No abstract

Abstract. The last decade has seen a dramatic rise in renewable energy converters connected to the grid, consisting mostly of intermittent distributed generators on the medium or low voltage grid. Due to this evolution in energy transmission, improved monitoring and control of the distribution grid is becoming mandatory in order to efficiently integrate the new power sources and guarantee power quality, efficiency and reliability. Our paper describes a reliable and precise power grid impedance estimation method using an innovative scheme to control the Pulse Width Modulator's pulse pattern on the inverters, in order to inject broad spectrum identification patterns. The generated harmonics and inter-harmonics will allow the online computation of the complete spectrum of the grid impedance at the Point of Common Coupling during normal operation. Simulations in typical grid situations verify that the proposed algorithm is robust to a realistic environment and can be used for automated feedback control.

No abstract

Abstract. Renewable energy technologies as DistributedEnergy Sources (DER) connected via power inverter on medium or low voltage grid are expected to become a more important part of future generation system. Therefore, it has to be ensured that their integration doesn't jeopardize the stability and performance of the power system which can only be attained with improved monitoring and control of system parameters on real time basis such as the equivalent grid impedance seen from the grid-tied DER. In order to ensure this, this paper investigates a reliable and precise method for online equivalent grid impedance estimation based on Pseudo-Random-BinarySequences (PRBS), which has been extensively used in system identification, communication and information theory. It allows real time computation of complete spectrum of grid impedance at the Point of Common Coupling (PCC) by injecting broad spectrum identification patterns of harmonics and interharmonics. The impedance spectrum thus, can be used for filter design, power quality evaluations, grid status determination and inverter tuning. In this paper, a PRBS-based active identification method is tested and implemented on an off-grid system consisting of a 3 phase inverter prototype developed in the lab and has been used to identify the grid impedance spectrum of a 3 phase purely inductive load connected at the output of the inverter. The results obtained confirm that the method estimates the grid impedance spectrum over a significant frequency range with high resolution on real time basis.

Abstract. The distribution grid has been the source of an increased amount of electricity production in recent years. Coupled with the adoption of open energy markets, this event has significantly complicated the powerflows on the distribution grid, urging network operators to invest in advanced control and monitoring tools in order to optimize the efficiency and reliability of the system. In this context, a method to estimate the connection status of distributed generators and the system topology is proposed in this paper, the goal being to obtain up to date information on the power system network's configuration. This will enable grid operators to have visibility on the status of the distribution grid and react proactively to problematic situations that might arise. The proposed topology estimation method relies on injected pilot signals through generators feeding in power. Pilot voltage stimulations are injected from distributed generators and the induced currents effects are measured at several nodes in the system. The measured data is evaluated through correlation, and a weighed least-square algorithm, applied to the network's dynamic model, estimates those unknown parameters and provides an accurate snapshot of the power network topology. The performance of the proposed method is evaluated on a small scale distribution network.