Abstract
This paper presents a nonlinear dynamic simulation model of an ultracapacitor (UC) bank and the associated control system. The control system at hand consists of two levels: the lower level controls the inverter of the UC bank, while the upper control level is responsible for providing charging/discharging active power set points to be followed by the lower control level. This paper focuses on the development of the upper control level for frequency control. Specifically, two simulation case studies are developed so as to assess the performance of the proposed control framework. In the first case study the upper control level is developed using a classical Proportional-Integral-Derivative (PID) controller. In the second case study the upper control level is devised using a Model Predictive Control (MPC) algorithm based on internal linear prediction model of a nonlinear UC bank. In both cases, a nonlinear UC bank simulation model is used. The simulation case studies are modelled and tested in Matlab/Simulink. The response of the MPC-controlled UC bank is compared to the 3 existing PID-control algorithms for frequency control. The simulation results show that the MPC algorithm outperforms the conventional PID controllers.
Highlights
T HE trend of increasing the share of inverter-interfaced generation (IIG) in power systems throughout the world and the subsequent reduction of synchronous inertia have motivated many research efforts to understand the stability of low-inertia systems as well as to develop new algorithms for enabling the IIG participation in system frequency control and otherManuscript received April 25, 2020; revised January 21, 2021; accepted March 15, 2021
The quality of the upper-level controller based on the Model Predictive Control (MPC) algorithm is compared with the response of a 3 standard PID control approaches: i) virtual inertia + transient droop (Fig. 4, Kd > 0; Ki > 0; τwd τwi > 0); ii) virtual inertia only (Kd = 0; Ki > 0; τwi > 0); iii) virtual inertia and droop with dynamic power limitation based on SoC estimation from [9] (Kd > 0; Ki > 0; τwd = τwi = 0)
The main goal of this paper is to show the potential benefits of applying an MPC algorithm to UC bank operation optimization for frequency control
Summary
T HE trend of increasing the share of inverter-interfaced generation (IIG) in power systems throughout the world and the subsequent reduction of synchronous inertia have motivated many research efforts to understand the stability of low-inertia systems as well as to develop new algorithms for enabling the IIG participation in system frequency control and otherManuscript received April 25, 2020; revised January 21, 2021; accepted March 15, 2021. T HE trend of increasing the share of inverter-interfaced generation (IIG) in power systems throughout the world and the subsequent reduction of synchronous inertia have motivated many research efforts to understand the stability of low-inertia systems as well as to develop new algorithms for enabling the IIG participation in system frequency control and other. The most prominent technologies for tackling the issues (e.g. voltage, frequency and angle stability, provision of balancing services [2]) brought upon by an increased share of inverter-interfaced generation are energy storage technologies such as batteries, flywheels, supercapacitors/ultracapacitors (SC/UC) [1]. Most attention has been paid to batteries as they are the most commercially mature and most versatile of all inverter-based fast storage technologies with a good trade-off between power density and energy density [3]. Relatively recently UC storage has been considered for bulk power system applications [4], [5]
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