Rotational Angle Calculation Using Dead-Time Compensation
Solution Overview
Problem
The existing methods for calculating the rotational position of a salient three-phase motor using high-frequency voltage signals can introduce audible noise and reduce accuracy due to the need to minimize the high-frequency voltage signal to mitigate noise, leading to errors in estimating the rotational angle.
Innovation Solution
A control system is developed that includes an inverter with switching elements, a superimposing element for high-frequency voltage signals, a calculating element for rotational angle calculation, and a dead-time compensating element to adjust switching durations, along with a current manipulating element to maintain accuracy by correlating the high-frequency voltage signal with the current flowing in the motor, thereby reducing noise and maintaining accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the high-frequency voltage signal magnitude is reduced to minimize audible noise, then noise level decreases, but the accuracy of rotational angle estimation deteriorates
Solution Approach 1:
The system performs preliminary dead time compensation by calculating correction values based on switching element states before they affect the high-frequency voltage signal. This advance correction prevents measurement errors from occurring in the first place, allowing accurate rotational angle estimation even with reduced signal magnitude.
Solution Approach 2:
The system uses feedback by continuously monitoring the actual high-frequency current signal and comparing it with expected values. The rotational angle calculation is refined through feedback loops that adjust estimates based on measured current deviations, maintaining accuracy despite lower signal magnitudes.
2Reliability
If dead time is introduced in switching elements to prevent short circuits, then inverter reliability improves, but error in high-frequency voltage signal increases
Solution Approach 1:
The dead time compensation calculation is performed in advance based on the switching element states during dead time periods. By pre-calculating the voltage error that would occur during dead time and applying correction values before they affect measurement, the system maintains signal accuracy while preserving the necessary dead time for reliable switching.
Solution Approach 2:
The system introduces an intermediary compensation mechanism that mediates between the conflicting requirements of dead time (for reliability) and signal accuracy. The compensation calculation acts as an intermediary that translates the effect of dead time into correctable error values, allowing both reliability and precision to coexist.
3Extent of automation
If the high-frequency voltage signal is superimposed on inverter output to estimate rotational angle, then rotational position measurement capability is enabled, but audible noise is generated
Solution Approach 1:
The system applies partial action by using just enough high-frequency voltage signal to obtain measurable current responses for rotational angle estimation. Rather than using full-strength signals, the system uses minimized magnitudes that are sufficient for measurement purposes while staying below the threshold for audible noise generation.
Solution Approach 2:
The system changes the frequency parameter of the superimposed voltage signal to be higher than the electrical angular frequency of the rotary machine. This parameter change allows the signal to be distinguished from fundamental frequency components during measurement while operating at frequencies less susceptible to audible noise perception.
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 system effectively reduces noise and maintains the accuracy of rotational angle calculation by compensating for dead time errors and manipulating currents, ensuring precise estimation of the motor's rotational position.
Implementation Method 1
An inverter IV is provided with a first pair of series-connected high- and low-side (upper- and lower-arm) switching elements Sup and Sun, a second pair of series-connected switching elements Svp and Svn, and a third pair of series-connected switching elements Swp and Swn
Implementation Method 2
a superimposing element configured to superimpose a high-frequency voltage signal on an output voltage of the inverter
Implementation Method 3
a calculating element configured to calculate a rotational angle of the rotary machine based on the measured high-frequency component value of a current flowing in the rotary machine
Implementation Method 4
a dead-time compensating element configured to shift a start edge and an end edge of an on duration for each of the first and second switching elements by a preset same time to compensate for an error due to the dead time
Data Source
AI summary
In a system for driving an inverter, a superimposing element superimposes, on an output voltage of the inverter. The high-frequency voltage signal is correlated with a measured high-frequency component value of a current flowing in the rotary machine. A calculating element calculates a rotational angle of the rotary machine based on the measured high-frequency component value. A dead-time compensating element shifts a start edge and an end edge of an on duration for each of first and second switching elements of the inverter by a preset same time to compensate for an error due to dead time. A current manipulating element manipulates a current flowing in the rotary machine to maintain an accuracy of calculation of the rotational angle.