Transformer Tap-Changing Circuit for EV Charging
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Solution Overview
Problem
Conventional tap-changing circuits for transformers are expensive and complex, limiting their ability to efficiently provide high currents to DC loads in applications such as electric vehicle charging, where battery voltage increases reduce current levels, necessitating a cost-effective and reliable solution.
Innovation Solution
A transformer-based apparatus with a secondary winding inductively coupled to a primary winding, featuring two rectifiers and a DC bus, where the first rectifier converts a higher AC voltage to a higher DC voltage and the second rectifier converts a lower AC voltage to a lower DC voltage, with a controller managing the voltage supply to maintain efficient current delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional tap-changing circuits with switch arrays and back-to-back thyristors are used to change transformer turns ratio, then the output voltage and current can be altered during battery charging, but the components become expensive and the control techniques become complicated
Solution Approach 1:
The patent divides the secondary winding into multiple discrete taps (first tap, second tap, third tap) with different voltage levels. Instead of using a complex continuous control system, the solution segments the voltage output into discrete levels that can be selectively connected to the DC bus, simplifying the control architecture while maintaining adaptability.
Solution Approach 2:
The patent implements dynamic tap selection based on real-time battery charging conditions. The controller dynamically switches between different taps on the secondary winding to maintain optimal charging current as battery voltage increases during charging, making the system adaptive without requiring complex continuous control.
2Ease of operation
If transformer impedance is used to limit current, then the current can be controlled during battery charging, but the transformer requires 15 to 20% impedance which limits design flexibility
Solution Approach 1:
The patent introduces an intermediary current-limiting inductor connected in series with the DC bus. This separate component handles the current limiting function, allowing the transformer itself to be designed with lower impedance (5-10%) for better efficiency and flexibility, while the inductor provides the necessary current protection.
Solution Approach 2:
The patent extracts the current limiting function from the transformer design itself and places it in a separate external inductor. This separation allows the transformer to be optimized for efficiency with lower impedance, while the extracted inductor component provides the current limiting capability.
3Device complexity
If a single rectifier is used to convert AC voltage to DC voltage, then the circuit is simpler, but the ability to maintain high current levels as battery voltage increases is reduced
Solution Approach 1:
The patent segments the rectification function by providing multiple rectifiers (first rectifier, second rectifier, third rectifier), each associated with different taps on the secondary winding. This segmentation allows the system to maintain efficient rectification across different voltage levels and sustain high current levels throughout the charging process.
Solution Approach 2:
The patent creates a multi-functional rectification system where multiple rectifiers can operate in different combinations based on charging requirements. The system can use individual rectifiers or multiple rectifiers simultaneously to maintain high current output across varying battery voltage 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
The solution provides a cost-effective and reliable method to maintain high current levels during battery charging by dynamically adjusting voltage and current through the use of rectifiers and a controller, optimizing energy transfer and extending battery life.
Implementation Method 1
a secondary winding configured to inductively couple to a primary winding when a current is passed through the primary winding from an energy source
Implementation Method 2
a first rectifier coupled to the secondary winding and configured to rectify a first AC voltage from the secondary winding into a first DC voltage
Data Source
AI summary
A transformer tap-changing circuit comprises an apparatus that includes a transformer comprising a secondary winding configured to inductively couple to a primary winding when a current is passed through the primary winding from an energy source, a first rectifier coupled to the secondary winding and configured to rectify a first AC voltage from the secondary winding into a first DC voltage, and a second rectifier coupled to the secondary winding and configured to rectify a second AC voltage from the secondary winding into a second DC voltage. The apparatus also includes a DC bus coupled to the first and second rectifiers and configured to receive the first and second DC voltages therefrom, wherein the first AC voltage is higher than the second AC voltage, and wherein the first DC voltage is higher than the second DC voltage.