Power Factor Correction Control for Bidirectional AC/DC Converters
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Solution Overview
Problem
Existing bidirectional AC/DC conversion systems, such as those used in plug-in hybrid electric vehicles, face inefficiencies due to reactive power caused by current shunted to capacitors in the power factor correction (PFC) circuit, which is not effectively canceled out, leading to suboptimal power factor correction and increased total harmonic distortion.
Innovation Solution
A power factor correcting device that includes a converter and a control unit with detection and calculation units to determine the magnitude of reactive current and calculate an operation amount for phase delay of switching elements, allowing the cancellation of advanced-phase reactive current and reduction of total harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a power factor correction circuit with capacitor is used, then reactive current flows through the capacitor causing advanced-phase current, but the power factor correction becomes suboptimal and total harmonic distortion increases
Solution Approach 1:
The control unit calculates the reactive current magnitude flowing through the capacitor and determines a phase delay amount to counteract the advanced-phase current. By applying this preliminary compensating action, the system cancels out the harmful reactive current effect before it degrades power factor correction performance, thereby reducing total harmonic distortion while maintaining capacitor-based PFC circuit functionality
2Object-generated harmful factors
If the switching phase is delayed to cancel reactive current, then power factor correction improves, but conversion efficiency may be affected by increased switching losses
Solution Approach 1:
The control unit calculates the precise phase delay amount needed to cancel the reactive current based on the detected current magnitude and capacitor characteristics. By applying only the necessary partial delay rather than excessive delay, the system achieves effective reactive current cancellation and power factor improvement while minimizing additional switching losses that would reduce conversion efficiency
3Object-generated harmful factors
If the converter switches AC voltage to DC voltage with phase control, then power factor is corrected, but the complexity of control increases
Solution Approach 1:
The control unit detects the magnitude of current flowing through the capacitor and uses this feedback information to calculate the appropriate phase delay amount. This feedback mechanism enables the system to dynamically adjust the switching phase to cancel reactive current while maintaining a relatively simple control structure, avoiding the need for complex control algorithms
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 corrects the power factor of total AC power including reactive power and reduces total harmonic distortion, improving the efficiency of bidirectional AC/DC conversion systems by controlling the phase delay of switching elements to align with the target phase delay, thereby enhancing power factor correction.
Implementation Method 1
a converter that converts, by switching, AC voltage into DC voltage
Implementation Method 2
a circuit with a capacitor through which reactive current flows
Data Source
AI summary
A power factor correcting device that controls switching of a converter that converts AC voltage inputted via a circuit with a capacitor through which reactive current flows into DC voltage calculates the magnitude of the reactive current based on the magnitude of the AC voltage inputted to the converter and the capacitance of the capacitor and corrects a power factor including the circuit, calculates a target value for a phase delay of the AC current with respect to the AC voltage based on the calculated magnitude and the magnitude of the AC current inputted to the converter or the magnitude of the DC power outputted from the converter, and calculates an operation amount for delaying the phase of the switching based on the calculated target value.