Reverse Recovery Current Prevention in Motor Driving Circuits
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Solution Overview
Problem
Existing motor driving apparatuses face issues with reverse recovery currents that can damage switching elements due to erratic microcomputer performance, leading to faulty switching and potential destruction of the switching element when the input current flows into the full wave rectifier.
Innovation Solution
A reverse recovery current prevention device that includes a switch control unit which prohibits the formation of a current pathway for reverse recovery currents by comparing voltage thresholds and zero-crossing detection results, preventing the switching element from turning on during inappropriate conditions, thereby preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching element is turned on and off to improve power factor, then the input current becomes a sine wave and voltage phase aligns with current phase, but the switching element may faultily turn on and reverse recovery current flows causing potential destruction
Solution Approach 1:
The control circuit detects the voltage between the negative-side output terminal and the cathode terminals before the switching element is turned on. When this voltage exceeds a predetermined threshold, the control circuit prohibits turning on the switching element in advance, preventing reverse recovery current from flowing before it can cause damage.
Solution Approach 2:
The control circuit acts as an intermediary between the switching element and the circuit, monitoring voltage conditions and making decisions about when to permit or prohibit switching element operation, thereby preventing harmful reverse recovery current while allowing beneficial power factor correction.
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3
AI summary
To prevent a switching element from being destroyed by a reverse recovery current, a reverse recovery current prevention device (2) comprises a full wave rectifier (21), first and second diodes (D22, D23), a switching element (24), and a switching element control unit (30). The full wave rectifier (21) rectifies a power source voltage (Vac) from an alternating current power source (10) inputted into first and second input terminals (s2, t2). Each of the anode terminals of the first and second diodes (D22, D23) is respectively connected to the first and second input terminals (s2, t2) of the full wave rectifier (21). The switching element (24) opens or shorts an electrical circuit between a negative-side output terminal of the full wave rectifier (21) and each of the cathode terminals (s3, t3) of the first and second diodes (D22, D23). The switching element control unit (30) prohibits the switching element (24) from shorting the circuit between the negative-side output terminal and each of the cathode terminals (s3, t3) in a case where the voltage between the negative-side output terminal and each of the cathode terminals (s3, t3) is at or greater than a threshold.