Flyback Converter Control for DC Link Capacitor Precharging
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Solution Overview
Problem
Existing methods for charging a DC link capacitor in a high-voltage network require additional components and space due to the use of a parallel current path with a switch and pre-charge resistor, leading to increased weight and cost.
Innovation Solution
A flyback converter is connected to both a low-voltage and high-voltage network, using a series circuit with a transformer and diode, and controlled by a control device to determine voltage and current levels for rapid charging, divided into current and voltage regulated phases to avoid overcurrents and overvoltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a parallel current path with switch and pre-charge resistor is used to charge the DC link capacitor, then the capacitor can be charged without excessive compensating currents, but additional components, space, weight and cost are required
Solution Approach 1:
The patent extracts and eliminates the pre-charge resistor and parallel current path from the circuit. Instead of using a separate charging circuit, the flyback converter's intrinsic circuitry is utilized to perform the charging function, thereby removing the problematic components that added complexity and cost while maintaining safe charging operation.
Solution Approach 2:
The flyback converter is designed to serve multiple functions: it acts as both the main power conversion device and the pre-charging device for the DC link capacitor. By controlling the duty cycle of the circuit breaker, the same converter that converts DC to AC also performs the pre-charging function, eliminating the need for dedicated pre-charge components.
2Reliability
If a parallel current path with pre-charge resistor is used, then compensating currents are limited to permissible levels, but additional weight and cost result from extra components
Solution Approach 1:
The flyback converter utilizes its own internal components (transformer, circuit breaker, diodes, capacitors) to limit and control the charging current. The duty cycle control of the circuit breaker inherently limits the current to permissible levels during the pre-charging phase, eliminating the need for external current-limiting resistors and reducing overall system weight.
3Productivity
If the DC link capacitor is charged rapidly, then the vehicle can be put back into service faster, but excessive currents and voltages may occur without proper control
Solution Approach 1:
The patent implements dynamic control of the circuit breaker's duty cycle during the pre-charging process. The duty cycle is adjusted based on the real-time voltage level of the DC link capacitor, allowing rapid charging when voltage is low while automatically reducing current as voltage approaches the target level, thus preventing excessive currents and voltages while maintaining high charging speed.
Solution Approach 2:
The control device monitors the voltage at the DC link capacitor and uses this feedback information to adjust the duty cycle of the circuit breaker. This closed-loop control ensures that charging current and voltage remain within safe limits while achieving rapid charging, as the system automatically responds to voltage changes and prevents overcurrent conditions.
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
Enables rapid, non-destructive charging of the DC link capacitor without additional components, reducing weight and cost while ensuring safe operation.
Implementation Method 1
a series circuit on the input side between the input terminals, consisting of a first circuit breaker and a primary winding of a transformer, and of a series circuit of a secondary winding of the transformer on the output side
Implementation Method 2
a series circuit of a secondary winding of the transformer on the output side between the output terminals and a first diode connected in the reverse direction
Implementation Method 3
a DC link capacitor in a high-voltage network disposed between a power source, preferably a DC voltage and/or a high-voltage power source
Data Source
AI summary
A method (100) of operating a flyback converter (250) to charge a DC link capacitor (210), with the steps of: determining (120) a voltage (Ux), characterizing the voltage at the DC link capacitor (210), specifying (140) a target charging current level (I_L) for charging the DC link capacitor (210) and specifying a corresponding duty cycle (Tx) for actuating the first circuit breaker (252) for as long as the determined voltage (Ux) falls below a first voltage level value (U1), specifying (150) a target charging voltage level (U_L), for as long as the determined voltage (Ux) corresponds to the first voltage level (U1) or the determined voltage (Ux) exceeds the first voltage level (U1) and the determined voltage (Ux) falls below a second voltage level (U2).