Load Control Device Current Detection Offset Calibration
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Solution Overview
Problem
Existing electric power steering devices face precision issues in current detection due to the influence of input offset voltage and common-mode rejection ratio in differential amplifiers, leading to decreased detection accuracy of current values in inverter circuits.
Innovation Solution
A load control device that includes a differential amplifier with a current detection resistor and a current calculation mechanism, where the device alternates switching elements between ON and OFF states to set an offset value during standby, allowing precise current calculation by subtracting the offset from the differential amplifier's output during motor drive control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a differential amplifier is used to amplify the voltage generated by the current detection resistor, then the output signal is amplified, but the detection precision decreases due to input offset voltage and common-mode rejection ratio errors
Solution Approach 1:
The patent applies preliminary action by measuring and storing the offset value of the differential amplifier during a standby state (when no current flows through the detection resistor) before actual current measurement. This pre-measured offset is then subtracted from subsequent measurements to eliminate systematic errors, thereby maintaining high detection precision while still utilizing the amplification capability of the differential amplifier.
2Duration of action of moving object
If the switching elements are kept in ON state to allow current flow to the load, then the load operates continuously, but the offset value cannot be measured and detection accuracy decreases
Solution Approach 1:
The patent implements periodic action by alternately switching between a standby state (where switching elements are OFF and offset value is measured) and a drive state (where switching elements are ON and current flows to the load). This periodic switching enables continuous offset calibration while maintaining substantial continuous operation of the load, resolving the contradiction between continuous operation and measurement accuracy.
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
This approach enables precise detection of current values within the circuit, enhancing the accuracy of assist torque delivery to the steering shaft by accounting for errors caused by the differential amplifier's characteristics, thereby improving the overall performance of the electric power steering system.
Implementation Method 1
a differential amplifier configured to amplify and output a voltage generated in the current detection resistor
Implementation Method 2
a load control means configured to ON/OFF operate switching elements on the basis of a PWM signal, the switching elements being interposed in each of an upper arm and a lower arm that connect a power source and a load
Implementation Method 3
a current detection resistor connected in series with the load; a differential amplifier configured to amplify and output a voltage generated in the current detection resistor
Data Source
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AI summary
A load control device includes a load control means that drives a load, a current detection resistor, a differential amplifier and a current calculation means. The load control means can switch between a standby state a drive state, a state in which a first of the switching elements is turned ON and a second of the switching elements is turned OFF and a state in which the first of the switching elements is turned OFF and the second of the switching elements is turned ON being alternately repeated in the standby state, in which both of the switching elements are turned ON in the drive state. The current calculation means calculates a current that flows to the current detection resistor on the basis of a value output from the differential amplifier in the drive state and an offset value output from the differential amplifier in the standby state.