Frequency converter

Abstract

Frequency converter (100), comprising: - an inverter (1) with a number of power semiconductors (7-12), wherein the inverter (1) is designed to control the power semiconductors (7-12) in a clocked manner such that a number of control signals (u, v, w) with a predetermined time profile are generated for controlling an electric motor (2), - terminals (13, 14, 15) at which the number of control signals (u, v, w) is output, and - a partial discharge detector (16) designed to detect partial discharges occurring in lines (17, 18, 19) between the frequency converter (100) and the electric motor (2) during the clocking of the power semiconductors (7-12), - wherein the partial discharge detector (16) comprises a partial discharge sensor (3) which is designed to extract partial discharge signals (TS) from signals present at the terminals (13, 14, 15) of the frequency converter (100).

Description

EP 3 796 012 A1 discloses a method and a device for detecting a partial discharge at a winding of an electric machine. For this purpose, measurement signals are decoupled and corrected from an interference frequency spectrum.EP 3 595 159 A1 discloses a converter with ground fault detection.EP 3 306 813 A1 discloses a power converter with short-circuit detection.The invention relates to a frequency converter which enables the safeest possible actuation of electric motors.The frequency converter comprises a conventional inverter with a number of power semiconductors. The inverter can have 6 power semiconductors, for example. The inverter is conventionally designed to actuate the power semiconductors in a clocked manner such that a number of, in particular pulse-width-modulated, actuation signals are generated with a predefined temporal profile for actuating an electric motor. For example, exactly three drive signals can be generated. In this respect, reference is also made to the relevant technical literature.The frequency converter further has terminals at which the number of drive signals is output.According to the invention, the frequency converter has a partial discharge detector which is designed to detect partial discharges during the pulsing of the power semiconductors, which partial discharges occur in or on lines between the frequency converter and the electric motor. The partial discharge detector can furthermore be designed to detect partial discharges which occur in the electric motor connected to the frequency converter.The partial discharge detector has a partial discharge sensor which is designed to couple out partial discharge signals from signals which are present at the terminals of the frequency converter.In one embodiment, the partial discharge sensor is designed to couple out the partial discharge signals capacitively, inductively, field-boundly, and / or directionally.In one embodiment, the partial discharge detector comprises a filter configured to separate the coupled-out partial discharge signals from interference signals caused by the pulsing of the power semiconductors.In one embodiment, the partial discharge detector has a processing unit which is designed to evaluate the filtered partial discharge signals for detecting partial discharges.In one embodiment, the processing unit for evaluating the partial discharge signals has an envelope curve detector.In one embodiment, the processing unit for evaluating the partial discharge signals has a root mean square RMS detector.One of the damage mechanisms for electric machines or electric motors is damage to winding insulation by so-called partial discharges. In this case, the insulation is damaged gradually until breakdown and thus destruction of the insulation system occurs.Partial discharges arise due to high field strengths in the insulation or due to rapid field strength changes. These problems are increasingly encountered during operation on a frequency converter or in switched-mode power supplies, in particular in the case of particularly low-loss, fast-switching frequency converters and switched-mode power supplies. By means of the invention, partial discharges can be detected during the operation of the electric machine, also at the frequency converter. Detection and maintenance can thus be carried out before the electrical machine fails, and standstill times in the sense of predictive maintenance can be eliminated. This also applies to other winding products under high load by switching elements, such as, among other things, in switched-mode power supplies.According to the invention, the partial discharge detector is integrated into a frequency converter with fast-switching semiconductor switches. Partial discharges in windings or their supply lines can thus be detected in the frequency converter itself, so that suitable countermeasures can be taken directly in the frequency converter, for example by appropriate control of the power semiconductors.The partial discharge detector is designed to reliably couple out a partial discharge signal at the terminals of an electric motor, a transformer and / or an inductance. Furthermore, the partial discharge detector is designed to separate a disturbance signal from the partial discharge signal. Furthermore, the partial discharge detector is designed to process the partial discharge signal in a suitable manner and to signal partial discharges internally in the device or to the outside.Decoupling of the partial discharge signal can be effected, for example, by capacitive coupling, inductive coupling, field-bound coupling and / or by directional coupling or other coupling mechanisms.Interference which arises, for example, by the converter must be removed from the decoupled or decoupled signal. For example, high-frequency filters can be used for this purpose.In order to detect the partial discharge, the partial discharge signal can be used directly in the case of very rapid detection. In order to simplify the processing directly in the frequency converter, an envelope curve or RMS detector can be used, for example.The data extracted from the partial discharge signal can be evaluated directly in the frequency converter, for example via an analog-to-digital converter. Alternatively, the measured values or raw data can also be passed on via a data connection to a superordinate controller for the evaluation there.By reliably decoupling the partial discharge signal from other signals at the terminals of the machine, a reliable partial discharge measurement can be carried out.A steep separation of partial discharge signal and interference signal can achieve a high interference voltage interval. This allows reliable detection.By using an envelope or RMS detector, the entire circuit can be kept simple and cost effective.By processing directly in the frequency converter, the frequency converter can be stopped already before a total failure with consequent damage when increased partial discharges occur. By connecting the frequency converter to a higher-order control, a message can be given via a data connection.Unlike in conventional partial discharge detectors, partial discharge detection takes place with clocked drive signals, which are also used for driving electric motors. Conventionally, sinusoidal voltages and currents are used instead.The invention will be described in detail below with reference to the drawings. The following shows: FIG. 1 schematically shows a block diagram of a frequency converter according to the invention with an inverter and a partial discharge detector.FIG. 1 shows a block diagram of a frequency converter 100.The frequency converter 100 has a conventional inverter 1 with six power semiconductors 7 to 12 in the topology shown, wherein the inverter 1 is conventionally designed to actuate the power semiconductors 7 to 12 in a clocked manner according to a PWM scheme in such a way that a number of sinusoidal actuation signals or actuation voltages u, v, w are generated with a predefined temporal profile for actuating an electric motor 2. In this respect, reference is also made to the relevant technical literature.The frequency converter 100 further has three terminals 13, 14, 15 at which the drive signals u, v, w are output.The frequency converter 100 further comprises a partial discharge detector 16 which is configured to detect partial discharges during the pulsing of the power semiconductors 7- 12 which occur in the electric motor 2 connected to the frequency converter 100 and / or in lines 17, 18, 19 between the frequency converter 100 and the electric motor 2.The partial discharge detector 16 has a partial discharge sensor 3 which is designed to couple out one or more partial discharge signals TS from signals or the drive signals u, v, w which are present at the connections 13, 14, 15 of the frequency converter 100.The partial discharge sensor 3 is designed to couple out the partial discharge signals TS capacitively, inductively, field-boundly, and / or directionally.The partial discharge detector 16 has a filter 4, for example in the form of a bandpass filter, which is designed to separate the coupled-out partial discharge signals TS from interference signals caused by the pulsing of the power semiconductors 7- 12.The partial discharge detector 16 has a processing unit 5, which is designed to evaluate the filtered partial discharge signals TS for detecting partial discharges.The processing unit 5 has, for example, an envelope curve detector 20 and / or a root mean square RMS detector 21 for evaluating the partial discharge signals TS.The partial discharge detector 16 has a control unit 6 connected downstream of the processing unit 5, which is configured, inter alia, to actuate the inverter 1 on the basis of the evaluation results of the processing unit 5.

Claims

Frequency converter (100), comprising: - an inverter (1) having a number of power semiconductors (7-12), wherein the inverter (1) is designed to actuate the power semiconductors (7-12) in a clocked manner such that a number of actuation signals (u, v, w) is generated with a predefined temporal profile for actuating an electric motor (2), - connections (13, 14, 15) at which the number of actuation signals (u, v, w) is output, and - a partial discharge detector (16) which is designed to detect partial discharges during the pulsing of the power semiconductors (7-12), which partial discharges occur in lines (17, 18, 19) between the frequency converter (100) and the electric motor (2), - wherein the partial discharge detector (16) has a partial discharge sensor (3) which is designed to detect partial discharges during the pulsing of the power semiconductors (7-12), Partial discharge signals (TS) can be decoupled from signals which are present at the connections (13, 14, 15) of the frequency converter (100).Frequency converter (100) according to Claim 1, characterized in that - the partial discharge sensor (3) is designed to couple out the partial discharge signals (TS) capacitively, to couple them out inductively, to couple them out in a field-bound manner and / or to couple them out in a directional manner.Frequency converter (100) according to one of the preceding claims, characterized in that - the partial discharge detector (16) has a filter (4) which is designed to separate the coupled-out partial discharge signals (TS) from interference signals which are caused by the clocking of the power semiconductors (7-12).Frequency converter (100) according to Claim 3, characterized in that - the partial discharge detector (16) has a processing unit (5) which is designed to evaluate the filtered partial discharge signals (TS) for detecting partial discharges.Frequency converter (100) according to Claim 4, characterized in that - the processing unit (5) for evaluating the partial discharge signals (TS) has an envelope curve detector (20).Frequency converter (100) according to Claim 4 or 5, characterized in that - the processing unit (5) for evaluating the partial discharge signals (TS) has a root mean square RMS detector (21).Frequency converter (100) according to one of the preceding claims, characterized in that - the partial discharge detector (16) is designed to detect partial discharges during the pulsing of the power semiconductors (7-12), which partial discharges occur in the electric motor (2) connected to the frequency converter (100).

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