Smart and Efficient BLDC Motor based Aquaponics System with MPPT

GRD Journals- Global Research and Development Journal for Engineering | Volume 5 | Issue 7 | June 2020 ISSN- 2455-5703

Smart and Efficient BLDC Motor based Aquaponics System with MPPT Aryaraj B. K PG Student Department of Electrical Engineering Adi Shankara College of Engineering & Technology, Kerala, India

Tony George Associate Professor Department of Electrical Engineering Adi Shankara College of Engineering & Technology, Kerala, India

Abstract Aquaponics system needs very high electricity for the aeration of the system moreover as pumping of water. The proposed system using alternative energy as a source of energy for designing and developing standalone Aquaponics system with longer life, less maintenance and better performance. The fundamentals building components of Aquaponics system are solar PV array, a zeta converter together with two voltage source inverter and two Brushless DC (BLDC) motors with a paddle wheel aerator and pump load coupled to their shaft. The proposed system improves the efficiency and control the speed of BLDC motor. This method is especially useful for rural areas that have a substantial amount of solar radiation and haven’t any access to grid system. The proposed system is mean to induce satisfactory system performance even under dynamic conditions. Suitability of the proposed system for various perturbations is evaluated by simulating the proposed system using MATLAB/Simulink.

Keywords- Solar PV Array, Zeta Converter, Voltage Source Inverter, BLDC Motor

I. INTRODUCTION Aquaponics system is a combination of both aquaculture and hydroponics system. Aquaculture means the production of aquatic animals such as snail, fish, prawns etc and hydroponics means the cultivation of plants without soil. Using the same technology Aquaponics systems vary in size from small indoor or outdoor units to large commercial units. It requires high electricity this was one of the main problem of this system. Electricity is required for aeration of the system as well as pumping of water. So that it can be constantly recycled and recirculated within the system. This problem can be overcome by using renewable energy. Among all the renewable energy solar is the abundant. The most important benefits of solar panel is that solar energy is a renewable energy, reduce electricity bills, does not require a lot of maintenance cost.[12] The process of extraction of power from the sun is costly. In recent years cost of solar panel and power electronic devices are reduced this leads various generations of household and industrial applications. Several researchers used the combination of DC-DC converters and motor in industrial applications [2-6]. From the reviews zeta converter and BLDC motor are mostly used in industries for improving the efficiency and speed control. BLDC motor does not require an additional control loop for the purpose of speed control. Brushless DC (BLDC) motor are highly reliable, high efficient, better speed verses torque characteristics, high dynamic response, noiseless operation, long operating life due to lack of electrical and friction losses, high speed ranges and no maintenance[9-13]. Due to these benefits of solar and BLDC motor is considered to develop a solar PV fed Aquaponics system which can operate for longer time as compared with brushed and induction motors [7-11]. The previous system is operated in solar PV fed air cooler application. Figure 1 shows the circuit diagram of solar PV fed air cooler. It consists of buck and boost converters for the operation of BLDC motors. It leads to the losses across the switches and components and also the system become bulky.

The challenging issue in designing solar PV array fed solar air cooler is to maintain constant speed of BLDC motors that drives the pump and the air blower [4-6]. In the process of maintain constant speed of both motors, there can be power imbalance between PV panel and the load. Hall sensors are used to find the speed and position of BLDC motors. The drawback of existing system is it cannot be used in high power application, speed is not controlled and efficiency of the system is less.

This paper is organized as follows; section 2 describes the block diagram of solar Photovoltaic (PV) array fed Aquaponics system. The designing equations for various components and speed control scheme for BLDC motors are described in sub sections.

Comparison of existing and modified system is explained by simulating these systems using matlab/SIMULINK model in section 3. Finally conclude the paper in section 4.

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Smart and Efficient BLDC Motor based Aquaponics System with MPPT (GRDJE/ Volume 5 / Issue 7 / 004)

Fig. 1: Circuit diagram of solar PV fed air cooler [1]

II. PROPOSED SYSTEM Figure 2 shows the block diagram of proposed Aquaponics system. It consists of solar PV panel, zeta converter, two voltage source inverters (VSI) , two BLDC motor with an aerator and pump load coupled to the their shaft. This was the building components of solar Aquaponics system. The input power is from solar PV panel. Maximum power is tracked by using Perturb & Observe (P&O) based Maximum Power Point Tracking (MPPT) controller. Voltage and current sensed from the output of solar PV panel by using MPPT and produce a duty cycle for the operation of zeta converter. The same amount of power is transferred to the output of zeta converter with a step up voltage. The voltage source inverter of individual BLDC motor converts the input dc power into AC power for driving the pump and aerator coupled to their respective shaft.

Fig. 2: Block diagram of proposed system

A. Solar PV Panel with Zeta Converter The proposed solar PV array model consists of 36 cells. Maximum power voltage (Vmp) is 34.54 V and current is 1.449 A. The solar PV panel is operated with perturb and observe algorithm based maximum power point tracking (MPPT). The P & O algorithm based MPPT generate duty cycle for the operation of zeta converter. Figure 3 shows the circuit diagram of zeta converter.

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Smart and Efficient BLDC Motor based Aquaponics System with MPPT (GRDJE/ Volume 5 / Issue 7 / 004)

Fig. 3: circuit diagram of proposed zeta converter

Zeta converter consists of two inductors and two capacitors which is capable of operating in either buck and boost operation. It is operated in continuous conduction mode (CCM) which reduced stress on its components and devices. For designing the parameters of zeta converter, maximum switch current is to be calculated for the minimum input voltage. Duty cycle for achieving maximum switch current is;

D

Vdc Vdc  Vmpp

(1)

Where Vdc is the dc output voltage of zeta converter which is same as the rating of BLDC motor.

An average current flowing through the zeta converter;

I dc 

Pmpp

L1 

DVmpp

(2)

Vdc

Estimation of L1, L2 & C1 as (3), (4) & (5);

L2 

f sw I L1 1  DVdc

(3)

(4)

f sw I L 2 DI dc C1  (5) f sw VC1 Where f sw is the switching frequency of the switch, L1 is the ripple current through L1, I L1  I mpp ; I L 2 is the ripple current through L2, same as I L 2  I dc ; VC1 is the voltage ripple across C1 same as VC1  Vdc The characteristics of IV and PV are shown in figure 4 and figure 5. Figure 4 represents current (Y axis) verses voltage (X axis). Figure 5 represents power (Y axis) verses voltage (X axis). When voltage increases current also increases at power reaches its peak current starts to decrease. The PV panel characteristics are drawn with a constant temperature at 25ºC and irradiance 1000 W/m2. Irradiance is directly proportional to output power ie, when the irradiance decreases output power also decreases. Temperature is inversely proportional to the output power ie, when the temperature increases power delivery capability decreases.

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Smart and Efficient BLDC Motor based Aquaponics System with MPPT (GRDJE/ Volume 5 / Issue 7 / 004)

Fig. 4: IV characteristics of solar PV panel with constant temperature and irradiance

Fig. 5: PV characteristics of solar PV panel with constant temperature and irradiance

Maximum power is obtained with the help of P & O algorithm and its flow chart is shown in figure 6. For every iteration small perturbation is introduced to change duty cycle in order to force to move the operating point near MPP. To determine new perturbation direction this algorithm compares power of previous step cycle with the power of new step cycle. When peak power is obtained, power at the next instant decreases and hence perturbation reverses. If the steady state is reached, algorithm oscillates amount the maximum peak point. Operating voltage also regularly increased or decreased based on the direction of current operating voltage location, in order to shift the operating voltage value near the maximum power point voltage.

Fig. 6: Implementation of P & O algorithm

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Smart and Efficient BLDC Motor based Aquaponics System with MPPT (GRDJE/ Volume 5 / Issue 7 / 004)

B. Electronic Commutation of Brushless DC Motor BLDC motor consists of permanent magnet as rotor which is the rotating part and coil winding as stator which is the stationary part. Based on the rotor position external inverter applies current to the coil winding for each phase. BLDC motor has no mechanical part for switching electric currents in the stator windings like brushed DC motor. In order to control electric currents applied to the stator windings, it is necessary to sense the positional relationship between the rotor and stator. BLDC motor requires an inverter circuit that generates AC current for the commutation of the stator windings. Hall sensors are used for the detection of rotor position.

Three phase bridge inverter consist of six switching devices for controlling the commutation pattern for 120º commutation of a BLDC motor. If one phase of the high side device is turned on then another phase of low side device is turned off. In 120º conduction mode each phase is conducted for 120º and off for 60º. Ie, each phase is conducted two times in one full cycle with a span of 120 electrical degrees each time. Hall sensors are placed at 120 degrees apart for the balanced operation of the BLDC motor. Switching pulses are generated based on the hall sensor signals as shown in table 1.

Table 1: switching states for the electronic commutation of the BLDC motor Switching states Hall signal state EMF of phase Ha 0 0 0 0 1 1 1 1

Hb 0 0 1 1 0 0 1 1

Hc 0 1 0 1 0 1 0 1

ea 0 0 -1 -1 +1 +1 0 0

eb 0 -1 +1 0 0 -1 +1 0

ec 0 +1 0 +1 -1 0 -1 0

Q1 0 0 0 0 1 1 0 0

Q2 0 0 1 1 0 0 0 0

Q3 0 0 1 0 0 0 1 0

Q4 0 1 0 0 0 1 0 0

Q5 0 1 0 1 0 0 0 0

Q6 0 0 0 0 1 0 1 0

The BLDC voltage source inverters are operated at fundamental frequency which is obtained by electronic commutation controller. System equations (6) can be derived from the above table 1.

Q1  H a H b H c  H a H b H c  H a H b ( H c  H c )  H a H b Q2  H a H b H c  H a H b H c  H a H b ( H c  H c )  H a H b

(6)

Q3  H a H b H c  H a H b H c  H b H c ( H a  H a )  H b H c Q4  H a H b H c  H a H b H c  H b H c ( H a  H a )  H b H c Q5  H a H b H c  H a H b H c  H a H c ( H b  H b )  H c H a Q6  H a H b H c  H a H b H c  H a H c ( H b  H b )  H a H c

C. Speed Control The speed of both BLDC motors is regulated by using Proportional Integral (PI) controller as shown in figure 7. Here taking the output speed of BLDC motor and it compare with our requested speed and creating an error using PI controller. Then the PI controller will compensate and creating pulses for our requested speed and given to the gates1.

Fig. 7: Speed control of BLDC motors using PI controller

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Smart and Efficient BLDC Motor based Aquaponics System with MPPT (GRDJE/ Volume 5 / Issue 7 / 004)

Figure 8 shows the pulses given to gates. According to the reference speed PI controller generate an error signal to gates as electro motive force (emf). In the gate block the error signals from the PI controllers is compared with the output of decoder and produce a single output for controlling the voltage source inverter. Speed control of both BLDC motors are done by using the same method.

Fig. 8: Pulses given to gate

III. SIMULATION RESULTS AND DISCUSSION The performance of solar PV powered zeta converter fed BLDC motor Aquaponics system is simulated in the MATLAB/Simulink.

High power rating Aquaponics system model is designed as per the equation mentioned. In this case both BLDC motors are considered with equal power rating with constant temperature 25º and irradiance 1000W/m2. Output current and voltage of solar PV panel is shown in figure 9.

Efficiency of zeta converter,  

Pout



45.57

 86.9% Pin 52.43 Efficiency is improved when compared with the simulation results of the previous system.

Fig. 9: Output current and voltage of solar PV panel

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Smart and Efficient BLDC Motor based Aquaponics System with MPPT (GRDJE/ Volume 5 / Issue 7 / 004)

Fig. 10: Torque of BLDC motor

Initially the irradiance of the system is 1000W/m2 and the requested speed of the system is constant at 1200 RPM and speed of BLDC motor is 1136 RPM during this case. When the input voltage of BLDC motor increases speed of the BLDC motor increases. Torque is inversely proportional to the speed of BLDC motor. When the torque decreases speed of the BLDC motor increases and vise versa.

Fig, 11: speed of BLDC motor connected to the shaft of aerator at irradiance 1000W/m2

Fig. 12: Speed of BLDC motor connected to the shaft of pump at irradiance 1000W/m2

A. Comparative Analysis of Proposed System with Conventional System Proposed Aquaponics system has several merits when compared with the existing system. Comparative analysis between existing and proposed system are presented in table 2. The proposed system is better than the existing one.

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Smart and Efficient BLDC Motor based Aquaponics System with MPPT (GRDJE/ Volume 5 / Issue 7 / 004)

Table 2: comparative analysis of proposed and conventional system

schemes Attributes Solar PV array BLDC motor DC-DC converters BLDC motor control Converter efficiency Switching losses Cost

sensors

Conventional

proposed

1-Voltage & 1-Current Hall signals, Speed & Current Boost converter & Buck converter Simple 59% High Medium

1-Voltage & 1-Current Hall signals & Speed Zeta converter Simple 86.9% Low Low

IV. CONCLUSION Standalone solar PV array fed Aquaponics system using pair of BLDC motors drive the pump and aerator load coupled to their individual shaft is implemented in MATLAB/SIMULINK. Maximum power is extracted by the P & O algorithm based MPPT from the solar PV panel and fed to the zeta converter. The use of zeta converter and BLDC motor increases the efficiency of the system. The speed of aerator and pump is maintained constant with the help of PI controller. The speed controller is used to change the speed of pump and aerator as per the requested speed and ensuring maximum possible power from the PV system.

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Ragnheidur Thorarinsdottir, “Aquaponics Guidelines” DOI: 10.13140/RG.2.1.4975.6880, August 2015, https://www.researchgate.net/publication/282732809 Jisha Anna Mathew, Juna John Daniel and Najma Habeeb “Switched Reluctance Motor Drive Water Pumping System Using Zeta Converter Powered By PV Array” International Journal of Innovative Research in Electrical, Electronics, Instrumentation and Control Engineering, Vol. 1, Special Issue 2, March 2018 Utkarsh Sharma ; Shailendra Kumar & Bhim Singh “Solar Array Fed Water Pumping System using Induction Motor Drive” 2016 IEEE 1st International Conference on Power Electronics, Intelligent Control and Energy Systems (ICPEICES), Conference Paper, 2016

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