Flywheel Buffer Torque Control for DC Link Power Peaks
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Solution Overview
Problem
In motor drive systems, flywheel-type power storage devices exhibit poor responsiveness to power discharge and storage commands due to time lag in speed control, complicating control of servomotors and leading to increased power peaks and operational costs.
Innovation Solution
A motor drive system with a torque limit value calculation unit and a motor control unit for buffer that adjusts the torque command limits to control the servomotor's rotation speed, allowing for efficient storage and discharge of DC power using a flywheel-based power storage device, thereby enhancing responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If speed control is used to control the servomotor for buffer, then the power storage device can store and discharge DC power, but the responsiveness is poor due to time lag in speed control
Solution Approach 1:
The patent changes the control parameter from speed to torque. By directly controlling the torque command to the servomotor for buffer, the system eliminates the time lag associated with speed control loops. The torque control allows immediate response to power storage and discharge commands, as torque can be adjusted instantaneously without waiting for speed changes to manifest.
2Device complexity
If the converter is configured as a common power supply unit for multiple inverters, then costs and space are reduced, but power peaks become larger during acceleration or deceleration
Solution Approach 1:
The patent employs the flywheel-based power storage device to perform preliminary energy storage during periods of low power demand. When the servomotor for drive decelerates, regenerative power is stored in the flywheel before potential power peaks occur. This preliminary action ensures that energy is already available in the power storage device to counteract upcoming power peaks, maintaining stable power supply without requiring additional converters.
3Reliability
If the servomotor for buffer rotates at constant speed during low power consumption, then the power storage device is ready to supply power, but control complexity increases
Solution Approach 1:
The patent extracts the speed control function from the overall control system and handles it separately through dedicated speed control means. This allows the torque control means to focus solely on responding to power storage and discharge commands, while speed is managed independently. The separation of control functions reduces the complexity of the main control logic, as each control aspect can be optimized and implemented independently.
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
The system achieves improved responsiveness and reduced power peaks by dynamically adjusting torque command limits based on rotation speed and DC power amounts, enabling efficient energy storage and supply, thus decreasing operational costs and power supply demands.
Implementation Method 1
a flywheel (21) capable of storing a rotation energy
Implementation Method 2
an inverter for buffer (23) configured to perform power conversion between a DC power in the DC link (4) and an AC power which is a drive power or a regenerative power of a servomotor for buffer (22)
Data Source
AI summary
A motor drive system includes: a converter connected to a DC link; an inverter for drive connected to the DC link; a power storage device configured to store a DC power from the DC link or supplies a DC power to the DC link; a torque limit value calculation unit configured to calculate a torque limit value of a servomotor for buffer in the power storage device on the basis of a rotation speed of the servomotor for buffer and a DC power amount stored or supplied by the power storage device; and a motor control unit for buffer configured to perform a torque control with respect to the servomotor for buffer while changing an upper limit value and a lower limit value of a torque command using the torque limit value so as to adjust a DC power amount stored or supplied by the power storage device.