JPH04364378A - Power conversion device for solar power generation - Google Patents

Abstract

PURPOSE:To convert the output of a solar battery without stopping an inverter by controlling the inverter by the output of CT of the output side of the inverter to be operated by the linkage with the commercial power sources through the conversion of the output of the solar battery. CONSTITUTION:An output from a solar electric power generator 1 is converted by an inverter 3, higher harmonics are filtered by a filter 6, and the power is linked to a commercial power system 4 after closing a switch 5. An output current II of the inverter 3 and a voltage VS of a power distribution system 4 are input to an AC detector 7 connected to the secondary side of CT10 of the output side of the inverter 3, an AC signal 7a' is determined and input to a control protection circuit 9. On the other hand, DC input VD is detected by a detector 8 and input to a control protection circuit 9. The control protection circuit 9 forms a drive signal 9a by signals VD and 7a', controls the inverter 3, and reduces a current II when the output current II exceeds the predetermined value. By doing this, the stop of inverter 3 is prevented even if a temporary fluctuation occurs in the power distribution system 4 and safe operation is continued.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a power conversion device for solar power generation that is linked to an existing AC power distribution system, and particularly relates to a power conversion device for solar power generation that does not stop due to temporary fluctuations in the power distribution system. It is something.

0002

2. Description of the Related Art FIG. 4 is a block diagram showing a conventional power conversion device for photovoltaic power generation disclosed in, for example, Japanese Patent Laid-Open No. 1-98008. In FIG. 4, 1 is a photovoltaic array that generates DC power Pd by the action of sunlight, Vd is the output voltage of photovoltaic array 1, and 2 is inserted on the output side of photovoltaic array 1 to prevent backflow of DC power Pd. 3 is an inverter that converts DC power Pd into AC power PI, V
I and II are the output voltage and output current of inverter 3, and 4
is the distribution system that is supplied with AC power PI and consumes it,
5 is a contactor that connects the power distribution system 4 to the output terminal side of the inverter 3. A filter 6 is inserted on the output terminal side of the inverter 3 to prevent harmonics output from the inverter 3 from flowing into the power distribution system 4, and is inserted between the output voltage VI of the inverter 3 and the voltage VS on the power distribution system 4 side. It also functions as a linkage reactor X (X is the magnitude of reactance) for maintaining the voltage phase difference δ.

7 is the voltage V on the AC side, that is, on the power distribution system 4 side.
An AC detector detects S and current IS and outputs an AC signal 7a, and 8 is a voltage V on the DC side, that is, on the photovoltaic array 1 side.
This is a DC detector that detects d. Reference numeral 9 denotes a control protection circuit that outputs a drive signal 9a to the inverter 3, which effectively supplies the DC power Pd to the power distribution system 4, and also outputs the AC signal 7 detected by the AC detector 7 and the DC detector 8.
a and DC voltage Vd to protect the inverter 3 in the event of an abnormality. 10 is a current transformer that detects the alternating current IS on the power distribution system 4 side.

FIG. 5 is a block diagram showing part of the internal structure of the control protection circuit 9. As shown in FIG. In FIG. 5, 12 is a protection detection circuit for protecting the inverter 3, and 13 is a control for effectively supplying the DC power generated by the photovoltaic array 1 to the power distribution system 4 and outputting a PWM (pulse width modulation) signal 13a. 14 is an AC overcurrent detection circuit provided in the protection detection circuit 12 and receives the AC signal 7a; 15 is a drive circuit that outputs the drive signal 9a; 12a is an inverter stop command output from the protection detection circuit 12; , 17
is the PWM signal 13a according to the inverter stop command 12a.
This is a stop circuit that stops the inverter 3 by cutting off the inverter 3.

Next, the operation of the conventional power converter for solar power generation shown in FIGS. 4 and 5 will be explained. Control of the inverter 3 consists of a reactive power control loop that performs voltage control using a PWM method, and an active power control loop that performs phase control. Assuming that the output voltage of the inverter 3 is VI, the system voltage of the distribution system 4 is VS, and the phase difference between them (that is, the voltage phase difference of the link reactor X) is δ, the active power P and reactive power Q output from the inverter 3 are It becomes as follows.

[0006]

[Math 1]

From the formula (2), it can be seen that the active power P changes by changing the phase difference δ, and from the formula (2), it can be seen that the reactive power Q changes by changing the output voltage VI of the inverter 3. To be more precise, the active power P and the reactive power Q have a correlation.

[0008] As can be seen from the formula, when the grid voltage VS increases, the reactive power Q increases and the utilization rate of the inverter 3 deteriorates, so normally Q=0, that is, VS=V
The output voltage VI of the inverter 3 is controlled so that it becomes I. At this time, in consideration of the output characteristics of the photovoltaic array 1, the conduction rate (pulse width) of the PWM control is changed without changing the output voltage Vd of the photovoltaic array 1.

Next, the operation of protecting the inverter 3 from overcurrent will be explained with reference to the waveform diagram shown in FIG. During normal operation when the power distribution system 4 is stable and VS=VI is satisfied, the output current II of the inverter 3 becomes a normal operation current 18 (see the solid line in FIG. 6(a)).

On the other hand, when the state of the power distribution system 4 suddenly changes, the output current II of the inverter 3 becomes the current 1 during normal operation.
A current (VS-VI)/X due to system voltage fluctuation is added to 8, resulting in a current 19 during system fluctuation (see the broken line in FIG. 6(a)). The current 19 at the time of grid fluctuation is detected by the AC overcurrent detection circuit 1.
When the AC overcurrent protection level 20 (see the dashed line in Fig. 6), which is set within 4 (see Fig. 5), is reached, the time tx
, the inverter stop command 1 is issued from the protection detection circuit 12.
2a is output. The stop circuit 17 receives the inverter stop command 12a, cuts off the PWM signal 13a, and stops the inverter 3. The waveform of the drive signal 9a at this time is as shown in FIG. 6(c). Note that the waveform of the drive signal 9a during normal operation is shown in FIG. 6(b).

[0011]

[Problems to be Solved by the Invention] The conventional power conversion device for solar power generation is constructed as described above, and the function of controlling the inverter 3 is mainly handled by the control circuit 13 in the control protection circuit 9. The protection detection circuit 12 in the control protection circuit 9 is mainly responsible for the function of protecting against overcurrent, and since the control function is not fast enough to follow sudden changes in the power distribution system 4, the protection detection circuit 12 is If the output current II reaches the AC overcurrent protection level 20 even for a short time that does not affect the inverter 3, the inverter 3
There was a problem in that it stopped the system and caused malfunction.

Furthermore, when the inverter 3 is stopped, the output current I
Since I suddenly becomes 0, an electromotive force is generated by the link reactor X in the filter 6, which causes the problem of accelerating the fluctuation of the power distribution system 4.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a power converter for photovoltaic power generation that does not stop the inverter due to temporary fluctuations in the power distribution system.

[0014]

[Means for Solving the Problems] A power conversion device for solar power generation according to the present invention is provided with a current detection means at the output terminal of the inverter corresponding to the connection point between the inverter and the filter, and the control protection circuit is configured by the current detection means. The feature is that the inverter is controlled based on the detected output current.

[0015]

[Operation] In this invention, when the output current detected at the output terminal of the inverter exceeds a predetermined level, the inverter's output current is throttled to prevent the inverter from stopping due to temporary fluctuations in the power distribution system. .

[0016]

【Example】

Example 1. FIG. 1 is a block diagram showing a first embodiment of the present invention, and 1 to 10 are the same as described above. In FIG. 1, a current detection means, that is, a current transformer 10 is provided at a connection point between an inverter 3 and a filter 6, and detects an output current II at an output terminal of the inverter 3. 7a' is inverter 3
This is an AC signal based on the output current II of the power distribution system 4 and the voltage VS on the power distribution system 4 side.

FIG. 2 is a block diagram of a portion of the control protection circuit 9 that controls the inverter 3, and 13 is the same as described above. In FIG. 2, 22 is an operational amplifier that amplifies the AC signal 7a', and 22a is an inverter current signal output from the operational amplifier 22 (output current I of the inverter 3).
23 is an absolute value circuit that converts the inverter current signal 22a into an absolute value signal 23a indicating its absolute value; 24 is a current suppression level that is a reference when suppressing the output current II of the inverter 3; 25 is a comparator that compares the absolute value signal 23a and the current suppression level 24 and outputs a suppression command signal 25a according to the comparison result; 26 is a filter that removes high frequency components from the AC signal 7a'; 27 is a filter 26
This is a pulse pattern circuit that generates a pulse pattern signal 27a corresponding to a rectangular wave of a fundamental wave component (commercial frequency) from the output signal of.

Reference numeral 28 denotes a suppression timing discrimination circuit, which detects, from the suppression command signal 25a and the pulse pattern signal 27a,
It is determined at what timing the output current II of the inverter 3 should be suppressed, and a suppression signal 28a is output. 30 is an AND circuit that takes the AND of the suppression signal 28a and the PWM signal 13a, and 30a is a suppression PWM signal output from the AND circuit 30.

Next, the operation of the first embodiment of the present invention shown in FIGS. 1 and 2 will be explained with reference to the waveform diagram in FIG. 3. FIG. 3 shows waveforms of some signals appearing in the configuration diagram of FIG. 2.

First, the output current II of the inverter 3 is detected by the current transformer 10 and becomes an alternating current signal 7a' via the alternating current detector 7. The AC signal 7a' is amplified by the operational amplifier 22 in the control protection circuit 9 and becomes an inverter current signal 22a. The inverter current signal 22a is converted into an absolute value by an absolute value circuit 23, and an absolute value signal 23a
becomes. Comparator 25 compares absolute value signal 23a and current suppression level 24, and when absolute value signal 23a exceeds current suppression level 24, activates suppression command signal 25a. For example, in the example shown in FIG. 3, the absolute value signal 23a exceeds the current suppression level 24 at time t1-t2 and time t3-t4 (dotted line portion), and at this time the suppression command signal 25a is activated. Ru. When the absolute value signal 23a does not exceed the current suppression level 24 (before time t1 in FIG. 3, from time t2 to t3, and from time t
4 and thereafter), the suppression command signal 25a is made non-active.

On the other hand, the AC signal 7a' is also input to the filter 26 to remove high frequency components, and the pulse pattern circuit 27 converts the AC signal 7a' into a pulse pattern signal 27a shown in FIG.
is converted to

Subsequently, the suppression command signal 25a and the pulse pattern signal 27a are input to a suppression timing determination circuit 28, and are converted into a suppression signal 28a. At this time, when the suppression command signal 25a is active, the suppression signal 28a also becomes active, and when the suppression command signal 25a is non-active, the suppression signal 28a also becomes non-active.

Furthermore, the suppression signal 28a is the PWM signal 1
3a is input to the AND circuit 30 and converted into the suppression PWM signal 30a. The suppressed PWM signal 30a is amplified by a drive circuit in the control protection circuit 9 to become a drive signal 9a. As shown in FIG. 3, the suppression PWM signal 30a is different from the PWM signal 13a at times t1 to t2 and from t3 to t4, and due to the effect of these parts, the inverter current signal 22a is changed as shown by the solid line in FIG. In this way, the current suppression level 24 is not exceeded. Thereby, the inverter output current II is also limited to a predetermined level or less.

[0024] In the above embodiment, the inverter 3 is
Although the explanation has been made based on the M method, other modulation methods may be used.

[0025]

As described above, according to the present invention, the current detection means is provided at the output terminal of the inverter corresponding to the connection point between the inverter and the filter, and the control protection circuit is based on the output current detected by the current detection means. Since the inverter is controlled by the inverter, it is possible to obtain a power converter for solar power generation that does not stop the inverter due to temporary fluctuations in the power distribution system.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a portion that controls the inverter of the present invention.

FIG. 3 is a waveform diagram of each signal appearing in the first embodiment of the present invention.

FIG. 4 is a configuration diagram showing a conventional power conversion device for solar power generation.

FIG. 5 is a block diagram showing part of the internal structure of a conventional control protection circuit.

FIG. 6 is a waveform diagram of each signal appearing in a conventional power conversion device for solar power generation.

[Explanation of symbols]

1 Photovoltaic array 3 Inverter 4 Power distribution system 9 Control protection circuit 10 Current transformer (current detection means)

Claims (1)

[Claims] 1. A photovoltaic array that generates DC power by the action of sunlight; an inverter that converts the DC power into AC power; a filter that removes harmonics from the AC power and supplies it to a power distribution system; A power conversion device for solar power generation, comprising: a control protection circuit that controls the inverter so that the output current of the inverter reaches a predetermined value and protects the output current from exceeding a predetermined level; A solar power generation system characterized in that a current detection means is provided at an output terminal of the inverter corresponding to a connection point of a filter, and the control protection circuit controls the inverter based on the output current detected by the current detection means. power conversion equipment.