Poly Phase Inverter Drive and its Parameter Estimation Using PIC Microcontroller

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International Journal of Recent Advances in Engineering & Technology (IJRAET)

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ISSN (Online): 2347 - 2812, Volume-3, Issue -8, 2015 20

Poly Phase Inverter Drive and its Parameter Estimation Using PIC Microcontroller

1S. S. Kumbhar, ²S. R. Kumbhar

1 JJTU Rajastahn, Ph. D. Scholar- India, ²Dept of Electronics, Willingdon College, Sanlgi (MS) India.

Abstract : In industrial applications single as well as three phase drives are prominently used in the industrial applications as prime mover. For driving heavy load applications, precisely three phase drives are preferably used. The three phase supply is not available in all circumstances. So the process has to run on the single supply. Ultimately the production and various parameters hampers. This problem was solved with single to three phase conversion. In order to drive the very heavy loads instead of three phase a poly phase i.e. six phase voltage source inverter based induction motor drive is suitable. It is essential to measure the various parameters of the induction motor. The data acquisition system play important role in the measurement of various parameters.

In the present research article 6 phase inverter drive using MOSFET is designed and fired with PWM through the software generated pulses. The required PWM pulses are generated using the PIC microcontroller. Each MOSFET is fired less than 60⁰. MOSFET requires very low power for their operation and operates at very high frequency.

The performance of the drive is tested. Various PWM techniques are used and as per the performance the best suitable firing scheme is used. The various parameters such as current, AC, DC voltage, Speed are sensed and the efficiency is calculated.

Keywords : Poly phase induction motor drive, Single to three phase conversion, Drive, Voltage source inverter, Microcontroller based poly phase drive.

I. INTRODUCTION

With industrial revolution in western Europe and the development of power devices many industrial sectors started using the motor. Initially the hand power drives were used which are now a days no industrial importance so it was replaced by the horse power drives.

These drives are replaces by mechanical drives but due to its low efficiency they were replaced by electrical drives. There are various electrical drives but the AC drives are dominant in industrial sector. Single phase drives are used for small load applications wile for higher load three phase drives are used. The three phase induction motors are widely used in the industrial applications. Generally the load driven by such motors is high. Even in circumstances the load may be very high the three phase is not quite suitable. But by some means the application task is completed. But the use of the poly phase is best suitable for such loads. In many places the three phase connection is major concern. So from the single phase supply, three phase and poly phase supply is possible. Such drive is design is the key issue in the present investigation. Such drive block diagram represents the Microcontroller as key control component, buffer, gate driver, snubber, and parameter sensing circuits. All the components are connected in a closed loop to from a drive.

II. SYSTEM DESIGN BLOCK DIAGRAM

Fig. 1 Proposed system configuration

Buffer

_Driver^Gate

Snubber

Line voltage rectifier

Microcontroller

Parameter Sensing circuits

6 phase inverter

M

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The system shown in Fig. 1 can work in closed or open loop configuration The microcontroller generates the PWM pulses whose current strength is not quite enough to drive the gate of the inverter MOSFET. The butter increases the required current capability having connected two transistors in darlington pair assembly.

The baser drive sign al has two parts : Isolator and amplifier. The isolator isolates the control circuit from the power circuit. For this the MCT2E is the best suitable. The amplifier strengthen the signal to drive the gates of the power MOSFETS. The poly phase invert has 12 MOSFETS and operated in pair only little less than the 60⁰. Each pair will conduct up to 60⁰. While PWM switching the surge pulses are generated that may damage the load and control circuit including the source. So the snubber is added in between the inverter and the Motor. The various parameters such as current, speed, voltage are sensed using the different sensors and recorded. The speed control parameters are set by the microcontroller and the control over the drive is achieved. The PWM will decide the power supplied to the motor and hence the speed of the drive.

III. DESIGN OF INVERTER

The inverter is designed with 12 MOSFETS as shown in the fig. 2. The rectified single voltage power is given to the inverter. The output of the MOSFET pair is

connect to the 6 phase motor. The gates G₁ to G₁₂ are driven by the PWM signal generated by the microcontroller. Each MOSFET is conduced during 60⁰ only. Initially G₁ and G₉ will conduct for 60⁰ then G₂ and G₉ conducts and so on. The appropriate power is supplied to the motor. While firing pulse generation the care is taken to keep the guard band in between the first pair OFF and second ON. Otherwise device may damage.

IV. PWM SCHEME

For the firing of the poly phase inverter the PWM is used. Six pulses are used for the firing of the inverter in pair form. Initially the simulation is carried out for the selection of better firing PWM scheme. The simulation is carried for Single, Three, five, seven and nine pulses per half cycles. The harmonic factor is also taken in to consideration. From the simulation results it is seen that the efficiency of the machine increases with increase in the speed. The efficiency also goes on improving for the increase in pulses per half cycle up to 7 pulses per half cycle. For nine pulses per half cycle it is observed that the performance of the drive is decrease to that of seven pulses. So seven pulses per half cycle scheme is selected for firing of inverter. Figure below shows the firing pulses of various PWM.

Fig. 2 Six Phase Inverter using MOSFET.

V. SENSING OF PARAMETERS

Speed sensing

For speed measurement the voltage supplied to the motor is read and using the software it represent the speed of the drive. For 0V, zero speed is taken and for 230V maximum 1400 rpm is represented for the given drive. As voltage increases the drive speed also increases. Here the V to F converter is used. Initially the sensed voltage in the rage 0-5V for the rpm 0-1400rpm.

AC Voltage Sensing

For AC voltage sensing the peak detector circuit is used.

The changes in the input is fed to the peak detector. The detector detects corresponding change and gives to ADC card through limiter circuit. Computer reads the data and applying the necessary correction and used for further processing. The proportional Voltage is scaled to 0-230V.

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DC Voltage Sensing Circuit

The potential divider is used for the measurement of DC voltage. The OP-AMP with unity gain is used. The output of the OPAMP is finally given to ADC. The output of ADC varies from 0 to 5V. which is proportional to 0 to 250 V. This measured voltage is scaled between the range 0 to 230V. .

Fig. 3 DC voltage sensing circuit Current Sensing Circuit

For measurement the simple arrangement is used. A good quality resistance of 1 ohm with 100 W is connected in series with the supply with the motor. The voltage developed across the resistance is proportional to current passing through the resistance. The developed voltage is passed through the transformer and limiter.

Then the developed voltage fed to ADC to read the proper voltage. The voltage across the ADC is in the range 0-5V and with the help of software it is scaled to 0-15 Ampere. The actual current sensing block diagram is shown in Fig. 4 (a) and its sensing arrangement is shown in Fig. 4(b).

Fig. 4 (a) block diagram of current sensing circuit.

Fig, 4 (b) current sensing experimental arrangement

VI. RESULTS AND DISCUSSION

Fig 5 : Speed Efficiency graph

Fig 6 : Voltage versus Speed

The fig. 5 shows the graphical representation of the speed efficiency characteristics. As the speed increases the efficiency increases up to 1300 rpm then the speed decreases due to the losses in the machine. The simulated and the experimental efficiency curves are similar in nature but the experimental results are somewhat little bit less than the simulated. This is due to the machine and switching losses. In order to increases the efficiency of the machine it is necessary to design the machine with minimum losses. The inverter firing must be utilized with the optimum switching.

The speed of the machine is measured by knowing the voltage. V to F converter gives the proper speed of the motor. The nature of the graph shows that the increase in voltage increases the speed of the motor. To control the speed of the motor. the power supplied to the motor must be controlled which is possible by the controlled firing of the gate of the MOSFETS. The MOSFETs are fired by the PWM generated by the microcontroller.

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VII. CONCLUSION

It is possible to control the speed of the motor by using the PWM technique. The large loads are driven by the three phase drives from the single phase supply with the help of the inverter technique. Similar way very large loads are also driven by the 6 phase inverter drive technique. If the number of phases increase the driving capability also increases. The efficiency of the drive is also comparable to that of the simulated drive. Various parameters are also measured for controlling the motor.

From single phase six phase conversion is done by using MOSFET based inverters and with the best firing pulse the inverter is fired. The snubber is also helping to reduce the transient responses and surge pulses.

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