Synchronous Motor Rotor Position Sensing With Opposite Voltage Pulses
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Solution Overview
Problem
Existing methods for determining the initial rotor position of synchronous motors, particularly permanent magnet synchronous motors (PMSMs), face challenges such as temporary rotation reversal and vibrations during start-up, especially when using sensorless closed-loop control systems, as they require large current pulses that induce noise and affect accuracy.
Innovation Solution
Applying pairs of voltage vector pulses with equal amplitudes but opposite polarities at pre-set motor angles to determine the initial rotor position based on the largest sum of stator currents or the change from negative to positive current, allowing for accurate position detection without rotor rotation and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large current pulses are applied to determine initial rotor position, then position detection capability is improved, but noise and chatter increase
Solution Approach 1:
The patent applies preliminary anti-action by using opposite polarity voltage pulses to counteract the harmful effects of large current pulses. The first pulse excites the stator winding to detect rotor position, while the second pulse with opposite polarity cancels out the residual current and reduces noise and chatter, thereby eliminating the harmful effects while maintaining position detection capability
Solution Approach 2:
The patent converts the harmful large current pulses into a beneficial detection mechanism. By applying voltage pulses that create controlled current flow, the system uses the resulting magnetic field interaction to detect rotor position. The opposite polarity second pulse then eliminates the harmful residual effects, transforming the potentially harmful large currents into a useful position sensing tool
2Speed
If open-loop start-up method with ramped current is used, then motor can start from standstill, but temporary rotation reversal may occur
Solution Approach 1:
The patent applies preliminary action by determining the initial rotor position before starting motor rotation. By detecting the rotor's starting position using voltage pulses and analyzing current responses, the system prepares the control algorithm with accurate position information, enabling smooth transition to closed-loop control and preventing rotation reversal during start-up
Solution Approach 2:
The patent uses feedback by continuously monitoring the current responses to applied voltage pulses and using this information to determine rotor position. The system measures the actual current flow and uses this feedback to calculate the rotor angle, ensuring accurate position detection and enabling stable start-up without rotation reversal
3Device complexity
If sensorless closed-loop control is used, then system complexity is reduced, but position estimation accuracy deteriorates at low speed
Solution Approach 1:
The patent applies periodic action by using periodic voltage pulses at predetermined motor angles to actively probe rotor position. Instead of relying solely on continuous back-emf measurement, the system periodically injects test pulses and measures current responses, creating a periodic position detection mechanism that works effectively at low speeds while maintaining sensorless operation
Solution Approach 2:
The patent uses parameter changes by varying the voltage pulse amplitude, frequency, and timing to optimize position detection at different operating conditions. The system adjusts the excitation parameters based on motor speed and load conditions, improving position estimation accuracy across the entire operating range while maintaining simple sensorless control architecture
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method improves the accuracy of initial rotor position determination, reduces noise and chatter, and enables smooth start-up of synchronous motors without rotor reversal, enhancing the reliability of sensorless closed-loop control systems.
Implementation Method 1
When three-phase electric conductors are placed in certain geometrical positions, which means at a certain angle from one another, an electrical field is generated. The rotating magnetic field rotates at a certain speed known as the synchronous speed. If a permanent magnet or electromagnet is present in this rotating magnetic field, the magnet is magnetically locked with the rotating magnetic field
Implementation Method 2
A permanent magnet motor uses permanent magnets the rotor to provide a constant magnetic flux which has a sinusoidal back-electromotive force (emf) signal
Data Source
AI summary
Described is a method of determining an initial rotor position on start-up of a synchronous motor. The method comprises applying at each of a plurality of pre-set motor angles a pair of voltage vector pulses, the pair of voltage vector pulses comprising a first and second pulses, each having the same amplitude but opposite polarities, the second pulse being applied immediately or near immediately after the first pulse. The method includes determining the stator current responses to said pairs of applied voltage vector pulses at said plurality of pre-set motor angles. Then, the initial rotor position can be determined from either of a stator angle corresponding to a pair of vector voltage pulses resulting in (a) a largest sum of stator currents or (b) where the sum of stator currents changes from a negative to a positive motor angle.