Sensorless Electric Drive Unit Using Back-EMF Zero-Crossing Detection
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Solution Overview
Problem
Existing sensorless control strategies for sinusoidal AC brushless motors in electric drive units face challenges such as high costs due to the need for costly sensors or complex integrated circuits for detecting zero crossings and phase currents, which can disrupt the sinusoidal trend of currents and increase acoustic noise.
Innovation Solution
An electric drive unit with a simple and cost-effective control architecture using a low-cost analogue unit to measure peak phase currents and detect zero crossings, eliminating the need for expensive sensors and complex ICs by employing a low-inductance shunt and a controller that calculates the optimum advance angle of the voltage relative to the CEMF, ensuring efficient and noiseless operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If costly sensors (absolute encoders, resolvers, Hall-effect sensors) are used to detect rotor angular position, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The motor's own back-EMF signals are used to provide position information. The controller detects zero-crossings of the back-EMF from the motor windings themselves, eliminating the need for external sensors. The motor serves its own measurement function through its inherent electrical characteristics.
Solution Approach 2:
Mechanical/physical sensors (encoders, resolvers, Hall-effect sensors) are replaced with an electrical measurement system. The controller uses electrical signal processing of back-EMF zero-crossings to determine rotor position, substituting a mechanical sensing approach with an electrical one.
2Loss of energy
If DSP-based FOC control is used to maintain orthogonal relationship between rotor and stator fields, then efficiency is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces expensive, complex DSP-based control systems with a simpler, lower-cost controller architecture. The simplified controller achieves adequate efficiency through back-EMF zero-crossing detection and basic commutation control, sacrificing some optimization capability for significant cost and complexity reduction.
Solution Approach 2:
The control approach changes from complex real-time field orientation control to a simpler method based on detecting back-EMF zero-crossings. This parameter change in the control strategy simplifies the system while maintaining acceptable efficiency for the application.
3Measurement precision
If current is held at zero for sufficient time to detect back-EMF zero crossing, then measurement precision is improved, but sinusoidal current trend is disrupted and acoustic noise increases
Solution Approach 1:
The controller rapidly detects back-EMF zero-crossings during natural current transitions without deliberately holding current at zero. By skipping the need for extended zero-current intervals and using brief natural zero-crossing moments for detection, the system maintains sinusoidal current flow and minimizes acoustic noise while still achieving accurate position detection.
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
The solution achieves efficient and noiseless operation with low energy consumption, maintaining the sinusoidal trend of currents and minimizing mechanical vibrations, thereby reducing costs and acoustic emissions.
Implementation Method 1
a brushless three-phase motor with permanent magnets generating a counter-electromotive force (CEMF) with a sinusoidal form
Implementation Method 2
employing a low-inductance shunt and a controller that calculates the optimum advance angle
Data Source
Figure 1
Figure 2~4
Figure 5
AI summary
Described is an electric drive unit (1) comprising an electric motor (2) with permanent magnets, an inverter (3) supplying electricity to the electric motor (2), a continuous current stage (4) supplying electricity to the inverter, a controller (8) comprising a modulator (5) for driving the inverter controlled by a first digital signal (Vs__act) representing the amplitude of the phase voltages to be applied to the electric motor and by a second digital signal (freq_act) representing the electrical frequency of the phase voltages; the electric drive unit (1) comprises an analogue/digital stage (6) for calculating the optimum value of the advance angle (d???) of the voltage applied to the electric motor relative to the counter-electromotive force as a linear function of the peak value of the phase current and an analogue/digital stage (12) for measuring the angle (fact) between the voltage applied to the electric motor and the phase current; the controller (8) is programmed for estimating, with a sampling at electrical frequency, the angle (?act) between the phase current and the counter-electromotive force as the difference between the aforesaid optimum value of the advance angle (dopt) and the angle (?act) measured between the voltage applied to the electric motor and the phase current.