DE102018115977A1 - Supply unit for a motor control with determination of the direct current component of a Rogowski flow measurement and method for determining the direct current component of a Rogowski current measurement at a supply unit for a motor control - Google Patents

Abstract

The invention relates to a supply unit for a motor control, with a three-phase supply input, a three-phase rectifier which is connected to the three-phase supply input; a DC voltage intermediate circuit which is connected to the three-phase rectifier, a computing unit and a Rogowski measuring device, set up to measure the phase current and output it to the computing unit. According to the invention, the supply unit has a network angle measuring device, a point in time being stored in the computing unit at which it can be assumed that the phase current is zero and the computing unit is set up to measure a phase current value measured by the Rogowski measuring device at the predetermined point in time save as offset value and correct a phase current value measured outside of the predetermined time by the Rogowski measuring device by subtracting the offset value and output the corrected phase current value or a value derived therefrom. The invention also relates to a corresponding method for determining the DC component of a Rogowski current measurement in a supply unit for an engine control.

Description

The invention relates to a supply unit for a motor control, which can be connected to a three-phase supply network and is used for DC voltage supply for a motor control.

Such a supply unit for a motor controller has a three-phase supply input that can be connected to a three-phase supply network. A typical supply network has a phase shift of essentially 120 ° between the individual phases and a frequency of around 50 Hz in Europe. The three phases of the supply input are connected to the AC side of a three-phase rectifier, which switches the individual phases in the correct phase by switching blocking elements DC side switches on. A DC voltage intermediate circuit is connected to the DC voltage side, to which a motor controller for its DC voltage supply can be connected. The DC voltage intermediate circuit can, for example, have a larger capacity in order to smooth the supply voltage rectified by the three-phase rectifier.

The supply unit and the motor control can also be arranged in a common housing. This combination of supply unit and motor control is usually called a frequency converter or servo converter.

In such supply units, it is advantageous if the phase current of the individual phases can be measured at the supply input. This is necessary, for example, to determine the total drive power of an axis system that can be connected to the supply unit with one or more motor controls. The RMS values of the individual phases are also important to protect individual components from overload. This is of particular interest for the protection of thyristors, which can be installed in three-phase rectifiers. Furthermore, the power distribution over the individual phases can also be determined by measuring the phase currents. Of particular interest is the measurement of leakage currents or fault currents, such as those that can occur in the event of a fault, for example due to a ground fault on one of the components. The fault current can be determined from the individual phase currents, since these add up to zero in the fault-free operation and only have a non-zero sum if there is a fault current. For safety reasons, it is desirable to detect such an error in order to be able to initiate appropriate measures, such as an emergency shutdown.

To measure the phase current, the supply unit therefore has a Rogowski measuring device which is arranged on one of the three phases of the supply input in order to measure the phase current of this phase.

A Rogowski measuring device in particular comprises a Rogowski coil, which can be designed, for example, as a toroidal air coil. The Rogowski coil can then be arranged, for example, concentrically around the conductor to be measured. An alternating current flowing through the current conductor generates a variable magnetic field, which in turn induces a voltage in the Rogowski coil surrounding it. If the voltage in the Rogowski coil is measured with high resistance, so that the current in the Rogowski coil is almost zero, then the measured voltage is proportional to the time derivative of the current in the conductor. In order to obtain the current itself from the time derivative of the current, a time integral must be formed. This is typically achieved by means of an integrator, for example in the form of an analog circuit. However, by measuring the time derivative and subsequent integration, the DC component of the phase current is lost. With a Rogowski measuring device, which consists at least of a Rogowski coil and an associated evaluation unit with integrator, only the AC component of the current can therefore be measured directly.

In addition to the AC component, however, the phase currents can also have a DC component. In particular, in the event of a fault, such as an earth fault, the phase currents can even contain mainly a direct component, whereas the alternating current component can be very small. The phase currents of the three phases are typically added for fault current detection. In fault-free operation, the currents of the three phases should add up to zero. If there is an earth fault, however, the sum of the phase currents is not equal to zero. Without the large DC component, however, only the small AC component remains for evaluation. This results in an unfavorably low measuring sensitivity for the detection of an earth fault. If the supply unit is to be switched off when there is an earth fault, it is necessary to set a correspondingly high threshold value for the switch-off to be used to avoid faulty shutdowns. However, this means that high-resistance earth faults, which lead to comparatively low fault currents, cannot be detected.

It is therefore an object of the invention to provide a supply unit with which a determination of the phase current including the DC component is possible.

The object is achieved by a supply unit for a motor control with a three-phase supply input, which can be connected to a three-phase supply network, and a DC voltage intermediate circuit for connection to a motor control for the DC supply of the motor control. The supply unit has a three-phase rectifier, the AC voltage side of which is connected to the three-phase supply input and the DC voltage side of which is connected to the DC voltage intermediate circuit. The current is measured by means of a Rogowski measuring device, which is arranged on at least one of the three phases of the supply input and is set up to measure the phase current of this phase. Due to its design, a Rogowski measuring device has a high-pass behavior with a typical cut-off frequency of less than 1 Hz. In measurement technology, lower cut-off frequencies of only a few milliseconds are reached, but the effort involved is very high. Typically, 0.5 Hz is sufficient and inexpensive to implement. Depending on the application, it can also be designed for significantly higher cut-off frequencies. The measured phase current value therefore only correctly reflects the AC component of the current. The great advantage of a Rogowski measuring device is, however, that the current in the conductor can be measured without the measuring device having to be a direct component of the circuit of the conductor. Large currents can therefore be measured with little effort and very inexpensively. The Rogowski measuring device is connected to a computing unit to which the measured phase current value is output. For this purpose, the Rogowski measuring device can, for example, send an analog signal to the computing unit, which can have an AD converter as an input for the phase current value. In this way, the analog signal can be scanned at high frequency by the computing unit in order to be processed as a digital value in the computing unit.

In a simple view of the basic circuit of the three-phase rectifier with a DC intermediate circuit connected behind it, only one current flows at any time between the phase with the most positive and the most negative potential. The current in the phase with the potential in between is therefore zero. However, inductances of the network and the various parameters of the supply unit result in shifts and widenings which lead to the area in which the phase current is practically zero in general being somewhat shorter and being at slightly different times. However, for all cases relevant in practice, a period can be specified for each phase when the phase current is zero. The time period can, for example, be measured directly for the respective supply unit or can be determined from experience values of typical supply units. Alternatively, a numerical simulation of the respective supply unit can be used to determine when the phase current is definitely zero.

Such a predetermined point in time and / or a predetermined period of time is then stored in the computing unit, at which it can be assumed that the phase current of the measured phase is zero. The time or period is accordingly referred to as no-stop time. The predetermined point in time and / or the predetermined period of time is related to the network angle, which indicates the point in time within an oscillation period. A period of oscillation can typically be divided into a network angle of 0 ° to 360 °. For example, one or more network angles, such as “5 °” or “1 ° to 30 °”, can be stored directly as the time or period. Alternatively, a point in time or a specific period of time can be stored after a specific network angle, such as “0.1 ms after the positive zero crossing of the phase voltage of the first phase”. The phase voltage is the voltage between an outer conductor and the network star point.

The supply unit for a motor controller accordingly has a network angle measuring device which is set up to determine the network angle at at least one of the three phases of the supply input and to output it to the computing unit. If the supply input is connected to a typical supply network, a sinusoidal supply voltage is present at each of the phases, which typically has a frequency of 50 Hz. In some countries, such as the United States, the power supply can also have a frequency of 60 Hz. The supply unit according to the invention can be used in both cases without any problems. For example, the network angle of the supply network is related to the positive zero crossing of the phase voltage of the first phase. In principle, however, any reference points are possible, since the three phases have an essentially fixed phase relationship with one another and are repeated at the same frequency.

The network angle measuring device advantageously determines the network angle on the basis of a voltage measurement of all three network voltages. A PLL (phase locked loop) is common here, for example in power measuring devices. A network angle determination using only one or two phases is also possible, for example in the event of a phase failure. A PLL can be coupled to at least one, advantageously all, of the phases of the three phases of the three-phase supply input. Since the line voltage is distorted by the rectifier (commutation dips) and is therefore subject to harmonics, the line angle can be determined particularly reliably by the PLL. The PLL locks onto the phase position of the fundamental voltage oscillation and is so sluggish that it is insensitive to line faults or commutation dips. The PLL can be constructed in hardware, but a PLL executed in software is preferred. It is transformed from a three-phase coordinate system to an orthogonal coordinate system in order to obtain the mains voltage according to the magnitude and phase angle. The phase angle is output to the PLL as the target phase. The PLL regulates the actual phase of a mains voltage pointer modeled in software in the orthogonal coordinate system so that it coincides with the target phase. The control loop is usually designed as a proportional integral controller. The integral component ensures that there is no permanent control deviation in the network angle, the proportional component is responsible for vibration damping.

The loop filter of the control loop is designed so that the phase control loop reacts very sluggishly. Line faults and commutation dips cannot disturb the line angle determined in this way. In addition, the PLL only clicks on the fundamental vibration. Harmonics on the mains voltage are irrelevant. The software PLL can also be used to control the thyristor rectifier in phase during precharging and during operation. The network angle determined with the PLL is output by the network angle measuring device to the computing unit.

The computing unit is then set up to store a phase current value measured by the Rogowski measuring device at the predetermined point in time and / or during the predetermined period or an average value from a plurality of phase current values measured during the period as an offset value. For this purpose, the computing unit can compare the network angle determined by the network angle measuring device and output to the computing unit with the predetermined point in time or the predetermined period of time (hereinafter “no-stop time”) stored in the computing unit in order to determine whether the no-stop time is present. In this case, the phase current is measured or the measured phase current value is read out and stored in a storage area for the offset value. Since the measured values can contain noise, it is expedient to take several measurements during the no-stop time, to form an average from the measured values and to save this average as an offset value. In particular, the phase current value can be sampled by the computing unit during the zero time and an average value can be formed from all phase current values.

If the arithmetic unit determines that one is outside the no-stop time, the phase current value measured by the Rogowski measuring device is corrected by subtracting the stored offset value from the measured phase current value. This corrected phase current value then contains the correct direct current component of the phase current. The corrected phase current value can be output by the computing unit or processed further in it and a value derived therefrom can be output.

Since the DC component can change over time, for example in the event of a sudden earth fault, the measurement of the offset value can be repeated. In particular, a corresponding measurement can be carried out for each oscillation period at the predetermined point in time or the predetermined period of time. Thus, the offset value is constantly updated and a corrected phase current value including the correct DC component can be determined at any time.

In a preferred embodiment of the invention, a separate Rogowski measuring device can be provided on each of the three phases of the three-phase supply input in order to measure the respective phase current of this phase. In this case, the computing unit is set up to calculate a corrected phase current value for each of these phases by subtracting an offset value. The corrected phase current values can then be output or a derived variable can be calculated from the corrected phase current values. For example, the current distribution and the power distribution over the three phases can be determined from the corrected phase current values.

In a particularly preferred embodiment of the invention, a predetermined point in time and / or a predetermined period of time (zero time), based on the network angle, is stored in the computing unit for which it can be assumed that the phase current of the respective phase is zero. For this purpose, three separate memory areas can actually be provided in the computing unit, in which for each phase Each own no-stop time is saved. Alternatively, a single value can be stored that is valid for all three phases. This value can then refer in particular to a separate reference point in the respective phase. For example, a point in time with reference to the positive zero crossing can be stored in the respective phase.

The computing unit is then set up to proceed for each of the three phases as has already been described for one phase. A phase current value of the phase measured by the Rogowski measuring device or an average of a plurality of phase current values measured during the predetermined period is therefore stored as an offset value of this phase for each phase at the predetermined time or during the predetermined period of the respective phase.

A separate offset value is therefore stored in the computing unit for each phase. Outside the predetermined point in time or the predetermined period of time, the phase current value measured by the Rogowski measuring device of the respective phase is corrected by subtracting the respective offset value of this phase. The corrected phase current values can then be output by the computing unit or further processed in the computing unit. An independent correction is therefore carried out for each individual phase.

The reference ground of the computing unit and the voltage measuring device can each be connected to the positive connection of the DC voltage intermediate circuit.

In a further particularly preferred embodiment of the invention, the supply unit is set up to carry out a fault current detection. For this purpose, the control unit can add the corrected phase currents of the three phases to a total value. In the error-free case, it can be assumed that the three phase currents add up to zero. If a residual value remains after the totalization of the corrected phase currents, there is a fault current. However, slight deviations from zero are normal due to the noise of the individual measured values. In order to avoid that it is erroneously assumed that there is an error, a non-zero threshold value is provided, and an error is only accepted and a corresponding signal is output when the threshold value is exceeded by the total value of the corrected phase currents. An alarm signal or a control signal, for example, can be output as a signal, which leads to the thyristor rectifier being switched off. As a result, the DC voltage side of the three-phase rectifier can be temporarily or permanently separated from the AC voltage side. This can prevent major damage, such as a cable fire, from occurring due to the fault current.

In a further preferred embodiment of the invention, the computing unit can be set up to apply low-pass filtering to the corrected phase current value or a value derived therefrom, in particular to the total value. Since the corrected phase current value also contains the DC component and only the AC component is smoothed by the low-pass filtering, the DC component can be determined in this way. This produces a much smoother signal, which can greatly increase immunity to interference. Alternatively, it is also possible to conclude an earth fault from the smoothed signal of a single phase if one of the phase currents reaches a value other than zero after low-pass filtering. With an ideal rectifier, a DC component only occurs in the event of an earth fault. In real thyristor rectifiers, however, a very small DC component in the phase current can also occur in earth-fault-free operation due to timing differences in the control, which is why the sum formation is the preferred variant. In particular, a sum value generated for leakage current detection can be smoothed by low-pass filtering. The threshold value for determining a fault current can then be selected to be particularly small without a false alarm being triggered by a noise on the measurement signals.

In a further preferred embodiment of the invention, the three-phase rectifier can be designed as an active rectifier, in particular a thyristor rectifier. In such an active three-phase rectifier, the individual blocking elements, for example transistors or thyristors, can be switched on and off by a computing unit. This can be done by the arithmetic unit of the supply unit described or alternatively by a separate arithmetic unit. With an active three-phase rectifier, it is possible to implement other functions beyond the normal rectifier function, which could also be performed by a passive diode rectifier. For example, in the event of a fault, a thyristor rectifier can be switched off completely by switching all the thyristors off. In the event of a fault, this ensures that the supply unit is switched off particularly quickly in order to avoid possible damage to the three-phase rectifier or other components of the supply unit or to the connected motor controller.

In a particularly preferred embodiment of the invention, the thyristor rectifier can be controlled by the computing unit and the computing unit can be set up to precharge the DC voltage intermediate circuit by phase gating when the supply unit is started up. When the supply unit is started, a capacitance contained in the DC voltage intermediate circuit is still uncharged. The phase cut enables the high voltage area to be cut out, so that charging is only carried out with a lower voltage in order to limit the currents. In this way, a secure loading of the capacity can be guaranteed without the working parameters of the individual components being exceeded. The current is limited by the line inductance, possibly in conjunction with a line reactor. The difference between the line voltage at the time of ignition of the thyristors (time of commutation) and the intermediate circuit voltage drops at the inductance and is called the commutation voltage.

The line reactor is usually arranged externally between the three-phase supply network and the three-phase supply input of the supply unit. An arrangement within the supply unit is also possible. The line choke is used to enable precharging when starting up and to ensure current limitation, especially in very hard networks with small inductance. Commutation drops in operation can also be reduced. The rectifier load during operation is also reduced. The line reactor reduces the effective phase current value and thus the current load of the rectifier and the supply network. A common value of 90 µH can be provided, for example, for the main inductance of a line choke of a supply unit with a rated power of 75 kW.

In a further preferred embodiment of the invention, the predetermined point in time or the predetermined period of time can be between a network angle of 1 ° and 30 ° and / or between 181 ° and 210 °, preferably between 7 ° and 25 ° and / or between 187 ° and 205 °, based on the positive zero crossing of the phase voltage of the respective phase. In the second phase, which has a phase shift of 120 ° to the first phase, this corresponds to a network angle between 121 ° and 150 ° and / or between 301 ° and 330 ° with respect to the zero crossing of the first phase. In the third phase, which has a phase shift of 240 ° to the first phase, a network angle between 241 ° and 270 ° and / or between 61 ° and 90 ° with respect to the zero crossing of the first phase.

• Im nachfolgenden Beispiel wird eine 90 pH-Netzdrossel verwendet, so wie sie typischerweise für eine Versorgungseinheit mit 75 kW Zwischenkreis-Dauerleistung und 180 kW kurzzeitige Zwischenkreis-Spitzenleistung vorgesehen wird. Diese Versorgungseinheit ist für eine dreiphasige Versorgungsspannung von 400 V bis 480 V bestimmt, bei einer zulässigen Toleranz der Netzspannung von ±10%.

At the times mentioned, it can be assumed for all cases relevant in practice that the phase current is zero. When a rectifier is commutated naturally on an inductive network, the commutation of the current of a current-carrying phase is delayed. The larger the commutating current and the greater the network inductance, the greater the delay. With a purely inductive network, the commutation time (delay) is longer than with an ohmic-inductive network with the same impedance. As the delay increases, the time in which the phase current is safely zero becomes smaller. The parameters of the supply unit also have an effect on no-stop time. This can be seen in the following examples:

• In the following example, a 90 pH line choke is used, as is typically provided for a supply unit with 75 kW DC link continuous power and 180 kW short DC link peak power. This supply unit is designed for a three-phase supply voltage from 400 V to 480 V, with a permissible tolerance of the mains voltage of ± 10%.

The mains short-circuit current is the theoretical current that can flow in one phase if all phases were short-circuited to the star point. It depends on the network inductance and the ohmic resistance of the network. Supply units of this performance class are usually connected to supply networks with a short-circuit current of 10 kA and more. Operation on supply networks with a much smaller short-circuit current is not possible or only possible to a limited extent with lower power.

The DC link capacitance is usually designed with 100 µF per kW DC link continuous power. For a supply unit with 75 kW DC link continuous power, it is usually 7500 µF. Depending on the application, the intermediate circuits can also be designed for significantly larger capacitance values of up to 30,000 µF, for example for the temporary storage of braking energy.

• Bei einer Variation der Kapazität des Zwischenkreises bei einer Netzspannung von 400 V, einem Netz-Kurzschlussstrom von 10 kA und einer Zwischenkreisleistung von 75 kW ergeben sich beispielsweise die folgenden Werte für die Nullzeit:

Zwischen kreis kapazität Nullzeit Anfang Nullzeit Ende Nullzeit Dauer 3750 µF 341° 34,2° 2,97 ms 7500 µF 342° 33,5° 2,89 ms 30000 µF 341° 33,7° 2,90 ms In the following, the no-stop time for a mains frequency of 50 Hz is determined by means of numerical simulation with variation of the relevant parameters within the expected design limits, whereby the typical values are listed in the middle line:

• With a variation of the capacity of the DC link with a mains voltage of 400 V, a mains short-circuit current of 10 kA and an intermediate circuit power of 75 kW, the following values for no-stop time result, for example:

Between circle capacity No-stop time No stop time No stop time 3750 µF 341 ° 34.2 ° 2.97 ms 7500 µF 342 ° 33.5 ° 2.89 ms 30000 µF 341 ° 33.7 ° 2.90 ms

With a variation of the intermediate circuit power at a mains voltage of 400 V, a mains short-circuit current of 10 kA and an intermediate circuit capacitance of 7500 µF, the following values for no-stop time result, for example: DC power No-stop time No stop time No stop time 37.5 kW 337 ° 33.7 ° 3.16 ms 75 kW 342 ° 33.5 ° 2.89 ms 180 kW 349 ° 33.2 ° 2.43 ms

With a variation of the mains short-circuit current at a mains voltage of 400 V, an intermediate circuit power of 75 kW and an intermediate circuit capacity of 7500 µF, the following values for no-stop time result, for example: Net short-circuit current No-stop time No stop time No stop time 5 kA 344 ° 32.7 ° 2.69 ms 10 kA 342 ° 33.5 ° 2.89 ms 20 kA 339 ° 32.6 ° 2.95 ms

With a variation of the mains voltage with an intermediate circuit power of 75kW, an intermediate circuit capacity of 7500 µF and a mains short circuit current of 10 kA, the following values for no-stop time result, for example: mains voltage No-stop time No stop time No stop time 360 V 343 ° 33.5 ° 2.83 ms 400 V. 342 ° 33.5 ° 2.89 ms 530V 338 ° 33.7 ° 3.11 ms

As an extreme case that can no longer be found in practice, a very soft network with a network voltage of 360 V, a network short-circuit current of 3.6 kA (purely inductive), and operation with an intermediate circuit power of 180 kW can be assumed , As shown above, the size of the DC link capacitance is of no importance for no-stop time.

This results in the following values for no-stop time: No-stop time No stop time No stop time 0.8 ° 30.2 ° 1.63 ms

Even for extreme cases of the boundary conditions encountered in practice, the phase current is therefore always zero between a network angle of 1 ° and 30 °. With a supply network of 50 Hz, the period in which the phase current is safely zero is always greater than 1.6 ms.

The beginning of the predetermined time period based on the positive zero crossing of the phase voltage of the phase under consideration can be between 1 ° and 12 °, preferably between 6 ° and 8 °, particularly preferably 7 °. At these times, it can be assumed with certainty that the respective phase current is already zero, so that the offset value can be measured.

The length of the predetermined period in relation to a supply network with 50 Hz can be between 0.1 ms and 1.6 ms, preferably 0.5 ms and 1.2 ms, particularly preferably 1 ms. This means that several averaging measurements can be carried out during the period in which the phase current is zero. At the same time, there is still a sufficiently large distance to the commutation time at the front and a sufficiently large distance to the beginning of the current flow, so that measurement errors of up to 5 ° can be tolerated when determining the network angle.

To store the predetermined period of time, for example, a start value and a time period or a start value and an end value can be stored in the computing unit. Angles or angular ranges are advantageously stored in the computing unit, which are the same for different network frequencies.

In a further preferred embodiment of the invention, the computing unit can be set up to permanently output the value zero as the corrected phase current during the predetermined period. Since it can be assumed during the predetermined period that the phase current is zero, no correction of the phase current has to be made. In addition, a possible noise on the measured phase current is not transmitted to the output.

Alternatively, the computing unit can be set up to correct the phase current value measured by the Rogowski measuring device for each phase during the predetermined time period by subtracting an offset value determined by the Rogowski measuring device at a previous predetermined time period.

In a further preferred embodiment of the invention, the Rogowski measuring device can have a Rogowski coil, which comprises conductor tracks on a printed circuit board. Such a Rogowski coil is particularly simple and inexpensive to manufacture, is particularly space-saving and can therefore be easily integrated in a supply unit. The large-volume and expensive AC current transformers usually used on the AC side of the three-phase rectifier can be dispensed with entirely, so that the construction volume and the manufacturing costs of the supply unit can be significantly reduced.

• - Messen eines Phasenstromwerts an einer Phase eines Versorgungseingangs der Versorgungseinheit während eines Zeitraums zu dem vorausgesetzt werden kann, dass der Phasenstrom der Phase null ist,
• - Speichern des gemessenen Phasenstromwerts als Offsetwert,
• - Messen eines Phasenstromwerts an der Phase des Versorgungseingangs der Versorgungseinheit außerhalb eines Zeitraums zu dem vorausgesetzt werden kann, dass der Phasenstrom der Phase null ist,
• - Korrigieren des gemessenen Phasenstroms durch Subtraktion des Offsetwerts;

The invention also relates to a method for determining the direct current component of a Rogowski current measurement in a supply unit for a motor control with the following steps:

• Measuring a phase current value at a phase of a supply input of the supply unit during a period when the phase current of the phase can be assumed to be zero,
• Storing the measured phase current value as an offset value,
• Measuring a phase current value at the phase of the supply input of the supply unit outside a period of time when it can be assumed that the phase current of the phase is zero,
• - correcting the measured phase current by subtracting the offset value;

The invention also relates to a supply unit for a motor control with a three-phase supply input for connection to a three-phase supply network and a three-phase rectifier, the AC side of which is connected to the three-phase supply input and a DC voltage intermediate circuit for connection to a motor control, in particular one of the supply units described above. The supply unit also has a brake chopper in the DC voltage intermediate circuit, with a braking resistor for dissipating energy and a switching element for switching the braking chopper between a deactivated state in which no current can flow through the braking resistor and an activated state in the current through the braking resistor can flow.

If a motor connected to the supply unit via a motor controller is braked, energy is typically returned to the DC link. To prevent the excess energy from causing damage, the energy supplied must be dissipated, for example, be converted into heat in a dissipative element. For this purpose, the brake chopper is provided in the DC link.

The brake chopper can be arranged, for example, between a positive and negative connection of the DC link. The switching element switches the braking resistor between the positive and negative connection of the DC link, so that a current can flow through the braking resistor. As a result, the electrical energy stored in the DC voltage intermediate circuit is converted into heat in the braking resistor, as a result of which the braking resistor heats up. The switching element can be controlled via hardware, so that when a limit voltage in the DC voltage intermediate circuit is exceeded, the switching element activates the brake chopper and current can flow through the braking resistor. Alternatively, the switching element can also be controlled by a computing unit, which switches the switching element as required to activate the brake chopper. If the switching element is not controlled by the computing unit, it can detect the actuation state of the switching element in order to obtain information about the state of the switching element.

A fault in the braking resistor, such as a short circuit or a partial short circuit, which leads to a reduced resistance value, can result in very large overload currents flowing through the braking resistor. As a result, leads to the braking resistor, in particular, which are not designed for such high currents, can overheat and even catch fire. Safety precautions should therefore be taken to quickly identify an overload and take appropriate measures.

To protect against overload in the braking resistor, the power converted in the braking resistor or the current flowing through the braking resistor must be determined. For this purpose, a voltage measuring device is arranged on the braking resistor, which is set up to measure the voltage drop across the braking resistor and to output it to the computing unit. The reference ground of the arithmetic unit and the voltage measuring device is advantageously arranged at the positive connection of the intermediate circuit because, for example, the upper thyristors of the three-phase rectifier can be controlled in a particularly simple manner and the mains voltage can also be measured particularly easily. The measurement of the voltage drop across the braking resistor is thus also particularly simple and inexpensive. However, since the resistance value of the braking resistor is not constant, in particular changes with temperature, the power determination by means of the voltage drop across the braking resistor alone is very imprecise. The supply unit therefore also comprises a Rogowski measuring device which is set up to measure the braking current through the braking resistor and to output it to the computing unit. The Rogowski measuring device can be arranged inside the device at the output terminal for an externally connected braking resistor. However, since a current measurement with a Rogowski measuring device can only determine the AC component of the braking current, it is likewise not possible to determine the braking power with the Rogowski measuring device alone, since the current through the braking resistor essentially has a DC component.

The computing unit therefore uses both the measured voltage drop across the resistor and the current value measured by the Rogowski measuring device to determine the braking current through the braking resistor. For this purpose, the computing unit is set up to carry out an offset measurement. At a time when the brake chopper is in a deactivated state, the brake current value measured by the Rogowski measuring device is stored as a brake offset value. Since no current can flow through the braking resistor while the brake chopper is deactivated, it can be assumed that the braking current is zero at this time. The current value measured by the Rogowski measuring device is therefore only to be interpreted as an offset and is therefore stored as a brake offset value.

The computing unit is also set up to carry out a reference measurement in a further step in order to determine the exact resistance value of the braking resistor. For this purpose, a braking current is measured by the Rogowski measuring device while the brake chopper is in an activated state. This is corrected by subtracting the brake offset value. At the same time as the braking current, the voltage drop across the braking resistor is measured by the voltage measuring device. This is divided by the corrected braking current value in order to calculate the resistance value of the braking resistor. This resistance value is stored in the computing unit. The braking current and / or the braking power can then be calculated at any time from the voltage drop across the braking resistor measured by the voltage measuring device and the resistance value stored in the computing unit. Since the resistance value is updated by offset and reference measurement, the braking current calculation from this value is much more precise than with a fixed resistance value.

In a preferred embodiment of the invention, the transition from the deactivated to the activated state of the brake chopper is measured. The offset measurement is carried out in the deactivated state, in particular immediately before the transition to the activated state. The offset measurement is carried out in the deactivated state, in particular in a period from 0.5 ms before the brake chopper is switched to the activated state. The reference measurement is then carried out in the activated state of the brake chopper, which directly follows the deactivated state of the brake chopper in which the offset measurement was carried out. The reference measurement takes place in the activated state, especially after a period of 0.5 ms after switching the brake chopper to 1 ms after switching the brake chopper.
This means that the reference measurement and offset measurement are separated from the deactivated state into the activated state only by a single switching operation.

Alternatively, the transition from the activated to the deactivated state of the brake chopper is measured: The reference measurement is then carried out in the activated state, in particular from 0.5 ms until immediately before the transition to the deactivated state. During this time the voltage drop across the braking resistor is measured. The offset measurement is carried out in the subsequently deactivated state, in particular after a period from 0.5 ms after switching the brake chopper to 1 ms after switching the brake chopper.

Alternatively, measurements can also be taken at both transitions, at the transition from the deactivated to the activated state and at the transition from the activated to the deactivated state.

Since the Rogowski measuring device can only correctly determine the alternating current component of the current, the measured current value is, in principle, only completely correct, despite the offset correction, directly after a switching operation into the activated state. The greater the inaccuracy, the greater the distance from the switching operation. The maximum possible value for the end of the measurement is 100 ms after the switching process if the evaluation electronics of the Rogowski coil have a lower cut-off frequency of a few milliseconds. However, settling and magnetic disturbances occur immediately after the switching process, which can also lead to inaccuracies in the measurement. Every braking resistor has a parasitic inductance. The electrical time constant for braking resistors for high braking power is typically around 15 µs. 500 µs after switching on, i.e. after about 33 time constants, the current in the braking resistor has settled completely. A current measurement can thus be carried out after about 500 µs. If very low-inductance braking resistors are used in connection with a fast switching element and the Rogowski measuring device is used in a magnetically insensitive arrangement, the measurements can be carried out after only about 10 to 50 µs.

It is therefore provided in a further preferred embodiment of the invention that the computing unit is set up in such a way that the reference measurement takes place over a period of 0.01 to 100 ms, preferably after 0.05 to 10 ms, particularly preferably after 0.5 to 1 ms after switching the brake chopper into the activated state. At this time, the current through the braking resistor has settled. Furthermore, disturbances in the measured value, such as those that can arise from magnetic coupling during the switching process, have surely subsided after this time. As the time interval from the switching process to the activated state increases, the current measurement by means of a Rogowski measuring device becomes increasingly inaccurate. During the specified period, the Rogowski measuring device can still output a very precise current value. This enables a particularly precise reference measurement to be carried out within a period of 0.01 to 100 ms after the brake chopper is switched to an activated state.

In a further preferred embodiment of the invention, the computing unit is set up to carry out the offset measurement for a period of 0.5 ms directly before the brake chopper is switched to an activated state. The offset measurement of the Rogowski current measurement is determined particularly precisely by the offset measurement immediately before the brake chopper is switched on, since it cannot change significantly until the reference measurement in a subsequent activated state.

In a special embodiment of the invention, the computing unit is set up to average over a predetermined measurement time when measuring the braking current in the deactivated state and / or when measuring the braking current in the activated state and / or when measuring the voltage drop across the braking resistor. By performing an averaging during the measurements, an influence by possible noise is minimized.

In a further preferred embodiment of the invention, the computing unit is set up to repeat the offset measurement and the reference measurement in an ongoing operation in order to constantly update the stored resistance value. As a result, fluctuations in the resistance value of the braking resistor that occur during operation are detected and taken into account, so that the correct braking current can be calculated at any time by means of the corrected resistance value and the voltage drop across the resistor.

In a further embodiment of the invention, the computing unit is set up to update the stored resistance value only by means of an offset measurement and a reference measurement if the brake chopper before switching to the state in which the reference measurement takes place previously more than 0.1 ms, preferably more than 0.5 ms, particularly preferably more than 1 ms was deactivated. This prevents incorrect measurements caused by rapid activation and deactivation from leading to an incorrect resistance value. In particular, in addition to the offset, the offset measurement could also have a portion of an actually flowing current and thus lead to an incorrect offset measurement. The current in the braking resistor has completely decayed 500 µs after the brake chopper has been switched to a deactivated state, that is to say after about 33 time constants. An offset measurement can thus be carried out about 500 µs after deactivation.

In a further preferred embodiment of the invention, the computing unit is set up to continuously scan the current value measured by the Rogowski measuring device and to store it in a FIFO memory. Such a “first-in-first-out” memory has a fixed number of memory locations and reads in a new measured value and overwrites the oldest stored measured value.

If a switching operation is detected from a deactivated state to the activated state, the current measured values stored in the FIFO memory can be read out and the mean value of the measured values can be formed. The measured values in the FIFO memory are then recorded during the deactivated state. Their mean value can therefore be stored in the computing unit as a brake offset value. After a predetermined time after activating the brake chopper, for example 1 ms after activating the brake chopper, the FIFO memory can be read out again and the mean value of the measured values, for example of the last 0.5 ms, can be formed. The predetermined time after activation can be selected so that the FIFO memory contains measured values when the brake chopper is activated. The mean value therefore corresponds to the measured braking current in the activated state and can be used for the reference measurement.

A FIFO memory can also be provided for the voltage measuring device, into which the voltage values of the voltage measuring device are continuously read. At the time of reading out the FIFO memory of the braking current, the FIFO memory of the voltage can also be read out in order to determine the voltage drop across the braking resistor. The resistance value can then be calculated from the two mean values.

The Rogowski measuring device can therefore be used to operate parameters such as Determine brake chopper current or brake chopper power.

The computing unit can be set up to provide the resistance value stored in the computing unit and constantly updated with a low-pass filtering, for example in order to reduce the influence of noise in the reference measurement, the offset measurement or the measurement of the voltage drop across the braking resistor to the calculated resistance value. With low-pass filtering, the noise can also be derived from the measurement values derived from the measurement of the voltage drop across the braking resistor and resistance calculation, e.g. Brake chopper current or brake chopper power can be reduced. Since the resistance value during operation e.g. can only change slowly due to heating of the braking resistor, this low-pass filtering is not disadvantageous for the derived measured values.

The Rogowski measuring device can have a Rogowski coil, which comprises conductor tracks on a printed circuit board. Such a Rogowski coil is particularly simple and inexpensive to manufacture, is particularly space-saving and can therefore be easily integrated in a supply unit. The large-volume and expensive DC current transformers, which are usually used in the brake chopper for recording the operating parameters, in particular in the case of large braking powers, can be dispensed with, so that the construction volume and the manufacturing costs of the supply unit can be significantly reduced.

• 1 zeigt eine erfindungsgemäße Versorgungseinheit für eine Motorsteuerung in einer schematischen Darstellung;
• 2 zeigt eine schematische Darstellung eines Dreiphasengleichrichters;
• 3 zeigt mehrere Graphen mit Strom- und Spannungswerten der Versorgungseinheit, ohne Erdschluss und mit Erdschluss;
• 4 zeigt mehrere Graphen mit Strom- und Spannungswerten der Versorgungseinheit, im Moment des Auftretens eines Erdschlusses;
• 5 zeigt eine schematische Darstellung einer Versorgungseinheit mit Bremschopper;
• 6 zeigt den tatsächlichen und den gemessenen Bremsstromverlauf einer Versorgungseinheit mit Bremschopper.

Further advantages, features and possible uses of the invention result from the following description of various embodiments and the drawings. All of the features described and / or illustrated represent the subject matter of the present invention, individually or in any combination, regardless of how they are summarized in the claims or their references.

• 1 shows a supply unit according to the invention for an engine control in a schematic representation;
• 2 shows a schematic representation of a three-phase rectifier;
• 3 shows several graphs with current and voltage values of the supply unit, without earth fault and with earth fault;
• 4 shows several graphs with current and voltage values of the supply unit, at the moment of occurrence of an earth fault;
• 5 shows a schematic representation of a supply unit with brake chopper;
• 6 shows the actual and the measured braking current curve of a supply unit with brake chopper.

In 1 is the supply unit according to the invention 1 shown schematically. The three-phase supply input 2 the supply unit 1 is connected to a normal three-phase network, the second phase of the first phase has a phase shift of 120 °, the second phase of the third phase has a phase shift of 120 ° and the third phase of the first phase has a phase shift of 120 °. The repetition frequency of the network is 50 Hz. The three phases of the supply input 2 are with the AC side 5 a three-phase rectifier 4 connected.

Such a three-phase rectifier 4 can be constructed as a passive rectifier in bridge circuit, as in 2 is shown. The switching states of the diodes change during operation such that for the most part exactly one phase is conductively connected to the positive output and one phase to the negative output. Short overlaps can also occur during the commutation time.

Instead of passive components like diodes 11 , Active components, for example transistors or thyristors, can also be provided, which are controlled by a computing unit 7 can be switched on or off. The basic principle of the three-phase rectifier is the same for active and passive rectifiers. By switching the individual blocking elements, the most positive of the three phases is switched to the positive output of the DC voltage side 6 and the most negative of the three phases to the negative output on the DC side 6 connected. Both blocking elements are in the blocking state for the middle phase in each case and there is therefore no connection to the DC voltage side for this phase 6 of the rectifier 4 ,

In the in 1 shown supply unit 1 are still at the three phases of the three-phase supply entrance 2 one Rogowski measuring device each 8th . 9 arranged. Each has a Rogowski coil 8th which is advantageously arranged concentrically or less advantageously eccentrically around the conductor of the respective phase. Because of the Rogowski measuring coil 8th output voltage signal is proportional to the time derivative of the current through the conductor, is an evaluation device 9 provided with an integrator. This integrates the voltage signal to a value for the phase current 19 . 20 . 21 to get and gives this to the computing unit 7 out. In principle, a Rogowski current measurement is not able to map direct currents. Rather, it has a high-pass behavior with a lower cut-off frequency of, for example, 0.5 Hz. That of the evaluation unit 9 to the computing unit 7 output phase current value 19 . 20 . 21 therefore consists of a correct AC component and any offset. This offset depends in particular on the history of the phase current. If there is a sudden increase in the phase current, this change in current is carried out by a Rogowski measuring device 8th . 9 first correctly detected. However, if the phase current subsequently remains constant, the mean value of the output signal from the Rogowski measuring device relaxes 8th . 9 but slowly towards zero. The DC component of the through the Rogowski measuring device 8th . 9 measured phase current 19 . 20 . 21 is therefore generally not correct. In the computing unit 7 are the measured phase current values 19 . 20 . 21 therefore corrected.

For this is in the computing unit 7 a predetermined period of time 22 . 23 . 24 based on the network angle 15 stored, it can also be assumed that the phase current 16 . 17 . 18 is zero. This period is called no-stop time 22 . 23 . 24 designated. The one in the arithmetic unit 7 No-stop time saved for the first phase 22 starts at a mesh angle 15 of 7 ° related to the positive zero crossing of the mains voltage (phase voltage) of the first phase 12 and lasts 1 ms. A second no-stop time 22 for the first phase begins at 187 ° and has a duration of 1 ms. No-stop time begins for the second phase 23 at 127 ° and 307 ° also related to the positive zero crossing of the mains voltage of the first phase 12 , The duration is also 1 ms. No-stop time begins for the third phase 24 at 247 ° and 67 ° also related to the positive zero crossing of the mains voltage of the first phase 12 , The duration is also 1 ms. The beginning of no-stop times 23 . 24 the second phase and the third phase correspond to 7 ° and 187 ° in relation to the positive zero crossing of the phase voltage 13 . 14 the respective phase itself, since they each have a phase shift of 120 °. The duration of the predetermined period relates to a network frequency of 50 Hz. At 60 Hz, the predetermined period would each last 833 microseconds.

To determine the current network angle 15 instructs the supply unit 1 a network angle measuring device 10 on, which is designed as software PLL. This is at the three-phase supply input 2 coupled and always gives the current network angle 15 to the computing unit 7 out.

The Rogowski measuring device 8th . 9 includes an analog evaluation circuit 9 , whose analog output signal at an input of the computing unit 7 is applied.

The computing unit 7 has an AD converter at the input to convert the analog signal into a digital value for further processing in the computing unit 7 convert. The analog value is sampled at a high frequency, for example at a frequency of 5 to 32 kHz. The higher the sampling frequency, the more samples are available for averaging. The sampling frequency is determined by the processor resources of the computing unit 7 limited and can be up to 100 kHz.

Alternatively, the voltage signal from the Rogowski measuring coil could 8th also given directly to the input of the AD converter and in the computing unit 7 to get integrated. However, this method would be disadvantageous because the voltage signal changes rapidly in the phase currents 16 . 17 . 18 can assume very large values and can exceed the dynamic range of the AD converter.

By the computing unit 7 is then in a first step that of the network angle measuring device 10 provided network angles 15 with that in the computing unit 7 stored no-stop time 22 . 23 . 24 compared. During no-stop time 22 . 23 . 24 becomes the phase current value 19 . 20 . 21 through the Rogowski measuring device 8th . 9 measured or on that with the Rogowski measuring device 8th . 9 connected input of the computing unit 7 read. Once the network angle 15 has a value of 7 °, the no-stop time begins 22 for the first phase. The computing unit 7 The read phase current values then begins for 1 ms 19 add up the first phase for averaging. At the end of no-stop time 22 the sum is divided by the number of measured values in order to obtain an average phase current value which is stored as an offset value for the first phase. Once the network angle 15 Corresponds to 127 °, the no-stop time begins 23 for the second phase. The arithmetic unit then averages the measured phase current values for 1 ms 20 the second phase and stores it as an offset value for the second phase. At a network angle of 247 ° 15 the corresponding measurement is carried out for the third phase and an offset value is saved for the third phase.

At 187 °, a further measurement is carried out for the first phase and that in the computing unit 7 stored offset value is overwritten by the newly determined mean value. Corresponding measurements are carried out at 307 ° and 67 ° for the second and third phases. The individual offset measurements are repeated in the subsequent oscillation periods. An offset measurement is therefore carried out twice for each phase per oscillation period. At a mains frequency of 50 Hz, the offset value of each phase is updated 100 times per second.

During the entire no-stop time 22 . 23 . 24 a phase is at an output of the computing unit 7 as a corrected phase current value 25 this phase output zero, or the value zero for further processing in the computing unit 7 used.

Outside of no-stop time 22 . 23 . 24 will be within no-stop time 22 . 23 . 24 determined offset value to the measured phase current value 19 . 20 . 21 applied. This is the phase current value 19 . 20 . 21 a phase through the Rogowski measuring device 8th . 9 measured or on which with a Rogowski measuring device 8th . 9 connected input of the computing unit 7 read in and in the computing unit 7 stored offset value of this phase from the measured phase current value 19 . 20 . 21 subtracted. The calculated value is called the corrected phase current value 25 issued for the respective phase.

3a shows three graphs with several parameters of the supply unit 1 , The top graph shows the line voltages 12 . 13 . 14 of the three phases, which each have a phase shift of 120 ° to one another. The network angle is further 15 drawn in, which has a sawtooth-shaped course. The network angle 15 is related to the positive zero crossing of the mains voltage 12 the first phase. At this point the grid angle is 0 ° and runs until the next positive zero crossing of the grid voltage 12 the first phase to 360 ° and then starts again at 0 °.

The middle graph of the 3a shows the actual phase currents 16 . 17 . 18 of the three phases. The course of the phase currents 16 . 17 . 18 is essentially identical except for a phase shift of 120 °. The curves each show two positive maxima, followed by a range in which the phase current is zero. This is followed by two negative maxima and another area in which the phase current is zero.

The lower graph shows the measured phase current 19 . 20 . 21 like he did with the Rogowski measuring device 8th . 9 is measured. The AC component of the phase currents 16 . 17 . 18 is measured in the phase currents 19 . 20 . 21 reproduced correctly. Since the phase current contains no DC component, the measured phase current contains no offset.

A zero time is representative of the lower and middle graph 22 . 23 . 24 for each phase as shown in the arithmetic unit 7 is saved. The no-stop time 22 . 23 . 24 is in the range in which the phase current of the respective phase is zero. During no-stop time 22 . 23 . 24 can be assumed for all extreme cases that the phase current of the respective phase is zero.

3b shows the graph of 3a in the event that the phase currents 16 . 17 . 18 contain a positive DC component. This occurs when the positive connection of the DC link has an earth fault. Through one-way rectification on the upper diodes / thyristors 11 of the three-phase rectifier are the phase currents 16 . 17 . 18 no longer zero symmetrical in the event of an earth fault. The arcs above the zero line get higher. Like the bottom graph with the measured phase currents 19 . 20 . 21 can be removed, the Rogowski measuring device 8th . 9 does not represent the DC component and consequently shifts the curve shape into the negative. This shift is compensated for by the offset correction. In the event of a fault with an earth fault, the phase current is always zero at no-stop times.

The computing unit 7 can therefore during no-stop time 22 the measured phase current in the first phase 19 save the first phase as an offset value for the first phase. In the case shown, this is approximately -30 A. The offset value can then be from the measured phase current 19 the first phase are subtracted to the actual phase current 16 reconstruct the first phase. The same procedure can be followed for the other two phases.

4 shows several parameters of the supply unit 1 in the event of a fault in which an earth fault occurs, representative of the first phase. The top graph are corresponding 3a and 3b the mains voltage 12 the first phase as well as the network angle 15 located. How, for example, can be recognized from the narrower vibrations of the top graph, is in the 4 represented a longer period of time.

The shows up to a time of about 0.1s 4 an error-free course. The phase current shown in the second graph 16 runs symmetrically. In the third graph is the Rogowski measuring device 8th . 9 measured phase current 19 located. In the case shown, this has no offset and therefore corresponds to the actual phase current 16 , The corrected phase current 25 in the fifth graph is therefore identical to the measured phase current 19 , In the eighth line is the sum 26 of the measured phase currents 19 . 20 . 21 shown. In the ninth line is the sum 27 the corrected phase currents 25 shown. This is identical to the total 26 , because the measured phase currents 19 . 20 21 have no offset. During the error-free course, up to 0.1 s, the sum of the phase currents is zero.

At the time at 0.1 s, an earth fault occurs, through which large currents can flow to earth. How the course of the phase current 16 in the second line, the average of the phase currents shown runs 16 clearly not equal to zero after the earth fault. This current therefore has a DC component. The measured phase current 19 can the actual phase current 16 display correctly shortly after the occurrence of the earth fault, but shifts after a short time and then no longer correctly displays the DC component. This can be seen in particular in the enlarged course of the measured phase current 19 in the fourth line. The DC component of the sum in the eighth line is also shown as almost zero after 0.5 seconds, at the right end of the graph. The corrected phase current value 25 can, however, the actual phase current 16 reproduce correctly including the DC component. This becomes particularly clear in the enlarged representation of the corrected phase current value in the sixth line and in the last line, in which the sum 27 the corrected phase currents 25 is shown. In the graph of the sums 26 and 27 a curve of the low-pass filtered values is also shown. These essentially only reflect the DC component of the sum. In the low-pass filtered signal, it can be clearly seen that the DC component of the sum for the uncorrected case 26 approaches zero, while the corrected sum correctly reflects the correct DC component. Since the low-pass filtered profile is also very smooth, very low threshold values can be selected in the case of a residual current detection, from which an error signal is output. Very high-resistance earth faults can therefore also be detected.

5 shows a supply unit according to the invention 1 with a three-phase supply input 2 with an AC side 5 a three-phase rectifier 4 connected is. The DC side 6 of the three-phase rectifier 4 is with a DC link 3 connected, in which a capacity for temporarily storing electrical energy is provided. There is also a braking resistor 30 with a switching element 31 as a brake chopper 30 . 31 between the positive and the negative side of the DC link 3 connected. The braking resistor 30 is with a first connection with the positive side of the DC link 3 connected and with its second connection via the switching element 31 with the negative side of the DC link 3 connected.

The supply unit 1 also has a Rogowski measuring device 8th . 9 on that a Rogowski coil 8th contains that in the connection line of the brake chopper 30 . 31 is arranged to the current through the braking resistor 30 to eat. An evaluation unit 9 determines a current value from the voltage signal output by the Rogowski coil and sends this to the computing unit 7 out. There is also a voltage measuring device 32 provided the voltage drop across the braking resistor 30 measures and to the computing unit 7 outputs.

The computing unit 7 is with the switching element 31 connected to the switching element 31 switch on when there is excess energy in the DC link 3 in the braking resistor 30 to be converted into heat. The computing unit 7 has a FIFO memory with sixteen memory locations, in which the measured values of the Rogowski measuring device are continuously stored 8th . 9 be imported. Because one in the arithmetic unit 7 provided AD converter has a sampling rate of 32 kHz, the memory content always corresponds to the measured values of the last 500 µs. The computing unit 7 furthermore has a second identical FIFO memory in which the voltage measurement values of the voltage measurement device are continuously stored 32 be imported.

6 shows an example of a time course of the braking current 33 and the associated measured values 34 the Rogowski measuring device 8th . 9 , During a first switching operation 35 from a deactivated state 36 in an activated state 37 becomes the brake chopper 30 . 31 activated and the braking current 33 rises to a value of around 200A with a steep edge. This rapid current change can be done by the Rogowski measuring device 8th . 9 in the measured current value 34 reproduced correctly, but the signal drops 34 after switching 35 slowly, although the braking current 33 in the activated state 37 remains constant. After deactivation of the brake chopper flows in the second deactivated state 36 ' no more current through the braking resistor 30 , the Rogowski measuring device 8th . 9 incorrectly returns a slightly negative value. In the second switching process 35 the braking current rises again to a value of around 200A, the Rogowski measuring device 8th . 9 gives however during the second activated state 37 ' a slightly lower current value 34 out.

The computing unit 7 is therefore set up to perform an offset measurement 38 perform the example of the second switching process 35 ' is explained. In the second switching process 35 ' The measured values of the braking current stored in the FIFO memory become the activated state 34 the Rogowski measuring device 8th . 9 averaged and as an offset value in the computing unit 7 stored. This value then corresponds to the mean value of the current measurement of the last 500 µs (38) before the switching process 35 ' , Approximately 1 ms after the switching process are used for a reference measurement 39 the measured values 34 the FIFO memory of the Rogowski measuring device 8th . 9 read out again and averaged. This mean value is corrected by subtracting the stored offset value and the braking current is reconstructed very precisely 1 ms after the switching process.

At the same time ( 39 ) becomes the second FIFO memory with the measured values of the voltage measuring device 32 read out and averaged. By dividing the averaged voltage value by the averaged and corrected current value, the current resistance value of the braking resistor can be calculated 30 be calculated. This value is in the computing unit 7 stored.

Because through the Rogowski measuring device 8th . 9 only shortly after the switching element is switched on 31 Correct current values of the braking current can be determined, the voltage measuring device will later 32 used for electricity calculation. For this purpose, the current measured voltage value is given by the in the computing unit 7 stored resistance value divided. Since the resistance value can be tracked as described for each switching operation, the current value output in this way is also correct at later times. With every switching operation, the Rogowski measuring device can 8th . 9 to correctly determine the braking current, to determine the exact resistance value and that in the computing unit 7 update stored resistance value.

LIST OF REFERENCE NUMBERS

1

supply unit

2

three-phase supply input

3

Dc link

4

Three-phase rectifier

5

AC side of the three-phase rectifier

6

DC side of the three-phase rectifier

7

computer unit

8th

Rogowski coil

9

evaluation

10

Power angle measuring device

11

diode

12

Mains voltage first phase

13

Mains voltage second phase

14

Mains voltage third phase

15

power angle

16

Phase current first phase

17

Phase current second phase

18

Phase current third phase

19

measured phase current value first phase

20

measured phase current value second phase

21

measured phase current value third phase

22

No phase first phase

23

Second phase no-stop time

24

No stop third phase

25

corrected phase current values

26

Sum of the measured phase current values

27

Sum of the corrected phase current values

30

braking resistor

31

switching element

32

Voltage detecting means

33

braking power

34

Measured values braking current

35

switching operation

35 '

switching operation

36

deactivated state

36 '

deactivated state

37

activated state

37 '

activated state

38

offset measurement

39

reference measurement

Claims (19)

Supply unit for at least one motor control, comprising - a three-phase supply input (2) for connection to a three-phase supply network; - A three-phase rectifier (4) with an AC voltage side (5) which is connected to the three-phase supply input (2); - A DC voltage intermediate circuit (3) for connection to at least one motor control, which is connected to a DC voltage side (6) of the three-phase rectifier (4); - a computing unit (7); - A Rogowski measuring device (8, 9) arranged on at least one of the three phases of the supply input (2) and configured to measure the phase current (16, 17, 18) of the phase and the phase current value (19, 20, 21) to the computing unit (7), characterized by - a network angle measuring device (10), configured to determine a network angle (15) at at least one of the three phases of the supply input (2) and to output it to the computing unit (7); - Wherein in the computing unit (7) a predetermined point in time and / or predetermined period (22, 23, 24) is stored in relation to the network angle (15), at which it can be assumed that the phase current (16, 17, 18) Phase is zero; - And wherein the computing unit is set up to measure a phase current value (19, 20, 21) or a mean value measured by the Rogowski measuring device (8, 9) at the predetermined point in time and / or during the predetermined period (22, 23, 24) save from a plurality of measured phase current values (19, 20, 21) as an offset value; - and correct a phase current value (19, 20, 21) measured outside the predetermined time and / or period (22, 23, 24) by the Rogowski measuring device (8, 9) by subtracting the offset value; - And output the corrected phase current value (25) or a value derived therefrom. Supply unit after Claim 1 , characterized in that one Rogowski measuring device (8, 9) is provided for each phase of the three-phase supply input (2), the computing unit (7) being set up to add a corrected phase current value (25) for each phase by subtracting an offset value to calculate. Supply unit after Claim 2 , characterized in that - in the computing unit (7) for each phase a predetermined point in time and / or period (22, 23, 24) in relation to the network angle (15) is stored, at which it can be assumed that the phase current (16 , 17, 18) of the respective phase is zero and - the computing unit (7) is set up for each phase at the predetermined point in time and / or during the predetermined period (22, 23, 24) of the respective phase one of the Rogowski Measuring device (8, 9) measured phase current value (19, 20, 21) or an average of several measured phase current values (19, 20, 21) of the respective phase as offset value of this phase and - for each phase one outside the predetermined period (22 , 23, 24) by the Rogowski measuring device (8, 9) of the respective phase measured phase current value (19, 20, 21) by subtracting the offset value of this phase. Supply unit after Claim 2 or 3 , characterized in that the computing unit (7) is set up to add the corrected phase currents (25) of the three phases to a sum value (27) and to compare this sum value (27) with a threshold value for fault current detection, and at If the threshold value is exceeded, a signal is output, in particular for switching off the thyristor rectifier (4). Supply unit according to one of the preceding claims, characterized in that the computing unit (7) is set up to apply low-pass filtering to the corrected phase current value or the value derived therefrom, in particular the total value (27). Supply unit according to one of the preceding claims, characterized in that the three-phase rectifier (4) is designed as a thyristor rectifier. Supply unit after Claim 6 , characterized in that the thyristor rectifier is controlled by the computing unit (7) and the computing unit (7) is set up to precharge the DC voltage intermediate circuit (3) by phase gating when the supply unit (1) is started. Supply unit according to one of the preceding claims, characterized in that the predetermined point in time and / or period (22, 23, 24) between 1 ° and 30 ° and / or 181 ° and 210 ° based on the positive zero crossing of the phase voltage (12, 13 , 14) of the respective phase, preferably between 7 ° and 25 ° and / or 187 ° and 205 °. Supply unit according to one of the preceding claims, characterized in that the computing unit (7) is set up to output the value zero as corrected phase current (25) at the predetermined point in time or during the predetermined period (22, 23, 24). Supply unit according to one of the preceding claims, characterized in that the Rogowski measuring device (8, 9) has a Rogowski coil (8) which comprises conductor tracks on a printed circuit board. Method for determining the DC component of a Rogowski measurement (8, 9) on a supply unit (1) for a motor control: - Measuring a phase current value (19, 20, 21) at a phase of a supply input (2) of the supply unit (1) during a period when it can be assumed that the phase current of the phase is zero (22, 23, 24); - storing an offset value based on the measured phase current value (19, 20, 21); - Measuring a phase current value (19, 20, 21) at the phase of the supply input (2) of the supply unit (1) outside a period at which it can be assumed that the phase current of the phase is zero (22, 23, 24); - correcting the measured phase current value (19, 20, 21) by subtracting the offset value; Supply unit for at least one engine control, in particular according to one of the Claims 1 to 10 , comprising - a three-phase supply input (2) for connection to a three-phase supply network; - A three-phase rectifier (4) with an AC voltage side (5) which is connected to the three-phase supply input (2); - A DC voltage intermediate circuit (3) for connection to at least one motor control, which is connected to a DC voltage side (6) of the three-phase rectifier (4); - A braking chopper (30, 31) in the direct voltage intermediate circuit (3) with a braking resistor (30) for dissipating energy and a switching element (31) for switching the braking chopper (30, 31) between a deactivated state in which no current through the Braking resistor (30) can flow and an activated state in which current can flow through the braking resistor (30); - a computing unit (7) which controls the switching element (31) and / or detects its state; - A voltage measuring device (32), arranged on the braking resistor (30) and configured to measure the voltage drop across the braking resistor (30) and to output it to the computing unit (7); - a Rogowski measuring device (8, 9), set up to measure the braking current (33) through the braking resistor (30) and output it to the computing unit (7), - the computing unit (7) being set up to carry out an offset measurement ( 38) to be carried out while the brake chopper (30, 31) is in a deactivated state (36, 36 '), in which a brake current (34) measured by the Rogowski measuring device (8, 9) is stored as a brake offset value; - To carry out a reference measurement (39) in which a brake current (34) measured by the Rogowski measuring device (8, 9) while the brake chopper (30, 31) is in an activated state (37, 37 ') by subtracting the Brake offset value is corrected and a voltage drop measured by the voltage measuring device (32) is divided by the corrected current value in order to calculate a resistance value of the braking resistor (30) and to store it in the computing unit (7) and - at a later point in time a braking current (33) from one of the voltage measuring device (32) measured voltage drop across the braking resistor (30) and the stored resistance value of the braking resistor (30). Supply unit after Claim 12 , characterized in that at a transition from a deactivated (36, 36 ') to an activated state (37, 37') of the brake chopper and / or at a transition from an activated (37, 37 ') to a deactivated state (36 , 36 ') of the brake chopper (30, 31) is measured. Supply unit after Claim 12 or 13 , characterized in that the computing unit (7) is set up to follow the reference measurement (39) over a period of 0.01 ms to 100 ms, preferably 0.05 ms to 10 ms, particularly preferably 0.5 ms to 1 ms switching the brake chopper (30, 31) into an activated state (37, 37 '). Supply unit according to one of the Claims 12 to 14 , characterized in that the computing unit (7) is set up to carry out the offset measurement (38) during a period of 0.5 ms before the brake chopper (30, 31) is switched to an activated state (37, 37 '). Supply unit according to one of the Claims 12 to 15 , characterized in that the computing unit (7) is set up to measure the braking current (33) in the deactivated state (36, 36 ') and / or to measure the braking current (33) in the activated state (37, 37' ) and / or to average the voltage drop across the braking resistor (30) over a predetermined measuring time. Supply unit according to one of the Claims 12 to 16 , characterized in that the computing unit (7) is set up to repeat the offset measurement (38) and the reference measurement (39) in an ongoing operation in order to constantly update the stored resistance value. Supply unit according to one of the Claims 12 to 17 , characterized in that the computing unit (7) is set up to update the stored resistance value only by offset measurement (39) and reference measurement (39) if the brake chopper (30, 31) before switching to the activated state (37, 37 ') was deactivated for more than 0.1 ms, preferably more than 0.5 ms, particularly preferably more than 1 ms. Supply unit according to one of the Claims 12 to 18 , characterized in that the computing unit (7) is set up to continuously scan the current value (34) measured by the Rogowski measuring device (8, 9) and to store it in a FIFO memory.

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