Sensorless Synchronous Motor Drive Using Neutral Point Potential
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Solution Overview
Problem
Existing sensor-less control methods for permanent magnet motors face challenges in low-speed operation due to reduced sensitivity and noise interference, particularly in non-salient rotor structures, and incur increased harmonic losses and switching losses when attempting to improve position estimation.
Innovation Solution
A driving system for synchronous motors that shifts the timing of inverter switch states to generate additional voltage vectors, allowing for precise estimation of rotor position using neutral point potentials without increasing switching frequency, thereby maintaining sinusoidal current drive at low speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If radio frequency wave is applied to detect rotor position, then position detection sensitivity is improved, but rotation pulsation, vibration, noise, and harmonic loss increase
Solution Approach 1:
The patent changes the detection parameter from current harmonics (caused by RF waves) to neutral point potential. This parameter change allows position detection without injecting RF waves, thereby avoiding rotation pulsation, vibration, noise, and harmonic loss while maintaining position detection sensitivity.
Solution Approach 2:
The patent introduces neutral point potential as an intermediary measurement point. By detecting the neutral point potential during PWM switching, the system obtains rotor position information without directly injecting RF waves into the motor, thus avoiding the harmful effects associated with RF wave injection.
2Loss of information
If induced voltage detection method is used for sensor-less control, then position information can be obtained, but sensitivity is reduced and position information may be buried in noise at low speeds
Solution Approach 1:
The patent performs position estimation by detecting neutral point potential during the PWM switching process itself, before the motor actually moves. This preliminary detection during the switching interval allows position information to be obtained even when the motor is stationary or moving at extremely low speeds, avoiding the noise burial problem of induced voltage methods.
3Loss of energy
If neutral point potential detection is performed without shifting PWM timing, then switching losses increase, but position estimation precision can be maintained
Solution Approach 1:
The patent dynamically adjusts the PWM switching timing to create specific switch states that enable neutral point potential detection. By shifting the PWM timing, the system creates detection opportunities during normal switching operations, allowing position estimation without requiring additional switching cycles or increasing overall switching frequency, thus maintaining energy efficiency.
4Measurement precision
If additional voltage vectors are generated by shifting switch states, then position detection precision is improved, but device complexity increases
Solution Approach 1:
The patent makes the PWM inverter perform multiple functions: both motor drive and position detection. By strategically timing the PWM switching, the same inverter circuit generates additional voltage vectors that serve dual purposes of motor control and rotor position estimation, eliminating the need for separate detection hardware or complex additional control circuits.
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
Enables efficient sensor-less driving with sinusoidal current at extremely low speeds, reducing switching losses and improving position detection precision without the need for additional hardware or complex control systems.
Implementation Method 1
a period of one cycle of pulse width modulation of an inverter, three or four types of switch states of which output voltage of the inverter is not zero vector are generated by shifting timing of switching of each phase
Implementation Method 2
a method for directly detecting induced voltage (speed electromotive force) induced when the rotor of the permanent magnet motor rotates
Implementation Method 3
obtain position information by detecting 'neutral point potential' which is a potential at the connection point of three-phase stator winding
Data Source
Figure 1
Figure 2(a)~3(b)
Figure 4(a)~4(e)
AI summary
A position sensor-less driving method is provided that can drive rotation speed/torque control of a permanent magnet motor using an inverter with an ideal sinusoidal current with the minimum number of switching, and can drive at a speed as low as an extremely low speed region close to zero speed. A neutral point potential of a permanent magnet motor 4 is detected in synchronization with PWM waveform of the inverter. A rotor position of the permanent magnet motor 4 is estimated from change of the neutral point potential. When the neutral point potential is detected, timing of each phase of the PWM waveform is shifted to generate three or four types of switch states of which output voltage of the inverter is not zero vector, and neutral point potentials in at least two types of switch states among them are sampled, whereby rotor position of the three-phase synchronous motor is estimated.