Frequency Inverter Pre-Charging Circuit with Choke and Semiconductor Switch
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Solution Overview
Problem
The existing frequency converters face the challenge of protecting the feed unit from damage due to high charging currents during the pre-charging phase of the intermediate circuit capacitor, which can lead to component destruction and potential overvoltages.
Innovation Solution
Incorporating a choke with a semiconductor switch and a freewheeling diode, allowing controlled current intensity during charging, and utilizing a commutation capacitor to manage inductive voltages, along with additional protection mechanisms like a switchable commutation capacitor and discharge resistor for safe energy dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the intermediate circuit capacitor is charged directly after the main contactor closes, then the capacitor charges quickly, but the charging current becomes excessively large and damages feed unit components
Solution Approach 1:
A pre-charging contactor is activated before the main contactor to charge the intermediate circuit capacitor through a pre-charging reactor. This preliminary charging action limits the initial inrush current while establishing sufficient voltage, preventing damage to the feed unit when the main contactor closes.
Solution Approach 2:
The pre-charging reactor serves as an intermediary element between the capacitor and the power source during the pre-charging phase. It mediates the charging process by limiting current while allowing voltage buildup, protecting the system from harmful inrush currents.
2Object-affected harmful factors
If a pre-charging circuit with semiconductor switches is used, then the charging current is controlled, but the thermal load on semiconductor switches increases
Solution Approach 1:
The charging process is segmented into two distinct phases: pre-charging through the pre-charging contactor and reactor, and main charging through the main contactor. This segmentation allows the semiconductor switches to operate only during the controlled pre-charging phase with limited current, reducing their thermal load while still achieving current control.
3Reliability
If the pre-charging contactor remains closed during operation, then the capacitor remains charged, but voltage jumps and overvoltages occur in the intermediate circuit
Solution Approach 1:
The pre-charging contactor is designed to be dynamically controlled - closed during the pre-charging phase to maintain capacitor charge, and opened during normal operation to prevent overvoltages. This dynamic switching behavior allows the system to adapt to different operational requirements, maintaining reliability when needed and preventing harmful effects during steady-state operation.
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 configuration effectively limits the charging current, prevents component damage, and provides protection against overvoltages and short-circuit currents, ensuring safe operation and reduced thermal loads on semiconductor switches.
Implementation Method 1
one of the circuit branches has a choke (58). One connection (66) of the choke (58) is connected to an intermediate circuit connection (56) of the feed unit (28)
Implementation Method 2
an intermediate circuit capacitor (22, 48) with a sufficiently large capacitance ensures that a ripple in the DC voltage U ZK generated in one of the conversion steps described is smoothed
Implementation Method 3
a semiconductor switch (46) is connected between the choke (58) and the intermediate circuit capacitor (48)
Data Source
Figure 1
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Figure 3
AI summary
The frequency converter (26) has first circuit branch with choke (L1) having first terminal connected to direct current (DC) input terminal of inverter (32) and second terminal connected to first terminal of freewheeling diode (60) and to first terminal of semiconductor switch. Second terminal of semiconductor switch is connected to DC terminal of alternating current (AC)-DC converter (28) in first circuit branch. Semiconductor switch controls a magnitude of an electrical current flowing from AC-DC converter into DC link capacitor (48) in accordance with control signal. An independent claim is included for a method for operating frequency converter.