Single-Sensor Motor Drive Control for DC Bus Voltage Stability
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Solution Overview
Problem
Existing motor drive systems face instability in current control loops due to negative spikes and oscillations in DC bus voltage caused by sudden changes in motor phase, leading to potential damage and inefficiencies.
Innovation Solution
A single current sensor system with a signal conditioner and feedback processor that blanks current feedback during motor phase changes, using a time period (tblanking) to stabilize the control loop by relying on prior sensor readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single current sensor is used to sense DC bus current, then device complexity and cost are reduced, but measurement precision and control reliability deteriorate due to negative spikes and oscillations during motor phase changes
Solution Approach 1:
The patent introduces a blanking mechanism as an intermediary between the current sensor and the control loop. During motor phase changes, the blanking function temporarily blocks the feedback signal from the single current sensor, preventing negative spikes and oscillations from affecting the control loop. This allows the use of a single sensor while maintaining measurement precision through selective signal filtering.
2Measurement precision
If current feedback is continuously monitored without blanking, then measurement precision is maintained, but stability of the control loop deteriorates due to negative spikes during phase changes
Solution Approach 1:
The patent extracts the problematic feedback signal during specific time periods (motor phase changes) by implementing a blanking function. This selectively removes the unstable portion of the current feedback signal that causes negative spikes and oscillations, while maintaining continuous monitoring during stable operation periods, thus preserving measurement precision while ensuring control loop stability.
3Reliability
If DC link capacitors are sized for worst-case oscillation scenarios, then reliability is improved, but device complexity and cost increase due to larger component requirements
Solution Approach 1:
The patent applies preliminary action by implementing the blanking function that proactively prevents negative spikes and oscillations before they can affect the control loop and DC bus voltage. By blocking the unstable feedback signal during motor phase changes, the system eliminates the need for oversized DC link capacitors, achieving reliability through control strategy rather than component oversizing.
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
Stabilizes the DC bus voltage and current control, improving accuracy and reducing the risk of oscillations, thereby enhancing motor control and potentially reducing the size of DC link capacitors.
Implementation Method 1
The single sensor can sense a voltage across and thereby a current passing through the sense resistor
Implementation Method 2
the sensor can include a signal conditioner that converts the analog voltage across the sense resistor into a digital output
Data Source
AI summary
A motor drive system includes a direct current (DC) power source and an inverter comprising a plurality of switching elements. The inverter is configured to receive a DC input from the DC power source and output an alternating current (AC) to three phases of a motor. The system also includes a single current sensor arranged to sense a current from the DC power source to the inverter and a control unit that controls the operation of the switching elements based in part on an output of the single current sensor. A control unit controls the operation of the switching elements based in part on an output of the single current sensor. The control unit is configured to determine that a Hall sensor change has occurred and to control the operation of the switching elements based on a prior sensor reading for a time period (tblanking) after the Hall sensor change.