Pulse duration modulation method and its device

Abstract

The invented pulse width modulation (PWM) method and device is used for the power supply or similar conversion facility of the electric power system related to AC / AC, AC / DC, or DC / DC. The method includes following steps. (1) Basic carrier cycle T is generated. The modified modualtion section is determined with the length of the section being as the N times of the cycle T, here N is an integer. (2) The alteration values with cycle T are generated randomly so as to make the sum of each alteration value equate to zero, but each alteration value is not all zeros. (3) In the said modulation section, the each alteration value is superimposed to the N pieces of the basic carrier cycle T in sequence so as to complete PWM. The invention makes the noise spectrum of the output voltage even so as to prevent the resonance with the mechanical stationary vibration. It is suitable to inverter.

Description

technical field [0001] The present invention relates to conversion equipment between AC and AC, between AC and DC, or between DC and DC as well as for power supply or similar power systems, especially a pulse width modulation method and device. Background technique [0002] Frequency conversion speed regulation technology has been widely used in the field of motor control. As shown in Figure 1, connecting the inverter in series between the power supply and the motor can easily meet the requirements for the motor speed, torque and other operating indicators, and the most common inverter control method is the space voltage vector PWM control. The space voltage vector PWM control method includes determining the basic carrier period T; determining the modulation coefficient m; determining the position angle θ of the space voltage command vector so as to determine the basic voltage vectors VA, VB, and VZ used to synthesize the space voltage command vector V; according to T, m a...

AI Technical Summary

Problems solved by technology

In this way, the generated noise is a performance of a series of energy fixed in a narrow frequency band. As shown in Figure 9, the noise power is concentrated and distributed in the frequency band area where the basic carrier period T is an integer multiple. Concentrated noise energy appears in the frequency band, making the EMI indicators worse near the frequency band area where the noise is sharp and the basic carrier period T is an integer multiple

[0015] Some methods have been applied to noise suppression, such as: changing the motor design, controlling the frequency point of system resonance, increasing the carrier, etc., but these methods either increase the cost of the equipment, especially after the system is constructed; The switch puts forward higher requirements, and brings unfavorable factors such as increased switching loss and large temperature rise

[0016] There are also some methods that adjust the position where the pulse occurs, so that the frequency of the higher harmonic component of the output voltage is dispersed within a predetermined frequency range, and the timing of the output voltage changes with time. This method changes the position of the pulse There are also certain limitations. For example, as the degree of pulse width modulation deepens, the area that can be used to modulate the pulse position becomes narrower and narrower.

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