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) that as such do not provide rotational inertia, are effectively displacing conventional generators and their rotating machinery. The traditional assumption that grid inertia is sufficiently high with only small variations over time is thus not valid for power systems with high RES shares. This has implications for frequency dynamics and power system stability and operation. Frequency dynamics are faster in power systems with low rotational inertia, making frequency control and power system operation more challenging.This paper investigates the impact of low rotational inertia on power system stability and operation, contributes new analysis insights and offers mitigation options for low inertia impacts.

Optimal control of Battery Energy Storage Systems (BESSs) is challenging because it needs to consider benefits arising in power system operation as well as cost induced from BESS commitment. The presented approach relies on the methodology of Model Predictive Control (MPC) for optimal BESS operation. Variable and strongly usage dependent battery degradation costs constitute the bulk of the marginal costs for BESS operation. Battery degradation is usually modeled with nonlinear functional dependencies or an implicit cycle counting approach unsuited for an MPC implementation. In this paper an explicit cost function considering battery degradation is developed, which sufficiently captures the nonlinearities and is applicable for arbitrary battery load patterns. The resulting piece-wise affine cost function leads to a mixed-integer quadratic programming problem allowing a standard hybrid MPC formulation.As proof-of-concept, a peak shaving algorithm relying on the proposed cost function and on adaptive soft limits is developed and implemented on the Zurich 1 MW BESS demonstration project, owned and operated by the utility of the Canton of Zurich (EKZ).

No abstract

No abstract

No abstract