Power Conversion Device Switching Frequency Control
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Solution Overview
Problem
Existing power conversion devices that convert AC power to DC and control switching frequency are complex and costly due to the use of oscillators and current sources, making it difficult to simply switch or increase the switching frequency without increasing hardware costs.
Innovation Solution
A power conversion device configuration that includes a rectifier circuit, a smoothing unit, a short-circuiting unit with a switching element, current and voltage detecting units, and a switching control unit with a switching frequency changing unit using logic circuits, allowing for frequency adjustment without additional hardware costs by utilizing general microcomputer functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an oscillator and current source are used to control switching frequency, then the switching frequency can be controlled, but the hardware configuration becomes complicated and costs increase
Solution Approach 1:
The patent extracts the frequency control function from dedicated hardware (oscillator and current source) and relocates it to software implementation within a microcomputer. The microcomputer's built-in timer and counter resources are utilized to generate PWM signals with variable frequency, eliminating the need for separate oscillator circuits and current sources while maintaining frequency control capability.
Solution Approach 2:
The patent replaces the mechanical/electrical hardware system (oscillator and current source) with a software-based control system running on a microcomputer. The microcomputer uses its digital processing capabilities to generate and modulate PWM signals, substituting physical frequency control hardware with programmable software logic that achieves the same function with reduced component count.
2Volume of moving object
If the switching frequency is increased to reduce reactor inductance value, then the reactor size can be reduced, but the hardware complexity and cost increase
Solution Approach 1:
The patent implements dynamic switching frequency adjustment capability through software control. The microcomputer can vary the PWM frequency based on operating conditions, allowing the system to optimize reactor size for different power levels and load conditions. This dynamic control enables the use of smaller reactors without requiring fixed high-frequency hardware designs.
Solution Approach 2:
The patent changes the operating parameter (switching frequency) from a fixed hardware-determined value to a software-controllable variable. By programmatically adjusting the PWM frequency, the system can achieve high-frequency operation that reduces reactor inductance requirements and physical size, while maintaining the flexibility to adapt frequency based on operational needs without hardware modifications.
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
Enables simple switching or increase of switching frequency without increasing costs, improving power factor and reducing harmonics while maintaining efficient operation and cost-effectiveness.
Implementation Method 1
a rectifier circuit unit that rectifies a voltage of the AC power source
Implementation Method 2
a smoothing unit that smooths a DC voltage on the load side of the rectifier circuit unit
Implementation Method 3
a switching element; a switching frequency changing unit that is disposed between the switching control unit and the short-circuiting unit and that is configured to be capable of changing a frequency of the control signal
Data Source
Figure 1~2
Figure 3(a)~4
Figure 5~6(c)
AI summary
In order to simply switch a switching frequency, a power conversion device (13) is disposed between an AC power source (1) and a load (12) and includes: a rectifier circuit unit (2) that rectifies a voltage of the AC power source (1); a smoothing unit (25) that smooths a DC voltage on the load (12) side of the rectifier circuit unit (2); a short-circuiting unit (24) that is disposed on the AC power source (1) side of the smoothing unit (25) and that short-circuits the AC power source (1); a step-up reactor (4) that is disposed on the AC power source (1) side of the short-circuiting unit (24); at least one of a reactor current detecting unit (8) that detects the current of the step-up reactor (4) and a bus voltage detecting unit (9) that detects an output voltage of the smoothing unit (25); a counterflow preventing element (6) that prevents a counterflow of the current from the smoothing unit (25) to the AC power source (1); a switching control unit (10) that generates a drive pulse from the output signal of the reactor current detecting unit (8) or the bus voltage detecting unit (9) and that outputs a control signal for the short-circuiting unit (24); and a switching frequency changing unit (11) that is disposed between the switching control unit (10) and the short-circuiting unit (24) and that changes a frequency of the control signal using a logic operation.