Inverter Switching Frequency Control for Motor Systems
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Solution Overview
Problem
Inverter systems for vehicles face challenges in efficiently managing switching frequencies to minimize losses, reduce AC current ripple, and decrease noise, vibration, and harshness (NVH) while maintaining torque smoothness, particularly in hybrid and electric vehicles where alternating current (AC) current ripple is high.
Innovation Solution
A motor control system that dynamically adjusts the switching frequency between a first predetermined frequency (e.g., 10 kHz) and a second predetermined frequency (e.g., 20 kHz) based on torque, speed, and current conditions of the electric motor, using a target frequency module to determine the optimal switching frequency for each phase of the inverter module, thereby reducing losses and AC current ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a fixed high switching frequency is used, then AC current ripple is reduced, but losses and noise increase
Solution Approach 1:
The patent implements dynamic switching frequency adjustment by transitioning from a fixed switching frequency to a variable switching frequency that adapts to operating conditions. The controller dynamically selects between a first switching frequency and a second switching frequency based on motor operating parameters, allowing the system to optimize between reducing AC current ripple and minimizing switching losses under different operating conditions.
Solution Approach 2:
The patent changes the switching frequency parameter based on motor operating conditions. The controller monitors motor parameters and adjusts the switching frequency between a first value and a second value, transforming the static parameter into a dynamic one that optimizes system performance across different operating points.
2Object-generated harmful factors
If a fixed high switching frequency is used, then AC current ripple is reduced, but noise and vibration increase
Solution Approach 1:
The system dynamically adjusts switching frequency to avoid resonant frequencies that cause noise and vibration. By varying the switching frequency between two discrete values based on operating conditions, the system can suppress acoustic resonance and reduce NVH (noise, vibration, and harshness) while maintaining adequate current ripple suppression.
Solution Approach 2:
The patent employs periodic modulation of the switching frequency, alternating between a first switching frequency and a second switching frequency based on the motor's operating state. This periodic variation helps distribute energy across different frequency bands, reducing concentrated harmonic content that causes noise and vibration.
3Loss of energy
If switching frequency is dynamically adjusted, then losses and AC current ripple are reduced, but system complexity increases
Solution Approach 1:
The patent segments the switching frequency control into discrete levels (a first switching frequency and a second switching frequency) rather than continuous adjustment. This segmentation simplifies the control logic while still achieving dynamic optimization, reducing the complexity compared to fully continuous frequency modulation.
Solution Approach 2:
The patent implements partial dynamic adjustment by using only two discrete switching frequency levels rather than full continuous variation. This partial action approach achieves sufficient optimization benefit while keeping the control system relatively simple, avoiding the complexity of continuous parameter adjustment.
Data Source
AI summary
A motor control system includes: a voltage command module configured to determine a target d-axis voltage for an electric motor and a target q-axis voltage for the electric motor; a target frequency module configured to: selectively set a target switching frequency to a first predetermined switching frequency; and selectively set the target switching frequency to a second predetermined switching frequency that is at least 2 kilohertz (kHz) greater than the first predetermined switching frequency; and a switching module configured to: based on the target d-axis voltage and the target q-axis voltage, determine target pulse width modulation (PWM) duty cycles for phases, respectively, of the electric motor; and switch switches of legs of an inverter module connected to the phases of the electric motor at the target PWM duty cycles, respectively, and the target switching frequency.