Motor Drive Short-Circuit Detection via DC Link Voltage Comparison
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Solution Overview
Problem
In motor drive apparatuses, short-circuit failures in series-connected capacitors can lead to excessive voltage applied to normal capacitors, potentially causing breakage or fire, especially in electrolytic capacitors, necessitating early detection without adding additional circuits to increase costs.
Innovation Solution
A motor drive apparatus with a short-circuit judgment unit that compares the DC link voltage to the peak power supply voltage to detect shorted capacitors and shuts off AC power flow when a short-circuit is detected, preventing excessive voltage from being applied to healthy capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional voltage monitoring circuits are added to detect short-circuit failures in capacitors, then detection capability is improved, but device complexity and cost increase
Solution Approach 1:
The control circuit that normally controls the contactor for motor operation is made multi-functional by adding capacitor short-circuit detection capability. The same control circuit now performs both motor control and capacitor fault detection, eliminating the need for separate monitoring circuits while maintaining detection capability.
Solution Approach 2:
The system uses its own existing voltage detection units and control circuits to perform capacitor short-circuit detection without requiring external monitoring equipment. The control circuit serves itself by monitoring system voltages to identify capacitor failures, making the system self-diagnostic.
2Strength
If series-connected capacitors are used to withstand high DC voltage, then voltage resistance is improved, but reliability deteriorates due to potential short-circuit failures
Solution Approach 1:
The control circuit continuously monitors the DC link voltage and compares it with the peak AC power supply voltage. When a short-circuit occurs in a capacitor, the DC link voltage drops below the expected peak AC voltage, providing feedback that triggers the control circuit to open the contactor and isolate the faulty capacitor, preventing further damage.
Solution Approach 2:
The control circuit is pre-programmed with the relationship between AC peak voltage and DC link voltage. When a short-circuit is detected, the system immediately opens the contactor to cushion or prevent the propagation of excessive voltage to other healthy capacitors, avoiding cascading failures before they can occur.
Data Source
AI summary
A motor drive apparatus includes a PWM converter configured to convert AC power of an AC power supply into DC power, a DC link unit including capacitors provided on the DC output side of the PWM converter and connected in series with each other, an inverter configured to convert the DC power of the DC link unit into AC power for driving a motor and output the AC power, a DC link voltage detection unit, a power supply voltage detection unit, a short-circuit judgment unit configured to judge that at least one of the capacitors has shorted when the DC link voltage value is smaller than the peak value of the power supply voltage, and a shut-off unit configured to shut off flow of AC power from the AC power supply into the PWM converter when the short-circuit judgment unit judges that at least one of the capacitors has shorted.