WO2019127184A1

WO2019127184A1 - Method and system for on-line condition monitoring of dc-link capacitor in power converter

Info

Publication number: WO2019127184A1
Application number: PCT/CN2017/119253
Authority: WO
Inventors: Junjie GE; Jinlei MENG; Wenliang Zhang; Tinho LI
Original assignee: Abb Schweiz Ag
Priority date: 2017-12-28
Filing date: 2017-12-28
Publication date: 2019-07-04

Abstract

A method and system for on-line condition monitoring of a direct current (DC) -link capacitor in a power converter. The method includes detecting a first waveform of voltage at the DC-link capacitor that is generated by applying a first control signal with a first duty cycle for at least one first switching period on the power converter (310). The method also includes detecting a second waveform of voltage at the DC-link capacitor that is generated by applying a second control signal with a second duty cycle for at least one second switching period following the at least one first switching period on the power converter (320), the second duty cycle deviating from the first duty cycle within a predetermined range. The method further includes determining, based on the second waveform, a parameter related to a health condition of the DC-link capacitor (330).

Description

METHOD AND SYSTEM FOR ON-LINE CONDITION MONITORING OF DC-LINK CAPACITOR IN POWER CONVERTER

TECHNICAL FIELD

Example embodiments of the present disclosure generally relate to capacitor monitoring and more particularly, to a method and system for on-line condition monitoring of a direct current (DC) -link capacitor in a power converter.

BACKGROUND

Capacitors, especially electrolytic capacitors (E-Cap) , are widely used in power electronic converters, specifically in the direct-current (DC) -link circuit. However, the capacitors will degrade with time and fail more frequently than other components in the power converters, which will threaten reliability of the power converters. To ensure reliability of power converters, it is desirable to carry out condition monitoring of the capacitors in the power converters so as to enable the indication of future failure occurrences and preventive maintenance.

The capacitor degradation usually manifests by a decrease in capacitance and an increase in equivalent series resistance (ESR) . Earlier detection of the ESR increase or capacitance decrease allows for preventive mitigation actions, such as scheduling shutdown and repairs. Moreover, it is also helpful with evaluation of the expected operational time until failure may happen. Preventing the increase of the ESR or decrease of the capacitance over a specified level provides maintaining the quality of converted power and protects the power converter from failure of DC-link capacitor (s) .

Methods for condition monitoring have been studied for a long time but most of them fail to be applied in real products. Most of the methods require additional hardware such as an external switching circuit, capacitor current sensor, or enhanced voltage sensor which includes an additional sample processing circuit. The impact on the main circuit, mechanical structure, or control circuit may lead to a redesign of the power converters, which is undesirable. Some condition monitoring methods may not require additional hardware, but provide low precision and/or have limited applications in some special scenarios or some certain converters. Moreover, some methods will suspend the normal operations of the power converters.

SUMMARY

Example embodiments of the present disclosure propose a solution for on-line condition monitoring of a direct current (DC) -link capacitor in a power converter.

In a first aspect, example embodiments of the present disclosure provide a method for on-line condition monitoring of a direct current (DC) -link capacitor in a power converter. The method includes detecting a first waveform of voltage at the DC-link capacitor that is generated by applying a first control signal with a first duty cycle for at least one first switching period on the power converter. The method also includes detecting a second waveform of voltage at the DC-link capacitor that is generated by applying a second control signal with a second duty cycle for at least one second switching period following the at least one first switching period on the power converter, the second duty cycle deviating from the first duty cycle within a predetermined range. The method further includes determining, based on the second waveform, a parameter related to a health condition of the DC-link capacitor.

In some embodiments, determining the parameter comprises: determining, based on the second waveform, a resonance frequency associated with the DC-link capacitor and an inductor coupled to the DC-link capacitor in the power converter; and determining, based on the resonance frequency, the parameter related to the health condition of the DC-link capacitor.

In some embodiments, determining the parameter based on the resonance frequency comprises: determining capacitance of the DC-link capacitor based on the resonance frequency and inductance of the inductor.

In some embodiments, determining the parameter based on the resonance frequency comprises: determining equivalent series resistance (ESR) or a change of the ESR of the DC-link capacitor based on energy of the second waveform of voltage at the resonance frequency and current flowing through a load in the power converter.

In some embodiments, the method is suspended in response to determining that a difference between an input power and an output power of the power converter exceeds a predetermined threshold.

In some embodiments, the DC-link capacitor includes at least one electrolytic capacitor.

In some embodiments, at least one of the first and second control signals includes a Pulse Width Modulation (PWM) control signal.

In a second aspect, example embodiments of the present disclosure provide a system for on-line condition monitoring of a direct current (DC) -link capacitor in a power converter. The system includes a detecting unit configured to detect a first waveform of voltage at the DC-link capacitor that is generated by applying a first control signal with a first duty cycle on the power converter for at least one first switching period, and detect a second waveform of voltage at the DC-link capacitor that is generated by applying a second control signal with a second duty cycle for at least one second switching period following the at least one first switching period on the power converter, the second duty cycle deviating from the first duty cycle within a predetermined range. The system also includes a determining unit configured to determine, based on the second waveform, a parameter related to a health condition of the DC-link capacitor.

In some embodiments, the determining unit is configured to: determine, based on the second wavefonn, a resonance frequency associated with the DC-link capacitor and an inductor coupled to the DC-link capacitor in the power converter; and determine, based on the resonance frequency, the parameter related to the health condition of the DC-link capacitor.

In some embodiments, the determining unit is configured to determine capacitance of the DC-link capacitor based on the resonance frequency and inductance of the inductor.

In some embodiments, the determining unit is configured to determine equivalent series resistance (ESR) or a change of the ESR of the DC-link capacitor based on energy of the second waveform of voltage at the resonance frequency and current flowing through a load in the power converter.

In some embodiments, the operations of the detecting unit and the determining unit are suspended in response to determining that a difference between an input power and an output power of the power converter exceeds a predetermined threshold.

In a third aspect, example embodiments of the present disclosure provide a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, cause the at least one processor to perform the method of the first aspect.

In a fourth aspect, example embodiments of the present disclosure provide a computer program product being tangibly stored on a computer readable storage medium and comprising instructions which, when executed on at least one processor, cause the at least one processor to perform the method of the first aspect.

In a fifth aspect, example embodiments of the present disclosure provide an Internet of Things (IoT) system. The system includes a power converter, and a system for on-line condition monitoring of a direct current (DC) -link capacitor in the power converter of the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the following detailed descriptions with reference to the accompanying drawings, the above and other objectives, features and advantages of the example embodiments disclosed herein will become more comprehensible. In the drawings, several example embodiments disclosed herein will be illustrated in an example and in a non-limiting manner, wherein:

Figs. 1A-1B i11ustrate curve graphs showing example degradation of ESR and capacitance of a DC-link capacitor;

Fig. 2 illustrates a diagram of an equivalent model of a capacitor;

Fig. 3 illustrates a flowchart of a process of on-line condition monitoring of a capacitor in accordance with some example embodiments of the present disclosure;

Fig. 4 illustrates a schematic diagram of an injection to a control signal used in a power converter in accordance with some example embodiments of the present disclosure;

Fig. 5A illustrates diagrams showing respective waveforms of voltage and current at a DC-link capacitor in accordance with some example embodiments of the present disclosure;

Fig. 5B illustrates diagrams showing respective zoom-in waveforms of voltage and current of the waveforms of Fig. 5A during a period of time in accordance with some example embodiments of the present disclosure;

Fig. 6A illustrates a diagram showing a waveform of voltage generated in accordance with some example embodiments of the present disclosure;

Fig. 6B illustrates a diagram showing a signal of high frequency components of the waveform of Fig. 6A in accordance with some example embodiments of the present disclosure;

Fig. 7 illustrates a diagram showing a Fast Fourier Transformation (FFT) result of the signal of Fig. 6B in accordance with some example embodiments of the present disclosure;

Figs. 8A-8B illustrate FFT results of high frequency components of signals generated for capacitors with different capacitances and ESRs in accordance with some example embodiments of the present disclosure;

Fig. 9A illustrates a curve chart of capacitance values estimated according to an example embodiment of the present disclosure at different real capacitance values of DC-link capacitors;

Fig. 9B illustrates a curve chart of capacitance errors at different real capacitance values of DC-link capacitors in accordance with some example embodiments of the present disclosure;

Fig. 10 illustrates a curve chart of example relationships of different magnitudes at the resonance frequency with different ESR values and load currents; and

Fig. 11 illustrates a block diagram of an example system in which embodiments of the present disclosure can be applied.

Throughout the drawings, the same or corresponding reference symbols refer to the same or corresponding parts.

DETAILED DESCRIPTION

The subject matter described herein will now be discussed with reference to several example embodiments. These embodiments are discussed only for the purpose of enabling those skilled persons in the art to better understand and thus implement the subject matter described herein, rather than suggesting any limitations on the scope of the subject matter.

The term “comprises” or “includes” and its variants are to be read as open terms that mean “includes, but is not limited to. ” The term “or” is to be read as “and/or” unless the context clearly indicates otherwise. The term “based on” is to be read as “based at least in part on. ” The term “being operable to” is to mean a function, an action, a motion or a state can be achieved by an operation induced by a user or an external mechanism. The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment. ” The term “another embodiment” is to be read as “at least one other embodiment. ”

Unless specified or limited otherwise, the terms “mounted, ” “connected, ” “supported, ” and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Furthermore, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. In the description below, like reference numerals and labels are used to describe the same, similar or corresponding parts in the Figures. Other definitions, explicit and implicit, may be included below.

As mentioned above, a decrease in capacitance and an increase in equivalent series resistance (ESR) can be used as indicators to manifest degradation of a DC-link capacitor in a power converter. Figs. 1A-1B illustrate

curves

101 and 102 of degradation of ESR and capacitance of a capacitor, respectively. The

curves

101 and 102 show a lifetime model of the DC-link capacitor. As shown, the capacitance value of the capacitor (C) , e.g., electrolytic capacitor, will decrease over time from its initial value C ₀, while the ESR of the capacitor will increase over time from its initial value R ₀. The widely accepted end-of-life criterion is that the ESR increases to double of the initial value (R ₀) and/or the capacitance decreases to 80%of the initial value (C ₀) . At that time (T _EoL) , the capacitor may be replaced with a new one to guarantee the reliability of the power converter.

It is important to detect the capacitance and/or ESR so as to carry out condition monitoring of the capacitor. Although many efforts have been devoted to the condition monitoring of capacitors, most of existing condition monitoring methods have disadvantages in various aspects which hinder the methods to be applied in real products. For example, most of the methods require additional hardware, leading to a redesign of the power converters. Some condition monitoring methods may not require additional hardware, but provide low precision and/or have limited applications in some special scenarios or some certain converters. Moreover, some methods will suspend the normal operations of the power converters.

According to embodiments of the present disclosure, there is provided a solution for on-line condition monitoring of a direct current (DC) -link capacitor in a power converter. In this solution, a duty cycle of a control signal used in the power converter is changed within a predetermined range to generate a new waveform of voltage at the DC-link capacitor. The waveform is analyzed to determine a parameter related to a health condition of the DC-link capacitor. By this way, it is helpful for assessing the health condition of the DC-link capacitor in a precise manner without suspending the operations of the power converter. Example embodiments of the present disclosure will be described in detail below with reference to the figures.

An equivalent model of a capacitor will be first introduced before the detailed description of the on-line monitoring of a DC-link capacitor. Fig. 2 shows such an equivalent model 200. In the equivalent model 200, a DC-link capacitor may be equivalent to a resistor 210 and an effective capacitor 220 connected in series to the resistor 210. The equivalent model 200 can be considered as an equivalent model for a single capacitor or an overall equivalent model for multiple capacitors deployed in a DC-link circuit of a power converter. In Fig. 2, i _in represents input current of the power converter, i _C represents current flowing through the DC-capacitor, i _out represents output current of the power converter, U _C represents voltage at the effective capacitor 220, and U _dc represents DC bus voltage.

Fig. 3 illustrates a flowchart of a process 300 in accordance with some example embodiments of the present disclosure. The process 300 can be implemented to carry out condition monitoring of a DC-link capacitor in a power converter, without suspending the operations of the power converter. In some embodiments, the process 300 can be implemented by a device having processing capability. Herein the DC-link capacitor to be monitored may include any type of one or more capacitors in the power converter. One example of the DC-link capacitor is an electrolytic capacitor (E-Cap) . The power converter may also be any type of power converters, such as a DC-DC converter, a DC-alternate current (AC) converter, an AC-DC converter, and the like.

At 310, a first waveform of voltage at the DC-link capacitor is detected. The first waveform of voltage is generated by applying a first control signal with a first duty cycle for at least one first switching period on the power converter. A control signal is used to control the voltage at the DC-link capacitor of the power converter, such as the DC bus voltage U _dc as shown in Fig. 2. Specifically, the control signal is used to control a switching element in the power converter to be on and off during switching periods, so that a certain level of voltage is generated at the DC-link capacitor. In some embodiments, the first control signal used for applying the first waveform of voltage is a Pulse Width Modulation (PWM) control signal. Other types of control signals that can be used to control the voltage generation in the power converter can also be used.

In embodiments of the present disclosure, the first control signal with the first duty cycle refers to a control signal that is used in normal operations of the power converter. That is to say, the power converter operates properly in the first switching period. To facilitate condition monitoring of the DC-link capacitor, in embodiments of the present disclosure, the first control signal with the first duty cycle used during the normal operations will be changed to a second control signal with a second different duty cycle for a period of time.

Specifically, at 320, a second waveform of voltage at the DC-link capacitor that is generated by applying the second control signal with the second duty cycle for at least one second switching period following the at least one first switching period on the power converter. During the at least one second switching period, by applying the second control signal with the second duty cycle, the voltage at the DC-link capacitor will form the second waveform that is different from the first waveform generated in the normal operations. In some examples, the second control signal may be a PWM control signal or any other types of control signals.

Since the second control signal is applied without suspending the operations of the power converter, the second duty is set as being deviating from the first duty cycle within a predetermined range. The predetermined range may be configured dependent on an acceptable or tolerable range of output voltage in the power converter. For example, it is acceptable if the second duty cycle is greater or lower than the first duty cycle by a value selected from a range of 1%to 3%. As such, during the switching period with the second control signal applied, the power converter can still work properly.

In some embodiments, the second control signal may be generated by injecting an additional signal into the first control signal that is used normally in the power converter to change the first duty cycle of the first control signal. The frequency of the injected signal may be set so that the second duty cycle of the second control signal deviates from the first duty cycle within the predetermined range. In some examples, the injected signal may be a low frequency signal, such as a 100 Hz square wave.

Fig. 4 illustrates a schematic diagram of an injection to a control signal used in a power converter. The first duty cycle of the first control signal 410 is set as D ₀, and the waveform of voltage generated at the DC-link capacitor will be relatively static. When the second control signal 420 with the second duty cycle d is applied in one or more switching periods, the waveform variation of the voltage at the DC-link capacitor will become larger.

In some embodiments, the voltage at the DC-link capacitor may be sampled with the normal voltage sensor and processing circuit included in the power converter, which is a component deployed in most of power converters. Thus, both the first and second waveforms can be easily detected from the power converter.

Generally, the voltage at the DC-link capacitor is a relatively static voltage during the switching period when the first control signal is applied. By applying the different second control signal, the variation of the voltage at the DC-link will be larger and can be used for analyzing the health condition of the DC-link capacitor. The large variation of the voltage at the DC-link may also reduce the precision requirement of the voltage sensor that is used to detect the second waveform from the power converter.

Fig. 5A shows example waveforms of voltage 510 and current 520 at the DC-link capacitor before, during, and after the second control signal is applied. It can be seen that the voltage 510 and current 520 are at relatively static levels. By applying the second control signal (for example, by injecting a signal to change the first duty cycle) in a time period of around 0.2s to 0.3s, there is an obvious resonance and variation in the voltage 510 as well as in the current 520. The resonance and variation can be seen more clearly in Fig. 5B, which shows waveforms of voltage 510 and current 520 during the specific period of 0.2s to 0.3s.

Referring back to Fig. 3, at 330 of the process 300, a parameter related to a health condition of the DC-link capacitor is determined based on the second waveform. The power converter typically includes an inductor, which is coupled directly or indirectly to the DC-link capacitor. When the second control signal is used, it is possible to cause LC resonance in the power converter due to the large variation on the voltage. The LC resonance phenomenon can be observed from the second waveform of voltage at the DC-link capacitor.

Fig. 6A illustrates an example of a second waveform of voltage 610 generated by applying the second control signal. In Fig. 6A, U _r0 represents the voltage at the DC-link capacitor generated when the first control signal is applied. U _d represents the voltage at the DC-link capacitor generated when the second control signal is applied. The variation of the second waveform of voltage U _d is caused by LC resonance when applying the second control signal. This second waveform 610 is analyzed to determine the parameter related to the condition monitoring of the DC-link capacitor.

In some embodiments, the second waveform 610 may be filtered, for example, by a band-pass filter, to obtain a signal 620 of high frequency components of the second waveform 610 as shown in Fig. 6B. The parameter related to the condition monitoring of the DC-link capacitor may be determined based on the signal 620 of the high frequency components. In some embodiments, the parameter related to the condition monitoring of the DC-link capacitor may include the capacitance and/or ESR of the DC-link capacitor. The determination of the capacitance and/or ESR based on the second waveform will be described in detail below.

To determine the capacitance of the DC-link capacitor, in a LC circuit formed by the DC-link capacitor and the inductor of the power converter, the principle equation may be represented as follows:

where f ₀ represents the resonance frequency, L represents inductance of the inductor, and C represents capacitance of the DC-link capacitor. Generally the inductance of the inductor L is known, it is possible to calculate the capacitance C if the resonance frequency f ₀ can be determined.

In some embodiments, a resonance frequency associated with the DC-link capacitor and the inductor may be determined based on the second waveform, for example, the high frequency components of the second waveform obtained after the band-pass filtering. The capacitance of the DC-link capacitor may be determined based on the resonance frequency and the inductance of the inductor.

The resonance frequency may be determined by performing frequency analysis on the second waveform, specifically, on the high frequency components of the second waveform (such as the one shown in Fig. 6B) . In some embodiments, the frequency analysis can be performed by applying Fast Fourier Transformation (FFT) on the high frequency components of the second waveform, such as the signal 620 in Fig. 6B. The result of the FFT calculation is shown in Fig. 7, which shows a relationship 710 between the frequency and the magnitudes of the FFT calculation. The magnitude at a respective frequency indicates energy of the second waveform at that frequency. The resonance frequency (f ₀) may be determined as the frequency with the maximum magnitude (M ₀) .

With the inductance L and resonance frequency f ₀ determined, the capacitance of the DC-link capacitor may be determined as follows:

Figs. 8A and 8B show examples of FFT results of high frequency components of signals generated for capacitors having different capacitances and ESRs. The FFT results indicate

relationships

810 and 820 of frequencies and magnitudes after the FFT calculations on the high frequency components of the waveforms generated by applying the second control signal. It shows that when capacitance and ESR of a DC-link capacitor vary, the determined resonance frequency varies accordingly. Thus, it is possible to determine the capacitance of the DC-link capacitor based on the resonance frequency.

Fig. 9A shows a curve 910 of capacitance values estimated according to an example embodiment of the present disclosure at different real capacitance values. Fig. 9B shows a curve 920 of the capacitance errors at different real capacitance values. As can be seen, the capacitance errors can be constrained to a low level, for example, lower than 2.5%in this example. With the high precision, the method of on-line condition monitoring of the present disclosure can be applied in real applications.

In some embodiments, the ESR may also be determined from the second waveform to indicate the condition monitoring of the DC-link capacitor. As shown in Figs. 8A and 8B, when the ESR varies, the magnitude at the resonance frequency in the second waveform varies. In addition, the magnitude at the resonance frequency is also influenced by current flowing through a load in the power converter. In some embodiments, the ESR of the DC-link capacitor may be determined based on the magnitude at the resonance frequency and the load current in the power converter.

For a certain level of load current, the magnitude at the resonance frequency varies as the ESR varies. Fig. 10 shows example relationships of different magnitudes at the resonance frequency with different ESR values and load currents. In this example, the curve 1010 shows the relationship between the magnitude and ESR when the load current is 3A, the curve 1020 shows the relationship between the magnitude and ESR when the load current is 5A, and the curve 1030 shows the relationship between the magnitude and ESR when the load current is 8A. In some embodiments of the present disclosure, one or more relationships like those shown in Fig. 10 may be determined and stored for use.

In determining the ESR for a certain DC-link capacitor, the current at the load may be measured, and the magnitude at the resonance frequency can be determined by the frequency analysis as described above. A curve fitting method may be applied to select one of a plurality of predetermined relationships based on the load current. Then the ESR is determined from the selected relationship based on the magnitude at the resonance frequency. In some embodiments, in order to achieve high precision, machine learning can be applied to learn the predetermined the relationships and select the fit one for determining the ESR.

As mentioned above, the second control signal is applied for the purpose of condition monitoring, and it is desirable to limit the impact on the operations of the power converter by the monitoring. In some cases, the on-line condition monitoring process 300 may be suspended in response to determining that a difference between an input power and an output power of the power converter exceeds a predetermined threshold. The predetermined threshold may be set as any value, such as 20%of the output power.

Since the on-line condition monitoring process is configured as an opened-loop control process, it may possibly result in a relatively large change in both the input power and output power. To suspend the online condition monitoring process by taking the input power and the output power into account, it is possible to guarantee the proper operations of the power converter. In addition, it is also helpful for reducing the likelihood of misjudging the condition monitoring of the DC-link capacitor.

According to the embodiments of the present disclosure, the capacitance and/or ESR of the DC-link capacitor in the power converter can be determined to indicate the health condition of the DC-link capacitor. In some embodiments, when the current capacitance and/or ESR of the DC-link capacitor are determined, it is also possible to determine changes of the capacitance and/or ESR during a period of time. In some embodiments, since the changes of the capacitance and/or ESR over time may follow respective curves, such as those shown in Figs. 1A and 1B, when the current capacitance and/or ESR is determined, it is possible to predict when the DC-link capacitor is about to reach the end of life. An alert may be issued to the maintainer of the power converter to notify of possible future failure and preventive maintenance, so that he/she can replace the DC-link capacitor in time.

By applying the on-line condition monitoring of the present disclosure, the capacitance and/or ESR can be calculated in a precise manner, without suspending the operations of the power converter. The on-line condition monitoring may also be implemented without requiring additional hardware to be introduced into the power converter, avoiding a redesign of the power converter. In some examples, the on-line condition monitoring process can be implemented in software, for example, as a program included in a device with processing capability. The on-line condition monitoring can be widely applied for any types of power converters deployed in any scenarios.

Fig. 11 illustrates an example system 1100 in which embodiments of the present disclosure can be applied. In some embodiments, the system 1100 may be deployed as an Internet-of-Things (IoT) system. In the system 1100, a power converter 1110 is connected wiredly or wirelessly to a system 1120 for on-line condition monitoring of a DC-link capacitor included in the power converter 1110. Although one power converter is shown, in some embodiments, more than one power converter may be included and connected to the system 1120 to monitor the condition of the DC-link capacitors included therein. In other examples, more than one system 1120 may be included to monitor the respective power converters in the system 1100.

As shown, the system 1120 includes a detecting unit 1122 configured to detect, from the power converter 1110, a first waveform of voltage at the DC-link capacitor that is generated by applying a first control signal with a first duty cycle on the power converter for at least one first switching period. The detecting unit 1122 is also configured to detect a second wavefonn of voltage at the DC-link capacitor that is generated by applying a second control signal with a second duty cycle for at least one second switching period following the at least one first switching period on the power converter, the second duty cycle deviating from the first duty cycle within a predetermined range. The system 1120 also includes a determining unit 1124 configured to determine, based on the second waveform, a parameter related to a health condition of the DC-link capacitor.

In some embodiments, the determining unit 1124 may be configured to determine, based on the second waveform, a resonance frequency associated with the DC-link capacitor and an inductor coupled to the DC-link capacitor in the power converter; and determine, based on the resonance frequency, the parameter related to the health condition of the DC-link capacitor.

In some embodiments, the determining unit 1124 may be configured to determine capacitance of the DC-link capacitor based on the resonance frequency and inductance of the inductor.

In some embodiments, the determining unit 1124 may be configured to determine equivalent series resistance (ESR) or a change of the ESR of the DC-link capacitor based on energy of the second waveform of voltage at the resonance frequency and current flowing through a load in the power converter.

In some embodiments, the DC-link capacitor includes at least one electrolytic capacitor. In some embodiments, at least one of the first and second control signals includes a Pulse Width Modulation (PWM) control signal.

In some embodiments, the system 1120 may be implemented as or implemented in a device with processing capacity. Examples of such device may include a computer, a server, a mobile terminal, and/or any other devices with processing capability. In some embodiments, the system 1120 may be implemented in a separate device or may be integrated into the power converter.

It should be appreciated that units included in the system 1120 correspond to the blocks of the process 300. Therefore, all operations and features described above with reference to Figs. 2 to 9 are likewise applicable to the units included in the system 1120 and have similar effects.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it will be appreciated that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the process or method as described above with reference to Fig. 3. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

The above program code may be embodied on a machine readable medium, which may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may bea machine readable signal medium or a machine readable storage medium. A machine readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. On the other hand, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A method for on-line condition monitoring of a direct current (DC) -link capacitor in a power converter, comprising:

detecting a first waveform of voltage at the DC-link capacitor that is generated by applying a first control signal with a first duty cycle for at least one first switching period on the power converter;

detecting a second waveform of voltage at the DC-link capacitor that is generated by applying a second control signal with a second duty cycle for at least one second switching period following the at least one first switching period on the power converter, the second duty cycle deviating from the first duty cycle within a predetermined range; and

determining, based on the second waveform, a parameter related to a health condition of the DC-link capacitor.
The method of claim 1, wherein determining the parameter comprises:

determining, based on the second waveform, a resonance frequency associated with the DC-link capacitor and an inductor coupled to the DC-link capacitor in the power converter; and

determining, based on the resonance frequency, the parameter related to the health condition of the DC-link capacitor.
The method of claim 2, wherein determining the parameter based on the resonance frequency comprises:

determining capacitance of the DC-link capacitor based on the resonance frequency and inductance of the inductor.
The method of claim 2 or 3, wherein determining the parameter based on the resonance frequency comprises:

determining equivalent series resistance (ESR) or a change of the ESR of the DC-link capacitor based on energy of the second waveform of voltage at the resonance frequency and current flowing through a load in the power converter.
The method of any of claims 1 to 4, wherein the method is suspended in response to determining that a difference between an input power and an output power of the power converter exceeds a predetermined threshold.
The method of any of claims 1 to 5, wherein the DC-link capacitor includes at least one electrolytic capacitor.
The method of any of claims 1 to 6, wherein at least one of the first and second control signals includes a Pulse Width Modulation (PWM) control signal.
A system for on-line condition monitoring of a direct current (DC) -link capacitor in a power converter, comprising:

a detecting unit configured to

detect a first waveform of voltage at the DC-link capacitor that is generated by applying a first control signal with a first duty cycle on the power converter for at least one first switching period, and

detect a second waveform of voltage at the DC-link capacitor that is generated by applying a second control signal with a second duty cycle for at least one second switching period following the at least one first switching period on the power converter, the second duty cycle deviating from the first duty cycle within a predetermined range; and

a determining unit configured to determine, based on the second waveform, a parameter related to a health condition of the DC-link capacitor.
The system of claim 8, wherein the determining unit is configured to:

determine, based on the second waveform, a resonance frequency associated with the DC-link capacitor and an inductor coupled to the DC-link capacitor in the power converter; and

determine, based on the resonance frequency, the parameter related to the health condition of the DC-link capacitor.
The system of claim 9, wherein the determining unit is configured to determine capacitance of the DC-link capacitor based on the resonance frequency and inductance of the inductor.
The system of claim 9 or 10, wherein the determining unit is configured to determine equivalent series resistance (ESR) or a change of the ESR of the DC-link capacitor based on energy of the second waveform of voltage at the resonance frequency and current flowing through a load in the power converter.
The system of any of claims 8 to 11, wherein the operations of the detecting unit and the determining unit are suspended in response to determining that a difference between an input power and an output power of the power converter exceeds a predetermined threshold.
The system of any of claims 8 to 12, wherein the DC-link capacitor includes at least one electrolytic capacitor.
The system of any of claims 8 to 13, wherein at least one of the first and second control signals includes a Pulse Width Modulation (PWM) control signal.
A computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, cause the at least one processor to perform the method according to any of claims 1 to 7.
A computer program product being tangibly stored on a computer readable storage medium and comprising instructions which, when executed on at least one processor, cause the at least one processor to perform the method according to any of claims 1 to 7.
An Internet of Things (IoT) system comprising:

a power converter; and

a system for on-line condition monitoring of a direct current (DC) -link capacitor in the power converter according to any of claims 8 to 14.