JPH08126344A - Interconnected inverter system and its control system - Google Patents

Abstract

PURPOSE: To reduce the cost of an interconnected inverter system by using a single digital microprocessor and, at the same time, to make the inverter to easily cope with the change of the kind of a switching element for power, etc., by calculating the maximum power control within a specific phase angle range based on the voltage of a power system by stopping the control of instantaneous value current. CONSTITUTION: A maximum power controller 241 which calculates the output current command value to an interconnected inverter system 2 so that the output of a solar battery 1 can become the maximum and an instantaneous value current controller 242 which sends a gate control signal to a switching section 22 so that the AC output current of the inverter 2 can coincide with the output current command value are respectively constituted of a single digital microprocessor. The controller 241 is operated within ranges from 30 deg. to 80 deg. and from 210 deg. to 260 deg. of the phase angle based on the voltage of a commercial power system 3 and the controller 242 is operated within the other phase angle ranges. Therefore, both the maximum power and instantaneous value current can be controlled by means of the single digital microprocessor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grid-connected inverter used in a solar power generation system and its control system.

[0002]

2. Description of the Related Art Photovoltaic power generation systems convert inexhaustible and clean solar energy into electric power and have great expectations. Especially in recent years, legal development has progressed in Japan as well, and grid-connected systems that convert DC power generated by solar cells into AC power using an inverter and feed it into a commercial power grid can now be used in earnest. It was
FIG. 10 shows an example of a general solar power generation system. The output of the solar cell 1 is connected to the commercial power system 3 via the system interconnection inverter 2. Inside the grid interconnection inverter, an input filter 21 composed of a coil and a capacitor,
There are a switch unit 22 as shown in FIG. 11 which is a semiconductor switch whose opening and closing is controlled by a gate control signal, an output filter 23 which is a coil and a capacitor, and a controller 24 which controls the operation of the inverter. The control device 24 includes a maximum power control device 241 and an instantaneous value current control device 242, and may also include a protection device and the like.

The maximum power control device 241 changes the operating point of the solar cell in accordance with changes in solar radiation intensity and temperature to extract the maximum power from the solar cell.
By inputting pv and the solar cell current Ipv, the output current command value of the inverter is calculated so that the solar cell output becomes maximum. More specifically, the voltage that maximizes the solar cell output power is calculated and calculated, and the current command value is controlled so that the solar cell voltage becomes the voltage. Generally, a digital microprocessor (so-called microcomputer) is used as the arithmetic unit. An example of such a maximum power control device is disclosed in JP-A-62-85312.

The instantaneous value current control device 242 inputs the current command value from the maximum power control device 241 and controls the switch section 22 by the gate control signal so that the inverter output current substantially matches the current command value. . An example of such an instantaneous value current control device is US Pat.
No. 57 is disclosed. An operation example of the instantaneous current controller will be described with reference to FIG. The instantaneous value current control device 242 changes the current command value to the maximum power control device 2
41, and sends a gate control signal (ON / OFF) command signal to the switch unit 22. Gate signal at this time,
FIG. 12 shows the relationship between the output current waveform and the current command value. As shown in FIG. 12, as the instantaneous value current control signal, the gate control signal is transmitted so that the output current substantially matches the current command value. That is, when the output current increases and the command value exceeds a certain value when the gate signal is H, the gate signal is reduced to L to reduce the output current, and when the output current falls below the command value to a certain amount, the gate signal is output again to H. Increase the current. By such control operation, the output current is made to substantially match the command value. In the inverter for a photovoltaic power generation system, the maximum frequency of the gate signal is considerably high at about 10 KHz to 30 KHz in order to reduce noise and output current distortion.

[0005]

By the way, these maximum power control device and instantaneous current control device are usually constructed separately. This is because the control speeds required for maximum power control and instantaneous current control are completely different. Since the maximum power control device only needs to follow the solar radiation fluctuation, a relatively slow control device can be used. According to the research conducted by the authors, it is sufficient to operate in a cycle of about 0.1 second.
However, the instantaneous value current control system must continuously compare the output current with the current command value and determine the ON / OFF state of the gate based on the result. In addition, in order to reduce the output current distortion and noise, the switch section must be turned on / off at 10 KHz or higher. For example, in order to achieve a switch speed of 10 KHz, the control cycle must be suppressed to less than 100 microseconds at the longest. There is. If both control operations are performed by a single digital microprocessor, all control logic can be built as software, which significantly increases the flexibility of the system. However, if this is normally performed, both the maximum power control and the instantaneous value current control are performed within the control cycle (for example, 100 μS),
It requires a very fast microprocessor and a very fast analog-to-digital converter. These are very expensive, and there is a problem that the inverter cannot be constructed inexpensively. Therefore, normally, the instantaneous value current control device configured by hardware and the maximum power control device configured by software as in the above-mentioned known example are combined. It is easy to control the instantaneous current control by hardware, but since it has two control devices, the hardware and the digital microprocessor, it is wasteful because it requires cost and installation place. Further, when a new switch element appears, it is necessary to change the hardware design of the current control unit.

The present invention has been made in view of the above-mentioned problems, and is inexpensive using a single digital microprocessor, and can be used for any switch element or solar cell without changing the hardware design. It is an object to provide an inverter that can perform control and maximum power control.

[0007]

The above object is to convert DC power from a solar cell into AC output through a switch section which is on / off controlled by a gate control signal, and convert the AC output power into commercial power through a filter. In a grid-connected inverter that supplies power to the grid, maximum power control that calculates the inverter output current command value so as to detect the output current and voltage of the solar cell and maximize the generated power from the solar cell, and the AC output current The same digital microprocessor performs the instantaneous value current control for controlling the switch unit by comparing the instantaneous value with the current command value, and performs the arithmetic operation for the maximum power control on the voltage of the commercial power system. Performing with the instantaneous value current control stopped within the range of 30 to 80 degrees or 210 to 260 degrees at the reference phase angle. Thus it is achieved.

[0008]

The operation of the inverter of the present invention will be described with reference to FIGS. FIG. 1 shows the basic configuration of a photovoltaic power generation system according to the present invention. The present invention is characterized in that the maximum power control device 241 and the instantaneous current control device 242 inside the control device 24 are integrally configured by the same digital microprocessor.

As the solar cell 1, an amorphous silicon solar cell, a crystalline silicon solar cell or the like can be used. Amorphous solar cells require less energy to manufacture, and are expected to significantly reduce costs in the future.

The input filter 21 is composed of a large-capacity electrolytic capacitor and a coil. It may be only a capacitor. This is used to suppress ripples in the solar cell output current.

The output filter 23 is composed of a capacitor and a coil. This filter is used to remove high frequency noise.

The control devices 241 and 242 include at least an analog-digital converter (A / D converter) for converting current or voltage into a digital value, and a digital microprocessor capable of processing the digital value and outputting a gate control signal. Need to be out. The digital microprocessor most suitable for the present invention from the viewpoint of downsizing of the control device and cost reduction is a so-called one-chip microcomputer in which peripheral elements such as an A / D converter and a memory are integrated on one chip. There are various types such as Mitsubishi Electric, NEC, Fujitsu, Hitachi, Motorola, etc., but for the control of the present invention, a relatively slow and inexpensive 8-bit CPU core can be used. is there.

Next, the operation of the instantaneous value current control and the maximum power control in the inverter of the present invention will be described with reference to FIG. Figure 2
(A) shows the operation of the conventional inverter, and (b) of the figure shows the operation of the inverter of the present invention. Figure 2
In, the horizontal axis is the phase angle with reference to the voltage of the commercial power system. This corresponds to one cycle of commercial frequency,
For example, at 50 Hz, the phase angle of 360 degrees is 20 ms, and at 60 Hz it is 16.6667 ms. Also,
A thick solid line shows that the control devices 241 and 242 are in an operating state, and a thick dotted line shows that they are in a stopped state.

In the conventional inverter, the instantaneous current controller and the maximum power controller are separately configured, so that both controllers operate continuously in parallel as shown in FIG. 2 (a). ing. In contrast, the present invention provides maximum power operation control with phase angles of 30 to 80 degrees and 210 to 26.
The feature is that the operation is performed at 0 degrees and the instantaneous value current control operation is performed at other points. By alternately performing the operations in this manner, both can be controlled by a single digital microprocessor. In addition, both control operations are performed in one control cycle (for example, 100 μ
The instantaneous value current control may be performed within one control cycle instead of time division in (S), and particularly the maximum power operation control is 50 degrees in phase angle (that is, about 2.3 at 60 Hz).
Since it only has to be executed in mS), a relatively low-speed microprocessor and A / D converter can be sufficiently used. The phase angle for performing maximum power point operation control has been found by the inventors of the present invention, and if it is removed, the output current distortion suddenly increases. The reason for this will be specifically described in the following examples.

[0015]

EXAMPLE FIG. 3 shows the configuration of a photovoltaic power generation system using an inverter according to an example of the present invention. In FIG. 3, as a solar cell 1, a USSC amorphous solar cell (trade name UPM880, rated output 22 W, voltage 15.
6V) and the switch unit 22 is a Hitachi MOSFET
(2SK1951) has a full bridge configuration. This output is an output AC filter 23 in which four inductors of 3 mH each (manufactured by Tamura Seiko Co., Ltd., trade name NAC-02-3000) L2 to L5 are connected in series, and an insulating transformer 231 having a transformation ratio of 6: 100. To a commercial system (100 V, 60 Hz) 3 via. Isolation amplifier (Bur-Brown, trade name IS
O122P) 243 was used to ensure electrical insulation from the AC detection portion, and then the detection signal was input to the analog-digital conversion unit 244 for measurement.

In FIG. 3, the DC filter 21 is 120
It consists of an mH inductor L1, 2200 μF capacitors C1 and C2 and 1000 μF capacitors C3, respectively. The current signal amplifier circuit 245 that amplifies the voltage between the terminals of the current detection resistor R1 is an operational amplifier (trade name: TL07).
1 (T1)) OP1, resistors R2 (= 910 kΩ) and R3
(= 82 kΩ), variable resistor VR1 for gain adjustment (= 3
0 kΩ), offset adjustment variable resistor VR2 (= 10
0kΩ), 100μF capacitors C5 and C6 respectively
Consists of In this embodiment, in order to confirm the principle of the present invention, a personal computer PC486M manufactured by Epson is used as the microprocessor 246 for analog-
For digital conversion, an A / D conversion board (trade name: AB98-35B, manufactured by ADTEC System Science, resolution 12 bits, conversion speed 25 microseconds) that can be mounted in an expansion slot of a personal computer was used.

In addition to the above, the maximum power control device and the instantaneous value current control device are constructed as software, and the PC
The control action was performed at 486M. FIG. 4 is a flowchart showing the overall operation of the microprocessor 246 in FIG. First, the inverter operation is started in synchronization with the commercial power system. Next, the phase angle is detected, and either instantaneous current control or maximum power control is performed according to the phase angle. That is, the phase angle is 30 to 80 or 2
If it is 10 to 260, the maximum power control process is performed, and otherwise, the instantaneous current control process is performed. When either processing is completed, the phase detection processing is returned to and the same loop processing is performed thereafter.

FIG. 5 is a flow chart of the system synchronization subroutine. The timing at which the instantaneous voltage of the commercial power system switches from negative to positive is detected, the SW mode (switching mode) is initialized, and the inverter operation is started. That is, the AC voltage (instantaneous value) Vac is read from the A / D converter, stored in the register Vac, and the contents of the register Vac are transferred to the register Vacp as the previous AC voltage data. Further, a new AC voltage (instantaneous value) Vac is read and stored in the register Vac, and this is compared with the AC voltage Vacp one time before. And 1
When the previous AC voltage register Vacp is negative and the newly read AC voltage Vac is positive, it is determined that the phase is 0, the phase flag Pflag is set to "0", and the SW mode is set to the current increasing mode. , Return to the main routine (FIG. 4). When it is determined that the phase is not 0, the process returns to the process of transferring the newly read AC voltage Vac to the register Vacp as the previous AC voltage, and the same loop process is performed thereafter.

FIG. 6 is a flow chart of the phase detection subroutine in FIG. Instantaneous voltage V of commercial power system
The values of ac and the phase flag Pflag are used as search keys in FIG.
The phase is obtained by referring to the phase table shown in. The phase is recorded in the phase table in the form of one-to-one correspondence with the voltage value and the value of the phase flag. In order to speed up the search, this table is preferably constructed so that the storage address of the phase information can be directly calculated from the phase flag and the voltage value. In FIG. 6, Vpeak is the peak value of the system voltage Vac, and the phase flag Pflag indicates "0", 90-180 degrees and 270-360 degrees when the phase of the system voltage Vac is 0-90 degrees and 180-270 degrees. Sometimes it is set to "1".

For the instantaneous value current control, it is easy to adopt a known method commonly called a hysteresis comparator method. This is described, for example, on pages 120 to 121 of "Power Electronics" (published by Kyoritsu Shuppansha, written by Takao Hirata). Specifically, the inverter output current is read by the A / D converter, and the SW mode is determined so that the difference from the reference current does not exceed a predetermined value. Other known methods can also be adopted.

As the maximum power control, a known method as described in the conventional method can be adopted. Here, the operation time assigned to the maximum power control is 50 degrees in phase angle (about 2.3 mS at 60 Hz).
That is, when the maximum power control operation (more accurately, the calculation operation therefor) is started when the phase angle is 30 degrees, the phase angle 80
The calculation operation for maximum power control is performed until the time. In this embodiment, the operation start phase angle is 30
It is in degrees. The output current waveform when the output current is 1.7 A (effective value) is shown in FIG. As described above, in the maximum power control operation range, the instantaneous value current control operation is not performed, so that the switching operation is not performed. In addition, the output current distortion rate at this time was 3.1%. The output current distortion of the interconnection inverter is required to be 5% or less in the "system interconnection guidelines", and the output current distortion rate is 3.1%.
Has cleared this standard.

In order to further clarify the effect of the present invention,
FIG. 9 shows the distortion rate at that time when the phase angle for starting the maximum power control operation is changed from 0 to 180 degrees while the phase range for performing the maximum power control remains 50 degrees. As shown in FIG. 9, it can be seen that the distortion rate sharply deteriorates at the starting phase angle such that the operating region exceeds 30 to 80 degrees. The reason for this is that the maximum power control operation is performed in the jagged portion of the waveform in FIG. 8, that is, in the portion where the current control system needs to work extremely finely. These facts have been found by the inventors' earnest research. Further, even at 180 to 360 degrees, the distortion rate can be suppressed low by operating in the range of 210 to 260 degrees for the same reason.

As described above, by executing the maximum power control operation in the phase angle range of 30 to 80 degrees or 210 to 260 degrees, the instantaneous current control and the maximum power control are processed by a single digital microprocessor. Moreover, the strain rate can be suppressed while being low.

[0024]

Other Embodiments In this embodiment, a one-chip microcomputer (M37710 manufactured by Mitsubishi) was used instead of the A / D converter and the personal computer of the previous embodiment. This has a built-in A / D converter and a memory, and is suitable for implementing the present invention. Of course, this is an example, and it goes without saying that other control microcomputers can be handled in the same manner. In this embodiment, the operation time of maximum power control is 30 degrees in phase angle (60 Hz).
Of about 1.39 mS), which is shorter than that of the previous example. Since the A / D converter with the built-in M37710 has a high conversion speed of 10 microseconds, such a setting was possible. In this way, when the relationship between the operation start phase angle and the distortion is examined, when the maximum power control operation is started at a temperature other than 30 to 80 degrees and 210 to 260 degrees, the distortion rate is as bad as 8% or more, and 30 to 80 degrees or 210 degrees. When operated in the range of from 260 to 260 degrees, the strain rate was suppressed to a small value of less than 5%.

As described above, it is highly preferable to use the one-chip microcomputer, especially the one-chip microcomputer having the built-in A / D converter, for implementing the present invention in terms of cost and mounting.

[0026]

[Other Embodiments] In this embodiment, the same control device as in the previous embodiment was used. And 200V as a solar cell
Using a simulated solar cell power supply with 2A output, MOSFE
As T, IRFBC40 manufactured by IR Far East Co. having a withstand voltage of 600 V was used. Since the inverter output voltage at this time is almost 100 Vrms, the transformer 231 of FIG. 3 is unnecessary. Thus, the output was directly connected to the commercial power system (100V, 60Hz). Also, according to the voltage and current used, the amplification factor of the detection circuit,
After adjusting the circuit constants of the filter, the control device used in the previous embodiment was used to perform the inverter operation.
As a result, again, 30 to 80 degrees or 210 to 2
When the maximum power control operation was performed within the range of 60 degrees, the inverter operation was possible without deteriorating the distortion rate. In this embodiment, the software is not particularly changed from the previous embodiment, but when a switch element having a property different from that of MOSFET, such as an IGBT or a power transistor, is used, the instantaneous value current is increased. It may be necessary to rewrite the software of the control unit. However, in the past, this current controller was composed of hardware, so compared to the fact that the hardware had to be recreated, it was possible to change the switch element by a very simple method of only rewriting the software. Can respond.

As described above, according to the present invention, the control device can be shared regardless of the output, which contributes to the cost reduction of the inverter.

In the embodiments shown in FIGS. 4 to 7, the maximum power control is repeated any number of times as long as the phase angle is within the range of 30 to 80 degrees or 210 to 260 degrees. However, the maximum power control may be performed only once when the phase angle reaches 30 degrees or 210 degrees, and then the current instantaneous value control may be performed again. In this case, the stop time of the instantaneous current value control is shortened, and the distortion rate can be further reduced.

[0029]

As described above, according to the present invention, the DC power from the solar cell is turned on / off by the gate control signal.
Converted to AC power via the switch unit that is controlled to be off,
In a grid-connected inverter that supplies output power to a commercial power system through a filter, the inverter output current command value is calculated by a digital microprocessor to detect the output current and voltage of the solar cell and maximize the generated power from the solar cell. Maximum power control device, which has an instantaneous value current control device for controlling the switch unit by comparing the instantaneous value of the output current with the current command value in the same digital microprocessor as described above, for maximum power control It is a grid-connected inverter that performs a calculation operation in the range of 30 to 80 degrees or 210 to 260 degrees with a phase angle based on the voltage of the commercial power system, and has the following effects. The maximum power control of the solar cell and the instantaneous value current control of the output current can be performed with only one relatively low-speed and inexpensive digital microprocessor. This makes it possible to construct an inexpensive inverter control device and provide an inexpensive inverter. Since both the current control unit and the maximum power control unit can be constructed as software, it is possible to flexibly deal with the change of the device of the switch unit and the change of the solar cell without the need to change the design of the hardware. With the above features, the control device can be a common component regardless of the type of the inverter, so that an inexpensive inverter can be provided by mass production. Even an inexpensive control device using such a single digital microprocessor does not increase output current distortion. Thus, it is convinced that the industrial value of the present invention is very high.

[Brief description of drawings]

FIG. 1 shows a basic configuration of a photovoltaic power generation system according to the present invention.

FIG. 2 is a time chart showing a control operation of the control device in FIG.

FIG. 3 is a block diagram of a photovoltaic power generation system using an inverter according to an embodiment of the present invention.

FIG. 4 is a flowchart showing a control operation of the control device in FIG.

5 is a flowchart showing a system synchronization subroutine process in FIG.

FIG. 6 is a flowchart showing a phase detection subroutine process in FIG.

7 is a phase table used in the processing of FIG.

FIG. 8 is an inverter output waveform diagram in FIG.

9 is a graph showing a relationship between a control operation start phase angle and an output current distortion rate in the control device of FIG.

FIG. 10 is a block diagram showing an example of a conventional solar power generation system.

FIG. 11 is a circuit diagram showing an example of an inverter switching unit.

FIG. 12 is an explanatory diagram showing an instantaneous value current control operation.

[Explanation of symbols]

1: solar cell, 2: grid-connected inverter, 21: input filter, 22: switching unit, 23: output filter,
24: control device, 241: maximum power control device, 242:
Instantaneous value current control device 244: A / D converter, 246:
Microprocessor, 3: commercial power system, Ipv: solar cell current, Vpv: solar cell voltage, Iac: inverter output current, Vac: commercial system voltage.

Claims (3)

[Claims] 1. A grid interconnection inverter that converts direct current power from a solar cell into alternating current output through a switch part that is on / off controlled by a gate control signal, and supplies this alternating current output power to a commercial power system through a filter. At
Maximum power control that calculates the inverter output current command value so as to maximize the generated power from the solar cell by detecting the output current and voltage of the solar cell, the instantaneous value of the AC output current as the current command value. By using the same digital microprocessor that performs instantaneous value current control for controlling the switch section by comparison, the phase angle is 30 to 80 degrees or 210 to 260 degrees with reference to the voltage of the commercial power system. In the range, the instantaneous value current control is stopped to perform the system interconnection inverter. 2. A system interconnection system in which direct current power from a solar cell is converted into alternating current output through a switch part which is on / off controlled by a gate control signal, and the alternating current output power is supplied to a commercial power system through an output filter. In the control method of the inverter, at least the maximum power control means for detecting the output current and voltage of the solar cell and outputting the inverter output current command value so as to maximize the generated power from the solar cell, and the instantaneous value of the AC output current. For controlling the switch unit by comparing the current command value with the current command value, for comparing the instantaneous value of the AC output current and the current command value, for controlling the switch unit and controlling the maximum power. Is executed by only one digital microprocessor, and the operation for maximum power control is performed by the commercial power system. The phase angle is 30 based on the standard voltage
To 80 degrees or 210 to 260 degrees, the control method of the grid interconnection inverter is characterized by performing the comparison between the instantaneous value of the AC output current and the current command value and stopping the control of the switch section. 3. A photovoltaic power generation system using the grid-connected inverter according to claim 1.