About Sine Pulse Width Modulation

Sine Pulse Width Modulation (SPWM)

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Introduction


Sinusoidal PWM has been a very popular technique used in AC motor control. This is a method that employs a triangular carrier wave modulated by a sine wave and the points of intersection determine the switching points of the power devices in the inverter.

Though this method is unable to make full use of the inverter’s supply voltage and the asymmetrical nature of the PWM switching characteristics produces relatively high harmonic distortion in the supply it is still popular for its simplicity.

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Block Diagram







• 8051 series Microcontroller• MOSFET• Gate Driver• Crystal Oscillator• Toggle Switches• Resistors• Capacitors• Diodes• Transformer• Regulator• Opto-isolators

Hardware Requirements







Software Requirements

Keil compiler

Languages: Embedded C or Assembly







Power Supply







The 230V AC supply is first stepped down to 12V AC using a step down transformer.

This is then converted to DC using bridge rectifier.

The AC ripples is filtered out by using a capacitor and given to the input pin of voltage regulator 7805.

At output pin of this regulator we get a constant 5V DC which is used for MC and other ICs in this project.

Power Supply







Microcontroller

It is a smaller computer

Has on-chip RAM, ROM, I/O ports.

RAM ROM

I/O Port

TimerSerial COM Port

Microcontroller

CPU

A single chip







Features of Micro Controller

8K Bytes of In-System Programmable (ISP) Flash Memory

4.0V to 5.5V Operating Range

Fully Static Operation: 0 Hz to 33 MHz

256 x 8-bit Internal RAM

32 Programmable I/O Lines

Three 16-bit Timer/Counters

Eight Interrupt Sources

Full Duplex UART Serial Channel







Microcontroller Pin Description







30 pF

30 pF

8.2 K

10 uF

+

11.0592 MHz

EA/VPPX1

X2

RST

31

19

189

Power On Reset Circuit







Opto-Isolator

Opto coupler is a 6 pin IC. It is a combination of 1 LED and a transistor.

Pin 6 of transistor is not generally used and when light falls on the Base-Emitter junction then it switches and pin5 goes to zero.

If input of the diode is zero and other end of diode is GND then the output is one.







When logic zero is given as input then the light doesn’t fall on transistor so it doesn’t conduct which gives logic zero as output.

When logic 1 is given as input then light falls on transistor so that it conducts, that makes transistor switched ON and it forms short circuit this makes the output is logic zero as collector of transistor is connected to ground.

Opto-Isolator







MOSFET

The MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is a Voltage controlled device.

This means that a voltage at the gate control the current flows from the drain to the source.

There are three terminals: Gate - connected to the input device.

Drain - connected to the positive, since electrons drain away to the positive. Source - the source of the electrons.







USES OF MOSFETS High power devices like motors and light bulbs give a large current output for a very tiny current input.

So a MOSFET can act as the interface between an integrated circuit that can give only a tiny current, and the motor that takes a big current.

In complimentary pairs they are used in hi-fi power amplifiers.

They produce less distortion as they are more linear than bipolar transistors.

Integrated circuits, as they can be made very compact.

MOSFET







IR2101 Features

Floating channel designed for bootstrap operation Fully operational to +600V Tolerant to negative transient voltage dV/dt immune.

Gate drive supply range from 10 to 20V.

Undervoltage lockout.

3.3V, 5V, and 15V logic input compatible.

Matched propagation delay for both channels.

Outputs in phase with inputs (IR2101) or out of phase with inputs (IR2102)







IR2101 Description

The IR2101(S)/IR2102(S) are high voltage, high speed power MOSFET and IGBT drivers with independent high and low side referenced output channels.

Proprietary HVIC and latch immune CMOS technologies enable ruggedized monolithic construction.

The logic input is compatible with standard CMOS or LSTTL output, down to 3.3V logic.

The output drivers feature a high pulse current buffer stage designed for minimum driver cross-conduction.







A star lamp load can be used to view the waveform only. This project uses an 8051 family microcontroller duly interfaced to the Opto-isolators for feeding to the bridge drivers. 3 no’s of dual bridge drivers are used to feed 3 phase bridge inverter with the DC supply developed from single phase AC after rectification.

Powering the circuit is achieved by a pair of control transformers with bridge rectifier and filter capacitors. One set of this power is used for the microcontroller and the other one is used for driving circuits of the three phase bridge.

Working

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The working principle of SPWM includes the following points

The frequency of triangular wave is the frequency of PWM.

Frequency of control voltage controls the fundamental frequency.

The peak value of control voltage controls the amplitude.

Modulation Index is defined by:

Where Vao1 = Fundamental component of Vao.







For Phase A: If Vcontrol > Vtriangle then Vao = Vd/2. If Vcontrol < Vtriangle then Vao = -Vd/2.

The working principle of SPWM includes the following points

For Phase B: If Vcontrol > Vtriangle then Vbo = Vd/2. If Vcontrol < Vtriangle then Vbo = -Vd/2.

For Phase C: If Vcontrol > Vtriangle then Vco = Vd/2. If Vcontrol < Vtriangle then Vco = -Vd/2.







Advantage

The main advantage of PWM is that power loss in the switching devices is very low.

When a switch is off there is practically no current, and when it is on, there is almost no voltage drop across the switch.

Power loss, being the product of voltage and current, is thus in both cases close to zero.

PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle.







Applications

In many industrial applications, Sinusoidal Pulse Width Modulation (SPWM), is used to control the inverter output voltage.

SPWM maintains good performance of the drive in the entire range of operation between zero and 78 percent of the value that would be reached by square-wave operation.

If the modulation index exceeds this value, linear relationship between modulation index and output voltage is not maintained and the over-modulation methods are required.

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For the generation of pure sinusoidal signal, SPWM is the most popular technique. In SPWM a digital waveform is generated and the duty cycle is modulated such that the average voltage of the waveform is corresponds to a pure sine wave. SPWM moves the voltage harmonic components to the higher frequencies. The SPWM technique treats each modulating voltage as a separate signal and compared to the common carrier triangular waveform.

Conclusion





About Sine Pulse Width Modulation

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