Power conversion device and air-conditioning device using same
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Solution Overview
Problem
Existing power converters face challenges in maintaining constant reactor current and reducing losses and noise, especially when the carrier frequency is decreased, due to pulsating input voltage from the rectifier.
Innovation Solution
A power converter system that includes a rectifier, a transformation circuit with a reactor and backflow prevention element, capacitors for smoothing, and a converter control unit that detects line and phase voltages, reactor current, and output voltage to control the switching element, using error accumulation and integration to generate a control amount and switching signal, thereby reducing noise and losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the carrier frequency is increased to control reactor current constant, then current control performance is improved, but loss and noise are increased
Solution Approach 1:
The patent applies preliminary action by calculating and storing reactive power command values in advance for multiple power supply voltage phases before actual operation. The reactive power command value calculation unit pre-calculates Q* for different voltage phases, and the selection unit quickly retrieves the appropriate pre-calculated value during operation. This eliminates the need for high-frequency real-time calculation, allowing carrier frequency to be reduced while maintaining control performance.
Solution Approach 2:
The patent implements dynamics by making the carrier frequency adjustable rather than fixed. The control system can dynamically set the carrier frequency based on operational requirements, enabling it to operate at lower frequencies during normal conditions to reduce losses and noise, while maintaining the capability to increase frequency when rapid current control is needed.
2Loss of energy
If the carrier frequency is decreased to reduce loss and noise, then converter efficiency is improved, but reactor current control performance deteriorates
Solution Approach 1:
The patent applies preliminary action by calculating and storing reactive power command values in advance for multiple power supply voltage phases before actual operation. The reactive power command value calculation unit pre-calculates Q* for different voltage phases, and the selection unit quickly retrieves the appropriate pre-calculated value during operation. This eliminates the need for high-frequency real-time calculation, allowing carrier frequency to be reduced while maintaining control performance.
3Stability of the object's composition
If a high carrier frequency is used to maintain constant reactor current, then current ripple is reduced, but switching loss and electromagnetic noise are increased
Solution Approach 1:
The patent applies preliminary action by calculating and storing reactive power command values in advance for multiple power supply voltage phases before actual operation. The reactive power command value calculation unit pre-calculates Q* for different voltage phases, and the selection unit quickly retrieves the appropriate pre-calculated value during operation. This eliminates the need for high-frequency real-time calculation, allowing carrier frequency to be reduced while maintaining control performance.
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 system effectively reduces noise and losses while suppressing reactor voltage fluctuations, even at lower carrier frequencies, by canceling errors in the switching command value and outputting control amounts at advanced phase angles, improving current control performance.
Implementation Method 1
a rectifier (10), which is configured to rectify three-phase AC power
Implementation Method 2
a transformation circuit (20), which includes a reactor (21), a switching element (23), and a backflow prevention element (22), and is configured to transform a voltage rectified in the rectifier
Implementation Method 3
a capacitor (25), which is configured to smooth an output voltage of the transformation circuit
Implementation Method 4
a switching element (23), and is configured to transform a voltage rectified in the rectifier
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A power converter includes a transformation circuit configured to transform a rectified voltage rectified by a rectifier to output the voltage, and a converter control unit configured to control an operation of a switching element of the transformation circuit. The converter control unit calculates a current command value based on a line voltage or the phase voltage, calculates a current deviation between the current command value and the reactor current, and calculates a switching command value from the current deviation calculated in a current subtractor. In this case, the converter control unit generates a control amount obtained by integrating the current deviation for each of different phase angles, and includes a plurality of integrators provided for the respective different phase angles of a power supply voltage. The integrator corresponding to a power supply phase angle is caused to accumulate the current deviation, and the integrator corresponding to a phase angle that is advanced by a set delay phase from the power supply phase angle is caused to output the control amount. A switching signal to be output to the switching element is generated with use of the control amount and the switching command value.