Described in this paper is a new circuit having the special output waveform suitable to drive the two-phase servomotor. The circuit “Twisted Waveform Magnetic Modulator” is composed of two saturable transformers and a (non-saturable) transformer. Primary winding pairs, either of which is made of the series connection of a primary winding of saturable transformer and the half of the center-tapped primary winding of the transformer in the same polarity, are connected to the voltage source (
Esm, sin ωt) in parallel but with reverse polarity to each other. The secondary winding of each transformer series-connected in the same polarity delivers output power. The waveform of output voltage is represented as follows,
ELm sin ωt, for -α<ωt -2π π<α
-
ELm sin ωt, for α<ωt -2nπ<2π-α
due to alternative saturation of each core of saturable transformers. Its saturation period is controlled by AC or DC current flowing through the control windings of saturable transformers, so that α goes to zero or π according to the polarity of control current. When the control current is zero, α =π/2 and the frequency of output voltage is twice as high as the frequency of powersupply, so that the output voltage has a twisted sinusoidal waveform, that is, the phase of fundamental sinusoidal voltage is abruptly reversed at each peak. When the control current flows, however, the output voltage waveform changes gradually into the normal sinusoidal waveform of the same frequency as that of the power supply. In this control, the peak value of the output voltage does not change and only the twisting angle α does. Then, the two-phase servomotor is easily driven to full rating by the Twisted Waveform Magnetic Modulator and there are not seen such defects as less damping, jump or hysteresis in the control characteristics and excessive circulating current all experienced in the magnetic servoamplifier.
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