GB1380730A - Waveform generators - Google Patents

Abstract

1380730 Controlling inverters INDUSTRIAL INSTRUMENTS Ltd 9 June 1972 [10 June 1971] 19936/71 Heading H2F In or for an inverter of the type in which switching elements are controlled so as to generate a pulse width modulated substantially sinusoidal waveform, a stepped, waveform X 2 is first generated having a frequency twice that of the required output, each step being compared with the instantaneous value of a triangular wave X 1 so as to derive a pulse width modulated sine wave X 3 of double frequency from which is derived a pair of push-pull waveforms X 4 , X 5 which are used to control the switching elements in two arms of a bridge so as to provide the required inverter output X 6 . As described, an astable circuit, which runs at 2 x 64 fo where fo is the required output frequency, triggers a J-K flip-flop and a monostable which enable a gate to provide 5 microsecond clock pulses at 64 fo as input to a reversible counter. The counter counts up to 15, the 16th pulse reverses the count and the 17th pulse begins to count down to the 31st pulse. The cycle is then repeated. A BCD decoder produces outputs which are fed to a summing amplifier S 1 via weighted resistors which provide a 16-step substantially sinusoidal waveform X 2 which is compared at A 11 with a triangular wave X 1 from an integrator A 1 thus producing the pulse width modulated wave X 3 . A bi-stable B 1 provides pushpull waveforms Q, # which are fed to transistors in adjacent arms of the bridge inverter (Fig. 1, not shown) and which thus periodically reverse the connections between the D.C. input and one side of the load. The transistors feeding the other side of the load are fed with push-pull pulse width modulated waveforms X 4 , X 5 derived from a logic circuit and switch the transistors so as to provide the required output X 6 .