The hysteresis control technique keeps the output current within a set band by switching ON or OFF when the current crosses upper or lower limits.
Execution Sample
Power Electronics
ref_current = 5.0
band = 0.5
upper_limit = ref_current + band
lower_limit = ref_current - band
if current > upper_limit:
switch = 'OFF'elif current < lower_limit:
switch = 'ON'
This code checks if the current is outside the hysteresis band and switches the device ON or OFF accordingly.
Analysis Table
Step
Measured Current (A)
Condition
Action
Switch State
1
4.6
4.6 > 5.5? No; 4.6 < 4.5? No
No switch change
Maintains previous state
2
5.6
5.6 > 5.5? Yes
Switch OFF
OFF
3
5.3
5.3 > 5.5? No; 5.3 < 4.5? No
No switch change
OFF
4
4.4
4.4 > 5.5? No; 4.4 < 4.5? Yes
Switch ON
ON
5
4.8
4.8 > 5.5? No; 4.8 < 4.5? No
No switch change
ON
6
5.7
5.7 > 5.5? Yes
Switch OFF
OFF
7
5.0
5.0 > 5.5? No; 5.0 < 4.5? No
No switch change
OFF
8
4.3
4.3 > 5.5? No; 4.3 < 4.5? Yes
Switch ON
ON
9
4.9
4.9 > 5.5? No; 4.9 < 4.5? No
No switch change
ON
10
5.6
5.6 > 5.5? Yes
Switch OFF
OFF
💡 Process repeats continuously to keep current within hysteresis band.
State Tracker
Variable
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
Step 8
Step 9
Step 10
Measured Current (A)
4.6
5.6
5.3
4.4
4.8
5.7
5.0
4.3
4.9
5.6
Switch State
ON (assumed)
OFF
OFF
ON
ON
OFF
OFF
ON
ON
OFF
Key Insights - 3 Insights
Why does the switch not change state when the current is within the hysteresis band?
Because the current is between the upper and lower limits, the control maintains the previous switch state to avoid rapid switching, as shown in steps 1, 3, 5, 7, and 9 in the execution_table.
What happens when the current exceeds the upper limit?
The switch turns OFF immediately to reduce the current, as seen in steps 2, 6, and 10 where the current is above 5.5A and the switch changes to OFF.
Why is there a lower limit in hysteresis control?
The lower limit prevents the switch from turning ON too early, avoiding rapid switching. When current falls below 4.5A, the switch turns ON, as in steps 4 and 8.
Visual Quiz - 3 Questions
Test your understanding
Look at the execution_table at step 4. What is the switch state after the action?
AON
BOFF
CNo change
DUndefined
💡 Hint
Refer to the 'Switch State' column at step 4 in the execution_table.
At which step does the current first exceed the upper limit causing the switch to turn OFF?
AStep 1
BStep 4
CStep 2
DStep 5
💡 Hint
Check the 'Condition' column for current > 5.5 in the execution_table.
If the hysteresis band was increased to 1.0 A, how would the switch behavior change at step 2?
ASwitch would still turn OFF
BSwitch would remain ON
CSwitch would toggle ON and OFF rapidly
DSwitch state would be undefined
💡 Hint
Look at the 'upper_limit' calculation and compare with current at step 2 in variable_tracker.
Concept Snapshot
Hysteresis control keeps output current within a band around a reference.
Switch turns ON if current < lower limit.
Switch turns OFF if current > upper limit.
Prevents rapid switching by allowing a band gap.
Common in power electronics for stable current control.
Full Transcript
Hysteresis control technique works by measuring the output current and comparing it to a reference current with an allowed band. If the current goes above the upper limit, the switch turns OFF to reduce current. If it falls below the lower limit, the switch turns ON to increase current. When the current is within the band, the switch state remains unchanged to avoid rapid switching. This cycle repeats continuously to maintain current stability. The execution table shows step-by-step current measurements, conditions checked, actions taken, and switch states. Key moments clarify why the switch does not change state inside the band and the role of upper and lower limits. The visual quiz tests understanding of switch states at specific steps and effects of changing the band size.
Practice
(1/5)
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
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.
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.
Final Answer:
To keep signals within set upper and lower limits by switching devices ON or OFF -> Option C
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
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.
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.
Final Answer:
Switch ON when signal is below lower limit, switch OFF when above upper limit -> Option A
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
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.
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.
Final Answer:
Keep the device ON until current exceeds 5A -> Option D
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
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.
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.
Final Answer:
Switch ON and OFF limits do not match hysteresis band -> Option A
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
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.
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.
Final Answer:
Switching frequency increases, causing higher losses and possible instability -> Option B
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
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