JP2008131756A - Power conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to reduce as much as possible a circulating current flowing between the input and the output of a power conversion device constructed of a converter and an inverter whose direct-current portions are connected in common. <P>SOLUTION: In zero voltage output state, the positive semiconductor switches 8, 10, 12 of the respective phases of the inverter are simultaneously brought into conduction or the semiconductor switches 9, 11, 13 of the respective phases are simultaneously brought into conduction. To prevent this zero voltage output state, a pattern of the switching operation of the semiconductor switches is devised to reduce a circulating current and prevent overvoltage in a direct-current intermediate capacitor 14. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention reduces the size of an apparatus that converts an AC voltage into an AC voltage having a different amplitude or frequency, or an uninterruptible power supply that compensates for fluctuations or interruptions in the amplitude or frequency of the AC voltage and supplies a stable voltage to a load. About.

FIG. 4 shows a configuration of a general power conversion device.
In FIG. 4, 1 is an AC power source, 2 to 13 are semiconductor switches, 14 is a DC capacitor, 15 to 20 are reactors, 21 to 26 are AC filter capacitors, and 27 is a transformer.
2 to 7, 14, 15 to 17, and 21 to 23 constitute a forward converter, which converts the AC input voltage of the AC power source 1 into a DC voltage by high-frequency switching of the semiconductor switches 2 to 7, Supply.

  On the other hand, 14, 8 to 13, 18 to 20, and 24 to 26 constitute an inverse converter, and AC filter capacitors 24 to 26 are formed by high frequency switching of the semiconductor switches 8 to 13 using the DC capacitor 14 as a DC voltage source. An alternating voltage of arbitrary amplitude and frequency is supplied to the load via This circuit continues power supply to the load even during AC power outages as a power supply device that converts AC input voltage into AC voltage of arbitrary amplitude and frequency, or by connecting a storage battery (not shown) to the DC unit 14 It is used as a so-called uninterruptible power supply.

  In FIG. 4, with the high-frequency switching operation of the semiconductor switches 2 to 7, the potential at the P point or the N point with respect to the R, S, and T points in FIG. Further, with the high frequency switching operation of the semiconductor switches 8 to 13, the potential with respect to the P point or the N point of the U, V, and W points in FIG. In general, in an AC power supply, one phase is often directly grounded or one phase to all phases are grounded via a capacitor. For this reason, the high-frequency potential fluctuation with respect to the AC input of each part of the circuit in FIG. 4 leads to the high-frequency potential fluctuation with respect to the ground potential. This high-frequency potential fluctuation can cause problems such as malfunction of electronic equipment and burnout of filter circuits to remove high-frequency noise, and in order to prevent this, reverse conversion to which loads such as electronic equipment are connected The output of the transformer is provided with a transformer 27 as shown so that potential fluctuations are not transmitted. However, this isolation transformer occupies a large volume and mass in the device, and hinders the reduction in size, weight and cost of the device.

Therefore, the applicant has previously proposed an apparatus as shown in FIG. 1 (Japanese Patent Application No. 2005-122251: also called a proposed apparatus).
This is for the purpose of enabling direct connection to the load without going through an insulation transformer, in order to suppress the high-frequency potential fluctuation of the output with respect to the input, and the common connection part of the AC filter capacitors 31 to 33 and the AC filter A common connection portion of the capacitors 34 to 36 is connected by a coupling capacitor 37. By selecting the capacitance of the coupling capacitor 37 so that the impedance is sufficiently low with respect to the switching frequency component and the impedance is sufficiently high (not significantly reduced) with respect to the frequency of the AC input voltage, The input and output are short-circuited in the high-frequency region, and the high-frequency potential fluctuation of the output with respect to the input is suppressed.

As a technique for suppressing the high-frequency potential fluctuation with respect to the ground potential, there is a technique shown in Patent Document 1 in addition to the proposed device.
Japanese Patent Laid-Open No. 11-235055

  However, in the apparatus of FIG. 1, a circulation path having the coupling capacitor 37 as a path is generated along with the high-frequency switching operation of the semiconductor switches 2 to 13, and a DC capacitor is generated by the circulating current that flows when the circulation path is formed. A path for charging 14 is generated. The charging operation may increase the voltage of the DC capacitor 14 and cause an overvoltage, which stops the apparatus. Here, the charging operation will be described in detail.

  In an operation in which a voltage is supplied from an AC power source and an AC voltage having an arbitrary amplitude and frequency is supplied to a load by a forward converter and an inverse converter, for example, three of the semiconductor switches 8, 10, 12 are in a conductive state, and the semiconductor switch 9 , 11 and 13 are in a non-conducting state, and when the voltage of the AC filter capacitor 31 is in a state in which a forward voltage is applied to the diode of the semiconductor switch 2, the semiconductor switch 8, 10, 12 and the reactor 15, the AC filter capacitors 31 to 36, the coupling capacitor 37, and the diode of the semiconductor switch 2 generate a circulation path, and a circulation current flows.

  Subsequently, when any one of the semiconductor switches 8, 10, and 12 is turned off, and the semiconductor switch that is paired with the semiconductor switches 8, 10, and 12 is turned on among the three semiconductor switches 9, 11, and 13. For example, when the switch 12 is turned off and the switch 13 is turned on, the current flowing through the switch 12 is transferred to the switch 13, so that the semiconductor switches 8, 10, the reactor 15, the AC filter capacitors 31 to 36, and the coupling capacitor 37. And a circulation path by the diode of the semiconductor switch 2, and a circulation path by using the DC capacitor 14 and the switch 13 as new paths, and the reactor 15, the AC filter capacitors 31 to 36, the coupling capacitor 37, and the diode of the semiconductor switch 2 as paths. Is generated. At this time, the current flowing through the DC capacitor 14 and the switch 13 as a new path becomes a current for charging the DC capacitor 14.

  In the switching operation of the inverse converter, in addition to the operation in which one semiconductor switch is turned on or off as described above, the three semiconductor switches may be turned on and off at the same time. For example, it is assumed that all three semiconductor switches 8, 10, and 12 that have been in a conductive state are simultaneously in a non-conductive state, and three semiconductor switches 9, 11, and 13 are in a conductive state at the same time. In this case, the circulating current through the semiconductor switches 8, 10, 12, the reactor 15, the AC filter capacitors 31 to 36, the coupling capacitor 37, and the diode of the semiconductor switch 2 passes through the DC capacitor 14 and the switches 9, 11, 13. As a new path, the circulating current flows through the reactor 15, the AC filter capacitors 31 to 36, the coupling capacitor 37, and the diode of the semiconductor switch 2. At this time, all the circulating current becomes a current for charging the capacitor.

  When the semiconductor switches 2 to 7 perform the switching operation and can return the power from the forward converter to the AC power supply side, the forward converter performs the operation of discharging the DC capacitor 14, and the above-described operation is performed. Voltage rise due to circulating current can be prevented. However, when the forward converter does not perform the switching operation, the circuit composed of the semiconductor switches 2 to 7 becomes a simple diode rectifier, and cannot perform the operation of returning power from the forward converter to the AC power source side. Since the capacitor 14 cannot be discharged, the voltage rises due to the circulating current. In addition, when the forward converter is composed of, for example, a mixed bridge, the operation of returning power from the forward converter to the AC power source cannot be performed, so the voltage of the DC capacitor 14 increases due to the circulating current. If an overvoltage occurs, the device is stopped.

When two sets of semiconductor switches 8, 10, 12 and 9, 11, 13 perform alternately conducting / non-conducting switching operations and the inverse converter outputs zero voltage, the voltage rise due to the circulating current is It occurs regardless of the connected load, and this case is the highest. When the inverse converter performs an operation of supplying an AC voltage having an arbitrary amplitude and frequency to the load, either one of the semiconductor switches 8, 10, 12 and 9, 11, 13 is turned on to output zero voltage Therefore, a circulation path for charging the DC capacitor is generated by the subsequent switching operation. At this time, if there is no load or light load, the amount of charge due to the circulating current will be larger than the amount of discharge of the DC capacitor due to the power consumption of the load, the voltage of the DC capacitor will rise, and the device will be stopped during output operation become.
Accordingly, an object of the present invention is to provide a stable voltage by coupling the input and output of a power conversion device, which is composed of a forward converter and an inverse converter, and in which both DC portions are connected in common, with a coupling capacitor. When supplying the load, the circulating current flowing between the forward and reverse converters is suppressed to prevent the DC capacitor voltage from rising.

In order to solve such a problem, in the invention of claim 1, a forward converter comprising a semiconductor switch, a reactor, and an AC filter capacitor and performing AC-DC conversion by a high-frequency switching operation of the semiconductor switch, a semiconductor switch, and a reactor And an AC converter capacitor, and an inverter that performs DC-AC conversion by high-frequency switching operation of the semiconductor switch, the DC portion is commonly connected, and one end of the AC filter capacitor of the forward converter is inverted Between one end of the AC filter capacitor of the capacitor and the impedance at the switching frequency of the semiconductor switch is sufficiently smaller than that of the reactor, and the impedance is higher than that of the AC filter capacitor at the input frequency or output frequency of the device. The power converter formed by connecting through a small capacitance coupling capacitor which does not become,
Each is composed of a series circuit of one or a plurality of positive-side semiconductor switches and negative-side semiconductor switches to form a conversion circuit for one phase, and this is connected in parallel for the number of phases to form an inverse converter. During operation, the switching pattern is selected so as to avoid a zero voltage output state in which all the positive-side semiconductor switches of each phase are turned on simultaneously or all the negative-side semiconductor switches of each phase are turned on simultaneously. It is characterized by that. That is, since it is a problem that the charging voltage of the DC capacitor rises until it becomes an overvoltage, in the present invention, in order to avoid this, the zero voltage output state is avoided as much as possible.

In the first aspect of the invention, when the zero voltage output state is required, only the switching pattern in which all the positive-side semiconductor switches of the respective phases are simultaneously turned on or the negative-side semiconductor of each phase is used. Only a switching pattern in which all of the switches are in a conductive state at the same time can be used (invention of claim 2), and in the invention of claim 1 or 2, depending on the output state or load state of the power converter. Thus, whether to avoid the zero voltage output state can be switched (invention of claim 3).
In any one of these claims, the inductor of the forward converter or the reactor of the inverse converter is in series with the reactor, or the DC common part of the forward converter and the inverse converter has an inductance greater than that of the reactor. A common mode coil having a sufficiently large value can be connected (invention of claim 4), or in series with the reactor of the forward converter or the reactor of the reverse converter, or the direct current of the forward converter and the reverse converter A saturable reactor whose inductance is sufficiently larger than that of the reactor when the current is small can be connected to the common portion (invention of claim 5).

  According to the present invention, the circulating current flowing between the forward and reverse converters is suppressed by devising the switching pattern of the reverse converter, and further by inserting a common mode coil and a saturable reactor. It is possible to prevent the voltage rise of the DC capacitor.

FIG. 1 is a circuit diagram for explaining an embodiment of the present invention. This is what has been described as the proposed device earlier, but it suppresses the rise in the DC capacitor voltage by waiting for the characteristics of the switching operation of the inverse converter, and specifically, as follows. (Method 1).
That is, in the switching operation of the inverse converter, when all of the semiconductor switches 8, 10, and 12, that is, all of the positive side semiconductor switches are simultaneously turned on, the AC output terminals U1, V1, and W1 are both connected to the DC capacitor 14. When three semiconductor switches 9, 11, and 13, that is, all of the negative-side semiconductor switches are in a conductive state at the same time, the AC output terminals U1, V1, and W1 become negative potentials of the DC capacitor 14 as described above. In a simple switching pattern, the line-to-line output of the inverse converter is zero voltage.

  The DC capacitor voltage rises because the circulating current that flows when all of the positive-side semiconductor switches are turned on simultaneously or all of the negative-side semiconductor switches are turned on simultaneously flows into the DC capacitor by the subsequent switching operation. Therefore, when it is necessary to set the line-to-line output of the inverter to a zero voltage state, all the positive side semiconductor switches of each phase are turned on simultaneously, or the negative side of each phase Not a switching pattern in which all semiconductor switches are turned on at the same time to output zero voltage instantaneously, but a switching pattern in which the voltage at the AC filter capacitor connection points U, V, and W of the inverse converter becomes zero voltage on average. To select.

  For example, the semiconductor switches 8, 11, and 13 are turned off, and the semiconductor switches 8, 11, and 13 are turned off only during a period when the semiconductor switches 9, 10, and 12 are turned off and during a period equivalent thereto. When 9, 10, and 12 are turned on, the average output voltage during the period of both states becomes zero. Even when not all of the positive side or negative side semiconductor switches are turned on at the same time, a circulating current flows through the semiconductor switch and the coupling capacitor 37 of each of the forward converter and the reverse converter. Since the amount of current is less than the circulating current that flows when all of the semiconductor switches on the side are in the conductive state at the same time, the circulating current that charges the DC capacitor is reduced in the subsequent switching operation, and the rise in the DC capacitor voltage is suppressed. be able to.

In FIG. 1, the following can be performed (method 2).
The operation of supplying an alternating voltage of arbitrary amplitude and frequency with the forward converter is, for example, an initial state of a switching pattern in which all the positive-side semiconductor switches are simultaneously turned on and all the negative-side semiconductor switches are simultaneously turned off. When the switching pattern in which all the positive-side semiconductor switches are simultaneously turned off and all the negative-side semiconductor switches are simultaneously turned on is set as the final state, the positive-side semiconductor switches are moved from the initial state to the final state one by one. This is implemented by setting the non-conductive state and simultaneously turning the paired negative-side semiconductor switches conductive. At this time, a circulating current flows through the coupling capacitor 37 in each switching pattern. However, the circulating current flowing in the switching pattern in the initial state flows only to each semiconductor switch and the coupling capacitor 37 of the forward converter and the inverse converter. Do not charge the DC capacitor. However, the circulating current flowing until the final state of the subsequent switching pattern becomes a charging current through the DC capacitor.

  Therefore, both the initial state and the final state of the switching pattern are switching patterns for setting the line-to-line output of the inverse converter to the zero voltage state. By returning to the state, the line output of the inverse converter is set to a zero voltage state, and a path for charging the DC capacitor is not taken. As a result, the circulating current for charging the DC capacitor is reduced, and an increase in the DC capacitor voltage can be suppressed.

In FIG. 1, the following can be further performed (method 3).
When the power can be returned from the forward converter to the AC power supply side, or the reverse converter operates to supply an AC voltage with an arbitrary amplitude and frequency to the load. However, when the amount of charge due to the circulating current is small, the DC capacitor voltage does not increase.
Therefore, depending on the output state or load state of the power conversion device, all the positive-side semiconductor switches for each phase are simultaneously turned off or all the negative-side semiconductor switches for each phase are turned on simultaneously. The switching of whether to avoid the zero voltage state is performed, and in the state where it is determined that the DC capacitor voltage rises, the switching operation of the method 1 or 2 is performed.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.
In the above methods 1 to 3, the circulating current for charging the DC capacitor 14 can be reduced, but the circulating current is not lost in any switching operation because the circulating path is formed. Therefore, the DC capacitor 14 is charged slowly, and eventually the voltage becomes larger than the specified value, and the device is stopped when an overvoltage occurs.

  Therefore, in FIG. 2, the coil 50 is installed on the AC input side, which is a circulation path, to suppress the circulation current. Since the circulating current becomes a common mode current for the coil 50, the coil 50 does not affect the input / output AC current of the apparatus by using a common mode coil, and its core has no effect on the circulating current. Therefore, even if the coil 50 is added, the size can be reduced as compared with the circuit of FIG. Here, the coil 50 is inserted on the AC input side, but it may be on the DC section or AC output side as long as it is in the circulation path. However, in order to avoid high-frequency potential fluctuation, which is a problem in the first place, an element having impedance cannot be inserted on the common input / output connection line.

FIG. 3 is a circuit diagram showing still another embodiment of the present invention.
When the purpose of circulating current suppression is only to prevent DC overvoltage at no load, supersaturated reactors 51, 52, and 53 may be inserted in place of the common mode coil 50 of FIG. The inductance value is small when the load current is sufficiently large and it is not necessary to suppress the circulating current, and becomes large near the no load. Similarly to FIG. 3, the core is not required to be saturated with respect to the circulating current, so that a smaller core than reactors 15 to 20 can be used.

  The insertion place may be any of the AC input side, DC section, or AC output side as in FIG. 3, but it is appropriate to insert it into the DC section in order to avoid the influence on the current and voltage control. At this time, since both the forward converter and the reverse converter require a DC capacitor, the illustrated capacitor 14 is arranged in parallel and a supersaturated reactor is provided between them. The same effect can be obtained even if the reactors 15 to 20 have characteristics (so-called swing characteristics) in which the inductance value becomes very large near zero current.

  Although the above description has mainly focused on the three-phase circuit, the present invention can be similarly applied to single-phase and multi-phase circuits.

Circuit diagram for explaining the embodiment of the present invention and the proposed apparatus Circuit diagram showing another embodiment of the present invention Circuit diagram showing still another embodiment of the present invention Circuit diagram showing a typical power converter

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... AC power source, 2-13 ... Semiconductor element switch, 14 ... DC intermediate capacitor, 15-20 ... Reactor, 31-36 ... Filter capacitor, 37 ... Coupling capacitor, 50 ... Common mode coil, 51-53 ... Saturable Reactor.

Claims (5)

A forward converter comprising a semiconductor switch, a reactor and an AC filter capacitor, which performs AC-DC conversion by a high-frequency switching operation of the semiconductor switch, and a DC switch by a high-frequency switching operation of the semiconductor switch, comprising a semiconductor switch, a reactor and an AC filter capacitor. An inverter for performing AC conversion, and the DC portion thereof is connected in common, and between one end of the AC filter capacitor of the forward converter and one end of the AC filter capacitor of the reverse converter, A capacitance coupling capacitor whose impedance is sufficiently lower than that of the reactor at a switching frequency and whose impedance is not significantly lower than that of the AC filter capacitor at the input frequency or output frequency of the device. The power converter formed by connecting via the capacitors,
Each is composed of a series circuit of one or a plurality of positive-side semiconductor switches and negative-side semiconductor switches to form a conversion circuit for one phase, and this is connected in parallel for the number of phases to form an inverse converter. During operation, the switching pattern is selected so as to avoid a zero voltage output state in which all the positive-side semiconductor switches of each phase are turned on simultaneously or all the negative-side semiconductor switches of each phase are turned on simultaneously. The power converter characterized by the above-mentioned.   When the zero voltage output state is required, use only a switching pattern in which all the positive-side semiconductor switches of each phase are simultaneously turned on, or all of the negative-side semiconductor switches of each phase are simultaneously turned on. The power converter according to claim 1, wherein only the switching pattern is used.   The power converter according to claim 1 or 2, wherein whether to avoid the zero voltage output state is switched according to an output state or a load state of the power converter.   A common mode coil having a sufficiently larger inductance than that of the reactor is connected in series with the reactor of the forward converter or the reactor of the reverse converter, or a direct current common part of the forward converter and the reverse converter. The power converter according to any one of claims 1 to 3.   A saturable reactor whose inductance is sufficiently larger than that of the reactor when the current is small is connected in series with the reactor of the forward converter or the reactor of the reverse converter or in a DC common part of the forward converter and the reverse converter. It connects, The power converter device as described in any one of Claims 1-3 characterized by the above-mentioned.

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