SRM State Machine Control for Rotor Overlap Switching
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Solution Overview
Problem
Existing motor control systems for Switched Reluctance Motors (SRMs) lack an efficient method to determine when rotor poles start to overlap with stator poles, leading to suboptimal torque production and reduced motor efficiency.
Innovation Solution
A state machine motor controller interface is developed, comprising an edge detector, sequencer, and counter, which uses position sensors to determine rotor states and generate control signals to energize stator poles at optimal overlap points, thereby maximizing torque and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional motor control systems are used for SRMs, then the system structure is simple, but the rotor position detection precision is insufficient leading to suboptimal torque production
Solution Approach 1:
The controller is segmented into distinct functional modules: edge detector module for detecting sensor transitions, sequencer module for state machine control, and counter module for timing. This segmentation allows each module to perform its specific function efficiently while maintaining overall system manageability despite increased complexity.
Solution Approach 2:
Position sensors serve as intermediaries between the rotor mechanical position and the control system. The sensors detect rotor position and provide signals to the edge detector, which then processes these signals through the state machine to generate appropriate control outputs for the power circuit.
2Productivity
If rotor position feedback is implemented to synchronize switching, then torque production improves, but the device complexity increases due to additional sensors and control circuitry
Solution Approach 1:
The state machine controller uses the position sensor signals directly to drive the state transitions and control output generation. The system serves itself by using the incoming sensor edges to automatically update the internal state and generate the corresponding phase control signals without requiring external intervention or complex processing.
Solution Approach 2:
The controller operates on periodic state transitions triggered by rotor position changes. The state machine cycles through predefined states in response to sensor edges, creating a periodic control pattern that synchronizes with the rotor motion to optimize torque production during each rotation cycle.
3Ease of operation
If simple polling-based QEI/PDEC interfaces are used, then the device complexity is low, but the initial rotor state cannot be determined requiring the rotor to be moved to a known position
Solution Approach 1:
The controller performs preliminary detection of the initial rotor position state when power is first applied or before operation begins. The state machine initializes by reading the current positions of all quadrature encoders and determining the starting state, allowing the motor to begin operation from its actual initial position without requiring manual intervention to move it to a predetermined position.
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
The proposed solution enables precise determination of rotor pole overlap, allowing for maximum torque production and increased motor efficiency, while also supporting all four-quadrant operation of the SRM.
Implementation Method 1
an edge detector having a plurality of first inputs and a plurality of first outputs, wherein each of the plurality of first inputs is adapted for coupling to a respective one of a plurality of position sensors whereby each of the plurality of position sensors indicates a different motor rotor angle range
Implementation Method 2
when a first input receives a sensor output from an associated position sensor, a state thereof is determined based upon a sensor output logic value, wherein each state is defined by a logic value stored in a register and compared with the sensor output logic value after the transition thereof
Implementation Method 3
a sequencer comprising: a state input coupled to the state output from the edge detector, a state change pulse input coupled to the state change pulse output from the edge detector, a valid state change event/interrupt output, and a plurality of definition registers for defining expected states, comparison logic for validating the state received from the edge detector with an associated one of the expected states
Implementation Method 4
a counter having a clock input coupled to a clock and a count value output, wherein the counter increments a count value for a clock pulse received until a valid state pulse is received from the sequencer, whereby the count value will be stored in a count register and the count value of the counter will be reset to zero
Implementation Method 5
The stator is constructed from magnetic materials and has conductors (windings) to produce magnetic fields
Implementation Method 6
The rotor rotates due to reluctance torque produced by the magnetic field generated in the stator windings
Implementation Method 7
The control circuit of a SRM may consist of pair of transistors/MOSFET's to control switching of each phase
Data Source
AI summary
A state machine motor controller (SMMC) interface comprises a plurality of states which defines a unique set of poles/motor phase/phases energized. Digital sensors capture the start of overlap of rotor poles with stator poles. The state change occurs when a rotor pole starts overlapping with a stator pole. The number of states depends on the number of phases and the design of the motor. The SMMC has up to four inputs to accept rotational information from digital sensors and can control motors having up to 16 states. A sequencer is used to keep track of state changes and provides a next state depending on forward/reverse direction setting and braking setting. A counter provides rotational speed based upon the number of clock pulses per time period for a state change. The sequencer checks for a faulty sensor(s) and generates a fault interrupt therefrom.