Three-Level Inverter for Direct AC Charging
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Solution Overview
Problem
Existing power conversion devices require a separate conversion circuit to convert three-phase AC voltage from a three-phase charger into DC voltage for charging a storage battery, increasing the size and cost of the system.
Innovation Solution
A power supply device with a three-level inverter connected in parallel to the storage battery, utilizing a capacitor unit and switching elements to convert three-phase AC voltage into DC voltage without a separate conversion circuit, allowing direct charging from a three-phase AC charger.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate conversion circuit is provided to convert three-phase AC voltage into DC voltage for charging the storage battery, then the charging function is achieved, but the device complexity and cost increase
Solution Approach 1:
The patent merges the three-phase AC to DC conversion function with the existing three-level inverter by connecting the three-phase AC charger to specific terminals (P11, P12, P13) and controlling the switching elements. The inverter's capacitor unit and switching elements are utilized to perform both the voltage conversion and charging functions, eliminating the need for a separate conversion circuit.
Solution Approach 2:
The three-level inverter is designed to perform multiple functions: it can operate as a power converter for motor drive, as a three-phase AC to DC converter for battery charging, and as a voltage regulator. By controlling the on-off states of the switching elements based on the connection configuration, the same hardware structure achieves different functions without requiring additional dedicated circuits.
2Reliability
If a separate conversion circuit is provided to convert three-phase AC voltage into DC voltage, then the charging function is achieved, but the size and cost of the power supply device increase
Solution Approach 1:
The conversion circuit functionality is merged into the existing inverter structure. The capacitor unit (C1, C2) and switching elements (S11-S44) that were originally designed for motor drive applications are repurposed to also perform AC-DC conversion for battery charging, thereby eliminating the need for separate conversion circuitry and reducing overall device size and cost.
Solution Approach 2:
The inverter system is designed with universal functionality to handle both motor drive operations and battery charging operations. The same hardware components can be controlled in different modes to achieve different functions, maximizing resource utilization and minimizing the total equipment footprint and cost.
3Device complexity
If the three-level inverter is used for both motor drive and three-phase AC charging, then the device complexity is reduced, but the control complexity increases
Solution Approach 1:
The patent implements preliminary configuration by pre-defining the connection relationships between the three-phase AC charger terminals and the inverter terminals. The control unit is programmed with predetermined control strategies for different operating modes (motor drive vs. charging), and the switching elements are pre-configured in specific on-off patterns based on the detected connection configuration, simplifying the real-time control decision-making process.
Solution Approach 2:
The control unit detects the connection configuration between the three-phase AC charger and the inverter, and based on this feedback information, automatically adjusts the control strategy for the switching elements. This feedback mechanism enables the system to intelligently switch between different operating modes and optimize the control parameters, managing control complexity through adaptive response.
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 efficient charging of the storage battery using a three-phase AC charger without a separate conversion circuit, reducing the size and cost of the power supply device while maintaining effective voltage conversion.
Implementation Method 1
turning on and off the first switching element, the second switching element, the third switching element, and the fourth switching element, and enabling three-level voltage to be output to a motor generator
Implementation Method 2
a capacitor unit having a first capacitor and a second capacitor connected in series with each other between a positive terminal and a negative terminal of the storage battery
Implementation Method 3
a first diode connecting between a portion between the first switching element and the second switching element and a portion between the first capacitor and the second capacitor, and a second diode connecting between a portion between the third switching element and the fourth switching element and the portion between the first capacitor and the second capacitor
Data Source
AI summary
A power supply device includes a storage battery; a capacitor unit having first and second capacitor; a three phase power converter, connected in parallel with the storage battery, each phase having first to fourth switching elements in series; three connection terminals electrically connectable to a three-phase AC charger; and a control unit, in a case where the three connection terminals and the three-phase AC charger are electrically connected between the first switching elements and the second switching elements for the respective three phases in the three-level inverter, before the storage battery is charged by means of the three-phase AC charger, charging the first capacitor with use of the storage battery and setting voltage of the second capacitor to 0 V.