Method for operating a drive system and drive system

Abstract

A method for operating a drive system and a drive system, the drive system comprising a rectifier, at least one inverter with an electric motor, wherein the electric motor is connected to a terminal on the AC voltage side of the inverter; wherein the terminal on the DC voltage side of the inverter is connected to the terminal on the DC voltage side of the rectifier via at least one inductance added to the line inductance; wherein a capacitor, in particular a non-polar capacitor, in particular a film capacitor, is connected to the terminal on the DC voltage side of the inverter and / or to the terminal on the DC voltage side of the rectifier; wherein a series circuit formed by a resistor and a controllable semiconductor switch, i.e. a brake chopper, is connected to the terminal on the DC voltage side of the inverter and / or to the terminal on the DC voltage side of the rectifier; wherein the brake chopper is operated at a single frequency f for a period of time during which the brake chopper is operated, in particular this frequency is spaced apart from the resonant frequency of a resonant circuit formed by the inductance and / or the capacitor.

Description

Technical Field

[0001] The invention relates to a method for operating a drive system and a drive system. Background Art

[0002] It is known that an electric machine can be operated as a generator or as a motor and that, therefore, if a capacitor is connected to a DC voltage-side terminal of an inverter supplying the electric machine, the voltage at this terminal increases during generator operation. Summary of the invention

[0003] The invention is based on the object of operating a drive system safely.

[0004] In a method for operating a drive system, wherein the drive system has a rectifier and at least one inverter with an electric motor, an important feature of the present invention is that the electric motor is connected to a terminal on the AC voltage side of the inverter; wherein the terminal on the DC voltage side of the inverter is connected to the terminal on the DC voltage side of the rectifier via at least one inductance that is additional to the line inductance / / an additional inductance that is additional to the line inductance; wherein a capacitor, in particular a non-polar capacitor, in particular a film capacitor, is connected to the terminal on the DC voltage side of the inverter and / or to the terminal on the DC voltage side of the rectifier; wherein a series circuit formed by a resistor and a controllable semiconductor switch, i.e. a brake chopper, is connected to the terminal on the DC voltage side of the inverter and / or to the terminal on the DC voltage side of the rectifier; wherein the brake chopper is operated at a single frequency f during its operating period, in particular this frequency is spaced apart from the resonant frequency of the resonant circuit formed by the inductance and / or the capacitor.

[0005] It is advantageous here that this frequency can be spaced apart from the resonant frequency of the drive system. This can avoid the excitation of oscillations and thus allow the drive system to be operated safely, in particular in terms of voltage. This is particularly advantageous if a plurality of inverters are supplied jointly from a DC voltage circuit, in particular an intermediate circuit. It is important here that the inductance and the capacitance cooperate to form an arrangement with a resonant frequency.

[0006] In an advantageous embodiment, the voltage supplying the series circuit, that is to say the intermediate circuit voltage, in particular the voltage present at the DC voltage-side connection of the inverter is detected. Advantageously, the operation of the brake chopper can be realized in a voltage-dependent manner. Thus, the control signal for the brake chopper can be generated by the control electronics, wherein the control signal can be generated on the one hand as a function of the intermediate circuit voltage and on the other hand as a function of the controllable time basis.

[0007] In an advantageous embodiment, the detected voltage value, i.e. the value of the intermediate circuit voltage, is digitized and transmitted as a digital serial data stream to a first digital filter, in particular a finite impulse response (FIR) filter, and to a second digital filter, in particular a finite impulse response (FIR) filter, wherein the second digital filter is started with a time difference relative to the first digital filter, in particular wherein the time difference is half the filter length. Advantageously, the error time can be reduced by being able to evaluate the digital data stream at a faster repetition rate.

[0008] In an advantageous embodiment, the output signals of the two filters are respectively transmitted to a comparison device for comparison with a first threshold value and a second threshold value; wherein the output signal of the comparison device is logically linked to a signal generated by a controllable time basis, in particular a controllable clock generator, in order to generate a control signal for the brake chopper. Advantageously, the voltage-related condition can be linked to the time-related condition. The control signal of the brake chopper can thus be generated in such a way that the brake chopper can always be operated at a particularly single fixed frequency when the intermediate circuit voltage is in a value range set for this. Compliance with the time-related condition ensures that the brake chopper is switched on at a frequency rhythm and switched off at a frequency rhythm. Operation is always carried out under the condition that the voltage is in a set range, because otherwise the brake chopper remains switched off.

[0009] In an advantageous embodiment, the brake chopper is always switched off when the intermediate circuit voltage falls below a threshold value U2 . Advantageously, the intermediate circuit voltage thus does not drop to an unexpectedly low value caused by the brake chopper.

[0010] In an advantageous embodiment, the brake chopper is switched on if the intermediate circuit voltage exceeds a first threshold value U1, in particular if either no switching-on has occurred previously or the last switching-on that occurred previously in time has occurred for more than a predetermined time period T, wherein the time period T is equal to the inverse of the frequency f. It is advantageous here that the brake chopper is switched on after exceeding U1, but only when the brake chopper is switched on again in a time-dependent manner for the first time or after an interruption in its operation. However, the interruption must have lasted longer than the inverse of the frequency and the intermediate circuit voltage must be greater than the threshold value U2.

[0011] In an advantageous embodiment, the first threshold value U1 is greater than the second threshold value U2. It is advantageous here that U1 is used as the switch-on threshold and U2 is used as the switch-off threshold.

[0012] In an advantageous embodiment, after the brake chopper has been switched on, the brake chopper is switched off, in particular at the latest after a time interval whose value is equal to the product of the duration T and a coefficient q (q×T); wherein the coefficient q has a value between zero and 1, in particular from a value in the range between 0.8 and 0.98.

[0013] This corresponds to a maximum continuous switching on of the brake chopper within the period T. A forced switching off is thus forced. The same applies to the reverse situation, so that a forced switching on occurs if the brake chopper was previously switched off to the maximum.

[0014] It is advantageous here that in order to comply with the frequency, a forced shutdown is also performed in the following case, i.e., if the intermediate circuit voltage is originally so high that the intermediate circuit voltage should be reduced, i.e., the energy of the intermediate circuit should be converted into heat by the brake chopper and the resistor connected in series as a brake resistor. Although it is disadvantageous that the brake chopper is designed for such compliance with the frequency, the excitation of resonance is prevented in this way. The brake chopper is preferably operable at the control limit. The brake chopper is then switched on for a maximum of 0.98×T and switched off for 0.02×T, instead of being switched on continuously. This loss in the control reserve / regulatory margin (Stellreserve) is taken into account in the planning / design of the brake resistor and is not a disadvantage in practice!!!

[0015] In an advantageous embodiment, the inverse of the duration T is greater than the resonant frequency of the resonant circuit formed by the inductor and / or the capacitor. Advantageously, a spacing of this frequency from the resonant frequency can be achieved, in particular a spacing of more than 40% of the value of the resonant frequency.

[0016] In an advantageous refinement, the brake chopper is switched off if the switch-on threshold U1 has been exceeded or reached at least once in the past and the intermediate circuit voltage U_ZK is above U2, if the time interval to the switch-off carried out previously in time reaches a time interval whose value is equal to the product of the duration T and the factor p (p×T), wherein the factor p has a value between zero and 1, in particular from a value in the range between 0.8 and 0.98. It is advantageous here to switch off the brake chopper in time so that the frequency is also maintained.

[0017] In an advantageous refinement, if the switch-on threshold U1 has been exceeded or reached at least once in the past and the intermediate circuit voltage U_ZK is above U2, the brake chopper is switched on if the time interval to the switch-on performed previously in time reaches a time interval whose value is equal to the product of the duration T and the factor q (q×T), wherein the factor q has a value between zero and 1, in particular from a value in the range between 0.8 and 0.98. It is advantageous here to switch on the brake chopper in time so that the frequency is also maintained.

[0018] In an advantageous embodiment, the factor q is equal to the factor p. It is advantageous here that the switch-on frequency and the switch-off frequency are identical and therefore no beat frequencies and their harmonics are additionally excited.

[0019] In an advantageous embodiment, the detected voltage value, i.e. the value of the intermediate circuit voltage, is digitized and transmitted as a digital serial data stream to a first digital filter, in particular a finite impulse response (FIR) filter, and to a second digital filter, in particular a finite impulse response (FIR) filter, wherein the second digital filter is started with a time difference relative to the first digital filter, in particular wherein the time difference is half the filter length. Advantageously, exceeding or falling below a threshold value can be detected more quickly.

[0020] In an advantageous embodiment, the output signals of the two filters are respectively transmitted to a comparison device for comparison with a first and a second threshold value, wherein the output signal of the comparison device is logically linked to a signal generated by a controllable time basis, in particular a controllable clock generator, in order to generate a control signal for the brake chopper. Advantageously, the voltage-related condition can be linked to the time-related condition.

[0021] An important feature of a drive system for implementing the above method is that the additional inductance is at least ten times, in particular at least one hundred times, greater than the line inductance. Advantageously, the resonant frequency is substantially independent of the line inductance. In this way, the additional inductance can be dimensioned such that the resonant frequency lies within a predetermined value range and the frequency for operating the brake chopper is sufficiently spaced apart from the resonant frequency.

[0022] The invention is not limited to the feature combinations of the individual claims. For a person skilled in the art, other meaningful combinations of the claims and / or the features of the individual claims and / or the features of the specification and / or the drawings may arise in particular from the objectives set out and / or from the comparison with the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will now be explained in more detail with reference to the accompanying schematic drawings.

[0024] Figure 1 Schematically describe the structure of the converter with brake chopper;

[0025] Figure 2 A drive system according to the present invention is schematically described;

[0026] Figure 3 shows the generation of a signal as a function of the intermediate circuit voltage;

[0027] Figure 4 Schematically shows the generation of a control signal for a brake chopper according to a signal implementation;

[0028] Figure 5 The resonant circuit formed by the line inductance and the capacitance C_ZK on the intermediate circuit side is shown without an additional intermediate circuit inductance L. DETAILED DESCRIPTION

[0029] like Figure 1 As shown, the converter has a rectifier 1 which can also be implemented as a feedback-supported rectifier. On the DC voltage side, a capacitor C is provided at the rectifier 1 which is of course implemented only as a non-polar capacitor, in particular as a film capacitor.

[0030] The voltage present at the capacitor C is detected and transmitted to the signal electronics 1 , which generates actuation signals for the controllable semiconductor switches arranged in the half bridge.

[0031] An electric machine M, in particular an AC motor, is supplied with power from the AC voltage-side connections of the inverter.

[0032] The voltage applied to the capacitor C is transmitted to the connection terminal on the DC voltage side of the inverter.

[0033] To protect against an excessively high voltage at the capacitor C, ie, against an excessively high intermediate circuit voltage, a series circuit is provided consisting of a braking resistor R and a controllable semiconductor switch 4 , wherein a freewheeling diode is likewise provided.

[0034] Therefore, with such a brake chopper, energy can be converted from the intermediate circuit into heat by means of a brake resistor, ie a brake resistor which essentially forms an ohmic resistor. In this way, excessively high system-critical voltage values ​​can be avoided.

[0035] The control signal for the semiconductor switch 4 is generated by the signal electronics 2 , to which the detected intermediate circuit voltage value is also transmitted.

[0036] The rectifier 1 is connected with its AC voltage-side connections to an AC voltage supply source.

[0037] The rectifier 1 can also be implemented as an AC / DC converter supporting feedback.

[0038] like Figure 2 As shown, according to the invention, a plurality of inverters can be connected to the intermediate circuit via an additional inductance L, so that in motor operation of an electric machine, in particular an AC machine, supplied by the corresponding inverter 20 , energy is extracted from the intermediate circuit, and in generator operation energy is supplied to the intermediate circuit.

[0039] A brake chopper with a brake resistor R is also assigned to each inverter 20 .

[0040] The capacitor C_ZK can be realized as a non-polar capacitor, in particular as a film capacitor.

[0041] For safe operation of drive systems with multiple inverters, however, only a single braking resistor must be connected to one inverter. The brake chopper of the other inverter can remain switched on.

[0042] Alternatively, in each inverter 20 , a capacitor C_ZK is connected to its respective DC voltage-side connection, to which a series circuit consisting of a respective controllable semiconductor switch, in particular a brake chopper, and a resistor, in particular a brake resistor, is connected in parallel.

[0043] On the one hand, the upper potential of the DC voltage side connection of the inverter 20 is connected to the upper potential of the intermediate circuit voltage U_ZK via the inductor L. On the other hand, the lower potential of the DC voltage side connection of the inverter 20 is connected to the lower potential of the intermediate circuit voltage U_ZK via the inductor L.

[0044] The intermediate circuit voltage is in turn generated by means of a mains-fed rectifier 21 , at the DC voltage-side connections of which non-polarized capacitors are arranged.

[0045] As in Figure 5 As shown, if no additional inductance is present, the capacitor C_ZK of the inverter is connected via the line inductance L_ZK. Thus, an excitation 50 is introduced into the drive system by the inverter 20, which excites the oscillation of the resonant circuit formed by the capacitor C_ZK and the line inductance L_ZK.

[0046] But because Figure 2 In addition, an inductance L shown in is present which is at least ten times greater than the line inductance L_ZK of the intermediate circuit, so that the resonant frequency thereby reaches a predetermined value range, for example 2 kHz, with a deviation of less than exactly 10%.

[0047] According to the invention, the brake chopper is operated at a frequency of 3 kHz, in particular at a network voltage of 400 V to 500 V, so that the brake chopper cannot excite oscillations of the resonant circuit. Since the pulse width modulation frequency of the controllable semiconductor switches of the inverter is also operated at a frequency above the value range, in particular at 4 kHz, 8 kHz or 16 kHz, the inverter cannot excite oscillations of the resonant circuit either.

[0048] In the case of lower mains voltages, such as, for example, 200 V to 240 V, the frequency can also be selected, by way of example, to be 5 kHz.

[0049] exist Figure 3 and 4 The operation mode and operating conditions of the brake chopper are further explained in Figure 3 The voltage-dependent conditions for the control of the brake chopper are shown schematically. Figure 4 The time-dependent conditions for controlling the brake chopper are shown schematically.

[0050] like Figure 3 As shown in FIG, the intermediate circuit voltage detected and converted into a serial digital data stream by means of a Delta-Sigma converter is transmitted to two digital filters, in particular finite-length unit impulse response (FIR) filters, whose corresponding start signals are offset in time from each other by half the filter length Ta / 2. The start signal is generated by a time base 30, to which a synchronization signal Sync is sent.

[0051] The digital filter 31 acts in the manner of a digital low-pass filter, ie in particular has an attenuation strength which has a window-shaped relationship with the frequency.

[0052] The output signals of the filters 31 are respectively transmitted to corresponding serial-parallel converters 32, whose digital parallel output signals are respectively transmitted to corresponding comparators 33, which compare the output signals, ie the detected corresponding voltage values, with the first threshold value U1 and the second threshold value U2.

[0053] The first threshold value U1 corresponds to the minimum voltage required to cause switching on when the brake chopper was previously switched off. The second threshold value U2 marks the voltage below which the brake chopper is switched off anyway.

[0054] The result of the comparison with the first threshold value U1 is respectively output on a signal line 37 .

[0055] The results of the comparison with the second threshold value U2 are each output on a second signal line 38 which leads to a combining device 39 .

[0056] In the means 34 for voltage monitoring, it is checked whether the first threshold value U1 is greater than zero. If not, then upon detection of a negative voltage, a shutdown of the drive system is initiated or the drive system is brought into a safe state.

[0057] For this purpose, a first signal line 37 leads from the respective comparator 33 to the respective AND connection 35 , with the respective result of the monitoring of the first threshold value U1 , ie with the output signal of the device 34 for voltage monitoring in order to shut down if a negative voltage is detected.

[0058] The comparator 33 is designed in such a way that it takes into account the hysteresis in each case in the corresponding comparison.

[0059] The connection means 39 combines the two signals on the two signal lines 38 into 2 bits of information, which are forwarded as BRC_Info. In this case, the information is encoded whether the two signals are zero, or whether at least one of the two signals is not zero, or whether both signals are not zero. This encodes whether the intermediate circuit voltage is greater than the switch-on threshold, less than the switch-off threshold, or lies between these two thresholds.

[0060] The output signal of AND connection 35 is also transmitted to signal generator 36 like the output signal of combining device 39. Signal generator 36 thus provides the above-mentioned signal BRC_Info and signal Ein_U_puls so that a setting is performed when threshold value U1 is exceeded and a reset is performed when it is undershot.

[0061] By following Figure 3 The double voltage processing with a time difference of half the filtering time enables a faster recognition of exceeding or falling below the threshold value (U1, U2).

[0062] like Figure 4 As shown in FIG. 1 , the signal BRC_Info is transmitted to the time base / time base 41 , the output signal of the time base 41 is transmitted to the connecting mechanisms 42 and 43 , and the output signals of the connecting mechanisms 42 and 43 are transmitted to the signal generating mechanism 44 .

[0063] In this way, according to Figure 3 and Figure 4 Consideration is given to time conditions and voltage conditions in generating the drive control signal BRC for the brake chopper.

[0064] On the one hand, if the voltage is above a threshold value U1 , the brake chopper is switched on, and if the voltage is below a threshold value U2 , the brake chopper is switched off.

[0065] U2 is smaller than U1 here.

[0066] If the intermediate circuit voltage U_ZK then rises from zero, the brake chopper is switched on only when U1 is exceeded. As soon as it falls below U2, the brake chopper is switched off anyway. After the brake chopper has been switched on, the brake chopper is switched off at the latest after a time period q×T, wherein the time period T is the reciprocal of a frequency predetermined for the brake chopper, in particular, for example, 3 kHz. The value of the coefficient q is between zero and 1 and is preferably selected to be large, for example, the coefficient q is 0.95.

[0067] Furthermore, if the switch-on threshold U1 has been reached at least once in the past and the intermediate circuit voltage U_ZK is still above U2, the brake chopper is switched off if the time period T has elapsed since the switch-off performed previously in time; the brake chopper is switched on if the time period T has elapsed after the switch-on performed previously in time.

[0068] The effect of this voltage and time condition is that, if the brake chopper is operated, it is operated at all events at a frequency f=1 / T. Otherwise, the brake chopper remains switched off.

[0069] In this way, operation of the brake chopper therefore does not induce undesired oscillations in the intermediate circuit.

[0070] Even if the different frequencies do not have infinitesimal amplitudes purely theoretically in a Fourier analysis of the time curve due to the resulting operating time of the brake chopper, the energy input at the resonance frequency is nevertheless too low to excite dangerous or undesirable oscillations.

[0071] In the invention, robust operation of a drive system with a plurality of inverters supplied with a common DC voltage and the avoidance of resonances and resonance growth are advantageously achieved. Furthermore, a reduction in the load on the individual components can be achieved, since the AC voltage component of the intermediate circuit current is reduced. Furthermore, information about the combined current intermediate circuit capacitance is not necessary. Therefore, it is not necessary to parameterize the control individually. In this way, even plug-and-play implementations can be achieved. Furthermore, it is advantageous that the inverter can also be switched on afterwards without the need for re-parameterization of the system. The hysteresis of the brake chopper automatically occurs correctly through the control. However, it is also possible to realize the connection points of the brake resistor at different positions.

[0072] List of reference numerals:

[0073] 1. Rectifier

[0074] 2Signal electronics

[0075] 3 Inverter

[0076] 4. Switches that can be driven, especially brake choppers

[0077] 5. Converter

[0078] 20Inverter

[0079] 21. Rectifier

[0080] 30 time basis

[0081] 31 Filters, especially digital filters

[0082] 32 serial-to-parallel converter

[0083] 33 Comparator with hysteresis

[0084] 34 Voltage monitoring to shut down when negative voltage is detected

[0085] 35 and connect

[0086] 36 Signal generation

[0087] 37 First signal line

[0088] 38 Second signal line

[0089] 39 Combination device

[0090] 40 Voltage-dependent logic devices

[0091] 41 Controllable time base, especially controllable counter

[0092] 42 Combination device

[0093] 43 Combination device

[0094] 44Signal generating mechanism

[0095] 50 Incentive

[0096] Clk clock signal

[0097] BRC is used for control signals of semiconductor switches, especially brake choppers.

[0098] BRC_Info for input signals of time base 41

[0099] Ein_U_puls connects the signal

[0100] Aus_U_puls shut down signal

[0101] Sync signal

[0102] Load charging signal

[0103] Koeff coefficient

[0104] Data Clock

[0105] U1 switch-on threshold

[0106] U2 shutdown threshold

[0107] RBrake resistor

[0108] M Motor

[0109] C Capacitor

[0110] L Inductance

[0111] L_ZK Line Inductance

[0112] C_ZK Capacitor on the intermediate circuit side of the corresponding inverter

Claims

1. A method for operating a drive system having a rectifier and at least one inverter with an electric machine, wherein: The motor is connected to a connection terminal on the AC voltage side of an inverter; wherein the connection terminal on the DC voltage side of the inverter is connected to a connection terminal on the DC voltage side of a rectifier via at least one additional inductance for a line inductance; wherein a capacitor is connected to a connection terminal on the DC voltage side of the inverter and / or to a connection terminal on the DC voltage side of the rectifier; wherein a series circuit formed by a resistor and a controllable brake chopper is connected to a connection terminal on the DC voltage side of the inverter and / or to a connection terminal on the DC voltage side of the rectifier; characterized in that the brake chopper is operated at a single frequency f during its operating duration, In this case, the voltage of the intermediate circuit supplying the series circuit is detected. wherein the detected value of the intermediate circuit voltage is transmitted as a digital serial data stream on the one hand to a first digital filter and on the other hand to a second digital filter; wherein the second digital filter is started with a time difference relative to the first digital filter; The output signals of the two filters are respectively transmitted to a comparison device for comparison with a first threshold value and a second threshold value; the output signal of the comparison device is logically linked with a signal generated by a controllable time basis to generate a control signal for the brake chopper.

2. The method according to claim 1, characterized in that This frequency is spaced apart from the resonant frequency of the resonant tank formed by the inductor and / or the capacitor.

3. The method according to claim 1, characterized in that The time difference is half the filter length.

4. The method according to claim 1, characterized in that: When the intermediate circuit voltage falls below a second threshold value U2 , the brake chopper is switched off.

5. The method according to claim 4, characterized in that When the intermediate circuit voltage exceeds a first threshold value U1 , the brake chopper is switched on if no switching has taken place previously or if the last switching that took place previously in time has elapsed for more than a predetermined time period T, wherein the time period T is equal to the inverse of the frequency f.

6. The method according to claim 5, characterized in that The first threshold value U1 is greater than the second threshold value U2.

7. The method according to claim 5, characterized in that After the brake chopper has been switched on, the brake chopper is switched off at the latest after a time interval whose value is equal to the product of the duration T and the factor q (q×T); the factor q has a value between zero and one.

8. The method according to claim 7, characterized in that The inverse of the time duration T is greater than the resonant frequency of the resonant circuit formed by the inductor and / or the capacitor.

9. The method according to claim 5, characterized in that If the switch-on threshold U1 has been exceeded or reached at least once in the past and the intermediate circuit voltage U_ZK is above U2, the brake chopper is switched off if the time interval to a switch-off performed previously in time reaches a time interval whose value is equal to the product of the duration T and a coefficient p (p×T), wherein the value of the coefficient p is between zero and 1.

10. The method according to claim 9, characterized in that If the switch-on threshold U1 has been exceeded or reached at least once in the past and the intermediate circuit voltage U_ZK is above U2, the brake chopper is switched on if the time interval to the switch-on performed previously in time reaches a time interval whose value is equal to the product of the duration T and the coefficient q (q×T), wherein the value of the coefficient q is between zero and 1.

11. The method according to claim 10, characterized in that The coefficient q is equal to the coefficient p.

12. The method according to claim 10, characterized in that The value of the coefficient q and the value of the coefficient p are between 0.8 and 0.

98.

13. The method according to claim 1, characterized in that The additional inductance is at least ten times the line inductance.

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