Power conversion device and refrigeration cycle apparatus
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Solution Overview
Problem
Existing power conversion devices face increased switching loss at high switching frequencies and larger reactor sizes to inhibit ripple current, while control methods that vary carrier frequency lead to increased ripple current and higher costs due to larger LCR filters.
Innovation Solution
A power conversion device with a booster circuit that includes a first and second backflow prevention element, switching elements, a reactor, and an intermediate capacitor, where the carrier frequency is adjusted based on the operation state to minimize switching loss and ripple current, allowing for reduced reactor and smoothing capacitor sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the switching frequency is increased to reduce the size of the reactor and smoothing capacitor, then the device size and cost are reduced, but the switching loss increases
Solution Approach 1:
The patent divides the booster circuit into two independent switching circuits: a first switching circuit with a first switching element and a second switching circuit with a second switching element. Each circuit operates at different switching frequencies, allowing the circuit to benefit from high-frequency operation (smaller components) while minimizing switching losses through coordinated control of the two circuits
Solution Approach 2:
The patent changes the switching frequency parameter differently for the two switching circuits. The first switching element operates at a higher frequency than the second switching element, optimizing the balance between component size and switching loss by using different frequency parameters in different parts of the system
2Loss of energy
If the switching frequency is decreased to reduce switching loss, then energy efficiency is improved, but the ripple current increases requiring larger reactors
Solution Approach 1:
The patent segments the switching operation into two independent circuits that can be controlled separately. The first switching circuit handles high-frequency switching with smaller ripple current, while the second switching circuit operates at lower frequency, collectively managing ripple current while maintaining low switching losses
Solution Approach 2:
The patent introduces an intermediate capacitor connected between the two switching circuits. This intermediate capacitor acts as a mediator that filters and stabilizes the voltage between the two circuits, reducing the overall ripple current while allowing the system to operate efficiently at optimized switching frequencies
3Adaptability or versatility
If the carrier frequency is varied linearly to control the booster circuit, then the output voltage range is expanded, but the noise frequency range increases requiring larger and more expensive filters
Solution Approach 1:
The patent segments the frequency control into two independent switching circuits operating at different carrier frequencies. This segmentation allows the system to expand the output voltage range through coordinated operation of the two circuits while each circuit operates within a narrower, more manageable frequency range, reducing the overall noise bandwidth
Solution Approach 2:
The patent changes the carrier frequency parameter differently for the two switching circuits. By assigning different frequency parameters to each circuit and coordinating their operation, the system achieves expanded output voltage range while keeping the noise frequency range of each individual circuit narrower and more easily filterable
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 configuration decreases switching loss and ripple current, reducing the size of the reactor and smoothing capacitor, thereby achieving cost reduction and improved efficiency.
Implementation Method 1
an intermediate capacitor connected in parallel with a series circuit of the second backflow prevention element and the first switching element. The intermediate capacitor is charged via the second backflow prevention element as a result of an ON operation of the second switching element, and the intermediate capacitor is discharged via the second backflow prevention element as a result of an ON operation of the first switching element
Implementation Method 2
a rectifier configured to rectify an AC voltage supplied from an AC power supply
Implementation Method 3
an inverter connected in parallel with the smoothing capacitor and configured to convert a DC voltage to an AC voltage and drive a motor
Data Source
AI summary
A rectifier, a booster circuit configured to boost an output voltage of the rectifier, a smoothing capacitor configured to smooth an output voltage of the booster circuit, and an inverter circuit configured to convert a DC voltage of the smoothing capacitor to an AC voltage and drive a motor forming a part of a device supplied with the voltage after the conversion, are included. In addition, a reactor, a first backflow prevention element, a second backflow prevention element, a first switching element, a second switching element, an intermediate capacitor, and a controller configured to control the first switching element and the second switching element, are included.