Voltage Regulation Characteristics Research Articles

A Low-Order Steady-State Model of Electric Springs for Conservation Voltage Reduction in Active Distribution Networks With Renewables

Electric spring (ES), as a new type of power electronic device, can flexibly regulate the voltage of noncritical load (NL) and improve the voltage quality of critical load (CL). It can further increase the energy savings of conservation voltage reduction (CVR) in active distribution networks (ADNs). However, the high-order nonlinearity of ESs steady-state model brings the difficulty of solving the CVR optimization problem Therefore, this paper proposes a low-order steady-state model of ESs for CVR in ADNs. The operation modes of ESs are extended based on analysis of voltage regulation characteristics, firstly. The equivalent circuit of the bus with an ES is also derived, and a steady-state model with low-order nonlinearity is further proposed. Then, considering significant difference in response speeds among ESs, distributed generation (DGs) and discrete control devices (DCDs), a two-stage coordinated operation model of ESs, DGs and DCDs is established. By means of convex envelope and linearization, the nonconvex nonlinear constraints are transformed into linear constraints, which can improve the convergence and solving efficiency of the optimization model. Finally, the case studies demonstrate that ESs can increase the CVR energy savings, and the proposed low-order steady-state model can improve the solving efficiency of this CVR optimization problem.

Control Strategy of Seamless Switching Between Grid-connected and Islanding Operation for Weak-connected Microgrid

A control strategy of seamless switching is proposed for the high-capacity microgrid, which is at the end of long-distance transmission. Firstly, the control modes of energy storage and diesel generator set under grid-connected conditions and islanding conditions are analyzed. Meanwhile, the seamless switching strategy for the microgrid, in which energy storage or diesel generator sets can be taken as the main power source adaptively, is proposed. During the switching from the grid-connected condition to the islanding condition, the connection line power is optimized according to the respective operational characteristics of the energy storage and diesel generator sets. And the interaction of the power step control with voltage blocking and the regulation characteristics of the line voltage regulator is utilized to effectively suppress the fluctuation of system voltage and frequency. Finally, the combination of auto-synchronization control and multiple synchronization control improves the success rate of switching from the islanding condition to the grid-connected condition. The on-site test results of an actual microgrid project verify the effectiveness of the proposed control strategy.

Cost‐effective secondary voltage control in dc shipboard integrated power system

AbstractFast and dramatic voltage disturbances caused by the electric propulsion and dynamic positioning process are severe issues in the DC shipboard integrated power system (DC‐SIPS). The secondary voltage control (SVC) equipped in the diesel genset (DG) and hybrid energy storage system (HESS) becomes an effective solution. However, the conventional SVC cannot distinguish the different voltage regulation characteristics between DG and HESS in a cost‐effective way when allocating the voltage regulation responsibility (VRR). The cost optimization achieved by the conventional tertiary control cannot be used for the DC‐SIPS due to frequent and unpredictable load fluctuations. In this paper, a cost‐effective secondary voltage control is proposed to realize voltage restoration and cost minimization simultaneously. First, the voltage regulation cost model is developed considering the different voltage regulation characteristics of DG and HESS. Then, the optimization problem of VRR distribution is addressed by minimizing the total voltage regulation cost function using a quadratic programming algorithm. Moreover, the voltage regulation ability of each energy storage system is fully used with the state of charge balance. Thus, the conflict among voltage restoration, cost minimization, and SoC balance is effectively addressed. Finally, promising hardware‐in‐loop test results illustrate the effectiveness of the proposed method.

Optimal Voltage Control Method for a Step Voltage Regulator Considering the Under-Load Tap Changer in a Distribution System Interconnected with a Renewable Energy Source

The voltage in distribution systems is controlled by the under-load tap changer of the substation and the pole transformer of the primary feeders. Recently, as one of the main countermeasures, a step voltage regulator is being introduced to solve voltage problems such as overvoltage phenomena in a distribution feeder interconnected with a renewable energy source and under voltage in a long-distance feeder. However, the tap of the step voltage regulator may be frequently operated due to its interdependent relationship with the under-load tap changer in the distribution system. Furthermore, given the existing operating characteristics of the step voltage regulator, it is difficult to perfectly maintain the customer voltage within an allowable limit using existing methods such as the line drop compensation method for a step voltage regulator. In addition, the existing line drop compensation method, considering the distributed generators, may be not able to control the proper voltage within an allowable limit. Therefore, in order to solve such voltage problems, this paper proposes a voltage control method for a step voltage regulator by considering the output voltage of an under-load tap changer that is operated via the line drop compensation method. In other words, to overcome the limitations of existing voltage control methods for step voltage regulators, this paper proposes an optimal control method to determine the optimal compensation rate for a step voltage regulator by considering the reverse power flow from a renewable energy source and the output voltage of the under-load tap changer of the main transformer.

Wind SRG-Based Bipolar DC Microgrid with Grid-Connected and Plug-In Energy Supporting Functions

Although a switched reluctance generator (SRG) is not the mainstream wind generator, it possesses the application potential and is worth developing for its many structural merits and high developed power ability. This paper presents a wind SRG-based bipolar DC microgrid having grid-connected and plug-in energy supporting functions. First, a surface-mounted permanent magnet synchronous motor (SPMSM)-driven wind turbine emulator (WTE) is established. Next, the wind SRG with an asymmetric bridge converter is developed. Good generating characteristics are obtained through proper designs of power circuit, commutation mechanism, external excitation source, voltage and current controllers. Third, a DC/DC boost interface converter and a bipolar voltage balancer are constructed to establish the 500 V microgrid bipolar DC-bus. To preserve the microgrid power supplying quality, a battery energy storage system (BESS) with bidirectional DC/DC interface converter is equipped. A dump load leg is added across the bus to limit the DC-bus voltage under energy surplus condition. In load side, a three-phase bidirectional load inverter is developed, which can be operated as a single-phase three-wire (1P3W) inverter or a three-phase three-wire (3P3W) inverter. Good sinusoidal voltage waveform and regulation characteristics are obtained using the proportional-resonant (PR) control. The microgrid to load and microgrid to grid operations are conductible. Finally, to further improve the powering reliability of microgrid, a three-phase T-type Vienna switch-mode rectifier (SMR) based plug-in energy supporting scheme is developed. When the microgrid energy shortage occurs, the possible harvested energy can be used to supply the microgrid.

A Simple Circuit and Control Topology to Produce Bipolar Non-Inverted and Inverted Voltage Step-Down Features

Single-phase AC–AC converters with a direct power conversion approach are receiving rapid development as they have the ability to produce the regulated non-inverting and inverting form of the input voltage at the output. This feature enables them to correct the line voltage profile once they are used as dynamic voltage restorers if there is an issue of voltage sag or swell in the power distribution system. The regulated non-inverting and inverting form of the output voltage may also be used to obtain the step change in the output frequency, as it is required in many industrial drive systems. However, the realization of such existing circuits needs a large number of components and semiconductor devices, especially switching transistors. The operating control (on and off) of the transistors is directly associated with the use of gate control circuits. The count of such circuits is critical as their volume and cost are much greater than the operating transistors. The number of conducting semiconductor devices in the existing converters is also a big source of high conversion losses, thus leading to lower efficiency. This article introduces a new circuit topology realized only with the use of one full bridge of four IGBTs and a full bridge of four diodes. The use of four switching transistors only requires four gate control circuits that drastically reduce the overall volume and size. All the operating modes of the proposed topology require the conduction of fewer semiconductor devices, which helps to lower the conduction losses. Detailed analysis and description were carried out to validate the attractive features of the developed circuit once compared with the existing circuit topologies. For validation purposes, the computer simulation was carried out on Simulink software. The results obtained from this environment were compared with the real results gained from a practically developed laboratory test bench. The voltage regulation characteristics of the output voltage by employing pulse width modulation (PWM) were confirmed for two values of the non-inverting and inverting outputs.

Determining the mode characteristics of voltage regulator with capacitive load

The tasks of dynamic compensation of reactive power are solved by means of flexible AC transmission systems using power electronics devices. The object of this study is a variable voltage regulator with a capacitive load. This paper considered the problem of the efficiency of phase voltage regulation on the capacitor battery to use it as a source to compensate for reactive power. The results of the study are presented, which justify the effectiveness of the technique for obtaining a dynamic source of reactive power based on the use of a thyristor voltage regulator with a capacitive load. A comparative study of two regimes of the regulator was carried out: the phase-controlled mode of closing fully controlled semiconductor gates and the phase-controlled mode for opening single-core semiconductor gates. Analytical expressions for angular characteristics of power according to the main harmonics are derived. It is shown that under the first mode the current through the capacitor is capacitive, which makes it possible to obtain a thyristor-adjustable capacitor battery for dynamic compensation of reactive power in power supply systems. It was found that under the second mode, simultaneously with the regulation of reactive power, there is a phenomenon of consumption from the active power supply network according to the main harmonics. This means that the regulation of current through an ideal capacity using ideal phase-controlled semiconductor gates is accompanied by the consumption of the active component of the current from the power supply network. The resulting component of active power in the electrical circuit without active resistances is proposed to be called "active artificial shear power". The results have been confirmed by studies on virtual models

Frequency Modulation Method and System of Photovoltaic Virtual Synchronous Generator Based on Computer Technology

With people’s attention to environmental protection, clean energy has become an important research and development direction. Among them, photovoltaic power generation has many advantages, such as simple process, no fuel consumption, no noise, no pollution and so on. The power grid capacity is becoming larger and larger, and has a great impact on the environment. Therefore, the grid connection of photovoltaic power generation will cause major problems for the planning, operation and dispatching of power grid. Virtual synchronous generator (hereinafter referred to as VSG) technology can simulate the inertia, primary frequency regulation and voltage regulation characteristics of synchronous generator, which has become an important way to improve the dynamic frequency response ability of the system. Therefore, VSG technology has become an important research technology of photovoltaic grid connected system, among which FM method will also become an important research direction. Firstly, this paper analyzes the VSG algorithm and its basic characteristics. Finally, this paper analyzes the control scheme of overall primary frequency regulation of photovoltaic power station (hereinafter referred to as PPS).

Analysis and Design for Output Voltage Regulation in Constant-on-Time-Controlled Fly-Buck Converter

Fly-buck converter is a multi-output converter with the structure of a synchronous buck converter structure on the primary side and a flyback converter structure on the secondary side, and can be utilized in various applications due to its many advantages. In terms of control, the primary side of the fly-buck converter has the same structure as a synchronous buck converter, allowing the constant-on-time (COT) control to be applied to the fly-buck converter. However, due to the inherent energy transfer principle, the primary-side output voltage regulation of COT controlled fly-buck converters may be poor, which can deteriorate the overall converter performance. Therefore, the primary output capacitor must be carefully designed to improve the voltage regulation characteristics. In this paper, a theoretical analysis of the output voltage regulation in COT controlled fly-buck converter is conducted, and based on this, a design guideline for the primary output capacitor considering the output voltage regulation is presented. The validity of the analysis and design guidelines was verified using a 5 W prototype of the COT controlled fly-buck converter for telecommunication auxiliary power supply.

A magnetically controlled series compensation-fault current limiter

This paper presents a magnetically controlled series compensation-fault current limiter (MCSC-FCL) which is composed of a magnetically controlled reactor (MCR) and a compensation capacitor. The device is improved from the traditional thyristor-controlled series compensation (TCSC), which has the characteristics of small output harmonics and simple control. The traditional saturated iron-core reactor is improved to increase the adjustable range of output reactance. During the fault, the MCR is connected to the grid alone to limit fault current; when the grid is normal, MCR and capacitor are used in series compensation mode. It effectively improves the utilization rate of the traditional current limiter MCR. In order to verify the effectiveness of the proposed MCSC-FCL, this paper analyzes the control characteristics of reactor models with different air gap structures by JMAG finite element analysis software, and verifies the voltage regulation characteristics and fault current limitation capabilities on MATLAB/Simulink platform.

A Transformer-Less Multiconverter Having Output Voltage and Frequency Regulation Characteristics, Employed with Simple Switching Algorithms

The attractive features of the direct AC-AC converters increase their use in many applications such as voltage control for a heavy-duty load that has a high time constant, AC machine drives, and heating systems based on the induction process. These converters process power in single-stage having simple circuit topologies with reduced switching devices and circuit components. These characteristics lead to the efficient power conversion process. The use of a low-frequency input transformer with multiple output tapping for the regulation of output voltage and frequency is one of the major sources of cost, size, and conversion losses. The complication in the switching algorithms is also the main concern in these converters. The preceding deficiencies lower their potency to be used in daily life. The costly controllers or processors are to be employed to realize the complex control techniques or algorithms. That increases the overall cost and circuit complication. This paper introduces the simple control techniques employed to a novel transformer less multi converter to have the various ac outputs for voltage and frequency regulation. The validation of power circuit and control schemes is tested through the simulation and practical results obtained in Simulink and practical setup respectively.

Development of Brushless Claw Pole Electrical Excitation and Combined Permanent Magnet Hybrid Excitation Generator for Vehicles

Aiming at the problems of large excitation loss and low power generation efficiency of silicon rectifier generators and the unstable output voltage of permanent magnet (PM) generators, a hybrid excitation generator (HEG) with suspended brushless claw pole electrical excitation rotor (EER) and combined magnetic pole PM rotor is proposed in the present work. With only one fractional slot winding stator, the generator adopts PM field as the main magnetic field and electrical excitation field as the auxiliary magnetic field, which not only retains the advantages of high efficiency of PM generators but also effectively reduces excitation consumption. The main structure parameters and the design method were analyzed, and a simulation analysis of no-load magnetic field distribution and flux regulation ability was carried out using finite element software to verify the rationality of the hybrid excitation parallel magnetic circuit design. Moreover, the no-load, load, regulation, and voltage regulation characteristics of the designed generator were tested, and the results show that the designed generator has a wide range of voltage regulation, which can ensure stable output voltage under variable speed and load conditions.

Research on a hybrid excitation PM synchronous generator with stator third harmonic winding excitation

This study presents a hybrid excitation permanent magnet synchronous generator (HEPMSG) with a stator third harmonic winding to solve the problems of adjusting the air-gap magnetic field of the permanent magnet synchronous machine (PMSM) and simplify the excitation system structure. The electromotive force (EMF) of the stator third harmonic winding, induced by the inherent third harmonic magnetic field in the air gap, provides the adjustable field current for the rotor field winding via the controllable rectification. The proposed machine structure is described, and the generation mechanism and the excitation principle of the stator third harmonic EMF are analysed. The conditions for maximum excitation current output are discussed, and the integrated design methods of the stator third harmonic winding and the rotor excitation winding are described. Based on the finite element method, the performances of the third harmonic excitation system are numerically compared for different stator third harmonic windings, and the open-circuit voltage regulation characteristics under different control angles are analysed. A 2.5 kW HEPMSG prototype with a stator third harmonic winding is manufactured and tested. The predicted and experimental results are in good agreement, which verifies the correctness of the excitation principle of the proposed HEPMSG.

Voltage regulation characteristics of a two-pack synchronous generator with combined excitation

The design, principle of operation, method for determining the inductance and the algorithm for plotting the voltage regulation characteristics of a two-packet synchronous generator with a combined excitation are described in this article. Characterization and inductance calculation were carried out for a prototype having a power of 11 kW, number of phases - 3, frequency of induced EMF in the AC winding - 550 Hz, number of pole pairs - 11.

Research on Multifunctional High-Power Grid Source Simulator System with Synchronous Generator, Line Impedance Imitation, and ZIP Load Emulator

As the penetration of distributed power sources in the power grid is getting higher and higher, the adverse effects are also increasing. It is necessary to adopt control technology to make the distributed power source participate in the power regulation of the power system. In this paper, a multifunctional high-power grid source simulator system is presented. For wider control bandwidth and better performance, a high-power, back-to-back converter and an auxiliary lower-power, back-to-back converter connected in cascade mode topology is proposed in this paper. The basic principle and implementation method of virtual synchronous generator (VSG) in the high-power, back-to-back converter are described to reflect the same power frequency characteristics and voltage regulation characteristics as synchronous generators. Amplitude closed-loop control is proposed to realize zero steady-state error in the lower-power, back-to-back converter, also with line impedance imitation. Meanwhile, a constant-impedance, constant-current, and constant-power (ZIP) load model is used to emulate static load in the grid simulator system. At last, a set of experimental results for a 2 MW grid simulator system is provided to verify the effectiveness and validity of the proposed approach.

Regulatory Features of Solar Battery Charger

The aim of the work is the analyze the of regulation characteristics of a switching voltage regulator of the step-up type. The case when the regulator's power source is a solar battery and the load is a rechargeable battery is considered. It is noted that in this mode, the switching voltage regulator operates in the mode of regulation of the output current (battery charging current). The case when the battery voltage is equal to the maximum no-load voltage of the solar battery is analyzed. It is shown that in this case regulation characteristic of the input current of the switching regulator coincide with the output characteristics of the solar battery, in which the axis of voltage is replaced by the axis of the relative open-time of the key of the switching regulator. Taking into account the received input regulation characteristics, the output regulation characteristics of the switching regulation were built. If the battery voltage is less than the maximum no-load voltage of the solar battery, the regulation characteristics of the switching regulation will coincide with a limited section of the output characteristics of the solar battery. In this case, the correspondence between the voltage scale and the scale of the relative open time of the key of the switching regulator will depend on the ratio between the battery voltage and the maximum no-load voltage of the solar battery. The conditions, under which the maximum amount of electrical energy will be obtain from the solar battery at different levels of illumination were analyzed. The condition, under which the inductance of the switching regulator will receive a discontinuous current mode were analyzed. For different levels of illumination of the solar battery, as well as depending on the magnitude of the inductance, the critical value of the relative open-time time of the key of the switching regulator, at which a discontinuous current mode occurs in the inductance were determined. Taking into account the possibility of the occurrence of such a mode, the adjustment of the previously obtained regulation characteristics were carried out. The normalized graphs of the regulation characteristics for the input and output current of the switching regulator, taking into account the possibility of the occurrence of a discontinuous current inductance in it are given. Recommendations on the expediency of using various sections of these characteristics, when charging batteries from a solar battery, are given. The dependence of the amount of under-received electrical energy from the solar battery, which is related to the pulsating nature of the input current of the switching regulator and the selected battery voltage value is analyzed. Recommendations regarding the choice of the battery voltage for a solar cell of the selected type are given.

Gravitational search algorithm based optimization technique for enhancing the performance of self excited induction generator

In wind based micro generation schemes, 3-phase self excited induction generators are prominently used in order to fulfil single phase load requirement. Hence in this context, this paper presents a 3-phase, 5.5 kW, 415 V, 50 Hz short shunt self excited induction generator for improving the voltage regulation and optimum performance of induction machine by using heuristic approach named as gravitational search algorithm. It is used in order to get the optimum capacitance values at specified speed for optimized voltage regulation and performance characteristics in terms of root mean square error and mean absolute error and mean square error. This optimization technique works on Newton law of gravity and it provides average best results for validating the performance in order to enhance machine parameters used in wind energy conversion system.

Voltage Management for Large Scale PV Integration into Weak Distribution Systems

In long distribution feeders, step voltage regulators (SVRs) with the line drop compensation have been widely implemented to control voltage profiles. After integration of photovoltaic (PV) systems, reactive power support from PV inverters can also be utilized in voltage regulation. Although both SVR and reactive power support can be effective to manage system voltage without coordination, problems such as large voltage variations and excessive SVR tap operations still exist in some strong PV power fluctuating days. In order to solve these issues, SVR and reactive power support should be assigned to different voltage regulation tasks according to their voltage regulation characteristics. Specifically, in a distribution system, an SVR should mainly deal with slowly changing quantities ( e.g. , load, upstream voltage), while the limited reactive power support should be used to counter fast fluctuating PV power. In this paper, the power factor droop parameters applied on PV inverters are optimally selected to achieve such coordination, so that voltage problems and excessive SVR tap operations can be successfully mitigated. The effectiveness of the proposed method is demonstrated via case studies. Future PV integration project in weak distribution systems can benefit from the innovative and practical methodology proposed in this paper.

A Distributed Voltage Control Strategy for Multi-Microgrid Active Distribution Networks Considering Economy and Response Speed

This paper presents a novel distributed voltage control strategy to maintain the voltage of active distribution networks containing multiple microgrids. Local voltage regulation characteristics, such as power reserve, adjustment cost, and regulating speed, are identified first. According to a neighbors’ voltage regulation characteristics, the microgrid coordinates neighborhood resources and asks them for coordination as soon as voltage problems occur. Microgrids schedule local resources based on a cooperative distributed model predictive control algorithm scheme with neighbor-to-neighbor communication. Tests are performed in an active distribution network with three microgrids. The numerical studies have shown that the proposed strategy mitigates the voltage fluctuation rapidly and efficiently with minimum operating cost.

Nonlinear Behavior Immunity Modeling of an LDO Voltage Regulator Under Conducted EMI

This paper presents a nonlinear behavior modeling method committed to the immunity of low-dropout (LDO) voltage regulator to conducted electromagnetic interference (EMI). A nonlinear behavior model is proposed to predict the immunity of LDOs, where the nonlinear characteristics of an LDO voltage regulator are described as a cascade of Taylor series and linear filter system. A test printed circuit board (PCB), using the direct power injection (DPI) method, is designed up to 2 GHz to measure the immunity of LDOs. A nonlinear behavior model, lump-parameter models of discrete components on PCB extracted from S -parameter measurement, and DPI method are used to predict the immunity of an LDO voltage regulator. The comparison of immunity between simulation and measurement shows that the model has a good fit up to 2 GHz.