Rotor Position Detection via Neutral-Point Voltage Ratios
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Solution Overview
Problem
Permanent magnet synchronous motors with saliency exhibit challenges in rotor position detection, particularly at zero and low speeds, where existing methods struggle to accurately control and estimate rotor position due to varying inductance of stator windings with rotor angle.
Innovation Solution
A method and arrangement for rotor position detection in permanent magnet synchronous motors using PWM excitation voltages with staggered waveforms, measuring voltage ratios at a common point to derive rotor position information, allowing identification of position ranges and discrimination between 180° electrical ranges, even at low speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If neutral-point potential detection is used for rotor position estimation, then position detection is enabled, but measurement precision deteriorates at zero and low speeds due to insufficient back EMF signals
Solution Approach 1:
The patent changes the detection parameter from direct back EMF measurement to neutral-point potential measurement during specific PWM switching states. By measuring the neutral-point potential when particular switch combinations are active, the system can derive rotor position information through voltage ratio comparisons, which remains effective at zero and low speeds where traditional back EMF methods fail.
2Measurement precision
If PWM excitation voltages with staggered waveforms are applied to create multiple excitation states, then rotor position detection capability is improved, but device complexity increases
Solution Approach 1:
The patent employs periodic PWM excitation with specific staggered switching sequences across three phases. By systematically cycling through different switch states (e.g., S1-S6 combinations) in a periodic manner, the system creates multiple excitation states that reveal rotor position information through neutral-point potential variations, achieving accurate detection without additional hardware.
Solution Approach 2:
The patent segments the detection process into discrete PWM switching states, where each state provides specific voltage ratio information. By dividing the full detection cycle into multiple segmented states with different switch configurations, the system can piece together complete rotor position information from individual state measurements, improving precision while using existing motor structure.
3Measurement precision
If voltage ratios are compared to identify rotor position ranges, then position detection accuracy is improved, but loss of energy increases due to additional PWM switching
Solution Approach 1:
The patent makes the PWM switching sequence serve dual functions: motor drive control and rotor position detection. The same staggered PWM excitation used for motor control creates the necessary voltage ratios for position detection, eliminating the need for separate detection switching sequences and reducing additional energy losses.
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 rotor position detection and control at zero and low speeds by comparing voltage ratios, improving motor control and efficiency, although it may introduce additional losses and limitations on modulation depth.
Implementation Method 1
A permanent magnet synchronous motor will have a rotor of permanent magnets, which turns either within or around the stator, and stator windings to which excitation voltages are applied to create magnetic interaction with the permanent magnets and cause the rotor to be driven
Implementation Method 2
The excitation voltages may be pulse-width modulated (PWM) voltages, in which case, current is controlled by changing the modulation
Implementation Method 3
The control means is further arranged to measure the voltage at the neutral point at sample times within the PWM periods and to generate from the measured voltages an estimation of the rotational position of the rotor
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Three windings (12) of a permanent magnet synchronousmotor10are connected from a common point (22) to respective feed points (24) and driven as a different phase of the motor 10by pwm excitation voltages from as witching circuit (28) under the control of a control circuit (38). Eight possible excitations state combinations exist for the circuit in Fig. 2 depending on whether the output of the circuit (28) is at supply voltage or ground for each of the three phases. Measurements are made of ratios of the voltage at the common point (22) as a proportion of the supply voltage, during various excitation states,and a comparison of these ratio values is used to derive position information for the rotor16of the motor (10).