Voltage Regulation in Distribution System with High Penetration of Residential Solar Energy


This research is to study the behavior of distribution systems with high penetration of residential solar energy. The U.S. Energy Information Administration (EIA) forecasts that small-scale solar, such as home rooftop panels, will add 9 GW of electricity-generating capacity in 2019 and 2020, an increase of 44% [1]. The increasing residential solar energy will lead to grid overvoltage issue. If successful, the findings of this project can help the distribution systems that are originally designed for no residential solar energy to adapt to high penetratial level of residential solar energy. The existing methods to regulate the distribution system with high penetration level involve empowering the photovoltaic (PV) system with volt-var/volt-watt control [2], re-designing the tap-changer control [3], and distributed reactive power compensator placement [4].


Voltage Regulation in Distribution System with High Penetration of Residential Solar Energy

A typical issue with high penetration of residential solar energy is the overvoltage at the customer side. The high penetration of residential PV will increase the voltage at customer side as the reverse power flow happens. To maintain the customer-side voltage within acceptable range, IEEE std. 1547 requires the DERs to provide reactive power to regulate local voltage profile [5].

To study the residential PVs impact on the distribution system, the following methodology has been adopted:

  • Modify available IEEE test feeders (IEEE8500) with high penetration of residential PV.
  • Develop detailed model of secondaries and incorporate with simulation study. The secondary modeling is focused on services transformers and building cables.
  • Implement Volt-Var/Volt-Watt control recommended from IEEE std. 1547.

A three-phase residential reactive power compensator is validated by simulation as a possible solution to deal with residential overvoltage issue [6]. The proposed three-phase reactive power compensator adopts innovative dc capacitor-less solid-state variable capacitor (SSVC) concept to minimize the dc-link capacitor.
Full bridge inverters typically need bulky electrolytic dc capacitors to absorb the unbalanced power from the ac side. These electrolytic capacitors normally have shorter lifetime than other components in the converter. In most full-bridge inverter applications, the dc voltage is required to be relatively constant. However, in reactive power compensation applications, such as SSVC, maintaining a constant dc-bus voltage is unnecessary since the dc bus is floating. The three-phase residential reactive power compensator adopted in this project removes the electrolytic dc capacitor from the circuit by releasing the constraints on dc bus voltage fluctuation. The dc voltage is supported by ac side voltage directly. For this residential reactive power compensator, the capacitance needed is only 3% of that required by a conventional three-phase inverter. The three-phase residential reactive power compensator is validated by simulation.

How WBG Can Help

The goal of this project is to regulate the distribution system voltage so that the conventional distribution system can better adapt to rapidly increasing residential solar energy penetration levels. This project has modified the IEEE 8500-bus distribution system test case with high penetration of solar energy. With the developed test case, the study related to medium voltage (MV) and low voltage (LV) can be conducted. The IEEE 8500-bus test case provide rich secondary models. The corresponding LV-side issues can be well captured and studied.

The three-phase dc capacitor-less SSVC has the potential to reduce the volume and the cost of residential reactive power compensator. The simulation study of the trhee-phase dc capacitor-less SSVC can be used for control verification and design reference.

Personnel Involved

  • Yunting Liu


[1] US Energy Information Administration, "EIA forecasts renewables will be fastest growing source of electricity generation", Jan. 2019, [Online]. Available: https://www.eia.gov/todayinenergy/detail.php?id=38053&src=email#
[2] T. Aziz and N. Ketjoy, "Enhancing PV Penetration in LV Networks Using Reactive Power Control and On Load Tap Changer with Existing Transformers," IEEE Access, vol. 6, pp. 2683-2691, 2017.
[3] T. T. Ku, C. H. Lin, C. S. Chen, C. T. Hsu, W. L. Hsieh, and S. C. Hsieh, "Coordination of PV Inverters to Mitigate Voltage Violation for Load Transfer between Distribution Feeders with High Penetration of PV Installation", IEEE Trans. Ind. Appl., vol. 52, no. 2, pp. 1167-1174, 2016.
[4] S. C. Hsieh, "Economic Evaluation of the Hybrid Enhancing Scheme with DSTATCOM and Active Power Curtailment for PV Penetration in Taipower Distribution Systems", IEEE Trans. Ind. Appl., vol. 51, no. 3, pp. 1953-1961, 2015.
[5] IEEE Standard Association, IEEE Std. 1547-2018. Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces. 2018.
[6] Y. Liu, L. Tolbert, F. Wang and F. Z. Peng, "Three-Phase DC Capacitor-Less Solid-State Variable Capacitor," IEEE Energy Conversion Congress and Exposition, Detroit, MI, USA, 2020, accepted.