Power Conversion Apparatus Reducing Switching Losses
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Solution Overview
Problem
Conventional power conversion systems experience high switching losses and inefficiencies when converting direct current power from solar cells or fuel cells to alternating current power, particularly due to high switching frequencies required in PWM-control inverters.
Innovation Solution
A power conversion apparatus utilizing a sequence of square wave voltage generators and a sinusoidal wave voltage generator, where square wave voltages are chopped at lower frequencies and then PWM-controlled to correct voltage differences, reducing switching losses and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PWM-control inverter switches at high frequency (around 18 kHz) to convert direct current to alternating current, then the power conversion can be achieved, but large switching loss occurs resulting in poor power conversion efficiency
Solution Approach 1:
The patent divides the power conversion process into two distinct stages: a chopper circuit that operates at low frequency to perform initial power conversion, and a PWM-control inverter that operates at high frequency to perform final power conversion. This segmentation allows each stage to operate at its optimal frequency, with the chopper circuit handling the bulk of power conversion at low frequency to minimize switching losses, while the PWM inverter provides precise control at high frequency.
Solution Approach 2:
The patent introduces periodic action by using the chopper circuit to perform power conversion at a low frequency that is periodically synchronized with the commercial power system frequency. This periodic low-frequency operation reduces switching losses compared to continuous high-frequency switching, while still achieving effective power conversion through the combination of chopper and PWM stages.
2Productivity
If conventional PWM-control inverter is used for power conversion, then direct current can be converted to alternating current, but the switching frequency must be high (around 18 kHz) causing large switching loss
Solution Approach 1:
The patent segments the power conversion function into two separate circuits: a chopper circuit for low-frequency power conversion and a PWM-control inverter for high-frequency power conversion. This segmentation enables the system to maintain full power conversion capability while reducing overall switching losses by distributing the conversion task across two stages operating at different frequencies.
Solution Approach 2:
The chopper circuit acts as an intermediary stage between the direct current source and the PWM-control inverter. It performs initial power conversion at low frequency, reducing the burden on the PWM inverter and allowing it to operate more efficiently with reduced switching losses while maintaining the required power conversion capability.
Data Source
Figure 1
Figure 2(A)~2(D)
Figure 3(A)~3(B)
AI summary
A first chopper circuit generates a first sequence of square wave voltages having a voltage level that changes to a positive side by chopping a direct current voltage at a system frequency. A second chopper circuit generates a second sequence of square wave voltages having a voltage level that changes to a negative side by chopping a direct current voltage at a frequency twice as high as the system frequency. The second chopper circuit further generates a third sequence of square wave voltages having a voltage level that changes to the positive and negative side in turns in the manner of sinusoidal wave by summing the first sequence of square wave voltages and the second sequence of square wave voltages. A third chopper circuit chops the third sequence of square wave voltages at a frequency determined by a timing that depends on if a voltage difference thereof to a sinusoidal wave voltage results in a positive value or a negative value and outputting the chopped third sequence of square wave voltages as a charge/discharge output. The third chopper circuit PWM-controls the charge/discharge output at a PWM frequency so that the difference is corrected to thereby generate a sinusoidal wave voltage that continuously changes to the positive and negative sides.