Motor Control Device Rotor Position Estimation Neutral Point Potential
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Solution Overview
Problem
Existing motor control devices face challenges in accurately estimating the rotor position of a three-phase synchronous motor at zero or low speed, particularly under high load conditions, leading to instability in braking force and extended braking distance due to decreased position estimation accuracy using neutral point potential methods.
Innovation Solution
A motor control device that includes a three-phase synchronous motor, an inverter, and a rotational position estimation unit which selectively uses detected neutral point potential values and voltage application states to accurately estimate the rotor position, even under varying load conditions, by employing redundant position detectors and advanced control algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rotational position detector is used to detect the rotor position, then the motor can be controlled accurately, but the system fails completely when the detector malfunctions
Solution Approach 1:
The patent creates a virtual copy of the rotational position detector by estimating rotor position through neutral point potential measurement. This software-based estimation replicates the function of hardware detectors without requiring additional physical sensors, thereby improving reliability through functional redundancy while avoiding the complexity and cost of adding more hardware detectors.
Solution Approach 2:
The patent introduces neutral point potential measurement as an intermediary method to obtain rotor position information. Instead of directly relying on rotational position detectors that may fail, the system uses the neutral point potential as an intermediate indicator that correlates with rotor position, providing an alternative pathway for position detection that enhances system reliability.
2Reliability
If a rotational position estimation unit based on induced voltage is used, then the motor can be driven stably at high speed, but the position cannot be estimated at low speed or zero speed
Solution Approach 1:
The patent changes the detection parameter from induced voltage (which is speed-dependent) to neutral point potential (which is position-dependent and valid at all speeds). By measuring the neutral point potential during PWM switching intervals, the system can estimate rotor position regardless of motor speed, thereby extending the operating speed range to include zero speed and low speed conditions while maintaining driving stability.
3Reliability
If multiple rotational position detectors are provided redundantly, then the system reliability improves, but the mounting space and cost increase
Solution Approach 1:
The patent creates a virtual copy of the rotational position detector functionality through software-based position estimation using neutral point potential measurement. This approach provides the reliability benefits of redundant detection systems without requiring additional physical detectors, thereby eliminating the need for extra mounting space while maintaining system reliability through functional redundancy.
4Reliability
If multiple rotational position detectors are provided redundantly, then the system reliability improves, but the cost increases
Solution Approach 1:
The patent creates a virtual copy of the rotational position detector through software-based estimation algorithms that process existing electrical measurements (neutral point potential). This approach provides the reliability benefits of redundant detection systems without requiring additional expensive hardware components, thereby reducing manufacturing costs while maintaining system reliability.
Solution Approach 2:
The patent enables the motor control system to self-diagnose and self-correct by using its own existing electrical measurements (neutral point potential during PWM operation) to estimate rotor position. This self-service approach eliminates the need for additional redundant detectors, reducing both cost and complexity while improving reliability through software-based fault tolerance.
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 solution enables accurate rotor position estimation regardless of load, enhancing the reliability of both motor control and brake control devices, thereby stabilizing braking force and reducing braking distance.
Implementation Method 1
a rotational position estimation unit for estimating a rotor position based on a neutral point potential of the three-phase winding
Implementation Method 2
an electromotive voltage (not an electromotive voltage according to a speed, but an electromotive voltage due to an imbalance in inductance) generated in a non-energized phase
Data Source
AI summary
Disclosed are a motor control device that can accurately estimate a rotor position based on a neutral point potential even when a load increases, and a brake control device that is driven by the motor control device. The motor control device 3 includes a three-phase synchronous motor 4 including a three-phase winding, an inverter 31 connected to the three-phase winding, a control unit 6 for controlling the inverter based on a rotor position of the three-phase synchronous motor, and a rotational position estimation unit 2 for estimating a rotor position θd based on a neutral point potential Vn of the three-phase winding. The rotational position estimation unit estimates a rotor position selectively using one or more of a plurality of detected values of the neutral point potential according to a pre-estimated value of the rotor position and a voltage application state to the three-phase winding.