Sensorless Synchronous Motor Control via Neutral Point Potential
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Solution Overview
Problem
Existing motor drive techniques for permanent magnet synchronous motors face challenges in low-speed operation due to high current harmonics and torque pulsation, and require manual adjustment of thresholds and neutral point potentials, making them unsuitable for mass-produced products and inexpensive microcomputers.
Innovation Solution
A synchronous motor control apparatus that automatically adjusts magnetic saturation characteristics and three-phase unbalance by using a Y-connected three-phase stator wiring, applying a pulse-shaped voltage to the rotor to acquire neutral point potential, and storing this value in a nonvolatile memory for position estimation, enabling high-torque sinusoidal wave drive from zero-speed without a rotor position sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sensorless control is used in low-speed range, then cost reduction and downsizing are achieved, but controllability and efficiency deteriorate due to low speed induced voltage
Solution Approach 1:
The invention changes the detection parameter from speed-induced voltage to magnetic saturation induced voltage, which can be observed even in stop state and low-speed range. This parameter change enables sensorless control to work effectively at low speeds where traditional speed-induced voltage methods fail.
Solution Approach 2:
The invention replaces the mechanical position sensor with a sensorless detection system that uses magnetic saturation induced voltage. This substitution eliminates the need for physical sensors while maintaining controllability in low-speed range through electrical measurement of the open-phase voltage.
2Extent of automation
If 120-degree conductive drive is used to observe magnetic saturation induced voltage, then position sensorless control is achieved, but current harmonics and torque pulsation increase
Solution Approach 1:
The invention performs preliminary detection of magnetic saturation induced voltage to determine rotor position, then uses this information to switch to optimal 180-degree conductive drive patterns. This preliminary action enables the system to avoid harmful current harmonics while maintaining sensorless operation.
Solution Approach 2:
The invention dynamically adjusts the conductive drive pattern from fixed 120-degree to variable 180-degree conduction based on detected rotor position. This dynamic adjustment optimizes current waveform to reduce harmonics and torque pulsation while maintaining effective sensorless control.
3Measurement precision
If manual adjustment of threshold and neutral point potential is performed, then position estimation accuracy is improved, but adjustment work and system complexity increase
Solution Approach 1:
The invention enables the system to automatically determine optimal threshold values and neutral point potentials through self-diagnosis routines. The controller performs automatic adjustment without manual intervention, reducing system complexity and adjustment work while maintaining high position estimation accuracy.
Solution Approach 2:
The invention implements feedback mechanisms where the controller continuously monitors magnetic saturation induced voltage and automatically adjusts threshold parameters based on detected rotor position. This feedback-based automatic adjustment eliminates manual calibration while ensuring accurate position estimation.
4Loss of information
If pulse voltage is applied to two phases to detect open phase voltage, then rotor position information is acquired, but the system requires complex phase switching control
Solution Approach 1:
The invention makes the inverter switches serve multiple functions: they perform both the detection function (by creating open-phase conditions for voltage measurement) and the drive function (by controlling motor operation). This multi-functionality simplifies the overall control system while enabling rotor position detection without additional sensors.
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 solution allows for sensorless drive in the low-speed range with reduced vibration and noise, enabling high-torque operation using a simple adjustment algorithm and inexpensive microcomputers, and accurately estimating rotor position for improved motor control.
Implementation Method 1
An induced voltage in the open phase is generated depending on a position of the rotor of the PM motor... The induced voltage is generated by a slight change in inductance in the motor due to a relationship between a permanent magnetic flux attached on the rotor of the PM motor and a conductive current by the pulse voltage, and can be observed also in the stop state. This is denoted as 'magnetic saturation induced voltage.'
Implementation Method 2
a neutral point potential of the Y-connected three-phase stator wiring is applied thereby to detect a rotor phase of the rotor
Implementation Method 3
a relationship between a permanent magnetic flux attached on the rotor of the PM motor and a conductive current by the pulse voltage
Data Source
AI summary
A method for detecting a potential (Vn) includes stator wirings in a Y connection, and automatically adjusting a relationship with a position of a rotor as a system for realizing rotor position-sensorless stable drive of an AC motor where the three-phase stator wirings are in Y connection in the stop and low-speed ranges. A synchronous motor control apparatus includes a three-phase synchronous motor in which three-phase stator wirings are in a Y connection, and an inverter for driving the motor, wherein the synchronous motor is DC-conducted thereby to move a rotor to a predetermined position, and is applied with a pulse-shaped voltage from the inverter in the moved state so that a neutral point potential as potential (Vn) of the Y connection point is acquired when the pulse voltage is applied, thereby driving the synchronous motor based on the acquired value.