A Two-Stage Architecture For Voltage/VAR Control In Power Distribution Systems

As a critical part of power systems,distribution system is the bridge between the transmis-sion system and end users.With the consideration of energy dilemma and environment issues,distributed generation(DG)integrated distribution system has been attracting wide attention.However,the integration of DG changes the traditional radial topology,and there will be bi-direction flow in distribution systems.Moreover,the output of the DG is deeply affected by factors such as weather,which bring prominent stochasticity and randomness.Considering the issues caused by the stochasticity and randomness,such as reactive power estimation deviation,there might be reactive power dis-balance in some areas of distribution systems.Hence,it is necessary to design a new volt/var optimization method in DG integrated distribution systems.In this paper,we analyzed the traditional centralized and decentralized method and then presented a two stage volt/var control strategy.In local stage,we presented a low complexity control algorithm,which stabilizes the bus voltages by DG’ s fast response to the voltage fluctu-ation.Utilizing the fuzzy comprehensive evaluation method,the state of the distribution system is evaluated online,and the global reactive power optimization is triggered when the evalua-tion characteristics does not been satisfied.In the global optimization stage,traditional reactive power compensation devices such as on-load tap-changing transformer and VAR-capable in-verter are re-dispatched to optimize the power loss,quality of electricity,and the allowance of the DG.Lastly,we presented a new state estimator,which can mitigate the reliability issues of the voltage regulation caused by the time skew problem.In order to verify the validity of the two-stage voltage and reactive power control scheme of this article,we select the IEEE 33 node distribution network for simulation.For each sub-segment,first,we verify the effectiveness of the control algorithm to deal with local power fluctuations in a short time.Then we take advantage of the fuzzy comprehensive evaluation method to assess the system running at a given time.The assessment was consistent with the expected results.Next,a simulation was used to verify the improvement of the overall quality of proposed voltage reactive power optimization algorithm and the decrease of network loss.On this basis,the overall design of the two-stage scheme is compared with the traditional reactive power optimization with fixed interval and existing two-phase control scheme.The results show that the proposed scheme ensures voltage quality as well as made a smaller power loss.Besides.number of global optimization times in proposed scheme is the minimal.Finally,comparative experiments were designed to prove the proposed state estimation algorithm.