Control Systems

Control of Power Systems

Summary

Contact Person:
Christian Hans

Our research in this area employs control methods for real-world applications in the domain of complex electrical power systems with a large share of decentralized, uncertain renewable generation. The overall objective is to enable carbon-free energy systems using automatic control. In what follows these applications are highlighted. They include distributed and decentralized low-level control as well as optimization-based high-level control, and control methods for wind power plants.

Distributed and decentralized control of future power systems

In future electrical power systems, conventional generators, such as coal power plants, will be mainly replaced by inverter-interfaced renewable sources and storage units. Our research in this field concerns different dimensions of low-layer control of such systems that comprise conventional and renewable generators as well as inverter-interfaced storage units. Modeling issues, which are a cornerstone for most control analysis and synthesis problems described below, were investigated in [Schiffer et al., 2016b].

Droop control, a simple decentralized scheme, has been a popular low-level control approach. Within the Control Systems Group, conditions for stability and power sharing under droop control were derived in [Schiffer et al., 2014a,b] for inverter-based microgrids and in [Schiffer et al., 2013] for grids with mixed rotational and electronic-interfaced units. In [Schiffer et al., 2015a, 2017], the analysis was extended to models that consider inaccurate clocks, induced by the fact that each individual unit is operated with its own digital processor. The effect of delays in grids with distributed rotational and electronic generation under droop control was thoroughly investigated in [Schiffer et al., 2016a].

The aforementioned analysis showed that droop control is not suitable to achieve reactive power sharing and typically leads to steady-state frequency deviations. As a consequence, in [Schiffer et al., 2015b, Schiffer. et al., 2014, Krishna et al., 2019] consensus-based distributed voltage control laws which guarantee reactive power sharing were proposed. Moreover, in [Krishna et al., 2017] different distributed secondary control schemes were thoroughly compared with respect to their steady-state frequency error, and in [Krishna et al., 2018], a consensus-based control law for accurate frequency restoration has been proposed. Furthermore, in [Krishna et al., 2020], robustness and steady-state performance of distributed secondary frequency control schemes have been investigated.

Operation control of single microgrids with very high renewable share

Microgrids are small power systems that can be operated connected to or isolated from a larger grid. They typically comprise storage units, renewable and conventional generators as well as loads. “Operation control” refers to the top, or tertiary, control level within a hierarchical control scheme and is typically based on comparatively simple models of the plant under low-level control. One central research question concerning microgrids is: how to operate microgrids with very high renewable share, i.e., how to control the energy of storage units, and how to maximize infeed from uncertain renewable sources without compromising a safe operation?

To answer this question, various model predictive control (MPC) schemes were derived within the Control Systems Group. They can be distinguished by the way they handle the uncertain load and renewable infeed: (i) certainty equivalence MPC [Hans et al., 2014], where a nominal forecast is fully trusted; (ii) minimax MPC [Hans et al., 2014, 2015a], where time-varying forecast intervals are assumed; (iii) risk-neutral stochastic MPC [Hans et al., 2015b], where a forecast probability distribution is fully trusted; and (iv) risk-averse MPC [Hans et al., 2020], where a forecast probability distribution is not fully trusted. The different approaches were thoroughly compared in different case studies in [Hans, 2021]. Moreover, in [Löser et al., 2019], fallback strategies for operation control of microgrids with communication failures were proposed. Additionally, in [Strenge et al., 2020b,a], learning based strategies for operation control were investigated. In [Strenge et al., 2019], a global controller is synthesized to improve the performance of a microgrid formed by interconnected prosumers.

Distributed optimization of interconnected microgrids

One approach to handle the operation of complex future energy systems with a large share of small-scale renewable energy sources is to partition the overall grid into smaller microgrids. To the outside world, each microgrid appears as a single entity that can provide or consume power. Allowing power exchange between these entities typically increases the overall system performance by exploiting effects like smoothing by geographical dispersion of renewable generators. One important research question in this area is: how to enable optimal trading among a network of interconnected microgrids while preserving the autonomy of each microgrid? Different distributed MPC schemes were derived within the Control Systems Group to answer this question. In [Hans et al., 2019], a hierarchical distributed MPC approach was presented. The approach considers a central coordinator that takes care of the transmission network which connects the individual microgrids. Power setpoints are found by consecutively solving (and communicating the results of) local optimization problems and a problem at the central coordinator. In [Sampathirao et al., 2021], the approach was extended by adding a condition that preserves the self-interests of each microgrid. Moreover, the central coordinator could be removed and the algorithm could be implemented in a fully distributed way that only requires peer-to-peer communication between neighboring microgrids.

Wind power plant control

Many wind farms are operated to a considerable extent in so-called power tracking mode in order to meet requirements of power system operators. In this mode, wind energy converters do not feed in the uncertain weather-dependent maximum possible power, but are operated with reduced power. Within current research activities at the Control Systems Group, existing degrees of freedom in the design of wind energy converters and wind farm controllers are exploited in order to achieve a better operation of the overall wind farm in power tracking mode.

People involved, projects and cooperations

Group members

Previous group members

  • J. Schiffer (joined Brandenburg University of Technology)
  • A. K. Sampathirao (joined Enervalis)
  • A. Krishna
  • M. Parada Contzen
  • T. D. Truong

Running projects

Completed projects

  • Mobil4Park
  • RETRAINER
  • Cybathlon 2016
  • iTRUST
  • STIMSWIM
  • BeMobil
  • APeroStim
  • MultiEMBI
  • SelfFEES
  • BigDysPro
  • MUNDUS
  • RehaRobES

Cooperations

Academia

  • A. Astolfi, Imperial College, UK
  • A. Bemporad, IMT Lucca, Italy
  • C. Bottasso, TUM, Germany
  • P. Braun, Australian National University, Australia
  • L. Grüne, Universität Bayreuth, Germany
  • F. Hellmann, PIK, Germany
  • R. Ortega, Supélec, France
  • J. Schiffer, Brandenburg University of Technology, Germany
  • P. Sopasakis, Queen’s University Belfast, UK
  • P. Patrinos, KU Leuven, Belgium

Industry

  • T. Heidt & E. Bosch, Autarsys GmbH, Germany
  • C. Reincke-Collon, Aggreko plc, Germany
  • T. Sezi, Siemens AG, Germany
  • A. K. Sampathirao, Enervalis, Belgium
  • Nordex SE

Publications related to this research area

2021

Sampathirao, A. K.; Hofmann, S.; Raisch, J.; Hans, C. A.
Distributed Conditional Cooperation Model Predictive Control of Interconnected Microgrids
Preprint
2021
Hans, C. A.
Operation control of islanded microgrids
Publisher: Shaker Verlag
2021
ISBN
978-3-8440-8300-2

2020

Strenge, Lia; Schultz, Paul; Kurths, Jürgen; Raisch, Jörg; Hellmann, Frank
A multiplex, multi-timescale model approach for economic and frequency control in power grids
Chaos: An Interdisciplinary Journal of Nonlinear Science, 30 (3) :033138
2020
Krishna, A.; Schiffer, J.; Raisch, J.
Distributed secondary frequency control in microgrids: Robustness and steady-state performance in the presence of clock drifts
European Journal of Control, 51 :135–145
2020
ISSN: 0947-3580
Strenge, Lia; Jing, Xiaohan; Boersma, Ruth; Schultz, Paul; Hellmann, Frank; Kurths, Jürgen; Raisch, Jörg; Seel, Thomas
Iterative learning control in prosumer-based microgrids with hierarchical control
IFAC-PapersOnLine, 53 (2) :12251-12258
2020
Hans, C. A.; Sopasakis, P.; Raisch, J.; Reincke-Collon, C.; Patrinos, P.
Risk-Averse Model Predictive Operation Control of Islanded Microgrids
IEEE Transactions on Control Systems Technology, 28 (6) :2136–2151
2020
Kral, T.; Hans, C. A.; Merk, P.
System for handling short circuits on an electrical network
2020

2019

Löser, I.; Sampathirao, A. K.; Hofmann, S.; Raisch, J.
Fallback Strategies in Operation Control of Microgrids with Communication Failures
58th IEEE Conference on Decision and Control (CDC), Page 3885-3891
December 2019
Strenge, Lia; Schafaschek, Germano; Raisch, Jörg
Modeling and control of prosumer-based microgrids: a Petri net approach
2019 IEEE 15th International Conference on Automation Science and Engineering (CASE), Page 209–215
IEEE
Publisher: IEEE, Vancouver, Canada
August 2019
Krishna, A.; Schiffer, J.; Monshizadeh, N.; Raisch, J.
A consensus-based voltage control for reactive power sharing and PCC voltage regulation in microgrids with parallel-connected inverters
European Control Conference (ECC), Page 542–547
June 2019
Hans, C. A.; Braun, P.; Raisch, J.; Grüne, L.; Reincke-Collon, C.
Hierarchical Distributed Model Predictive Control of Interconnected Microgrids
IEEE Transactions on Sustainable Energy, 10 (1) :407–416
January 2019
ISSN: 1949-3029

2018

Krishna, A.; Schiffer, J.; Raisch, J.
A Consensus-Based Control Law for Accurate Frequency Restoration and Power Sharing in Microgrids in the Presence of Clock Drifts
European Control Conference (ECC), Page 2575–2580
June 2018

2017

Krishna, A.; Hans, C. A.; Schiffer, J.; Raisch, J.; Kral, T.
Steady state evaluation of distributed secondary frequency control strategies for microgrids in the presence of clock drifts
25th Mediterranean Conference on Control and Automation, Page 508–515
Publisher: Valletta, Malta
2017

2016

Schiffer, J.; Zonetti, D.; Ortega, R.; Stanković, A. M.; Sezi, T.; Raisch, J.
A survey on modeling of microgrids—From fundamental physics to phasors and voltage sources
Automatica , 74 :135 - 150
2016
ISSN: 0005-1098
Schiffer, J.; Fridman, E.; Ortega, R.; Raisch, J.
Stability of a class of delayed port-Hamiltonian systems with application to microgrids with distributed rotational and electronic generation
Automatica , 74 :71 - 79
2016
ISSN: 0005-1098

2015

Hans, C. A.; Sopasakis, P.; Bemporad, A.; Raisch, J.; Reincke-Collon, C.
Scenario-Based Model Predictive Operation Control of Islanded Microgrids
54th IEEE Conference on Decision and Control (CDC), Page 3272–3277
Publisher: Osaka, Japan
December 2015
Schiffer, J.; Ortega, R.; Hans, C. A.; Raisch, J.
Droop-Controlled Inverter-Based Microgrids are Robust to Clock Drifts
American Control Conference (ACC), Page 2341–2346
Publisher: Chicago, IL, USA
July 2015
Hans, C. A.; Nenchev, V.; Raisch, J.; Reincke-Collon, C.
Approximate Closed-Loop Minimax Model Predictive Operation Control of Microgrids
European Control Conference (ECC), Page 241–246
Publisher: Linz, Austria
2015
Efimov, D.; Ortega, R.; Schiffer, J.
ISS of multistable systems with delays: application to droop-controlled inverter-based microgrids
American Control Conference (ACC)
2015
Schiffer, J.; Fridman, E.; Ortega, R.
Stability of a class of delayed port-Hamiltonian systems with application to droop-controlled microgrids
54th IEEE Conference on Decision and Control (CDC)
2015

2014

Schiffer., J.; Seel, T.; Raisch, J.; Sezi, T.
A Consensus-Based Distributed Voltage Control for Reactive Power Sharing in Microgrids
European Control Conference (ECC), Page 1299–1305
Publisher: Strasbourg, France
2014
Schiffer, J.; Ortega, R.; Astolfi, A.; Raisch, J.; Sezi, T.
Conditions for Stability of Droop-Controlled Inverter-Based Microgrids
Automatica, 50 (10) :2457–2469
2014
Publisher: Elsevier
ISSN: 0005-1098
Hans, C. A.; Nenchev, V.; Raisch, J.; Reincke-Collon, C.
Minimax Model Predictive Operation Control of Microgrids
19th IFAC World Congress, Page 10287–10292
Publisher: Cape Town, South Africa
2014
Schiffer, J.; Ortega, R.; Astolfi, A.; Raisch, J.; Sezi, T.
Stability of Synchronized Motions of Inverter-Based Microgrids Under Droop Control
19th IFAC World Congress, Page 6361–6367
Publisher: Cape Town, South Africa
2014

2013

Schiffer, J.; Goldin, D.; Raisch, J.; Sezi, T.
Synchronization of Droop-Controlled Microgrids with Distributed Rotational and Electronic Generation
52nd IEEE Conference on Decision and Control (CDC), Page 2334–2339
Publisher: Firenze, Italy
December 2013