Open-Winding Motor Inverter Control for Zero-Phase Current Suppression
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Solution Overview
Problem
Existing methods for estimating the magnetic pole position of open-winding motors driven by two inverters are inadequate due to the presence of zero-phase current, which interferes with precise position estimation, especially at low speeds.
Innovation Solution
A control system that generates three-phase PWM signals using two inverters, incorporating a zero-phase current suppressing unit to manage current flow direction and a PWM signal generating unit that synchronizes phase shifts to detect current variations within a carrier period, allowing accurate magnetic pole position estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If two inverters are used to drive an open-winding motor, then the motor can be controlled with enhanced power and flexibility, but zero-phase current appears which interferes with magnetic pole position estimation
Solution Approach 1:
The patent extracts and eliminates the harmful zero-phase current component from the three-phase currents before performing magnetic pole position estimation. By removing this interfering component, the estimation precision is restored despite using two inverters for enhanced motor power.
Solution Approach 2:
The patent changes the processing parameters of the current signals by applying specific coordinate transformations and filtering operations to separate and eliminate the zero-phase current component, thereby enabling accurate position estimation while maintaining the power benefits of dual inverter operation.
2Speed
If current variation detection is performed within a carrier period, then high-speed position estimation is achieved, but at low speeds the induced voltage amplitude is reduced making accurate estimation difficult
Solution Approach 1:
The patent introduces an intermediary processing step that detects current variations within the carrier period and uses these variations as a mediator to estimate position at low speeds, bypassing the limitation of reduced induced voltage amplitude that normally prevents accurate low-speed estimation.
Solution Approach 2:
The patent utilizes periodic current variation detection synchronized with the carrier wave period to extract position information even when the motor is stationary or moving at very low speeds, where traditional induced voltage methods fail due to insufficient voltage amplitude.
3Device complexity
If zero-phase current is not suppressed, then the control system is simpler, but current detection accuracy deteriorates due to interference
Solution Approach 1:
The patent replaces complex hardware modifications with software-based signal processing methods to suppress zero-phase current. Through coordinate transformations and selective filtering in the control algorithm, the system achieves accurate current detection without adding complex physical components.
Data Source
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AI summary
An open-winding motor drive device according to an embodiment includes a primary side inverter having three-phase wires that are independent from each other and are connected to three output terminals of a motor having an open-winding structure including six output terminals, a secondary side inverter connected to three remaining output terminals of the motor, a current detecting unit that detects three-phase currents applied to the motor, a current variation detecting unit that outputs a difference between values of the three-phase currents detected twice as a current variation, a magnetic-pole-position estimating unit that estimates a magnetic pole position based on the current variation of the motor, a control unit that controls current to be applied to the motor and a rotating speed, a zero-phase current suppressing unit that suppresses zero-phase current flowing in the same direction through the three-phase wires of the motor via paths between the primary side and secondary side inverters and the motor, and a PWM signal generating unit that compares three-phase duty ratios calculated based on a command voltage and a direct-current voltage acquired from the control unit and the zero-phase current suppressing unit with a carrier and generates three-phase PWM signals of each of the primary side and secondary side inverters. For 64 voltage vectors, which are combinations of ON/OFF patterns of the primary side and secondary side inverters, the PWM signal generating unit divides a hexagonal spatial vector is divided into six sectors, the hexagonal spatial vector having, as its center, a point where two second switching patterns are located and having, as its vertices, points where two first switching patterns are located, the second switching pattern not generating zero-phase voltage and not generating voltage that acts on between the phases of the motor, the first switching pattern not generating zero-phase voltage and generating voltage that acts on between the phases of the motor, and for three-phase duty ratios of the primary side and secondary side inverters of each sector, and shifts the phases by synchronizing between the primary side and the secondary side such that a time is provided for the current variation detecting unit to detect a difference between current values of the three phases twice for each of a maximum, medium and minimum phases classified based on the magnitudes of the duty ratios.