Volt-VA control using multi-port converters for voltage management in low voltage feeders

Abstract

The increase in quantity and electrification of energy in residential areas pushes the existing distribution network to its limits. If left unchanged, the network will suffer from voltage violations caused by the increase of electric vehicle (EV) charging, energy generation by Photovoltaics (PV) panels and the phasing out of natural gas. Typically, cables are reinforced to cope with increased demand, but upgrading large parts of the Dutch electricity network is expensive. By not expanding the network, the remaining capacity of the network needs to be optimally used. This situation encourages the switch to an active distribution network, which opens up a new possibility for voltage management and optimal use of the distribution network.
One of these prospects is the multi-port converter. This converter combines the usually separate converters of EV, PV and battery energy storage system (BESS) to a single entity. Combined with an optimal charging algorithm, the energy management system (EMS) of the multi-port converter decides when to (dis)charge the BESS and EV, using a moving horizon window. By controlling the previously nondispatchable loads, flexibility is generated on the demand side. Using a network of multi-port converters on its own is insufficient to cope with voltage problems in the distribution network due to the overlap of (dis)charging schedules and lack of communication.
A Voltage management system (VMS) is used to coordinate the EMS of all the multi-port converters in the network to stay within the voltage range. This controller aims to prevent and correct voltage problems by varying the input or output of the multi-port converter. The prevention is done by actively reserving energy and changing prices to encourage changes in the (dis)charge schedule of the multi-port converter. The correction of the voltage profile is achieved by active power (Volt-Watt), reactive power (Volt-VAR)and apparent power (Volt-VA) control. 
Due to the stochastic nature of solar energy and load demand, the actual battery capacity and voltage profile may deviate. To combat the change in battery capacity, a reference tracker is installed. For the change in voltage, a real-time controller is implemented, used for rapid response. These controllers are placed inside the EMS under the optimal charging algorithm. 
The main focus of this thesis is to design a control structure, which can be gradually deployed, to prevent and correct voltage problems in a low voltage feeder in various time scales. By using multiple intertwined controllers, the proposed hierarchical control structure achieves fast operation, prevention and correction of the voltage profile over an extended period.
The simulations have been validated on the IEEE European low voltage test feeder. Results demonstrate that a limited number of multi-port converters is needed to keep the voltage profile within limits. The various correction methods have been tested for effectiveness to correct voltage deviations. Both active (Volt-Watt) and apparent (Volt-VA) power show capabilities of voltage control. Furthermore, the real-time controller is capable of removing individual load usage from the network and prevent voltage violations caused by uncontrolled PV and EV.