JP2002270876A - Solarlight power generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a solarlight power generator of a type using a linkage inverter of a high-frequency link type by particularly improving an efficiency of the linkage inverter of a low output side. SOLUTION: The solarlight power generator comprises a means for monitoring a DC input voltage and input current of the high-frequency inverter 21 of a DC/DC converter 19 and operating the inverter 21 under the control (Pmax control) of tracking a maximum power point of the solar battery 17, a means for raising a modulation of the converter 19 under the control of the operation of the inverter 21 so as to raise the DC input voltage in the operating state of the Pmax control when the DC input voltage of the DC/AC inverter 20 is lower than the upper limit voltage, and a means for regulating the modulation of the converter 19 under the control of the operation of the inverter 21 so that, when the DC input voltage of the inverter 21 is raised to the upper limit voltage, the DC input voltage is held at the upper limit voltage in the operating state of the Pmax control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts a DC output of a solar cell into an AC of a system output of a system frequency by a high-frequency link system interconnection inverter and outputs the AC of the system output to the system side. The present invention relates to a photovoltaic power generator, and more particularly, to a drive control thereof.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 3, this type of photovoltaic power generator is formed by connecting a high-frequency link type interconnection inverter 2 to a solar cell 1, and the interconnection inverter 2 is connected to an input side DC power supply. A DC / AC converter section 3 and an output DC / AC inverter section 4.

[0003] The DC output of the solar cell 1 is DC / D
The high frequency inverter 5 of the C converter unit 3 converts the high frequency alternating current into a high frequency AC of several KHz to several tens KHz, for example, and supplies the high frequency AC to a rectifying / smoothing unit 7 via a high frequency transformer 6 for input / output insulation. 7 is rectified and smoothed by a diode rectifier circuit 8 and a smoothing LC filter 9 and is converted into a DC power supply of a DC / AC inverter unit 4.

Further, the DC power is converted by the DC / AC inverter unit 4 into a single-phase or three-phase AC having a system frequency synchronized with the system power 10, and the AC is supplied to the system.

Incidentally, the high-frequency inverter 5 and the DC /
The low-frequency inverter 11 of the AC inverter unit 4 performs a switching operation by the PWM drive pulses of the respective drive control units 12 and 13.

Then, the voltage and current of the DC output of the solar cell 1 are measured by the voltage detector 14 and the current detector 15 on the input side of the high-frequency inverter 5, and based on the monitoring of these measurement results, the driving unit 12 High-frequency inverter 5 in maximum power point tracking control (hereinafter referred to as Pmax control) of battery 1
To drive.

[0007] The drive control unit 13 has a system frequency PL.
Under the L control, the low-frequency inverter 11 is operated in a linked manner, assuming that its DC input voltage is a constant voltage of a command value (set value).

[0008] By this interconnection operation, the low-frequency inverter 1
The output of the output 1 increases or decreases according to the difference between the voltage of the DC power supply supplied from the DC / DC converter 3 and the voltage of the command value.

At this time, the upper limit value (upper limit voltage) of the DC input voltage determined from the element withstand voltage of the low frequency inverter 11 and the like.
Is 420V and the allowable DC input voltage range is 420V
Assuming that it is ~ 320V, conventionally, the voltage of the command value is set to approximately 380V, which is the intermediate value.

Then, the duty ratio of the switching operation of the high-frequency inverter 5 according to the increase or decrease of the DC output of the solar cell 1 so that the voltage of the DC power supply of the DC / DC converter unit 3 becomes the constant voltage of the command value. Is varied, and the modulation (modulation amount) of the DC / DC converter unit 3 is adjusted while maintaining the high-frequency inverter 5 in the operation state of the Pmax control. Note that reference numeral 16 in FIG. 3 denotes a system wiring inductance.

[0011]

In this type of conventional solar power generation apparatus, the modulation of the DC / DC converter section 3 is performed so that the DC input voltage of the DC / AC inverter section 4 becomes a constant voltage of a command value. Since the Pmax control operation of the high-frequency inverter 5 is variably realized, as described below, when the DC output of the solar cell 1 is low, the modulation of the DC / DC converter unit 3 is low. There is a problem that the efficiency of the entire interconnected inverter is reduced.

That is, the interconnection inverter 2 shown in FIG.
kW inverter, and the DC output voltage of the solar cell 1 is 2
70V, transformation ratio of high frequency transformer 6 is 1: 1.5, DC
Assuming that the DC input voltage of the / AC inverter unit 4 is 380 V, the DC output of the solar cell 1 is sufficiently large and the rated DC operation at the time of the rated operation to operate as a 10 kW inverter is performed.
The modulation of the / DC converter unit 3 is M (10)
Then, the modulation M (10) becomes
As shown in the equation, the value becomes as high as 0.94.

[0013]

## EQU1 ## M (10) = 380V ÷ (270V × 1.5)
= 0.94

On the other hand, when the DC output of the solar cell 1 is low, for example, 50% of the rated (maximum output), and the modulation of the DC / DC converter unit 3 at this time is M (5), This modulation M (5)
Is very low at 0.47 as shown in the following equation (2).

[0015]

M (5) = 0.5 × {380V} (270V ×
1.5)｝ = 0.47

If the output current (effective value) of the DC / DC converter section 3 flowing to the DC / AC inverter section 4 via the filter 9 is defined as I _DC , the current I _{DC is} obtained from the following equation (3).

[0017]

I _DC = AC output power of inverter unit 4 (= output power of converter unit 3) 電 圧 DC voltage of solar cell 1 (= input voltage of converter unit 3) ÷ modulation of converter unit 3

When the modulation M (5) has a low output, the AC output power of the DC / AC inverter unit 4 is 5 k
W (= 5000 W) and is, at this time, when 270V DC voltage of the solar cell 1, 39.4A becomes as shown in Formula 4 Formula of current I _DC Hatsugi, modulation M
(10) A large current equivalent to that at the time of the rated output of 0.94 is obtained.

[0019]

## EQU4 ## 5000W ÷ 270V ÷ 0.47 = 39.4A

In the case of interconnected outputs having the same magnitude, as the current _IDC increases, the output waveform and the like deteriorate, and the efficiency of the interconnected inverter 2 as a whole decreases.

The present invention relates to a photovoltaic power generator of this type using a high-frequency link type interconnection inverter,
It is an object to improve and improve the efficiency of a grid-connected inverter at the time of low output.

[0022]

In order to solve the above-mentioned problems, a photovoltaic power generator according to the present invention employs a DC / DC converter.
Means for monitoring the voltage and current of the DC input of the high-frequency inverter of the converter section to operate the high-frequency inverter by Pmax control of the solar cell; and for controlling the Pmax control when the DC input voltage of the DC / AC inverter section is lower than the upper limit voltage. Means for controlling the operation of the high-frequency inverter to increase the modulation of the DC / DC converter so that the DC voltage increases in the operating state; and operating the Pmax control when the DC input voltage increases to the upper limit voltage. Means for controlling the operation of the high-frequency inverter and adjusting the modulation of the DC / DC converter so that the DC input voltage is maintained at the upper limit voltage in the state.

Therefore, the DC / DC converter section is designed so that the DC input voltage of the DC / AC inverter section rises to its upper limit voltage (eg, 420 V) as much as possible at the time of low output of the interconnection inverter having a small DC output of the solar cell. The modulation increases in the operating state of the Pmax control.

In this case, the DC input voltage of the DC / AC inverter section is reduced to a constant voltage lower than the upper limit voltage (for example, 380
Since the modulation of the DC / DC converter section is higher than that of the conventional device fixed to V), the current I _DC obtained from the equation (3) is reduced, the waveform ratio is improved, and the efficiency of the entire interconnected inverter is improved. Has been improved and improved.

Also, during rated operation of the interconnection inverter having a sufficiently large output from the solar cell, the DC input voltage of the DC / AC inverter is maintained at the upper limit voltage.
Since the DC input voltage of the / AC inverter is higher than the DC input voltage of the conventional device, the efficiency of the interconnection inverter is improved and improved.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an overall configuration of a photovoltaic power generation device, which is formed by connecting a high-frequency link type interconnection inverter 18 to a solar cell 17, and the interconnection inverter 18 has an input side DC corresponding to the converter unit 3 in FIG.
A DC / AC converter section 19 and an output DC / AC inverter section 20 corresponding to the inverter section 4 in FIG.

The DC output of the solar cell 17 is DC /
The high-frequency inverter 21 of the DC converter 19 converts the high-frequency AC into a high-frequency AC of several KHz to several tens of KHz, for example, and supplies the high-frequency AC to a rectifying and smoothing unit 23 via a high-frequency transformer 22 for input / output insulation. Rectified and smoothed by a diode rectifier circuit 24 and a smoothing LC filter 25, and converted into a DC power supply of the DC / AC inverter unit 20.

At this time, the voltage detector 26 and the current detector 27 provided on the DC input side of the high-frequency inverter 21 use the DC output voltage and current of the solar cell 17, in other words, the input voltage and the input of the high-frequency inverter 21. The current is measured, and the measurement output is supplied to a control circuit 29 provided in the drive control unit 28 of the high-frequency inverter 21.

Under the software control of the control circuit 29, the DC input voltage and current of the high-frequency inverter 21 are monitored based on the measurement results of the detectors 26 and 27, and the high-frequency inverter 21 is operated under the Pmax control of the solar cell 17. The driving circuit 30 of the driving control unit 28 outputs the high-frequency inverter 21 based on the operation control of this means.
Is supplied with a driving PWM pulse, and the high frequency inverter 21 is subjected to the Pmax control operation by the PWM pulse.

Further, the DC power supply of the filter 25 is DC /
It is supplied to the low frequency inverter 31 of the AC inverter section 20.

The measurement result of the DC voltage of the voltage detector 33 provided on the DC input side of the low-frequency inverter 31 and the measurement result of the AC voltage of the instrument transformer 34 provided on the AC output side, and the drive control Based on the Pmax control state notification from the unit 29, a PWM pulse for driving the low-frequency inverter 31 is formed by the drive control unit 35. With this pulse, the low-frequency inverter 31 is connected to the system power supply 32 to operate. The power is converted into a single-phase or three-phase AC having a system frequency, and this AC is supplied to the system.

At this time, the PWM of the low-frequency inverter 31
The duty ratio of the pulse is determined by the DC / AC inverter unit 20.
Varies according to the voltage of the command value (set value) of the drive control unit 35 for setting the DC input voltage of the drive control unit 35. In FIG. 1, reference numeral 36 denotes a system wiring impedance.

Next, the solar cell 17 has the highest open-circuit voltage, and the Pmax control operation of the high frequency inverter 21 is performed by increasing or decreasing the duty ratio of the PWM pulse. This is done by detecting points.

At this time, the DC input power of the high-frequency inverter 21 changes along a mountain-shaped characteristic line having a peak at the maximum power point of the output of the solar cell 17. The inverter 21 is in an operation state before reaching the maximum power point, and when it is on the right side of the mountain, the high-frequency inverter 21 is in an operation state after the maximum power point.

The drive control circuit 29 determines the operating state of the high-frequency inverter 21 that changes every moment, and sends the information on the left or right side of the mountain of the determination result to the drive control unit 35 as the Pmax control state notification. send.

Further, based on this state notification, the drive control unit 35 variably corrects the pulse width of the PWM pulse of the high-frequency inverter 21 via the drive circuit 30 of the drive control unit 28, controls its operation, and controls the DC / AC The DC input voltage of the inverter section 20 is corrected so as to approach the upper limit voltage of, for example, 420 V set based on the element withstand voltage of the low-frequency inverter 31 as much as possible.

That is, the interconnection inverter 18 maintains the high-frequency inverter 21 in the Pmax control operation state when the DC input voltage of the DC / AC inverter section 20 is lower than the upper limit voltage by software control of the drive control section 35. The operation of the high-frequency inverter 21 is controlled so that the DC input voltage of the DC / AC inverter unit 20 increases,
Means for increasing the modulation ratio of the DC / DC converter section 19 by increasing the duty ratio of the driving is formed. When the DC input voltage of the DC / AC inverter section 20 rises to the upper limit voltage, the high frequency inverter 21 is switched off. The operation of the high-frequency inverter 21 is controlled so that the DC input voltage of the DC / AC inverter unit 20 is maintained at the upper limit voltage while maintaining the operation state of the Pmax control, and the duty ratio of the drive is varied to change the DC / DC converter unit 19. Is also formed. Specifically, the operation control shown in the flowchart of FIG. 2 is performed by these two means.

In this operation control, the voltage of the command value of the DC input voltage of the DC / AC inverter unit 20 is set to V _{DC · REF.}
Assuming that the upper limit voltage of the DC input voltage is 420 V, the drive control unit 35 determines in step S ₁ that V _{DC · REF} <
To determine 420V or not, V _{DC · REF} <at 420V DC /
When the DC input voltage of the AC inverter 20 is lower than the upper limit voltage, the program proceeds from step S ₁ to step S _2.

Then, the drive controller 35 corrects the duty ratio of the drive pulse output from the drive circuit 30 by a unit amount to increase the modulation of the DC / DC converter 19.

[0040] Further, the process proceeds to step S _3, based on Pmax control status notification from the drive control unit 29, the drive control unit 35 is the operation state of the high-frequency inverter 21 determines whether the left or right side of the mountain.

The result of this determination is on the left side of the mountain (at the maximum power point
Before), the output taken from the solar cell 1 is small.
Step S_ThreeTo step S_FourTo DC / AC
Voltage V of command value of inverter unit 20_{DC / REF}Deduct the unit amount
Conversely, the judgment result is on the right side of the mountain (after passing the maximum power point).
If necessary, increase the voltage to improve the conversion efficiency.
S_ThreeTo step S_FiveTo DC / AC inverter
Voltage V of command value of unit 20 _{DC / REF}Is raised by a unit amount.

Then, step S₁To step S_Two, S
_ThreeThrough step S_FourIs Step S _FiveControl processing
By repeating, high frequency of DC / DC converter section 19
Inverter 21 operates even when solar cell 17 has a low output.
Is controlled to an operation state in which electric power at a high power point is taken out, and D
The low frequency inverter 31 of the C / AC inverter section 20 is
The DC input voltage approaches the upper limit voltage (420V) as much as possible.
To be pulled up.

At this time, as the DC input voltage of the low frequency inverter 31 rises, the DC / DC converter 19
Is increased, the voltage of the high-frequency AC of the high-frequency inverter 21 is increased, and D
The voltage of the DC power supplied to the low-frequency inverter 31 of the C / AC inverter unit 20 increases.

When the direct current output of the solar cell 17 is low, for example, 50% of the interconnected inverter, the DC / DC
When the voltage of the DC power supplied from the converter 19 to the DC / AC inverter 20 is raised to 420 V,
Modulation M of DC / DC converter section 19
(5) ′ becomes M (5) ′ = 0.52 as shown in the following equation (5), which is similar to the equation (2), and is obtained from the modulation M (5) = 0.49 of the conventional device. Get higher.

[0045]

M (5) ′ = 0.5 × {420} (270 ×
1.5)｝ = 0.52

Further, the modulation M (5) '
Assuming that the output current of the DC / DC converter unit 19 is I _DC ′, the output current I _DC ′ becomes I _DC ′ = 35.6 A, as shown in the following equation (6). It decreases from I _DC = 39.4A.

[0047]

I _DC '= 5000 W ÷ 270 V ÷ 0.52 = 35.6 A

Then, due to the decrease of the current I _DC ′, DC
The waveform ratio of the / DC converter unit 19 is improved compared to the prior art,
The efficiency of the entire interconnection inverter 18 is improved and improved.

Next, during the rated operation of the interconnection inverter where the DC output of the solar cell 1 is sufficiently large, the voltage V _{DC · REF} of the command value of the DC / AC inverter section 20 rises to the upper limit voltage. moves from step S ₁ in FIG. 2 in step S _6, the DC input voltage of the DC / AC inverter section 20 is fixed to the upper limit voltage while maintaining a voltage V _{DC · REF} to the upper limit voltage (420 V) by the drive control unit 35 , Low frequency inverter 31
To prevent excessive DC voltage.

[0050] Further, the process proceeds to step S _7, the control circuit on the basis of the Pmax control status notification from 29, the drive controller 35 Step S ₃ high-frequency inverter in the same manner as 2
It is determined whether the operation state 1 is the left or right side of the mountain.

Then, if it is on the left side of the mountain (before reaching the maximum power point), the drive control unit 35 proceeds from step S ₇ to step S ₈ , and through the drive circuit 30, switches the duty ratio of the switching of the high-frequency inverter 21. And DC /
The modulation of the DC converter 19 is increased.

On the right side of the mountain (after passing the maximum power point),
If so, step S₇To step S ₉To step
S₈On the contrary, the switching of the high frequency inverter 21
DC / DC converter unit 1 by reducing the duty ratio of
DC / DC converter with low modulation of 9
The section 19 is operated by the Pmax control.

At this time, assuming that the modulation of the DC / DC converter 19 is M (10) ′, the modulation M (10) ′ is the DC / AC inverter 2
Since the DC input voltage of 0 rises from 380V of the conventional device to 420V, the modulation M (10) of the conventional device is performed.
= 0.94. Therefore, the interconnection inverter 1
8 at high output is also improved.

Since the efficiency at the time of low output is greatly improved, the interconnection inverter 18 is connected to the system power supply 32 with high efficiency regardless of the output state, and the high-frequency link type interconnection inverter is operated. It is possible to provide a highly efficient photovoltaic power generation device using the same.

[0055]

The present invention has the following effects. Interconnected inverter 1 with small DC output of solar cell 17
8, when the high-frequency inverter 21 of the DC / DC converter unit 19 performs the maximum power point tracking control operation,
By increasing the modulation of the C / DC converter 19, the DC input voltage of the DC / AC inverter 20 can be increased so as to reach its upper limit voltage (eg, 420 V) as much as possible.

In this case, the DC input voltage of the DC / AC inverter section 20 is changed to a constant voltage lower than the upper limit voltage (for example, 38
0V), the modulation of the DC / DC converter 19 is higher than that of the conventional device that performs the maximum power point tracking control operation of the high frequency inverter 21 of the DC / DC converter 19, and the current flowing from the converter 19 to the inverter 20. _IDC can be reduced to improve the waveform ratio, and the efficiency of the interconnection inverter 18 as a whole can be improved and improved.

During the rated operation of the interconnection inverter 18 having a sufficiently large output from the solar cell 17, the DC input voltage of the DC / AC inverter section 20 is maintained at the upper limit voltage. The inverter 20 can perform the maximum power point tracking control operation.
Since the DC input voltage of the / AC inverter unit 20 is higher than the DC input voltage of the conventional device, the efficiency of the interconnection inverter 18 can be improved and improved.

Therefore, in this type of solar cell power generator using a high-frequency link type interconnection inverter, the system power supply 3 can be operated with high efficiency regardless of the output state of the solar cell 17.
2 can be connected and operated.

[Brief description of the drawings]

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

FIG. 2 is a flowchart for explaining the operation of FIG. 1;

FIG. 3 is a block connection diagram of a conventional example.

[Explanation of symbols]

 Reference Signs List 1,17 Solar cell 2,18 Interconnected inverter 3,19 DC / DC converter 4,20 DC / AC inverter 5,21 High frequency inverter 6,22 High frequency transformer 7,23 Rectifying smoothing part 10,32 System power supply

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F051 KA03 KA04 5G066 HB06 5H420 BB03 BB12 CC03 DD03 DD04 EB09 EB11 EB26 EB29 EB39 FF03 FF24 FF25 GG07

Claims (1)

[Claims] 1. A high frequency link type interconnection inverter D
The DC output of the solar cell is converted to a high-frequency AC by a high-frequency inverter provided in a C / DC converter, and the high-frequency AC is converted to a DC / D signal through a high-frequency transformer.
The DC / AC inverter supplies a rectified and smoothed portion to the rectifying and smoothing portion, and the rectifying and smoothing portion rectifies and smoothes the high-frequency AC to form a DC power supply for a subsequent DC / AC inverter. In a photovoltaic power generation device that converts a power supply into an alternating current of a grid frequency output and outputs the alternating current to a grid side, a DC voltage and a current of the high-frequency inverter are monitored, and the high-frequency inverter tracks the maximum power point of the solar cell. Means for controlling the operation of the high-frequency inverter so that the DC input voltage increases in the operation state of the maximum power point tracking control when the DC input voltage of the DC / AC inverter section is lower than an upper limit voltage. Means for increasing the modulation of the DC / DC converter section by controlling the DC / DC converter section, when the DC input voltage rises to the upper limit voltage, Means for controlling the operation of the high-frequency inverter and adjusting the modulation of the DC / DC converter so that the DC input voltage is maintained at the upper limit voltage in the operating state of the maximum power point tracking control. A solar power generation device characterized by the above-mentioned.