Accurate Power Control Research Articles

Accurate Power Control for Hybrid PV-Battery/Supercapacitor System

Accurate Power Control for Hybrid PV-Battery/Supercapacitor System

Decentralized Control for Multi-Terminal Cascaded Medium-Voltage Converters Considering Multiple Crossovers

Decentralized control with multiple droop characteristics can significantly improve the accuracy of power flow in medium-voltage direct-current (MVdc) networks. However, multiple crossovers caused by different control characteristics can lead to the drifts of power and voltage and instability issues. When this type of control is implemented in the cascaded three-level neutral-point-clamped (C3L-NPC) converters, on one hand, the mechanism of such the power and voltage drifts was not investigated. On the other hand, power control accuracy, dc voltage balancing across submodules (SMs) and multiple crossovers should all be considered, which requires suitable control methods. To address the challenges, firstly, the mechanism behind the power and dc voltage drifts is analyzed. Secondly, a control scheme is presented to improve the power control accuracy and dc voltage balancing and concurrently, to avoid the multiple crossovers. This is achieved by suitable droop gain design and adding a secondary power compensator. The presented control scheme is verified in MATLAB/Simulink simulation and experimentally validated in a three-terminal MVdc testbed. Results show that the accuracy of steady-state power flow is improved by 15% due to the elimination of multiple crossovers, while the power accuracy at dynamics improved by 13% with the secondary power compensator.

Accurate and Continuous Reactive Power Control of Three-terminal Hybrid DC Transmission System

Accurate and Continuous Reactive Power Control of Three-terminal Hybrid DC Transmission System

Color tuning halide perovskites: Optical amplification and lasing

Light emission with delicate wavelength control generates fundamental colors that are essential for vision-based applications such as displays, information communication, visual and augmented reality. Yet these light emitting technologies critically rely on the development of photonic sources for proper lighting and color matching. Halide perovskites have recently emerged as excellent and efficient photonic sources due to their outstanding photophysical properties, such as low defect trap densities, long carrier lifetime, large absorption coefficient, high quantum yield and optical gain. On a par with the rapid advances of light-emitting diodes (LEDs), perovskite-based optical amplifiers and lasers have made great strides in the past few years, which have much more accurate control of color-matched lighting, high power, spatial and wavevector control of color emission. In this review, we aim to review the recent progress of perovskite lasers at micro-, nano- and subwavelength scales, discuss the properties of halide perovskites and optical cavity structures that benefit color light emission, and examine the remaining challenges in the field for the future development of perovskite-based lasing technologies.

Energy storage steady-state PCS power allocation algorithm based on SOC dynamic sequencing

A power allocation algorithm for energy storage PCS based on SOC sequencing is proposed, aiming at the problem that the energy management system (EMS) can allocate the power of the energy storage unit power converter (PCS) in the existing centralized electrochemical energy storage station steady-state power control, and cannot take into account the equalization of the state of charge (SOC) of the energy storage unit and the power control accuracy of the whole station. Based on the analysis of the characteristics of PCS power allocation algorithms commonly used in engineering, this paper proposes an algorithm to determine the PCS control priority based on the SOC ranking results, and then realize PCS power allocation. The simulation results show that compared with other steady-state PCS power allocation algorithms, the algorithm proposed in this paper can enable the whole station to achieve a better balance of the SOC of the energy storage unit under the premise of satisfying the power control accuracy, so that the energy storage station can provide better steady-state power support for the power grid.

Accurate power control of grid forming power converters for improving large-signal stability

Accurate power control of grid forming power converters for improving large-signal stability

An accurate power control strategy for electromagnetic rotary power controllers

AbstractWith the rapid development of active distribution networks, the “petal”‐type distribution network has become the mainstream power supply structure. Power control methods for active distribution networks should be further studied to ensure the safe and reliable power supply of a distribution system. An electromagnetic rotary power flow controller (RPFC) is a feasible solution for controlling power in active distribution networks. However, when testing the effectiveness of the PQ decoupled control method for RPFC based on instantaneous reactive power theory, difficulties were encountered with the synchronous control of the rotor position angle of two rotating‐phase transformers, and the accuracy of power control was unsatisfactory. Given this condition, PQ control is improved in three ways. First, the system's periodic oscillation problem is solved via variable speed control. Second, the servo motor‐rotary phase‐shifting transformer synchronous rotation scheme, which reduces power control error and improves stability, is designed. Third, the overshoot phenomenon in power control is improved using the variable‐domain fuzzy proportional‐integral adaptive method. Experimental results show that the proposed advanced control scheme exhibits good dynamic and static performance in power control scenarios and achieves effective improvement in RPFC.

Conservation Voltage Reduction Strategy for Autonomous Microgrid with Improved Voltage-CurrentDroop-Based Inverter Control Framework

In a conventional AC distribution system, the conservation voltage reduction (CVR) strategy is widely employed to lower down the voltage of specific load to lower the power consumption. The wide applicability of demand side management (DSM) using CVR in a stand-alone microgrid through VSI-based energy sources is a thrust area, that is, not examined yet and needs to be explored. The fast dynamics and flexible control are the characteristics of the voltage-current droop method which further increases the inertia of the voltage source inverter. For utilizing these advantages of this droop method, it is required to determine the accurate droop gain to properly coordinate the distribution of power among DGs. In this paper, the voltage-current droop method is utilized to carry out the function of DSM, and a modified droop computation method for voltage-current droop is formulated to determine the impedance from initial of the DG point to the downstream end for multifeeder network. As most of the droop control techniques emulate the conventional power grid such as Q-V droop control which reduces voltage with the increase of reactive power, the research prospect is very high in devising the new droop computation method for voltage-current droop for accurate control of power. In addition to it, the work is extended to apply the benefits of voltage-current droop to execute DSM strategy in standalone MG. Moreover, the capability of the proposed estimation of droop parameter is implemented on a standalone 5-bus single-feeder multi-DGs network, and furthermore, the scheme is applied to IEEE-9 bus multifeeder multi-DGs network to show the applicability of the proposed scheme. The simulation results produced from MATLAB/Simulink are compared with the decentralized power-based droop method and conventional voltage-current droop technique to analyse the performance of the devised scheme.

Efficient Phase-Only Dual- and Multi-Beam Pattern Synthesis With Accurate Beam Direction and Power Control Employing Partitioned Iterative FFT

In this communication, a novel phase-only method based on a partitioned iterative Fourier transform (PIFT) is presented to efficiently synthesize dual- and multibeam patterns for uniformly spaced linear and planar arrays. To achieve accurate mainlobe peak directions, the PIFT integrates a partitioned beam calibration strategy into the IFT to successively calibrate the beams by partitioning the multibeam pattern into single-beam patterns and calibrating them individually. Besides, the peak powers of the multiple beams are precisely controlled through proper mainlobe corrections. Several numerical examples of synthesizing dual- and multibeam patterns with accurately controlled peak directions and beam powers as well as reduced sidelobe levels (SLLs) are presented to demonstrate the effectiveness and efficiency of the proposed method. Synthesized results are validated with full-wave simulation. Comparisons with other phase-only methods are also presented to show the superiority of the proposed method.

Direct Power Control of a Bipolar Output Active Rectifier for More Electric Aircraft Based on an Optimized Sector Division

This paper presents a novel direct power control (DPC) strategy based on an optimized sector division for a three-phase coupled inductor-based bipolar output active rectifier (TCIBAR) applied in more electric aircraft (MEA). First, based on the instantaneous power theory, the power model of the TCIBAR is built in the synchronous rotating coordinate system. Second, to implement the hysteresis power control of TCIBAR without causing the runaway of the zero-sequence current in the three-phase coupled inductor (TCI), a set of new voltage vectors that have the same zero-sequence voltage (ZSV) component are synthesized and adopted in the proposed DPC strategy. Third, by quantitatively analyzing the effect of the new synthesized voltage vectors on the power variation of TCIBAR, an optimized sector division method is proposed to improve the accuracy of power control and reduce the phase current harmonics in TCIBAR. Finally, to maintain the voltage balance of the bipolar dc ports in TCIBAR, voltage balance control is studied in the proposed DPC strategy. The proposed DPC strategy is researched on an experimental platform of TCIBAR, and the results show that the proposed DPC strategy is feasible and has good static and dynamic performance.

Mobile Hybrid Energy System for Modern Drives of Smart Energy Transition

Mainly driven by the climate change, electric power systems are globally going through a transition. In order to cut carbon dioxide emissions and slow down global warming, traditional systems consisting of concentrated, easily controllable and often fossil-based power plants are step-by-step replaced by the ones which are typically distributed, renewable and carbon dioxide free. Often this green and renewable production is weather-dependent and much more difficult to predict than the traditional fossil-based one. In the smart energy transition we are dealing with these critical and topical issues: how to ensure the balance in the power grid, when the controllability of production gets more and more difficult. New solutions, such as flexible loads, demand response and growing role of energy storage, are called for to ensure high quality of electric energy. In all these solutions, more accurate power control is called for. In addition, it is important to realize that such new solutions of modern electric drives always require sophisticated power electronics combined with smart control. To be able to demonstrate these modern electric drives of smart energy transition, a mobile and technically versatile hybrid energy system was designed and built at Tampere University of Applied Sciences. In addition to easy transfer enabled by a trailer solution, the goal of design and construction was in technical diversity. The hybrid energy system presented in this paper has not been tailored to any specific use, but instead, we wanted to be able to demonstrate even such modern electric drives that were not predictable in the design phase of the system. Thus, the technical diversity of the system deserves to be emphasized. In this paper we present the design, the operational principles, smart control properties and some successful demonstrations of energy transition related modern electric drives.

Design and assessment of a core-power controller for lithium-cooled space nuclear reactor based on the concept of fuzzy model predictive control

Thanks to its unique characteristics of high power-to-mass ratio, shallow reactivity poisoning, and quick response to reactivity control, power supply system based on lithium-cooled space nuclear reactor is preferred for various exploration missions into outer and deep space. However, due to its nature of few-people or even unmanned on-duty, an intelligent autonomous control of the reactor system, especially an accurate control of the reactor core power following the demanding power output, is of vital importance for such a space nuclear reactor. In this study, a core-power controller for a megawatt ultra-small lithium-cooled space nuclear reactor was designed based on the concept of fuzzy model predictive control (FMPC) combining model predictive control and T-S fuzzy theory. Performance of the FMPC controller was simulated and assessed with the Simulink platform for five typical operation transients including ramp, step and disturbance transient. The results show that the intelligent FMPC controller possesses an excellent load-following ability and anti-interference ability, both of which are of vital importance for space exploration missions. When compared with the classical PID controller, the FMPC controller designed in this study shows also a much better performance with smaller overshoot, lesser adjusting time and lower integral time-squared error.

Frequency Regulation of Electric Vehicle Aggregator Considering User Requirements with Limited Data Collection

High penetration of renewable energy in the power grid causes serious frequency deviations. Large-scale integrations of electric vehicles (EVs) in the power grid provide considerable vehicle-to-grid potential for frequency regulation. Existing frequency regulation strategies with aggregated EVs realize accurate power control that relies on complete information interaction between the EV aggregator and individual EVs. However, the data collection for all EV parameters is not applicable due to privacy protection and the limited communication environment. Considering the limited data collection from grid-connected EVs, this paper provides a novel frequency regulation strategy and tends to address the uncertain influence from EV users’ charging requirements, the EV aggregator’s power regulation, and the frequency regulation performance. Firstly, considering the influence of the limited data collection by EVs on the users’ requirement of traveling and regulation preference, a probabilistic evaluation model for the available regulation capacity of the EV aggregator and the probabilistic control method for EVs are developed. Then, a frequency regulation strategy with error correction control and progressive regulation recovery is developed to simultaneously guarantee the system frequency regulation performance and the regulation requirements of EV users. Finally, case studies are carried out to validate the effectiveness of frequency regulation strategy for decreasing the uncertain influence from the limited data collection, ensuring the EV users’ requirements, and improving the system frequency stability.

Expert knowledge-based peak current mode control of electrosurgical generators for improved output power regulation.

Electrosurgical generators (ESG) are widely used in medical procedures to cut and coagulate tissue. Accurate control of the output power is crucial for surgical success, but can be challenging to achieve. In this paper, a novel expert knowledge-based peak current mode controller (EK-PCMC) is proposed to regulate the output power of an ESG. The EK-PCMC leverages expert knowledge to adapt to changes in tissue impedance during surgical procedures. We compared the performance of the EK-PCMC with the classical peak current mode controller (PCMC) and fuzzy PID controller. The results demonstrate that the EK-PCMC significantly outperformed the PCMC, reducing the integral square error (ISE) and integral absolute error (IAE) by a factor of 3.88 and 4.86, respectively. In addition, the EK-PCMC outperformed the fuzzy PID controller in terms of transient response and steady-state performance. Our study highlights the effectiveness of the proposed EK-PCMC in improving the regulation of the output power of an ESG and improving surgical outcomes.

Wide Frequency PWM Rectifier Control System Based on Improved Deadbeat Direct Power Control

The precision of deadbeat direct power control depends on the parameters of the system model. In wide frequency applications, such as multi- electric aircraft and electric vehicles, variations in frequency and resistive parameters will affect the control effect. The AC side voltage frequency of the generator rectifier varies widely, which will lead to a steady-state reactive power error in the deadbeat direct power control. In addition, the large temperature variation range during the operation of the multi-electric aircraft and electric vehicles leads to large changes in the filter inductance and line resistance of the AC side, and the model parameters do not match the actual parameters, which will further deteriorate the control accuracy. In this paper, a PWM rectifier control method is proposed for the occasions when the frequency and temperature change are in a wide range. Using repetitive control and power compensation, it solves the problems of steady-state reactive power error and control accuracy degradation caused by the mismatch of model parameters under severe operating conditions. The control method can precisely adjust the output DC voltage of PWM rectifier, and it also can maintain unity power factor and reduce the total harmonic distortion rate of the input current. The effectiveness of the proposed control method is verified by the experimental results.

Enhancing dynamic stability performance of hybrid ac/dc power grids using decentralised model predictive control

High voltage direct current (HVDC) networks are transforming ac power grids to hybrid ac/dc power grids; hence hybrid ac/dc power grids are facing new stability challenges. In this paper, a decentralised control scheme based on model predictive control (MPC) is proposed to enhance the stability of hybrid ac/dc power grids under disturbances. The proposed scheme controls the dc voltage, frequency, active and reactive power simultaneously with minimum deviations from steady-state values. A communication network is used to share the sampled grid data with the local MPC of each voltage source converter (VSC). Hence, the central controller can be avoided. Moreover, the active power-sharing between converters can be pre-designed. Thus, fast and accurate active power control can be realised. Finally, the proposed control scheme is validated using a five-terminal VSCHVDC test system with MATLAB. The VSCHVDC network with the proposed control scheme shows a smaller deviation and a faster response compared with the conventional droop control scheme and centralised MPC scheme under small disturbances. Under large power variations, the proposed control scheme assists to reach the steady-state rapidly with a minimum impact on the entire power grid. The proposed control scheme has also proved its robustness under communication delays and outages.

Sensitivity analysis for active electromagnetic field manipulation in free space

ABSTRACT This paper presents a detailed sensitivity analysis of the active manipulation scheme for electromagnetic (EM) fields in free space. The active EM fields control strategy is designed to construct surface current sources (electric and/or magnetic) that can manipulate the EM fields in prescribed exterior regions. The active EM field control is formulated as an inverse source problem. We follow the numerical strategies in our previous works, which employ the Debye potential representation and integral equation representation in the forward modelling. We consider two regularization approaches to the inverse problem to approximate a current source, namely the truncated singular value decomposition (TSVD) and the Tikhonov regularization with the Morozov discrepancy principle. Moreover, we discuss the sensitivity of the active scheme (concerning power budget, control accuracy, and quality factor) as a function of the frequency, the distance between the control region and the source, the mutual distance between the control regions, and the size of the control region. The numerical simulations demonstrate some challenges and limitations of the active EM field control scheme.

Energy control technology for MMC during fault ride through

Integrating the energy dissipation unit inside the converter is a cost-effective solution for fault ride-through of surplus power in offshore wind power systems. To address the problem of low accuracy of the existing self-consuming converter control strategy, an energy dissipation unit control strategy based on DC voltage hysteresis control and step throwing is proposed to achieve accurate control of the dissipated power during fault ride-through, and to control the DC bus voltage and sub-module capacitance voltage to fluctuate within the allowable range. Simulation results show that the proposed self-consuming converter control strategy can effectively achieve fault ride-through under different fault strength conditions, and the capacitor voltage ripple is reduced by more than 20% when using the optimized control strategy than the basic control strategy.

Suppression of laser power error in a miniaturized atomic co-magnetometer based on split ratio optimization

A miniaturized atomic spin-exchange relaxation-free (SERF) co-magnetometer measures angular velocity using a balanced polarimetry technique which is easily affected by the laser power. A laser power closed-loop control system is usually used to suppress the fluctuation of the laser power. Although this method can greatly eliminate the fluctuation of the in-loop laser power (the feedback laser), it cannot fully eliminate the fluctuation of the out-of-loop laser power (the signal measurement laser). This leads to SERF gyroscope laser power error, which reduces the inertial measurement accuracy. In this paper, the influence mechanism of the split ratio (the ratio of the in-loop laser power to the out-of-loop laser power) on the out-of-loop laser power control accuracy is analyzed by establishing a laser power transmission model inside and outside the loop. Moreover, a method is developed to improve the out-of-loop laser power stability by optimizing the split ratio. Comparative experiments showed that the relative Allan standard deviation of the out-of-loop laser power decreased from 5.48 × 10−6 to 2.62 × 10−6 at 100 s, and decreased by an order of magnitude from 1.76 × 10−5 to 3.30 × 10−6 at 1000 s. Correspondingly, the rate ramp coefficient in the Allan standard deviation curve of the SERF gyroscope test data decreased from 1.312 [(°/h)/h] to 0.246 [(°/h)/h]. And the bias stability increased from 0.032 °/h to 0.019 °/h. Therefore, the proposed method can improve the long-term stability of the probe laser power and effectively suppress the laser power error of the SERF gyroscope.

Coordinated Reactive Power Control with a Variable Shunt Reactor and an Inverter-Based Wind Power Plant

Underground or submarine cables have a higher capacitance component than overhead lines, and they inject a large amount of capacitive reactive power into the system. A separate reactive power compensation device is required in order for a wind power plant (WPP) connected to the public network with a cable to meet the reactive power requirements required by the grid code. In this paper, a reactive power control using a variable shunt reactor (VSR) was proposed to satisfy the reactive power requirement required by the grid code for a WPP connected to the grid through a cable. The proposed reactive power control method compensates for the capacitive reactive power of the cable by using a VSR, and it follows the reactive power command through the reactive power control of a WPP. In the section where it is difficult to follow the WPP reactive power command only with the reactive power capacity of a WPP due to cable losses or a cable reactive power compensation error of the VSR, the reactive power control is additionally supported through the hysteresis control of the VSR. The proposed method satisfies the grid codes, and it enables fast and accurate reactive power control. The performance of the proposed method was verified through simulation using MATLAB/Simulink.