The main objective of this chapter is the experimental validation of active and reactive power control at the connection point for a three-phase grid connected inverter. It gives an overview on the adopted vector control strategy, regulation of the angle of orientation of the blades (pitch control), synchronization grid side converter to the power network using phase closed loop (PLL). Once the experimental test bench is described, the authors devote a first part to the design of the block circuit diagram of the experimental platform and the control strategy implemented in the DSPace DS1104, and they suggest some steps to associate the inverter to the electrical network. Subsequently, they discuss the experimental results validating the proposed power control. The purpose of this experimental results is the DSPACE real-time implementation of PQ control using three-phase inverter and development of a startup algorithm of the experimental test bench.
TopIntroduction
To overcome the problem of global warming, some countries have turned to new forms of so-called “renewable” energies such as hydro, solar and wind power. These renewable energies provide solutions to climate change ((GWEC), 2018), which ensures the liberalization of the electricity market and the development of decentralized production (production of electricity at the places of use themselves). They give rise, in the field of Electrical Engineering, to several new technical problems. These problems are caused by the impact of new types of energy source on the grid. One of these sources of energy is wind power, which represents a promising and growing technology ((GWEC), 2018).
It is non-polluting, inexhaustible energy (wind energy), reliable in isolated regions and can be complementary to traditional sectors. Its advantages have led to a gradual increase in the injection of wind energy into the electricity grid in many countries.
Most manufacturers build a large-scale wind turbine of megawatts. These wind turbines are based on three types of generators and large-scale back-to-back converters. The permanent magnet synchronous generator (PMSG) (without gearbox), the double feed induction generator (DFIG) and the squirrel cage induction generator (SCIG). The comparison between DFIG, PMSG and SCIG, shows that the SCIG has a simple construction, low cost and more robust in terms of the impact of fault clearance time and disconnection of the wind turbine from the power grid. These generators can be used in fixed speed wind turbine (Duong, et al., 2014) or variable speed wind turbine (Errami, et al., 2015; Elyaalaoui, et al., 2019; Martinez, et al., JUNE 2012; Folly & Sheetekela, 2009). Regarding fixed speed wind turbines, the generator is connected directly to the grid, which allows the operation for only a specific wind speed, which demand the use of variable speed wind turbine equipped with back-to-back converters to achieve this objective (Elyaalaoui, et al., 2014; Elyaalaoui, et al., 2016). The WT is connected into the network through filter and transformer (Elyaalaoui, et al., 2019).
The power produced by the SCIG and PMSG is completely injected into grid through the AC/DC/AC converter, the filter and the transformer. The DC/AC converter can be used for solar energy (Abedi, et al., 2020) and wind energy conversion system (Elyaalaoui, et al., 2020). The control type of DC/AC converter plays an important goal in power quality improvement (Elyaalaoui, et al., 2020; Gui, et al., 2018) and system robustness against grid faults (Elyaalaoui, et al., 2018; Xu, et al., 2007; Ouassaid, et al., 2016; Elyaalaoui, et al., 2021). The control of wind energy conversion system is divided into two parts: the generator side converter control and the grid side converter control (Ouassaid, et al., 2016). The MPPT algorithm is adopted to generate the torque reference in order to extract the maximum active power control from the wind. But the rotor flux control is developed to orient rotor flux on d-axis and ensure decoupling between flux and torque. Mechanical power is limited to nominal power by “pitch control” strategy. In the grid-side converter control system, the active and reactive power, injected to the grid, are regulated to satisfy the requirements imposed by the Transmission System Operator (TSO) and to maintain the DC bus voltage constant. Therefore, a sufficient amount of reactive power should be available to satisfy the new grid code recommendations and reactive power demand (Santos-Martin, et al., 2008). The new grid code is imposed for the WF to produce or consume the reactive power (Ghennam, et al., 2009).
The TSO impose for renewable power system to satisfy the demanded active and reactive power near the PCC because it causes additional losses in the transmitting lines of the power network and cannot be transmitted over long distances (Elyaalaoui, et al., 2019). To solve the problem of regulating reactive power at the point of common coupling (PCC), a PQ control method of the grid side converter must be developed to track its reference generated by the supervision system. This reactive power is also necessary for the LVRT (Low Voltage Ride-Through) control to satisfy the TSO's recommendations (Elyaalaoui, et al., 2019).