JP5523297B2 - Power converter - Google Patents

Description

  The present invention relates to an improved power converter for reducing harmonics.

  In a power converter having a rectifier circuit for converting from alternating current to direct current, a three-phase bridge rectifier is multiplexed using an insulating transformer to reduce input harmonics. In such a system using an isolation transformer, the relationship between the degree of multiplexing and the magnitude of input harmonics is clear, and multiplexing is performed using a number of three-phase bridge rectifiers for the required degree of input harmonic reduction. It is possible to find out what should be done by a simple calculation. However, an insulating transformer having a secondary winding with an appropriate phase difference is expensive and large.

  On the other hand, a method has been proposed in which a non-insulated single-winding transformer is used as an input transformer and the phase difference of the secondary winding is shifted by 40 ° (see, for example, Patent Document 1).

US Pat. No. 5,124,904

  The technique disclosed in Patent Document 1 has the advantage that the voltage applied to the three-phase bridge rectifier always has the maximum amplitude, so that harmonics due to an abnormal rectification path peculiar to the single-winding transformer do not occur. In order to shift each of the windings by 40 °, for example, it is necessary to increase the amount of windings for shifting the phase as compared with the method of shifting by 15 °, so that the single-winding transformer becomes large.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power conversion device capable of reducing harmonics using a small single-winding transformer.

  In order to achieve the above object, a power conversion device according to a first aspect of the present invention includes a rectifier that rectifies an AC voltage of a three-phase AC power source through a balance reactor, and a primary AC voltage of the three-phase AC power source. The input phase of the secondary winding is 60 ° / M (M is an odd number of 3 or more) phase difference intervals symmetrical to the plus side and the minus side centered on 0 °. A single-winding transformer having windings, (M-1) three-phase rectifiers that rectify output voltages of the (M-1) secondary windings, and a total of M three-phase rectifiers. It is characterized by comprising M zero-phase current-suppressing DC reactors, each of which is an input and each output is connected in parallel to a common load.

  The power conversion device according to the second aspect of the present invention has an AC voltage of a three-phase AC power supply as a primary input, and a phase difference between windings is 60 ° / N (N is an integer of 2 or more). A single-winding transformer having N secondary windings, N three-phase rectifiers for rectifying the output voltages of the N secondary windings, and the N three-phase rectifiers as inputs. , And N outputs zero-phase current suppression DC reactors whose outputs are connected in parallel to a common load.

  According to the present invention, it is possible to provide a power conversion device capable of reducing harmonics using a small single-winding transformer.

The circuit block diagram of the power converter device which concerns on Example 1 of this invention. The voltage vector figure of the power converter device which concerns on Example 1 of this invention. The circuit block diagram of the power converter device which concerns on Example 2 of this invention. The circuit block diagram of the power converter device which concerns on Example 3 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  Hereinafter, the power converter concerning Example 1 of the present invention is explained with reference to FIG.1 and FIG.2.

  FIG. 1 is a circuit configuration diagram of a power conversion apparatus according to Embodiment 1 of the present invention. Power is supplied from the three-phase AC power source 1 to the three-phase rectifiers 4B and 4C via the single-winding transformer 2 and to the three-phase rectifier 4A via the balance reactor 3. Each of the three-phase rectifiers 4A, 4B, and 4C has a configuration in which diodes are bridge-connected, and outputs a DC voltage. The single-winding transformer 2 has a primary winding 21 and secondary windings 22 and 23, and a counter feed end of the primary winding is commonly connected as a neutral point N. The secondary winding 22 supplies a three-phase voltage having a phase advanced by 15 ° with respect to the primary winding 21 to the three-phase rectifier 4B. Similarly, the secondary winding 23 supplies a three-phase voltage having a phase delayed by 15 ° with respect to the primary winding 21 to the three-phase rectifier 4C. Here, the balance reactor 3 is provided for adjusting the input voltage of the three-phase rectifier 4A to the three-phase rectifiers 4B and 4C in consideration of the impedance drop of the secondary windings 22 and 23.

  The DC outputs of the three-phase rectifiers 4A, 4B, and 4C are connected in parallel to a common load 6 via zero-phase current suppressing DC reactors 5A, 5B, and 5C, respectively. Here, the load 6 does not necessarily have to be a DC load composed of passive elements, and may be an active load such as an AC motor driven by an inverter, for example. The zero-phase current suppressing DC reactor 5 has windings on the positive side and the negative side, and when the current flowing through the positive side winding changes, the impedance flows when this current flows back through the negative side winding. It works to minimize. Here, “minimum” means that the reactances of the positive side and the negative side cancel each other and become zero, and in principle, the impedance becomes only the resistance of the winding.

  Hereinafter, the operation of the power conversion apparatus according to the first embodiment of the present invention will be described with reference to FIG. FIG. 2 shows the voltages applied to each of the three-phase rectifiers 4A, 4B, and 4C as vectors. As shown in the figure, line voltages UA-VA, VA-WA, and WA-UA that are 120 ° out of phase are applied to the three-phase rectifier 4A. Here, UA, VA, and WA indicate the U-phase, V-phase, and W-phase input terminals of the three-phase rectifier 4A, respectively, and the same applies to the other three-phase rectifiers. The three-phase rectifier 4B is applied with line voltages UB-VB, VB-WB, WA-UA having a phase interval of 120 ° relative to each other, with a phase advance of 20 ° from the above voltages. The line voltages UC-VC, VC-WC, and WC-UC, which are delayed by 20 ° from each voltage of the phase rectifier 4A and have a phase interval of 120 °, are applied. If balanced rectification is performed in this state, the current flowing from the AC power source 1 into the power converter becomes a current equivalent to so-called 18-pulse rectification, and the harmonics are considered to be greatly reduced.

  However, since the phases of the single-winding transformer 2 are not insulated from each other, as shown by broken lines in FIG. 2, voltages higher than the line voltage applied to each three-phase rectifier (for example, UB-VC, VB-WC, WB-UC) is applied across the three-phase rectifier. For this reason, for example, the current flowing from the U phase (UB) of the three-phase rectifier 4B flows through the load 6 through the positive side winding of the zero-phase current suppression DC reactor 5B, and the zero-phase current suppression DC reactor 5B is negative. A current route is generated that returns to the V phase (VC) of the three-phase rectifier 4C through the negative side winding of the zero-phase current suppressing DC reactor 5C instead of the side winding. When such a ripple current flows, not only the harmonic component of the current flowing from the AC power supply 1 into the power converter increases, but also an extra ripple occurs in the DC voltage applied to the load 6, depending on circumstances. In such a case, the DC voltage may become an overvoltage, causing the protection device to operate.

  The zero-phase current suppressing DC reactor 5 is provided to suppress such a zero-phase current across the three-phase rectifier. That is, with respect to the route passing through the negative side winding of the zero-phase current suppressing DC reactor 5C through the positive side winding of the zero-phase current suppressing DC reactor 5B as described above, the zero-phase current suppressing DC reactor 5 is used. The impedance of is the sum of both positive and negative. Accordingly, the impedance is extremely larger than the impedance when the zero-phase current suppressing DC reactor 5B is passed from the positive side to the negative side. For this reason, the magnitude of the ripple current is limited, and the DC voltage is also prevented from being overvoltage.

  In the first embodiment, an output equivalent to 18-pulse rectification is obtained using the three-phase rectifiers 4B and 4C whose phases are shifted by 20 ° positively and negatively around the three-phase rectifier 4A having the same phase as that of the AC power supply 1. Further, it is possible to obtain an output equivalent to 30 pulse rectification by adding two three-phase rectifiers. In this case, four secondary windings of the single-winding transformer 2 are provided, and two three-phase rectifiers shifted by 12 ° and 24 ° to the positive side around the three-phase rectifier having the same phase as the AC power source 1 and the negative side Two three-phase rectifiers that are shifted in phase by 12 ° and 24 ° may be used.

  If further expanded, a rectifier that rectifies the AC voltage of the three-phase AC power supply through a balance reactor and the AC voltage of the three-phase AC power supply as the primary input, and the output phase of the secondary winding is positive around 0 °. (M-1) / 2 secondary windings at a phase difference interval of 60 ° / M (M is an odd number of 3 or more) on the side, and 60 ° / M (M is an odd number of 3 or more) on the negative side A single-winding transformer having (M−1) / 2 secondary windings at a phase difference interval, and (M−1) three-phase rectifiers for rectifying the output voltage of each of these secondary windings; What is necessary is just to comprise a power converter device from the M zero-phase current suppression DC reactor which takes each of the three-phase rectifiers which become M in total as an input, and connects the output to a common load in parallel.

  In the above description, M is an odd number, but M may be an even number if the balance of the output phase centered on 0 ° is not taken into consideration. In this case, it is sufficient to provide one more secondary winding on the plus side or minus side of the single-winding transformer.

  FIG. 3 is a circuit configuration diagram of the power conversion apparatus according to the second embodiment of the present invention. About each part of this Example 2, the same part as each part of the power converter device which concerns on Example 1 of this invention of FIG. 1 is shown with the same code | symbol, and the description is abbreviate | omitted. The difference between the second embodiment and the first embodiment is that a switch 7 for separating the primary winding, a current detector 8 for detecting a load current, and a switch controller 9 are provided. The switch controller 9 has a load current of a predetermined value. It is the point which set it as the structure which turns off the switch 7 when it becomes below.

  As described above, the magnitude of the ripple current described above is limited by the effect of the DC reactor 5 for suppressing the zero-phase current and the DC voltage is suppressed from being overvoltage. The effect of the current suppressing direct current reactor 5 is weakened, the direct current voltage fluctuates greatly and becomes an overvoltage, and the protection device is operated. To prevent this, the switch 7 is turned off when the load current detected by the current detector 8 becomes a predetermined value or less. When the switch 7 is turned off, the maximum voltage across the phases indicated by the broken line in FIG. 2 is not applied. However, the phase shift by the secondary windings 22 and 23 is not performed at the same time, and an AC voltage having the same phase as that of the AC power supply 1 is basically applied to each of the three-phase rectifiers 4A, 4B, and 4C. It becomes a waveform and the input harmonics increase. However, in this case, the load current is below a predetermined value, and the absolute value is small. Accordingly, since the fluctuation of the DC voltage can be suppressed in this way, the device will not be overvoltaged to operate the protection device.

  Although FIG. 3 shows the connection of the single-winding transformer as a star connection having a neutral point N, the same effect can be obtained if the primary winding is disconnected and the excitation current is cut off even in the case of the delta connection. It is clear that is obtained.

  FIG. 4 is a circuit configuration diagram of the power conversion apparatus according to the third embodiment of the present invention. The same parts of the third embodiment as those of the power conversion apparatus according to the first embodiment of the present invention shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. The third embodiment is different from the first embodiment in that the balance reactor 3, the three-phase rectifier 4A and the zero-phase current suppressing reactor 5A for rectifying the same phase as the AC power supply are omitted, and the single transformer 2A is used as a secondary. The four-winding type is used, and the outputs of the secondary windings 24 and 25 are given to the three-phase rectifiers 4D and 4E, respectively. 6 is a configuration in which power is supplied to 6.

  The power converter in Example 3 constitutes a harmonic suppression system equivalent to 24-pulse rectification. Therefore, the secondary windings 22, 23, 24, and 25 of the single-winding transformer 2A have phases of −22.5 °, −7.5 °, + 7.5 °, and + 22.5 ° with respect to the AC power supply 1, respectively. What should I do? As described above, if the necessary phase shift is realized by using only the secondary winding of the single-winding transformer 2A without using the balance reactor shown in the first embodiment, the secondary winding of the single-winding transformer 2A is Although it increases, there is an advantage that the degree of freedom of voltage applied to the three-phase rectifier is increased.

  Further, as a modification of the third embodiment, it is possible to configure a harmonic suppression system equivalent to 12-pulse rectification by using the secondary winding of the single-winding transformer as two pieces of −15 ° and + 15 °. In summary, in order to construct a harmonic suppression system equivalent to 6N pulse rectification, each of N secondary windings having a phase difference of 60 ° / N (N is an integer of 2 or more) by a single-winding transformer. It can be seen that it may be configured so that the outputs of N are supplied to N three-phase rectifiers.

  The power converter shown in the third embodiment is provided with the switch 7, the current detector 8 and the switch controller 9 shown in FIG. 3, and opens and closes when the load current becomes a predetermined value or less by the switch controller 9. Obviously, if the device 7 is turned off, fluctuations in the DC voltage can be suppressed even if the load current is reduced, so that overvoltage of the device can be prevented.

  Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof. For example, a DC voltage may be detected instead of the current detector 8 in the second embodiment, and the switch 7 may be turned off when the DC voltage exceeds a predetermined value. Further, it is not always necessary to detect the load current by the current detector 8, and this may be substituted by the input current of any three-phase rectifier 4.

DESCRIPTION OF SYMBOLS 1 AC power source 2, 2A Single volume transformer 3 Balance reactor 4, 4A, 4B, 4C, 4D, 4E Three-phase rectifier 5, 5A, 5B, 5C, 5D, 5E Zero-phase current suppression reactor 6 Load 7 Switch 8 Current Detector 9 Open / close controller

Claims (6)

A rectifier that rectifies the AC voltage of the three-phase AC power source through a balance reactor;
A phase difference interval of 60 ° / M (M is an odd number of 3 or more) symmetrically on the plus side and the minus side with the AC voltage of the three-phase AC power supply as the primary input and the output phase of the secondary winding as a center around 0 °. A single-winding transformer having (M-1) secondary windings,
(M-1) three-phase rectifiers for rectifying the output voltage of each of the (M-1) secondary windings;
A power conversion apparatus comprising: a total of M three-phase rectifiers as inputs, and M zero-phase current-suppressing DC reactors each having an output connected in parallel to a common load. A single-winding transformer having N secondary windings having an AC voltage of a three-phase AC power supply as a primary input and a phase difference between the windings of 60 ° / N (N is an integer of 2 or more);
N three-phase rectifiers for rectifying the output voltage of each of the N secondary windings;
A power conversion device comprising N number of three-phase rectifiers as inputs and N number of zero-phase current suppressing DC reactors whose outputs are connected in parallel to a common load.   2. The power converter according to claim 1, wherein the phase difference interval is 20 °, and the phase difference of the secondary winding viewed from the AC power source is −20 ° and + 20 °, respectively.   The phase difference between the windings is 15 °, and the phase differences viewed from the AC power source are −22.5 °, −7.5 °, + 7.5 °, and + 22.5 °, respectively. The power conversion device according to claim 2.   The power converter according to claim 2, wherein a phase difference between the windings is 30 °, and a phase difference viewed from the AC power supply is −15 ° and + 15 °, respectively. A switch that can be opened so that the primary winding of the single-winding transformer is not excited by the AC power supply;
The power converter according to any one of claims 1 to 5, wherein the switch is opened when a current flowing through the load substantially becomes a predetermined value or less.

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