Multi-Motor Inverter Control Using Time-Shared AD Sampling Circuit
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Solution Overview
Problem
Low-cost MCUs with only one AD sampling circuit struggle to accurately control multiple permanent magnet synchronous motors due to the complexity and high cost of individual AD sampling circuits, making it difficult to sample phase currents effectively.
Innovation Solution
A motor control system that employs a rectifier, filter circuit, operation controller, voltage sampler, inverters, and current samplers, where the phase current signals of multiple motors are time-share sampled through a single AD sampling circuit, with staggered sampling during rising or falling half cycles of triangular carrier signals to avoid conflicts, allowing a low-cost MCU to control multiple motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple independent AD sampling circuits are used to control multiple permanent magnet synchronous motors, then the control accuracy and reliability are improved, but the device complexity and cost increase
Solution Approach 1:
The patent combines multiple AD sampling circuits into a single shared circuit that time-division multiplexes the sampling of phase currents from multiple motors. The controller sequentially samples each motor's phase current through the same ADC at different time slots, eliminating the need for separate ADCs for each motor while maintaining control accuracy through proper timing coordination with PWM carrier signals.
Solution Approach 2:
The single AD sampling circuit is designed to serve multiple functions by sampling phase currents from multiple different motors through time-division multiplexing. The same ADC resource is universally applied to monitor all motor phases across multiple motors, making the system more cost-effective without sacrificing the ability to accurately control each motor independently.
2Device complexity
If a single AD sampling circuit is used to control multiple motors, then the cost is reduced, but the sampling accuracy and reliability deteriorate due to sampling conflicts
Solution Approach 1:
The patent implements periodic time-division multiplexed sampling where the single AD sampling circuit periodically alternates between sampling different motors' phase currents in a cyclic manner. Each motor receives dedicated sampling time slots within each PWM period, ensuring that sampling occurs at appropriate intervals without conflict, thereby maintaining measurement precision while using a single ADC resource.
Solution Approach 2:
The controller preliminarily determines the sampling timing for each motor's phase current before actual sampling occurs, coordinating the sampling schedule with the PWM carrier signals. By pre-planning which motor to sample at each time slot and ensuring sampling occurs during appropriate phases of the PWM cycle, the system avoids sampling conflicts and maintains accuracy without requiring multiple ADCs.
3Device complexity
If phase currents of multiple motors are sampled simultaneously through a single AD sampling circuit, then the cost is reduced, but sampling conflicts occur leading to control failure
Solution Approach 1:
The patent segments the sampling process into distinct time slots for each motor, dividing the continuous sampling requirement into discrete periodic intervals. Each motor's phase current is sampled in its designated time slot within the PWM period, preventing simultaneous sampling conflicts while using a single ADC. This segmentation of the sampling timeline enables cost-effective control of multiple motors without sacrificing control efficiency.
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
Enables accurate and simultaneous control of multiple motors using a single AD sampling circuit, reducing costs and improving operational efficiency by preventing sampling conflicts and ensuring accurate phase current sampling.
Implementation Method 1
a rectifier configured to perform a full-wave rectification of an AC input voltage
Implementation Method 2
a filter circuit connected in parallel with the DC bus, the AC input voltage is converted into a DC bus voltage after being processed by the rectifier and the filter circuit
Data Source
AI summary
A motor control system includes a plurality of inverters each configured to be connected to a corresponding one of a plurality of motors, a plurality of current samplers coupled to the plurality of inverters, respectively, and each configured to sample a phase current of a corresponding one of the plurality of motors to generate a phase current signal for the corresponding one of the plurality of motors, and an operation controller including an analog-digital (AD) sampling circuit. The operation controller is configured to synchronously generate a plurality of triangular carrier signals each corresponding to one of the plurality of motors, and sample the phase current signals of the plurality of motors in a time sharing manner through the AD sampling circuit in rising half cycles or falling half cycles of the plurality of triangular carrier signals, respectively. The half cycles of the triangular carrier signals for sampling the phase current signals of the plurality of motors are staggered in time from each other.