JP7366076B2 - Three-phase inverter and uninterruptible power supply system - Google Patents

Description

The present invention relates to a three-phase inverter for supplying three-phase AC voltage as a power source for, for example, computer air conditioning equipment, and an uninterruptible power supply system equipped with this three-phase inverter.

Conventionally, an inverter that outputs a three-phase AC voltage of 200 [V] as an AC power source for a motor is described, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2012-231567).
Furthermore, as inverters for air conditioning equipment, those described in, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2011-160559) and Patent Document 3 (Japanese Patent Laid-Open No. 2012-65376) are known.

Usually, AC power supplies using three-phase inverters are of medium or large capacity, but there are relatively few small capacity ones. For this reason, for example, it is desired to realize a small-capacity three-phase inverter that can be connected to a 48-volt battery and supply a three-phase AC voltage of 200-volts (effective value) to a load during a power outage.

As shown in FIG. 8, Patent Document 4 (Japanese Unexamined Patent Publication No. 2017-195739) discloses that the voltage of an AC power supply 101 is rectified and smoothed by a converter 102 to generate a DC voltage of 48 [V], and this DC voltage is A power supply device 100 is disclosed that supplies voltage from a DC bus 103 to a battery 104 and an inverter 105, and also to a load 200 via an output section 106. In FIG. 8, 107 is a control circuit that controls the converter 102, battery 104, and inverter 105, and 108 is an external interface provided between the DC bus 103 and an external circuit.

Japanese Patent Application Publication No. 2012-231567 Japanese Patent Application Publication No. 2011-160559 JP2012-65376A JP 2017-195739 ([0012] to [0021], Figure 2, etc.)

According to the power supply device described in Patent Document 4 (Japanese Unexamined Patent Publication No. 2017-195739), for example, when the AC power supply 101 is out of power, the DC voltage (48 [V]) of the battery 104 is converted to the AC voltage (200 [V]) by the inverter 105. V]) and can be supplied to the load 200, thereby making it possible to perform so-called power outage compensation.
However, this power supply device includes an external interface 108 for exchanging DC power between an external DC power source and the DC bus 103, which has the problem of complicating the circuit configuration.

Therefore, the problem to be solved by the present invention is to convert a DC voltage (for example, 48 [V]) into a three-phase AC voltage (for example, 200 [V]) of a predetermined size using a simple configuration, and to convert this three-phase AC voltage into a computer. An object of the present invention is to provide a small-capacity, compact three-phase inverter that can be supplied as a power source for air conditioning equipment, etc., and an uninterruptible power supply system equipped with this three-phase inverter.

In order to solve the above problem, a three-phase inverter according to claim 1 includes:
DC power supply and
A converter having a plurality of current averaging converters for respectively converting the DC voltage of the DC power supply into pulsed rectangular wave voltages whose phases are shifted from each other, and the plurality of current averaging converters are connected in parallel with each other;
A transformer having a plurality of unit transformers for respectively boosting the output voltage of the current averaging converter to a predetermined magnitude, and the plurality of unit transformers are connected in parallel to each other;
a rectifying and smoothing circuit that rectifies and smoothes the output voltage of the transformer;
a DC/AC conversion circuit that converts the output voltage of the rectification and smoothing circuit into a three-phase AC voltage;
Equipped with
input currents of the plurality of current averaging converters are averaged;
The DC/AC conversion circuit is
A DC voltage of a predetermined magnitude is assumed to be a virtual 0 [V], and internal control is performed so that a voltage vector centered on this 0 [V] rotates within a positive voltage range and a predetermined line voltage is output. A three-phase AC voltage is output by controlling the on/off of the switching elements.

A three-phase inverter according to a second aspect of the present invention is the three-phase inverter according to the first aspect, wherein the DC power source is a single positive power source.

The three-phase inverter according to claim 3 is the three-phase inverter according to claim 1 or 2, wherein the current averaging converter includes a switching element connected in series to the primary winding of the unit transformer and a current detecting element. It is characterized by having a resistance.

The three-phase inverter according to claim 4 is the three-phase inverter according to any one of claims 1 to 3, wherein the DC/AC conversion circuit is connected in series to an internal switching element that is controlled to be turned on and off. It is characterized by having an inductance component.

The uninterruptible power supply system according to claim 5 includes a storage battery that is charged with a DC voltage obtained by rectifying an AC power supply voltage, and a storage battery that converts the DC voltage of the storage battery into a three-phase AC voltage and outputs it during a power outage of the AC power supply. A three-phase inverter according to any one of claims 1 to 4 is provided.

According to the three-phase inverter of the present invention, for example, during a power outage, the DC voltage of a storage battery or the like can be converted into a three-phase AC voltage of a predetermined magnitude, and this can be supplied as a power supply voltage to the air conditioning equipment of a computer, etc. It is possible to maintain continuous operation of the computer and compensate for power outages.
Furthermore, with the uninterruptible power supply system equipped with this three-phase inverter, it is possible to continuously supply a three-phase AC voltage to a load using the DC power of the storage battery even during a power outage of the AC power supply.

FIG. 1 is a block diagram showing the overall configuration of a three-phase inverter according to an embodiment of the present invention. (a) is a circuit diagram showing a current averaging converter together with a unit transformer, and (b) is a voltage waveform at point _P1 in (a). (a) is a circuit diagram showing a unit transformer and its secondary side rectifying and smoothing circuit, and (b) is a voltage waveform at point _P2 in (a). FIG. 2 is a configuration diagram of a DC/AC conversion circuit (unit conversion circuit) for one phase. FIG. 2 is a diagram illustrating the principle of outputting three-phase alternating current voltage by a DC/AC conversion circuit. FIG. 2 is a diagram illustrating the principle of outputting three-phase alternating current voltage by a DC/AC conversion circuit. 1 is a configuration diagram of an uninterruptible power supply system equipped with a three-phase inverter according to the present invention. FIG. 4 is a configuration diagram of a power supply device described in Patent Document 4.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of a three-phase inverter according to this embodiment.
In FIG. 1, a DC voltage (for example, 48 [V]) is input from a storage battery or the like to a DC input terminal 1, and noise components are removed from this DC voltage by an input filter 2, and an overcurrent cutoff circuit 3 and an inrush current prevention circuit 4 are input sequentially. The overcurrent cutoff circuit 3 uses a fuse or the like to cut off overcurrent, and the inrush current prevention circuit 4 uses switching elements and The input current is limited by the operation of the current limiting resistor.

The converter 5 connected to the latter stage of the inrush current prevention circuit 4 operates as a so-called chopper, and for example, four converters are connected to each other so as to generate rectangular wave voltages whose phases are shifted from each other from the output voltage of the inrush current prevention circuit 4. The current averaging converter is connected in parallel.

FIG. 2(a) is a circuit diagram showing the current averaging converter 5A together with the unit transformer 6A. Here, a plurality (four) of unit transformers 6A are provided corresponding to the current averaging converters 5A, and in FIG. The unit transformers 6A are collectively referred to as transformer 6.

In FIG. 2A, the current averaging converter 5A has a parallel circuit of two switching elements 51 and a parallel circuit of two current detection resistors 52 connected in series to the primary winding 61 of the unit transformer 6A. It is configured as follows. Here, the reason why two sets of series circuits of the switching element 51 and the current detection resistor 52 are provided is to divide the current and prevent heat generation.In principle, the switching element 51 and the current detection resistor It is sufficient to provide one set of series circuits with 52.
As shown in FIG. 2(b), the switching timing of the pulsed rectangular wave voltages output from the four current averaging converters 5A connected in parallel is controlled so that their phases are shifted by 1/4 period. be done. Note that FIG. 2(b) shows the voltage waveform at point _P1 in FIG. 2(a).

The reason why four 5A current averaging converters are connected in parallel and switched while shifting the phase is to average and reduce the influence of noise superimposed on the input current. To do this, the current flowing through the primary winding 61 of the unit transformer 6A is detected by the current detection resistor 52, and the switching timing is controlled so that the detected values are equal, so that the input current of the current averaging converter 5A is averaged. be converted into

FIG. 3A is a circuit diagram of the unit transformer 6A and the rectifying and smoothing circuit 7 connected to its secondary side.
The unit transformer 6A functions as a step-up transformer, and a rectifying and smoothing circuit 7 including a diode 71 and a capacitor 72 is connected to both ends of its secondary winding 62. The rectifying and smoothing circuit 7 may be provided corresponding to each of the four unit transformers 6A, or the secondary windings 62 of the four unit transformers 6A may be connected in parallel and connected to the input of a single rectifying and smoothing circuit 7. You can also connect them all at once on the side. Alternatively, four circuits each including a unit transformer 6A and a diode 71 may be connected in parallel, and a single capacitor 72 may be connected to the output side of the circuit.

In this embodiment, the primary voltage is stepped up by the unit transformer 6A, and the peak value of the secondary voltage is, for example, a rectangular wave voltage of 385 [V]. FIG. 3(b) shows the voltage waveform at _two points P in FIG. 3(a). Although not shown, the secondary voltage of the four unit transformers 6A has a phase similar to the voltage waveform in FIG. 2(b). are shifted by 1/4 period.

The DC voltage rectified and smoothed by the rectification and smoothing circuit 7 shown in FIG. 3(a) is input to the DC/AC conversion circuit 8 as shown in FIG.
The DC/AC conversion circuit 8 converts a DC voltage of 385 [V] into a three-phase AC voltage with an effective value of 200 [V], for example, by the on/off operation of a switching element, and the unit for one phase is The conversion circuit 8A is shown in FIG. Three phases (U, V, W phases) of this unit conversion circuit 8A are connected in parallel, and the DC/AC conversion circuit 8 of FIG. 1 is constituted by these three-phase unit conversion circuits 8A.

In the unit conversion circuit 8A shown in FIG. 4, a DC voltage of 385 [V] is input to a series circuit consisting of a coil 83, a switching element 81, a coil 84, and a switching element 82. are connected in parallel. Here, the coils 83 and 84 are for slowing down the change in current flowing through the switching elements 81 and 82 in order to perform zero current switching of the switching elements 81 and 82.
Further, free wheel diodes 87 and 88 are connected in antiparallel to the series circuit of the coil 83 and the switching element 81 and the series circuit of the coil 84 and the switching element 82, respectively.

Furthermore, a series circuit consisting of a reactor 89 and a capacitor 90 is connected between the connection point between the freewheeling diodes 87 and 88 and the ground GND, so that one phase of AC voltage is output from the connection point between the two. ing.
The principle of outputting a three-phase AC voltage with an effective value of 200 [V] from the DC/AC conversion circuit 8 in which three phases of the above unit conversion circuits 8A are connected in parallel will be explained later.

Returning to FIG. 1, between the DC/AC conversion circuit 8 and the AC output terminal 11, an overcurrent cutoff circuit 9 consisting of a fuse or the like and an output filter 10, which is a noise filter, are connected.
In addition, 22 is a temperature detection circuit for detecting an overheating state inside the device, 23 and 24 are current/voltage detection circuits, 25 is a current detection circuit, and 21 is a converter based on the detection signal from each detection circuit 22 to 25. 5 and the switching elements of the DC/AC conversion circuit 8, such as a CPU. This control circuit 21 is also used to control a display device, a cooling fan, etc. (not shown), and to transmit each detection signal to the outside, as necessary.

In the above configuration, it is desirable that the converter 5 and the DC/AC conversion circuit 8 be mounted on separate boards. In that case, as the control circuit 21, a CPU that controls the converter 5 and a CPU that controls the DC/AC conversion circuit 8 are provided and mounted on separate boards, and two temperature detection circuits 22 are also provided on each board. It is good to implement each of them.

Next, the principle of outputting a three-phase AC voltage with an effective value of 200 [V] from the DC/AC conversion circuit 8 will be explained with reference to FIGS. 5 and 6.
First, 385 [V], which is the output voltage of the rectifying and smoothing circuit 7 in FIG. 3(a) described above (input voltage of the unit conversion circuit 8A in FIG. It is set by [V]=220×√3.

_In the DC/AC conversion circuit ₈ , as _shown in FIG. Consider rotating voltage vectors that have a phase difference of 120° and a magnitude (radius) of 163 [V] so that the voltage vector is 200 [V]×√2). Here, as a voltage value of 385 [V] or less, which is the input voltage of the unit conversion circuit 8A, and based on the maximum value of the rated output voltage, 200×√3≒345 [V], the radius is 163 [V] The vector circle around which the voltage vector (or phase-to-phase voltage vectors V _uw , V _wv , V _vu ) rotates is from 345 [V] to 19 [V] (=345 [V] - 163 [V] within the positive voltage range). x2).
Furthermore, in this embodiment, 182 [V] as the voltage value at which the center of the vector circle is located is assumed to be a virtual 0 [V] (common return line), and the inter-phase voltages V _uw , V _wv , V _vu are approximately The switching elements 81 and 82 in the DC/AC conversion circuit 8 are turned on and off so that 283 [V] is output.

As a result, as shown in Figures 5 (a) to (c), a voltage vector of magnitude 163 [V] moves inside the vector circle with the voltage 182 [V] corresponding to the virtual 0 [V] as the center. As it rotates, phase-to-phase voltages V _uw , V _wv , and V _vu of approximately 283 [V] are output. Note that FIG. 6 shows the output voltages of each phase (U, V, and W phases).
Conventionally, a voltage vector of 163 [V] is rotated around the actual 0 [V] to output phase-to-phase voltages V _uw , V _wv , V _vu of approximately 283 [V]. In other words, +163 [V] ] and -163 [V] power supplies (positive and negative power supplies), but according to this embodiment, by rotating a voltage vector with a radius of 163 [V] within the positive voltage range, the positive power supply It is possible to output phase-to-phase voltages V _uw , V wv , and V _vu of predetermined magnitudes from the DC/AC conversion circuit 8 by using only the voltages V uw , V _wv , and V vu of predetermined magnitudes.
The three-phase AC voltage thus generated is supplied to various loads such as the electric motor of the air conditioning equipment via the AC output terminal 11 of FIG.

FIG. 7 is a configuration diagram of an uninterruptible power supply system equipped with a three-phase inverter according to the present invention.
In FIG. 7, an AC voltage from an AC power source 300 such as a commercial power source is converted into a DC voltage by a rectifier circuit 400, which charges a storage battery 500 and is supplied to a distribution board 600. In the distribution board 600, by turning on the switch 601, a DC voltage of 48 [V] is input to the DC input terminal 1 of the three-phase inverter 700 according to the present invention. Note that 602 is a switch for supplying DC voltage to other loads.

The configuration of the three-phase inverter 700 is as shown in FIG. 1, and a three-phase AC voltage with an effective value of 200 [V] is generated as an output. Supplied to various loads.
When the AC power supply 300 is healthy, the DC voltage output from the rectifier circuit 400 is supplied to the three-phase inverter 700 via the switch 601, and when the AC power supply 300 is out of order, the DC voltage of the storage battery 500 is supplied to the three-phase inverter 700 via the switch 601. By supplying the three-phase AC voltage to the three-phase inverter 700 through the three-phase inverter 700, a three-phase AC voltage of a predetermined magnitude can be stably supplied to the load 800 even during a power outage.

1: DC input terminal 2: Input filter 3: Overcurrent cutoff circuit 4: Inrush current prevention circuit 5: Converter 5A: Current averaging converter 6: Transformer 6A: Unit transformer 61: Primary winding 62: Secondary winding 7: Rectifier smoothing circuit 71: Diode 72: Capacitor 8: DC/AC conversion circuit 8A: Unit conversion circuit 81, 82: Switching element 83, 84: Coil (inductance component)
85 to 88: Diode 89: Reactor 90: Capacitor 9: Overcurrent cutoff circuit 10: Output filter 11: AC output terminal 21: Control circuit 22: Temperature detection circuit 23, 24: Current/voltage detection circuit 25: Current detection circuit 300 : AC power supply 400: Rectifier circuit 500: Storage battery 600: Distribution board 601, 602: Switch 700: Three-phase inverter 800: Load

Claims (5)

DC power supply and
A converter having a plurality of current averaging converters for respectively converting the DC voltage of the DC power supply into pulsed rectangular wave voltages whose phases are shifted from each other, and the plurality of current averaging converters are connected in parallel with each other;
A transformer having a plurality of unit transformers for respectively boosting the output voltage of the current averaging converter to a predetermined magnitude, and the plurality of unit transformers are connected in parallel to each other;
a rectifying and smoothing circuit that rectifies and smoothes the output voltage of the transformer;
a DC/AC conversion circuit that converts the output voltage of the rectification and smoothing circuit into a three-phase AC voltage;
Equipped with
input currents of the plurality of current averaging converters are averaged;
The DC/AC conversion circuit is
A DC voltage of a predetermined magnitude is assumed to be a virtual 0 [V], and an internal control is performed so that a voltage vector centered on this 0 [V] rotates within a positive voltage range and a predetermined phase-to-phase voltage is output. A three-phase inverter that outputs three-phase AC voltage by controlling on/off of switching elements. In the three-phase inverter according to claim 1,
A three-phase inverter, wherein the DC power source is a single positive power source. In the three-phase inverter according to claim 1 or 2,
A three-phase inverter, wherein the current averaging converter includes a switching element and a current detection resistor connected in series to the primary winding of the unit transformer. In the three-phase inverter according to any one of claims 1 to 3,
The DC/AC conversion circuit is
A three-phase inverter characterized by having an inductance component connected in series to an internal switching element that is controlled on and off. 5. A storage battery that is charged with a DC voltage obtained by rectifying an AC power supply voltage, and a DC voltage of the storage battery that is converted into a three-phase AC voltage and outputted when the AC power supply is interrupted. An uninterruptible power supply system comprising the three-phase inverter described above.

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