Drive comprising an electric motor supplied by a converter, and method for operating a drive

Abstract

drive comprising an electric motor supplied by an inverter (6), wherein the converter (6) has an inverter (12) which has a DC-side connection and an AC-side connection, where a series circuit is supplied from the DC-side connection and the motor is supplied from the AC-side connection, wherein the series circuit has a resistance and a controllable semiconductor switch (11) for controlling the current flowing through the series circuit, wherein the voltage available at the DC-side connection of the inverter (12) is detected, characterized by the fact that - a comparator is set up in such a way and is operatively connected to a controllable semiconductor switch (11) such that an output signal of the comparator controls the controllable semiconductor switch (11), wherein the comparator is set up and is in operative connection with a utilization determination device (21) such that the output signal is also supplied to the utilization determination device (21) and the utilization determination device (21) determines a signal value from it, - the resistance has a braking resistance (1), - the comparator is set up in such a way that it monitors the recorded voltage value for exceeding a first threshold and falling below a second threshold, - the utilization determination device (21) has a counter whose counting direction depends on the value of the detected voltage and / or on the control signal (4) provided for the controllable semiconductor switch (11), - the utilization determination device (21) is set up such that a respective counting speed is provided during downward counting depending on the signal value.

Description

[0001] The invention relates to a drive comprising an electric motor supplied by a converter, and a method for operating a drive.

[0002] It is generally known that a drive has a converter-fed motor, wherein the converter has a rectifier and an inverter that can be fed from the DC-side connection of the rectifier.

[0003] From DE 27 34 467 A1, a brake control arrangement for a traction motor drive system is known as the closest prior art.

[0004] From DE 10 2013 014 609 A1 a motor control device with at least two resistance discharge units is known.

[0005] From JP 2003 - 333873 A a method for protection against overheating in a resistor is known.

[0006] The invention is therefore based on the objective of further developing a drive system, with the aim of increasing safety.

[0007] According to the invention, the problem is solved in the drive according to the features specified in claim 1 and in the method according to the features specified in claim 8.

[0008] Important features of the invention for the drive are that it has an electric motor supplied by a converter, wherein the converter is an inverter having a DC-side connection and an AC-side connection, wherein a series circuit is supplied from the DC-side connection, in particular the intermediate circuit voltage connection, and the motor is supplied from the AC-side connection, wherein the series circuit has a resistance and a controllable semiconductor switch, in particular for controlling the current flowing through the series circuit, where the voltage available at the DC-side connection of the inverter, in particular the intermediate circuit voltage, is measured, wherein a comparator generates an output signal that controls the controllable semiconductor switch, wherein the output signal is also supplied to a utilization determination device and the utilization determination device determines a signal value from it, in particular which can be used as a measure of the temperature of the resistance. in particular, wherein the signal value is fed to a second comparator which, upon exceeding a threshold value, supplies the inverter with a shutdown signal, which causes the respective switches of the inverter electrically connected to the AC-side connection to open or leads to a safe stop of the drive in accordance with the safety standard.

[0009] An advantage of this is that if a critical load on the braking resistor is exceeded, i.e., if a critical temperature is exceeded, the energy supply to it can be disconnected.

[0010] Furthermore, the wiring and use of a bimetallic switch in the braking resistor for its thermal monitoring are eliminated. An advantage of this is that a braking resistor can also be thermally monitored without a bimetallic switch using a computational model. This reduces the wiring effort and allows for the use of simpler, less expensive braking resistors without a bimetallic switch, or even non-intrinsically safe braking resistors.

[0011] In an advantageous embodiment, the resistor has a braking resistance, in particular wherein the resistor comprises a first braking resistor which is arranged inside the housing of the inverter, or a second braking resistor which is arranged outside the housing of the inverter, In particular, the first and second braking resistors can be operated in series, parallel, or alternatively. An advantage of this is that the braking resistor dissipates energy generated by the motor as thermal heat flow to the environment when the DC link voltage exceeds a first threshold value and the inverter switches are thus at risk due to excessive DC link voltage.

[0012] In an advantageous embodiment, the comparison device monitors the detected voltage value for exceeding a first threshold and falling below a second threshold. in particular where the second threshold is smaller in absolute value than the first threshold, In particular, the comparator is configured such that when the first threshold is exceeded, the output signal controls the controllable semiconductor switch in such a way that current is supplied to the resistor, and when the second threshold is undershot, the output signal controls the controllable semiconductor switch after a minimum switching time in such a way that no current flows through the resistor. An advantage of this is that when the first threshold is exceeded, the DC link voltage is reduced again by supplying energy to the braking resistor, i.e., closing the controllable semiconductor switch and thus enabling the current supply from the DC link to the resistor. When the second threshold, which is lower than the first threshold, is undershot, the current supply is stopped after a minimum switching time. The switch-on time ends after a minimum switching time. Because the first and second thresholds are different, hysteresis is created. The minimum switch-on time prevents excessively frequent switching of the semiconductor on and off, thus reducing the switching power loss in the semiconductor switch.

[0013] In an advantageous embodiment, the utilization determination device has a counter whose counting direction depends on the value of the detected voltage or on a control signal provided for the controllable semiconductor switch. in particular where the direction of counting of the counter, in particular the counting upwards or downwards of the counter, is positive when the first threshold is exceeded and negative when the second threshold is not reached, In particular, a higher counting rate is used for upward counting than for downward counting, which depends on the load. An advantage of this approach is that a measure of the temperature can be determined very easily. However, the physically correct exponential temperature curve is not determined and / or used; instead, only linear temperature curves are determined and / or applied. When the temperature rises, only a single counting rate is used, i.e., only a single linear curve. When the temperature falls, several linear curves, i.e., different counting rates, are used. The counting rate decreases monotonically with the temperature, but not strictly monotonically. Each temperature range is uniquely assigned its counting rate. The counting rate corresponds to the clock signal at the counter's input.The counter reading therefore increases per time period according to the counting speed, if long-term averaging is used and / or the time period is an integer multiple of the cycle time.

[0014] In an advantageous embodiment, the utilization determination device is arranged such that, during downward counting, a respective counting speed is provided, and in particular applied, depending on the signal value, in particular the utilization or temperature of the braking resistor, and in particular wherein a first counting speed is applied in a first value range of the signal value and a second counting speed is applied in a second value range of the signal value. in particular, the first counting speed is greater in magnitude than the second counting speed, In particular, the signal values ​​of the second range are larger in magnitude than the signal values ​​of the first range. An advantage of this is that a measure of the temperature can be determined in a particularly simple way, without having to define an exponential function.

[0015] In an advantageous embodiment, only a single counting speed is used for the upward counting. The advantage here is that a particularly simple method of determining the temperature is employed, which deviates from the physically correct method but requires very little effort to implement.

[0016] In an advantageous embodiment, the utilization determination device is set up such that a respective counting speed is provided during downward counting, depending on the signal value. The counting speed decreases monotonically with decreasing signal values, but not strictly monotonically. An advantage of this is that slower counting speeds occur at small signal values ​​than at larger ones. This allows the temperature profile to be easily simulated without requiring particularly high computing power.

[0017] Important features of the method for operating a drive, in particular the aforementioned one, are that the drive has a braking resistor that can be supplied from an intermediate circuit of the drive, wherein a utilization rate is determined from the detected intermediate circuit voltage and / or from the control signal provided for the controllable semiconductor switch by operating a counter in upward counting mode when the detected intermediate circuit voltage exceeds a first threshold value, and by operating the counter in downward counting mode when the detected intermediate circuit voltage falls below a second threshold, where the counting speed in downward counting operation depends on the magnitude of the detected intermediate circuit voltage and / or on the load on the braking resistor, in particular where the respective counting speed - with decreasing absolute values ​​of the recorded intermediate circuit voltage- - and / or with decreasing absolute values ​​of temperature or load on the braking resistor, which is switched off when the controllable semiconductor switch is switched off, i.e. when the second threshold is undershot, and after the minimum duty cycle has elapsed, decreases monotonically in absolute value, but in particular does not decrease strictly monotonically. in particular, where, when a predetermined counter value is exceeded, the supply of the braking resistor from the intermediate circuit is terminated and / or the inverter of the drive's converter is blocked and / or the switches of the drive's inverter are opened or made high-impedance.

[0018] An advantage of this is that a measure for the temperature of the braking resistor can be easily determined, and thus, if a critical temperature is exceeded, the inverter can be brought into a safe state, for example by not supplying any further energy to the braking resistor and / or by opening the switches of the inverter.

[0019] The invention will now be explained in more detail with the help of illustrations: In the Fig. Figure 1 shows a schematic representation of the drive system.

[0020] As in Fig. As shown in Figure 1, the drive comprises an inverter-fed electric motor M, wherein the inverter 6 has a rectifier 13 which is supplied from an electrical supply network 10, in particular a three-phase network. On the output side, the rectifier 13 provides a unipolar voltage, in particular a DC voltage, which is also referred to below as the intermediate circuit voltage.

[0021] The inverter 12 is supplied from the intermediate circuit voltage, and its output voltage, i.e. alternating voltage, in particular three-phase voltage, feeds the motor M.

[0022] The intermediate circuit voltage is buffered with an intermediate circuit capacitor 5.

[0023] A series circuit is supplied from the intermediate circuit voltage. This circuit consists of a controllable semiconductor switch 11, specifically a braking chopper, and at least one resistor. The resistor can optionally be implemented as a first braking resistor 1, located inside the housing of the inverter 6, or as a second braking resistor 1a, located outside the housing of the inverter 6, i.e., externally. A jumper must be arranged accordingly for this purpose. A parallel or series connection of the first and second braking resistors is also possible.

[0024] A light-emitting diode (LED) is arranged in parallel with the first braking resistor 1, so that the operation of the semiconductor switch can be monitored with galvanic isolation by means of a phototransistor. The voltage signal generated by the phototransistor is fed as a feedback signal 2 to a control electronics unit 3, which is designed to generate the control signals for the braking chopper 4. This control electronics unit then generates a corresponding control signal for the controllable semiconductor switch 11, i.e., for the braking chopper. Monitoring for the use of the first or second braking resistor is also possible (1, 1a). Preferably, the control signal 4 is pulse-width modulated, with the pulse-width modulation ratio corresponding to the modulation level.

[0025] The voltage value 8 of the intermediate circuit voltage, detected by a voltage sensing device V, is supplied to the control electronics 3 - as is the feedback signal 2.

[0026] As in Fig. As shown in Figure 2, the DC link voltage is monitored for exceeding or falling below threshold values ​​by means of a monitoring device 20. If the DC link voltage exceeds a first threshold value U1, the controllable semiconductor switch 11 is activated such that a current driven by the DC link voltage flows through the resistor, thus converting power from the DC link into ohmic heat. If the DC link voltage falls below a second threshold value U2, which is lower than the first threshold value U1, the controllable semiconductor switch 11 is opened after a minimum on-time has elapsed.

[0027] Thus, the intermediate circuit voltage is regulated to a value between U1 and U2 - at least in generator mode.

[0028] The control electronics 3 for generating the control signals 4 for the controllable semiconductor switch, in particular the brake chopper, is preferably implemented as a freely programmable gate array (FPGA) or as a DSP. This makes the control electronics 3 particularly quick and easy to provide.

[0029] The load is determined by means of the load determination device 21 arranged in the control electronics 3. For this purpose, a counter is incremented for the duration of the current being drawn from the intermediate circuit to the resistor and incremented otherwise.

[0030] The counter reading n is therefore a measure of the thermal utilization rate, i.e., a measure of the temperature of the braking resistor.

[0031] When counting up, the counting speed is much faster than when counting down; therefore, the counting speed n+ during counting up is greater in absolute value than the counting speed n- during counting down. In a first implementation, the counting up is performed using the system clock CLK. Since this results in a linear increase in the temperature value over time at a constant load level, there is indeed a deviation from an exponential function that would occur in the idealized case. However, only the temperature range below the wire's breaking point—that is, the temperature range in which the braking resistor is usable—is approximated by the linear function.

[0032] When counting down, the exponential function that occurs in the idealized case is not approximated as a single linear function. Instead, the entire temperature range in which the braking resistor can be used is divided into several adjacent temperature ranges. Each of these individual temperature ranges is assigned a specific counting speed n-, whereby this counting speed n- decreases with decreasing temperature, in particular monotonically. The lowest temperature range is therefore assigned the slowest counting speed n- when counting down.

[0033] The temperature ranges are easily defined by dividing the utilization level into, for example, ten ranges. In this example, increments of 10% are advantageously used: a first range from 0 to 10%, a second range from 10% to 20%, a third range from 20% to 30%, and so on up to a final range from 90% to 100%. If the utilization exceeds 100%, the braking resistor's functionality is not guaranteed, and failure is likely, for example, due to a broken wire or similar issue.

[0034] As in Fig. Figure 2 shows the downward counting rate n- assigned to each area in the utilization determination average 21. For this purpose, the utilization rate n is compared with the threshold values ​​X_0 to X_m that characterize the areas, whereby each area is assigned a slower counting rate n- by supplying a correspondingly reduced system clock CLK_0 to CLK_m.

[0035] The utilization level n is only available as an output signal if a release signal 2 is also present, especially when using a first braking resistor 1. Otherwise, an error condition exists.

[0036] The invention therefore relates to a drive comprising an electric motor supplied by a converter, wherein the converter is an inverter having a DC-side connection and an AC-side connection. wherein a series circuit is supplied from the DC-side connection, in particular the intermediate circuit voltage connection, and the motor is supplied from the AC-side connection, wherein the series circuit has a resistance and a controllable semiconductor switch, in particular for controlling the current flowing through the series circuit, where the voltage available at the DC-side connection of the inverter, in particular the intermediate circuit voltage, is measured, wherein a comparator generates an output signal that controls the controllable semiconductor switch, wherein the output signal is also supplied to a utilization determination device and the utilization determination device determines a signal value from it, in particular which can be used as a measure of the temperature of the resistance. in particular wherein the signal value is fed to a second comparator which, when a threshold value is exceeded, supplies the inverter with a shutdown signal, which causes the respective switches of the inverter to be electrically connected to the AC-side connection to be opened.

[0037] In another embodiment according to the invention, there are not ten temperature ranges, but a different number of temperature ranges, for example between five and fifteen. Reference symbol list 1. First braking resistor, internal, i.e., within the housing of the drive's inverter 1a second braking resistor, optional 2 Binary feedback signal 3 Control electronics for generating the control signals for the brake chopper 4 Control signal for the brake chopper, especially pulse width modulated 5 Intermediate circuit capacitor 6 inverters 7 FPGA 8. Recorded DC link voltage value 10 electrical supply network, in particular three-phase network 11 controllable semiconductor switches, in particular brake choppers 12 inverters 13 rectifiers 20 monitoring devices for monitoring voltage 21 Utilization determination tools for determining thermal utilization

Claims

[1] Drive comprising an electric motor supplied by an inverter (6), wherein the converter (6) has an inverter (12) which has a DC-side connection and an AC-side connection, where a series circuit is supplied from the DC-side connection and the motor is supplied from the AC-side connection, wherein the series circuit has a resistance and a controllable semiconductor switch (11) for controlling the current flowing through the series circuit, wherein the voltage available at the DC-side connection of the inverter (12) is detected, characterized by , that - a comparator is set up in such a way and is operatively connected to a controllable semiconductor switch (11) such that an output signal of the comparator controls the controllable semiconductor switch (11), wherein the comparator is set up and is in operative connection with a utilization determination device (21) such that the output signal is also supplied to the utilization determination device (21) and the utilization determination device (21) determines a signal value from it, - the resistance has a braking resistance (1), - the comparator is set up in such a way that it monitors the recorded voltage value for exceeding a first threshold and falling below a second threshold, - the utilization determination device (21) has a counter whose counting direction depends on the value of the detected voltage and / or on the control signal (4) provided for the controllable semiconductor switch (11), - the utilization determination device (21) is set up such that a respective counting speed is provided during downward counting depending on the signal value. [2] Drive according to claim 1, characterized by , that the signal value is fed to a second comparator which, when a threshold value is exceeded, supplies a shutdown signal to the inverter (12), which causes the respective switches of the inverter (12) electrically connected to the AC-side connection to be opened. [3] Drive according to claim 1 or 2, characterized by , that the resistor has a first braking resistor (1) which is located inside the housing of the inverter (6) and / or a second braking resistor (1a) which is located outside the housing of the inverter (6). [4] Drive according to at least one of the preceding claims, characterized by, that the comparator is set up such that when the first threshold is exceeded, the output signal controls the controllable semiconductor switch (11) in such a way that current is supplied to the resistor, and when the second threshold is undershot, the output signal controls the controllable semiconductor switch (11) in such a way that after an additional minimum on-time no current flows through the resistor. [5] Drive according to at least one of the preceding claims, characterized by , that the counting direction of the counter is positive when the first threshold is exceeded, i.e., counting upwards, and negative when the second threshold is not reached, i.e., counting downwards. [6] Drive according to claim 5, characterized by , that a higher counting speed is provided for when counting upwards than when counting downwards. [7] Drive according to at least one of the preceding claims, characterized by , that A first counting speed is applied in a first value range of the signal value, and a second counting speed is applied in a second value range of the signal value. where the first counting speed is greater in magnitude than the second counting speed, where the signal values ​​of the second value range are larger in magnitude than the signal values ​​of the first value range. [8] Drive according to at least one of the preceding claims, characterized by , that only a single counting speed is used when counting upwards. [9] Drive according to at least one of the preceding claims, characterized by , that the utilization determination device (21) is set up such that, when counting down, a respective counting speed is provided depending on the signal value, where the respective counting speed decreases monotonically in magnitude with decreasing signal values, but does not decrease strictly monotonically. [10] Method for operating a drive, wherein the drive has a braking resistor (1) that can be supplied from an intermediate circuit of the drive, characterized by , that a utilization rate is determined from the detected intermediate circuit voltage and / or from the control signal (4) for a controllable semiconductor switch (11) which is intended to control the current in the braking resistor (1), by operating a counter in upward counting mode when the detected intermediate circuit voltage exceeds a first threshold value, and by operating the counter in downward counting mode when the detected intermediate circuit voltage falls below a second threshold, where the counting speed in downward counting operation depends on the value of the detected intermediate circuit voltage and / or the thermal load. [11] Method according to claim 10, characterized by , whereby the respective counting speed decreases monotonically in magnitude with decreasing values ​​of the detected intermediate circuit voltage and / or the thermal load, but does not decrease strictly monotonically. [12] Method according to claim 10 or 11, wherein, when a predetermined counter value is exceeded, the supply of the braking resistor (1) from the intermediate circuit is terminated and / or the inverter (12) of the converter (6) of the drive is blocked and / or the switches of the inverter (12) of the drive are opened.

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