Inverter Phase Modulation With Offset Compensation for Delay Reduction
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Solution Overview
Problem
Existing motor drive systems experience delays in voltage reference utilization due to sequential execution of current regulator and modulation routines, leading to overshoot and torque ripple, which can be mitigated by increasing switching frequency or using expensive hardware, but these solutions introduce additional drawbacks.
Innovation Solution
A method that allows for simultaneous execution of current regulator and modulation routines within the same switching period, using standard transducers and maintaining balanced three-phase voltage by determining and applying offset values to compensate for phase voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sequential execution of current regulator and modulation routines is used, then device complexity is reduced, but delay in voltage reference utilization increases causing overshoot and torque ripple
Solution Approach 1:
The modulation routine is executed preliminarily using voltage reference data from the previous switching period to generate switching signals for the current period. This preliminary execution eliminates the delay caused by sequential execution, as the modulation is already prepared before the current regulator completes its calculation. The system uses predicted or previously calculated voltage reference values to maintain continuous control without waiting for the current regulator to finish.
Solution Approach 2:
The system dynamically adapts the execution timing and data sources of the modulation routine based on the completion status of the current regulator. When the current regulator completes early, the newly calculated voltage reference is immediately utilized. When it completes late, the system seamlessly switches to using previous period data. This dynamic adaptation allows the system to maintain optimal performance across varying operating conditions without fixed sequential constraints.
2Loss of time
If increasing switching frequency is used to reduce delay, then voltage reference utilization delay is reduced, but power losses and device complexity increase
Solution Approach 1:
The modulation routine executes preliminarily using previously available voltage reference data before the current regulator completes its calculation. This approach eliminates the need to increase switching frequency to reduce delay, as the modulation is already prepared in advance using available data from the previous switching period, thereby avoiding additional switching losses.
3Speed
If using voltage reference from previous switching period is used, then continuous voltage control is maintained, but voltage balance between phases deteriorates
Solution Approach 1:
The system applies asymmetric offset compensation to different phases based on which voltage reference data is being used. When using previous period voltage reference data, specific phases receive offset adjustments to compensate for the delay-induced imbalance. The offset values are calculated to counteract the differential delay effects, restoring symmetry to the three-phase voltage outputs despite the asymmetric data timing.
Solution Approach 2:
The system implements feedback mechanisms to detect and correct voltage balance deviations caused by using previous period voltage reference data. Offset values are calculated based on the difference between current and previous voltage reference values, and this feedback is applied to restore phase balance. The feedback loop continuously monitors and adjusts the offset compensation to maintain voltage symmetry.
Data Source
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AI summary
A power converter is configured to measure an output current and to determine a multiphase voltage reference as a function of the output current. Within the same switching period the voltage reference is determined, a modulation routine determines a modulation index for each phase of the output voltage. In some instances, one or more phases must start modulation during the switching period before the new modulation index is determined. The modulation routine stores the value of the modulation index generated from the prior switching period and uses the stored value when a new value is not yet ready. An offset value for the phase voltage which used a modulation index from the prior switching period is determined in order to compensate the phase voltages of the other phases and to maintain a desired line-to-line voltage output from the power converter.