CA2136602A1 - Enhanced traction system for trolleybuses powered from a 600 volt direct current power line - Google Patents

Abstract

An electrically driven vehicle, powered from a 600 volt direct current power line in which the vehicle current collectors are united electrically as the vehicle passes by power line as switching points and crossings and in which a circuit permits regeneration of electrical attraction and breaking power comprising a three phase vehicle voltage and frequency current inverter and a three phase a synchronises attraction motor.

Description

;~3~02 APPLICATION OF THE lNV~L.llON

This invention relates to the electronic circuits which are necessary to use an industrial inverter in the regenerative electrical traction and braking of a trolleybus powered from a 600V direct current power line, in which the vehicle's current collectors are united electrically as the vehicle passes by power line switch points and crossings.

RACR~ROUND OF THE lNV~NllON
1. PRESENT TECHNIQUE. Trolleybuses are presently powered by an electrical and mechanical system formed by a thyristor (chopper)-based electronic inverter and a direct current motor with non-regenerative composite excitation.

2. TECHNIQUE A~nl~v~ WITH THE lNV~NLlON. The trolleybus is powered by an electrical and mechanical system formed by an inverter which produces a three-phase variable voltage and frequency current and a three-phase asynchronous motor, and thereby offers the advantages related to a three-phase, asynchronous, squirrel cage, four-pole, fully-enclosed, external fan motor (TEFC). It is the simplest prime motor in electrical and mechanical technology, as the same needs no collector, brushes, auxiliary excitation circuits, etc.

The squirrel cage, three-phase asynchronous motor is the most popular officially approved motor in the electrical and mechanical market, and is available in many brands.

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The antifriction bearings are the only pieces of the squirrel cage three-phase asynchronous motor that wear off and may be long-lasting if properly lubricated. It is not necessary to disassemble the motor in order to lubricate them.

The squirrel cage three-phase asynchronous motor need not be cleaned internally because it is fully enclosed and does not have inside any element that causes dirt particles, as is the case of the direct current motor, which causes conductor debris, copper from the collector and carbon from the brushes.

The squirrel cage three-phase asynchronous motor has the easiest to replace coil and the least copper content; it is a single-coil motor, as opposed to the direct current motor with assembly coils, series field, parallel field and exchange poles.

The inverter used is readily available in the industrial electrical and mechanical market and may be purchased from many makers.

Thanks to the inverter's great computational power it is possible to implement innumerable protective and informative functions of the motor, inverter and the vehicle's operation and driving.

The inverter does not need sophisticated reactors (inducers) due to the following basic reasons: (i) it uses the ~3~i6~2 greater intrinsic inductance of induction motors, and (ii) it generates a quasi-sine current wave.

The inverter's efficiency is greater than that of the chopper. An inverter is a great deal smaller and lighter than a chopper. The vehicle's kinetic energy is automatically recovered in the inverter, which sends this energy to the overhead line, if the line voltage is not too high.

The inverter/asynchronous motor combination is less expensive than the chopper/direct current motor combination, and the world trend is to reduce the price even more.

The inverter is made up by easy-to-reach basic parts: a D.C. bus contactor; a D.C. bus with capacitors; a power transistor package; a transistor-based control printed circuit;
a printed circuit with a microprocessor.

SUMMARY OF THE lN V~N'l'lON
Trolleybus braking efficiency is achieved through regenerative braking. The trolleybus is capable of driving in zones where current collectors are electrically united. The trolleybus has a low maintenance cost thanks to the use of a squirrel cage asynchronous traction motor. The trolleybus is a low-price vehicle because industrial components are used and is therefore cost-efficient.

~1 366~2 BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example, in the accompanying drawings in which:
Figure 1 is an inverter traction motor circuit according to the invention;

Figure 2 is a modified inverter circuit according to the invention;

Figure 3 is a inverter polarity protection circuit according to the invention;

Figure 4 illustrates a current collector power line crossing according to the invention;

Figure 5 is an electric vehicle current inducer according to the invention;

Figure 6 is a current collector disconnection detection circuit according to the invention;

Figure 7 is an inverter power pedal input signal circuit 30according to the invention;

Figure 8 is an inverter digital electronic output circuit according to the invention;

Figure 9 is a vehicle brake transducer circuit according to the invention;

Figure 10 is an inverter activation digital input circuit according to the invention; and ~3~;6~2 Figure 11 is an inverter analog electronic forward and reverse speed limit input circuit according to the present nvent lon .

DETAILED DESCRIPTION OF THE lNV~L.llON

The industrial inverter (Ul) must meet the following characteristics (Fig. 1):
1. Enough electric power to propel and regeneratively brake the vehicle with a 440V three-phase asynchronous traction motor (Ml).

2. Input voltage: 440V 3O 60Hz.

3. Output voltage: 0-440V 3O 1-120Hz.

4. Internal bus voltage: 450V DC Minimum.
750V DC Maximum.

5. Digital electronic input port (R) (Fig. 1) to activate the inverter (Ul).

6. Digital electronic input port (A) (B) for a two-channel square encoder for use as traction motor feedback (Ml).

7. Analog electronic input port (T) to control the traction motor's motive torque (positive) or regenerative torque (negative).

8. Analog electronic input port (SM) to limit the traction motor's (Ml) positive or negative speed.

~13~02 9. Digital electronic output port (MS) which changes value as the traction motor (M1) reaches a minimum speed.

10. Analog electronic output port (P) in proportion to the algebraic value of the traction motor (M1) power.

11. Analog electronic output port (S) in proportion to the traction motor (M1) speed.

The embodiment of the invention may be divided into three parts:
1. A modification of the commercial inverter to permit the use of 600V DC power.

2. Modification of the commercial inverter to prevent its capacitors from discharging due to a short circuit in the current collectors.

3. Interface circuits between the vehicle driver and the inverter.

Part 1 The commercial inverter has six diode packages (gl to 6) (Fig. 2), which are necessary to rectify the three-phase alternating current.

Z1 ~6602 These diodes are eliminated with the current input (L3) and the varistors (V2) and (V3).

The diode (g7) (Fig. 3) protects from connection with the wrong polarity. These changes allow the inverter to be connected to 600V DC supplies and in addition to send to the network the electric power produced by the regenerative brake.

Part 2 Since the current collectors are electrically united (short-circuit), when the vehicle goes through power line crossings and switch points it is necessary to disconnect the current collectors inverter. This operation must be made quickly and therefore cannot be accomplished with electrical and mechanical means. The short circuiting is preceded by a disconnection as the current collector passes through the insulating fiber, as shown in Figure 4.

This disconnection is detected in the circuit shown in Figure 6, as follows:

The current used or generated by the electric vehicle flows through the inducer (M5), inducer used to reduce (di/dt), on Figures 5 and 6. This current is pulsating due to the frequency of the carrier wave which is necessary to produce the variable frequency sine current that the inverter (Ul) applies to thé
traction motor (Ml). If the voltage induced by this current is missing in the reactor (M5) it means that a current collector has contracted the insulating fiber. This voltage is connected through (Rloo~ and (Kloo) to the two ~ED's of the optic couplings (ulO0) and (ulOl) connected in antiparallel fashion. The Zener diodes (dZ100) and (dZ101) protect the LED's of the optic couplings (ulO0) and (ulOl) from transient voltage.

~ 3~i602 The current collectors and the inverter are disconnected through (Ql) (Fig. 5) to prevent the discharging of the inverter (Ul) capacitors. The diode (gl8) conducts the current used by the inverter (Ul).

The contacts (Cl) and (C2) belong to the same class as the contactors used to select the proper polarity for the inverter (Ul).

The diode (gl7), the capacitor (Cl) and the resistance (R3) protect the package (Ql), (gl8) and inverter (Ul) from transient current and voltage.

The two output transistors of the optic couplings (ulO0) and (ulOl) connected in parallel fashion (Fig. 6) therefore conduct power if the current collectors are energized, and communicate a logical high to one of the inputs of gate AND
(u102).

The analog output (P) of inverter (Ul) is carried to a comparator (u103) which will produce a logical high in the output if the signal (P) is negative (regeneration). The output signal of (u103) is carried to an optic coupling (u104). The optic coupling's (u104) output transistor produces a logical high if the vehicle is regenerating. This logical high is communicated to the other input of gate AND (u102).

The output gate AND (u102) is carried to an amplifier (u105) which causes Ql to be conducted when the following two conditions are concurrently met:
(a) That the vehicle be regenerating.
(b) That the current collectors have not been disconnected.

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Part 3 The driver controls the trolleybus run through a power pedal or accelerator and a brake pedal. The brake pedal operates the friction brakes through pneumatic actuators.

The power pedal varies in proportion to the magnitude of the analog electronic signal communicated to the inverter's (Ul) input port (T).

This takes place as follows (Fig. 7):
The distance between the analog proximity sensor (b5) and a metallic shadow is varied by the power pedal so that the amplifier (U7) produces a current ranging from 4 to 20mA through the resistor (R20) and the LED of the optic coupling (U13), so that the current in the LED of the optic coupling (u13) increases as the pedal is pushed.

The field effect output transistor of u13 is carried through (R2) and (R1) to the amplifying circuit formed by (R4), (P2), operation amplifier (u14), (R3) and (P1). The amplifier output is carried to the optic insulator (u5b) field effect output transistor to the inverter circuit formed by the operational amplifier (u15), (R6) and (R7). The operational amplifier output (u15) is carried through the field effect output transistor of the optic insulator (u7b) to the inverter's analog input port (T).

Thus, by pushing the power pedal and if the field effect output transistors of the optic coupling (u5b) and (u7b) are in conduction mode, the absolute value of the voltage applied to the inverter's analog input port increases (T) and the vehicle will run at the speed that the acceleration conditions, vehicle weight, road slope and other factors permit, propelled by the magnitude of the motive torque requested to the inverter (U1) through the position of the power pedal.

~3~2 -The optic coupling (u7b) (Fig. 7) conducts if the vehicle driver selects forward drive by moving a switch to a position that excites the optic coupling (u7b) LED through R17, optic coupling (u7b) and (u12).

The inverter circuit formed by the amplifier (u15), (R6) and (R7) (Fig. 7) also receives an analog signal from the inverter's (U1) analog output port (S) through the optic couplings (u4a), (ulla), (u6) and the potentiometers (P5) and (P6).

The optic coupling (u4a) is normally excited. The optic coupling (ulla) is excited only if the motor speed exceeds the minimum speed. This takes place thanks to the transistor (ql) (Fig. 8) to whose base is connected the digital exit port (MS) of the inverter (U1), which produces a logical high if the motor (M1) is operated at more than the minimum programmed speed.

The analog optic coupling (U6) (Fig. 9) is excited in proportion to the air pressure of the actuators of the vehicle brakes. The transducer (U6) converts the pressure into voltage.
The potentiometer (P1) divides this voltage, which is carried to the operational amplifier (ul).

The operational amplifier output (ul) is carried to the transistor base (u2) which in turn handles the excitation of the LED of the analog optic insulator (u6).

From the above description, it appears that upon releasing the power pedal the analog optic coupling (u5b) ceases to conduct (Fig. 7), and thereby predominates the positive signal produced by the analog output port (S) which is proportional to the motor (M1) speed.

The inverter amplifier (u14) transforms the positive signal into a negative signal, so that as the power pedal is released the analog input port (T) of the inverter (U1) receives a negative voltage which the inverter (Ul) transforms into a negative torque applied to the motor (Ml) which creates a regenerative braking.

This braking is proportional to the motor (Ml) speed and ceases when the motor (Ml) speed is reduced as a result of optic coupling (ulla) ceasing to conduct.

If in addition to releasing the power pedal the brake pedal is pushed, the output field effect transistor of the optic coupling (u6) (Fig. 7) increases the effect of the inverter amplifier (u15) (increasing even more the regenerative braking which is now proportional to the position of the brake pedal and the motor (Ml) speed).

In order to reverse, the excitation of the optic insulator (u7b) (Fig. 7) is eliminated and the optic insulator (u8b) is excited through a logical high to (R18). Thus, a negative signal is sent to the inverter's (Ul) analog input port (T) and thus the motor (Ml) reverses. The regenerative braking does not work when the vehicle is reversing.

To activate the inverter (Ul) (Fig. 10), it is necessary to apply a logical low to the digital input port (R), which is achieved by exciting the optic coupling (u12) and the optic coupling (u5a) (Fig. 7).

In order that at the time of releasing the power pedal, and bearing in mind that so doing eliminates the excitation, the inverter (Ul) is not disactivated and the regenerative braking is lost, the path of (u5a) is replaced with the output transistor of the optic coupling (ullb). The optic coupling (ullb) reacts just as the optic coupling (ulla) (Fig. 8) does.

The forward and reverse speed limits must be capable of being adjusted separately.

The reverse speed must be very low due to the geometry formed by the current collectors and the overhead line.

The voltage divider formed by (P4) and (R11) (Fig. 11) is used to limit the forward speed. Such voltage divider communicates the voltage selected in (P4) through the optic coupling (u7a) to the analog input port (SM) of the inverter (U1). This limits the forward speed.

The voltage divider formed by (P3) and (R10) is used to limit the reverse speed. Such voltage divider communicates the voltage selected in (P4) through the optic coupling (u8a) to the analog input port (SM) of the inverter (U1). This limits the reverse speed.

While the invention has been described in connection with a specific embodiment thereof and in a specific use, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims.

The terms and expressions which have been employed in this specification are used as terms of description and not of limitations, and there is no intention in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claims.

Claims (5)

1. In an electrically driver vehicle such as a trolleybus powered from a 600V direct current power line and in which the vehicle current collectors are united electrically as the vehicle passes by power line switching points and crossings, the improvement comprising a circuit which permits regeneration of electrical traction and braking power comprising a three-phase vehicle voltage and frequency current inverter and a three-phase asynchronous traction motor.

2. The circuit of claim 1, wherein the inverter has the following characteristics:
(a) Enough electric power to propel and regeneratively brake the vehicle with a 440V three-phase synchronous traction motor;
(b) Input voltage: 440V 3o 60Hz;
(c) Output voltage: 0-440V 3o 1-120Hz;
(d) Internal bus voltage: 450V DC Minimum;
750V DC Maximum;
(e) Digital electronic input port to activate the inverter;
(f) Digital electronic input port for a two-channel square encoder for use as traction motor feedback;
(g) Analog electronic input port to control the traction motor's motive torque (positive) or regenerative torque (negative);
(h) Analog electronic input port to limit the traction motor's positive or negative speed;
(i) Digital electronic output port which changes value as the traction motor reaches a minimum speed;

(j) Analog electronic output port in proportion to the algebraic value of the traction motor power; and (k) Analog electronic output port in proportion to the traction motor speed.

3. The circuit of claim 2, wherein the inverter is modified by a varistor circuit that eliminates the diodes for rectifying the three-phase alternating current.

4. The circuit of claim 2, wherein the current collectors and inverter are disconnected when the vehicle goes through power line crossing and switching points, to prevent discharge of the inverter capacitors due to short circuit in the current collector.

5. The circuit of claim 2, wherein the invertor is connected to a power pedal input signal circuit, whereby depression of the power pedal increases torque applied to the traction motor and release of the power pedal, or depression of the brake pedal is transferred into a negative torque applied to the traction motor which creates a regenerative braking.