Electric Motor Control System PWM Synchronization
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Solution Overview
Problem
Existing three-phase electric motor control systems face challenges with thermal management due to switching and conduction losses, which limit power handling capacity, and the use of multiple independent sub-motors introduces unsynchronized PWM control leading to increased DC bus voltage ripple and complexity.
Innovation Solution
A control system that synchronizes two electric motor control devices without a dedicated synchronization signal, using a communication bus to offset PWM counter values and minimize DC link capacitance and electromagnetic noise, thereby reducing the cost, complexity, and weight of the motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a larger power rating is desired for a conventional three phase motor, then the motor diameter must be increased, but the peripheral speed of the rotor increases requiring reduced coil turns which decreases inductance and increases current requirements
Solution Approach 1:
The motor is divided into multiple independent sub-motors, each with its own control device and inverter. Each sub-motor handles a portion of the total power requirement, allowing the use of smaller switching devices with lower current ratings while maintaining the overall high power output. This segmentation reduces the current per switching device and consequently reduces I²R losses and thermal management requirements.
2Loss of energy
If multiple independent sub-motors are used to reduce current per switching device, then switching losses and thermal management improve, but PWM control becomes unsynchronized leading to increased DC bus voltage ripple
Solution Approach 1:
The control devices exchange synchronization information through a communication bus, allowing each device to adjust its PWM timing based on feedback from others. This feedback mechanism ensures synchronized PWM control across all sub-motors, minimizing DC bus voltage ripple while maintaining the benefits of reduced switching losses.
3Reliability
If a dedicated synchronization line is used between controllers, then PWM synchronization is achieved, but the cost, complexity and weight increase due to isolation connections and additional processing requirements
Solution Approach 1:
The dedicated hardware synchronization line is replaced with a communication bus that transmits synchronization information digitally. This substitution eliminates the need for isolation connections and complex hardware synchronization circuits, reducing system complexity, cost, and weight while maintaining reliable PWM synchronization through software-based coordination.
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 allows for efficient power management, reduced thermal losses, and simplified synchronization of PWM counters, enhancing the motor's power handling capacity and reducing electromagnetic noise and DC link capacitance.
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
PWM control works by using the motor inductance to average out an applied pulse voltage to drive the required current into the motor coils
Data Source
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AI summary
A control system for an electric motor, the control system comprising a first control device arranged to control an operation of a first component of the electric motor; a second control device arranged to control an operation of a second component of the electric motor, wherein the first control device is arranged to transmit to the second control device a first signal for indicating the transmission of data over a first communication link to the second control device, wherein the second control device is arranged to use the timing of the first signal to synchronise the operation of the second component with the operation of the first component.