A Novel Control Scheme for Standalone Hybrid Renewable Energy System

I J C T A, 8(5), 2015, pp. 2459-2467 International Science Press A Novel Control Scheme for Standalone Hybrid Renewable Energy System Booma J.*, Arul Pragash I.**, Dhana Rega A.J.*** Abstract: This paper proposed an integrated control scheme for standalone hybrid renewable energy system with battery management. The Standalone Hybrid Renewable Energy System comprised of Photo Voltaic system and Wind Generation System can provide low cost, reliable green energy to the rural areas. In this paper, an integrated control logic of power flow management with voltage regulation for standalone hybrid renewable energy system is proposed to provide reliable and regulated power supply to residential loads (both DC and AC loads). The modelling of the proposed system consist of three power sources (Tata TB305LBZ solar panel model with maximum power of 3050 W, PMSG based Wind Generation System with 1500 W rating, and Nickel Metal Hydride battery with maximum capacity of 1000 AH) and three power sinks (DC load of 500 W, AC load of 2000 W and battery unit during charging conditions). The performance of the proposed standalone system is verified under different environmental conditions by using MATLAB/Simulink tool and results are effectively validated at different system conditions. Index Terms: Standalone Hybrid Renewable Energy System, Wind Generation System (WGS), Battery storage system, Maximum Power Point Tracking (MPPT), power regulation, photovoltaic (PV), Positive Buck-Boost converter, voltage regulation. 1. INTRODUCTION In remote and isolated area, Diesel generators are commonly used for electric power generation due to their reliability, low installation cost, easy of starting, compact power density and portability. But it requires high operating cost and also polluting environment. Renewable Energy (RE) based standalone hybrid power generation system can provide environmental friendly alternative for diesel generator based standalone system and also reliable and cost-effective. Solar, wind, Bio-mass, Geo-thermal and tidal energy are used as a primary power sources for Hybrid Generation System. Among them, wind and solar energy sources are the most promising RE sources [1], [2]. Due to the intermittent nature of RE sources, they can t able to match the instantaneous load demand variations. Therefore, Energy Storage Systems (EES) are essential for reliable operation and to provide transient stability during sudden environmental and load variations [3], [4], [5]. There are different energy storage systems such as flywheel energy storage, pumped hydro, batteries, superconducting magnetic energy storage and super-capacitors are used in different applications for different purposes. In our proposed work, Batteries are used as backup source, as they are having higher energy densities, and very fast response time [6]. The most widely used Incremental conductance algorithm based MPPT control logic is proposed in our work. Positive Buck-Boost converter is used to provide voltage regulation as it can able to step up or step down the input voltage [7], [8], [9]. This paper proposes, an integrated control logic of power flow management with voltage regulation for standalone hybrid renewable energy system to provide reliable and regulated power supply to residential loads (both DC and AC loads). The modelling of the proposed system by using MATLAB/Simulink software * Assistant Professor PSNA College of Engineering and Technology, Tamilnadu-624002, India, Email: boomakumar2005@gmail.com ** PG Scholar PSNA College of Engineering and Technology, Tamilnadu-624002, India, Email: iarulpragash@gmail.com *** Assistant Professor Anand Institute of Higher Technology, Chennai, Tamilnadu, India, Email: dhanrega.jayapalan@gmail.com

2460 Booma J., Arul Pragash I., Dhana Rega A.J. consist of three power sources (Tata TB305LBZ solar panel model with maximum power of 3050 W, PMSG based Wind Generation System with 1500 W rating, and Nickel Metal Hydride battery with maximum capacity of 1000 AH) and three power sinks (DC load of 500 W, AC load of 2000 W and battery unit during charging condition). The performance of the proposed standalone system is studied and analysed under different environmental conditions by using MATLAB/Simulink tool and results are effectively validated at different system conditions. 2. SYSTEM DESCRIPTION The proposed system consist of the following modules, 1) Hybrid Electrical Energy Generation System (PV panel, Wind turbine with PMSG), 2) MPPT control logic with DC-DC Boost converter to extract maximum power from both PV system and WGS, 3) Closed loop positive Buck-Boost voltage regulator, 4) Battery storage with power regulation unit to control the power flow between source and load, 5) Residential Loads. In our proposed system, PV panel and Wind Generation System is connected to the DC-DC boost converter with MPPT control logic to extract the maximum power from PV panel and WGS irrespective of solar irradiation and wind speed [10], [11]. Battery storage unit with charge controller is connected in between Hybrid Generation System (HGS) and the residential load unit, to produce backup power and also to provide power regulation between source and load. Closed loop Positive Buck-Boost voltage regulator is used for voltage regulation to produce constant voltage to satisfied load requirements as well as to charge the battery with constant voltage. The power flow management is done by controlling charging and discharging of the battery unit by using suitable control logic through the availability of input power and state of charge (SOC) of the battery unit. 2.1. Modelling of PV system For modelling the PV panel, Tata Power Solar System TP305LBZ MATLAB module is chosen in the proposed system with maximum power of 3050 watts. Figure 2 shows the I_V characteristics of a solar module and gives idea about open circuit voltage, short circuit current and the maximum power point. Figure 1: Block Diagram of the proposed system

A Novel Control Scheme for Standalone Hybrid Renewable Energy System 2461 Figure 2: I-V and P-V characteristics of Tata TP305LBZ under standard and varying environmental conditions Therefore at a particular value of V mpp and I mpp, maximum power point is obtained depending on the solar irradiation and ambient temperature. In order to supply 2500 W of total load unit, 10 number of Tata TP305LBZ modules are connected in series to produce maximum power of 3050 W at the standard environmental conditions of 1000 (W/m 2 ) irradiation and 25 0 c temperature. 2.2. Modelling of Wind Generation System The WECS model includes a Wind Turbine (WT), a PMSG, and PWM rectifier in generator-side as intermediate DC circuit. The generator-side rectifier is used to track the maximum wind power. For Modelling the Wind Generation System, MATLAB wind turbine model with the rating of 1500 W is connected to a three phase, Permanent Magnet Synchronous Generator. Tata Tp305lbz Solar Module Table 1: Parameters Of Tata Tp305lbz Solar And Wind Turbine Module Wind Turbine Module Maximum power, P max (W) 305.3 Nominal Mechanical output power, (W) 1500 Voltage at maximum power point, V mpp (V) 36.7 Base power of electrical generator (VA) 1500/0.9 Current at maximum power point, I mpp (I) 8.32 Base wind speed Short circuit current, I sc (I) 8.78 Maximum power at base wind speed (p. u) 0.8 Open circuit voltage, V oc (V) 44.5 Base rotational speed (p. u) 1 2.3. Maximum Power Point Tracking The efficiency of the solar cell and wind turbine system is very low. In order to increase the efficiency, methods are to be undertaken to match the source and load properly. One such method is the Maximum Power Point Tracking (MPPT). This is a technique used to obtain the maximum possible power from varying sources [12]. I-V curve of photovoltaic systems and the power curve of wind system is non-linear, thereby making it difficult to be used to power a certain load. This is done by utilizing a boost converter whose duty cycle is varied by using a MPPT algorithm. There are several MPPT algorithms available to track maximum power point, among them Incremental conductance based MPPT algorithm can track changing conditions more rapidly than the conventional Perturb and Observation algorithm. In our proposed system Incremental conductance based MPPT control logic with Boost converter is used to extract maximum power from PV panel and Wind Generation System. In these method, the PV array terminal voltage is m s 12

2462 Booma J., Arul Pragash I., Dhana Rega A.J. CONTROL LOGIC: If, di/dv = - (I/V) at Maximum Power Point If, di/dv > - (I/V) Left of MPP. If, di/dv < - (I/V) Right of MPP. always adjusted according to the MPP voltage and it is based on the incremental and instantaneous dp conductance of the PV module and the rectifier output voltage is adjusted according to the MPP in dv Wind Generation System [13]. In Figure 3, the slope of P-V curve is zero at MPP, increasing on the left of MPP and decreasing on the right hand side of the MPP. From the equations shown in the above figure, Maximum power point is achieved when the change in ratio of change in the output conductance is equal to negative output conductance.the duty cycle for the dc-dc boost converter is obtained from the MPPT algorithm and it is changed based on the solar irradiation in PV system and wind speed in WGS. 2.4. Voltage Regulation Figure 3: Flow chart and control logic for Incremental Conductance algorithm Closed-Loop positive Buck-Boost converter is used for voltage regulation to provide a constant voltage for battery charging as well as to meet the load requirement [14]. The positive or non-inverting buck-boost converter is a cascaded combination of a buck converter followed by a boost converter. It can able to step up or step down the input voltage, to provide a constant voltage without changing the input voltage polarity.positive Buck-Boost converter can be operated in buck-boost, buck or boost modes of operation. Higher efficiency conversion is possible only in either buck/boost mode of operation compared to the buck-boost mode due to the reduced conduction losses and power dissipation. Therefore, in the proposed system either separate buck or boost mode of operation is considered for voltage regulation. As shown in the above figure, in Buck mode, Switch Q2 is to be always OFF, and output voltage is regulated by controlling Q1 as like a typical buck converter in the continuous conduction mode (CCM). The output voltage is same as that of a typical buck converter and which is always less than the input voltage. The output voltage of converter in buck mode is, Where, D = Duty cycle of the controlling switch Q1. V OUT = D V IN (1) In Boost mode, Q1 is always ON, D1 is reverse biased and the output voltage is regulated by controlling Q2 switch as in a typical boost converter shown in figure. The output voltage of the converter is same as that of a typical boost converter and which is always greater than the input voltage.

A Novel Control Scheme for Standalone Hybrid Renewable Energy System 2463 (a) Buck mode of operation (b) Boost mode of operation Figure 4: Circuit Diagram for modes of operation of Positive Buck-Boost Converter V OUT Where, D = Duty cycle of the controlling switch Q2. VIN (2) 1 D In both buck and boost mode of operation, to obtain a constant reference voltage, the converter is operated in closed loop control. In a closed loop control, the output voltage is compared with reference voltage to generate the error signal. The error signal is fed to the PI controller and the output of PI controller is fed to the pulse generation block to control the switches. 2.5. Battery Management with Power Regulation In order to provide an uninterruptable power supply to the residual loads, battery storage unit with a suitable power flow management system is proposed in these paper. The power regulation is made by controlling charging and discharging of the battery unit with load management [15]. As shown in Figure 5 based on the output power form the boost converter and the State Of Charge of battery (SOC), the power flow from sources to sinks is controlled by using the control logic. The battery is charged by the constant voltage charging method and the constant voltage for charging the battery is obtained from closed loop positive buck-boost converter. Whenever, the Hybrid Generation System output power is more than the load requirement, the battery is switched to the charging mode to store the excess amount of power and during some unfavourable environmental conditions, if the source is not able to meet the load requirement than the battery is switched to the discharging mode to deliver the required amount of power. From the Figure 6 the control logic for battery management with power regulation is obtained by controlling the charging and discharging of battery with load management based on the output power from source and SOC of battery. 3. SIMULATION RESULTS OF OVER ALL SYSTEM As proposed in these paper, to provide an uninterruptable, regulated power supply to the residential loads from standalone Hybrid Generation System, simulation models are built in the MATLAB-Simulink environment. The overall system performance for standard and varying environmental conditions is analysed and verified through the simulation results.in the MATLAB model, Tata solar system TP305LBZ type PV panel model with maximum power of 3050 watts and PMSG based Wind Generation System maximum power of 1500 watts at standard environmental conditions are used as main sources. Nickel-Metal-Hydride battery model with maximum capacity of 1000Ah is used as a backup source. To provide regulated voltage

2464 Booma J., Arul Pragash I., Dhana Rega A.J. P dc Outputpower from Boost converter. SOC State Of Charge of Battery. C Charging Mode. D Discharging Mode. L1 Load of 500 watts (DC). L2 Load of 1500 watts (AC). Figure 5: Control logic for power flow management proposed system to loads and charging the battery, closed loop positive buck-boost converter is designed with suitable reference voltage. Power regulation between sources and loads is controlled by using suitable control logic for charging and discharging the battery. The performance of the proposed system can be analysed by considering two cases based on their operating environmental condition. Case 1: Hybrid System under Standard Environmental Conditions (1000 W/m 2 Irradiation, 12 m/s Wind Speed) Figure 6(a) shows the simulation results of the proposed system, under standard environmental conditions with 1000 W/m 2 solar irradiation and 25 o c panel ambient temperature for PV system and 12 m/s wind speed for Wind Generation System. Under these conditions, solar panel canable to produce the power more than 2500 watt and Wind Generation System can able to produce more than 1000 watts of power under these conditions. Therefore, the input power alone can able to satisfy the 500 watts of DC load and 2000 watts of AC load. And the excess amount of power is stored in the battery unit.to extract the maximum power from Hybrid Generation System, incremental conductance based MPPT control logic is proposed separately for each sources and which continuously tracks the suitable duty cycle for boost converter. Case 2: Hybrid System under Varying Environmental Conditions (continuously varying solar irradiation and wind speed) Under varying environmental conditions like different solar irradiation and wind speed, the output power from the Hybrid system is also varied consequently. Figure 6(b) shows the variation of output power for continuously varying solar irradiation (varying from 250 to 1000 W/m 2 ) and wind speed (varying from

A Novel Control Scheme for Standalone Hybrid Renewable Energy System 2465 Table 2 Power Regulation Of Hybrid System Under Varying System Conditions Solar Duty cycle Output Wind Output Battery unit DC AC Irradiation for boost power speed power form operating mode load load (w converter form PV system m m 2) s wind system (W) (W) (W) 1000 0.5439 2997 8 982 charging mode 500 2000 500 0.4459 1447 14 1154 charging mode 500 2000 250 0.3889 652 16 1278 discharging mode 500 2000 0 0 0 0 0 discharging mode 500 500 (a) Hybrid System Under Standard Environmental Conditions (b) Hybrid System Under Varying Environmental Conditions Figure 6: Proposed system results under standard and varying environmental conditions

2466 Booma J., Arul Pragash I., Dhana Rega A.J. 8 to 16 m/s). The MPPT controller continuously tracks the maximum power form Hybrid system by varying the duty cycle with respect to the corresponding solar irradiation and wind speed. Even though, the output power from hybrid system is varied from its maximum to minimum, but it can able to satisfy the loads due to the effective usage of battery unit.the performance of the proposed system under different solar irradiation and wind speed can be analysed by using Table 2. From the simulation data, it is observed that the proposed system can able to provide reliable regulated power supply to loads under varying environmental conditions. The above tabulation shows the hybrid system performance under different operating conditions. Load management is taken into the account based on the battery operating conditions. 4. CONCLUSION In this work, the proposed integrated control for standalone hybrid renewable energy system is developed to provide regulated and reliable power supply to residential loads. The main features of the proposed system are, it can able to provide an uninterruptable, regulated power to residual loads irrespective of any environmental and load conditions.the control strategy of the proposed system is done by two components, 1) Incremental conductance based MPPT control logic with DC-DC boost converter. 2) Closed loop positive buck-boost converter based voltage regulation. The power flow management is done by controlling charging and discharging of the battery unit by using suitable control logic through the availability of input power. MATLAB/Simulink tool is used to model the hybrid system. The performance of the proposed standalone system is verified under different environmental conditions by using MATLAB/Simulink tool and results are effectively validated at different environmental and system conditions. References [1] Osman Haruni A.M., Michael Negnevitsky, Enamul Haque.Md and Ameen Gargoom, A Novel Operation and Control Strategy for a Standalone Hybrid Renewable Power System, IEEE Trans. Sustainable energy, vol. 4, no. 2, April 2013. [2] R. J. Best, D. J. Morrow, D. J. McGowan, and P. A. Crossley, Synchronous islanded operation of a diesel generator, IEEE Trans. PowerSyst., vol. 22, no. 4, pp. 2170 2176, Nov. 2007. [3] T. Zhou and B. François, Energy management and power control of a hybrid active wind generator for distributed power generation and grid integration, IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 95 104, Jan. 2011. [4] S. D. G. Jayasinghe, D. M. Vilathgamuwa, and U. K. Madawala, Direct integration of battery energy storage systems in distributed power generation, IEEE Trans. Energy Convers., vol. 26, no. 2, pp. 977 685, Jun. 2011. [5] C. Wang and M. H. Nehrir, Powermanagement of a stand-alone wind/ photovoltaic/fuel cell energy system, IEEE Trans. Energy Convers., vol. 23, no. 3, pp. 957 967, Sep. 2008. [6] N. Gyawali and Y. Ohsawa, Integrating fuel cell/electrolyzer/ultracapacitor system into a stand-alone microhydro plant, IEEE Trans. EnergyConvers., vol. 25, no. 4, pp. 1092 1104, Dec. 2010. [7] T. Esram and P. L. Chapman, Comparison of photovoltaic array maximum power point tracking techniques, IEEE Trans. Energy Convers., vol. 22, no. 2, pp. 439 449, Jun. 2007. [8] A Yazdani and P. P. Dash A control methodology and characterization of dynamics for a photovoltaic (PV) system interfaced with a distribution network, IEEE Trans. Power Del., vol. 24, no. 3, pp. 1538-1551, Jul. 2009. [9] K Kobayashi, H Matsuo and Y Sekine, An Excellent Operating Point Tracker of the Solar-Cell Power Supply System, IEEE Trans. Ind.Electron., vol. 53, no2, pp. 495-499, April. 2006. [10] H. Camblong, Digital robust control of a variable speed pitch regulated wind turbine for above rated wind speeds, Control Eng. Practice, vol. 16, no. 8, pp. 946 958, Aug. 2008. [11] E. Muljadi and C. P. Butterfield, Pitch-controlled variable-speed wind turbine generation, IEEE Trans. Ind. Appl., vol. 37, no. 1, pp. 240 246, Jan./Feb. 2001. [12] T. Yoshida, K. Ohniwa, and O. Miyashita, Simple control of photovoltaic generator systems with high-speed maximum power point tracking operation, EPE J., vol. 17, pp. 38 42, 2007. [13] L. Yang, J. Cao and Z. Li, Principles and implementation of maximum power point tracking in photovoltaic system, IEEE conference on Mechanic Automation and Control Engineering, 2010.

A Novel Control Scheme for Standalone Hybrid Renewable Energy System 2467 [14] A. Hajizadeh, M. A. Golkar, and A. Feliachi, Voltage control and active power management of hybrid fuel-cell/energystorage power conversion system under unbalanced voltage sag conditions, IEEE Trans.Energy Convers., vol. 25, no. 4, pp. 1195 1208, Dec. 2010. [15] D. Ipsakis, S. Voutetakis, P. Seferlis, F. Stergiopoulos, and C. Elmasides, Power management strategies for a stand-alone power system using renewable energy sources and hydrogen storage, Int. J. HydrogenEnergy, vol. 34, no. 16, pp. 7081 7095, 2009.