactive (VAR) support. However, an efficient CVR methodology is much needed for proper coordination of multiple traditional volt/VAR control devices and advanced power-electronics-based devices. Therefore, this article introduces a multistage coordinated CVR methodology incorporating IDG and SOP devices for offline (i.e., day-ahead scheduling) and online (i.e., real-time dispatch) studies. For day-ahead scheduling, stochastic CVR formulation has been developed considering intermittency and uncertainties in power loads and generations. In contrast, online simulations have been performed in two stages for near-real-time operation using an inner-day rolling control model based on model-predictive control and real-time control through modified volt/VAR droop (VVD) control by optimal VVD curve selection. To validate the proposed scheme, a real-time cosimulation platform using a real-time digital simulator and a MATLAB-GAMS interface has been built. The efficacy of the proposed method has been validated on various case studies and also tested on sudden external disturbances such as sudden cloud transient, cloud cover, and substation voltage changes. Furthermore, the robustness of the proposed method has also been checked under faulty conditions. The test results demonstrate the significance of the proposed methodology on voltage violation mitigation, energy loss, energy consumption minimization, and service restoration.

A Deep Learning Approach for the Detection and Classification of Power Quality Disturbances with Windowed Signals

The modernization of Power Systems (PSs) to smart grids, the expansion of microgrids, the ever-increasing presence of distributed power generation, the more frequent use of non-linear and voltage-sensitive loads by the consumers have caused problems to the Power Quality (PQ). The studies in PQ are commonly related to disturbances that alter the sinusoidal characteristics of the voltage waveforms and/or current. The first step to analyzing the PQ is to detect and then classify the disturbances, since by identifying the disturbance, it is possible to know its causes and deliberate over strategies to mitigate it. Thus, this paper proposes a deep-learning approach using voltage signals, without pre-processing, extraction, nor manual selection of features in order to detect and classify PQ disturbances automatically. The proposed approach is composed of convolution layers, a pooling layer, a long short-term memory layer, and batch normalization. A 1D convolution was used to adapt the data from the voltage signals. Overlapping windowed signals with different Signal–Noise Ratio (SNR) (40 dB, 30 dB, 20 dB and 0 dB) and with different sampling rates (16, 32, and 64 samples/cycle) were used. For a more in-depth view of the results, the proposed approach was evaluated for its accuracy, precision, recall, and F1-Score in different scenarios. An analysis of the obtained results shows that even for the worst case scenario (SNR of 20 dB and sampling rates of 16 samples/cycle), the approach performs satisfactorily with values above 0.97 for the analyzed metrics, allowing, thus, consumer action in a demand-side management scenario.

Risk-based dynamic expansion planning of distribution network’s reliability and power quality

ABSTRACT Today’s advanced society with high level of digitalisation suffers from power outages even if it takes just a few minutes. Also, higher voltage drop causes higher power losses and also damages home appliances. In a competitive environment, higher power losses and lower reliability are converted to economic losses. So, Distribution Companies (DisCos) try to provide reliable power supply with higher power quality, of course, in lowest possible costs to their consumers. In this regard, simultaneous switch placement and capacitor allocation can be eco-technically efficient. Due to the limited budget of DisCo, the investments must be applied in different years and in accordance with the level of accepted risk by DisCo. So, this paper is aimed to optimise both the reliability-oriented risk-based – and power quality – objective functions; by finding the timing and sitting of both capacitors and switches, sizing of installed capacitors and determining the kind of installed switches (Recloser and sectionliser), using MOPSO. Also, the uncertainties of load demand and electricity price, voltage-sensitive loads and load priority in power supply are applied to the planning problem. To evaluate the effectiveness of the suggested method, the computer simulation is done on a 33-Bus IEEE distribution network and the results are discussed.

Determinations of Annual Investments of DisCo and Private Sector in Expansion Planning of Distribution Network

Ever-increasing load-demand, threaten the continuity of power supply and diminishes power quality causing serious technical challenges in distribution networks. In this regards, commonly used cheaper practices like capacitor allocation and network configuration, can enhance operational parameters of the network. On the other hand, supplying the future loaddemand, requires installing new substations or distributed generations (DGs). Because of DGs inherent technical and economic advantages, Distribution Company (DisCo), encourage private investment to install DGs, by signing long-term Power Purchase Agreement (PPA) with DG owners (DGO). In such a situation created, DG allocation and simultaneously capacitor allocation and network configuration can be economical for both DisCo and DGO and also can enhance the reliability and power quality. So, this paper is aimed to find the annual instants for network configuration; timing, sizing and sitting of capacitors and DGs, and PPA rates using Multi-Objective Particle Swarm Optimization (MOPSO). Also, the uncertainties of load-demand and electricity-price, voltage-sensitive loads and load priority in power supply are applied into the planning problem. Voltage deviation and voltage stability are considered as constraints which must be better in optimum solution. The effectiveness of the proposed scheme, is validated by computer simulation done on a 33-Bus IEEE distribution network and the outcomes are discussed.

Two-Stage Active and Reactive Power Coordinated Optimal Dispatch for Active Distribution Network Considering Load Flexibility

A high proportion of renewable energy connected to the power grid has caused power quality problems. Voltage-sensitive loads are extremely susceptible to voltage fluctuations, causing power system safety issues and economic losses. Considering the uncertainty factor and the time-varying characteristic, a linearized random ZIP model (constant impedance (Z), constant current (I), and constant power (P)) with time-varying characteristics was proposed. In order to improve the voltage quality of the voltage-sensitive loads in the day-here stage in an active distribution network (ADN), a linearized two-stage active and reactive power coordinated stochastic optimization model was established. The day-ahead active and reactive power coordination optimization was to smooth the large voltage fluctuation and develop a reserve plan to eliminate the unbalanced power caused by the prediction error in the day-here optimization. In the day-here real-time redispatch, the voltage was further improved by the continuous reactive power compensation device. Finally, the simulation results on the IEEE-33 bus system showed that the control strategy could better eliminate the unbalanced power caused by the prediction error and obviously improve the voltage of sensitive loads in the real-time stage on the premise of maintaining economic optimality.

Control of Pervasive Domestic-Scale Inverters for Minimizing Total Feeder Power

This paper proposes a method for studying the potential benefits of reactive power control by domestic-scale inverters, considering network losses, inverter losses, and load-voltage sensitivity. The model is developed as a mixed-integer quadratically constrained quadratic program (MI-QCQP), using a linearization of the unbalanced distribution load flow equations. Networks both with and without on-load tap changers are studied, with the test cases covering both European and North American-style circuits. The use of domestic inverter control is shown to increase benefits compared to conventional tap control by 20%, reducing the total feeder power draw by as much as 0.5% of the feeder load. In contrast, the minimization of either load or losses in isolation is shown to increase the amount of power that a feeder draws in five of the seven circuits. To reduce the communications overhead of the approach, a control scheme is proposed that specifies the reactive power of all inverters on each phase identically; this approach is shown to realise up to 98% of the potential benefits of inverter reactive power control.

Research on dynamic control of low‐voltage distribution network with high penetration of electric heat pumps based on μPMU measurements and data‐driven approach

Electric heat pump (EHP) is a kind of high-power load, which causes power impact and voltage sag during its start-up process. With the increasing penetration of EHP loads, serious low-voltage and overload problems occur in the low-voltage distribution network, resulting in malfunction of voltage-sensitive load. This study analyses the start-up characteristics of the EHP and proposes a data-driven approach for identifying the starting state and model of EHP based on high-frequency micro-phasor measurement unit (μPMU) measurements. The state criterion based on the starting model can be used to quickly determine whether there is a starting impact at the present time. The identification method based on superposition fitting can be used to identify the number of EHPs that cause a start-up impact. Then, a dynamic control algorithm is proposed to solve the problem of low voltage and voltage sag of EHP loads. Simulation results show that the proposed quadratic model can better reflect the starting characteristics of the EHP, and the proposed dynamic control method of EHP based on data-driven approach can identify the state of EHP using µPMU measurement accurately in a very fast manner, effectively avoiding the overshoot of EHP start-up impact.

Enhanced grid frequency support by means of HVDC-based load control

The two major frequency incidents in Continental Europe and UK call for faster frequency regulation. Hvdc systems can dynamically adjust the power output to support the frequency regulation by means of droop characteristics. Adding derivative terms in the power controller enables inertia emulation that improves the system initial response. As drawback, due to the fast power transfer variation, the HVDC-connected areas suffer from temporary power imbalance and hence frequency deviation. To overcome this limitation, HVDC-based load controllers can be implemented at HVDC terminals to shape the consumption of nearby voltage-sensitive loads by means of controlled voltage variations, with the goal to minimize the frequency deviation in the supporting areas. In multi-terminal systems, the frequency support can be optimally shared among terminals depending on the load sensitivity. This minimizes the voltage deviation in supporting areas and limits the hvdc reactive power, while providing the same frequency damping in the faulty area.

Optimizing the Droop Characteristics of AC/DC Hybrid Microgrids for Precise Power Sharing

AC/DC hybrid microgrids (HMGs) represent a promising architecture that allows the hosting of a mix of ac/dc energy resources and ac/dc loads. Despite their potential, when islanded, HMGs impose operational challenges among of which are precise and stable power sharing, frequency restoration, and voltage regulation. Imprecise power sharing can result in some distributed generators (DGs) being overloaded, while others being underloaded. This article proposes an optimal-power-flow-based optimal power sharing (OPS) scheme to optimize the droop characteristics of DGs and interlinking converters for global power sharing in a multi-DG HMG regardless of DG location and type. The optimized droop parameters might jeopardize the microgrid stability. Thus, the proposed OPS scheme preserves stable power sharing through stability-constrained optimization of the droop characteristics. In addition to DG overloading because of unequal power sharing, voltage-sensitive loads could possibly suffer from voltage deviations because of drooping the voltage with the load increase. The proposed OPS strategy enjoys the ability to regulate the ac/dc voltage within a desired range and restore the nominal frequency. Steady-state and time-domain simulations verify the effectiveness of the proposed sharing scheme in achieving the underlying objectives. Test results also prove the capability of the OPS scheme in zonal power sharing in the case of a distribution grid with multizone ac/dc microgrids.

Fully DSP-Based Control of an Active Voltage Conditioner

One of the main problems in low voltage (LV) networks is related to sensitive load voltage stabilization close to the nominal value. This paper presents the analysis, design, and implementation of a back-to-back converter based active voltage conditioner for low voltage (LV) distribution grids to compensate short-term voltage sags or swells. The proposed voltage regulator contains an indirect AC/DC/AC converter and uses linear control associated with the pulse width modulation technique. To verify the practical usefulness of the proposed novel concept, a 5kVA three-phase prototype active voltage conditioner has been constructed, and the control system has been implemented based on 32-bit floating-point digital signal processor (DSP) TMS320F28377s. The effectiveness of the proposed method is demonstrated through the comprehensive experimental results.

A New PV-Open-UPQC Configuration for Voltage Sensitive Loads Utilizing Novel Adaptive Controllers

In this article, a novel topology for photovoltaic (PV) fed open unified power quality conditioner has been proposed focusing on the requirement of voltage sensitive loads. It has incorporated the advantages of open unified power quality conditioner (UPQC) and grid connected PV systems by providing a possible solution towards the demand of different power quality levels at end user. Increasing the system robustness for various voltage and current distortions, adaptive controllers have been implemented for series and shunt compensators of UPQC. Adaptive notch filter based improved Syncronous Reference Frame (SRF) scheme has been utilized for the control of series compensator. An adaptive logarithmic absolute algorithm has been implemented for shunt part of proposed system. The utilization of moving average filter (MAF) instead of low pass filter (LPF) for dc bus voltage regulation has neglected the chance of high as well as low frequency ripples. A feed forward component has been added to the shunt controller to regulate the grid current at constant level in presence of grid disturbances. The proposed controllers are verified on a developed prototype of proposed system in the laboratory. The system performance is found satisfactory under various grid conditions like voltage sags, voltage swells, voltage unbalance, voltage harmonics, sudden load addition and removal, and variation in solar irradiation.