Active and Reactive Power Control Through P-Q Controller Base System to Replicate the Behavior of Full Power Converter of Wind Turbine

This paper presents a technique to simulate the active and reactive power control phenomenon of a full power converter base wind turbine. The implementation of full power converter in the wind turbine has enhanced the quality of power supply to the grid. It has the ability to increase better controllability and full control over real and reactive power. The active and reactive powers are the essential area of control for the grid manager. The conventional energy generation companies provide some margin of reactive power support with the active power to the grid. But for the case of renewable energy producers it is the matter of concern. In this paper a P-Q controller is introduced for controlling active and reactive power of the full power converter base wind turbine which injects power to the PCC. The design technique implements PI controller base system with externally control current source. The simulation model has been prepared in PSCAD/EMTDC. Keywords— P-Q controller, Point of common coupling (PCC), Transmission system operator (TSO), Grid code, Full power converter, voltage source converter (VSC). INTRODUCTION The driving force of a society is the development of its energy producing infrastructure. As the world is advancing day by day, eventually it is essential to find new sources of energy to meet the future energy demand. It cannot be based solely on the conventional sources of energy such as thermal, nuclear and hydro power, because of the rapid decline of the sources and their impact on the environment is quite alarming for the society. To find the better solution modern, energy technology is moving towards the renewable energy sources i,e wind, solar and wave energy . So far, their contribution to meet demand is quite modest. The main disadvantages of these renewable energy sources that they are quite expensive and less flexible compared to conventional power plants. But their enormous potential to collect from nature and environment friendly characters make them the alternative choice for the future energy. Currently the most effective wind power plants have efficiency of about 50% and now the consideration is to make it cheaper, more reliable and more flexible [1]. The technological development of wind power is vast in Europe, America and some of the countries of Asia like India and China. To make the renewable energy sources to perform well and overcome their limitation, the major challenge is the efficient integration with the conventional grid. The characters of the conventional energy sources are known to the system operators but the behaviors of the renewable energy sources are quite unpredictable because they directly rely on nature, suppose for the case of PV shell it depends on sun irradiation and for wind energy it depends on the wind speed, which has a variation on hour to hour, day to day and also month to month basis. The system operators expect that these renewable energy sources should provide some control over the active and reactive power, which is included in the grid code for them. Control over active power and reactive power in steady state and in the time of system dynamics are the area of concern. But with the help of modern technology the full power converter base system of the wind turbine can overcome this problem. In this paper a simple way is presented to represent the real and reactive power effect to simulate the behavior of wind turbine in providing real power to the grid and in some case the reactive power support to the grid. A P-Q controller base system is presented to simulate the active and reactive power control phenomenon of a full power base wind turbine both in normal and abnormal condition of the grid. International Journal of Engineering Research and General Science Volume 2, Issue 5, August-September, 2014 ISSN 2091-2730 642 www.ijergs.org EVITCA DNA EVITCAER REWOP LORTNOC FO A DIRG Electric grids are basically two types, which are ac grid and dc grid. In a dc grid the total power is calculated from active power, which is the multiplication of voltage and current. The conduction loss depends only on the active power. For the case of conventional ac grid the total power is calculated through its apparent power, which is the geometric sum of active and reactive power [8]. In an AC grid the voltage and current both are sinusoidal quantities which oscillate with the frequency of 50 or 60 hz. The product of these two will be the power and it will be only the active power if there is no phase difference between the voltage and current. However, if there is any phase shift between the voltage and current the output power is oscillating with its positive and negative value [8]. If the phase difference between current and voltage is 90 then the total power is the reactive power because the active power is oscillating with equal and opposite value and the average of active power is zero. This situation can arise, if the system is dealing with pure inductive or capacitive element. For the case of pure inductive element the current lags behind the system voltage by 90 and in the case of pure capacitive element the current leads the voltage by 90. If a transmission grid is considered, where it is connected to renewable energy source like wind turbine, there exists reactive components with the resistive components for the line. Now if a transformer is presented in between the generating source and the grid, it also has inductive reactance. On the consumer side of the load are mostly inductive. So for the grid it is essential to prepare the compensation arrangement for reactive power, because the reactive power is not consumed by the load it just go forward and backward in the system and just participate in the system conduction loss. That’s why the compensation is required. Generally the big generating station supply active power with leading power factor that means they have reactive power compensation for the inductive load. To compete with the conventional energy sources the wind firms also have to provide support for the reactive power, which is imposed by the transmission system operators (TSO) through the grid code criteria. TROPPUS REWOP EVITCAER DNA EVITCA HTIW ENIBRUT DNIW ESAB RETREVNOC REWOP LLUF NONEMONEHP The improvement and modification of modern technology has helped a lot to develop some essential fetchers of wind turbine like the size, quality of output power and technology used. One of the most important improvements is the development of full power converter with variable speed operation. In a full power converter base wind turbine the generator may be a permanent magnet synchronous generator or an induction generator. They may or may not use gear box as shown in the Figure -1. The energy produced in this kind of wind turbine passes through the converter, so it can isolate the system in the time of major disturbance of the grid. With the variation of wind speed the electrical frequency of the generator can change otherwise the power frequency in the grid remains unchanged. Thus allow the variable speed operation of the wind turbine [3]. Induction / Synchronous generator Power Electronic Converter Figure-1 Full power converter base wind turbine[5]. A full power converter is consisting of two voltage source converter, one is responsible two control the generator side and the second one is responsible for the grid side. Each of the converters has the ability to absorb or generate the reactive power independently [7]. The generator side converter is basically a diode rectifier or a Pulse width modulated converter, where as the grid side converter is a conventional PWM converter [3]. The output power from the generator depends on the rotor speed which depends on wind speed. The wind speed has a wide variation and the rotor speed also varies with it as shown in figure-2, a controllable output power is possible by the rotor side converter which helps the rotor to adjust its speed. Whereas the grid side converter provide a controllable International Journal of Engineering Research and General Science Volume 2, Issue 5, August-September, 2014 ISSN 2091-2730 643 www.ijergs.org active power output without consuming reactive power, Rather than it has the ability to provide some reactive power it needed by the grid [4]. Figure-2 Power and Rotor speed curve with respect to wind speed. DESIGN OF THE SYSTEM A P-Q controller based system is designed to replicate the behavior of a full power converter considering the nature of wind turbine and how it behaves with the connected grid. The essential features of the P-Q controller are the control over the active power which is performed by the generator side converter and the control over the reactive power which is performed by the as the grid side converter. Thus by using a P-Q controller the full power converter base wind turbine can be eliminated from the network during the time of grid code analysis simulation work to make the system more simple. As mentioned before, the wind power generation varies with the wind speed, so it is expected that at PCC of grid power injection in a controlled way. The task can be performed by the grid side converter of full power converter. In this designed model the reference value of active and reactive power is set at PCC and it is expected that the turbine side converter should achieve the value by its controllability [5]. The P-Q controller can exchange a given amount of real and reactive power at the point of common coupling. Figure-3 shows the connection of load to the PCC [5]. Figure-3 Externally control current source [5]. At the PCC the voltage is to be maintained constant, so the power at that point can be controlled by controlling the current through that point or vice verse. The design block is shown in figure-4. The entire system can be presented by the block diagram as shown in figure-5. It can be divided in to the following blocks:  llanretxE .ecruos tnerruc lortnoc y  3 .tnemerusaem egatlov esahp  .tnemerusaem rewop evitcaer dna evitcA International Journal of Engineering Research and General Science Volume 2, Issue 5, August-September, 2014 ISSN 2091-2730 644 www.ijergs.org  .kcolb LLP  ot βα dna βα ot qd 3 .retrevnoc tnerruc esahp  .rellortnoc Q-P Externally controlled 3-phase current source PCC 3-phase Voltage measurement Active and Reactive power measurenemt