Dual source auxiliary power supply

Abstract

An auxiliary power supply system for providing controlled alternating current in an electric motor traction vehicle driven by a prime mover through a traction alternator. During normal traction operation the prime mover operates at a high constant rotational speed to directly drive an auxiliary alternator which provides the auxiliary power, while in standby operation the prime mover operates at a reduced constant rotational speed and the auxiliary power is obtained from the traction alternator at the desired frequency and voltage.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to electrical power supply systems for electrically propelled traction vehicles and more particularly to alternating current auxiliary power supply systems utilized in electrically propelled vehicles, wherein alternating current generating means, driven by a thermal prime mover, energizes the propulsion motors of the vehicle.

Traction vehicles, such as diesel electric locomotives, commonly utilize a thermal prime mover to drive a traction alternator whose output provides electrical power to the traction motors. The prime mover, such as a diesel engine or the like is operated at various speeds by throttle control in accordance with the power requirements of the alternator.

In addition to traction power, it has also been necessary to provide auxiliary power for lighting, heating and air conditioning. Frequently, it is desirable to provide alternating current auxiliary power for this purpose. Historically, this power has been provided by an auxiliary alternator which is driven by an auxiliary prime mover at a constant rotational speed to ensure an auxiliary power supply of constant frequency and voltage. The auxiliary prime mover and alternator are thus operated continuously to provide the required power both during periods of normal traction operation and during standby operation, wherein the vehicle is standing idle as when awaiting call. During standby, auxiliary power is required, but to a much lesser extent than when in normal traction operation. This varying of the load on the auxiliary prime mover, which has traditionally been a diesel engine, causes considerable problems in maintenance with attendant costs. The expense of an extra diesel engine is thus substantial when considering original installation costs and subsequent overhaul demands.

It is therefore desirable to eliminate the auxiliary prime mover and to drive the auxiliary alternator directly from the traction prime mover which has sufficient available power. However, in conventional diesel electric vehicles the speed of the prime mover is varied during operation, by changing the setting of the throttle lever. This variation of prime mover speed would result in a change in auxiliary alternator speed with a corresponding change in output voltage and frequency.

Energization of the auxiliary power source by the prime mover is further complicated because of standby operation of the vehicle. During time periods wherein the vehicle is in a standby condition, the auxiliary power is still required, but the traction power is not, and thus the operation of the prime mover at the constant high speed is impractical. The resulting noise in residential areas is extremely undesirable. A reduction in prime mover speed will reduce the noise level, but would in turn excessively reduce the frequency of the auxiliary alternator. The use of gears to maintain the alternator speed while slowing the prime mover speed would involve unnecessary expense and difficulty.

It is therefore an object of this invention to provide an improved system for generating alternating current of substantially uniform frequency, for use as auxiliary power in a traction vehicle wherein alternating current generating means driven by prime FIG. 2859,848winding 79. The excitation panel comprises a pulse width modulator 106, a power transistor bridge circuit 107, and an exciter coil 108. The pulse width modulator which is electrically connected across the d-c power source 84 at terminals 109 and 111, has an outlet line 112 which carries an amplified signal to the base of a power transistor 113 of the bridge circuit 107. The bridge circuit has input terminals 107a and 107b and output terminals 107c and 107d, the input terminals being connected across the d-c power source by leads 114 and 116, and the output terminals having connected therebetween the exciter coil 108. The NPN power transistor is connected between the terminals 107b and 107d with its emitter nearest the terminal 107b. Connected in the other legs of the bridge circuit are the resistors 117, 118 and 119 connected between terminals 107d and 107a, 107a and 107c, and 107c and 107b, respectively. The PWN is a self-saturating reactor with a main a-c winding and several d-c control windings. The a-c winding is connected from one output of an oscillator to the power transistor, and the d-c windings are connected to line 70. The oscillator provides a square wave a-c to turn the transistor off and on at approximately 800 times a second. The PWM responds to the feedback signals in line 70 and causes the transistor to turn off and on in response thereto, the ratio of off to on time being determined by the power demand and varied accordingly by the signals from the ACCR and VCR. The exciter field is thus fed from the vehicle battery in relation to the transistor on and off control, and the alternator output is varied accordingly.

During normal operation of the traction vehicle, the auxiliary alternator 29, driven by the prime mover at a constant speed through coupling 31, provides three-phase current through its output leads 32 to the trainline 33, and through the power transfer switch contacts 41(a) which are set in the indicated position. Voltage limitation is provided wherein voltage feedback signals pass through leads 34 to the input of voltage regulator 36. In the voltage feedback system the leg having the highest voltage is used to generate a limiting signal. The voltage regulator applies one of the three line-to-line voltages to an excitation control circuit 20 which provides a d-c current to the field winding circuit 35. Various known circuits may be used to accomplish this regulation, FIG. 3 shows one arrangement which is commonly used in the art and includes a bridge rectifier 39, voltage measuring means 40, and an a-c power source 56. The bridge rectifier 39, is connected to legs 34a and 34b at its terminals 39a and 39b. The alternating inputs from these legs is rectified to enter line 57 through the output terminal 39d. A d-c current is thus provided to the field winding 35 and returns along line 65 to the rectifier input terminal 39c. The a-c power supply 56, such as a chopper or oscillator or the like, is responsive to the voltage measuring means 40 to increase or decrease the flow of current to the exciter field winding 35. The output of the auxiliary alternator 29 is thus voltage regulated. Locomotive battery current from the d-c source 84 is provided by lines 55 and 60 to supply the field current for the initial alternator build-up. The switches 125a and 125b are actuated and displaced from the positions shown in FIG. 3 during initial build-up, and are returned to their indicated positions by relays when sufficient current is being provided by the alternator 29 to maintain the field. The current being delivered to the trainline is limited by a conventional current limiter circuit 38 which receives current feedback signals through an ammeter 75 from the current transformers 53 connected to the respective legs of the three-phase output. A rectifier 80 is connected to the output of the current limiter to provide a d-c signal to the current control winding 95 along lines 45.

During periods of standby operation, wherein the traction alternator is providing auxiliary power, the drive switches 105 are opened thereby opening the circuits to the traction motors and to the current feedback shunt 48. Similarly, the power transfer switch is actuated and contacts 41b and 41c as well as 41(a) are actuated and displaced from the position shown in FIG. 2 thereby connecting terminals 101, 102 and 103 respectively. The reference current then is a constant current signal coming from the voltage regulator 36 through line 104, which current is directed through the comparison circuit 30 to the terminal 102 through the line 106, to line 87, the power source 84, line 86, terminal 90 and hence back to the voltage regulator 36. The reference current is provided to line 104 from a constant current source 115 which is connected to the vehicle battery 84, across the lines 55 and 60. This constant current source is obtained by conventional circuitry and its output value is appropriately chosen to be equal to the current that flows through the VCR 62 when a specified voltage appears at the output of the traction alternator, (for example, 21 milliamps when the voltage is 480 volts). Similarly, the rectified current feedback in the circuit 44 is adjusted in amplitude by resistors 120 so as to obtain the desired milliamp/volt relationship, wherein when the current being delivered to the trainline reaches a specific predetermined level the ACCR will generate the proper signal to reduce the excitation to the traction alternator, thereby limiting the trainline current to the desired level.

As previously discussed, during normal traction operation, a voltage feedback signal originates at the rectified portion of the traction circuit and is applied by line 25 to the control winding 47 of the voltage measuring reactor 62. During standby operation, this feedback signal continues to be applied from the rectifiers 16. Thus, a voltage limit control is maintained in the same manner as in normal operation.

As stated hereinbefore, current limit control during normal operation is maintained through the control winding 47. However, during periods of standby operation, the opening of the drive switches acts to switch out the shunt 48 and hence the reaction control winding 48. It is necessary, therefore to provide another current feedback circuit when the power transfer switch contacts 41d are closed. When a circuit is provided for a current feedback signal to enter from the voltage regulator, along line 45, to the control winding 95 whose signal changes the primary winding impedance and hence modulates the a-c signal from the supply 71.

The current feedback signal output of the current measuring reactor 61 is thus applied to the bridge rectifier 58 and the voltage feedback signal output of the VCR 62 is applied to the bridge rectifier 59. The output of the bridge rectifiers are connected serially by lines 83, 76 and 77 in the reference current circuit. Accordingly, a comparison is effected between the reference current and the voltage or current feedback signal having the larger magnitude. If the voltage and/or current feedback signals exceed the reference current signal in magnitude, a current signal proportional to the difference between the greater one of the feedback signals and the reference current, is applied to the PWM winding through line 70, which PWM winding responds thereto by causing a reduction in excitation to the traction alternator and thus a reduction in voltage. This arrangement limits the maximum voltage and current outputs of the traction generator in reference to current and voltage being delivered to the auxiliary machinery. The excitation circuit is one such as is commonly used in the art and is not considered to be unique. The embodiment which is hereinafter described represents only one manner of controlling the excitation to the traction alternator.

Claims

1. In a traction vehicle of the type wherein thermal prime mover means drives a traction alternator having a predetermined number of commutating poles and adapted to energize traction motor means, an auxiliary power arrangement adapted to produce alternating current, the combination comprising:

a. an auxiliary alternator having a plurality of commutating poles greater less than the number of poles of said traction alternator;

b. means for mechanically coupling said prime mover means to said auxiliary alternator;

c. governor control means for maintaining the shaft speed of said prime mover at a first predetermined shaft speed during normal operation of said traction vehicle and at a second predetermined reduced speed during standby operation of the traction vehicle;

d. an alternating current circuit having an output adapted to energize auxiliary power circuits and an input;

e. switching means to connect said input to the output of said auxiliary alternator during normal operation of said traction vehicle, and to connect said input to the output of said traction alternator during standby operation of said traction vehicle;

f. wherein the number of commutating poles of said auxiliary alternator is substantially equal to the product of the number of commutating poles of said traction alternator and the ratio of said first second predetermined shaft speed to said second first predetermined shaft speed.

2. The auxiliary power source of claim 1 and including control means having an input connected to be responsive to the traction power applied to said traction motors and an output connected to regulate the excitation of said traction alternator, wherein during standby operation of said vehicle, said control means is connected to be responsive to the output of said alternating current circuit.

3. A traction vehicle propulsion system as defined in claim 2 wherein said control means is effected by a reference current, said reference current during normal operation being variably responsive to said governor control means and during standby operation being a constant current of of a predetermined magnitude.