Power converter arrangement and method for determining the state of elements of a power converter

Abstract

The invention relates to a power converter arrangement having power modules (1, 2, 3) of a power converter and a control device (4) for power modules, an intermediate circuit capacitor arrangement (5) in the intermediate circuit of the power converter and a monitoring device (6, 7, 8, 14) for determining the state of elements of the power converter, in particular for determining the state of the intermediate circuit capacitor arrangement, wherein the monitoring device has a monitoring AC voltage source (6) which can be controlled independently of the intermediate circuit voltage, is electrically conductively connected to the terminals (13, 14) of the intermediate circuit by means of a coupling capacitor (7) and connecting lines (11, 12) and applies a monitoring AC voltage to the intermediate circuit, wherein the following elements are provided for efficient monitoring: a voltage detection device (8a) for detecting the time-dependent monitoring AC voltage created, a current detection device (8b) for detecting a time-dependent monitoring current which is created when the monitoring AC voltage is applied, a voltage threshold detector (8c) for detecting the times of threshold crossings, in particular voltage zero crossings, of the monitoring AC voltage, a current threshold detector (8d) for detecting the times of threshold crossings, in particular current zero crossings, of the monitoring current, and a timing device (9) for determining the phase shift between the monitoring voltage and the monitoring current on the basis of the detected times of the threshold crossings, in particular the zero crossings, of the monitoring voltage and monitoring current, and a processing device (10) which assigns an age state to the determined phase shift on the basis of a comparison with reference values.

Description

[0001] Power converter arrangement and method for determining the condition of power converter elements. The invention lies in the field of electrical engineering and power electronics and is applicable to power converters in various application areas, such as power distribution, generator and motor control, as well as wind energy and solar technology. The components in the power path of power converters are subject to aging / degradation during their life cycle. This degradation process is ubiquitous and depends on a multitude of different factors. The progressive aging during the life cycle leads to changes in the electrical and mechanical properties of the components.Due to different failure characteristics of the various components, there is a risk that if a component is suddenly destroyed or if certain aging thresholds are exceeded, other components of the power converter may be damaged and / or downtime of the power converter or the higher-level system may occur due to necessary repairs or urgent maintenance.

[0002] Solutions are already known that enable the detection of aging effects in a power converter system. Especially in the area of ​​thermomechanical fatigue phenomena in power modules, there are already publications describing the monitoring of packaging and connection technology. Such approaches often utilize the recording of load accumulation (cycle counters) and employ temperature-sensitive electrical parameters to calculate and / or predict aging and fatigue states using computational models.

[0003] Our understanding of the degradation processes and mechanisms in converter electronic power modules has also increased significantly in recent years thanks to intensive research projects. Another important component in the converter system is the DC link capacitors, which have also been shown to fail relatively frequently. Due to their importance in the converter system and the amount of energy stored, defects in the DC link are often associated with component destruction.

[0004] In addition, there are studies in the field of detecting moisture-induced degradation in power converters that focus on leakage current monitoring or monitoring the reduction in the blocking strength of the power modules. However, such methods can only be transferred to other components in the power path to a limited extent. Furthermore, leakage current measurement during converter operation is extremely difficult due to the fact that the load current is superimposed on the comparatively small leakage current and that the power semiconductor switching operations continuously couple disturbances into the system being monitored. Approaches also exist in the field of impedance spectroscopy.

[0005] The publication by W. Zhou, M. Wang, and Q. Wu, "A Model-Based Monitoring Method for Offline Accelerated Testing of DC-Link Capacitor in Three-Phase Inverter Systems," IEEE Transactions on Power Electronics, Vol. 36 No. 1, pp. 61-67, 2021, presents an approach based on injecting an alternating signal into a DC link via a coupling capacitor. However, the setup described therein only allows limited operation under field conditions. In particular, the coupling capacitance was chosen to be very large compared to the DC link capacitance in the publication. This is very difficult or even impossible to implement in practice, since such a large capacitance with the necessary dielectric strength would require a considerable amount of space and could not be meaningfully integrated. In addition, the setup measures the voltage and current in the DC link and uses them as the basis for further calculations.

[0006] Against the background of the prior art, the present invention is based on the object of creating an arrangement and a method that enable the monitoring of aging states for components of a power converter arrangement in a simple, accurate, and reliable manner. This object is achieved with the features of the invention by a power converter arrangement according to claim 1 and a method for determining the state of elements of a power converter. The subclaims present possible implementations of the power converter arrangement and the method for determining the state.

[0007] The invention thus relates to a power converter arrangement with power modules of a power converter and a control device for power modules, an intermediate circuit capacitor arrangement in the intermediate circuit of the power converter and a monitoring device for determining the state of elements of the power converter, in particular for determining the state of the intermediate circuit capacitor arrangement, wherein the monitoring device has a monitoring AC voltage source which is controllable independently of the intermediate circuit voltage and which is electrically connected to the terminals of the intermediate circuit by means of a coupling capacitor and connecting lines and impresses a monitoring AC voltage on the intermediate circuit.

[0008] Such a converter arrangement also has the following features to solve the problem:

[0009] A voltage detection device for detecting the resulting, time-dependent monitoring alternating voltage, a current detection device for detecting a time-dependent monitoring current that is established with the impression of the monitoring alternating voltage, a voltage threshold detector for detecting times of threshold crossings, in particular zero voltage crossings, of the monitoring alternating voltage, a current threshold detector for detecting times of threshold crossings, in particular zero current crossings, of the monitoring current, as well as a time measuring device for determining the phase shift between the monitoring voltage and the monitoring current based on the detected times of the threshold crossings, in particular zero crossings, of the monitoring voltage and monitoring current and a processing device,which assigns an ageing state to the determined phase shift based on a comparison with reference values.

[0010] The arrangement according to the invention is primarily intended to monitor an intermediate circuit capacitor arrangement, which may comprise one or more intermediate circuit capacitors. Furthermore, the aging of the remaining components of the converter, such as the power modules, can also influence the measured variables and thus be monitored. In this context, the power modules can be understood as a pair of power semiconductor units that are controlled by a control device and each control the current in a branch of the converter.

[0011] The core of the invention lies in determining the degradation, specifically from the phase shift of the injected current compared to the injected voltage. The injected voltage is generated by a monitoring AC voltage source independent of the other elements of the converter arrangement and coupled into the intermediate circuit via a coupling capacitor. The injected current then appears as the system response and can be measured outside the intermediate circuit in the area of ​​the monitoring AC voltage source at a measuring resistor in the form of the voltage drop across it. The coupling capacitor is selected to have a smaller capacitance than the capacitor arrangement of the intermediate circuit capacitor(s).Although the voltage division results in a relatively high voltage drop across the coupling capacitor, which is fundamentally undesirable, it limits the size of the coupling capacitor to such an extent that it can be structurally integrated into the control section of the power converter. The capacitance of the coupling capacitor can be less than 1 mF, for example, in the range of 10 μF to 10 μF (depending on the dielectric strength). The monitoring AC voltage source, the voltage measuring device, and the current measuring device can be located outside the DC link.The described arrangement allows for a much simpler measurement of the phase shift of the injected current, measured by the current detection device, relative to the injected voltage, measured by the voltage detection device, compared to full-scale impedance spectroscopy. For example, using threshold detectors and a time-to-digital converter (TDC), the phase shift can be evaluated / assessed using a microcontroller. The evaluated data and events can be forwarded to the power converter controller and / or a condition monitor.

[0012] A possible implementation of the power converter arrangement can provide that the voltage detection device and the current detection device are directly electrically connected to the connecting lines between the monitoring AC voltage source and the potential terminals of the intermediate circuit.

[0013] A further possible implementation of the power converter arrangement can provide that the current detection device has a measuring resistor which is electrically connected in series with a connecting line between the monitoring AC voltage source and the terminals of the intermediate circuit capacitor arrangement and at which a voltage drop is measured.

[0014] It can also be provided that the voltage detection device is designed to detect the resulting time-dependent monitoring voltage independently of the voltage applied to the intermediate circuit capacitor arrangement.

[0015] This allows the injected voltage and the injected current resulting from the system response to be measured independently of the load current in the converter itself and the DC link voltage, allowing the system response to be easily detected using these variables. If measured in the converter itself, the injected variables would represent only a small portion of the voltages and currents flowing there.

[0016] A possible embodiment can thus provide that the current detection device is designed to detect the time-dependent monitoring current generated by the monitoring AC voltage source independently of the load currents flowing in the power converter.

[0017] In a power converter arrangement of the type described, it can also be provided that the monitoring AC voltage source is structurally combined with an electronic assembly of the power converter, in particular a control device for power modules or a measuring device for an intermediate circuit voltage, in such a way that the terminals of the monitoring AC voltage source are connected or can be connected to the potential terminals of the intermediate circuit.

[0018] For this purpose, the monitoring AC voltage source can be arranged directly on a common circuit board with a control device for power modules or a measuring device for an intermediate circuit voltage, or it can be connected to such a circuit board as a module, for example, plugged onto it. In any case, the monitoring AC voltage source can be arranged in a common housing or on a common support with a control device. This reduces the construction effort and allows the power supply of the various units to be combined. Furthermore, the potentials of the intermediate circuit and the monitoring device can be matched to each other.

[0019] A further possible implementation of the power converter arrangement can provide that the voltage detection device and / or the current detection device are structurally combined with an electronic assembly of the power converter, in particular a control device for power modules or a measuring device for an intermediate circuit voltage, in particular on a common printed circuit board or in an electronic module.

[0020] The voltage detection device and / or the current detection device can thus also be arranged together with the monitoring AC voltage source on a common printed circuit board and / or a carrier or in a common housing.

[0021] In a power converter arrangement of the type described, it can also be provided that the processing device is designed to determine a relationship between detected current and voltage values ​​of the monitoring current and the monitoring alternating voltage, to compare this with stored reference values ​​and to take the result of the comparison into account when assigning an aging state.

[0022] Since, in addition to the phase shift between the injected alternating voltage and the injected current, the amplitude ratio between these two quantities also depends on the aging state of the elements of the intermediate circuit, in particular the intermediate circuit capacitor arrangement, this amplitude ratio can also be used or taken into account as an indicator for determining an aging state.

[0023] In addition to a power converter arrangement of the type described above, the invention also relates to a method for determining the state of elements of a power converter with power modules and an intermediate circuit, in particular for determining the state of an intermediate circuit capacitor arrangement of a power converter, in which a monitoring alternating voltage is impressed on the intermediate circuit capacitor arrangement by means of a monitoring alternating voltage source that can be controlled independently of the load currents of the power converter via a coupling capacitor, in which the resulting, time-dependent monitoring voltage is detected by a voltage detection device, the time-dependent monitoring current generated by the monitoring alternating voltage source is detected by a current detection device, times of threshold crossings, in particular the voltage zero crossings, of the monitoring alternating voltage are detected by a voltage threshold detector,by a current zero-crossing detector, the times of threshold crossings, in particular the current zero crossings, of the monitoring current are detected, by a time measuring device the phase shift between the monitoring voltage and the monitoring current is determined on the basis of the detected times of the threshold crossings of the monitoring voltage and the monitoring current, and by a processing device an ageing state is assigned to the determined phase shift on the basis of a comparison with reference values.

[0024] A possible implementation of the method mentioned can provide that the ratio of absolute values, in particular the ratio of the peak values, of monitoring current and monitoring voltage is determined and taken into account when assigning an aging state.

[0025] In the following, the invention is shown using exemplary embodiments in figures of a drawing and described below.

[0026] This shows

[0027] Figure 1: a symbolic circuit diagram of a power converter arrangement,

[0028] Figure 2: the course of the injected alternating voltage relative to a measured voltage drop, which represents the course of the injected current and

[0029] Figure 3 shows a schematic overview of the functional elements of a power converter arrangement. Figure 1 shows a power converter arrangement according to the invention with three power modules 1, 2, 3, each containing pairs of power semiconductor elements S1 and S2, S3 and S4, and S5 and S6. The power modules can also be designed as individual switch modules. The individual pairs of power semiconductor elements each switch one phase of a load current on and off. An intermediate circuit is defined by an intermediate circuit capacitor 5 and its connections to the power modules 1, 2, 3. The right-hand part of Figure 1 shows an equivalent circuit diagram of the intermediate circuit capacitor with a capacitance 5a, an ohmic resistor 5b connected in parallel with it, an ohmic resistor 5c connected electrically in series with the capacitance 5a, and an inductance 5d connected electrically in series with the capacitance 5a.

[0030] A control device 4 of the power modules 1, 2, 3 has gate drivers 4a, 4b. The gate drivers are each connected in a conventional manner to the control terminals of the power semiconductor elements S1, S2, S3, S4, S5, S6, namely via the auxiliary emitter high-side (AEHS), auxiliary emitter low-side (AELS), auxiliary collector high-side (ACHS), gate high-side (G HS), and gate low-side (G LS) terminals. For reasons of clarity, only the gate driver for one of the half-bridge branches is shown as an example in Figure 1.

[0031] An electronic circuit integrated at the level of the gate drivers 4a, 4b, i.e., the control device 4 of the power modules 1, 2, 3, superimposes an alternating signal in the form of a monitoring alternating voltage Ui on the intermediate circuit voltage. The amplitude of the monitoring alternating voltage Ui is significantly smaller than the intermediate circuit voltage, for example, less than 5%, in particular less than 2% or less than 1%, more particularly less than 0.1% or even less than 0.01% of the intermediate circuit voltage, and the voltage is generated by a monitoring alternating voltage source 6. The coupling is galvanically isolated, capacitive, and implemented by means of a coupling capacitor 7.The monitoring AC voltage source 6 is connected on one side by means of the connecting line 12 to a potential connection 14 (earth potential, or the negative intermediate circuit potential DC, Auxiliary emitter low-side (AELS)) and the intermediate circuit, while on the other side the connection of the coupling capacitor 7 facing away from the monitoring AC voltage source 6 is connected by means of the connecting line 11 to the high-voltage potential connection 13 (Auxiliary collector high-side (ACHS)) of the intermediate circuit. The potential connection 14 can advantageously be at the same potential as the GNDLS connection so that the circuit of the AC voltage source is closed and the impressed alternating signal can flow back to the source.

[0032] The injected voltage Ui is detected by a voltage detection device 8a. The injected current is detected by a current detection device 8b using a voltage drop U2 across the measuring resistor 15. For more precise detection of the waveforms of the voltages Ui and U2, zero-crossing detection is performed by the voltage threshold detector 8c and the current threshold detector 8d in order to generate logic levels from the analog signal waveforms. A time measuring device 9, for example in the form of a time-to-digital converter, determines the phase shift between the monitoring voltage and the monitoring current based on the detected signal edges occurring at different times, specifically the times of the zero crossings of the monitoring voltage and current.A processing device 10, for example in the form of a microcontroller, assigns an aging state to the determined phase shift based on a comparison with stored reference values.

[0033] The temporal curves of the monitoring current (the injected current) relative to the monitoring voltage (the injected AC voltage) are sketched in Figure 2 for various aging states of a DC link capacitor arrangement or a power converter and are intended to show the behavior with progressive aging. The values ​​of the temporal offset of the signals U2, which represent the resulting injected current, compared to the signal curve of the monitoring AC voltage, which is represented by the measured voltage Ui, are determined experimentally or by simulation calculations for various aging states. Arrow 16 indicates the direction in which the curves representing U2 and thus the current curve of the injected current shift with increasing aging. Furthermore, it is evident from Figure 2 that with increasing aging, the amplitude of U2 also increases relative to the amplitude of Ui.Thus, the amplitude ratio between U2 and Ui (the quotient of U2 and Ui) is also an indicator of aging that can be used for analysis.

[0034] The advantage of phase shift as a damage or aging indicator is that it is easy to evaluate as a single variable, eliminating the need for complex further data processing. In principle, the method offers the possibility of monitoring degradation during converter operation. The invention can be integrated into gate units during the construction of a converter arrangement or integrated into an existing system as a retrofit solution.

[0035] Figure 3 shows an overview of the measurement concept in connection with the functional units 17, 18, 19 of the power converter.

[0036] Functional unit 17 comprises the converter controller with the closed-loop control, the measured value acquisition, and the communication interfaces. Functional unit 18 comprises the gate unit with the gate drivers 4a, 4b for the power semiconductor modules S1-S6, as well as protective devices at the power semiconductor level. Functional unit 19 comprises the actual power section of the converter with the power semiconductor modules S1-S6, the load connections, the phase connections (busbars), and the elements of the intermediate circuit, in particular the intermediate circuit capacitor(s) 5.The monitoring device according to the invention with the monitoring AC voltage source, the current and voltage detection devices 8a, 8b, the threshold detectors 8c, 8d and the time measuring device 9 as well as the processing device 10 is designated 20 in Figure 3 and is shown integrated into the functional unit 18 - either integrated into it during production or retrofitted as part of a retrofit.

[0037] If the monitoring device is systematically integrated into the power converter arrangement and a circuit board with an electronic circuit for measuring the intermediate circuit voltage is provided there, it is possible to arrange the monitoring device on this circuit board.

Claims

Patent claims 1. A power converter arrangement with power modules (1, 2, 3) of a power converter and a control device (4) for power modules, an intermediate circuit capacitor arrangement (5) in the intermediate circuit of the power converter and a monitoring device (6, 7, 8, 14) for determining the state of elements of the power converter, in particular for determining the state of the intermediate circuit capacitor arrangement, wherein the monitoring device has a monitoring AC voltage source (6) which is controllable independently of the intermediate circuit voltage and which is electrically connected to the terminals (13, 14) of the intermediate circuit by means of a coupling capacitor (7) and connecting lines (11, 12) and impresses a monitoring AC voltage on the intermediate circuit, characterized by a voltage detection device (8a) for detecting the resulting, time-dependent monitoring AC voltage (U i, U inj), a current detection device (8b) for detecting a time-dependent,a monitoring current (I inj) which is established upon application of the monitoring alternating voltage, a voltage threshold detector (8c) for detecting times of threshold crossings, in particular zero voltage crossings, of the monitoring alternating voltage, a current threshold detector (8d) for detecting times of threshold crossings, in particular zero current crossings, of the monitoring current, and a time measuring device (9) for determining the phase shift between the monitoring voltage and the monitoring current based on the detected times of the threshold crossings, in particular zero crossings, of the monitoring voltage and monitoring current, and a processing device (10) which assigns an aging state to the determined phase shift based on a comparison with reference values.

2. Power converter arrangement according to claim 1, characterized in that the voltage detection device (8a) and the current detection device (8b) are electrically connected directly to the connecting lines (11, 12) between the monitoring AC voltage source (6) and the potential terminals (13, 14) of the intermediate circuit.

3. Power converter arrangement according to claim 1 or 2, characterized in that the current detection device (8b) has a measuring resistor (15) which is electrically connected in series with a connecting line (11) between the monitoring AC voltage source (6) and the terminals (13) of the intermediate circuit capacitor arrangement (5), at which a voltage drop is measured.

4. Power converter arrangement according to claim 1, 2 or 3, characterized in that the voltage detection device (8a) is designed to detect the resulting time-dependent monitoring voltage (U inj ) independently of the voltage applied to the intermediate circuit capacitor arrangement (5).

5. Power converter arrangement according to one of claims 1 to 4, characterized in that the current detection device (8b) is designed to detect the time-dependent monitoring current (linj) generated by the monitoring AC voltage source (6) independently of the load currents flowing in the power converter.

6. Power converter arrangement according to one of claims 1 to 5, characterized in that the monitoring AC voltage source (6) is structurally combined with an electronic assembly of the power converter, in particular a control device (4) for power modules (1, 2, 3) or a measuring device for an intermediate circuit voltage, in such a way that the terminals of the monitoring AC voltage source are connected or can be connected to the potential terminals (13, 14) of the intermediate circuit.

7. Power converter arrangement according to one of claims 1 to 6, characterized in that the voltage detection device (8a) and / or the Current detection device (8b) with an electronic assembly of the power converter, in particular a control device (4) for power modules (1, 2, 3) or a measuring device for an intermediate circuit voltage, structurally combined, in particular on a common printed circuit board or in an electronic module.

8. Power converter arrangement according to one of claims 1 to 7, characterized in that the processing device (10) is designed to determine a relationship between detected current and voltage values ​​of the monitoring current and the monitoring alternating voltage, to compare these with stored reference values ​​and to take the result of the comparison into account when assigning an aging state.

9. Method for determining the state of elements of a power converter with power modules (1, 2, 3), in particular for determining the state of an intermediate circuit capacitor arrangement (5) of a power converter, in which a monitoring alternating voltage (Ui, U inj) is impressed on the intermediate circuit capacitor arrangement (5) by means of a monitoring alternating voltage source (6) that can be controlled independently of the load currents of the power converter via a coupling capacitor (7), in which the resulting, time-dependent monitoring voltage is detected by a voltage detection device (8a), the time-dependent monitoring current (I inj) generated by the monitoring alternating voltage source is detected by a current detection device (8b), times of threshold crossings, in particular of the voltage zero crossings, of the monitoring alternating voltage are detected by a voltage threshold detector (8c), times of threshold crossings are detected by a current zero crossing detector (8d),in particular the current zero crossings of the monitoring current are detected, the phase shift between the monitoring voltage and the monitoring current is determined by a time measuring device (9) on the basis of the detected times of the threshold crossings of the monitoring voltage and the monitoring current and, A processing device (10) assigns an aging state to the determined phase shift based on a comparison with reference values.

10. The method according to claim 9, characterized in that the ratio of absolute values, in particular the ratio of the peak values, of the monitoring current and the monitoring voltage is determined and taken into account when assigning an aging state.

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