JP2000217365A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress DC offset produced in a single-phase or 3-phase AC system, enable the employment of an economical ripple detecting means, reduce the cost and minimize the influences of temperature change and change with time to improve reliability. SOLUTION: A power converter has an AC unit, a DC unit, a switching unit 1 connected between the AC unit and the DC unit and converts power by its switching operation and a control unit 6 which controls the switching unit 1. A ripple detecting means which detects a ripple component appearing on the DC side is provided in the DC unit. If a DC component is contained in the output current of the AC unit, a ripple component whose frequency is the same as that of the AC frequency of the AC unit output current is superposed on the output current of the DC unit. As the ripple detecting means is provided in the DC unit, the ripple component contained in the DC unit output current is detected and, in order to control the DC component contained in the current of the AC unit, the switching unit 1 is controlled by control signals including DC component compensation signals to compensate DC offset.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter which operates between a DC power system and a single-phase or three-phase AC power system. More specifically, the present invention relates to control of a DC component included in an AC output current of this type of power converter. The power conversion device according to the present invention includes an inverter device, an active filter, a converter device, and the like.

[0002]

2. Description of the Related Art Semiconductor power converters using semiconductor switching elements are used for various purposes. DC /
A forward conversion device and an inverse conversion device that perform power conversion during AC are representative examples of this. According to the above-described semiconductor power conversion device, electric energy can be converted into a desired form with high efficiency by a combination of a control technique and a sensor circuit and an electronic circuit for realizing the control technique.

Conventionally, power converters that perform forward conversion, reverse conversion, or bidirectional conversion for use by connecting to a three-phase AC power system include sine-wave input type forward converters and distributed power supplies. Inverting devices, active filters, and the like to be used are listed.

[0004]

This type of power converter can achieve a desired power conversion by utilizing a control technique and an electronic circuit technique for realizing the control technique. However, on the other hand, even a slight error in a signal in a sensor circuit or an electronic circuit constituting the control device is reflected as an input / output error of the power conversion device. There was a risk of damaging the equipment. For example, the DC component or the low-frequency component included in the AC output component of the power converter demagnetizes the iron core of the transformer, causing an excessive inrush current and damaging the equipment. One.

[0005] As an example, "Distributed power system interconnection technical guideline (JEAG 9701, JEAG 9701)" applied to a distributed power system interconnection inverter, describes the AC output of the inverter. It is stated that as a countermeasure for preventing the pole transformer from being demagnetized due to the DC component contained in the DC output component, the DC component contained in the AC output current must be suppressed to within 1.0% of the rated effective current.

For this reason, as a conventional measure, for example, Japanese Patent No. 2774685 has proposed that a DC component included in an output current is detected by a sensor and the DC component of the output current is compensated based on the signal. I have. As another example, in a grid-connected inverter for photovoltaic power generation,
A technology that uses a circuit that omits a transformer installed on the AC output side is a collection of lectures (papers) of the Joint Research Meeting of the Japan Solar Energy Society and the Japan Wind Energy Association (November 30, 1995 to December 1, 1995). No. 13). In the inverter disclosed in this paper, in order to prevent the DC component from flowing out to the AC output side, a current detector with good linearity is used as a current detector for AC current detection,
By adding an automatic zero adjustment circuit to the current detector,
The zero-point drift correction of the detector is always performed.

However, in the conventional countermeasures against the DC component disclosed in the above patent, the DC output error is detected by a detection circuit combining a sensor and an amplifier circuit. Limited by
For this reason, there remains a problem in terms of cost such as the need to use highly accurate and reliable parts for the analog parts used in the sensor and compensator, and the necessity of making adjustments at the factory before shipping. Was.

Further, since the detection circuit is affected by the ambient temperature environment or the like, it is necessary to measure the temperature characteristics of the detection circuit in advance and perform compensation based on information from the temperature sensor. In order to avoid such inconvenience, it is necessary to adopt parts such as individual parts having small variations in temperature characteristics and to arrange a temperature sensor, so that the system configuration and the design procedure become complicated. It was inevitable. In addition, conventional methods for preventing DC component outflow in grid-connected inverters omitting transformers, as introduced in the above-mentioned papers of the proceedings, rely on the performance of the current detector for basic DC detection. Therefore, it is necessary to use an expensive detector. Further, since the output of the current detector is corrected by the automatic zero-adjustment circuit, there is a problem that a complicated and sophisticated circuit is required.

Further, when a compensating circuit for suppressing the DC component of the output current is provided based on the DC component signal detected by the detector, the compensating circuit is required to have characteristics with less offset and drift, and high quality is required. There is a problem that a circuit is required. In particular, in a distributed power generation system such as a photovoltaic power generation that is expected to spread due to lower prices, the use of expensive components may increase the overall cost and affect the spread of the entire system.

One object of the present invention is to provide a power converter capable of suppressing the occurrence of a DC offset in a single-phase or three-phase AC system.

Another object of the present invention is to provide a power conversion device which can use inexpensive ripple detecting means and can reduce the price of the entire device.

Still another object of the present invention is to provide a highly reliable power converter capable of minimizing the effects of temperature change and aging.

[0013]

In order to solve the above-described problems, a power supply is connected between the DC power system and the AC power system to transfer power between the DC power system and the AC power system. The power converter of the present invention, an AC unit connected to the AC power system, a DC unit connected to the DC power system,
A switching unit is connected between the DC unit and the AC unit and performs power conversion by a switching operation, and a control unit that controls the switching unit.

The DC section is provided with ripple detecting means for detecting a ripple component appearing on the DC side and generating a ripple detection signal. The difference from the conventional one is that the ripple detecting means is provided not in the AC section but in the DC section. The current output from the switching unit to the AC unit (hereinafter referred to as “output current”) includes a DC component (hereinafter “DC offset”).
) Is included in the DC section, a ripple component having the same frequency as the AC frequency of the AC section output current is superimposed. In the present invention, by providing the ripple detection means in the DC section, the ripple component appearing in the DC section is detected by the ripple detection means as a reflection of the DC offset included in the output current.

The control section receives a ripple detection signal from the ripple detection means, generates a DC component compensation signal for controlling a DC component included in the current of the AC section based on the ripple detection signal, The switching unit is controlled by a control signal including a compensation signal to compensate for a DC offset. The compensation of the DC offset in the control unit is to make the DC offset substantially zero. Such an operation is based on the ripple detection signal detected by the ripple detection means.
This is achieved by controlling the switching operation of the switching unit so that the component of the AC frequency is not included.

In the present invention, it is necessary to provide a ripple detecting means in the DC section which is the input side of the switching section. The ripple detecting means has a function of detecting a single-phase or three-phase AC frequency component. Just prepare. That is, since there is almost no influence of the DC offset or gain error of the ripple detecting means, an inexpensive ripple detecting means can be used, and the cost of the entire apparatus can be reduced. In addition, since the influence of temperature change and aging can be suppressed to a minimum, a highly reliable device can be obtained.

The power converter according to the present invention includes a DC-AC inverter for converting DC to single-phase or three-phase AC, an AC-DC converter for converting single-phase or three-phase AC to DC, Filter etc. are included. Further, the control unit may be a computer, a dedicated analog processing circuit, a digital processing circuit, or a combination of both.

Further, a power conversion device according to another aspect of the present invention is a power conversion device including a DC connection portion connected to a DC power supply and an AC connection portion connected to an AC power supply, and an output of the power conversion device. Output power control means for controlling power; modulation means for calculating an AC current command value based on an output power command signal provided by the output power control means to generate an AC current command signal; A current control means for controlling the power conversion means based on the current command signal; a current detection means for detecting a DC side current of the power conversion means; and an AC output appearing at an AC connection portion based on a current detected by the current detection means. DC component outflow prevention means for detecting a DC component included in the DC component and generating a signal for removing or reducing the DC component. In one aspect of the present invention, the DC component outflow prevention unit is synchronized with a system including a filter unit that extracts a current component having the same frequency as the AC fundamental wave component from a current signal output from the current detection unit, and an AC power supply. A multiplier for multiplying the reference sine wave by the output signal of the filter means, and a compensation means for compensating for the DC component of the AC output current according to the output of the multiplier. In this case, the multiplier is a digital multiplier, the filter means and the compensation means are also configured as digital means, and the DC component outflow prevention means is provided with a reference sine wave digital signal synchronized with a system including an AC power supply. Preferably, the multiplication of the reference sine wave and the output signal of the filter means is performed digitally. Further, the DC component outflow prevention means calculates the compensation signal for compensating the DC component of the AC output current based on the output of the multiplier by the compensation means, and adds the compensation signal to the AC current command signal in reverse polarity. Is preferred.
The current detecting means may be omitted from the DC current detecting function, so that a low-cost current detecting means can be used.

[0019]

FIG. 1 is a block diagram showing a configuration of a power converter according to the present invention. FIG. 1 shows a three-phase AC interconnection inverter device. The power converter according to the present invention includes the switching unit 1, the ripple detection unit 17, and the control unit 6. Reference numeral 2 denotes a filter circuit.

The switching unit 1 includes DC connection units d and e,
It includes three-phase AC connections a, b, and c. Switching unit 1
Performs power conversion between the DC side DC connected to the DC connection parts d and e and the three-phase AC side AC connected to the three-phase AC connection parts a, b and c. When the power transmission goes from the DC side DC to the three-phase AC side AC as indicated by an arrow F1, the switching unit 1 operates as a DC-AC inverter (inverse conversion). In this case, the switching unit 1 may use any type of inverter circuit such as a non-insulated inverter such as a full-bridge inverter and an NPC inverter, or an isolated inverter. Power transmission is indicated by arrow R
As shown by 1, when going from the three-phase AC side AC to the DC side DC, the switching unit 1 operates as an AC-DC converter (forward conversion). Also in this case, various circuit systems can be adopted as in the case of the DC-AC inverter.

A DC power supply 5 and a capacitor 4 are provided at the DC connection sections d and e of the switching section 1, and the switching section 1 is connected to the DC power supply 5 or a DC load. The three-phase AC system 3, the capacitor 4, and the DC power supply 5 may be considered as external requirements or internal requirements of the power converter.

The ripple detecting means 17 detects a ripple component appearing on the DC side DC as a reflection of the DC offset included in the output current. The embodiment will be described on the assumption that the ripple component of the current appearing on the DC side DC is detected. In this case, a current transformer is typically used as the ripple detecting means 17. However, any other type of ripple detecting means can be used as long as the means detects ripples.

The control unit 6 is supplied with the ripple detection signal y from the ripple detection means 17 and supplies the supplied ripple detection signal y
, A signal for controlling the DC component included in the three-phase AC side AC is generated, and the switching unit 1 is controlled by the control signal S0 including the signal to compensate the DC component included in the three-phase AC side AC. I do.

The embodiment has current sensors 15 and 16 for detecting the alternating currents ia and ib. The control unit 6 controls the switching operation of the switching unit 1 based on the current detection signals S1 and S2 of the current sensors 15 and 16 such that the output currents ia to ic of the respective phases a, b and c become equal to the command values. I do. Further, in the embodiment, the control unit 6 receives the terminal voltage signal Vc of the capacitor 4 and the phase signal S3 detected by the voltage detection unit 19 coupled to the three-phase AC system 3, and has a predetermined phase. A sine-wave current command value is calculated, and a current command signal corresponding to the current command value is generated. The control unit 6 controls the control signal S0 including the current command signal.
To the switching unit 1 to control the switching operation of the switching unit 1. Further, the current sensors 15, 16
And a filter 2 between the three-phase AC connection portions a, b, and c. The filter 2 selectively passes the component of the three-phase AC frequency f.

The ripple detecting means 17 is different from the conventional one,
It is provided not on the three-phase AC side AC but on the DC side DC. Output currents ia to ic output to three-phase AC side AC
Includes a DC offset,
A ripple having the same frequency as the frequency f of the three-phase alternating current is superimposed. This point will be described with reference to FIGS.

FIG. 2A shows waveforms of an output current i not including a DC offset and a voltage V. The output current i is a current viewed in one phase of the three-phase alternating current, and the voltage V is a phase voltage. There is a phase difference θ between the voltage V and the output current i.

FIG. 2B is a power waveform diagram at the time of the phase difference θ shown in FIG. 2A. As is well known, power P
= V · i · cos (θ). In FIG. 2B, the power P
Includes an average power (DC component) and a frequency component 2f that is twice the three-phase AC frequency f. FIG. 2B shows the output current i
Does not include a DC offset, the power P is a straight line having no level fluctuation with time.
The current Idc flowing to the DC side DC is proportional to the power P. Therefore, the current Idc flowing to the DC side DC also shows a constant value with no temporal level fluctuation.

FIG. 3A shows waveforms of the output current i and the voltage V when a DC offset is included. Because of the DC offset △ Idc, the waveform of the output current i is raised by the DC offset △ Idc. For this reason, the power P fluctuates as shown in FIG. In this case, the power P fluctuates at the three-phase AC frequency f.
Since the current Idc flowing in the DC side DC is proportional to the power P, a ripple fluctuating at the three-phase AC frequency f appears in the current Idc flowing in the DC side DC.

In the present invention, the ripple detecting means 17
Is provided on the DC side DC, so that the ripple component of the DC side DC, which is a reflection of the DC offset 出力 Idc included in the output current i, is detected by the ripple detecting means 17.

The control section 6 generates a signal for controlling the DC offset included in the three-phase AC side AC based on the ripple detection signal y supplied from the ripple detection means 17,
The switching unit 1 is controlled by the control signal S0 including this signal.
To compensate for the DC offset ΔIdc. The compensation of the DC offset △ Idc in the control unit 6 is to make the DC offset △ Idc substantially zero. Such an operation is achieved by controlling the switching operation of the switching unit 1 so that the ripple detection signal y detected by the ripple detection unit 17 does not include the component of the system frequency f.

In the present invention, the ripple detection means 17 is required on the DC side DC.
Need only have a function of detecting the three-phase AC frequency component f appearing on the DC side DC. That is, since there is almost no influence of errors in the DC offset and gain of the ripple detecting means 17, an inexpensive current sensor can be used, and the cost of the entire apparatus can be reduced. In addition, since the influence of temperature change and aging can be suppressed to a minimum, a highly reliable device can be obtained.

FIG. 4 shows a more specific circuit diagram of the power converter according to the present invention. The switching unit 1 is configured by a full bridge circuit using a semiconductor switching element. The filter 2 is constituted by an LC filter. The control unit 6 includes an output power control unit 8 for controlling DC / AC conversion power, current command calculation units 9 and 11, a reference wave generation unit 1
0, current control units 12, 13 and PWM modulation unit 14.

The reference wave generator 10 is constituted by, for example, a combination of a PLL circuit and a data table.
9, synchronized with the voltage of the three-phase AC system 3 detected by
Further, reference sine wave signals x and z having reference amplitudes are calculated.

The operation of the three-phase power converter of this configuration is, for example,
POWER ELECTRONICS (Ned Mohan et al., 1989 JOHN WILEY &
SONS, Inc.) and so on, and details of the basic operation will be omitted.

A feature of the embodiment shown in FIG. 4 is that it has a DC component outflow prevention means 7. FIG. 5 shows DC outflow prevention means 7.
Is shown. The illustrated DC component outflow prevention means 7 includes a filter 71, multipliers 721 and 722, and compensators 731 and 7
32, filters 741, 742 and two-phase / 3-phase converter 7
5 and so on. In the present invention, the multiplication units 721 and 7
22, compensators 731 and 732, and two-phase / 3-phase converter 75
And the like indicate the circuit configuration or the order of signal processing.

The ripple detection signal y from the ripple detecting means 17 is input to one of the input terminals of the multipliers 721 and 722 via the filter 71. The reference sine wave signals x and z from the reference sine wave generator 10 are input to the other terminals of the multipliers 721 and 722. The reference sine wave signals x and z are sine wave signals having the same frequency f as in the three-phase AC system, and have a phase difference of 90 degrees. For example, the reference sine wave signal x is selected as a sine wave signal synchronized with the phase voltage of the first phase (connection terminal a) of the three-phase AC system.
A sine wave delayed by 90 degrees from the reference sine wave signal x can be selected.

The reference sine wave signals x and z are generated by the reference sine wave generator 10. The reference sine wave generator 10 generates reference sine wave data from the data table based on the phase synchronization signal of the PLL circuit, and adds sine wave data corresponding to the reference sine wave signals x and z to the data table. Can be created.

The multiplying units 721 and 722 are connected to the ripple detecting means 1
7 and the reference sine wave signals x and z are respectively multiplied. Output M of multipliers 721 and 722
α and Mβ are input to filters 741 and 742, respectively. The filters 741 and 742 can be omitted. The outputs of the filters 741 and 742 are output to a compensator 731,
732 and the outputs of the compensators 731 and 732 are 2
It is input to the phase / three-phase converter 75 and added to the detection outputs of the current sensors 15 and 16 provided on the AC side.

Next, the operation of the DC component outflow prevention means 7 shown in FIG. 5 will be described with reference to the waveform diagrams of FIGS.
FIG. 6 is a waveform diagram when the output current does not include a DC offset, and FIG. 7 is a waveform diagram when the output current includes a DC offset.

When ignoring high frequency components caused by the switching operation in the switching unit 1, the output currents ia to ic and the output voltages (phase voltages) va to vc of the switching unit 1 can be written as follows. it can. va = Vm cos (ωt) vb = Vm cos (ωt-2π / 3) vc = Vm cos (ωt-4π / 3) (1) ia = Im cos (ωt + θ) + Iad ib = Im cos (ωt + θ−2π / 3) + Ibd ic = Im cos (ωt + θ−4π / 3) + Icd (2) Vm is the maximum value of the output phase voltage, Im is the maximum value of the output current, ω
Represents the angular frequency of the fundamental wave, and Iad, Ibd, and Icd represent DC offsets included in the output currents ia to ic. θ
Is the phase angle of the output currents ia-ic.

If the output currents ia to ic do not include a DC offset, iad = Ibd = Icd = 0 holds, and the waveforms are as shown in FIGS. 6 (a) and 6 (b). As a specific example in the case where the output current includes a DC offset, for example, ia = 1.5 A for the a phase, ib = −3.
FIGS. 7A and 7B show voltage and current waveforms when a DC offset of 0 A is included.

Here, in analyzing the instantaneous value of the three-phase alternating current, a method of converting the three-phase alternating current into an equivalent two-phase alternating current and analyzing it is applied. Such analysis methods are well known to those skilled in the art. According to this analysis method, the three-phase voltage and current are converted into equivalent two-phase alternating current by the following equations (3) and (4). Here, vα, vβ, iα, and iβ represent the voltage and current components of each phase when equivalent two-phase alternating current is set to α phase and β phase, respectively. By the conversion as described above, the three-phase alternating current shown in FIG. 9A or the equations (1) and (2) is converted into the three-phase alternating current shown in FIG.
As shown in the figure, each phase has an equivalent two phase difference of 90 degrees.
It is converted into phase exchanges vα and vβ.

The two-phase voltage v converted as described above
Regarding the waveforms of α and vβ and the waveforms of the currents iα and iβ,
FIGS. 6C and 6D show the case where no DC offset is included, and FIGS. 7C and 7D show the case where the DC offset is included. In the current waveform diagram of FIG. 7D, the currents iα and iβ each include a DC offset, and the DC offset included in the three-phase AC is converted into an equivalent two-phase DC offset in the equivalent two-phase AC model. You can see that it is done. When the voltages and currents shown in Expressions (1) and (2) are converted into two-phase voltage and current by Expressions (3) and (4), the following expression is obtained. The underlined portion is the DC offset on the equivalent two-phase AC.

Here, considering the instantaneous value p of the output power on the two-phase alternating current, p = vα · iα + vβ · iβ (7) The output power p is the output power of the α-phase of two-phase AC (vα
Iα) and the output power of the β phase (vβ · iβ).

FIGS. 6 (e) and 6 (f), and FIGS.
(F) shows the instantaneous output power waveforms of the equivalent two-phase alternating current α-phase and β-phase, and FIGS. 6 (g) and 7 (g) show the instantaneous waveform diagrams of the total total power.

In the waveform diagram of FIG. 6, which does not include the DC offset, the output power of the α-phase and β-phase has the average output power (DC component) superimposed with the ripple of the frequency twice as high as the three-phase AC frequency f. It is observed as a waveform as shown. Since the ripple of the frequency 2f, which is twice the three-phase AC frequency f included in the α-phase output power and the β-phase output power, has a phase difference of 180 degrees, the total output power is only a DC component. (See FIG. 6 (f)).

FIG. 7 in which DC offset is included in output current
In the waveform diagram of FIG. 4, the output power of the α-phase and the β-phase include not only the average output power (DC component) and the frequency component 2f twice as high as the three-phase AC frequency f, but also the same frequency as the three-phase AC frequency f. Ripple is superimposed. The waveform diagram of FIG. 7 or equation (5),
As is clear from (6) and (7), the three-phase AC frequency f
The component a having the same frequency as has the same phase as the α-phase voltage, and the component b has the same phase as the β-phase voltage waveform. However, since the DC offset included in the β phase has a negative polarity,
The phase is inverted by 180 degrees. When the DC current is included in the output current, the output power of the α phase is pa = vαiα = (3/4) VmImcos (θ) + (3/4) VmImCos (2ωt + θ ) + (3/2) Vm ・ Im ・ cos (ωt) (8) The output power of β phase is pb = vβ ・ iβ = (3/4) Vm ・ Im ・ cos (θ) + (3/4) Vm・ Im ・ cos (2ωt + θ) + (√3 / 2) Vm ・ (Iad + Ibd) ・ sin (ωt) (9) The total output power is p = (3/2) Vm ・ Im ・ cos (θ) + (3/2) Vm · Iad · cos (ωt) + (3/2) Vm · (Iad + Ibd) · sin (ωt) (10) The underlined third term in the above equations (8) and (9) is a DC offset having the same frequency f as the three-phase AC.

The instantaneous waveform of the total power is given by the above equation (8).
Since the sum of (9) is obtained, a ripple having the same frequency as the three-phase AC frequency f is included, and the power obtained by synthesizing the waveforms of the components included in the α phase and the components included in the β phase (under the expression (10)) The line portion) is superimposed as shown in FIG.

The DC component outflow prevention means 7 according to the present invention compensates for the DC offset included in the output current using the above characteristics. That is, a component having the same frequency as the three-phase AC frequency f included in the output power is detected, and three-phase DC offset is compensated from the amplitude and phase of the ripple.

If the smoothing capacitor 4 is sufficiently large and its terminal voltage Vc is a DC voltage with little ripple, the waveform of the current flowing through the DC side DC becomes a waveform proportional to the output power waveform. And a ripple detecting means 17 comprising a current detecting element. The ripple detecting means 17 measures a DC input current. This makes it possible to detect a current ripple component having the same frequency component as the three-phase AC fundamental frequency f.

In FIG. 5, a filter 71 removes high-frequency noise due to the switching operation of the switching section 1 and extracts a low frequency component near the fundamental frequency of the three-phase AC frequency f included in the output power.

Next, the multipliers 721 and 722 once decompose the same frequency component as the three-phase AC frequency f output from the filter 71 into α-phase and β-phase signals. The input signal y to the DC component outflow prevention means 7 is a signal proportional to the total output power p (see Equation 10). That is, The reference wave signals x and z are given as x = cos (ωt) z = sin (ωt), respectively.

The output Mα of the multiplication unit 721 is expressed as follows: Mα = y × x = k1 × {(3/2) Vm ・ Im ・ cos (θ) + (3/2) Vm ・ Iad ・ cos (ωt) + (3 / 2) Vm ・ (Iad + Ibd) ・ sin (ωt)} cos (ωt) = (3/2) k1 ・ Vm ・ Im {(1/2) cos (ωt-θ) + (1/2) cos (ωt + θ)} + (3/2) k1 ・ Vm ・ Iad ・ {1/2 + (1/2) ・ cos (2ωt) + (√3 / 2) k1 ・ Vm ・ (Iad + Ibd) ・(1/2) ・ sin (2ωt) (11)

The output Mβ of the arithmetic unit 722 is given by Mβ = y · z = k1 · {(3/2) Vm · Im · cos (θ) + (3/2) Vm · Iad · cos (ωt) + (3 / 2) Vm ・ (Iad + Ibd) ・ sin (ωt)} sin (ωt) = (3/2) k1 ・ Vm ・ Im ・ cos (θ) ・ sin (ωt) + (3/2) k1 ・ Vm Iad · (1/2) · sin (2ωt) + (√3 / 2) k1 · Vm · (Iad + Ibd) · {1 / 2−cos (2ωt)} (12) The outputs Mα and Mβ of the multiplication units 721 and 722 include:
In addition to the necessary DC component, an unnecessary three-phase AC frequency f component and a ripple component having a frequency twice as high as the three-phase AC frequency f are included. The filters 741 and 742 have a role of removing frequency components that are one and two times the three-phase AC frequency f.

As a result, only the DC components of equations (11) and (12) are extracted from the outputs of the filters 741 and 742, respectively. When rewritten, the following equations (13) and (14) are obtained. The output Fα of the filter 741 and the output Fβ of the filter 742 are as follows: Fα = (3/4) k1 · Vm · Iad = (√3 / 2√2) k1 · Vm × (√3 / √2) Iad (13 Fβ = (√3 / 4) k1 · Vm · (Iad + Ibd) = (√3 / 2√2) k1 · Vm × (1 / √2) (Iad + Ibd) (14) Equation (13) and When Expression (14) and Expression (6) are compared, they both show the underlined portion (DC component) in Expressions (13) and (14) and the underlined expression in Expression (6). A proportional relationship is recognized between the calculated portion (DC component). That is, the filters 741 and 74
2 are proportional to the DC component (represented by the underline in equation (6)) in an equivalent two-phase AC system. Therefore, the output F of the filters 741 and 742
When α and Fβ become zero, the DC offset included in the three-phase AC becomes zero. The compensating units 731 and 732 calculate compensation signals for setting the outputs Fα and Fβ of the filters 741 and 742 to zero.

It is desirable that the compensators 731 and 732 have a configuration having an integral element. If an integrator or a proportional-integrator is used, a steady DC current can be reduced to zero in principle. Also,
If an integrator or a proportional-integrator is selected as the compensating units 731 and 732, they have a high gain for low frequency components,
The filter 741 has a characteristic that the gain is low with respect to the high frequency component, that is, the characteristic of the low pass filter.
742 may be omitted for simplification.

The compensation signals cα and cβ calculated by the compensating units 731 and 732 are compensation signals for the two-phase AC system. Phase / three-phase conversion,
A three-phase compensation signal is generated. The conversion equation is given by equation (15).
As shown below. In equation (15), compensation signals Ca, Cb and Cc are:
These are three-phase compensation signals converted from the two-phase compensation signals cα and cβ. In the case of three-phase alternating current, once the conditions of the two phases are determined, the conditions of the remaining one phase are automatically determined. Therefore, among the compensation signals Ca, Cb and Cc, for example, the compensation signals Ca and Cb It is sufficient to calculate the two.

As shown in FIG. 4, the compensation signals Ca and Cb converted by the phase number converter 75 are added to the adder 61,
At 62, the outputs S1, S of the current sensors 15, 16 are output.
2 is added in the opposite polarity. This compensates for the DC offset.

FIG. 8 is a diagram showing a compensation operation when a DC offset is included in the three-phase AC side in the power converter shown in FIG. 4. FIG. 8 (a) shows an a-phase output current waveform, and FIG.
8B shows a b-phase output current waveform, FIG. 8C shows an output power waveform, FIG. 8D shows a compensation signal waveform, and FIG. 8E shows an offset compensation error waveform. In the case of FIG.
A DC offset of 0.5 A transiently occurs in the path to the phase due to disturbance such as an output error of the current sensor (see FIG. 8D). Referring to FIG. 8D, a compensation signal is calculated for this DC offset. Even if the DC offset changes with time, the compensation signal follows it. The compensation signal is based on the current sensor outputs S1 and S2.
Since the DC offset is added in the opposite polarity (see FIG. 4), if a DC offset occurs in the current sensor due to disturbance or the like, this can be reliably canceled and an output current that does not include the DC offset can flow.

In the case of the present invention, it is necessary to provide the DC side DC with a ripple detecting means 17 such as a current sensor, but the ripple detecting means 17 only needs to have a function of detecting the component of the fundamental frequency f. In other words, it is hardly affected by DC offset and gain errors of the current sensor,
Since an inexpensive sensor can be used, the cost of the entire system can be reduced, and the influence of a change in temperature or aging can be minimized, and reliability can be improved. Further, since the DC offset of the output current is adjusted by focusing on the specific frequency component included in the DC power supply, not only the influence of the DC offset and drift of the current sensor, but also the filter, the A / D converter circuit, DC offset and drift of peripheral circuits such as an A / A converter circuit can be collectively compensated, and are not affected by the characteristics of these peripheral circuits at all. Therefore, even if the peripheral circuit is an inexpensive element or circuit configuration,
Accurate DC offset compensation is possible, and further improvement in reliability and cost reduction can be achieved.

In particular, in special applications requiring high speed, safety, and higher reliability, this method is used in combination with the conventional method of operating while correcting the DC offset of the current sensor installed on the AC side. Thus, the DC offset included in the AC output current can be more effectively suppressed.

FIG. 11 is a block diagram showing another embodiment of the power converter according to the present invention. This embodiment shows a circuit configuration that can be adopted when the capacity of the smoothing capacitor 4 provided on the DC side DC is small. Smoothing capacitor 4
Is small, the terminal voltage Vc includes a ripple component that changes at the frequency f of the three-phase AC corresponding to the DC offset included in the three-phase AC side AC. Therefore, when the capacity of the smoothing capacitor 4 is small, the ripple detecting means 1
As 7, a voltage sensor can be used.

The voltage signal detected by the voltage sensor 17 is supplied to the phase shift means 18. The phase shifting means 18 shifts the phase of the ripple component fluctuating at the three-phase AC frequency f by 90 degrees. The output signal of the phase shift means 18 is supplied to the DC component outflow prevention means 7, and the above-described offset compensation action is performed. Considering that the ripple voltage included in the terminal voltage Vc of the smoothing capacitor 4 has a phase delay of 90 degrees, the reference sine waves x and z supplied to the DC component outflow prevention means 7 are replaced in advance. If the polarity is adjusted, the phase shifter 18 can be omitted.

FIG. 12 is a block diagram showing another embodiment of the power converter according to the present invention. This embodiment includes a first ripple detecting means 171 composed of a ripple detecting element and a second ripple detecting means 172 composed of a voltage sensor. Then, the operation unit 64 multiplies the ripple detection signal output from the first ripple detection unit 171 by the voltage detection signal output from the second ripple detection unit 172 to calculate the power. Then, the multiplication signal is supplied to the DC component outflow prevention means 7 to compensate for the DC component outflow.

The present invention relates to a converter device having a similar operation principle, for example, a sine wave input type AC / DC converter,
It can also be applied to active filters. The following is an example.

FIG. 13 is a block diagram showing still another embodiment of the power converter according to the present invention. In the figure, FIG.
Are denoted by the same reference numerals. In the embodiment, the DC side DC includes a DC power supply 50 and a DC load 100. DC power supply 50 may include, for example, a solar power supply,
DC load 100 is shown as a circuit including DC-DC converter 110 and load 120. The load 120 may be optional. The circuit configuration of the DC load 100 is not limited to the embodiment. For example, a DC load that does not have the DC-DC converter 110 may be used. Other configurations are shown in FIG.
The configuration is the same as that described in 4, 5, etc., and the same operation or processing is performed.

That is, the power generated by the DC power supply 50 is supplied to the DC load 100 and also to the switching unit 1. The switching unit 1 switches DC power supplied from the DC power supply 50 and the smoothing capacitor 4 and outputs the DC power to the three-phase AC side AC.

The control section 6 generates a signal for controlling the DC offset included in the three-phase AC side AC based on the ripple detection signal y supplied from the ripple detection means 17. The control unit 6 controls the switching unit 1 by the control signal S0 including this signal, and compensates for the DC offset included in the three-phase AC side AC. The compensation of the DC offset is performed so that the ripple detection signal detected by the ripple detection means 17 does not include the component of the three-phase AC frequency f.
This is achieved by controlling the switching operation of the switching unit 1.

FIG. 14 is a block diagram showing still another embodiment of the power converter according to the present invention. In the figure, FIG.
Are denoted by the same reference numerals. The illustrated embodiment shows a power conversion device used as an uninterruptible device. The switching unit 1 operates as an AC-DC converter that switches the three-phase AC system 3 and converts it into DC. The power converted to DC by the switching unit 1 is used for charging a DC power supply 51 composed of a secondary battery or the like,
The DC-AC inverter 200 converts the power to, for example, three-phase AC and supplies the AC to a three-phase load 300.

When the three-phase AC system 3 loses power, the energy stored in the DC power supply 51 is transferred to the DC-AC inverter 2
00 and is supplied to a three-phase load 300.

The point that the ripple detecting means 17 is provided on the DC side DC and the function of preventing the DC component from flowing out by the control unit 6 are the same as those of the above-described embodiments. That is, the control unit 6 generates a signal for controlling the DC offset included in the three-phase AC side AC1 based on the ripple detection signal y supplied from the ripple detection unit 17. Then, the switching unit 1 is controlled by the control signal S0 including this signal, and 3
The DC offset included in the phase AC side AC1 is compensated.

FIG. 15 is a block diagram showing still another embodiment of the power converter according to the present invention. In the figure, FIG.
Are denoted by the same reference numerals. The illustrated embodiment shows a power converter used as an uninterruptible power supply. The three-phase AC system 3 is connected to the three-phase load 300 via the power failure detection switch 400. The power failure detection switch 400
Opened when the three-phase AC system 3 loses power.

The three-phase AC connections a to c of the power converter are:
A stage following the power failure detection switch 400, the three-phase load 30
In the preceding stage of 0, it is connected to the three-phase system, and when the three-phase AC system 3 is out of power, instead of the three-phase AC system 3,
Power is supplied to the three-phase load 300. The power converter can adopt the circuit configuration described with reference to FIGS. 1 to 12.

In the power conversion device according to the present invention, the control section 6 can be configured as a digital processing device. When the control unit 6 is configured as a digital processing device,
A DSP (digital signal processor) can be used. Alternatively, a computer may be used. FIG.
Shows an example of a power conversion device in which the control unit 6 is configured as a digital processing device. In the figure, the same components as those shown in FIG. 1 are denoted by the same reference numerals. In the control unit 6, the detection signals S1 to S3,
Analog and digital converters (hereinafter, referred to as A / D converters) 651 to 655 are provided at input terminals of y and Vc. If the A / D converters 651 to 655 are already provided inside the control unit, these can be omitted.

Since the ripple frequency component of the ripple detection signal y is important, a filter 661 for extracting the ripple is provided before the A / D converter 651. A similar filter 662 is provided before the A / D converter 652 also when detecting the ripple of the terminal voltage Vc of the smoothing capacitor 4.

FIG. 17 is a block diagram of the DC component outflow prevention means 7. 17, the same reference numerals as those shown in FIG. 5 denote the components that perform the same processing. The difference from FIG. 5 is that the ripple detection signal y is extracted by a filter 661 and then supplied to an A / D converter 651 to be converted into a digital signal.
The point is that the signal is supplied to one of the input terminals of the multipliers 721 and 722. 5 also differs from the DC component outflow prevention unit 7 shown in FIG. 5 in that each unit of the DC component outflow prevention unit 7 performs digital processing.

In the analog system, when there are errors such as the reference sine waves x and z synchronized with the three-phase system and the DC offsets in the multipliers 721 and 722, errors may occur in the compensation signal. According to digital processing, this problem can be completely solved. In particular, in a system interconnection inverter device in which a control device is originally implemented digitally, only a slight change in software is required.

Most of the other parts included in the control unit 6 are the DSP
And performs digital processing. Specifically, for example, in FIG. 4, the output power control unit 8, the current command calculation units 9, 11, the reference wave generation unit 10, the current control unit 12,
13 and the PWM modulator 14 all perform digital processing. Even when the control unit 6 is configured by a computer, it is basically represented by a block diagram as shown in FIG.

As described above, according to the above embodiment of the present invention, the following effects can be obtained. (A) It is possible to provide a power converter capable of suppressing the occurrence of a DC offset in a three-phase AC system. (B) An inexpensive ripple detector can be used, and a power converter that can reduce the price of the entire device can be provided. (C) It is possible to provide a highly reliable power converter capable of minimizing the effects of temperature change and aging.

FIG. 18 shows the present invention applied to an inverter device.
An example is shown below. The inverter device embodying the present invention includes:
An inverter main circuit 101 is provided. Inverter main cycle
The output of the path 101 is output via a filter circuit 102 to an output terminal.
Output terminals a and b are connected to commercial AC power supplies.
Is connected to the AC power supply system 103 as shown in FIG. Inverter
-Connect the input side of the main circuit 101 to the DC power supply 105
Capacitor 104 is provided.
4, input terminals d and e of the inverter main circuit 101
Are respectively connected. The inverter main circuit 101
Full-bridge inverter and half-bridge inverter
Inverters such as inverters and NPC inverters
-Or any type of inverter, such as an isolated inverter
An inverter may be used. Inverter main circuit 1
01 switches the terminal voltage of the capacitor 104
Output to the AC power supply system 103 via the filter 102
You. This inverter device controls the output power.
Output power control means 106 is provided. Operating reference voltage
The operation reference voltage command signal R which determines
Terminal voltage V_cIs input to the output power control means 106
And the output power control means 106
To calculate the output power and output power command signal S_TenForm
You. Under constant power factor conditions, this output power control
Power command signal S which is the output of stage 106 _TenIs the output current
An amplitude command value is given.

The output of output power control means 106 is input to one input terminal of modulator 108. AC power system 3
And a reference sine wave oscillating means 110 for receiving a phase signal from the AC power supply system 103 to form a reference sine wave signal x including phase information of the AC power in the AC power supply system 103. The output of the reference sine wave oscillating means 110 is The signal is input to the other input terminal of the modulator 108. The modulator 108 is connected to the output power control unit 10.
Power command signal S ₁₀ from 6 the reference sine wave oscillation means 110
Based on the phase information signal X from calculates a current command value of sinusoidal having a predetermined phase, to form a current command signal S ₁₁ corresponding to the current command value.

The current command signal S ₁₁ from the modulator 108 is
The signal is input to the comparator 112. Inverter main circuit 101
Is provided with a current detection element 115, and a current detection signal I ₀ of the current detection element 115 is input to the comparator 112. The comparator 112 is connected to the modulator 10
8 inverter main circuit 101 a current command signal S ₁₁ from
Is compared with the output current detection signal I _0, and the difference signal S ₁₂ between the two is input to the output current control means 109. The output current controller 109, a control signal S ₁₃ is formed on the basis of the difference signal S _12, and inputs the control signal S ₁₃ to the pulse width modulation control unit 11. Pulse width modulation control unit 11, a control signal S ₁₄ which is pulse width modulated to form the basis of the control signal S _13, giving the control signal S ₁₄ to the inverter main circuit 1, and controls the switching operation. In this way, control is performed such that the AC output current represented by the current detection signal I ₀ of the current detection element 15 becomes equal to the command value R. The configuration and operation of the above-described inverter device are described in Japanese Patent Application Laid-Open No. 8-123561, and further detailed description is omitted here.

In the embodiment of the present invention shown in FIG.
In addition to the configuration of the inverter device described above, a current detection element 116 is provided at a position adjacent to the DC input terminal e of the inverter main circuit 101. This current detecting element 11
6 is input to the DC outflow prevention circuit 107. The DC component outflow prevention circuit 107 also
The reference sine wave signal x from the reference sine wave oscillator 110 is also input.

FIG. 19 shows the configuration of the DC component outflow prevention circuit 107, which includes a filter circuit 171 and a multiplier 172.
And the compensation circuit 173 as a main component. Multiplier 1
A filter circuit 74 may be provided between 72 and the compensation circuit 173. The current detection signal y from the current detection element 116 is
The signal is input to one input terminal of the multiplier 172 via the filter circuit 171. The reference sine wave signal x from the reference sine wave oscillating means 110 is input to the other input terminal of the multiplier 172. The multiplier 172 multiplies the current detection signal y from the current detection element 116 by the reference sine wave signal x, and outputs the output of the multiplier 172 via the filter circuit 174 to the compensation circuit 1.
Give to 73. The filter circuit 174 may be omitted.

The operation of the DC outflow prevention circuit 107 shown in FIG. 19 will be described below. Assuming that the high frequency component caused by the switching operation in the inverter main circuit 1 is ignored, when the output voltage v and the output current i of the inverter device are controlled to be sine waves, the following conditions are satisfied. _{v = V m Cos (ωt)} i = I m Cos (ωt + α) + I d Here, the maximum value of V _m is the output voltage, I _m is the maximum value of the output current, omega is the fundamental angular frequency, I _d is Each represents a DC component included in the output current. At this time, the instantaneous output power is expressed as follows. p = v · i = (V m I m / 2) Cos α + (V m I m / 2) Cos (2ωt + α) + V m I d Cos first term in (.omega.t) (16) Equation (16) Inverter The average output power of the device, the second term is the ripple power component having twice the power supply frequency due to the asymmetry of the single-phase AC, and the third term is the same as the power supply frequency caused by the DC component of the output current The frequency components are respectively represented.

On the other hand, if the high-frequency component accompanying the switching operation in the inverter main circuit 100 is ignored, the instantaneous value of the DC current in the inverter device is as follows. _Id-inv = (p + _ploss ) / _Vdc Here, _ploss represents the _loss of the inverter, and _Vdc represents the DC voltage. Considering the high-frequency component accompanying the switching operation in the inverter main circuit 1 ignoring,
Normally, p _loss is mainly composed of a DC component and a frequency component twice as high as the power supply frequency, and can be expressed as follows. p _loss = v _m I _loss 0 + v _m I _loss 2Cos (2ωt +
β) Therefore, the DC current of the inverter device can be expressed by the following equation. _{I d-inv = (V m} I m / 2V dc) Cos α + (V m I m / 2V dc) Cos (2ωt + α) + (V m I loss 2 / V dc) Cos (2ωt + β) + (V m I _d / _Vdc ) Cos (ωt) (17) In equation (17), the first term represents the DC component, the second term and the third term
The term represents a component having twice the fundamental frequency, and the fourth term represents a fundamental frequency component. Among the components of the DC side current, the DC component included in the AC output current has an effect only on the fourth term. Therefore, by monitoring the fundamental frequency component of the DC side current of the inverter device, The DC component included in the current can be detected. In other words, when the fundamental frequency component of the DC current of the inverter device becomes zero, the DC component included in the AC output current becomes zero.

Actually, the DC current of the inverter device contains many high-frequency components due to the switching operation in the inverter main circuit 100. In the circuit 107 shown in FIG. 19, the filter circuit 171 operates to remove this high frequency component included in the DC current. The current detection signal y from which the high frequency component has been removed is input to the multiplier 172 as described above. The multiplier 172 performs the following operation. _{I d-inv xCos (ωt)} = [(V m I m / 2V dc) Cos α + (V m I m / 2V dc) Cos (2ωt + α) + (V m I loss 2 / V dc) Cos (2ωt + β) _{+ (V m I d / V} dc) Cos (ωt)] · Cos (ωt) = (V m I m / 2V dc) Cos α · Cos (ωt) + (V m I m / 4V dc) [Cos ( ωt + α) + Cos (2ωt + α)] + (V m I loss 2 / V dc) [Cos (ωt + β) + Cos (2ωt + β)] + (V m I d / 2V dc) Cos (2ωt) + V m I d / 2V dc ( 18) When the output of the multiplier 172 is passed through a low-pass filter to remove the AC component, the last term (V
_m I _d / 2V _dc) leaving only. This signal has a relationship proportional to the DC component included in the current on the AC side of the inverter device. By obtaining this signal, the DC component flowing to the AC side is detected.

FIG. 20 shows the output voltage waveform on the AC side, the AC current waveform, and the current on the DC side of the inverter device. The output voltage V _ac on the AC side has a sinusoidal shape as shown in FIG. It becomes a wave. The output current i _ac on the AC side is shown in FIG.
It becomes a waveform shown in FIG. 1B and may include a DC component in the form of an offset value. FIG. 20C shows the waveform of the current I _d-inv on the DC side of the inverter device. When the output on the AC side includes a DC component, the current I _d-inv on the DC side
Includes a swell component as shown by a broken line in FIG. 20 (c). The frequency of the undulation component is the same as the frequency of the AC-side output voltage _Vac . If the offset value, which is a DC component in the AC output current i _ac, is positive, the phase of the swell component is the same as the AC output voltage V _ac . If the offset value is negative, the phase of the swell component is opposite to the output voltage _Vac on the AC side. The above-described calculation in the multiplier 172 and the processing by the filter circuit 174 are for detecting an offset component from the undulation component. From the output of the multiplier 172 represents the DC component of the resultant AC side through the filter circuit _{174 (V m I d / 2V} dc)
Is guided to the compensation circuit 173. Compensation circuit 173
Is preferably provided with an integrating element, and can be formed by an integrator or a proportional-integrator, and forms a compensation signal z that makes the output from the filter circuit 174 zero. The compensation signal z is input to the comparator 12 in the opposite polarity is added to the current command signal S _11. The integrator and the proportional-integrator have a characteristic of a low-pass filter in which the gain is high for the low-frequency component and the gain is low for the high-frequency component. When configured with a proportional-integrator, the filter circuit 174 can be omitted, thereby simplifying the configuration of the DC component outflow prevention means 7.

With the configuration described above, it is possible to remove the DC component in the output on the AC side. In this configuration, if there is an error such as an offset in the multiplier and a reference sine wave synchronized with the AC power supply system, an error may occur in the compensation signal. In order to solve this problem, a digital circuit may be used instead of the reference sine wave oscillating means 110, and the multiplier 172 may be constituted by a digital circuit. Further, it is preferable that the filter circuit 174 and the compensation circuit 173 are also configured as digital circuits. In particular, in a grid-connected inverter device in which the control device is implemented digitally, the present invention can be adopted by slightly changing the software.

In the present invention, the inverter main circuit 1
Although a current detection element is required on the input side of 01, this current detection element only needs to have a function of detecting a basic network frequency component included in the current. That is, since there is almost no influence from errors in the offset and gain of the current detection element, an inexpensive current detection element can be used, and the cost of the entire apparatus can be reduced. In addition, since the influence of temperature change and aging can be suppressed to a minimum, a highly reliable device can be obtained. The present invention detects the offset current of the output current by focusing on a specific frequency component included in the DC-side input current of the inverter device,
Not only the influence of the offset and drift of the current detecting element, but also the offset and drift of the filter circuit and other peripheral devices can be compensated collectively, and the configuration can be made so as not to be affected by the peripheral circuit at all. Therefore, inexpensive elements and circuit configurations can be adopted for the peripheral circuit. In particular, in special applications where high speed, safety, and higher reliability are required, using the method of the present invention together with the conventional method of correcting the offset of the current detection element installed on the AC side, It is possible to effectively suppress or remove the DC component included in the AC output component. FIG.
18 shows an operation when an offset voltage is forcibly applied to the output signal I ₀ of the AC-side output current detection element 15 in FIG. 18 in order to experimentally show the effect of the present invention. FIG. 21 (a)
As shown in FIG. 21, when an offset current corresponding to about 2% of the rated current is added, the compensation signal z output from the compensation circuit 173 increases as shown in FIG. With the increase of the compensation signal z, the offset error is returned to zero as shown in FIG. FIG. 22 shows the effect of the present invention when a 200 V single-phase commercial AC power supply system is connected to an inverter device having a rated power of 3 kW and a DC input voltage of 350 V. The inverter output is 0.9%, which is 30% of the rating.
When operating at kW output and applying a step disturbance of 0.6 A, which is 4.0% of the output current, an offset is temporarily generated in the inverter output, but this offset is instantaneously settled.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a power conversion device according to an embodiment of the present invention.

FIGS. 2A and 2B are voltage-power waveform diagrams of the power converter illustrated in FIG. 1, in which FIG. 2A illustrates a voltage-current waveform when a three-phase AC unit does not include a DC offset, and FIG. The power waveform diagrams of FIG.

FIGS. 3A and 3B show voltage-power waveform diagrams in the power converter shown in FIG. 1, wherein FIG. 3A shows a voltage-current waveform when a three-phase AC unit includes a DC offset, and FIG. Each shows a power waveform diagram.

FIG. 4 is a more specific circuit diagram of the power converter according to the embodiment of the present invention.

5 is a diagram showing a configuration of a DC component outflow prevention unit included in a control unit of the power conversion device shown in FIG.

FIG. 6 shows a three-phase voltage waveform (a), a three-phase current waveform (b), and a two-phase voltage waveform (c) when the DC offset is not included in the three-phase AC side in the power converter shown in FIG. , 2
FIG. 3 is a diagram showing a phase current waveform (d), an α-phase output power waveform (e), a β-phase output power waveform (f), and a total power waveform (g).

FIG. 7 shows a three-phase voltage waveform (a), a three-phase current waveform (b), and a two-phase voltage waveform (c) when the three-phase AC side includes a DC offset in the power converter shown in FIG. 2
FIG. 3 is a diagram showing a phase current waveform (d), an α-phase output power waveform (e), a β-phase output power waveform (f), and a total power waveform (g).

8 is an a-phase output current waveform (a), a b-phase output current waveform (b), and an output power waveform (c) when the three-phase AC side includes a DC offset in the power converter illustrated in FIG. FIG. 6 is a diagram showing a compensation signal waveform (d) and an offset compensation error waveform (e).

FIG. 9A is a circuit diagram showing a basic circuit of three-phase alternating current, and FIG.
It is a figure which shows the vector display (b) of a phase voltage.

10A is a circuit diagram illustrating the conversion between the three-phase alternating current and the two-phase alternating current illustrated in FIG. 9 and FIG.

FIG. 11 is a block diagram showing still another embodiment of the power converter according to the present invention.

FIG. 12 is a block diagram showing still another embodiment of the power converter according to the present invention.

FIG. 13 is a block diagram showing still another embodiment of the power converter according to the present invention.

FIG. 14 is a block diagram showing still another embodiment of the power converter according to the present invention.

FIG. 15 is a block diagram showing still another embodiment of the power converter according to the present invention.

FIG. 16 is a block diagram showing still another embodiment of the power converter according to the present invention.

FIG. 17 is a diagram showing a configuration of DC component outflow prevention means that can be used in the power converter shown in FIG.

FIG. 18 is an overall block diagram of an inverter device showing another embodiment of the present invention.

FIG. 19 is a block diagram showing a configuration of a DC component outflow prevention means used in the circuit of FIG. 18;

FIG. 20 is a chart showing an AC voltage waveform, an AC current waveform, and a DC current waveform in an inverter device for explaining the principle of DC component detection according to the present invention.

21 is a table showing the effect of the embodiment of FIG. 18, wherein (a) shows the offset current given by disturbance, and (b)
Indicates a compensating signal generated thereby, and (d) indicates an offset error appearing in the inverter output.

FIG. 22 is a table showing a convergence state of offset when a disturbance is applied to the AC output of the inverter device in a step-like manner.

[Explanation of symbols]

1. Switching section, 2. Filter circuit, 3 ...
Three-phase AC system 4 DC smoothing capacitor 5 DC power supply 6
Control unit 7 DC outflow prevention means 101 Inverter main circuit 102 Filter circuit 103 AC power supply system 104 Capacitor 105 DC power supply 106
..Output power control means 107.DC outflow prevention means 108.Modulation means.
109 output current control means 110 reference sine wave oscillation means 111 pulse width modulation means 171 filter circuit 172 multiplier 173
.Compensation means, 174..Filter circuits

Claims (16)

[Claims] 1. A power converter connected between a DC power system and an AC power system for transmitting and receiving power between the DC power system and the AC power system, the power conversion device comprising: An AC unit connected thereto; a DC unit connected to the DC power system; a switching unit connected between the DC unit and the AC unit to perform power conversion by a switching operation; and controlling the switching unit. A control unit, wherein the DC unit is provided with a ripple detection unit that detects a ripple component appearing on the DC side to generate a ripple detection signal, and the control unit transmits a ripple detection signal from the ripple detection unit. Receiving a DC component compensation signal for controlling a DC component included in the current of the AC section based on the ripple detection signal, and generating the DC component compensation signal by the control signal including the DC component compensation signal. A power converter, comprising: controlling a switching unit to compensate for a DC component included in the AC unit. 2. The power conversion device according to claim 1, wherein the ripple detection unit includes a current detection element that detects a current ripple that appears in the DC unit. 3. The power conversion device according to claim 1, wherein the ripple detection unit includes a voltage detection element that detects a voltage ripple that appears on the DC side. , Power conversion equipment. 4. One of claims 1 to 3
In the power conversion device described in the paragraph, the AC power system is a three-phase AC power system, the control unit includes a DC component outflow prevention unit, and the DC component outflow prevention unit includes a first filter and , A first multiplying unit, a second multiplying unit, a first compensating unit, a second compensating unit, and a phase number converting unit. Extracting a component having the same frequency as the fundamental wave component of the phase alternating current; the first multiplying unit outputs a signal supplied from the first filter and a first signal having the same frequency as the fundamental frequency of the three-phase alternating current; The second multiplying unit has a signal supplied from the first filter and the same frequency as a fundamental wave frequency of three-phase alternating current, and The sine wave is multiplied by a second reference sine wave having an electrical phase difference of 90 degrees, A first compensating unit that generates a compensation signal for compensating for a DC component included in the output current of the three-phase alternating current, according to an output of the first multiplying unit; A compensation signal for compensating for a DC component included in the output current of the three-phase AC is generated according to an output of the second multiplication unit. The phase number conversion unit includes the first compensation unit and the second compensation unit. A power conversion device adapted to convert two compensation signals supplied from two compensation units into the same number of phases as three-phase alternating current. 5. The power converter according to claim 4, wherein the DC component outflow prevention unit includes a second filter and a third filter, and the second filter includes a first filter and a second filter. Extracting a low-frequency component of the signal output from the multiplying unit, supplying the extracted signal to the first compensating unit, the third filter configured to extract a low-frequency component of the signal output from the third multiplying unit; A power converter configured to extract a frequency component and supply the extracted signal to the second compensator. 6. Any one of claims 1 to 5
The power conversion device according to any one of the preceding claims, wherein the control unit performs digital processing. 7. One of claims 1 to 6
The power converter according to claim 1, wherein the DC power system includes a DC power supply connected to the DC unit, and the AC power system is connected to the AC unit. 8. The power converter according to claim 7, wherein the AC power system is a three-phase AC power system with a neutral point and not grounded. 9. The power conversion device according to claim 7, wherein the power conversion device is a DC-AC conversion device or an AC-DC conversion device, or A power converter that constitutes an AC-DC bidirectional converter. 10. The power converter according to claim 7, further comprising a DC load. 11. The power converter according to any one of claims 7 to 10, wherein the power converter includes an uninterruptible power supply. 12. Power conversion means comprising a DC connection part connected to a DC power supply and an AC connection part connected to an AC power supply, output power control means for controlling output power of the power conversion means, A modulating means for calculating an ac current command value based on an output power command signal given by the output power control means to generate an ac current command signal; and the power conversion means based on a current command signal given by the modulating means. A power control device including a current control means for controlling the power conversion means, the power conversion apparatus being used by being connected to an AC power supply, wherein a current detection means for detecting a DC side current of the power conversion means; DC outflow prevention means for detecting a DC component included in the AC output appearing at the AC connection portion and generating a signal for removing or reducing the DC component is provided. Power converter. 13. The power converter according to claim 12, wherein the DC component outflow prevention unit extracts a current component having the same frequency as an AC fundamental component from a current signal output from the current detection unit. Filter means, a multiplier for multiplying a reference sine wave synchronized with a system including the AC power supply by an output signal of the filter means, and a compensation means for compensating a DC component of an AC output current according to an output of the multiplier. A power converter, comprising: 14. The power converter according to claim 13, wherein said multiplier is a digital multiplier, said filter means and said compensation means are configured as digital means, and said DC component outflow prevention means is said digital means. A power converter comprising a reference sine wave digital signal synchronized with a system including an AC power supply, wherein the reference sine wave is multiplied digitally by an output signal of the filter means. 15. The power converter according to claim 13, wherein the DC component outflow prevention unit compensates for a DC component of an AC output current based on an output of the multiplier. A compensation signal to be calculated by the compensation means, and the compensation signal is added to the AC current command signal in reverse polarity. 16. The electric power converter according to claim 12, wherein said current detecting means does not have a DC current detecting function. Conversion device.