JP3086574B2 - Grid-connected inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current control type for converting electric power generated by a solar cell into alternating current, supplying electric power to a load in connection with an existing commercial power supply, and supplying surplus electric power to a commercial power system. It relates to a grid-connected inverter.

[0002]

2. Description of the Related Art In a conventional grid-connected inverter, a pulse width modulation (PWM) control is performed when a DC output from a solar cell is converted into an AC and supplied to an existing commercial power supply. This is a method of converting DC power into a sine wave AC output of a commercial frequency by giving a pulse example in which a pulse width and positive / negative polarity are controlled as a gate signal of a switching element forming an inverter bridge.

FIG. 5 shows an example of a conventional grid-connected solar power generation system. Referring to FIG. 2, a grid-connected inverter 1 controlled by PWM is connected to a solar cell 2 and connected to an existing commercial power supply 3 via a commercial transformer 20 at an output end of the grid-connected inverter 1. Here, the interconnecting relay 10 turns ON after confirming that the output voltage of the inverter is established.
N, the inverter output is connected to a commercial power supply to supply power. Further, the arithmetic circuit 21 detects the inverter input voltage, current (solar cell output voltage, current) and the voltage of the commercial power supply, and calculates the magnitude of the inverter output current corresponding to the solar cell output. That is, a current command signal 25 having an amplitude value proportional to the magnitude of the inverter output current and controlled to have the same phase as the voltage waveform of the commercial power supply is output to the error amplifier 22. Further, an error signal between the current command signal 25 and the inverter output current signal detected by the current detector 17 is amplified by the error amplifier 22, and this signal is output to the PWM modulation control unit 23 as a sine wave error signal 26. , P
A pulse train signal subjected to WM modulation control is generated. The ON / OFF control of the switching elements constituting the inverter bridge 5 is performed by the pulse train signal via the gate drive signal generator 24 at the subsequent stage.
By the above operation, the feedback control in which the actual amount of the output current of the interconnection inverter 1 changes in proportion to the amplitude value of the current command signal 25 is realized.

Here, a method of determining the amplitude value of the current command signal 25 in the arithmetic circuit 21 will be described. A current command signal which is a sine wave signal having one or more amplitude values and a commercial frequency is stored in advance. When controlling the magnitude of the inverter output current by the amplitude value of the current command signal, the arithmetic circuit actively changes the amplitude value of the current command signal, according to the resulting change in the output power of the solar cell, The amplitude value was controlled in the direction of increase and decrease. That is, first, the inverter input power (= solar cell output power) when the current command signal having the minimum amplitude value is output to the error amplifier is detected and stored. Next, the arithmetic circuit actively selects or outputs a current command signal having an amplitude value smaller by a minute value than the previous time. Then, the inverter input power after changing the current command signal is similarly detected and compared with the stored power value of the former. As a result, if the latter power value is large, a current command signal that is larger by the minute value of the amplitude value is output more actively, and the latter power value is stored in place of the stored former power value. By repeating the above operations, the amplitude value of the current command signal is increased until the output power of the solar cell reaches the maximum value, and when the output power exceeds the maximum value, the amplitude value is reduced by the minute value. By the above control, the present inverter is always controlled by the current command signal having an amplitude value corresponding to the maximum output of the solar cell, and can always supply power corresponding to the maximum output of the solar cell to the commercial power supply.

However, a problem in this case is that, in addition to actively changing the amplitude value of the current command signal, the current command signal is used to control the pulse width modulation method. Response is poor, and control delay is inevitably caused. For this reason, when the amplitude value of the current command signal is increased to a small value near the maximum power point of the solar cell, the effect does not immediately appear in the change of the inverter input power (solar cell output). The control proceeds in the direction of increasing the amplitude value of the value, and the amplitude value is increased more than necessary beyond the maximum output point. In addition, the result of the above control is reflected, and even if the amplitude value is reduced by a small value when the input power exceeds the maximum point, the inconvenience that the result is further delayed in the input power is repeated. It is. As a result, the solar cell, which is the input source of the inverter, cannot supply the power required by the inverter, the voltage of the solar cell (inverter input voltage) drops sharply, and the operating point of the solar cell is pulled to the short-circuit current side. A phenomenon occurs. As a countermeasure for this, a large-capacity (10000 to 15000 μF) input capacitor is provided at the inverter input section, and therefore, the shape and weight of the entire interconnected inverter device are large. Furthermore, when the maximum point of the solar cell output is tracked and controlled due to the above control delay, when the solar radiation intensity is constant, the maximum point can be almost tracked by the action of the input capacitor. However, even when the intensity fluctuates, the delay of the tracking control influences, and a sufficiently good tracking characteristic cannot be obtained.

[0006]

With respect to the output current control and the solar cell maximum point tracking control in the grid-connected inverter, when the inverter output current is controlled in accordance with the maximum output of the solar cell, an excellent circuit configuration is achieved. Responsiveness of current control can be obtained, and therefore, the capacitance of the input capacitor can be reduced, and the size and weight of the device can be reduced. Moreover, since the control responsiveness is high, good maximum point tracking characteristics can be realized even in the event of sudden changes in solar radiation.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to convert a power generated from a DC power supply from a solar cell into an AC power and supply it to an existing commercial power supply. A system type inverter, wherein an inverter output current is used as a control amount, and an upper limit value and a lower limit value of a current command signal are set for the control amount so that the actual value of the control amount is the upper limit value and the lower limit value of the current command signal. In a grid-connected inverter that controls the switching element to turn on and off so that it repeatedly reciprocates within a range having a certain width between the values, the output power or current of the solar cell associated with a small increase or decrease in the inverter output current at each switching It is also possible to provide a grid-connected inverter that performs maximum point tracking control of a solar cell by detecting a small increase or decrease in the current command signal and making a small change in the amplitude of the current command signal. It is.

That is, the present invention relates to a system interconnection inverter inserted between a solar cell and an existing commercial power supply, for converting the output of the solar cell into an alternating current and supplying power to a load in conjunction with the existing commercial power supply. Means for detecting an inverter output current, means for detecting solar cell output power or current, means for comparing an output current signal and a current command signal with hysteresis, and an inverter with an output of the hysteresis comparing means. Means for ON / OFF control of the switch element, and a solar cell output power or current is detected for an output current that repeatedly increases and decreases with a constant width determined by the hysteresis width, and the output current increases and decreases and the Means for changing the amplitude value of the current command signal that determines the magnitude of the inverter output current by comparing the increase and decrease of the battery output. It is made.

[0009]

The system interconnection inverter according to the present invention uses a comparator having hysteresis with the inverter output current as a control amount, and outputs the inverter output current and a current command signal (sine wave signal).
And turning on / off the gate pulse signal of the switching element constituting the inverter bridge circuit so that the actual value of the inverter output current falls within a range having a certain width above and below the current command signal. Perform control. That is, the inverter output current repeatedly increases and decreases slightly between the upper limit and the lower limit of the current command signal by ON / OFF control of the switching element, and follows the current command signal in an oscillatory manner.

On the other hand, the magnitude of the inverter output current is determined by the amplitude value of the sine wave signal of the current command signal, and the magnitude of the amplitude value depends on the maximum output of the solar cell which is the input power supply of the inverter. Is determined, the maximum output point tracking control of the solar cell output which fluctuates depending on the amount of solar radiation and the element temperature can be realized.

From the above, in the repetition of the minute increase and decrease of the inverter output current described above, the minute increase and decrease of the inverter output current and the increase and decrease of the solar cell output power or current as the inverter input source are detected. When the input power is also increasing when the output current is increasing slightly,
It is determined that “maximum solar cell output ≧ inverter output”, and the amplitude of the current command signal is increased to increase the inverter output current. Alternatively, if the input power decreases or does not change when the output current is slightly increased, “the maximum output of the solar cell ≦
Inverter output is determined, and the amplitude value of the current command signal is reduced. By performing the above control, when the solar cell output according to the solar radiation intensity is obtained, the inverter output increases to the point where the output equivalent to the maximum output of the solar cell is obtained, and the equivalent output is obtained. When the point is obtained, the point is vibrated, and the maximum point tracking control of the solar cell can be realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and control method of a grid-connected inverter according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is an example of a system interconnection inverter of the present invention.
Referring to FIG. 1 below, the grid-connected inverter 1 is inserted between the solar cell 2 and the existing commercial power supply 3,
The DC power generated by the solar cell 2 is converted into AC power of 60/50 Hz, and the DC power is connected to the commercial power supply 3 and supplied to the load.

In the system interconnection inverter 1 of the present invention,
The input capacitor 4 changes the output of the solar cell
Alternatively, it is provided to control a sudden change in the input voltage of the inverter 1 due to a minute change in the inverter output due to the output current control. The DC power input to the interconnection inverter 1 is converted into high frequency and alternating current by the instantaneous current value control in the high frequency inverter bridge 5 composed of switching elements Q1 to Q4, and supplied to the primary side of the high frequency transformer 6. . This high-frequency alternating current is rectified by the diode bridge 7 on the secondary side of the high-frequency transformer 6, and the high-frequency and ripples are smoothed by the DC reactor 8 to become a current. This current is converted into AC power of the commercial frequency by the return control in the commercial frequency inverter bridge 9 composed of the switching elements S1 to S4, and the interconnection relay, A
It is connected to the commercial power supply 3 via the C filter 11.

The signal processing and operation circuit 12 includes a voltage signal V _IN of the solar cell 1, a current signal I _IN detected by the current detector 16, and a primary-side current of the high-frequency transformer (inverter output) detected by the current detector 17. A current signal I _T and a voltage signal V _OUT of the commercial power supply 3 are input, and a current command signal 18 and a polarity determination signal 19 are output. The hysteresis comparator 13 detects the high-frequency transformer 6 detected by the current detector 17.
Enter the primary current I _T and the current command signal 18, the primary current of the high frequency transformer 6 are repeatedly reciprocate within a predetermined width with upper and lower limits around the current command signal 18 As described above, switching elements Q1, Q4 and Q2, Q3 constituting the high-frequency inverter bridge are set to NO.
On / off control is performed alternately via the T circuit 14. The return control circuit 15 receives the polarity determination signal 19 and
Switching elements S1, S1 constituting a commercial frequency inverter bridge according to the polarity of voltage signal V _OUT of commercial power supply 3
ON / OFF of S4, S2, and S3 is alternately switched.

Next, the operation will be described. Basically, the current command signal (I
_REF ) 18, an upper limit value I ⁺ having a fixed value ΔI and a lower limit value I ⁻ are given to the hysteresis comparator 13 as set values. Then, the actual current signal value at which the high-frequency transformer primary side I _T of the control amount of the present invention is detected by the current detector 17, and inputs with the current command signal 18 to the hysteresis comparator 13. Then, the current signal I _T is the actual value of the control amount is OFF the upper limit set value _{^{I + (I + = I REF}} + ΔI) exceeds the switching element Q1 of the high frequency inverter bridge 5, Q4, via a NOT circuit 14 as the decreasing direction of the current gradient and ON the Q2, Q3 by, and the current signal I _T decreases, the lower limit set value I ^- (I ^- =
When I _REF −ΔI), FQ1 and Q4 are turned on, and Q
3, Q4 is turned OFF, and the current signal I _T is controlled to increase. Such actual value of the current signal I _T by performing a switching control I ⁺ and I ^- to remain so as to reciprocate in each switched between. Here, when a sine wave signal having an arbitrary amplitude value at the same frequency as the commercial power supply is used as the current command signal (I _REF ), the current signal _IT is shown in FIG. In this manner, a sinusoidal current waveform that changes so as to repeatedly reciprocate and follow the current command signal in a width of ± ΔI around the current command signal and is proportional to the amplitude value of the current command signal at the commercial frequency can be obtained. As described above, the magnitude of the current on the primary side of the high-frequency transformer in the system interconnection inverter 1, that is, the magnitude of the inverter output current can be controlled by the amplitude value of the current command signal (I _REF ).

Here, the amplitude value of the current command signal (I _REF ) is determined by the signal processing operation circuit 12. First, the signal processing operation circuit 12 outputs the current signal I _IN and the voltage signal V of the solar cell.
_IN , the high-frequency transformer primary-side current signal I _T , and the commercial power supply voltage signal V _OUT are input at a sampling cycle that is at least twice the switching frequency of the high-frequency inverter, and the solar cell current signal I _IN and voltage signal V _IN And calculates the output power of the solar cell and stores the calculated value. And for small changes that repeatedly increases and decreases of the current signal I _T of the primary side of the high-frequency transformer, wherein depending on whether the solar cell output power is how to change, determine whether the maximum solar cell output power and the arithmetic output Then, the amplitude value of the current command signal is determined. Then, control is performed so as to output an inverter output current corresponding to the maximum output of the solar cell. To explain this control in detail, the sampling period of more than 2 times the switching frequency of the high frequency inverter, reads the value of the current signal I _T, and a voltage signal V _IN and the current signal I _IN of the solar cell, the latter 2 The solar cell output power is calculated from the values, and the respective values are stored. And further, as above
Current signal I _T to the value of the voltage signal V _IN of the solar cell, reads the current signal I _IN, by calculating the value of the photovoltaic output power, compared with the has stored values, FIG. 3
When the output power of the solar cell is similarly increased from the previous time when the current signal _IT has a slightly increased current gradient as shown in (2), the amplitude value of the current command signal is increased by the minute value, and the inverter output current is increased. Is controlled to be larger.
Also when the solar cell output when the current gradient of the current signal I _T is increased minute conversely does not decrease or change, current signal I _T
Is controlled until the current gradient of the current command signal decreases in a decreasing direction, and the amplitude value of the current command signal is reduced by a minute value. Wherein the stored currently read instead of the value was a value, and stores the calculated value, further new current signal I _T to the value of the voltage signal V _IN of the solar cell, reads the current signal I _IN, sun By repeating the operation of calculating the value of the battery output power and comparing it with the stored value, the inverter output current increases until the maximum power of the solar cell output at the solar radiation intensity at that time is reached, Control that tracks the maximum point while vibrating the inverter output when the maximum point is reached can be realized.

On the other hand, when the signal processing operation circuit 12 outputs the current command signal 18, the voltage signal V
_By synchronizing with _OUT , the primary side current (inverter output current) of the high-frequency transformer, which is the control amount, can be controlled to have the same phase (power factor 1) as the voltage of the commercial power supply. Further, the signal processing operation circuit 12 detects the polarity of the voltage signal V _OUT , outputs a polarity determination signal 19 to the return control circuit 15, and performs ON / OFF control of the switching element of the commercial frequency inverter bridge 9 to perform waveform control. Is performed. By this control, as shown in FIG. 4, the DC current rectified by the diode bridge 7 becomes an AC inverter output at the subsequent stage of the commercial frequency inverter bridge 9.

[0018]

As can be seen from the above, the present invention employs instantaneous output current control in a grid-connected inverter, and the actual value of the inverter output current, which is the control amount, is controlled by the current command that gives a desired current value. By following the signal while repeating the increase / decrease of the upper and lower limits in a certain range, the change of the inverter input (solar cell output) accompanying the increase / decrease of the output current is detected and the maximum point of the solar cell is tracked. Control. This makes it possible to configure the control circuit with a simple circuit configuration, and the responsiveness of current control is greatly improved when controlling the inverter output current according to the solar cell output. Ratio 1 /
The size can be reduced to 3 to 〜, and the size of the apparatus can be reduced. In addition, due to the improvement of control responsiveness, a very good tracking characteristic can be realized even at the time of sudden change of solar radiation as compared with the conventional maximum point tracking characteristic.

[Brief description of the drawings]

FIG. 1 is a block diagram of a system interconnection inverter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a current command signal I _REF and an actual value of an inverter output current.

FIG. 3 is a diagram showing actual values of a current command signal and an inverter output current according to one embodiment of the present invention.

FIG. 4 is a diagram showing a current waveform of each part according to an embodiment of the present invention.

FIG. 5 is a block diagram of a system interconnection inverter according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Grid connection inverter 2 Solar cell 3 Commercial system power supply 4 Input capacitor 5 High frequency inverter bridge 6 High frequency transformer 7 Diode bridge 8 DC reactor 9 Commercial frequency inverter bridge 10 Interconnection relay 11 AC filter 12 Signal processing operation circuit 13 Hysteresis comparator 14 NOT circuit 15 Return control circuit 16 Current detector 17 Current detector 18 Current command signal 19 Correction judgment signal

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI H02M 7/527 H02M 7/527 (72) Inventor Satoshi Fujii 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (58 ) Surveyed field (Int.Cl. ⁷ , DB name) G05F 1/67 H02M 7/48

Claims (1)

(57) [Claims] 1. A grid-connected inverter that converts DC power generated from a DC power supply from a solar cell into AC and supplies the AC power to an existing commercial power supply, wherein the inverter output current is used as a control amount, and On the other hand, an upper limit value and a lower limit value of the current command signal are set, and the switching element is set so that the actual value of the control amount repeatedly reciprocates within a range having a certain width between the upper limit value and the lower limit value of the current command signal. In a system-interconnected inverter that controls on / off control of the power supply, a small increase or decrease in the solar cell output power or a current associated with a small increase or decrease in the inverter output current is detected for each switching, and a magnitude of the amplitude value of the current command signal is detected. A grid-connected inverter characterized by performing maximum point tracking control of a solar cell by minutely changing its length.