AND A MINING VEHICLE

F1ELD OF THE INVENTION

The invention relates to a system and method for supplying electric energy to a mining vehicle and a mining vehicle.

BACKGROUND OF THE INVENTION

Underground mining vehicles require high power during their use. lf electric energy is used for supplying the mining vehicles, the voltage level of the components should not be very high because high voltage level requires large clearances and insulations, for example. This leads to large, complicated, and ex pensive components. Typically, the mining vehicles should, however, be as com pact as possible. On the other hand, lower voltage level causes that the currents in the system rise. High current requires thick conductors, for example, in the supply system and in the mining vehicle thereby raising the costs. BR1EF DESCRIPTION [D1SCLOSURE] OF THE INVENTION

An object of the invention is to provide a new system, method and a mining vehicle. The invention is characterized by what is stated in the independ ent claims. Some embodiments of the invention are disclosed in the dependent claims.

ln the presented solution electric energy is supplied to a mining vehi cle using a system comprising a bipolar LVDC supply having a certain total volt age. The mining vehicle comprises at least a first energy unit and a second energy unit. The first energy unit is connected to a part of said certain total voltage and the second energy unit is connected to another part of said certain total voltage. Thereby the components of the first and second energy unit need to tolerate a voltage level that is only a part of the total voltage. However, bipolar LVDC supply supplies power on the total voltage to the mining vehicle whereby the supplied power may be high although the current is moderate.

According to an embodiment, the bipolar LVDC supply comprises a positive pole and a negative pole and a neutral point between the positive pole and the negative pole. The first energy unit may be connected between the posi tive pole and the neutral point and the second energy unit may be connected be tween the negative pole and the neutral point. Thereby the voltage balance is reli able in the mining vehicle. According to another embodiment, the bipolar LVDC supply comprises a first converter and a second converter connected in series. The converters may be used for keeping the voltage balanced in both halves of the mining vehicle lt is possible to arrange the neutral point between the first and second converters.

According to another embodiment, the first energy unit and the second energy unit comprise traction motors of the mining vehicle.

According to another embodiment, the first energy unit and the second energy unit comprise batteries and the mining vehicle comprises connecting means and a control unit. The control unit may be arranged to connect the batter ies in parallel in drive mode and arranged to connect the batteries in series in charge mode ln drive mode the connect in parallel means that the voltage level required for the vehicle DC-bus and the components in the vehicle is rather low. ln charge mode a higher charging voltage is supplied. This allows for a use of a simple and cheap plug-socket connection and smaller and lighter cables for high power fast charging.

BR1EF DESCRIPTION OF THE DRAW1NGS

ln the following the invention will be described in greater detail by means of embodiments with reference to the attached drawings, in which

Figure 1 is a schematic of an electric system of a mining vehicle;

Figure 2 is a schematic showing how to connect the batteries of the mining vehicle;

Figure 3 is a schematic of another electric system of a mining vehicle; and

Figure 4 is a schematic of another embodiment how to connect the batteries of the mining vehicle.

DETA1LED DESCRIPTION OF THE INVENTION

Figure 1 shows a schematic of an electric system of a mining vehicle. The mining vehicle may be a dump truck, a LHD (load-haul-dump vehicle), an un derground mining truck or a drill rig, for example.

Reference numeral 1 depicts a bipolar LVDC (low voltage direct cur rent) supply ln the embodiment shown in Figure 1 the total voltage of the bipolar LVDC supply is 1500 V. However, the total voltage may be lower or higher than that, such as 400 V, 800 V, 1000 V or 5 kV. However, a voltage level of 1500 V or less is advantageous because such voltage level is still considered as low voltage according to the 1EC rules and the European Union directive 2014/35/EU i.e. low voltage directive, for example. Higher voltage would result in requirements with larger clearances etc. leading to larger, complicated and expensive components.

The mining vehicle comprises connectors 2a and 2b for connecting the mining vehicle to the bipolar LVDC supply 1. The connectors 2a and 2b may be trolley connections connecting the mining vehicle to a trolley line, for example. Further, the connectors 2a and 2b may be a charging connector/coupler of a charging device, for example. The connectors 2a and 2b may be separate connect ors or connected to the same charging connector/coupler.

Reference numerals 3a, 3b and 3c depict the DC bus of the mining ve hicle. 3a is the positive pole bus bar, 3b is the negative pole bus bar and 3c is the neutral or 0V bus bar. The total voltage of the bipolar LVDC supply is divided in to two halves that are substantially equal. Thus, if the total voltage of the bipolar LVDC supply is 1500 V, for example, in the mining vehicle the total voltage is sep arated to two halves to comprise +750 V, 0 V and -750 V levels.

The mining vehicle comprises a first traction battery 4a and a second traction battery 4b. The traction batteries 4a and 4b may be used as a power source when the mining vehicle is used without a contact to the outside power supply, thus, outside of a trolley line, for example.

For connecting the traction batteries 4a, 4b to the DC bus of the mining vehicle, DC/DC converters 5a, 5b may be used. The first traction battery 4a is connected to a first part of the total voltage and the second traction battery 4b is connected to another part of the total voltage.

The DC/DC converters 5a, 5b are not necessary for connecting the traction batteries 4a, 4b to the DC bus of the mining vehicle. This is the case when an external charger is used providing that the charger itself controls its voltage, for example.

The mining vehicle further comprises a first traction motor 6a and a second traction motor 6b. The mining vehicle may comprise two separate traction motor drives, that is one traction motor drive per axle. The two traction motor drives may also be connected together into a summation gear.

The first traction motor 6a is connected to the first part of the total voltage and the second traction motor 6b is connected to the another part of the total voltage. The traction motors 6a and 6b are connected to the DC bus of the mining vehicle with inverters 7a and 7b.

According to an embodiment, the mining vehicle may comprise a plu rality of wheel hub motors, that is a plurality of traction motors. Each wheel may comprise a wheel hub motor ln such case, a four-wheel mining vehicle comprises four wheel hub motors or traction motors, for example lf the mining vehicle comprises more than four wheels, the mining vehicle may also comprise more than four wheel hub motors. The mining vehicle may also comprise odd number of wheel hub motors ln the mining vehicle the first energy unit connected to a part of said certain total voltage of the bipolar LVDC supply may comprise one or more traction motors such as wheel hub motors and the second energy unit con nected to another part of said certain total voltage of the bipolar LVDC supply may comprise one or more traction motors such as wheel hub motors.

The mining vehicle further comprises a first brake resistor 8a and a second brake resistor 8b. The brake resistors 8a and 8b may be connected to the DC side of the inverters 7a and 7b.

lt is advantageous to keep the voltage balanced in both halves. When the mining vehicle is disconnected from the LVDC supply and energy is supplied from the batteries, it is possible that the traction motors 6a and 6b experience different loads at the same time, which can cause voltage imbalance in the DC bus. This voltage imbalance may be prevented or decreased with the DC/DC convert ers 5a and 5b connected to each DC bus halves and charging or discharging the batteries 4a and 4b.

Additionally, the brake resistors 8a and 8b may be switched to each DC bus halves to maintain the voltage symmetry. The brake resistors 8a and 8b may be used for maintaining the voltage symmetry during downhill drive, especially.

Figure 2 shows a schematic how to connect the batteries of the mining vehicle. The electric system of the mining vehicle may comprise two or more even numbered amount of batteries ln drive mode of the mining vehicle, the batteries are connected in parallel ln charge mode of the mining vehicle, the batteries are connected in series.

The contactors Kl, K2, K4, K5, K6, K7 and K8 are connecting means that are used for providing the connecting in parallel and the connecting in series. Contactor Kl is a positive pole charging contactor and contactor K2 is a negative pole charging contactor. Contactors K4 and K6 are used for positive pole discon nection for charging busbars. Contactors K5 and K7 are used for negative pole disconnection for charging busbars. Contactor K8 is a neutral pole connection device for charging busbars.

The control unit 9 controls the contactors. The battery energy for use is taken from the drive mode output 9 depicted in the Figure 2. Referring to the Figure 2, while batteries are parallel-connected, the charging contactors Kl, and K2 are open (not contacting), contactors K4, K5, K6, and K7 are closed (contacting), and K8 is open (not contacting).

To ready the batteries for bipolar charging, contactors K4, K5, K6, and K7 are opened (break contact), after which the contactor K8 is closed (make con tact). When charging is started, the contactors Kl and K2 are closed (make con tact).

lt should be noted that the bipolar charging of the batteries does not necessarily require a neutral point connection from the charging system because the batteries are normally parallel-connected and share the same SOC and volt age. The neutral point N is at 0V inherently.

Figure 3 shows a solution similar to shown in Figure 1 but with an im provement relating to voltage balance ln addition to the positive pole connector 2a and the negative pole connector 2b, the mining vehicle comprises a neutral point connector 2c. The neutral point connector 2c connects the centreline or 0 V or neutral point of the bipolar LVDC supply 1 to the mining vehicle.

The improved voltage balance using the neutral point in the LVDC supply is advantageous especially if the mining vehicle comprises odd number of traction motors, for example. Further balancing may be performed using the brake resistors 8a, 8b and/or DC/DC converters 5a, 5b.

The bipolar LVDC supply 1 is supplied from an electric grid 11. The bi polar LVDC supply 1 may comprise a transformer 12. ln Figure 3 the transformer 12 comprises two secondaries 12a, 12b. According to an embodiment the number of secondaries of the transformer 12 is one. According to another embodiment the number of the secondaries of the transformer 12 is more than two.

The bipolar LVDC supply 1 further comprises a first converter 13a and a second converter 13b. The first converter 13a and the second converter 13b are connected in series whereby the neutral point is arranged between the first and second converters. Thereby the centerline of the mining vehicle is effectively bal anced and thus the voltage balance is maintained on a high level.

lnstead of the converters in series, as shown in Figure 3, the bipolar LVDC supply with the neutral point may also be provided using one converter ln such case the converter may be a three level NPC (Neutral-Point-Clamped) in verter, for example.

Figure 4 shows a solution where the improvement relating to voltage balance is implemented in a manner similar to the solution in Figure 3. ln addition to the positive pole charging contactor K1 and the negative pole charging contac tor K2 the mining vehicle comprises a neutral pole charging contactor K3.

ln the solution shown in Figure 2 different voltage levels in the batter ies 4a and 4b would cause that the point between the batteries would not be neu- tral (0 V). However, the solution shown in Figure 4 provides for the voltage bal ance and thereby protects the charger itself, for example.

According to an embodiment the mining vehicle may comprise a three level NPC inverter or any other multi level inverter for driving a motor having a higher voltage level. Such a motor may be connected between the positive pole and the negative pole and possibly to the neutral pole, also.

Thus, an energy unit may be connected between the positive pole and the negative pole with neutral connection using a three level NPC inverter, for example lf such an energy unit is bipolar as such and comprises a neutral point or it comprises components connected in series over which the voltage divides natu- rally, the components of the energy unit need to tolerate a lower voltage, only. Thus, the energy unit connected to a part of said certain total voltage may com prise a traction motor and/or a battery and/or any other electrical component.

lt will be obvious to a person skilled in the art that, as technology ad vances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.