Hysteresis control technique in Power Electronics - Mini Project: Build & Apply

Hysteresis Control Technique

📖 Scenario: You are working on a simple power electronics project where you need to control the output current of an inverter. To keep the current within a safe range, you will use the hysteresis control technique.This technique helps maintain the current close to a reference value by switching the inverter output on or off depending on the current's position relative to upper and lower limits.

🎯 Goal: Build a step-by-step understanding of the hysteresis control technique by defining the reference current, setting hysteresis band limits, applying the control logic, and completing the control decision process.

📋 What You'll Learn

Define a reference current value

Set upper and lower hysteresis band limits

Implement the hysteresis control logic to decide switching

Complete the control decision with output switching states

💡 Why This Matters

🌍 Real World

Hysteresis control is widely used in power electronics to maintain current or voltage within safe limits, improving device reliability and efficiency.

💼 Career

Understanding hysteresis control is essential for engineers working with inverters, motor drives, and power converters in industries like renewable energy, automotive, and manufacturing.

1

Define the reference current

Create a variable called i_ref and set it to the exact value 10.0 representing the reference current in amperes.

Power Electronics

# Create the reference current variable i_ref
# Your code here

Hint

The reference current is the target current you want to maintain using hysteresis control.

2

Set hysteresis band limits

Create two variables called upper_limit and lower_limit. Set upper_limit to i_ref + 0.5 and lower_limit to i_ref - 0.5 to define the hysteresis band around the reference current.

Power Electronics

i_ref = 10.0
# Define upper_limit and lower_limit for hysteresis band
# Your code here

Hint

The hysteresis band creates a range around the reference current to decide when to switch the output.

3

Implement hysteresis control logic

Create a variable called i_actual and set it to 10.3 representing the measured current. Then write an if-else statement that sets a variable switch_state to "OFF" if i_actual is greater than upper_limit, and to "ON" if i_actual is less than lower_limit. If i_actual is within the band, keep switch_state unchanged and initialize it to "ON" before the conditions.

Power Electronics

i_ref = 10.0
upper_limit = i_ref + 0.5
lower_limit = i_ref - 0.5
# Define i_actual and hysteresis control logic
# Your code here

Hint

This logic turns the switch off if the current is too high, on if too low, and keeps it on if within limits.

4

Complete the hysteresis control decision

Add a final line that creates a variable called output_signal and sets it to 1 if switch_state is "ON", or 0 if switch_state is "OFF". Use a simple if-else statement for this.

Power Electronics

i_ref = 10.0
upper_limit = i_ref + 0.5
lower_limit = i_ref - 0.5
i_actual = 10.3
switch_state = "ON"
if i_actual > upper_limit:
    switch_state = "OFF"
elif i_actual < lower_limit:
    switch_state = "ON"
# Set output_signal based on switch_state
# Your code here

Hint

The output signal controls the inverter switch: 1 means switch on, 0 means switch off.

Practice

1. What is the main purpose of the hysteresis control technique in power electronics?

easy

A. To convert AC signals into DC signals

B. To increase the frequency of switching devices continuously

C. To keep signals within set upper and lower limits by switching devices ON or OFF

D. To measure the power consumption of a device

Solution

1. Step 1: Understand the role of hysteresis control

   Hysteresis control is designed to maintain a signal within a specific range by switching devices ON or OFF when the signal crosses set limits.

2. Step 2: Compare options with this role

   Only To keep signals within set upper and lower limits by switching devices ON or OFF describes this behavior correctly. Other options describe unrelated functions.

3. Final Answer:

   To keep signals within set upper and lower limits by switching devices ON or OFF -> Option C

4. Quick Check:

   Hysteresis control = signal limits control [OK]

Hint: Remember: hysteresis controls signal range by switching [OK]

Common Mistakes:

• Confusing hysteresis control with signal conversion
• Thinking it increases switching frequency continuously
• Assuming it measures power consumption

2. Which of the following correctly describes the switching action in hysteresis control?

easy

A. Switch ON when signal is below lower limit, switch OFF when above upper limit

B. Switch OFF when signal is below lower limit, switch ON when above upper limit

C. Switch ON and OFF randomly without limits

D. Switch ON only when signal equals the upper limit

Solution

1. Step 1: Recall hysteresis switching rules

   In hysteresis control, the device switches ON when the signal falls below the lower limit and switches OFF when it rises above the upper limit.

2. Step 2: Match options with this rule

   Switch ON when signal is below lower limit, switch OFF when above upper limit matches this exactly. Other options describe incorrect or random switching.

3. Final Answer:

   Switch ON when signal is below lower limit, switch OFF when above upper limit -> Option A

4. Quick Check:

   Switch ON below lower limit = correct switching [OK]

Hint: ON below lower limit, OFF above upper limit [OK]

Common Mistakes:

• Reversing ON and OFF conditions
• Assuming random switching
• Switching only at exact limits

3. Consider a hysteresis controller with upper limit 5A and lower limit 3A controlling current. If the current is 4A and rising, what will the controller do next?

medium

A. Ignore the current and maintain previous state

B. Switch OFF the device immediately

C. Switch ON the device immediately

D. Keep the device ON until current exceeds 5A

Solution

1. Step 1: Analyze current position relative to limits

   The current is 4A, which is between the lower limit (3A) and upper limit (5A), and it is rising.

2. Step 2: Apply hysteresis control logic

   The device remains ON until the current exceeds the upper limit (5A), then it switches OFF. Since current is rising but below 5A, device stays ON.

3. Final Answer:

   Keep the device ON until current exceeds 5A -> Option D

4. Quick Check:

   Current rising between limits = device stays ON [OK]

Hint: Device switches OFF only after exceeding upper limit [OK]

Common Mistakes:

• Switching OFF too early before upper limit
• Switching ON again unnecessarily
• Ignoring current trend

4. A hysteresis controller is designed with upper limit 10V and lower limit 8V. If the controller switches ON at 9V and OFF at 11V, what is the error in design?

medium

A. Switch ON and OFF limits do not match hysteresis band

B. Switching ON at 9V is correct

C. Switching OFF at 11V is within limits

D. No error, design is correct

Solution

1. Step 1: Compare given switching points with hysteresis limits

   The hysteresis band is between 8V (lower) and 10V (upper). The controller should switch ON at or below 8V and OFF at or above 10V.

2. Step 2: Identify mismatch in switching points

   Switching ON at 9V (above lower limit) and OFF at 11V (above upper limit) does not match the defined hysteresis band, causing incorrect control.

3. Final Answer:

   Switch ON and OFF limits do not match hysteresis band -> Option A

4. Quick Check:

   Switch points must match hysteresis limits [OK]

Hint: Switch points must align exactly with hysteresis limits [OK]

Common Mistakes:

• Ignoring mismatch in switching thresholds
• Assuming switching at any point is valid
• Confusing upper and lower limits

5. In a power converter using hysteresis control, if the hysteresis band is made very narrow, what is the likely effect on the switching frequency and system performance?

hard

A. System stops switching and remains fixed

B. Switching frequency increases, causing higher losses and possible instability

C. No change in switching frequency or performance

D. Switching frequency decreases, improving efficiency

Solution

1. Step 1: Understand effect of hysteresis band width

   A narrow hysteresis band means the signal crosses limits more frequently, causing the controller to switch ON and OFF more often.

2. Step 2: Analyze impact on switching frequency and performance

   Higher switching frequency leads to increased switching losses and can cause instability due to rapid switching.

3. Final Answer:

   Switching frequency increases, causing higher losses and possible instability -> Option B

4. Quick Check:

   Narrow band = more switching = losses [OK]

Hint: Narrow band means more switching, more losses [OK]

Common Mistakes:

• Assuming narrow band reduces switching frequency
• Thinking performance improves with narrow band
• Ignoring switching losses