Electric Motor Power Calculation for Zero-Speed Holding Loads
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Solution Overview
Problem
Existing methods for calculating consumed power of an electric motor in industrial machines, such as injection molding machines, inaccurately report zero power consumption when the motor is not rotating, despite actual power being consumed, particularly during pressure holding steps.
Innovation Solution
A method to calculate consumed power using the equation Wm=2π·Tm·Rm/(ηm·ηp)/60+Pw, where Tm is output torque, Rm is rotational speed, ηm is motor efficiency, ηp is power factor, and Pw is switching loss, which accounts for power generated by inverters even when the motor is not rotating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If consumed power is calculated based on current and rotational speed only, then voltage detection and voltmeter are not required, but consumed power is calculated as zero when rotational speed is zero even though power is actually consumed
Solution Approach 1:
The patent changes the calculation parameters from only current and rotational speed to include current, rotational speed, and inverter output voltage. This parameter expansion allows accurate calculation of consumed power even when rotational speed is zero, as the voltage parameter captures the power consumption state during static operation phases like pressure holding.
Solution Approach 2:
The patent introduces the inverter output voltage as an intermediary parameter that bridges the gap between current detection and accurate power calculation. By detecting the inverter output voltage and incorporating it into the power calculation formula, the system can accurately measure consumed power without adding a voltmeter to the motor side, thus maintaining simplicity while improving accuracy.
2Productivity
If simple calculation method using only current and rotational speed is used, then calculation is simple, but power consumption during pressure holding step is not detected
Solution Approach 1:
The patent expands the calculation parameters to include inverter output voltage while maintaining computational efficiency. The enhanced formula Wm = (Im × Rm × 2π)/(60 × ηm × ηp) + (Vu × Im × ηinv) accurately captures power consumption during pressure holding steps without significantly increasing calculation complexity, as the additional term uses readily available inverter output voltage data.
3Measurement precision
If inverter output voltage is detected and included in calculation, then consumed power is accurately calculated even at zero rotational speed, but detection complexity and device requirements increase
Solution Approach 1:
The patent uses the inverter output voltage as an intermediary measurement that can be obtained from the inverter's existing control circuitry. This approach avoids the need for additional voltage sensors on the motor side, as the inverter already possesses the capability to detect its own output voltage through its control system, thus minimizing additional device requirements.
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
Accurately calculates consumed power even when the rotational speed of the electric motor is zero, enabling precise energy consumption monitoring and reduction in overall industrial apparatus power usage.
Implementation Method 1
the DC power is converted by the inverter into a three-phase AC current of a desired current at a desired frequency
Implementation Method 2
three-phase AC power supplied from a factory is converted into DC power by the converter
Implementation Method 3
Wm=2π·Tm·Rm/(ηm·ηp)/60+Pw, where Tm is an output torque, Rm is a rotational speed, ηm is a motor efficiency, ηp is a power factor, and Pw is a switching loss
Data Source
AI summary
A consumed power calculation method for an electric motor for calculating consumed power of the electric motor in an industrial machine including one or more electric motors supplied with a current and driven by an inverter, the consumed power calculation method including: measuring a current Im supplied to the electric motor; obtaining an output torque Tm of the electric motor based on the current Im; and calculating consumed power Wm of the electric motor by the equation: Wm=2π·Tm·Rm/(ηm·ηp)/60+Pw, where Rm is a rotational speed of the electric motor, ηm is a motor efficiency of the electric motor, ηp is a power factor, and Pw is a switching loss of the inverter.