Multi-phase Drive Capacitor Voltage Balancing
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Solution Overview
Problem
In multi-phase electric drives, the voltage across electrolytic capacitors is not adequately monitored, leading to potential thermal instability and violent explosions due to unequal voltage sharing among series-connected capacitors, which poses safety and secondary damage risks.
Innovation Solution
A multi-phase electric drive system that includes a voltage measurement device to monitor the voltage across each capacitor set in the capacitor bank, connected in series, and a control system to adjust power unit operations based on measured voltages, preventing over-voltage and unbalanced voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If multiple electrolytic capacitors are connected in series to achieve higher voltage ratings, then the voltage handling capability is improved, but unequal voltage sharing among capacitors occurs due to parameter variations and aging, leading to thermal instability and potential explosions
Solution Approach 1:
The patent implements voltage sensing circuits that continuously monitor the voltage across each capacitor in the series string. These sensing circuits provide feedback signals to the control system, which then adjusts the switching patterns of the power electronics to equalize voltage distribution among capacitors, preventing any single capacitor from exceeding its voltage rating and avoiding thermal instability or explosions
Solution Approach 2:
The patent employs active voltage balancing techniques that dynamically change operating parameters (such as switching duty cycles and pulse widths) to compensate for parameter variations and aging effects in capacitors. By adjusting these parameters in real-time based on measured voltage conditions, the system maintains uniform voltage sharing across all series-connected capacitors despite manufacturing tolerances and degradation over time
2Device complexity
If the overall voltage of series-connected capacitors is monitored, then system-level voltage control is achieved, but individual capacitor voltage imbalances due to aging or defects cannot be detected, posing safety risks
Solution Approach 1:
The patent divides the overall voltage monitoring function into segmented individual capacitor monitoring units. Each capacitor is equipped with its own voltage sensing circuit that measures its specific voltage condition independently. This segmentation allows the system to detect voltage imbalances and faults at the individual capacitor level rather than only at the system level, enabling early fault detection and prevention of catastrophic failures
Solution Approach 2:
The patent introduces intermediate voltage sensing circuits as mediators between the capacitors and the control system. These sensing circuits act as intermediaries that translate individual capacitor voltage conditions into detectable signals, enabling the control system to identify and respond to individual capacitor faults, aging effects, and voltage imbalances before they lead to safety hazards
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
The system effectively protects capacitors from over-voltage and unbalanced voltage issues, preventing thermal instability and explosions, thereby ensuring safety and maintaining the reliability of the multi-phase electric drive.
Implementation Method 1
a rectifier, being adapted for converting incoming power from the corresponding secondary windings into a DC voltage
Implementation Method 2
a capacitor bank, being connected to an output of said rectifier through DC+ and DC-; wherein: said capacitor bank includes a plurality of capacitor sets connected in series
Data Source
Figure 1
Figure 2A~2B
Figure 2C
AI summary
It is provided a multi-phase electric drive for use with a multi-phase AC load and the power unit thereof. The multi-phase electric drive includes a multi-phase power transformer with at least one primary winding and a plurality of secondary windings. The primary winding may be electrically connected to a source of multi-phase AC power. Power units may have an input connected with a corresponding one of said plurality of secondary windings and may have a single-phase controllable output to such multi-phase AC load. The power units may be serially connected with respective others of said power units in each phase output line and are connectable to said multi-phase AC load.