JP7347338B2 - Power converter and its operating method - Google Patents

Description

The present disclosure relates to a power conversion device and a method of operating the same.

The power conversion device is provided between a DC line and an AC line of a commercial power system, performs DC/AC power conversion, and can operate in a grid-connected manner with the commercial power system. In Japan, single-phase three-wire systems are mainly used for low-voltage commercial power systems. Here, among the single-phase three wires, the voltage line is the U line, the V line, and the neutral line is the O line. In a power converter equipped with an inverter that forms a two-leg (four switching elements) full-bridge circuit, when connected to the grid, for example, 202V is output between the U line and the V line, but not output to the O line. .

In a power conversion device equipped with an inverter that constitutes a full bridge circuit with three legs (six switching elements), for example, the current command value of the O line is always set to 0, and the current command value is set to the U line and V line. By setting the current command values to sinusoidal waves with a phase difference of 180° from each other, it is possible to connect three wires to a single-phase three-wire commercial power system and perform grid-connected operation (for example, the patent (See Reference 1). Moreover, such a power conversion device can also perform self-sustaining operation by performing voltage control based on a voltage command value.

Japanese Unexamined Patent Publication No. 7-163153

In a power converter equipped with a 3-leg inverter as described above, when performing single-phase 3-wire independent output, for example, the DC positive terminal of the inverter is connected to the U line, V line reactor, and O line via the The inductance of the current path leading to the DC side negative electrode of the inverter is the combined value of the inductances of the reactors installed on the U line and the V line. Assuming that the inductance of each reactor is the same value, the combined value will be half of that value. Therefore, in order to ensure a desired inductance in the current path and reduce current ripple and leakage current, the inductance of the reactor installed in the U line and the V line must be set to be large.

On the other hand, when interconnecting with the grid, no current flows through the O line. Therefore, the combined inductance of the current path is twice the inductance of each of the U-line and O-line. In other words, there is no need for such a large inductance when connecting to the grid. However, the inherent inductance of each reactor must be set to a larger value, that is, a value necessary for independent single-phase three-wire output. As a result, a reactor with excessive inductance is used when interconnecting with the grid.

In order to increase the inductance of the reactor, it is necessary to increase the number of turns. Furthermore, the cross-sectional area of the core must be increased to prevent magnetic saturation of the core. As a result, the length of the winding and the volume of the core increase, making it difficult to downsize the reactor and also increasing the power loss generated in the reactor.

In view of such problems, the present disclosure provides a power conversion device that can select between a single-phase two-wire grid-connected output and a single-phase three-wire independent output, by making the reactor more compact and reducing losses. With the goal.

This disclosure includes the following inventions. However, the present invention is defined by the scope of the claims.

(Power converter)
The power conversion device of the present disclosure includes:
A power conversion device provided between a positive and negative two-wire DC circuit connected to a DC power supply and a single-phase three-wire AC circuit,
a power converter including an inverter that is provided between the DC circuit and the AC circuit and configures a 3-leg full bridge circuit;
A control unit that controls the power conversion unit,
The power conversion section includes:
A first reactor and a second reactor each provided in two lines that are AC side voltage lines of the inverter;
a third reactor that is provided on the neutral line on the AC side of the inverter and has an inductance larger than either the inductance of the first reactor or the inductance of the second reactor;
It is equipped with

(How to operate a power converter)
The method of operating the power conversion device of the present disclosure includes:
A method of operating a power conversion device provided between a positive and negative two-wire DC circuit connected to a DC power source and a single-phase three-wire AC circuit, the method comprising:
The power conversion device includes an inverter that constitutes a three-leg full bridge circuit, and a first reactor, a second reactor, and a third reactor for each of the three AC side wires of the inverter, and the third reactor. Under the condition that the inductance of the reactor is larger than either of the inductance of the first reactor and the inductance of the second reactor,
When interconnecting with a commercial power system, two of the three legs are operated to switch and connected to the AC power line via the first reactor and the second reactor,
During self-sustaining operation, all three legs are switched, the leg connected to the voltage line is connected to the AC line via the first reactor and the second reactor, and the leg connected to the neutral line is connected to the AC power line via the third reactor;
This is a method of operating a power conversion device.

According to the present disclosure, in a power conversion device that can select between a single-phase two-wire output and a single-phase three-wire independent output, the reactor can be made more compact and losses can be reduced.

FIG. 1 is a circuit diagram showing an example of a power conversion device. FIG. 2 is a diagram schematically showing an example of the shape of the U-line and V-line reactors. In Figure 3, the inductance of each reactor for the U line and V line is 600 μH, there is no reactor for the neutral line, the load on the U phase (between the U line and the V line) is 3 kW, and the load on the V phase (between the V line and the O line) is 3 kW. FIG. 3 is a waveform diagram when independent output operation is performed. FIG. 4 is a waveform diagram when independent output operation is performed with the inductance of each of the reactors for the U line and the V line being 100 μH, no reactor for the neutral line, a U phase load of 3 kW, and a V phase load of 3 kW. Figure 5 is a waveform diagram when independent output operation is performed with the inductance of each reactor for the U line and V line being 100 μH, the inductance of the reactor for the neutral line being 300 μH, a U phase load of 3 kW, and a V phase load of 3 kW. be. Figure 6 is a waveform diagram when grid-connected operation is performed with the inductance of each reactor for the U line and V line being 100 μH, the inductance of the reactor for the neutral line being 300 μH, a U phase load of 3 kW, and a V phase load of 3 kW. It is. Figure 7 shows that the U-line and V-line reactors are a common core, and the neutral line reactor is independent, and the self-inductance of each winding of the U-line and V-line reactors is 52 μH, the mutual inductance is 50 μH, and the neutral It is a waveform diagram when the inductance of the line reactor is 300 μH, the U-phase load is 3 kW, and the V-phase load is 3 kW, and independent output operation is performed. Figure 8 shows that the U-line and V-line reactors are a common core, the neutral line reactor is independent, and the self-inductance of each winding of the U-line and V-line reactors is 52 μH, the mutual inductance is 50 μH, and the neutral It is a waveform diagram when grid-connected operation is performed with the inductance of the line reactor being 300 μH, the U-phase load being 3 kW, and the V-phase load being 3 kW. Figure 9 shows that all three-wire reactors have a common core, the self-inductance of each winding of the U-line and V-line reactors is 52 μH, the self-inductance of the winding of the neutral wire reactor is 200 μH, and the UV winding has a self-inductance of 52 μH. It is a waveform diagram when self-sustaining output operation is performed with a mutual inductance between the windings of 50 μH, a mutual inductance between the UO and VO windings of 100 μH, a U-phase load of 3 kW, and a V-phase load of 3 kW. Figure 10 shows that all 3-wire reactors have a common core, the self-inductance of each winding of the U-line and V-line reactors is 52 μH, the self-inductance of the winding of the neutral wire reactor is 200 μH, and the UV winding It is a waveform diagram when grid-connected operation is performed with a mutual inductance between the windings of 50 μH, a mutual inductance between the UO and VO windings of 100 μH, a U-phase load of 3 kW, and a V-phase load of 3 kW. FIG. 11 is a diagram showing an example in which all three-wire reactors are a shared core, which is a prerequisite for FIGS. 9 and 10. FIG. 12 is a circuit diagram illustrating an example of the configuration of a hybrid power converter including a part of the power converter of FIG. 1 when there are multiple DC power sources.

[Description of embodiments of the present disclosure]
The embodiment of the present disclosure includes at least the following as its gist.

(1) This is a power conversion device installed between a positive and negative two-wire DC line connected to a DC power supply and a single-phase three-wire AC line, and between the DC line and the AC line. The power conversion unit includes a power conversion unit including an inverter that is installed in a three-leg full bridge circuit, and a control unit that controls the power conversion unit. The power conversion unit is provided with a first reactor and a second reactor provided in two voltage lines on the AC side of the inverter, respectively, and a neutral line on the AC side of the inverter, and is provided on the neutral line of the AC side of the inverter, and and a third reactor having an inductance larger than both the inductance and the inductance of the second reactor.

In the power conversion device of (1) above, when the single-phase three-wire voltage lines are the U line and V line, and the neutral line is the O line, there is a reactor in each line. Since there is a reactor on the O line, when performing independent output in a single-phase three-wire system, the inductance of two reactors can be obtained for each of the U line-O line and the V line-O line. Therefore, the ripple of the current flowing through each reactor can be reduced without increasing the inductance of the reactor for the U line, V line, and each reactor, and similarly, single-phase three-wire independent output is possible. .

By making the inductance of the O-line reactor larger than the inductance of the U-line and V-line reactors, the inductance of the U-line and V-line reactors can be changed to a single-phase, two-wire grid-connected output, The optimum value can be set for both single-phase three-wire independent output. Therefore, the three reactors as a whole can be made small and have low loss.
In this way, the reactor can be made more compact and losses can be reduced in a power conversion device that can select between a single-phase two-wire grid-connected output and a single-phase three-wire independent output.

(2) The power converter according to (1) above includes a series body of a pair of capacitors connected between the positive and negative two wires, and three capacitors star-connected to the single-phase three wires of the AC circuit. a bypass path that short-circuits the interconnection portion of the pair of capacitors and the neutral point of the star connection; and a common mode choke coil provided in the power converter within a range bypassed by the bypass path. It is preferable to have the following. The control unit switches two legs of the inverter connected to the first reactor and the second reactor using a unipolar pulse width modulation method.

By switching the inverter using the unipolar pulse width modulation method, the amplitude of the pulse voltage applied to both ends of the reactor winding is halved compared to the bipolar pulse width modulation method, and the operating frequency is twice the switching frequency. become. Therefore, the inductance of each reactor for U line and V line can be reduced to 1/4. In addition, the unipolar pulse width modulation method can be used both when the system is connected to the grid, which is a two-wire output of U-line and V-line, and when it is independent, which is a single-phase three-wire output.

When an inverter is operated using the unipolar pulse width modulation method or single-phase three-wire independent output, the ground potential of the DC line fluctuates due to the inverter's switching operation, causing leakage via the ground stray capacitance of the DC line and the ground on the AC side. Current flows more easily. However, leakage current can be suppressed by short-circuiting the DC line and the AC line via a capacitor using a bypass path.
A common mode choke coil suppresses common mode current and leakage current.

(3) In the power converter according to (1) or (2), the first reactor and the second reactor may share a core and be connected together.
In this case, the first reactor and the second reactor are integrated, and the overall structure can be made compact.

(4) In the power conversion device of (1) or (2), the first reactor, the second reactor, and the third reactor may share a core.
In this case, the first reactor, the second reactor, and the third reactor are integrated, and the whole can be configured compactly.

(5) From the viewpoint of the method, this is a method of operating a power conversion device provided between a positive and negative two-wire DC circuit connected to a DC power supply and a single-phase three-wire AC circuit. The power conversion device includes an inverter that constitutes a three-leg full bridge circuit, and a first reactor, a second reactor, and a third reactor for each of the three AC side wires of the inverter, and the third reactor. Under the condition that the inductance of the reactor is larger than both the inductance of the first reactor and the inductance of the second reactor, two of the three legs are operated for switching when interconnected with a commercial power system. , is connected to the AC line through the first reactor and the second reactor, and during self-sustaining operation, all three legs are switched, and the leg connected to the voltage line is connected to the first reactor and the second reactor. A leg that is connected to the AC line via the AC line and connected to the neutral wire is connected to the AC line via the third reactor.

In this way, it is possible to realize a power conversion device that can select between a single-phase two-wire grid-connected output and a single-phase three-wire independent output, and also to make the reactor more compact and reduce losses.

[Details of embodiments of the present disclosure]
《Example of configuration of power converter》
Hereinafter, specific examples of the power conversion device of the present disclosure will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing an example of a power conversion device. In the figure, a power converter 100 is provided between a positive and negative two-wire DC line 2 connected to a DC power source 1 and an AC line 4 to which a load 3 is connected. The load 3 may be a load R _UO or R _VO in a narrow sense that only consumes power, or may be a load in a broad sense, that is, a commercial AC power source. The AC line 4 is a single-phase three-wire type, with voltage lines being U and V lines, and a neutral line being O line. The O wire is grounded.

The DC power source 1 is, for example, a storage battery or a solar power generation device. The DC power supply 1 has ground stray capacitances 5 and 6 in parallel as an equivalent circuit. There is an equivalent relationship in which the midpoint of a pair of series bodies of ground stray capacitances is grounded.

The power converter 100 includes a pair of capacitors 7 and 8 connected in series between the positive and negative lines of the DC circuit 2 . The capacitance of each capacitor 7, 8 is the same. A smoothing capacitor 11 is connected between the positive and negative lines of a DC bus 10 that passes from the DC line 2 through the common mode choke coil 9. Voltage sensor 12 detects the line voltage of DC bus 10 and sends an output signal to control section 13 . An inverter 14 is connected between two lines of the DC bus 10.

The inverter 14 constitutes a three-leg full bridge circuit with switching elements Q1, Q2, Q3, Q4, Q5, and Q6. The switching elements Q1, Q2, Q3, Q4, Q5, and Q6 are, for example, MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors), but instead of MOSFETs, they are IGBTs (Insulated Gate Bipolar). Transistor) can also be used.

The AC side of the legs of switching elements Q1 and Q2 is the _U1 line connected to the U line. The AC side of the legs of switching elements Q3 and Q4 is the _V1 line connected to the V line. The AC side of the legs of switching elements Q5 and Q6 is the _O1 line connected to the O line. The U ₁ line and the V ₁ line reach the U ₂ line and the V ₂ line via reactors L _U and L _V and current sensors 15 and 16. The O ₁ line reaches the O ₂ line via reactor Lo. A capacitor 17 and a voltage sensor 19 are connected between the _U2 wire and _{the O2} wire. A capacitor 18 and a voltage sensor 20 are connected between the _V2 line and the _O2 line.

The U ₂ line, O ₂ line, and V ₂ line are connected to the U line, O line, and V line, respectively, via the common mode choke coil 21 on the AC side. The capacitors 22, 23, and 24 are connected to the U line, O line, and V line in a star connection within the power conversion device 100. A neutral point _NAC of the star connection is connected to an interconnection point _NDC between a pair of capacitors 7 and 8 on the DC side by a bypass path 25.

The control unit 13 includes, for example, a computer, and implements necessary control functions by the computer executing software (computer program). The software is stored in a storage device (not shown) of the control unit. The control unit 13 acquires output signals from the voltage sensors 12, 19, 20 and the current sensors 15, 16, and controls switching of the six switching elements Q1, Q2, Q3, Q4, Q5, and Q6. Power conversion device 100 includes this control section 13 and other power conversion sections 100a.

《Operation of power converter》
The power conversion device 100 configured as described above converts the DC power supplied from the DC line 2 to the DC bus 10 into AC power using the inverter 14 and supplies the AC power to the AC line 4. When the DC power source 1 is a storage battery, the inverter 14 can also perform reverse conversion from AC to DC and charge the storage battery.

From the viewpoint of an operation method regarding grid connection/self-sustaining operation of the power conversion device 100, it can be expressed as follows.
The power conversion device 100 includes an inverter 14 that constitutes a three-leg full bridge circuit, and reactors L _U , L _V , and L _O on the three AC side wires of the inverter 14, respectively, and the inductance of the reactor L _O is , is operated under the condition that the inductance is larger than the inductance of each of the reactors L _U and L _V . (i) When interconnecting with the commercial power grid, two of the three legs are operated to switch and connected to the AC line 4 via the reactors L _U and L _V , and (ii) during autonomous operation, , all three legs are operated in a switching manner, and the leg connected to the voltage line is connected to the AC line 4 via the reactors L _U and L _V , and the leg connected to the neutral line is connected to the AC line 4 via the reactor L _O. The operating method is to connect it to 4. Switching control of the two legs connected to the reactors L _U and L _V is performed using a unipolar pulse width modulation (PWM) method.

《Specific example of control during autonomous operation》
An example of the control operation of the control unit 13 when the inverter 14 performs power conversion from DC to AC will be described. Switching control of the two legs connected to the reactors L _U and L _V is performed using a unipolar pulse width modulation method.
First, the control unit 13 operates based on the difference between the voltage target value of the U phase (between the U line and the O line) and the U phase voltage detected by the voltage sensor 19 and the U phase current detected by the current sensor 15. Then, the U-phase voltage reference value Vinvu ^* is determined.

Similarly, the control unit 13 determines the difference between the voltage target value of the V phase (between the V line and the O line) and the V phase voltage detected by the voltage sensor 20 and the V phase current detected by the current sensor 16. Based on this, the V-phase voltage reference value Vinvv ^* is determined.

Next, the control unit 13 sets the voltage reference for the two legs (switching elements Q1, Q2, Q3, Q4) of the inverter 14 based on the difference between the U-phase voltage reference value Vinvu ^* and the V-phase voltage reference value Vinvv ^* . Find the value Vinv_ref.
The control unit 13 also sets the voltage reference value Vinvo_ref for the neutral leg (switching elements Q5, Q6) of the inverter 14 based on the sum of the U-phase voltage reference value Vinvu ^* and the V-phase voltage reference value Vinvv ^* . demand.

Based on the voltage reference value Vinv_ref and the input voltage to the inverter 14 detected by the voltage sensor 12, the control unit 13 controls each gate of the four switching elements Q1, Q2, Q3, and Q4 of the two legs. Find the control signal. Further, the control unit 13 determines respective gate control signals for the two switching elements Q5 and Q6 of the neutral leg based on the voltage reference value Vinvo_ref and the input voltage to the inverter 14.

Through such control, the two reference values are determined using the reference values Vinv_ref and Vinvo_ref obtained by comparing the line voltage between the U line and the O line and the line voltage between the V line and the O line with their respective target values. The difference is taken as the PWM reference value that controls the leg connected to the output of the U line and the V line, and the sum of the two reference values is taken as the PWM reference value that controls the leg connected to the output of the O line. In this way, the voltage required for a single-phase three-wire system can be provided by PWM control. The control unit 13 sets the V-line PWM reference value to be the one in which the sign of the U-line PWM reference value is inverted, and outputs three levels of UV line voltage (unipolar PWM).

《Example of reactor shape》
FIG. 2 is a diagram showing a simplified example of the shape of the reactors L _U and L _V. The U-line and V-line reactors L _U and L _V share a ring-shaped core 26 and have their windings connected in a harmonic manner. Note that the number of turns is simplified and is not the actual number of turns. Since it is an alternating current, the direction of the current changes, but if it flows as shown, the reactors L _U and L _V can be integrated and miniaturized.

《Waveform example》
In Figure 3, the inductance of each reactor L _U and L _V is 600 μH, there is no reactor for the neutral line, the U phase (between the U line and the V line) has a load of 3 kW, and the V phase (between the V line and the O line) has a load of 3 kW. , is a waveform diagram when independent output operation is performed. From top to bottom, they represent the following:
(a): AC output voltage (between U line and V line),
(b): Voltage across the reactor L _U of the U line,
(c): Voltage across V line reactor L _V ,
(d): Voltage across the O line reactor L _O (none) (=0),
(e): U line reactor current (peak-to-peak ripple 8A)
(f): V line reactor current (peak-to-peak ripple 8A),
(g): O line reactor current (peak-to-peak ripple 19A)
(h): Leakage current 6.5mA (horizontal line with a constant value at the center of amplitude), bypass path current: 0.86A (one with amplitude)

FIG. 4 is a waveform diagram when independent output operation is performed with the inductance of each of the reactors L _U and L _V being 100 μH, no reactor in the neutral line, and a U-phase load of 3 kW. From top to bottom, they represent the following:
(a): AC output voltage (between U line and V line),
(b): Voltage across the reactor L _U of the U line,
(c): Voltage across V line reactor L _V ,
(d): Voltage across the O line reactor L _O (none) (=0),
(e): U line reactor current (peak-to-peak ripple 50A)
(f): V line reactor current (peak-to-peak ripple 50A),
(g): O line reactor current (peak-to-peak ripple 100A)
(h): Leakage current 9.4 mA (horizontal line with a constant value at the center of amplitude), bypass path current: 0.87 A (one with amplitude)

According to FIG. 3, it can be seen that since there is no reactor in the O line, the current ripple of the single-phase three-wire independent output cannot be reduced unless the inductance of the U line and the V line is increased.
According to FIG. 4, it can be seen that if the inductance of the U-line and V-line reactors is made small (100 μH), the ripple becomes large and the loss becomes too large to be practical.

Figure 5 is a waveform diagram when independent output operation is performed with the inductance of each of the reactors L _U and L _V being 100 μH, the inductance of the reactor L _O of the neutral line being 300 μH, the U phase load being 3 kW, and the V phase load being 3 kW. It is. From top to bottom, they represent the following:
(a): AC output voltage (between U line and V line),
(b): Voltage across the reactor L _U of the U line,
(c): Voltage across V line reactor L _V ,
(d): Voltage across the reactor L _O of the O line,
(e): U line reactor current (peak-to-peak ripple 8A)
(f): V line reactor current (peak-to-peak ripple 8A),
(g): O line reactor current (peak-to-peak ripple 14A)
(h): Leakage current 4.4 mA (horizontal line with a constant value at the center of amplitude), bypass path current: 0.60 A (one with amplitude)

According to FIG. 5, since there is a reactor L _O in the O line, the current ripple in the single-phase three-wire independent output can be reduced even if the inductance of the U line and the V line is reduced. Since there is a bypass path and a common mode choke coil, it can be seen that leakage current and common mode current are small even with 2-leg unipolar PWM and single-phase 3-wire independent output.

Figure 6 shows the waveforms when grid-connected operation is performed with the inductance of each reactor L _U and L _V being 100 μH, the inductance of the reactor L _O of the neutral line being 300 μH, the U-phase load being 3 kW, and the V-phase load being 3 kW. It is a diagram. From top to bottom, they represent the following:
(a): AC current (between U line and V line), current total distortion rate 2%
(b): Reactor ( _LU , _LV ) current (peak-to-peak ripple 8A)
(c): Leakage current 4.0 mA (horizontal line with a constant value at the center of amplitude), bypass path current: 0.58 A (one with amplitude)

According to FIG. 6, even when connected to the grid, the ripple of the reactor current is comparable to that of single-phase three-wire, and it can be seen that a distortion-free sine wave can be output.

FIG _. 7 shows that the reactors L _{U and} L _V share a core (FIG. 2), and the reactor L _O is independent. It is a waveform diagram when independent output operation is performed with an inductance of _O being 300 μH, a U phase load of 3 kW, and a V phase load of 3 kW. From top to bottom, they represent the following:
(a): AC output voltage (between U line and V line),
(b): Voltage across the reactor L _U of the U line,
(c): Voltage across V line reactor L _V ,
(d): Voltage across the reactor L _O of the O line,
(e): U line reactor current (peak-to-peak ripple 8A)
(f): V line reactor current (peak-to-peak ripple 8A),
(g): O line reactor current (peak-to-peak ripple 16A)
(h): Leakage current 4.3 mA (horizontal line with a constant value at the center of amplitude), bypass path current: 0.58 A (one with amplitude)

FIG _. 8 shows that the reactors L _{U and} L _V share a core (FIG. 2), and the reactor L _O is independent. It is a waveform diagram when grid-connected operation is performed with an inductance of _O being 300 μH, a U-phase load of 3 kW, and a V-phase load of 3 kW. From top to bottom, they represent the following:
(a): AC current (between U line and V line), current total distortion rate 2%
(b): Reactor ( _LU , _LV ) current (peak-to-peak ripple 8A)
(c): Leakage current 4.1mA (horizontal line with a constant value at the center of amplitude), bypass path current: 0.60A (one with amplitude)

According to FIG. 6, even if the reactor is made smaller by sharing the core of the U line and the V line, the ripple of the reactor current is small, and the leakage current and common mode current are small. It can be seen that even when connected to the grid, the ripple of the reactor current is the same as the independent output, and a distortion-free sine wave is output.

FIG. 9 shows that the reactors L _U , L _V , and L _O all have a common core (see FIG. 11 described later), and that the self-inductance of each winding of the reactors L _U and L _V is 52 μH, and that of the winding of the reactor L _O. Self-inductance is 200 μH, mutual inductance between reactors L _U and L _V is 50 μH, mutual inductance between reactors L _U and L _O and between reactors L _V and L _O is 100 μH, U phase load is 3 kW, V phase load is 3 kW, It is a waveform diagram when independent output operation is performed. From top to bottom, they represent the following:
(a): AC output voltage (between U line and V line),
(b): Voltage across the reactor L _U of the U line,
(c): Voltage across V line reactor L _V ,
(d): Voltage across the reactor L _O of the O line,
(e): U line reactor current (peak-to-peak ripple 8A)
(f): V line reactor current (peak-to-peak ripple 8A),
(g): O line reactor current (peak-to-peak ripple 12A)
(h): Leakage current 4.7mA (horizontal line with a constant value at the center of amplitude), bypass path current: 0.65A (one with amplitude)

FIG. 10 shows that the reactors L _U , L _V , and L _O all have a common core (see FIG. 11 described later), and that the self-inductance of each winding of the reactors L _U and L _V is 52 μH, and that of the winding of the reactor L _O. Self-inductance is 200 μH, mutual inductance between reactors L _U and L _V is 50 μH, mutual inductance between reactors L _U and L _O and between reactors L _V and L _O is 100 μH, U phase load is 3 kW, V phase load is 3 kW, It is a waveform diagram when grid-connected operation is performed. From top to bottom, they represent the following:
(a): AC current (between U line and V line), current total distortion rate 2%
(b): Reactor ( _LU , _LV ) current (peak-to-peak ripple 8A)
(c): Leakage current 4.1mA (horizontal line with a constant value at the center of amplitude), bypass path current: 0.60A (one with amplitude)

According to FIGS. 9 and 10, even if the reactor is further downsized by sharing the core of the U line, V line, and O line, the ripple of the reactor current is small, and the leakage current and common mode current are small. It can be seen that even when connected to the grid, the ripple of the reactor current is the same as the independent output, and a distortion-free sine wave is output.

《3-wire shared core》
FIG. 11 is a diagram showing an example in which the reactors L _U , L _V , L _O are all shared cores, which is a prerequisite for FIGS. 9 and 10 . The reactors L _U , L _V , L _O shown in FIG. 11 share one core 27 that serves as a magnetic path, and are configured by winding coils around three core legs 27 _U , 27 _O , and 27 _V. There is. The solid arrows in the figure represent the case where unnecessary current components flowing in the same direction through the U line and the V line return to the O line in the independent output. The dotted arrows represent the magnetic fluxes mf1 and mf2 within the core 27 when current flows in this manner. In this case, since the magnetic flux mf1 and the magnetic flux mf2 strengthen each other in the core leg portion _27O , unnecessary current components can be suppressed. On the other hand, for normal mode current flowing between the U line and the V line in independent output and grid connection, the magnetic flux strengthens each other in the core leg 27 _U and core leg 27 _V , suppressing current ripple. can do. As a result, the reactors L _U , L _V , and L _O can be integrated, and the size of the reactor can be reduced as a whole.

《Summary of disclosure》
The power conversion device of the present disclosure can be summarized as follows.

(Reactor placement)
As shown in FIG. 1, by installing reactors L _U , L V , and L _O on the U line, V _line , and O line, respectively, there is also a reactor L _O on the O line. Therefore, when performing independent output in a single-phase three-wire system, the current path between the U line and the O line and the current path between the V line and the O line can be Sufficient inductance can be secured with two reactors. Thereby, ripples in the current flowing through each reactor can be reduced. Further, the U-line and V-line reactors can be made smaller and have lower losses.

(control method)
By driving the two legs of the inverter 14 that controls the currents of the U and V lines with unipolar PWM, the amplitude of the pulse voltage applied to both ends of the reactor windings is halved, and the operating frequency is 2 times the switching frequency. Since it is doubled, the inductance of the U-line and V-line reactors can be reduced to 1/4. Unipolar PWM can be used for both two-wire output during grid connection and single-phase three-wire output during independent output. Since there is a reactor in the O line, single-phase three-wire independent output is possible even if the inductances of the U and V lines are relatively small.

(Bypass route)
When the inverter 14 is operated with unipolar PWM or single-phase three-wire independent output, the ground potential of the DC line fluctuates due to the switching operation of the inverter 14, and the stray capacitance to ground of the DC power supply 1 and DC line 2 as well as the AC side Leakage current tends to flow through the ground. However, by providing a common mode current bypass path 25 that short-circuits the DC line 2 and the AC line 4 via the capacitors (7, 8, 22, 23, 24), leakage current can be suppressed.

(Common mode choke coil)
By installing the common mode choke coils 9 and 21 within the range of the main circuit between both ends of the bypass path 25, common mode current and leakage current can be suppressed.

(Reactor inductance)
By making the inductance of the O line larger than the inductance of the U line and V line, the inductance of the reactors L _U and L _V of the U line and V line can be adjusted to 2-wire output when connected to the grid, and single-wire output when independent output. The optimum value can be set for both phase and three-wire output. As a result, the inductances of the three reactors L _U , L _V , and L _O can be set to optimal values, and the overall size and loss can be reduced.

"others"
FIG. 12 is a circuit diagram illustrating an example of the configuration of a hybrid power converter 200 including a part of the power converter 100 when there are a plurality of DC power sources. In the figure, the capacitor 11 and DC bus 10 of the power converter 100 and the right side thereof are the same as those in FIG. 1. A DC power supply 1B, which is a storage battery, is connected to the DC bus 10 via a DC/DC converter 28. Further, the other DC power source 1P is a solar power generation panel. The DC power supply 1P has ground stray capacitances 31 and 32 in parallel as an equivalent circuit. Further, the midpoint of the series body of the pair of ground stray capacitances 31 and 32 is in an equivalent state where it is grounded.

A pair of capacitors 33 and 34 connected in series are connected between the positive and negative lines of the DC circuit 30, which are both ends of the series body of the ground capacitances 31 and 32. The capacitance of each capacitor 33, 34 is the same. An interconnection point _NDC between the pair of capacitors 33 and 34 is connected to a bypass path 25 of the power conversion device 100. A common mode choke coil 35 and a DC/DC converter 36 are connected to two wires of the DC line 30. The output of the DC/DC converter 36 is connected to the DC bus 10. Although only one set of DC power supply unit 37 is shown in FIG. 12, multiple sets of DC power supply units can be connected in parallel to the DC bus 10.

In this way, in the hybrid power converter 200 in which a plurality of DC power supplies are connected to a common DC bus 10, the bypass path 25 is located between the positive and negative two wires of the DC circuit 30 in one or more sets of DC power supply units. It is connected to a potential interconnection point _NDC .

《Addendum》
It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered restrictive. The scope of the present invention is indicated by the claims, and it is intended that all changes within the meaning and range equivalent to the claims are included.

1 DC power supply 1B DC power supply (storage battery)
1P DC power supply (solar power generation panel)
2 DC line 3 Load 4 AC line 5, 6 Stray capacitance to ground 7, 8 Capacitor 9 Common mode choke coil 10 DC bus 11 Capacitor 12 Voltage sensor 13 Control unit 14 Inverter 15, 16 Current sensor 17.18 Capacitor 19.20 Voltage sensor 21 Common mode choke coil 22, 23, 24 Capacitor 25 Bypass path 26 Core (U line V line shared core)
27 core (U line, V line, O line shared core)
28 DC/DC converter 30 DC line 31, 32 Stray capacitance to ground 33, 34 Capacitor 35 Common mode choke coil 36 DC/DC converter 37 DC power supply unit 100 Power converter 100a Power converter 200 Power converter Lu, Lv, Lo Reactor mf1, mf2 Magnetic flux N _AC neutral point N _DC interconnection point Q1, Q2, Q3, Q4, Q5, Q6 Switching element

Claims (5)

A power conversion device provided between a positive and negative two-wire DC circuit connected to a DC power supply and a single-phase three-wire AC circuit,
a power converter including an inverter that is provided between the DC circuit and the AC circuit and configures a 3-leg full bridge circuit;
A control unit that controls the power conversion unit,
The power conversion section includes:
A first reactor and a second reactor each provided in two lines that are AC side voltage lines of the inverter;
a third reactor that is provided on the neutral line on the AC side of the inverter and has an inductance larger than either the inductance of the first reactor or the inductance of the second reactor;
A power converter equipped with a series body of a pair of capacitors connected between the positive and negative two wires;
three capacitors star-connected to the single-phase three wires of the AC line;
a bypass path that short-circuits the interconnection portion of the pair of capacitors and the neutral point of the star connection;
a common mode choke coil provided in the power converter within a range bypassed by the bypass path,
The power conversion device according to claim 1, wherein the control unit switches two legs of the inverter connected to the first reactor and the second reactor using a unipolar pulse width modulation method. The power conversion device according to claim 1 or 2, wherein the first reactor and the second reactor share a core and are harmonically connected. The power conversion device according to claim 1 or 2, wherein the first reactor, the second reactor, and the third reactor share a core. A method of operating a power conversion device provided between a positive and negative two-wire DC circuit connected to a DC power source and a single-phase three-wire AC circuit, the method comprising:
The power conversion device includes an inverter that constitutes a three-leg full bridge circuit, and a first reactor, a second reactor, and a third reactor for each of the three AC side wires of the inverter, and the third reactor. Under the condition that the inductance of the reactor is larger than either of the inductance of the first reactor and the inductance of the second reactor,
When interconnecting with a commercial power system, two of the three legs are operated to switch and connected to the AC power line via the first reactor and the second reactor,
During self-sustaining operation, all three legs are switched, the leg connected to the voltage line is connected to the AC line via the first reactor and the second reactor, and the leg connected to the neutral line is connected to the AC power line via the third reactor;
How to operate a power converter.

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