JP4493460B2 - Power converter - Google Patents

Description

The present invention relates to a power conversion device , for example , a power conversion device used as an uninterruptible power supply device in which a direct transmission switch is connected in series to a system.

  2. Description of the Related Art Conventionally, various non-instantaneous power supply devices having various circuit configurations have been proposed. For example, as shown in JP-A-1-222635 (see Patent Document 1) and JP-A-8-223822 (see Patent Document 2). There is something to be done.

  The conventional uninterruptible power supply shown in Patent Document 1 is a constant-voltage constant-frequency power supply (CVCF) that once converts an AC input voltage to DC and then reversely converts it to AC, and bypasses the CVCF. A bypass circuit composed of a semiconductor switch is provided, and a configuration is adopted in which alternating current is once converted to direct current through a converter both at normal time and when the voltage drops, and the direct current is converted into alternating current by an inverter. For this reason, there is a problem that current always passes through the semiconductor even in a normal state, a loss is always generated, the overall efficiency of the entire apparatus is lowered, and the apparatus is enlarged for cooling. Moreover, since the output of the inverter requires a PWM-controlled rectangular wave, there is a problem that a large filter is required for smoothing the output.

  In addition, in the conventional uninterruptible power supply shown in Patent Document 2, the commercial line is directly connected to the load by a direct transmission switch when it is normal, but when the commercial line drops below a certain voltage, the direct transmission switch is disconnected. The battery power is supplied to the load through the inverter and step-up transformer. In such a configuration, the step-up transformer needs to have a function of smoothing the rectangular voltage generated by the inverter and needs to transmit a commercial frequency voltage, so that the voltage time product (the amount of magnetic flux) is large. Therefore, there is a problem that a large and expensive system is required.

JP-A-1-222635 JP-A-8-223822

  The present invention has been made to solve the above-described problems. By combining outputs of a plurality of single-phase inverters, the system voltage is compensated for in a normal state, and the system is reduced to a predetermined voltage or less. Thus, there is provided an uninterruptible power supply apparatus that can realize voltage supply to a load at low cost by fine waveform control even after the direct switch is disconnected.

  An uninterruptible power supply according to the present invention is inserted in parallel in a system connecting a power source and a load, and a single-phase inverter group in which respective AC side terminals are connected in series with each other, and a single-phase inverter group connected in series with the system A single-phase inverter, and a DC-DC converter connected to the DC terminals of each of the single-phase inverter group and the single-phase inverter and controlling power from a DC power supply and supplying the DC-DC converter to each inverter. The group and the single-phase inverter are configured to transmit and receive energy via the DC-DC converter.

  According to the uninterruptible power supply device of the present invention, by combining one isolation transformer and a plurality of single-phase inverters, in any voltage state such as voltage increase / decrease compensation during normal operation, voltage compensation during power failure, etc. In addition, there is an effect that stable voltage supply to the load can be realized at low cost by fine waveform control.

Embodiment 1 FIG.
FIG. 1 shows a schematic configuration diagram of an uninterruptible power supply according to Embodiment 1 of the present invention. In FIG. 1, a power source 1 is usually a commercial AC power source having a system voltage Vo, and directly supplies power to a load 2 via a direct switch 3 composed of a mechanical switch such as a relay. The load 2 is connected to a single-phase inverter group 4, 5, 6 in which each AC side terminal is inserted in parallel with the system, and a single-phase inverter 7 inserted in series with the system. Yes. Capacitors 8 to 11 are connected to the DC-side terminals of the single-phase inverters 4 to 7, respectively, and the energy of the respective voltages VB4, VB3, VB2, and VB1 is passed through the DC-DC converter 12 to the single-phase inverter group 4, 5 and 6 and the single-phase inverter 7 can be exchanged with each other.

The DC-DC converter 12 is supplied with a predetermined DC voltage from the battery 13 via the chopper 14, and the output from the chopper 14 is also supplied to the DC side terminal of the single-phase inverter 4. The output terminals of the single-phase inverter groups 4, 5 and 6 are respectively connected in series and connected to the load 2 via a filter 15.
Here, as shown in FIG. 2, each of the single-phase inverters 4 to 7 includes switches 20 to 23 such as MOSFETs connected in a single-phase bridge, and parasitic diodes 24 to 27 connected in antiparallel to each element, A well-known configuration comprising gate drive circuits 30 to 33 for driving the gates of the switches can be employed.

  Next, as shown in FIG. 3, the chopper circuit 14 includes a reactor 41 and switches 41 and 42 such as MOSFETs, diodes 43 and 44, and gate circuits 45 and 46, and is connected to an input terminal. The voltage of the battery 13 is boosted and output from the output terminal. Further, as shown in FIG. 4A, the DC-DC converter 12 is provided in series with a transformer 50 having a plurality of windings N1, N2, N3, and N4 and the respective windings N1 to N4. Switches 51 to 54 such as MOSFETs, diodes 55 to 58, and gate circuits 59 to 62 are configured, and converter control is performed by controlling the switches 51 to 54. FIG. 4B shows an example of the conduction control of the switches 51 to 54, which will be described in detail later. Further, FIG. 5 shows an example of a gate circuit. In the figure, the photocoupler 65 and the DC power supply 66 are constituted by a resistor 67 and an amplification buffer 68.

  Next, the operation of the uninterruptible power supply shown in FIG. 1 will be described with reference to FIGS. Under normal conditions, the direct transmission switch 3 is closed, and the system voltage Vo is directly supplied from the system power supply 1 to the load 2 through this switch. At this time, the single-phase inverters 4, 5, and 6 function as rectifiers, charge the respective DC-side capacitors 8, 9, and 10, and the single-phase inverter 7 outputs zero. The operation of the uninterruptible power supply can be roughly divided into two. One is a voltage increasing / decreasing voltage compensating action when the voltage of the system 1 is lowered or increased, and the other is a voltage compensating action when the power system is interrupted.

  First, consider the case where the voltage of system 1 is reduced. In FIG. 6, if the system voltage Vo drops at time to, the inverter 7 starts to operate. The DC capacitor 11 of the inverter 7 is charged with the DC voltage VB1, and the inverter 7 outputs the AC voltage VB1out in synchronization with the frequency of the system, so that the load voltage Vd has a waveform increased by VB1 for each polarity. . As a result, the system voltage drop can be compensated. Note that power transmission and reception by the DC capacitor 11 will be described in the second embodiment.

On the other hand, when the system voltage Vo increases, a predetermined voltage is applied to the load voltage (not shown) if the output of the inverter 7 is generated with the opposite polarity to the system voltage Vo.
Next, a case where the power failure occurs in the system will be described. When a power failure occurs in the system, first, the direct transmission switch 3 is disconnected and the chopper circuit 14 is operated to supply power from the battery 13 to the DC capacitor 8 of the single-phase inverter 4. In addition, power is transmitted from the direct current capacitor 8 to the direct current capacitors 9, 10, 11 by the DC / DC converter 12. For example, the relationship between the voltages VB1 to VB4 of the DC capacitors is, for example, 1: 2: 4: 8. Actually, many other DC capacitor relationships are possible, for example, 1: 3: 9: 27, and the voltages can be exactly the same.

  When the direct transmission switch 3 is disconnected, the four inverters 4 to 7 are all connected in series to the load, so that the outputs of the four inverters can be combined to generate a desired waveform. For example, in the case of 1: 2: 4: 8, it is possible to output a voltage of 16 levels (including zero) on one side by a combination of binary numbers. Since a voltage waveform of 16 levels on one side can be output, a substantially sinusoidal voltage can be supplied to the load in combination with the effect of the output filter. FIG. 7 shows a pseudo sine wave generated at 16 levels on one side. Thus, by combining the outputs of the four inverters, it is possible to supply power to the load 2 even during a power failure of the system. In the case of a 1: 3: 9: 27 relationship, it is possible to output a 40-level waveform on one side. Furthermore, if at least one inverter is operated by PWM, finer waveform control is possible.

  Next, transmission / reception of electric power by the capacitor 11 when the system voltage decreases or increases will be described. The power of VB1 by the capacitor 11 flows from the load 2 side when the system voltage Vo increases, and flows out to the load 2 when the system voltage Vo decreases. Therefore, the DC / DC converter 12 needs to transmit and receive the electric power. Since the three inverters 4 to 6 can also generate a sine wave or the like depending on the combination of their output voltages, for example, the relationship of the voltages from VB2 to VB4 is set to 3: 9: 27, the maximum one side By outputting the 14-level voltage, the output level is approximated to a sine wave and smoothed by the filter 15, so that power can be discharged from each inverter to the system.

  For example, when the voltage Vo of the system drops, in order to compensate with the output voltage VB1out of the single-phase inverter 7, it is necessary to send power from the DC capacitors 8, 9, 10 to the DC capacitor 11 through the DC / DC converter 12. . For this purpose, power must be injected from the system to the DC capacitors 8, 9, 10. Specifically, as shown in FIG. 8 (a), if the inverters 4 to 6 output a voltage lower than the system voltage, that is, rectifier operation, current flows from the system to the inverters 4 to 6, and the DC capacitor 8 , 9 and 10 are charged. That is, the total power of the DC capacitors 8, 9, 10 increases. Thereby, power can be supplied from the DC capacitors 8, 9, and 10 to the DC capacitor 11 through the DC / DC converter 12.

  On the contrary, when the system voltage Vo increases, in order to compensate by the output voltage VB1out of the single-phase inverter 7, this time, power is supplied from the DC capacitor 11 to the DC capacitors 8, 9, 10 through the DC / DC converter 12. I need to send it. For this purpose, it is necessary to inject total power from the VB2, VB3, and VB4 of the DC capacitors 8, 9, and 10 into the system. Specifically, as shown in FIG. 8B, if the inverters 4 to 6 output a voltage higher than the system voltage, current flows from the inverters 4 to 6 to the system, and the total of the DC capacitors 8, 9, 10 Electric power decreases. Thus, power can be supplied from the DC capacitor 11 to the DC capacitors 8, 9, 10 through the DC / DC converter 12. That is, power can be returned from VB1 to the grid. By performing such control, the entire voltage waveform from VB2 to VB4 becomes very fine, and the smoothing filter 15 requires a much smaller capacity than the conventional case.

Embodiment 2. FIG.
Next, details of the DC / DC converter 12 will be described. FIG. 4A is a circuit diagram of the DC / DC converter 12 according to the present invention. As is apparent from FIG. On the primary side of the insulating transformer 50, a known circuit unit including a winding N1, a switch 51 such as a MOSFET, a diode 55, and a gate circuit 59 is connected. Further, on the secondary side of the insulating transformer 50, a circuit unit including a winding N2 and a switch 52 such as a MOSFET, a diode 56, and a gate circuit 60, a winding 53 and a switch 53 such as a MOSFET, and a diode 57. A circuit unit comprising a gate circuit 61, a winding N4, a switch 54 such as a MOSFET, a diode 58, and a circuit unit comprising a gate circuit 62 are connected in series.

  At this time, the windings N1 to N3 and the winding N4 are configured to reverse the winding directions and to reverse the voltage generation timing. That is, the DC / DC converter 12 comprises a bidirectional forward type DC / DC converter by the windings N1 to N3 and the switches 51 to 53 connected thereto, and the winding N1. The winding N4 constitutes a bidirectional flyback type DC / DC converter by the switches 51 and 54 connected thereto.

By configuring as described above, the gate voltages of the switches 51, 52, 53 become H at the same timing as shown in the upper part of FIG. 4B, and each switch becomes conductive. The output of the DC / DC converter 12 generates a voltage proportional to the turn ratio of the windings N1 to N3. As a result, the capacitors 8 to 10 are also charged with voltages proportional to the turns ratio of the windings N1 to N3, and VB2 = VB4 * N2 / N4 and VB3 = VB4 * N3 / N4. In the above equation, N2, N3, and N4 represent the number of turns of the windings N2, N3, and N4.
By adopting such a configuration, the voltage relationship of the DC portions of the inverters 4 to 6 can be fixed to the winding ratio of the windings N1 to N3.
By making the switching frequency of each of the switches 51 to 53 sufficiently higher than the load current changing speed, that is, the commercial frequency, power transfer is performed quasi-statically, so that an efficient converter can be formed.

On the other hand, a bidirectional flyback DC / DC converter constituted by winding N1 and winding N4 and switches 51 and 54 connected to them will be described. As shown in the lower part of FIG. 4B, the gate voltage of the switch 54 is inverted in logic from the gate voltage of the switch 51. Therefore, the excitation energy is stored in the transformer 50 and the switch is turned off. It can operate to supply power to the other party. As a flyback type operation, when the exciting current of the transformer 50 does not continuously become zero (current continuous mode), the following relationship is established.
VB4 * d = VB1 * (1-d) * N1 / N4
VB1 = VB4 * d / (1-d) * N4 / N1

Here, d = Td / To (duty ratio), N4 and N1 represent the number of turns of the windings N4 and N1. That is, the voltage of VB1 is represented by the voltage of VB4 and the duty ratio d,
Therefore, by changing the duty ratio d, the magnitude of VB1 can be changed according to the change in the system voltage Vo.
By adopting the configuration of the DC / DC converter as described above, the inverters 4, 5, and 6 always maintain the fixed voltage value and the fixed voltage relationship, and freely change the value of VB1 by changing d. be able to. Accordingly, it is easy to supply a constant voltage to the load when the system voltage decreases or increases while outputting stable voltage using the inverters 4, 5, and 6 to transmit and receive power to the system. .

Since the inverters 4 to 6 can output a sine wave, the inverters 4 to 6 can be operated as a parallel reactive power compensation circuit. The operation is shown in FIG. FIG. 9A shows a case where the load is operated with a delayed load, that is, the phase of the load current Id is delayed with respect to the system voltage V ₀ . Here, the single-phase inverters 4, 5, 6 perform an operation of flowing the current Ix into the system so that the system current I ₀ has the same phase as the system voltage V ₀ . That is, each output level is controlled or PWM control is performed so that Ix flows into the system from the single-phase inverters 4, 5, 6, and Ix is smoothed by the effect of the smoothing filter 15. As a result, the system current I ₀ and the system voltage V ₀ are in phase with each other, so that when viewed from the system, it appears that a load with a power factor of 1 is connected, so that reactive power can be compensated for and the system using harmonic components Backflow into the can be prevented. Furthermore, since the effective value of the current flowing through the system can be reduced, the loss of cables and the like is reduced.

FIG. 9B is an operation example when a rectifier load is connected. As with In the case of (a), the single-phase inverters 4, 5, 6 so that the current flows _{I 0} of unity power factor to the grid, pouring current Ix to the grid. Since the single-phase inverters 4, 5, and 6 can control a fine waveform, even when a current change such as a rectifier load is severe, it is possible to control the current I ₀ having a power factor of 1 to flow reliably. This is because the gain of the control system can be increased by the filter 15 having a small capacity. In such an operation, the amount of current flowing into and out of the single-phase inverters 4, 5, and 6 is almost different, and the voltage relationship between VB2 and VB4 is easily broken. In order to correct this, as described above, the DC-DC converter 12 is operated, and the DC-DC converter 12 exchanges energy so that the voltages VB2 to VB4 maintain predetermined values, respectively. As a result, the current flowing through the system is limited to the active power, and the effective current value and harmonics on the system side are reduced, which can be connected to noise reduction and loss reduction.

Embodiment 3 FIG.
In the third embodiment, a gate power source such as a single-phase inverter and a DC-DC converter constituting the uninterruptible power supply device of the present invention as described above is shared, and the unit configuration is simplified. FIG. 10 shows a detailed circuit including the chopper circuit portion 14, the DC-DC converter portion 12, and the inverter portion 3 of the uninterruptible power supply device of the present invention. As shown in the figure, all of the switches such as MOSFETs constituting each part require a gate drive circuit, and all of these also require a power source. However, in the configuration in which single-phase inverters are connected in series as described above, the concept that each single-phase inverter is a unit unit is common, so it is generally accepted that each gate power supply is provided in a unit unit. Existed as. However, if gate power supplies are prepared as many as the number of switches, it goes without saying that the configuration becomes complicated and the cost increases.

Conventionally, there has been a technique for sharing a gate power supply with a plurality of inverters having a common bus (see, for example, Japanese Patent Application Laid-Open No. 2002-199743). However, a common bus is used as in the embodiment of the present invention. In an unstructured configuration, the gate power source was not shared for the following reasons.
That is, in a so-called series multiple inverter in which inverters are connected in series and a part of the output terminal is shared by each inverter, a high-frequency current due to PWM normally flows in the output line, so a large potential fluctuation occurs in the output line. To do. Therefore, a large potential fluctuation occurs at a high frequency even in the same potential portion in direct current, and this tends to increase noise current and leakage current.

For this reason, from the viewpoint of reducing the influence of these noise currents and leakage currents on the gate power supply, it has been generally considered difficult to share the gate power supply. However, according to the inverter configuration according to the present embodiment, as described above, since the output waveform is generated by the combination of the inverter outputs, the switching frequency is greatly reduced. Therefore, each inverter is switched at a low frequency. Is sufficient, and the noise current and leakage current are drastically reduced. As a result, it becomes possible to share the gate power supply of the portion having the same potential in terms of DC.
That is, as shown in FIG. 10, in an N-stage inverter (N = 4 in this case), the terminal connected to the inverter N-1 at the output terminal of the inverter N is the source terminal of the inverter N side. It is possible to share the gate power supply of the switch (4S3) and the switch (3S1) on the inverter N-1 side connected to the terminal led to the inverter N-1.

Further developing the idea, combinations having a common source terminal on the N-side bus of each inverter, that is, 4G4 and 4G2, 46 and 59, and 3G4, 3G2, 60, and 2G4, 2G2, 61, and 1G4, 1G2 , 62 are assigned PS1, PS2, PS3, and PS4, respectively.
Next, PS6, PS7, and PS8 are assigned to the pairs 4G3, 3G1, and 3G3, 2G1, and 2G3, 1G1, respectively, in which the source portions are shared by the lines connecting the inverters in series. By doing so, the number of power supplies for the gate is greatly reduced. This is shown in FIG. As shown in FIG. 11, power is supplied to each pair or combination of gate circuits, that is, PS1 to PS4 and PS6 to PS8, by one common gate power source.
Therefore, according to the present embodiment, since the number of gate power supplies can be greatly reduced, a simple and inexpensive circuit configuration can be realized.

It is a schematic block diagram of the uninterruptible power supply device which concerns on Embodiment 1 of this invention. The circuit example of the inverter part of the uninterruptible power supply device shown in FIG. 1 is shown. The circuit example of the chopper part of the uninterruptible power supply device shown in FIG. 1 is shown. The block diagram and the operation | movement waveform diagram of the DC-DC converter part which concern on Embodiment 2 of this invention are shown. The circuit example of the gate circuit part of the uninterruptible power supply device shown in FIG. 1 is shown. It is a wave form diagram explaining the voltage increase operation | movement of the uninterruptible power supply device shown in FIG. It is a pseudo sine waveform which shows an example of the output waveform of the uninterruptible power supply which concerns on Embodiment 1 of this invention. It is a figure explaining transmission and reception of electric power between each inverter and a system according to change of system voltage. It is a wave form diagram at the time of making the single phase inverter group of the uninterruptible power supply device shown in FIG. It is a detailed circuit diagram of the uninterruptible power supply device which concerns on Embodiment 3 of this invention. In FIG. 10, it is a conceptual diagram explaining common use of a gate power supply.

Explanation of symbols

1 AC power supply, 2 load,
3 Direct switch, 4, 5, 6 Single-phase inverter group,
7 single-phase inverter, 8, 9, 10, 11 capacitor,
12 DC-DC converter, 13 battery,
14 choppers, 15 filters,
50 Insulation transformer.

Claims (5)

A single-phase inverter group that is inserted in parallel to the system connecting the power source and the load and whose AC side terminals are connected in series to each other, a single-phase inverter connected in series to the system, the single-phase inverter group and the single-phase inverter group A DC-DC converter connected to each DC side terminal of the phase inverter and controlling power from a DC power source and supplying the DC-DC converter to each inverter, and the single-phase inverter group and the single-phase inverter include the DC- A power conversion apparatus, wherein energy is transmitted and received through a DC converter. 2. The DC-DC converter includes one insulating transformer having a plurality of windings individually connected to a DC side terminal of either the single-phase inverter group or the single-phase inverter. The power converter device described in 1. 2. A capacitor is connected to each DC side terminal of the single-phase inverter group and the single-phase inverter, and a voltage value charged in these is set to a predetermined ratio by the insulating transformer. Or the power converter device of Claim 2. 3. The insulation transformer of the DC-DC converter adopts a forward configuration between the single-phase inverter groups and a flyback configuration between the single-phase inverter groups and the single-phase inverters. The power converter device described in 1. In the case where the single-phase inverter group has an N-stage serial configuration, the terminal connected to the inverter N-1 at the output terminal of the inverter N is a switch on the inverter N side that is the source terminal, and the switch is connected to the inverter N-1. The power converter according to claim 2, wherein the gate power supply is shared with the switch on the inverter N- 1 side connected to the connected terminal.

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