Two-Stage AC-DC Converter for Low-Voltage Three-Phase PFC
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Solution Overview
Problem
Existing three-phase boost-type PFC converters face challenges when the required output voltage is low, leading to stress on converter components and increased costs due to the need for over-dimensioning, especially when the battery is largely depleted.
Innovation Solution
An electrical converter with two converter stages and a current injection circuit, controlled by a control unit, allows for pulse width modulation to achieve a DC voltage higher than the instantaneous full-wave rectified voltage, reducing stress on components by operating in a second mode when low voltage is required, and maintaining sinusoidal current and unity power factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the isolated DC/DC converter stage fully absorbs a high voltage ratio when the required output voltage is low, then the converter can operate, but stress on converter components increases and over-dimensioning is required
Solution Approach 1:
The patent implements dynamic operation modes (first mode with boost converter active, second mode with boost converter inactive) that adapt to the required output voltage level. When output voltage is low, the system switches to the second mode, dynamically changing the voltage ratio absorption distribution between converter stages to avoid excessive stress on components
Solution Approach 2:
The control unit changes operational parameters by switching between different modes based on the required output voltage. In the second mode, the boost converter is deactivated and the isolated DC/DC converter operates with a reduced voltage ratio, thereby reducing stress on components and extending service life
2Adaptability or versatility
If the isolated DC/DC converter stage fully absorbs a high voltage ratio when the required output voltage is low, then the converter can operate, but over-dimensioning of converter components is required, increasing cost
Solution Approach 1:
The system dynamically switches between operation modes based on the required output voltage. In the second mode for low output voltage, the voltage ratio absorption is redistributed, allowing the use of smaller, less expensive components instead of over-dimensioned components that would be required if the converter always operated in the first mode
Solution Approach 2:
By changing the operational mode parameter, the system allows the isolated DC/DC converter to operate with a lower voltage ratio in the second mode, enabling the use of cost-effective components rather than expensive over-dimensioned components
3Reliability
If the converter operates in the second mode with low output voltage, then stress on components is reduced, but the voltage between DC bus terminals is lower than the full-wave rectified AC voltage
Solution Approach 1:
The system dynamically adapts the DC output voltage to match the required load demand. When operating in the second mode, the DC output voltage naturally follows the full-wave rectified AC voltage profile, which is appropriate for applications like battery charging where the load can accept variable voltage
Solution Approach 2:
The converter is designed to universally handle different output voltage requirements by supporting two operation modes. The second mode is particularly suitable for battery charging applications where the battery voltage varies with state of charge, making the converter adaptable to different charging stages
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 reduces stress on converter components and lowers costs by allowing the converter to operate efficiently at low output voltages, maintaining sinusoidal current and unity power factor, especially when connected to a DC/DC converter or DC/AC converter in constant power mode.
Implementation Method 1
The first converter stage is configured for converting between the AC signal at the three phase terminals and a first signal, e.g. a (switched) voltage or a current, at the first and second intermediate nodes
Implementation Method 2
The second converter stage is operable to convert between a second signal, e.g. a (switched) voltage or a current, at the third and fourth intermediate nodes and a DC signal at the first and second DC terminals
Implementation Method 3
The current injection circuit is operable to connect between the phase terminal having a smallest absolute instantaneous voltage value of the three phase voltages and the first and second DC terminals
Data Source
AI summary
An AC-DC converter includes three phase terminals, first and second DC terminals, a first converter stage for converting between the AC signal and a first signal at first and second intermediate nodes, a second converter stage to convert between a second signal at third and fourth intermediate nodes and the DC signal at the first and second DC terminals. The second converter stage has a first active switch. A link connects the first and third intermediate nodes and the second and fourth intermediate nodes. A current injection circuit has second active switches. In a first mode, the first active switch and the second active switches are operated through PWM. In a second mode, the third and fourth intermediate nodes are continuously connected to the first and second DC terminals such that the second converter stage is inoperative and the second active switches are operated through PWM.