Sinusoidal PWM (SPWM) technique in Power Electronics - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the carrier wave frequency in SPWM.

Power Electronics

carrier_frequency = [1]  # Frequency of the triangular carrier wave

Drag options to blanks, or click blank then click option'

A1000

B50

C5000

D60

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing the output frequency instead of the carrier frequency.

The carrier frequency in SPWM is typically high, often around 1 kHz or more, to allow smooth modulation of the output waveform.

2fill in blank

medium

Complete the code to calculate the modulation index in SPWM.

Power Electronics

modulation_index = [1] / carrier_amplitude  # Ratio of reference to carrier amplitude

Drag options to blanks, or click blank then click option'

Acarrier_amplitude

Breference_amplitude

Coutput_voltage

Dfrequency_ratio

Attempts:

3 left

💡 Hint

Common Mistakes

Using carrier amplitude as numerator instead of denominator.

The modulation index is the ratio of the reference (sinusoidal) amplitude to the carrier (triangular) amplitude.

3fill in blank

hard

Fix the error in the code that generates the SPWM signal.

Power Electronics

spwm_signal = 1 if reference_signal > [1] else 0

Drag options to blanks, or click blank then click option'

Acarrier_signal

Boutput_voltage

Cmodulation_index

Dreference_signal

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing reference_signal to itself instead of carrier_signal.

In SPWM, the reference sinusoidal signal is compared to the carrier triangular signal to generate the PWM pulses.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps angles to SPWM values.

Power Electronics

spwm_map = {angle: 1 if [1] > [2] else 0 for angle in range(0, 360)}

Drag options to blanks, or click blank then click option'

Amath.sin(math.radians(angle))

Bmath.cos(math.radians(angle))

Ccarrier_wave_value

Dmodulation_index

Attempts:

3 left

💡 Hint

Common Mistakes

Using cosine instead of sine for the reference signal.

The sinusoidal reference is the sine of the angle, compared to the carrier wave value to decide the PWM output.

5fill in blank

hard

Fill all three blanks to generate SPWM pulses with modulation index control.

Power Electronics

spwm_output = {angle: 1 if ([1] * [2]) > [3] else 0 for angle in range(0, 360)}

Drag options to blanks, or click blank then click option'

Amath.sin(math.radians(angle))

Bmodulation_index

Ccarrier_wave_value

Dmath.cos(math.radians(angle))

Attempts:

3 left

💡 Hint

Common Mistakes

Using cosine instead of sine.

Not multiplying by modulation index.

The SPWM output is generated by multiplying the sine of the angle by the modulation index and comparing it to the carrier wave value.

Practice

1. What is the main purpose of the Sinusoidal PWM (SPWM) technique in power electronics?

easy

A. To store electrical energy in capacitors

B. To generate a smooth AC output voltage by comparing a sine wave with a carrier wave

C. To convert DC voltage directly into DC current

D. To measure the frequency of an AC signal

Solution

1. Step 1: Understand SPWM function

   SPWM uses a sine wave and a carrier wave to create a smooth AC output voltage.

2. Step 2: Compare options with SPWM purpose

   Only To generate a smooth AC output voltage by comparing a sine wave with a carrier wave correctly describes SPWM's role in generating AC output by wave comparison.

3. Final Answer:

   To generate a smooth AC output voltage by comparing a sine wave with a carrier wave -> Option B

4. Quick Check:

   SPWM creates smooth AC output = To generate a smooth AC output voltage by comparing a sine wave with a carrier wave [OK]

Hint: SPWM = sine wave compared with carrier wave for AC output [OK]

Common Mistakes:

• Confusing SPWM with DC-DC conversion
• Thinking SPWM stores energy
• Mixing SPWM with measurement tools

2. Which waveform is used as the carrier signal in the Sinusoidal PWM (SPWM) technique?

easy

A. Triangular wave

B. Square wave

C. Sine wave

D. Sawtooth wave

Solution

1. Step 1: Identify carrier waveform in SPWM

   SPWM compares a sine wave with a triangular carrier wave to generate pulses.

2. Step 2: Match carrier waveform to options

   Only the triangular wave is the carrier signal used in SPWM.

3. Final Answer:

   Triangular wave -> Option A

4. Quick Check:

   Carrier wave in SPWM = Triangular wave [OK]

Hint: Carrier in SPWM is always a triangular wave [OK]

Common Mistakes:

• Choosing sine wave as carrier instead of modulating signal
• Confusing square wave with carrier
• Selecting sawtooth wave incorrectly

3. In SPWM, if the amplitude of the sine reference wave is increased while keeping the carrier frequency constant, what happens to the output voltage?

medium

A. Output voltage decreases

B. Output voltage remains the same

C. Output voltage increases

D. Output voltage becomes zero

Solution

1. Step 1: Understand effect of sine amplitude in SPWM

   Increasing sine amplitude increases the modulation index, which raises output voltage.

2. Step 2: Analyze options based on modulation index effect

   Only Output voltage increases correctly states output voltage increases with sine amplitude.

3. Final Answer:

   Output voltage increases -> Option C

4. Quick Check:

   Sine amplitude up -> output voltage up [OK]

Hint: Higher sine amplitude means higher output voltage [OK]

Common Mistakes:

• Assuming output voltage decreases with sine amplitude
• Thinking output voltage stays constant
• Confusing frequency effects with amplitude effects

4. A student implemented SPWM but noticed the output waveform is distorted and not smooth. Which of the following is the most likely cause?

medium

A. Using a square wave instead of a triangular carrier wave

B. Using a triangular carrier wave with frequency much higher than sine wave

C. Using a sine wave amplitude equal to zero

D. Using a sine wave with too low frequency compared to carrier wave

Solution

1. Step 1: Identify correct carrier waveform for smooth SPWM

   SPWM requires a triangular carrier wave; using a square wave distorts output.

2. Step 2: Evaluate options for distortion causes

   Only Using a square wave instead of a triangular carrier wave mentions wrong carrier waveform causing distortion.

3. Final Answer:

   Using a square wave instead of a triangular carrier wave -> Option A

4. Quick Check:

   Wrong carrier wave -> distorted output [OK]

Hint: Carrier must be triangular, not square, for smooth SPWM [OK]

Common Mistakes:

• Ignoring carrier waveform type
• Confusing frequency effects with waveform shape
• Assuming zero amplitude sine wave causes distortion

5. In an SPWM inverter controlling an AC motor, if the carrier frequency is increased while keeping the sine wave frequency and amplitude constant, what is the expected effect on the motor's performance?

hard

A. Motor speed increases significantly

B. Motor overheats immediately

C. Motor torque drops to zero

D. Output voltage quality improves, reducing motor vibration

Solution

1. Step 1: Understand carrier frequency effect in SPWM

   Increasing carrier frequency improves output waveform quality by producing more pulses per cycle.

2. Step 2: Relate waveform quality to motor performance

   Better waveform quality reduces motor vibration and noise, improving performance without changing speed.

3. Final Answer:

   Output voltage quality improves, reducing motor vibration -> Option D

4. Quick Check:

   Higher carrier frequency -> better voltage quality -> less vibration [OK]

Hint: Higher carrier frequency means smoother output, less motor vibration [OK]

Common Mistakes:

• Assuming motor speed changes with carrier frequency
• Thinking torque drops to zero
• Believing motor overheats immediately