RU2352052C2 - Reversible direct current drive with sequential excitation motor (versions) - Google Patents

Abstract

FIELD: electrics. ^ SUBSTANCE: electric drive includes contacts of two reverse contactors in armature circuit, adjustable key connecting motor excitation winding over additional low-voltage source and two diodes with armature outputs, two other diodes connected between excitation winding outputs and power source clamp. Another motor power source clamp is connected to one or another low-voltage power source. Contact of additional contactor closed in traction mode and open in recuperate halt braking mode is connected between power source clamp connected to second diode couple and commutation elements of reverse switch. ^ EFFECT: provisions for recuperate halt braking mode of electric drive. ^ 2 cl, 2 dwg

Description

The invention relates to a direct current electric drive with pulse speed control and can be used on electrified vehicles, for example, electric carts, electric forklifts powered by a battery motor, including the conversion of an existing fleet of battery powered vehicles.

Known reversible direct current electric drive with a sequential excitation motor, containing a reversing switch in the armature circuit, a controlled key element in the power circuit of the electric motor, a shunt diode and a low-voltage excitation coil recharge source connected to one terminal with a controlled key element and the other terminal through two diodes with clamps of the anchor chain of the electric motor (see AS 483752 USSR, MKI Н02Р 1/22, decl. 03.19.1973, publ. 09.09.1975, Bulletin No. 33). As the closest to the proposed drive, it is adopted as a prototype.

Known electric drive provides:

- reverse of the electric motor using a special switch in its anchor chain;

- engine operation on a soft mechanical characteristic at high loads and a rigid characteristic of speed limits in the region of small and negative loads, with an automatic transition from the motor mode to the regenerative braking mode and vice versa;

- non-reactive start-up and pulse speed control, both in the motor mode and in the mode of regenerative braking when the vehicle is moving on a scooter slope;

- steady stopping braking with pulse regulation in a wide range of speeds.

To implement the specified operating modes in the electric drive, a five-position manual switch with movement from the zero position in one or the other direction, depending on the chosen direction of vehicle movement, was used.

Manual reversing switches are widely used on some rail vehicles (for example, mine electric locomotives), but they are almost unacceptable for electrified vehicles with steering (trolley buses, electric cars, battery trolleys and forklifts). As a rule, they use indirect contactor control by means of a command controller with a foot drive. Depending on the chosen direction of movement, one of the two reverse contactors is switched on, which closes the corresponding pair of contacts in the anchor chain of the traction motor. Similar technical solutions were used, for example, on electric forklifts of domestic and Bulgarian production (see Machulsky SA Electric Forklifts. Handbook. - M .: Transport, 1992).

However, it is not possible to realize the circuit diagram of the switching elements of the reversing switch required for stopping regenerative braking of the vehicle with this embodiment of the reverse unit.

The aim of the invention is the expansion of the use of a reversible electric drive with a set of prototype functions for vehicles with indirect contactor control, i.e. implementation of regenerative stop braking when using contactor reverse in the anchor chain of the traction motor.

The claimed technical result is achieved due to the fact that between the clamp of the power source connected to the shunt diode and a pair of switching elements of the reverse node, the contact of an additional contactor is introduced, closed in traction mode and open in the mode of stop regenerative braking. In this case, the second clamp of the power source can be connected to one or the other terminal of the make-up source.

Figure 1 shows a circuit diagram of the proposed electric drive, figure 2 a, b is a diagram of the closure of the contacts of the controller and the dependence of the reference voltage U _{0 of} the control device of the key element on the angular movement of the control pedal.

The motor armature 1 is included in the diagonal of the reversing switch on the switching elements 2 to 5 (contacts of the reverse contactors 6, 7). Between the common point of the switching elements 5, 3 and the clamp of the additional low-voltage direct current source 8 (feed source of the field coil) are included: the field winding 9 of the motor, a current sensor 10 and a controlled key element 11, for example, an IGBT transistor with a control device 12. The second clamp of the make-up source 8 is connected through the diodes 13 and 14 to the terminals of the armature 1. Between the controlled key element 11 and the clamp of the power supply, a shunt diode 15 is connected, and between the specified clamp of the power supply of the electric drive and the common contact 16 of the additional contactor 17 is inserted by the point of the switching elements 2, 4 of the reverse node 17. Another clamp of the power supply in the first embodiment of the electric drive is connected to the connection point of the make-up source 8 with the key element (points a), and in the second version - to the connection point of the make-up source 8 and diodes 13, 14 (point b in figure 1).

The key element control device 12 can be performed, for example, on the basis of one of the pulse-width modulator (PWM) microcircuits with a current limiting unit, which are widely used in stabilized DC power supplies.

As a low-voltage source of make-up 8, it is advisable to use a transistor DC-to-DC converter with galvanic separation of circuits (DC-DC converter).

To control the contactors 6, 7, 17, a command controller 18 with a foot drive and a reversing switch 19 are intended. A driving element 20 is connected to the pedal, forming a driving action U ₀ for the control device 12 of the key element 11, the dependence of which on the pedal angle α has the form shown figure 2, b. Such a dependence can be obtained, for example, by using a circular potentiometer as a setting element, the engine of which makes a full revolution when the pedal is moved through the angle α ₃ -α ₁ .

The structure of the power circuit of the electric drive and its performance are maintained while changing the polarity of the sources, electric valves and the controlled key element.

The proposed electric drive in the first embodiment is as follows.

In the initial position of the controller 18, both of its contacts cd and ef are open, the coils of the contactors 6, 7, 17 are de-energized, contacts 2-5, 16 are open and the engine is off. To start the engine “forward”, the reversing switch 19 prepares to turn on the contactor 6. When the pedal is subsequently moved to the angle α _{1, the} contact cd of the controller 18 closes, which leads to the inclusion of the contactor 6 and the closure of its contacts 2, 3 in the motor armature circuit. Further movement of the pedal causes a change in the driving voltage U ₀ according to the dependence U ₀ (α) shown in FIG. 2, b, and to the closure of the contact ef of the controller when the angle of rotation α _{2 is} reached. As a result, the contactor 17 is turned on and closes the contact 16 in the power supply circuit of the electric motor. Then there appears a control voltage U ₀ at the input of the control device 12, which increases linearly with increasing angle α, as a result of which pulses are formed at the output of the device 12, which enable the opening and closing of the key element 11 with an adjustable duty ratio γ = t _AND / T,

where t _And - the duration of the closed state of the key;

T is the period of its switching.

This changes the average voltage at the terminals of the motor

U _cp = γ · U, which ensures smooth acceleration of the electric motor and regulation of the vehicle speed when moving the control pedal in the range of rotation angles α ₂ - α ₃ . When the key is closed, the full voltage U of the power source is applied to the motor and the armature current rises. When the key is open, the current gradually drops, closing under the influence of the EMF of self-induction of the motor armature circuit through the diode 15. Upon completion of the acceleration of the motor, the key element 11 is put into a constantly closed state.

If in the process of regulating the duty cycle γ or because of an increase in the load on the motor shaft, its current reaches a certain maximum permissible value, the current limiting unit 10 activates the current limiting unit of the control device 12, maintaining the average current value at a set limit level.

When the key element 11 is closed, the additional make-up source 8 is connected to the field winding of the motor 9 through the closed switching element 3 of the contactor 6 and the diode 14. If the voltage drop across the field winding caused by the flow of the armature current exceeds the EMF of the additional source 8, the diode 14 is closed, the winding recharge there is no excitation and the engine runs on a soft mechanical characteristic with sequential excitation.

When reducing the load on the motor shaft, and consequently, the current consumed by it, the voltage drop across the field winding 9 decreases, the diode 14 is unlocked and the source 8 feeds the field excitation motor, maintaining magnetic flux while further reducing the armature current. As a result, the proposed electric drive has a boundary speed even with a negative load on the shaft (for example, when the vehicle is moving on a scooter slope), when the emf of rotation exceeds the emf of the power source of the traction motor, the latter automatically switches to regenerative braking mode.

The recuperation current is closed by the circuit: motor armature 1 - closed switching element 2 of the contactor 6 - power source - additional make-up source 8 - diode 14 - armature 1. The field winding is fed through the circuit: output b of make-up source 8 - diode 14 - closed switching element 3 of the contactor 6 - field winding 9 - key element 11 - output a source 8.

With the appearance of a positive load on the motor shaft, the electric drive automatically returns to motor mode.

When the control pedal is returned to the position with the angular position α _{2, the} reference voltage U ₀ becomes zero, the key element control device 12 stops the formation of unlocking pulses, the key element 11 is locked and disconnects the electric motor from the power source. The release of the pedal leads to the opening of the contact ef of the controller 18, the contactor 17 is de-energized and the contact 16 further breaks the power supply circuit of the electric motor. Subsequent deceleration of the vehicle can be carried out by standard means of braking.

To put the drive into regenerative braking mode in order to reduce the speed or stop the vehicle, when returning the control pedal to the angular position α _{2 with} switch 19, turn off the coil of the contactor 6 and turn on the coil of the contactor 7. As a result, the switching elements 2, 3 in the armature circuit of the electric motor will open, and switching elements 4, 5 are closed - the contacts of the contactor 7. When the pedal is subsequently smoothly returned to the direction of decreasing the angular position α, the contact ef will open Weller 18 turns off the contactor 17, and opens the contact 16 in the circuit of the motor supply. At the output of the master element 20, a voltage U ₀ will appear, and the control device 12 will begin to generate pulses for opening and closing the key element 11.

When the key element 11 is closed, the motor is short-circuited and self-excited with current closure along the circuit: armature 1, switching element 5, field winding 9, current sensor 10, key element 11, make-up source 8, diode 14, armature 1. Fast and efficient excitation the engine at any speed of rotation is provided due to the fact that the source 8 is connected to the excitation winding 9 of the engine through the diode 13.

With the subsequent opening of the thyristor switch, the motor current, decreasing in time, continues to flow along the circuit: armature 1, switching element 5, field coil 9, current sensor 10, diode 15, motor power supply, recharge source 8, diode 14, armature 1.

By moving the pedal, changing the value of the reference voltage U ₀ , you can adjust the duty cycle γ, and therefore the intensity of the braking mode.

When the current reaches the set maximum value by the signal of the current sensor 10, the current limiting unit of the key element control device 12 is activated, maintaining the average value of the braking current at a set limit level.

To stop braking and switch to coast, it is enough to return the control pedal to the initial zero position, and to return to the traction mode, switch 19 to the on position of the contactor 6 and by pressing the control pedal switch it to the angular position α> α ₂ corresponding to the duty cycle γ.

To start the engine “backward”, the reversing switch 19 prepares the inclusion of the contactor 7. When the pedal is subsequently moved to the angle α _{1, the} contact cd of the controller 18 closes, which leads to the inclusion of the contactor 7 and the closure of its contacts 4, 5 in the motor armature circuit. Subsequent start-up and speed control are carried out in the same way as during "forward" rotation. The excitation winding 9 is fed from the source 8 with the key element 11 closed through the diode 13 and the closed switching element 5 of the contactor 7. The recovery current with a negative load on the motor shaft is closed by the circuit: armature 1, switching element 4 of the contactor 7, the motor power source, source make-up 8, diode 13, armature 1.

To put the drive into regenerative braking mode in order to reduce the speed or stop the vehicle, when returning the control pedal to the angular position α _{2 with} switch 19, turn off the coil of the contactor 7 and turn on the coil of the contactor 6. As a result, the switching elements 4, 5 in the armature circuit of the electric motor will open, and switching elements 2, 3 are closed - the contacts of the contactor 6. With the subsequent smooth return of the pedal to the direction of decreasing the angular position α, the contact ef will open Weller 18 turns off the contactor 17, and opens the contact 16 in the circuit of the motor supply. At the output of the master element 20, a voltage U ₀ will appear, and the control device 12 will begin to generate pulses for opening and closing the key element 11.

When the key element 11 is closed, the self-excitation of the engine occurs along the circuit: armature 1, switching element 3, field winding 9, current sensor 10, key element 11, make-up source 8, diode 13, armature 1. Fast and efficient excitation of the engine at any speed of rotation is ensured due to the fact that the source 8 is connected to the excitation winding 9 of the motor through the diode 14. Upon subsequent opening of the thyristor switch, the motor current, decreasing in time, continues to flow along the circuit: armature 1, switching element 3, the excitation winding 9, current sensor 10, diode 15, motor power supply, recharge source 8, diode 13, armature 1.

The electric drive according to the second embodiment works similarly to that described above for the first embodiment and performs the same functions. The differences relate to the operating modes of the make-up source and the type of mechanical characteristics of the drive in the recovery mode when the vehicle is moving on a scooter slope.

In the first version of the drive in the motor mode from the low-voltage source, only the excitation winding recharge current is consumed, while in the regenerative braking mode, the total recharge and recuperation current flows through it. In this case, due to a voltage drop on the internal resistance of the make-up source, the engine is counter-compounding - with an increase in the armature current in the braking mode, the excitation current decreases and the rotation frequency increases. With comparable values of the resistance of the field winding and the make-up source, the mechanical characteristic of the electric drive becomes excessively soft, which limits the range of permissible braking conditions.

In the second version of the drive, on the contrary, in the motor mode, the make-up source is additionally loaded with the current of the anchor circuit, whereas in the braking mode only excitation current is consumed from it. In this case, there is no anti-compounding of the engine, and the electric drive in the recovery mode when the vehicle is moving on a scooter slope has a rigid mechanical characteristic that provides automatic speed limitation in a wide range of brake currents. However, since most of the time the drive operates in motor mode, the second version of its implementation will require, as a rule, the use of a larger power source. Therefore, when choosing a particular drive option, it is necessary to take into account the features of its operation mode.

Claims (2)

1. A reversible DC drive with a sequential excitation motor, comprising a reversing switch in the armature circuit, a controlled key connecting the motor excitation winding through an additional low-voltage voltage source and two diodes with armature leads, as well as a shunt diode connected between the excitation winding terminal and the source clamp power, and another clamp of the motor power source is connected to a common point of the low voltage voltage source and the key, characterized in that between the clamp m of the motor power source connected to the shunt diode, and the switching elements of the reversing switch, an auxiliary contactor contact is introduced, closed in traction mode and open in the mode of regenerative braking. 2. A reversible DC drive with a sequential excitation motor, comprising a reversing switch in the armature circuit, a controlled key connecting the motor excitation winding through an additional low-voltage voltage source and two diodes with armature leads, as well as a shunt diode connected between the excitation winding terminal and the source clamp characterized in that the other terminal of the motor power source is connected to a common point of the low voltage source and the first pair of diodes, and between the terminal a power point connected to a shunt diode, and switching elements of the reversing switch, an auxiliary contactor contact is introduced, closed in the traction mode and open in the stop regenerative braking mode.

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