JP3205762B2 - Grid-connected inverter controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts DC power output from a DC power supply such as a solar cell into AC power for linking to a commercial system power supply, and always keeps the output power from the DC power supply in a maximum state. The present invention relates to a system interconnection type inverter control device adapted to supply to a general load.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a grid-connected solar power generation system to which a conventional grid-connected inverter control device is applied. In the case of this conventional example, a constant input voltage control method is adopted as a control method. In this system, DC power of a solar cell 2 is converted into AC power by a grid-connected inverter 1 controlled by PWM (pulse width modulation), and is connected to a commercial power supply 3 to supply power to a load 4. is there.

The system interconnection inverter 1 has functions of an input capacitor 5, an FET bridge 6, an output filter, and
It comprises an output choke coil 7 for converting a WM-modulated rectangular wave into a sine wave, a smoothing capacitor 8, and a control unit 9. The control unit 9 includes an input voltage detection circuit 10, a bandpass filter (BPF) 11, an output current detector 12,
DC voltage constant control circuit 13, DC voltage reference voltage source 14,
Multiplier 15, error amplifier 16 for output current control, PWM
It comprises a modulation circuit 17 and a gate drive circuit 18 for driving the FET bridge 6.

Hereinafter, a control method will be described.

[0005] An inverter input voltage _VDC is detected by an input voltage detection circuit 10 and a constant DC voltage control circuit 13 controls the inverter input voltage _VDC and a DC voltage reference voltage source 14.
An error signal S1 with respect to the reference voltage _VREF is generated, and this error signal S1 is used as one input of the multiplier 15. Further, the commercial system voltage V _CS is detected, only the fundamental wave component is extracted by the band pass filter 11, and the reference sine wave signal S 2 is used as the other input of the multiplier 15. The multiplier 15 multiplies the input error signal S1 by the reference sine wave signal S2 to generate an inverter output current reference signal S3.

The error amplifier 16 receives the inverter output current reference signal S3 from the multiplier 15 and the inverter output current I _OUT detected by the output current detector 12, and outputs a modulation reference error signal S4 obtained by amplifying the difference between the two. PWM modulation circuit 1
7 is output. PWM modulation circuit 17 performs PWM control based on the modulation reference error signal S4 inputted by driving the FET bridge 6 via the gate drive circuit 18, the reference voltage V _{RE F} to the matched inverter input voltage V _DC is Control to obtain. That is, the solar cell 2
The input characteristics of the grid-connected inverter 1 are controlled by the operating voltage of.

In the FET bridge 6, when the transistors Q1 and Q2 are simultaneously turned on, the transistors Q3 and Q4 are simultaneously turned off.
3 and Q4 are simultaneously turned on, the transistors Q1, Q2
Are controlled to be turned off simultaneously.

[0008] Due to the characteristics of the solar cell 2, the operating voltage at which the maximum power can be extracted changes every moment depending on weather conditions such as the amount of solar radiation and the element temperature. By the way, the feature of the above-mentioned conventional method is that the operation voltage is simulated at the maximum output point of the solar cell 2 on the assumption that the operating voltage can be approximated by a constant voltage regardless of the amount of solar radiation or the element temperature.

However, it is naturally expected that the predetermined constant voltage value does not match the voltage value at which the maximum power can be obtained. In this case, it operates at a point shifted from the maximum output point, and cannot output the maximum power. In particular, when the amount of solar radiation is large, a large amount of power is wasted. Further, since the maximum output point voltage greatly changes depending on the element temperature, it is necessary to change a predetermined constant voltage value depending on the season, which is complicated.

[0010]

A major feature of a solar cell is that its output characteristics are greatly affected by weather conditions, and that even under the same weather conditions, its output differs depending on the operating point. No.

Therefore, in order to effectively utilize the power generated by the solar cell, it is conceivable that the maximum power point tracking control should be performed. There is a fundamental problem that the output power cannot be actively controlled by changing the operating point on the characteristic curve.

As is well known, the output characteristics of the solar cell are as shown in FIG. 3. If the weather conditions are constant, the output characteristic of the solar cell depends on the impedance of the load provided on the output side of the solar cell. The values of the output voltage and the output current of the solar cell change on the output characteristic curve, and accordingly, the output power value of the solar cell also changes.

Here, assuming that the impedance of the load provided at the output terminal of the solar cell is R as shown in the figure, the output voltage and output current of the solar cell at this time are the values at point p on the characteristic curve. By changing the load impedance R, the operating point p of the solar cell moves on the characteristic curve,
Each value of the output voltage, output current, and output power of the solar cell changes. In order to extract the maximum power of the solar cell, control may be performed so that the load impedance R seen from the solar cell side is optimal even when the weather conditions change.

When the maximum power point tracking control of the solar cell is to be performed by the output current control type inverter, the amplitude of the output current reference signal is manipulated, and the error signal between the output current reference signal and the detected output current signal is calculated. PWM modulation is performed to drive the inverter. As a result of the operation, it is determined whether the input power has increased or decreased, and the amplitude of the next output current reference signal is changed.

When starting from the open voltage side of the solar cell and gradually increasing the amplitude of the output current reference signal, the error signal from the detected output current signal increases, and the switching duty ratio increases in PWM modulation. Become. Then, the inverter input impedance, that is, the impedance viewed from the solar cell, becomes small, and the output power increases according to the solar cell output characteristic curve. Since the inverter output voltage is considered to be substantially constant at the voltage of the commercial system power supply 3, as the output power increases, the inverter output current also increases.

However, as the amplitude of the output current reference signal gradually increases, the output power continues to increase,
Assume that the maximum power point has been reached. Then, when the amplitude of the output current reference signal is further increased to exceed the maximum power point, the inverter input power decreases, and the inverter output current also decreases.

At this time, the output current signal to be fed back becomes small and the error signal from the output current reference signal becomes large, so that the duty ratio of the switching becomes large and the input impedance becomes small in the PWM modulation. Above, the operating point attempts to move to the short circuit side. Then, since the output power decreases, the output current further decreases, and a state occurs where the error signal from the output current reference signal further increases. As a result, when the maximum power point is exceeded, the operating point moves to the short-circuit side. Then, the maximum power point tracking control cannot be performed as it is.

Therefore, when the output current signal exceeds the maximum power point, the output current reference signal needs to be decreased in accordance with the decrease in the output current signal. The characteristics of the solar cell depend on the amount of solar radiation or element temperature at that time. Also, in the control, in order to change the amplitude of the next output current reference signal in a feedforward manner by increasing or decreasing the input power as a result of manipulating the amplitude of the output current reference signal, the changed The battery operating point cannot be predicted.

That is, with the above control, an increase or decrease in the input power is detected, and the amplitude of the output current reference signal is changed.
It is extremely difficult to perform maximum power point tracking control.

The present invention has been made in view of such circumstances, and performs a maximum power point tracking control satisfactorily even if the voltage-current characteristics of a DC power supply such as a solar cell fluctuate. It is an object of the present invention to be able to always extract maximum power from a DC power supply.

[0021]

A system interconnection type inverter control device according to the present invention controls ON / OFF of a bridge of a switching element based on a switching pattern signal, and controls a DC power input from a DC power source such as a solar cell. To AC power, means for supplying to a load in connection with a commercial system power supply, means for generating the switching pattern signal by pulse width modulation based on a reference sine wave signal, and a detected inverter output current value Means for storing
Grid-connected inverter controllers with different amplitudes
A reference sine in which a plurality of the reference sine wave signals are stored in advance.
Wave signal storage means, and zero voltage
Point, and synchronize with the zero cross point.
Storing the reference sine wave signal in the reference sine wave signal storage means.
Means for reading and outputting al, and means for varying the amplitude of the reference limit wave in a direction to increase or decrease by periodically one step, and means for storing the detected inverter output current value, the stored previous A determination means for determining the direction of change of the output current value by comparing the output current value of the output current value with the current output current value; and , based on the determination result of the determination means , when the change direction of the output current value increases. Means for maintaining the change direction of the amplitude of the reference sine wave signal as it is, and inverting the change direction of the amplitude of the reference sine wave signal when the change direction of the output current value decreases. is there.

[0022]

According to the present invention, a reference limit is generated in the same phase state based on detection of a commercial system voltage, a pulse width modulation is performed based on the reference sine wave signal to generate a switching pattern signal, and a switching pattern signal is generated based on the switching pattern signal. The bridge of the switching element is ON / OFF controlled to convert DC power from a DC power supply such as a solar cell into AC power, and connect the AC power to a commercial system power supply to supply the load. By periodically changing the amplitude of the reference sine wave signal, the inverter output current value is detected and stored, and it is determined whether the output current value is increasing or decreasing by comparing with the previous output current value. The direction of the amplitude change of the reference sine wave signal is maintained (increase in the increase direction, decrease in the decrease direction),
When the reference sine wave signal is decreasing, the amplitude change direction of the reference sine wave signal is inverted (decrease in the increase direction, increase in the decrease direction), and the amplitude of the reference sine wave signal is increased by 1 in the determined direction.
Change by steps. By repeating the above, the maximum power point tracking control that always sets the output power of the DC power supply to the maximum power point can be performed. Also, a plurality of reference sine wave signals having different amplitudes are reserved.
And memorize them in synchronization with the zero cross point.
Maximum power point tracking control can be performed by outputting a sinusoidal signal.
When performing the operation, the voltage of the commercial
Just detect the voltage waveform and value.
Therefore, the detection circuit can be simplified.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a system interconnection type inverter control device according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a configuration diagram of a grid-connected solar power generation system to which a control device according to an embodiment of the present invention is applied.
In the present system, the solar cell 32 is connected to the grid-connected inverter 31, and the grid-connected inverter 31 converts the DC power output from the solar cell 32 into AC power in the same phase as the commercial grid power supply 33 by PWM control. System power supply 3
3, and supplies power to a load 34 such as a general household electric appliance.

The system interconnection inverter 31 is a voltage-type current control type inverter, and includes an input capacitor 35 for suppressing a change in input power from the solar cell 32, an FET bridge 36 as a switching element for DC-AC conversion, and an output filter. An output choke coil 37 and a smoothing capacitor 38 for converting a PWM-modulated rectangular wave into a sine wave, and an interconnection relay 39 for disconnecting the system interconnection inverter 31 from the commercial system power supply 33 and the load 34 when an abnormality occurs. It comprises a control unit 40.

A flywheel diode is connected to each of the four transistors Q1 to Q4 in the FET bridge 36 in reverse polarity. FET bridge 36
Is controlled by a gate drive circuit 42 described later.
When the transistors Q1 and Q2 are simultaneously turned on, the transistors Q3 and Q4 are simultaneously turned off. Conversely, when the transistors Q3 and Q4 are simultaneously turned on, the transistors Q1 and Q4 are turned off.
Q2 is configured to be turned off simultaneously.

The control section 40 comprises the following elements. That is, a control circuit 41 that performs maximum power point tracking control, output current control, and system protection of the system interconnection inverter 31, a gate drive circuit 42 that drives and controls the FET bridge 36, and a reference sine wave output from the control circuit 41. A PWM modulation circuit 43 for generating a switching pattern signal S12 by PWM modulating the signal S11 and outputting the switching pattern signal S12 to the gate drive circuit 42, and a synchronization signal detector 44 for setting the output of the inverter 31 to the same phase as the commercial system power supply 33. And the positive / negative direction detector 45 and the output current detector 4
6 is comprised.

The control circuit 41 is a digital circuit,
An A / D converter 47 for converting a signal detected by the output current detector 46 into a digital signal; a CPU 48 for performing various operations required for control; and a reference sine wave serving as a source of each pulse width for PWM control. A reference sine wave signal record that stores waveform pattern data and the like for producing the signal S11.
ROM 49 as storage means, RAM 50 as temporary storage memory, and digital waveform pattern data
The D / A converter 51 converts the reference sine wave signal S11 into an analog reference sine wave signal S11 and outputs the reference sine wave signal S11 to the PWM modulation circuit 43.

The operation of the system configured as described above will now be described.

The system interconnection inverter 31 performs a PWM control by the PWM modulation circuit 43 and outputs a pair of switching transistors Q1 and Q2 and a pair of switching transistors Q1 and Q2 in the FET bridge 36 based on the gate pulse signal S13 output from the gate drive circuit 42. By switching the switching transistors Q3 and Q4 alternately on and off to perform switching, the output current of the grid interconnection inverter 31 is controlled, and the output of the solar cell 32 is supplied to the load.

In this case, the PWM modulation circuit 43 has a D / A
By comparing the reference sine wave signal S11 from the converter 51 with a triangular wave serving as a switching carrier, PWM
A switching pattern signal S12 as a waveform is generated and output to the gate drive circuit. Gate drive circuit 42 receiving switching pattern signal S12
Outputs the gate pulse signal S13 to the FET bridge 36, and outputs the transistors Q1 and Q2 and the transistor Q
3, Q4 is turned on / off to generate a rectangular wave. The rectangular wave is output from the output choke coil 37 and the smoothing capacitor 38.
The current is converted into a sine wave current by the output filter, and supplied to the load 34 via the interconnection relay 39. The reference sine wave signal S11 is controlled to have the same phase as the voltage waveform of the commercial system power supply 33, and the duty ratio of the PWM pattern is determined by the magnitude of the amplitude.

Next, the reference sine wave signal S11 will be described. As described above, PW is generated by the reference sine wave signal S11.
The duty ratio of the M pattern is determined, and the operating point of the solar cell 32 is determined.
Is obtained. By the way, in order to perform the solar cell maximum power point tracking control, the amplitude of the reference sine wave signal S11 must be variable. Below is the reference sine wave signal S
11 shows a method of varying the amplitude of the eleventh example.

The reference sine wave signal pattern when the duty ratio of the system interconnection inverter 31 is the maximum is defined as the largest one, and the data for one cycle of the maximum reference sine wave signal is decomposed at certain time intervals. The amplitude value is represented as a digital value. In this embodiment, the frequency is 60 Hz and 1
The cycle is 1/60 second, which is divided into 256 equal parts, about 65.1μ
sec is a unit cycle. In this case, one cycle of the reference sine wave signal is composed of 256 digital values in the time axis direction. The set of digital values for one cycle is considered as a unit. Next, for each of a large number of reference sine wave patterns obtained by dividing the amplitude of the maximum reference sine wave signal at equal intervals (in this embodiment, equal to 200), one cycle of each of the patterns is similarly performed as described above. Consider a set of 256 digital values. That is, the reference sine wave signal is a waveform pattern formed by a set of 256 digital values, and there are a total of 200 types of such waveform patterns having different amplitudes.

The data of such 200 kinds of reference sine wave patterns are stored in the ROM 49 of the control circuit 41 in advance. Number 1 for each reference sine wave pattern
When a reference sine wave pattern is designated by a number to the ROM 49, the CPU 48 sequentially reads out 256 digital values from the ROM 49 for the designated sine wave pattern of the designated number, and the D / A converter 51 To send to. The D / A converter 51 has a CP
U48 generates an analog reference sine wave signal S11 having a reference sine wave pattern corresponding to the number designated by U48,
The signal is output to the M modulation circuit 43.

The timing at which the CPU 48 reads the digital value of the reference sine wave pattern is as follows. At the same time when the synchronization signal detector 44 reads out the zero-cross point of the commercial system voltage V _CS by a commercial system power source 33 as a synchronization signal, CPU 48 reads the first data to start the internal timer, 256 such one cycle of 1/60 sec The second data is read after a lapse of 65.1 μsec. That is, the digital values of the reference sine wave pattern of the designated number are sequentially read out every 65.1 μsec, and these digital values are D / A converted by the D / A converter 51 to perform the reference sine wave signal S11.
Is generated and output to the PWM modulation circuit 43. At this time, the synchronization signal detector 44 detects the zero cross point of the commercial system voltage V _CS , and the positive / negative direction detector 45 detects the positive or negative direction of the waveform of the commercial system voltage V _CS ,
The PU 48 outputs data in accordance with the positive and negative directions, thereby converting the reference sine wave signal S11 to the commercial system voltage V.
It can be output in the same phase as _CS .

Further, the control circuit 41 performs the following control simultaneously. The CPU 48 converts the output current I _OUT of the inverter 31 detected by the output current detector 46 into an A / D signal at a relatively long fixed cycle by the A / D converter 47.
The data is converted and temporarily stored in the RAM 50. Then, the inverter output current value stored last time is compared with the inverter output current value input this time to determine whether the inverter output current value has increased or decreased. According to the result of the determination, it is determined whether the number of the next reference sine wave pattern is to be increased or decreased. The details are as follows.

In the first time, "0" is set as the previous inverter output current value, the number of the reference sine wave pattern is designated as the minimum value "1", and the number change direction of the reference sine wave pattern increases. Set in the direction of. To determine the direction of increase or decrease of the reference sine wave pattern number after the second time, compare the previous inverter output current value with the current inverter output current value, and if the inverter output current value increases, The change direction of the number is maintained as it is, and when the inverter output current value decreases, the change direction of the number is reversed. In other words, when the inverter output current value increases, if the number change direction is in the increasing direction, it is maintained in the increasing direction as it is, and if the number change direction is in the decreasing direction, it is maintained in the decreasing direction as it is. . Conversely, when the inverter output current value decreases, if the number change direction is in the increasing direction at that time, it is reversed to be a decreasing direction, and if the number changing direction is in the decreasing direction, it is reversed to be the increasing direction. That is.

Setting the number change direction of the reference sine wave pattern in the increasing direction means outputting the reference sine wave signal S11 having a sine wave pattern having a larger amplitude. Setting the number change direction in the decreasing direction means outputting a reference sine wave signal S11 having a sine wave pattern with a smaller amplitude. In the present embodiment, there are 200 reference sine wave pattern numbers, 1 to 200. When increasing or decreasing this number, it is assumed that the number is increased or decreased by one.

In this embodiment, the above control is performed by the control circuit 4
1 is realized by software control using a microcomputer including a CPU 48, a ROM 49, and a RAM 50.

By performing the above-described control, when the weather condition is constant, the solar cell operating point is moved from the open voltage side to the maximum power point every time the amplitude of the reference sine wave signal S11 is increased. When the inverter output current value decreases beyond the maximum power point, the direction of change in the amplitude of the reference sine wave signal S11 is inverted to reduce the amplitude, thereby bringing the solar cell operating point closer to the maximum power point again. be able to.

Therefore, thereafter, by controlling the amplitude change direction in the same manner, the solar cell 32 can always be operated near the maximum power point, and the operating point moves to the short-circuit side as in the conventional example. Does not occur. It is not necessary to decrease the output current reference signal in accordance with the decrease of the output current signal, and the input current increases or decreases as a result of performing the amplitude operation of the output current reference signal. This is because there is no need to change the amplitude.

Also, no matter how the characteristics of the solar cell change due to changes in weather conditions, the amplitude of the reference sine wave signal S11 can be reduced by performing the above-described control in accordance with the situation of increase or decrease in the inverter output current value. By performing the control, it is possible to quickly move the solar cell operating point to the maximum power point. That is, regardless of weather conditions and load fluctuations,
Maximum power point tracking control can always be performed well.

[0043]

As described above, according to the present invention, even when the output characteristics of a DC power supply such as a solar cell fluctuate, the maximum power point tracking control can be easily performed, and the maximum power point can always be controlled from the DC power supply. Can be taken out. In addition, multiple
The reference sine wave signal of
Output the reference sine wave signal in synchronization with the
When performing maximum power point tracking control,
Only needs to detect the zero-crossing point.
Since there is no need to detect the pressure waveform / value,
Can be simplified.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a grid-connected solar power generation system to which a grid-connected inverter control device according to an embodiment of the present invention is applied.

FIG. 2 is a configuration diagram of a grid-connected solar power generation system to which a grid-connected inverter control device according to a conventional example is applied.

FIG. 3 is a voltage-current characteristic diagram of a solar cell.

[Explanation of symbols]

31 ... grid-connected inverter 32 ... solar cell 33 ... commercial power supply 34 ... load 35 ... input capacitor 36 ... FET bridge 37 ... output choke coil (filter) 38 ... smoothing capacitor (filter) 39 ... Interconnection relay 40... Controller 41... Control circuit 42... Gate drive circuit 43... PWM modulation circuit 44... Synchronous signal detector 45... Positive and negative direction detector 46. ... A / D converter 48 ...... CPU 49 ...... ROM 50 ...... RAM 51 ...... D / A converter S11 ...... reference sine wave signal S12 ...... switching pattern signal S13 ...... gate pulse signal V _CS ...... commercial system voltage I _OUT …… Inverter output current

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI H02M 7/77 H02M 7/77 (72) Inventor Hiroshi Nakata 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (56 References JP-A-62-166730 (JP, A) JP-A-5-46265 (JP, A) JP-A-2-228715 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB G05F 1/67 G05F 1/10

Claims (1)

(57) [Claims] An ON / OFF control of a bridge of a switching element based on a switching pattern signal converts DC power input from a DC power supply such as a solar cell into AC power, and connects the AC power to a commercial system power supply to a load. Bei means for supplying and means for generating the switching pattern signal by a pulse width modulation based on the reference sine wave signal, and means for storing the detected inverter output current value
A plurality of reference sine wave signals having different amplitudes are stored in advance.
A reference sine wave signal storage means for detecting a zero cross point of the voltage of the commercial power supply
And the reference sine wave is synchronized with the zero cross point.
Read and output a signal from the reference sine wave signal storage means
Means for periodically increasing or decreasing the amplitude of the reference limited wave by one step, means for storing the detected inverter output current value, and the stored previous output current value When determining the hand to determine the direction of change of the output current value by comparison between the current output current value
And stage, based on a determination result of said determining means, when the changing direction of the output current value is increased to maintain the direction of change of the amplitude of the reference sine wave signal, when the change direction of the output current value is reduced Means for inverting the direction of change in the amplitude of the reference sine wave signal.