JP2001028882A - System-interconnection inverter apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exclude the distortion of an output voltage waveform generated due to an error in an output voltage by installing a repetitive compensator which controls an output current. SOLUTION: For example, the feedforward control of a capacitor current ic is executed in order to control the power factor '1' of a linkage-point current is. Since an inverter output current ia can be controlled directly by an inverter, the feedforward control of the capacitor current ic is performed to a linkage- point current command value is* so as to obtain an output-current command value ia*. Then, the inverter output current ia and the linkage-point current is are detected, and the capacitor current ic is detected as their difference portion. Then, Δia* is found from a current control error Δia by a repetitive compensator 4. On the basis of it, a voltage value Vcon is found by a current controller 9. The output Vrd* of a dead-time correction circuit 6 is added so as to obtain an output-voltage command value V*. Based on this, a PWM control operation is executed, and a sine-wave output current of a power factor '1' can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system-linked inverter device for converting a DC voltage generated by a power generator into an AC voltage and outputting the AC voltage to a system link.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a configuration of a system-linked inverter. Here, the system-linked inverter 30 uses the DC voltage detector 3 to detect the DC voltage V _dc generated by a power generation device such as a solar cell.
4, which is converted into an AC voltage having a predetermined frequency and supplied to a connected system link. The output current of the inverter 30 is generally controlled by an output current detector 35,
Linkage point voltage detector 36, and the respective detector output of the zero cross detector 37, a current control unit 32 is the reference sine wave i _s ^*
And the output current i amplifies the current error between _a, further performing the feedforward control of the link point voltage v _s in obtaining the inverter output voltage command value v ^* PWM signal generator 31
To be sent to

A PWM signal generator 31 generates a PWM signal according to an inverter output voltage command value v ^* from the current control unit 32 and drives an inverter including a bridge circuit 38 to realize a sine wave output current. are doing.

[0004]

However, the dead time T provided for preventing the upper and lower arms of the switching element constituting the inverter from being short-circuited.
Due to _d , an error occurs in the voltage actually output from the inverter, and it is difficult to output the voltage as the command value. Since the error in the output voltage substantially depends only on the sign of the output current, the effect is particularly large at the timing when the sign of the output current is switched, causing a large distortion in the waveform of the output current.

Conventionally, in order to compensate for the periodic disturbance caused by the dead time, a method called a simple dead time compensation method in which the amount of voltage compensation is switched according to the sign of the output current has been adopted.

This is because dead time T_dOutput voltage
The sign of the error is the inverter output current i _aEqual to the sign of
The value of the error takes a substantially square wave change. Therefore,
Force current i_aDead if the absolute value of
Time correction amount v_Td ^*Is 0, and if it is large,
V determined in consideration of switching delay, etc._TdBy
Next formula

[0007]

(Equation 1)

[0008] This is a calculation method.

However, even in this method, the correction amount v _Td
^Since it is difficult to determine the sign of the current in the vicinity of the zero crossing point where ^* changes, the error in the output voltage cannot be completely compensated for, especially when the output current value is small. Will be noticeable.

[0010] Figure 7 shows the results obtained by experiments output current waveform of the system interconnection inverter that performs the control as described above, a large waveform in the current value i _s ^* zero cross point shown by I in FIG. It can be seen that distortion has occurred. This indicates that the error of the output voltage cannot be completely compensated by the conventional simple dead time compensation method.

In the system link, an LC filter 33 as shown is indispensable in order to prevent the current of the carrier frequency component from flowing out to the system link.

[0012] However, since the current i _c proceeds to filter capacitor C flows, the power factor of the link point current i _s is deteriorated. Conventionally, output current control for compensating the phase has been performed in order to improve the power factor. However, it has been difficult to realize a link point current having a power factor of “1” particularly at a low output of the inverter due to control delay. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to eliminate distortion of an output current waveform caused by an error in an output voltage without taking a complicated circuit configuration as much as possible. It is an object of the present invention to provide a system-linked inverter device capable of performing such operations.

[0014]

According to the first aspect of the present invention,
In a system-linked inverter device that generates an AC voltage from an input DC voltage and outputs the generated AC voltage to a system, a repetitive compensator that controls an output current is provided.

With this configuration, it is possible to eliminate the distortion of the output current waveform caused by the output voltage error.

According to a second aspect of the present invention, in the first aspect of the present invention, the repetition compensator has a low-pass filter, and a dead time of the repetition compensator is reduced by a phase characteristic of the low-pass filter. The gain of the repetition compensator is improved at a cycle that is an integral multiple of the frequency of the AC voltage output from the inverter device.

With this configuration, in addition to the operation of the first aspect, the repetition compensator can be driven more efficiently.

According to a third aspect of the present invention, in the first aspect of the present invention, the system-linked inverter device has a filter circuit using a capacitor for preventing a current of a carrier frequency component from flowing out to the system. A feedforward correction control for the current value flowing through the capacitor is performed.

With this configuration, in addition to the operation of the first aspect of the invention, the power factor of the link point current can be maintained at a high value.

According to a fourth aspect of the present invention, in the third aspect of the invention, there is provided an arithmetic means for calculating a value of a current flowing through the capacitor from a difference between an inverter output current and a link point current.

With such a configuration, in addition to the effect of the third aspect of the invention, the configuration for detecting the value of the current flowing through the capacitor can be simplified.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit configuration of a current control system of the system-linked inverter device according to the embodiment, in which a repetitive compensator 4 is used as a means for correcting an output current control error.

In order to make the DC voltage V _dc generated by a power generation device such as a solar cell follow the target command value V _dc ^* , the DC peak voltage command value I _s ^* is obtained by using the DC voltage controller 1. For control realizing power factor of the linking point current "1", associated point voltage v _s reference sine wave signal generated using a zero-cross detector 2 and the reference sine wave generator 5 from sinθ
And then multiplying the linkage point current crest command value I _s, which is the output of the DC voltage controller 1 obtains the association point current command value i _s ^*.

Since it is the output current i _a that can be directly controlled by the inverter, feedforward control of the capacitor current i _{c in} the circuit including the low-pass filter 3 and the limiter 18 is performed, and the output current command value i _a ^* And Capacitor current i _c may be detected directly, here obtains the difference i _c = i _a -i _s by detecting the inverter output current i _a and the connection point current i _s, further low-pass filter 3 Is used to remove the carrier frequency component included in the capacitor current _ic , so that a new current detecting means is not required.

The current control error Δi by the repetitive compensator 4_a
From Δi_a ^*And find this Δi_a ^*Based on current control
The voltage value v_conAnd then dead tie
Output v of the system correction circuit 6_Td ^*And the output voltage command value
v^*And This command value v ^*Based on the inverter
By executing the PWM control of the output voltage, the power factor "1"
A sine wave output current can be obtained.

FIG. 2 shows a specific circuit of the iterative compensator 4.
Illustrates the configuration and compensates for the effects of periodic disturbances
Output current command value i_a ^*And inverter output current i
_aCurrent control error Δi which is the deviation of_aAgainst the disturbance
The dead time element “e” of L ′ shorter than the period L^-L'sWith 402
The current controller input Δi_a ^* To
Ask. Further, in this iterative compensator 4, the stability of the control system is improved.
The low-pass filter 401 with a time constant T
Useless time element "e^-L's"402 is additionally arranged at the preceding stage.

[0028] With such a configuration, produces a phase delay of the current control error .DELTA.i _a caused by the influence of the disturbance to the phase characteristic by passing the low-pass filter 401. Therefore, the compensator gain is reduced at an integral multiple of one-fourth of the disturbance period, and a sufficient current distortion reduction effect cannot be obtained.

FIG. 3 is an example of a closed-loop gain diagram in the circuit configuration shown in FIG. 2, in which a first-order low-pass filter having a filter time constant T [s] is used. In the figure, a broken line A indicates a case where the time constant T of the low-pass filter 401 is 0.35 [ms] and the power supply cycle L = 16.67 [ms], which is a disturbance cycle, is a dead time. The gain at integer multiples is low. Therefore, the low-pass filter 40
In order to improve the compensator gain by setting the dead time L 'to be shorter than the disturbance period L in consideration of the phase characteristic of No. 1, the dead time L' is calculated using the above equation (1).

[0030]

(Equation 2)

Is obtained as follows. The solid line B in FIG.
Is the compensation when the dead time L '= 16.32 [ms] obtained by the above equation (2), assuming that the filter time constant T = 0.35 [ms] and the power supply cycle L = 16.67, which is a disturbance cycle. It can be seen that the gain has been greatly improved when the power supply frequency is an integral multiple.

[0032] Thus, the present embodiment as shown in FIG. 1 is for performing the feedforward control of the capacitor current for control to achieve a power factor of the link point current i _s "1". Since it can be directly controlled by the inverter is the inverter output current i _a, linkage point current command value i _s ^*
To perform feedforward control of the capacitor current i _c, the output current command value i _a ^*. Capacitor current i
_c may be detected directly, by obtaining as a difference by detecting the inverter output current i _a and the connection point current i _s, and the good configuration without using a new current detecting means.

The sine wave of these results, even for the change of the inverter output from the low output to the rated output, and even when the system voltage v _s is varied, in conjunction point surely the power factor "1" Output current can be obtained.

[0034] Figure 4 shows the experimental result of the output current waveform i _s shown in FIG. 1, can be sufficiently reduced compared with the case where the waveform distortion II in zero cross position of the current shown in FIG 7, It can be seen that a sine waveform is obtained.

Note that a circuit configuration as shown in FIG. 5 may be used instead of the circuit configuration shown in FIG.

FIG. 5 shows another circuit configuration of the system-linked inverter current control device according to the present embodiment. In the figure, the repetitive compensator 4 is used as a means for correcting a link point current command value. That is, repeated deviation of the link point current command value i _s ^* a linkage point current detection value i _s input to the compensator 4, obtaining the i _s ^** as output.

[0037] Since it can be directly controlled by the inverter is the output current i _a, performs feedforward control of the capacitor current i _c of the circuit including the low-pass filter 3 and the limiter 18, the output current command value i _a ^* And Capacitor current i _c may be detected directly, here obtains the difference i _c = i _a -i _s by detecting the inverter output current i _a and the connection point current i _s, further low-pass filter 3 Is used to remove the carrier frequency component included in the capacitor current _ic , so that a new current detecting means is not required.

[0038] Then, determine the voltage value v _con from the current control error .DELTA.i _a by the current controller 9 adds the linkage point voltage v _s obtained by this voltage value v _con detecting means further dead time correction circuit 6 v by adding _Td ^* and output voltage command value v ^* is output. By executing the PWM control of the output voltage by the inverter based on the command value v ^* , a sine wave output current with a power factor of “1” can be obtained.

Even in the circuit configuration of FIG.
Flow i_sCapacitor for control to realize power factor of "1"
Executes current forward control. Inverter
Can be directly controlled by the inverter output current i_aIs
And the link point current command value i_s ^* And the capacitor current i_cNo
The feedforward control is performed, and the output current command value i_a ^*
And

The capacitor current i _c may be detected directly, by obtaining as a difference by detecting the inverter output current i _a and the connection point current i _s, may not be used a new current detection means configured I have to.

The sine wave of these results, even for the change of the inverter output from the low output to the rated output, and even when the system voltage v _s is varied, in conjunction point surely the power factor "1" An output current can be obtained.

Although the above embodiment has been described with respect to a system-linked single-phase inverter, the present invention is not limited to this, and it can be easily applied to a three-phase inverter. it is obvious.

In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0044]

According to the first aspect of the present invention, it is possible to eliminate the distortion of the output current waveform caused by the error of the output voltage.

According to the second aspect of the invention, in addition to the effect of the first aspect, the repetition compensator can be driven more efficiently.

According to the third aspect of the invention, in addition to the effect of the first aspect of the invention, the power factor of the link point current can be maintained at a high value.

According to the fourth aspect of the present invention, in addition to the effect of the third aspect of the present invention, the configuration for detecting the value of the current flowing through the capacitor can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of a current control system of a grid-linked inverter according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a specific circuit configuration of the iterative compensator in FIG. 1;

FIG. 3 is a closed loop gain diagram in the circuit of FIG. 2;

FIG. 4 is a diagram showing an output current waveform of the system-linked inverter device of FIG. 1;

FIG. 5 is a block diagram showing another circuit configuration of a current control system of the grid-linked inverter device according to the embodiment;

FIG. 6 is a block diagram illustrating a configuration example of a system-linked inverter device.

FIG. 7 is a diagram showing an output current waveform of the system-linked inverter device of FIG. 6;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 DC voltage controller 2 Zero cross detector 3 Low-pass filter 4 Repetitive compensator 401 Low-pass filter 402 Dead time element 5 Reference sine wave generator 6 Dead time correction circuit 9 Current Controller 30 ... System-linked inverter 31 ... PWM signal generator 32 ... Current control unit 33 ... LC filter 34 ... DC voltage detector 35 ... Output current detector 36 ... Coupling point voltage detector 37 ... Zero cross detector 38 ... Bridge circuit

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kenichi Aiba 1-chome Takamichi, Iwazuka-cho, Nakamura-ku, Nagoya-shi, Aichi Prefecture Nagoya Machinery Works, Mitsubishi Heavy Industries, Ltd. 3-1-1, Machi-cho, Mitsubishi Heavy Industries, Ltd. Air Conditioner Works (72) Inventor Hidehiko Sugimoto 16-4 F-term of 3-4, Iwanaridai, Kasugai-shi, Aichi (reference) 5G066 HA30 HB05 5H007 AA02 BB05 BB07 CB05 DA05 DA06 DB01 DC02 DC05 EA02

Claims (4)

[Claims] 1. A system-linked inverter device for generating an AC voltage from an input DC voltage and outputting the generated AC voltage to a system-linked device, comprising a repetitive compensator for controlling an output current. 2. The repetition compensator has a low-pass filter, sets a dead time of the repetition compensator based on a phase characteristic of the low-pass filter, and sets a frequency of an AC voltage output by the inverter device. 2. The system-coupling inverter device according to claim 1, wherein the gain of the repetition compensator is improved by an integral multiple of the following. 3. The system-linked inverter device has a filter circuit using a capacitor for preventing current of a carrier frequency component from flowing out to an output system, and performs feedforward correction control on a current value flowing through the capacitor. The system-linked inverter device according to claim 1, wherein: 4. The system-linked inverter device according to claim 3, further comprising a calculating means for calculating a value of a current flowing through said capacitor from a difference between an inverter output current and a link point current.