Three-Level Rectification Converter for High-Voltage Bidirectional DC/DC
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional DC/DC converters face challenges in handling high-voltage applications, particularly in electric vehicle on-board chargers, due to limitations in withstand voltage and electromagnetic interference (EMI), and struggle with bidirectional operation and high efficiency across wide output voltage ranges.
Innovation Solution
A three-level rectification DC/DC converter with a resonant circuit that includes a primary circuit, resonant tank circuit, and secondary circuit, utilizing a transformer, flying capacitor, and switch bridge arm to achieve bidirectional operation and high voltage gain through controlled switching of secondary switches, allowing energy storage by short-circuiting the secondary circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SiC component with 1200V withstand voltage is used to handle 800V applications, then the withstand voltage requirement is met, but the cost increases and high dv/dt causes EMI problems
Solution Approach 1:
The patent applies segmentation by dividing the voltage handling into multiple levels. The three-level rectification circuit segments the 800V voltage into multiple lower voltage stages (e.g., 400V per stage), allowing the use of lower voltage switches (650V rated) that operate at lower dv/dt rates, thereby reducing EMI while still achieving the required 800V output through series connection of multiple voltage levels.
Solution Approach 2:
The patent transitions from a conventional single-level voltage conversion to a multi-level voltage conversion architecture. By adding the vertical dimension of voltage levels (from single level to three levels), the system achieves the required voltage handling capability while operating each switch at lower voltage stress, thus reducing EMI without requiring expensive SiC components.
2Adaptability or versatility
If GaN device is used in high-voltage (800V) work environment, then the development trend is followed, but the limited withstand voltage makes it hard to be directly applied
Solution Approach 1:
The patent segments the high-voltage application into multiple lower-voltage stages that can be handled by GaN devices. By operating GaN switches at their optimal voltage range (below 650V per switch) within the three-level architecture, the system leverages the high-frequency switching capability of GaN while avoiding its limitation of insufficient withstand voltage for direct 800V operation.
Solution Approach 2:
The patent introduces intermediate voltage levels and energy storage elements (inductors, capacitors) as mediators between the GaN switches and the 800V output. These intermediaries allow GaN devices to operate at lower voltages where they excel, while the overall system achieves the required 800V output through the multi-level conversion process.
3Reliability
If dual-active-bridge circuit with multiple phase shift technique is used, then zero-voltage switching is achieved under wide output range, but the control becomes complicated and high turn-off current causes high turn-off stress and EMI
Solution Approach 1:
The patent extracts the phase shift control complexity from the switching operation by using a different control approach. Instead of using multiple phase shifts between primary and secondary bridges, the invention uses a single-phase-shift control on the primary side combined with synchronous rectification on the secondary side, simplifying the control architecture while maintaining zero-voltage switching capability.
Solution Approach 2:
The patent inverts the conventional approach by placing the active switches and phase shift control on the primary side only, while using passive synchronous rectification switches on the secondary side. This inversion reduces the number of controlled switches and simplifies the control system, eliminating the need for complex multi-phase-shift control while achieving soft switching.
4Ease of operation
If LLC circuit with variable frequency control is used, then all switches achieve zero voltage switching and implementation is easy, but the bidirectional work requirement cannot be met
Solution Approach 1:
The patent enhances the functionality of the DC/DC converter by enabling bidirectional power flow capability. The three-level rectification circuit with controlled switching allows the converter to operate in both rectification modes (PFC and DC/DC conversion), making it a universal solution that can handle both unidirectional and bidirectional applications, unlike the conventional LLC resonant converter which is limited to unidirectional operation.
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 enables efficient bidirectional operation and high voltage gain while reducing the stress on secondary switches, making it easier to select components and dissipate heat, thus improving efficiency and reducing costs.
Implementation Method 1
the three-level rectification DC/DC converter has the characteristic of a resonant circuit and can meet the bidirectional work requirement
Implementation Method 2
A primary winding of the transformer is coupled between the first and second primary terminals. A secondary winding of the transformer is coupled between a first secondary terminal and a second secondary terminal of the resonant tank circuit
Data Source
AI summary
The present disclosure provides a three-level rectification DC/DC converter including primary and secondary circuits and a resonant tank circuit. A voltage between two primary terminals is a first voltage. The secondary circuit includes a flying capacitor, a switch bridge arm, and a capacitor bridge arm. The switch bridge arm includes four switches serially connected. Two terminals of the flying capacitor are respectively connected between the first and second switches and connected between the third and fourth switches. Two secondary terminals are respectively connected between the second and third switches and connected between two output capacitors of the capacitor bridge arm. In two consecutive periods of the first voltage, the first and second switches are in an on state for a preset time length after two falling edges respectively, and the third and fourth switches are in the on state for the preset time length after two rising edges respectively.