A WIND SOLAR HYBRID SYSTEM USING SOLID STATE TRANSFORMER (SST) FOR REACTIVE POWER COMPENSATION M.GOPINATH 1 S.RAVICHANDRAN 2 1 PG Student, Department of EEE, Arunai Engineering College, Tiruvannamalai,Tamilnadu, India. 2 Assistant Professor, Department of EEE,Arunai Engineering College,Tiruvannamalai,Tamilnadu, India. Abstract This paper presents a wind solar hybrid system using Solid State Transformer (SST) for reactive power compensation. The proposed hybrid system using SST can effectively suppress the voltage fluctuation. This work deals with the holistic modeling approach of a combined Photovoltaic and Wind power system. The controller design has to be done with fuzzy and sliding mode controller along with SST. This approach enables the design and implementation of efficient controllers for Distributed Energy Resource (DER) hybrid systems. The simulation of proposed work is carried out using MATLAB Keywords renewable energy, control systems, modeling, power systems. Need for DER system I. INTRODUCTION Due to climate change concerns, the DER (Distributed Energy Resources) constitute increasingly appealing alternatives to traditional energy sources. The DER provide a significant and growing contribution to the grid, as well as being widely used as stand-alone generators for relatively small power networks or those associated with isolated locations. A hybrid DER energy system, combining wind and photovoltaic power as main energy sources, with the possibility to integrate a fuel cell or grid connection, in order to supply continuous power to variable loads and the control of the hybrid system is the key to optimizing its efficiency. But the above mentioned sources do not have a closed loop control with efficient control actions so as to maintain the output constant. II. CONVENTIONAL SYSTEM Wind power is an uncontrollable resource, which, when combined with the nature of wind induction generators like the fixed-speed squirrelcage induction generator (SCIG), makes for a challenging integration of large WFs into the grid, particularly in terms of stability and power quality [3]. To address this issue, utilities generally need to install reactive power compensation devices, such as static compensators (STATCOMs) [3] [11]. Additionally, a large step-up power transformer is necessary to interface the low voltage wind generator to the distribution system, as well as any STATCOM used in the system. Fig.1 wind energy conversion system DISADVANTAGES IN CONVENTIONAL SYSTEM Higher cost.
Increased volume and weight. Voltage fluctuations. III. EXISTING SYSTEM A family of existing wind energy systems has been shown in Fig. 2. It shows the case of a WF with SCIG, where the SST acts as the grid interface. The local capacitor bank, two conventional transformers, and the STATCOM as shown in Fig.1 are all functionally integrated into a single SST. Fig. 3 Functional representation of SST. THREE-PHASE SST Fig.2 Wind Farms with Squirrel Cage Induction Generator interfaced by SST IV. SST Conventional copper-and-iron-based transformers have been challenged by solid-state technologies. Specifically, a conventional transformer in ideal terms represents a simple input output voltage and current transformation; thus, disturbances on one side, which are typical active and reactive powers, are fully reflected on the opposite side. Overcoming this seeming drawback, the SST has been a promising technology in recent years [13] [18]. Potential advantages of SST over conventional transformers include low volume and weight (due to its high-frequency operation compared with 60-Hz transformer), fault isolation, voltage regulation, unsusceptible to harmonics, easy integration of renewable energy resources and energy storage, etc. [12]. As functionally shown in Fig. 3. The SST is typically composed of a highvoltage ac/dc rectifier that regulates a high-voltage dc bus (and ac voltage when for reactive power compensation), an isolated high-frequency operated dc/dc converter to regulate the secondary dc bus, and a dc/ac inverter to regulate the output terminal ac voltage. A high-voltage and high-power SST that can be interfaced with the distribution system is also not easy with state-of-the-art technology. Numerous technologies are being investigated and may be feasible for this high-voltage and high-power application, such as advanced power device. Fig.4 Three-phase SST for control illustration The wind energy systems using solid-state transformer (SST) can effectively suppress the voltage fluctuation without additional reactive power compensator. A cascaded-type three-phase SST is shown in Fig.4. Its first stage is a three-phase bidirectional ac/dc pulse width modulation (PWM) rectifier, which can also be used in the dc/ac power conversion stage as depicted. Its dc/dc stage is embodied by a dual active bridge (DAB) converter, which represents the most attractive candidate for high-power applications requiring isolation, as it can perform zero-voltage switching in a wide operation range [19], [20]. V. THE PROPOSED SCHEME AND CONTROL TECHNIQUES By integrating both wind and solar, it is possible to get uninterrupted steady source of power at all times is the basic idea of proposed system as shown in Fig.5.
Fig.5 Proposed energy conversion system Both the controllers are to be designed as a closed loop controllers. Hence the load voltage is maintained very constantly in spite of variations. VI. Effectively reduces voltage fluctuations. Integrated function of active power transfer, reactive power compensation and voltage conversion. SIMULATION RESULTS OF PROPOSED SCHEME THREE PHASE SST OUTPUT Fig.6 Proposed Block diagram From the solar panel the powers are obtained, this voltage is stepped up to high voltage DC using DC-DC converter. This is designed as a closed loop controller using Fuzzy logic based controller, Fuzzy logic controller is basically a rule based decision maker.the FLC allows one to use a control strategy expressed in the form of linguistic rules for the definition of an automatic control strategy. Here we achieve a wide span of input voltage. So the Boost DC to DC converter can do the best even if the input solar power comes down beyond a threshold level. From the wind energy the AC obtained is first converted into DC using a rectifier circuit. So later this voltage is stepped up to high voltage DC using DC-DC converter. In order to connect the output of these power sources to the GRID, it has to be now inverted. For inverter design again we employ some type of controller called sliding mode controller.the sliding mode control methodology has been widely used for robust control of nonlinear systems. This control based on the theory of variable structure systems. The main advantage of sliding mode control is robustness against structured and unstructured uncertainties. The system invariance properties are observed only during the sliding phase. It need not be precise and will not be sensitive to parameter variations that enter into the control channel. Fig.7 Output waveform for Three phase SST with available AC Source WIND FARM USING SST WITH SLIDING MODE CONTROLLER Fig.8 Output waveform for Wind farm using SST with sliding mode controller PV WITH FUZZY CONTROLLER ADVANTAGES OF PROPOSED SYSTEM
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