Half-Bridge PWM Shutdown Using Inductor Current Freewheeling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In power conversion apparatuses connected to a grid through a bidirectional switch, inappropriate timing of stopping the PWM driver gating signal can lead to high voltage across switching transistors due to inductor current cutoff, potentially damaging them, especially in harsh environments like lightning strikes where voltage polarity can be incorrectly determined.
Innovation Solution
A power conversion apparatus with a controller that quickly turns off all switching transistors in the half-bridge circuit when the inductive device current is within set thresholds, ensuring only one transistor remains on for freewheeling, minimizing the impact of fault or emergency events and maintaining circuit safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If all switching transistors are directly blocked to stop sending PWM driver gating signal, then the shutdown response is fast, but the inductor current is cut off causing high voltage generation that damages switching transistors
Solution Approach 1:
The patent applies preliminary action by detecting the inductor current direction before shutdown and pre-configuring the bidirectional switch states. When shutdown is required, the system has already determined which switching transistors to block and which to maintain, preventing inductor current cutoff while achieving fast shutdown. This resolves the contradiction by preparing the circuit state in advance based on current flow direction detection.
2Reliability
If blocking is performed only when the inductor current is zero, then switching transistor safety is maintained, but it takes up to half a switching periodicity to perform the action
Solution Approach 1:
The system performs preliminary detection of inductor current direction through the bidirectional switch before shutdown is required. By knowing the current flow direction in advance, the system can immediately block the appropriate switching transistors when shutdown is triggered, rather than waiting for current to naturally reach zero. This eliminates the half-period delay while maintaining transistor safety.
Solution Approach 2:
The patent uses feedback by continuously monitoring the inductor current direction through the bidirectional switch and using this information to control the shutdown process. The current direction detection provides real-time feedback that enables the controller to make informed decisions about which switching transistors to block, achieving both fast response and transistor protection.
3Device complexity
If the inductor current direction is not detected, then the control logic is simple, but voltage polarity may be incorrectly determined in harsh environments like lightning strikes
Solution Approach 1:
The patent introduces an intermediary element - the bidirectional switch - that facilitates safe current flow during shutdown. By detecting current direction through this intermediary device and using it to control switching transistor blocking, the system achieves accurate voltage polarity determination even in harsh environments. The bidirectional switch acts as a mediator between the inductor and the switching transistors, providing reliable current direction information.
Data Source
Figure 1a~1b
Figure 2a
Figure 2b
AI summary
This application provides a power conversion apparatus and a control method of stopping sending a PWM driver gating signal thereof. When the power conversion apparatus is faulty or receives a shutdown instruction, a controller controls all switching transistors in a half-bridge circuit to be turned off. Specifically, when an inductor current is not zero, a part of switching transistors in an upper half bridge arm or a lower half bridge arm that is turned on are controlled to be turned off, and all switching transistors in the lower half bridge arm or the upper half bridge arm that is turned off are controlled to be turned off. After the inductor current freewheels to approximately zero, all switching transistors of the upper half bridge arm or the lower half bridge arm that is turned on are controlled to be turned off, so that all switching transistors in the half-bridge circuit of the power conversion apparatus are turned off. When the inductor current is approximately zero, all switching transistors in an on state in the upper half bridge arm and the lower half bridge arm are controlled to be simultaneously turned off, so that all the switching transistors in the half-bridge circuit of the power conversion apparatus are turned off. In a process of stopping sending a PWM driver gating signal, driving of more switching transistors can be blocked as quickly as possible to reduce impact of an emergency or fault event.