Controlled Voltage Source Research Articles

CONSIDERATIONS ON THE ANALYSIS OF THE OPERATING CHARACTERISTICS OF THE HORIZONTAL SYNCHRONOUS MOTORS EQUIPPING THE HYDRO AGGREGATES IN HIGH-POWER ENERGY PUMPING STATIONS

In this paper, the authors present modelling and analysis of the operating characteristics of the synchronous motor with electromagnetic excitation, for driving the centrifugal pump that equips hydro aggregates in high-power energy pumping stations, motor powered from fixed or adjustable voltage sources. Two operating scenarios were considered, namely: the stationary operation of the synchronous motor fed from an ideal, controllable voltage source and the case of its supply from the industrial network. For solving, algorithms and calculation programs developed in the Mathcad programming environment were designed. For example, a representative case study of one of the three identical hydro aggregates from one of a high-power energy pumping station of an existing hydropower facility in Romania was chosen. The hydro aggregate is driven by a horizontal synchronous motor with electromagnetic excitation powered at medium voltage (6 kV).

The Influence of Switching Frequency on Control in Voltage Source Inverters

This paper aims to show how the switching frequency influences the properties of the digitally controlled voltage source inverter (VSI). The measurements of the Bode plots of the inverter are shown and discussed to present the existing signal delays and power conversion efficiency, depending on the switching/sampling frequency. Two types of controllers are presented, Single-Input–Single-Output (SISO) and Multi-Input–Single-Output (MISO), and adequate prediction units (the Smith Predictor for SISO—Coefficient Diagram Method and the full-state Luenberger Observer for MISO—Passivity Based Control) were used to compensate for the delays. It will be shown by comparing the THD of the VSI output voltage that prediction is useful with low VSI switching frequency (about 10 kHz) but is not important for the middle switching frequencies (about 25 kHz) or the high switching frequency (>50 kHz). This paper shows that increasing the switching frequency simplifies digital control without reasonably decreasing efficiency. The theoretical considerations, the Matlab/Simulink 2021b simulations, the final experimental laboratory verification are presented.

Double closed loop PI control with full compensation arc elimination based on zero sequence voltage of neutral point

Aiming at the problem of zero sequence voltage generated by unbalance parameters of line to ground, which affects arc suppression effect of grounding fault of controllable voltage source. By analyzing the influence of ground unbalance parameters on the arc suppression effect of controllable voltage source under different grounding modes, the mechanism of full compensation arc suppression based on zero sequence voltage of neutral point is revealed, and on this basis, a fully compensated arc suppression model of controllable voltage source controlled by double closed loop PI is established, and the deviation control is carried out by using the neutral voltage of distribution network and the voltage of fault phase supply. The residual voltage ring adopts the ground fault phase residual voltage for closed loop control. The simulation results show that the dual-closed-loop PI control algorithm can continuously stabilize the output waveform of the controllable voltage source. When the transition resistance is 0.1 ~ 10 kΩ, the residual voltage stabilization time of the independent controllable voltage source grounding method is 43 ms ~ 2.4 s, and the parallel arc suppression coil grounding method is 43 ms ~ 4.7 s. The proposed dual closed-loop PI control method for neutral point voltage deviation and fault residual voltage can stabilize the residual voltage of the grounded fault phase to below 10 V, forcing reliable arc extinction at the grounded fault point, exhibiting good stability. Low-voltage simulation tests have also proved the feasibility of the algorithm.

Research on Voltage Coordinated and Stability Control of Condensers Based on Reactive Power Replacement

Abstract In this research, we investigated condenser voltage coordination and stability control systems by analyzing voltage coordinated control mode among excitation, voltage coordination and stability as well as automatic-voltage reactive power control systems. By using dynamic excitation regulation and steady-state regional voltage source control replacement, dynamic reactive power quickly output under fault condition as well as optimized regional reactive power under steady state were realized. The correctness and practicability of the proposed strategy was verified through engineering application. Adopting the reactive power displacement of voltage coordination control system to solve local voltage instability problem after UHV DC blocking. The proposed method realized multi-time scale emergency, recovery and steady-state control of the system under steady and dynamic states.

Effect of Semiconductor Materials on the Current Control Voltage Source Trancitor Hall Voltage

Effect of Semiconductor Materials on the Current Control Voltage Source Trancitor Hall Voltage

Sizing and experimental validation of a selfsync droop-based grid forming inverter with direct voltage control

Currently, the transient stability of the grid is mainly ensured by the inertial behavior of its synchronous generators. The increase of renewable energy sources connected to the grid through grid following (GFL) inverters is severely affecting the inertia of the grid and its stability is beginning to be compromised. Moreover, in case of a large disturbance, these renewable energy sources disconnect from the grid by design, thus exacerbating the problem. The idea of mimicking the behavior of synchronous generators in an inverter and participating in the grid stability gave birth to the so-called grid forming (GFM) inverters. This implies a change in paradigm from current controlled sources (GFL) to voltage-controlled sources (GFM). Despite known stability issues in current controlled converters, a typical approach to GFM converters with LCL output filters is based on cascaded current and voltage control loops. An internal current loop controls the inverter’s output currents and an external voltage loop controls the filter capacitors’ voltages. The problem is that this solution is complex and is also marginally stable. Alternatively, in this paper we explore a direct voltage control, which is based on droop control. The proposed control’s output is used for the direct control of the inverter’s output voltage in amplitude and phase. A complete analysis is performed, and a method is proposed to determine the appropriate control parameters as well as the sizing of the inverter components. Finally, an experimental setup is presented and the effectiveness of the proposed method is shown in simulations as well as in real-life experiments.

A novel resistance-capacitance model for evaluating urban building energy loads considering construction boundary heterogeneity

To address the problems associated with the accuracy of existing resistance-capacitance (RC)-based urban building energy modeling (UBEM) being low, a novel RC-based UBEM was developed. This model takes into account construction boundary heterogeneity by clustering and lumping together building construction elements with similar boundary conditions. In addition to buildings with single thermal zone, the novel RC model was extended to buildings with multiple thermal zones by using voltage-controlled voltage sources (VCVSs). The model was validated by four ASHRAE 140 cases with single thermal zone and two real urban building cases with multiple thermal zones. To verify the effectiveness of the proposed lumping concept, comparisons between the proposed RC model and the existing RC models were conducted. The results show that the novel RC-based UBEM could reach the balance between accuracy and efficiency. The hourly heating/cooling loads of the novel RC model agree well with those produced by the benchmark model EnergyPlus. The novel model has shown an efficiency improvement of approximately 78% compared to EnergyPlus. The 4R1C model is more accurate than 3R2C model especially for cases with large capacitance and resistance differences between interior and exterior construction components. The accuracy of the proposed RC-based UBEM is significantly improved compared with the existing RC-based UBEM. Thus, it is necessary to consider the construction boundary heterogeneity in the RC models for evaluating urban building energy loads.

Voltage and Current Control Strategy for Grid Connected WECS Employing Two and Three Level Voltage Source Converters

This paper presents voltage and current control strategy for grid connected variable speed wind turbine induction generator employing two and three level voltage source inverters. Induction generators are widely used because of its low cost, robust construction and capability of feeding active power to load without getting reactive power from separate source. The mechanical energy required to drive the generator is obtained from a variable speed wind turbine. Three phase induction machine is excited from a three phase voltage source converter. The DC voltage of the capacitor is inverted and fed to the three phase grid using a current controlled voltage source inverter. Control strategy has been developed for maintaining the DC link voltage constant and also to feed the power at unity power factor to the grid, even though there is variation in wind speed. It is also shown that the harmonics are considerably reduced when a two level inverter is replaced by a three level inverter. The simulation study has been carried out using MATLAB/Simulink. Simulation results indicate the feasibility of control strategy.

Static Series Compensator for the compensation of voltage-quality disturbances based on particle swarm optimization techniques

Static Series Compensator (SSC) is a power electronic based device that provides three-phase controllable voltage source to restore the load voltage to pre-sag conditions within few milliseconds. This paper proposes a new control technique based on an adaptive tunning PI controller that uses a selective controller to describe the effectiveness of SSC for mitigating voltage sags in power distribution systems at critical loads. The integral of time multiply squared error (ITSE) index is minimized to reach the optimal tuning of PI controllers based on particle swarm optimization (PSO) technique to determine whether the best fitting solution is achieved. The controller is designed in a synchronously-rotating reference frame. Independent (homopolar component, d-axis component and qaxis component) controllers are used to tackle balanced and unbalanced voltage supplies. Simulation is done using Simulink “SimPowerSystem” Toolbox to illustrate the principle and performance of an SSC operation in load voltage compensation

Multiresolution Models of DC Traction Power Supply Systems With Reversible Substations

Reversible substations (RSs) permitting bidirectional power flows can recover the regenerative braking energy of trains in DC traction power supply systems (TPSSs), increasing the energy efficiency of railway systems. To predict their effects on system dynamics and energy savings, the paper develops multiresolution models (MRMs) to simulate the RS roles with different fidelities. A high‐resolution model for the transient simulation replicates a particular topology where a three‐level voltage source inverter is connected to the secondary winding of an existing 12‐pulse rectifier transformer and regulated to keep a constant DC voltage in the inverting mode. Furthermore, it can model the transient effects of pantograph‐to‐line arcing by inserting arc voltage profiles at the train’s input stage. To increase the computation speed in the long‐term energy flow simulation, a low‐resolution model simplifies the rectifiers into a series connection of a diode and a controlled voltage source depicting their nonlinear output characteristics and then places a DC voltage source in parallel to form a reverse path for braking power recovery. In addition, nonlinear conversion efficiencies are introduced to calculate energy flows across substations. The MRMs are tested based on a 1.5 kV DC TPSS and discussed alongside system dynamics under normal operation or pantograph arcing and the consistencies between different models. The RS using bidirectional voltage source converters only is additionally modelled to compare the technical performance of the two topologies in terms of system dynamics and energy efficiencies.

Simulation of the influence of parameters of disturbing vibration accelerations on the operation of a new two-channel transformer gravimeter

A new two-channel transformer gravimeter of an automated aviation gravimetric system was considered, the accuracy of which is higher than gravimeters known today. Its design was described. The influence of the parameters of disturbing vibrational accelerations on the operation of a new two-channel transformer gravimeter was simulated. The influence of frequencies and amplitudes of perturbing accelerations for the most unfavorable resonant cases on the operation of a two-channel transformer gravimeter was studied using a computer. After all, today there are no scientific, theoretical and practical works devoted to researching the possibility and expediency of using a two-channel transformer gravimeter as an AGS gravimeter. The transformer gravimeter contains a sensitive element consisting of a magnetic circuit, a movable armature, a primary excitation winding and a secondary output winding having two identical sections. Two sections of the secondary winding are connected in series-opposite, and the movable armature is connected to the motor, which, with a certain period, lowers the armature down and lifts it up along the magnetic circuit, and the motor is controlled by a switching device connected to the control voltage source, and the output signal from the secondary output winding is fed to the input of the output signal calculator, where an output signal is generated that is proportional to twice the value of the gravitational acceleration. A transformer gravimeter is a means of measuring the vertical component of the gravitational acceleration vector from an aircraft and can be used in the field of geodesy, geophysics, in particular, in the formation of reference gravimetric grids in hard-to-reach areas of the globe, as well as in aircraft and rocket building. The transformer gravimeter is part of the aviation gravimetric system placed on the aircraft.

Comparison of a Dynamic Model of Electric Arc Furnace with Actual Operation Data for Voltage Flicker Analysis in Electrical Power Network

Electric arc furnaces (EAFs) used in the iron and steel manufacturing industry for melting and refining scrap metals are one of the most disturbing loads that exhibit unbalanced and highly nonlinear characteristics. Serious voltage fluctuations occur in the power system as a result of the rapid change in the current drawn from the grid by the EAF. Voltage fluctuations lead to a power quality problem known as flicker, which is defined as observable changes in light sources that affect the production environment, cause eye fatigue in personnel, and lower the work concentration levels. To investigate the voltage flicker problem, an accurate mathematical model describing the behavior of the EAF load is required. In this study, a dynamic EAF model that can be adjusted to different operating conditions has been developed in the time domain. The electric arc voltage has been modeled as an externally controllable voltage source. The instantaneous arc voltage has been expressed as a function of the arc length independent of the current. The arc resistance, which varies with time and is nonlinear, has also been calculated with differential equations using the instantaneous arc voltage value. To measure the short-term flicker severity index caused by the EAF in the power system, a flicker meter in compliance with the International Electrotechnical Commission (IEC) 61000-4-15 standard has been designed. The current-voltage characteristics of the EAF, its effect on the power system, and the flicker severity occurring at the point of common coupling (PCC) have been analyzed with simulation studies using the PSCAD/EMTDC software. Besides, the simulation results of the dynamic model of the EAF have been compared with the results obtained from the model based on the measured field data.

Saturable Voltage-Behind-Reactance Models of Induction Machines Including Air-Gap Flux Harmonics

Accurate and numerically efficient models of induction machines are of critical importance for reliable analysis and simulation of large-scale power systems. Specifically, modeling magnetic saturation that causes air-gap flux harmonics, which can significantly affect machine dynamics, has been the focus of many research efforts. In this paper, two voltage-behind-reactance (VBR) models are proposed for induction machines which formulate the air-gap flux harmonics caused by the main flux saturation. Specifically, the proposed constant-parameter VBR (CPVBR) model can be conveniently interfaced with the external network using constant <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RL</i> branches and controlled voltage sources. The numerical performance of the two proposed VBR models is validated and benchmarked against the state-of-the-art models of induction machines with saturation and air-gap flux harmonics. It is shown that the proposed models offer superior numerical performance (i.e., higher accuracy and simulation speed) compared to the existing models, which would be beneficial for offline and/or real-time simulations of power systems.

Small-Signal Synchronous Stability of a New-Generation Power System With 100% Renewable Energy

The traditional power system dominated by synchronous generators (SGs) is now evolving into a new-generation power system dominated by voltage source converter (VSC)-based renewable energy, causing substantial changes in the dynamical behavior. This paper investigates the small-signal synchronous stability of a new-generation power system composed solely of grid-following and/or grid-forming power electronics devices in the absence of an infinitely strong bus. The phase-lock-loop (PLL)-based VSC is taken as a representative of grid-following devices and treated as a controlled-current source whose phase is driven by the power factor angle. In sharp contrast, the virtual synchronous generator (VSG)-based VSC is taken as a representative of grid-forming devices and treated as a controlled-voltage source whose phase is driven by the active power. Small-signal synchronization stability models are established for multiconverter power systems within the framework of the classical Phillips–Heffron model for traditional power systems. Explicit expressions for equivalent inertia, damping, and synchronization coefficients are obtained. We find that both PLL-based and VSG-based VSCs show similar synchronization principles and contribute to the inertia and damping of the system. All these findings are well supported and verified by our modal analysis and time-domain simulations.

Two-stage PV grid-connected control strategy based on adaptive virtual inertia and damping control for DC-link capacitor dynamics self-synchronization

Conventional DC-link voltage-controlled voltage source converter (VQ-VSC) controls DC-link capacitor voltage and reactive power output by using phase locked loop (PLL) for synchronous grid connection of new energy sources such as PV. However, the deterioration of dynamic performance in PLL can lead to instability in VQ-VSC control within a weak grid. To improve the stability of VQ-VSC grid connection, the DC-link capacitor dynamic self-synchronous grid-connected control strategy without using PLL is proposed in this paper. The converter virtual rotational inertia variability and virtual inertia damping frequency characteristics are analyzed based on the synchronous generator rotor rotation characteristics. The proposed control strategy provides adaptive virtual inertia and damping coefficients for DC-link capacitor self-synchronous units to dynamically match the inertia and damping requirements during frequency synchronization, and enables VQ-VSC to operate in grid-forming mode without changing the grid synchronization unit. Compared with constant virtual inertia-damping control and adaptive virtual inertia-damping control based on change rate of frequency, the simulation results demonstrate the effectiveness of the proposed control strategy, which significantly improves the grid connection stability of PV systems in weak grids.

Adaptive fault ride through control of VSM Grid-forming converters

Recently, many high voltage direct current (HVdc) transmission lines are being constructed with the intention of becoming “backbones” of future power grids. Grid-forming (GFM) controlled Voltage Source Converters (VSCs) are anticipated to provide significant stability advantages compared with Grid-following (GFL) VSCs in HVdc converters connected to weak ac grids or to grids with high penetration of renewable inverter-based resources (IBRs). This paper proposes an adaptive fault ride through controller for Virtual Synchronous Machine (VSM) GFM control, which has significantly improved fault ride through capability over the more conventional GFM control with cascaded or switchable current limiting. The performance of the proposed adaptive control is investigated using Electromagnetic Transient (EMT) simulation. The results show that the proposed adaptive control has superior post disturbance recovery from ac faults as well as phase angle shifts, and overcomes the instability reported in GFM converters connected to strong ac networks.

Modelling and control of current full compensation system‐based controllable voltage source

AbstractCurrent active suppression technology of arc overvoltage in distribution network has small capacity of controllable voltage source and complex control and cannot flexibly adjust the zero‐sequence voltage of neutral point. This study proposes a controllable voltage source system to fully compensate the arc current of ground fault for solving these problems. A controllable voltage source model based on passive supply voltage converter is established, utilising Dyn transformer to carry unbalanced load for a long time. The model output voltage is the same amplitude and frequency as that of single‐phase ground fault phase, but opposite phase. The compensation switch is operated when a ground fault occurs. The output voltage amplitude of the controllable voltage source is controlled, the fault phase voltage is controlled to be 0 in the closed loop, the grounding fault arc current is eliminated and the arc grounding overvoltage is suppressed. The control strategy was verified by the PSCAD/EMTDC simulation model of single‐phase grounding fault arc in 10 kV distribution network and the real single‐phase fault experiment platform of 0.4 kV distribution network. Results proved the model and strategy's accuracy and effectiveness. It provides an engineering practical method for active suppression of arc grounding overvoltage in distribution network.

출력변동에 대응한 유도발전기의 역률 보상 제어

Induction generators are widely used in micro hydroelectric power plants. When the flow rate and the head change in the power plants, it becomes a parameter that changes the output of the induction generator. Induction generator has a low power factor even when operated at rated output with an inductive load. Also, if the induction generator is operated lower than the rated value or its output power is fluctuated, the change in the power factor becomes larger at a lower power factor. Therefore, a power factor compensation device such as a single capacitor or STATCOM is applied for power factor compensation. When the generator output is fluctuated, the converter voltage of STATCOM has the characteristic of fluctuating in conjunction with it. In this study, we propose the constant voltage source control method in STATCOM for power factor correction of induction generator and its feasibility is verified by the simulation in which the performance of power factor compensation by the capacitor, STATCOM without constant voltage control and STATCOM with constant voltage control are simulated and quantitatively compared. As a results, we confirmed that the STATCOM with constant voltage control can improve the power factor of induction generators a little comparing to the single capacitor or STATCOM without constant voltage control even if the generator output is fluctuated.

Comparative assessment of single-loop droop controlled grid-forming converter and its damping enhancement

As the penetration of power electronic interfaced power sources increases rapidly, grid-forming controlled voltage source converters (VSCs) are deemed as an effective alternative to synchronous generators. As a typical grid-forming control scheme, droop control is commonly utilized due to its simplicity of construction and stability of operation. VSCs driven by droop controls, such as multi-loop droop control (MLDC) and single-loop droop control (SLDC) are capable of actively establishing voltage and frequency of grid-forming converters. However, the transient performance of SLDC at different faults is less explored to date. In this work, an in-depth comparative assessment of large-signal stability against the established MLDC is first presented by means of phase portrait. It is revealed that, both control strategies have similar transient behaviors with their basic scheme. However, with the introducing of the low-pass filters which can emulate the inertia, SLDC generally exhibits a larger power angle overshoot during the fault and therefore has poorer transient stability as compared that of MLDC. To address this issue, this work improves the damping of SLDC by incorporating differential compensation link into it. Furthermore, a parameter design guideline that balances damping and inertia, hence the transient stability and frequency stability, is proposed. The analysis is supported by real-time hardware-in-the-loop experimental results.

Single Tuned Filter Design for Mitigating Harmonic Distortion in (30 KV) ALTAHRER Substation

Nowadays, due to the fast growth of electronic devices, harmonic issues have become a main matter for current day electrical operators. Some of the causes of harmonics are: a) ripples in voltage waveform of machines, b) flux distortion in the synchronous machines, c) transformer magnetizing currents, d) non-linear loads such as static power converters, arc furnaces, and e) static-var compensators as suppliers of continuously variable var sources. The harmonic filtering is one of the solutions for preventing the worrying harmonics from entering the rest of the system. There are basically two types of filters: i) passive, where the filter components are passive elements such as resistor, inductor, and capacitor, and ii) active, where the filter has a controlled current or voltage source. This peper introduces a single-tuned passive filter to minimize the harmonic distortion of AL-TAHRER substation (30KV). The offered filter and studied system modeling are built by ETAP software. Results show the effectiveness of the proposed filter in mitigating total harmonic distortion of studied system