Power conversion device and air conditioning device using same
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Solution Overview
Problem
Existing power conversion devices for air-conditioning systems, particularly those using three-phase full-wave rectification, struggle to effectively suppress both low-order and high-order harmonics, leading to increased total harmonic distortion (THD) and partial weighted harmonic distortion (PWHD).
Innovation Solution
A power conversion device comprising a rectifier, transformation circuit with a reactor and switching element, smoothing capacitor, inverter, and a converter control unit that calculates and adjusts switching signals based on current deviations to manage reactor current, thereby controlling the operation of the switching element to bring the current deviation close to a target value, using a combination of current control, switching command value calculation, and error accumulation units to manage harmonics across different power supply phase angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a direct current reactor is provided immediately after the three-phase rectifier to control current, then the power supply current can be controlled, but the device complexity increases
Solution Approach 1:
The invention makes the existing reactor serve multiple functions: it continues to provide current smoothing while also being integrated into the control system as a sensing element for current deviation detection. The control unit uses the reactor current information to calculate duty adjustments, eliminating the need for separate current control circuitry and reducing overall system complexity.
Solution Approach 2:
The control system uses the reactor's own current output as the feedback signal for control decisions. By detecting the current through the reactor and using this same signal for duty calculation, the system makes the reactor self-sufficient for both its traditional smoothing function and the new control function, avoiding additional sensors or circuitry.
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 suppresses both low-order and high-order harmonics, reducing total harmonic distortion (THD) and partial weighted harmonic distortion (PWHD), while improving current control performance and allowing for higher carrier frequencies with wide bandgap semiconductors, enhancing harmonic control.
Implementation Method 1
a rectifier, which is configured to rectify an AC voltage supplied from a three-phase AC power supply
Implementation Method 2
a smoothing capacitor, which is configured to smooth an output voltage from the transformation circuit
Implementation Method 3
an inverter, which is configured to convert a DC voltage smoothed in the smoothing capacitor into an AC voltage
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Provided is a power conversion device including: a rectifier configured to rectify an AC voltage supplied from a three-phase AC power supply; a transformation circuit including at least a reactor, a switching element, and a backflow prevention element, and being configured to transform the voltage rectified in the rectifier; a smoothing capacitor configured to smooth an output voltage from the transformation circuit; an inverter configured to convert a DC voltage smoothed in the smoothing capacitor into an AC voltage; a power supply voltage detector configured to detect, as a power supply voltage, at least any one of at least one line voltage and at least one phase voltage of the three-phase AC power supply; an output voltage detector configured to detect the output voltage from the transformation circuit; a current detector configured to detect a reactor current flowing through the reactor; and a converter control unit configured to control an operation of the switching element so as to bring a current deviation of the reactor current from a preset current value close to a preset current deviation based on the power supply voltage, the output voltage, and the reactor current.