ANPC Inverter Zero-Crossing Switching Overvoltage Prevention
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Solution Overview
Problem
Active neutral point clamped (ANPC) inverters face the risk of overvoltage during zero-crossing switching due to asynchronous switching actions of switches, which can lead to voltage exceeding the safe limit for switches in the bridge leg.
Innovation Solution
A zero-crossing switching method and apparatus for ANPC inverters that control switch states according to a preset logic, transitioning through a sequence of safe switch state combinations to ensure the maximum voltage borne by switches is clamped to a safe limit value, specifically one-half of the direct-current bus voltage, thereby preventing overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional modulation scheme is used to operate inner transistors at high frequency, then switching speed is improved, but overvoltage risk increases during zero-crossing switching
Solution Approach 1:
The patent applies preliminary action by detecting zero-crossing switching events in advance and preemptively adjusting the switching sequence of transistors. When zero-crossing is detected, the control system prepares a special switching sequence that ensures outer transistors switch before inner transistors, preventing overvoltage before it can occur. This advance preparation resolves the contradiction by maintaining high switching speed while eliminating overvoltage risk through proactive control.
Solution Approach 2:
The patent implements dynamics by making the switching sequence adaptive rather than fixed. The control system dynamically adjusts the switching sequence based on real-time detection of zero-crossing events. During normal operation, conventional high-frequency switching is used for efficiency, but during zero-crossing transitions, the sequence is dynamically changed to ensure safe switching order. This dynamic adaptation allows the system to maintain high speed performance while preventing overvoltage only when necessary.
2Productivity
If simultaneous switching of multiple switches is attempted at zero-crossing, then productivity is improved, but voltage control precision deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the simultaneous switching action into sequential steps. Instead of attempting to switch multiple transistors at the exact same moment, the control system segments the switching into a defined sequence: first outer transistors are switched, then inner transistors are switched afterward. This segmentation maintains productivity by completing all necessary switches in rapid succession while ensuring precise voltage control through the enforced switching order that prevents overvoltage.
3Adaptability or versatility
If clamping diode is replaced with controllable switch, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent applies feedback by implementing a control system that monitors the switching state and output voltage, then adjusts the switching sequence accordingly. The control system detects zero-crossing events and provides feedback to modify the switching pattern, ensuring that the controllable switches operate in the correct sequence. This feedback mechanism manages the increased complexity by using intelligent control logic to coordinate the additional controllable switches, thereby maintaining adaptability while controlling device complexity through automated coordination.
Data Source
AI summary
An ANPC inverter, a zero-crossing switching method and a zero-crossing switching apparatus of the ANPC inverter are provided. The method includes: controlling switch states of switch devices in a bridge leg to change according to a preset logic when zero-crossing switching occurs in an output voltage instruction of the bridge leg, so as to prevent overvoltage in the switch device in the bridge leg. The preset logic includes switching among a sequence of switch state combinations. Switch state combinations of the switch devices before and after the zero-crossing switching occurs are defined as the first and second switch state combinations of the sequence. The second to the penultimate switch state combinations are all safe switch state combinations selected in advance, in each of which a maximum voltage borne by the switch devices in the bridge leg is clamped to a safe limit value.