JP6884029B2 - Power converter and diagnostic method of power converter - Google Patents

Description

The present invention relates to a power conversion device and a method for diagnosing a power conversion device, and more particularly to a power conversion device and a method for diagnosing a power conversion device suitable for diagnosing a smoothing capacitor constituting a main circuit.

Power converters using semiconductor switching elements are widely used in fields such as industry, home appliances, transportation, automobiles, and electric power / social infrastructure systems. For example, in an industrial power converter of several hundred kW or more, a forward converter (hereinafter referred to as a converter (CONV)) that converts AC power into DC power in order to connect to a load such as a power system or a motor, or A system is composed of a plurality of converters as an inverse converter (hereinafter referred to as an inverter (INV)) that converts DC power into AC power. In such a system, each converter (CONV / INV) has a smoothing capacitor to smooth the fluctuations associated with power conversion. In each converter, the input power or the output power is smoothed by a smoothing capacitor. Such a power converter is described in, for example, Japanese Patent Application Laid-Open No. 2008-11606.

Japanese Unexamined Patent Publication No. 2008-11606

Each converter (CONV / INV) is provided with a smoothing capacitor that smoothes fluctuations associated with power conversion, and this smoothing capacitor deteriorates according to the ambient temperature, applied voltage, and current flow. When the smoothing capacitor deteriorates and the capacitance decreases, the fluctuation of the DC voltage becomes large, which may cause distortion in the current flowing to the power system and the load. Therefore, in order to use such a power converter for a long period of time, regular maintenance is required to confirm that the capacitance of the smoothing capacitor has not deteriorated and is the required capacitance. It was.

For example, in order to detect a decrease in capacitance due to deterioration of the smoothing capacitor, it is conceivable to use the rising time of the charging current or the falling time of the discharge current of the smoothing capacitor as the judgment value when the power converter is started or stopped. .. The charge or discharge time determined by the CR time constant is used, but it is necessary to detect the rise of the charging current of the smoothing capacitor from the state where the power converter is stopped, and the power converter for the time required for maintenance work. The operating time of is shortened. That is, since it is not possible to detect the deteriorated state of the capacitance while the power converter is continuously operated, there is a problem that the operating rate of the system is lowered.

An object of the present invention is to provide a power conversion device and a method for diagnosing a power conversion device that can detect deterioration of a smoothing capacitor while maintaining the system operating rate.

In order to achieve the above object, the present invention has a plurality of power converters for converting power from AC to DC or DC to AC, and the plurality of power converters are connected to a common DC voltage unit. Each of the plurality of power converters has a smoothing capacitor, and the smoothing capacitor can be obtained by analyzing the current flowing from the smoothing capacitor of any of the plurality of power converters to the smoothing capacitor of the other power converter. It is configured to have a function to detect the deterioration state.

Alternatively, in a power converter that converts power from alternating current to direct current or from direct current to alternating current, the power converter is composed of a plurality of power converters, and the power converters have smoothing capacitors individually and the power converter is used. The DC voltage section of the power converter is connected to a common DC voltage section, and has the function of observing or estimating the current flowing in the DC voltage section to which each power converter is connected, and has the function of observing or estimating the DC. It has a function to detect the deteriorated state of the smoothing capacitor mounted on each power converter by analyzing the current of the voltage section, and has a mechanism to output the deteriorated state to the outside through an external interface.

According to the present invention, deterioration of a smoothing capacitor can be detected while maintaining the system operating rate.

This is the configuration of the power converter according to the first embodiment of the present invention. It is a flowchart which detects the deterioration state of the DC smoothing capacitor in the 1st and 4th Examples of this invention. It is a figure explaining the outline of the frequency analysis of the DC voltage part current in the 1st and 4th Examples of this invention. This is the configuration of the power converter according to the second embodiment of the present invention. It is another configuration of the power converter in the third embodiment of the present invention. It is a figure explaining the outline of the frequency analysis of the DC voltage part current in the 2nd, 3rd, 5th and 6th Examples of this invention. It is a configuration of a power converter according to a fourth embodiment of the present invention. It is a configuration of the power converter in the fifth embodiment of the present invention. This is the configuration of the power converter according to the sixth embodiment of the present invention.

Embodiments (Examples) for carrying out the present invention will be described below with reference to the drawings.

Figure 1 shows the configuration of the power converter. In this embodiment, a three-phase two-level converter will be described as an example. Two power converters (101a / 101b) consisting of a semiconductor switching element and a DC smoothing capacitor (also referred to as a smoothing capacitor; the same shall apply hereinafter) (103a / 103b) are connected to the DC voltage section (100a / 100b). ing. Since it is a two-level converter, the DC voltage section (100a / 100b) has a positive electrode side (100a) and a negative electrode side (100b). A current sensor (102) is provided. Even if the current sensor (102) is provided on the positive electrode side (100a), the effects shown below are the same.

Each power converter (101a / 101b) is controlled by an operation command (107a / 107b) from the controller (105) to control an input or an output (104a / 104b). The controller (105) outputs the operating state (108) of each power converter to the deterioration diagnosis unit (106) of the DC smoothing capacitor (103a / 103b), and the deterioration diagnosis unit (106) outputs the DC voltage unit (100a / 103b). The deterioration state is detected by calculating the decrease in capacitance of the DC smoothing capacitors (103a and 103b) in combination with the current information (109) of 100b). The deteriorated state shows only the deteriorated state of the DC smoothing capacitors (103a and 103b), and does not include information on the operating rate of the power converter.

Here, the operating state (108) of each power converter (101a / 101b) is the frequency, modulation factor, and gate pulse pattern of the output or input current of each power converter (101a / 101b). In addition, in order to identify the deterioration factor of the DC smoothing capacitor (103a / 103b), the output or input current value of each power converter (101a / 101b), the inside of the board of each power converter (101a / 101b), The external temperature, the DC voltage value of each power converter (101a / 101b), and the ground current value of the device / control panel of the power converter (101a / 101b) may be included.
In this embodiment, the power converter (101a) converts the DC power from the DC voltage section (100a / 100b) into a three-phase AC according to the operation command (107a) from the controller (105) and converts it into an AC output section. Output to (104a). In addition, the power converter (101b) converts the DC power from the DC voltage section (100a / 100b) into three-phase AC according to the operation command (107b) from the controller (105), and the AC output section (104b). Output to.
Here, regarding the power converter (101a / 101b), AC power is input from the terminal (104a / 104b), converted to DC by the power converter (101a / 101b), and DC to the DC voltage section (100a / 100b). It may be configured to supply power. Alternatively, one of the power converters (101a / 101b) may be configured to convert from alternating current to direct current, and the other of the power converters (101a / 101b) may be configured to convert from direct current to alternating current.

Further, the conversion to AC power may be connected to the power system as a constant frequency, or may be supplied to an electric motor or the like as a variable frequency.

Figure 2 shows a flowchart for detecting the deterioration state of the DC smoothing capacitors (103a and 103b) executed by the deterioration diagnosis unit (106). The power converter (101a / 101b) calculates the resonance frequency of the DC voltage section (100a / 100b) in the operating state (S101) (S102).

The general idea of the calculation of the resonance frequency will be explained first, and the details of the specific calculation will be explained later. Figure 3 shows a schematic diagram of frequency analysis of the current of the DC voltage section (100a / 100b). Frequency analysis can be obtained, for example, by performing a Fourier transform operation on the output of the current sensor (102) in the deterioration diagnosis unit (106). The current of the DC voltage section (100a / 100b) includes the frequency components (200a / 200b) determined by the operation pattern of each power converter (101a / 101b) and the frequency determined by the carrier frequency of each power converter (101a / 101b). In addition to the components (201a and 201b), the component (202) of the resonance current (113) between the DC smoothing capacitors (103a and 103b) mounted on each power converter (101a and 101b) is included.

The current component determined by the operating pattern and carrier frequency of the power converters (101a / 101b) changes depending on the operating conditions, but the static DC smoothing capacitors (103a / 103b) mounted on each power converter (101a / 101b) are static. The frequency of the resonance current determined by the capacitance and the parasitic inductance of the DC voltage section (100a / 100b) connecting each power converter (101a / 101b) is constant for a relatively short period of time regardless of the operating condition. .. However, when the DC smoothing capacitors (103a and 103b) deteriorate and the capacitance decreases, the resonance frequency (202) moves to a higher frequency.

Therefore, when the detection signal (109) related to the operating state (108) of each power converter (101a / 101b) and the current (113) of the DC voltage unit (100a / 100b) is analyzed and the power converter is shipped. By comparing with the measured resonance frequency, it is possible to detect the deterioration state of the DC smoothing capacitors (103a and 103b).

Further, the detection of the deterioration state of the DC smoothing capacitors (103a and 103b) executed by the deterioration diagnosis unit (106) will be described in detail. In the flowchart shown in FIG. 2, when the resonance frequency of the DC voltage section (100a / 100b) exceeds the specified value 1, the DC smoothing capacitor (103a / 103b) outputs a deteriorated alarm (S104a). Here, as the resonance frequency of the DC voltage section (100a / 100b), a frequency lower than the resonance frequency of the DC voltage section (100a / 100b) at the time of shipment of the power converter shown _{below as f 0 is cut by filtering, and then.} It may be compared with the specified value 1 (the same may be applied when comparing with the specified value 2). The alarm is output to, for example, a monitor or the like (112a, 112b) provided in the power converters (101a and 101b) shown in FIG.

In this example, the case where the deterioration state of the DC smoothing capacitors (103a and 103b) is output in two stages is shown. Deterioration state 1 indicates a state in which the capacitance of the DC smoothing capacitor (103a / 103b) is reduced, but the operation of the power converter (101a / 101b) can be continued. Deterioration state 2 indicates that the power converters (101a and 101b) have become difficult to operate stably.

Here, the capacitance of the DC smoothing capacitor (103a / 103b) at the time of shipment of the power converter (101a / 101b) is C _0, and the capacitance in the deteriorated state is C ₁ and C ₂ (C _1). > C ₂ ). The resonance frequency of the DC voltage section is expressed by the following equation by the parasitic inductance L of the bus bar or wiring connecting between the power converters (101a and 101b) and the capacitance.

When the specified value is the state where the capacitance of the first stage of deterioration is reduced by 5% from the initial state and the state where the capacitance of the second stage of deterioration is reduced by 10% from the initial state is the specified value of the resonance frequency change. 1 is 1.026 times the initial state, and the specified value 2 is 1.054 times the initial state. Assuming that the capacitance in the initial state is 2 mF and the parasitic inductance between the power converters (101a and 101b) is 500 nH, the resonance frequency in the initial state is about 5 kHz, and the resonance frequency in the deteriorated state 1 is about 5.2 kHz ( At f ₁ ), the resonance frequency in the deteriorated state 2 is about 5.3 kHz (f ₂ ).

Here, for example, the capacitance of the first stage of deterioration state (specified value 1) is selected as the specified value from the range of 5% to 15% reduction from the initial state, and the static electricity of the second stage of deterioration state (specified value 2) is static. The capacitance may be selected as a specified value from a range that is larger than the first stage of the deteriorated state and reduced by 10% to 20% from the initial state.

After outputting the alarm (S104b), stop the power converters (101a and 101b) (S105). By outputting the deteriorated state in multiple stages in this way, the operator or maintenance staff of the power converter (101a / 101b) recognizes that the replacement time of the DC smoothing capacitor (103a / 103b) is approaching. It becomes possible to make it.
Here, while the power converter (101a / 101b) is being operated, the resonance frequency is calculated at a constant or arbitrary time interval, and the transition of the resonance frequency is sequentially observed to obtain a DC smoothing capacitor (103a / 101b). It is possible to detect the deterioration state of 103b).
In this way, the deterioration state is analyzed by the deterioration diagnosis unit (106) of the DC smoothing capacitor (103a / 103b) and output as deterioration information of the DC smoothing capacitor (103a / 103b) (110). The deterioration information is notified to the maintenance worker by displaying it on the monitor (112a) provided in the power converter (101a / 101b) or the maintenance device such as a personal computer connected to the power converter at the time of maintenance. Alternatively, by notifying the monitoring center (112b) in a remote location connected by the network (111), the deterioration state of the DC smoothing capacitor (103a / 103b) is maintained while the operating state of the power converter (101a / 101b) is maintained. Can be observed.

In the first embodiment, the deterioration diagnosis of the DC smoothing capacitor is performed by calculating the resonance frequency, but the deterioration diagnosis of the DC smoothing capacitor may be performed based on another factor corresponding to the resonance frequency.

Fig. 4a shows an example of a three-phase three-level converter, and Fig. 5 shows a schematic diagram of frequency analysis of the DC voltage section current in this embodiment. Two power converters (301a, 301b) composed of a semiconductor switching element and a DC smoothing capacitor (303a, 303c, 303b, 303d) are connected to a DC voltage section (300a, 300b, 300c). In this embodiment, the current sensor of the DC voltage section (300c) is connected to the common (300c) in which both the resonance current (313a) on the positive side (300a) of the DC voltage section and the resonance current (313b) on the negative side (300b) of the DC voltage section flow. 302) is provided to supply the current (309) of the DC voltage section to the deterioration diagnosis section (106) of the DC smoothing capacitor. In this embodiment, since there are two resonance paths, frequency peaks (402a and 402b) corresponding to the two resonance frequencies appear. In general, power converters are configured with objectivity, so the resonance frequency on the positive electrode side and the resonance frequency on the negative electrode side often almost match, but in Fig. 5, they are represented by different resonance frequencies.

Similar to Example 1, it is possible to observe the deteriorated state of the DC smoothing capacitors (303a, 303c, 303b, 303d) while continuing the operating state of each converter (301a, 301b).

Fig. 4b shows another example of a three-phase three-level converter, and Fig. 5 shows a schematic diagram of frequency analysis of the DC voltage section current in this example. In this embodiment, current sensors (302a and 302b) are provided to observe the resonance current (313a) on the positive electrode side (300a) of the DC voltage section and the resonance current (313b) on the negative electrode side (300b) of the DC voltage section, respectively. In this embodiment, since there are two resonance paths, frequency peaks (402a and 402b) corresponding to the two resonance frequencies appear. In general, power converters are configured with objectivity, so the resonance frequency on the positive electrode side and the resonance frequency on the negative electrode side often almost match, but in Fig. 5, they are represented by different resonance frequencies.

Similar to Example 1, it is possible to observe the deterioration state of the DC smoothing capacitor while continuing the operating state of each converter.

Figure 6 shows another example of a three-phase, two-level converter. In this embodiment, the signal (509) of the voltage sensors (502a and 502b) of the DC smoothing capacitor is used, and the current of the DC voltage section is estimated from the potential difference of each voltage sensor. After calculating the current in the DC voltage section, the resonance current flowing in the DC voltage section is observed in the same manner as in Example 1 to detect the deterioration state of the DC smoothing capacitor.

Figure 7 shows another example of a three-phase, three-level converter. Similar to Example 3, the current of the DC voltage section is estimated from the signal (609) of the voltage sensor (602a, 602c, 602b, 602d) of the DC smoothing capacitor (303a, 303c, 303b, 303d). The current on the positive side (300a) of the DC voltage section is the potential difference between the voltage sensor (602a) and the voltage sensor (602b), and the current on the negative side (300b) of the DC voltage section is the potential difference between the voltage sensor (602c) and the voltage sensor (602d). Estimated by. After calculating the current of the DC voltage section (300a, 300b, 300c), the frequency peak (402a, 402b) of the resonance current flowing in the DC voltage section is observed in the same manner as in Example 2, and the deterioration of the DC smoothing capacitor is observed. Detect the state.

Figure 8 shows another example of a three-phase, three-level converter. Similar to the fourth and fifth embodiments, the current of the DC voltage section is estimated from the signal (709) of the voltage sensor (702a / 702b) of the DC smoothing capacitor (303a / 303c / 303b / 303d). In this embodiment, a voltage sensor is used for the positive electrode and the negative electrode of the DC voltage section (300a, 300b, 300c), and the combined current of the positive electrode side (300a) and the negative electrode side (300b) of the DC voltage section is estimated. .. After calculating the current of the DC voltage section (300a, 300b, 300c), the resonance current frequency peak (402a, 402b) flowing through the DC voltage section (300a, 300b, 300c) is observed in the same manner as in Example 2. Detects the deterioration state of the DC smoothing capacitor.

100a / 300a ... DC voltage part (positive side), 100b / 300b ... DC voltage part (negative side), 101a / 101b / 301a / 301b ... Power converter, 102/302/302a / 302b ... Current sensor, 103a / 103b / 303a・ 303b ・ 303c ・ 303d… DC smoothing capacitor, 104a ・ 104b… AC output unit, 105… Power converter control unit (controller), 106… DC smoothing capacitor deterioration diagnosis unit, 107a ・ 107b… Power converter control Signal, 108 ... Power converter operation information, 109/309 ... DC voltage section current information, 110 ... DC smoothing capacitor deterioration information, 111 ... Network line, 112a ... Power conversion during monitoring or maintenance installed in the power converter Maintenance equipment such as personal computers connected to the device, 112b ... Remote monitoring center, 113 ... Resonant current path, 200a / 200b ... Frequency caused by the operating state of the power converter, 201a / 201b ... Carrier frequency of the power converter Frequency caused by, 202, 402a, 402b ... Resonance frequency between power converters, 300c ... DC voltage section (common), 502a, 502b, 602a, 602b, 602c, 602d, 702a, 702b ... Voltage sensor, 509, 609・ 709… DC voltage section information, S101… The state where the converter is operating, S102… DC voltage section resonance frequency calculation, S103a… Comparison with the specified value 1 of the resonance frequency, S103b… The specified value 2 of the resonance frequency Comparison, S104a: Deterioration alarm 1 output of DC smoothing capacitor, S104b: Deterioration alarm 2 output of DC smoothing capacitor, S105: Converter stopped

Claims (10)

It has a plurality of power converters that convert power from AC to DC or DC to AC, the plurality of power converters are connected to a common DC voltage section, and the plurality of power converters are each smoothing capacitors. It has a function to detect the deterioration state of the smoothing capacitor by analyzing the current flowing from the smoothing capacitor of any of the plurality of power converters to the smoothing capacitor of the other power converter. A power conversion device having a calculation unit that frequency-analyzes the current of the DC voltage unit, and detecting a deteriorated state of the smoothing capacitor based on a calculation performed by the calculation unit. The power conversion device according to claim 1, wherein the current to be analyzed is a current sensor that detects the current of a DC voltage unit that connects each power converter. The power according to claim 1, wherein the voltage sensor for measuring the voltage of the smoothing capacitor mounted on each power converter is provided, and the analyzed current is estimated based on the detection of the voltage sensor. Converter. The power conversion device according to any one of claims 1 to 3 , wherein the deteriorated state of the smoothing capacitor mounted on the detected power converter is displayed on a monitor mounted on the power converter panel. The power conversion according to any one of claims 1 to 3 , wherein the deteriorated state of the smoothing capacitor mounted on the detected power converter is observed by connecting a maintenance device to the control panel of the power converter. apparatus. The power conversion device according to any one of claims 1 to 3 , wherein the deteriorated state of the smoothing capacitor mounted on the detected power converter is transmitted via a network line for observing at a remote location. The power conversion device according to any one of claims 1 to 6 , wherein the deterioration state of the smoothing capacitor mounted on the power converter is detected while the power converter is in operation. In claim 1, an alarm is output when the deterioration state of the first stage is reached, and when the deterioration state of the second stage, which is a deterioration state advanced from the first stage, is reached, the first stage is described. A power conversion device characterized by outputting an alarm with a higher warning level than the stage. According to claim 8, wherein the first stage of the degradation state and the second stage of deterioration state, a power conversion apparatus characterized by being detected on the basis of the frequency component included in the current. It has a plurality of power converters that convert power from AC to DC or DC to AC, the plurality of power converters are connected to a common DC voltage section, and the plurality of power converters each have a smoothing capacitor. In the diagnostic method for diagnosing the power converter, the current flowing from one of the smoothing capacitors of the plurality of power converters to the smoothing capacitor of the other power converter is detected, the detected current is analyzed, and the DC voltage is analyzed. A diagnostic method for a power converter that performs an operation to analyze the frequency of the current of a unit and detects the deterioration state of the smoothing capacitor based on the operation.

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