GB1602958A - Electric vehicle traction motor control - Google Patents

Description

(54) ELECTRIC VEHICLE TRACTION MOTOR CONTROL (71) We, LUCAS INDUSTRIES LIMITED, a British Company of Great King Street, Birmingham, Bl9 2XF, England; do hereby declare the invention for which we pray that a Patent may be granted to us and the method by which it is to be performed to be described in the following statement:- This invention relates to an electric vehicle motor control of the general kind in which motor current is controlled by periodically making and breaking a main current path to the motor when the motor current falls below a lower limit and rises about an upper limit respectively, the limits being variable under the control of the vehicle driver.

In one known arrangement the main current path is constituted by a first thyristor connected in series with the motor between a pair of supply rails. To turn off the main thyristor it is required to divert all the motor current through a communicating path which consists of a second thyristor, tlrst inductor and a capacitor in series with a second inductor across the capacitor and is arranged when fired to reverse the voltage across the capacitor.

An electric vehicle traction motor control circuit in accordance with the invention comprises a main thyristor in series with the motor armature between a pair of supply rails, a second thyristor arranged on firing to divert current from the main thyristor into a commutating capacitor, a third thyristor connected in series with an inductor across the commutating capacitor and arranged on firing to reverse the voltage on the commutating capacitor, driver operable control means for determining upper and lower motor current limits, first firing control means for firing the main thyristor when the actual armature current is less than said lower limit, second firing control means for firing the second thyristor when the actual armature current exceeds the upper limit and third firing control means sensitive to the cessation of flow of current into the commutating capacitor and firing the third thyristor when such current flow ceases.

An example of the invention is shown in the accompanying drawings in which: Figure 1 is a circuit diagram of a thyristor chopper and motor circuit; Figure 2 is a circuit diagram of a commutating capacitor voltage sensing circuit; Figure 3 is a circuit diagram of a current comparator circuit and the firing circuit for one of the thyristor of the chopper circuit of Figure 1; Figures 4 and 5 are circuit diagrams of firing circuits for the two other thyristors of Figure 1 respectively; and Figures 6 and 7 are circuit diagrams of other logic circuit elements included in the control circuit.

Referring firstly to Figure 1 the motor in this case has an armature winding 10 and a field winding 11. A contact F connects one side of the armature winding 10 to a positive supply rail 12 (at about 200 V relative to a rail 13) and a contact R connects the other side of the armature 10 to the rail 12. The two sides of the armature 10 are also connected to two fixed contacts of a change-over switch F/RB, the common contact of which is connected via an inductor 14 the field winding 11, a main thyristor SCR1 and a main fuse 15 in series to the rail 13.Four diodes D1 to D4 connect the two sides of the armature 10 to the rails 12, 13, with the diode Dl having its anode connected to the same side of the armature as the contact F and its cathode connected to the rail 12, the diode D2 having its cathode connected to the anode of the diode Dl and its anode connected to the rail 13, the diode DA having its anode connected to the other side of the armature 10 and its cathode connected to the rail 12 and the diode D4 having its cathode connected to the anode of the diode D3 and its anode connected by a brake current fuse 16 to the rail 13. A further diode D5 has its anode connected to the anode of the thyristor SCRI and its cathode connected to the rail 12.A sixth diode D6 has its cathode connected to the common contact of the switch F/RB and its anode connected to the rail 13.

For commutating the current through the thyristor SCRI there is a second thyristor SCR2 connected in series with a saturable core inductor 17, a fuse 18 and a commutating capacitor 19 between the anode of the thyristor SCRI and the rail 13.

A third thyristor SCR3 is connected in series with an inductor 20 across the canacitor 19.

For normal forward motoring the contact F is closed and the switch F/RB is closed to the right by contactors driven by circuits which do not form part of the present invention and an understanding of which is not necessary for an understanding of the present invention. When the main thyristor is conductive current flows through contact F, "forwardly" through the armature through the switch F/RB, the inductor 14, the field winding 11, the thyristor SCRI and the main fuse 15. When the thyristor SCR2 is fired (assuming that there is a negative voltage on the "upper" plate of the capacitor 19 at this stage), the current referred to is diverted from the main thyristor SCR1 into the capacitor 19 via the inductor 17. This causes the thyristor SCR1 to turn off.The diverted current causes the capacitor 19 to charge up until the voltage on the upper plate of the capacitor 19 is the same as that at the anode of the thyristor SCRI. At this stage the inductor 17 continues to cause current to flow into the capacitor 19 and the inductor 14 acts to maintain current in the armature and field windings via the "freewheel" diode D,.

Inductor 17 and capacitor 19 acts as a resonant circuit but when the voltage on capacitor 19 reaches its peak, (i.e. when the current in the inductor 17 falls to zero) the thyristor SCR2 turns off and the charge is then held on the capacitor 19. The armature and field winding current decays away.

Firing of the thyristor SCR3 causes the inductor 20 to be connected across the charged capacitor 19. The capacitor 19 thus dischargees into the inductor 20, current continuing to flow until a peak negative voltage is attained, which peak is held until the next commutation is required.

For reverse running contact F is opened, contact R is closed and switch F/RB is closed to the left. For regenerative braking when the motor is running forwardly both contacts F and R are opened and switch F/kB is closed to the left. Current induced in the armature, then flows through the switch F/RB, the inductor 14, the field winding 11, the thyristor SCRI, the fuses 15 and 16 and the diode D4.

Figure 1 also shows an armature current sensing arrangement comprising a ferromagnetic loop 21 surrounding one of the conductors leading to the armature winding 10, a Hall effect device 22 in a gap in this loop and a differential amplifier A1 with its inputs connected by resistor Rl and R2 to the terminals of the device 22. A feedback resistor R3 connects the inverting input terminal of the amplifier A1 to its output terminal and a bias resistor R4 connects the non-inverting terminal to earth. A resistor and thermistor network 23 is provided at the output of the amplifier A1 to provide temperature compensation.

A circuit is also provided to detect the instant at which the voltage on the inductor 17 reverses and the diode D5 starts to conduct during commutation. In the example shown this circuit includes a diode D7, a resistor R5 and the light emitting diode of an opto-coupler O connected in series across the inductor 17. The transistor of the opto-coupler is included in a "ready" circuit (not shown in detail) which produces an output pulse at a terminal 24 for as long as there is a reversed voltage on the inductor 17. The "ready" pulse may alternatively be generated by means of a current detector on the conductor associated with the freewheel diode D5. Such detector may be a current transformer or another Hall effect type detector, the latter being preferred.

Turning now to Figure 2 there is shown a circuit which is used to monitor the voltage on the capacitor 19 after firing of the thyristor SCR3. This circuit includes a pnp transistor Ql which has its collector connected to the rail 13 and its base connected by a high ohmic value resistor R, to the capacitor 19. The emitter of the transistor Ql, is connected via a current limiting resistor R6 and the light emitting diode of an optocoupler 2 to a rail 25.A resistor R, is connected between the base of the transistor Ql and the rail 25 and a diode D8 has its cathode connected to the rail 25 and its anode connected to the base of transistor Ql to provide protection of the transistor Ql in the period whilst the capacitor voltage is positive following commutation. The rail 25 has a zener diode regulated supply from the rail 12. To this end a resistor R9 connects the rail 12 to the rail 25 and a zener diode ZDI has its cathode connected to the rail 25 and its anode connected to the rail 13, a smoothing capacitor Cl being connected across the zener diode ZDI.

The phototransistor of the opto-coupler O2 has its collector connected to a +15V supply rail 26 associated with a ground rail 27 and a -15V supply rail 28 ofappwer supply which is isolated from the main traction power supply rails 12, 13. The emitter of this phototransistor is connected by a resistor Rlo to the rail 27 and a resistor Rl, connects its base to its emitter. The phototransistor of another opto-coupler O3 is likewise connected with resistors Rl2 and R,3. The emitters of these two transistors are also connected by resistors R,4 and R,5 respectively to the inverting and noninverting input terminals of an operational amplifier A,.A resistor R,6 connects the non-inverting input terminal of the amplifier A, to the rail 27 and the output terminal of the amplifier A, is connected to the cathode of a diode D9 with its anode connected to the base of an pnp transistor Q2 with a potentiometer Rl7 connecting the emitter of the transistor Q2 to the rail 27.

The collector of the transistor Q2 is connected via light emitting diode of the opto-coupler O3 to the rail 28. A resistor Rl8 connects the base of the transistor Q2 to the rail 27. The emitter of the transistor Q2 is connected by a resistor R19 and a capacitor C2 in parallel to the inverting input terminal of the amplifier Al.

The circuit described provides a voltage across the potentiometer Rl7 which is substantially linearly related to the voltage across the capacitor 19 (except when this latter voltage is positive following commutation). The use of the opto-isolator O3 in the feedback loop of the amplifier A provides compensation for the non-linearity and variations of gain with temperature of the opto-isolator 02, assuming the two optoisolators O2 and O3 to be reasonably matched.

The slider of the potentiometer Rí7 is connected both to a sample and hold circuit based on operational amplifiers A and A3 and to a threshold voltage detector based on an operational amplifier A4. The sample and hold circuit includes an n-channel field effect transistor Q3 with its drain connected to the output terminal of the amplifier A2 and its source connected to one side of a capacitor C3 which has its other side connected to the rail 27. The inverting input terminal of the amplifier A2 is connected by a resistor Rl9 to the slider of the potentiometer Rl7 and its non-inverting input terminal is connected by a resistor R, to the rail 27 and by a resistor R21 to the rail 28.A feedback resistor R22 connects the output terminal of the amplifier A2 to the inverting input terminal thereof so that the amplifier A2 acts as a linear inverting amplifier.

A bias resistor R23 connects the output terminal of the amplifier A2 to the gate of the field effect transistor Q3 which is also connected to the anode of a diode D1n. The cathode of the diode D1 is connected by.

resistor Ru to the collector of an npn transistor Q4 which has its emitter connected to the rail 28 and its collector connected by a resistor R, to the rail 26.

The base of the transistor Q4 is connected to the common point of two resistors R,, RD in series between the collector of a pnp transistor Q3 and the rail 28. The emitter of the transistor Q5 is connected to the rail 26 and it is biased off by a resistor R28 connected between the rail 26 and the base of the transistor Q5 which is also connected by a resistor R29 to a terminal 29 (see Figure 7).

Whilst the terminal 29 is at a voltage close to that on the rail 26, the transistors Q4 and Q5 are off and the field effect transistor Q3 is non-conductive. When the voltage on the terminal 29 falls as will be explained hereinafter, the transistor Q4 and Q5 turn on and the field effect transistor Q3 assumes a low resistance state, allowing the capacitor C3 to charge or discharge rapidly to the voltage then existing at the output termimal of the amplifier A2.

The amplifier A3 is connected as a voltage follower to provide a very high input impedance so as not to discharge the capacitor C3. A resistor R, connects the capacitor C3 to the non-inverting input terminal of the amplifier A3, a resistor R31 connecting the output terminal of the amplifier A3 to its inverting input terminal.

The output terminal of the amplifier A3 is also connected to the cathode of a diode Dull, of which is connected by a normally closed relay contact to a terminal 30 (Figure 3).

The amplifier A4 is connected as a comparator with hysteresis. Its inverting input terminal is connected by a resistor R32 to the slider of the potentiometer R,7, and its non-inverting input terminal is connected to the common point of a pair of resistors R33, R34 in series between the rails 27, 28 and also, by a resistor R35, to its output terminal which is connected to a terminal 31.

Turning now to Figure 3, there is shown schematically the arrangement in which the signals from the current transducer circuit of Figure 1 and the capacitor voltage circuit of Figure 2 are used. The current signal is applied via a resistor R41 to the inverting input terminal of an operational amplifier A5 connected as a comparator with hysteresis. The required hysteresis is obtained by means of resistors R42, R43 connected in series between the output terminal of the amplifier A5 and the rail 27 with their common point connected to the non-inverting input terminal of the amplifier A5. The inverting input terminal of the amplifier A3 is connected by a resistor R, to a motor current demand signal generating circuit 32, of which the output stage is shown.It receives input signals from a speed transducer circuit 33 and from accelerator and brake pedal operated potentiometers 34 and 35 and produces a d.c. output signal representative of the desired average motor current varying in accordance with a complex function of speed and pedal depression. Details of a similar circuit arrangement may be found in prior U.K. Patent Serial No. 1545202, 8364/75.

The output stage is constituted by an operational amplifier Aloo which operates either in inverting or non-inverting mode according to whether a transistor Q100 is on or not. The inverting input terminal of the amplifier Aioo is connected by a resistor R150 to a point in the circuit 32 and two resistors Rl5l, Rl52 of the same value connect the same point to the non-inverting input terminal. A resistor Rl53 combined with a capacitor Cl00 in series connect the output terminal of the amplifier Aloo to the earth rail 27.A resistor Rl54 connects the junction of the resistor Rl53 with the capacitor Cl00 to the anode of a diode Dloo, the cathode of which is connected to the base of a transistor Q101 connected as an emitter follower. Two resistors Rl55, R56 in series connect the emitter of the transistor Q101 to the rail 27 with the junction of these resistors connected to the inverting input terminal of the amplifier Aloo by a feedback resistor Rl57. The emitter of the transistor Qlol is connected by the resistor R, to the inverting input terminal of the amplifier A5.

The terminal 30 is connected to the base of the emitter follower transistor Qlol If the output of the amplifier A5 is high the voltage at its non-inverting input terminal is at a fixed positive level which must be exceeded by the voltage at its inverting input terminal before the amplifier output can go negative.

Similarly when the output of the amplifier A5 is low, there is a fixed negative voltage applied to the non-inverting input terminal of the amplifier A5. The signals applied via resistors R41 and R, are of opposite polarity and these resistors may be regarded as forming a potential divider so that for a given demand signal the output of the amplifier A5 will go low when an upper current limit is exceeded and will go high when the motor current is less than a low current limit, both limits being variable by the driver using the pedals 34, 35.

The effect of the capacitor voltage signal applied via terminal 30 is to decrease the level to which the current demand signal may rise if capacitor voltage is too low.

The output terminal of the amplifier A5 is connected by a diode D12 and a resistive potential divider R46, R47 to the base of an npn transistor Q6 with its emitter grounded to the rail 27 and its collector connected by a resistor R48 to the rail 26. The collector of the transistor Q6 is connected to a terminal 36 (Figure 4) and also to the cathode of a diode D13 with its anode connected by a resistor R49 to the rail 26. A diode D14 connects the anode of the diode D13 to a terminal 39 (Figure 7). A zener diode ZD2 has its cathode connected to the anode of the diodes D13 and D,4 and its anode connected by a resistor R, to the rail 27.

The resistor R49 and the zener diode ZD2 are chosen so that the zener diode ZD2 does not conduct if either of the diodes D,3, D14 is conducted, i.e. if the transistor Q6 is on or the terminal 39 voltage is low.

An npn transistor Q7 has its emitter connected to the rail 27 and its base connected to the anode of the zener diode ZD2, its collector being connected by a resistor R51 to the rail 26. The transistor Q7 turns on whenever the zener diode ZD2 is conducting.

The emitter of the transistor Q7 is connected by a resistive potential divider R52, R53 to the base of an npn transistor Q8 which controls an oscillator based on a unijunction transistor Q9 and a capacitor C4.

The secondary base of the unijunction transistor Q9 is connected by two resistors R54, R55 in series to the rail 27 and its primary base is connected by a resistor R56 to the rail 26. There are two separate charging paths for the capacitor C4 which determine the frequency of the oscillator.

One such path is constituted by a resistor R57 connected in series with the capacitor C4 between the rails 26, 27. The other path is constituted by a resistor R58, a diode Dl5, a diode D16 and a resistor R59 in series across the resistor R57, the total resistance of the resistors R58 R59 being significantly less than the resistance of the resistor R57. A diode D17 is connected across the series combination of the resistor R59 and the diode Dl6, with its polarity reversed relative to that of the diode Dl6. The anode of the diode D16 and the cathode of the diode D17 are connected to the collector of the transistor Q8. The andde of the diode D15 is connected to the anode of a thyristor SCR4 which has its cathode connected to the rail 27.

When the transistor Qs is conducting, the oscillator does not operate since the capacitor C4 is held discharged. When the transistor Q8 is turned off, i.e. when the transistor Q7 turns on, the oscillator starts to run at a relatively high frequency until the thyristor SCR4 is fired as will be explained hereinafter. Thereafter, for as long as the transistor Q8 is off, the oscillator will operate at a low frequency determined by the resistor R57.

The common point of the resistors R54, R55 is connected to the base of a transistor Qlo which has its emitter connected to the rail 27 and its collector connected by a resistor R, to the rail 26.

The collector of the transistor Q10 is connected to the TRIGGER terminal of an integrated circuit timer Tri (shown as one half of a dual timer circuit type NE556 manufactured by signetics). The Discharge and Threshold terminals of this timer circuit are connected to the junction of a resistor R6, and a capacitor C5 in series between the rails 26 and 27. The Control Voltage terminal of the circuit is connected to the rail 27 by a capacitor C6 and the RESET terminal is connected to the collector of an npn transistor Q" which has its emitter connected to the rail 27 and .4s collector connected by a resistor R62 to the rail 26.

The base of the transistor Q" is connected by a resistor R63 to the rail 27 and by a resistor RM to the cathode of a diode D,g having its anode connected to the collector of the transistor Q7. The base of the transistor Q11 is also connected by a resistor R, to the cathode of a diode D,, the anode of which is connected to a terminal 40.

The OUTPUT terminal of the timer circuit T1 is connected to a terminal 41 and thence to the gate of the main thyristor SCR1. This OUTPUT terminal is also connected by a normally closed override contact 42 and a resistor R, to gate of the thyristor SCR4, this gate being also connected by a resistor RR to the rail 27.

Assuming the voltage at terminal 40 is low and that at terminal 89 is high turning off of the transistor Q6 by a negative transition in the output of the current comparator operational amplifier A5 causes transistor Q7 to turn on which in turn causes the oscillator to commence oscillating at relatively high frequency, and, because, in these circumstances, the transistor Q11 is turned off, the timer T1 will be triggered the resistors R58 and R59 and the capacitor CA fixing the delay before such triggering at approximately 70,aS. The timer OUTPUT terminal now goes high for 20,us, set by the resistor R61 and the capacitor C5.This output pulse fires the thyristors SCR1 and SCR4, the latter interrupting the previous charging path for the capacitor C4. The resistor R57 and the capacitor C4 set the repetition frequency of the oscillator at approximately 200 Hz so that additional firing pulses are produced by the timer T1 at this frequency, in case the current level in the thyristor SCRI is insufficient for it to hold the thyristor SCRI conductive.When the output of the current comparator operational amplifier A5 goes high (indicating that the actual current has reached the upper limit), transistor Q6 turns on, turning off transistor Q7 which turns on transistors Q8 and Q". Transistor Q" holds the RESET terminal of the timer T, low so that it cannot be triggered and transistor Q1 maintains the capacitor C4 discharged so that the oscillator ceases to run.

The terminals 36, 39 and 40 provide input signals to the circuit of Figure 4 which controls firing of the thyristor SCR2. A resistor R70 connects the terminal 36 too the anode of a zener diode ZD3, the cathode of which is connected by a resistor R71 to the rails 26 so that the zener diode ZD3 only conducts when the transistor Q6 of Figure 3 is on (i.e. when the current comparator operation amplifier A5 output is high). The cathode of the zener diode ZD3 is connected to the base of a pnp transistor Ql2, the emitter of which is connected to the rail 26 and the collector of which is connected to the rail 27 by a resistor R72.

The collector of the transistor Q1, is connected by a resistor R73 and a capacitor C in series to the base of a npn transistor Q,3 -which has its emitter connectëd to the rail 27 and its collector connected by a resistor R74 to the rail 26. The base of the transistor Q,3 is connected to the cathode of a protective diode D, which has its anode grounded to rail 27 and is also connected by a resitor R,5 to the rail 27 to bias the transistor Q,3 off.

It will be appreciated that when the transistor Q,2 turns on the transistor Q,3 will be turned on for as long as its takes the capacitor to charge up (the time constant R,3 C6 being approximately lows).

The collector of the transistor Q,2 is also connected by a resistor R,6 and a diode D, in series to one side of a capacitor C7, the other side of which is connected to the rail 27. Said one side of said capacitor C7 is connected to the emitter of a unijunction transistor Q,4, which has its secondary base connected by a resistor R77 to the rail 27 and its primary base connected to the rail 26 by a resistor R78. The secondary base of the unijunction transistor Q,4 is also connected by a resistor R79 and a diode D, in series to the base of the transistor Q,3.

The resistor R,6, capacitor C, and unijunction transistor Ql4 form an oscillator, operating under the control of the transistor Ql2 at a frequency of about 3KHz. This oscillator is arranged to be inhibited by an npn transistor Ql5 with its collector emitter connected across the capacitor C, and biased off by a resistor RN connected between its base and the rail 27.The base of the transistor Qls is also connected to the cathode of a thyristor SCR5 the anode of which is connected by a resistor R61 to the collector of the transistor Ql2. The base of the transistor Ql5 is further connected to the collector of an npn transistor Qi6 having its emitter connected to the rail 27 and its base connected by a resistor R, to the rail 27. A diode D24 has its cathode connected to the base of the transistor Ql6 and its anode connected by a resistor R83 to the terminal 40.A diode D, connects the anode of the diode D, to the terminal 39 so that the transistor Q,6 can only turn on when the signals at both terminals 39 and 40 are high.

The thyristor SCR5 has its gate connected by a resistor R", a diode D26 and a normal closed override contact 43 to the OUTPUT terminal to another integrated circuit timer T2 (constituted by the other half of the NE556 circuit of time T,). The INPUT terminal of the timer T2 is connected to the emitter of the transistor Q,3 and its Control Voltage terminal is connected by a capacitor Ca to the rail 27.

The Threshold and Discharge terminals of the timer T2 are both connected by a resistor R15 to the rail 26 and by a capacitor C9 to the rail 27, the resistor R, and the capacitor C9 setting the on-time of the monostable multivibrator constituted by the timer T2 and its associated components at about 20us. The OUTPUT terminal of the timer T2 Is also connected to the gate of the second thyristor SCR2 (Figure 1) and to a terminal 44.

The RESET terminal of the timer T2 is connected by a resistor RS6 to the rail 26 and by the collector-emitter path of an npn transistor Q7 to the rail 27. The base of the transistor Q,7 is connected by a resistor R" to the rail 27 and by a resistor Rg, to the anode of a zener diode ZD4 having its cathode connected to the cathode of three diodes D26, D27, and D28 respectively. The anodes of the diodes D, D27, D= and D, are connected to three terminals 45, 46 and 47 see Figure 5 respectively, so that a high voltage signal at any of these terminals will turn on the transistor Qx7 and reset the timer T2.A capacitor C,0 is connected between the cathode of the zener diode ZD4 and the rail 27.

Provided that the signal voltages at the terminals 45, 46 and 47 are all low when the transistor Q,2 is turned on by output of the current comparator operational amplifier A5 going high, the timer T2 will be triggered immediately and the oscillator around the unijunction transistor Ql4 starts to run providing further triggering pulses to the timer T2. The first output pulse from the timer T2 turns on the thyristor SCR5 which, unless the transistor Q,6 is on, turns on the transistor Ql5 on, thereby holding the capacitor C7 discharged and stopping the oscillator from running.

A normally open contact 48 connects the terminal 36 via a resistor R, and a diode D to the emitter of the unijunction transistor Qu. so that when the contact 48 is closed (when a "creep" condition has been selected) the oscillator runs at a significantly lower frequency of say 400Hz when the output of the current comparator operational amplifier A5 is high. In this condition the transistor Ql2 is off so that -firing of the thyristor SCR5 does not provide current to turn on the transistor Ql5 and stop the oscillator.

Turning now to Figure 5 the OUTPUT terminal of the timer T2 (Figure 4) is connected via the terminal 44 through two resistors Rgo, Rgl in series to the rail 27. The common point of these resistors is connected-to the base of an npn transistor Q,,, the emitter of which is grounded to the rail 27. The collector of the transistor Qis is connected by a resistor R92 to the rail 26 and is also connected to the Trigger terminal of another timer integrated circuit T3 which is connected as a monostable multivibrator with a pulse duration of about 2.5 mS.The Threshold and Discharge terminals of the timer T3 are connected to the rail 27 by a capacitor C11 and to the rail 26 by a resistor R93 and variable resistor R, in series. A capacitor C12 connects the Control Voltage terminal of the timer T3 to the rail 26 and the Reset terminal is connected to a terminal Rl. The Output terminal is connected to a terminal 49 (Figures 6 and 7).

The output terminal of the timer T3 is also connected via a capacitor C13 to one end of a resistor R95 the other end of which is connected to the rail 26. A diode D, has its cathode connected to the rail 26 and its anode connected to the junction between the capacitor C13 and the resistor R95 so that a negative going pulse is produced at this junction when the timer T3 resets.This junction is also connected to the Trigger terminal of another timer T4, again connected as a monostable multivibrator with a pulse duration of about 20us. The Threshold and Discharge terminals of the timer T4 are connected to the rail 26 by a resistor Rg6 and to the rail 27 by a capacitor Cl4. A capacitor C15 connects the Control Voltage terminal of the timer T4 to the rail 27 and its Reset terminal is connected to a terminal R2. The output terminal of the timer T4 is connected via the terminal 45 to the gate of the thyristor SCR3 and also to the reset circuit of the timer T2 (Figure 4).

The Output terminal of the timer T4 is also connected by two resistors Rugs, R, in series to the rail 27, the junction of these resistors being connected to the base of an npn transistor Ql9 which has its emitter connected to the rail 27.The collector of the transistor Ql9 is connected by a load resistor R100 to the rail 26 and is also connected to the Trigger terminal of yet another timer T5 connected as a mono stable multivibrator with a pulse duration of 300,us. The Threshold and Discharge terminals of the timer T5 are connected to the rail 27 by a capacitor C16 and to the rail 26 by a resistor R101 and a variable resistor Rl02 in series. The Control Voltage terminal of the timer T5 is connected by a capacitor C17 to the rail 27 and its Reset terminal is connected directly to the rail 26.

A capacitor C18 connects the Output terminal of the timer T5, which terminal is also connected to the terminal 46, to the Trigger terminal of a further timer circuit T6 connected as a monostable multivibrator with a pulse length of 100,us. The Threshold and Discharge terminals of the timer T6 are connected to the rail 27 by a capacitor C19 and to the rail 26 by a resistor Rl03. The Control Voltage terminal of the timer T6 is connected by a capacitor C to the rail 26 and its Reset terminal is connected directly to the rail 26.The Trigger terminal is connected by a resistor R1M and a diode D, to the rail 26 so as to convert the trailing edge of the output pulse of the timer T5 into a negative-going triggering inpulse for the timer T6. The output terminal of the timer T is connected to the terminal 47.

Turning now to Figure 6, there is shown a simple circuit which converts the low signal which exists at terminal 31 when the capacitor 19 voltage is too low into a high level signal for use in the circuits of Figure 3 and 4. This circuit includes a resistor R110 connecting the anode of a diode D31 to the rail 26. The terminal 31 is connected to the anode of this diode by a normally closed contact which is energised if it is required to override the low control signal. The cathode of the diode D31 is connected by a resistor R,ll to the base of an npn transistor QN which base is also connected by a resistor Rill2 to the rail 27. The transistor Q20 has its emitter connected to the rail 27 and its collector connected to the terminal 40 and by a resistor Rill3 to the rail 26.

The R2 reset signal for resetting the timer T4 is generated by inverting a demand cutoff signal generated under certain circumstances during change overs between forward and reverse motoring and braking.

This particular feature is not essential to the present invention and the derivation of the demand cutoff signal will not be described herein. The demand cutoff terminal 50 is connected by a resistor Rill4 to the base of an npn transistor Q21 which has its emitter connected to the rail 27. A resistor Rll5 connects the base of the transistor Q21 to the rail 27 and a resistor Rill6 connects the collector of the transistor Q21 to the rail 26, which collector is also connected to the terminal R2 and to the cathode of a diode D32. The anode of the diode is connected by a capacitor C21 to the rail 26 and also to the anodes of two diodes D33, D34 and a zener diode ZD5.The cathode of the diode D3J is connected to terminal 49 and that of the zener diode ZD5 is connected by two resistors R"7 and R118 in series to the rail 26. The junction of this resistor is connected to the base of a pnp transistor Q22 with its emitter connected to the rail 26 and its collector connected by a resistor Rill9 to the rail. The cathode of the diode D34 is connected to the collector of an npn transistor Q23 with its emitter grounded to rail 27 and its collector connected by a resistor Rl20 to the rail 26.The base of the transistor Q23 is connected by a resistor R121 to the rail 27 and also to the anode of a zener diode ZD6 the cathode of which is connected to the terminal 24 and, by a resistor R,22 to the rail 26. This transistor Q22 can be turned on by a positive going signal at the terminal 24 or at the terminal 50 or a negative going signal at the terminal 49.

The collector of the transistor Q22 is connected to the Trigger terminal of another timer circuit T7 connected as a monostable multivibrator with a pulse duration of 104us. The Threshold and Discharge terminals of the timer T7 are connected by a capacitor C22 to the rail 27 and by a resistor Rl23 to the rail 26. The Control Voltage terminal is connected by a capacitor C23 to the rail 27 and the Reset terminal is connected directly to the rail 26.

The output terminal of the timer T7 is coupled by a capacitor C, to the Trigger terminal of another timer T8. This Trigger terminal is connected to the rail 26 by a resistor Rl24 and a diode D35 in parallel so that the timer T9 is triggered by the falling edge of the output pulse of the timer T7. The timer T9 is connected as a monostable multivibrator with a pulse duration of 50 s. Its Threshold and Discharge terminals are connected to the rail 27 by a capacitor C, and to the rail 26 by a resistor Rl25. The Control Voltage terminal of the timer T8 is connected to the rail 27 by a capacitor C26.The Reset terminal of the timer T8 is connected to the collector of an npn transistor Q24 which has its emitter grounded to rail 27 and its collector connected to the rail 26 by a resistor Rl26.

The base of the transistor Q24 is connected to the collector of an npn transistor Q25, the emitter of which is connected to the rail 27 and the collector of which is connected by a resistor Rl2, to the rail 26. The base of the transistor Q25 is connected to the junction of two resistors Rl28 Rl29 connected in series between the Output terminal of the timer T9 and the rail 27 and also connected by a resistor Rl30 to the cathode of a diode D36 with its anode connected to the collector of the transistor Q23.

The Output terminal of the timer T8 is also connected by two resistors R,3, and R,32 in series to the rail 27, with the junction of these resistors connected to the base of an npn transistor Q26. The emitter of the transistor Q26 is connected to the rail 27 and its collector is connected via a normally closed override contact 51 to the R, terminal and also by a resistor Rl33, to the rail 26.

The timer T7 is triggered when the transistor Q22 turns off either as a result of the signal at terminal 49 going high (caused by triggering of timer T3) or as a result of the signal at terminal 24 going low. At the end of the output pulse from the timer T7, the timer T, is triggered, provided the signal at terminal 24 remains low. Once triggered the timer T, is not reset if the signal at terminal 24 goes high.

Turning finally to Figure 7, two simple logic circuits are shown. Firstly there is an npn transistor Q27 controlling the signal at the terminal 29 in accordance with the signals at the terminal 46 and 49. The emitter of the transistor Q2, is connected to the rail 27 and its base is connected to the same rail by a resistor R. This base is also connected to the anode of a zener diode ZD7, the cathode of which is connected by a resistor Rl3* to the cathodes of two diodes D37 and D38, which have their anodes connected to the terminals 46 and 49 respectively. A capacitor C2, is connected between the cathodes of these diodes and the rail 27.The collector of the transistor Q2, is connected to the terminal 29 and by a resistor R,3, to the rail 26. It will be appreciated that the signal at the terminal 29 goes high to cause the field effect transistor Q3 (Figure 2) to become conductive, only when the signals at terminals 46 and 49 are both low.

The remainder of Figure 7 controls the signal at terminal 37 in accordance with the signals at terminals 46, 47 and 49. An npn transistor Q2a has its emitter connected to the rail 27 and its base connected to the same rail by a resistor R,. This base is also connected to the anode of a zener diode ZD8, the cathode of which is connected by a resistor Rl4, to the cathodes of three diodes D39, D, and D41 with their anodes connected to the terminals 46, 47 and 49 respectively. A capacitor C, is connected between the cathodes of these diodes and the rail 27. The collector of the transistor Q2, is connected to the terminal 37 and also, by a resistor Rl42 to the rail 26.

In normal running the sequence of operations is as follows:- The thyristor SCRI is fired when the output of the current comparator operational amplifier A5 goes low provided that the signal at terminal 39 is high (i.e.

There are currently no pulses being produced by timers T3, T5 and T6) and the signal at terminal 40 is low (i.e. there is an adequate charge for commutation on the capacitor 19).

When the output of the amplifier A5 goes high the timer T1 is held reset (it will not still be producing its output pulse) via transistor Q11 turning on when transistor Q6 turns on.

Also, transistor Ql2 turns on, causing transistor Ql3 to turn on momentarily and triggering the timer T2 provided that the signals at terminals 45, 46 and 47 are all low (i.e. provided none of timers T5, T6 or T7 is producing a pulse). This causes firing of the thyristor SCR2 to commutate the main thyristor SCRI current.

When the thyristor SCR2 ceases to conduct (indicating completion of commutation) the signal at the terminal 24 goes low, so that, provided the signal at terminal 49 is high (which condition exists for 2.5 mS following firing of the thyristor SCR2 because of timer T3), the timer T7 is triggered. At the end of the timer T7 output pulse timer T8 is fired (assuming that the signal at the terminal 24 has not meanwhile gone high) and the output of the timer T8 turns on the transistor Q26 and thereby resets the timer T3. Such resetting of the timer T3 causes triggering of the timer T4 which fires the thyristor SCR3. In the event of the reset pulse at Rl being "missed" for any reason, the timer T3 resets and triggers the timer T4 after its full 2.5 mS delay.

Firing of the thyristor SCR3, causing triggering of the timer T5 which triggers the timer T6 after 304us, i.e. sufficient time for the voltage on the capacitor 19 to reverse and settle. During the 100us pulse duration of the timer, T6, the f.e.t. Q3 is conductive and the voltage on the capacitor 19 is sampled so that the signal at terminal 30 is adjusted to set the upper and lower current limits for the next cycle. Only when the signal at the terminal 47 goes low at the end of this 109us does the signal at the terminal 37 go high again to allow the next cycle to start.

Firing of thyristors SCR1 and SCR2 is prevented if the signal at terminal 31 goes low, but this can be overridden if required, for test purposes.

In the creep mode contact 48 is closed and the thyristors SCR2 and SCR3 are fred alternately whilst the signal at terminal 36 is high (i.e., after the motor current falls below its lower limit) so that some current can flow in the motor. When the signal at terminal 36 goes low such alternate firing ceases until the motor current falls again below its lower limit.

Our copending Application Nos. 9839/77, 9840/77 and 9841/77 (Serial Nos. 1602955, 1602956, 1602957) describe and claim electric vehicle traction motor control circuits having features in common with that described and claimed herein.

WHAT WE CLAIM IS: 1. An electric vehicle traction motor control circuit comprising a main thyristor in series with the motor armature between a pair of supply rails, a second thyristor arranged on firing to divert current from the main thyristor into a commutating capacitor, a third thyristor connected in series with an inductor across the commutating capacitor and arranged on firing to reverse the voltage on the commutating capacitor, driver operable control means for determining upper and lower motor current limits, first firing control means for firing the main thyristor when the actual armature current is less than said lower limit, second firing control means for firing the second thyristor when the actual armature current exceeds the upper limit and third firing control means sensitive to the cessation of flow of current into the commutating capacitor and firing the third thyristor when such current flow ceases.

2. An electric vehicle traction motor control circuit as claimed in claim 1 in which there is a further inductor in series with said second thyristor and the commutating capacitor, said means sensitive to the cessation of current flow into the commutating capacitor being connected across the further inductor.

3. An electric vehicle traction motor control circuit as claimed in claim 2 in which said means sensitive to cessation of current flow into the commutating capacitor comprises a diode, a resistor and current sensing element in series across the further inductor, the diode being connected to permit recirculating current flow through the resistor and current sensing element when current flow into the commutation capacitor ceases.

4. An electric vehicle traction motor control circuit as claimed in claim 3 in which the current sensitive element is the light-emitting diode of an opto-isolator.

5. An electric vehicle traction motor control circuit as claimed in claim 4 in which there is a recirculation diode connected between the anode of the second thyristor and one of the supply rails arranged to carry the motor current after the current flow into the commutating capacitor has ceased, said means sensitive to cessation of current flow into the commutating capacitor comprises means sensitive to the commencement of current flow in said recirculation diode.

6. An electric vehicle traction motor control circuit as claimed in claim 5 in which the means sensitive to commencement of current flow in the recirculation diode comprises a current transformer in series with the recirculation diode.

7. An electric vehicle traction motor control circuit as claimed in claim 5 in which the means sensitive to the commencement of current flow in the recirculation diode comprises a ball-effect element associated with a conductor in series with the recirculation diode.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. control circuits having features in common with that described and claimed herein. WHAT WE CLAIM IS:

1. An electric vehicle traction motor control circuit comprising a main thyristor in series with the motor armature between a pair of supply rails, a second thyristor arranged on firing to divert current from the main thyristor into a commutating capacitor, a third thyristor connected in series with an inductor across the commutating capacitor and arranged on firing to reverse the voltage on the commutating capacitor, driver operable control means for determining upper and lower motor current limits, first firing control means for firing the main thyristor when the actual armature current is less than said lower limit, second firing control means for firing the second thyristor when the actual armature current exceeds the upper limit and third firing control means sensitive to the cessation of flow of current into the commutating capacitor and firing the third thyristor when such current flow ceases.

2. An electric vehicle traction motor control circuit as claimed in claim 1 in which there is a further inductor in series with said second thyristor and the commutating capacitor, said means sensitive to the cessation of current flow into the commutating capacitor being connected across the further inductor.

3. An electric vehicle traction motor control circuit as claimed in claim 2 in which said means sensitive to cessation of current flow into the commutating capacitor comprises a diode, a resistor and current sensing element in series across the further inductor, the diode being connected to permit recirculating current flow through the resistor and current sensing element when current flow into the commutation capacitor ceases.

4. An electric vehicle traction motor control circuit as claimed in claim 3 in which the current sensitive element is the light-emitting diode of an opto-isolator.

5. An electric vehicle traction motor control circuit as claimed in claim 4 in which there is a recirculation diode connected between the anode of the second thyristor and one of the supply rails arranged to carry the motor current after the current flow into the commutating capacitor has ceased, said means sensitive to cessation of current flow into the commutating capacitor comprises means sensitive to the commencement of current flow in said recirculation diode.

6. An electric vehicle traction motor control circuit as claimed in claim 5 in which the means sensitive to commencement of current flow in the recirculation diode comprises a current transformer in series with the recirculation diode.

7. An electric vehicle traction motor control circuit as claimed in claim 5 in which the means sensitive to the commencement of current flow in the recirculation diode comprises a ball-effect element associated with a conductor in series with the recirculation diode.