Active discharge of a high-voltage bus line

Abstract

A method for actively discharging a common bus line (116) of a machine (100) comprising a power machine (102), a generator (112), a drive motor (124) and one or more auxiliary devices (126), wherein the method comprises: monitoring a rotational speed of the power machine (102) with respect to a first lower threshold; monitoring a voltage of the common bus line (116) with respect to a second upper threshold; and activating one or more of the following: the generator (112), the motor (124) and the auxiliary devices (126), if the rotational speed of the power machine (102) falls below the first lower threshold and if the voltage exceeds the second upper threshold, in order to discharge voltage from the common bus line (116).

Description

Technical FieldThe present disclosure relates generally to electric drive assemblies, and more particularly to systems and methods for actively discharging electrical bus lines.Prior ArtA common or electrical bus is used in a variety of applications including work machines, vehicles, and computers. Electrical bus lines may also be used in high voltage applications to carry power from a power source to the electrical devices. An electric bus line is substantially a parallel circuit used to connect a plurality of electric devices together with power sources such as solar cells, batteries, and the like. In addition, bus lines can be used in direct current (DC) applications and have a positive line and a negative line or ground line, via which a potential difference can be provided.One problem that may occur in DC voltage applications is that electrical devices may store electrical energy. As a result, the electrical devices may continue to supply the stored electrical energy to the electrical bus line when the electrical bus line is disconnected from a power source. Thus, a comparatively long period of time may be required for the electric bus line to return to a low energized state in which the electric potential difference between the positive line and the negative line is minimal. When technicians are forced to wait for the electrical bus to return to their low energized state before they begin repair operations, the time required for repair and maintenance of such machines, as well as the associated costs, increases dramatically.Many existing high voltage electrical bus lines use a discharge resistor to assist in the dissipation of stored energy once the power supply associated therewith is turned off or disconnected. For example, US 2009 / 0141412 A1 to Hickam discloses a discharge circuit having a power resistor connected between the positive and negative lines of the associated electrical bus line to discharge current flow therein. While such discharge resistors allow a certain degree of energy dissipation, the rate of discharge is limited to a natural discharge rate, which still requires a significant wait time, particularly for high voltage applications. Moreover, such discharge circuits and discharge resistors are prone to errors, which may represent a significant risk in devices not equipped with secondary safety facilities as a catch solution.DE 10 2005 015 379 A1 discloses an electric drive system having a direct current bus voltage controller, having a power source, a generator, at least one capacitor for storing a power supply, a common bus for conducting the power output to the capacitor, at least one motor for receiving power from the common bus, and a control device in connection with the at least one motor and the generator.The disclosed system and method are directed to overcoming one or more of the problems set forth above and associated with the prior art.SUMMARY OF THE DISCLOSUREThe object of the present invention is achieved by a method and a system for the active discharge of a common bus line of a machine in each case according to the main claims. The dependent claims relate to preferred embodiments of the invention.In one aspect of the present disclosure, a method for actively discharging a common bus line of a machine including an engine, a generator, a drive motor, and one or more auxiliary devices is provided. The method monitors a speed of the engine relative to a first lower threshold, monitors a voltage of the common bus line relative to a second upper threshold, and activates one or more of the generator, the motor, and the accessories if the speed of the engine falls below the first lower threshold and the voltage exceeds the second upper threshold to discharge voltage from the common bus line.In another aspect of the present disclosure, a method for actively discharging a common bus line of a machine including an engine and a generator is provided. The method determines a speed threshold for the engine, determines a voltage threshold for the common bus line, compares a current speed of the engine to the speed threshold, compares a current voltage of the common bus line to the voltage threshold, and switches the generator to a powering mode if the current speed falls below the speed threshold and the current voltage of the common bus line exceeds the voltage threshold to partially drain excess charge from the common bus line.In yet another aspect of the present disclosure, an active discharge system is provided for an engine having an engine, a generator, a drive motor, and one or more auxiliary devices. The active discharge system comprises a common bus line and a control unit. The common bus line is in electrical communication with at least one of the following: the generator, the drive motor and the accessories of the machine. The control unit is in electrical communication with at least the engine of the machine and the common bus line. The controller is further configured to monitor a speed of the engine relative to a first lower threshold, monitor a voltage of the common bus line relative to a second upper threshold, and activate one or more of: the generator, the motor, and the accessories; if the engine speed falls below the first lower threshold and the voltage exceeds the second upper threshold, to discharge voltage from the common bus line.Brief Description of the DrawingsFIG. 1 is a diagrammatic view of a machine constructed in accordance with an exemplary embodiment of the present disclosure; FIG. 2 is a schematic view of an exemplary embodiment of an active discharge system as applied to a typical electric drive machine; and FIG. 3 is a flow diagram of an example method for actively discharging an electrical common bus line of a machine.Detailed DescriptionReference will now be made in detail to specific embodiments or characteristics illustrated in the accompanying drawings as examples. In general, corresponding reference numerals are used throughout the drawings to reference like or corresponding parts.FIG. 1 diagrammatically illustrates a mobile machine 100 that may use electric drive means to cause movement. More specifically, the machine 100 may include a primary power source 102 coupled to an electric drive 104 to cause movement by a propulsion device 106. Such a mobile machine 100 may be used as a work machine for performing a particular type of work associated with an industry such as mining, construction, agriculture, transport, or any other suitable industry known in the art. For example, the machine 100 may be an earthmoving machine, a watercraft, an aircraft, a tractor, a off-road vehicle, a road vehicle, or any other suitable mobile machine.Referring now to FIG. 2, an example discharge system 108 as applied to an electric drive 104 of a machine 100 is provided. The electric drive 104 may include a primary power source 102, such as a diesel engine, a gasoline engine, a natural gas engine, or any other type of internal combustion engine commonly used to generate power. The electric drive 104 may also be used in conjunction with any suitable power source, such as a fuel cell or the like. The engine 102 may be configured to directly or indirectly transfer power to parasitic loads 110 via belts, hydraulic systems, or the like. The engine 102 may also be configured to mechanically transfer power to a generator 112 via a clutch or axially rotating driveshaft 114.The generator 112 of FIG. 2 may be a switched reluctance generator (SR), or any other suitable generator configured to generate electrical energy in response to rotational drive by the engine 102. As is well known in the art, the generator 112 may include a rotor (not shown) rotatably disposed within a fixed stator (not shown). The rotor of the generator 112 may be rotatably coupled to an output of the engine 102 via a direct crankshaft, transmission train, hydraulic circuit, or the like. The stator of the generator 112 may be coupled to a common bus line 116 of the electric drive 104 by means of a converter circuit 118 comprising rectifiers, converters, capacitors and the like. During a generator mode of operation, when the rotor of the generator 112 is rotated within the stator by the primary power source 102, electrical current may be induced and supplied to the converter circuit 118. The converter circuit 118 may convert the electrical signals to the appropriate direct current (DC) voltage for distribution to the various electrical devices and subcomponents of the machine 100. In addition, the generator 112 may be capable of causing rotation of the rotor in response to electrical signals supplied to the stator from the common bus 116, for example, during a motor mode of operation.The common bus line 116 may include a positive line 120 and a negative or ground line 122, via which the common bus line 116 may distribute a common DC bus line DC voltage between one or more electrically parallel components of the machine 100. For example, the common bus 116 may distribute power supplied by the engine 102 and the generator 112 to one or more motors 124 to cause movement by a propulsion device 106. In particular, the first converter circuit 118 associated with the generator 112 may provide a DC signal that is communicated to a second converter circuit 118 associated with one or more motors 124. The second converter circuit 118 may convert the DC signal into the appropriate phase signals necessary to drive the motors 124. The common bus line 116 may also distribute the common DC voltage to additional devices 126 of the machine 100, including, for example, heating ventilation and cooling systems (HVAC) 128, high voltage pumps 130, high voltage fans 132, or any other device driven with the common DC voltage. The additional devices 126 may also include a second power source or hybrid system 134 configured to store any portion of the common DC voltage within a rechargeable energy storage device 136, such as a battery. In such embodiments, the common bus line 116 may be configured to selectively distribute the energy stored within the energy storage device 136 to the generator 112 and / or the one or more motors 124 such that the fuel consumed by the power source 102 is minimized. In still further embodiments, the additional devices 126 may be provided with a switched discharge resistor 138 that may be selectively switched between the positive and negative lines 120, 122, thereby discharging any excess voltage in the common bus line 116.For example, as shown in FIG. 2, the common bus line 116 may also be provided with a means for actively discharging or draining excess voltage stored within the common bus line 116. In particular, the discharge system 108 may be provided with a controller 140 in electrical communication with at least the common bus line 116 and the primary power source or engine 102 of the machine 100. The control unit 140 may monitor the current operating conditions of the engine 100 and determine whether the common bus voltage should be drained based on these operating conditions. The operating conditions may indicate, for example, the load on the machine 100, a travel speed of the machine 100, the desired operation of the machine 100 as input by the operator, and the like. Based on such operating conditions of the machine 100, if the controller 140 determines that the common bus voltage is to be derived, the controller 140 may release the bus voltage by activating one or more of the generator 112, the drive motor 124, the additional devices 126, and any other device that receives power from the common bus 116.In a particular embodiment, the controller 140 may activate the generator 112 in a motor mode of operation to release at least partially excess bus voltage. Accordingly, the control unit 140 of the unloading system 108 may communicate with the generator 112 to determine or select its operating mode. The control of a switched reluctance generator can be effected, for example, by means of direct connections to the switches and / or the windings of the switched reluctance generator. The controller 140 may also be configured to discharge the voltage of the bus line through the drive motor 124, the HVAC system 128, the high voltage pumps 130, the high voltage fans 132, and any combination thereof. When using the hybrid system 134, the control unit 140 may also be configured to condition the discharged voltage of the bus line and store it in the energy storage device 136 for later use. By activating such devices, the controller 140 may securely discharge the voltage of the bus line using existing components and operations typically performed within the machine 100.The operation of the unloading system 108 may be integrated or embedded in the existing controller of the machine 100. Additionally, the controller 140 may be implemented using one or more of the following: a processor, a microprocessor, a microcontroller, an electronic control module (ECM), an electronic control unit (ECU), or any other suitable means for electronically controlling the functionality of the unloading system 108. The controller 140 may be configured to operate according to a predetermined algorithm or set of instructions to control the unloading system 108 based on the various operating conditions of the machine 100. Such an algorithm or set of instructions may be preprogrammed or included in the memory of the controller 140, as is conventional in the art.Referring to the flowchart of FIG. 3, an example method for actively discharging or draining a common bus 116 of a machine 100 is disclosed. The disclosed method may be implemented as an algorithm or set of program codes by which the controller 140 is configured to operate. As shown, the controller 140 may initially determine a set of thresholds from which it monitors one or more parameters of the machine 100 that are relevant to the common bus voltage. For example, the control unit 140 may determine a first threshold value or a lower limit for the engine speed as well as a second threshold value or an upper limit for the voltage of the common bus line. The appropriate first and second thresholds may be determined, for example, based on a combination of operating conditions of the machine 100, such as the load on the machine 100, the travel speed of the machine 100, the operator input, and the like. Alternatively, the machine speed and bus voltage thresholds may be predetermined values that are preprogrammed into the controller 140. In other alternatives, a plurality of predetermined thresholds may be stored with respect to various operating conditions of the machine 100 to enable the controller 140 to extract the ideal set of thresholds to be used based on the detected current operating conditions.For example, the controller 140 of FIG. 2 may communicate with at least the engine 102 and the common bus 116 of the electric drive 104 to monitor instantaneous machine speed and voltage of the bus during normal operation of the machine 100, as shown in FIG. 3. In addition, the control unit 140 may continuously compare the present speed of the engine with the threshold value for the speed of the engine, and also compare the present voltage of the common bus line with the threshold value of the voltage of the common bus line. If both thresholds are reached, for example, if the current speed of the engine falls below the minimum threshold speed and the voltage of the common bus exceeds the maximum threshold voltage, the controller 140 may determine that a potentially unsafe level of electrical power is stored in the common bus 116 without adequate dissipation thereof. Accordingly, as shown in FIG. 3, the controller 140 may continue to discharge the charge on the common bus 116 by activating the generator 112, the drive motor 124, one or more auxiliary devices 126, or a combination thereof. By supplying the voltage of the bus line to the generator 112, the drive motor 124, the HVAC system 128, the high voltage pumps 130 or fans 132, the common bus line 116 may be safely discharged out of the machine 100 while performing typical operations or functions required by the machine 100 or its operator.In the embodiment of FIG. 3, the control unit 140 may be configured to switch the generator (112) to a motor operating mode if the current speed of the engine falls below the minimum speed threshold and the common bus voltage exceeds the maximum voltage threshold. The manner in which the controller 140 activates the motoring mode of operation of the generator 112 may vary based on the configuration and type of generator 112 used. In configurations where the generator 112 is a switched reluctance generator, the controller 140 may activate the motor mode of operation by, for example, inducing a switched electric current in each of the phases of the generator 112 and providing the appropriate pulse sequence to each phase by chopping, pulse width modulation, or any other suitable means known in the art. By diverting the energy stored in the common bus 116 back to the generator 112 and causing the rotor of the generator 112 to rotate, the controller 140 can efficiently discharge the common bus voltage to a safe level. In such a manner, the controller 140 may maintain the generator 112 activated in the motoring mode until one or more of the thresholds are cleared. For example, if the voltage of the common bus line falls below the maximum threshold voltage or if the speed of the engine is determined to exceed the minimum threshold speed, the control unit 140 may stop inducing electric current from the common bus line 116 to the generator 112 and end the motor mode, as shown in FIG. 3. Once the controller 140 completes the motor mode, the controller 140 may return to monitoring the speed of the engine and the common bus voltage. Alternatively, the controller 140 may return to set new thresholds for the speed of the engine and the voltage of the bus line before returning to the step of driving.Industrial applicabilityIn general, the foregoing disclosure finds application in various industrial applications such as agriculture, construction or mining industry by providing more efficient discharging of electrical bus lines in high voltage mobile work vehicles and / or machines, such as tractors, backhoe loaders, compressors, feller-off machines, forest machines, industrial cranes, skid steer loaders, wheel loaders, and the like. The systems and methods disclosed herein discharge the energy stored on electrical bus lines by activating one or more of the existing devices of the machine in a motor mode of operation. Because the electrical bus line can be discharged quickly and technicians can work quickly, the downtime expended for repairs and / or maintenance is significantly reduced. From the foregoing, it will be appreciated that while only certain embodiments have been set forth for purposes of illustration, alternatives and modifications will be apparent to those skilled in the art from the above descriptions. These and other alternatives are considered equivalents and within the scope of the appended claims.

Claims

A method for actively discharging a common bus line (116) of a machine (100) comprising an engine (102), a generator (112), a drive motor (124), and one or more auxiliary devices (126), the method comprising: monitoring a speed of the engine (102) relative to a first lower threshold; monitoring a voltage of the common bus line (116) relative to a second upper threshold; and activating one or more of the generator (112), the motor (124), and the auxiliary devices (126) if the speed of the engine (102) falls below the first lower threshold and if the voltage exceeds the second upper threshold to discharge voltage from the common bus line (116).The method of claim 1, wherein the auxiliary devices (126) comprise one or more of the following: a heating ventilation and cooling system HVAC (128), a high voltage pump (130), a high voltage fan (132), and a discharge resistor (138) to passively discharge electrical energy in the common bus line (116).The method of claim 1, wherein the auxiliary devices (126) comprise a hybrid system (134) for conditioning and storing the voltage discharged into an energy storage device (136) through the common bus line (116).The method of claim 1, wherein the generator (112) is switched to a motor mode of operation if the speed of the engine (102) falls below the first lower threshold and the voltage exceeds the second upper threshold to discharge voltage from the common bus line (116).The method of claim 4, further comprising a step of switching the generator (112) from the motor mode of operation if the voltage of the common bus line (116) falls below the second upper threshold.The method of claim 1, wherein the first lower threshold is based on at least one of a load on the machine (100), a travel speed of the machine (100), and an operator input.The method of claim 1, wherein the generator (112) is a switched reluctance generator.An active discharge system (108) for an engine (100) comprising an engine (102), a generator (112), a drive motor (124), and one or more auxiliary devices (126), the active discharge system (108) comprising: a common bus line (116) in electrical communication with at least one of the generator (112), the drive motor (124), and the auxiliary devices (126) of the engine (100); A controller (140) in electrical communication with at least the engine (102) of the engine (100) and the common bus line (116), the controller (140) being configured to monitor a speed of the engine (102) with respect to a first lower threshold, monitor a voltage of the common bus line (116) with respect to a second upper threshold, and activate one or more of: the generator (112), the motor (124), and the accessories (126) if the speed of the engine (102) falls below the first lower threshold and the voltage exceeds the second upper threshold to discharge voltage from the common bus line (116).The system (108) of claim 8, wherein the controller (140) switches the generator (112) to a motor mode of operation if the speed of the engine (102) falls below the first lower threshold and the voltage exceeds the second upper threshold, and switches the generator (112) from the motor mode of operation if the voltage of the common bus line (116) falls below the second upper threshold.The system (108) of claim 8, wherein the controller (140) is configured to determine the first lower threshold based on one or more current operating conditions of the machine (100) and is configured to determine the second upper threshold based on one or more current operating conditions of the machine (100).

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