Totem-Pole AC/DC Converter Control for Smaller DC Capacitors
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Solution Overview
Problem
Conventional power conversion devices face challenges in reducing the capacitance and size of the DC capacitor while maintaining accurate control of input current and voltage, due to interference between high power factor control and voltage control, and a long charging/discharging time constant relative to the AC power supply cycle.
Innovation Solution
A power conversion device with a totem pole type AC/DC converter circuit that includes a rectification bridge circuit, leg circuit with semiconductor switching elements, and a reactor, where a control circuit generates switching patterns to alternately excite and reset the reactor, and adjusts duty cycles to separate the control of input current and capacitor voltage, allowing for high-frequency PWM control to achieve both high power factor and voltage control with reduced capacitor capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If control is switched at a cycle of the AC power supply, then high power factor control is achieved, but the charging/discharging time constant of the DC capacitor becomes greater than or equal to 1/4 of the AC cycle, making it difficult to reduce capacitor capacitance and size
Solution Approach 1:
The patent divides the control cycle into multiple sub-cycles, performing high power factor control at a finer time resolution than the AC power supply cycle. This segmentation allows the DC capacitor to be charged and discharged in smaller, more frequent steps, reducing the required capacitance while maintaining control accuracy.
Solution Approach 2:
The patent implements dynamic switching control where the switching frequency is decoupled from the AC power supply frequency. The control unit dynamically adjusts switching timing within each AC cycle to independently optimize both power factor and capacitor voltage, enabling faster response than traditional AC-cycle-synchronized control.
2Manufacturing precision
If the charging period and discharging period of the DC capacitor are adjusted within a switching cycle, then voltage control for the DC capacitor is improved, but interference with high power factor control of input current occurs, making it difficult to maintain control accuracy
Solution Approach 1:
The patent segments the control functions into separate processing stages: high power factor control calculations are performed independently from capacitor voltage control calculations. This functional segmentation prevents interference between the two control objectives while maintaining both accuracies.
Solution Approach 2:
The control unit performs preliminary calculations for high power factor control switching timing before executing capacitor voltage control adjustments. By establishing the power factor control baseline first, then superimposing voltage control modifications, the patent prevents conflicting control actions and maintains both control accuracies.
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 effectively suppresses interference between input current and voltage control, enabling high-accuracy control and reducing the capacitance and size of the DC capacitor, thus promoting the downsizing of the power conversion device.
Implementation Method 1
A power conversion device that includes a circuit having a plurality of semiconductor switching elements connected in series, a DC capacitor for energy transfer, and a reactor, and that outputs multi-level DC power by utilizing charging and discharging of the DC capacitor
Data Source
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AI summary
Provided is a power conversion device that can suppress interference between control of input current from an AC power supply and voltage control for a DC capacitor to perform both the controls with high accuracy, and can reduce the capacitance and size of the DC capacitor. A power conversion circuit (1) includes a rectification bridge circuit (3), a leg circuit (4) having upper and lower legs (4a, 4b) connected in series, a DC capacitor (Cf), a smoothing capacitor (Cdc), and a reactor (L). A control circuit (7) performs PWM control of the leg circuit (4) by generating a duty cycle so as to control a voltage of the DC capacitor (Cf) while controlling an input current from an AC power supply (2), in a control cycle. When the duty cycle is generated, a sum of duty cycles is made constant in one cycle for each leg (4a, 4b).