Electric Motor Control Device Torque Fluctuation Suppression
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Solution Overview
Problem
Existing control devices for electric motors face challenges in reducing calculation load while preventing torque fluctuations during output increases, often resulting in sudden changes in current and torque shocks.
Innovation Solution
A control device with an inverter circuit and control circuit that manage switching elements to seamlessly transition between one-phase modulation and rectangular wave control, using duty ratios and phase switching to minimize torque fluctuations and calculation load, incorporating an electric angle detection unit and modulated wave generation to determine optimal switching times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the control device transitions from three-phase modulation control to rectangular wave control when motor output increases, then the motor can deliver higher power, but the switching element ON time suddenly increases causing current change and torque shock
Solution Approach 1:
The control device dynamically adjusts the control mode based on the motor output level. At low output levels, it uses three-phase modulation control with PWM switching. When output increases and the modulation wave reaches the carrier wave maximum/minimum values, it transitions to rectangular wave control. This dynamic adaptation allows the system to optimize for either efficiency or power delivery depending on operating conditions, resolving the contradiction between power output and torque stability.
2Ease of operation
If the control device uses a map to determine drive signals for transitioning between control modes, then torque can be controlled, but calculation load increases due to map interpolation requirements
Solution Approach 1:
The control device changes the control parameter from continuous PWM duty ratios to discrete rectangular wave patterns (always on/off states). This parameter change simplifies the control logic by eliminating the need for complex map interpolation calculations, while still maintaining effective torque control through the binary switching states of the inverter elements.
Solution Approach 2:
The control space is segmented into distinct regions: one for three-phase modulation control and another for rectangular wave control. The transition between these segments occurs when the modulation wave reaches the carrier wave boundaries. This segmentation allows the system to use simpler control logic in each region without requiring continuous interpolation across the entire operating range, reducing calculation load.
Data Source
AI summary
There is provided a control device for an electric motor. The control device includes an inverter circuit and a control circuit. In a control cycle of the electric motor, the control cycle includes first to third sections. The control circuit outputs a first modulated wave in accordance with an output of the electric motor and outputs a minimum value or maximum value of a carrier wave as second and third modulated waves in the first section with a peak of first alternate-current voltage, and outputs the second modulated wave in accordance with an output of the electric motor and outputs the minimum value or maximum value of the carrier wave as the first and third modulated waves in the second section with a peak of second alternate-current voltage. The same output is applied in the third section with a peak of third alternate-current voltage.