DC Link Capacitance Decline Detection in Motor Drive Devices
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Solution Overview
Problem
Conventional motor drive devices cannot detect capacitance decline in DC link capacitors outside of initial charging operations and cannot individually detect capacitance decline in multiple inverter sections connected to a converter section.
Innovation Solution
A motor drive device with first and second current detection parts, a voltage detection part, and a capacitance decline detection part that calculates the change in electric charge and voltage over a predetermined time to determine capacitance decline, allowing detection even during normal operation and in individual capacitors within multiple inverter sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitance decline detection is performed only during initial charging operation, then the detection method is simple, but capacitance decline cannot be detected outside of initial charging operations
Solution Approach 1:
The patent transitions from a static detection method (only during initial charging) to a dynamic detection method that can operate at multiple timing points including during normal operation. The control unit calculates capacitance values at different operational stages, enabling continuous monitoring capability while maintaining system adaptability.
2Reliability
If multiple inverter sections are connected to a converter section, then system capacity increases, but individual capacitance decline detection becomes difficult
Solution Approach 1:
The patent divides the detection system into segment-specific current detection parts and voltage detection parts for each inverter section. By calculating capacitance values individually for each section using section-specific measurements, the system can detect capacitance decline in individual capacitors even when multiple inverter sections are connected to a single converter section, without requiring complex centralized detection infrastructure.
3Measurement precision
If AC power supply is interrupted for capacitance detection, then detection accuracy improves, but operational continuity deteriorates
Solution Approach 1:
The patent enables continuous capacitance monitoring by performing capacitance value calculations during normal operational periods rather than requiring power interruption. The control unit utilizes current and voltage measurements taken during regular operation to calculate capacitance values, allowing continuous monitoring without interrupting the AC power supply or operational workflow.
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
Enables detection of capacitance decline in DC link capacitors beyond initial charging and in individual capacitors across multiple inverter sections, without interrupting AC power supply, facilitating continuous monitoring and threshold adjustment.
Implementation Method 1
a DC link capacitor provided to each of the reverse converters in a DC link between the forward converter and reverse converter
Implementation Method 2
a first current detection part that detects current flowing between the forward converter and the DC link capacitor in the DC link; a second current detection part that detects current flowing between the DC link capacitor and the reverse converter in the DC link
Implementation Method 3
a voltage detection part that detects a voltage of the DC link capacitor
Data Source
AI summary
A motor drive device includes: reverse converter that converts DC power from a forward converter into AC power; a DC link capacitor provided in a DC link; a first current detection part that detects current flowing between the forward converter and capacitor; a second current detection part that detects current flowing between the capacitor and reverse converter; a voltage detection part that detects a voltage of the capacitor; and a capacitance decline detection part that obtains a change value in electric charge of the capacitor from a n integrated value by integrated a predetermined time of a difference in current values detected by the current detection parts, obtains a capacitance value of the capacitor based on the obtained change amount in electric charge and change amount in voltage of the capacitor for the predetermined time, and detects a capacitance decline in the capacitor based on the obtained capacitance value.