US 5,402,054 A · Variable speed AC drive control

Abstract

A method for controlling the speed of an AC machine (12) is described. The AC machine (12) receives three output phases (A,B,C) supplied from a cycloconverter (10) which is connected to an input supply (R,Y,B) of frequency f.sub.1. The cycloconverter (10) is caused to operate in three modes under control of a microprocessor (25). The first mode supplies the AC machine (12) in the frequency range 0 to f.sub.0, by conventional cycloconverting to generate a near continuum of frequencies. The second mode operates the cycloconverter (10) to synthesize a number of frequency steps in the frequency range f.sub.0 to f.sub.1 from the input supply (R,Y,B) and provides speed control of the AC machine (12) by phase control of the output voltage (A,B,C) between each frequency step. The third mode operates the cyclonverter (10) to be transparent, such that the input frequency f.sub.1 is effectively directly supplied to the AC machine (12) without speed regulation being applied.

Claims13

Dependent claims

A method of controlling the speed of a rotating AC machine, the AC machine being connected to a frequency converter which includes a plurality of switching elements connected to respective phases of a multi-phase input power supply and a control for selectively switching the switching elements, the method comprising:

operating the AC machine in three exclusive speed ranges within the range 0 to the frequency of the input supply, f.sub.1, wherein each of the three speed ranges corresponds to a separate operating mode of the frequency converter, and
(i) in the first mode, synthesizing a near continuum of frequencies in the range 0 to f.sub.0, where f.sub.0 is less than f.sub.1 by switching said switching elements to synthesize the near continuum of frequencies from the multi-phase input power supply,
(ii) in the second mode, synthesizing a number of output waveforms of intermediate frequency steps between the frequencies f.sub.0 to f.sub.1 by switching said switching elements to synthesize the intermediate frequency steps from the multi-phase input power supply, and between each frequency step, adjusting the phase of the input supply to obtain voltage control over the AC machine, and
(iii) in the third mode, connecting said switching elements so that the AC machine is effectively connected directly to said multi-phase input power supply, whereby the AC machine receives the input supply frequency f.sub.1.

1 more element

A method of operating an AC-AC frequency converter which includes a plurality of switching elements connected to the respective phases of a multi-phase input power supply with frequency, f.sub.1, and a control for selectively switching the switching elements to connect the multi-phase input power supply to an output of the frequency converter, comprising:

(i) operating the frequency converter in a first mode within the frequency range 0 to f.sub.0, where f.sub.0 is less than f.sub.1, said step (i) of operating synthesizing a near continuum of frequencies in the said range from said multi-phase input power supply,
(ii) operating the frequency converter in a second mode by synthesizing a number of output waveforms of intermediate frequency steps between the frequencies f.sub.0 to f.sub.1 from the multi-phase input power supply, and between each frequency step providing further control by adjusting the phase of the multi-phase input power supply to obtain control over the output voltage from the frequency converter, and
(iii) operating the frequency converter in a third mode by connecting said switching elements so that the output is effectively connected directly to said multi-phase input power supply so as to provide at the at the output of the converter, the input supply frequency, f.sub.1.

Dependencies are inferred from the claim text.

Variable speed AC drive control

Life of this patent

Variable speed AC drive control

Life of this patent

Abstract

Claims13