Single Phase Grid Connected PV-Wind-Diesel-Battery System Operated Three Phase Induction Motor for Aqua-Farms

. Sustainable Aqua Farms requires continuous power supply to drive three phase induction motors for maintaining good oxygen levels. Unfortunately many places are suffering from frequent power cuts as well as availability of only single phase supply. Hence, 1-Φ to 3 - Φ conversion is essential to operate 3-Φ motors as well as required operatio n of diesel generators during no supply from grid. However, consumption of heavy diesel causes many problems in aqua culture which is not sustainable. Hence, in order to reduce diesel consumption, and increase eco-friendly environment, photovoltaic (PV) and wind generator system can be integrated to system. A proper energy management system is required among all these sources to achieve cost effective system with best performance. The battery is used for responding in transient time periods. The proposed energy management system can reduce consumption of diesel by operating it at maximum efficiency. In case of any excess power available from wind and PV, the surplus power can be transmitted to single phase grid to reduce electricity bill. In order to maintain stable dc-link voltage, Sliding Mode Controller (SMC) based DC to DC converters are incorporated. The proposed controller reduces the ripples in motor torque to improve the life time of components used in system as well as can reduce power consumption with the addition these renewable energy resources. For reduction of ripples in torque, a TS-Fuzzy based speed sensor less direct torque controller is implemented to run induction motor through three phase inverter.


Introduction
Water is main resource for human life as well as plays a vital role in development of any nation.The supplying of water from underground is required now a days due to lack of water resources available near to human civilizations.Hence, water pumping systems becoming a part of human life for applications of both crop/field as well as drinking purpose.Apart from these, sufficient water supply is mandatory to run aqua farm effectively.To fulfil this, an induction motor needs to be coupled with water pump [1][2][3].
However, high power/torque motors are required to lift high quantity of water from high depth of underground water.Hence, three phase motors are most suitable for water pumping system [4][5][6][7][8].Unfortunately only single phase supply is available in many places ____________________________________ for usage of electrical supply.Hence in order to run three phase motor, first we need to convert single phase to DC through diode rectifier.This DC voltage may not be sufficient to run three phase motor through inverter.Therefore, a boost converter is needed to step-up the DC link voltage.A Sliding Mode Controller (SMC) is implemented [9] for stabilizing the DC output of boost converter.This stabilizing input voltage of inverter can provide fewer harmonic to motor which can improve the life time of motor as compared to high harmonics.Hence three phase induction motor (IM) is chosen for development of pumping system in this paper.Generally submersible pumps are used in water pumping system which will be creating problems in sensing speed of the motor.To avoid this issue, speed sensorless controller [10][11][12] is implemented in this paper.In order to reduce ripples in torque, Direct torque controller (DTC) has been implemented for running the motor through inverter.Further to generate reference electromagnetic torque by using Takagi-Sugeno (TS) fuzzy based controller [13] is incorporated with DTC.However, using diesel generators consumes heavy diesel and emits toxic gases which damages aqua lives.Hence, to diminish the consumption of diesel, solar and wind Renewable Energy Sources (RES) are integrated to the system for sustainable environment.However, the output from PV and wind is not constant, hence a battery bank is integrated to the system.

System Description
The proposed system for water pumping system with three phase induction motor from single phase supply is shown in Fig. 1.The system consists of single phase diode rectifier to converter single phase to DC, boost converter to step-up dc voltage to maintain constant DC-link voltage which is input to the three phase inverter which is required to run the three phase induction motor to drive the water pump.To stabilize DC-link voltage, a SMC is implemented to generate pulses for Q1.Compared with proportional and integral (PI) controller, TS-Fuzzy controller can helps to reduce ripples in torque, since the reference electromagnetic torque is generating from TS-Fuzzy controller.The TS-Fuzzy controller can able to generate smooth output (i.e., reference signal of electromagnetic torque) due to its simple defuzzification rules.The DTC is applied to regulate the speed of motor.The controlling speed can also regulate the quantity of discharging water from pump.Space vector pulse width modulation is implemented for generating pulses for inverter.The general components involved in the Fig. 1 are discussed briefly as follows.The PV and wind generators are having their own MPPT converters for their best utilization [14][15].The DC generator (DCG) is for generating dc supply.The battery is integrated to dc-bus over bidirectional dc to dc converter [16][17][18].In case of more power generated from Renewable Energy Sources(RES), the surplus power will be feed to grid through 1-phase bidirectional converter.However, the battery is not allowing to charge from grid, hence a diode is placed between dc-bus and 1-phase bidirectional converter.

Selection of Motor rating and Pump
Generally, there is a static friction which is due to the rotating parts of the system.To overcome this the breakaway torque (Tb) of motor/pump should be about 10-25% of the nominal-torque.The pump starts supplying water only when the speed reaches a threshold value (ωt) [19][20][21].The rate of flow of water (Q, gal/min) linearly proportional with the speed of pump/motor (ω), as expressed in (1) and also the head of the system having nonlinear equation which is represented by equation ( 2) and required horse power capacity of motor is calculated by equation Where, a, a0, a1, a2 and b are the constants and Whp = necessary HP and ' H' represents the total dynamic head (in feet) .The actual power required to run a pump should be higher than Whp.The brake horse power (BHP) is the power required at the pump shaft to pump a predetermined flow rate against a predetermined H represented by equation ( 4).Assuming Qmax as 100 gal/min; H=50m , pump efficiency=1, drive efficiency=0.95.As per the equation ( 4), approximately 5hp motor is required to lift the required water.The maximum speed of the motor((≈1800rpm)is obtained from the equation ( 2 The torque on motor i.e., load torque is estimated from maximum speed and maximum power as TL =25 Nm.However, load torque will grow linearly from Tb to TL as water flows from underground to ground level because the weight of the water on the motor increases (i.e., quantity of water from pump to outlet or ground point).It appears that the load torque will be relatively low at first, then build like a ramp as the water drains to the ground level.Finally, as the water reaches ground level, the load torque will be constant.Furthermore, the friction between the pipe and the water will add some extra load torque to the engine.Additionally, if any additional pipe is added to supply water to another place for utilisation, this load torque will rise.Generally this rating of 5 hp motor is using for supply water to crop in agriculture sector [21].Similarly 5 hp motor is also using in aqua sector for circulating oxygen in pounds.

Sensorless control of Induction Motor
Submersible pumps are used in the majority of water pumping systems, with the engine being submerged.Sensing motor speed is required to design speed control of an induction motor, which is unfortunately difficult to do at high depths where the motor is submerged.Hence, estimation of speed by using mathematical equations can help to design sensor less speed controller of the induction motor.In sensorless speed control, speed estimation is very important [22][23][24] and it can be achieved by mathematical expressions .However, speed estimation requires both input voltage and currents of IM.Hence, both voltage and current sensors are required.Moreover, two current sensors are sufficient to sense the 3-phase currents, and input voltages [25]can be obtained by phase voltage reconstruction.The output of the inverter (i.e., input of IM) is depending on both Vdc and pulses which are generated by the PWM generator [26][27].Hence, inverter voltages can be obtained with the help of mathematical expressions .Therefore, physical voltage sensors are not required to sense the input voltage of IM.It makes the system more cost-effective.

( ) ( )
The rotor speed is calculated by below equation Slip speed can be estimated by below equation, ( ) ( ) The speed estimation is done with the help of equation from ( 5) to (9).

TS-Fuzzy Controller
When compared to Proportional plus Integral (PI) controller, the performance of TS-Fuzzy controller is very good and operation is smooth under quick changes in dc-link voltage.Therefore, TS-Fuzzy controllers are used in this work.The considered input variables for designing the TS-Fuzzy controller are voltage/current error variations (xi) and its derivative ) as shown in Fig. 2. By using the membership functions positive (p) and negative (N) the realization of inputs fuzzification is done as shown in Fig. 2.The rules corresponding to TS-Fuzzy controller are given in Table 1.
In Table 1, the calculated output of the TS-Fuzzy operation is characterized by Z1, Z2, Z3, and Z4.K denotes the sampling instant.a1,a2, a3, a4 and a5 designate the fuzzy constants, attuned by a tuning process that diverges from one controller to another.TS-Fuzzy is implemented to generate reference torque from comparing speed of motor to its reference speed, hence the output Y is dynamically adjusted to improve the performance and stability during system dynamics.In this proposed system smooth reference torque signal can help to minimize ripples in generated electromagnetic torque from induction motor.

TS-Fuzzy based Direct Torque Control
DTC is one of the best methods used in VFD's [16] to control the torque of three-phase induction motors.To achieve this, motor flux and torque are to be estimated by measuring the current and voltage of motor.Hysteresis controller needs high quality measuring devices without noise.The performance of the DTC method is very good even in the absence of speed sensors.In general, integration of motor phase voltages decides the flux estimation.Hence, controlling of motor is difficult if there is a zero-output frequency from the VFD (variable frequency drive).The induction motor can be started at standstill with maximum torque by designing the control system such that frequency range should be 50 Hz to 1 Hz.The speed reversal is also possible.A position sensor or speed sensor could be added to the DTC system for continuous low speed operations and even for zero frequency operations also.Using these sensors speed control and torque is maintained at high accuracy for total speed range.In direct torque control, the magnitude of the stator flux and torque instantaneous errors are considered to choose the non-zero and zero voltage vectors of the inverter The inverter switching frequency can be limited by adjusting the large hysteresis band and the range of that frequency is determined by the thermal limit [28][29] of power devices.In lower speed regions, the performance of the system will decrease.While controlling the torque, the hysteresis controller is set to change the elapsing time from lower limit to upper limit proportional to operating conditions [30][31].The model diagram of TS-Fuzzy based DTC of induction motor is shown in Fig. 3.The phase reconstruction block also implemented to obtain three phase voltages without measuring voltage at output of inverter.It can help to decrease the number of voltage sensors results in decrease of the cost.

Rule2
N P

Results and Discussions
The system represented in Fig. 1 is modelled in MATLAB/Simulink and the results are presented in Simulink platform.All aqua farms required variable speed to regulate oxygen levels in SAF.Similarly the variable speed is required to regulate discharging of water quantity in many industries as well as in apartments.Hence the response of the system is tested under change in reference signal of speed.The reference speed is altered from 1000 rpm to 1500 rpm at t=1.0 sec.In order to track reference speed of the motor, the TS-fuzzy based DTC generates required pulses to inverter.The reference speed and speed generated by motor is depicted in Fig. 4.   The flux components of direct axis and quadrature axis are depicted in Fig. 5.It seems, the flux components are having smooth shape which can represents smooth operation of speed of motor.The resultant total flux is depicted in Fig. 6.The reference flux is set to be at unity value, hence the total flux becomes stable at unit value.This seems the motor is under safe operation with respect to both saturation and flux weakening mode.Generally load on the motor depends on both depth of the water as well as quantity to be discharged.During the starting of the motor, the depth of water is less as it is just from motor to underground.Once water reaches to outlet, the torque will be increased due to weight of the water as well as due to friction between water and pipe.Hence it is very important to analyze the controllers during change in torque.Moreover, the response of electromagnetic torque generated by motor is depicted in Fig. 7. From Fig. 7, it is concluded that the ripples in torque with TS-Fuzzy controller has reduced compared with PI controller.Hence, there is significant priority of using TS-Fuzzy controller while designing DTC for induction motor.

Conclusion
The TS-Fuzzy and sliding mode controllers are implemented for water pumping system driven by 3-Φ IM fed from a single phase supply.The sensorless controller has suggested in this paper as it is considered submersible pump.The results are presented under change in torque as well as change in reference speed of the motor for various applications.Moreover, the comparison of electromagnetic torque generated by motor using PI controller and TS-Fuzzy controller is evaluated and find that there is a significant priority by using TS-Fuzzy controller.Hence, it is concluded that the ripples are minimized in torque by implementing TS-Fuzzy controller in DTC of induction motor.To reduce consumption of diesel,and to improve the sustainability in future,renewable energy sources like PV, wind and battery bank is integrated to system.Further, with the help of proposed controllers, the surplus power will be transferred to the grid when load power is less than the generation for future sustainable eco friendly environment.

Fig. 1 .
Fig.1.Single phase to Three phase conversation to drive induction motor for water pumping using Wind-PV system.

Fig. 4 .
Fig. 4. Response of speed under change in reference speed

Table 1 .
The TS-Fuzzy controller rules.