Elevator Drive Control Strategy for Back-EMF Reduction
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Solution Overview
Problem
Elevator drive systems face limitations in accelerating current requirements, leading to increased costs and reduced drive lifetime due to fixed voltage capabilities and motor design constraints, which restrict duty loads and speeds.
Innovation Solution
A control strategy that selectively adds a current out of phase with the EMF voltage of the electric motor during constant speed operations, reducing back-EMF voltage and increasing current, allowing for higher motor speeds without increasing accelerating current ratings, thereby reducing the cost and enhancing drive lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the motor rated voltage is set close to the drive sinusoidal output voltage limit to minimize rated current, then the rated current of the motor and drive is minimized, but the accelerating current rating of the drive must be increased to accommodate voltage transients and inaccuracies, which increases drive cost and reduces drive lifetime
Solution Approach 1:
The patent changes the operating parameters of the motor by introducing a negative d-axis current component that modifies the back-EMF voltage. This parameter change allows the motor to operate at higher speeds without requiring increased accelerating current rating, thereby maintaining drive lifetime while achieving higher performance
Solution Approach 2:
Instead of increasing the accelerating current rating to accommodate voltage transients and achieve higher motor speeds, the patent inverts the approach by introducing a negative current component that reduces the back-EMF voltage. This inverted strategy allows higher speeds without increasing the current rating, thus preserving drive reliability and lifetime
2Productivity
If the accelerating current rating of the drive is increased to accommodate voltage transients and allow higher motor speeds, then higher duty loads and speeds can be accommodated, but more robust or larger switching devices are required, which increases drive cost
Solution Approach 1:
The patent modifies the current parameters by adding a negative d-axis current component that reduces the back-EMF voltage. This parameter modification enables the motor to achieve higher speeds without requiring larger or more robust switching devices, thereby maintaining device simplicity while enhancing productivity
Solution Approach 2:
Rather than increasing the current rating and switching device capacity to achieve higher speeds, the patent inverts the conventional approach by reducing the effective back-EMF voltage through negative current injection. This allows higher duty speeds to be achieved with the same switching devices, avoiding increased device complexity and cost
3Reliability
If the motor rated voltage is lowered to accommodate DC bus voltage variations and transients, then voltage reliability is improved, but the accelerating current rating must be increased, which increases drive cost
Solution Approach 1:
The patent changes the voltage parameter by introducing a negative d-axis current that reduces the back-EMF voltage. This allows the motor to operate reliably with the actual DC bus voltage variations without requiring a lowered rated voltage, while avoiding the need to increase the accelerating current rating and drive complexity
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 lowers the accelerating current requirement, reduces the cost of the drive assembly, and extends the drive's lifetime while enabling higher duty loads and faster duty speeds.
Implementation Method 1
Most arrangements include electric motors that cause desired movement of an elevator car responsive to the signals and power provided through the drive
Implementation Method 2
selectively adding a current out of phase with an EMF voltage of the electric motor
Data Source
AI summary
An elevator drive assembly (30) includes a voltage regulator (40) that selectively introduces current under certain conditions. In one example, the voltage regulator (40) introduces a negative flux current to an electric motor (32) when the motor (32) is operating under conditions corresponding to constant speed movement of an elevator car (22). In one example, the added negative flux current effectively reduces the back-EMF voltage of the motor (32) during the constant velocity portion of an elevator run. A disclosed example includes controlling the added current to maintain control over a motor torque constant, which becomes a function of the added current.