Marcelo G. Cendoya

Wind Farm to Weak-Grid Connection using UPQC custom power device

Wind Farms (WF) employing squirrel cage induction generator (SCIG) directly connected to the grid, represent a large percentage of the wind energy conversion systems around the world. In facilities with moderated power generation, the WF are connected through medium voltage (MV) distribution headlines. A situation commonly found in such scheme is that the power generated is comparable to the transport capacity of the grid. This case is known as Wind Farm to Weak Grid Connection, and its main problem is the poor voltage regulation at the point of common coupling (PCC). Thus, the combination of weak grids, wind power fluctuation and system load changes produce disturbances in the PCC voltage, worsening the Power Quality and WF stability. This situation can be improved using control methods at generator level, or compensation techniques at PCC. In case of wind farms based on SCIG directly connected to the grid, is necessary to employ the last alternative. Custom power devices technology (CUPS) result very usefull for this kind of application. In this paper is proposed a compensation strategy based on a particular CUPS device, the Unified Power Quality Compensator (UPQC). A customized internal control scheme of the UPQC device was developed to regulate the voltage in the WF terminals, and to mitigate voltage fluctuations at grid side. The internal control strategy is based on the management of active and reactive power in the series and shunt converters of the UPQC, and the exchange of power between converters through UPQC DC-Link. This approach increase the compensation capability of the UPQC with respect to other custom strategies that use reactive power only. Simulations results show the effectiveness of the proposed compensation strategy for the enhancement of Power Quality and Wind Farm stability.

Investigation of UPQC for sag compensation in wind farms to weak grid connections

In the last years, the wind power generation incorporated into standard grids has been increased significantly. This situation forced the revision of grid connection code requirements, to guarantee the reliability in systems with high wind power penetration. In case of three phase short circuit, voltage sags are observed near the point of failure, and characterized by a sudden voltage reduction and lagging phase jump. For induction generator based wind farms connected to weak grids, such sag may lead to wind farm outage, due to limited low voltage ride through capability of induction generators. In this work a voltage sag compensation strategy is proposed for amplitude and phase jump restoration, and compared with amplitude only compensation strategy. These strategies were implemented using an Unified Power Quality Compensator UPQC. Unlike other Custom Power Devices like DVR and D-Statcom, the UPQC has the feature of active power sharing between shunt and series converters through DC-link; thus, series voltage injection with any phase angle may be maintained without the need of power source installed in DC bus. Results shows a better wind farm performance in proposed strategy than that found in magnitude only compensation schemes. Thus, considering the improvement in performance, the proposed strategy is recommended in retrofitting the existing installed fixed speed induction generators based wind farms.

Low-cost sliding-mode power controller of a stand-alone photovoltaic module

This work presents a simple and low-cost power electronic system that allows a flexible control of the operating conditions of the photovoltaic module. The system consists of a buck converter with sliding mode control. Control algorithms for maximum power tracking, module voltage and load current regulation are proposed. Moreover, these algorithms can be readily combined to have a complete control of the energy conversion system. The dynamic analysis reveals that there may be regions of instability that are avoided by appropriate switching logics. Operation and main features of the proposed electronic power controller are validated through simulation and experimental results.

RDG in weak grid for desalination plant. System topology and control strategy

Renewable Distributed Generation (RDG), such as production of electric power near to the load, is particularly beneficial when the distribution network is “weak” against specific demands, as in potable water production systems connected to coastal electrification networks. In these areas, the wind resource may be suitable for this type of generation. This work proposes the topology, the operation mode and the control strategy for a Reverse Osmosis Desalination Plant, “assisted” by a weak AC grid and “powered” by a variable speed wind turbine based on a three-phase BDFIG machine. The wind energy conversion is optimized through adequate control of the generator. The high pressure pump of the desalination plant is controlled for the maximum utilization of the generated power. The electric power fluctuations due to win turbulence are compensated through a controlled energy storage system based on a flywheel. The system configuration, its operation mode and control are presented.

A microgrid with EMS based on a standard data network. Analysis and evaluation

In order to achieve optimal operation conditions in a microgrid with Energy Management System (EMS), a communication system is needed. It is important to consider in depth different characteristics of communication systems regarding issues like determinism, time constrains, cost effectiveness etc. This paper reviews different type of network protocols which can be used in order to fulfill the different communication needs for protection, management and automation in a microgrid. We also present simulations about the behavior of different networks protocols, showing whether some of the above conditions are met or not.

Stand-alone hybrid microgrid for remote areas. Topology and operation strategy

In remote regions, were a main Utility System for energy distribution is not available, the implementation of Microgrids with hybrid generation are very useful. In this context, a Stand-Alone wind/diesel/gas/battery/supercapacitors Hybrid Microgrid topology is proposed. The main scope is to create a low cost system to feed Residential loads through a local AC bus, using wind energy obtainable at system location. The random characteristics of the wind makes necessary to smooth the fluctuating supply in order to minimize the disturbances on local grid electric parameters. To overcome these problems, a Wind Turbine based on a DFIG machine and Strategies to control the power of a Storage Energy System are employed. An appropriate Supervisor Module with a reliable communication network is used to balance generation and loads, in order to properly operate the Microgrid. The system structure, operation modes and mathematical models for simulation and validation are presented.

Microgrid for remote areas with Water Pumping, based on wind-diesel DER and Energy Storage

In remote regions were a main distribution grid is not available, the implementation of Microgrids with Distributed Energy Resources (DERs) are very useful. In this context, a Stand-Alone Wind/Diesel Microgrid with modular architecture is proposed. The main scope is to feed Residential loads and a Water Pumping System through a local AC BUS. The random characteristics of the wind makes necessary to smooth the fluctuating supply in order to minimize disturbances in the pump and diesel generator. To overcome this problem, a compensation control strategy based in the power control of a Storage Energy System and the Water Pumping System is employed. An appropriate and reliable communication network is used to supervise and balance generation and loads, to maintain the correct functioning of the Microgrid. The system structure, operation and mathematical models for simulation and validation are presented.