An induction motor's speed is set by the supply frequency, so controlling speed means controlling frequency — but reducing frequency alone drives the machine into saturation, because flux is proportional to voltage divided by frequency. A variable frequency drive therefore reduces voltage in proportion to frequency, holding the ratio constant so the flux stays where the designer intended. This project builds that drive: a rectifier and DC link, a three-phase inverter switched with sinusoidal PWM, a V/f profile with a low-frequency voltage boost, and a Simulink model validated against the hardware waveforms.
Not just the parts. Teams budget from a component list, then run out in week six on wire, connectors and the driver board they destroyed. These are the lines that catch them.
| Line | Cost |
|---|---|
Components and materials From the bill of materials | Rs 12,750 to Rs 31,900 |
Spares and replacements 15 % — you will destroy something | Rs 1,913 to Rs 4,785 |
Consumables and hardware Wire, connectors, headers, screws, heatshrink | Rs 1,530 to Rs 3,828 |
PCB fabrication | Rs 350 to Rs 900 |
Report, printing and binding Two or three bound copies, plots and the plagiarism check | Rs 400 to Rs 1,200 |
| Total | Rs 16,943 to Rs 42,613 |
| Each, split 3 ways | Rs 5,648 to Rs 14,204 |
Indicative bands last checked in August 2026 — a guide, not a quotation. Prices move and vary by seller, and anything you can borrow from the lab comes straight off the total. The 7 week figure assumes 16 person-weeks of work shared between 3; students past 4 add coordination rather than output, so the estimate stops improving there.
The same chain in words
The rectifier and capacitor produce a stiff DC link. A pre-charge resistor limits the inrush into that capacitor at power-up, and is bypassed by a contactor once it is charged.
The controller generates three sinusoidal references 120 degrees apart at the commanded frequency, and compares each against a triangular carrier to produce the switching pattern for the three legs.
The amplitude of those references is scaled with frequency so that volts per hertz stays constant, which keeps the airgap flux constant and the motor's torque capability unchanged across the speed range.
Below a few hertz the stator resistance drop is a significant fraction of the applied voltage, so a fixed boost is added to the profile, otherwise the flux collapses and the motor cannot produce starting torque.
Above base frequency the voltage cannot rise any further, so volts per hertz falls, flux weakens and available torque falls with it. That is the field weakening region and it is a limit, not a fault.
This is the chapter that separates an engineering project from an assembly job. Every value below carries the formula that produced it and the assumptions it rests on — check them against your own ratings before you use them, because your motor is not this motor.
V/f = rated voltage / rated frequency
415 / 50 = 8.3. At 25 Hz the drive therefore applies 207.5 V, at 10 Hz it applies 83 V, and so on down the profile.
Ns = 120 x f / P
120 x 50 / 4 = 1500. Actual shaft speed is lower by the slip, which for a small machine is a few percent.
Add the estimated stator IR drop to the linear profile
At 5 Hz the linear profile applies only 41.5 V, and several volts of that are dropped across the stator resistance rather than producing flux. Without boost the motor will not start under load; with too much boost it saturates and overheats at low speed.
Vdc = sqrt(2) x V line for a three-phase rectifier
1.414 x 415 = 587 V. Every device in the inverter must be rated well above this, and the DC link capacitors have to be rated for it continuously plus the ripple.
Peak phase fundamental = m x Vdc / 2, with m at most 1 in the linear range
At m = 1 the peak phase voltage is 293.5 V, so phase RMS is 207.5 V and line RMS is 359 V. The drive cannot reach the motor's rated 415 V with plain SPWM in its linear range — which is the point of the next line.
Peak phase = Vdc / sqrt(3) with space vector modulation
587 / 1.732 = 339 V peak phase, which is 240 V phase RMS and 415 V line RMS. Space vector modulation injects a zero sequence component that lets the fundamental go higher for the same DC link, at no extra hardware cost. It is the single strongest technical point available in this project.
| Item | Qty | Unit cost |
|---|---|---|
IGBT or MOSFET module Three-phase bridge, 1200 V, 15 A, or six discrete devices | 1 | Rs 1,800 to Rs 5,000 |
Isolated gate drivers Optically isolated drivers with dead-time and desaturation protection | 1 | Rs 900 to Rs 2,600 |
Controller board STM32 or a DSP board with three-phase complementary PWM | 1 | Rs 900 to Rs 3,000 |
Rectifier and DC link Three-phase bridge rectifier, 470 uF 900 V DC link capacitors | 1 | Rs 1,200 to Rs 3,200 |
Pre-charge circuit Power resistor with a bypass contactor and timer | 1 | Rs 350 to Rs 900 |
Current sensors Hall effect sensors on two output phases | 2 | Rs 350 to Rs 900 |
Isolated voltage sensing DC link voltage divider with an isolation amplifier | 1 | Rs 400 to Rs 1,100 |
Heatsink and fan Extruded heatsink with forced air | 1 | Rs 500 to Rs 1,500 |
Three-phase motor 0.75 kW (1 HP), 415 V, 4 pole Normally borrowed from the machines lab. | 1 | Rs 4,500 to Rs 9,000 |
MCB, enclosure, wiring Four pole MCB, metal panel, ferrules, shielded signal cable | 1 | Rs 1,500 to Rs 3,800 |
MATLAB with Simulink Student or institutional licence Use the college licence — do not budget for this. | 1 | — |
Specifications are written as ratings rather than brands, so any equivalent part works. Where a line says to borrow from the lab, do — it is usually the largest number on the page, and the total drops to Rs 12,443 at the low end without them.
None of these blocks you — they are learnable inside a semester. Each one you do not have costs a couple of weeks, so count them into your plan.
Anything marked required is a blocker, not a difficulty. Arrange the access before you commit to the project, not after.
Use these when your guide says the scope is too small, or when you want something in the results chapter that nobody else in your batch will have.
The structure below is what a project report is marked against, with the mistake that costs marks in each chapter. There is no template to download and there will not be one: the writing is your work, and a site that did it for you would be helping you cheat rather than helping you pass.
A final year report is normally 60 to 90 pages with a substantial literature survey, and many departments expect a paper submission alongside it.
The full report guide — front matter, conventions and page countsOne paragraph covering what the problem is, what you built, and what the result was. Written last, even though it appears first.
Loses marks: Describing the problem and the method but never stating a result. If there is no number in your abstract, it is not finished.
Why the problem matters, the context it sits in, and a clear statement of the objectives your project set out to meet.
Loses marks: Objectives written so vaguely that nobody can tell at the end whether they were met. Write objectives you can tick off in the conclusion.
What has already been done, what each approach achieved, and the specific gap your work addresses.
Loses marks: A list of paper summaries with no comparison and no gap. The survey exists to justify your design choice, so end it by saying what you chose and why.
The system as a whole: the block diagram, what each block does, and the signal or power path between them.
Loses marks: A block diagram copied from a datasheet or another report. Draw yours to match what you actually built, including the parts that are inconvenient.
Every component value and rating, with the formula, the assumptions and the arithmetic that produced it. This is the chapter that distinguishes an engineering project from an assembly job.
Loses marks: Component values with no justification. If a resistor is 10 kOhm, the report must say why it is not 1 kOhm.
The circuit as built, the PCB or wiring, the flowchart, and the parts of the code that carry the actual logic.
Loses marks: Twenty pages of pasted source listing. Include the flowchart and the few functions that matter, and put the full listing in an appendix.
What you measured, in tables and graphs, compared against what you predicted in the design chapter — including where they disagreed.
Loses marks: Photographs of the working model presented as results. A photograph is evidence that it exists, not evidence that it works. Results are measurements.
Whether each objective was met, what the measured performance was, and what the honest next step would be.
Loses marks: Future scope written as a wish list of unrelated features. It should follow from a limitation you actually hit.
Every source in a consistent style, plus datasheets, full code listings and the complete bill of materials.
Loses marks: Citing a blog or a video where a datasheet or a standard exists. Cite the primary source for anything you relied on.
The demonstration is half the assessment. These are the questions this project invites, and the answers are written the way you would give them out loud.
Because the airgap flux is proportional to voltage divided by frequency. If frequency is reduced at constant voltage, the flux rises, the magnetic circuit saturates, the magnetising current becomes very large and the machine overheats. Holding volts per hertz constant keeps the flux at its design value across the whole speed range.
The drive cannot produce more voltage than the DC link allows, so above rated frequency the voltage stays fixed while frequency keeps rising. Volts per hertz therefore falls, flux weakens, and the available torque falls roughly inversely with speed. Power stays approximately constant, which is why it is called the constant power or field weakening region.
The V/f profile assumes that the applied voltage all appears across the magnetising branch, but part of it is dropped across the stator resistance. At 50 Hz that drop is a negligible fraction of 415 V, but at 5 Hz the profile applies only about 41 V and the same resistive drop is now a large fraction of it. Adding a fixed boost compensates for the drop so the flux is maintained and the motor can develop starting torque.
Because in a three-wire motor the neutral is not connected, so any common-mode component added to all three phase references cancels in the line-to-line voltages that actually drive the machine. Space vector modulation exploits this by effectively adding a third-harmonic zero-sequence component, which lowers the peak of each reference and allows the fundamental to be increased by about 15.5 percent before the modulator saturates.
At power-up the DC link capacitor is empty, so it looks like a short circuit to the rectifier and would draw an enormous inrush current, damaging the diodes and welding contactor contacts. The pre-charge resistor limits that current while the capacitor fills, and once the link is near full voltage a contactor shorts the resistor out so it does not carry the running current.
The two devices in a leg cannot switch instantaneously, so if one is commanded on at the moment the other is commanded off, both conduct briefly and short the DC link through themselves. Dead time is a deliberate gap where both are off. Its cost is a small error in the output voltage each switching cycle, which appears as low-order harmonic distortion and torque ripple, worst at low output voltage.
Normally taken as a B.E. final year project (7th/8th sem) project. If yours is a different course, the extensions above scope it up and the simpler half of the design scopes it down — the arithmetic does not change. Back to all projects.