Sam Weckx

Combined Central and Local Active and Reactive Power Control of PV Inverters

The increasing amount of photovoltaic (PV) generation results in a reverse power flow and a violation of the overvoltage limits in distribution networks. PV inverters can curtail active power or consume reactive power to avoid these excessive high voltages. Local controllers of active and reactive power that are based on measurements of the produced PV power have a fast response to the changing production levels of the PV installation. The performance of these local controllers depends on the tuning of the control parameters, which are grid and time dependent. In this paper, local control functions are defined as piecewise linear functions. The parameters of all the local control functions are regularly reoptimized. This results in an optimal use of reactive power and a minimum amount of curtailed active power, while respecting network limitations. The optimization of these parameters is formulated as a convex optimization problem, which can be solved sufficiently fast. The performance of the control is evaluated on an existing three-phase four-wire distribution grid and is compared with different local control methods.

Load Balancing With EV Chargers and PV Inverters in Unbalanced Distribution Grids

Balanced three-phase four-wire distribution grids can host significantly more distributed generation and electric vehicles. Three-phase photovoltaic (PV) inverters and electric vehicle (EV) chargers can be adapted to transfer power from highly loaded to less loaded phases, without overloading the inverter or charger. Grid conditions will be improved due to a more balanced operation of the network and more PV panels and EVs can be connected before the limits of the network are reached. A classic coordinated charging strategy for EVs is adapted in this paper. It is shown that the charging of EVs can be improved when power can be transferred from one phase to another. Using PV inverters with a balancing inverter, the power injected in each phase will become a controllable variable as the total amount of produced power does not necessarily need to be equally divided across the three phases. The improvements made by using EV chargers and PV inverters that can balance the network are investigated. Several load flow simulations with realistic data show a positive effect on the system losses, the grid voltage, and voltage unbalance. Finally, a local controller is proposed to control the balancing between the phases when a real-time communication channel is not available.

Primary and Secondary Frequency Support by a Multi-Agent Demand Control System

Decentralized demand control can help to ensure the balance between electricity demand and supply. In this paper, a multi-agent demand control system is proposed where residential demand is controlled to provide spinning reserves. With the proposed control framework, an aggregator of dynamic demand is able to control the consumption and the response on frequency changes of a cluster of loads. The primary frequency support by the cluster of loads can emulate the primary control of a conventional generator. The total customer welfare remains maximal during the frequency support by applying utility functions for each device.

LV distribution network feeders in Belgium and power quality issues due to increasing PV penetration levels

In this paper, the impact of residential distributed energy resources (DER) on the power quality is investigated in four feeder types of the electrical LV distribution network in Flanders, Belgium. The investigated power quality issues are over-voltage, under-voltage and unbalance. The results of the simulations are discussed in detail. The paper leads to an estimation of the compliance to the power quality standard EN 50160, and a summary of issues in the distribution grids when increasing the amount of DER.

Multiagent Charging of Electric Vehicles Respecting Distribution Transformer Loading and Voltage Limits

In this paper, a market based multiagent control mechanism that incorporates distribution transformer and voltage constraints for the charging of a fleet of electric vehicles (EVs) is presented. The algorithm solves a utility maximization problem in a distributed way, assigning most charging power to the EVs with the highest need for energy. The algorithm does not rely on an iterative exchange of messages, but finds the optimal solution after the exchange of just one single message. A substation agent is responsible for guaranteeing a safe network operation. It uses the remaining capacity of each of the EV chargers for reactive voltage control. The performance of the algorithm is evaluated on an existing three-phase four-wire distribution grid. Simulation results show that the fleet of EVs can be charged at a minimal increase of costs, without jeopardizing the network.

Parameter identification of unknown radial grids for theft detection

This paper proposes an algorithm to detect the stealing of electricity by illegal connections in smart grids with unknown or uncertain cable lengths. Many new applications in the rising smart grid context will require information of the grid topology. We show that with measurement data of smart meters, the grid can be identified, as well as the phase of connection. One of the applications requiring grid information is the detection of electricity theft by double feeding. Electricity theft is a problem faced by all power utilities. Financial impacts are a reduced income for the system operator and the necessity to charge more to other customers. Stealing of electricity by double feeding can not be detected by the smart meter or by analysing the load profiles. Therefore it is suggested in this paper to use measurements of smart meters to identify the grid parameters and detect irregularities of specific customers.

Optimal real-time pricing for unbalanced distribution grids with network constraints

In this paper, a real-time pricing algorithm is described that allows different energy providers to share one common network, without violating the network constraints. We consider a smart grid equipped with a two-way communication system. Energy producers, system operator and end-users exchange information through the communication infrastructure in order to converge to the optimal power consumption schedules without violating network limitations. A distributed gradient algorithm automatically manages the interactions between the different agents. Customer behaviour is modelled by utility-functions, based on concepts from microeconomics. The proposed algorithm is applied to a 3-phase 4-wire radial grid.

Voltage Sensitivity Analysis of a Laboratory Distribution Grid With Incomplete Data

New voltage control algorithms are necessary to cope with the increasing amount of distributed generation and electric vehicles in distribution networks. Many of the newly proposed voltage control algorithms are based on linearized dependencies between the voltage magnitude, and the active and reactive power consumption. These linearized dependencies are normally obtained by algorithms, which rely on accurate grid topology information. Due to the traditionally passive operation of low voltage (LV) distribution networks, this information is typically missing, incomplete, or inaccurate. Therefore, this paper introduces a method to extract these linear dependencies based on historical smart meter data only. No information about the grid topology is required. The model adapts to the changing load conditions in the network. The algorithm has a low complexity and is applied to an unbalanced LV distribution network. Data of a practical laboratory setup is used to validate the proposed method in real-life conditions. With the obtained voltage sensitivity factors a voltage management strategy was implemented for the laboratory grid.

Reducing grid losses and voltage unbalance with PV inverters

In this paper, three-phase PV inverters are used to reduce the losses and the voltage unbalance in three-phase four-wire distribution grids. PV inverters rarely operate at maximal power production. If the PV inverter has four or six inverter legs it can supply negative- and zero-sequence currents. This makes it possible for the majority of the produced power to be injected into the phase with the highest power consumption, or to transfer power from highly loaded to less loaded phases, without overloading the PV inverter. Grid conditions will be improved due to a more balanced operation of the network. A benchmark solution is computed, where a central controller optimally controls the balancing inverters to minimize system losses. A local control approach for the balancing inverters is compared to the benchmark solution. Several load flow simulations with realistic data show a positive effect on the system losses, the grid voltage and the voltage unbalance.

LS-SVM-based on-load tap changer control for distribution networks with rooftop PV's

This paper discusses voltage regulation using on-load tap changers (OLTC) with line drop compensation (LDC) on low-voltage distribution networks with a high penetration of photovoltaic generation (PV). Load flow simulations show that PV generators affect the performance of classical LDC in a negative way. However, when a database exists where voltages measured by smart-meters are stored, Least-Squares support vector machines (LS-SVM) can be used to estimate the maximum and minimum voltage in the system, without needing a grid model, nor real-time communication. Control of the OLTC can then be executed to widen the gap between the system voltage and the acceptable limits, based on the maximum and minimum system voltage estimates.