Mitigation of Voltage Variation by REMS for Distribution Feeders

Abstract:

This study develops a renewable energy management system (REMS) for the control of photovoltaic (PV) smart inverters to mitigate the voltage violation of distribution systems with high penetration of PV installation. The impact analysis of distribution feeders with PV system integration for decision making of smart inverter control has been embedded in REMS to solve the voltage violation problem. To verify the effectiveness of the proposed REMS to enhance the system voltage quality, a PV system installed in a distribution feeder of Taiwan Power Company (Taipower) has been selected for field testing. The real power, reactive power and voltage of the study PV system have been collected. The impact analysis of PV integration is performed to solve the mitigation of voltage variation by the control of reactive power compensation of smart inverters. It is found that the voltage at the test PV system is very consistent to the field test results. The computer simulation of a distribution feeder with a large PV farm has been executed to illustrate that the control of smart inverters can enhance the utilization of solar energy by reducing the curtailment of renewable power generation dramatically for a distribution system with high penetration of PV systems. 

 

Existing System:

To the present, considerable efforts have been devoted to mitigate the overvoltage problem introduced by the injection of intermittent renewable power generation. Reactive compensation facilities such as STATCOM have been used at the connection point of large renewable power generation to reduce the problem of voltage flicker [11]. Active power curtailment techniques have been proposed to reduce the real power injection in case of peak solar irradiation when high penetration PV systems have been installed in the distribution feeders [12]-[13]. For conventional PV inverters, the power factor is fixed at 1.0 so that only the real power is generated. When the output terminal voltage of PV systems violates the overvoltage constraint, the output active power of the PV inverter must be reduced by changing its operation mode from the maximum power point towards the open circuit voltage of PV panel. The operation mode of minimum power output will be adopted if the overvoltage problem at point of common coupling (PCC) cannot be completely solved by reducing PV power generation [14]-[15]. Stetz et al. [16] propose autonomous control of inverters for voltage improvement using the reactive power consumption and curtailment of the feed-in active power. A two-stage voltage control architecture for PV generation is proposed in [17]. The optimal control of the reactive power output by PV inverters to reduce voltage violation with respect to a control reference is proposed in [18]. In [19], the authors present an optimization strategy applied to a new algorithm for decentralized voltage control based on sensitivity analysis [20]. Reference [21] analyzes impacts of the cloud effect on voltage stability to find that reactive power support provided by PV inverters can solve the instability problem.

 

Proposed System:

  To provide more effective control of PV renewable power generation that can help solve the overvoltage problem due to high PV penetration in a distribution system, this study develops a renewable energy management system (REMS) to control PV smart inverters and thereby enhance system voltage quality [24]. The hourly PV power generation of field PV systems is predicted according to day-ahead weather forecasting data. The three phase load flow analysis is then executed to solve the possible voltage rise at the PCC of all PV systems. The control algorithm is then applied in the REMS master station to derive the proper power factor setting and even the real power curtailment for each PV system. The public 4G communication system is used to transmit the control command to the gateway of PV smart inverters. The voltage, real power and reactive power generation of the PV system after executing the control command are then reported to the master station. To support the impact analysis of PV integration in distribution system, system data of the distribution feeder must be determined using the interface programming to retrieve the attributes of the line segment and integrated PV systems from the database of a digital mapping system. A topology process is executed to find the network configuration of the study distribution feeder based on the connectivity attributes of line segments. Based on the simulation results, the decision making process is then derived for the control of PV smart inverters to adjust the power factor and the real power output of PV system when a voltage violation occurs due to excessive PV power generation during peak solar energy periods.

 

Conclusion:

  A renewable energy management system has been proposed in this study to provide the highly effective control of PV smart inverters to enhance the utilization of solar energy and to prevent the overvoltage problem for distribution system with high penetration of PV systems. The real power generation by each PV system connected in the distribution feeder is determined according to the installation capacity, the hourly solar irradiation forecasting and the PV panel temperature. An impact analysis software has been embedded in the REMS system, which will retrieve the attributes of distribution components from the facility database to build the network topology of study feeder and generate the input data files for impact analysis. The decision making for the control of PV inverters has been derived to adjust the power factor setting and real power generation curtailment for the PV system when the service voltage exceeds the operation constraint. To verify the accuracy of the impact analysis due to PV integration and to demonstrate the effectiveness of the proposed REMS, a rooftop PV system with capacity of 352 kWp has been selected for field testing and computer simulation. It is found that the voltage variation at the PCC after the control of power factor and real power curtailment by the smart inverters is very consistent with the results of impact analysis of PV system integration.

Reference:

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[3] Renewable Energy Report, Bureau of Energy, Ministry of Economic Affairs, Taiwan, Feb. 2015, [Online]. Available: http:// http:// http://web3.moeaboe.gov.tw/ECW/populace/web_book/WebReports.asp x?book=M_CH&menu_id=142.

 

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[10] A. Ellis, “Grid operations and high penetration PV,” presented at the Utility/Lab Workshop PV Technol. Syst., Tempe, AZ, USA, Nov. 8–9, 2010.