MOTOR VEHICLE WITH HYBRID POWER SUPPLY SYSTEM AND METHOD FOR OPERATION THEREOF

Abstract

A motor vehicle has an electric drive motor (6), an input instrument (9) for inputting a power request from the drive motor (6) by a driver, and a hybrid power supply system. The hybrid power supply system comprises a fuel cell arrangement (2), a battery (4), a power converter unit (3) for supplying a consumer (5), formed at least partially by the motor (6), 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) which is 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 charge state of the battery (4).The control unit (8) is connected to the input instrument (9) and is configured to vary the target charge state (Q1, Q2, Q') as a function of the power requirement (ϑ).

Description

The present invention relates to an automobile having a hybrid power supply system 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 system motor vehicle in which the likelihood of such limitations is minimized.According to one aspect of the invention, the object is achieved by a motor vehicle having an electric drive motor, an input instrument for inputting a power demand of the drive motor by a driver, and a hybrid power supply system, wherein the hybrid power supply system comprises 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 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 a deviation between the actual and desired state of charge of the battery, and is connected to the input instrument, typically an accelerator pedal, in order to vary the desired state of charge as a function of the power requirement.When the accelerator pedal is actuated, the driver intuitively takes into account a requirement for traction and the expected acceleration behavior that is variable depending on the road gradient and surface properties, vehicle load, etc.; as a result, although it is variable in the short term, it reflects a drive load to be expected and can be used to increase the setpoint state of charge when the load is high to be expected and thus to ensure that the power supply system maintains a high-load state for a long time before the battery is discharged to such an extent that the power must be reduced.Due to variability in the actuation of the input instrument, varying the desired state of charge should be based on a moving average of the power demand or a magnitude derived from the power demand.The duration of a time period over which the moving average value is formed can be a few 10 s to a few minutes, in particular approximately 60 s.According to the distinction between operation of the vehicle with normal and with increased power demand, the control unit can be configured to switch between two stationary desired states of charge, a high and a low as a function of the power demand.In order to bring about a gradual transition between the two and to avoid inefficient, abrupt changes in the operating conditions of the fuel cell arrangement, it can be provided that the control unit controls the operation of the battery on the basis of non-stationary target states of charge, the values of which lie between those of the high and the low target state of charge, during a changeover between the stationary target states of charge. That is to say, while the control unit can maintain the stationary target states of charge for arbitrarily long times, provided that the driver's power demand permits this, the non-stationary target states of charge are only possible temporarily, in the course of the changeover from one stationary target state of charge to the other.The decision as to which of the stationary target states of charge is to be used can be based on a comparison of the moving average value with a limit value. In particular, the control unit can be configured to change to the high desired state of charge if the moving average value rises above a first limit value and to change to the low desired state of charge if the moving average value falls above a second limit value. If the first limit value is greater than the second limit value by a hysteresis value, a threshold value which reduces the number of switching processes and thus the proportion of less efficient transient operating phases can be kept small.The object is furthermore achieved by a method for operating a motor vehicle having an electric drive motor, an input instrument for inputting a power demand of the drive motor by a driver, and a hybrid power supply system, wherein the hybrid power supply system comprises a fuel cell arrangement, a battery, a power converter unit for selectively supplying an at least partially motor-formed 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:detecting a power request input from the driver via the input instrument;varying a desired state of charge of the battery as a function of the power demand;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 supply system; FIG. 2 is a flowchart of a process of a control unit of the hybrid power supply system; and FIG. 3 shows an exemplary characteristic curve of the fuel cell setpoint power P as a function of the state of charge Q of the battery.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.During travel, the control unit 8 determines the setpoint value of the charge state Q continuously on the basis of the position of an accelerator pedal 9 actuated by the driver by cyclic repetition of the method of FIG. 2.In step S 1, the control unit 8 queries the current displacement θ of the accelerator pedal, stores the obtained displacement value and calculates (S 2) an average value θ≅from this and displacement values stored from previous iterations of the last 60 s.In S 3, the average value θξ is compared with an upper limit value θ 1. If this is exceeded, then a high value Q 1 is set as a target setpoint value Q T of the state of charge of the battery 4 (S 4); otherwise, the method branches to step S 5.In S 5, the average value θξ is compared with a lower limit value θ 2. If this value is undershot, then a low value Q 2 is set as the target setpoint value of the state of charge of the battery 4 (S 6); otherwise, the setpoint value remains unchanged with respect to the previous iteration.The setting of the target setpoint value in steps S 4 and S 6 is not to be understood as meaning that it would have to be changed; the target setpoint value set in the previous iteration can also be confirmed unchanged.In S 7, an instantaneous setpoint value Q M still stored from the previous iteration is compared with the target setpoint value Q T. If both are identical, the instantaneous setpoint value Q M remains unchanged. If they are different, the present target value Q M is approximated to the target target value Q T by a predetermined increment ΔQ (S8). Thus, in the event of a change in the target set value, the instantaneous set value Q M gradually and delayedly matches it.In step S 9, the control unit 8 determines the current state of charge Q of the battery 4 via any suitable measuring instrument 10.FIG. 3 shows as characteristic curve C 2 a conventional relationship between the state of charge of the battery 4 and the nominal power of the fuel cell arrangement 2 predefined by a conventional control unit not taking into account the power requirement of the driver 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 that, at a continuously high power requirement of the consumer 5, a critically low state of charge is achieved in which 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 control unit 8 according to the invention selects (S 11) the characteristic curve C 2 for defining the power of the fuel cell arrangement as a function of the state of charge Q if the power demand of the driver is low and the instantaneous setpoint value Q M is equal to Q 2 (S 10).A second characteristic curve C 1 in FIG. 3 is obtained from the characteristic curve C 2 by shifting to the right, here, for example, by 20 percentage points of the state-of-charge scale Q. 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%. Therefore, the control unit 8 uses the characteristic line C 1( S 13) when the driver's power demand is high and the current target value Q M is Q 1 (S 12).As described above in connection with step S8, the present target value Q M may temporarily assume non-stationary values between these two extremes besides the stationary values Q 1 and Q 2 as well.When the present target value Q M is between Q 1 and Q 2 the control unit 8 generates a temporary characteristic curve C by shifting the characteristic curve C 1 or C 2 along the Q axis in the graph of FIG. 3 so that the power value at which the curve C 2 becomes the target value Q 2( or the curve C 1 becomes the target value Q 1) at the temporary characteristic curve C corresponds to the present target value Q M (S14).From the characteristic curve thus obtained, in S 15, the value of the power P is determined, which corresponds to the state of charge Q detected in S 9, and the fuel cell arrangement 2 is controlled in order to supply this power P.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 Accelerator pedal 10 Measuring instrument

Claims

Motor vehicle having an electric drive motor (6), an input instrument (9) for inputting a power demand of the drive motor (6) by a driver, and a hybrid power supply system, wherein the hybrid power supply system comprises a fuel cell arrangement (2), a battery (4), a power converter unit (3) for supplying an electrical energy from the fuel cell arrangement (2) and / or the battery (4) to a load (5) formed at least in part by the motor (6), and for charging the battery (4) with electrical energy from the fuel cell arrangement (2) and / or regenerated electrical energy from the load (5), and a control unit (8) which is configured to, 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 the desired state of charge of the battery (4), characterized in that the control unit (8) is connected to the input instrument (9) and is configured to vary the desired state of charge (Q 1, Q 2, Q') as a function of the power requirement (θ).Motor vehicle according to claim 1, wherein the function of the power requirement (θ) comprises forming a moving average (θ≅) of the power requirement or a quantity derived from the power requirement (θ).Motor vehicle according to Claim 2, in which a time period over which the moving average value (θ≅) is formed has a duration of a few 10 s to a few minutes, in particular approximately 60 s.Motor vehicle according to one of the preceding claims, in which the control unit (8) is configured to switch between two stationary desired states of charge, a high state of charge (Q 1) and a low state of charge (Q 2), as a function of the power request (θ).Motor vehicle according to Claim 4, in which the control unit (8) is configured to control (S14, S15), during a changeover between the stationary desired states of charge (Q 1, Q 2) the operation of the battery (4) on the basis of non-stationary desired states of charge (Q M) the values of which lie between those of the high (Q 1) and of the low desired state of charge (Q 2).Motor vehicle according to claim 2 or 3 and claim 4 or 5, wherein the control unit (8) is configured to change to the high desired state of charge (Q 1) if the moving average (θ≅) increases above a first limit value and to change to the low desired state of charge (Q 2) if the moving average falls above a second limit value, optionally wherein the first limit value is greater than the second limit value by a hysteresis value.Method for operating a motor vehicle having an electric drive motor (6), an input instrument for inputting a power request of the drive motor (6) by a driver, and a hybrid power supply system, wherein the hybrid power supply system comprises a fuel cell arrangement (2), a battery (4), a power converter unit (3) for supplying an electrical energy from the fuel cell arrangement or the battery (4) to a load (5) formed at least in part by the motor (6), 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: - detecting (S1) a power request input by the driver via the input instrument; varying (S 10-S 14) a setpoint state of charge (Q M) of the battery (4) as a function of the power demand; regulating (S 15) 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 6 causes the computer to carry out the method of claim 7.

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