Single MAG AMP control system for regulating bipolar voltage output of a power converter

Abstract: A power converter embodying the principles of the invention, and having a positive and negative output utilizes a single magnetic amplifier controller to control two saturable inductor cores utilized to regulate the positive and negative outputs by modulating the positive and negative pulse output of the power converter transformer. The magnetic amplifier controller monitors and sums the two voltage outputs and derives an offset from average representative output signal. This offset from average representative output signal is compared with a reference signal to derive an error signal. A current responsive to the error signal is generated and utilized to periodically reset the two saturable inductor cores and regulate the positive and negative output voltages.

Description: This invention relates to power supplies. A multiple output power supply whose output is regulated by using magnetic amplifiers conventionally has two saturable inductor cores in each output and a separate magnetic amplifier controller for each output. While this provides precise regulation, the number of magnetic cores required and the need for a separate magnetic amplifier controller for each output is expensive and often provides regulation with more precision than is needed for a particular application. US-A-3 452 268 discloses a power supply energized by a bipolar alternator for applying power to a rectifier through two paralleled magnetic amplifier gate windings to a primary transformer winding. A split secondary winding is connected to a rectifier which is connected to provide a positive and negative output voltage. According to this invention there is provided a power supply as claimed in claim 1. A two output power converter embodying the invention utilizes a single magnetic amplifier controller to control two saturable inductor cores utilized to regulate the positive and negative outputs of a converter by modulating the positive and negative pulse output of the power converter transformer. The magnetic amplifier controller monitors and sums the two voltage outputs and derives an offset from average representative output signal. This offset from average representative output signal is compared with a reference signal to derive an error signal. A current responsive to the error signal is generated and utilized to periodically reset the two saturable inductor cores and regulate the positive and negative output voltages. The invention will now be described with reference to the accompanying drawing, in which: FIG. 1 is a schematic of a power converter embodying the invention; and FIG. 2 is a schematic of a magnetic amplifier controller suitable for use in the power converter of FIG. 1. Referring to FIG. 1, a power converter includes an inverter switching circuit 101 which switches a DC voltage supplied by a DC energy source applied to input terminals 102 and 103. This inverter switching circuit 101 is not shown in detail since inverter switching circuits are well known in the art. It operates by periodically switching the applied DC voltage to produce an AC pulse signal which is applied to the primary winding 106 of power transformer 105. A secondary winding of the power transformer is center tapped at node 104 to produce two secondary windings 107 and 108 connected in series with each other. The center tap ( node 104 )is connected via lead 110 to a return terminal 111 which is common to two output terminals 112 and 113 which supply regulated DC voltage outputs of opposite polarity. A positive DC voltage output is supplied at terminal 112 and a negative DC voltage output is supplied to terminal 113. A regulated positive DC voltage output at output terminal 112 is derived from secondary winding 107 when its pin 1 is positive with respect to the node 104. This voltage is coupled to the positive output terminal 112 through the magnetic amplifier winding 121 of magnetic amplifier core 120, rectifying diode 131 and winding 141 of filter inductor coil 140. A regulated positive DC output voltage is also derived from secondary winding 108 when its pin 2 is positive with respect to the node 104 and is coupled to the output terminal 112 through winding 126 of magnetic amplifier core 125, rectifying diode 132 and winding 141 of filter coil 140. Similarly a regulated negative DC voltage output is derived at output terminal 113 from secondary winding 108 when its pin 2 is negative with respect to the node 104. This voltage is coupled to the negative output terminal 113 through the magnetic amplifier winding 122 of magnetic amplifier core 120, rectifying diode 134 and winding 142 of filter inductor coil 140. A regulated negative DC output voltage is also derived from secondary winding 107 when its pin 1 is negative with respect to the node 104 and is coupled to the output terminal 113 through winding 127 of magnetic amplifier core 125, rectifying diode 133 and winding 142 of filter coil 140. Regulation of the DC output voltage at terminals 112 and 113 is controlled by a single magnetic amplifier controller 150. The magnetic amplifier controller 150 monitors the positive and negative output voltages at output terminals 112 and 113 via leads 152 and 153, respectively. It sums the two sensed voltage outputs and derives an offset voltage representative of an average output voltage This representative offset voltage of the average output voltage is compared with a reference voltage and an error voltage is general A current responsive to the error voltage is generated and applied on lead 151 wherein it is transmitted via diodes 137 and 138, which are switched by the voltage polarities, to transmit the reset current and periodically reset the two saturable inductor cores 120 and 125. While a representative voltage of the average output voltage is derived in this particular example with regulated output voltages of opposite polarity a conventional average voltage could he used if the two output voltages were of the same polarity. An understanding of the invention may be readily attained by describing the operation of the circuit. The inverter switching circuit 101 applies a train of pulses of alternating polarity to the primary winding 106. Assume that a pulse in the secondary winding 107 is positive at pin 1 of that winding with respect to the center tap 104. Initially the transmission of this pulse to the output 112, via inductor winding 121, is blocked by the inductance of the saturable inductor core 120. The time delay of the leading edge of the pulse caused by this block is determined by the level at which the core was reset following transmission of the previous pulse transmitted. At the end of this time delay the positive pulse is transmitted and goes via rectifying diode 131 and the output filter comprising capacitor 161 and inductor winding 141 to the positive output terminal 112. A negative output is supplied at output terminal 113 from the negative pin 2 of winding 108 and after the time delay determined by the reset level of saturable inductor core 120 is transmitted by winding 122 and diode 134 to the output filter comprising capacitor 162 and inductor winding 142 and from there to output terminal 113. A similar process occurs when pin 2 of winding 108 becomes positive. Winding 126 of the saturable inductor core 125 delays the pulse as determined by the reset level to which it was set following transmission of the previous pulse. The rectifying diodes 132 and 133 rectify the positive and negative pulses respectively. Capacitor 161 and filter winding 141 filters the positive pulse and capacitor 162 and filter winding 142 filters the negative pulse. Hence a positive DC output voltage appears at output terminal 112 and a complimentary negative DC output voltage appears at output terminal 113. The DC voltage outputs at terminals 112 and 113 are sensed and coupled via leads 152 and 153 to the magnetic amplifier controller 150. The magnetic amplifier controller 150 sums the magnitude of both the sensed output voltages to obtain an offset representation voltage which is representative of the average magnitude of the two output voltages. This representative voltage is compared with a fixed reference voltage level by an error amplifier to obtain an error voltage. This error voltage of the error amplifier is transformed to a reset current for the two magnetic amplifier cores 120 and 125. This reset current is applied to the magnetic amplifier core 120 through diode 137 when the pulse train at pin 1 of winding 107 is negative with respect to the center tap node 104. Similarly a reset current is applied to the magnetic amplifier core 125 through diode 138 when the pulse train is negative at pin 2 of winding 108 with respect to the centertap node 104. This reset current periodically resets the magnetic amplifier cores 120 and 125 by the exact amount necessary to maintain the average output voltage magnitude at a desired regulated value when the load at the outputs 112 and 113 varies or is changed. Two free wheeling diodes 163 and 166 are included to maintain continuity of current in the filter windings 141 and 142 for both positive and negative currents during dead time between pulses and diode blocking of the pulse train. An illustrative controller is disclosed in FIG. 2. The two output voltages are coupled, via leads 252 and 253, to an offset voltage divider comprising the resistors 270 and 271 which are selected to be different in value. This voltage divider sums the two opposite polarity output voltages and derives a voltage representative of an average voltage value at the two output terminals. This representative voltage is applied to an error amplifier 272 which compares it to a reference voltage 273 and generates an error voltage which it applies to a transconductance amplifier 274. The transconductance amplifier 274 converts the error voltage to a reset current which appears on its output lead 251 connected to the cores of the saturable inductors.

Claims: A power supply for providing first and second output voltages at first and second output terminals (112,113), respectively, including means (101,105) for generating bipolar pulse voltage outputs at first and second nodes (1,2), a magnetic amplifier (120,121,122; 125,126,127) for regulating the first and second output voltages, means (150) for deriving from the first and second output voltages a control signal for controlling the magnetic amplifier, the control signal heing representative of an average output voltage as compared to a reference voltage, and characterised in that the means for generating bipolar pulse voltage outputs includes an inverter (101) for inverting an input DC voltage, the magnetic amplifier includes a first saturable inductor core (120) having a first inductor winding (121) connecting the first node (1) to the first output terminal (112) and a second inductor winding (122) connecting the second node (2) to the second output terminal (113),and a second saturable inductor core (125) having a first inductor winding (126) connecting the second node (2) to the first output terminal (112) and a second inductor winding (127) connecting the first node (1) to the second output terminal (113), and the deriving means (150) is adapted to apply said control signal as a reset current to the first windings (121,126) of the first and second saturable cores to reset the first and second saturable cores (120,125). A power supply as claimed in claim 1 wherein the generating means includes a power transformer (105) having first and second secondary windings, the first and second nodes being at one end of the first and second secondary windings respectively, and there is provided first rectifying means (131,132) for coupling positive voltages from the first inductor windings of (121,126) the first and second saturable cores to the first output terminal (112), and second rectifying means (133,134) for coupling negative voltages from the second inductor windings of the first and second saturable cores to the second output terminal (113). A power supply as claimed in claim 1 or 2 including diode means (137,138) oriented to periodically enable the reset current to flow. A power supply as claimed in claim 1,2 or 3 including a filter inductor (140) having a first and a second winding (141,142) connected in series with the first and second output terminals respectively. A power supply as claimed in claim 1,2,3 or 4 wherein the deriving means includes a voltage divider connected to the first and second output terminals and having unequal first and second impedances (270,271) to generate a voltage representative of an average of the first and second output voltages.

Inventors: BUCK ROBERT J, WALK RALPH, ZAVERI PRADHUMAN S, BUCK, ROBERT J., WALK, RALPH, ZAVERI, PRADHUMAN S.
Applicants: AMERICAN TELEPHONE & TELEGRAPH, AMERICAN TELEPHONE AND TELEGRAPH COMPANY
Application year: 1989
Main classification: G05F1
IPC codes: H02M3, G05F1, H02M7