GB2050089A

GB2050089A - Traction equipment

Info

Publication number: GB2050089A
Application number: GB8010472A
Authority: GB
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1979-03-29
Filing date: 1980-03-28
Publication date: 1980-12-31
Also published as: SE416435B; FR2452814A1; JPS55131202A; SE7902800L; GB2050089B; DE3010327A1; IT8067482A0

Abstract

Traction equipment comprises a vehicle F with an electric a.c. motor M and with an accumulator battery B for feeding the motor via an inverter VR. The vehicle is provided with means, such as a switch SW and a plug AM, for connecting the a.c. side of the inverter to a stationary a.c. voltage source TR for charging the battery via the inverter. In addition, the vehicle has means such as a charging regulator CR, a comparison circuit JF, a current regulator IR, amplifiers FR-FT, delay devices DR-DT and a potentiometer P, for controlling the inverter and thus the charging current while charging the battery. Members FR-FT, DR-DT are responsive to voltages URUSUT of the source TR to control the phase position of the inverter voltage relative to the voltage of source TR. Potentiometer P is adjusted to minimize the reactive power between the inverter and source TR while charging the battery. A time programme may control the charge current instead of sensing the battery voltage by potentiometer SD. <IMAGE>

Description

SPECIFICATION Traction equipment Technical Field This invention relates to traction equipment of the kind comprising a vehicle with an electric a.c. motor and with an accumulator battery for feeding the motor via an inverter.

In the operation of battery-operated electric vehicles it has so far been necessary to arrange special charging units, usually stationary, for charging the batteries of the vehicles.

Such charging units normally comprise a transformer and a controllable rectifier as well as control circuits for controlling the charging process. The rated power of such a charging unit is relatively high because of the limited charging time, and the unit is therefore relatively expensive.

The present invention aims to provide traction equipment of the kind referred to, in which the charging equipment may be considerably simplified and may be made considerably less expensive compared with previously known devices, without appreciably increasing the complexity, weight and price of the vehicle itself.

Disclosure of the Invention According to the invention, in a traction equipment comprising a vehicle with an electric a.c. motor and with an accumulator battery for feeding the motor via an inverter, the vehicle is provided with connection members for connecting the a.c. side of the inverter to a stationary alternating voltage source for charging the battery via the inverter and with control members for controlling the inverter and thus the charging current while charging the battery.

Brief Description of Drawings The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a circuit diagram of one embodiment of traction equipment in accordance with the invention, and Figures 2 and 3 are circuit diagrams of modified parts of the equipment of Fig. 1.

Description of Preferred Embodiments Fig. 1 shows a vehicle F (the units within the dash-lined rectangle), which may be a battery-operated electric truck, an electric car, or the like. The vehicle has a drive motor M, which is a three-phase asynchronous motor, and an accumulator battery B. A three-phase inverter VR has its two d.c. connections connected to the battery B and its a.c. connections connected to the motor M via a twoposition electric switch SW.

The inverter is self-commutated and may thus independently generate a three-phase alternating voltage. The inverter is of a type known per se and consists of a bridge connection of six thyristors T1-T6 provided with turn-off means. Each thyristor is provided with a feedback valve, and these consist of the diodes D1-D6. The inverter has a control pulse device SPD which delivers control pulses to the thyristors and their turn-off means in such a manner that a three-phase alternating voltage is obtained at the output terminals R, S, T of the inverter.

In normal operation of the vehicle, the control pulse device controls the inverter such that the frequency and amplitude of the alternating voltage are variable for control of the motor. For example, the control pulse device may comprise a voltage-controlled oscillator for controlling the frequency, and the amplitude of the output alternating voltage is suitably controlled (for example, through pulse width modulation) such that its amplitude is proportional to the frequency. The mode of operation of such an inverter and its construction and control circuits are previously well known. In normal operation, the switch SW is in the position shown in full lines, and the battery B supplies the motor M via the inverter. By varying the frequency of the inverter, the slip and torque of the motor are affected.

If the frequency of the inverter is reduced to the extent that the slip becomes negative, the motor feeds back power to the battery and regenerative braking is obtained. The control circuits and control members which are used in normal operation are previously well known and are therefore not shown in detail.

For charging the battery of the vehicle, the switch SW is put in the position shown by dashed lines, the motor thus being disconnected from the inverter and the latter being connected to the plug AM arranged in the vehicle. The plug AM is interconnected with a stationary socket outlet AFI for charging the battery.

The a.c. source for charging the battery consists of a three-phase transformer TR with connections RN, 5N and TN for permanent connection to an a.c. mains network. The transformer steps down the mains voltage to a level suitable for charging the battery, for example 50-100 V. The secondary voltage of the transforner is supplied to the socket outlet AFI via the inductors LiR, L,, and LIT.

The plug AM and the socket outlet AFI have three main pins and sockets, respectively, for connecting the main circuits of the inverter via the switch SW and the inductors LIR, L15 and L1T to the transformer TR. Further, the plug AM and the socket outlet AF have three auxiliary pins and sockets, respectively, for connecting the phase control circuits of the inverter directly to the transformer TR.

During charging, the inverter is controlled as follows: The inverter generates a stable alternating voltage at its terminals R, S, T. The secondary voltage of the transformer TR is also a stable alternating voltage. These two voltages are connected to each other via the inductors LiR, Lis and LIT. If the phase difference between the two voltages is small, the flux of active power is, with a good approximation, proportional to the phase difference between the two voltages, and the flux of reactive power is proportional to the difference between the amplitudes of the two voltages.

The amplitude of the voltage of the inverter is suitably controlled so that it becomes approximately equal to the amplitude of the secondary voltage of the transformer TR, which provides a minimization of the reactive power flux between the network and the inverter. For this purpose the amplitude control input AC of the control pulse device SPD of the inverter is supplied with an analogue voltage adaptation signal Su, which is adjusted by means of a potentiometer P such that the amplitude of the output voltage of the inverter acquires the desired value.

For controlling the phase position of the output voltage of the inverter, the three phase voltages UR, Us and UT are supplied to amplifiers FR, F5 and FT, respectively, where the amplitude of the voltages is limited so that the output voltages U'R, U'5 and U'T of the amplifiers will consist of square voltages which are similar to UR, Us and UT, respectively, with regard to phase and frequency. These signals are supplied to delay devices DR, D5 and DT with controllable time delay.

The output voltages SR, Ss and ST from the delay devices are supplied to the synchronizing input Sc of the control pulse device SPD of the inverter, which control pulse device controls the output voltages of the inverter into being equal to the voltages SR, Ss and ST in frequency and phase.

A charging regulator CR of a kind known per se generates a desired value Iso for the charging current. This desired value may be controlled in a known manner in dependence on the battery voltage U5 (which is obtained from a voltage divider SD) and in dependence on the time such that the charging current acquires the desired characteristic. The actual value IB of the charging current is obtained from a measuring shunt SH and is compared with the desired value Iso in a comparison circuit JF. The deviation Al is supplied to a current regulator IR having PI characteristic, the output signal Sp of which is supplied to the delay devices DR, D5, DT and controls the time delay therein.

The phase position of the control signals SR, SS, ST and thus of the e.m.f. of the inverter will therefore be automatically controlled such that the charging current IB follows the desired value Iso generated by the charging regulator CR.

The invention offers considerable advantages compared with previously known traction equipment. The vehicle itself presents all the advantages, known per se, of a.c. operation of the drive motor. The drive motor may consist of an inexpensive and practically maintenance-free asynchronous motor. The control of the motor is carried out smoothly and rapidly and with low losses by means of the inverter. The vehicle may be braked regeneratively, which has proved to provide a considerable increase of the running distance for a given battery capacity or, inversely, a considerable reduction of the magnitude of the battery for a given running distance.

The necessary supplementary units in a traction equipment according to the invention consist of the switch SW and of the control circuits for the battery charging operation shown in the Figure and located outside the inverter. Since the switch SW only has to be operated in currentless state, it may be simple and inexpensive. The control circuits may consist of simple supplementations of the control equipment which is part of the vehicle. Neither the switch nor the control circuits will therefore cause any significant increase in the price or weight of the vehicle.

However, a considerable simplification of the stationary charging equipment is obtained, resulting in a considerable saving compared with previously known traction equipment. In principle, said charging equipment consists of a single transformer. If several vehicles are to be charged simultaneously, the transformer need only be provided with several socket outlets. An additional socket outlet AF2 of this kind is shown in Fig. 1. It is identical with the socket outlet AFI. The main sockets of the outlet AF2 are connected to the secondary side of the transformer TR via inductors L2R, L25 and L2T, and its auxiliary sockets are connected directly to the transformer. The socket outlets may be located at different positions within, for example, a factory area and may be connected to a transformer arranged at a suitable location. Because of the simultaneity factor, the rated power of the transformer may be lower than the sum of the rated powers of the socket outlets. If an alternating voltage of a suitable magnitude for battery charging is already available, the transformer may be completely dispensed with, and the stationary equipment then consists of the socket outlets and their inductors only.

A traction equipment according to the invention may consist of one or more vehicles and possibly also comprise the stationary equipment for charging the batteries of the vehicle.

In the example described above, the motor supplied from the battery via the inverter is a propulsion motor for an electrically operated truck or car. However, the invention may just as well be employed for other types of electrical vehicles. For example, the motor may be a drive motor for the lifting motion of a fork-lift truck.

The control system for the battery charging operation described above may be designed in a great many other ways within the scope of the invention. For example, instead of the simple control of the inverter voltage shown, a closed control circuit may be provided, which controls the inverter voltage or the reactive power flux to the desired value.

The inverter itself may, of course, be designed in a great many ways other than that described above.

The control of the charging current may be performed in other ways than that described above. For example, the charging programme and the sensing of the battery voltage may then be eliminated.

From the above description, it is clear how the battery of the vehicle is charged from a three-phase a.c. network. Alternatively, the battery charging may be carried out from a single-phase a.c. network. During battery charging the inverter is then driven as a single-phase inverter, only two of the three phase groups of the inverter then being used.

The a.c. terminals of these two phase groups, for example R and S, are then connected to an a.c. network via a single-phase connection device. An inductor (for example L1R) is then required only in one of the two phase conductors.

Fig. 2 shows a traction equipment which corresponds to that shown in Fig. 1 but with the exception that the inductors LIR, L15 and L, l are arranged on the vehicle between the plug AM and the switch SW. The voltages UR, Us, UT for phase control of the inverter may then be taken out between the inductors and the plug. The plugs and socket outlets then become considerably simplified, since no auxiliary sockets/pins are needed to transmit the voltages UR, Us, UT. Further, it is not necessary to have a set of inductors for each socket outlet, as in Fig. 1; only one single set of inductors placed on the vehicle is required.

Fig. 3 shows how the transformer TR may be located on the vehicle F. The socket outlets may then be connected to an existing a.c.

network, for example an ordinary 380 V three-phase supply network. The stationary part of the traction equipment then consists only of conventional socket outlets AF1 AF2, Ar3, which may be positioned in a simple and inexpensive manner in a desired number and at desired locations within, for example, a factory area. Socket outlets of this type are often already arranged at locations suitable for charging vehicles. This embodiment provides maximum flexibility, at little or no cost as regards the stationary part, when it comes to charging an arbitrary number of vehicles at arbitrary locations. The transformer is suitably located in the vehicle in such a way that it has a benefical effect on the stability of the vehicle.In, for instance, a fork-lift truck, it may be mounted at the end of the vehicle opposite from the lifting mechanism. The transformer may wholly or partially replace existing counterweights in the vehicle, and it will then add little or nothing to the total weight of the vehicle.

In the traction equipment of Fig. 3, the transformer may be designed so that its leakage inductance is so high that the inductors L1R, L15 and LIT may be eliminated. The same can be done in the embodiments according to Figs. 1 and 2, if only one stationary socket outlet, for example Ari, is arranged for charging the vehicle.

The embodiments according to Figs. 1 and 2 may be modified so that part of the necessary inductance is arranged in the vehicle and the remainder is arranged in series with the respective socket outlets.

The above description shows how the mains alternating voltage (UR, Us, UT) is sensed and used as a reference for controlling the phase position of the inverter voltage and thus of the flux of active power (the charging current). It has been known previously to control a converter by means of a freewheeling oscillator with controllable frequency which (possibly via auxiliary circuits) generates control pulses to the valves of the converter. If the inverter in the vehicle has, or is provided with, such an oscillator, it may be used for controlling the inverter also during the charging operation.The difference between, for example, the desired and actual values of the charging current is then adapted to influence the frequency of the oscillator and thus of its phase position, thus forming a closed control system which controls the acutal value of the charging current into correspondence with its desired value. The sensing of the mains voltage UR, Us, UT shown in Figs. 1-3, then becomes redundant, as well as the auxiliary sockets/pins on the plugs and socket outlets AM, Ari, Ar2 shown in Fig. 1.

In the above description a vehicle with an inverter and a drive motor M has been described. The invention may, of course, also be applied to vehicles having several drive motors, for example one for each wheel, which are supplied by a common inverter or by separate inverters. The inverter (or one or more of the inverters) may then be used in the manner described above for charging the battery of the vehicle.

In vehicles of the kind referred to here there is often required a contactor for disconnecting the supply voltage to the motor. This contactor may then be designed as a switch and be used as the switch SW shown in Figs. 1-3.

Claims

1. Traction equipment comprising a vehicle with at least one electric a.c. motor and with an accumulator battery for supplying the motor via an inverter, wherein the vehicle is provided with connection members for con necting the a.c. side of the inverter to a stationary alternating voltage source for charging the battery via the inverter and with control members for controlling the inverter and thus the charging current while charging the battery.

2. Traction equipment according to claim 1, in which the inverter is a self-commutated inverter and said control members comprise members for controlling the phase position of the inverter voltage relative to the voltage of the alternating voltage source.

3. Traction equipment according to claim 2, comprising voltage-controlling members for controlling the output voltage of the inverter such that the flux of reactive power between the inverter and the alternating voltage source is minimized while charging the battery.

4. Traction equipment according to any of the preceding claims, comprising a stationary alternating voltage source which is provided with at least one further connection member for connecting the source to the inverter of a vehicle for charging the vehicle battery.

5. Traction equipment according to claim 4, in which said alternating voltage source comprises a transformer with a primary winding arranged for connection to an a.c. network and with a secondary winding which is connected to said at least one further connection member.

6. Traction equipment according to any of claims 1 to 3, comprising a transformer arranged on the vehicle between said connection members and the inverter.

7. Traction equipment according to claim 6, in which the alternating voltage source consists of an ordinary low voltage network.

8. Traction equipment according to claim 6 or 7, in which said transformer is arranged in the vehicle in such a way that it has a benefical effect on the stability of the vehicle.

9. Traction equipment according to claim 4 or 5, in which the alternating voltage source comprises inductive means arranged in series with said at least one further connection member.

10. Traction equipment according to any claims 1 to 8, comprising inductive means arranged on the vehicle between said connection members and the inverter.

11. Traction equipment constructed and arranged substantially as herein described with reference to, and as illustrated in, Fig. 1, or Fig. 1 as modified by either of Figs. 2 and 3, of the accompanying drawings.