Power Conversion Device Relay Control for Capacitor Lifespan
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Solution Overview
Problem
Existing power conversion apparatuses face instability in power supply to motors and reduced robustness to environmental changes, particularly during power supply imbalances, due to the connection of resistors and smoothing capacitors, which leads to increased voltage pulsation and reduced lifespan of components.
Innovation Solution
A power conversion apparatus with a second relay that controls the flow of current through smoothing capacitors, allowing for selective use of capacitors based on operational states, thereby stabilizing power supply and extending the lifespan of components by dispersing heat and ripple current loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a smoothing capacitor is connected to the input stage of the inverter to stabilize voltage, then power supply stability is improved, but inrush current increases several times during startup
Solution Approach 1:
The relay is opened before power startup to prevent inrush current from charging the smoothing capacitor. By performing this preventive action in advance, the patent eliminates the harmful inrush current while maintaining the necessary voltage stabilization function when the relay is closed during normal operation.
Solution Approach 2:
A relay is introduced as an intermediary component between the power supply and the smoothing capacitor. The relay acts as a controlled switch that mediates the connection, allowing the system to prevent inrush current during startup while enabling voltage stabilization during normal operation through controlled opening and closing.
2Object-generated harmful factors
If an inrush current preventing circuit with resistor and relay is connected in series to the smoothing capacitor, then inrush current is suppressed, but power supply stability deteriorates when the smoothing capacitor is not used
Solution Approach 1:
The relay provides dynamic control over the smoothing capacitor connection, switching between connected and disconnected states based on operational requirements. This dynamic approach allows the system to suppress inrush current when needed while maintaining power supply stability when the capacitor is actively used, adapting to different operational conditions.
Solution Approach 2:
The system changes the operational parameter of the smoothing capacitor by controlling the relay state. When the relay is open, the capacitor is effectively removed from the circuit; when closed, it is activated for voltage stabilization. This parameter change allows optimization for different operational phases.
3Stability of the object's composition
If the relay is kept closed to maintain power supply stability, then voltage stabilization is improved, but the smoothing capacitor is continuously exposed to heat and ripple current reducing its lifespan
Solution Approach 1:
Instead of continuous connection, the relay provides periodic control of the smoothing capacitor connection. The capacitor is connected only when voltage stabilization is required, and disconnected during periods when it is not needed, reducing cumulative exposure to heat and ripple current while maintaining stability when necessary.
Solution Approach 2:
The smoothing capacitor is extracted from the continuous circuit path by opening the relay when its stabilizing function is not required. This removes the capacitor from exposure to harmful heat and ripple current during periods when voltage stabilization is not needed, extending its operational lifespan.
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 solution ensures stable power supply to motors and enhances robustness to environmental changes by extending the lifespan of smoothing capacitors and preventing premature failure due to heat and ripple currents, while reducing the impact of power supply imbalances.
Implementation Method 1
A commercial alternating current is converted into a direct current by a rectifier
Implementation Method 2
a smoothing capacitor is connected to an input stage of the inverter, to thereby stabilize a voltage
Implementation Method 3
a relay 31B and an inrush preventing resistor 32B, and the second relay 31B is connected in series to a second smoothing capacitor 40B
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A power conversion apparatus includes: a rectifier for rectifying an AC voltage supplied from an AC power supply; a first smoothing capacitor and a second smoothing capacitor connected in parallel to each other, configured to smooth and charge an output from the rectifier; an inrush current preventing circuit connected in series to the first smoothing capacitor, the inrush current preventing circuit including an inrush preventing resistor for suppressing an inrush current and a first relay connected in parallel to the inrush preventing resistor; a second relay connected in series to the second smoothing capacitor; an inverter circuit for converting the output smoothed by the first smoothing capacitor and the second smoothing capacitor into an AC voltage and outputting the AC voltage to a load; and relay controlling means for controlling a switching operation of the first relay and the second relay. Further, the relay controlling means sets, when the operation of the inverter circuit is started, the first relay to an on state and the second relay to an off state, and controls, while the inverter circuit is operated, the operation of the second relay based on the state of the load.