Load Switching Research Articles

Adaptive Droop Control for Voltage and Frequency Regulation in Virtual Power Plant under Power System Contingencies

The frequent penetration of distributed energy resources in microgrid environment often faces operational challenges like stability and reliability issues. In order to overcome these challenges, the concept of the virtual power plant is suggested. Practically, the chance of voltage and frequency fluctuation increases in virtual power plant scenarios under critical power system contingencies like faults and sensitive load switching. Therefore, implementation of efficient controllers is required to address this issue. Further, the fixed gain droop control topology reported in literature is insufficient to accomplish seamless voltage and frequency regulation of the virtual power plants. Therefore, this paper proposes an adaptive droop control scheme to regulate system’s frequency and voltage (as per IEEE 1547) in presence of critical power system contingencies under virtual power plant scenarios. Further, a small signal stability analysis is carried out considering the system Eigenvalues to investigate the effectiveness of the proposed adaptive droop controller. Additionally, a comparative analysis between traditional and proposed droop controller is performed considering critical power system contingencies under MATLAB / Simulink environment. The dynamic responses establish the improved performance of the proposed controller over the traditional control scheme in terms of transient and steady-state stability.

Exploiting the operational flexibility of AC-MTDC distribution system considering various flexible resources

Due to inherent volatility and uncertainty, the large-scale renewable energy integration has led to surge demands for operational flexibility in distribution system. Though various flexible resources in distribution system can help smooth the fluctuation of renewable energy, they also increase the complexity of dispatching. In order to enhance the flexibility of AC-MTDC distribution system, this paper proposes an economic and flexible scheduling model comprehensively considering source-grid-load-storage flexible resources, which exploits the potential flexibility by power flow controlling through VSC, control mode switching of MTDC and scheduling of flexible loads. Firstly, MTDC control strategy and mathematical models for various flexible resources are established. Then, the mechanism of flexibility supply–demand balance is analyzed, and three flexibility evaluation indices are presented from the perspective of flexibility supply–demand matching, network transmission flexibility and overall system flexibility respectively. Furthermore, a novel optimal scheduling model considering flexibility constraints is established to improve system flexibility. Finally, the proposed method is verified in a 47-bus AC-MTDC distribution network. Results show that the coordinated dispatching with power flow regulation, control mode switching of MTDC and flexible loads scheduling can greatly improve the flexibility of AC-MTDC distribution system and reduce the operation cost.

DEVELOPMENT OF AN ENERGY SUPPLY SYSTEM BASED ON THE PROTOTYPE «KAZEOSAT – 2»

"This article discusses the development of a prototype power supply system «KAZEOSAT -2» for which two types of load behaviour are modeled and described. In the first approach, the analysis focused on using load duty cycles to simulate the average power consumption per orbit in order to study the behaviour of the subsystem for various orbit scenarios. The second approach consisted in modeling the load switching behaviour taking into account the event of the mission flight sequence. The article also analyses the state of the energy balance based on the events of the mission flight sequence, as well as predicts the effect of power peaks on battery discharge behaviour. Busbar regulation was implemented, the converter block and converter efficiency were modeled using resistive resistance in parallel to its input ports. It is noted that the fill factor of the converter was controlled using a PI controller and a comparator, which measure the load voltage and compare it with the reference value. Keywords: reliability, block diagram, modelling, block, subsystem"

A State Machine-Based Droop Control Method Aided with Droop Coefficients Tuning through In-Feasible Range Detection for Improved Transient Performance of Microgrids

The cascaded droop-voltage-current controller plays a key role in the effective operation of microgrids, where the controller performance is critically impacted by the desigheme, a constant value n of the droop controller. Moreover, in critical loading (e.g.: connection/disconnection of large inductive load), the pre-set value of the droop coefficient brings asymmetry in transient performance leading to instability. Hence, to improve symmetry by reducing the trade-off between transient response and stability margin, this paper proposes a state machine-based droop control method (SMDCM) aided with droop coefficients’ tuning through in-feasible range detection. Here, to realize the issues and the role of the droop controller’s dynamics on the microgrid’s stability, a small-signal stability analysis is conducted, thereby, an in-feasible range of droop values is identified. Accordingly, safe values for droop coefficients are implemented using the state machine concept. This proposed SMDCM is compared with the conventional constant droop control method (CDCM) and fuzzy logic-based droop control method (FLDCM) in terms of frequency/power/voltage characteristics subjected to different power factor (PF) loading conditions. From the results, it is seen that CDCM failed in many metrics under moderate and poor PF loadings. FLDCM is satisfactory under moderate PF loading, but, showed 54 Hz/48 Hz as maximum/minimum frequency values during poor PF loading. These violate the standard limit of ±2%, but SMDCM satisfactorily showed 50.02 Hz and 49.8 Hz, respectively. Besides, FLDCM levied an extra burden of 860 W on the system while it is 550 W with SMDCM. System recovery has taken 0.04 s with SMDCM, which completely failed with FLDCM. Similarly, voltage THD with FLDCM is 58.9% while with SMDCM is 3.08%. Peak voltage due to capacitive load switching is 340V with FLDCM and 150 V with SMDCM. These findings confirm that the proposed SMDCM considerably improved the transient performance of microgrids.

A review on techniques for improving power quality: research gaps and emerging trends

Many issues have arisen for the electricity sector because of the widespread use of gadgets that rely on electrical power. India's energy demands are rising rapidly due to the country's rapid economic development. These days, almost every industry makes extensive use of electrical machinery and equipment. Electronic gadgets add a non-linear demand to the power grid, which can cause power quality (PQ) problems such as voltage fluctuations that can damage electrical equipment and even knock the grid down. As the use of DG units becomes more commonplace, complications related to power conversion interfaces, load switching, and other factors emerge as potential bottlenecks in service. Power filters were first created several decades ago to address problems with PQ and to dampen harmonics caused by nonlinear loads. This document summarises previous studies that have investigated the effectiveness of power filters and other techniques for enhancing power quality. There are also descriptions of research that is still going on and where it stands, as well as a look ahead to what its possible future benefits might be.

Transient Enhanced Mode design based on DC-DC Buck-Boost converter

With the rapid development of electronic products, a system may suddenly start operating from a dormant state. In order to provide a stable supply voltage to a system with a rapidly changing load and to improve the transient response of the DC-DC, a Buck-Boost type DC-DC with a Transient Enhancement Mode is proposed, which improves the transient response during load switching and reduces the overshoot/undershoot voltage and recovery time. The oscillator part can respond to different load transients and output different frequency clock signals to finally achieve fast charging and slow discharging of the inductor. The specific circuit design and physical implementation of the proposed method are verified based on a 0.18μm high-voltage BCD process. The test results show that the minimum overshoot/undershoot voltage can reach 40mV and the fastest recovery time can reach 14μs, and the transient voltage and recovery time are reduced by 66% and 88% respectively compared with the DC-DC design without a fast Transient Enhancement Mode.

Invention of a contactless voltage relay with an adjustable reset ratio

The purpose of this article is to apply the relay effect observed in semiconductor circuits to create a contactless relay voltage with an adjustable return coefficient, connected in one device sensitivity to the input voltage and switching of powerful loads to high currents. A dynamic circuit is investigated, consisting of an adjustable semiconductor, in series with a parallel circuit of a capacitor and a resistor, which is one of the parts of the proposed relay device with a sinusoidal frequency of voltage fluctuations on the load. To study the operating modes and analyze the device circuits, it is recommended to use numerical methods using computer technology.The principle of operation and experimental characteristics of the developed device are presented.

A Deep Learning Technique for Detecting High Impedance Faults in Medium Voltage Distribution Networks

Utility companies always struggle with the High Impedance Fault (HIF) in the electrical distribution systems. In this article, the current signal is seen in situations involving 10,400 different samples, with and without HIF, like linear, non-linear load, and capacitance switching. A better method that processes signals very fast and with low sample rates, requiring less memory and computational labor, is demonstrated by Mathematical Morphology (MM). For HIF identification, Deep Convolution Neural Networks (DCNNs) are being developed. This paper presents a novel method for signal processing with low sample rates, high signal processing speed, and low computational and memory requirements. The suggested six-layer DCNN is compared with other models, such as the four-layer and eight-layer DCNN models and the results are discussed.

A Unified Control for PFC Converter With Seamless Transition Between PWM/PFM Modes

Discontinuous conduction mode is often used in boost power factor correction converter. This article proposes a unified control method to achieve both pulsewidth modulation control and pulse frequency modulation control, which is based on the virtual impedance principle. The control modes can easily be changed by only adjusting one control parameter. Consequently, by comprehensively considering current ripple, switching frequency, and efficiency, the converter can operate flexibly in the situation of variable loads. This article first introduces the operation principle of the proposed unified control method. Then, the operation condition for each control mode is discussed. Besides, the current ripple, the switching frequency, and the power loss are analyzed. Finally, the experimental results of steady-state test and load switching test are presented. And the efficiency of the converter is more than 95% in the range from half load to full load. These experimental results fully verify the effectiveness of the proposed control.

An Non-Intrusive Load Event Detection Approach Based on CEEMDAN-WTD-F Test

<p>To improve the perception of the switch state of the electrical equipment and realize the identification of the non-intrusive load switching process more accurately, a non-intrusive load event detection method based on the CEEMDAN-WTD-F test is proposed in this paper. Firstly, the adaptive median filter is used to reduce the noise fluctuation of power data of electric equipment and the discrete sequence derivative is used to reduce turn-on transition time for individual loads. Then, based on the principle of decomposition denoising and statistical testing, Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) and Wavelet Threshold De-noising (WTD) are used to process the input signal, and then the F test is used to determine whether an event occurs. Then, the proposed detection method is verified on the BLUED public data set, and a comparison experiment is carried out with the existing detection algorithm. The experimental results fully show that the proposed method has a lower missed detection rate and false detection rate than other detection algorithms, and the detection precision rate, recall rate, and F1 value are higher than 97%.</p> <p> </p>

Salp swarm algorithm for optimal load balancing in low voltage networks

Distribution networks for low voltage (LV) are three-phase networks. It mostly serves single-phase end customers with a variety of load characteristics. Because each customer's load behavior differs, the current on the LV networks feeder is shared unequally, leading in an im-balance problem. This research investigates an efficient distribution of single-phase loads amongst three phase networks using the salp swarm algorithm (SSA) to phase swap consumers between phases. Customers are rearranged and their loads are switched from heavy to light to achieve phase shifting. Jordan's electricity distribution company (EDCO) has provided a full load feeder as a case study. The results of switching loads to a three-phase feeder show that the im-balance index and power losses can be decreased significantly.

Enhancing active reconfigurable intelligent surface

A Reconfigurable Intelligent Surface (RIS) panel comprises many independent Reflective Elements (REs). One possible way to implement an RIS is to use a binary passive load impedance connected to an antenna element to achieve the modulation of reflected radio waves. Each RE reflects incoming waves (incident signal) by using on/off modulation between two passive loads and adjusting its phase using a Phase Shifter (PS). However, this modulation process reduces the amplitude of the reflected output signal to less than unity. Therefore, recent RIS works have employed Reflection Amplifiers (RAs) to compensate for the losses incurred during the modulation process. However, these systems only improve the reflection coefficient for a single modulation state, resulting in suboptimal RE efficacy. Thus, this paper proposes a strategy for optimising RE by continuously activating the RA regardless of the switching load state. The performance of the proposed scheme is evaluated in two scenarios: (1) In the first scenario (Sc1), the RA only operates to compensate for high-impedance loads, and (2) in the second scenario (Sc2), the RA runs continuously regardless of the RE loads. To benchmark the performance of Sc1 and Sc2, various metrics are compared, including signal-to-noise ratio, insertion loss, noise figure, communication range, and power-added efficiency. Numerical examples are provided to demonstrate the effectiveness of the proposed scheme. It is found that the proposed system in Sc2 leads to better overall performance compared to Sc1 due to the increased gain of the RIS reflection.

Degradation monitoring of SiC MOSFET gate-oxide based on differential mode conducted interference spectrum

The gate-oxide degradation of power devices has an important impact on the normal operation of electrical equipment. Therefore, the research on the condition monitoring of gate oxide is of great significance to improve the operation reliability. In this article, a new monitoring method for the gate oxide in silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) is proposed. Firstly, the degradation mechanism of gate oxide and its influence on the change rate of drain current (di/dt) during device switching are analyzed. Secondly, taking the Buck converter composed of SiC MOSFET as the research object, combined with the EMI equivalent model and conducted interference coupling path of the converter, the relationship between differential mode electromagnetic interference (DM EMI) signal and gate-oxide degradation is established. Finally, the amplitude of DM interference signal is used as the characteristic parameter to monitor the condition of SiC MOSFET gate oxide, and the effectiveness of the monitoring method is verified by experiments. The monitoring method proposed in this paper is applicable to different switching frequencies and load currents, and can monitor the healthy state of gate oxide in SiC MOSFET under laboratory environment and actual working conditions, which has strong practicability.

Dynamic response and stability performance of a proton exchange membrane fuel cell with orientational flow channels: An experimental investigation

The dynamic response of proton exchange membrane fuel cells with the load switching determines the operation stability and life of fuel cells. To investigate the dynamic response of proton exchange membrane fuel cells from the perspective of gas and water delivery, the dynamic response of the fuel cell with the parallel and orientational flow channels was tested under different loads and operating conditions. The experimental results show that the dynamic performance of the fuel cell with orientational flow channels is good after the current and voltage loads are switched. The orientational flow channels improve water management, make the water distribution of the flow channels uniform, increase the membrane hydration, and prevent flooding in the local electrode. The voltage variation coefficient of the cell with orientational flow channels is 1.57%, which is smaller than that of the cell with parallel flow channels 35.6%. Thus, the dynamic performance and stability are improved. The overshoot and undershoot of pressure drop are observed which is due to the changing of gas transferring to the electrode when the load is switched. The orientational flow channels improve the gas transfer capacity, which makes more gas enter the electrode to participate in reactions, thus the orientational flow channels improve dynamic performance and decrease dynamic time constant.

Decision tree approach for fault detection in a TCSC compensated line during power swing

Detection of fault in a thyristor-controlled series capacitor (TCSC)-compensated transmission line is more difficult compared to normal transmission lines. The fault detection problem becomes further complicated in such lines, especially during power swings. In this paper, a new approach is proposed for detecting fault during power swing in a TCSC-compensated transmission line, using only local end current measurements as input to a decision tree (DT)-based classifier. It is the first-ever use of the DT-based method for this application. The performance of the proposed method has been validated on numerous test cases generated on the WSCC 9-bus 3-machine system and the modified IEEE 39-bus New England system through EMTDC/PSCAD by varying the different parameters such as fault resistance, fault type, fault location, fault inception angle, firing angle of the TCSC, load switching, current transformer saturation, etc. The sensitivity of the proposed fault detection technique is found to be 100%, which is superior compared to the existing methods. Thus, justify the effectiveness of the proposed method.

A Coordination Optimization Method for Load Shedding Considering Distribution Network Reconfiguration

Load shedding control is an emergency control measure to maintain the frequency stability of the power system. Most of the existing load shedding methods use the extensive form of directly cutting off the outlet of the substation, featuring low control accuracy and high control cost. A network reconfiguration technique can adjust the topology of the distribution network and offers more optimization space for load shedding control. Therefore, this paper proposes a reconfiguration–load shedding coordination optimization scheme to reduce the power loss caused by load shedding control. In the proposed method, a load shedding mathematical optimization model based on distribution network reconfiguration is first established. The tie switches and segment switches in the distribution network are used to perform the reconfiguration of the distribution network, and the load switches are adopted to realize the load shedding. To improve the solving efficiency of the model, a solving strategy that combined a minimum spanning tree algorithm with an improved genetic algorithm is trailed to address the nonlinear and nonconvex terms. The application of the proposed method and model are finally verified via the IEEE 33 bus system, and the advantages in reducing the loss cost and the number of outage users are accordingly proven.

Short-Circuit Characteristic of Single Gate Driven SiC MOSFET Stack and Its Improvement With Strong Antishort Circuit Fault Capabilities

The single gate driven series connected power device stack possesses the advantages of high compactness and low cost. However, research of its short circuit (SC) characteristic remains uncovered. This article fills this gap and points out that, with the single gate driver it has the potential of over-current limitation. Furthermore, based on it, an improved single gate driven silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(mosfet)</small> stack with strong antishort circuit fault capabilities is proposed. By adding auxiliary circuits to adjust the driving process of the single gate driver, the SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> stack can be automatically turned <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> in both SC conditions of fault under load and hard switch fault, while the normal working principle of the stack is not influenced. Neither active control nor overcurrent detection is required, which is the biggest merit of the proposed topology. Its design and analysis are presented in detail, followed by the validation by conducting simulations and experiments.

Supervised Learning of Overcomplete Dictionaries for Rapid Response-Based Dynamic Stability Prediction

This paper develops a supervised learning of overcomplete dictionaries (SLOD) to efficiently perform online analysis and prediction of dynamic stability (DSP) in large power systems. To this end, multiple post-contingency signals with varying faults, load and generator switching are acquired by phasor measurement units (PMUs) based monitoring of all generators to form the training dataset. The SLOD approach then jointly learns a sparse feature dictionary and a stability status classifier using dynamic singular value decomposition (D-KSVD) and orthogonal matching pursuit (OMP). The aim is to learn features of the signals while adding a stability status term to the optimization problem. This enabled stable/unstable classes to be represented. The proposed SLOD manages to improve online DSP shortly after a contingency. It does this without any prior assumptions or signal preprocessing except for dynamic state estimation to get rotor speed from generator terminal PMU data. Test results on the IEEE 2-area 4 machines, 39 and 68 -bus test systems demonstrate that the SLOD gives more than satisfactory performance in all cases (i.e., ∼99.99% accuracy, ∼99.99% reliability, and 100% security) compared to Statistics and Machine Learning Toolbox™ -MATLAB that use time-series-based high-dimensional stability indices as input for DSP.

A signed correlation index-based differential protection scheme for inverter-based islanded microgrids

The different fault characteristics of the inverter-based distributed generation (IBDG) units make the protection of the inverter-based islanded microgrids (IBIMGs) a formidable task. According to IEEE Std 1547.4, the limited fault current levels associated with the IBIMGs may result in misleading decisions of the traditional protective relays during fault occurrence. In this paper, a new differential protection scheme for the IBIMGs is introduced based on the signed correlation technique. The proposed scheme is formulated based on the signs of the instantaneous phase currents at both line ends instead of the current magnitudes. In addition, a signed correlation index is defined to measure the similarity between the signs of the instantaneous phase currents at both line ends employing only a time window of half-cycle. Moreover, a fault detection index is introduced to discriminate the internal faults from other events. In order to validate the proposed scheme, the 9-bus IBIMG and the modified IEEE 33-bus system are simulated on the PSCAD/EMTDC platform, and several scenarios are conducted, including load switching, outage of IBDG units, external bus faults, and internal faults. The obtained results emphasize that the proposed scheme operates correctly considering all types of faults, different fault resistances and inception angles, as well as measurement and synchronization errors.

Research on Multi-Energy Integrated Ship Energy Management System Based on Hierarchical Control Collaborative Optimization Strategy

The propulsion systems of hybrid electric ship output and load demand have substantial volatility and uncertainty, so a hierarchical collaborative control energy management scheme of the ship propulsion system is proposed in this paper. In a layer of control scheme, the traditional perturbation algorithm is improved. Increasing the oscillation detection mechanism and establishing the dynamic disturbance step length realizes the real-time stability of maximum power point tracking control. In the second-layer control scheme, the power sensitivity factor and voltage and current double closed-loop controller is introduced. By designing a two-layer coordinated control strategy based on the dynamic droop coefficient, the problem of voltage and frequency deviation caused by load switching is solved. In the third-layer control scheme, due to the need of the optimal scheduling function, the multi-objective particle swarm optimization algorithm was improved through three aspects: introducing the mutation factor, improving the speed formula, and re-initializing the strategy. Compared with other algorithms, this algorithm proves its validity in day-ahead optimal scheduling strategy. The superiority of the hierarchical collaborative optimization control schemes proposed was verified, in which power loss was reduced by 39.3%, the overall tracking time was prolonged by 15.4%, and the environmental cost of the diesel generator was reduced by 8.4%. The control strategy solves the problems of the steady-state oscillation stage and deviation from the tracking direction, which can effectively suppress voltage and frequency fluctuations.