Design Control Schemes of Three Phase Induction Motor Connected PV System with Voltage Source Inverter

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 7, Issue 10, October 2017)

18

Design Control Schemes of Three Phase Induction Motor

Connected PV System with Voltage Source Inverter

Dr. R. Arulmurugan

1

, T. Anushalini

2

1_{Associate Professor,}2_{Assistant Professor, Dept. of EEE, S R Engineering College, Warangal, India.}

Abstract— This paper presents the simulation output of the three phase induction motor connected to PV system regulated by the voltage source interver.The simulation implementation of perturb and observe (P&O ) maximum power point tracking (MPPT) used in solar array power systems with Voltage Source Inverter (VSI). The main difference of the proposed system to existing MPPT systems includes elimination of the proportional–integral control loop and investigation of the effect of simplifying the control circuit. Contributions are made in several aspects of the whole system, including VSI, boost converter design, system simulation, controller programming. The resultant system is capable of tracking MPPs efficacious and produce the alternating current output through VSI for three phase induction drive. The P&O MPPT algorithm is used to track MPPs because it is simple and easy to track the solar irradiation. MATLAB and Simulink were employed for simulation studies was used to program a proposed system.

Keywords— solar photovoltaic, voltage source inverter, maximum power point tracking, boost converter, three phase induction motor

I. INTRODUCTION

Recently, energy generated from clean, efficient, and environmentally friendly sources has become one of the major challenges for engineers and scientists [1]. Among all renewable energy sources, solar power systems attract more attention because they provide excellent circumstances to generate electricity while greenhouse emissions are reduced [2]–[3]. It is also gratifying to lose dependant conventional electricity generated by burning coal and natural gas. Regarding the endless aspect of solar energy, it is worth saying that solar energy is a unique prospective solution for energy crisis equivalent. However, despite all the aforementioned advantages of solar power systems, they do not present desirable efficiency [4], [5].The efficiency of solar cells depends on many factors such as temperature, insolation, spectral characteristics of sunlight, dirt, shadow, and so on.

Changes in insolation on panels due to fast climatic changes such as cloudy weather and increase in ambient temperature can reduce the photovoltaic (PV) array output power. In other words, each PV cell produces energy pertaining to its operational and environmental conditions [6], [7].

In addressing the poor efficiency of PV systems, some methods is proposed, among which is a new concept called ―maximum power point tracking‖ (MPPT). All MPPT methods follow the same goal which is maximizing the PV array output power by tracking the maximum power on every operating condition [8] [9].

There are a large number of algorithms that are available to track MPPs. Some of them are simple, such as those based on voltage and current feedback, and some are more complicated, such as perturbation and observation (P&O) or the incremental conductance (IncCond) method. They also vary in complexity, sensor requirement, speed of convergence, cost, range of operation,popularity, ability to detect multiple local maxima, and their applications [10]– [15].

II. PROPOSED THREE PHASE INDUCTION DRIVE CONNECTED PV SYSTEM WITH VSI

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International Journal of Emerging Technology and Advanced Engineering

[image:2.612.54.278.144.261.2]

19 Fig. 1 Equivalent circuit of PV model

2.1 PV Model

The basic structural unit of a solar module is the PV cells. A solar cell converts the energy in the photons of sunlight into electricity by means of the photoelectric phenomenon found in certain types of semiconductor materials such as silicon and selenium. A single solar cell can only produce a small amount of power. To increase the output power of a system, solar cells are generally connected in series or parallel to form PV modules. PV module characteristics are comprehensively discussed in [3], [6], [11], which indicate an exponential and nonlinear relation between the output current and voltage of a PV module. The main equation for the output current of a module is [1]

(1) Where Io is the PV array output current, V is the PV output Voltage, Iph is the cell photocurrent that is proportional to solar

Irradiation, IRS is the cell reverse saturation current that mainly depends on temperature, KO is a constant, ns represent the number of PV cells connected in series, and np represents the number of such strings connected in parallel.

In (2), the cell photocurrent is calculated from

(2) Where:

Iscr cell short-circuit current at reference temperature and Radiation;

KI short-circuit current temperature coefficient; TR cell reference temperature;

S solar irradiation in milliwatts per square centimeter. Moreover, the cell reverse saturation current is computed from

(3)

Where

TR cell reference temperature; Irr reverse saturation at TR;

EG band-gap energy of the semiconductor used in the cell.

2.2 Three faze inverters

Some examples where voltage source inverters are used are: uninterruptible power supply (UPS) units, adjustable speed drives (ASD) for ac motors, electronic frequency changer circuits etc. Most of us are also familiar with commercially available inverter units used in homes and offices to power some essential ac loads in case the utility ac supply gets interrupted. In such inverter units, battery supply is used as the input dc voltage source and the inverter circuit converts the dc into ac voltage of desired frequency.

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International Journal of Emerging Technology and Advanced Engineering

20 The power circuit of the three-phase VSI is shown in Fig 5. The power circuit of this inverter is implemented using insulated gate bipolar transistors (IGBTs); however, other semiconductor switches can be used depending on the power and switching characteristics of the inverter. Moreover, this inverter consists of three half-bridge inverters, which are connected in parallel and have the same phase output voltages with a phase difference of 120°. Therefore, for the specific inverter topology, the following equations hold: image below

2.3 Three phase induction drive

[image:3.612.325.563.153.313.2]

The three phase induction motor as the self starting induction motor, running at the synchronous speed. As the squirrel cage induction motor is simple and maintains constant speed from the low to high level of load conditions. The various parameters that are looked into are its normal power, voltage and frequency. The other important aspects are stator and rotor parameters namely the stator resistance and inductance parameters and also the rotor resistance and inductance with the inductance values are maintained appropriately.

Fig. 3 Parameters of three phase induction motor load

[image:3.612.56.283.411.590.2]

2.4 DC Boost converter with MPPT

Fig.2 Boost converter

The power converter selected in this study is a kind of step-up chopper, it is inserted in order to interface the PV output to the resistor as shown in Fig 2. Its objective is to track the MPP of the PV array. A coil, a capacitor, a diode and an IGBT controlled with a PWM signal, build this converter and it transforms input voltage to the output voltage as a step up transformer as shown in Fig 5, two sensors are required for measuring Vpv and Ipv. The MPPT algorithm adjusts incessantly the DC–DC Boost converter duty cycle. Comparing this duty ratio to a saw signal, a PWMsignal is generated. The control input u is the switch position; it takes 0 when the switch is open or 1 when the switch is closed. Based on the Kirchhoff‘s first and second rules, the dynamic model of the converter can be written

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Where VO and oil are the load voltage and the current across the inductor, respectively. The output voltage of the boost converter VO can be expressed in function of the input voltage Vpv and its duty cycle d:

[image:3.612.332.462.502.546.2]

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International Journal of Emerging Technology and Advanced Engineering

21 Eq. (5) demonstrates that incrementing (decrementing) the voltage reference Vpv can be done by decrementing (incrementing) the converter duty cycle d.

2.5 Perturb and observe MPPT algorithm

The basic concept of Perturb and Observe (P&O) algorithm involves the perturbation of solar PV operation point Corresponding to the sign of the last increment of PV power [16, 18]. In this method, any changes of perturb voltage ∆V are commanded by the algorithm to the PV module operating voltage. P&O will determine whether the operating voltage should be increased or decreased by ∆V after the process of observing output power has taken place. Figure 1 shows more detail on the operation of the conventional P&O algorithm. Based on the obtained information, P&O algorithm is able to predict when the operating voltage is approaching the VMPP by comparing the actual and the previous state of the power, P, and voltage, V. In short, the next perturbation to reach the MPP will be the same if there is an increment of P and vice versa as shown concluded in Table 1.

Fig.4. Perturb and observe MPPT algorithm

Table.1.

Function of P&O MPPT algorithm

Purtubation ∆P Next purtubation

Positive Positive Positive

Positive Negative Negative

Negative Positive Negative

Negative Negative Positive

III. RESULTS AND DISCUSSION

The overall simulation setup shows the input and output blocks clearly, the input is given to the VSI through the PV panel. The output from the panel is a DC output, as it is a DC –DC converter its gives DC output wich is fed into the voltage source inverter inorder to get AC output to feed the 3 phase induction motor to run at appropriate speeds. The renewable energy is utilized or irradiation is efficaciously trapped by the PV panel to run the motor. The voltage source inverter comprising of six switches works with the phase difference of 120°. Turn on and off according to the duty cycle to run the motor at appropriate speeds. The output from the motor are reflected as the output waveforms.

Fig.5 overall proposed simulation setup

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International Journal of Emerging Technology and Advanced Engineering

22 Fig.6 output waveform of three phase induction motor (a). Inverter input voltage of DC, (b). Top three pulse generator, (c) bottom three

pulses generator. (d) Rotor speed of induction motor (d) Electromagnetic torque)

The most important part of the simulation revolves around how effectually the motor is going to maintain the speed limit of the motor by turning ON and OFF of the top three switches and bottom three switched which switched alternative by taking turns as two above and one below and vice versa. These pulse waveforms are observed below fig7.

Fig.7 Pulse generator waveform of voltage source inverter (a) Top three pulses (b) Bottom three pulses

A comparitve study has been done with the three phase synchronous motor and the waveforms are observed in the laboratory. This study helps to find out difference in the two different motor operation and the pros and cons with various parameter could be measured and analysed as waveforms in the below shown fig 8.

Fig.8 Output waveform of three phase synchronous machines.

IV. CONCLUSION

In this paper, a simple perturb and observe MPPT method was employed to drive the three phase induction motor through voltage source inverter. The proposed system was simulated and constructed, and the functionality of the designed control concept was proven. From the results acquired during the simulations experiments, it was confirmed that, with a well-designed system including a proper boost converter and voltage source inverter and selecting an efficient and proven algorithm, the implementation of MPPT is simple and can be easily constructed to achieve an acceptable efficiency level of the PV modules. The results also indicate that the proposed method is capable of tracking and working three phase induction drive effectively and reduces low power loss of system and cost.

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International Journal of Emerging Technology and Advanced Engineering

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