JPS5875479A - Control system of dc-ac converter - Google Patents

Abstract

PURPOSE:To put a separately excited converter into stable operation by a method wherein constant current and voltage control circuits are provided and respective output is input input into the phase lag priority circuit to control the separately excited converter by means of the phase lag signals. CONSTITUTION:The output of photocell 1 generating DC power making use of sunshine is converted into AC by means of a separately excited converter 2 transmitting it to AC system 5. At this time, the DC current is detected by a detector 11 and its vlaue and the deviation from the setter 21 are input into the phase lag priority circuit 15 through the intermediary of the constant current control circuit 23 while the DC voltage is detected and its value and the deviation from the setter 31 are also input into said phase lag priority circuit 15 through the intermediary of the constant voltage control circuit 33. Then the signals with phase lag are selected to control the separately excited converter 12. Through these procedure, when the characteristics curve of said photocell 1 is shifted due to fluctuation of sunshine, said separately excited converter may be put into stable operation eliminating the operation unabled point.

Description

Detailed Description of the Invention a) Description of the Technical Field The present invention uses a photovoltaic cell as a power source and is a DC-AC converter that converts the DC power generated by the light source into sound current power using a separately excited converter. Regarding the device, in particular, the control method of the DC-AC converter to ensure stable operation at all times regardless of changes in the amount of solar radiation incident on the photovoltaic cell. A schematic block diagram of a DC-AC converter used as a power source is shown. In FIG. 1, a photovoltaic cell that receives 1ri solar radiation and generates countercurrent power ti, a passive converter 2, and a photovoltaic cell I are connected via a DC reactor 3. The passive converter 2 is connected to an AC system 5 via a converter transformer 4. □In a DC-AC converter that uses a photovoltaic cell as a power source and converts DC to AC Kf using a converter, the passive converter may fail to operate under constant current control. That is, the DC current is 1 iL for detecting this t.
I5! The detected value of the DC current is led to the sampling circuit 22 via the transformer 11 and a current-voltage conversion circuit 1z for converting it into a value that can be easily handled by a control circuit. The other input of the plowing circuit 22 is the tth fixed current value for operating the passive converter under constant current control, and the value is regulated by the current setting device 21. The switching circuit 22 outputs the difference between the current setting value and the detected DC current value, and the constant ti
The signal is input to the L flow control circuit 23. In the constant current control circuit 23, 1 kL (the difference between the At setting value and the detected value of the DC current increases) is output to the phase control circuit 1111.The phase control circuit 16 outputs the output signal of the constant current control circuit 23 Corresponding to the well phase, separately excited conversion mxri skin, sending out arc pulses 0
With the configuration described above, the DC-AC converter is operated so that a DC current corresponding to the current setting value always flows through the constant current control circuit of the separately excited converter.

In other words, the operating characteristics of the DC-AC converter are shown in FIG.
In Figure 2, (1) is the characteristic curve of photovoltaic cell I, (2) Fi
1 is a characteristic curve of the separately excited exchanger 1. As already explained, the ninth I is operated with separately excited conversion erFi constant current control.
[000m with constant current characteristics as shown in (2) in Figure 2]
Although the explanation is omitted here, there is a margin angle IJ to prevent commutation failure of the separately excited converter.
Characteristic 111 that is synthesized with the @ part! ill! have. Therefore, the Kum Pond IC in Figure 842)~Sexual Cocoon Legs (Z)
The DC-AC converter is operated at point A, which is the intersection of the characteristic -m (J) of the separately excited converter 2. By the way, Marugame? Ti! The output of L increases or decreases in response to changes in the amount of solar radiation, but today the withstand capacity has decreased and the % characteristics of the light
Assuming that (1) K has changed from CI in the figure to point feed, the externally excited converter 2 lowers the DC flt voltage in an attempt to flow a DC current corresponding to the first set value determined by the current setting device 21. Although the DC voltage is lowered to @ of (2) in Figure 2, even in this state, the intersection of (Iy and (2) cannot be made), so the DC-AC converter 1 becomes unable to operate and shuts down. There is.

C) Object of the invention Object of the invention Fi Eliminate the above-mentioned drawbacks, always direct current
An object of the present invention is to provide a control method for a DC-current converter for stably operating an AC converter.

d) #lt construction of the invention A schematic block diagram of an embodiment of the present invention is shown in FIG. Examples are omitted.

Friendly voltage changer 1 that detects direct current voltage! j, shi11 and
OI# is used as a control circuit to convert it to a small value.
The DC voltage is input to the construction circuit 11 as a detected DC voltage value via the L voltage-voltage conversion circuit 14.
The other input of the switching circuit 32 is a predetermined voltage setting value for operating the separately excited converter under constant voltage control.
The difference between the positive pressure set value and the detected value of the DC voltage is outputted and inputted to the constant voltage control circuit JJK. In the constant voltage control circuit S3,
The difference between the voltage setting value and the detection width of the DC voltage is amplified and input to the phase lag priority circuit 15 ◎ Among the output signals of the phase lag priority circuit 15Fi, the constant current control circuit 23, and the constant voltage control circuit S3 , the third signal outputs the signal whose phase is delayed as the phase of the ignition pulse given to the separately excited converter 2, and inputs it to the phase control circuit 1-.
The diagram is composed of 0・-) Effect of the invention Effect of the invention The effect of the invention will be explained using the blocks in Fig. 3 and the characteristic diagram of the DC-current conversion device according to No. .

As shown in No. 4-, the characteristics of the photovoltaic cell 1-1iI(1
) and separately excited conversion (to) characteristic curve 2 and current characteristic region 6
It is assumed that the DC-AC converter is operated at point A, which is the intersection of @kaku. Here, the amount of solar radiation decreases, and the light ma
Assume that the characteristic curve changes from (Z) to (1) as shown by the dotted line.At this time, in the conventional control circuit, there is no intersection and the operation becomes impossible, but in the case of the present invention, An intersection point is formed and operation is possible. This imaginary will be explained in detail below. Now, the characteristic curve of light 1 [pond] is shown by the dotted line (1
y, the constant current control circuit IS of the separately excited converter 2 advances to phase 1 of the ignition pulse given to the separately excited converter 2 in order to flow the DC current at the current setting value, as described above. It operates in the direction of lowering the DC voltage. In other words, Sadaki style @
The output signal of the circuit ZS changes in the direction of advancing the phase.

On the other hand, the constant voltage setting circuit 33 provided in the present invention operates when the constant current control circuit 2S operates and the DC voltage tube is lowered significantly so that the voltage becomes lower than the voltage setting value of the DC voltage determined by the voltage setting device 31. , the output signal of the voltage control circuit 31 operates in such a direction as to prevent the ignition pulse applied to the separately excited conversion@:2 from being avoided any further. That is, the output signal of the constant voltage control circuit 33 changes in the direction of delaying the phase. Therefore, when the DC voltage becomes lower than the voltage setting value, the phase delay priority circuit 15
The output of the current constant 'K lf+ is transferred from the signal of the control circuit JJ to the signal of the constant voltage control circuit 33. As a result, the operating characteristics of the externally excited energy converter 2 become constant voltage characteristics, eD in Fig. 4.
Becomes visible to mosquitoes. That is, at point B, the photocell IO characteristic curve←
The CIP and the characteristic curve of the passive converter 2 intersect at the point 1 in the constant voltage region, and the DC-AC transition can continue to operate stably.

Conversely, if the characteristic curve of the photovoltaic cell changes from (Iy to (1)), a detailed explanation will be omitted, but if you try to operate with the DC voltage determined by the voltage setting value of constant voltage control path 1 31, a turtle current will occur. In the ninth stage, when a DC current higher than the set value flows, the foot current control circuit 23 operates and the entire DC pressure is applied in order to maintain the DC current at the set value ◎To do this, the phase of the ignition pulse is delayed. The output of the phase interlocking priority circuit I6 is controlled by the constant current control 1g1lIII from the output signal of the constant voltage control circuit 33.
Moving on to the output signal of S, point A in FIG. 4 becomes the operating point of the DC-AC converter.

f) Overall effect As explained above, the constant current control circuit and constant pressure control Igl
DC-AC converter fl1 that can continue stable operation by configuring it via a phase delay priority circuit with the road.
1t- can be provided. In history, in order to operate a DC-AC converter under constant single pressure control, the current setting value of the constant current control circuit was usually set to It is also possible to set the value □ to prevent overload operation of the separately excited conversion system.

[Brief explanation of the drawing]

1st vgUt: l A schematic diagram of a conventional current-AC converter, 25th Q is an operating characteristic diagram of a conventional DC-AC converter, and Figure 3 is a schematic block diagram of a DC-AC converter according to the present invention. Figure 4 shows the operating characteristics of the present invention. 1...Photovoltaic cell, 2...Separately excited variable! Im! Vessel, 3...
DC reactor, 4...Main pressure number for conversion number, 5...AC system, IK...current transformer, I2...current-voltage conversion circuit, 13...voltage transformer, 14...・Pressure-voltage conversion circuit, 2I... Potentiometer for current setting value, meter, 3I... Botensilometer for voltage setting value, 22.3
2...Summing circuit, ZS...constant current control circuit, 3
3... Constant voltage control circuit, 15... Phase delay priority circuit, 16... Phase control circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 2

Claims (1)

[Claims] In a DC-AC converter made up of a photovoltaic cell that outputs DC and a separately excited converter that converts the DC output of the light source into AC, as a control circuit for the other j121 converter,
It is equipped with a constant i [control circuit that controls the DC current and a constant voltage *L+ control circuit that controls the DC voltage, and when the DC voltage exceeds a certain set value voltage, the separately excited conversion is performed by constant current control. , and when the DC voltage is below the set value voltage, the separately excited conversion device is operated under constant voltage control.