Electric Motor PWM Ramp Control for Active Short-Circuit Transition
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Transitioning an electric motor to an active short circuit mode can cause high peak inductive current spikes, potentially damaging the rotor magnets and inverter switches due to coil winding inductance.
Innovation Solution
Implement a soft-start ramp limit mechanism that gradually reduces the PWM modulation depth during the transition to active short circuit mode, controlling the inductive current flow to prevent high peak currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric motor is transitioned to active short circuit mode to avoid high back EMF voltages, then the motor protection is improved, but high peak inductive current spikes are generated that can damage rotor magnets and inverter switches
Solution Approach 1:
The patent applies preliminary action by gradually reducing the PWM modulation depth over a predetermined time period before fully transitioning to active short circuit mode. This ramping down of the PWM signal prevents sudden current spikes by preparing the circuit in advance, allowing the inductive current to decrease progressively rather than abruptly when the short circuit mode is activated.
2Productivity
If PWM voltage is applied to coil windings to drive the electric motor, then the motor operation is maintained, but transitioning to short circuit mode causes high current spikes due to coil winding inductance
Solution Approach 1:
The patent applies dynamics by making the PWM modulation depth variable over time rather than abrupt. The system dynamically adjusts the PWM signal, gradually reducing its depth over a predetermined time period during the transition to active short circuit mode. This dynamic adjustment allows the inductive current to follow a controlled trajectory, preventing sudden power spikes while maintaining motor operation during the transition.
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
Minimizes peak inductive current flow, preventing damage to the rotor magnets and inverter switches by smoothly transitioning the electric motor to short circuit mode.
Implementation Method 1
A three phase electric motor typically includes three coil sets, where each coil set is arranged to generate a magnetic field associated with one of the three phases of an alternating voltage
Implementation Method 2
Electric motors work on the principle that a current carrying wire will experience a force when in the presence of a magnetic field
Implementation Method 3
As the rotor rotates relative to the coil windings a back electromotive force, otherwise known as a back EMF, is generated that opposes the original applied voltage and consequently acts against the current flow that causes the rotor to rotate
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A method for controlling an electric motor, the method comprising receiving a command to place the electric motor in a short circuit mode; varying a limit to an available pulse width modulation depth for controlling current flow in the electric motor to a predetermined value over a predetermined time period or at a predetermined rate of change; wherein upon the pulse width modulation depth limit being varied to the predetermined value placing the electric motor in the short circuit mode.