Method for operating an electric vehicle and electric vehicle

Abstract

The present invention relates to a method for operating an electric vehicle and an electric vehicle, the electric vehicle comprising: a first energy storage device, which is in particular designed as a rechargeable battery device; a second energy storage device, which is in particular designed as a double-layer capacitor device and / or is in particular capable of being charged and discharged faster than the first energy storage device; an energy supply unit, which in particular intermittently provides energy for charging the first energy storage device and / or the second energy storage device; a first electrical consumer, which is connected to the second energy storage device via an intermediate circuit; wherein an intermediate circuit voltage is present in the intermediate circuit; wherein the first energy storage device is connected to the energy supply unit via a bidirectional converter device; wherein the second energy storage device is connected to the energy supply unit; wherein a first power flow occurs from the first energy storage device to the second energy storage device when the intermediate circuit voltage drops below a definable voltage; and wherein a second power flow from the second energy storage device to the first energy storage device is prevented, in particular prevented at all times.

Description

Technical Field

[0001] The invention relates to a method for operating an electric vehicle and an electric vehicle. Background Art

[0002] Preferably, the unmanned, mobile assistance system is provided as an electric vehicle. Alternatively, such a vehicle may also be referred to as an unmanned guided vehicle (FTF) or an AGV (automated guided vehicle).

[0003] Document DE 10 2007 002 242 A1 discloses an unmanned transport vehicle for transporting goods. This type of load transport can be described as an intralogistics application. The unmanned transport vehicle is powered inductively.

[0004] Document DE 195 45 544 A1 discloses a front-end transport rail system that supplies electrical energy to vehicles via contact wires. To enable operation without an external energy source, electrolytic capacitors or gold capacitors (also known as supercapacitors, supercapacitors, or double-layer capacitors) are proposed as the energy source.

[0005] US Pat. No. 6,265,851 B1 discloses a supercapacitor energy supply for an electric vehicle, which has two energy storage devices that can be used selectively to drive the vehicle.

[0006] EP 2 419 364 A1 discloses an unmanned transport system having two energy storage devices (a double-layer capacitor device and a battery device). In normal operation, the double-layer capacitor device supplies energy to the drive device, ie, the electric motor.

[0007] In an emergency, that is, when the voltage in the double-layer capacitor device drops below a certain level, the device switches to battery operation. The drive device is then powered solely by the battery device until the double-layer capacitor device is recharged at a charging station.

[0008] DE 10 2017 005 153 A1 discloses a method for operating an electric vehicle and an electric vehicle, wherein the vehicle has a hybrid storage device and a double-layer capacitor device. Both storage devices can optionally provide energy for a traction drive.

[0009] A charging station and a corresponding electric vehicle are known from US 2008 277 173 A1. Summary of the Invention

[0010] The object of the present invention is to improve and optimize the energy management of an electric vehicle, in particular a driverless mobility assistance system, having two different types of energy storage devices.

[0011] According to the invention, this object is achieved with respect to a method for operating an electric vehicle and with respect to an electric vehicle according to the features described below.

[0012] An important feature of the present invention in a method for operating an electric vehicle, in particular an unmanned mobility assistance system (MAS) for intralogistics applications, is that the vehicle has: a first energy storage device, which is in particular designed as a rechargeable battery energy storage device; a second energy storage device, which is in particular designed as a double-layer capacitor device and / or can be charged and discharged faster than the first energy storage device; an energy supply unit, which in particular intermittently provides energy for charging the first energy storage device and / or the second energy storage device; and a first electrical consumer, in particular for driving the vehicle. A travel drive or a lifting device or an operating device or a transport device; wherein a first electrical consumer is connected to a second energy storage device via an intermediate circuit, wherein an intermediate circuit voltage is present in the intermediate circuit, wherein the first energy storage device is connected to an energy supply unit via a bidirectional converter device, wherein the second energy storage device is connected to the energy supply unit, wherein a first power flow from the first energy storage device to the second energy storage device occurs when the intermediate circuit voltage drops below a definable / predeterminable voltage, wherein a second power flow from the second energy storage device to the first energy storage device is prevented, in particular prevented at all times.

[0013] In other words, two energy storage devices are used to supply energy to the electrical consumers. The second energy storage device is directly connected to the electrical consumers via a so-called intermediate circuit. Advantageously, multiple electrical consumers can also be connected to the second energy storage device via the intermediate circuit. The electrical consumers are thus connected in parallel to the second energy storage device. The second energy storage device supplies the required energy to one or more electrical consumers, but it can also absorb energy fed back by one or more electrical consumers. By preventing power flow from the second energy storage device to the first energy storage device at all times, it is ensured that the energy stored in the second energy storage device is only available to the vehicle's electrical consumers. This prevents equalization charging from the second energy storage device to the first energy storage device at all times. As soon as the voltage in the intermediate circuit drops below a defined voltage, the first energy storage device is used to charge the second energy storage device. In this case, power flows from the first energy storage device to the second energy storage device. The first energy storage device advantageously has a larger capacity than the second energy storage device, thereby compensating for the second energy storage device's lower energy content. The second energy storage device is advantageously dimensioned so that it can buffer brief power peaks from the electrical consumers. The first energy storage device is dimensioned for the continuous, ie average, power consumption of the electrical consumer.

[0014] This has the advantage that the second energy storage device is always charged at least to a definable voltage, ie always has an at least definable energy content.

[0015] The second energy storage device is advantageously designed as a double-layer capacitor device and / or can be charged and discharged more quickly than the first energy storage device. Double-layer capacitor devices are characterized by being able to charge within seconds and fully discharge to zero voltage. They have a cycling stability in the range of one million cycles, meaning they have a very high number of charge / discharge cycles. Therefore, they are advantageously suitable for providing peak power to electrical consumers in electric vehicles.

[0016] The first energy storage device is advantageously designed as a battery energy storage device. A battery energy storage device can be charged and discharged more slowly than a double-layer capacitor device, which is an advantageous embodiment of the second energy storage device. Advantageously, the first energy storage device has a higher energy density and actually has a lower power density and a lower number of charge / discharge cycles than the second energy storage device. An example of a battery energy storage device is a device consisting of one or more secondary electrochemical elements, in particular nickel-based and / or iron-based. Such a secondary electrochemical element comprises a negative electrode, a positive electrode, a porous diaphragm separating the negative electrode and the positive electrode from each other, and an in particular aqueous alkaline electrolyte, with which the electrodes and the diaphragm are impregnated. Such a nickel-based and / or iron-based secondary electrochemical element can provide high pulse currents very quickly, like a capacitor, but in other respects exhibits more battery properties, in particular the capacitor equations Q=CU and W=1 / 2CU 2 This is not applicable to this battery energy storage device. This battery energy storage device has high cycle stability. This cycle stability ranges between 1,000 and 20,000. Therefore, more frequent charge and discharge cycles can be performed before the power requirements of the battery energy storage device are no longer met. Furthermore, this battery energy storage device has overcharge and overdischarge stability. It can be fast-charged at up to 15C. Another example of a battery energy storage device is a lithium-ion battery.

[0017] In an advantageous embodiment, the first electrical consumer is a traction drive for driving movement, in particular traction, of the vehicle or a lifting device or an operating device.

[0018] These consumers here each include, by way of example, a drive motor, in particular a three-phase AC motor, which is supplied with a three-phase voltage by an inverter. The inverter is in turn connected to the intermediate circuit and converts the DC voltage into a three-phase current.

[0019] In an advantageous embodiment, the energy supply unit is supplied with energy in a contact- or contactless manner.

[0020] In the case of a contact-based energy supply, it is advantageous that the energy storage device can be easily charged, for example by means of a plug.

[0021] In contactless energy supply, the advantage is that the energy storage device can be reliably charged, for example, by induction. In one advantageous embodiment, the energy supply unit includes a rectifier that is supplied by the secondary inductance of the electric vehicle. In particular, the rectifier connects capacitors in series or parallel so that the resonant frequency of the resulting resonant circuit is equal to the frequency of the alternating current applied to the stationary primary inductance. Inductive energy transmission also increases safety, and the wear of the charging contacts that would otherwise be required is eliminated. Furthermore, a contact-proof design can be easily implemented.

[0022] In an advantageous embodiment, the energy supply unit is supplied with energy intermittently during driving.

[0023] The advantage here is that energy can be supplied over a portion of the travel route, allowing both energy storage devices to be recharged or kept fully charged, thus extending their lifespan because they undergo as few complete charging cycles as possible, and in particular, are not frequently fully charged or discharged. This reduces aging. The energy supply can, for example, be carried out contact-free via a contact wire. Alternatively, a stationary primary conductor can be arranged along the travel route, via which the energy is inductively transferred to a secondary inductor arranged in the electric vehicle.

[0024] In an advantageous embodiment, the second energy storage device has a charge completion voltage and a discharge completion voltage, wherein the value of the definable voltage is greater than the value of the discharge completion voltage and less than the value of the charge completion voltage.

[0025] Advantageously, the electrical consumer can be dimensioned for a definable voltage value. This definable voltage value can also be referred to as the switching point. This is the point at which the first energy storage device is used to supply energy to the intermediate circuit or the second energy storage device in order to maintain the voltage at the definable voltage value. This has the advantage that, at the same power, the electrical consumer must consume less current, so the electrical consumer can be dimensioned for a smaller maximum current and a smaller operating voltage range. Consequently, when an electric motor is used as the electrical consumer, the motor can be mechanically designed to be smaller, meaning that a smaller motor size can be used.

[0026] Typical values ​​of the charge completion voltage U1 and the discharge completion voltage U3 are U1 = 360 V and U3 = 120 V. Assuming that only the second energy storage device is used and the maximum allowable current for the electrical consumer is I V,max =10A, the maximum allowable power consumption is P V,max=1200W power. Only in this way can it be ensured that the second energy storage device can always provide the required power for the electrical consumer. If the first energy storage device is used in addition and the switching point is set to U2=150V, then at the same power P V,max =1200W, the maximum current I V,max =1200W / 150V=8A.

[0027] In an advantageous embodiment, the definable voltage value depends on the average power required by the first electrical consumer.

[0028] Advantageously, the power transferred from the first energy storage device to the second energy storage device corresponds to the average, i.e., the power of the consumer. This allows the second energy storage device to be dimensioned smaller, as it only needs to buffer power peaks. The first energy storage device bears the base load, i.e., the average load.

[0029] In one advantageous embodiment, the vehicle has a vehicle control unit for controlling the driving motion, in particular, the vehicle control unit receiving commands, in particular wirelessly, from a higher-level control unit. Advantageously, the vehicle control unit can be supplied with energy from a first energy storage device. In particular, a battery, such as a lithium-ion battery, can be used as the first energy storage device, whose voltage level is in the low-voltage range, in particular, 12 V, 24 V, 48 V, or 96 V.

[0030] In an advantageous embodiment, the definable voltage value is dynamically varied during operation of the vehicle.

[0031] This advantageously allows for reacting to changing conditions in intralogistics applications. For example, if it is known that different average powers are required for different travel sections, the definable voltage value can be adapted for each travel section. The adaptation of the definable voltage value can be implemented, for example, by the vehicle control system. With multiple electrical consumers, such as a drive and a lift, it is conceivable, for example, to set a different definable voltage value for the travel section between two workstations than when loading and unloading a load using the lift while the vehicle is stationary.

[0032] In an advantageous embodiment, the definable voltage value is equal to the quotient of the maximum power required by the first electrical consumer and the maximum current permitted for the first electrical consumer.

[0033] It is advantageous here that the operating mode of the second energy storage device can be adapted to the requirements of the electrical consumers.

[0034] In one advantageous refinement, the second power flow is prevented by a diode arranged between the second energy storage device and the converter device.

[0035] The advantage here is that the blocking of the second power flow is easily achieved.

[0036] In an advantageous embodiment, an actual value of a recharging current (Umladestrom) flowing between a first connection point and a second connection point is detected, in particular by means of a current measuring device, wherein the first connection point is connected to the energy supply unit and the converter device, and wherein the second connection point is connected to the second energy storage device and the electrical consumer, wherein a second power flow is prevented in that the converter device is deactivated at least with respect to charging the first energy storage device when the detected actual value of the recharging current falls below a minimum recharging current limit value, in particular a non-negative value.

[0037] The advantage here is that the second power flow is prevented from a control perspective, and a diode between the first and second energy storage devices can be omitted. Thus, the function of a diode is simulated from a control perspective. Here, if the actual value of the current measuring device is less than the minimum recharge current limit, the converter device is deactivated, at least with respect to the charging process of the first energy storage device. This ensures that energy from the second energy storage device is not supplied to the first energy storage device. In other words, in the absence of an external energy supply and when the recharge current is less than the minimum recharge current limit, a unidirectional converter device is derived from the bidirectional converter device, which only allows power flow from the first energy storage device. Alternatively, deactivation can also be performed completely, so that no power can flow from or to the first energy storage device at all.

[0038] In the present invention, the following definitions apply to the flowing current:

[0039] When the vehicle has an external energy supply, the energy supply unit provides a supply current. This supply current can be used to charge the first energy storage device and / or the second energy storage device and / or to supply energy to the first electrical consumer. By definition, the supply current always has a positive value because the energy supply unit is designed only for energy supply and not for energy recirculation.

[0040] The current flowing through the converter device is referred to as the first charging current. If energy is supplied to the first energy storage device, i.e., the first energy storage device is charged, the first charging current is defined as positive. If energy is withdrawn from the first energy storage device, i.e., it is discharged, the first charging current is correspondingly negative.

[0041] Accordingly, the current flowing through the second energy storage device is referred to as the second charging current. If energy is supplied to the second energy storage device, i.e., the second energy storage device is charged, the second charging current is defined as positive. If energy is withdrawn from the second energy storage device, i.e., it is discharged, the second charging current is correspondingly negative.

[0042] The current flowing through the first electrical consumer is called the load current. By definition, the load current is positive when energy is supplied to the first electrical consumer. For example, when the drive motor is operating as a motor. The load current is correspondingly negative because the first electrical consumer feeds energy back into the intermediate circuit. For example, when the drive motor is operating as a generator.

[0043] Finally, the recharging current is defined. The recharging current flows between the first energy storage device and the second energy storage device. Here, the recharging current is the difference between the supply current and the first charging current. If there is no external energy supply, that is, the supply current is zero, then the recharging current corresponds exactly to a negative charging current. In addition, the recharging current is divided into a second charging current and a load current. Therefore, the recharging current is the sum of the second charging current and the load current. When the current flows from the first energy storage device or from the energy supply unit in the direction of the second energy storage device or the first electrical consumer, the recharging current is positive according to the definition. Therefore, a negative recharging current means that the current flows from the second energy storage device or from the first electrical consumer in the direction of the first energy storage device or the energy supply unit.

[0044] In an advantageous embodiment, the actual value of the recharging current flowing between a first connection point and a second connection point is detected, in particular by means of a current measuring device, wherein the first connection point is connected to the energy supply unit and the converter device, and wherein the second connection point is connected to the second energy storage device and the electrical consumer, wherein the actual value of the intermediate circuit voltage is detected, in particular by means of a voltage measuring device, wherein the converter device includes a choke, a DC transformer and a regulator with a cascade control device, wherein the second power flow is prevented as follows: the cascade control device sets or regulates the converter voltage applied to the DC transformer as a function of the detected actual value of the recharging current and the detected actual value of the intermediate circuit voltage, i.e., a negative recharging current is prevented.

[0045] Advantageously, the second power flow is prevented using open-loop control technology, and a diode between the first and second energy storage devices can be omitted. Thus, the function of a diode is simulated using open-loop control technology. Advantageously, when the actual value of the recharging current falls below the recharging current limit, the converter device is not completely deactivated directly, but rather only the first charging current is limited. This allows the energy supply unit to still charge the first energy storage device while simultaneously preventing the second power flow.

[0046] In an advantageous embodiment, a first power flow from the first energy storage device to the second energy storage device occurs when the intermediate circuit voltage is less than the charge completion voltage and the voltage in the first energy storage device is above a definable minimum voltage.

[0047] This has the advantage that the second energy storage device can be charged to a higher voltage as long as there is still power reserve in the first energy storage device.

[0048] In an advantageous embodiment, the cascade control device comprises a current regulator with a superimposed voltage regulator and a limiting device arranged between the voltage regulator and the current regulator, wherein the limiting device limits a setpoint value of the recharging current to a value that is greater than a particularly non-negative minimum recharging current limit value.

[0049] It is advantageous here that the cascade control device allows the second energy storage device to be regulated to a defined voltage value and simultaneously controls the recharging current.

[0050] In an advantageous embodiment, the vehicle comprises, in addition to the first electrical consumer, further electrical consumers, wherein all electrical consumers are connected to the second energy storage device via an intermediate circuit, in particular in parallel.

[0051] The advantage here is that energy can be exchanged via the intermediate circuit. If, for example, the drive motor of a traction drive is operated as a generator, the energy generated can be used, for example, to operate a lifting device on the vehicle.

[0052] An important feature of the electric vehicle according to the invention, in particular for carrying out the above-mentioned method, is that the vehicle comprises a first energy storage device, a second energy storage device, an energy supply unit, and a first electrical consumer, the first energy storage device being in particular designed as a rechargeable battery device, the second energy storage device being in particular designed as a double-layer capacitor device and / or the second energy storage device being capable of being charged and discharged more rapidly than the first energy storage device, the energy supply unit providing energy for charging the first energy storage device and / or the second energy storage device in particular intermittently, the first electrical consumer being connected to the second energy storage device via an intermediate circuit, wherein an intermediate circuit voltage is present in the intermediate circuit, the first energy storage device being connected to the energy supply unit via a bidirectional converter device,

[0053] The second energy storage device is connected to the energy supply unit.

[0054] The vehicle is designed in such a way that, when the intermediate circuit voltage drops below a definable voltage, a first power flow occurs from the first energy storage device to the second energy storage device and a second power flow from the second energy storage device to the first energy storage device is prevented.

[0055] The same advantages result here as in the method according to the invention.

[0056] In an advantageous embodiment, the energy supply unit is designed as a controllable current source.

[0057] An advantage here is that this can be realized very easily, in particular for inductively coupled energy supply units.

[0058] In an advantageous embodiment, the first energy storage device can be detachably arranged on the electric vehicle, so that the first energy storage device can be replaced.

[0059] This has the advantage that the first energy storage device can be easily replaced if it wears out. The first energy storage device is therefore not permanently installed or integrated in the vehicle, but rather is removably mounted on the vehicle. In particular, when a low protective voltage is used for the first energy storage device, the advantage is that the first energy storage device can be easily replaced even by personnel who are not appropriately trained. This is particularly advantageous when the first energy storage device is not designed for the service life of the vehicle and is therefore a wearing part.

[0060] In an advantageous embodiment, overvoltage protection and / or undervoltage protection and / or overcurrent protection are provided on the first energy storage device by means of current measurement and / or voltage measurement, and / or overheating protection is provided on the first energy storage device by means of temperature measurement, and / or overvoltage protection and / or overcurrent protection are provided on the second energy storage device by means of current measurement and / or voltage measurement, and / or overheating protection is provided on the second energy storage device by means of temperature measurement.

[0061] The advantage here is that the safety of the energy storage device is increased and it cannot be damaged. This is particularly important when energy is fed back into the energy storage device via a consumer.

[0062] The present invention is not limited to the above-mentioned feature combinations. For a person skilled in the art, in particular in view of the objectives proposed and / or the objectives proposed by comparison with the prior art, other reasonable combinations of the above-mentioned feature combinations and / or individual features and / or features of the description and / or features of the drawings will be apparent to those skilled in the art. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] exist Figure 1 A mobility assistance system according to the invention with an electrical consumer is schematically shown in FIG. This mobility assistance system is also referred to as MAS below.

[0064] exist Figure 2 The figure shows the intermediate circuit voltage U when energy is supplied to the consumers from the intermediate circuit. ZK Curve of change relative to time.

[0065] exist Figure 3 A second exemplary embodiment of a mobility assistance system according to the invention with a consumer is schematically shown in FIG.

[0066] exist Figure 4 The regulator structure for the second embodiment is schematically shown in FIG. DETAILED DESCRIPTION

[0067] Figure 1A block diagram schematically illustrates those components of a MAS that are considered part of the vehicle's energy management system. The MAS includes an energy supply unit 1 for energy supply, which in this exemplary embodiment is designed as a regulated power supply. To this end, the power supply unit 1 includes a regulator (not shown in further detail) that regulates the supply current I0 of the power supply unit 1 and thereby provides a supply voltage U0. This supply voltage U0 is a DC voltage, which for the MAS is advantageously in the range of 120 V to 600 V. Reference to voltage in this disclosure always refers to a DC voltage unless an AC voltage is explicitly specified.

[0068] The power supply unit 1 for the MAS can be configured in different ways. For example, it can be implemented as a simple charger with a plug-in connector, so that the MAS can be supplied with energy in a contact-type manner at a specific charging station. Similarly, during the travel of the MAS, a contact-type energy supply can be implemented, for example, by means of a contact wire. As an alternative, a contactless energy supply, such as an inductive energy supply, can be implemented. This can be done by coupled primary and secondary inductors. In this case, both power supply at a fixed charging station and power supply during the travel of the MAS can be considered - for example, by a primary wire laid in or on the workshop floor.

[0069] If an external energy supply is present, a supply current I0, which is positive as specified, is provided by the energy supply unit 1. If no external function is present, for example because the MAS is traveling on a section without a contact line or inductive power supply, no supply current is provided or the supply current I0 is zero.

[0070] The charger 1 is connected to a bidirectional converter device 2, to which a first energy storage device 3 is in turn connected. In this example, the bidirectional converter device 2 is designed as a bidirectional DC / DC converter, and the first energy storage device 3 is designed as a battery. Thus, energy can be supplied to or withdrawn from the battery 3 via the bidirectional DC / DC converter 2. The DC / DC converter can be designed as a non-potentially isolated or, advantageously, as a potential-isolated DC / DC converter.

[0071] Advantageously, the battery 3 has a voltage U1 in the low-voltage range, advantageously a voltage of 12 V, 24 V or 48 V.

[0072] The current input to DC / DC converter 2 is referred to as first charging current I1. When battery 3 is supplied with energy, i.e., when it is being charged, first charging current I1 is positive by default. When battery 3 is being drawn from, i.e., when it is being discharged, first charging current I1 is correspondingly negative.

[0073] Here, DC / DC converter 2 selectively converts supply voltage U0 into battery voltage U1 when battery 3 is charging, and converts battery voltage U1 into supply voltage U0 when battery 3 is discharging. This charging and discharging can occur with or without an external energy supply, depending on the requirements of the intralogistics application. Voltage level U0 is then provided by energy supply unit 1 and / or by DC / DC converter 2.

[0074] Furthermore, the charger 1 is connected to a second energy storage device 4, which in this embodiment is implemented as a double-layer capacitor 4. It is applicable that, instead of a double-layer capacitor, an arrangement consisting of multiple double-layer capacitors connected in parallel and / or in series can also be used. Therefore, the following description of double-layer capacitors applies analogously to the double-layer capacitor arrangement. Here, the double-layer capacitor 4 and the DC / DC converter 2 are connected in parallel to the charger 1. Furthermore, a consumer 5 is connected in parallel to the double-layer capacitor 4, which in this embodiment is a traction drive for vehicle traction. For example, the traction drive can be implemented as a three-phase AC motor with a pre-installed three-phase inverter. In this case, the inverter converts the DC voltage applied to the inverter into a three-phase AC voltage in a known manner, which is used to operate a three-phase motor, such as a squirrel-cage rotor. The traction drive 5 can also include multiple motors, each of which can be operated by its own inverter. Furthermore, the inverter can also be designed to be regenerative, so that when the drive motor is in generator mode, energy can be regenerated to charge the double-layer capacitor 4.

[0075] In addition to the drive for pulling the MAS, other electrical consumers can also be considered, such as a lifting device for receiving a load or a handling device for moving an object, such as a robot arm. These can be connected in parallel with the first electrical consumer, for example.

[0076] exist Figure 1 In the embodiment shown, a diode 6, whose function will be described below, is provided between a first connection point 7 of the DC / DC converter 2 and a second connection point 8 of the double-layer capacitor 4. Two voltage levels are obtained via the diode 6. At the first connection point 7, the voltage level U0 is present, while the double-layer capacitor 4 and the traction drive 5 are at the intermediate circuit voltage U0 at their common second connection point 8. ZK The voltage level U ZK That is, the double-layer capacitor 4 and the drive 5 are connected via a common intermediate circuit and separated from the DC / DC converter 2 by a diode. Therefore, the DC / DC converter 2, the double-layer capacitor 4 and the drive 5 can be supplied with the supply voltage U0 when an external function is present. If the intermediate circuit U ZKIf the voltage in the intermediate circuit is less than the supply voltage U0, the intermediate circuit rises until it has reached the level of the supply voltage U0. Due to the voltage drop across the diode 6, this voltage will be slightly lower than the supply voltage U0. However, since the supply voltage U0 is usually in the range of 120V or more, the voltage drop across the diode 6 is negligible in this case. If there is no external energy supply and the DC / DC converter 2 does not feed energy, the supply voltage U0 can be less than U ZK , while the intermediate circuit voltage is always maintained at a positive level by the double-layer capacitor. In this case, diode 6 permanently, i.e., constantly, prevents equalization charging from the double-layer capacitor 4 to the battery 3. Therefore, in principle, energy transfer from the double-layer capacitor 4 to the battery 3 is neither possible nor desirable.

[0077] The current supplied to the double-layer capacitor 4 is referred to as the second charging current I2. If energy is supplied to the double-layer capacitor 4, i.e., the double-layer capacitor is charged, the second charging current I2 is positive as intended. If energy is withdrawn from the double-layer capacitor 4, i.e., it is discharged, the second charging current I2 is correspondingly negative.

[0078] The current supplied to the traction drive 5 is called load current I3. When energy is supplied to the traction drive 5, that is, when the drive motor is operating as a motor, load current I3 is positive as specified. When the traction drive 5 is feeding back energy, for example because the drive motor is operating as a generator during braking, load current I3 is correspondingly negative.

[0079] The diode 6, arranged between the connection points 7 and 8, prevents energy from reaching the DC / DC converter 2 or, via the DC / DC converter 2, the battery 3 from the intermediate circuit. Consequently, energy from the double-layer capacitor 4 to the battery 3 is prevented from being charged back into the battery at all times. In other words, the diode prevents energy from flowing from the double-layer capacitor to the battery. Energy flow in the opposite direction is permitted and desirable. This means that energy from the battery 3 can be used to increase the voltage U in the intermediate circuit. ZK That is, the double-layer capacitor 4 can be charged by the charger and / or by the battery, while the battery can only be charged by the charger.

[0080] The current flowing between the two connection points 7, 8 and thus through the diode 6 is referred to as the recharging current I 1,2 If the current flows from the first connection point 7, i.e. from the DC / DC converter or from the charger 1, to the second connection point 8, i.e. in the direction of the intermediate circuit or in the direction of the double-layer capacitor 5 and the traction drive 5, the recharging current is positive as specified. 1,2In the present first exemplary embodiment, this is prevented by the diode 6. Once energy has been stored in the double-layer capacitor 4, it should no longer be used to charge the battery 3.

[0081] The double-layer capacitor 4 has a charge completion voltage U L , that is, the maximum voltage it can reach to the maximum extent of charging, and has a discharge completion voltage U E , i.e., in particular, a minimum voltage greater than zero. These characteristic voltage values ​​are defined by the type of construction of the double-layer capacitor. Typical values ​​are, for example, U L =350V, U E = 120V. Therefore, the traction drive 5 must be able to supply the required power within this voltage range. Therefore, if only the double-layer capacitor 4 is used as a single energy storage device, the traction drive 5 will be designed for the minimum voltage and therefore the maximum current for the expected maximum power. This usually results in the use of a larger structural size, for example, in the drive motor. In order to improve this design in terms of being able to use a smaller structural size, the DC / DC converter 2 with the battery 3 is responsible for ensuring that the intermediate circuit voltage U ZK Does not drop to a limitable voltage level U S Below. This is Figure 2 The situation in which the drive 5 continuously requires energy and there is no external energy supply is schematically shown. First, the double-layer capacitor 4 is charged at a voltage level U L Fully charged. As time goes by, the voltage U ZK decreases until it reaches the limited switching voltage U S At the latest at this point in time, the DC / DC converter 2 is then operated so that energy is transferred from the battery 3 into the intermediate circuit in order to maintain the voltage level there at least at U S Intermediate circuit voltage U ZK For example, it can be determined by means of a simple voltage measurement. Overall, the drive can be designed to be smaller. The voltage U S It can then be used as a nominal voltage for dimensioning the power electronics and the drive and is referred to here as the switching voltage U S .

[0082] The activation command of the DC / DC converter 2 can be executed, for example, by a vehicle control unit (not shown in the figure). Such a vehicle control unit controls the energy management of the vehicle and the corresponding driving movement. Alternatively or additionally, it is also conceivable that the DC / DC converter itself has control electronics, the measured intermediate circuit voltage U ZK The value is fed to the control electronics, which then switches the voltage below the switching voltage U S When the load is turned on, appropriate steps are taken to transfer energy to the intermediate circuit.

[0083] The battery has a large capacity and compensates for the low energy content of the double-layer capacitor. If the power supplied from the battery to the intermediate circuit corresponds to the average power of the intralogistics application, the voltage across the double-layer capacitor and therefore in the intermediate circuit remains at U S This results in favorable operating conditions for the double-layer capacitors. The double-layer capacitors buffer any power peaks of the drive, while the battery can be designed for the continuous consumption of the drive. If a larger power reserve is available at the DC / DC converter, the double-layer capacitors can also be recharged to the full charge voltage U L .

[0084] Therefore, for the above U L =350V and U E = 120V, the following advantages are obtained compared to a system with only one double-layer capacitor: The maximum current of the power electronics of the drive is limited to I V,max =10A, for the E =120V single double layer capacitor, then P V,max =U E I V,max = 1200 W. If the switching point is selected to be, for example, U S =180V, then we get P V,max =U S I V,max =1800W.

[0085] When the drive device 5 is operated as a generator, the energy generated thereby can be used to recharge the double-layer capacitor 4. It is advantageously ensured that the voltage applied to the double-layer capacitor 4 does not exceed the charging completion voltage U L This can be easily implemented, for example, with the aid of an overvoltage protection device.

[0086] As mentioned above, the task of the diode 6 is to prevent the recharging of the double-layer capacitor 4 into the battery 3. The energy once absorbed by the double-layer capacitor 4 should no longer enter the battery 3 and should be used only by the traction drive 5. As an alternative to the diode, in the second embodiment, a particularly permanent blockage of this power flow can also be implemented using closed-loop control technology or open-loop control technology. For this purpose, the recharging current I is measured by means of a current measuring device. 1,2 The current measuring device replaces the Figure 1 The diode is shown in Figure 2. Apart from this, all currents are defined as for the Figure 1 The same applies to the second embodiment. The current measuring device measures the recharging current I 1,2The actual value of the detected 1,2_ist is transmitted to the DC / DC converter 2, which in this case comprises, for example, signal electronics. A defined minimum recharging current limit value I 1,2_min When the minimum recharging current limit is fallen below, the DC / DC converter is deactivated, at least with respect to charging the battery. This means that this deactivation only includes the voltage conversion from voltage level U0 to voltage level U1, while the opposite voltage conversion direction is not deactivated.

[0087] Alternatively, the DC / DC converter can also be completely deactivated, ie switched off. 1,2_min is preferably positive and in particular well above the value zero, so that the recharging current I 1,2 Due to any time delay, the voltage does not fall below zero, i.e., it does not become negative. This means that power flow from the double-layer capacitor 4 to the battery 2 is prevented from occurring for control purposes. Advantageously, deactivating the DC / DC converter 2 only involves the voltage conversion from voltage level U0 to voltage level U1. Therefore, the opposite voltage conversion direction is not deactivated.

[0088] exist Figure 3 and Figure 4 Here, as in the second embodiment, the recharging current I between the first connection point 7 and the second connection point 8 is 1,2 The current is measured by means of a current measuring device 12 arranged between these connection points. That is, the power flow from the double-layer capacitor to the battery is blocked in open-loop control technology. The current measuring device 12 replaces the Figure 1 The diode 6 is shown in FIG. The current measuring device 12 recharges the current I 1,2 The measured actual value I 1,2_ist The current is transmitted to the converter device 2 shown in more detail here. The converter device 2 includes a cascade regulator 9, a bidirectional DC transformer 11 and a choke 10 described below. The names of the currents or the definitions of the current directions are the same as in the first embodiment. The DC transformer 11 is connected to the DC transformer 11 with U W The converter voltage shown is converted into the battery voltage U1 and vice versa. Since no diode is present in the present case, the voltage level U0 is equal to the intermediate circuit voltage U ZK The converter voltage U W Can be compared with the intermediate circuit voltage U ZK This is because an inductor 8 is provided between the DC transformer 11 and the first connection point 7. In this example, the inductor 10 is part of the converter device 2, so that the voltage supplied to the converter device 2 corresponds to the supply voltage U0.

[0089] In this case, as described below, the cascade controller 9 prevents the compensation charging from the double-layer capacitor 4 to the battery 3 using open-loop control technology. 1,2_ist In addition to the actual value of the intermediate circuit voltage U ZK The actual value of U ZK_ist The actual value U ZK_ist With the help of Figure 3 is obtained by measuring the voltage not shown.

[0090] exist Figure 4 , a cascade control device implemented in a cascade controller 9 is shown, comprising a current regulator 15 with a superimposed voltage regulator 13. A setpoint value limiting device 14 is arranged between the two regulators 13, 15.

[0091] First, the intermediate circuit voltage U is specified, for example, by the vehicle control unit. ZK_soll Compare it with the actual value of the detected intermediate circuit voltage U ZK_ist The comparison is performed and the difference is fed as an input variable to the voltage regulator 13. The voltage regulator 13 generates a recharging current I 1,2_soll To avoid negative recharging current I 1,2 , the rated value of the recharging current is limited to a value greater than the minimum recharging current limit I by the limiting device 14. 1,2_min In other words, for the rated value I 1,2_soll >I 1,2_min , the limiting device 14 is not changed, and the value of the rated value I 1,2_soll <I 1,2_min , the limiting device 14 sets it to the minimum recharge current limit I 1,2_min . Minimum recharge current limit I 1,2_min is a non-negative value. For an ideal regulator, we can also consider I 1,2_min = 0. The limiting device 14 generates the recharging current I 1,2_soll The new value of the rated value is compared with the recharge current I 1,2_ist The actual values ​​of are compared and the difference is supplied as input variable to the current regulator 15. The current regulator finally generates the current for the converter voltage U as output variable. W_Stell This means that only the converter voltage U W_Stell , without performing open-loop control on it.

[0092] exist Figure 2 In the situation schematically shown in FIG, ie when there is no external energy supply (I0=0) and energy is continuously supplied to the traction drive 5, the cascade regulator can be used to implement the following: the intermediate circuit voltage U ZK_sollThe rated value is set to the conversion voltage U S If the intermediate circuit voltage U ZK Greater than the conversion voltage U S , that is U ZK_ist >U S =U ZK_soll , the voltage regulator 13 will try to recharge the current I 1,2_soll Specifying a negative rated value to reduce the intermediate circuit voltage U ZK However, the rated value is set to the minimum recharge current limit I by the limiting device. 1,2_min , for example I 1,2_min =0.1A.

[0093] If the recharge current is higher than this limit, I 1,2_ist >0.1A, the voltage regulator 15 will change U W_Stell The setting value of I is such that the recharging current is reduced, i.e. the battery 3 does not support the double-layer capacitor 4. 1,2_min This ensures that the cascade regulator can react promptly when the current falls below this limit, so that the recharging current I 1,2 Does not become negative.

[0094] If the intermediate circuit voltage U ZK Due to the energy consumption of the traction drive 5, the voltage drops to the conversion voltage U S Below, the current regulator 13 specifies a larger positive setpoint value I 1,2_soll , so as to maintain the voltage level at U S .

[0095] Even in other cases where a negative recharge current I 1,2 In the event of a sudden interruption of the external energy supply or energy regeneration of the traction drive 5, the cascade controller 9 also ensures that, in the end, no power flows from the double-layer capacitor 4 to the battery 3. It should be pointed out in this context that, in the present invention, a power flow, for example, from the double-layer capacitor 4 to the battery 3, is always understood to mean a charge transfer that significantly changes the energy content of the energy storage device.

[0096] Reference Signs List

[0097] 1 energy supply unit

[0098] 2Bidirectional DC / DC converter

[0099] 3. First energy storage device

[0100] 4 Second energy storage device

[0101] 5 electrical appliances

[0102] 6 diodes

[0103] 7First connection point

[0104] 8 Second connection point

[0105] 9 Cascade Regulators

[0106] 10 chokes

[0107] 11 DC transformer

[0108] 12 Current measuring device

[0109] 13 Voltage Regulator

[0110] 14 Restraining devices

[0111] 15 Current regulator

[0112] U L Charging completion voltage

[0113] U S Conversion voltage

[0114] U E Discharge completion voltage

[0115] I0 supply current

[0116] I1 first charging current

[0117] I2 second charging current

[0118] I 1,2 Recharge current

[0119] I3 load current.

Claims

1. A method for operating an electric vehicle, the electric vehicle comprising: - a first energy storage device (3), - a second energy storage device (4) capable of being charged and discharged faster than the first energy storage device (3), an energy supply unit (1) which provides energy for charging the first energy storage device (3) and / or the second energy storage device (4), - a first electrical consumer (5), in, The first electrical consumer (5) is connected to the second energy storage device (4) via an intermediate circuit, In the intermediate circuit, there is an intermediate circuit voltage (U ZK ), The first energy storage device (3) is connected to the energy supply unit (1) via a bidirectional converter device (2). The second energy storage device (4) is connected to the energy supply unit (1). It is characterized by: When the intermediate circuit voltage (U ZK ) drops to a limited voltage (U S ), a first power flow occurs from the first energy storage device (3) to the second energy storage device (4), and A second power flow from the second energy storage device (4) to the first energy storage device (3) is prevented at all times.

2. The method according to claim 1, characterized in that The electric vehicle is an unmanned mobility assistance system for intralogistics applications.

3. The method according to claim 1, characterized in that The first energy storage device is designed as a rechargeable battery device; and / or The second energy storage device is designed as a double-layer capacitor device.

4. The method according to claim 1, wherein The energy supply unit intermittently provides energy for charging the first energy storage device (3) and / or the second energy storage device (4).

5. The method according to claim 1, characterized in that The first electrical consumer is a driving drive or a lifting device or a transport device for the driving movement of the electric vehicle.

6. The method according to any one of claims 1 to 5, It is characterized by: The energy supply unit (1) is supplied with energy in a contact-type or contactless manner, wherein the energy supply unit (1) is supplied with energy intermittently during driving.

7. The method according to any one of claims 1 to 5, It is characterized by: The second energy storage device (4) has a charging completion voltage (U L ) and discharge completion voltage (U E ), Among them, the voltage that can be limited (U S ) is greater than the discharge completion voltage (U E ) value and is less than the charging completion voltage (U L ) value.

8. The method according to any one of claims 1 to 5, It is characterized by: The voltage that can be limited (U S ) depends on the average power required by the first electrical consumer (5) (P V ).

9. The method according to any one of claims 1 to 5, It is characterized by: Dynamically change the voltage (U S ) value.

10. The method according to any one of claims 1 to 5, It is characterized by: The voltage that can be limited (U S ) is equal to the maximum power (P V,max ) and the maximum current (I V,max )'s quotient.

11. The method according to any one of claims 1 to 5, It is characterized by: The second power flow is prevented by a diode (6) arranged between the second energy storage device (4) and the converter device (2).

12. The method according to any one of claims 1 to 5, It is characterized by: The recharging current (I) flowing between the first connection point (7) and the second connection point (8) is detected by means of a current measuring device. 1,2 ) actual value (I 1,2_ist ), The first connection point (7) is connected to the energy supply unit (1) and the converter device (2), The second connection point (8) is connected to the second energy storage device (4) and the electrical consumer (5). Among them, when the recharge current (I 1,2_ist ) is lower than the minimum recharge current limit (I 1,2_min ), the converter device (2) is deactivated at least with respect to charging the first energy storage device (3).

13. The method according to claim 12, characterized in that The minimum recharge current limit is non-negative.

14. The method according to any one of claims 1 to 5, It is characterized by: The recharging current (I) flowing between the first connection point (7) and the second connection point (8) is detected by means of a current measuring device (12). 1,2 ) actual value (I 1,2_ist ), The first connection point (7) is connected to the energy supply unit (1) and the converter device (2), The second connection point (8) is connected to the second energy storage device (4) and the electrical consumer (5). The intermediate circuit voltage (U ZK ) actual value (U ZK_ist ), The converter device (2) comprises a choke (10), a DC transformer (11) and a regulator (9) with a cascaded regulation device. The second power flow is prevented in the following manner: the cascade control device is controlled according to the detected actual value of the recharging current (I 1,2_ist ) and the detected actual value of the intermediate circuit voltage (U ZK_ist ), the converter voltage (U W ) is set or adjusted so that a negative recharge current (I 1,2 ).

15. The method according to claim 14, It is characterized by: The cascade regulating device comprises a current regulator (15) with a superimposed voltage regulator (13) and a limiting device (14) arranged between the voltage regulator (13) and the current regulator (15). The limiting device sets the rated value of the recharging current (I 1,2_soll ) is limited to the following value: This value is greater than the minimum recharge current limit (I 1,2_min ).

16. The method according to claim 15, characterized in that The minimum recharge current limit is non-negative.

17. The method according to any one of claims 1 to 5, It is characterized by: The second energy storage device (4) has a charging completion voltage (U L ) and discharge completion voltage (U E ), when the intermediate circuit voltage (U ZK ) is less than the charging completion voltage (U L ) and the voltage in the first energy storage device (3) is higher than the minimum voltage (U min ), the first power flow occurs.

18. The method according to any one of claims 1 to 5, It is characterized by: The electric vehicle comprises not only the first electrical consumer (5) but also other electrical consumers, wherein all the electrical consumers are connected in parallel to the second energy storage device (4) via an intermediate circuit.

19. An electric vehicle, comprising: - a first energy storage device (3), - a second energy storage device (4) capable of being charged and discharged faster than the first energy storage device (3), an energy supply unit (1) which provides energy for charging the first energy storage device (3) and / or the second energy storage device (4), a first electrical consumer (5) which is connected to the second energy storage device (4) via an intermediate circuit, wherein: The intermediate circuit voltage (U ZK ), The first energy storage device (3) is connected to the energy supply unit (1) via a bidirectional converter device (2). The second energy storage device (4) is connected to the energy supply unit (3). It is characterized by: The electric vehicle is designed such that when the intermediate circuit voltage (U ZK ) drops to a limited voltage (U S ), a first power flow occurs from the first energy storage device (3) to the second energy storage device (4), and A second power flow from the second energy storage device (4) to the first energy storage device (3) is prevented at all times.

20. The electric vehicle according to claim 19, characterized in that The electric vehicle is an unmanned mobility assistance system for intralogistics applications.

21. The electric vehicle according to claim 19, wherein: The first energy storage device is designed as a rechargeable battery device; and / or The second energy storage device is designed as a double-layer capacitor device.

22. The electric vehicle according to claim 19, wherein: The energy supply unit intermittently provides energy for charging the first energy storage device (3) and / or the second energy storage device (4).

23. The electric vehicle according to any one of claims 19 to 22, characterized in that The electric vehicle is used to perform the method according to any one of claims 1 to 18.

24. The electric vehicle according to any one of claims 19 to 22, It is characterized by The energy supply unit (1) is configured as an adjustable current source, and / or The first energy storage device (3) is detachably arranged on the electric vehicle in such a manner that the first energy storage device (3) can be replaced.

25. The electric vehicle according to any one of claims 19 to 22, It is characterized by Providing overvoltage protection and / or undervoltage protection and / or overcurrent protection on the first energy storage device (3) by means of current measurement and / or voltage measurement, and / or providing overheating protection on the first energy storage device (3) by means of temperature measurement, and / or Providing overvoltage protection and / or overcurrent protection on the second energy storage device (4) by means of current measurement and / or voltage measurement, and / or Overheating protection is provided at the second energy storage device (4) by means of temperature measurement.

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