Variable Voltage Converter for HEV DC Bus Voltage Control
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Solution Overview
Problem
Hybrid electric vehicles face inefficiencies due to the limited range of DC bus voltage in existing variable voltage converters, leading to high inverter switching and conduction losses, especially when operating at low rotor speeds or when the battery voltage exceeds the required voltage for the electric machine, causing distortion in current signals and other system inefficiencies.
Innovation Solution
A variable voltage converter system with a switch in series with a capacitor and an inductor in parallel, configured to operate in boost mode over a duty cycle range from 0 to less than 0.5, allowing for a corresponding voltage output that ranges from 0 to the maximum of the converter, thereby adjusting the DC bus voltage to meet the requirements of different motor/generator speeds and minimizing inverter power losses and harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the DC bus voltage range is limited in existing variable voltage converters, then the converter structure remains simple, but inverter switching and conduction losses increase especially at low rotor speeds or when battery voltage exceeds required voltage
Solution Approach 1:
The patent implements a dynamic voltage conversion system that can adaptively adjust the DC bus voltage range based on operating conditions. The variable voltage converter dynamically switches between different conversion modes (voltage reduction when battery voltage exceeds inverter requirements, voltage maintenance when battery voltage is insufficient) to optimize inverter efficiency across varying rotor speeds and load conditions, thereby reducing switching and conduction losses while maintaining broad adaptability
Solution Approach 2:
The system changes the operating parameters of the variable voltage converter based on real-time conditions. When battery voltage is higher than required, the converter operates in voltage reduction mode with adjusted duty cycle to lower the DC bus voltage to optimal levels for the inverter, minimizing conduction losses. When battery voltage is insufficient, the converter maintains voltage to ensure proper inverter operation, thus optimizing energy efficiency across different operating points
2Reliability
If the battery voltage exceeds the required voltage for the electric machine, then the energy source capacity is sufficient, but current signal distortion and system inefficiencies occur
Solution Approach 1:
The variable voltage converter serves as an intermediary device between the battery and the inverter. When battery voltage exceeds the required voltage for the electric machine, the converter actively regulates and reduces the voltage to the appropriate level, preventing current signal distortion and system inefficiencies. This intermediary function ensures that the inverter receives optimal voltage input, maintaining current signal quality and overall system efficiency
Solution Approach 2:
The system employs feedback control mechanisms where the variable voltage converter continuously monitors the battery voltage and inverter requirements. When voltage mismatch is detected (battery voltage exceeding inverter needs), the converter adjusts its duty cycle and operating mode to reduce voltage to the optimal range, thereby preventing current distortion and maintaining system efficiency. The feedback loop ensures reliable operation across varying operating 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 system achieves an expanded operating voltage range, minimizing inverter switching and conduction losses, maintaining high modulation index, and reducing total harmonic distortion, thus enhancing the efficiency and performance of the power conversion system.
Implementation Method 1
an inductor in parallel with the capacitor and switch
Implementation Method 2
a capacitor in series with one of the switches
Data Source
AI summary
A system includes a bus, and a variable voltage converter (VVC) having a switch in series with a capacitor, and an inductor in parallel with the capacitor and switch, and configured such that operation of the switch in boost mode over a duty cycle range from 0 to less than 0.5 results in a corresponding voltage output to the bus from 0 to a maximum of the VVC.