Motor Inverter Current Sensing for In-Run Offset Voltage Detection
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Solution Overview
Problem
Existing motor control devices require a dedicated component to detect offset voltage, which increases costs and complicates the detection process, and often necessitate stopping the motor to perform accurate offset voltage detection.
Innovation Solution
A control device that includes an inverter circuit, a shunt resistor, and a control circuit capable of switching elements to temporarily prevent current flow through the shunt resistor during regular motor operation, allowing for offset voltage detection without stopping the motor and eliminating the need for a dedicated component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated component is used to detect offset voltage, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the offset voltage detection function with the existing current detection circuit by utilizing the shunt resistor and amplifier circuit already present in the motor control system. The control circuit integrates both current measurement and offset voltage detection capabilities, eliminating the need for separate dedicated components while maintaining detection accuracy.
Solution Approach 2:
The shunt resistor and amplifier circuit are designed to serve multiple functions: they detect both the operating current during motor operation and the offset voltage when no current flows. This multi-functionality reduces device complexity by using existing components for dual purposes rather than requiring separate dedicated detection circuits.
2Measurement precision
If the motor is stopped to detect offset voltage, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The control circuit periodically switches the switching element to an off state at predetermined intervals during motor operation to detect offset voltage. This periodic action allows offset voltage measurement without requiring the motor to be stopped, as the switching element can be temporarily turned off while the motor continues to rotate through inertia or external drive.
Solution Approach 2:
The system maintains continuous motor operation by detecting offset voltage during periodic intervals when the switching element is off, rather than requiring a complete motor stop. The motor continues to receive power through other phases or through inertia, ensuring uninterrupted useful action while enabling offset voltage detection.
3Productivity
If the switching element is kept on continuously, then productivity is improved, but measurement precision worsens
Solution Approach 1:
The control circuit implements periodic switching of the switching element between on and off states. During the off state intervals, the control circuit measures the offset voltage by detecting the voltage across the shunt resistor when no current flows through that phase. This periodic switching enables accurate offset voltage measurement while maintaining overall high productivity through continuous motor operation.
Solution Approach 2:
The control circuit performs offset voltage detection at predetermined intervals or at specific timing within the PWM cycle, preparing accurate offset compensation values in advance. This preliminary action ensures that offset voltage data is available for compensation during motor operation without requiring continuous switching element interruption.
4Measurement precision
If a dedicated component is used for offset voltage detection, then measurement precision is improved, but ease of manufacture worsens
Solution Approach 1:
The patent combines offset voltage detection functionality with the existing current detection circuit components (shunt resistor, amplifier, and control circuit). By merging these functions into a single integrated circuit design, the manufacturing process is simplified as fewer separate components need to be assembled, tested, and calibrated, while still achieving accurate offset voltage detection.
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 highly accurate detection of offset voltage while the motor is rotating, reducing costs and operational complexity by avoiding the need for a dedicated component and allowing continuous motor operation.
Implementation Method 1
a shunt resistor provided between a ground-side potential line of the inverter circuit and a ground, or between a high potential line of the inverter circuit and a power supply section
Implementation Method 2
an amplifier circuit configured to amplify the voltage converted from the current by the shunt resistor and output the amplified voltage to the control circuit
Data Source
AI summary
A control device includes an inverter circuit having a plurality of switching elements forming three upper and lower arms corresponding one-to-one to the phases of a three-phase motor. The control device includes a shunt resistor, a control circuit that outputs a PWM drive signal to the inverter circuit, and an amplifier circuit. During a regular control, a motor control section changes a pulse signal that controls switching of the switching element. The motor control section sets the switching element included in the arm located on a potential line side to which the shunt resistor is connected to a state in which current does not flow by changing the pulse signal. In this state, the current value acquisition section acquires the offset voltage converted by the shunt resistor.