Parallel Motor Drive Circuit Using Vector Control
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Solution Overview
Problem
Operating multiple electric motors in parallel with a single inverter is challenging due to differences in load balancing and speed synchronization, particularly for permanent magnet (PM) motors, which often require dedicated drives and result in higher costs and instability issues.
Innovation Solution
A drive circuit system that selects a target PM motor with the largest torque output and uses a digital signal processor (DSP) to execute a vector control algorithm, generating a complex command voltage vector for PWM signals to synchronize and stabilize all motors, allowing them to operate at the same speed under varying loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple PM motors are operated in parallel with a single inverter, then cost and complexity are reduced, but load balancing and speed synchronization become difficult to control
Solution Approach 1:
The patent segments the control of multiple PM motors by selecting one motor as the 'synchronization reference' whose rotor position and speed are used to generate the common PWM control signals for all parallel motors. This segmentation approach allows a single inverter to control multiple motors while maintaining synchronization, as the reference motor's control parameters are applied to all other motors in the parallel configuration.
Solution Approach 2:
The system implements feedback by continuously monitoring the rotor position and speed of the synchronization reference motor, and using this information to dynamically adjust the PWM control signals. The feedback loop ensures that all parallel motors remain synchronized by comparing their actual performance against the reference motor's operational parameters and making real-time corrections.
2Power
If each PM motor uses a dedicated drive, then speed control and torque management are optimized, but cost and system complexity increase
Solution Approach 1:
The patent merges multiple dedicated drive functions into a single inverter by implementing a centralized control architecture that uses the synchronization reference motor's parameters to control all parallel motors. Instead of having separate inverters for each motor, the system combines the control functions by applying the reference motor's PWM signals to all motors, thereby reducing the number of drive devices while maintaining torque control capability.
Solution Approach 2:
The single inverter is designed to perform multiple functions by controlling multiple PM motors simultaneously. The inverter universalizes the control approach by using a common PWM generation mechanism that adapts to all parallel motors based on the synchronization reference motor's operational state, allowing one drive device to replace multiple dedicated drives.
3Adaptability or versatility
If multiple motors operate at varying speeds under varying loads, then load adaptability is improved, but system stability deteriorates
Solution Approach 1:
The patent creates equipotentiality in the parallel motor system by forcing all motors to operate at the same speed and synchronization point as the reference motor. By equating the operational parameters (speed, frequency, PWM duty cycle) of all motors to the reference motor's parameters, the system maintains stability while adapting to varying loads through the reference motor's performance adjustments.
Solution Approach 2:
The system adapts to varying loads by dynamically changing the PWM control parameters based on the synchronization reference motor's operational state. When the reference motor's load changes, its rotor position and speed parameters are updated, and these parameter changes are automatically applied to all parallel motors, maintaining stability while adapting to different load conditions.
Data Source
AI summary
A method of operating a drive circuit for parallel electric motors is provided. The method includes receiving measurements of stator phase currents in the parallel electric motors. The method includes selecting a target PM motor, from among the parallel electric motors, that generates a largest torque output. The method includes executing a vector control algorithm to generate a complex command voltage vector for the target PM motor. The method includes generating and transmitting a pulse width modulation (PWM) signal based on the complex command voltage vector for controlling an inverter. The method includes operating the inverter according to the PWM signal to supply three-phase alternating current (AC) power to the parallel electric motors.