Motor Control Circuit With Switchable Gain Current Feedback
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Solution Overview
Problem
Existing control circuits for electric motors face challenges in achieving precise and accurate driving due to noise levels in current measurement, which are influenced by the least significant bit (LSB) resolution of analog-to-digital converters (ADCs). Current solutions either increase ADC bits at high cost, use fast low-resolution ADCs with increased feedback loop lag, or reduce current sensor maximum levels, all of which impact dynamic performance.
Innovation Solution
A control circuit for electric motors that includes low and high voltage subcircuits separated by a galvanic isolation barrier, utilizing an isolator with a limited number of channels to select low or high gain driving modes based on current measurements. The analog front-end applies different gains depending on the current level, optimizing current feedback and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of bits of the ADC is increased to improve LSB resolution and reduce noise, then measurement precision is improved, but device cost increases
Solution Approach 1:
The patent applies dynamics by making the ADC gain configurable and switchable between different modes (first gain and second gain higher than the first gain) based on operating conditions. This allows the system to adapt the measurement resolution dynamically - using higher gain for low current measurements to achieve better LSB resolution, and lower gain for high current measurements to maintain appropriate measurement range, thereby eliminating the need for a permanently high-resolution ADC.
Solution Approach 2:
The patent changes the parameter of ADC gain to resolve the contradiction. By switching between different gain values in the analog front-end, the system can achieve variable effective resolution without changing the physical ADC bit depth. This parameter change allows the same hardware to operate at different precision levels depending on the current measurement range required.
2Measurement precision
If a fast ADC with limited bits is used and multiple current measurement samples are averaged to improve resolution, then measurement precision is improved, but feedback loop response time increases
Solution Approach 1:
The system dynamically switches between different gain modes based on current measurement requirements. When high precision is needed at low currents, the higher gain mode provides better resolution without requiring extensive averaging. This dynamic adaptation reduces the need for multiple samples and averaging, thereby maintaining fast feedback loop response while achieving high measurement precision when required.
Solution Approach 2:
By changing the ADC gain parameter dynamically, the system achieves variable measurement resolution without relying on statistical averaging methods. The higher gain provides increased resolution for low current measurements directly at the hardware level, eliminating the time-consuming averaging process while maintaining measurement precision.
3Measurement precision
If the current sensor maximum current level is reduced to improve LSB resolution, then measurement precision is improved, but dynamic performance deteriorates
Solution Approach 1:
The patent implements dynamic gain switching that adapts to the current measurement range. The system uses the higher gain mode for low current measurements to achieve high LSB resolution, and switches to lower gain mode for high current measurements during dynamic operation. This dynamic adaptation allows the system to maintain high precision at low currents without sacrificing the ability to measure large currents during acceleration and dynamic phases.
Solution Approach 2:
The system changes the ADC gain parameter based on operating conditions rather than fixing the sensor maximum current level. This parameter change allows the same hardware to achieve high effective resolution for low current measurements while maintaining the full dynamic range capability for high current measurements, thus preserving both precision and dynamic performance.
4Measurement precision
If different driving modes are implemented according to motor operating range to optimize current feedback, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent implements a dynamic gain switching mechanism controlled by a simple comparator that monitors the current measurement range. When the current exceeds a threshold, the system automatically switches between gain modes. This dynamic adaptation achieves different driving modes for optimized current feedback without requiring complex control logic, maintaining relatively simple device architecture while improving measurement precision across different operating ranges.
Data Source
AI summary
A control circuit for an electric motor includes low and high voltage subcircuits, and an isolation barrier therebetween. The low voltage subcircuit comprises a current controller configured to generate a driving signal, and a feedback loop. The high voltage subcircuit comprises a power bridge configured to output a current that drives the motor, a current sensor configured to measure the current, an analog front-end and an analog-to-digital converter (ADC). The analog front-end is configured to apply as a function of the measured current. The isolation barrier comprises an isolator having: first and second channels to pass respectively a clock signal and a control signal from the low to high voltage subcircuit to select the gain; and third and fourth channels to pass respectively an output signal of the ADC and a replica of the clock signal from the high to low voltage subcircuit.