Rotor Position Detection Using Phase Voltage During Zero-Crossing
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Solution Overview
Problem
Existing methods for determining rotor position in permanent magnet synchronous motors (PMSM) face challenges at low speeds or standstill conditions due to low or zero back-EMF voltage amplitude, requiring additional sensors and increasing complexity and cost, while sensorless techniques struggle to accurately detect position without causing noise and vibrations.
Innovation Solution
A method using pulse width modulation (PWM) to generate sinusoidal phase currents, allowing for rotor position detection through phase voltage measurement by disconnecting a phase at zero current crossing, utilizing mutual inductance variations to determine rotor position without additional sensors, enabling accurate position detection at low speeds and reducing noise and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensorless back-EMF control technique is used to measure rotor position, then cost is reduced and reliability is improved by eliminating additional parts, but measurement precision deteriorates at low speed operation where back-EMF voltage amplitude is very low or zero
Solution Approach 1:
The patent changes the measurement parameter from back-EMF voltage (which is speed-dependent) to phase voltage during zero-current intervals (which is measurable at all speeds). By measuring phase voltage when phase current is zero, the system obtains rotor position information without relying on back-EMF amplitude, thus maintaining measurement precision at low speeds while keeping the system sensorless
Solution Approach 2:
The patent uses phase voltage measurement as an intermediary to indirectly determine rotor position. Instead of directly measuring back-EMF voltage which fails at low speeds, the system measures phase voltage during zero-current intervals and uses this intermediate measurement to calculate rotor position, bypassing the limitation of back-EMF-based direct measurement
2Measurement precision
If additional sensors and transducers are added to detect rotor position, then measurement precision is improved, but device complexity increases and reliability decreases due to additional failure points
Solution Approach 1:
The patent makes the motor's own phase windings serve dual purposes: both for generating motor torque and for sensing rotor position. By measuring phase voltage during zero-current intervals in the existing phase windings, the system obtains position information without needing separate sensing windings or external sensors, thus reducing device complexity while maintaining measurement precision
Solution Approach 2:
The patent makes the phase windings universal by having them perform both motor function (generating torque through current flow) and sensing function (providing position information through voltage measurement during zero-current intervals). This multi-functionality eliminates the need for separate sensing components, reducing device complexity while maintaining measurement capability
3Measurement precision
If current pulses are injected to detect rotor position at standstill, then measurement precision is improved at zero speed, but harmful factors increase due to acoustic noise and shaft vibrations
Solution Approach 1:
The patent inverts the conventional approach of injecting current pulses to create magnetic field for position detection. Instead, it applies voltage during zero-current intervals when the motor is already producing torque, utilizing the existing magnetic field and current-free periods to measure phase voltage and determine position, thereby avoiding the harmful effects of pulse injection while maintaining measurement precision
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 reliable rotor position detection at zero speed and low rotational speeds without additional sensors, improving motor control reliability and reducing noise and vibrations, while maintaining high motor torque during startup.
Implementation Method 1
Three phase currents flow through the motor windings... The phase currents create a rotating electro-magnetic field which causes angular motion of the rotor
Implementation Method 2
a measurement unit (14) for measuring a phase voltage value on a respective phase during a zero current crossing interval
Data Source
AI summary
A device for determining a rotor position in a polyphase electric motor has a power control unit for applying drive voltages according to a pulse width modulation scheme so as to synchronously drive the motor. A measurement unit is arranged for measuring a voltage value on a respective phase by determining a zero-crossing interval where the phase current is around zero, disconnecting the phase from the respective drive voltage during the zero-crossing interval, and measuring the voltage value when the drive voltage of a first other phase is the supply voltage and the drive voltage of a second other phase is the zero voltage. A position unit is arranged for determining the rotor position based on the voltage value.