HYBRID POWER SUPPLY SYSTEM AND METHOD FOR ITS OPERATION

Abstract

A hybrid power supply system comprises a fuel cell arrangement (2), a battery (4), a power converter unit (3) for selectively supplying an external consumer (5) with electrical energy from the fuel cell arrangement (2) or the battery (4) and for charging the battery (4) with electrical energy from the fuel cell arrangement (2) or regenerated electrical energy from the consumer (5), and a control unit (8) configured to control the power of the fuel cell arrangement (2) and the distribution of electrical energy from the fuel cell arrangement (2) to the battery (4) and the consumer (5) based on a deviation between the actual and target state of charge of the battery (4) and to vary the target state of charge (Q1Q2, Q') as a function of an expected power consumption of the consumer (5).

Description

The present invention relates to a hybrid power supply system, particularly a hybrid power supply system for automotive applications, and an operation method thereof.Such a hybrid power supply system conventionally comprises an arrangement of one or more fuel cells, a tank for supplying the fuel cell arrangement with a power carrier, typically hydrogen gas, a battery, a power converter unit for supplying an external load with electrical energy from the fuel cell arrangement or the battery and for charging the battery with electrical energy from the fuel cell arrangement or regenerated electrical energy from the load, and a control unit which is configured to control the power of the fuel cell arrangement and the distribution of electrical energy of the fuel cell arrangement to the battery and the load on the basis of, inter alia, a deviation between the actual and target state of charge of the battery.Since the electrical energy generated by the fuel cell arrangement is more expensive than grid-bound electrical energy, it is generally not economical, in the case of a power supply system for a motor vehicle, to configure the fuel cell arrangement so powerful that it can permanently cover the energy requirement of the vehicle alone. It is more economical for a user to charge the battery of such a vehicle whenever possible on the grid and to use the fuel cell arrangement only if a route to be traveled exceeds the range that can be achieved with battery operation. By thus making the fuel cell assembly small in size, costs, installation space and weight can be saved on the vehicle.A disadvantage of this approach is that the fuel cell arrangement alone is not capable of satisfying the high demand for tractive force, which may result from a combination of high payload, hill climbing and / or high vehicle speed.Therefore, the battery must compensate for these power gaps. Critical situations occur when the battery cannot be discharged due to thermal constraints or a low state of charge (SOC) of the battery. In such situations, the electrical power of the engine conventionally has to be throttled. This results in lower acceleration or speed of the vehicle and is unsatisfactory for the user of the vehicle.It is therefore an object of the invention to provide a hybrid power supply system in which the likelihood of such limitations is minimized.According to one aspect of the invention, the object is achieved by a hybrid power supply system having a fuel cell arrangement, a battery, a power converter unit for selectively supplying an external load with electrical energy from the fuel cell arrangement or the battery and for charging the battery with electrical energy from the fuel cell arrangement or regenerated electrical energy from the load, and a control unit which is designed to control the power of the fuel cell arrangement and the distribution of electrical energy of the fuel cell arrangement to the battery and the load on the basis of a deviation between the actual and desired state of charge of the battery, and to vary the desired state of charge as a function of an expected power consumption of the load.By increasing the desired state of charge when the high power consumption is expected, the fuel cell arrangement can be put into operation already at a higher state of charge of the battery than at normal or low power consumption, and even if the actual power consumption is constantly higher than that of the power of the fuel cells, the time interval until the battery is discharged, which is obligatory for power restrictions, can be extended and, in the ideal case, delayed until the destination of the journey is reached.In the simplest case, it can be assumed that the user knows the destination and can estimate whether long-lasting operation with high power, for example during highway or hill travel, is required to reach this destination. Therefore, the control unit can be connected to an input means, via which the expected power consumption of the consumer can be specified by the user.If the vehicle has a navigation system into which the user can input a destination in a known manner in order to subsequently be permitted to move to this destination along a route planned by the navigation system, the control unit should be connected to the navigation system and be configured to select the expected power consumption of the consumer on the basis of the route planned by the navigation system.In order to manage without user inputs, the control unit can, according to a preferred embodiment, be connected to an operating state sensor of the consumer and be configured to select the expected power consumption of the consumer on the basis of a measured value of the operating state sensor.As an operating state sensor, in particular in a hybrid power supply system for a motor vehicle, a tachometer, a power meter or a torque sensor is primarily considered. On the basis of the tachometer signal, by evaluating average or peak speeds, it is possible to distinguish between driving in city traffic and on an expressway; a hill approach can be detected on the basis of a torque measured in the drive train or a ratio of drive power to speed. It is also conceivable to detect an acceleration of the vehicle by means of the tachometer and, on the basis of a comparison of this acceleration with an acceleration expected under predefined conditions, for example the road inclination and the vehicle load, to estimate the torque acting in the drive train or to detect a hill approach or a high load of the vehicle and, on the basis thereof, to estimate the expected power consumption of the consumer.In order to avoid abrupt changes in the operating conditions of the fuel cell arrangement, the control unit should be configured to change the power of the fuel cell arrangement continuously and at a rate which does not exceed a predetermined maximum rate. This is also possible indirectly by the setpoint state of charge being changed only continuously and with a limited rate of change.The invention furthermore relates to a motor vehicle having a hybrid power supply system as described above and an electric drive motor which forms at least part of the external load.The object is furthermore achieved by a method for operating a hybrid power supply system having a fuel cell arrangement, a battery, a power converter unit for selectively supplying an external load with electrical energy from the fuel cell arrangement or the battery and for charging the battery with electrical energy from the fuel cell arrangement or regenerated electrical energy from the load, having the steps:estimating an expected power consumption of the load;defining a target state of charge of the battery as a function of the expected power consumption;controlling the power of the fuel cell arrangement on the basis of the desired state of charge.A further subject matter of the invention is a computer program, for example in form stored on a data carrier, comprising computer-executable instructions, the execution of which, by a computer arranged as a control unit in a hybrid power supply system as described above, causes the computer to execute the method defined above.Further features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the appended figures. They show FIG. 1 is a block diagram of a motor vehicle having a hybrid power system; FIG. 2 shows an exemplary characteristic curve of the fuel cell setpoint power as a function of the state of charge of the battery; and FIG. 3 is a flowchart of a process of a control unit of the hybrid power supply system.FIG. 1 shows a schematic of a motor vehicle with a hybrid power supply system. A hydrogen tank 1 is connected in a manner known per se to a fuel cell arrangement 2 for supplying it with hydrogen gas which is reacted in the fuel cells of the arrangement with atmospheric oxygen in order to generate electrical energy.A power converter unit 3 connects the fuel cell arrangement 2 to a battery 4 and to a load 5 in the form of an electric motor 6, which acts on a drive train 7 of the vehicle, and possibly other electrically operated equipment such as infotainment system, windshield wipers, fans or control electronics.The control electronics include, among other things, a control unit 8, the task of which is to control the power of the fuel cell arrangement 2 in such a way that the fuel cell arrangement 2 and the battery 4 meet the demand of the consumer 5 and the state of charge Q of the battery 4 is kept in the vicinity of a predefined setpoint value.During a major part of the operating time, the power consumption of the load 5 is positive; so that if it exceeds the output power of the fuel cell arrangement 2, missing power must be fired from the battery 4. If the power consumption of the consumer is below the output power of the fuel cell arrangement 2, the battery 4 is charged with the excess energy. This also applies to the case of regenerative operation; if the motor operates as a generator during braking or when driving downhill, the power consumption of the consumer 5 is negative, then the battery 4 should be able to absorb this energy. Therefore, the set value for the state of charge of the battery 4 is at least so much smaller than 100% that the battery 4 always has sufficient residual capacity for realistically expected regenerated energy.In the individual case, the control unit 8 determines the setpoint value of the state of charge Q on the basis of at least one of a plurality of criteria. If the vehicle has a navigation system 9, the control unit 8 queries it as to whether a planned route is present, which the vehicle is expected to follow. If so, it can be checked whether a destination or a landing point of the trip is higher by at least a predefined limit value than the height above normal zero at which the vehicle is located at the query time. If so, an above-average power demand on the route is to be expected, and a high setpoint value Q 1 of the state of charge is selected in order to ensure that a driving operation in which the power consumption of the motor is higher than the power of the fuel cell can be maintained for a long time before the battery state of the battery becomes so low that the motor power must be limited. An above-average power requirement on the route can also be assumed when the planned route runs over an expressway and a high driving speed is to be expected.If the difference in elevation is below the limit value, the route does not run on an expressway, or there is no information about a planned route (whether because the user of the vehicle has not entered a destination or because no navigation system is connected to the control unit 8), the control unit 8 refers to information about the current and previous movement states of the vehicle for the decision about a target value of the state of charge. For this purpose, the control unit 8 is connected, for example, to a tachometer 10 and is set up to identify a road currently being traveled as an expressway (and accordingly to select the high setpoint value Q 1 of the state of charge) if a travel speed is measured over a time period of a predefined length of, for example, several minutes, which travel speed is above the maximum speed permissible for traffic on expressways.Furthermore, the control unit 8 can be connected to a torque sensor 11 on the drive train 7 in order to compare the torque occurring there with a stationary torque required for driving at constant speed on a level route. Torque peaks associated with accelerating the vehicle may last only a short time until a target speed is reached. If a high torque clearly exceeding the steady-state torque is measured over a longer time, for example more than a few 10 s, this is attributable to hill climbing, and the high setpoint value Q 1 of the state of charge is selected.In all other cases, the control unit selects a low set point Q 2 of the state of charge.Alternatively, the control unit 10 can estimate the torque in the drive train 7 on the basis of a known relationship between the power consumption of the electric motor 6, the speed of the vehicle detected by the tachometer 10 and the torque generated by the electric motor 6. Based on the ratio between this torque and the acceleration of the vehicle resulting therefrom, an uphill travel can be detected and the setpoint value of the state of charge can be selected accordingly, as described above.It is also conceivable to estimate the charge of the vehicle on the basis of the ratio between the torque of the engine 6 and an acceleration (or, in the case of recuperation operation, deceleration) of the vehicle resulting therefrom and to select the high setpoint value Q 1 of the charge state if the estimated charge is above a predefined limit value.Input means 12 such as a switch may be provided on the dashboard of the vehicle, allowing a user of the vehicle to replace an automatically made selection of the set point as described above with his own selection. Since the driver of the vehicle can know about an imminent gradient or expressway route even if no data from a navigation system is present or before measurements make it possible for the control unit 8 to identify such a route, the driver can already make a suitable selection Q 1 or Q 2 for the setpoint value of the state of charge at an earlier point in time. Likewise, he can correct a decision of the control unit to boost the setpoint value of the state of charge via the input means 12 if he knows that the route conditions which the control unit 8 has caused to make the decision will no longer apply in the short time.FIG. 2 shows an exemplary characteristic curve C 2 of the relationship between the state of charge of the battery 4 and the setpoint power of the fuel cell arrangement 2 predefined by the control unit 8 as a function of this state of charge. At a low state of charge, between 0 and approximately 40% of the charging capacity, the fuel cell arrangement 2 is operated with maximum power in order to avoid a critically low state of charge being reached when the power demand of the consumer 5 is constantly high, in which state of charge the power available for the consumer 5 has to be throttled under the need of the consumer 5 in order to protect the battery 4, or to delay such a situation at least for as long as possible. In a middle range of the state of charge, here between about 40% and about 55%, the sol power is a linearly decreasing function of the state of charge; with an even higher state of charge, the dependence of the sol power on the state of charge decreases ever further and finally reaches the value zero at about 90%. A setpoint value of the state of charge cannot be read unambiguously from this curve; the setpoint value of the state of charge can be considered here to be that state of charge which is set in the long term during driving under standardized conditions, e.g. on a level roadway at a predefined speed. For purposes of this description, it may be assumed that the set point for the characteristic Q shown is 2= 50%.The characteristic curve C 1 is obtained from the characteristic line C 2 by shifting to the right, here, for example, by 20 percentage points of the state of charge scale. It can be directly understood that if instead of the characteristic curve C 2 the characteristic curve C 1 were used as the basis for the control of the fuel cell arrangement 2, this would correspond to a setpoint value Q 1= 70%.FIG. 3 is a flowchart showing a process of the control unit 8, in which two processes are cyclically repeated. The first process is for setting a target value for the charge state of the battery 4; in step S 1, the speed is sensed by the sensor 10, and the torque is sensed by the sensor 11 or calculated on the basis of motor power and acceleration as described above. In step S2, it is determined whether a target value, Q 1 or Q 2, is input by the driver at the input means 12. If yes, the selected value is transmitted to the second process (S 5). If no, it is checked (S3) whether route data are available from a navigation system 9 and selection of the target value is possible from these as explained above. If yes, the selected value is also transmitted to the second process (S 5). Otherwise, the control unit makes a decision about the setpoint value (S 4) on the basis of torques and speeds measured in the current and previous iterations in step S 1 and transmits this to the second process (S 5).The second process may be repeated at shorter time intervals than the first. Step S11 compares the target value Q 1 or Q 2 transmitted from the first process with a current target value Q* of the second process, and if both differ, corrects the target value Q* of the second process by a predetermined increment or decrement toward the transmitted target value. Transferred to the diagram of FIG. 2, this corresponds to the shift of a characteristic curve C currently used for the control of the fuel cell arrangement 2, provided it does not already correspond to C 1 or C 2 by a predefined step width in the direction of one of these two characteristic curves C 1 or C 2. It is thus achieved that, if a new setpoint value is established in the first process, the setpoint value Q* used in the second process for controlling the charging of the battery 4 is not adapted immediately, but rather gradually matches the new setpoint value over the course of a plurality of iterations at a predefined rate of change.In step S12, the control unit 8 uses a suitable measuring instrument 13 to determine the current state of charge Q' of the battery 4; in step S13, a setpoint power P' of the fuel cell arrangement 2 is assigned to this state of charge Q' on the basis of the characteristic curve Q*, which may be updated in S11, and is output to the fuel cell arrangement 2.Reference numerals denote reference numerals1 Tank 2 Fuel cell arrangement 3 Power converter unit 4 Battery 5 Load 6 Electric motor 7 Drive train 8 Control unit 9 Navigation system 10 Tachometer 11 Torque sensor 12 Input means 13 Measuring instrument

Claims

Hybrid power supply system having a fuel cell arrangement (2), a battery (4), a power converter unit (3) for supplying an external load (5) with electrical energy from the fuel cell arrangement (2) or the battery (4) and for charging the battery (4) with electrical energy from the fuel cell arrangement (2) or regenerated electrical energy from the load (5), and a control unit (8) which is configured to control the power of the fuel cell arrangement (2) and the distribution of electrical energy of the fuel cell arrangement (2) to the battery (4) and to the load (5) on the basis of a deviation between the actual and desired state of charge of the battery (4), characterized in that the control unit (8) is configured to control the desired state of charge (Q 1 Q 2, q') as a function of an expected power consumption of the load (5).Hybrid power supply system according to Claim 1, in which the control unit (8) is connected to an input means (12) via which the expected power consumption of the load (5) can be specified by a user.Hybrid power supply system according to Claim 1 or 2, in which the control unit is connected to an operating state sensor (10, 11) of the load (5) and is configured to select the expected power consumption of the load on the basis of a measurement value of the operating state sensor (10, 11).The hybrid power supply system of claim 3, wherein the operating condition sensor is a tachometer (10), a power meter, or a torque sensor (11).Hybrid power supply system according to one of the preceding claims, in which the control unit (8) is connected to a navigation system (9) and is set up to select the expected power consumption of the load (5) on the basis of a route planned by the navigation system (9).Hybrid power supply system according to one of the preceding claims, in which the control unit (8) is configured to change the desired state of charge (Q 1 Q 2, Q') or the power (P') of the fuel cell arrangement (2) continuously and at a rate which does not exceed a predefined maximum rate.Motor vehicle having a hybrid power supply system according to one of the preceding claims and an electric drive motor (6) which forms at least part of the external load (5).Method for operating a hybrid power supply system having a fuel cell arrangement (2), a battery (4), a power converter unit (3) for selectively supplying an external load (5) with electrical energy from the fuel cell arrangement or the battery (4) and for charging the battery (4) with electrical energy from the fuel cell arrangement (2) or regenerated electrical energy from the load (5), having the steps: - estimating (S1-S5) an expected power consumption of the load; - defining (S12) a setpoint state of charge (Q') of the battery (4) as a function of the expected power consumption; - regulating (S13) the power of the fuel cell arrangement (2) on the basis of the setpoint state of charge.A computer program comprising computer executable instructions, execution of which by a computer arranged as a controller (8) in a hybrid power supply system according to any one of claims 1 to 7 causes the computer to carry out the method of claim 8.

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