PWM Inverter Control System Modulation Factor Adjustment
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Solution Overview
Problem
Conventional control systems for PWM inverters struggle to effectively reduce noise when operating at high modulation factors, as the on-off pattern of PWM pulses becomes constant, limiting the spreading of switching frequency components.
Innovation Solution
A control system that adjusts the modulation factor by varying the step-up command value to the converter, allowing the modulation factor to be changed within a predetermined range, thereby altering the on-off pattern of PWM pulses and spreading the switching frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the PWM inverter operates at a high modulation factor, then the voltage command amplitude is large, but the on-off pattern of PWM pulses becomes almost constant making it difficult to spread switching frequency components
Solution Approach 1:
The patent applies dynamics by making the carrier frequency variable rather than fixed. The control device changes the carrier frequency dynamically based on the modulation factor, specifically using a higher carrier frequency when the modulation factor is high and a lower carrier frequency when the modulation factor is low. This dynamic adjustment ensures that the on-off pattern of PWM pulses changes even at high modulation factors, effectively spreading switching frequency components and reducing noise.
Solution Approach 2:
The patent changes the parameter of carrier frequency based on the modulation factor. When the modulation factor increases, the carrier frequency is increased proportionally. This parameter change relationship is expressed as: when modulation factor is high, use high carrier frequency; when modulation factor is low, use low carrier frequency. This ensures optimal noise reduction across different operating conditions while maintaining effective PWM control.
2Object-generated harmful factors
If the carrier frequency is randomly changed to spread switching frequency components, then noise is reduced, but when operating at high modulation factor the on-off pattern becomes constant reducing effectiveness
Solution Approach 1:
Instead of using random carrier frequency changes, the patent implements a dynamic carrier frequency adjustment mechanism that responds to the modulation factor. The carrier frequency is changed systematically based on operating conditions, ensuring that the on-off pattern of PWM pulses remains variable even at high modulation factors. This dynamic approach maintains reliability of noise reduction by adapting to different operating conditions rather than relying on random variations.
Solution Approach 2:
The patent employs feedback by using the modulation factor as a basis for determining the carrier frequency. The control device continuously monitors the modulation factor and adjusts the carrier frequency accordingly. This feedback mechanism ensures that the noise reduction remains effective across different operating conditions, as the carrier frequency is always appropriately matched to the current modulation factor, preventing the on-off pattern from becoming constant.
3Object-generated harmful factors
If the on-off pattern of PWM pulses is changed to spread switching frequency components, then noise is reduced, but at high modulation factor the frequency of PWM pulse on-off reduces
Solution Approach 1:
The patent changes the carrier frequency parameter in response to changes in modulation factor. When the modulation factor is high, the carrier frequency is increased to compensate for the reduced on-off frequency, thereby maintaining the effectiveness of switching frequency component spreading. This parameter change strategy ensures that noise reduction remains effective across different modulation factors while adapting to the changing on-off frequency characteristics.
Solution Approach 2:
The patent implements a dynamic relationship between carrier frequency and modulation factor. Rather than using a fixed carrier frequency, the system adjusts the carrier frequency dynamically based on the modulation factor. This dynamic adjustment compensates for the reduced on-off frequency at high modulation factors, maintaining the ability to spread switching frequency components effectively and reduce noise across all operating conditions.
Data Source
AI summary
A control system for controlling an electric rotating machine includes an inverter for driving the electric rotating machine, a converter that converts an input voltage thereof to an output voltage equal to a step-up command value, and supplies the output voltage to the inverter, a pulse generation section that generates PWM pulses from a carrier for controlling the inverter in accordance with result of comparison between the carrier and a voltage command to the electric rotating machine, and a command generation section that generates the step-up command value. The command generation section includes a command control section that controls the step-up command value such that a modulation factor defined as an amplitude of the voltage command divided by the output voltage of the converter is changed within a predetermined modulation factor range.