Power Conversion Device PWM Control for High Power Factor
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Solution Overview
Problem
Conventional DC/DC electric power conversion devices fail to achieve high-power-factor control for input current and maintain constant voltage of a DC capacitor when connected to an AC power supply, due to inability to control the phase of the AC power supply.
Innovation Solution
An electric power conversion device comprising a rectification circuit, a switching section with semiconductor elements, and a control circuit that performs high-frequency PWM control to rectify AC input, step up voltage, and smooth output, enabling high-power-factor control and constant DC capacitor voltage through precise control of the switching elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional DC/DC electric power conversion device is used with AC power supply, then device can perform voltage conversion, but high-power-factor control for input current cannot be performed and voltage of energy transfer capacitor cannot be controlled to be constant
Solution Approach 1:
The patent divides the control function into two independent control loops: one for controlling the sum of ON periods of switching elements to achieve high-power-factor input current control, and another for controlling the ratio of ON periods to maintain constant energy transfer capacitor voltage. This segmentation allows each control objective to be achieved independently without interference.
Solution Approach 2:
The patent changes the control parameters by introducing dual PWM control with different duty cycle relationships. The first PWM signal controls the overall ON period sum while the second PWM signal controls the duty cycle ratio, enabling independent adjustment of input current power factor and capacitor voltage stability.
2Volume of moving object
If device configuration is downsized by reducing reactor and capacitor capacity, then device size is reduced, but control precision may be affected
Solution Approach 1:
The patent employs dynamic PWM control where the duty cycles of switching elements are continuously adjusted based on feedback. This dynamic control allows the system to maintain precise control over input current and capacitor voltage even with reduced energy storage component sizes, as the control adapts to maintain stability.
Solution Approach 2:
The patent implements feedback control mechanisms where the actual capacitor voltage and input current are monitored and used to adjust the PWM duty cycles. This feedback ensures that even with reduced reactor and capacitor capacities, the system maintains precise control and stability through continuous correction.
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 solution allows for reliable high-power-factor control of input current and constant voltage of the DC capacitor, reducing the capacity of reactors and capacitors, leading to a downsized device configuration.
Implementation Method 1
a rectification circuit for rectifying input from an AC power supply
Implementation Method 2
a reactor having a first end connected to a positive side terminal of the rectification circuit
Implementation Method 3
a first semiconductor element, a second semiconductor element, a first switching element, and a second switching element for each controlling conduction and block of current
Implementation Method 4
a smoothing capacitor for smoothing the output of the switching section
Data Source
AI summary
An electric power conversion device which performs conversion to desired voltage using charge and discharge of a DC capacitor includes: a reactor connected to a rectification circuit; a leg part in which diodes and first and second switching elements are connected in series between positive and negative terminals of a smoothing capacitor, and to which the reactor is connected; and the DC capacitor. A control circuit performs high-frequency PWM control for the first and second switching elements using the same drive cycle, with their reference phases shifted from each other by a half cycle, and controls a sum and a ratio of ON periods of the first and second switching elements in one cycle, thereby allowing both high-power-factor control for input AC current and voltage control for the DC capacitor.