PMSM Current Sensor Balancing via Shoot-Through Sampling
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Solution Overview
Problem
Existing methods for balancing scaling errors in multiple current sensors for three-phase inverter-PMSM control face challenges in eliminating sampling dead zones and optimizing direct current voltage utilization, leading to torque fluctuations and current distortion.
Innovation Solution
The method involves setting an impedance network between the DC power supply and the three-phase inverter, using shoot-through vectors for current sampling, and calculating correction coefficients to balance scaling errors, thereby eliminating sampling dead zones and improving voltage utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current sampling methods are used in three-phase inverter-PMSM control, then the control system operates with standard current sensors, but sampling dead zones occur in high modulation regions leading to torque fluctuations and current distortion
Solution Approach 1:
The patent applies periodic shoot-through vectors at specific intervals (e.g., every 6 electrical degrees) to create additional current sampling opportunities. This periodic injection of shoot-through vectors transforms the single sampling window into multiple sampling windows throughout each PWM cycle, eliminating the sampling dead zones that occur in conventional continuous modulation methods.
Solution Approach 2:
The patent changes the modulation parameter by introducing shoot-through vectors that temporarily alter the inverter switching states. This parameter change creates distinct current sampling moments during the shoot-through periods, allowing accurate current measurement without restricting the overall voltage utilization of the inverter system.
2Ease of operation
If scaling errors of multiple current sensors are not balanced, then the control system uses all available current sensors, but torque fluctuations occur due to unbalanced scaling errors
Solution Approach 1:
The patent implements a feedback mechanism where current sampling errors are detected during shoot-through vectors, and correction coefficients are calculated and applied to balance the scaling errors of multiple current sensors. This feedback loop continuously monitors and corrects sensor inaccuracies, eliminating torque fluctuations caused by unbalanced scaling errors while maintaining system simplicity.
Solution Approach 2:
The patent replaces the need for complex mechanical sensor calibration with an electrical correction approach. By using mathematical correction coefficients derived from shoot-through vector sampling, the system electronically compensates for sensor scaling errors without requiring physical sensor adjustment or replacement.
3Measurement precision
If shoot-through vectors are used for current sampling, then additional sampling windows are provided, but the DC power supply may experience short-circuit conditions
Solution Approach 1:
The patent introduces an impedance network as an intermediary element between the DC power supply and the inverter. This impedance network acts as a protective mediator that limits current during shoot-through vectors, preventing direct short-circuit conditions while still allowing the shoot-through vectors to function for current sampling purposes.
Solution Approach 2:
The patent applies beforehand cushioning by pre-installing the impedance network in the DC power supply path before any shoot-through vectors are executed. This protective measure is in place beforehand to cushion against potential short-circuit currents, ensuring that even if shoot-through vectors cause excessive current flow, the impedance network will limit the damage to the DC power supply.
Data Source
AI summary
The invention discloses a control method for balancing scaling errors of multiple current sensors for PMSM. An impedance network is set between a direct current power supply and a three-phase inverter connected to a PMSM to avoid positive and negative poles of the direct current power supply being short-circuited under actions of shoot-through vectors. Under actions of two shoot-through vectors in a PWM cycle, three-phase current sensors are used to respectively sample the sum of currents in each branch of three-phase output branches of the three-phase inverter and a branch of the same bridge arm of the three-phase inverter, according to the sampled currents, operating to obtain the relationship between the scaling error coefficients of the three-phase current sensors. Then, correction coefficients are calculated. The correction of the scaling errors of the current sensors is implemented using correction coefficient feedback control.