JP2003088139A - Power converter for system interconnection and method of controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent flow of zero-phase current among inverters with a simplified means without taking any measure in the hardware among inverters. SOLUTION: This power converter for system interconnection has a structure that a distributed power supply B is connected in common in the DC side while a system power supply Vs is connected in the AC side via an interconnection transformer TR, a plurality of inverters INV1 , INV2 for converting the DC power of the distributed power supply B to the AC power through ignition of the switching elements S1 to S6 are connected in parallel in multiplex, and the output currents of the inverters INV1 , INV2 are controlled through ignition of the switching elements S1 to S6 with the gate pulse based on the PWM control of the triangular wave comparison system. In this power converter for system interconnection, a control unit E is further provided to detect the zero-phase element of an output currents I of the inverters IVN1 , INV2 and shifts, based on the polarity and amplitude of the zero-phase current, the triangular wave signal from the reference phase to generate the gate pulse G of the switching elements S1 to S6 through which the zero-phase current flows.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion device for grid interconnection, and more specifically, to connect a distributed power source such as a solar cell or a fuel cell to a power system, a plurality of power sources are connected between the distributed power source and the grid power source. The present invention relates to a power conversion device for grid interconnection in which inverters are connected in parallel.

[0002]

2. Description of the Related Art For example, in a system interconnection system in which a distributed power source such as a solar cell or a fuel cell is connected to an electric power system, inverters for converting DC power of the distributed power source into AC power may be connected in parallel and in multiples. 12 to 16 show configuration examples of a power conversion device in which a plurality of (for example, two) three-phase inverters INV ₁ and INV ₂ are connected in parallel.

The power converter shown in FIGS. 12 to 16 has a configuration in which inverters INV ₁ and INV ₂ are connected in parallel and multiple connections, and the DC side of both inverters INV ₁ and INV ₂ is connected to a distributed power source B in common. At the same time, the AC side is connected to a system power source Vs for three-phase AC through a coupling transformer TR to form a system.

Each of the inverters INV ₁ and INV ₂ is provided with switching elements S _{1 to} S ₆ of a full bridge structure, an electrolytic capacitor C is connected to the DC side thereof, and an output filter three-phase reactor FL is connected to the AC side thereof, and the AC side thereof. PW based on the output current I detected by the current transformer CT provided in the
A control unit E for generating a gate pulse G for firing the switching elements S _{1 to} S ₆ by M control is provided.

In this power converter, the DC power output from the distributed power source B is charged in the electrolytic capacitor C, the charged power is converted into AC by switching the inverters INV ₁ and INV ₂ , and the AC power is fed to the power system. A load (not shown) is supplied. Inverter IN
In the power conversion device in which V ₁ and INV ₂ are connected in parallel and multiple, PW is performed by the control unit E of each inverter INV ₁ and INV _2.
The gate pulse G for firing the switching elements S _{1 to} S ₆ is independently generated by the M control.

As described above, since the control unit E of the inverters INV ₁ and INV ₂ generates the gate pulse G by the original PWM control, the respective inverters INV ₁ and INV ₁
A phase shift of the gate pulse G may occur at INV ₂ . Deviation occurs an arc timing point of the switching elements S ₁ to S ₆ between the inverter INV ₁ and INV ₂ by the phase shift of the gate pulse G, referred to as cross current between the inverter INV ₁ and INV ₂ as shown in FIG. 17 This causes a problem that the zero-phase current I ₀ flows.

Therefore, in the conventional power converter, the inverters INV ₁ and INV ₂ are provided by the following means ( ₁₎ to ( _3).
The zero-phase current I ₀ flowing between them is suppressed.

Control unit E of inverters INV ₁ and INV ₂
The synchronization signal D for matching the firing timing and the pulse width of the gate pulse G is transmitted and received between them (FIG. 12).
reference). With this synchronization signal D, it is possible to achieve perfect matching of the firing timing and pulse width of the gate pulse G output from each control unit E.

Isolation transformers T are provided on the AC sides of the inverters INV ₁ and INV ₂ (see FIG. 13). Since the insulation transformer T makes the zero-phase impedance between the inverters INV ₁ and INV ₂ infinite in principle, even if the zero-phase voltage is generated at the switching frequency level in both control units E, the inverter INV ₁ The zero-phase current I ₀ does not flow between INV ₂ .

An inductance (for example, a filter F called a common mode choke coil) that has a high impedance only when the zero-phase current I ₀ flows is inserted on the DC side of the inverters INV ₁ and INV ₂ (see FIG. 14). . Due to the blocking (filtering) effect that this inductance exhibits, the inverters INV ₁ and INV
It is possible to prevent the zero-phase current I ₀ from flowing between V ₂ .

A three-phase reactor FL for an output filter provided on the AC side of the inverters INV ₁ and INV ₂ (see FIG. 12)
(See FIG. 14), three single-phase reactors FLu,
FLv and FLw are provided on the AC side of the inverters INV ₁ and INV ₂ respectively (see FIG. 15). Three-phase reactor FL
In the case of, since the zero-phase impedance between the inverters INV ₁ and INV ₂ becomes extremely small, the inverters INV ₁ ,
Since there is no blocking (filtering) effect on the zero-phase voltage generated from INV _2, it is necessary to separately provide the means for suppressing the zero-phase current I ₀ as described above. On the other hand, the single-phase reactors FLu, FLv,
In the case of FLw, since an inductance that can exert a blocking (filtering) effect on the zero-phase voltage generated from the inverters INV ₁ and INV ₂ is secured, the single-phase reactor itself can suppress the zero-phase current I _0. it can.

LCL π-type filters FL ₁ , FC, FL ₂ are provided on the AC side of the inverters INV ₁ , INV ₂ (see FIG. 16). That is, it is composed of the first filter reactor FL ₁ forming the three-phase reactor, the filter capacitor FC, and the second filter reactor FL ₂ for interconnection. Since the LC filter composed of the first filter reactor FL ₁ and the filter capacitor FC removes the voltage component of the switching frequency level generated from the inverters INV ₁ and INV ₂ , the zero phase voltage at the switching level is generated. Since it does not, the zero-phase current I ₀ can be suppressed. The second filter reactor FL ₂ has a function of connecting impedance between the inverters INV ₁ and INV ₂ or between the inverter and the power system, and has a system configuration similar to parallel operation of AC power supplies.

[0013]

By the way, as described above,
Sea urchin inverter INV₁And INV₂Zero-phase current I flowing between
₀Power conversion device of the related art including means for suppressing
Then, we have to take measures in terms of hardware,
Each had the following problems.

Control unit E of inverters INV ₁ and INV ₂
In the case where a means for transmitting and receiving a synchronization signal D for synchronizing the gate pulse G (see FIG. 12) is adopted, the synchronization signal D includes information on the firing timing of the gate pulse G and the pulse width. There must be. Here, the switching frequency is, for example, 10 kHz to 20 kHz, and one cycle is approximately 20 μsec to 100 μsec.

For example, in the control section E of the inverter INV ₁ on the signal transmission side (master side), it is necessary to calculate the information of the synchronization signal D, that is, the firing timing and pulse width of the gate pulse G. After this arithmetic processing, the synchronizing signal D is transmitted to the control unit E of the inverter INV ₂ on the signal receiving side (slave side), but the control time in both the inverters INV ₁ and INV ₂ on the signal transmitting side and the signal receiving side is transmitted. Since it is too short, it becomes difficult to execute transmission / reception of the synchronization signal D.

A pulse transmission system in which the gate pulse G is directly transmitted from the signal transmitting side to the signal receiving side is conceivable. However, since it is necessary to insulate the control section E of both inverters INV ₁ and INV ₂ , transmission / reception pulse An insulating circuit section (for example, an optical signal is adopted) must be provided. Since these signal transmission means are changed depending on the number of parallel multiplexing of the inverters INV ₁ and INV ₂ , it is difficult to standardize the power conversion device.

When the means (see FIG. 13) for providing the insulating transformers T on the AC sides of the inverters INV ₁ and INV ₂ respectively is adopted, the rated frequency of the insulating transformers T provided on the AC sides of the inverters INV ₁ and INV ₂ is Since it is a system frequency, the insulation transformer T needs to be large and heavy, which leads to an increase in size and cost of the power conversion device.

A means (see FIG. 14) is provided on the DC side of the inverters INV ₁ and INV ₂ for inserting a filter F (for example, a common mode choke coil) having an inductance that becomes high impedance only when the zero-phase current I ₀ flows. When adopted, the filters F provided on the DC side of the inverters INV ₁ and INV ₂ are large and heavy, as in the case described above, which leads to an increase in size and cost of the power conversion device.

Three single-phase reactors FLu, FLv,
When adopting the means (see FIG. 15) for providing FLw on the AC side of each of the inverters INV ₁ and INV ₂ , the cost and size are double and the installation man-hours are doubled as compared with the case of one three-phase reactor FL. Is tripled, which is not suitable for a general-purpose power conversion device that requires cost reduction.

When means for providing LCL π-type filters FL ₁ , FC, FL ₂ on the AC side of the inverters INV ₁ , INV ₂ (see FIG. 16) is adopted, the filters are large and large, as in the case described above. Since it becomes heavy, it causes an increase in the size and cost of the power conversion device.

Therefore, the present invention has been proposed in view of the above problems, and an object thereof is to provide a zero phase between inverters by a simple means without taking measures in terms of hardware between the inverters. An object of the present invention is to provide a power conversion device for grid interconnection that can prevent current from flowing and a control method thereof.

[0022]

As technical means for achieving the above object, the present invention is characterized by the following points from the viewpoint of a PWM control method (triangular wave comparison method, hysteresis comparator method, vector method). To do. Where P
Among the WM control methods, the triangular wave comparison method is a PWM waveform (based on comparison of a carrier (carrier) signal (eg, triangular wave or sawtooth wave) that changes linearly with time and a modulation signal (eg, sine wave). (Switching element drive waveform) means a method to obtain output, and the hysteresis comparator method inputs the error signal between the inverter output and the command value to a comparator with hysteresis width so that the error is within the threshold of the comparator. This means a method to follow vibrationally, and the vector method means that the inverter generates 8
This means a method of converting the voltage vector into a pulse width signal so that the average value of the voltage vector at a certain time matches the voltage command vector based on the individual voltage vectors. Regardless of which method is adopted, the present invention can suppress the zero-phase current between the inverters by PWM control according to the method without taking a hardware measure between the inverters.

(1) Triangular wave comparison system In the device of the present invention, a distributed power source is commonly connected to the DC side, a system power source is connected to the AC side through a interconnection transformer, and a switching element is ignited. For grid interconnection, connecting multiple inverters that convert DC power of distributed power supply to AC power in parallel and control the output current of the inverter by igniting switching elements by gate pulse based on PWM control of triangular wave comparison method In the power converter,
A zero-phase component of the output current of the inverter is detected, and based on the polarity and magnitude of the zero-phase current, a triangular wave signal for generating a gate pulse of a switching element through which the zero-phase current flows is phase-shifted from a reference phase. It is characterized in that it is provided with a control unit.

The control unit detects a zero-phase component of the output current of the inverter, a calculation unit that calculates the polarity and magnitude of the zero-phase current, and a polarity and magnitude of the zero-phase current. Based on this, it is possible to adopt a configuration including a pulse generator that generates the gate pulse of the switching element through which the zero-phase current flows by shifting the triangular wave signal from the reference phase.

According to the method of the present invention, a plurality of inverters are connected in parallel to be connected to a system power source, and a triangular wave comparison type PWM is used.
By controlling the output current of the inverter by firing the switching element by the gate pulse based on the control,
In a method of controlling a grid interconnection power converter that converts DC power of a distributed power supply provided in common to each inverter into AC power, a zero-phase component of the output current of the inverter is detected, and the zero-phase current The triangular wave signal for generating the gate pulse of the switching element through which the zero-phase current flows is shifted from the reference phase based on the polarity and the magnitude.

According to the present invention, based on the PWM control of the triangular wave comparison system, the triangular wave signal is shifted from the reference phase by the correction value according to the polarity and the magnitude of the zero-phase current generated in the inverter. It is possible to correct the phase shift of the gate pulse between them, and as a result, it is possible to completely match the switching timings of the switching elements in each inverter to achieve synchronization.

(2) Hysteresis comparator system In the device of the present invention, a distributed power source is commonly connected to the DC side, a system power source is connected to the AC side through an interconnection transformer, and a switching element is ignited. For connecting to multiple grids, which connects the DC power of the distributed power supply to AC power in parallel and controls the output current of the inverter by firing the switching element by the gate pulse based on the PWM control of the hysteresis comparator method. In the power converter, the zero-phase component of the output current of the inverter is detected, and the hysteresis width for generating the gate pulse of the switching element through which the zero-phase current flows is detected based on the polarity and magnitude of the zero-phase current. It is characterized by comprising a control unit for adjusting with respect to an output current reference value of the inverter.

The control section adjusts the hysteresis width with respect to the output current reference value of the inverter according to the polarity and the magnitude of the zero phase current detecting section for detecting the zero phase component of the output current of the inverter. A configuration including a hysteresis width determination unit and a correction target selection unit that selects a switching element of an inverter that adjusts the hysteresis width can be provided.

In the method of the present invention, a plurality of inverters are connected in parallel to be connected to a system power supply, and a switching element is fired by a gate pulse based on PWM control of a hysteresis comparator system to control the output current of the inverter. Thus, in the control method of the grid interconnection power converter for converting the DC power of the distributed power source provided in common to each inverter into the AC power, the zero phase component of the output current of the inverter is detected, and the zero phase is detected. The hysteresis width for generating the gate pulse of the switching element in which the zero-phase current flows is adjusted with respect to the output current reference value of the inverter based on the polarity and magnitude of the current.

According to the present invention, the hysteresis width with respect to the output current reference value of the inverter is increased or decreased by the correction value according to the polarity and the magnitude of the zero-phase current generated in the inverter based on the PWM control of the hysteresis comparator system. As a result, the gate pulse of the desired switching element selected based on the polarity of the zero-phase current can be corrected, and as a result, the switching timing of the switching element in each inverter can be perfectly matched and synchronized.

(3) Vector system In the device of the present invention, a distributed power source is commonly connected to the DC side, a system power source is connected to the AC side through an interconnection transformer, and a switching element is ignited. Multiple inverters that convert DC power from distributed power supplies to AC power are connected in parallel, and the grid switching based on vector-based PWM control fires switching elements to control the output current of the inverters. In the device, a zero-phase component of the output current of the inverter is detected, one of the switching elements through which the zero-phase current flows is selected based on the polarity and magnitude of the zero-phase current, and the selected switching element is turned off. It is characterized by comprising a control unit for determining an output voltage vector to be controlled.

The control section selects one of a zero-phase current detecting section for detecting a zero-phase component of the output current of the inverter and a switching element through which the zero-phase current flows based on the polarity and magnitude of the zero-phase current. However, it is possible to adopt a configuration including a vector determination unit that determines an output voltage vector for turning off the selected switching element.

According to the method of the present invention, a plurality of inverters are connected in parallel to be connected to the system power source, and the switching element is fired by the gate pulse based on the PWM control of the vector system to control the output current of the inverter. In a control method of a grid interconnection power converter for converting DC power of a distributed power source provided in common to each inverter to AC power, a zero phase component of the output current of the inverter is detected and the zero phase current is detected. It is characterized in that any one of the switching elements through which the zero-phase current flows is selected based on the polarity and the magnitude of, and the output voltage vector for turning off the selected switching element is determined.

In the present invention, one of the switching elements through which the zero-phase current flows is selected based on the polarity and magnitude of the zero-phase current generated in the inverter based on the PWM control of the vector system, and the selected switching is performed. By determining the output voltage vector that turns off the element,
The gate pulse between each inverter can be corrected,
As a result, the zero-phase current between the inverters can be suppressed.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION First to third embodiments of the present invention will be described in detail below. The first embodiment is a triangular wave comparison type P
When the WM control is used, the second embodiment uses the hysteresis comparator type PWM control, and the third embodiment uses the vector type PWM control. In the first to third embodiments, The PWM control method is different and the hardware configuration is common.

FIG. 1 shows a hardware configuration of a grid interconnection power conversion device common to the first to third embodiments. The power conversion device shown in the figure is installed in a grid interconnection system that links a distributed power source B such as a solar cell or a fuel cell to an electric power grid, and includes a plurality of (eg, two) three-phase inverters. It has a configuration in which INV ₁ and INV ₂ are connected in parallel, the DC side of both inverters INV ₁ and INV ₂ is connected in common to the distributed power source B, and the AC side thereof is a three-phase AC through the interconnection transformer TR. The system is configured by connecting to the system power supply Vs.

Each of the inverters INV ₁ and INV ₂ is provided with switching elements S _{1 to} S ₆ of a full bridge structure, an electrolytic capacitor C is connected to the DC side thereof, and a three-phase reactor FL for output filter is connected to the AC side thereof, and the AC side thereof. PW based on the output current I detected by the current transformer CT provided in the
A control unit E for generating a gate pulse G for igniting the switching elements S _{1 to} S ₆ by M control is provided, and the DC power output from the distributed power source B is charged in the electrolytic capacitor C, and the charging power is charged. AC conversion is performed by switching the inverters INV ₁ and INV ₂ , and the AC power is supplied to a load (not shown) in the power system.

By the way, in the power converter in which the inverters INV ₁ and INV ₂ are connected in parallel multiplex, the gate pulse for igniting the switching elements S _{1 to} S ₆ by the PWM control in the control unit E of the respective inverters INV ₁ and INV _2. G is generated. Inverter INV
_Since the control unit E of ₁ and INV ₂ generates the gate pulse G by its own PWM control, the phase shift of the gate pulse G may occur in the respective inverters INV ₁ and INV ₂ . Due to the phase shift of the gate pulse G, the switching element S ₁ is switched between the inverters INV ₁ and INV _2.
There is a deviation in the firing timing of ~ S ₆ and the inverter IN
Zero-phase current I ₀ flows between V ₁ and INV ₂ (see FIG. 17).
The problem occurs.

(First Embodiment) In order to prevent the inconvenience that the zero-phase current I ₀ flows, in the first embodiment, the inverters INV ₁ and INV ₁ are based on the PWM control by the triangular wave comparison method in the control unit E. The phase shift of the gate pulse G between ₂ is corrected.

As shown in FIG. 2, the power converter of the first embodiment has a zero-phase current detector 1 for detecting the zero-phase component of the output currents of the inverters INV ₁ and INV ₂ , and its zero-phase current I. _{Based on} the polarity and magnitude of the zero-phase current I ₀ , the calculator 2 that calculates the polarity and magnitude of ₀ by PI control, and the gate pulse G of the switching elements S _{1 to} S ₆ through which the zero-phase current I ₀ flows. Is provided with a pulse generator 3 for shifting the triangular wave signal for generating the signal from the reference phase and outputting the gate pulse G of the switching elements S _{1 to} S ₆ .

Generally, in the PWM control of the triangular wave comparison system, as shown in FIG. 3, the reference sine wave signal I generated by the control unit E and the triangular wave signal II are compared to compare the inverters INV ₁ and INV _{2 with each} other. A gate pulse G for firing the switching elements S _{1 to} S ₆ is generated. Here, the polarity and magnitude of the zero-phase current I ₀ generated in the inverters INV ₁ and INV ₂ are detected by the zero-phase current detection unit 1, and the polarity and magnitude of the zero-phase current I ₀ are set as reference value = 0. After comparison, the calculation unit 2 calculates the bias value (correction value) α based on the polarity and magnitude of the zero-phase current I ₀ by PI control. The pulse generator 3 corrects the triangular wave signal II by shifting it from the reference phase based on the bias value α.

That is, as shown in FIG. 4, the bias value α
If becomes positive (triangular wave signal II 'shown by the chain line in the figure),
By shifting the triangular wave signal II from the reference phase so that the firing timing of the gate pulse G is advanced, the phase shift of the gate pulse G is corrected (the gate pulse G ′ shown by the chain line in the figure). On the contrary, if the bias value α becomes negative (triangular wave signal II ″ shown by the broken line in the figure), the gate pulse G
The phase shift of the gate pulse G is corrected by shifting the phase of the triangular wave signal II from the reference phase so that the firing timing of is delayed (gate pulse G ″ shown by the broken line in the figure).

In the first embodiment, the inverters INV ₁ and INV ₂ are based on the PWM control of the triangular wave comparison system.
The phase shift of the gate pulse G between the inverters INV ₁ and INV ₂ is corrected by shifting the triangular wave signal II from the reference phase by the bias value α in accordance with the polarity and the magnitude of the zero-phase current I ₀ generated at. As a result, the switching timings of the switching elements S _{1 to} S ₆ in both inverters INV ₁ and INV ₂ can be perfectly matched and synchronized, and the zero-phase current I can be obtained between the inverters INV ₁ and INV _{2. 0} stops flowing.

To correct the phase shift of the gate pulse, _{one of} the _two inverters INV ₁ and INV ₂ (eg, INV ₁ ) is used as a reference, and the other inverter (eg, INV ₂ ) is compared with a triangular wave. The triangular wave signal II may be shifted from the reference phase by the bias value α by the PWM control of the method. In the PWM control of the triangular wave comparison method, the phase shift of the gate pulse G is corrected for each of the U phase, V phase, and W phase.

(Second Embodiment) In the second embodiment,
In order to prevent the above-described inconvenience that the zero-phase current I ₀ flows, the inverters INV ₁ and IN ₁ are controlled by the control unit E based on the PWM control by the hysteresis comparator method.
The gate pulse G between V ₂ is corrected.

Generally, in the PWM control of the hysteresis comparator system, in the control unit E, the output current reference value I of the inverters INV ₁ and INV ₂ as shown in FIG.
^ref (U-phase current reference value Iu ^ref , V-phase current reference value I
v ^ref , the W-phase current reference value Iw ^ref ) and the hysteresis width ΔI (fixed) for the output current reference value I ^ref are preset, and the output current I (U of the inverters INV ₁ and INV ₂ is set.
Phase current Iu, V-phase current Iv, W-phase current Iw), the inverter INV ₁ , so that the output current I falls within the range of the output current reference value I ^ref ± hysteresis width ΔI (see FIG. 6). A gate pulse G (U-phase, V-phase, W-phase gate pulse Gu, Gv, Gw) that fires the switching elements S _{1 to} S ₆ of INV ₂ is generated.

In FIG. 5 and FIG. 7, what is described as “up ON” and “up OFF” is the inverter INV of FIG.
₁ , a switching element S ₁ connected to the P side of INV ₂ ,
It means igniting S ₃ and S ₅ , and conversely, "down ON"
Means "below OFF" to ignite the switching element S _2, S _4, S _6, which is connected to the N side of the inverter INV _1, INV _2.

The power converter of the second embodiment, as shown in FIG. 8, has a zero-phase current detecting section 5 for detecting a zero-phase component of the output current I of the inverters INV ₁ and INV ₂ , and the zero-phase current thereof. Depending on the polarity and magnitude of I ₀ , the inverter INV ₁ ,
A hysteresis width determination unit 6 for adjusting the hysteresis width [Delta] I with respect to the output current reference value I ^ref of INV _2, inverter INV ₁ should adjust the hysteresis width [Delta] I, INV ₂
The correction unit selecting unit 7 for selecting the switching elements S _{1 to} S ₆ of _{No. 1} and the control unit E in which the pulse generating unit 4 is added.

In the PWM control of the hysteresis comparator system, as described above, the output current I of the inverters INV ₁ and INV ₂ is the output current reference value I ^ref ± hysteresis width Δ.
Inverter INV so that it falls within the range of I (see FIG. 6)
₁ , a gate pulse G for igniting the switching elements S _{1 to} S ₆ of INV ₂ is generated.

That is, the polarity and the magnitude of the zero-phase current I ₀ generated in the inverters INV ₁ and INV ₂ are detected by the zero-phase current detector 5 and the correction is made according to the polarity and the magnitude of the zero-phase current I _0. The hysteresis width determination unit 6 adjusts the value α by adding and subtracting the fixed hysteresis width ΔI. Inverter I whose hysteresis width ΔI should be adjusted
NV _1, the switching element S ₁ to S ₆ of INV ₂ selected in the correction target selector 7, the correction signal H (U-phase for the switching element S ₁ to S _6, V-phase, W-phase correction signals Hu, H
The gate pulse G (U-phase, V-phase, W-phase gate pulse Gu, Gv, Gw) is corrected by v, Hw). The correction value α is varied in proportion to the zero-phase current I ₀ by multiplying the zero-phase current I ₀ by a constant gain k.

The adjustment in the hysteresis width determining section 7 is as follows.
If the polarity of the zero-phase current I ₀ is positive, the inverter IN
The upper hysteresis width is reduced from the fixed hysteresis width ΔI by the correction value α so as to shorten the switching time of the switching elements S ₁ , S ₃ and S ₅ connected to the P side of V ₁ and INV ₂ . On the contrary, if the polarity of the zero-phase current I ₀ is negative, the lower hysteresis is set so as to shorten the switching time of the switching elements S ₂ , S ₄ , S ₆ connected to the N side of the inverters INV ₁ , INV _2. The width is reduced from the fixed hysteresis width ΔI by the correction value α.

FIG. 7 specifically illustrates the latter case, for example.
The zero-phase current I₀Has a negative polarity,
Inverter INV₁, INV₂Switch connected to the N side of
Element S₂, S_Four, S₆The switching time of
The lower hysteresis width is fixed to a fixed hysteresis width ΔI
Therefore, the correction value α is reduced. The dotted line in the figure is the one before
Inverter INV₁, INV₂Output current I, solid line is corrected
Later inverter INV ₁, INV₂Output current I'of it
Shows each.

In the second embodiment, the hysteresis
Based on the PWM control of the comparator system, the inverter I
NV₁, INV₂Zero-phase current I generated in₀Polar and large
Inverter INV depending on the size₁, INV₂Output current of
Reference value I^refFor the correction value α
The zero-phase current I₀Based on the polarity of
Desired switching element S selected by₁~ S₆Gate of
The loss G can be corrected, and as a result, both inverters
INV₁, INV₂Switching element S in ₁~ S₆of
Synchronize by making the switching timing completely the same
be able to.

The correction of the gate pulse G is based on one of the two inverters INV ₁ and INV ₂ (eg, INV ₁ ) as a reference, and the other inverter (eg, INV ₂ ) is of a hysteresis comparator type. The hysteresis width ΔI may be increased or decreased by the correction value α by PWM control. In the case of the PWM control of the hysteresis comparator method, the gate pulse G is corrected for each of the U phase, V phase, and W phase.

(Third Embodiment) In the third embodiment, in order to prevent the above-described inconvenience that the zero-phase current I ₀ flows, the control unit E uses the vector-based PWM.
The gate pulse G between the inverters INV ₁ and INV ₂ is corrected based on the control.

Here, the inverter INV₁, INV₂From
Output voltage vector V that can be generated₀~ V₇Is shown in FIG.
As shown in (b), the switching element S₁~ S₆The eight
It consists of a firing pattern and is suitable for vector type PWM control.
The output voltage vector V ₀~ V₇Selection and departure
I try to control my life time. In addition, in FIG.
Switching element S₁~ S₆In the firing pattern of
Itching element S₁And S₂, S₃And S_Four, S_FiveAnd S₆Is that
It is fired in the opposite direction.

With reference to these eight output voltage vectors V _{0 to} V ₇ (hereinafter referred to as reference output voltage vectors), correction output voltages as shown in FIG. 10 are obtained with respect to the reference output voltage vectors V _{0 to} V ₇ . The vectors VN _{1k to} VN _6k are newly defined. In the corrected output voltage vector VN _{1k to} VN _6k ,
N shown in FIG. 10 is the switching elements S ₁ , S ₃ , S ₅ and N connected to the P side of the inverters INV ₁ , INV _2.
This means that both of the switching elements S ₂ , S ₄ , S ₆ connected to the side are turned off. Further, k means that the switching elements S _{1 to} S ₆ of the phase in which the zero-phase current I ₀ is flowing are selected. In the U phase, k = 1, in the V phase, k = 2, In the case of the W phase, k = 3.

The power converter of the third embodiment is shown in FIG.
As shown in 11, the inverter INV ₁, INV₂Output power
Zero-phase current detector 8 for detecting the zero-phase component of the flow I, and its zero-phase
Current I₀Zero-phase current I based on the polarity and magnitude of₀Flow
Switching element S₁~ S₆Select one of the
Selected switching element S of₁~ S₆To turn off
Outputs the vector determination unit 9 that determines the output voltage vector
The control unit E added to the current control unit 10 is provided.

In this vector type PWM control, the switching element of the phase in which the zero-phase current I ₀ generated between the inverters INV ₁ and INV ₂ flows, that is, the inverter I
Switching element S connected to the P side of NV ₁ and INV _2
1, S _3, S ₅ or the switching element S ₂ which is connected to the N side, S _4, the reference output voltage vector V ₀ ~V ₇ and the correction output voltage vector output voltage vector to OFF at least one of S ₆ It is selected from VN _{1k to} VN _6k , and thereby a gate pulse G for igniting the switching elements S _{1 to} S ₆ of the inverters INV ₁ and INV ₂ is generated.

That is, the polarity and magnitude of the zero-phase current I ₀ generated in the inverters INV ₁ and INV ₂ are detected by the zero-phase current detector 8. Here, when the zero-phase current I ₀ is detected, the dead zone β is preset to prevent excessive hunting from occurring in the switching elements S _{1 to} S ₆ of the inverters INV ₁ and INV ₂ . .
Therefore, if the zero-phase current I ₀ is within the dead zone β, the normal vector control by the reference output voltage vectors V _{0 to} V ₇ is executed. If the zero-phase current I ₀ is out of the range of the dead zone β, the reference output voltage vectors V _{0 to} V ₇ and the corrected output voltage vector V ₀ due to the difference in the flow direction of the zero-phase current I _0.
The following vector control for selecting a desired output voltage vector from N _{1k to} VN _6k is executed.

When the zero-phase current I ₀ is larger than the dead zone + β, normal output voltage vectors V ₁ , V ₂ , V ₄ (switching elements S ₁ , S connected to the P side of each inverter INV ₁ , INV ₂₎ are output. ₍ Only one of S ₃ and S ₅ is ON), the reference output voltage vector V ₀ is selected, and other normal output voltage vectors V ₃ , V ₅ and V ₆ are corrected output voltage vector VN _3k. , VN _5k , VN _6k are selected.
On the contrary, when the zero-phase current I ₀ is smaller than the dead zone −β, the normal output voltage vectors V ₃ , V ₅ , V ₆ (each inverter IN
V _1, for the switching element S ₂ which is connected to the N side of the INV _2, S _4, only one of S ₆ is ON), and selects a reference output voltage vector V _7, other conventional output voltage For the vectors V ₁ , V ₂ and V ₄ , the corrected output voltage vectors VN _{1 k} , VN _2k and VN _4k are selected.

As described above, in the third embodiment, the inverters INV ₁ , I are based on the PWM control of the vector system.
A switching element in a phase in which a zero-phase current I ₀ generated between NV ₂ is flowing, that is, P of the inverters INV ₁ and INV ₂ .
The reference output voltage vector V ₀ is an output voltage vector for turning off at least one of the switching elements S ₁ , S ₃ , S ₅ connected to the side or the switching elements S ₂ , S ₄ , S ₆ connected to the N side. ~ V ₇ and the corrected output voltage vectors VN _{1k to} VN _6k , the gate pulse G between the inverters INV ₁ and INV ₂ can be corrected, and as a result, both inverters INV ₁ and INV ₁
The zero-phase current I ₀ between V ₂ can be suppressed.

The correction of the gate pulse G is performed by two units.
Inverter INV₁, INV₂One of the INVA
Data (eg INV₁) As a reference
Data (eg INV₂) About vector system PWM system
Zero-phase current I₀Switching element S₁~ S₆of
Select one of the selected switching elements S
₁~ S₆If you decide the output voltage vector to turn off
Yes. In the case of this vector type PWM control, the gate pulse
The correction of the scan G is collectively performed for the U phase, the V phase, and the W phase.

[0064]

According to the present invention, P of the triangular wave comparison system is used.
Means for shifting the triangular wave from the reference phase by the correction value according to the polarity and magnitude of the zero-phase current generated in the inverter based on the WM control, and the zero generated in the inverter based on the PWM control of the hysteresis comparator method. Means for increasing / decreasing the hysteresis width with respect to the reference value of the output current of the inverter according to the polarity and magnitude of the phase current, and the polarity and magnitude of the zero-phase current generated in the inverter based on the PWM control of the vector system. Take a measure in terms of hardware between the inverters by selecting one of the switching elements through which the zero-phase current flows based on the above, and by determining the output voltage vector that turns off the selected switching element. It is possible to prevent the zero-phase current from flowing between the inverters by simple means. As a result, it is easy to reduce the cost and size of the product.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a hardware configuration of a power conversion device for grid interconnection in an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a control unit in PWM control of a triangular wave comparison method in the power conversion device of FIG.

FIG. 3 is a waveform diagram for explaining a procedure for generating a gate pulse by comparing a triangular wave signal and a sine wave signal in PWM control of the triangular wave comparison method.

FIG. 4 is a waveform diagram for explaining a procedure for phase-shifting a triangular wave signal to correct a gate pulse in PWM control of the triangular wave comparison method.

FIG. 5 is a block diagram showing a configuration for explaining a procedure for setting a hysteresis width for an output current reference value of an inverter and generating a gate pulse in PWM control of a hysteresis comparator system.

FIG. 6 is a waveform diagram showing an output current obtained by setting a hysteresis width with respect to an output current reference value of an inverter in a hysteresis comparator type PWM control.

FIG. 7 is a waveform diagram for explaining the procedure for correcting the gate pulse by adjusting the hysteresis width in the hysteresis comparator PWM control.

FIG. 8 is a block diagram showing a configuration of a control unit by PWM control of a hysteresis comparator method in the power conversion device of FIG.

9A and 9B are reference output voltage vectors that can be generated by an inverter in vector-based PWM control, where FIG. 9A is a vector diagram and FIG. 9B is a vector table.

FIG. 10 is a table showing a newly defined corrected output voltage vector in vector-based PWM control.

FIG. 11 is a block diagram showing a configuration of a control unit under vector-based PWM control in the power conversion device of FIG. 1.

FIG. 12 is a circuit diagram showing a first conventional example of a power conversion device for grid interconnection.

FIG. 13 is a circuit diagram showing a second conventional example of a power conversion device for grid interconnection.

FIG. 14 is a circuit diagram showing a third conventional example of a power interconnection device for grid interconnection.

FIG. 15 is a circuit diagram showing a fourth conventional example of a power conversion device for grid interconnection.

FIG. 16 is a circuit diagram showing a fifth conventional example of a power conversion device for grid interconnection.

FIG. 17 is a partial circuit diagram for explaining a mechanism of a zero-phase current flowing between inverters.

[Explanation of symbols]

B Distributed power source S _{1 to} S ₆ Switching element TR Interconnection transformer Vs System power source INV ₁ and INV ₂ Inverter E Control unit I ₀ Zero-phase current I Output current G Gate pulse I ^ref Output current reference value ΔI Hysteresis width V _{0 to} V ₇ Output voltage vector (reference output voltage vector) VN _{1k to} VN _6k Output voltage vector (correction output voltage vector) 1 Zero-phase current detection unit 2 Calculation unit 3 Pulse generation unit 5 Zero-phase current detection unit 6 Hysteresis width determination unit 7 Correction Target selection unit 8 Zero-phase current detection unit 9 Vector determination unit

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5G066 CA08 DA08 HA15 HB03 HB06                       HB07 JB04                 5H007 BB07 CA01 CB05 CC05 CC32                       DA05 DB01 DC02 EA02 FA13

Claims (9)

[Claims] 1. A distributed power source is commonly connected to the DC side, a system power source is connected to the AC side via an interconnection transformer, and a DC power of the dispersed power source is AC power by igniting a switching element. In a power conversion device for grid interconnection, in which a plurality of inverters for converting to are connected in parallel and a switching element is ignited by a gate pulse based on PWM control of a triangular wave comparison method to control the output current of the inverter,
A zero-phase component of the output current of the inverter is detected, and based on the polarity and magnitude of the zero-phase current, a triangular wave signal for generating a gate pulse of a switching element through which the zero-phase current flows is phase-shifted from a reference phase. An electric power converter for grid interconnection, comprising a control unit for controlling the electric power. 2. The controller includes a zero-phase current detector that detects a zero-phase component of the output current of the inverter, a calculator that calculates the polarity and magnitude of the zero-phase current, and a polarity of the zero-phase current. And a pulse generator for generating a gate pulse of the switching element through which the zero-phase current flows based on the magnitude and the magnitude thereof by shifting the triangular wave signal from the reference phase. Power converter for grid interconnection. 3. A plurality of inverters are connected in parallel to be connected to a system power supply, and a switching element is fired by a gate pulse based on PWM control of a triangular wave comparison method to control the output current of each inverter. In a method for controlling a grid interconnection power conversion device for converting DC power of a distributed power source provided in common to an inverter into AC power,
A zero-phase component of the output current of the inverter is detected, and based on the polarity and magnitude of the zero-phase current, a triangular wave signal for generating a gate pulse of a switching element through which the zero-phase current flows is phase-shifted from a reference phase. A method for controlling a power conversion device for grid interconnection, comprising: 4. A distributed power supply is commonly connected to the DC side, a system power supply is connected to the AC side through an interconnection transformer, and a DC power of the distributed power supply is AC power by igniting a switching element. In the power conversion device for grid interconnection, in which a plurality of inverters for converting into inverters are connected in parallel and the output current of the inverters is controlled by igniting the switching element by a gate pulse based on PWM control of a hysteresis comparator method, the output of the inverters Detects the zero-phase current, and based on the polarity and magnitude of the zero-phase current, the hysteresis width for generating the gate pulse of the switching element through which the zero-phase current flows is set to the output current reference value of the inverter. A power conversion device for grid interconnection, comprising a control unit for adjusting. 5. The zero-phase current detection unit for detecting the zero-phase component of the output current of the inverter, and the hysteresis width for the output current reference value of the inverter according to the polarity and magnitude of the zero-phase current. The power conversion device for grid interconnection according to claim 4, further comprising: a hysteresis width determining unit to be adjusted, and a correction target selecting unit to select a switching element of an inverter to adjust the hysteresis width. 6. A PW of a hysteresis comparator type in which a plurality of inverters are connected in parallel and are connected to a system power supply.
Power conversion for grid interconnection that converts DC power of a distributed power source provided in common to each inverter into AC power by controlling the output current of the inverter by firing a switching element by a gate pulse based on M control In the control method of the device, detecting the zero-phase component of the output current of the inverter, based on the polarity and magnitude of the zero-phase current,
A control method for a grid interconnection power conversion device, characterized in that a hysteresis width for generating a gate pulse of a switching element through which the zero-phase current flows is adjusted with respect to an output current reference value of an inverter. 7. A distributed power source is commonly connected to the DC side, a system power source is connected to the AC side via an interconnection transformer, and a DC power of the dispersed power source is AC power by igniting a switching element. In a power conversion device for grid interconnection, in which a plurality of inverters for converting into inverters are connected in parallel, and a switching element is ignited by a gate pulse based on vector system PWM control to control the output current of the inverter, the output current of the inverter Control for detecting the zero-phase component, selecting one of the switching elements through which the zero-phase current flows based on the polarity and magnitude of the zero-phase current, and determining the output voltage vector that turns off the selected switching element. A power conversion device for grid interconnection, comprising: 8. The control unit is one of a zero-phase current detection unit that detects a zero-phase component of the output current of the inverter, and a switching element through which the zero-phase current flows based on the polarity and magnitude of the zero-phase current. And a vector determination unit that determines an output voltage vector that turns off the selected switching element. 8. The power interconnection device for grid interconnection according to claim 7, further comprising: 9. A plurality of inverters are connected in parallel to be connected to a system power supply, and a switching element is ignited by a gate pulse based on a PWM control of a vector system to control an output current of each inverter. In a method of controlling a grid interconnection power converter that converts DC power of a distributed power source provided in common to AC power, a zero-phase component of the output current of the inverter is detected, and a polarity of the zero-phase current and A control method of a power conversion device for grid interconnection, comprising selecting one of switching elements through which a zero-phase current flows based on a magnitude and determining an output voltage vector for turning off the selected switching element.