Motor Current Feedback Circuit With Isolated Dynamic Gain Switching
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Solution Overview
Problem
Existing control circuits for electric motors face challenges in optimizing current feedback as a function of the motor's operating range, leading to suboptimal dynamic performances and noise levels.
Innovation Solution
A control circuit with a low voltage subcircuit and a high voltage subcircuit separated by a galvanic isolation, featuring an isolator with limited channels to pass control data and select between low and high gain driving modes based on current thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of bits of the ADC is increased to reduce LSB resolution and improve noise level, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies dynamic gain switching in the analog front-end, changing the gain value based on the current operating range. This allows a fixed-resolution ADC to achieve variable effective resolution, improving measurement precision without increasing ADC bit depth or complexity.
Solution Approach 2:
The patent changes the analog gain parameter dynamically based on current magnitude. By switching between different gain values (first gain for high current, second gain for low current), the system optimizes measurement precision for different operating conditions without modifying the ADC itself.
2Measurement precision
If the current sensor maximum current level is reduced to improve LSB resolution, then measurement precision is improved, but the dynamic performances (acceleration, speed, torque) deteriorate because large currents cannot be measured
Solution Approach 1:
The system dynamically switches between different gain modes based on the measured current magnitude. This allows the measurement system to adapt to both large currents during acceleration and small currents during steady-state operation, maintaining both measurement precision and dynamic performance capability.
Solution Approach 2:
The current measurement range is segmented into different operating zones (high current range and low current range), each handled by a specific gain mode. This segmentation allows optimal measurement precision in each zone while maintaining overall measurement capability across the full current range.
3Measurement precision
If an average from multiple current measurement samples is calculated to increase effective ADC bits, then measurement precision is improved, but the lag in feedback loop increases, limiting dynamic performances
Solution Approach 1:
The system dynamically adjusts the analog gain based on real-time current magnitude, providing immediate response without requiring temporal averaging. This eliminates feedback loop lag while maintaining measurement precision through instantaneous analog signal conditioning.
Data Source
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AI summary
The invention relates to a control circuit (10) for an electric motor comprising at least one phase. The control circuit (10) comprises a low voltage subcircuit (12a), a high voltage subcircuit (12b) and an isolation barrier (50) therebetween. The low voltage subcircuit (12a) comprises a current controller (16) adapted to generate a driving signal, and a feedback loop (19) whose output is fed back to the input of the current controller (16). The high voltage subcircuit (12b) is adapted to output a current for driving the motor, an analog front-end (44) and an ADC (46). The isolation barrier (50) comprises an isolator (54) adapted to pass the output signal of the ADC (46) across the isolation barrier (50) from the high voltage subcircuit (12b) to the low voltage subcircuit (12c). The analog front-end (44) is adapted to apply a low or high gain as a function of the current in the at least one phase. The isolator (54) comprises a first and a second channel to pass respectively a clock signal (CLK) and a control signal (ICS) from the low to the high voltage subcircuit (12a, 12b) to select the low or high gain (G) of the analog front-end (44). The isolator (54) further comprises a third and a fourth channel to pass respectively the output of the ADC (46) and a replica of the clock signal (CLK") from the high to the low voltage subcircuit (12a, 12b).