Abstract
This paper studies the distributed secondary control of DC microgrids (MGs) in the case of asynchronous sampling, including both the stability condition and accurate consensus algorithm. The asynchrony means that the update actions of each distributed generation (DG) based on the local information and information received from neighbors are independent of the actions of others at sampled discrete times, which would cause deviation from the accurate convergence and even lead to instability in the worst case. First, a small-signal model of MG installed with secondary voltage control is established to include the individual sampling periods. A stability criterion based on the periodic continuity of sampling instant offset is thus formulated to reveal a stability mapping of multiple sampling. By quantifying the accuracy deviations caused by the asynchrony, an improved ratio consensus strategy is proposed that allows the deviation to be estimated accurately via an auxiliary signal and compensated with respect to the eventual equilibrium to produce an exact solution. Our approach customizes the stability and accuracy for distributed secondary control considering asynchronous sampling in MG, which has been ignored in most existing literature. The effectiveness of the proposed methodology is verified by simulations.
Highlights
With the increasing penetration of renewable energy resources, the microgrid (MG) has emerged as a promising concept for integration of distributed generations (DGs), storages and loads within an identifiable electrical boundary [1,2,3]
(1) Given that each DG unit in a distributed control system updates its dynamics independently, the distributed secondary control in MG with regard to asynchronous sampling is first investigated in this paper, including both the stability condition and an accurate consensus algorithm
Case studies are performed to investigate the secondary control performance under asynchronous sampling conditions using a test DC microgrid shown in Figure 6, where the system and control parameters are listed in Table 1 and the desired power sharing ratio among the three DG units is 1:1:1
Summary
With the increasing penetration of renewable energy resources, the microgrid (MG) has emerged as a promising concept for integration of distributed generations (DGs), storages and loads within an identifiable electrical boundary [1,2,3]. To realize spontaneous power sharing without critical communication links, primary control is often implemented using the droop paradigm, which would lead to poor power sharing because of the distinct output impedance and voltage deviations involved To overcome these disadvantages of primary control, secondary control schemes ranging from centralized to distributed approaches have been proposed. (1) Given that each DG unit in a distributed control system updates its dynamics independently, the distributed secondary control in MG with regard to asynchronous sampling is first investigated in this paper, including both the stability condition and an accurate consensus algorithm. (2) A small-signal MG model with distributed secondary control is established using the normalized periodicity of sampling offset among the interactive DGs, which allows for the stability assessment of MG with asynchronous sampling. It can be observed from (2) and (3) that the average consensus and the dynamic average consensus as basis of distributed secondary control have an important effect on system performance
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