Inverter Control Device Dynamic Carrier Frequency Ripple Mitigation
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Solution Overview
Problem
Inverters for electric vehicles face challenges in reducing the size, weight, and cost of intermediate circuit capacitors due to high-frequency ripple voltages, which increase with lower DC-side voltages, necessitating larger capacitors that occupy more space and incur higher manufacturing costs.
Innovation Solution
A control device that adjusts the carrier frequency of pulse width modulated switching signals based on DC-side voltage, increasing the frequency as the voltage decreases to mitigate ripple voltage peaks without significantly increasing total losses, allowing for a smaller, lighter, and cheaper capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the capacitance of the DC link capacitor is increased to reduce ripple voltage, then the ripple voltage decreases, but the installation space, weight, and manufacturing costs increase
Solution Approach 1:
The patent dynamically changes the carrier frequency parameter based on the DC link voltage level. When voltage decreases, the carrier frequency is increased to compensate for the resulting increase in ripple voltage, thereby maintaining acceptable ripple levels without requiring oversized capacitance
Solution Approach 2:
The control device dynamically adjusts the carrier frequency in response to changing operating conditions (DC link voltage). This dynamic adaptation allows the system to maintain optimal performance across varying voltage levels without requiring a capacitor sized for worst-case scenarios
2Object-affected harmful factors
If the capacitance of the DC link capacitor is increased to reduce ripple voltage, then the ripple voltage decreases, but the installation space increases
Solution Approach 1:
The control device changes the carrier frequency parameter dynamically based on DC link voltage measurements, increasing frequency when voltage drops to counteract ripple voltage increases, thereby eliminating the need for larger capacitor physical dimensions
3Object-affected harmful factors
If the carrier frequency is increased to reduce ripple voltage at low DC-side voltages, then the peak-to-valley value of ripple voltage decreases, but the switching losses of the switching elements increase
Solution Approach 1:
The control device dynamically adjusts the carrier frequency parameter based on real-time DC link voltage measurements, increasing frequency only when voltage drops to a level that would cause excessive ripple, thereby minimizing switching losses during normal operation while maintaining ripple control when needed
Solution Approach 2:
The system dynamically adapts the carrier frequency to operating conditions, applying high-frequency switching only when necessary to control ripple at low voltage levels, rather than maintaining high frequency continuously, thus reducing overall switching losses
Data Source
Figure 1
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AI summary
Control device (8) for an inverter (2) supplying an electrical machine (3), wherein the control device (8) is configured to provide pulse-width modulated switching signals (15) with a carrier frequency for controlling switching elements (12) of the inverter (2), wherein the control device (8) is configured to obtain voltage information (17) describing a DC-side voltage of the inverter (2) and to determine the carrier frequency at least within a voltage interval (23) of the DC-side voltage and at least during an operating mode of the control device (8) as a function of the voltage information (17) such that the carrier frequency increases with decreasing DC-side voltage.