Pre-Charging DC-Bus Capacitors in Modular Power Systems
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Solution Overview
Problem
Existing power conversion systems for medium-voltage applications face challenges such as large size and high cost due to the need for medium-voltage elements, inability to hot-plug power modules, risk of system failure if pre-charging circuit components fail, limited pre-charging capability to one time, and unbalanced capacitor voltage, especially when grid voltage changes.
Innovation Solution
A power conversion system with independently pre-charging units in each power module, connected in parallel to DC-Bus capacitors, using auxiliary power sources for pre-charging, allowing each module to charge independently and reducing the size and power consumption of the pre-charging circuit, enabling hot-plugging and balancing capacitor voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-charging circuit uses medium-voltage elements to charge DC-Bus capacitors, then pre-charging function is achieved, but system size and cost increase
Solution Approach 1:
The pre-charging circuit is segmented into multiple independent pre-charging units, each responsible for charging a specific DC-Bus capacitor. This segmentation allows each unit to use lower-voltage elements rather than requiring a single medium-voltage pre-charging circuit, thereby reducing the size and cost of individual components while maintaining the overall pre-charging function.
Solution Approach 2:
The patent introduces auxiliary power sources as intermediaries to provide charging current to each pre-charging unit. These auxiliary power sources enable the pre-charging process without requiring the main power circuit to handle the full medium voltage, allowing the use of smaller, lower-voltage rated components in the pre-charging path.
2Reliability
If pre-charging circuit components fail, then pre-charging function is compromised, but system reliability is maintained through redundancy
Solution Approach 1:
By dividing the pre-charging circuit into multiple independent units, the failure of one unit does not affect the others. Each unit operates autonomously, so if one pre-charging unit fails, the remaining units can still charge their respective DC-Bus capacitors, maintaining overall system reliability without requiring complex redundancy mechanisms.
Solution Approach 2:
Each pre-charging unit is designed to be self-contained with its own auxiliary power source and control logic. This self-service capability means that each unit can detect and respond to its own failure conditions independently, simplifying the overall system control while maintaining reliability through distributed fault tolerance.
3Reliability
If pre-charging is performed once for all modules, then initial charging is achieved, but voltage balance cannot be maintained during operation
Solution Approach 1:
Each pre-charging unit is equipped with voltage detection circuitry that continuously monitors the voltage across its associated DC-Bus capacitor. Based on this feedback, the control unit can determine when re-charging is needed and activate the pre-charging function accordingly, maintaining voltage balance without requiring continuous or frequent pre-charging operations.
Solution Approach 2:
The pre-charging system transitions from a static, one-time charging approach to a dynamic, on-demand charging mechanism. Each pre-charging unit can be independently activated based on real-time voltage conditions, allowing the system to adapt to changing operational requirements and maintain voltage balance flexibly throughout the system's operation.
4Loss of energy
If power modules are connected in series at input and parallel at output, then power conversion efficiency is improved, but pre-charging becomes more complex
Solution Approach 1:
The pre-charging circuit is segmented to match the modular structure of the power conversion system. Each power module has its own dedicated pre-charging unit, which simplifies the pre-charging process by allowing independent charging of each module's DC-Bus capacitor without requiring complex coordination across the entire series-connected system.
Solution Approach 2:
Each pre-charging unit is designed with a universal structure that can be replicated across all power modules. This modular universality means that the same pre-charging circuit design can be used for each module in the series-connected system, reducing overall complexity through standardization while maintaining the ability to charge multiple modules simultaneously or independently.
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 smaller, more efficient pre-charging circuits with lower power loss, allows for independent pre-charging of each power module, and prevents system failure if a pre-charging unit fails, while maintaining balanced capacitor voltage and enabling hot-plugging of power modules.
Implementation Method 1
a pre-charging unit electrically connected to the charging input end for receiving direct current and electrically connected to the DC-Bus capacitor for pre-charging the DC-Bus capacitor
Data Source
AI summary
The present invention discloses a power conversion system and a method for pre-charging DC-Bus capacitors therein. The power conversion system comprises a plurality of power modules, each including a power input end; a charging input end; a power output end; at least one power conversion unit, each of the power conversion unit including at least one DC-Bus capacitor and being electrically connected to the power input end and the power output end; and a pre-charging unit electrically connected to the charging input end for receiving direct current and electrically connected to the DC-Bus capacitor for pre-charging the DC-Bus capacitor. The power input ends of the plurality of power modules are connected in series and then electrically connected to an AC power source, and the power output ends of the plurality of power modules are connected in parallel.