Center-Aligned PWM Short Pulse Extension
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Solution Overview
Problem
In conventional PWM motor control schemes, short pulses occur when the phase duty cycle approaches 100%, leading to a low-side on-time of zero, which is not sufficient to meet the minimum on-time requirement, causing inefficiencies in motor control, particularly in 48-volt systems used in hybrid electric vehicles.
Innovation Solution
A microcontroller-controlled system that extends the duty cycle of the low-side switch into the next period to ensure a minimum on-time duration by outputting a PWM signal that is center-aligned to the off-time, preventing short pulses and maintaining deterministic PWM control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a buffered center-aligned PWM scheme is used to create an effective phase duty cycle, then the PWM control accuracy is improved, but short pulses occur on the low-side when the phase duty cycle approaches 100%
Solution Approach 1:
The patent applies preliminary action by detecting when the low-side on-time would become zero before it actually occurs, and proactively extending the pulse into the next period to ensure the minimum on-time requirement is met. This prevents the short pulse problem before it happens while maintaining the center-aligned PWM scheme.
Solution Approach 2:
The patent introduces dynamic adjustment to the PWM duty cycle by extending the low-side pulse into the next period when needed. This dynamic modification ensures the pulse duration always meets the minimum on-time requirement while maintaining the overall center-aligned PWM control structure.
2Stability of the object's composition
If the low-side PWM is center-aligned to the off-time, then the PWM signal symmetry is improved, but the low-side on-time becomes zero when the phase duty cycle is high
Solution Approach 1:
The patent detects in advance when the center-aligned PWM would result in zero low-side on-time and proactively extends the pulse into the next period. This preliminary intervention maintains the symmetric center-aligned structure while ensuring adequate pulse duration.
Solution Approach 2:
By extending the low-side pulse into the next PWM period, the patent ensures continuous useful action is maintained on the low-side switch, preventing gaps or zero-duration pulses that would occur with strict center-alignment at high duty cycles.
3Reliability
If deadtime is applied by delaying the start of the end pulse, then the switching safety is improved, but the pulse duration is shortened below the minimum on-time
Solution Approach 1:
The patent proactively extends the pulse duration into the next period before the deadtime reduction can cause the pulse to fall below the minimum on-time requirement. This preliminary extension compensates for the deadtime effect and ensures adequate pulse duration is maintained.
Solution Approach 2:
The patent applies beforehand cushioning by adding extra duration to the pulse in advance, creating a buffer that compensates for the duration reduction caused by deadtime application. This ensures the pulse always meets the minimum on-time requirement despite deadtime delays.
Data Source
AI summary
A system includes an electric motor, at least one pair of high side and low side switches connected to the electric motor, and a microcontroller connected to the high side and low side switches. At least the low side switches have a minimum on-time requirement. The microcontroller controls the switches by outputting a pulse-width modulation (PWM) signal. At least the PWM signal outputted to the low side switch is center-aligned to the off-time. When a request is made to the microcontroller resulting in a low side on-time of zero with a previous duty cycle request that is greater than a predetermined threshold, the microcontroller is constructed and arranged to extend the duty cycle of the low side switch of the at least one pair of switches into the next period to a duration of the required minimum on-time.