Transient Detection Circuit for Rotor Position Ripple Counting
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Solution Overview
Problem
Existing motor control systems struggle to accurately determine the position of a rotor in electric motors when the frequency of the PWM signal is below a threshold frequency, leading to incorrect pulse counting and potential motor damage.
Innovation Solution
A motor control circuit that includes a transient detection circuit to detect current transients and a pulse counter to update the rotor position, with logic to prevent incorrect pulse output by extending the pulse duration based on expected commutation times and using edge blanking to avoid parasitic transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ripple counting technique is used to determine rotor position, then rotor position can be determined without sensors, but the technique fails when PWM signal frequency is similar to ripple frequency caused by commutation
Solution Approach 1:
The patent extracts and isolates the commutation ripple signal from the total current by using a high-pass filter to remove the PWM carrier frequency components. This allows the ripple counting technique to accurately detect rotor position even when operating at low PWM frequencies where the carrier frequency would otherwise interfere with the commutation ripple frequency.
Solution Approach 2:
The patent introduces an intermediary processing stage between current sensing and ripple counting that includes filtering and signal conditioning circuits. This intermediary stage separates the commutation ripple signal from PWM switching artifacts, enabling accurate position detection without being affected by PWM frequency variations.
2Loss of energy
If PWM frequency is reduced below threshold frequency, then switching losses are reduced and efficiency improves, but the controller cannot accurately count ripples in the current
Solution Approach 1:
The patent extracts the commutation ripple signal from the total current waveform using filtering techniques that specifically remove PWM carrier frequency components. This extraction allows accurate ripple counting to proceed even when the PWM frequency is reduced to minimize switching losses.
Solution Approach 2:
The patent changes the frequency parameters of the signal processing filters to match the reduced PWM operating frequency. By dynamically adjusting the filter characteristics based on the PWM frequency, the system maintains accurate ripple detection across a wide range of operating conditions including low-frequency operation.
3Measurement precision
If pulse width modulation is used to control the rotor, then motor control precision is improved, but parasitic transients are generated that interfere with position detection
Solution Approach 1:
The patent converts the harmful parasitic transients generated by PWM switching into useful information by detecting their characteristic patterns. The system uses these transients as timing references to synchronize the ripple counting process, transforming what would be noise into a useful synchronization signal for accurate position detection.
Solution Approach 2:
The patent introduces intermediary signal processing circuits that filter and condition the current signal to eliminate parasitic transient interference. These circuits use band-pass filtering and synchronous detection techniques to pass only the commutation ripple frequencies while rejecting PWM switching artifacts.
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 improves the accuracy of rotor position determination, reducing incorrect pulse counts and lowering the risk of motor damage by distinguishing between commutation and parasitic current transients, even at low PWM frequencies.
Implementation Method 1
a technique known as ripple counting, which includes counting the number of ripples in the current caused by the back electromagnetic force (BEMF) and the commutation of the rotor
Implementation Method 2
counting the number of ripples in the current caused by the back electromagnetic force (BEMF) and the commutation of the rotor
Data Source
AI summary
A motor control circuit for controlling an electric motor may include at least one switching device configured to receive, from a pulse modulation device, a pulse modulated signal and output, based on the pulse modulated signal and to the electric motor, a current. In some examples, a frequency of the pulse modulated signal is below a threshold frequency. The motor control circuit may also include a transient detection circuit configured to detect a current transient, and responsive to detecting the current transient, output a pulse. The motor control circuit may further include a pulse counter configured to update, based on the pulse, a value indicative of a position of a rotor of the electric motor; and output the value indicative of the position of the rotor.