Motor Bus Current Compensation for Small-Capacitance AC Supplies
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Solution Overview
Problem
Conventional motor control circuits without large electrolytic capacitors experience unstable bus voltage and current due to small capacitance, leading to unstable motor output, especially when operating with different AC power supplies and fluctuating load conditions.
Innovation Solution
A motor control circuit with a power supply, first and second rectification circuits, a driving circuit, and a controller that obtains a periodic bus voltage waveform, samples it multiple times, linearly fits voltage values to determine slopes, calculates power frequency, and generates a control signal to compensate the bus current, thereby stabilizing the motor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a large electrolytic capacitor is used to stabilize bus voltage, then voltage stability is improved, but circuit board volume increases
Solution Approach 1:
The patent changes the control parameters by introducing a power frequency correction value that dynamically adjusts the current control based on the detected power frequency. This parameter change enables the system to maintain stable bus voltage and current without requiring a large electrolytic capacitor, thus reducing circuit board volume while maintaining voltage stability.
Solution Approach 2:
The patent implements a feedback mechanism where the controller detects the power frequency from the bus voltage waveform, calculates a correction value, and uses this correction value to adjust the current control. This closed-loop feedback system compensates for voltage instability that would otherwise require large capacitance, enabling voltage stabilization with smaller capacitors.
2Adaptability or versatility
If power frequency correction is implemented for multi-power supply compatibility, then adaptability is improved, but measurement precision deteriorates due to waveform fluctuation
Solution Approach 1:
The patent performs preliminary sampling of the bus voltage waveform at multiple predetermined time points before calculating the power frequency. By collecting voltage values at multiple time points and performing linear fitting, the system prepares accurate data in advance, which compensates for waveform fluctuations and enables precise power frequency detection across different power supplies.
Solution Approach 2:
The patent uses excessive sampling by measuring voltage at multiple time points (t1, t2, t3, t4) rather than a single point. This excessive measurement approach provides redundant data that can be processed through linear fitting to extract accurate power frequency information even when the waveform fluctuates, thereby maintaining measurement precision while achieving broad power supply adaptability.
Data Source
AI summary
A current control method and a motor control circuit are provided. The motor control circuit includes a first rectification circuit and a second rectification circuit connected in parallel between a live wire and a natural wire of a power supply, a sampling resistor, and a controller connected to the second rectification circuit. The first rectification circuit is connected to the motor. The current control method include obtaining a periodic waveform signal of a bus voltage; collecting a bus current value through the sampling resistor; sampling the periodic waveform signal for a plurality of times; linearly fitting multiple voltage values obtained at a plurality of sampling time points to obtain multiple slopes; obtaining a power frequency according to the multiple slopes; calculating a compensation current value according to the power frequency; and generating a control signal according to the compensation current value and the bus current value.