Voltage Regulation In Distribution Grids Research Articles

Cooperative Peak Shaving and Voltage Regulation in Unbalanced Distribution Feeders

This paper considers the co-operation of distributed generators (DGs), battery energy storage systems (BESSs) and voltage regulating devices for integrated peak shaving and voltage regulation in distribution grids through a co-optimization framework, which aims to minimize the operational costs while fulfilling the operational constraints of network and devices. To account for the uncertainties of load demand and generation, we then convert the co-optimization model into a two-stage stochastic program where state-of-charge (SoC) trajectories of BESSs and operation of voltage regulating devices are optimized at the first stage for day-ahead scheduling, while the reactive powers of DGs and BESSs are left at the second stage for potential intra-day scheduling to handle short-term voltage issues. The proposed co-optimization scheme is validated on the IEEE 37-node test feeder and compared with other practices.

Joint Chance Constraints in AC Optimal Power Flow: Improving Bounds Through Learning

This paper considers distribution systems with a high penetration of distributed, renewable generation and addresses the problem of incorporating the associated uncertainty into the optimal operation of these networks. Joint chance constraints, which satisfy multiple constraints simultaneously with a prescribed probability, are one way to incorporate uncertainty across sets of constraints, leading to a chance-constrained optimal power flow problem. Departing from the computationally heavy scenario-based approaches or approximations that transform the joint constraint into conservative deterministic constraints; this paper develops a scalable, data-driven approach which learns operational trends in a power network, eliminates zero-probability events (e.g., inactive constraints), and accurately and efficiently approximates bounds on the joint chance constraint iteratively. In particular, the proposed framework improves upon the classic methods based on the union bound (or Boole’s inequality) by generating a much less conservative set of single chance constraints that also guarantees the satisfaction of the original joint constraint. The proposed framework is evaluated numerically using the IEEE 37-node test feeder, focusing on the problem of voltage regulation in distribution grids.

Designing Reactive Power Control Rules for Smart Inverters Using Support Vector Machines

Smart inverters have been advocated as a fast-responding mechanism for voltage regulation in distribution grids. Nevertheless, optimal inverter coordination can be computationally demanding, and preset local control rules are known to be subpar. Leveraging tools from machine learning, the design of customized inverter control rules is posed here as a multi-task learning problem. Each inverter control rule is modeled as a possibly nonlinear function of local and/or remote control inputs. Given the electric coupling, the function outputs interact to yield the feeder voltage profile. Using an approximate grid model, inverter rules are designed jointly to minimize a voltage deviation objective based on anticipated load and solar generation scenarios. Each control rule is described by a set of coefficients, one for each training scenario. To reduce the communication overhead between the grid operator and the inverters, we devise a voltage regulation objective that is shown to promote parsimonious descriptions for inverter control rules. Numerical tests using real-world data on a benchmark feeder demonstrate the advantages of the novel nonlinear rules and explore the trade-off between voltage regulation and sparsity in rule descriptions.

An MPC based optimized control approach for EV-based voltage regulation in distribution grid

This paper presents a model predictive control (MPC) method, which allows EVs to participate in the grid voltage regulation as a reactive power compensation device to maintain the grid voltage within a stable range while keeping EVs charged to the desired state. According to the number of the connected EVs, the EVs can assist or even replace the traditional reactive power compensation device to achieve control objectives. The proposed method uses a two-stage hierarchical control scheme based on model predictive control to minimize the deviation of voltage profile while satisfying system constraints. The applicability of the proposed method is verified through a 19-bus radial distribution system. Simulation results show that based on the proposed scheme, EVs can assist or replace traditional reactive power compensation devices to participate in grid voltage regulation and achieve better voltage control performance.

Parallel Operation of Transformers With on Load Tap Changer and Photovoltaic Systems With Reactive Power Control

In recent years, the number of active grid components for voltage regulation in distribution grids has increased significantly. Besides voltage regulators, such as transformers with on load tap changers (OLTCs), distributed generators can provide a certain voltage support by means of reactive power control (RPC). The different control entities, OLTC, and RPC by photovoltaic (PV) systems, usually operate based on local measurements and control characteristics. Hence, unintended interactions between the control entities cannot be excluded in general. This paper analyzes the parallel operation of OLTC transformers with a voltage-based control and PV systems with different RPC strategies (e.g., Watt/power factor control PF(P), volt/var control (Q(V)) in a distribution system environment. The focus is on unintended interactions, such as an increase of OLTC switching operations by PV RPC. The contribution and novelty of this paper is to raise awareness for the likelihood of these unintended interactions and to provide a first methodology to assess the parallel operation of OLTC control and PV RPC in detail. The results show that the impact of PV RPC on the number of OLTC switching operations and the effectiveness in parallel operation can differ considerably between the applied PV RPC strategies.

Integrated voltage regulation in distribution grids with photovoltaic distribution generation assisted by telecommunication infrastructure

Massive penetration of Distributed Generation Photovoltaic Systems – DGPV – connected to the power distribution grid through electronic inverters can contribute, in an aggregate scenario, to the performance of several power system control functions, notably in voltage regulation along a distribution feeder. In this context, the supervision and control of these generating units through a standardized, flexible and capillary communication infrastructure becomes a key factor in enabling large-scale integration. Present voltage regulation methods adopted in distribution grids using DGPV units are based on the local interaction of each source with the power grid, without exploiting the potential benefits of a wide integration among them. This paper proposes the use of an optimization method for voltage regulation, focused on reactive power injection control, based on a communication architecture model that coordinates the interaction among the inverters of DGPV units. This architecture enables each distributed source to perform in accordance with its operational characteristics and location, while dynamically coordinated by a DGMS (Distributed Generation Management System). The proposed communication infrastructure is based on the connectivity and interoperability requirements established by the international standard IEC 61850 and the IEEE 2030 reference model. A sensitivity analysis regarding the performance of voltage regulation and communication infrastructure, based on a co-simulation of PSCAD and MatLab, shows the effectiveness of the proposed optimization method. This work analyses the impact of communication network delay and unavailability in voltage regulation process.

Multi-objective coordinated droop-based voltage regulation in distribution grids with PV systems

High penetrations of photovoltaic (PV) systems in distribution grids have caused new challenges such as reverse power flow and voltage rise. Reactive power contribution by PV systems has been proposed by grid codes and literature as one of the remedies for voltage profile violation. Recent German Grid Codes (GGC), for instance, introduce a standard active power dependent reactive power characteristic, Q(P), for inverter-coupled distributed generators. Nevertheless, the GGC recommends a voltage dependent reactive power characteristic Q(V) for the near future, recognizing that the Q(P) characteristic cannot explicitly address voltage limits. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to develop a coordinated Q(V) characteristic for each PV system along a radial feeder using only the local measurement and drooping technique concepts. The aim of this paper is using a multi-objective design to adjust the parameters of the Q(V) characteristic in the proposed droop-based voltage regulation in order to minimize the reactive power consumption and line losses. On the other hand, it is also possible to adjust the parameters in order to reach equal reactive power sharing among all PV systems. A radial test distribution grid, which consist of five PV systems, is used to calculate power flow and, in turn, the voltage sensitivity matrix. The comparison of results demonstrates that both approaches in the proposed droop-based voltage regulation can successfully regulate the voltage to the steady-state limit. Moreover, it is shown that the profile of reactive power consumption and line losses are considerably reduced by the multi-objective design.

Coordinated Active Power-Dependent Voltage Regulation in Distribution Grids With PV Systems

High penetrations of photovoltaic (PV) systems in distribution grids have brought about new challenges such as reverse power flow and voltage rise. One of the proposed remedies for voltage rise is reactive power contribution by PV systems. Recent German Grid Codes (GGC) introduce an active power dependent (APD) standard characteristic curve, ${\rm Q}({\rm P})$ , for inverter-coupled distributed generators. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to locally and systematically develop a coordinated ${\rm Q}({\rm P})$ characteristic for each PV system along a feeder. The main aim of this paper is to evaluate the technical performance of different aspects of proposed ${\rm Q}({\rm P})$ characteristics. In fact, the proposed method is a systematic approach to set parameters in the GGC ${\rm Q}({\rm P})$ characteristic. In the proposed APD method the reactive power is determined based on the local feed-in active power of each PV system. However, the local voltage is also indirectly taken into account. Therefore, this method regulates the voltage in order to keep it under the upper steady-state voltage limit. Moreover, several variants of the proposed method are considered and implemented in a simple grid and a complex utility grid. The results demonstrate the voltage-regulation advantages of the proposed method in contrast to the GGC standard characteristic.

Comparison of Different Innovative Technical Solutions for Voltage Regulation in Distribution Grids

Comparison of Different Innovative Technical Solutions for Voltage Regulation in Distribution Grids