Abstract

This diploma thesis examines the voltage rise phenomenon caused by the penetration of distributed photovoltaic generators to low voltage networks, and studies various methods to confront it. In this framework, we model and study two rural Low Voltage networks, with different line features, and we execute simulations for different scenarios of PV production and consumer load profiles.

Initially, the basic characteristics of photovoltaic systems are mentioned, and the impacts of environmental conditions on their operation are briefly explained. We are introduced to the concept of microgrids, and the devices of the laboratory microgrid are described. We examine the impacts of PV connection to LV networks, and the specifications for this connection are mentioned. We present methods to mitigate voltage rise, and we emphasize on the active power curtailment method (apc), as well as the power factor control method (pfc). Power flow analysis, and first order voltage sensitivity analysis are discussed. Subsequently, we describe the real-time digital simulator (RTDS), which will be used to conduct experiments.

Regarding the experimental part of this thesis, at first we study the aforementioned networks using the load flow analysis code in Matlab. Additionally, we design them in Simulink, and we present the results of the voltage levels at the connection nodes, by implementing various production-consumption scenarios. We implement apc, or pfc, or both methods in order to reduce voltage rise. The response of the network voltage and the designed controllers is observed at transient states. A PV module and an MPPT algorithm are modeled, while a PV array is constructed by connecting the above modules. We calculate the PV array power production during a day, using insolation and module temperature time series. A consumer load profile time series is selected, and both load and production time series are inserted in the second LV network. Both voltage levels and active and reactive power profiles at nodes are recorded.

Finally, an LV network and both controllers are modeled for simulations in RTDS. Once more, voltage and active and reactive power profiles are recorded, while the results are compared to the ones resulting from Simulink simulations for the same network.

Keywords: photovoltaic systems, microgrid, RTDS, voltage rise due to photovoltaic connection, PV modeling, MPPT, load flow analysis, voltage sensitivity analysis, active power curtailment, power factor control, time series.

Author: Fanis Korlos

Responsible PhD: Panos Kotsampopoulos / kotsa@power.ece.ntua.gr

Supervising Professor: Nikos Hatziargyriou / nh@power.ece.ntua.gr

PDF: Full version (Greek) and Short version (English)