Curtailment Control Research Articles

Battery-less uncertainty-based control of a stand-alone PV-electrolyzer system

Solar photovoltaic (PV) energy is variable. The output power can change considerably in a matter of minutes, imposing challenges on the control of systems connected downstream. The power from these systems can be smoothed using electric storage, potentially increasing the system cost. An alternative is to deliberately curtail the power before it starts to change. This strategy relies on ultra-short-term forecasting to determine the curtailment point. Unfortunately, forecasting is prone to errors and high uncertainty even in the very short-term, leading to control errors. We propose an active power curtailment control strategy for a stand-alone solar photovoltaic system powering an electrolyzer. Our work’s novelty relies on the controller’s ability to deal with large forecasting errors and high uncertainty, combining artificial intelligence for predicting the power ramps and fuzzy logic to account for imperfect prediction. We validated our approach using a hardware emulator of the photovoltaic system, power converter and electrolyzer. Under clear sky conditions, the curtailment results in unnecessary energy loss, while under variable irradiance, the controller successfully smooths the power ramps within 10% of the PV system’s nominal power. Although our approach was designed for a stand-alone system, its concept can be directly applied to grid-connected systems as well.

Novel Curtailment Control Strategy for Wind Power Plants Based on the SQP Optimization

As the penetration level of renewable energy sources (RESs) increases, the output power of RESs needs to be curtailed to balance the power supply and load demand. Nevertheless, depending on the curtailment control strategy for wind power plants (WPPs), while the total amount of output power curtailment remains the same, the overall stored inertial energy within WPPs may vary. Furthermore, this stored inertial energy within WPPs can be used during disturbances to enhance frequency stability. This paper proposes a novel curtailment control strategy based on the sequential quadratic programming (SQP) optimization algorithm to effectively curtail WPPs and increase the overall stored inertial energy within WPPs. Then, the proposed solution can enhance frequency stability by providing a more inertial response from WPPs during disturbances. To verify the effectiveness of this novel curtailment control strategy, several case studies are conducted using the IEEE 39-bus system. The results show that the proposed curtailment control strategy effectively increases the stored inertial energy within WPPs while satisfying the required output power curtailment.

PV Power Curtailment and BESS Management for Distribution Networks: A Practical Approach

Voltage and thermal limits in distribution feeders are the main features assessed to determine their hosting capacity (HC) due to the integration of distributed generation (DG), especially photovoltaic systems (PV). This paper proposes a PV active power curtailment control strategy combined with the management of battery energy storage systems (BESS) under high penetration of PV systems. In addition, the voltage imbalances rate is included in the evaluated operating parameters in order to reduce voltage and thermal issues and avoid or postpone the feeder reinforcement costs. The study uses Monte-Carlo and stochastic simulations to determine the HC and the PV system's random location. Also, several PV systems capacities are proposed by using statistics. Mexican standards are used for the HC estimation and to perform the power curtailment control strategy. The use of smart PV inverters is considered to reduce or increase the PV active power generation. The BESSs are capable of regulating their charge and discharge cycle independently. The results show the advantages of using strategies separately and in combination can be beneficial to improve the feeder performance.

Selection of Inertial and Power Curtailment Control Methods for Wind Power Plants to Enhance Frequency Stability

As renewable energy penetrates the power system, system operators are required to curtail output power from generation units to balance the power supply and demand. However, large curtailment from wind power plants (WPPs) may instantly cause excessive output power decrement, causing system frequency to drop significantly before reaching its nominal value. In order to solve this problem, this paper proposes a cooperative control framework to determine the operation of WPPs in two control methods, which are the stepwise inertial control (SIC) method and the curtailed control method. The proposed framework first determines the WPPs to operate in the curtailed control method to provide the required power curtailment. Next, it determines the WPPs to operate in the SIC method considering their releasable kinetic energy to provide an effective inertial response and compensate for the sudden excessive output power decrement caused by other WPPs operated in the curtailed control method. Therefore, each WPP is operated in one of two control methods to provide required power curtailment while reducing the sudden excessive output power decrement. To verify the effectiveness of the proposed cooperative control framework, several case studies are carried out on the practical South Korea electric power system.

Synthetic control chart with curtailment for monitoring shifts in fraction non-conforming

The integration of the curtailment method with control charts considerably improves the detection speed by signalling an out-of-control condition prior to the inspection of the whole sample. To date, few research works have focused on the incorporation of the curtailment method to improve the performance of control charts. Thus, this paper incorporates the curtailment approach with the synthetic chart to propose a synthetic with curtailment (Curt_Syn) control chart for detecting upward shifts in the fraction non-conforming, p. We compare the newly developed Curt_Syn chart with the synthetic, exponentially weighted moving average (EWMA), cumulative sum (CUSUM), EWMA with curtailment (Curt_EWMA), and CUSUM with curtailment (Curt_CUSUM) charts. From an overall perspective, the results reveal that the Curt_Syn chart surpasses the synthetic chart by 38% under various conditions. For all p shifts, the Curt_Syn chart outperforms the CUSUM and EWMA charts. When the p shift is large, the Curt_Syn chart is superior to the Curt_CUSUM and Curt_EWMA charts. To demonstrate the implementation of the Curt_Syn chart, an illustrative example is provided. [Received: 30 April 2019; Accepted: 7 April 2021]

Evaluation of Power Maximization and Curtailment Control Methods for Converters in Wearable Photovoltaic Energy Harvesting Applications

As wearables become more widely adopted, powering them from ambient energy sources can improve reliability and reduce reliance on batteries. Solar photovoltaic (PV) power is a viable power source for such emerging applications. However, because wearable applications bend and move with the user&#x0027;s motion, the PV panels used in these applications experience varying light intensities over multiple PV cells that reduce power generation in traditional series-string configurations. To address the PV power reduction problem, a configuration of boost converters with parallel-connected outputs are utilized, which is effective in uneven lighting conditions. Depending on the load demand and available solar power, a converter control system should quickly transition between maximum power point tracking (MPPT) and power curtailment operation. This work evaluates MPPT (perturb &amp; observe and constant-voltage) algorithms and power curtailment (over-voltage shut-off and flexible power point tracking) methods on their effectiveness in wearable applications. Experimental results verify that the perturb &amp; observe with flexible power point tracking effectively adapts to changes in the load and light conditions while maintaining 30&#x0025; and 31&#x0025; higher output power, respectively. It also maintains the maximum component temperature below <inline-formula><tex-math notation="LaTeX">$29{}^{\circ }$</tex-math></inline-formula>C which is a safe temperature for wearable applications.

A Fair Incentive Scheme for Participation of Smart Inverters in Voltage Control

The increasing trend of renewable energy sources integration in the distribution systems may cause voltage fluctuations and voltage limit violations. The smart inverters with reactive power capability and active power curtailment (APC) control can solve the grid voltage issues. In this article, three-phase optimal power flow (TPOPF) is applied to dispatch the APC and reactive power injection (RPI) of inverters. The TPOPF takes smart meter measurements as inputs. The nonproportional APC and proportional APC are examined. In this article, a fair incentive scheme for APC by the inverters is proposed, appropriate for both utility and renewable energy producers. Similarly, unequal RPI and equal RPI by the inverters to maintain the system voltage are studied. The RPI incentive scheme is analyzed by accounting for the costs incurred in overrating of the inverters, power losses, and life reduction due to reactive power supplied by the inverters. The effective location of inverters for APC and RPI in the distribution network is explored. The incentive schemes are implemented in 27-node distribution system and IEEE European low-voltage distribution system.

Analysis and Mitigation of the Impact of Ancillary Services on Anti-Islanding Protection of Distributed Generators

The incorporation of ancillary services on distributed generators (DGs) at utility level has imposed several challenges on the existing distribution networks. To address one of such problem, this paper discusses the impact of ancillary services, mainly the voltage ride through (VRT) capability and active power curtailment control (APCC) of DGs on their anti-islanding protection scheme (AIPS). In this study, different types of load models (viz. ZIP, induction motor (IM) and composite loads) have been considered and non-detection zone (NDZ) characteristics are obtained for a modified IEEE 1547/ UL 1741 test system for analyzing the problem. Further demonstration of this issue has been carried out by conducting time domain simulations in PSCAD/EMTDC platform on modified IEEE 1547 and CIGRE low voltage benchmark test system having composite loads at each of the load buses. Finally, an appropriate mitigation framework has been proposed by incorporating a hybrid islanding detection technique to enable simultaneous implementation of VRT, APCC and AIPS in DGs. The online implementation of the proposed framework is realized in MATLAB/Simulink platform and real-time simulations are performed in OPAL-RT (OP5600) test bed on the modified IEEE 1547/ UL 1741 test system for validating its efficacy.

Coordinated Control of Parallel DR-HVDC and MMC-HVDC Systems for Offshore Wind Energy Transmission

Parallel operation of a diode rectifier-based high-voltage direct current (DR-HVDC) and modular multilevel converter (MMC)-based HVDC (MMC-HVDC) for transmitting offshore wind energy is investigated in this article. An enhanced active power control scheme of the offshore MMC station is proposed to improve the power flow distribution between the MMC-HVDC and DR-HVDC links which are both connected to the offshore wind farm (OWF) ac network. By regulating the offshore voltage, all the wind powers are transmitted via the DR-HVDC link in low wind conditions while the offshore MMC power is controlled around zero to reduce transmission losses, considering the efficiency superiority of DR-HVDC over its MMC counterpart. When the DR-HVDC is out of service, wind energy is transferred via the MMC-HVDC and the wind turbine (WT) generated power is automatically limited by slightly increasing the offshore ac voltage to avoid potential MMC-HVDC overload. A power curtailment control is also proposed which slightly increases the dc voltage of the DR-HVDC to enable autonomous reduction of the generated wind power so as to avoid DR-HVDC overload during MMC-HVDC outage. The proposed coordinated control only uses local measurements and, without the need for communication, can seamlessly handle transitions including various faults. The proposed scheme enables fault ride-through operation and provides a high efficient solution with flexible operation for integrating large OWFs. Simulation results confirm the proposed control strategy.

Impact of Power Output Curtailment Control of Photovoltaic Power Generation on Grid Frequency

In a power system with very high penetration photovoltaic power (PV) generation, the curtailment of PV power will be necessary to maintain a power supply and demand balancing. PV power output can be effectively utilized by controlling the curtailment at a certain interval based on forecasting and nowcasting of aggregated power output of PV systems. By using an optimum unit commitment scheduling model, this paper assesses the effect of a scheduled curtailment control at 30 min interval on the reduction of curtailed PV power output in comparison with a fixed curtailment control throughout a day. Then, by using an electricity supply - demand simulation model, this paper discusses the effect of ramp rate control of curtailed PV power output for avoiding the steep change in grid frequency due to the stepwise change in curtailment.

The Power Simulation of Water-Cooled Central Air-Conditioning System Based on Demand Response

With rapid development of smart grid, terminal power load is paid more and more attention, especially that of air conditioning system, which constitute an integral part of summer peak electricity load. In this paper, through controlling indoor air temperature deduced by equivalent thermal parameters-model, daily energy consumption and energy consumption during peak hours can be adjusted and reduced to realize demand side management. To reduce peak load of grid and ensure stable and reliable operation of grid, four temperature control strategies, including constant setting temperature control strategy, pre-cooling control strategy, curtailment control strategy and improved curtailment control strategy were proposed. Meanwhile, three operation schemes of the chiller were also employed. Furthermore, considering the power consumption and curtailment, five indicators including hourly average load, hourly average load ratio, energy saving ratio, load-shedding ratio during peak hours and coefficient of performance (COP) have been proposed to evaluate the performance. Results showed that the operation scheme of operating numbers control obtained better effect. Energy saving ratio was highest of 32.5% with curtailment control strategy, while load-shedding ratio during peak hours was optimal with improved curtailment control strategy. However, COP was maximum at 3.66 when pre-cooling control strategy was employed. This study can guide the operation of water-cooled air conditioning system through energy saving ratio and COP, also it has more benefits on economy of power system by hourly average load and load-shedding ratio.

Coordinative Low-Voltage-Ride-Through Control for the Wind-Photovoltaic Hybrid Generation System

The wind-photovoltaic (PV) hybrid renewable energy system (HRES), which consists of permanent-magnet synchronous generators (PMSG) and PV arrays, is becoming a cost-effective electric source for powering islanded areas. However, high penetration of renewables makes the power system vulnerable to transient voltage faults, which undermines the stability of the future inverter-dominated grid. To address this issue, a coordinative low-voltage-ride-through (LVRT) control scheme is proposed for the operation of the wind-PV HRES in this article. This control scheme will exploit the maximum energy inertia of the HRES for incorporating the power imbalance between the faulted grid and the renewable generators. An optimization problem is formulated to maximize the renewable energy harvesting within the operational and environmental limitations. To cope with different working conditions, four control processes are coordinated in an optimized manner during the LVRT period: 1) adaptive dc-link voltage control; 2) PMSG rotating speed control; 3) PV energy curtailment control; and 4) blade pitch angle control. Besides, this control scheme applies a direct output control that can generate stable and accurate current as per grid code requirements. The results of the hardware-in-the-loop (HIL) experiment and the MATLAB/Simulink simulation are provided to verify the effectiveness of the proposed control scheme.

Two-stage voltage control strategy for PV plants based on variable droop control

ABSTRACTVoltage violation is an important factor that restricts grid-connected photovoltaic system. The utilization of PV plant’s reactive power capability is an effective measure to mitigate voltage violation. This paper proposes two-stage voltage control strategy to enhance the voltage support capability of photovoltaic grid-connected system. In first stage, adaptive gains are set according to the maximum reactive capacity of each PV plant in order to distribute reactive power among PV plants more reasonably, avoiding certain PV plants operating in the limit state for a long time. In second stage, when the reactive power capacity is insufficient, the priority of active power curtailment for each PV plant is calculated in real time. Active power curtailment control will be performed in PV plants with high priority to released more reactive power capacity for voltage support. The simulation results carried out by PSCAD/EMTDC software demonstrated that this strategy can effectively solve the voltage violation problem. Meanwhile, the proposed strategy not only can exploit reactive capacity of each PV plant as much as possible to avoid certain PV plants operating in the limit state for a long time, but also can reduce the amount of active power curtailment when reactive power adequacy is insufficient.

Operation of Stand-Alone Microgrids Considering the Load Following of Biomass Power Plants and the Power Curtailment Control Optimization of Wind Turbines

Various stand-alone hybrid power systems are widely used to fulfil the electric loads for remote, rural villages. Although there are many investigations based on various aspects of renewable hybrids energy microgrids, the discussions about the application of biomass combustion power plants are rare. Also, detailed investigations of the system steady and transient stability analysis, and the power curtailment control optimization of wind turbines in these stand-alone hybrid systems are seldom found. This paper focuses on wind/biomass/diesel/battery stand-alone microgrids and discusses the system operation, energy management and dispatch issues detailed. The renewable and controllable biomass power is localized to follow the load fluctuations over a long timescale to decrease the power production from diesel and the peak-load shifting demands of the battery banks. An optimization strategy of the wind power curtailment control is also proposed to effectively decrease the frequency and amplitude of the pitch actor and, to some extent, improve the power generation through the combination of the active turbine speed control and pitch regulation. Then a parallel double-mode optimal operation strategy with a “fault detector” is presented to realize economic optimization dispatch under the normal mode and emergency power control for large disturbance scenarios. Finally, case studies of a microgrid on a remote Canadian aboriginal community are conducted to demonstrate the performance of the proposed methods.

On wind turbine down-regulation control strategies and rotor speed set-point

The use of down-regulation or curtailment control strategies for wind turbines offers means of supporting the stability of the power grid and also improving the efficiency of a wind farm. Typically, wind turbine derating is performed by modifying the power set-point and subsequently, the turbine control input, namely generator torque and blade pitch, are acted on to such changes in the power reference. Nonetheless, in addition to changes in the power reference, derating can be also performed by modifying the rotor speed set-point. Thus, in this work, we investigate the performance of derating strategies with different rotor speed set-point, and in particular, their effect on the turbine structural fatigue and thrust coefficient were evaluated. The numerical results obtained from the high-fidelity turbine simulations showed that compared to the typical derating strategy, the derated turbines might perform better with lower rotor speed set-point but it is crucial to ensure such a set-point does not drive the turbine into stalled operations.

Techno-economic analysis of battery storage and curtailment in a distribution grid with high PV penetration

Global solar PV capacity continues growing and this technology is a central solution for the global energy transition based on both economic growth and decarbonisation. PV technology is mainly being installed in distribution networks next to the consumption centres but it is an intermittent source which does not offer demand matching capability therefore calling for the redesign of distribution networks. In this study, battery storage and PV curtailment are compared as solutions for a residential area in Zurich (Switzerland) with large PV penetration from a techno-economic perspective. The techno-economic analysis focuses on the implications of the location (and related size) of battery storage and the type of curtailment control (fixed versus dynamic) for relevant stakeholders such as consumers and the distribution network operator. PV energy time-shift, the avoidance of PV curtailment and the upgrade deferral of the distribution transformer are the energy services provided by battery systems. Residential batteries offer more value for PV management than grid-scale solutions despite higher levelized cost but PV curtailment is the most cost-effective solution since only up to 3.2% of total PV electricity generation in energy terms should be curtailed for avoiding the transformer upgrading. We conclude that shared ownership models for PV curtailment could considerably improve its acceptance among consumers.

Estimation and forecast accuracy of regional photovoltaic power generation with upscaling method using the large monitoring data in Kyushu, Japan

Abstract In order to optimize photovoltaic (PV) output curtailment control, forecasting a regional PV power generation are an important issue. Its estimation is also important as a basic step prior to forecasts. Upscaling algorithm is general approach for evaluating and forecasting a regional PV power generation because the number of monitored plants is usually limited. However, the method leads to large error when the characteristics of monitored plants differ from those of unknown plants in a region. In this paper, we analysed the errors on estimation and forecast of regional PV power generation with upscaling method by using monitoring data obtained from 2219 small PV plants in Kyushu, Japan. As the results, random sampling method has sufficient accuracy for day-ahead and short-term forecasts in case of the large number of reference plants, and unlike forecasts the minimum estimation error does not remain flat and continued to decrease as the number of power plants increased.

Optimal coordinated voltage control in active distribution networks using backtracking search algorithm.

The growing interest in distributed generation (DG) in recent years has led to a number of generators connected to a distribution system. The integration of DGs in a distribution system has resulted in a network known as active distribution network due to the existence of bidirectional power flow in the system. Voltage rise issue is one of the predominantly important technical issues to be addressed when DGs exist in an active distribution network. This paper presents the application of the backtracking search algorithm (BSA), which is relatively new optimisation technique to determine the optimal settings of coordinated voltage control in a distribution system. The coordinated voltage control considers power factor, on-load tap-changer and generation curtailment control to manage voltage rise issue. A multi-objective function is formulated to minimise total losses and voltage deviation in a distribution system. The proposed BSA is compared with that of particle swarm optimisation (PSO) so as to evaluate its effectiveness in determining the optimal settings of power factor, tap-changer and percentage active power generation to be curtailed. The load flow algorithm from MATPOWER is integrated in the MATLAB environment to solve the multi-objective optimisation problem. Both the BSA and PSO optimisation techniques have been tested on a radial 13-bus distribution system and the results show that the BSA performs better than PSO by providing better fitness value and convergence rate.

Enhanced Network Voltage Management Techniques Under the Proliferation of Rooftop Solar PV Installation in Low-Voltage Distribution Network

The proliferation of rooftop solar PV distributed generator (PVDG) installation in a low-voltage distribution network (LVDN) imposes voltage fluctuation challenges that are a threat to distribution system operators. Reactive power control (RPC) methods are insufficient in isolation to combat the overvoltage fluctuations manifested in an LVDN with a significant number of grid-tied PVDG installations, whereas active power curtailment (APC) control can alleviate the voltage fluctuation in such situations and it is achieved at the cost of reduced active power injection. This paper explores how deficiencies in both RPC and APC as separate approaches can be mitigated by suitably combining RPC and APC algorithms. Strategies combining two RPCs and one RPC in conjunction with APC are proposed as two coordinating algorithms by means of an instantaneous measurement of node voltage and active power. These coordinating algorithms are embedded in all the rooftop PVDG grid-tied inverters (GTIs), where the GTI coordinates among them for voltage support without exceeding individual inverter volt-ampere rating. The result of the combined approach shows a significant improvement in managing and stabilizing the voltage and allows the penetration of PVDG to be increased from 35.65% to 66.7% of distribution transformer kilovolt-ampere rating.

Autonomous Curtailment Control in Distributed Generation Planning

While enabling prominent growth of renewable-based distributed generation (DG) and matching energy harvesting, nonfirm connection policy requires accompanying active and reactive power dispatch control. Centralized control often implies comprehensive communication infrastructure and notable capital investment. Hence, DG planning models tailored for decentralized management of thermal and voltage constraints are found wanting. This paper presents a DG planning methodology, which successfully incorporates a new decentralized active power curtailment control and also includes decentralized voltage control. It optimizes autonomous control settings for each generator individually, such that the net energy export from the distribution to transmission level, per unit of installed capacity, is maximized. Comparative time series analysis validates the methodology.