METHOD AND SYSTEM FOR OPERATING A SYSTEM INCLUDING AN ENERGY STORAGE DEVICE AND RESISTOR

Abstract

In a method and system for operating a system having an energy storage device and a resistor, and in order to discharge the energy storage device, an electric power that is constant over time is continuously supplied to the resistor, e.g., during a time period, e.g., until the resistor has practically been fully discharged, the time period, e.g., being greater than the time constant of the temperature rise of the resistor induced by a continuous electric power that is constant over time and supplied to the resistor.

Claims

16. A method for operating a system that includes an energy storage device and a resistor, comprising: continuously supplying an electric power, that is constant over time, to the resistor to discharge the energy storage device.

17. The method according to claim 16, wherein the electric power is continuously supplied to the resistor during a time period that is greater than a time constant of a temperature rise of the resistor induced by the continuous supply of electric power that is constant over time and supplied to the resistor.

18. The method according to claim 16, wherein the electric power is continuously supplied to the resistor until the resistor has been substantially fully discharged.

19. The method according to claim 16, further comprising: acquiring a voltage applied at a series circuit that includes the resistor and a controllable semiconductor switch, the series circuit being fed directly from a voltage supplied by the energy storage device and/or via a DC/DC converter from the voltage supplied by the energy storage device; and conveying, to the controllable semiconductor switch, a pulse width modulated actuation signal having a pulse width modulation ratio as a function of a value of the acquired voltage.

20. The method according to claim 19, wherein a pulse width modulation ratio corresponding to (1/U)*(P*R){circumflex over ( )}½, U representing the acquired voltage, P representing the power that is constant over time, R representing resistance of the resistor, the controllable semiconductor switch being continuously closed in response to the acquired dropping below a threshold value.

21. The method according to claim 20, wherein the threshold value corresponds to (P*R){circumflex over ( )}½.

22. The method according to claim 19, wherein the controllable semiconductor switch includes a brake chopper.

23. The method according to claim 16, wherein the system includes a supply module that includes a mains-operated rectifier and whose DC-voltage-side terminal is connected to a DC-voltage-side terminal of an inverter and to a first terminal of a DC/DC converter, a second terminal of the DC/DC converter being connected to a terminal of the energy storage device supplying the voltage, an electric motor and/or a three-phase motor being connected at an AC-voltage-side terminal of the inverter.

24. The method according to claim 23, wherein a DC/DC actuator is arranged between the DC-voltage-side terminal of the rectifier and the DC-voltage-side terminal of the supply module, which stops a power flow from the rectifier to a series circuit that includes the resistor R and a controllable semiconductor switch during discharging of the energy storage device.

25. The method according to claim 24, wherein, during the discharging, heat is generated on a particular power module on which diodes of the rectifier and the controllable semiconductor switch are arranged in an integrated fashion, by the controllable semiconductor switch and/or by the diodes of the rectifier.

26. The method according to claim 23, wherein the inverter includes a power module on which controllable semiconductor switches arranged in half bridges are arranged.

27. The method according to claim 23, wherein the power is lower than a power maximally recoverable by the electric motor via the inverter to the DC-voltage-side terminal of the inverter in a generator-mode operation of the electric motor.

28. The method according to claim 19, wherein a pulse width modulation frequency of the actuation signal is varied while the power is supplied, and values, different values, and/or discrete values are used successively in time as the pulse width modulation frequency.

29. The method according to claim 16, further comprising acquiring current flowing through the resistor, determining an instantaneous resistance value of the resistor from a time-averaged voltage supplied via a brake chopper and the time-averaged current, and determining an instantaneous temperature of the under consideration of a characteristics curve that represents a temperature dependency of the resistor.

30. The method according to claim 29, further comprising monitoring whether the determined temperature of the resistor exceeds a threshold value, and performing an emergency shutoff of the brake chopper in response to the determined temperature of the resistor exceeding the threshold value.

31. The method according to claim 29, wherein the determined temperature is controlled to a setpoint temperature by setting the power as an actuation value of a controller and/or a PI controller.

32. A system, comprising: an energy storage device; an inverter; a DC/DC converter; a supply module that includes a mains-operated rectifier and whose DC-voltage-side terminal is connected to a DC-voltage-side terminal of the inverter and to a first DC-voltage-side terminal of the DC/DC converter, a second DC-voltage-side terminal of the DC/DC converter being connected to the energy storage device; and an electric motor and/or a three-phase motor connected at an AC-voltage-side terminal of the inverter.

33. The system according to claim 32, wherein the energy storage device includes an accumulator system, a dual-layer capacitor system, and/or an ultracap system.

34. The system according to claim 32, wherein a DC/DC actuator is arranged between a DC-voltage-side terminal of a rectifier and the DC-voltage-side terminal of the supply module.

35. The system according to claim 32, wherein a controllable semiconductor switch arranged in series with a brake resistor is arranged in a housing of the DC/DC converter.

36. The system according to claim 32, wherein a controllable semiconductor switch arranged in series with a brake resistor is integrated on a power module that includes diodes arranged in half bridges and/or controllable semiconductor switches.

37. The system according to claim 36, wherein the power module is arranged in a housing of the inverter or the supply module.

38. The system according to claim 32, wherein the system includes a resistor and is adapted to perform a method that includes continuously supplying an electric power, that is constant over time, to the resistor to discharge the energy storage device.

39. The method according to claim 16, wherein the system includes: an inverter; a DC/DC converter; a supply module that includes a mains-operated rectifier and whose DC-voltage-side terminal is connected to a DC-voltage-side terminal of the inverter and to a first DC-voltage-side terminal of the DC/DC converter, a second DC-voltage-side terminal of the DC/DC converter being connected to the energy storage device; and an electric motor and/or a three-phase motor connected at an AC-voltage-side terminal of the inverter.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0023] FIG. 1 schematically illustrates a system according to an example embodiment of the present invention.

DETAILED DESCRIPTION

[0024] As schematically illustrated in FIG. 1, a supply module 1 supplied by an AC voltage supply network 8 delivers a unipolar voltage at its DC-voltage-side terminal.

[0025] The DC-voltage-side terminal of an inverter 2 is connected to this terminal, and at the AC-voltage-side terminal of inverter 2, inverter 2 supplies a three-phase voltage to an electric motor 4, e.g., an AC motor, a three-phase motor, etc.

[0026] The inverter is actuated by a control electronics 3, control electronics 3, for example, generating pulse width modulated actuation signals for the controllable semiconductor switches of the inverter which are arranged in half bridges and switched in parallel with one another, this parallel circuit of half bridges being supplyable from the unipolar voltage.

[0027] The semiconductor switches, i.e., for example, six controllable semiconductor switches, are integrated on a module on which a further controllable semiconductor switch, which may be referred to as a brake chopper, is integrated as well.

[0028] The brake chopper is connected in series with a resistor which may be denoted as a brake resistor 7, and this series circuit is likewise supplyable from the unipolar voltage.

[0029] A terminal of a DC/DC converter 5 is also connected to the DC-voltage-side terminal of supply module 1 so that this DC/DC converter 5 is switched in parallel with inverter 2.

[0030] An energy storage device 6 is connected at the other terminal of DC/DC converter 5. DC/DC converter 5 thus allows for a power flow from energy storage device 6 to the intermediate circuit having the unipolar voltage or vice versa, even if the amount of the unipolar voltage differs significantly from the amount of the voltage applied at energy storage device 6.

[0031] Energy storage device 6 is implementable as an electrolyte capacitor system, as a dual-layer capacitor system, and/or, e.g., as an accumulator system.

[0032] Supply module 1 may be arranged as a mains-operated rectifier. However, a DC/DC actuator is, for example, situated between the mains-operated rectifier and the DC-voltage-side terminal of supply module 1 so that the power flow from the AC-voltage supply network 8 into the intermediate circuit is controllable.

[0033] The rectifier, for example, has a module again on which the diodes of the rectifier are disposed in an integrated fashion and on which a further controllable semiconductor switch is additionally integrated, which may be denoted as a brake chopper.

[0034] The brake chopper is connected in series with a further resistor 10, which may be referred to as a brake resistor, and this series circuit is likewise supplyable from the DC-voltage-side terminal of the rectifier.

[0035] DC/DC converter 5 also includes a further controllable semiconductor switch, which may be referred to as a brake chopper.

[0036] This brake chopper is connected in series with a further resistor 9, which may be referred to as a brake resistor, and this series circuit is also supplyable from the DC-voltage-side terminal of the rectifier or from the voltage applied at energy storage device 6.

[0037] A plurality of brake choppers may thus be provided in the system.

[0038] According to example embodiments of the present invention, the safety of the system is increased in that the discharging of the energy storage device can be carried out in a controlled manner.

[0039] This is important not only when the energy storage device is transported but also when maintenance work is performed on the system and the energy storage device is to be discharged. Moreover, a discharge is also important in special types of energy storage devices when a memory effect is to be prevented. NiCd accumulators, for instance, are discharged at regular time intervals.

[0040] The discharging hereof takes place such that the brake chopper of the respective brake resistor (7, 9, 10) is actuated as a function of the unipolar voltage or the voltage U applied at the series circuit that includes the brake resistor and the associated brake chopper, such that a constant power is continuously supplied to the respective brake resistor R.

[0041] This electric power P continuously supplied to the respective brake resistor until the energy storage device is practically completely discharged is specified to be as high as possible. It therefore, for example, equals the nominal power of brake resistor R.

[0042] For this purpose, voltage U is acquired and the respective brake chopper is actuated, e.g., with the aid of a pulse width modulation ratio (1/U)*(P*R)){circumflex over ( )}½. The power supplied to the respective brake resistor thereby remains constant even given a dropping voltage U.

[0043] The nominal power, i.e., also power P, e.g., is lower than the power maximally recoverable by electric motor 4 via inverter 2 in a generator-mode operation of the electric motor.

[0044] The Ohmic resistance of respective brake resistor R may thus be selected to be very low and a practically complete discharge may therefore be obtained within a short time.

[0045] If the voltage drops below a threshold value, the pulse width modulation may even be replaced by a continuous closing of the controllable switch. This allows for a particularly rapid deep discharge. As soon as the voltage then drops below a second, even lower threshold value, the switch is opened again so that the destruction of accumulator cells is prevented.

[0046] In the described manner, energy from the intermediate circuit thus is convertible into heat via the brake resistors (7, 9, 10).

[0047] If the series circuit that includes brake resistor 9 and its allocated brake chopper is fed directly from the voltage applied at the energy storage device, a simple deep discharge of the energy storage device is readily possible because the DC/DC converter is unable to operate without a minimum voltage, which means that no discharge through brake resistors 7 and 10 can be carried out below the minimum voltage. This is because the series circuit formed by the respective brake chopper and brake resistor 7 or 10 is supplied only indirectly via DC/DC converter 5 from the energy storage device.

[0048] When the energy storage device is discharged, the supply module is unable to conduct electric power from the AC voltage supply network to the intermediate circuit.

[0049] In further exemplary embodiments, the current flowing through the respective brake resistor is acquired and the instantaneous resistance value of the brake resistor is determined from the time-averaged voltage supplied via the brake chopper and also from the acquired time-averaged current, and the instantaneous temperature of the respective brake resistor is determined under consideration of a characteristic curve, which represents the temperature dependency of the brake resistor.

[0050] On the one hand, it may thus be monitored whether the temperature of the brake resistor exceeds a threshold value and an emergency shut-off of the brake chopper is therefore required. On the other hand, it is alternatively possible to set a power that is adapted to the determined temperature. This means that power P is adjusted to the temperature. As a result, a change in the ambient temperature or a worsening of the heat transfer resistance effective from the brake resistor to the environment is able to be taken into account.

[0051] In further exemplary embodiments, no constant pulse width modulation frequency is used, but the pulse width modulation frequency instead is varied intermittently or continuously. This makes it possible to achieve a less interfering noise emission.

LIST OF REFERENCE NUMERALS

[0052] 1 supply module [0053] 2 inverter [0054] 3 control electronics [0055] 4 electric motor [0056] 5 DC/DC converter [0057] 6 energy storage device [0058] 7 brake resistor [0059] 8 AC voltage supply network [0060] 9 brake resistor [0061] 10 brake resistor [0062] Claims 1 to 15. (Canceled).