Electric Motor Magnetic Field Detection Using Pulse-Width Measurement
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Solution Overview
Problem
Sensorless motor systems face challenges in detecting rotor location at low speeds or when stationary, requiring complex and costly hardware and software, leading to delayed starting and instability under viscous loads and load fluctuations.
Innovation Solution
A method using a three-phase half bridge inverter circuit with stored conduction patterns and a comparator to detect magnetic field location by measuring pulse-width times and peak currents, allowing for simple and low-cost closed-loop control of 120° rectangular-wave conduction to start the motor from a stationary state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a setup starting manner with stationary excitation is used to locate the rotor, then the rotor location can be detected at zero speed, but it requires large current, takes long time to locate, and delays motor starting
Solution Approach 1:
The patent applies periodic high-frequency voltage injection to the motor phases and measures the resulting current responses at different excitation states. By periodically switching between different phase excitations and measuring current amplitudes, the system determines rotor location without requiring continuous large current application, thus reducing starting time while maintaining detection accuracy.
Solution Approach 2:
The patent changes the injection voltage frequency to a high frequency range and measures current response amplitudes at different excitation states. By utilizing the relationship between injection voltage, current response amplitude, and rotor position, the system achieves rapid location detection without the time-consuming stationary excitation method.
2Measurement precision
If a high frequency wave injection manner is used to detect rotor location, then location can be detected at zero speed, but three current sensors, high-speed A/D converter, and complex mathematical model are required
Solution Approach 1:
The patent extracts only the essential measurement requirement by using a single current sensor to measure current amplitudes during high-frequency voltage injection. Instead of requiring three current sensors and high-speed A/D converters, the invention simplifies the detection circuit to basic components while maintaining the ability to detect rotor location through amplitude comparison at different excitation states.
Solution Approach 2:
The patent replaces expensive, complex detection equipment (three current sensors, high-speed A/D converter, complex mathematical models) with simple, low-cost components (single current sensor, basic microcontroller). The system uses straightforward amplitude comparison logic instead of complex mathematical modeling, significantly reducing hardware and software complexity.
3Ease of manufacture
If conventional sensorless driving manner is used, then the motor structure is compact and low-cost, but the rotor cannot be started when speed is zero because no voltages are induced
Solution Approach 1:
The patent applies preliminary high-frequency voltage injection to the motor phases before正式启动 the motor. By injecting high-frequency voltages and measuring current responses at different excitation states, the system determines the initial rotor location. This preliminary action enables the motor to be started from zero speed while maintaining the compact, sensorless structure.
Solution Approach 2:
The patent introduces high-frequency voltage injection as an intermediary mechanism to enable zero-speed operation. The high-frequency injection serves as a mediator that provides the necessary voltage excitation and location information without requiring the motor to be already rotating, thus bridging the gap between stationary state and rotational operation.
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 instantaneous detection of permanent-magnet field location, reducing production costs and measurement time, improving motor starting reliability, and allowing for precise control and operation in various applications, including reciprocating mechanisms.
Implementation Method 1
comparator means for comparing a detecting voltage corresponding to the coil current detected by the current detecting means with a reference voltage corresponding to a current threshold capable of detecting magnetic resistance change caused by magnetic field polarity
Implementation Method 2
timer means for measuring a pulse-width time from starting to apply sensing conduction to the three-phase coils until the coil current detected by the comparator means reaches the current threshold
Implementation Method 3
a conduction-off step in which all output of the output means to the three-phase coils is blocked immediately before applying the sensing conduction and stored energies stored in all of the coils are released so as to produce a period of a zero current state where the coil current is zero
Data Source
AI summary
The present invention addresses the problem of providing a method for detecting a magnetic field location in an electric motor, said method making it possible to lower costs using simple hardware and software, and instantaneously detect permanent-magnet field location. As a means for solving said problem, an MPU (51) sequentially selects one from six conduction patterns using a phase at which one-phase conduction occurs without branching at a neutral point among three-phase coils as a phase to be measured, applies a sensing current to the three-phase coils, and uses a timer (56) to measure a pulse-width time until the coil current detected by a current sensor (53) reaches a current threshold, and stores the same as measurement data. Following the forward-direction conduction pattern, a reverse-direction conduction pattern is selected and a current is applied to the phase to be measured, after which the same conduction pattern is repeated for the remaining two phases, whereby a current is applied for all six conduction patterns. Conduction times are stored as measurement data, and the permanent-magnet field location are identified from the field location information corresponding to the conduction pattern having the shortest conduction time among the measurement data of the conduction times corresponding to the six conduction patterns.