US2492812A - Electronic control system - Google Patents

Description

2 l 2 9 2 K A w O N F B 9 4 9 l 7 2 a D ELECTRONIC CONTROL SYSTEM s Shets-Sheet 1 Filed Aug. 21, 1948 mmxmim INVENTOR.

BY Edward F Nowa/r ELECTRONIC CONTROL SYSTEM Filed Aug. 21, 1948 I5 Sheets-Sheet 2 V/ ANODE VOLTA G5 4, T 1E: Z i

POINT HOLD OFF VOLTA GE PULSE F OM 735 V5 M we ANODE VOLTAGE E U CURRE/VT VG F/QES A 774/5 PO/NT 00A DPA TURE VOLTAGE V/ F/HES AT 774/5 POI/VT V/ ANO0 V LTAGE HOLD OFF VOLTAGE PUL 85 FROM T65 V6 ANODE VOLTAGE IN VEN TOR.

QUADRATURE VOLTAGE foward F Nowak ATTORNEY Dec. 27, 1949 E. F. NOWAK 2,492,812

ELECTRONIC CONTROL SYSTEM Filed Aug. 21, 1948 3 Sheets-Sheet 5 A CRITICAL (ER/D T1 I Q Th1; i

A MODE 1? A/VODE 1/04 TA GE (JR/D VOL TA CE W (HIT/CAL 09/0 VOLTAGE CR/D VOL TA G5 IN VEN TOR fem/0rd ff Nam/0k lTTOHNE Y Patented Dec. 27, 1949 ELECTRONIC CONTROL SYSTEM Edward F. Nowak, Hartford, Conn., assignor to Federal Electric Products Company, Newark,

N. J., a corporation Application August 21, 1948, Serial No. 45,537

14 Claims- (Cl. 318-317) The present invention relates to electronic control systems for motor or other loads operable by direct current obtained from an alternating current source.

One object of the invention is the provision of a system wherein the control circuits are isolated, electrically, from the power circuits.

Another object is the provision of a motor control system which provides an exceedingly quickacting control of the motor speed so as to maintain constant motor speed, comparable to constant speedeharacteristic of a synchronous motor, and to eliminate hunting.

A further object is to provide a control circuit for firing grid-controlled rectifiers by pulses from auxiliary rectifiers, the magnitude of the pulses being considerably greater than required, thereby permitting one design of control circuit to be used in control systems of a wide range of sizes or current ratings.

A further object is the provision of a failsafe electronic motor-control circuit, precluding increase in the speed of the motor in the event of defective control or control failure.

Another object is the provision of a control circuit wherein a glow-discharge tube is utilized for limiting the load current, whereby a sharp current-limiting action is obtained. Further, in connection with this object of the invention, the glow-discharge tube provides a visual indication of overloading.

At the present time existing control systems of the general type to which this invention relates are not entirely satisfactory because they have one or more of the following objections and disadvantages:

l. A control device, such as a saturable reactor is used and its inherent inductive lag causes the control to respond slowly. This is particularly objectionable under conditions of rapidly changing load.

2. The auxiliary control tubes are not isolated electrically from the power tubes. This usually results in poor auxiliary tube performance.

3. Failure of an auxiliary control tube causes an unsafe condition, i. e. a motor speed which may be many times higher than the desired preset speed.

4. If the main power tubes are of the mercury vapor type, changes in ambient temperature affeet their characteristics to the point where performance of the control is impaired.

The control system of the present invention overcomes these disadvantages of existing control systems. There is no saturable reactor to slow the response; instead the main power tubes are fired through pulse transformers by small inert gas thyratrons, which are in turn controlled, preferably by the quadrature method. In this way, the auxiliary control tubes are isolated electrically from the main power tubes, resulting in improved performance. The auxiliary control tubes are so arranged that a failure of any of them will not result in a condition that will increase the conductivity of the main power tubes, therefore the control will always fail safe. Since the small thyratrons which fire the main power tubes are of the inert gas type, they are not adversely affected by temperature changes. Since the main power tubes will always fire when the small thyratrons fire, the main power tubes can be of the mercury vapor type and the performance of the control will not be adversely affected by temperature changes. In addition, this control system provides other useful features including a novel current limiting circuit utilizing the breakdown of a glow discharge device. This provides a very sharp action, as well as providing a visual indication of the current limiting action, the advantages of which are obvious. The accomplishment of these results constitutes an object of the present invention.

The above and other objects, features and advantages of this invention, as well as objects ancillary thereto, will be fully understood from the following description considered in connection with the accompanying illustrative drawings:

In the accompanying drawings:

Fig. 1 is a circuit diagram of the presently preferred embodiment of the invention;

Figs. 2a, 2b, 2c and 2d are graphic illustrations of the concomitant discharge or firing of the control and power tubes;

Fig. 3 is a diagram illustrating the discharge or firing of certain of the tubes by the quadrature method;

Figs. 4 and 5 are graphic illustrations of the power-output action of the power tubes.

Power is supplied by the transformer secondary TISI to the motor armature MA through a full wave rectifier consisting of electric valves VI and V2, which are controlled grid rectifiers. Transformer secondary TZS! provides a hold-off voltage so that with no signals from transformer secondaries T33 and TtS, electric valves VI and V2 do not conduct for any portion of the cycle. A pulse from transformer secondary T3S will fire electric valve VI, and a pulse from transformer secondary T48 will fire electric valve V2. So by controlling the point in each cycle that the transformer pulses occur, the point in the cycle at which electric valves VI and V2 begin to conduct can be controlled, thereby controlling the armature voltage. Condensors CI and C2 are used to drain ofi any excess charge from the grids of electric valves VI and V2 to prevent mis-firing. Resistances RI and R2 are used to limit the grid current of electric valves VI and V2. Resistances R3 and R4 are used to load transformer secondaries TBS and T48 to prevent excessively high voltages. Pulses appear across transformer secondaries T38 and T48, of course, when their respective transformer primaries, TtP and T4? are energized. Transformer primaries T3P and T4P are energized by transformer secondary T3S4 through the auxiliary grid-controlled rectifier valves V3 and V9. These last mentioned valves are smaller than the power supply valves VI and V2.

Figs. 2a, 2b, 2c and 2d are graphic illustrations of this pulse firing, showing two sets of operating conditions for tubes V8 and VI respectively. Tubes V2 and V9 operate in the same manner on the other half cycle. The point in the cycle at which electric valves V8 and V9, and therefore electric valves VI and V2, are fired is determined by the grid control of electric valves V8 and V9, according to the quadrature method. The control is accomplished by applying to the grids a voltage of anode frequency but lagging the anode voltage by 90 electrical degrees. Under this condition, as shown in Fig. 3, the grid voltage will reach the critical value, that which starts tube conduction, when the anode voltage is ap proximately maximum and the tubes will conduct for approximately one-half of each positive half cycle of anode voltage indicated by the shaded area. A direct current voltage of variable magnitude and polarity is inserted in series with the quadrature voltages. By controlling the magnitude and polarity of this direct current voltage, it is possible to control the output of the thyratrons. This is illustrated in Figs. 4 and 5. If the direct current voltage is zero, the same condition exists as in Fig. 3 and the thyratrons conduct approximately one-half of each cycle. If the direct current voltage is made positive and of a magnitude equal to the peak value of the quadrature voltage the condition is as shown in Fig. 4 and the thyratrons conduct for the entire cycle. If the direct current voltage is made negative and of a magnitude equal to the peak value of the quadrature voltage, the condition is as shown in Fig. and the thyratrons do not conduct for any part of the cycle. Therefore, by varying this direct current voltage from the negative maximum to the positive maximum it is possible to control the thyratrons from full on to full oif.

Transformer secondary T283 provides the alternating current voltage which is shifted in phase by resistance R25 and condensor CIil. Resistances R23 and R24 form a divider network for this quadrature voltage. Resistances R26 and R21 are used to limit the grid current of electric valves VB and V9. Condensors CI! and CIZ are used to drain any excess charge from the grids of electric valves V8 and V9. The direct current voltage, variable in magnitude and polarity, which controls electric valves V8 and V9 by the quadrature method is obtained from the bridge consisting of electric valve V6 and resistances RI8, RI 9 and R20. Valve V6 is a vacuum triode. This bridge is supplied with a direct current voltage from a voltage doubler rectifier consisting of transformer secondary T2S2, resistance R22,

4 rectifiers DDRI, DDR2, resistance R2 I, condensors C8 and C9. The output voltage of this voltage doubler is stabilized by the voltage regulator tube V'I which is a glow-discharge tube. This stabilized voltage is also used as a reference voltage which is applied to potentiometer Rl5.

The magnitude and polarity of the output voltage of the bridge is controlled by the condition of conductivity of electric valve V6, which is in turn dependent upon the grid to cathode potential of said valve V6. Thus, a change in the grid to cathode potential of valve V6 changes the output voltage of the bridge, which changes the point in the cycle at which auxiliary valves V8 and V9 are fired and therefore changes the point in tne cycle at which power valves VI and V2 are fired. The entire system is so sensitive that a change of approximately 0.3 volt in the grid to potential of valve V6 will change electric valves VI and V2 from the condition of no conductivity to full conductivity.

The voltage components which make up the grid to cathode voltage of electric valve V6 are the voltage across resistance RE, which is proportional to the terminal voltage of the motor armature, the voltage across resistance RII, which opposes the voltage across resistance R6 and therefore compensates for the IR drop of the armature, and the voltage across resistance R54, which is proportional to the setting of resistance RI 5 which is the speed setting for armature control. Valve V5 is a vacuum triode and is normally at full and constant conductivity. The voltage difference between the voltage across resistance R5 and the voltage across resistance RI I is compared with the reference voltage across resistance RI4, and then electric valve V6 acts to operate the circuits described above to control the condition of conductivity of electric valves VI and V2 so as to keep the counter E. M. F. of the armature, and therefore its speed, assuming constant field excitation, at the desired value as set on resistance RI5,

The voltage across resistance RII, which is proportional to armature current, is obtained in the manner which will now .be described. Current transformer T5 has its split primaries TEPI and T5P2 in the anode leads of electric valves VI and V2 so that alternate half-cycles of current create an alternatin flux in its core. Although these primaries are shown in the anode leads, they will function equally as well in the cathode leads. This alternating flux produces an alternating current voltage in the transformer secondary T5S. The output of transformer secondary TES is rectified by a full wave rectifier V3. Resistance R8 is used to prevent excessively high voltages across transformer secondary T58. Resistances RH and RI2 form a simple divider network across the output of the rectifier so that the voltage across resistance RII is proportional to the output of the rectifier and therefore to the armature current.

Resistance RIO and electric valve V4 form the principal elements of the current limiting system. Electric valve V4 which is normally nonconducting is a glow-discharge device such as a neon lamp. The voltage applied to electric valve V4 is Varied by changing the setting of resistance R9. Electric valve V4 will break down at various values of armature current depending on the setting of resistance R9, which is the current-limit setting. When electric valve V4 breaks down, it provides a visual indication that the armature current has reached the pre-set limit.

In addition, it allows current to flow through resistance RIO which is in the grid-cathode path of both electric valves V5 and V6. This changes the conductivity of electric valve Vii directly, due to the appearance of a voltage across resistance RID, and indirectly by the change in conductivity of electric valve V5 which changes the volt-- age across resistance Rid which in turn changes the grid-cathode potential of electric valve V6. These effects acting together are sufficient to change the conductivity of electric valve V6, which in turn operates through previously described circuits to decrease the conductivity of electric valves VI and V2 and limit the armature current to substantially the preset value regardless of the degree of the over-load, includin a locked armature.

Condensor C3 is used to filter the voltage across resistance RH], and C4, C5 and C5 are by-pass condensors. C6 and Rid act to filter the alternating current component of the voltage across R6. RIB together with RI! act as current limiting resistances of the grid of V6.

The motor-field control will now be described:

Power is supplied by the transformer second-- ary TISZ to the motor field MF through a full wave rectifier, consisting of electric valves Vii and VIZ which are controlled grid rectifiers. The grids of electric valves Vii and V52 are controlled directly by the quadrature method without auxiliary gas tubes as in the armature control. This is quite acceptable here, because the motor is protected from loss of field by the field failure relay FFCR. It will be readily understood that a failure of an auxiliary tube which a will increase the field voltage to full value, will not result in an unsafe condition. Transformer secondary T256 provides the alternating current voltage which is shifted in phase by resistance R33 and condenser CH5, resistances R35 and R3? form a divider network for this quadrature voltage. Resistances R39 and E i-ii are used to limit the grid current of electric valves Vii and V12. The direct current voltage, variable in polarity and magnitude, which is used to control electric valves VII and V12 by the quadrature method is obtained from the bridge made up of resistances RSI, R32, R33 and electric valve V58, the latter being a vacuum triode. The voltage supply for this bridge is provided by the voltage doubler rectifier consisting of transformer secondary T2S5, resistance R29, rectifiers DDR3, DDR5, condensors CH3, CH5 and resistance R35).

Resistances R4! and RM form a simple divider network across the field so that the voltage across resistance RM is proportional to the field voltage of the motor. The grid to cathode voltage of electric valve Vlfl is made up of the voltage as set by resistance R35 (field voltage setting) and the voltage across resistance RM. Electric valve VIO compares these two voltages which are in opposition, and when the Voltage across resistance RM differs from that set by resistance R35, the conductivity of electric valve We is changed, which in turn changes the conductivity of electric valves VH and V12, to return the field voltage to its desired preset value.

The coil of the current sensitive relay FFCR is placed in series with the field MF and its contact interlocks the 3 wire magnetic control of the armature contactors, so that the armature can remain energized only when the field is energized. The contact of a time delay relay, TD, is also placed in series with the field so that neither the field nor the armature can be energized until the tube cathodes have been energized for a sufiicient time to reach the proper operating temperature. The magnetic control (three wire, reversing) and the dynamic braking which includes the resistance R5 and the relays CRF and CRR are conventional and therefore need not be described. OL designates the heater of the usual thermal overload relay the normally closed contacts of which are indicated at OLC.

The auxiliary relay CRA is arranged so that it is energized when either of the directional contactors are energized. One normally closed contact CRA! of CRA is used to short circuit parts of resistance R35 so that when CRA is deenergized., the field voltage is at full value, regardless of the setting of the field voltage control. This assures starting at full field. At starting when CRA is energized, this normally closed contact opens, but condenser 0E5 has assumed a charge which puts the field value at full until this charge is drained off by resistance R34. This results in full field starting with a gradual return to the preset value of field voltage. The other normally closed contact CRAZ of CRA short circuits resistance RI9 when CRA is deenergized. This means that VI and V2 are non-conducting and when the directional contactor and CRA are energized at starting this contact opens, and the voltage across resistance R19 increases gradually as condenser Cl discharges. This insures a smooth start without excessive armature current. An extra contact SBI of the stop button SB is inserted between resistance R20 and resistance R2 I.- When the stop button is depressed this opens causing the output of the bridge to be negative and thus causing VI and V2 to be non-conducting. This happens before relays CRF or CRR can operate, therefore relays CRR and CRF are not required to rupture the armature current.

Thus it is seen that the system hereinbefore described is well adapted to accomplish the several objects of the invention. It will be understood however that various changes may be made without departing from the underlying idea or principles of this invention within the scope of the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent, is:

1. In an electronic control system for a load operable by direct current, means including unidirectional electric valve means for supplying uni-directional current to said load from a source of alternating current, said valve means having control electrode-means therein for determining the instant of conduction thereof, uni-directional electric valve means the output circuit of which is operatively connected to said control electrodemeans of said first mentioned valve means for effecting the conduction of the latter, said second valve means having control electrode-means for determining the instant of conduction thereof, and means including phase-shifting means for energizing said last mentioned control electrodemeans in predetermined phase relation with the anode means of said second valve means.

2. In an electronic control system for a load operable by direct current, means including unidirectional electric valve means for supplying uni-directional current to said load from a source of alternating current, said valve means having control electrode-means therein for determining the instant of conduction thereof, uni-directional electric valve means the output circuit of which is connected to said control means of said first mentioned valve means, said second valve means having control electrode-means for determining the instant of conduction thereof, means for impressing on said last mentioned control means a composite voltage comprising voltage which is in quadrature phase relation with the anode means of said second valve means and a direct current voltage variable in polarity and amount in series with said quadrature voltage.

3. In an electronic control system for a load operable by direct current, means including unidirectional electric valve means for supplying unidirectional current to said load from a source of alternating current, said valve means having control electrode-means therein for determining the instant of conduction thereof, uni-directional electric valve means the output circuit of which is connected by transformer means to said control means of said first mentioned valve means, said second valve means having control electrodemeans for determining the instant of conduction thereof, means for impressing on said last mentioned control means a composite voltage comprising voltage which is in quadrature phase relation with the anode means of said second valve means and a direct current voltage variable in polarity and amount in series with said quadrature voltage.

4. In an electronic control system for a load operable by direct current, means including unidirectional electric valve means for supplying uni-directional current to said load from a source of alternating current, said valve means having control electrode-means therein for determining the instant of conduction thereof, uni-directional electric valve means the output circuit of which is connected to said control means of said first mentioned valve means, said second valve means having control electrode-means for determining the instant of conduction thereof, mean for impressing on said last mentioned control means a voltage which is in quadrature phase relation with the associated anode means, and means for supplying a direct current voltage variable in polarity and amount in series with said quadrature voltage, said last mentioned means comprising a bridge including uni-directional electrical valve means in one circuit thereof.

5. In an electronic control system for a load operable by direct current, means including unidirectional electric valve means for supplying unidirectional current to said load from a source of alternating current, said valve means having control electrode-means therein for determining the instant of conduction thereof, uni-directional electric valve means the output circuit of which is connected by transformer means to said control means of said first mentioned valve means, said second valve means having control electrodemeans for determining the instant of conduction thereof, means for impressing on said last mentioned control means a voltage which is in quadrature phase relation with the associated anode means, and means for supplying a direct current voltage variable in polarity and amount in series with said quadrature voltage, said last mentioned means comprising a bridge including uni-directional electrical valve means in one circuit thereof.

6. In an electronic control system for a load operable by direct current, means including unidirectional electrical valve means for supplying to said load direct current derived from an alternating current source, said valve means including control electrode-means operable to determine the instant of conduction of said valve means,

means for impressing on said control means an alternating current voltage which is out of phase in relation to the anode voltage of said valve means, and means for supplying in series with said voltage a direct current of variable amount and polarity, said last mentioned means comprising a bridge including uni-directional electrodecontrolled electrical valve means in one circuit thereof.

7. In an electronic control system for a load operable by direct current, means including unidirectional electric valve means for supplying unidirectional current to said load from a source of alternating current, said valve means having control electrode-means therein for determining the instant of conduction thereof, unidirectional electric valve means the output circuit of which is connected to said control means of said first mentioned valve means, said second valve means having control electrode-means for determining the instant of conduction thereof, means for impressing on said last mentioned control means a voltage which is in quadrature phase relation with the associated anode means, means for supplying a direct current voltage variable in polarity and amount in series with said quadrature voltage, and means including a glow discharge tube operable under the control of the current through said load and acting through said direct current voltage supply means and said second valve means to limit the current supplied to said load.

8. In an electronic control system for a load operable by direct current, means including unidirectional electric valve means for supplying unidirectional current to said load from a source of alternating current, said valve means having control electrode-means therein for determining the instant of conduction thereof, uni-directional electric valve means the output circuit of which is connected to said control means of said first mentioned valve means, said second valve means having control electrode-means for determining the instant of conduction thereof, means for impressing on said last mentioned control means a voltage which is in quadrature phase relation with the associated anode means, means for supplying a direct current voltage variable in polarity and amount in series with said quadrature voltage, said last mentioned means comprising a bridge including uni-directional electrical valve means in one circuit thereof, means for providing a reference voltage, means for providing a voltage proportional to the terminal voltage of said load, and means for providing a voltage opposite to said terminal voltage and proportional to the voltage drop across the load, the output of said valve of the bridge being controlled by the dinerence between said two last mentioned voltages and by said reference voltage.

9. In an electronic control system for a load operable by direct current, means including unidirectional electric valve means for supplying unidirectional current to said load from a source of alternating current, said Valve means having control electrode-means therein for determining the instant of conduction thereof, uni-directional electric valve means the output circuit of which is operatively connected to said control electrodemeans of said first mentioned valve means for effecting the conduction of the latter, said second valve means having control electrode-means for determining the instant of conduction thereof, and means including phase-shifting means for energizing said last mentioned control electrodemeans in predetermined phase relation with the anode means of said second valve means, said second valve means being of the inert gaseous type and said first mentioned valve means being of the mercury vapor type.

10. In an electronic control system for a load operable by direct current, means includin unidirectional electric valve means for supplying unidirectional current to said load from a source of alternating current, said valve means having control electrode-means therein for determining the instant of conduction thereof, uni-directional electric valve means the output circuit of which is operatively connected to said control electrodemeans of said first mentioned valve means for effooting the conduction of the latter, said second valve means having control electrode-means for determining the instant of conduction thereof, and means including phase-shifting means for energizing said last mentioned control electrodemeans in predetermined phase relation with the anode means of said second valve means, said second valve means having a smaller power output than said first valve means.

11. In an electronic control system for a load operable by direct current, means including unidirectional electric valve means for supplying unidirectional current to said load from a source of alternating current, said valve means having control electrode-means therein for determining the instant of conduction thereof, uni-directional electric valve means the output circuit of which is connected by transformer means to said control means of said first mentioned valve means, said second valve means having control electrodemeans for determining the instant of conduction thereof, means for impressing on said last mentioned control means a composite voltage comprising voltage which is in quadrature phase relation with the anode means of said second valve means and a direct current voltage variable in polarity and amount in series with said quadrature voltage, said second valve means being of the inert gaseous type and said first mentioned valve means being of the mercury vapor type.

12. In an electronic control system for a load operable by direct current, means including unidirectional electric valve means for supplyin unidirectional current to said load from a source of alternating current, said valve means having control electrode-means therein for determining the instant of conduction thereof, uni-directional electric valve means the output circuit of which is connected by transformer means to said con trol means of said first mentioned valve means, said second valve means having control electrodemeans for determining the instant of conduction thereof, means for impressing on said last mentioned control means a composite voltage comprising voltage which is in quadrature phase relation with the anode means of said second valve means and a direct current voltage variable in polarity and amount in series with said quadrature voltage, said second valve means having a smaller power output than said first valve means.

13. A control system, comprising a gaseous rectifier which is grid controlled by pulses from the secondary winding of a transformer, said control system comprising a source of alternating current and an auxiliary gaseous rectifier connested in series with the primary of said transformer, a source of alternating current phase shifted approximately behind the anode voltage of said auxiliary rectifier, a source of direct current voltage variable in magnitude and polarit superimposed on said phase shifted Voltage and said phase shifted voltage with the superposed direct current voltage connected between the grid and cathode of said auxiliary rectifier to convert a small change in direct current voltage to a change in phase of 0 to of the said pulses.

14. A control system for a direct current motor, controlled-grid rectifier means for supplying current for operating said motor from an alternating current source, auxiliary controlled-grid rectifier means operativel connected to said first rectifier means for supplying pulses to the latter for determining the instant of conduction of said first rectifier means, means for providing a reference voltage, means for providing a voltage proportional to the terminal voltage of said motor, means for providing a voltage opposed to said terminal voltage and proportional to the armature current of said motor, and means operatively connected to the grid-control means of said auxiliary rectifier means and operable in response to the difference between said reference voltage and the resultant of said last two mentioned voltages for determining the instant of conduction of said auxiliary rectifier means.

EDWARD F. NOWAK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,654,937 Knight Jan. 3, 1928 2,066,943 Philpott Jan. 5, 1937 2,249,840 Levy July 22, 1941 2,312,117 Moyer eta-1 Feb. 23, 1943

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