Dual-Active-Bridge PWM Control for Low HV Voltage Efficiency
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Solution Overview
Problem
Single-stage DC-DC converters for electric vehicles exhibit high conversion losses and inefficiency at low high-voltage DC voltages, necessitating complex, expensive, and space-consuming multi-stage designs.
Innovation Solution
A DC-DC converter with a transformer, low-voltage and high-voltage semiconductor bridge circuits, and a control unit that adjusts pulse-width modulation (PWM) duty cycles and frequencies to optimize power transmission, particularly at low high-voltage DC voltages, using a control unit to determine and adjust PWM duty cycles based on detected voltages and transformer turns ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage DC-DC converter is used, then the device complexity is reduced, but conversion losses increase at low high-voltage DC voltages
Solution Approach 1:
The patent implements dynamic PWM frequency adjustment where the switching frequency changes based on the duty cycle requirements. When duty cycle is below 50%, a higher frequency is used to maintain efficiency, while at 50% duty cycle, the frequency is reduced. This dynamic adaptation allows the single-stage converter to maintain efficiency across different operating conditions without requiring multiple fixed stages.
Solution Approach 2:
The patent changes the PWM frequency parameter dynamically based on the duty cycle. By adjusting the frequency parameter in response to duty cycle conditions, the converter optimizes its performance at low voltages while maintaining simplicity. This parameter adaptation enables efficient operation without adding structural complexity.
2Reliability
If PWM duty cycle is limited to minimum 50%, then reliable voltage conversion is ensured, but control flexibility is reduced
Solution Approach 1:
The patent introduces frequency as an additional control dimension to compensate for the restricted duty cycle range. By varying the PWM frequency in addition to duty cycle, the system achieves the necessary control flexibility despite the minimum 50% duty cycle constraint, maintaining both reliability and adaptability.
Solution Approach 2:
The patent uses periodic PWM switching with dynamically adjusted frequency and duty cycle. The periodic nature of the switching allows the system to achieve effective voltage conversion control while maintaining the minimum 50% duty cycle requirement, using frequency modulation to provide the necessary control range.
3Productivity
If PWM frequency is increased to compensate for low duty cycle, then power transmission efficiency improves, but switching losses increase
Solution Approach 1:
The patent dynamically adjusts PWM frequency based on operating conditions, increasing frequency only when duty cycle is below 50% to maintain efficiency. When duty cycle reaches 50%, the frequency is reduced to minimize switching losses. This dynamic balance optimizes the trade-off between transmission efficiency and switching losses.
Solution Approach 2:
The patent changes the PWM frequency parameter in response to duty cycle conditions, creating an adaptive system that optimizes the efficiency-loss trade-off. By adjusting frequency as a variable parameter rather than fixing it, the system achieves high power transmission efficiency while minimizing unnecessary switching losses.
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 efficient power transmission without additional stages, reducing conversion losses and maintaining simplicity and efficiency across varying high-voltage DC levels.
Implementation Method 1
a transformer with a low-voltage winding and a high-voltage winding, wherein the low-voltage winding and the high-voltage winding are magnetically coupled
Data Source
Figure 1
Figure 2
AI summary
DC-DC converter (100) comprising: a control device (8) for controlling LV semiconductor switches (4.1a - 4.1d) and HV semiconductor switches (7.1a - 7.1d) by means of pulse-width modulated control signals (S-LV, S-HV), wherein the control device (8) is configured to detect the LV DC voltage (Ug-LV) and the HV DC voltage (Ug-HV), to determine a theoretical pulse-width modulation duty cycle (Dt) based on the LV DC voltage (Ug-LV), the HV DC voltage (Ug-HV) and a turns ratio (n) of a transformer (3) and to generate a pulse-width modulated control signal (S-LV, S-HV) depending on the theoretical pulse-width modulation duty cycle (Dt).