Motor Current Sampling Circuit With Dynamic Resistor Switching
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Solution Overview
Problem
Existing current sampling methods for permanent magnet synchronous motors, such as single-resistor and multi-resistor sampling, suffer from issues like loud motor noises and degraded performance due to inappropriate voltage utilization and current distortion, particularly in high-speed and low-speed applications.
Innovation Solution
A current sampling circuit that switches between single-resistor and multi-resistor sampling based on motor parameters, using a switching control unit to determine the appropriate method for different application scenarios, thereby optimizing current sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dual-resistor sampling is used at voltage zero vector moment, then current sampling is achieved, but voltage utilization is reduced in high-speed applications
Solution Approach 1:
The patent dynamically switches between dual-resistor sampling and single-resistor sampling methods based on the motor's operating speed. At low speeds, dual-resistor sampling is used for accurate current measurement, while at high speeds, single-resistor sampling is used to maximize voltage utilization. This dynamic adaptation resolves the contradiction by selecting the appropriate sampling method according to operational conditions.
2Productivity
If single-resistor sampling is used at voltage effective vector moment, then voltage utilization is improved, but current distortion occurs in low-speed and sector transition regions
Solution Approach 1:
The system dynamically selects the sampling method based on operating conditions. In low-speed and sector transition regions where single-resistor sampling causes current distortion, the system switches to dual-resistor sampling to ensure accurate current measurement. This dynamic switching resolves the contradiction between voltage utilization and current sampling accuracy.
3Loss of time
If PWM phase shifting is applied to extend voltage effective vector time, then current sampling time is sufficient, but current distortion is introduced causing loud motor noises
Solution Approach 1:
The patent segments the operating range into different speed regions and applies different sampling strategies. Instead of using PWM phase shifting across all operating conditions, the system uses dual-resistor sampling at low speeds to naturally provide sufficient sampling time without introducing current distortion. This segmentation approach eliminates the need for harmful PWM phase shifting while ensuring adequate sampling time.
Data Source
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AI summary
A frequency converter and a current sampling circuit thereof, and a three-phase current sampling method for a motor. The frequency converter (1000) is suitable for driving a motor (M) in a compressor. The current sampling circuit comprises: a single-resistor sampling unit (10) configured to perform current sampling at a voltage effective vector moment to obtain three-phase currents of the motor (M); a multi-resistor sampling unit (20) configured to perform current sampling at a voltage zero vector moment to obtain three-phase currents of the motor (M); and a switching control unit (30) configured to acquire a parameter of the motor (M), determine a switching index on the basis of the parameter of the motor (M), and select one of the single-resistor sampling unit (10) and the multi-resistor sampling unit (20) on the basis of the switching index to perform current sampling.