Scenario-based model predictive operation control of islanded microgrids

Abstract

Abstract-We propose a model predictive control (MPC) approach for the operation of islanded microgrids that takes into account the stochasticity of wind and load forecasts. In comparison to worst case approaches, the probability distribution of the prediction is used to optimize the operation of the microgrid, leading to less conservative solutions. Suitable models for time series forecast are derived and employed to create scenarios. These scenarios and the system measurements are used as inputs for a stochastic MPC, wherein a mixedinteger problem is solved to derive the optimal controls. In the provided case study, the stochastic MPC yields an increase of wind power generation and decrease of conventional generation.

Steady state evaluation of distributed secondary frequency control strategies for microgrids in the presence of clock drifts

“…Fig. 3c depicts the internal frequencies and active power ratios of the MG, controlled with strategy (20). It can be observed that the steady state frequency error of unit 1 and at the busbar goes to zero.…”

“…Note that only the internal frequencyω i is available to every unit. Furthermore, ω d ∈ R is the frequency set point, k i ∈ R >0 the droop coefficient, P d i ∈ R the active power set point from a higher control level, e.g, energy management [20], and ξ i ∈ R is the control input. The measured active power P m i ∈ R is obtained by filtering the power output P i in (1) by a first order low pass filter with time constant τ i ∈ R >0 .…”

“…Hence, the approach presented in (20) partially fulfils the control objectives as a zero steady state frequency error can be reached. However, power sharing cannot be guaranteed.…”

“…3b indicates that a zero steady state frequency error is hard to be achieved with (18). Control approaches that use a very accurate central frequency measurement at a node with non-zero pinning gain as in (20) and (22) are able to realise zero steady state frequency error in the presence of clock drifts. In steady state, power sharing can be achieved by using a distributed frequency secondary control that is parametrized as described in Section IV-C.…”

“…Remark 1: The control approaches (20) and (22) can also be implemented with central frequency measurement at a bus bar. Then, the busbar is added to the secondary control layer and the frequency reference ω d is provided only to the busbar.…”