Three-Phase Charging Converter with Buck Stage for Power Factor Correction
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Solution Overview
Problem
Existing devices for charging electrical energy stores from three-phase AC voltage sources face inefficiencies and additional hardware requirements, particularly in achieving sinusoidal phase currents in phase with the AC voltage source and ensuring compliance with power factor correction standards.
Innovation Solution
A device comprising three half-bridges with inductors connected between switch nodes and a phase of the AC voltage source, along with a buck converter connected to an intermediate circuit capacitor, where the buck converter switch is cyclically actuated to form sinusoidal phase currents, and can be bypassed in regular mode, utilizing a control device to manage switch states for efficient charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a known device with active B6 bridge and buck converter is used for three-phase charging, then power factor correction can be achieved, but additional hardware components and increased device complexity are required
Solution Approach 1:
The converter device is designed to perform multiple functions: it operates as a drive converter during motor operation and as a charging converter when connected to an electrical energy store. The same converter circuitry, including the six switches and inductors, serves both purposes, eliminating the need for separate power factor correction hardware and reducing overall device complexity
Solution Approach 2:
The invention merges the charging function and power factor correction function into a single integrated converter device. The buck converter is integrated with the existing converter circuit, and the same intermediate circuit capacitor serves both the drive function and charging function, reducing the number of required hardware components
2Reliability
If separate charging and drive converter devices are used, then functional requirements are met, but device complexity and hardware requirements increase
Solution Approach 1:
A single converter device is designed to universally handle both drive operation (powering a motor) and charging operation (storing energy in an electrical energy store). The converter's topology with six switches and three inductors remains the same, but its function changes based on operational mode, eliminating the need for separate drive and charging converters
Solution Approach 2:
The converter device dynamically switches between different operational modes. A control device manages the switching states of the six switches to adapt the converter's function: in drive mode, it operates as a standard voltage source converter; in charging mode, it operates as a charging converter with power factor correction, allowing one device to fulfill multiple functional requirements
3Productivity
If the buck converter switch is cyclically switched in charging mode, then charging current is generated, but additional control complexity is introduced
Solution Approach 1:
In charging mode, the buck converter switch is cyclically switched at a predetermined frequency to generate charging current. This periodic switching action allows the buck converter to transfer energy from the intermediate circuit capacitor to the electrical energy store in controlled pulses, enabling efficient charging while using the existing converter infrastructure
Solution Approach 2:
The control device monitors the operational state and switch positions to determine whether the system is in drive mode or charging mode. Based on this feedback, it adjusts the switching strategy: in drive mode, it controls the six switches for motor operation; in charging mode, it enables cyclic switching of the buck converter switch to generate charging current, optimizing control based on real-time conditions
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
This solution enables efficient, cost-effective three-phase charging with reduced harmonic emission, utilizing existing converter devices for both drive and charging modes, and supports sinusoidal phase currents in phase with AC voltage, enhancing power factor correction and reducing hardware needs.
Implementation Method 1
an inductor is connected electrically between a respective node point of two switches of one of the half-bridges and a respective phase of the AC voltage source
Implementation Method 2
a buck converter device electrically connected to an intermediate circuit capacitor of the converter device
Data Source
AI summary
The invention relates to a device (100) for charging an electrical energy store (B) from a three-phase AC voltage source (U1, U2, U3), said device having: —a converter device (20) electrically connected to the AC voltage source (U1, U2, U3) and with three half-bridges (H1, H2, H3), each having two series-connected switches (S1, S2; S3, S4; S5, S6), wherein an inductor (L1, L2, L3) is connected electrically between a respective node point of two switches (S1 . . . S6) of one of the half-bridges (H1, H2, H3) and a respective phase of the AC voltage source (U1, U2, U3); —a buck converter device (TS) electrically connected to an intermediate circuit capacitor (C1) of the converter device (20), wherein a switch (STS) of the buck converter device (TS) is cyclically switched in a charging mode of the device (100) and is open in a regular mode of the converter device (20); and —a switch (SF) by means of which the buck converter device (TS) can be bypassed in regular mode of the converter device (20); —wherein, depending on the phase voltages of the AC voltage source (U1, U2, U3) and currents through the inductors (L1, L2, L3), the switch (STS) of the buck converter device (TS) and the switches (S1 . . . S6) of the half bridges (H1, H2, H3)of the converter device (20) can be switched by means of a control device (10) in such a manner that a charging current for the electrical energy store (B) drawn from the AC voltage source (U1, U2, U3)in order to charge the electrical energy store (B) is formed such that each phase current of the AC voltage source (U1, U2, U3) is substantially sinusoidal, the phase currents being substantially in phase with the corresponding phase voltages of the AC voltage source (U1, U2, U3).