Interconnection inverter device

An interconnection inverter device includes a pair of capacitors connected in series to a pair of direct-current buses each connecting a direct-current power supply and the inverter; an opening/closing unit connected to either one of the pair of direct-current buses; voltage monitor units that monitor terminal voltages of the pair of capacitors respectively; and a controller that controls opening or closing of the opening/closing unit based on monitor voltages detected by the voltage monitor units.

TECHNICAL FIELD

The present invention generally relates to an inverter device. The present invention specifically relates to an interconnection inverter device for interconnecting direct-current power from a solar cell, a fuel cell, or the like, to an alternating-current power system.

BACKGROUND ART

Interconnection inverter devices for interconnecting with an alternating-current power system include a smoothing unit for stabilizing a voltage of input direct-current power. The smoothing unit has conventionally been configured by using an electrolytic capacitor for high power.

On the one hand, among interconnection inverter devices in which the direct-current power is an output of a solar cell, an interconnection inverter device with a high-voltage specification, such that an input voltage reaches even 700 VDC, requires a product with a high-breakdown voltage of about 850 WV (working voltage) allowing for derating as a breakdown voltage of an electrolytic capacitor for smoothing.

However, the electrolytic capacitor with such a high-breakdown voltage is not common in terms of its cost and configuration, and it is, therefore, difficult to be adopted into home electric appliances. Based on this background, the high-breakdown voltage is ensured in the interconnection inverter devices each with a high-voltage specification by serially connecting low-cost, high-availability two general-purpose electrolytic capacitors of about 450 WV or 500 WV.

There are few documents, related to the interconnection inverter device, which directly disclose measures against problems for this type of electrolytic capacitors. This is because it is thought common that circuit operation of a converter circuit or of an inverter circuit is directly stopped as safety measures upon device malfunction.

On the other hand, there is Patent document 1 as follows as a document which discloses not safety measures for protecting the device but safety measures for persons handling the device.

The Patent document 1 takes up the problem such that a service person may get a shock under a condition as follows, and discloses an interconnection inverter device as measures against the problem. The condition is such that he/she may get a shock upon operation of a detection function for preventing the device from being destroyed caused by overvoltage or overcurrent occurring inside the interconnection inverter device, because the device is in the stopped state in which the charge in an output capacitor connected to a final stage of the device is not being discharged. And the interconnection inverter device, disclosed as the measures against it, stops an oscillation operation of a booster converter and of the inverter as soon as possible when the overvoltage or the overcurrent occurs inside the device, and quickly discharges the charge from the output capacitor connected to the final output stage of the device.

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

Because the general-purpose electrolytic capacitor with high-breakdown voltage has generally 450 WV or 500 WV, it is necessary to ensure a desired breakdown voltage by serially inserting two electrolytic capacitors of, for example, 450 WV to between 700-VDC input lines of the interconnection inverter device.

On the other hand, if any unexpected event occurs, that is, if a short-circuit fault occurs in either one of the two electrolytic capacitors connected in series, a voltage exceeding the breakdown voltage is applied to the other electrolytic capacitor, and burst may inevitably occur. The electrolytic capacitor where the burst has occurred causes blowout of gas or liquid leakage. This brings about a problem that the blowout of gas or the like badly affects other circuits and deteriorates other circuit components, and also a fear that the blowout of gas or the like may lead to fire of the device under flammable bad environment.

The present invention has achieved to solve at least the problems in the conventional technology, and it is an object of the present invention to provide an interconnection inverter device capable of detecting anomaly in an electrolytic capacitor and safely stopping the device.

Means for Solving Problem

To solve the above problems, and to achieve the above objects, according to an aspect of the present invention, an interconnection inverter device that includes an inverter for converting direct-current power supplied from a direct-current power supply to alternating-current power and that interconnects an output of the inverter to an alternating-current power system includes a pair of capacitors connected in series to a pair of direct-current buses each connecting the direct-current power supply and the inverter; a switch unit connected to either one of a positive bus and a negative bus that constitute the pair of direct-current buses; a pair of voltage monitor units each of which detects a terminal voltage of a corresponding one of the pair of capacitors; and a controller that controls the switch unit based on a terminal voltage detected by at least one of the voltage monitor units.

EFFECT OF THE INVENTION

The interconnection inverter device according to the present invention includes a pair of capacitors connected in series between a pair of direct-current buses each connecting the direct-current power supply and the inverter, and controls opening or closing of the opening/closing unit inserted to either one of the positive-electrode-side bus and the negative-electrode-side bus based on the monitor voltages obtained by monitoring terminal voltages of the pair of capacitors. Therefore, even if a short-circuit fault occurs in a capacitor, it is possible to prevent a situation, which may arise, where a high voltage is applied to a normal capacitor, and to safely stop the device.

EXPLANATIONS OF LETTERS OR NUMERALS

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Exemplary embodiments of an interconnection inverter device according to the present invention are explained in detail with reference to the accompanying drawings. The present invention is not to be limited by these embodiments. Moreover, the circuit configurations explained below are exemplary, i.e., it is possible for a person skilled in the art to modify the circuit configurations without departing from the technical spirit of the present invention.

First Embodiment

FIG. 1is a circuit diagram of an interconnection inverter device1according to a first embodiment of the present invention. The interconnection inverter device1is configured as a power system in such a manner that its input terminals IN1and IN2are connected to a solar cell11which is a direct-current power supply and power is interconnected to an alternating-current power system (not shown) through its output terminals OUT1and OUT2which are alternating current output terminals. In the solar cell11as the direct-current power supply, serial and parallel combinations of cells can arbitrarily be configured. Therefore, an output voltage can be set in a wide range from tens of VDC to hundreds of VDC.

The circuit configuration of the interconnection inverter device1according to the first embodiment shown inFIG. 1is explained below. The interconnection inverter device1includes component units such as an inverter21, a switching element13such as IGBT (Insulated Gate Bipolar Transistor); a switching element controller14that controls the switching element13; a relay12; capacitors15aand15bsuch as an electrolytic capacitor; voltage monitor units16aand16bthat monitor voltages of the capacitors15aand15brespectively; and a CPU22as a controller that controls the relay12and the switching element controller14.

The inverter21is connected at its input terminals to a bus5being a direct-current bus on a positive-electrode side and to a bus6being a direct-current bus on a negative-electrode side, and is connected at its output terminals to the output terminals OUT1and OUT2respectively to interconnect with the alternating-current power system. The capacitor15aand the capacitor15bare connected in series to be inserted between the bus5and the bus6. The relay12is inserted to the bus6, and a first terminal (e.g., collector of IGBT) and a second terminal (e.g., emitter of IGBT) of the switching element13are connected to the bus6so that the relay12is sandwiched by the terminals. Furthermore, one end of the switching element controller14is connected to a control end (base of IGBT) of the switching element13to control on/off of the switching element13. The CPU22communicates with such component units as the voltage monitor units16aand16b, the switching element controller14, and the relay12so as to control the switching element controller14and the relay12based on monitor voltages by the voltage monitor units16aand16b.

The operation of the interconnection inverter device1is explained below. The voltage monitor units16aand16bmonitor respective voltages of the capacitors15aand15bconnected in series, and output the monitor voltages detected to the CPU22. For example, if a short-circuit fault occurs in the capacitor15a, the monitor voltage (voltage of the capacitor15b) of the voltage monitor unit16bbecomes a predetermined threshold (e.g., 400 VDC) or more, and the voltage exceeding the threshold is detected by the CPU22. At this time, the CPU22controls the relay12inserted to the bus6to be turned off. The supply of the direct-current power from the solar cell11is shut off through the control, and the operation of the device to be safely stopped.

In this manner, the interconnection inverter device1forms a capacitor protection circuit when electrolytic capacitors with low breakdown voltage connected in series are used for a high voltage unit, and is characterized as follows. That is, each voltage of the capacitors connected in series is monitored, and if a short-circuit fault occurs in either one of the capacitors, then it is detected that the voltage of the other capacitor becomes the threshold or more, and the relay inserted to the input line is controlled to be turned off.

Although the switching element13is connected to the bus6in addition to the configuration of the relay12in the above manner, the main purpose of this configuration is to protect contact points of the relay12. In other words, according to the present invention, a purpose that the device is safely stopped can be achieved without the switching element13, but in terms of the protection of the contact points of the relay12, it is effective to control the switching element13as explained in the following.

As shown inFIG. 1, for example, when a short-circuit fault occurs in the capacitor15a, the monitor voltage of the capacitor15bbecomes the predetermined threshold or more, and it is detected by the CPU22. At this time, it is preferable that the CPU22first control the relay12to be turned off while the on-state of the switching element13is maintained, and then, control the switching element13to be turned off. On the other hand, for example, when the capacitor15ahaving failed the short circuit is replaced to recover the interconnection inverter device1, it is preferable that the CPU22first control the switching element13to be turned on, complete charging to the capacitors15aand15b, and then, control the relay12to be turned on. These controls allow prevention of contact-point degradation due to direct-current arc of the relay12. Moreover, these controls allow the solar cell11and the capacitors15aand15bto be connected when an output voltage of the solar cell11is low, to thereby suppress an inrush current to the capacitors15aand15b. By monitoring the output voltage of the solar cell11, the switching element13can be automatically turned on, for example, when the output voltage of the solar cell11is low, and this enables suppression of the inrush current to the capacitors.

During the processes, it is determined whether a terminal voltage of a capacitor, different from the capacitor having failed the short circuit, or a voltage at a connecting terminal, to which the capacitor is connected, has exceeded a predetermined threshold (first threshold). But, it may be determined whether a terminal voltage of the capacitor having failed the short circuit or a voltage at a connecting terminal to which the capacitor is connected is below a predetermined threshold (second threshold) which is different from the first threshold. Furthermore, it is possible to control a voltage using both the first threshold and the second threshold. The flow in this case is shown inFIG. 2.

InFIG. 2, the voltage monitor unit16amonitors a terminal voltage (Vc1) of the capacitor15a, while the voltage monitor unit16bmonitors a terminal voltage (Vc2) of the capacitor15b(step S101). The CPU22determines whether each of monitor voltages (Vc1, Vc2) of the capacitors15aand15bhas exceeded the predetermined first threshold (Vth1) (step S102). If it is determined that either one of the monitor voltages (Vc1, Vc2) has exceeded the predetermined first threshold (Vth1) (step S102, Yes), the control is performed on the relay12and the switching element13(step S104). On the other hand, if it is determined that neither of the monitor voltages (Vc1, Vc2) has exceeded the predetermined first threshold (Vth1) (step S102, No), then it is determined whether each of the monitor voltages (Vc1, Vc2) is below the predetermined second threshold (Vth2) (step S103). If it is determined that either one of the monitor voltages (Vc1, Vc2) is below the predetermined second threshold (Vth2) (step S103, Yes), then the process at step S104is executed. If it is determined that neither of the monitor voltages (Vc1, Vc2) is below the predetermined second threshold (Vth2) (step S103, No), then the process proceeds to step S101, where monitoring of each terminal voltage of the capacitors is continued.

In the flow, the order of the processes at step S102and step S103may be interchanged with each other. Furthermore, either one of the processes at step S102and step S103can be omitted.

As explained above, in the interconnection inverter device1, a pair of capacitors connected in series is inserted between a pair of direct-current buses each connecting the solar cell and the inverter, and opening or closing of the opening/closing unit inserted to either the positive-electrode-side bus or the negative-electrode-side bus is controlled based on the monitor voltages obtained by monitoring terminal voltages of the pair of capacitors. Therefore, even if a short-circuit fault occurs in a capacitor, it is possible to prevent the situation, which may arise, where a high voltage is applied to a normal capacitor, and to safely stop the device.

In the configuration ofFIG. 1, a large amount of inrush current is about to flow from a high-voltage (e.g. 700 VDC) solar cell to a capacitor with almost zero voltage upon turning on the device, but, for example, by inserting a desired resistor to the emitter side or the collector side of the switching element13, it is possible to suppress the large amount of inrush current. Even if the resistor is inserted to the switching element, the switching element is turned on and then the relay connected in parallel thereto is turned on, and a switching element circuit is thereby bypassed. Therefore, the insertion of the resistor does not lead to an increase in loss.

In the circuit configuration ofFIG. 1, the relay12and the first and the second terminals of the switching element13are inserted or connected to the bus6being the direct-current bus on the negative-electrode side, but may be inserted or connected to the bus5being the direct-current bus on the positive-electrode side.

Second Embodiment

FIG. 3is a circuit diagram of an interconnection inverter device30according to a second embodiment of the present invention. The interconnection inverter device30is configured, based on the configuration according to the first embodiment ofFIG. 1, to include a converter25, which changes (to boost voltage and/or to step down voltage) an input voltage supplied from the solar cell11, provided in the input stage of the inverter21. The rest parts of the configuration are the same as or equivalent to these of the configuration according to the first embodiment shown inFIG. 1, and therefore, the same reference numerals are assigned to those component units, and explanation thereof is omitted.

InFIG. 3, the converter25includes coils17aand17b, switching elements18aand18bsuch as IGBT, diodes19aand19b, and capacitors20aand20b. In the converter25, the switching element18aand the switching element18bare connected in series to be inserted between the bus5and bus6, and the capacitor20aand the capacitor20bare connected in series to be inserted between the bus5and the bus6at connection points closer to the side of the inverter21than those of the switching elements18aand18b. The diode19ais inserted between connection points of the switching element18aand the capacitor20aon the bus-5side so that a direction in which a current (direct current) flows is a forward direction of its own. The diode19bis inserted between connection points of the switching element18band the capacitor20bon the bus-6side so that a direction in which a current (direct current) flows is a forward direction of its own. The coil17ais inserted between connection points of the switching element18aand the capacitor15aon the bus-5side, while the coil17bis inserted between connection points of the switching element18band the capacitor15bon the bus-6side. Elements of the capacitors15aand15b, those of the switching elements18aand18b, and those of the capacitors20aand20bare connected to connection points respectively, and the connection points are connected to a common bus7.

InFIG. 3, when a short-circuit fault occurs in either one of the switching elements18aand18barranged in parallel with the capacitors15aand15brespectively, the capacitor15aor the capacitor15bconnected in parallel with a switching element having failed the short circuit is short-circuited by the relevant switching element. This causes the same situation as that of the first embodiment to occur. In this case also, by performing control in the same manner as that of the first embodiment, the operation of the interconnection inverter device30can be safely stopped.

Furthermore, in the converter25, when a short-circuit fault occurs in either one of the capacitors20aand20barranged in parallel with the switching elements18aand18brespectively, the capacitor15aor the capacitor15bconnected in parallel with a capacitor having failed the short circuit is short-circuited by the relevant capacitor. This causes the same situation as that explained above to occur. In this case also, by performing control in the same manner as that of the first embodiment, the operation of the interconnection inverter device30can be safely stopped.

The converter25as shown inFIG. 3indicates the circuit configuration when each voltage stored in the capacitors15aand15bis boosted, but the configuration is not limited by this. Therefore, even if a circuit that steps down the voltages stored in the capacitors15aand15bor a circuit that boosts/steps down the voltages is connected to the converter25, it is obvious that this circuit can be applied in the same manner as above.

As explained above, in the interconnection inverter device30, even if the converter that boosts and/or steps down an input voltage supplied from the solar cell is provided, opening or closing of the opening/closing unit can be controlled in the same manner as that of the first embodiment based on a terminal voltage of the capacitor monitored, and the same effect as that of the first embodiment is obtained.

Third Embodiment

FIG. 4is a circuit diagram of an interconnection inverter device40according to a third embodiment of the present invention. The interconnection inverter device40is configured, based on the configuration according to the first embodiment ofFIG. 1, so that three or more capacitors (three in the example ofFIG. 4) are inserted between the bus5and the bus6. The rest parts of the configuration are the same as or equivalent to these of the configuration according to the first embodiment shown inFIG. 1, and therefore, the configuration except the main component units is omitted fromFIG. 4, and explanation thereof is omitted.

InFIG. 3, the capacitors15a,15b, and a capacitor15c(C1, C2, C3) are connected in series to be inserted between the bus5and the bus6. Based on this configuration, even if a short-circuit fault occurs in any one of the capacitors, the breakdown voltage can be ensured by the remaining two capacitors. If three or more capacitors are connected, the breakdown voltage can be ensured by the remaining two or more capacitors.

For example, in the case of a high voltage specification such that an output voltage of the solar cell11is 700 VDC, the whole breakdown voltage of the capacitors15a,15b, and15cconnected in series requires a product with a high-breakdown voltage of about 850 WV allowing for derating and the like. On the other hand, by serially connecting low-cost, high-availability three general-purpose electrolytic capacitors of about 450 WV, even if a short-circuit fault occurs in one of the capacitors, a breakdown voltage of 900 WV as a total breakdown voltage of the remaining two capacitors can be ensured. Therefore, a wider selection is provided such that the operation of the device can be continued in addition to stopping of the device. Based on the configuration in the above manner, a capacitor having failed can be fixed at any time when it is convenient for a user or a repair person, which allows improvement of the operation rate and the reliability of the device.

As explained above, in the interconnection inverter device40, a capacitor group including three or more capacitors connected in series is inserted between a pair of direct-current buses each connecting the direct-current power supply and the inverter. And opening or closing of the opening/closing unit inserted to either the positive-electrode-side bus or the negative-electrode-side bus is controlled based on each monitor voltage obtained by monitoring each terminal voltage of the capacitor group. Therefore, even if a short-circuit fault occurs in a capacitor, it is possible to prevent the situation, which may arise, where a high voltage is applied to a normal capacitor, and to safely stop the device.

INDUSTRIAL APPLICABILITY

As can be seen, the interconnection inverter device according to the present invention is useful as an interconnection inverter device for interconnecting direct-current power from the solar cell, the fuel cell, or the like, to an alternating-current power system. And it is particularly suitable for an interconnection inverter device with a high-voltage specification in which an input voltage is comparatively high.