JPH10210760A - Control method for inverter for power generation by sun ray - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the biased magnetization of a transformer, in a sun ray power generation system which supplies load with the output voltage of an inverter whose input is the output of a solar battery through the above transformer. SOLUTION: The formation of the output voltage of an inverter is performed by the PWM control which performs the comparison between a triangular wave carriage signal and a new sine wave command signal which is obtained by adding the output of an ACR 34, which receives the input of the deviation between the detection signal IINV of the inverter output current by CT1 and the detection signal IAC of a load current by CT2, to a modified sine wave command signal being obtained by adding the output of an instantaneous AVR 33, which receives the input of the deviation between a command signal and the detection signal VAC of load voltage by PT, to the sine wave command signal which constitutes the reference of the load voltage, being outputted by a sine wave generator 32. Then, DC components within the output current of an inverter which causes the biased magnetization of the transformer are removed, and the increase of the resonance current in an LC resonance system on output side of the transformer is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic power generation system for converting an output voltage of an inverter which receives an output of a solar cell into a predetermined alternating current to an appropriate voltage via a transformer and feeds the load to a load. The present invention also relates to a method for controlling a photovoltaic power generation inverter for preventing the transformer from being demagnetized and reducing the resonance current between the transformer and its output-side capacitor.

[0002]

2. Description of the Related Art As a conventional inverter control in this type of photovoltaic power generation system, there is known an inverter control performed as shown in a control block diagram illustrated in FIG. In addition, the main circuit diagram of FIG. 4 shows whether the solar power generation system shown in FIG. 3 operates in parallel with the external AC power supply system and the load in common, or whether the two power supply systems individually supply power to the load, It is an example of a main circuit configured so that any operation is possible.

First, in the main circuit diagram of FIG. 4, 1 is a solar cell, 2A is an inverter device, 3 is an external AC power supply such as a commercial power supply, and 4 is a load. Here, the inverter device 2A
, 21 is an inverter that receives the DC output of the solar cell 1 and converts it into an AC having a predetermined voltage and frequency.
22 is a transformer for converting the output voltage of the inverter 21 into a required load power supply voltage, 23 is a reactor, 24 is a capacitor for smoothing the output of the inverter 21 via the transformer 22, 25 is generated in an inverter output smoothing system. This is a braking resistor for suppressing the resonance current.

[0004] MC is an electromagnetic contactor for parallel operation of the external AC power supply 3 and the photovoltaic power generation system including an inverter 21 and the like, and COS is the photovoltaic power generation system and the external AC power supply 3
And CB1 to CB3 are switching switches for switching the power supply path when power is independently supplied to the load 4. That is, the electromagnetic contactor MC is opened, and the switching switch CO
When S is closed at the output side of the transformer 22, the solar power generation system supplies power to the load 4 alone, and when the MC is opened and the COS is closed on the side of the external AC power supply 3, the external power is supplied. The AC power supply 3 supplies power to the load 4 alone,
Further, if the COS is closed at the output side of the transformer 22 and the MC is closed in a synchronized state between the photovoltaic power generation system and the external AC power supply system, both the photovoltaic power generation system and the external AC power supply 3 are used. To the load 4.

Since the photovoltaic power generation system operates in parallel with the external AC power supply 3, the inverter 21 becomes equal to the external AC power supply 3 at the output frequency and the output voltage transformed by the transformer 22. It is controlled as follows. Next, the control block diagram of FIG. 3 shows a configuration of a control system for the inverter 21 of the photovoltaic power generation system main circuit shown in FIG. Therefore, the description of the main circuit elements shown in FIG.
And is omitted here.

In FIG. 3, a λ setter 31 is a control parameter λ in PWM control (pulse width modulation control).
Is set. Here, the parameter lambda is the desired output voltage and its sine wave command signal amplitude is proportional to the frequency of the same inverter amplitude V _M and the ratio between the amplitude V _C of the triangular wave carrier signal (lambda = V _M / V _C ). Also,
The offset setting unit 38 sets the zero level transition width of the sine wave command signal in order to eliminate the DC component in the output of the inverter, which constitutes the demagnetization component of the transformer 22, and the sine wave generator 32 has the parameter A sine wave having an amplitude specified by λ and having a zero-level shift having a width specified by the setting unit 38 is output as a sine wave command signal in the PWM control.

Further, the instantaneous AVR 33 includes a sine wave generator 3
As input a deviation between the load voltage V _AC detected by a sine wave command signal output from the 2 and instrument transformer PT instantaneous operation type that outputs a correction instruction for the deviation for each waveform of the sine-wave command signal In the automatic voltage regulator, the voltage deviation correction command is added to a sine wave command signal output from the sine wave generator 32, and a corrected sine wave command signal in the PWM control is newly formed.

Next, the triangular wave generator 35 outputs a triangular wave carrier signal having an amplitude defined by the parameter λ and changing at a predetermined carrier frequency as a comparison signal with respect to the sine wave command signal in PWM control. is there.
Further, a PWM 36 is a pulse width modulation control circuit, which converts a pulse train whose pulse width is modulated in accordance with the result of the magnitude comparison operation between the sine wave command signal and the triangular wave carrier signal into a solar cell output DC input to the inverter 21. This is output as a voltage intermittent basic signal.

Further, the gate signal distributor 37 is provided with the PWM
The pulse train modulated by the pulse width output from the circuit is transformed into three sets of pulse trains having an electrical phase difference according to the number of output phases of the inverter 21, for example, an electrical angle of 120 degrees when outputting three phases. This is output as an intermittent control signal for each phase switching element in the main circuit.

[0010]

Generally, the magnetizing of a transformer is caused by the superposition of a direct current component on an alternating current which passes through the windings and becomes an iron core exciting current. The direct current component in the exciting current strengthens the excitation in the superimposing direction, breaks the symmetry in the core excitation, and distorts the waveform of the transformer secondary output voltage. That is, it causes the generation of harmonic components in the secondary output voltage of the transformer.

In the present invention, the transformer exciting current is an output current of a solar cell output conversion inverter which is a primary alternating current. On the other hand, as described above, the conventional method of controlling an inverter for photovoltaic power generation uses an amplitude designation by the λ setting device and a zero by the DC component in the inverter output current, which causes a transformer demagnetization, by the offset setting device. In accordance with the offset setting corresponding to the level shift width, control is performed so that the load voltage is equal to a sine wave command signal formed asymmetrically in the amplitude direction according to the offset setting.
Note that no consideration is given to the formation of the sine wave command signal for the state of the load current that forms the load voltage.

However, the DC component in the inverter output current, which causes the transformer demagnetization, depends on the difference in switching characteristics between the upper and lower arm elements in the bridge configuration of the inverter main circuit or the difference in time characteristics in the switching command signal system. And the magnitude thereof changes according to the load state of the inverter or the fluctuation of the input voltage, and is not a constant value.

Therefore, in the conventional control method in which the DC component in the inverter output current is regarded as constant and the fixed offset is set so that the zero level transition width with respect to the sine wave command signal becomes a constant value, the change in the load state or the input voltage Cannot cope with the change of the offset level due to the fluctuation of the output voltage, resulting in the waveform distortion of the secondary output voltage of the transformer and the generation of the secondary harmonics, and also the leakage reactance and the output smoothing of the transformer. There is a danger that the harmonic current in the LC resonance system formed with the capacitor increases due to the harmonics.

In view of the above, the present invention relates to a photovoltaic power generation system which receives an output of a solar cell and converts the output to a predetermined AC, converts the output voltage of the inverter to an appropriate voltage via a transformer, and supplies the voltage to a load. It is another object of the present invention to provide an inverter control method for preventing the transformer from being demagnetized and reducing the resonance current between the transformer and an output-side capacitor thereof.

[0015]

To achieve the above object, the present invention provides a method for controlling an inverter for photovoltaic power generation according to the present invention. 1) The invention according to claim 1 receives a DC output of a solar cell and controls An inverter for converting the output voltage of the inverter into an AC voltage, a transformer for converting an output voltage of the inverter into a required load power supply voltage, and a transformer output smoothing capacitor provided on a secondary side of the transformer. With respect to the inverter in the photovoltaic power generation system, a deviation between a sine wave command signal having a required load voltage and its amplitude proportional and having the same frequency and a detection signal of the load voltage is input and each wave of the command signal is inputted. A pulse width modulation system based on a comparison between a corrected sine wave command signal obtained by adding an output of an instantaneous operation type automatic voltage adjusting means for outputting a waveform correction signal every time to the command signal and a triangular carrier signal. And controlling the inverter in a photovoltaic power generation system configured to maintain the load voltage at the required value through inverter output voltage control. The method for detecting an inverter output current between the inverter and a transformer And a load current detecting means between the smoothing capacitor and the load, an automatic current adjusting means having a deviation between the detected inverter output current and the load current converted into a transform ratio as its input, And the output signal of the automatic current adjusting means is used as an addition correction signal to the corrected sine wave command signal in the pulse width modulation control.

According to a second aspect of the present invention, in the method of controlling an inverter for photovoltaic power generation according to the first aspect, a Hall element type current transformer including a Hall element as a basic element of the inverter output current detecting means. And 3) The invention according to claim 3 is the method of controlling an inverter for photovoltaic power generation according to claim 1, wherein the means for detecting the inverter output current is constituted by a shunt as its basic element.

As described above, the present invention relates to a DC component in the inverter output current and a resonance current in an LC resonance system formed on the transformer output side, as a deviation between the inverter output current and the load current converted into a transformer ratio. Detects the combined state of the two, and transforms the detected value as a current component correction signal that is quantitatively and temporally appropriate through an automatic current regulator, and converts this current component correction signal to a sine wave generator. PWM based on the corrected sine wave command signal obtained by adding the sine wave command signal output by
By performing control to form an inverter output voltage, the DC component in the inverter output current that causes the transformer demagnetization and the LC resonance system resonance current due to harmonics resulting from waveform distortion due to the demagnetization To reduce or eliminate both.

Further, as a means for detecting the inverter output current including a direct current component, a Hall element type current transformer or a current divider is constituted by an operational amplifier or the like as a basic element. By using the shunt type, accurate current detection is achieved regardless of whether the DC component is contained.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to a control block diagram of FIG. 1 and a main circuit diagram of FIG. 1 and 2 and FIG. 3 showing an embodiment of the prior art.
4 and FIG. 4, the same reference numerals are given to the components having the same functions. First, the main circuit diagram of the photovoltaic power generation system shown in FIG.
And a current transformer CT1 provided between the transformer 22 and the load 4 for detecting the output current of the inverter, and a current transformer CT2 provided between the transformer 22 and the load 4 via the COS. The output of each CT is applied to an inverter 21, and a resistor 2 for suppressing a resonance current connected in series to a capacitor 24.
5 is omitted.

Next, the control block diagram of FIG.
In response to the change in the main circuit diagram of FIG.
Inverter output current detection signal I by current transformer CT1
An automatic current regulator (ACR) 34 is provided for inputting a deviation (I _AC -I _INV ) between _INV and the load current detection signal I _AC by the current transformer CT 2, and outputs both the sine wave generator 32 and the instantaneous AVR 33. By adding the output of the ACR 34 to the sine wave command signal formed as the sum of
It is configured to obtain a new and modified sine wave command signal in PWM control for forming an inverter output voltage.

That is, by correcting the sine wave command signal by a current corresponding to the current deviation (I _AC −I _INV ), the sine wave command signal changes irregularly in accordance with the operation state of the inverter, and the transformer demagnetization. The automatic offset setting operation that follows the direct current component in the inverter output current and automatically selects the zero level shift width in the inverter output voltage to an appropriate value becomes possible, and the reduction of the direct current component in the inverter output current is possible. The waveform distortion of the secondary output voltage of the transformer is reduced or eliminated, and the harmonic content contained in the secondary output voltage of the transformer is also reduced or eliminated, thereby reducing the transformer leakage reactance and the smoothing capacitor. The resonance current due to the harmonics in the LC resonance system to be formed is also reduced or eliminated.

Although the circuit configuration is not shown, each of the CTs shown in FIG.
The content of is that a Hall element type current transformer in which a Hall element is used as a basic detection element and a required operational amplifier is combined with the Hall element type current transformer, or a shunt is used as a basic detection element and a required operational amplifier is combined with the element. It is a shunt type current transformer.

[0023]

According to the present invention, an inverter which receives an output of a solar cell and converts it into a predetermined alternating current, a transformer which converts an output voltage of the inverter into a required load power supply voltage, and a transformer For the inverter in a photovoltaic power generation system configured with an output smoothing capacitor, a deviation between a required load voltage and a sine wave command signal whose amplitude is proportional and whose frequency is the same and a detection signal of the load voltage. Pulse width modulation (PWM) by comparing the corrected sine wave command signal obtained by adding the output of the instantaneous operation type automatic voltage adjusting means having the 2.) In the method of controlling an inverter according to claim 1, wherein between the detection signal of the output current of the inverter and the detection signal of the load current converted based on a transformation ratio of the transformer. The output signal of the automatic current adjusting means having the deviation as its input is added to the sine wave command signal, and the sine wave command signal to be compared with the triangular wave carrier signal in the PWM control is corrected by a current corresponding to the current deviation. By performing the above, it is possible to perform an automatic offset setting operation that follows a change in the DC component in the inverter output current that causes the transformer demagnetization and automatically selects an appropriate zero-level transition width in the inverter output voltage. As described above, the waveform distortion of the secondary output voltage of the transformer accompanying the reduction of the DC component is reduced or eliminated, and the harmonic content contained in the secondary output voltage of the transformer is also reduced or eliminated. Accordingly, the transformer leakage reactance is reduced. Also, the resonance current due to the harmonic in the LC resonance system formed by the capacitor and the smoothing capacitor is reduced or eliminated. Further, as a means for detecting an inverter output current including a direct current component, a Hall element type current transformer or a shunt type having an operational amplifier or the like as a basic element thereof is used as a means for detecting an inverter output current including a DC component. This makes it possible to accurately detect a current including a DC current or a harmonic current.

[Brief description of the drawings]

FIG. 1 is a control block diagram showing an embodiment of the present invention.

FIG. 2 is a main circuit diagram showing an embodiment of the present invention.

FIG. 3 is a control block diagram showing an embodiment of the prior art.

FIG. 4 is a main circuit diagram showing an embodiment of the prior art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Inverter device 2A Inverter device 3 External AC power supply 4 Load 21 Inverter 22 Transformer 23 Reactor 24 Capacitor 25 Resistance 31 λ setting device 32 Sine wave generator 33 Instantaneous AVR (instantaneous operation type automatic voltage regulator) 34 ACR ( Automatic current regulator) 35 Triangular wave generator 36 PWM (pulse width modulation control circuit) 37 Gate signal distributor 38 Offset setting device CB _n breaker (n = 1 to 3) COS switching switch CT _n current transformer for instrument ( n = 1,2) MC Magnetic contactor PT Transformer for instrument

Claims (3)

[Claims] An inverter for receiving a DC output of a solar cell and converting it into a predetermined AC, a transformer for converting an output voltage of the inverter into a required load power supply voltage, and a secondary side of the transformer And a detection of the load voltage and a sine wave command signal whose amplitude is proportional to the required load voltage and whose frequency is the same with respect to the inverter in the photovoltaic power generation system having the transformer output smoothing capacitor provided in A modified sine wave command signal obtained by adding to the command signal the output of the instantaneous operation type automatic voltage adjusting means for inputting a deviation from the signal and outputting a waveform correction signal for each wave of the command signal. And a triangular wave carrier signal to perform pulse width modulation control, and the inverter in the photovoltaic power generation system configured to maintain the load voltage at the required value through inverter output voltage control. In the method of controlling a motor, the inverter output current detecting means between the inverter and the transformer, the load current detecting means between the smoothing capacitor and the load, the detected inverter output current and the transformer ratio Automatic current adjusting means having as its input a deviation from the converted load current, and adding an output signal of the automatic current adjusting means to the corrected sine wave command signal in the pulse width modulation control. A method for controlling an inverter for photovoltaic power generation, wherein the method is used as a correction signal. 2. The method for controlling an inverter for photovoltaic power generation according to claim 1, wherein said means for detecting the inverter output current is a Hall element type current transformer having a Hall element as its basic element. How to control a solar power inverter. 3. The method for controlling an inverter for photovoltaic power generation according to claim 1, wherein said means for detecting the output current of said inverter comprises a shunt as its basic element. Method.