Cascaded DC-DC Converter Voltage Equalization
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Solution Overview
Problem
Existing high-voltage DC-DC conversion systems with series-connected DC-DC power modules face challenges in voltage equalization during startup or standby states, leading to increased volume and cost due to the need for discharge circuits and high-voltage relays.
Innovation Solution
A cascaded conversion system with DC-side capacitors connected in series and switching units comprising bridge arms with first and second switches, controlled by a control unit to generate a switching frequency signal for alternating on/off states, ensuring voltage equalization across capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discharge circuits and parallel resistors are used to equalize input voltage, then voltage equalization is achieved, but device volume and cost increase
Solution Approach 1:
The patent extracts the voltage equalization function from separate external components (discharge circuits and parallel resistors) and integrates it into the existing switching units of the DC-DC power modules. By utilizing the existing switching devices and control circuits, the need for additional equalization components is eliminated, thereby reducing device volume while maintaining voltage equalization capability
Solution Approach 2:
The switching units in the patent are designed to perform multiple functions: both power conversion and voltage equalization. The same switching devices and control circuits used for normal operation are also utilized for voltage equalization during startup and standby states, eliminating the need for dedicated equalization components and reducing overall device volume
2Reliability
If discharge circuits and parallel resistors are used to equalize input voltage, then voltage equalization is achieved, but manufacturing cost increases
Solution Approach 1:
The patent extracts the voltage equalization function from separate external components (discharge circuits and parallel resistors) and integrates it into the existing switching units of the DC-DC power modules. By utilizing the existing switching devices and control circuits, the need for additional equalization components is eliminated, thereby reducing device volume while maintaining voltage equalization capability
Solution Approach 2:
The switching units in the patent are designed to perform multiple functions: both power conversion and voltage equalization. The same switching devices and control circuits used for normal operation are also utilized for voltage equalization during startup and standby states, eliminating the need for dedicated equalization components and reducing overall device volume
3Reliability
If high-voltage DC relays are used for voltage adjustment, then voltage control is achieved, but insulation requirements and space occupation increase
Solution Approach 1:
The patent extracts the voltage control function from external high-voltage DC relays and implements it within the integrated switching units. By using the existing switching devices and control circuits already present in each DC-DC power module, the need for separate high-voltage relays and their associated insulation structures is eliminated, thereby reducing space occupation
Solution Approach 2:
The patent replaces mechanical relay-based voltage control with electronic switching control. The switching units use electronic switches and control circuits to adjust voltage, eliminating the need for mechanical relays and their associated insulation requirements and space occupation
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 approach reduces the volume and cost of voltage equalization by utilizing switching loss to adjust capacitor voltages, achieving equalization without the need for large discharge circuits or high-voltage relays.
Implementation Method 1
utilizing switching loss to adjust capacitor voltages
Data Source
AI summary
A cascaded conversion system and a voltage equalizing control method thereof are provided. The cascaded conversion system includes a plurality of conversion circuits connected in cascade. Each conversion circuit includes a DC-side capacitor, a switching unit and a control unit. The DC-side capacitors of the conversion circuits are electrically connected in series. In each conversion circuit, the switching unit is connected to the DC-side capacitor in parallel and includes a plurality of bridge arms. Each bridge arm includes a first switch and a second switch. The control unit controls the switches according to the voltage across the DC-side capacitor. The control unit controls the first and second switches to be turned on alternately. All the first switches are turned on and off simultaneously, and all the second switches are turned on and off simultaneously, thereby making the voltages across the DC-side capacitors of the conversion circuits equal.