Solid-State Precharge Apparatus for Power Conversion Systems
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Solution Overview
Problem
Existing power conversion systems face challenges in efficiently precharging DC bus capacitors while minimizing inrush current and avoiding the costs, size, and weight associated with traditional precharging methods, such as contactors or circuit breakers.
Innovation Solution
The use of solid-state precharge switching circuitry with thyristors and reverse diodes coupled in AC circuit paths, along with a precharge resistor, controlled by a controller that turns off thyristors until a non-zero DC bus voltage threshold is reached, allowing the capacitor to charge through the resistor and then switching on to bypass the resistor for normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional precharging methods using contactors or circuit breakers are employed, then the DC bus capacitor can be precharged, but the system incurs increased cost, size, and weight
Solution Approach 1:
The patent replaces mechanical precharging devices (contactors or circuit breakers) with solid-state semiconductor switching devices. The semiconductor switches are integrated into the power conversion system and controlled by switching logic to perform the precharging function, eliminating the need for separate mechanical precharging apparatus and thereby reducing cost, size, and weight while maintaining the precharge function.
2Reliability
If traditional precharging methods using contactors or circuit breakers are employed, then the DC bus capacitor can be precharged, but the system complexity increases
Solution Approach 1:
The patent merges the precharging function with the main power conversion system by integrating semiconductor switching devices that serve dual purposes: precharging the DC bus capacitor and performing normal power conversion operations. This integration eliminates the need for separate precharging apparatus and reduces overall system complexity compared to traditional methods requiring additional contactors or circuit breakers.
Solution Approach 2:
The semiconductor switching devices in the patent are designed to perform multiple functions: they act as precharge switches during startup and as power conversion switches during normal operation. This multi-functionality reduces the need for dedicated precharging components and simplifies the overall system architecture.
3Productivity
If the DC bus capacitor is charged directly without precharging, then the system responds faster, but inrush current damages components
Solution Approach 1:
The patent implements preliminary action by precharging the DC bus capacitor through semiconductor switching devices before closing the main circuit breaker. The switching logic controls the semiconductor switches to charge the capacitor gradually, preventing inrush current from damaging the circuit breaker and other components, while still enabling fast system response once precharged.
Solution Approach 2:
The semiconductor switching devices serve as intermediaries between the AC input and the DC bus capacitor during the precharging phase. They control the charging current to prevent inrush current while still enabling the capacitor to charge to the required voltage level, thus protecting downstream components without sacrificing system response speed.
4Object-affected harmful factors
If precharge resistors are used in AC circuit paths, then inrush current is limited, but the resistor dissipates energy and reduces efficiency
Solution Approach 1:
The patent employs dynamic control of semiconductor switching devices to manage the precharging process. The switching logic dynamically adjusts the switching states to limit inrush current during capacitor charging, and then transitions to bypass the precharge resistors once charging is complete. This dynamic switching minimizes energy dissipation in the precharge resistors while still protecting against inrush current.
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 inrush current, mitigates stress on system components, and eliminates the need for complex switching logic, providing a cost-effective and efficient method for precharging DC bus capacitors and filter capacitors, thereby preventing undesired tripping of the converter.
Implementation Method 1
A precharge resistor is coupled in one or more of the AC circuit paths. A controller turns all the thyristors off to allow the DC bus capacitor to charge through the precharge resistor
Implementation Method 2
thyristors or other semiconductor switching devices and reverse diodes coupled in AC circuit paths between AC input lines and a rectifier
Data Source
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AI summary
Power conversion systems, methods and precharge systems are disclosed to charge a DC bus capacitor, including thyristors and reverse diodes coupled in AC circuit paths between AC input lines and a rectifier, a precharge resistor coupled in one or more of the AC circuit paths, and a controller to turn all the thyristors off to allow the DC bus capacitor to charge through the precharge resistor, and to turn all the thyristors on when the DC bus voltage reaches a non-zero threshold value.