Brushless PM Motor Control Using Phase Current Polarity Prediction
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Solution Overview
Problem
Brushless permanent magnet motors face challenges in accurately determining the timing of control signals for inverter switches due to switching dead time, which can lead to undesirable delays and impact motor performance, often requiring current sensors that increase component costs and complexity.
Innovation Solution
A method that monitors phase current in one winding to predict the polarity of current in another winding, allowing for the determination of control signal timing without direct measurement, thereby reducing the need for current sensors and compensating for switching dead time by advancing or retarding the control signal based on current direction and voltage vector considerations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sensors are installed in all phase windings to directly measure current for accurate control timing, then measurement precision is improved, but device complexity and component cost increase
Solution Approach 1:
The patent creates a virtual copy of the current measurement capability by predicting current polarity in unmeasured phases based on the measured phase's zero-crossing point. This prediction model allows the system to obtain current information for all phases without installing physical sensors in each phase, thereby reducing sensor quantity while maintaining control accuracy
Solution Approach 2:
The patent introduces the zero-crossing point detection as an intermediary mechanism. By detecting the zero-crossing point in one phase and using it to predict current polarity in other phases, the system mediates between limited sensor availability and comprehensive current knowledge required for accurate control timing
2Reliability
If switching dead time is increased to prevent short circuits in the inverter, then reliability is improved, but productivity decreases due to delayed voltage vector application
Solution Approach 1:
The patent performs preliminary determination of the correct voltage vector timing by predicting current polarity before the switching event occurs. This allows the control system to prepare and apply the appropriate voltage vector immediately after the mandatory dead time, minimizing the impact of dead time on overall productivity while maintaining safety
Solution Approach 2:
The patent dynamically adjusts the control strategy based on predicted current polarity. By determining whether current is flowing in positive or negative direction in each phase, the system can optimally select and time the application of voltage vectors, thereby reducing the effective impact of fixed dead time delays on motor performance
3Productivity
If switching dead time is reduced to improve voltage vector application timing, then productivity is improved, but reliability worsens due to increased short circuit risk
Solution Approach 1:
The system performs preliminary prediction of current polarity before switching occurs, enabling the control algorithm to determine the optimal timing for voltage vector application. This advance preparation allows the system to minimize dead time while ensuring that voltage vectors are applied at the most effective moment, thereby maintaining productivity without compromising reliability
Data Source
AI summary
A method of controlling a brushless permanent magnet motor having a plurality of phase windings and an inverter for applying voltage vectors to the plurality of the phase windings, the method including monitoring phase current flowing through a first phase winding to determine a zero-crossing point of the phase current flowing through the first phase winding. The method includes predicting a polarity of phase current flowing through a second phase winding based on the determined zero-crossing point of the phase current flowing through the first phase winding, and determining a timing of a control signal to control switches of the inverter to apply a voltage vector to the phase windings. The timing of the control signal is determined using the predicted polarity of phase current flowing through the second phase winding.