EV Charger PFC Pre-Charge Circuit With Single Shared Resistor
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Solution Overview
Problem
Existing charging devices for electric vehicles require multiple pre-charging resistors and relays to limit input current, leading to a complex and bulky solution.
Innovation Solution
A simplified circuit topology using a single switching element and a pre-charging resistor in parallel with the PFC stage, allowing controlled charging of the intermediate capacitor without the need for individual pre-charging resistors and relays, and utilizing a multiphase input terminal unit to distribute charging current across phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple pre-charging resistors and relays are used to limit input current, then input current is limited and power grid-side faults are avoided, but device complexity and component quantity increase
Solution Approach 1:
The patent merges multiple pre-charging resistors (one per phase) into a single pre-charging resistor that is shared across all phases. The single switching element controls this shared resistor to limit inrush current during charging operation, eliminating the need for multiple individual resistors and relays while maintaining current limitation functionality.
Solution Approach 2:
The single pre-charging resistor serves all phases simultaneously, performing the current limitation function universally across the multiphase input. The single switching element also performs multiple functions: controlling the pre-charging resistor, managing inrush current, and enabling/disabling charging operation across all phases.
2Reliability
If pre-charging resistors are used in each connecting line to limit input current, then excessive current is prevented, but the charging device becomes bulkier and less compact
Solution Approach 1:
The patent combines multiple distributed pre-charging resistors into a single centralized pre-charging resistor. This consolidation dramatically reduces the physical space required for these components while maintaining the same current limitation effect across all phases through the shared resistor and switching element.
3Device complexity
If a single switching element with pre-charging resistor is used, then device complexity and component quantity are reduced, but control of input current limitation must be achieved with fewer components
Solution Approach 1:
The single switching element is designed to perform multiple control functions: it switches the pre-charging resistor into the circuit during charging operation to limit inrush current, and can be controlled to manage current distribution across phases. This multi-functional design simplifies the control architecture despite the reduced component count.
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 approach reduces the number of components, minimizes input current, and prevents excessive current flow, resulting in a more compact and efficient charging system.
Implementation Method 1
A first stage, the so-called power-factor-correction stage, the PFC stage, converts the sinusoidal input voltage from the alternating voltage power grid into a direct voltage
Implementation Method 2
An intermediate capacitor is arranged between the two stages, which buffers the power pulsation in the double frequency of the alternating voltage current of the power source
Implementation Method 3
One wide-spread implementation for input current limitation is the limitation via pre-charging resistors in the connecting lines between the alternating voltage power system and the PFC stage
Implementation Method 4
A second stage consists of a direct voltage converter or DC/DC converter that ensures galvanic isolation via a transformer and adjusts the voltage levels
Data Source
AI summary
Charging device for a vehicle, wherein the input side of the charging device (500) comprises an input terminal unit (100) for connecting a single-phase or multiphase alternating voltage and a PFC stage (200) for providing a direct voltage at an intermediate terminal (300), wherein the PFC stage (200) comprises a half-bridge (210, 220, 230) for each phase of the n-phases, wherein a first switching element (S1) is connected on one side to the positive ends of the half-bridges and on the other side to the positive intermediate terminal (310) and being designed to enable or interrupt a current flow between the positive ends of the half-bridges and the positive intermediate terminal (310) via the first switching element (S1).