Bus Capacitor Discharge Control Using Bridge Arm Switches
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Solution Overview
Problem
Conventional discharge control methods for bus capacitors in power converter systems are costly, complex, and inefficient, requiring high-voltage relays and additional discharge elements, which lead to increased power loss and extended discharge times, posing safety risks and complicating system maintenance.
Innovation Solution
A discharge control method utilizing pulse control signals to manage power semiconductor switches in bridge arms, forming a discharge loop between the bus capacitor's terminals, allowing for adjustable discharge times and reducing the need for additional discharge elements by using phase dislocation modulation to control the discharge current effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-voltage relay and discharge resistor are used for bus capacitor discharge, then the discharge function is achieved, but the system cost and complexity increase
Solution Approach 1:
The patent extracts the discharge function from the main power converter circuit by utilizing the inherent bridge arm switches. Instead of adding a separate relay and discharge resistor circuit, the invention reuses the existing IGBT switches and diodes in the bridge arms to create a discharge path, thereby eliminating the need for additional high-voltage relay and discharge resistor components
Solution Approach 2:
The bridge arm switches in the power converter are designed to serve multiple functions: power conversion during normal operation and capacitor discharge during shutdown or fault conditions. By controlling the bridge arm switches in a specific configuration, the same hardware components perform both the primary conversion function and the safety discharge function, reducing overall system complexity
2Loss of time
If a discharge resistor with small resistance value is used, then the discharge time is reduced, but the power loss increases
Solution Approach 1:
The patent implements dynamic control of the discharge process by adjusting the switching states of bridge arm switches based on the real-time voltage level of the bus capacitor. During the discharge process, the control strategy dynamically modifies which switches are conductive, allowing the system to achieve rapid initial discharge when voltage is high while transitioning to a lower power loss state as voltage decreases, thus optimizing both discharge time and power loss throughout the entire discharge cycle
Solution Approach 2:
The discharge process is controlled through periodic switching of the bridge arm switches, creating a controlled oscillation or stepped discharge pattern. This periodic switching allows the capacitor to discharge in controlled intervals, achieving rapid discharge when needed while managing power loss through the periodic nature of the switching action rather than continuous high-power dissipation
3Loss of energy
If a discharge resistor with large resistance value is used, then the power loss is reduced, but the discharge time increases
Solution Approach 1:
The control strategy dynamically adjusts the discharge path configuration based on the capacitor voltage level. When voltage is high, the system configures switches to create a lower effective resistance path for rapid discharge. As voltage decreases, the switching configuration changes to maintain safe discharge while reducing power loss, thus dynamically optimizing the trade-off between discharge time and power loss throughout the discharge process
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 method enables efficient and controlled discharge of bus capacitors, reducing system complexity and cost by utilizing existing power semiconductor switch devices, ensuring safe and rapid discharge within allowable current ranges without additional high-voltage relays or discharge resistors.
Implementation Method 1
using phase dislocation modulation to control the discharge current effectively
Data Source
AI summary
The present disclosure discloses a method of discharging a bus capacitor in a power converter, the method comprising: outputting a plurality of pulse control signals to the corresponding plurality of power semiconductor switch groups when the working state of the power converter is in a discharge state and the state of the main circuit breaker is open to control the ON and OFF of the plurality of power semiconductor switch groups, respectively, so as to form a discharge loop between the positive terminal and the negative terminal of the bus capacitor within at least a preset time, thereby causing the bus capacitor to discharge. Since a discharge loop is formed by the bus capacitor and the bridge arms and the energy of the bus capacitor is consumed by a power device, thereby the peak value and discharge rate of discharge current can be effectively controlled without adding additional discharge elements.