Braking Chopper Circuit for DC Link Voltage Control
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Solution Overview
Problem
In adjustable speed drive systems, the load can act as a generator, causing the DC link voltage to rise, and existing braking chopper circuits are inadequate in effectively managing this energy feedback.
Innovation Solution
A braking chopper circuit with a braking resistor connected between the DC link capacitors and a neutral point, controlled by a switching module with specific switching states and a control circuit that adjusts switching frequency based on DC link voltage and IGBT junction temperature to efficiently discharge the capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a braking chopper circuit is used to dissipate energy at the DC link, then the DC link voltage can be reduced, but the existing circuits are inadequate in effectively managing energy feedback when the load acts as a generator
Solution Approach 1:
The patent implements dynamic switching control where the braking chopper circuit transitions between different operational states (first switching state for energy dissipation, second switching state for energy feedback management) based on real-time DC link voltage conditions. This dynamic adaptability allows the circuit to effectively handle both voltage reduction and generator-mode energy feedback, resolving the contradiction between reliability and adaptability.
2Productivity
If switching frequency is increased to improve capacitor discharge speed, then DC link voltage reduction efficiency improves, but IGBT damage risk increases
Solution Approach 1:
The patent employs periodic switching control where the braking chopper operates in alternating switching states with controlled duty cycles. This periodic action allows the system to achieve effective capacitor discharge through repeated on-off cycles rather than continuous high-frequency switching, thereby maintaining discharge productivity while reducing thermal stress and damage risk to IGBTs.
Solution Approach 2:
The control circuit monitors DC link voltage and switching state to dynamically adjust the braking chopper operation. This feedback mechanism ensures that switching frequency and duty cycle are optimized in real-time, achieving fast capacitor discharge when needed while automatically reducing switching intensity to prevent IGBT damage, thus resolving the productivity-harmful factors contradiction.
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 effectively reduces DC link voltage by discharging capacitors through controlled switching states, ensuring safe operation by capping switching frequency to prevent IGBT damage, thus maintaining system stability and efficiency.
Implementation Method 1
A braking chopper circuit with a braking resistor connected between the DC link capacitors and a neutral point
Implementation Method 2
a control circuit that adjusts switching frequency based on DC link voltage and IGBT junction temperature
Data Source
AI summary
A circuit comprising a first power node for connection to a positive voltage of a DC link, a second power node for connection to a negative voltage of the DC link and a mid-point power node for connection to a mid-point voltage of the DC-link, the circuit further comprising a three-level neutral point clamped converter module and a brake resistor connection.