Rotating Electric Machine Controller Using Current Estimation
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Solution Overview
Problem
In systems with rotating electric machines, inverter control devices face challenges in maintaining control when phase currents become undetectable in at least two out of three phases based on voltage values from shunt resistors, particularly during abnormal conditions or specific operation states.
Innovation Solution
The control device employs a method to estimate phase currents and control the rotating electric machine by using a position sensor-less control strategy, calculating instruction voltages and currents in a γδ coordinate system, and adjusting switching modes and time ratios to ensure continuous control, even when phase currents are not detectable in all phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase currents are detected using voltage values from shunt resistors, then current detection is achieved, but control cannot be maintained when phase currents become undetectable in at least two phases
Solution Approach 1:
The patent introduces an intermediary estimation mechanism that uses detectable phase currents and mathematical relationships (including zero-sequence current calculations) to infer undetectable phase currents. This intermediary approach allows the system to maintain control continuity by substituting direct measurement with indirect estimation when shunt resistor detection fails in at least two phases.
Solution Approach 2:
The system implements feedback by continuously monitoring the detectability of phase currents and switching between direct detection mode and estimation mode. When undetectability is detected in at least two phases, the system activates the estimation mechanism using feedback from the single detectable phase and mathematical relationships, ensuring control continuity through adaptive response.
2Reliability
If modulation ratio is limited to ensure detectability of phase currents in at least two phases, then detection reliability is improved, but machine size increases and responsiveness decreases
Solution Approach 1:
The patent applies dynamics by making the detection strategy adaptive rather than static. The system dynamically switches between direct detection and estimation modes based on real-time detectability conditions. This allows the modulation ratio to operate at optimal levels for performance while the system adaptively compensates for detection limitations through the estimation mechanism when needed.
Solution Approach 2:
The system changes operational parameters by switching between different detection modes based on detectability conditions. When at least two phases are undetectable, the system changes from relying on direct voltage measurement to using current estimation based on mathematical relationships and zero-sequence current calculations, allowing flexible operation across different modulation ratios without being constrained by detection limitations.
3Device complexity
If shunt resistors are connected to only one of upper and lower arms in each phase, then device complexity is reduced, but phase current detection becomes unreliable in certain operation states
Solution Approach 1:
The patent uses mathematical relationships and zero-sequence current calculations as intermediaries to compensate for the limited shunt resistor configuration. By leveraging the relationship between phases and the properties of zero-sequence currents, the system can accurately estimate phase currents even with simplified shunt resistor connections to only one arm per phase, maintaining measurement precision while reducing device complexity.
Solution Approach 2:
The system replaces direct mechanical/electrical measurement (voltage detection across shunt resistors in all phases) with mathematical estimation methods. By using computational approaches based on detectable phase currents and mathematical relationships, the system substitutes physical measurement infrastructure with algorithmic inference, reducing hardware complexity while maintaining detection accuracy.
Data Source
AI summary
A controller of a rotating electric machine performs a control on a control amount of the rotating electric machine by (a) calculating a voltage instruction value for controlling the control amount based on voltage detection values of the shunt resistors when shunt resistors in at least two phases have an electric current flowing therein, and (b) performing a drive control of each of switches in an inverter based on the calculated voltage instruction value. The controller determines whether a phase current flowing in a winding is detectable in at least two of three phases based on voltage values of the shunt resistors, and, when determining that the phase current is not detectable in the at least two phases, the controller performs the drive control based on a past current value or a past voltage value in a two-phase rotating coordinate system of the rotating electric machine.