JP2022167803A - Power conversion device and control method thereof - Google Patents

Abstract

To achieve miniaturization and suppression of phase voltage imbalance in a power conversion device capable of providing a self-sustaining output in a single-phase three-wire system.SOLUTION: A power conversion device that provides AC output to a single-phase three-wire AC circuit includes a series body of a first capacitor and a second capacitor, provided between two lines of a DC bus and having a midpoint voltage at an interconnection point, a midpoint voltage control unit provided between two lines of the DC bus and controlling the midpoint voltage, and a control unit that performs bipolar pulse width modulation control on the inverter and controls the midpoint voltage control unit, and an AC reactor has a core common to two lines from the output end of the inverter to a first voltage line and a second voltage line, and the control unit controls the inverter such that the line voltage between the first voltage line and the second voltage line reaches a target value, and adjusts the midpoint voltage by controlling the midpoint voltage control unit such that the absolute values of the first phase voltage and the second phase voltage are equal to each other.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a power conversion device and its control method.

A power converter capable of providing a single-phase, three-wire, self-contained output is proposed, for example, in Patent Document 1. The power conversion device of Patent Document 1 includes a two-phase half-bridge inverter and a converter that adjusts the midpoint potential of a DC bus. In this inverter, a series body of a first high-side switching element and a second low-side switching element, and a series body of a third high-side switching element and a fourth low-side switching element are provided between two lines of a DC bus. ,It is connected. The converter that controls the midpoint potential of the DC bus controls the potential at the interconnection point in the series body of a pair of capacitors connected between the two lines of the DC bus so that it becomes midway between the potentials of the two lines of the DC bus. do. This interconnection point is directly connected to the single-phase three-wire neutral wire.

The controller of the inverter controls opening and closing of the four switching elements by unipolar pulse width modulation control (PWM (Pulse Width Modulation) control). By alternately turning on the first switching element and the second switching element, the U-phase voltage between the first voltage line (U line) and the neutral line (O line) of the single-phase three-wire system is output. . By alternately turning on the third switching element and the fourth switching element, the W-phase voltage between the second voltage line (W line) and the neutral line (O line) of the single-phase three-wire system is output. .

JP 2014-87160 A (Fig. 1)

In the power conversion device described above, opening and closing of the first switching element and the fourth switching element and opening and closing of the second switching element and the third switching element are not synchronized with each other. Therefore, the ground potential of the DC bus fluctuates greatly due to switching, and a large amount of common mode noise is generated at the AC output terminal. In order to suppress this common mode noise, an expensive and large filter circuit including a common mode choke coil and a Y capacitor is required. In addition, a reactor for smoothing must be arranged on each of the U line and the W line. Therefore, it is difficult to miniaturize the power converter. Moreover, a large iron loss occurs in each reactor.

On the other hand, when the stand-alone output is supplied to a single-phase three-wire AC load, if there is an imbalance between the U-phase load and the W-phase load, the U-phase voltage and the W-phase voltage will not match. In this case, it is not possible to match the U-phase voltage and the W-phase voltage by controlling the midpoint potential as described above.

An object of the present disclosure is to achieve miniaturization and suppression of phase voltage imbalance in a power conversion device capable of providing self-sustained output in a single-phase three-wire system.

The present disclosure includes the following inventions. However, the present invention is defined by the claims.

(power converter)
Disclosed is a power converter for providing AC output to a single-phase, three-wire AC electrical circuit, comprising:
an inverter;
an AC reactor provided between the inverter and the AC electric circuit;
a DC bus that supplies a DC voltage to the inverter;
a series body of a first capacitor and a second capacitor provided between two lines of the DC bus and having a midpoint voltage at an interconnection point;
a midpoint voltage control unit provided between two lines of the DC bus for controlling the midpoint voltage;
AC side voltage for acquiring a first phase voltage between the first voltage line and the neutral line of the AC line and a second phase voltage between the second voltage line and the neutral line of the AC line a sensor;
a control unit that performs bipolar pulse width modulation control on the inverter and controls the midpoint voltage control unit.
The AC reactor has a core common to two lines from the output end of the inverter to the first voltage line and the second voltage line,
The control unit
controlling the inverter so that the line voltage between the first voltage line and the second voltage line becomes a target value;
The midpoint voltage is adjusted by controlling the midpoint voltage controller so that the absolute values of the first phase voltage and the second phase voltage are equal to each other.

(Control method for power converter)
an inverter, an AC reactor provided between the inverter and a single-phase three-wire AC electric circuit, a DC bus for supplying a DC voltage to the inverter, and an interconnection provided between two wires of the DC bus A series body of a first capacitor and a second capacitor having a point at a midpoint voltage, a midpoint voltage control section provided between two lines of the DC bus for controlling the midpoint voltage, and a bipolar capacitor for the inverter. and a control unit that controls the midpoint voltage control unit, and provides an AC output to the AC electric circuit, a control method by the control unit, ,
controlling the inverter so that the line voltage between the first voltage line and the second voltage line of the AC electric circuit becomes a target value;
The midpoint voltage is adjusted by controlling the midpoint voltage controller so that the absolute values of the first phase voltage and the second phase voltage as viewed from the neutral line of the AC electric circuit are equal to each other.

Advantageous Effects of Invention According to the present disclosure, it is possible to achieve miniaturization and suppression of phase voltage imbalance in a power converter capable of providing a self-sustained output in a single-phase three-wire system.

FIG. 1 is a circuit diagram showing an example of a power converter. FIG. 2 is a control block diagram relating to the control of the inverter and the control of the midpoint voltage control unit, which are executed in the control unit. FIG. 3 is a graph showing an AC output waveform when a resistive load is connected only between the U line and the O line of the AC electric circuit, and no load is applied between the W line and the O line. FIG. 4 is another control block diagram different from FIG. 2 regarding the control for the inverter and the control for the midpoint voltage control section executed in the control section. FIG. 5 is another control block diagram, different from FIGS. 2 and 4, relating to the control of the inverter and the control of the midpoint voltage control section executed in the control section. FIG. 6 is a graph showing an AC output waveform when a half-wave rectification resistive load is connected only between the U and O lines of the AC electric circuit, and no load is applied between the W and O lines. FIG. 7 is a graph showing the AC output waveform and the midpoint control current when no load is placed between the U and O lines of the AC electric circuit and a 1.5 kW resistive load is connected between the W and O lines. FIG. 8 is a graph showing an AC output waveform and a midpoint control current when no load is placed between the U line and the O line of the AC electric circuit and a 3 kW resistive load is connected between the W line and the O line. FIG. 9 is a diagram for explaining signals output from the AC code instruction section of the second example. FIG. 10 is a block diagram showing the internal configuration of the AC code instruction section in the fourth example. FIG. 11 is a diagram for explaining a signal output from the AC code instruction section of the fourth example. FIG. 12 is a graph showing the AC output waveform and the midpoint control current when no load is placed between the U and O lines of the AC electric circuit and a 3 kW resistive load is connected between the W and O lines. FIG. 13 is a block diagram showing the internal configuration of the AC code instruction section in the fifth example. FIG. 14 is a block diagram showing the internal configuration of the AC code instruction section in the sixth example. FIG. 15 is an enlarged graph showing each voltage in FIG. 9A when the line voltage zero cross is detected. FIG. 16 is a block diagram showing the internal configuration of the AC code instruction section in the seventh example.

[Description of Embodiments of the Present Disclosure]
Embodiments of the present disclosure include at least the following as gists thereof.

(1) The power conversion device of the present disclosure is a power conversion device that provides AC output to a single-phase three-wire AC electric circuit, and includes an inverter and an AC reactor provided between the inverter and the AC electric circuit. a DC bus that supplies a DC voltage to the inverter; a series body of a first capacitor and a second capacitor that are provided between two lines of the DC bus and whose interconnection point serves as a midpoint voltage; A midpoint voltage control unit provided between two lines for controlling the midpoint voltage, a first phase voltage between a first voltage line and a neutral line of the AC electric line, and a second phase voltage of the AC electric line AC-side voltage sensor that acquires the second phase voltage between the voltage line and the neutral line; and control that performs bipolar pulse width modulation control on the inverter and controls the midpoint voltage control unit. and The AC reactor has a core common to two lines extending from the output end of the inverter to the first voltage line and the second voltage line, and the control unit controls the first voltage line and the second voltage line. The inverter is controlled so that the line-to-line voltage between the voltage lines becomes a target value, and the midpoint voltage control is performed so that the absolute values of the first phase voltage and the second phase voltage are equal to each other. It is a power conversion device that controls a part to adjust the midpoint voltage.

In such a power conversion device, the inverter does not control the phase voltages during the self-sustained operation, but operates to match the line voltage between the first voltage line and the second voltage line to the target value. The control unit controls the midpoint voltage control unit to adjust the midpoint voltage so that the absolute values of the first phase voltage and the second phase voltage are equal to each other. The midpoint voltage is not limited to the median value, and may deviate to either one of the median values. In addition, the bipolar pulse width modulation control stabilizes the ground voltage of the DC bus, reduces common mode noise, and allows the use of an AC reactor having a common core for two voltage lines. As a result, the size of the noise filter and the AC reactor can be reduced, so that the size of the power converter can be reduced.

(2) In the power conversion device of (1), the control unit controls the midpoint voltage control unit such that the midpoint voltage deviates from the midpoint value of the voltage between the two lines of the DC bus. .
In this case, even if the AC load of the first phase and the AC load of the second phase are uneven, the midpoint voltage deviates from the median value, so that the first phase voltage and the second phase voltage They can be equal to each other in absolute value.

(3) In the power conversion device of (1) or (2), the control unit causes the phase of the first phase voltage to match the phase of the inverted voltage obtained by inverting the second phase voltage by: The midpoint voltage is adjusted by controlling the midpoint voltage controller.
As a result, the midpoint control current can be reduced while adjusting the phase voltage on the AC side, compared to the case where the phase difference between the first phase voltage and the inversion voltage is not adjusted. As a result, it is possible to use a DC reactor with a small current rating, thereby suppressing an increase in the size of the DC reactor, suppressing an increase in cost, and suppressing an increase in loss.

(4) In the power conversion device of (1) or (2), the control unit controls the phase of the first phase voltage or the phase of the inverted voltage obtained by inverting the second phase voltage, and the phase of the line voltage. The midpoint voltage is adjusted by controlling the midpoint voltage controller so that the phases match.
As a result, while adjusting the phase voltage on the AC side, the midpoint control current can be reduced compared to the case where the phase difference between the first phase voltage or the inversion voltage and the line voltage is not adjusted. As a result, it is possible to use a DC reactor with a small current rating, thereby suppressing an increase in the size of the DC reactor, suppressing an increase in cost, and suppressing an increase in loss. In addition, since it is only necessary to calculate one of the phases of the first phase voltage and the second phase voltage, the circuit configuration can be further simplified.

(5) In the power conversion device of (3) above, the control unit applies a positive or negative bias voltage to the midpoint voltage when there is a phase difference between the first phase voltage and the inversion voltage. reducing the phase difference;
By applying a positive or negative bias voltage to the midpoint voltage based on the phases of the first phase voltage and the inversion voltage, the phase difference between the first phase voltage and the inversion voltage is brought close to zero (or made zero). can be adjusted.

(6) In the power conversion device of (4) above, the control unit causes the midpoint voltage to be positive or negative when there is a phase difference between the first phase voltage or the inversion voltage and the line voltage. is applied to reduce the phase difference.
By applying a positive or negative bias voltage to the midpoint voltage based on the phase of the first phase voltage or the inversion voltage and the phase of the line voltage, the first phase voltage or the inversion voltage and the line voltage The phase difference can be adjusted to near (or zero) zero.

(7) In the power conversion device of (3) or (4), the control unit controls the first phase voltage when detecting the zero crossing of the line voltage and the first phase voltage when detecting the zero crossing of the line voltage. A positive or negative bias voltage is applied to the midpoint voltage to reduce the phase difference between the first phase voltage and the inversion voltage based on at least one of the two phase voltages.
As a result, the bias voltage can be applied based on each voltage when the zero crossing of the line voltage is detected, instead of the phases of the first phase voltage and the second phase voltage. It can be simplified.

(8) In the power conversion device of (1) or (2), the control unit positively or negatively biases the midpoint voltage when there is a difference between the first phase voltage and the second phase voltage. A voltage is applied to reduce the difference.
Even if the AC load of the first phase and the AC load of the second phase are uneven, the first phase The voltage and the second phase voltage can be adjusted to be equal to each other in absolute value.

(9) In the power converter according to any one of (5) to (8), the bias voltage is a rectangular wave, a sine wave, or a triangular wave.

(10) In the power converter of (1) or (2), the first phase voltage and the second phase voltage are instantaneous values or effective values.
Both instantaneous values and effective values can be used as the first phase voltage and the second phase voltage. If the instantaneous value is used, the control response is quick, but the control is slightly sensitive. When the effective value is used, the control response is slower than the instantaneous value, but it becomes a stable control that does not become hypersensitive.

(11) In the power conversion device according to any one of (1) to (10), the AC reactors are additively connected.
In this case, the size of the AC reactor can be reduced.

(12) From the viewpoint of a control method, an inverter, an AC reactor provided between the inverter and a single-phase three-wire AC electric circuit, a DC bus that supplies a DC voltage to the inverter, and the DC A series body of a first capacitor and a second capacitor provided between two lines of the bus and having a midpoint voltage at an interconnection point; and a midpoint provided between the two lines of the DC bus and controlling the midpoint voltage. A power converter that provides an AC output to the AC circuit, comprising a voltage control unit and a control unit that performs bipolar pulse width modulation control on the inverter and controls the midpoint voltage control unit 3. The control method by the control unit, wherein the inverter is controlled so that the line voltage between the first voltage line and the second voltage line of the AC electric circuit becomes a target value, and A control method for a power converter, comprising: controlling the midpoint voltage control section to adjust the midpoint voltage so that the absolute values of the first phase voltage and the second phase voltage seen from the sex line are equal to each other. is.

According to such a control method for a power converter, during self-sustained operation, the inverter does not control the phase voltage and operates to match the line voltage between the first voltage line and the second voltage line to the target value. . As a control method, the midpoint voltage controller is controlled to adjust the midpoint voltage so that the absolute values of the first phase voltage and the second phase voltage are equal to each other. The midpoint voltage is not limited to the median value, and may deviate to either one of the median values. In addition, the bipolar pulse width modulation control stabilizes the ground voltage of the DC bus and reduces common mode noise.

[Details of the embodiment of the present disclosure]
Hereinafter, specific examples of the power conversion device and the control method thereof according to the present disclosure will be described with reference to the drawings.

<<Configuration of Power Converter>>
FIG. 1 is a circuit diagram showing an example of a power converter. The power converter 100 is provided between the DC power supply 20 and the AC electric circuit 31 . The power conversion device 100 is capable of grid-connected operation with a commercial power system, or self-sustained operation in a state of being disconnected from the commercial power system. In the present disclosure, self-sustained operation will be described.

The AC electric line 31 is of a single-phase three-wire type, and has voltage lines U and W and a grounded neutral line O. A U-phase load 32u is connected to the U-phase of the AC electric circuit 31 (between the U line and the O line). A W-phase load 32w is connected to the W-phase of the AC electric circuit 31 (between the W line and the O line). 101 V is applied between the U line and the O line, 101 V is applied between the W line and the O line in the opposite phase to the U phase, and 202 V is applied between the U line and the W line.

The power conversion device 100 includes a DC/DC converter 1 connected to a DC power supply 20, a DC bus 2 on the high voltage side of the DC/DC converter, a smoothing capacitor 3 connected between two lines of the DC bus 2, A midpoint voltage controller 4 connected between two lines of the DC bus 2, a series body 5 of DC bus capacitors 5H and 5L connected between the two lines of the DC bus 2, and connected to both ends of the DC bus capacitor 5H. a voltage sensor 6H connected to both ends of a DC bus capacitor 5L, a voltage sensor 6L connected to both ends of the DC bus capacitor 5L, an inverter 7 connected between two lines of the DC bus 2, an AC reactor 8, AC side capacitors 9u and 9w, It includes voltage sensors 10u and 10w and a controller 11 . The DC side voltage sensor is composed of a voltage sensor that detects the voltage between two lines of the DC bus 2 and a voltage sensor that detects the voltage across either one of the DC bus capacitors 5H and 5L. good too.

Voltage sensor 6H detects voltage _VH across DC bus capacitor 5H and sends a detection signal to controller 11 . The voltage sensor 6L detects the voltage _VL across the DC bus capacitor 5L and sends a detection signal to the controller 11. FIG. DC bus capacitors 5H and 5L have the same capacitance.
The voltage sensor 10 u detects the voltage V _uo across the AC side capacitor 9 u and sends a detection signal to the control section 11 . The voltage sensor 10 w detects the voltage _Vwo across the AC side capacitor 9 w and sends a detection signal to the controller 11 . The AC side capacitors 9u and 9w have the same capacitance.

The DC/DC converter 1 is configured by connecting a DC reactor 12, a high-side switching element Q7, and a low-side switching element Q8 as shown. A diode d7 is connected in anti-parallel with the switching element Q7, and a diode d8 is connected in anti-parallel with the switching element Q8. This DC/DC converter 1 is a booster circuit, and boosts the voltage of the DC power supply 20 to the voltage required for the DC bus 2 . The DC/DC converter 1 is controlled by the controller 11 .

Note that the DC/DC converter 1 can be omitted if the voltage of the DC power supply 20 is sufficiently high. Furthermore, if the voltage of the DC power supply 20 is too high, a step-down circuit may be adopted as the DC/DC converter. The voltage between the two lines of DC bus 2 is smoothed by smoothing capacitor 3 .

The midpoint voltage control unit 4 is a DC/DC converter, and is configured by connecting a high-side switching element Q5, a low-side switching element Q6, and a DC reactor 13 as shown. DC reactor 13 is connected to midpoint M of series body 5, which is the interconnection point of DC bus capacitors 5H and 5L. A diode d5 is connected in anti-parallel with the switching element Q5, and a diode d6 is connected in anti-parallel with the switching element Q6. The midpoint voltage controller 4 is controlled by the controller 11 .

It is the voltage _VL that the midpoint voltage controller 4 is trying to control directly. Assuming that the voltage between the two lines of the DC bus 2 is V _B , the voltage V _H is (V _B −V _L ). These voltages are
V _L =V _H =(V _B /2), or
_VL >( _VB /2)> _VH , or _VL <( _VB /2)< _VH
It may be. Since the middle point M of the series body 5, which is the interconnection point of the DC bus capacitors 5H and 5L, is directly connected to the O line on the AC side, the "potential" is the ground potential.

The inverter 7 has four switching elements Q1, Q2, Q3, Q4. Diodes d1, d2, d3 and d4 are connected in anti-parallel to the switching elements Q1, Q2, Q3 and Q4, respectively. The inverter 7 outputs 202V between the U line and the W line of the AC electric circuit 31 through a filter circuit including the AC reactor 8 and the AC side capacitors 9u and 9w. The AC reactor 8 for smoothing the output of the inverter 7 has U-wire and W-wire windings wound around a common core, and has a summing connection that reinforces the magnetic flux with respect to the normal current.

The voltage _Vuw between the U line and the W line of the AC electric circuit 31 is the difference between the voltage _Vuo detected by the voltage sensor 10u and the voltage _Vwo detected by the voltage sensor 10w. A voltage sensor may be provided to directly detect the voltage _Vuw between the U line and the W line. A voltage sensor may be provided to detect the voltage V _uw between the U line and the W line instead of either one of the voltages V _uo and V _wo . In short, the voltages V _uw , V _uo , and V _wo may be obtained as long as they can be detected or calculated.

The control unit 11 includes, for example, a computer, and the computer executes software (computer program) to implement necessary control functions. The software is stored in a storage device (not shown) of control unit 11 .

The switching elements Q1 to Q8 illustrated in FIG. 1 are all IGBTs (Insulated Gate Bipolar Transistors), but MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) can also be used instead.

<<Control of Power Converter>>
Next, the control (control method) for the inverter 7 and the midpoint voltage control section 4 in the power converter 100 configured as described above will be described.

(first example)
FIG. 2 is a control block diagram relating to the control of the inverter 7 and the control of the midpoint voltage control unit 4 executed in the control unit 11. As shown in FIG. Such control can be implemented entirely by software, or partially implemented by hardware. In FIG. 2, the target value of the AC voltage (instantaneous value) is indicated by the _Vuw voltage reference indicating section B1. A comparator B2 obtains a deviation between this target value and the actually detected voltage _Vuw between the U line and the W line. The deviation is added to the target value through the proportional integral calculator B3 (adder B4). Based on the corrected voltage value obtained by the addition, the voltage command signal generator B5 generates a voltage command signal. The voltage command signal is compared with a carrier signal (triangular wave or sawtooth wave) output from the carrier signal generating section B6 in the PWM control section B7 to generate a PWM control signal.

This PWM control signal is generated from a common voltage command signal and carrier signal, thereby controlling switching elements Q1, Q2, Q3 and Q4. This control is a bipolar PWM type control in which opening and closing of the pair of switching elements Q1 and Q4 are synchronized, and complementarily, opening and closing of the pair of switching elements Q2 and Q3 are synchronized.

As a result, the inverter 7 operates so that the voltage _Vuw between the U line and the W line matches the target value. Bipolar PWM control stabilizes the ground potential of the DC bus. Therefore, common mode noise can be reduced. In addition, since the cores of the reactors for the U line and the W line can be made common for additive connection, the AC reactor 8 (FIG. 1) can be integrated into one to be miniaturized.

For reference, in the power converter of Patent Document 1, the pair of switching elements Q1 and Q2 and the pair of _Q3 and _Q4 are provided with When different voltage command signals are applied, the opening and closing of the pair of switching elements Q1 and Q4 in the diagonal direction of the bridge and the opening and closing of the pair of switching elements Q2 and Q3 are not synchronized. Therefore, the ground potential of the DC bus fluctuates due to switching, and a large amount of current flows through the AC reactor. Further, if the cores of the AC reactor of the U line and the AC reactor of the W line are made common and connected together, control becomes impossible. Therefore, it is not possible to reduce the size of the AC reactor by integrating it into one.

Next, in FIG. 2, the adder B8 adds the U-phase voltage V _uo detected between the U line and the O line and the W-phase voltage V _wo detected between the W line and the O line. Since the U-phase voltage V _uo and the W-phase voltage V _wo have opposite phases and opposite signs, the addition result is 0, or the difference between the absolute values is the sign of the larger absolute value. is the value with This value becomes a correction value added by an adder B11 to the midpoint voltage reference designated by the midpoint voltage reference designation section B10 through the proportional integral calculation section B9. The midpoint voltage reference is, for example, the midpoint value ( _VB /2), where _VB is the voltage between two lines of the DC bus.

The addition result in the adder B11 is compared with the voltage _VL in the comparator B12. The deviation of the comparison result, that is, deviation from _VL (bias voltage) is sent to the voltage command signal generator B14 via the proportional integral calculator B13. Then, a voltage command signal is generated in the voltage command signal generator B14. The voltage command signal is compared with a carrier signal (triangular wave or sawtooth wave) output from the carrier signal generator B15 in the PWM controller B16, and becomes a PWM control signal for the switching elements Q5 and Q6.

Thus, if there is a difference between the U-phase voltage _Vuo and the W-phase voltage _Vwo , the midpoint voltage is corrected to deviate from the midpoint value according to the difference. If the midpoint voltage control unit 4 basically controls the voltages V _L and V _H to be equal to each other, the U-phase voltage V _uo and the W-phase voltage V _wo are generally the same in amplitude and out of phase. An inverted voltage waveform is obtained. However, when there is a large difference in the capacity of the loads connected between the U-line and the O-line and between the W-line and the O-line, the U-phase voltages _{V uo} and _W The amplitudes of the phase voltages _Vwo do not match each other.

Therefore, as described above, a correction value is added to the midpoint voltage reference so that the sum of the U-phase voltage _Vuo and the W-phase voltage _Vwo is always zero.
In addition, a necessary correction value may be given so that the U-phase voltage V _uo or the W-phase voltage V _wo respectively match the control target value.
In short, the U-phase voltage V _uo and the W-phase voltage V _wo should be controlled to be equal to each other in terms of absolute values.

FIG. 3 is a graph showing an AC output waveform when a resistive load is connected only between the U line and the O line of the AC electric circuit, and no load is applied between the W line and the O line. The numerical value on the horizontal axis is time [seconds], and the numerical value on the vertical axis is voltage [V]. The frequency of alternating current is 50 Hz. The AC waveform with the larger amplitude is the voltage _Vuw between the U and W lines. The two AC waveforms having smaller amplitudes and having phases inverted to each other are the U-phase voltage V _uo and the W-phase voltage V _wo . The DC waveform is the midpoint voltage _VL of the DC bus. From this result, it can be seen that the line voltage V _uw , the U-phase voltage V _uo , and the W-phase voltage V _wo that match the target values are obtained even if the loads are uneven. In addition, the midpoint voltage _VL fluctuates slightly every moment, and the phase voltage adjustment on the AC side is performed by biasing the midpoint voltage.

(Second example)
FIG. 4 is another control block diagram different from FIG. The difference from FIG. 2 is the middle point voltage correction section P1 on the upper left. In the upper left midpoint voltage corrector P1, the effective value calculator B20 calculates the effective value based on the U-phase voltage _Vuo . Similarly, the effective value calculator B21 calculates the effective value based on the W-phase voltage _Vwo .

The U-phase effective value and the W-phase effective value are compared with each other in a comparator B22. The difference obtained by the comparison is subjected to proportional integration by the proportional integral calculator B23, and then multiplied by the sign indicated by the AC sign indicating unit B24 by the multiplier B25. Since this multiplication has the same sign as the effective value for both the U phase and the W phase, it is necessary to decide whether to add or subtract the correction value according to the deviation of the effective value of the U phase and W phase. means. The correction value processed by the multiplier B25 is added to the midpoint voltage reference indicated by the midpoint voltage reference indicating section B26 (adder B27). The midpoint voltage reference is, for example, the midpoint value ( _VB /2), where _VB is the voltage between two lines of the DC bus.

The addition result in the adder B27 is compared with the voltage _VL in the comparator B28. The deviation of the comparison result, that is, the deviation from _VL (bias voltage) is sent to the voltage command signal generator B14 via the proportional integral calculator B29. The subsequent processing and the control block diagram regarding the control of the inverter 7 are the same as in FIG.

When power is supplied to the load connected between the U line and the O line, current flows from the DC bus capacitor 5H between the plus side electric path of the DC bus 2 and the midpoint M during the period when the U-phase voltage is positive. During the period when the U-phase voltage is negative, a current flows from the DC bus capacitor 5L between the midpoint M and the negative electric path of the DC bus 2. Therefore, when the effective value of the U-phase voltage V _uo is smaller than the effective value of the W-phase voltage V _wo , V _L >V _H in the negative period so that V _H >V _L in the positive period. If the DC bus midpoint voltage V _L is controlled such that the effective values of the U-phase voltage V _uo and W-phase voltage V _wo match each other.

For reference, in the power conversion device described in the above-mentioned Patent Document 1, the midpoint voltage control is only performed so that the voltages _VL and _VH are equal, and the voltages are biased (bias voltage is given) is not performed.

(Third example)
FIG. 5 is another control block diagram different from FIGS. The difference from FIG. 2 is the middle point voltage correction section P2 on the upper left. In the upper left midpoint voltage corrector P2, the effective value calculator B20 calculates the effective value based on the U-phase voltage _Vuo . Similarly, the effective value calculator B21 calculates the effective value based on the W-phase voltage _Vwo .

The U-phase effective value and the W-phase effective value are compared with each other in a comparator B22. The difference obtained by the comparison is subjected to proportional integration by the proportional integral calculator B23, and then multiplied by the sign indicated by the AC sign indicating unit B24 by the multiplier B25. Since this multiplication has the same sign as the effective value for both the U phase and the W phase, it is necessary to decide whether to add or subtract the correction value according to the deviation of the effective value of the U phase and W phase. means. The correction value processed by the multiplier B25 is added to the midpoint voltage reference indicated by the midpoint voltage reference indicating section B26 (adder B27). The midpoint voltage reference is, for example, the midpoint value ( _VB /2), where _VB is the voltage between two lines of the DC bus.

The addition result of the adder B27 is sent to the voltage command signal generator B14. Subsequent processing and control block diagrams relating to the control of the inverter 7 are the same as those in FIGS.

In the case of the third example, as in the second example, when power is supplied to the load connected between the U line and the O line, during the period when the U-phase voltage is positive, the plus side electric path of the DC bus 2 and the midpoint A current flows from the DC bus capacitor 5H between M. During the period when the U-phase voltage is negative, a current flows from the DC bus capacitor 5L between the midpoint M and the negative electric path of the DC bus 2. Therefore, when the effective value of the U-phase voltage V _uo is smaller than the effective value of the W-phase voltage V _wo , V _L >V _H in the negative period so that V _H >V _L in the positive period. If the DC bus midpoint voltage V _L is controlled such that the effective values of the U-phase voltage V _uo and W-phase voltage V _wo match each other.

FIG. 6 is a graph showing an AC output waveform when a half-wave rectification resistive load is connected only between the U and O lines of the AC electric circuit, and no load is applied between the W and O lines. The numerical value on the horizontal axis is time [seconds], and the numerical value on the vertical axis is voltage [V]. The frequency of alternating current is 50 Hz. The midpoint voltage control is according to the third example. The AC waveform with the larger amplitude is the voltage _Vuw between the U and W lines. The two AC waveforms having smaller amplitudes and having phases inverted to each other are the U-phase voltage V _uo and the W-phase voltage V _wo . The DC waveform is the midpoint voltage _VL of the DC bus. From this result, it can be seen that the line voltage V _uw , the U-phase voltage V _uo , and the W-phase voltage V _wo that match the target values are obtained even if the loads are uneven. In addition, the midpoint voltage _VL fluctuates slightly every moment, and the phase voltage adjustment on the AC side is performed by biasing the midpoint voltage.

(Fourth example)
In the second example described above, in order to match the effective value of the U-phase voltage V _uo and the effective value of the W-phase voltage V _wo with each other, a current (hereinafter referred to as “midpoint (referred to as the control current I _L ). The current flows from the DC bus capacitor 5H or the DC bus capacitor 5L to control the DC bus midpoint voltage _VL .

Here, in the AC electric circuit, the greater the degree of imbalance between the load connected between the U line and the O line and the load connected between the W line and the O line, the more the effective value of the U-phase voltage V _uo . and the effective value of the W-phase voltage _Vwo , the midpoint control current _IL tends to increase.

7 and 8 are graphs showing the AC output waveform (a) and the midpoint control current (b) in the power converter 100 of the second example. FIG. 7 is a graph when no load is applied between the U line and the O line of the AC electric circuit, and a 1.5 kW resistance load is connected between the W line and the O line. FIG. 8 is a graph when no load is applied between the U line and the O line of the AC electric circuit, and a 3 kW resistance load is connected between the W line and the O line. That is, FIG. 8 is a graph showing a state in which the degree of load imbalance is greater than that in FIG.

In the graphs of FIGS. 7 and 8, the numerical values on the horizontal axis are time [seconds], the numerical values on the vertical axis in (a) are voltage [V], and the numerical values on the vertical axis in (b) are current [A]. . The frequency of alternating current is 50 Hz. The AC waveform with the larger amplitude is the voltage _Vuw between the U and W lines. The two AC waveforms with smaller amplitudes are the U-phase voltage V _uo and the inverted voltage V _ow (=−V _wo ) obtained by inverting the W-phase voltage V _wo . 3 and 6 _show the U-phase voltage V _uo and the W-phase voltage V _wo , but from FIG. 7 _onwards , the inversion voltage V _ow .

The effective value of the midpoint control current IL is _31.1 A in FIG. 7(b) (load difference of 1.5 kW), whereas it is 62.1 A in FIG. 8(b) (load difference of 3 kW). It is 0 A, and the midpoint control current IL increases as the degree of load _imbalance increases.

In order to flow more _midpoint control current IL, a DC reactor 13 with a higher current rating is required, which causes problems such as an increase in the size and cost of the DC reactor 13 . In addition, as the current rating of the DC reactor 13 increases, the loss in the DC reactor 13 increases.

Based on the above, the inventors found that when the load imbalance between the U line and the O line and between the W line and the O line is large, the absolute values of the U-phase voltage V _uo and the W-phase voltage V _wo are equalized. The phase difference between the U-phase voltage V _uo and the inversion voltage _{V ow} was focused on in order to invent a method of suppressing the increase in the midpoint control current IL while compensating for it.

Here, in FIG. 7A, the phase difference between the U-phase voltage _Vuo and the inversion voltage _Vow is _4.34 °, whereas in FIG _. The phase difference is 8.55°. Thus, the phase difference between the U-phase voltage V _uo and the inversion voltage V _ow increases as the degree of load imbalance increases.

In the second example described above, midpoint control is performed so that the effective values of the U-phase voltage _Vuo and the W-phase voltage _Vwo match each _{other .} are not controlled to match.

FIG. 9 is a diagram for explaining the signal output from the AC code instructing section B24 of the second example. FIG. 9(a) is a graph showing an enlarged part of FIG. 8(a), and FIG. 9(b) is a graph showing a signal output from the AC code indicator B24 of the second example. FIG. 9A exaggerates the phase difference between the U-phase voltage V _uo and the inverted voltage V _ow of the W-phase voltage V _wo for the sake of explanation.

In the case of the second example, the AC sign indicator B24 outputs +1 or -1 according to the sign of the line voltage _Vuw . That is, the output phase of the AC sign indicator B24 matches the phase of the line voltage _Vuw . In such a case, although the effective values of the U-phase voltage _Vuo and the W-phase voltage _Vwo can be made to match each other, a phase difference may occur between the U-phase voltage _Vuo and the inversion voltage _Vow .

Therefore, in this example, the U-phase voltage _Vuo and the W-phase voltage _Vwo are equal in absolute value, and the midpoint is set so that the phase of the U-phase voltage _Vuo and the phase of the inversion voltage _Vow match each other. The voltage controller 4 is controlled to adjust the midpoint voltage _VL . That is, the midpoint voltage controller 4 is controlled to adjust the midpoint voltage _VL so that the phase of the U-phase voltage _Vuo and the phase of the W-phase voltage _Vwo are 180°. As a result, while adjusting the phase voltage on the AC side, the midpoint control current _IL is reduced compared to the case where the phase difference between the U-phase voltage _Vuo and the inversion voltage _Vow is not adjusted.

FIG. 10 is a control block diagram showing the internal configuration of the AC code instructing section B241 in this example. The power conversion apparatus 10 of this example differs from the second example in configuration in that it includes an AC code instruction section B241 in place of the AC code instruction section B24 of the second example (FIG. 4), and the other points are common.

In the AC sign instruction section B241, the phase calculation section B30 calculates the phase of the U-phase voltage _Vuo based on the U-phase voltage _Vuo . The phase calculator B31 calculates the phase of the inversion voltage _{Vow based on the W-phase voltage Vwo (} that is, the phase obtained by inverting the phase of the W-phase voltage _Vwo by 180°). The phase calculator B32 calculates the phase of the line voltage _Vuw based on the line voltage _Vuw . The phase calculators B30 to B32 may be, for example, zero cross detection circuits or phase locked loop (PLL) circuits.

The phase of U phase and the phase of W phase are compared with each other in comparator B33. The deviation obtained by the comparison is added to the phase of the line voltage _Vuw through proportional integration by the proportional integration calculation section B34 (adder B35). The AC code instructing section B241 outputs the phase corrected by the addition to the multiplier B25 as a phase output φ. The multiplier B25 multiplies the difference between the effective values of the respective phases passed through the comparator B22 and the proportional-integral calculator B23 by the value indicated by the AC sign indicating section B241.

That is, the control unit 11 applies a positive or negative bias voltage to the midpoint voltage V _L based on the phase of the U-phase voltage V _uo and the phase of the W-phase voltage V _wo to obtain the U-phase voltage V _uo and the phase difference of the W-phase voltage _Vwo . In this manner, the midpoint voltage _VL is not necessarily set to an intermediate value, but biased by application of the bias voltage, so that even if the U-phase AC load and the W-phase AC load are unequal, , the U-phase voltage _Vuo and the W-phase voltage _Vwo can be adjusted to be equal to each other in absolute value. Furthermore, based on the phase of the U-phase voltage _Vuo and the phase of the W-phase voltage _Vwo , by applying a positive or negative bias voltage to the midpoint voltage V _L , the U-phase voltage V _uo and the inversion voltage V _wo can be adjusted so that the phase difference between .

FIG. 11 is a diagram for explaining the signal output from the AC code instructing section B241. FIG. 11A is a graph showing an enlarged AC output waveform in the power conversion device 100 of this example, and FIGS. It is a graph showing.

The AC sign instruction section B241 performs a phase output φ by performing feedback control so that the difference between the phases of the U phase and the W phase becomes 0 by the proportional integral calculation section B34. Since the phase output φ is obtained according to the difference between the phases of the U phase and the W phase, it does not always match the phase of the line voltage _Vuw . The phase output φ is, for example, a rectangular wave, as shown in FIG. 11(b). When the phase output φ is a square wave, the phase output φ has the following values.

The phase output φ may be a sine wave (sin φ) as shown in FIG. 11(c). Also, the phase output φ may be a triangular wave as shown in FIG. 11(d). When the phase output φ is a triangular wave, the phase output φ has the following values.

As shown in FIG. 11(a), by matching the phases of the U-phase voltage _Vuo and the inversion voltage Vow by the AC sign instructing section _B241 , the midpoint control current _IL can be reduced.

FIG. 12 is a graph showing the AC output waveform (a) and the midpoint control current (b) in the power converter 100 of this example. FIG. 12 is a graph when no load is applied between the U line and the O line of the AC electric circuit, and a 3 kW resistance load is connected between the W line and the O line. The numerical value on the horizontal axis is time [seconds], the numerical value on the vertical axis in (a) is voltage [V], and the numerical value on the vertical axis in (b) is current [A]. The frequency of alternating current is 50 Hz. The AC waveform with the larger amplitude is the voltage _Vuw between the U and W lines. The two AC waveforms with smaller amplitudes are the U-phase voltage _Vuo and the W-phase inversion voltage _Vow .

As shown in FIG. 12(a), the phase difference between the U-phase voltage V _uo and the inverted voltage V _ow (that is, the phase difference obtained by inverting the phase of the U-phase voltage V _uo and the phase of the W-phase voltage V _wo by 180°) ) is almost 0. The effective value of the midpoint control current I _L in FIG. 12(b) is 39.7 A, and the value (62.0 A) in FIG. is lower than

As described above, the midpoint control current _IL can be reduced by adjusting the midpoint voltage _VL so that the phases of the U-phase voltage _Vuo and the inversion voltage _Vow are approximately the same. As a result, a reactor with a small current rating can be used as the DC reactor 13, so that it is possible to suppress an increase in the size of the DC reactor 13, suppress an increase in cost, and suppress an increase in loss. .

(Fifth example)
FIG. 13 is a control block diagram showing the internal configuration of the AC code instructing section B242 in this example. The power conversion device 100 of this example differs from the fourth example in terms of configuration in that it includes an AC code instruction section B242 instead of the AC code instruction section B241 of the fourth example (FIG. 10), and other points are common.

In the AC sign instruction unit B241, three phase calculation units B30 to B32 calculate the phases of the U-phase voltage V _uo , the W-phase voltage V _wo and the line voltage V _uw . On the other hand, in the AC sign instruction unit B242, the phase of the line voltage _Vuw is an intermediate value between the phase of the U-phase voltage _Vuo and the phase of the W-phase voltage _Vwo . The difference between the phase of _Vuo and the phase of the line voltage _Vuw is controlled to be zero. Since the phase of the W-phase voltage _Vwo is interlocked with the phase of the U-phase voltage _Vuo , the phase of the inversion voltage _Vow is also made to match the phase of the line voltage _Vuw by this control.

In the AC sign indicator B242, the comparator B33 compares the phase of the U-phase voltage _Vuo calculated by the phase calculator B30 and the phase of the line voltage _Vuw calculated by the phase calculator B32 to determine the deviation. Calculate The deviation is added to the phase of the line voltage _Vuw through proportional integration by the proportional integral calculation section B34 (adder B35). The AC code instructing section B242 outputs the phase corrected by the addition to the multiplier B25 as a phase output φ.

That is, the control unit 11 applies a positive or negative bias voltage to the midpoint voltage V _L based on the phase of the U-phase voltage V _uo and the phase of the line voltage V _uw to obtain the U-phase voltage V _uo and the phase difference of the line voltage _Vuw . In this manner, the midpoint voltage _VL is not necessarily set to an intermediate value, but biased by applying a bias voltage. The phase voltage _Vuo and the W-phase voltage _Vwo can be adjusted to be equal to each other in absolute value. Furthermore, based on the phase of the U-phase voltage _Vuo and the phase of the W-phase voltage _Vwo , by applying a positive or negative bias voltage to the midpoint voltage V _L , the U-phase voltage V _uo and the inversion voltage V _wo can be adjusted to bring the phase difference of .

According to the AC code instruction section B242, one phase calculation section B31 can be omitted compared to the AC code instruction section B241, so that the circuit configuration can be further simplified.

Note that the AC sign instructing section B242 may perform control so that the difference between the phase of the inversion voltage _{Vow and the phase of the line voltage Vuw is} zero. In this case, the comparator B33 compares the phase of the inversion voltage _{Vow calculated by the phase calculator B31 and the phase of the line voltage Vuw calculated} by the phase calculator B32 to calculate the deviation.

That is, in this case, the control unit 11 applies a positive or negative bias voltage to the midpoint voltage V _L based on the phase of the inversion voltage V _ow and the phase of the line voltage V _uw to obtain the inversion voltage V _ow and the line voltage _Vuw . Since the phase of the U-phase voltage _Vuo is interlocked with the phase of the inversion voltage _Vow , the phase of the U-phase voltage _Vuo is also made to match the phase of the line voltage _Vuw by this control.

(6th example)
FIG. 14 is a control block diagram showing the internal configuration of the AC code instructing section B243 in this example. The power conversion device 100 of this example differs from the fourth example in terms of configuration in that it includes an AC code instruction section B243 in place of the AC code instruction section B241 of the fourth example (FIG. 10), and other points are common.

FIG. 15 is an enlarged graph showing each voltage at the time of zero-cross detection of the line voltage _Vuw in FIG. 9(a). The instantaneous value of the U-phase voltage _Vuo at the time when the instantaneous value of the line voltage _Vuw becomes zero (that is, when the zero cross is detected) is referred to as "instantaneous value X1". Also, the instantaneous value of the inverted voltage _Vow of the W-phase voltage _Vwo at the time of zero-cross detection of the line voltage _Vuw is referred to as "instantaneous value X2". Here, the instantaneous value X1 is a pair of positive and negative values of the instantaneous value X2 (X1=-X2). That is, the instantaneous value X1 of the U-phase voltage _Vuo and the instantaneous value (-X2) of the W-phase voltage _Vwo at the time of zero-cross detection of the line voltage _Vuw are equal.

In this example, by controlling the instantaneous value X1 of the U-phase voltage _Vuo when the zero crossing of the line voltage _Vuw is detected to be zero, the phase of the U-phase voltage _Vuo and the phase of the line voltage _Vuw match. Since the phase of the W-phase voltage _Vwo is interlocked with the phase of the U-phase voltage _Vuo , the phase of the inversion voltage _Vow is also made to match the phase of the line voltage _Vuw by this control.

In the AC sign instruction section B243, the instantaneous value calculation section B36 calculates the instantaneous value X1 of the U-phase voltage _Vuo when the line voltage _Vuw detects the zero crossing based on the U-phase voltage _Vuo and the line voltage _Vuw . do. The comparator B33 compares the instantaneous value X1 calculated by the instantaneous value calculator B36 with zero to calculate a deviation. The deviation is added to the phase of the line voltage _Vuw through proportional integration by the proportional integral calculation section B34 (adder B35). The AC code instructing section B243 outputs the phase corrected by the addition to the multiplier B25 as a phase output φ.

The phase output φ controls the instantaneous value X1 to be zero. According to the AC code instruction section B243, the two phase calculation sections B30 and B31 can be omitted compared to the AC code instruction section B241, so that the circuit configuration can be further simplified.

Note that the AC sign instruction unit B243 controls so that the instantaneous value of the W-phase voltage _Vwo when the line voltage _Vuw detects the zero crossing (the instantaneous value is equal to the instantaneous value X1 as described above) becomes zero. may In this case, the instantaneous value calculator B36 calculates the instantaneous value of the W-phase voltage _Vwo at the time of detecting the zero crossing of the line voltage _Vuw based on the W-phase voltage _Vwo and the line voltage _Vuw .

That is, the control unit 11 controls the instantaneous value X1 (the voltage of the U-phase voltage V _uo when the zero cross of the line voltage V _uw is detected) or the instantaneous value −X2 (the W-phase voltage V _wo when the zero cross of the line voltage V _uw is detected). ), the phase difference between the U-phase voltage V _uo and the inversion voltage V _ow is reduced by applying a positive or negative bias voltage to the midpoint voltage V _L .

(Seventh example)
FIG. 16 is a control block diagram showing the internal configuration of the AC code instructing section B244 in this example. The power conversion device 100 of this example differs in configuration from the sixth example in that it includes an AC code indication section B244 in place of the AC code indication section B243 of the sixth example (FIG. 14), and other points are common.

In the sixth example, the instantaneous value X1 is controlled to be zero. On the other hand, in this example, the difference between the instantaneous value X1 of the U-phase voltage _Vuo when the zero crossing of the line voltage _Vuw is detected and the instantaneous value X2 of the inversion voltage _Vow when the zero crossing of the line voltage _Vuw is detected is controlled to be zero. That is, control is performed so that the instantaneous value X1 and the instantaneous value X2 are equal to each other.

In the AC sign instruction section _B244 , the instantaneous value calculation section B37 calculates the instantaneous value X2 of the inversion voltage _{Vow when the line voltage Vuw detects} the zero crossing based on the inversion voltage Vow and the line voltage _Vuw . The comparator B33 compares the instantaneous value X1 calculated by the instantaneous value calculator B36 and the instantaneous value X2 calculated by the instantaneous value calculator B37 to calculate a deviation. The deviation is added to the phase of the line voltage _Vuw through proportional integration by the proportional integral calculation section B34 (adder B35). The AC code instructing section B244 outputs the phase corrected by the addition to the multiplier B25 as a phase output φ.

The phase output φ controls the instantaneous value X1 and the instantaneous value X2 to be equal to each other. According to the AC code instruction section B244, two phase calculation sections B30 and B31 can be omitted compared to the AC code instruction section B241, so that the circuit configuration can be further simplified.

That is, the control unit 11 applies a positive or negative bias voltage to the midpoint voltage _VL based on the instantaneous value X1 and the instantaneous value X2, thereby _adjusting the phase difference between the U-phase voltage _Vuo and the inversion voltage Vow. Reduce.

《Summary of Disclosure》
The above disclosure can be generalized and expressed as follows.
A power conversion device 100 that provides an AC output to a single-phase three-wire AC electric circuit is provided between two lines of a DC bus 2, and has a DC bus capacitor 5H and a DC bus capacitor 5H whose interconnection point is a midpoint voltage _VL . A 5L series body 5 and a midpoint voltage control section 4 provided between two lines of the DC bus 2 for controlling the midpoint voltage _VL are provided. The control unit 11 of the power conversion device 100 performs bipolar pulse width modulation control on the inverter 7 and controls the midpoint voltage control unit 4 . The AC reactor 8 has a common core for two lines extending from the output terminal of the inverter 7 to the U line and the W line. The control unit 11 controls the inverter 7 so that the line voltage between the U line and the W line becomes a target value, and the U-phase voltage _Vuo and the W-phase voltage _Vwo become equal in absolute value. Thus, the midpoint voltage _VL is adjusted by controlling the midpoint voltage controller 4 .

In such a power converter 100, the inverter 7 does not control the phase voltage and operates to match the line voltage between the U line and the W line to the target value during the self-sustained operation. The control unit 11 controls the midpoint voltage control unit 4 to adjust the midpoint voltage _VL so that the U-phase voltage and the W-phase voltage are equal in absolute value. The midpoint voltage _VL is not limited to the median value, and may be biased (shifted) from the median value to one side. Moreover, the voltage to ground of the DC bus 2 is stabilized by the bipolar pulse width modulation control, and common mode noise can be reduced. A reactor 8 can be used. As a result, the size of the AC reactor 8 can be reduced, so that the size of the power converter 100 can be reduced.

The control unit 11 can control the midpoint voltage control unit 4 so that the midpoint voltage _VL deviates from the median value of the voltage between the two lines of the DC bus 2 . As a result, even if the U-phase AC load and the W-phase AC load are unequal, the midpoint voltage shifts from the midpoint value, causing the U-phase voltage _Vuo and the W-phase voltage _Vwo to They can be equal to each other in absolute value.

In other words, when there is a difference between the U-phase voltage _Vuo and the W-phase voltage _Vwo , the control unit 11 applies a positive or negative bias voltage to the midpoint voltage V _L to reduce the difference. be able to. In this manner, the midpoint voltage _VL is not necessarily set to an intermediate value, but biased by application of the bias voltage, so that even if the U-phase AC load and the W-phase AC load are unequal, , the U-phase voltage _Vuo and the W-phase voltage _Vwo can be adjusted to be equal to each other in absolute value.

The AC reactor 8 can be miniaturized by being connected in sum.
Both instantaneous values and effective values can be used as the U-phase voltage and the W2-phase voltage. If the instantaneous value is used, the control response is quick, but the control is slightly sensitive. When the effective value is used, the control response is slower than the instantaneous value, but it becomes a stable control that does not become hypersensitive.

《Supplement》
It should be noted that the embodiments disclosed this time should be considered as examples in all respects and not restrictive. The scope of the present invention is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope of equivalence to the scope of claims.

1 DC/DC Converter 2 DC Bus 3 Smoothing Capacitor 4 Midpoint Voltage Control Section 5 (Capacitor) Series 5H, 5L DC Bus Capacitors 6H, 6L Voltage Sensor 7 Inverter 8 AC Reactor 9u, 9w AC Side Capacitor 10u, 10w Voltage Sensor 11 Control Unit 12, 13 DC Reactor 20 DC Power Supply 31 AC Circuit 32u U-phase Load 32w W-phase Load 100 Power Converter d1, d2, d3, d4, d5, d6, d7, d8 Diodes Q1, Q2, Q3, Q4 , Q5, Q6, Q7, Q8 Switching element B1 _Vuw voltage reference indication unit B2 Comparator B3 Proportional integration operation unit B4 Adder B5 Voltage command signal generation unit B6 Carrier signal generation unit B7 PWM control unit B8 Adder B9 Proportional integration operation Section B10 Midpoint voltage reference indication section B11 Adder B12 Comparator B13 Proportional integration calculation section B14 Voltage command signal generation section B15 Carrier signal generation section B16 PWM control section B20, B21 Effective value calculation section B22 Comparator B23 Proportional integration calculation section B24 AC sign indicator B25 Multiplier B26 Midpoint voltage reference indicator B27 Adder B28 Comparator B29 Proportional integral calculator B30, B31, B32 Phase calculator B33 Comparator B34 Proportional integral calculator B35 Adder B36, B37 Instantaneous value calculator Part B241, B242, B243, B244 AC sign indication part M Midpoint P1, P2 Midpoint voltage correction part X1, X2 Instantaneous value

Claims (12)

A power converter that provides AC output to a single-phase three-wire AC circuit,
an inverter;
an AC reactor provided between the inverter and the AC electric circuit;
a DC bus that supplies a DC voltage to the inverter;
a series body of a first capacitor and a second capacitor provided between two lines of the DC bus and having a midpoint voltage at an interconnection point;
a midpoint voltage control unit provided between two lines of the DC bus for controlling the midpoint voltage;
AC side voltage for acquiring a first phase voltage between the first voltage line and the neutral line of the AC line and a second phase voltage between the second voltage line and the neutral line of the AC line a sensor;
a control unit that performs bipolar pulse width modulation control on the inverter and controls the midpoint voltage control unit;
The AC reactor has a core common to two lines from the output end of the inverter to the first voltage line and the second voltage line,
The control unit
controlling the inverter so that the line voltage between the first voltage line and the second voltage line becomes a target value;
controlling the midpoint voltage control unit to adjust the midpoint voltage so that the absolute values of the first phase voltage and the second phase voltage are equal to each other;
Power converter. The control unit controls the midpoint voltage control unit such that the midpoint voltage deviates from an intermediate value of voltages between two lines of the DC bus.
The power converter according to claim 1. The control unit controls the midpoint voltage control unit to adjust the midpoint voltage so that the phase of the first phase voltage and the phase of the inverted voltage obtained by inverting the second phase voltage match. ,
The power converter according to claim 1 or 2. The control unit controls the midpoint voltage control unit such that the phase of the first phase voltage or the phase of the inverted voltage obtained by inverting the second phase voltage matches the phase of the line voltage. adjusting the midpoint voltage with
The power converter according to claim 1 or 2. When there is a phase difference between the first phase voltage and the inversion voltage, the control unit applies a positive or negative bias voltage to the midpoint voltage to reduce the phase difference.
The power converter according to claim 3. When there is a phase difference between the first phase voltage or the inversion voltage and the line voltage, the control unit applies a positive or negative bias voltage to the midpoint voltage to reduce the phase difference. ,
The power converter according to claim 4. Based on at least one of the first phase voltage when the zero crossing of the line voltage is detected and the second phase voltage when the zero crossing of the line voltage is detected, the control unit controls the midpoint applying a positive or negative bias voltage to the voltage to reduce the phase difference between the first phase voltage and the reversal voltage;
The power converter according to claim 3 or 4. When there is a difference between the first phase voltage and the second phase voltage, the control unit applies a positive or negative bias voltage to the midpoint voltage to reduce the difference.
The power converter according to claim 1 or 2. The bias voltage is a square wave, a sine wave or a triangular wave,
The power converter according to any one of claims 5 to 8. The first phase voltage and the second phase voltage are instantaneous values or effective values,
The power converter according to claim 1 or 2. The AC reactor is sum-actively connected,
The power converter according to any one of claims 1 to 10. an inverter, an AC reactor provided between the inverter and a single-phase three-wire AC electric circuit, a DC bus for supplying a DC voltage to the inverter, and an interconnection provided between two wires of the DC bus. A series body of a first capacitor and a second capacitor having a point at a midpoint voltage, a midpoint voltage control section provided between two lines of the DC bus for controlling the midpoint voltage, and a bipolar capacitor for the inverter. and a control unit that controls the midpoint voltage control unit, and a control unit that provides an AC output to the AC electric circuit. ,
controlling the inverter so that the line voltage between the first voltage line and the second voltage line of the AC electric circuit becomes a target value;
controlling the midpoint voltage control unit to adjust the midpoint voltage so that the absolute values of the first phase voltage and the second phase voltage viewed from the neutral line of the AC electric circuit are equal to each other;
A control method for a power converter.

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