DC Link Capacitor Voltage Imbalance Detection via Sense Resistors
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Solution Overview
Problem
Current technologies for detecting unbalanced DC link capacitor voltage are costly and inefficient, especially when dealing with multiple series-connected capacitors, leading to uncertainties in feedback control and potential damage to capacitors due to abnormal voltage distribution.
Innovation Solution
A detection apparatus using sense resistors and current sensors is implemented, where one end of each sense resistor is connected to a common node of two capacitors and the other end to a common node of two balanced resistors, allowing a current sensor to measure currents flowing through the sense resistors to determine if the DC voltage is balanced, thereby preventing abnormal voltage situations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If isolation DC/DC converters are used to detect capacitor voltage, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces sense resistors as intermediary components connected in parallel with each capacitor. These resistors convert voltage information into current information that can be measured by a single current sensor. The sense resistors act as mediators between the high-voltage capacitor nodes and the low-voltage measurement circuit, enabling accurate voltage detection without requiring complex isolation DC/DC converters for each capacitor.
Solution Approach 2:
The patent creates a simplified measurement model by using sense resistors to replicate the voltage information in current form. Instead of directly measuring high-voltage capacitor voltages with complex converters, the system copies the voltage information through the sense resistors to a single current sensor, achieving the same detection goal with simpler components.
2Measurement precision
If multiple voltage detection circuits are used for each capacitor, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple voltage detection functions into a single current sensor by using sense resistors connected in parallel with each capacitor. The current sensor measures the total current through the sense resistors, which contains information about the voltage balance across all capacitors. This combining approach eliminates the need for separate voltage detection circuits for each capacitor, reducing overall system complexity while maintaining detection accuracy.
3Measurement precision
If complex detection circuits are implemented, then measurement precision is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent replaces expensive, complex isolation DC/DC converters with simple, inexpensive sense resistors and a single current sensor. The sense resistors are basic passive components that are cheap and easy to manufacture, and the overall detection circuit becomes much simpler to assemble and maintain, significantly improving ease of manufacture while retaining adequate detection precision.
4Reliability
If detection circuits are added to monitor capacitor voltage, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the current sensor continuously monitors the current through the sense resistors, which reflects the voltage balance status of the capacitors. The control circuit receives this feedback information and can take corrective actions when voltage unbalance is detected, improving system reliability. The feedback loop uses simple components rather than complex detection circuits, minimizing the increase in device complexity.
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
This solution effectively determines whether the DC voltage is balanced across multiple capacitors, eliminating the risk of abnormal voltage and reducing operational costs by simplifying the detection process without interfering with the main circuit operation.
Implementation Method 1
One end of each sense resistor is coupled to a common-connected node of two capacitors, and the other end of each sense resistor is coupled to a common-connected node of two balanced resistors. The current sensor is coupled to one of the sense resistors, and measures a current value of a current flowing through the sense resistor coupled to the current sensor.
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A detection apparatus for unbalanced DC link capacitor voltage, the DC link provides a DC voltage (VDC) and includes a plurality of capacitors (C11-C1N) coupled in series to two ends of the DC link and a plurality of balanced resistors (RB11-RB1N) coupled in series to two ends of the DC link and corresponding to the capacitors (C11-C1N). The detection apparatus includes a plurality of sense resistors (RS1-RSM) and a current sensor (A). One end of each sense resistor (RS1-RSM) is coupled to a common-connected node of two capacitors (C11-C1N), and the other end thereof is coupled to a common-connected node of two balanced resistors (RB11-RB1N). The current sensor (A) is coupled to one of the sense resistors (RS1-RSM) and measures a current value (IS) of a current flowing through the sense resistor (RS1-RSM) coupled to the current sensor (A).