PWM Control Device for Torque Pulsation Suppression
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Solution Overview
Problem
Existing power conversion devices, such as inverters, face issues with symmetry of PWM control pulses when the frequency of the carrier wave is close to the frequency of the voltage command value, leading to increased lower order harmonics and torque pulsation, which can cause shaft vibration and turbine trip in gas turbine power generation systems and affect ride quality in electric vehicles.
Innovation Solution
A control device that generates symmetrical PWM control pulses by using a negative phase creation unit to invert and delay the pulse signals, ensuring that the half cycles of the PWM pulse are symmetrical, even when the load frequency changes, thereby suppressing torque pulsation due to lower order harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If asynchronous PWM control is used with carrier wave frequency close to voltage command frequency, then device complexity is reduced, but symmetry of PWM pulse is lost causing increased lower order harmonics and torque pulsation
Solution Approach 1:
The patent applies asymmetry principle by intentionally creating asymmetrical control between positive and negative half cycles through the negative phase creation unit. Instead of maintaining symmetrical PWM patterns, the invention deliberately generates asymmetrical pulse widths in negative half cycles to cancel out lower order harmonics, thereby reducing torque pulsation while keeping the control circuit relatively simple.
2Object-generated harmful factors
If synchronous PWM control is used to maintain pulse symmetry, then lower order harmonics are suppressed, but control circuit complexity increases
Solution Approach 1:
The patent applies inversion principle by creating negative phase PWM signals that are inverted relative to the positive phase signals. The negative phase creation unit generates control pulses with inverted polarity and adjusted width to compensate for harmonics, achieving harmonic suppression through this inverted control approach rather than traditional synchronous PWM methods.
3Adaptability or versatility
If frequency of voltage command value is changed to adapt to variable speed operation, then adaptability is improved, but symmetry of voltage half cycles is lost causing torque pulsation
Solution Approach 1:
The patent applies dynamics principle by making the PWM control adaptable to changing operating conditions. The control device dynamically adjusts the negative phase PWM pulse widths based on the instantaneous voltage command frequency and motor rotational speed, allowing the system to maintain harmonic suppression effectiveness across variable speed operations while adapting to frequency changes.
Data Source
AI summary
A control device for power conversion device controls a power conversion device in a system driven by the power conversion device to which an electric motor outputs AC power, and includes: a control pulse generation unit configured to generate a control pulse of the power conversion device; and a negative phase creation unit configured to input a pulse signal output by the control pulse generation unit and rotational speed information of the electric motor, and to generate an inverted signal of an output signal of the control pulse generation unit, wherein the pulse signal of a half cycle during one cycle of voltage, the pulse signal being generated by the control pulse generation unit, and a pulse signal of a next half cycle during the one cycle of voltage, the pulse signal being generated by the negative phase creation unit, are symmetrical in positive and negative relationship of voltage.