Active Reflected Wave Cancellation for SiC Motor Drives
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Solution Overview
Problem
Wide-Bandgap semiconductor-based motor drives, particularly those using silicon carbide (SiC) MOSFETs, experience reflected wave phenomena that cause high voltage spikes at motor terminals, leading to insulation damage and reduced lifespan due to increased switching speeds and dv/dt, which conventional passive dv/dt filters struggle to mitigate effectively in medium to high power applications due to bulkiness, high power loss, and reliability issues.
Innovation Solution
An active reflected wave canceller (ARWC) is attached to each phase of the motor drive, comprising a pulse generator and power inductor that injects controlled nanosecond pulses to break the inverter output voltage edges into two steps, canceling reflected waves at the motor terminals, thereby reducing overvoltage without requiring the load current to flow through the pulse generator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive dv/dt filters are used to mitigate reflected wave phenomenon, then overvoltage at motor terminals is reduced, but the filter becomes bulky and experiences high power loss in medium to high power applications
Solution Approach 1:
The patent replaces the passive mechanical dv/dt filter with an active electronic system that uses controlled voltage injection through power electronic switches. This substitution eliminates the need for bulky inductors and resistors while achieving the same overvoltage mitigation function through active control of reflected waves.
Solution Approach 2:
The invention changes the approach from passive parameter-based filtering to active parameter control by dynamically adjusting the injection voltage magnitude and timing based on the detected reflected wave characteristics. This allows optimal mitigation performance without the energy losses inherent in passive components.
2Object-affected harmful factors
If passive dv/dt filters are used to mitigate reflected wave phenomenon, then overvoltage at motor terminals is reduced, but the filter becomes bulky in medium to high power applications
Solution Approach 1:
The patent replaces the passive mechanical dv/dt filter with an active electronic system that uses controlled voltage injection through power electronic switches. This substitution eliminates the need for bulky inductors and resistors while achieving the same overvoltage mitigation function through active control of reflected waves.
Solution Approach 2:
The active reflected wave canceller integrates multiple functions including overvoltage mitigation, signal detection, and controlled voltage injection within a single compact electronic system, replacing the need for separate bulky passive filter components.
3Productivity
If switching frequency is increased to improve system performance, then productivity increases, but reflected wave phenomenon becomes more severe
Solution Approach 1:
The system uses feedback to detect the reflected wave characteristics and dynamically adjusts the injection voltage parameters to counteract the reflected waves. This feedback mechanism enables effective mitigation even at high switching frequencies where the reflected wave characteristics change rapidly.
Solution Approach 2:
The active reflected wave canceller employs periodic injection of compensating voltage pulses synchronized with the switching frequency and the reflected wave period. This periodic action effectively counteracts the reflected waves without requiring reduction of the switching frequency.
Data Source
AI summary
An active reflected wave canceller (ARWC, or RWC) can attached to each phase at the output of a motor drive (i.e., inverter). The reflected wave canceller is generally comprised of a pulse generator and a power inductor. The power inductor is used to by-pass the load current, so it doesn't flow through the pulse generator. The pulse generator injects an accurately controlled nanoseconds narrow-width pulse into the system. The injected narrow pulse breaks the rising and falling edge of the inverter output voltage into two steps, which generates two traveling waves along the cable that cancel each other at the motor terminals.