Inverter Dead Time Compensation Using Fundamental Wave Phase
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Solution Overview
Problem
Existing motor control systems face challenges in accurately compensating for output voltage fluctuations during dead time in inverter circuits, particularly when the polarity of the motor current changes due to high-frequency content, leading to overcompensation and affecting transient characteristics.
Innovation Solution
A motor control device with a dead time compensation unit that includes a current phase calculation unit, base compensation voltage calculation unit, and variable gain calculation unit, which calculates and adjusts dead time compensation voltages based on the amplitude of the fundamental wave and high-frequency ripple of the motor current to ensure accurate compensation of output voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dead time compensation is performed based on fundamental wave phase, then compensation is applied, but overcompensation occurs when high-frequency content causes polarity changes
Solution Approach 1:
The patent applies preliminary action by predicting the polarity of motor current during dead time based on the phase of the fundamental wave component before the dead time occurs. This allows the control system to pre-determine the compensation voltage polarity, avoiding the problem of detecting polarity changes caused by high-frequency content during the dead time itself.
Solution Approach 2:
The patent segments the motor current into two distinct components: the fundamental wave component and the high-frequency ripple component. By analyzing only the fundamental wave phase to determine polarity, the system isolates the relevant information from the fundamental wave while filtering out the disruptive high-frequency content, thus achieving accurate polarity detection without overcompensation.
2Reliability
If dead time compensation is suspended when motor current is small, then overcompensation is prevented, but output voltage fluctuation remains uncompensated
Solution Approach 1:
The patent changes the parameter used for compensation decision-making from the absolute value of motor current to the phase relationship between the fundamental wave and the compensation voltage. This allows the system to maintain compensation even when current is small, by relying on phase information which remains reliable regardless of current magnitude, thus preventing both overcompensation and uncompensated fluctuations.
3Measurement precision
If feedback compensator compensates for voltage fluctuation during dead time suspension, then fluctuation is compensated, but transient characteristics are affected
Solution Approach 1:
The patent ensures continuous dead time compensation by using fundamental wave phase information that remains valid even when motor current amplitude is small. This eliminates the need to suspend compensation, maintaining continuous useful action in voltage fluctuation compensation and preventing the feedback compensator from having to compensate for dead time effects, thus preserving transient characteristics.
Data Source
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AI summary
To provide a motor control device capable of properly compensating the fluctuation in inverter output voltage during a dead time. The motor control device is for an inverter including switching elements composing upper and lower arms to convert a direct-current voltage to an alternating-current voltage and apply the alternating-current voltage to a motor thereby controlling a current of the motor to be a current target value, the motor control device including a dead time compensation unit (20) that compensates fluctuation in inverter output voltage during a dead time with each switching between the upper and lower arms by a dead time compensation voltage, wherein the dead time compensation unit (20) acquires an input parameter that determines a polarity of motor current during the dead time in a half-cycle of a fundamental wave of the motor current, and varies the dead time compensation voltage according to magnitude of the input parameter.