Power conversion device, motor drive device, and refrigeration-cycle application apparatus
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Solution Overview
Problem
Existing power conversion devices that convert AC power into desired power for applications like air conditioners face challenges in reducing vibrations of compressors, leading to increased size due to higher current requirements for smoothing capacitors when torque control is varied.
Innovation Solution
A power conversion device that adjusts input current to the converter based on frequency pulsations, reducing the current flowing to the smoothing unit by pulsating the input power in synchronization with motor rotational speed, allowing for the use of smaller capacitors and minimizing apparatus size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If torque control is performed to vary output torque in accordance with load torque variations, then compressor vibrations are reduced, but capacitor current increases requiring larger capacitors
Solution Approach 1:
The invention applies periodic action by controlling the converter input current to pulsate at specific frequencies (first frequency matching motor rotational speed, second frequency matching AC power supply frequency). This periodic current control creates corresponding power pulsations that reduce the capacitor current required for smoothing, thereby resolving the contradiction between vibration reduction and capacitor current management
Solution Approach 2:
The invention changes the parameter of input current characteristics by introducing controlled pulsations at specific frequencies. Instead of maintaining constant current, the system varies current magnitude periodically according to the motor speed and power supply frequency, which reduces the RMS current through the capacitor while maintaining effective torque control
2Object-affected harmful factors
If capacitor current tolerance is increased to handle torque control variations, then vibration reduction control becomes feasible, but apparatus size increases
Solution Approach 1:
By implementing periodic current pulsations synchronized with motor speed and power supply frequency, the system reduces the effective capacitor current requirement. This allows vibration reduction control to be achieved without increasing capacitor size or selecting capacitors with higher current tolerance ratings
Solution Approach 2:
The invention creates a controlled copy of the torque pulsation pattern through current control, where the input current pulsations mirror the load torque variations. This copying approach enables the system to anticipate and compensate for torque variations without requiring oversized capacitors to handle uncontrolled current spikes
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 approach effectively reduces the size of the power conversion device by minimizing capacitor current and capacitance requirements, achieving cost reduction and size reduction while maintaining vibration reduction and high power factor control.
Implementation Method 1
a converter rectifying a first alternating-current power supplied from an alternating-current power supply and boosting a voltage of the first alternating-current power rectified
Implementation Method 2
a smoothing unit connected to an output end of the converter... the smoothing capacitor is provided at the preceding stage of the inverter in order to smooth a current output from a converter
Data Source
AI summary
A power conversion device includes a converter that rectifies a first alternating-current power supplied from an alternating-current power supply and boosts a voltage of the power rectified; a smoothing unit connected to an output end of the converter; and a control unit that controls the converter to cause an input current to the converter to change in accordance with at least one of a first frequency or a second frequency, and that reduces a current flowing to the smoothing unit, the first frequency being a frequency of pulsation of input power to a load unit connected across the smoothing unit, the second frequency being a frequency of pulsation of input power to the converter due to a frequency of the alternating-current power supply.