Battery Load Emulator Circuit for Constant-Voltage Charger Testing
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Solution Overview
Problem
Conventional test loads, such as banks of power dissipating resistors, fail to accurately emulate the behavior of high-capacity rechargeable batteries used in electric vehicles due to their resistive nature, which does not resemble the constant voltage characteristic of actual batteries, leading to improper functioning of charging devices.
Innovation Solution
An electrical circuit that includes a regulator circuit with a voltage sensing circuit, comparator circuit, and controllable load circuit to maintain a constant terminal voltage, mimicking the behavior of a battery by controlling current flow to emulate the battery's electrical characteristics, using a controllable load circuit with additional resistive elements to handle varying current levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional test loads (banks of power dissipating resistors) are used, then the device complexity is reduced and ease of manufacture is improved, but the measurement precision and reliability of battery charging device testing deteriorate because resistive loads do not emulate the constant voltage characteristic of actual batteries
Solution Approach 1:
The patent implements a feedback control mechanism where the microcontroller continuously monitors the voltage across the battery emulator terminals and adjusts the duty cycle of the PWM signal to maintain a constant voltage output. This closed-loop feedback system ensures the emulator accurately replicates battery behavior under varying load conditions, resolving the contradiction between emulation accuracy and system simplicity.
Solution Approach 2:
The patent replaces the conventional mechanical/resistive test load approach with an electronic switching circuit using MOSFETs and PWM control. This substitution transforms the emulation mechanism from passive resistive elements to an active electronic system that can dynamically adjust its characteristics to match battery behavior, significantly improving measurement precision while maintaining manageable device complexity through integrated control.
2Adaptability or versatility
If the controllable load circuit uses additional resistive elements to handle varying current levels, then the adaptability to different current levels is improved, but the device complexity and power dissipation requirements increase
Solution Approach 1:
The patent employs periodic pulse-width modulation (PWM) switching to control the controllable load circuit. By switching the MOSFETs on and off at high frequency with variable duty cycles, the circuit can precisely control the average current flow through the resistive elements. This periodic action allows the system to handle varying current levels adaptively while minimizing continuous power dissipation, as the resistive elements only dissipate power during the on-periods of the PWM cycle.
Solution Approach 2:
The patent implements a dynamic control system where the PWM duty cycle is continuously adjusted based on feedback from the voltage sensing circuit. This dynamic adjustment allows the controllable load circuit to adapt its effective resistance and current handling capability in real-time, matching the varying current requirements of different battery types and charging scenarios without requiring fixed high-power resistive elements that would continuously dissipate excessive energy.
3Reliability
If the regulator circuit maintains constant voltage by controlling current flow, then the reliability of charging device testing is improved, but the device complexity increases due to multiple circuit components
Solution Approach 1:
The patent designs the regulator circuit components to perform multiple functions. The operational amplifier serves both as a voltage sensing amplifier and as an error amplifier in the feedback loop. The MOSFETs function as both the controllable load elements and as the power switching devices for current regulation. The same RC networks provide both timing functions for PWM generation and filtering functions for voltage sensing. This multi-functionality reduces the overall number of discrete components while maintaining reliable constant voltage control.
Solution Approach 2:
The patent combines several circuit functions into integrated blocks. The voltage sensing circuit is merged with the error detection function, eliminating the need for separate sensing and comparison circuits. The PWM generator is integrated with the MOSFET driver circuitry, combining timing generation and power switching control in one module. The feedback network is merged into the operational amplifier configuration, creating a unified control loop. These merges reduce component count and simplify the overall circuit architecture while preserving the reliability of constant voltage maintenance.
Data Source
AI summary
An electrical circuit that emulates a battery, e.g., an EV battery, when being charged may comprise: terminals configured to connect to a battery charging device; and a regulator circuit including: a voltage sensing circuit for sensing the voltage at the terminals and providing a voltage proportional thereto; a comparator circuit responsive to the difference between the voltage sensing circuit and the reference voltage; a controllable load circuit connected to the terminals and including a controllable element responsive to the comparator circuit for causing a current to flow between the terminals; whereby the current flowing in the controllable load circuit is controlled to maintain the voltage between the terminals at a voltage that is proportional to the reference voltage.