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Power systems that need to integrate renewables at a large scale must account for the high levels of uncertainty introduced by these power sources. This can be accomplished with a system of many distributed grid-level storage devices. However, developing a cost-effective and robust control policy in this setting is a challenge due to the high dimensionality of the resource state and the highly volatile stochastic processes involved. We first model the problem using a carefully calibrated power grid model and a specialized hidden Markov stochastic model for wind power which replicates crossing times. We then base our control policy on a variant of stochastic dual dynamic programming, an algorithm well suited for certain high dimensional control problems, that is modified to accommodate hidden Markov uncertainty in the stochastics. However, the algorithm may be impractical to use as it exhibits relatively slow convergence. To accelerate the algorithm, we apply both quadratic regularization and a risk-directed importance sampling technique for sampling the outcome space at each time step in the backward pass of the algorithm. We show that the resulting policies are more robust than those developed using classical SDDP modeling assumptions and algorithms., Comment: 42 pages, 7 figures, Replacement: added additional references

We consider an energy storage problem involving a wind farm with a forecasted power output, a stochastic load, an energy storage device, and a connection to the larger power grid with stochastic prices. Electricity prices and wind power forecast errors are modeled using a novel hidden semi-Markov model that accurately replicates not just the distribution of the errors, but also crossing times, capturing the amount of time each process stays above or below some benchmark such as the forecast. This is an important property of stochastic processes involved in storage problems. We show that we achieve more robust solutions using this model than when more common stochastic models are considered. The new model introduces some additional complexity to the problem as its information states are partially hidden, forming a partially observable Markov decision process. We derive a near-optimal time-dependent policy using backward approximate dynamic programming, which overcomes the computational hurdles of classical (exact) backward dynamic programming, with higher quality solutions than the more familiar forward approximate dynamic programming methods., Comment: 36 pages, 7 figures, replacement: up to date version, additional references added