Bidirectional DC/DC Converter Charging Intermediate Circuit Capacitor
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Solution Overview
Problem
In electric or hybrid vehicles, the high-voltage battery must be periodically disconnected for maintenance, leading to potentially high and rapidly increasing currents when reconnecting, which can exceed component limits due to recharging of the intermediate-circuit capacitor, necessitating a complex mechanical switch and incurring losses in charging resistors.
Innovation Solution
A bidirectional DC/DC converter with a discharge transformer configuration, utilizing a series inductor with a second winding and discharge diode, allows controlled and current-limited charging of the intermediate-circuit capacitor from the low-voltage battery, eliminating the need for additional charging circuits and mechanical switches, and enabling charging to any desired voltage without connecting the high-voltage battery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the high-voltage battery is disconnected for maintenance and then reconnected, then the maintenance operation can be performed, but potentially high and rapidly increasing currents flow due to recharging of the intermediate-circuit capacitor
Solution Approach 1:
The patent charges the intermediate-circuit capacitor from the low-voltage battery before reconnecting the high-voltage battery, so that when the high-voltage battery is reconnected, the voltage difference is minimized and excessive currents are prevented
Solution Approach 2:
The patent introduces a charging device with a charging resistor as an intermediary component to limit the charging current from the low-voltage battery to the intermediate-circuit capacitor, preventing excessive currents when the high-voltage battery is reconnected
2Object-generated harmful factors
If a charging device with mechanical switch and charging resistor is used to charge the intermediate-circuit capacitor, then excessive currents are limited, but device complexity increases and energy losses occur in the charging resistor
Solution Approach 1:
The patent replaces the mechanical switch with electronic switching components (transistor or MOSFET) controlled by a control unit, eliminating the need for mechanical moving parts while achieving the same current limiting function
Solution Approach 2:
The patent integrates the charging function into the existing DC/DC converter circuitry, allowing the same electronic components to serve both normal power conversion functions and the specialized function of charging the intermediate-circuit capacitor before high-voltage battery reconnection
3Object-generated harmful factors
If a charging resistor is used to charge the intermediate-circuit capacitor, then current is limited, but energy losses occur in the charging resistor
Solution Approach 1:
The patent replaces the passive resistive current limiting with active electronic switching and control, where the transistor or MOSFET regulates current flow through pulse-width modulation or similar control techniques, significantly reducing energy dissipation compared to resistive limiting
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 solution prevents excessive currents, reduces losses, and increases efficiency by allowing controlled charging of the intermediate-circuit capacitor from the low-voltage battery, eliminating the need for complex mechanical switches and enabling universal use in various converter types.
Implementation Method 1
an intermediate-circuit capacitor in the high-voltage network. One or more transformers ensure the galvanic isolation of the low-voltage network from the high-voltage network, in such a way that energy transmission takes place only via the inductive coupling between the transformer coils
Implementation Method 2
a series inductor in the low-voltage network is used to smooth the current pulses in the low-voltage circuit
Implementation Method 3
the series inductor is configured as a discharge transformer, wherein the term discharge transformer refers to the inductive discharging of the energy stored in the series inductor
Data Source
AI summary
The invention relates to a bidirectional DC/DC converter for transmitting energy between a high-voltage grid (HV) and a low-voltage grid (LV), comprising connections for a high-voltage battery (UHV) and a low-voltage battery (UNV). The converter comprises the following:—one or more transformers (1) for galvanically isolating the low-voltage grid (LV) from the high-voltage grid (HV), an intermediate circuit capacitor (CZK) in the high-voltage grid (HV),—electronic switches (D1 to D4, M1 to M4) for connecting and reversing the polarity of the coil of the transformer (1) on the high-voltage grid (HV) and on the low-voltage grid (LV),—a controller (2) for controlling the electronic switches (D1 to D4),—and a series inductance (W1) in the low-voltage grid (NV). The series inductance (W1) is designed as a discharge transformer (3) for discharging the energy stored in the series inductance (W1), wherein a second coil (W2) is connected in series to a discharge switch (S) and a diode (D), and the series inductance (W1) is discharged to the low-voltage battery (UNV) when the discharge switch (S) is activated. The invention additionally relates to a method for charging the intermediate circuit capacitor (CZK) of the converter to the high-voltage grid potential from the low-voltage battery (UNV).