Carrier frequency calculation method and device for PWM rectification variable-frequency system

Abstract

The invention discloses a carrier frequency calculation method for a PWM rectification variable-frequency system. The carrier frequency calculation method comprises the following steps: calculating an initial carrier frequency according to a predetermined carrier frequency formula; collecting current values of a predetermined number of parallel capacitors, and calculating a root-mean-square value of the currents of the parallel capacitors according to the current values and the number of the parallel capacitors; calculating a rated current value of the parallel capacitors, and amplifying the rated current value by a predetermined multiple so as to obtain a comparison current value; comparing the root-mean-square value with the comparison current value; taking the initial carrier frequency as the carrier frequency required in the PWM rectification variable-frequency system when the root-mean-square value is less than the comparison current value; and performing self-optimization calculation when the root-mean-square value is greater than the comparison current value till the carrier frequency determined by self-optimization is used as the required carrier frequency when the root-mean-square value is less than the comparison current value. By means of the method, influence on the system after the parallel compensation capacitors are connected can be inhibited, such that, the security of the system can be ensured. The invention further discloses a carrier frequency calculation device for the PWM rectification variable-frequency system.

Description

technical field [0001] The invention relates to the field of electrical technology, in particular to a carrier frequency calculation method and device in a PWM rectification and frequency conversion system. Background technique [0002] State Grid's "Power System Voltage and Reactive Power Management Regulations" stipulates that for users of transformers above 100KVA, the power factor must be greater than 0.9. In order to meet the needs of the power supply system, reactive power compensation must be carried out. [0003] At present, the mainstream compensation method is to connect compensation capacitors in parallel on the low-voltage side of the transformer; however, for PWM controllable rectification variable-frequency loads, affected by the carrier frequency (limited by the switching frequency of the device), system harmonics always exist, and are related to the carrier frequency , Fundamental frequency into a certain mathematical relationship, high-order harmonic compone...

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Problems solved by technology

[0003] At present, the mainstream compensation method is to connect compensation capacitors in parallel on the low-voltage side of the transformer; however, for PWM controllable rectification variable-frequency loads, affected by the carrier frequency (limited by the switching frequency of the device), system harmonics always exist, and are related to the carrier frequency , Fundamental frequency into a certain mathematical relationship, the high-order harmonic components are particularly prominent; at the same time, the high-order harmonics are easily amplified by the joint action of parallel capacitors and transformer impedance, causing pollution to the public power grid, and the environment in which electrical equipment is used is harsh. It will bring harm to the surrounding communication system and equipment outside the public power grid. In severe cases, the local parallel resonance and series resonance of the power transmission and distribution system will burn the parallel capacitor and cause the system to collapse, resulting in damage to the safety of equipment and personnel. Therefore, how to effectively calculate The carrier frequency makes the harmonic components of the PWM rectification and frequency conversion system controllable, away from the harmonic times that can be amplified by the combined effect of parallel capacitors and short-circuit impedance, suppresses the frequency point generated by resonance, and suppresses the impact on the system after the parallel compensation capacitor is connected, ensuring The safety of the system is a technical problem that those skilled in the art need to solve urgently

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