JP2892183B2 - Power converter for photovoltaic power generation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for photovoltaic power generation which is connected to an existing AC power distribution system, and more particularly to a power converter for photovoltaic power generation which is not stopped due to a temporary fluctuation of the distribution system. It is about.

[0002]

2. Description of the Related Art FIG. 4 is a configuration diagram showing a conventional power converter for photovoltaic power generation disclosed in, for example, JP-A-1-98008. In FIG. 4, reference numeral 1 denotes a photovoltaic array that generates DC power Pd by the action of sunlight, Vd denotes an output voltage of the photovoltaic array 1, and 2 denotes a reverse flow of the DC power Pd inserted into the output side of the photovoltaic array 1. prevention diode, an inverter for converting DC power Pd to AC power P _I 3, V _I and I _I the output voltage and output current of the inverter 3, the power distribution system to consume it is supplied AC power P _I 4 Reference numerals 5 and 5 are contactors for interconnecting the distribution system 4. 6
Between is a filter harmonic is inserted into the output terminal side of the inverter 3 so as not to flow into the distribution system 4 which is output from the inverter 3, the output voltage V _I of the inverter 3 and the voltage V _S of the distribution system 4 side communicating to keep the voltage phase difference δ in
It also has a function as a system reactor X (the magnitude of the reactance is X).

[0003] Reference numeral 7 denotes a voltage V on the AC side, that is, the distribution system 4 side.
AC detector for outputting an AC signal 7a detects the _S and the current I _S, 8 the voltage Vd of the direct current side, that the photovoltaic array 1 side
Is a DC detector that detects 9 is a control and protection circuit for outputting a drive signal 9a to the inverter 3, the photovoltaic A
DC power Pd obtained by Ray 1 is efficiently converted to AC power
Converted to P _I, it causes supplied to effectively power distribution system 4 the DC power Pd, according to the detected AC signals 7a and DC voltage Vd by the AC detector 7 and DC detector 8, protects the inverter 3 at the time of abnormality. Reference numeral 10 denotes a current transformer that detects the AC current I _S on the distribution system 4 side.

FIG. 5 is a block diagram showing a 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 distribution system 4 and outputting a PWM (pulse width modulation) signal 13a. A circuit 14, an AC overcurrent detection circuit provided in the protection detection circuit 12 to receive the AC signal 7a; a drive circuit 15 for outputting the drive signal 9a; 12a, an inverter stop command output from the protection detection circuit 12 , 17
Is a PWM signal 13a according to the inverter stop command 12a.
Is a stop circuit that stops the inverter 3 by shutting off the power supply.

Next, the operation of the conventional power converter for photovoltaic power generation shown in FIGS. 4 and 5 will be described. The control of the inverter 3 includes a reactive power control loop for performing voltage control using a PWM method and an active power control loop for performing phase control. Assuming that the output voltage of the inverter 3 is V _I , the system voltage of the distribution system 4 is V _S , and the phase difference between them (that is, the voltage phase difference of the interconnection reactor X) is δ, the output is from the inverter 3. The active power P and the reactive power Q are as follows.

[0006]

(Equation 1)

[0007] From equation found to be active power P is changed by changing the phase difference [delta], it can be seen that the reactive power Q is varied by varying the output voltage V _I of the inverter 3 from the equation. Strictly speaking, the active power P and the reactive power Q have a correlation.

As can be seen from the equation, when the system voltage V _S increases, the reactive power Q increases and the utilization factor of the inverter 3 deteriorates. Therefore, normally, Q = 0, ie, V _S = V _I
Controlling the output voltage V _I of the inverter 3 so that.
At this time, considering the output characteristics of the photovoltaic array 1 , the PWM
The duty ratio (pulse width) of the control is changed.

Next, the operation of protecting the inverter 3 from overcurrent will be described with reference to the waveform diagram of FIG.
During the normal operation in which the distribution system 4 is stable and satisfies V _S = V _I , the output current I _I of the inverter 3 becomes a normal operation current 18 (see the solid line in FIG. 6A).

On the other hand, when the state of the power distribution system 4 changes suddenly, the output current I _I of the inverter 3 becomes 1
8 applied current (V _S -V _I) / X by system voltage variations, so that the system change during current 19 (see FIG. 6 (a) broken lines). The system fluctuation current 19 is supplied to the AC overcurrent detection circuit 14.
When the AC overcurrent protection level 20 (see the dash-dot line in FIG. 6) set in FIG.
a 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. FIG. 6B shows the waveform of the drive signal 9a during the normal operation.

[0011]

The conventional power converter for photovoltaic power generation is configured as described above, and the function of controlling the inverter 3 is mainly performed by the control circuit 13 in the control protection circuit 9. The function of protecting from overcurrent is mainly handled by the protection detection circuit 12 in the control protection circuit 9, and the control function is not fast enough to follow a sudden change of the power distribution system 4. When the output current I _I reaches the alternating overcurrent protection level 20 even short time extent is not affected to the inverter 3, there is a problem that results in a cause malfunction of the inverter 3 is stopped.

When the inverter 3 is stopped, the output current I
_{Since I} suddenly becomes 0, an electromotive force is generated by the interconnection reactor X in the filter 6, and there is a problem that the fluctuation of the distribution system 4 is accelerated. Further, JP-A-63-2
74374 and JP-A-63-206165.
The control circuit of the power converter to be referred to is also proposed.
However, it is not possible to achieve overcurrent suppression with an inexpensive circuit configuration.
I can't. That is, JP-A-63-274374 discloses
The described device is an instantaneous current control using a current minor loop.
Overload control by following the current command value according to the load.
Current to generate high-performance output voltage and current.
And high-speed arithmetic circuits and electronic components.
Required, complicated configuration and cost increase
There was a point. Also, Japanese Patent Application Laid-Open No. 63-206165 discloses
Applicable device applies to uninterruptible power supply (UPS)
Power that is connected to the existing AC distribution system
It can not be applied to a conversion device, and after all, it is simple and inexpensive
If the circuit configuration cannot suppress only instantaneous overcurrent
There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems , and an inexpensive and simple circuit configuration of a photovoltaic power conversion device that does not stop an inverter due to a temporary fluctuation of a distribution system. The purpose is to gain.

[0014]

A power converter for photovoltaic power generation according to the present invention is provided with current detecting means at an output terminal of an inverter corresponding to a connection point between the inverter and a filter, and the control protection circuit comprises a current detecting means. Including a suppression circuit that controls the inverter based on the output current detected by the control circuit , when the output current exceeds the suppression level.
The present invention is characterized in that the suppression signal is activated and a suppression signal for suppressing the drive signal of the inverter is output.

[0015]

According to the present invention, the output current of the inverter is narrowed down when the output current detected at the output terminal of the inverter exceeds a predetermined level, so that the inverter is not stopped due to a temporary fluctuation of the distribution system. .

[0016]

【Example】

Embodiment 1 FIG. FIG. 1 is a configuration diagram showing a first embodiment of the present invention, and 1 to 10 are the same as those described above. In FIG. 1, a current detecting means, that is, a current transformer 10 is provided at a connection point between the inverter 3 and the filter 6 and detects an output current I _I at an output terminal of the inverter 3. 7a 'is an AC signal based on the output current I _I of the inverter 3 and the voltage V _S of the distribution system 4 side.

FIG. 2 is a block diagram of a portion for controlling the inverter 3 in the control protection circuit 9, and 13 is the same as that described above. In FIG. 2, reference numeral 22 denotes an operational amplifier for amplifying the AC signal 7a ', and 22a denotes an inverter current signal output from the operational amplifier 22 (output current I of the inverter 3).
_I indicates the value of _I ), 23 is an absolute value circuit for converting the inverter current signal 22a into an absolute value signal 23a indicating its absolute value, and 24 is a current suppression level serving as a reference when suppressing the output current I _I of the inverter 3. , 25 are comparators for comparing the absolute value signal 23a with the current suppression level 24 and outputting a suppression command signal 25a according to the comparison result, and 26 is an AC signal 7a '.
Filter for removing high frequency components from the filter, 27 is filter 2
6 is a pulse pattern circuit that generates a pulse pattern signal 27a corresponding to a square wave of a fundamental wave component (commercial frequency) from the output signal of FIG. Comparator 25, based on the output current I _I
To activate the suppression command signal 25a, and
The inverter 3 is controlled in cooperation with a switching discrimination circuit (described later).
To form a suppression circuit for control.

Reference numeral 28 denotes a suppression timing discriminating circuit, which determines the suppression timing signal 25a and the pulse pattern signal 27a from each other.
It determines at what timing the output current I _I of the inverter 3 is suppressed, and outputs a suppression signal 28a. Numeral 30 denotes an AND circuit for calculating the logical product of the suppression signal 28a and the PWM signal 13a, and reference numeral 30a denotes 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 described with reference to the waveform diagram of FIG. FIG. 3 shows waveforms of some signals appearing in the configuration diagram of FIG.

First, the output current I _I of the inverter 3 is detected by the current transformer 10 and becomes an AC signal 7 a ′ via the AC 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 the absolute value circuit 23, and the absolute value signal 23a
Becomes The comparator 25 compares the absolute value signal 23a with the current suppression level 24, and activates the suppression command signal 25a when the absolute value signal 23a exceeds the current suppression level 24. For example, in the example shown in FIG. 3, the absolute value signal 23a is (dotted line) at time t ₁ ~t ₂ and time t ₃ ~t _4, it exceeds the current suppression level 24, this time inhibition command signal 25a Is activated. When the absolute value signal 23a does not exceed the current suppression level 24 (time t ₁ earlier in FIG. 3, the time t ₂ ~t ₃ and time t ₄ after), suppression command signal 25a is non-active.

On the other hand, the AC signal 7a 'is also inputted to a filter 26 to remove high-frequency components, and 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 discriminating circuit 28 and converted into a suppression signal 28a. At this time, when the suppression command signal 25a is active, the suppression signal 28a is also active, and when the suppression command signal 25a is non-active, the suppression signal 28a is also non-active.

Further, the suppression signal 28a is a PWM signal 1
The signal is input to the AND circuit 30 together with 3a, and is converted into a suppressed PWM signal 30a. The suppression 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, suppression PWM signal 30a is, PW at time t ₁ ~t ₂ and time t ₃ ~t ₄
Unlike the M signal 13a, the effect of this portion makes the inverter current signal 22a not exceed the current suppression level 24 as shown by the solid line in FIG. Thus, inverter output current I _I is limited below a predetermined level.

In the above embodiment, the inverter 3 is connected to the PW
Although described as the M type, another modulation type 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 detects the output current detected by the current detection means. includes a suppression circuit for controlling the inverter on the basis of, suppression circuitry, the output current is suppressed
When the level exceeds the level, the suppression signal is activated and a suppression signal for suppressing the drive signal of the inverter is output.Therefore, a power conversion device for photovoltaic power generation that does not stop the inverter due to temporary fluctuations in the distribution system There is an effect that can be obtained at a low cost and with a simple circuit configuration.

[Brief description of the 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 an inverter according to 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 photovoltaic power conversion device.

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photovoltaic array 3 Inverter 4 Distribution system 9 Control protection circuit 10 Current transformer (current detection means)

Claims (1)

(57) [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 the AC power to a distribution system, A power protection device for photovoltaic power generation, comprising: a control protection circuit that controls the inverter so that the output current of the inverter becomes a predetermined value and protects the output current so that the output current does not exceed a predetermined level. a current detecting means to an output terminal of the inverter provided corresponding to the connection point of the filter, the control protection circuit, suppress times for controlling said inverter based on the detected output current by said current detecting means
And wherein the suppression circuit determines that the output current has exceeded a suppression level.
A power conversion device for photovoltaic power generation, comprising: activating a suppression signal at the time of power generation and outputting a suppression signal for suppressing a drive signal of the inverter.