Göran Andersson

ETH Zurich | ETH Zürich · Department Information Technology and Electrical Engineering

This work develops and compares several networked control and estimation algorithms to manipulate the power consumption of a population of residential thermostatically controlled loads to fulfill PJM frequency regulation requests given an imperfect communication network and modeling error. The algorithms rely on a model of the plant to reduce the e...

Due to high power in-feed from photovoltaics, it is expected that more battery systems will be installed in the distribution grid in near future to mitigate voltage violations and thermal line overloading. In this paper, we present a two-stage centralized model predictive control (MPC) scheme for distributed battery storage that consists of a sched...

Stochastic optimal power flow (OPF) formulations that minimize the expected operating costs over forecast scenarios generally result in lower costs than the standard (deterministic) OPF problem for power systems with significant forecast error, for example, from renewable energy sources. However, this type of stochastic OPF problem is more computat...

Dynamic line rating (DLR) models the transmission capacity of overhead lines as a function of ambient conditions. It takes advantage of the physical thermal property of overhead line conductors, thus making DLR less conservative compared to the traditional worst-case oriented nominal line rating (NLR). Employing DLR brings potential benefits for gr...

Due to increasing shares of renewable energy sources, more frequency reserves are required to maintain power system stability. In this paper, we present a decentralized control scheme that allows a large aggregation of refrigerators to provide Primary Frequency Control (PFC) reserves to the grid based on local frequency measurements and without com...

Higher shares of electricity generation from renewable energy sources and market liberalization is increasing uncertainty in power systems operation. At the same time, operation is becoming more flexible with improved control systems and new technology such as phase shifting transformers (PSTs) and high voltage direct current connections (HVDC). Pr...

This paper proposes a novel algorithm to optimally size and place storage in low voltage (LV) networks based on a linearized multiperiod optimal power flow method which we call forward backward sweep optimal power flow (FBS-OPF). We show that this method has good convergence properties, its solution deviates slightly from the optimum and makes the...

Rechargeable lithium-ion batteries are promising candidates for building grid-level storage systems because of their high energy and power density, low discharge rate, and decreasing cost. A vital aspect in energy storage planning and operations is to accurately model the aging cost of battery cells, especially in irregular cycling operations. This...

To stabilize power system frequency both in normal operation and after a contingency, a hierarchy of distributed-proportional and centralized-integral controllers is employed in most power systems. Providing proportional control–commonly referred to as primary frequency control or droop–with conventional generators constitutes significant cost. Thi...

In this paper, we propose a framework to jointly schedule energy and frequency control reserves in islanded systems, taking into account the system dynamic response. In islanded power systems, the control of system frequency differs considerably comparing to large interconnections, and dynamic models are employed to study the system behaviour. We s...

This paper proposes a novel algorithm to optimally size and place storage in low voltage (LV) networks based on a linearized multiperiod optimal power flow method which we call forward backward sweep optimal power flow (FBS-OPF). We show that this method has good convergence properties, its solution deviates slightly from the optimum and makes the...

With increasing shares of renewable energy sources (RES) and intensified electricity trading, the transmission system is operated closer to its limits. Dynamic line rating (DLR) can be used to obtain additional transmission capacity on existing lines by considering current meteorological factors. DLR is hence in general less conservative than nomin...

Over the past years, the share of electricity production from wind power plants has increased to significant levels in several power systems across Europe and the United States. In order to cope with the fluctuating and partially unpredictable nature of renewable energy sources, transmission system operators (TSOs) have responded by requiring wind...

Due to the increase of intermittent renewable energy sources, it is becoming more important to consider renewable generation forecast error when solving the optimal power flow (OPF) problem. The stochastic OPF, which uses multiple forecast scenarios, generally leads to a lower cost compared to the standard deterministic OPF, which uses a single for...

This paper is the first part of a two-part series in which we present results from an experimental demonstration of frequency regulation in a commercial building test facility. In Part I, we introduce the test facility and develop relevant building models. Furthermore, we design a hierarchical controller that consists of three levels: a reserve sch...

This paper is the second part of a two-part series presenting the results from an experimental demonstration of frequency regulation in a commercial building test facility. In Part I, we developed relevant building models and designed a hierarchical controller for reserve scheduling, building climate control and frequency regulation. In Part II, we...

Forecast uncertainty related to the power production from renewables frequently leads to significant changes between the scheduled and the actual power injections. Larger and more frequent fluctuations in the power production require new approaches to handle congestion and ensure system security. In this paper, we investigate how different strategi...

We investigate how a wind power plant with energy storage can be optimally controlled to comply with power gradient restrictions. For this purpose we use the kinetic energy stored in the turbine rotor and an additional battery storage. As a main contribution we propose a two level control scheme combining a supervisory controller with a low level c...

In this paper, a novel modeling framework is proposed, the multi-horizon modeling approach. This approach allows a very detailed and transparent modeling of many problems in hydro power planning by simultaneously being computationally very efficient. The model is applied to a complex pumped storage hydro power plant in a liberalized market environm...

Over the past years, the share of electricity production from wind power plants has increased to significant levels in several power systems across Europe and the United States. In order to cope with the fluctuating and partially unpredictable nature of renewable energy sources, transmission system operators (TSOs) have responded by increasing thei...

The extensive installation of gas-fired power plants in many parts of the world has led electric systems to depend heavily on reliable gas supplies. The use of gas-fired generators for peak load and reserve provision causes high intra-day variability in withdrawals from high pressure gas transmission systems. Such variability can lead to gas price...

In this paper we propose a distributed dynamic controller for sharing frequency control reserves of asynchronous AC systems connected through a multi-terminal HVDC (MTDC) grid. We derive sufficient stability conditions, which guarantee that the frequencies of the AC systems converge to the nominal frequency. Simultaneously, the global quadratic cos...

Large-scale deployment of Renewable Energy Sources (RES) has led to significant generation shares of variable RES in power systems worldwide. RES units, notably inverter-connected wind turbines and photovoltaics (PV) units that do not provide rotational inertia, are effectively displacing conventional generators and their rotating machinery. This h...

In this paper, we present distributed controllers for sharing primary and secondary frequency control reserves for asynchronous AC transmission systems, which are connected through a multi-terminal HVDC grid. By using Lyapunov arguments, the equilibria of the closed-loop system are shown to be globally asymptotically stable. We quantify the static...

Due to thermal inertia, commercial buildings can provide power system frequency reserves with the heating, ventilation and air-conditioning (HVAC) systems. In this paper, we follow up on a recently proposed framework for scheduling and provision of secondary frequency control (SFC) reserves within a building aggregation. We extend this framework wi...

Higher penetration of renewable energy sources and market liberalization increase both the need for transmission capacity and the uncertainty in power system operation. New methods for power system operational planning are needed to allow for efficient use of the grid, while maintaining security against disturbances. In this paper, we propose a ris...

In this paper, we present an optimization tool to investigate the cost-optimal placement and sizing of battery storage as a PV integration measure in distribution grids. Additionally, potential synergies between PV generation, battery storage, PV curtailment and electric mobility are also explored. The optimization tool is based on the two basic Op...

This paper proposes a new methodology to maximize the feasible set of power injections and cross-border power transfers in meshed multi-area power systems. The approach used polyhedral computation schemes and is an extension to the classic procedure for cross-border transfer capacity assessment in the European power network, including the computati...

Imbalance settlement markets are managed by the system operators and provide a mechanism for settling the inevitable discrepancies between contractual agreements and physical delivery. In European power markets, settlements schemes are mainly based on heuristic penalties. These arrangements have disadvantages: First, they do not provide transparenc...

This paper focuses on the self-scheduling problem of an aggregator of plug-in electric vehicles (PEVs) purchasing energy in the day-ahead market, and offering balancing services for a wind power producer, i.e., committing to compensate the forecast errors of wind power plants. The aggregated charging and discharging flexibility of the PEV fleet is...

The growing amount of fluctuating renewable infeeds and market liberalization increases uncertainty in power system operation. To capture the influence of fluctuations in operational planning, we model the forecast errors of the uncertain in-feeds as random variables and formulate a security constrained optimal power flow using chance constraints....

Demand response could provide reserves to power systems and market designs should enable cost-efficient exploitation of these resources. In direct load control programs, consumers provide demand response in exchange for incentive payments. The success of such contracts is a function of level of information sharing, consumer costs, and power system...

The number of renewable energy sources in electricity grids is growing and with it the associated uncertainty. For power system operation a good tradeoff between security and cost becomes increasingly important. We consider the problem of including uncertainty from renewable in-feed in a DC security constrained optimal power flow (SCOPF) by formula...

The reserve grid is a redundant MV grid, which serves as an emergency power system (EPS). It is designed to compensate interruptions of the MV grid or substations by offering an independent connection to an additional substation. The challenge is to find the optimal topology regarding costs and reliability. The locations of the customers and the su...

Robust programs with modulated uncertainty sets are problems in which the uncertainty sets are treated as optimization variables. In many applications, these uncertainty sets can be interpreted as reserve capacities for which rewards are offered. One example is the provision of frequency reserve capacities to the power grid by demand-side resources...

A major challenge in power system operation is the integration of renewable energy in-feed in large scale. Currently, the responsibility to cope with uncertainty in power injection is transferred to a central authority, i.e. the system operator, while renewable energy in-feed is supported via a tariff system. In this paper we propose market partici...

When energy storage units, such as batteries, are installed to support photovoltaics and defer power system upgrades they are inactive or only partially used most of time. Their unused capacities could be used to provide frequency control, allowing them to generate additional revenues. However, the challenge is to decide how much of their energy an...

The use of multi-terminal HVDC grids is a promising option to tackle the coming challenges in long distance power transmission, but the combined operation of HVDC and AC grids will bring certain challenges. The dynamic interaction from the fast controllable converter station with the rotational inertia dependent AC grids has to be investigated in d...

This paper puts forward the vision of fully decoupling market operations from security considerations through controllable power flows. In "A Fully Controllable Power System", power system security is no longer dependent on the location of the power injection points. In the ideal case, this leads to the elimination of redispatching costs, which amo...

It has been shown that the heating, ventilation, and air conditioning (HVAC) systems of commercial buildings can offer ancillary services to power systems without loss of comfort. In this paper, we propose a new control framework for reliable scheduling and provision of frequency reserves by aggregations of commercial buildings. The framework incor...

Increased distributed Photo-Voltaic (PV) generation leads to an increase in voltages and unwarranted backflows into the grid. This paper investigates Demand Response (DR) with Electric Water Heaters (EWHs) as a way to increase the PV hosting capacity of a low-voltage feeder. A control strategy relying only on power measurements at the transformer i...

Long-term simulations of electric power systems are an essential tool for power system planning and operation. As power systems are extraordinarily complex, simplifying assumption have to be made to find computational tractable model formulations. In this paper we define aggregation methods 1) for simulation time, 2) for generation units and 3) for...

Typically, the charging of Plug-in Electric Vehicles (PEVs) can be shifted in time. This flexibility can be used to reduce the cost and/or network impact of charging, and even to provide ancillary services. The focus of this paper is on the use of charging flexibility for cost minimization, either from the perspective of PEVs or from the society's...

In the past few years, the share of renewable power generation has been growing significantly, leading to increased uncertainties in power system operation. In this paper, the effect of wind in-feed uncertainties on power flow in the AC grid is investigated. The wind power in-feed deviations from initial forecast are modelled as Gaussian random var...

Due to high power in-feed from photovoltaics, it is expected that more battery systems will be installed in the distribution grid in near future. In this paper, we present a method to optimally control multiple battery sets in real-time to collectively provide services to power systems. The method is based on a Model Predictive Control (MPC) framew...

Thermal loads can, in principle, provide ancillary services to power systems. In this paper, we propose a new, practical frequency control scheme that allows different types of thermal loads to collaboratively offer reserves in parallel to generators. Primary reserves are provided by residential refrigerators in a decentralized fashion based on loc...

In this paper an algorithm is developed for solving the Optimal Power Flow (OPF) and Security Constrained OPF (SCOPF) problem in mixed AC/DC grids. Non-linear models are used for power lines and AC/DC and DC/DC converters. The converter models include terminal losses and power rating constraints. The formulation of the SCOPF problem is such that it...

In this paper we propose a distributed dynamic controller for sharing frequency containment reserves of asynchronous AC systems connected through a multi-terminal HVDC (MTDC) grid. We derive sufficient stability conditions, which guarantee that the frequencies of the AC systems converge to the nominal frequency. Simultaneously, the global quadratic...

An on-going debate in the energy economics and power market community raises the question if energy-only power markets are increasingly failing due to growing feed-in shares from subsidized renewable energy sources (RES); the argument being essentially that the merit-order effect of RES production depresses day-ahead spot market prices, which in tu...

Congestion management is crucial to maintain an efficient and reliable power system operation, and thus it is an important task for any transmission system operator. Different congestion management approaches are currently implemented by different TSOs. In this paper, we consider two market schemes. The first one considers the transmission constrai...

Due to the increasing amount of electricity generated from renewable sources, uncertainty in power system operation will grow. This has implications for tools such as Optimal Power Flow (OPF), an optimization problem widely used in power system operations and planning, which should be adjusted to account for this uncertainty. One way to handle the...

The optimal operation of an integrated electricity and natural gas system is investigated. The couplings between these two systems are modeled by energy hubs, which serve as interface between the loads and the transmission infrastructures. Previously, we have applied a distributed control scheme to a static three-hub benchmark system. In this paper...

In this paper, we present distributed controllers for sharing primary and secondary frequency control reserves for asynchronous AC transmission systems, which are connected through a multi-terminal HVDC grid. By using passivity arguments, the equilibria of the closed-loop system are shown to be globally asymptotically stable. We quantify the static...

This paper proposes a formulation for a stochastic security constrained unit commitment, dispatch and reserve scheduling, considering non-spinning reserves. We employ a randomized optimization technique that is based on scenario generation of the uncertain variables, in this case the wind power, and offers probabilistic certificates regarding the r...

This paper proposes a formulation for a stochastic security constrained unit commitment, dispatch and reserve scheduling, considering N-1 security and non-spinning reserves. We employ a randomized optimization technique that is based on scenario generation of the uncertain variables, in this case the wind power, and offers probabilistic certificate...

This paper formulates a probabilistic security-constraint optimal power flow considering a combination of an AC system and a multi-terminal HVDC grid that can depict the future power systems. The probabilistic formulation is discussed considering uncertainty in the generation infeed (e.g. wind power). To achieve a tractable problem we use a lineari...

In this paper, we propose a simulation-based method for primary control reserve (PCR) reallocation in large power systems, taking into account the variability of renewable energy sources' (RES) in-feed. Our goal is to identify technically feasible pairwise PCR reallocations between generally non-neighboring control areas (CAs). To achieve this goal...

Recent research has shown that thermostatically controlled loads (TCLs) can provide power system services. However, a key challenge is to achieve coordinated control of large populations of resources using existing communication and control infrastructure or with minimal addition of new infrastructure. In this paper, we assume that we only have acc...

Electricity market designs must evolve to incorporate efficiently the large-scale penetration of renewable energy sources and demand side participation. Current renewable energy support schemes and fixed tariff systems fail to address two major power system operation issues and therefore create additional system costs. First, unlike other commodity...

This paper includes security constraints in OPF calculations for combined HVAC and HVDC grids. Two formulations of the problem are considered: a preventive and a corrective formulation. The outages of lines, generators and terminal stations are included. The preventive control method assumes that no control actions are taken after a contingency hap...

It is known that in some cases, switching some transmission lines of an electric power system off may improve the optimal economic dispatch cost. This modification of the economic dispatch problem is known as optimal transmission line switching. Unfortunately, the modified problem involves binary decision variables which make the problem difficult...

This paper introduces linear current distribution factors for use in: (a) SCOPF formulations, and (b) in analytical approximations of corrective control actions for HVDC lines. These are relationships based on complex numbers, which can be used in the context of full AC power flow equations. Three distribution factors are introduced: the linear AC...

This paper proposes a novel algorithm to identify degradation in batteries used for power system applications. Unlike conventional battery control methods that try to extend battery lifetime by applying heuristic rules, this approach allows us to maximize battery lifetime within an optimal control framework. We use an online Least Squares (LS) iden...

Demand Response (DR) is widely held to be an essential part of future power systems. DR is expected to support integration of distributed generation from Renewable Energy Sources (RES) as well as to facilitate demand-side participation in power and ancillary service markets. This paper critically analyzes several business models from both a Distrib...

In this paper we present three different algorithms for the placement of multi-terminal HVDC interconnections. The speciality is the quantitative incorporation of operational flexibility in the placement algorithms. The first algorithm tries to find the most economical placement, the second algorithm looks for the placement which yields the highest...

This paper presents a novel approach for the predictive power dispatch of a large number of power system units that can be diverse in their power as well as power ramp ratings and can be dispersed both in distribution grids and transmission networks. In particular, the involved unit portfolio consists of Renewable Energy sources (RES), conventional...

With a large-scale introduction of plug-in electric vehicles (PEVs), a new entity, the PEV fleet aggregator, is expected to be responsible for managing the charging of, and for purchasing electricity for, the vehicles. This book chapter deals with the problem of an aggregator bidding into the day-ahead electricity market with the objective of minim...

In this paper, an equivalent single-infeed model of a multi-infeed HVDC system is derived to lend theoretical basis for defining an index called equivalent effective short-circuit ratio (EESCR), which can resolve the ambiguity when applying the effective short-circuit ratio (ESCR) concept for the single-infeed to multi-infeed HVDC systems. Moreover...

Power systems are traditionallymonitored and controlled by an IT infrastructure, referred to as Supervisory Control and Data Acquisition (SCADA) system. The cyber-physical interaction of power systems (physical) and SCADA systems (cyber) rises security issues, since the links between those systems are vulnerable to cyber-attacks that can potentiall...

Demand response can provide services to the power network, however, coordination of spatially distributed demand response resources generally requires coping with imperfect communication networks. This work investigates methods to manage communication constraints (e.g., Delays and bandwidth limitations), faced by demand response aggregators who man...

Operational flexibility is an important property of electric power systems and plays a crucial role for the transition of existing power systems, many of them based on fossil fuels, toward power systems that can efficiently accommodate high shares of variable renewable energy sources (RESs). The availability of sufficient operational flexibility in...

The Global Grid advocates the connection of all regional power systems into one electricity transmission system spanning the whole globe. Power systems are currently forming larger and larger interconnections. Environmental awareness and increased electricity consumption leads more investments toward renewable energy sources, which are abundant in...

Deliverable (D) No: 4.2 Report on new methods to maximize integration of EV and DER in distribution grids (methods for optimization under uncertainty, for storage modelling and for statistical behaviour of EV and DER)

Primary frequency control, also known as primary frequency response or droop, is one of the essential ancillary services guaranteeing stable operation of any power system. Provision of primary and secondary frequency control reserves creates high costs to the system operator. Demand Response, that is an automatic contribution by flexible loads, may...

Dynamic Thermal Line Rating (DLR) is deemed to be an effective way to increase transmission capacities and therefore enabling additional operational flexibility. The transmission capacities are dynamically determined based on current or expected weather conditions. First pilot projects have proven its efficiency. In this paper we present two approa...

In this paper we propose an algorithm to calculate the Hourly Price Forward Curve (HPFC) under market coupling conditions. The algorithm uses the supply and demand curves, transfer capacity, weather and seasonal indicators to calculate the HPFC based on the Market Coupling (MC) algorithm using implicit capacity auctions.

Plug-in electric vehicles (PEVs) can be considered flexible loads, as the time when they are charged can be shifted to a certain extent without impacting the drivers' mobility. An aggregator coordinating these flexible resources aims to minimize the costs of charging, subject to individual PEV constraints, imposed by battery and charging infrastruc...

This paper presents a decentralized controller for sharing primary AC frequency control reserves through a multi-terminal HVDC grid. By using passivity arguments, the proposed controller is shown to stabilize the closed-loop system consisting of the interconnected AC and HVDC grids, given any positive controller gains. The static control errors res...

In this paper we present a framework to efficiently characterize the available operational flexibility in a multi-area power system. We focus on the available reserves and the tie-line flows. The proposed approach is an alternative to the current calculation of the Available Transfer Capacity (ATC), as it considers location and availability of rese...

Higher penetration of renewable energy and market liberalization increase both the need for transmission capacity and the uncertainty in power system operation. New methods for power system operational planning are needed to allow for efficient use of the grid, while maintaining security and robustness against disturbances. In this paper, we propos...

This paper presents a medium-term self-scheduling optimization of pumped hydro storage power plants with detailed consideration of short-term flexibility. A decomposition of the problem into inter- and intrastage subproblems, where the intrastage problems themselves are formulated as multi-stage stochastic programs, allows the detailed consideratio...

This paper demonstrates the stabilization of a large power system with a high penetration of Renewable Energy Sources, such as wind or photovoltaic, using Voltage Source Converter based HVDC links. Due to the reduction of system inertia, frequency oscillations are expected to increase unless additional control measures are added to the system. Base...

This paper presents a market-based control approach to minimize the charging costs of plug-in electric vehicles (PEVs) without impacting their end-use. In the proposed framework, vehicles are modeled as agents actively placing bids to purchase electricity in the spot market. Their bids depend on status variables which represent the urgency to charg...

The grid integration of intermittent Renewable Energy Sources (RES) causes costs for grid operators due to forecast uncertainty and the resulting production schedule mismatches. These so-called profile service costs are marginal cost components and can be understood as an insurance fee against RES production schedule uncertainty that the system ope...

Model Predictive Control (MPC) is a widely used method in process industry for the control of multi-input and multi-output systems. It possesses features that make it attractive for power system applications. Power systems exhibit complex characteristics such as hybrid nature (mixed continuous and discrete dynamics), nonlinear dynamics, and very la...

This paper presents two algorithms for solving a medium-term hydro optimization. Considered are risk-averse operation, provision of spinning reserves as well as short- term production flexibility. Proposed is a variant of stochastic dual dynamic programming (SDDP) and stochastic dynamic programming as a benchmark. A risk measure is introduced in bo...

Battery energy storage systems (BESSs), while at the moment still expensive, are from a technical point of view exceptionally well suited to support a distribution system operator (DSO) in the challenges created by increasing distributed, fluctuating and uncertain generation from renewable energy sources (RES), as well as by the unbundling of elect...