Power Stack Buck-Boost Control for EV Ripple Current Reduction
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Solution Overview
Problem
Electric vehicle (EV) systems face inefficiencies due to battery internal losses and radio interference caused by ripple current from pulse-width modulation (PWM) in motor controllers, leading to heat generation and reduced performance, with existing solutions being costly and inefficient.
Innovation Solution
The Versatile Power Stack Unit (VPSU) system uses a combination of inductors and capacitors to store excessive PWM current, upconverts PWM frequency, and incorporates a DC/DC converter to minimize ripple voltage and current, allowing for high-efficiency operation with small, low-cost components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PWM control is used to control motor power, then motor speed and torque control is improved, but battery internal losses and heat generation increase due to ripple current
Solution Approach 1:
The battery pack is divided into multiple independent battery stacks, each connected to its own DC/DC converter. This segmentation allows each stack to be controlled independently, reducing the overall ripple current impact on any single battery while maintaining PWM motor control efficiency.
Solution Approach 2:
DC/DC converters are introduced as intermediary devices between the battery packs and the motor controller. These converters act as buffers that smooth out the ripple current from PWM switching, reducing battery internal losses while preserving the ability to control motor speed and torque effectively.
2Reliability
If DC link capacitors are used to reduce ripple current, then battery performance is improved, but device volume and cost increase significantly
Solution Approach 1:
The function of reducing ripple current is extracted from the traditional DC link capacitor approach and implemented instead through DC/DC converters connected to segmented battery stacks. This eliminates the need for large, bulky capacitors while achieving the same ripple reduction effect, significantly reducing controller volume.
Solution Approach 2:
The system changes the operating parameters by using multiple battery stacks with DC/DC converters operating at optimized duty cycles. This parameter change allows ripple current reduction without requiring large capacitance values, thereby reducing the volume of stationary components in the controller.
3Loss of energy
If battery internal resistance is reduced to improve power efficiency, then power losses are reduced, but this requires operating at optimal state of charge which limits flexibility
Solution Approach 1:
The system dynamically adjusts the duty cycle of each DC/DC converter based on real-time battery state of charge and load requirements. This dynamic control allows the system to operate at optimal efficiency points when possible, while maintaining the flexibility to adapt to various operating conditions and state of charge levels, thus preserving versatility.
Solution Approach 2:
The DC/DC converters are designed to perform multiple functions: they provide ripple current reduction, enable flexible power distribution between segmented battery stacks, and allow operation across a wide range of state of charge levels. This multi-functionality maintains operating flexibility while minimizing power losses through optimized control.
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 VPSU significantly reduces power losses and extends battery life by minimizing heat generation and ripple current, improving the overall efficiency and cost-effectiveness of EV systems.
Implementation Method 1
An inductor and a capacitor are used to provide comprises magnetic field storage and voltage charge storage
Implementation Method 2
An inductor and a capacitor are used to provide comprises magnetic field storage and voltage charge storage
Implementation Method 3
incorporates a DC/DC converter to achieve high efficiency at a nominal 50% PWM duty cycle
Data Source
AI summary
A “Versatile Power Stack Unit” (VPSU) for controlling electrical devices such as motors for electric vehicles is disclosed. The VPSU uses a DC/DC buck-boost converter that generates output voltage. By varying the voltage according to need, the system can maintain a Pulse-Width Modulation duty cycle of 50% without introducing any ripple current or voltage into the batteries or system, while minimizing losses due to internal resistance. Any number of VPSUs can be connected one to the other in order to provide the voltage and current needed to power the electrical device. Not only does the VPSU minimize ripple current and losses due to internal resistance, but it enables recharging at low voltage and according to the needs of small numbers of batteries with minimal temperature rise during the charging, thereby extending battery lifetime and improving battery performance.