Active Voltage Control Research Articles

Fuzzy Switched Active Disturbance Rejection Voltage Control of Generators With Load Switchings

Fuzzy Switched Active Disturbance Rejection Voltage Control of Generators With Load Switchings

Graph Multi-Agent Reinforcement Learning for Inverter-Based Active Voltage Control

Graph Multi-Agent Reinforcement Learning for Inverter-Based Active Voltage Control

Physics-Guided Multi-Agent Deep Reinforcement Learning for Robust Active Voltage Control in Electrical Distribution Systems

Physics-Guided Multi-Agent Deep Reinforcement Learning for Robust Active Voltage Control in Electrical Distribution Systems

Physics-Informed Multi-Agent deep reinforcement learning enabled distributed voltage control for active distribution network using PV inverters

With the recent rapid uptake of photovoltaic (PV) resources, the overvoltage condition during low load periods or intermittent renewable generation is one of the most critical challenges for electricity distribution networks. Traditional model-based local or centralized control methods that rely on proper system parameters are difficult to mitigate rapid changes in power systems. Utilizing model-free/data-driven multiagent deep reinforcement learning (MADRL) has been recognized as an effective solution to active voltage control. However, existing MADRL-based control approaches trained solely on data are agnostic to the underlying real-world physics principles. Therefore, this paper aims to incorporate physical knowledge of regional distribution networks into MADRL’s decision-making. The main contributions of this paper are summarized as follows. First, a novel physics-informed MADRL -based distributed voltage control method is proposed, which is still under a centralized training and distributed execution framework and only requires local measurements. Second, graph neural networks are employed to help MADRL agents learn graph knowledge (node features and topological information). Further, transformer is introduced to extract discriminative representations and ensure agents’ cooperative control. Third, we adopt a physics-guided architecture of neural networks in the actor network to stabilize the training process and improve sample efficiency. Finally, simulation results based upon modified IEEE 33-bus and 141-bus networks validate the proposed method's effectiveness, robustness and computation efficiency.

MULTIFUNCTIONAL GRID CONNECTED INVERTER BY WIND ENERGY CONVERSION SYSTEM

Non-conventional mode of generation of electricity has several advantages over conventional sources of generation. It is eco-friendly, cost effective, damage free, long lasting and more over harmless. Electricity generation through wind energy is considered as socially beneficial and economically feasible for several applications. Domestic and industrial devices use more and more circuits having a non- linear behaviour. They create non-sinusoidal currents causing high harmonic currents in the distribution networks. In the proposed method, a three-phase multifunctional grid-connected inverter interfaced with a wind energy conversion system (WECS) is introduced. This system consists of a permanent magnet synchronous generator (PMSG) based wind turbine, a rectifier and a three-phase voltage source inverter connected to the utility at the point of common coupling. To ensure the multifunctional feature, we propose a direct power control (DPC) which is applied to eliminate line current harmonics, compensate reactive power and feeding wind power into the utility. The simulation results show that the control algorithm of system is effective for eliminating harmonic currents, reactive power compensation and inject the active power available from the PMSG wind turbine into the load and/or grid. Key Words: Wind Energy Conversion System, Double Fed Induction Generator, Self-Excited Induction Generator, Self- Excited Induction Generator, Permanent Magnet Synchronous Generator, Shunt Active Power Filter, Static Compensator, Voltage and Frequency Controller, Photo Voltaic Generator.

Low Frequency Oscillation Suppression Strategy in New Power System Based on Virtual Synchronous Generator

With the blend of massive new energy into power network systems, the inertia and damping features of new power systems are reduced, which is prone to cause low-frequency oscillations (LFO) in the power systems. Virtual synchronous generators (VSG) have received widespread attention by simulating the external characteristics of synchronous generators (SG) to enhance the inertia of new power systems and help suppress low-frequency oscillations. By analyzing the mathematical model of VSG, the control links of each part of VSG are established, the traditional reactive power-voltage (Q-V) of VSG is improved, and the formulas of active voltage control and reactive power control droop coefficient are deduced.Finally, a simulation model of VSG is created by MATLAB/Simulink platform, and new methods for suppressing LFO in power systems are compared and analyzed. The correctness of the formula and the improvement effect of reactive power and voltage control are verified.

Physics-Shielded Multi-Agent Deep Reinforcement Learning for Safe Active Voltage Control With Photovoltaic/Battery Energy Storage Systems

While many multi-agent deep reinforcement learning (MADRL) algorithms have been implemented for active voltage control (AVC) in power distribution systems, the safety of electrical components involved in the operation of these algorithms are mostly ignored. In this work, a safe MADRL control scheme is proposed to regulate the reactive and active power control of photovoltaics (PVs) to alleviate power congestion and improve voltage quality by coordinating battery energy storage systems (BESSs) and static var compensators (SVCs). Uniquely, the learning algorithm designed in this paper can limit the action of the agent when approaching a dangerous state to ensure the safety of BESSs during the training process, which is realized by developing a multi-agent twin delayed deep deterministic (MATD3) policy gradient algorithm with a physics-based shielding mechanism. Specifically, actions that lead to dangerous states, the state-of-charge (SoC) of BESSs is fully loaded or drained, are replaced by the shielding mechanism with safe actions while maintaining system stability. Furthermore, each PVs node in the power distribution network is treated as an agent under the fact of reactive and active power sensitivities to voltage in the MATD3 algorithm, which is beneficial for improving scalability. Training, testing and comparative results on IEEE 33-bus and 141-bus with real-world data are provided to demonstrate the effectiveness and superiority of the proposed algorithm.

An Improved Carrier-Based PWM Strategy with Reduced Common-Mode Voltage for a Three-Level NPC Inverter

Double modulation wave carrier-based pulse width modulation (CBPWM) is a solution for eliminating the deviations of the neutral-point voltage (NPV) in three-level neutral-point clamped inverters. In this paper, a new hybrid CBPWM strategy is proposed that not only eliminates the neutral-point voltage oscillations but also reduces the common-mode voltage (CMV) by half. Furthermore, the harmonic content is also reduced compared with the available reduced CMV modulation by adjusting the modulation waves based on the location of the reference vector in the space vector diagram. An active neutral-point voltage controller is also realized in order to maintain the performance of the modulation strategy under the NPV perturbations. The performance of the proposed algorithm is compared to the available CBPWM-based techniques in the literature. The effectiveness of the proposed method is also verified by experimental results.

Modern Active Voltage Control in Distribution Networks, including Distributed Generation, Using the Hardware-in-the-Loop Technique

Voltage constraints usually place restrictions on how distributed generation (DG) can be connected to weak distribution networks. As DG capacity increases, active voltage control techniques are needed. Active approaches can greatly lower connection costs while boosting the capacity of connectable DG when used in place of the passive strategy. In this article, a modified active voltage control algorithm is used on an IEEE 33 bus system to test the robustness and reliability of the control algorithm under severe conditions. The simulations are carried out using the hardware-in-the-loop (HIL) method. Real-time simulations are used to test data transfer and the reliability of the control algorithm’s execution. The analysis is based on a three-phase symmetric power system.

Three-Phase Flying Capacitor Clamped Current Source Converter With Active Capacitor Voltage and CMV Control

AC-type flying capacitor (FC) concept has been proposed for current source converter (CSC) topologies recently, which offers unique merits over the traditional CSCs, such as lower <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> with improved dc-link voltage quality as well as flexible common-mode voltage (CMV) control. To cope with the main-stream three-phase industrial applications, in this article, the three-phase flying-capacitor-clamped CSC is introduced and extensively investigated for the first time. A novel space vector modulation is proposed, featuring a modular design process, active FC voltage control, and CMV suppression. The detailed commutation principles and the capacitor clamping voltage influence under different switching states are comprehensively addressed. Then, the redundant switching states are optimized to fulfill the multiple targets simultaneously. Simulation and experimental results are performed to demonstrate the superior dc-link power quality and CMV performance compared with the traditional three-phase CSC topology.

A novel arc suppression method based on active voltage control

The passive current arc-suppression cannot compensate the active and harmonic components, active current arc-suppression has poor reliability and economy, the passive voltage arc-suppression is easy to enlarge the fault range. The paper analyses the essential mechanism of ground fault arcing, proposes a novel active voltage arc suppression technology. The method adjusts the fault phase voltage by changing different winding numbers of grounding transformer. The fault phase voltage drops below the arc restriking voltage critical point to realize active arc suppression. A typical 10 kV distribution network is used to verify the proposed method.

Droop-based active voltage regulation control and robust stability analysis for VSCs in the large-scale RES-integrated power system

New features like high penetration level, low inertia, and weak damping are decreasing voltage support capacity in the power system as it sees large-scale renewable energy source (RES) integration continuously. The reasonable solution to this challenge is developing an additional active voltage regulation function for voltage source converters (VSCs). This study proposes a droop-based active voltage control strategy for VSCs in large-scale RES-integrated power systems to make VSCs continue to operate and regulate the voltage at the point of common coupling (PCC) during a fault without causing overcurrent. In order to meet the requirements of RESs and grid code, all control boundary conditions are designed based on practical engineering data. Meanwhile, plant uncertainty and parameter disturbance are introduced into a robust stability margin analysis model based on the component connection method (CCM) and structured singular value (SSV) to improve the engineering application prospect. The effectiveness and feasibility of this control strategy are proved by logical deduction and practical simulation based on a generalized small-signal model.

A Linear–Nonlinear Switching Active Disturbance Rejection Voltage Controller of PMSG

This article investigates a modified linear–nonlinear switching active disturbance rejection control (LNSADRC) voltage controller which is suitable for the permanent magnetic synchronous generator (PMSG) high-speed operation in electrified aircraft scenarios. The improved LNSADRC voltage controller integrates the power approach law of sliding mode into the extended state observer (ESO), which is more robust compared with the linear active disturbance rejection control (LADRC). Then, the stability of the proposed LNSADRC voltage controller is proved by constructing multiple Lyapunov functions. Finally, the effectiveness of the proposed voltage controller is validated by the experiment results of the 5.5-kW PMSG platform. The experimental results illustrate that the voltage recovery time of the LNSADRC voltage controller is smaller than the LADRC voltage controller when the PMSG faces load resistor change and prime mover speed change, and the time of voltage establishment for the LNSADRC is faster than the LADRC.

Dynamic equivalence of doubly-fed wind turbines based on parameter identification and optimization

The dynamic equivalence and modeling of large-scale wind farms is the basis for studying the problem of multi-temporal and spatial scale wind farms grid connection, and the establishment of a high-precision equivalence model is a key issue among them. This paper takes doubly-fed wind turbines as the research object. Aiming at the problem of large dynamic errors in direct aggregation of equivalents into a single unit, an equivalent model combined with particle swarm optimization algorithm is established to improve the accuracy of dynamic equivalents. The electrical parameters, reactive power reference values, active power controller parameters, and active DC voltage controller parameters are optimized using particle swarm optimization. The research results show that the equivalent model after optimizing the parameters of the active power and DC bus voltage controller is the closest to the detailed model in describing the dynamic characteristics of multiple machines.

Active Damping Injection Output Voltage Control with Dynamic Current Cut-Off Frequency for DC/DC Buck Converters

With regard to DC/DC buck converter applications, the objective of this study is to expand the admissible range of the output voltage cut-off frequency while lowering the steady-state current cut-off frequency as possible. This study fortifies the inner loop by incorporating the novel subsystems such as an auto-tuner (for the dynamic current cut-off frequency) and active damping injection invoking the pole-zero cancellation nature with the particular designed feedback gain structure. The outer loop active damping control renders the closed-loop speed transfer function to be a first-order low-pass filter with the cooperation of the specially structured design parameters; in addition, it provides time-varying disturbance attenuation. The experimental results obtained for a 3-kW buck converter validate the feasibility of the proposed technique by showing a 34% performance enhancement (at least) compared with the recent active damping controller.

Facilitating higher photovoltaic penetration in residential distribution networks using demand side management and active voltage control

AbstractFuture power networks are certain to have high penetrations of renewable distributed generation such as photovoltaics (PV). At times of high PV generation and low customer demand (e.g., summer), network voltage is likely to rise beyond limits mandated by grid codes resulting in a curtailment of PV generation, unless appropriate control means are used. This leads to a reduction in energy yield and consequently reduces the economic viability of PV systems. This work focuses on scenario‐based impact assessments underpinned by a net prosumer load forecasting framework as part of power system planning to aid sustainable energy policymaking. Based on use‐case scenarios, the efficacy of smart grid solutions demand side management (DSM) and Active Voltage Control in maximizing PV energy yield and therefore revenue returns for prosumers and avoided costs for distribution networks between a developed country (the UK) and developing country (India) is analyzed. The results showed that while DSM could be a preferred means because of its potential for deployment via holistic demand response schemes for India and similar developing nations, technically the combination of the weaker low voltage network with significantly higher solar resource meant that it is not effective in preventing PV energy curtailment.

A Virtual Space Vector PWM With Active Neutral Point Voltage Control and Common Mode Voltage Suppression for Three-Level NPC Converters

Virtual space vector pulsewidth modulation (VSVPWM) provides a new approach to neutral point voltage (NPV) control and common mode voltage (CMV) suppression. Few values of coefficients configured in the virtual vectors cannot adjust the NPV continuously. An improved VSVPWM (IVSVPWM) with active neutral point voltage control (ANPVC) and CMV suppression is proposed in this article. Continuously variable coefficients configured in the virtual vectors adjust the NPV actively and continuously for any load power factor over the full modulation indexes. Failure of CMV suppression is analyzed, and the undesired vectors with high CMV are avoided by limiting the range of the variable coefficients. The limited variable coefficients and the selected basic vectors with low CMV suppress the CMV effectively. Simulation and experimental results are given to validate the proposed novel IVSVPWM, which can achieve quicker ANPVC and reduce CMV to half of the conventional VSVPWM simultaneously.

Active Gate Driver and Management of the Switching Speed of GaN Transistors during Turn-On and Turn-Off

The paper investigates the management of drain voltage and current slew rates (i.e., dv/dt and di/dt) of high-speed GaN-based power switches during the transitions. An active gate voltage control (AGVC) is considered for improving the safe operation of a switching cell. In an application of open-loop AGVC, the switching speeds vary significantly with the operating point of the GaN HEMT on either or both current and temperature. A closed-loop AGVC is proposed to operate the switches at a constant speed over different operating points. In order to evaluate the reduction in the electromagnetic disturbances, the common mode currents in the system were compared using the active and a standard gate voltage control (SGVC). The closed-loop analysis carried out in this paper has shown that discrete component-based design can introduce limitations to fully resolve the problem of high switching speeds. To ensure effective control of the switching operations, a response time fewer than 10 ns is required for this uncomplex closed-loop technique despite an increase in switching losses.

Suppression of residual amplitude modulation of ADP electro-optical modulator in Pound-Drever-Hall laser frequency stabilization

We report a simple and robust approach to reduce the residual amplitude modulation (RAM) by employing an ammonium dihydrogen phosphate (ADP) crystal to provide optical phase modulation in the Pound-Drever-Hall frequency stabilization system. The birefringence-related amplitude modulation can be suppressed due to the insensitivity to the ambient temperature of the crystal. The proposed RAM can be significantly reduced to 20 ppm level, which is comparable with the electro-optic modulator (EOM) under critical active temperature and bias voltage control. The RAM-induced frequency instability is below 2 × 10−17 for integration times from 1 to 1000 s, which is lower than the fundamental thermal noise limit of the reference cavity and meets the requirements for realization of the ultra-stable laser and high-precision measurement.

A Loss Redistribution Technique for the Power Devices in the NPC Converter by PWM Zero-Sequence Injection

The neutral-point-clamped (NPC) converter suffers from uneven power loss distribution among semiconductor devices under the conventional modulation technique, which degrades its reliability. In this article, a zero-sequence voltage injection technique is proposed to address this issue. Its effectiveness of power loss redistribution is not restricted by operation conditions, and no extra devices are required. Its performance in reducing the power loss of the most stressed device in the NPC converter is verified by simulation and experiment tests under different power factors. A compatible active neutral-point voltage control strategy is designed and validated by laboratory tests. The output current quality and common-mode voltage are discussed as well.