JP5325507B2 - Grid interconnection inverter - Google Patents

Description

  The present invention relates to a grid-connected inverter that converts an output of a power generation device into an alternating current and outputs it to a commercial power system.

A grid-connected inverter that converts (boosts) the output of power generators such as solar cells, biomass, and fuel cells to a DC voltage with a converter, converts the converted DC voltage to AC by switching, and outputs it to the commercial power system. Is known (for example, Patent Document 1).
In such a grid-connected inverter, the capacity of the power generator can be improved by executing MPPT control (Maximum Power Point Tracker) that adjusts the output of the converter so that the power generated by the power generator is maximized. Can be maximized.
JP-A-9-308263

  However, during the execution of MPPT control, the generated power of the solar cell frequently increases and decreases in the vicinity of the maximum generated power, and may not easily converge to the maximum generated power.

  The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a grid-connected inverter capable of quickly converging the generated power of the power generator to the maximum generated power.

A grid-connected inverter according to a first aspect of the present invention is a converter that converts power generated by a power generator into a DC voltage, an inverter that converts the output of the converter into AC, and the power generated by the power generator is maximized. MPPT control means for adjusting the output of the converter, and outputs the output of the inverter to the commercial power supply system, wherein the MPPT control means is an average generated power per unit time of the power generator And a determination for determining whether the current average power generation amount detected by the detection unit is an increase or a decrease relative to the previous average power generation amount detected by the detection unit. means and the determination result of the determining means is operable to maintain the direction of the adjustment time increase, the determination result is the decrease amount decreasing reverse the direction of the adjustment when the predetermined amount or more Adjustment direction control means, and adjustment means for adjusting the adjustment amount for the output of the converter in a decreasing direction when the average generated power detected by the detection means is within a predetermined range over a set time. .

  According to the grid-connected inverter of the present invention, the generated power of the power generator can be quickly converged to the maximum generated power.

[1] A first embodiment of the present invention will be described below with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a power generation device such as a solar cell (PV), which is installed on a roof of a house, etc., and receives a direct solar radiation to output a DC voltage. This output is applied to the capacitors 3 and 4 via the switch 2, and the voltage of the capacitors 3 and 4 is supplied to a converter, for example, a boost chopper 5. The step-up chopper 5 is a so-called DC-DC converter having a DC reactor 6, a transistor such as an IGBT 17, a backflow prevention diode 8, and a capacitor 9, and the IGBT 7 is turned on / off in accordance with a PWM signal supplied from the control unit 60. Thus, the generated power (DC voltage) of the solar cell 10 is boosted to a predetermined reference level DC voltage.

  The output of the step-up chopper 5 is supplied to the single-phase inverter 20. The single-phase inverter 20 includes four transistors, for example, a full bridge circuit composed of IGBTs 21, 22, 23, and 24, a free wheel diode D connected in reverse parallel to the IGBTs 21, 22, 23, and 24, and a PWM supplied from the control unit 60. Gate driving circuits 31, 32, 33, and 34 that drive the on / off (switching) of the IGBTs 21, 22, 23, and 24 in response to signals, and the input voltage (DC voltage) from the boost chopper 5 is the system voltage and Convert to AC voltage that matches system frequency.

  A capacitor 42 is connected to the output terminal of the single-phase inverter 20 via an AC reactor 41 serving as a noise filter. A commercial power system (single-phase) is connected to the capacitor 42 via relay contacts 43 and 44 and output capacitors 45 and 46. A three-wire AC 200V) 47 is connected.

  A commercial power supply system (single-phase single-wire AC 100 V) 50 for independent operation is connected to the capacitor 42 via a relay contact 48 and an output capacitor 49.

  Note that the generated voltage (PV voltage) of the solar cell 10, the current between the capacitors 3 and 4 (current for detecting a ground fault of the solar cell 10), the generated current (PV current) of the solar cell 10, and the boosted chopper 5 The control unit 60 detects the voltage, the output current of the single-phase inverter 20, the output voltage of the single-phase inverter 20, and the system voltage between the relay contacts 43 and 44.

  The control unit 60 includes an MCU 61 as a control center. An EEPROM 62, an A / D converter 63, a PWM generator 64, and an A / D converter 65 are connected to the MCU 61. The EEPROM 62 is for storing various data. The A / D converter 63 converts the power generation voltage (PV voltage), the ground fault detection current, the power generation current (PV current), and the boost voltage into digital signals and takes them in. The PWM generator 64 generates a PWM signal for a boost chopper having a period and on / off duty according to the MPPT command value from the MCU 61, and is used for an inverter having a period and on / off duty according to the command from the MCU 61. A PWM signal is generated. The boosting PWM signal is supplied to the boosting chopper 5, and the inverter PWM signal is supplied to the single-phase inverter 20. A / D converter 65 converts the output current of single-phase inverter 20, the output voltage of single-phase inverter 20, and the system voltage into digital signals and captures them.

  The MCU 61 has MPPT control means as a main function. This MPPT control means performs MPPT control (Maximum Power Point Tracker) for adjusting the output of the boost chopper 5 (adjusting the MPPT command value) so that the output of the solar cell 10 becomes the maximum power. The following means (1) to (4) are included.

  (1) Detection means for detecting (calculating) the average generated power amount Ppv_avg per unit time 100 msec of the solar cell 10.

  (2) Whether the current average power generation amount Ppv_avg detected by the detection means is higher than the previous average power generation amount (maximum average power generation power so far) Ppv_avg detected by the detection means Determining means for determining whether it is a decrease

  (3) An adjustment direction in which the adjustment direction with respect to the output of the boost chopper 5 is maintained as it is when the determination result of the determination means is increased, and the adjustment direction with respect to the output of the boost chopper 5 is reversed when the determination result is decreased. Control means. Specifically, when the determination result is increased, the adjustment direction with respect to the output of the boost chopper 5 is maintained as it is. The determination result is decreased and the decrease amount is a predetermined amount (for example, 2 of the previous average generated power amount Ppv_avg). In the case of the above, the adjustment direction with respect to the output of the step-up chopper 5 is reversed.

  (4) When the average generated power amount Ppv_avg detected by the detecting means is within the predetermined range over the set time Ts1, the average generated power amount Ppv_avg is determined to be in the stable state near the maximum generated power amount Ppv_max. Adjustment means for adjusting the adjustment amount Width with respect to the predetermined amount of the adjustment direction control means and the output of the boost chopper 5 in the decreasing direction.

  Next, the operation will be described with reference to FIG. 2, FIG. 3, FIG. 4, and FIG. FIG. 2 shows the control of the MCU 61. FIG. 3 shows the relationship between the change in the amount of generated power, the change in the MPPT command value, and the direction and amount of adjustment. FIG. 4 shows how the generated power of the solar cell 10 increases toward the optimum operating point (maximum generated power) for MPPT control. FIG. 5 shows how the generated power of the solar cell 10 repeats increasing and decreasing in the vicinity of the optimum operating point of MPPT control.

  First, the generated voltage Vpv_ad and the generated current Ipv_ad of the solar cell 10 are A / D converted and read. Further, a timer count is executed, and it is determined whether or not the timer count has reached a unit time, for example, 100 msec. When the timer count reaches a unit time of 100 msec, the timer count is cleared, and an average generated voltage (also referred to as average input voltage) Vpv_avg and average generated current (also referred to as average input current) Ipv_avg in the unit time of 100 msec are calculated. The average generated power amount Ppv_avg in a unit time of 100 msec is calculated by the product of the average generated voltage Vpv_avg and the average generated current Ipv_avg.

  Then, in order to increase the calculated average generated power amount Ppv_avg, a prescribed adjustment amount Width for the output of the boost chopper 5 is set.

  Subsequently, it is determined whether or not the calculated average generated power amount Ppv_avg is within a predetermined range between a preset allowable stability upper limit value Ppv_Hi and a stable allowable lower limit value Ppv_Li. If it is within the predetermined range, timer count (power generation amount stabilization detection counter count) stable_cnt is started, and it is determined whether or not the timer count stable_cnt has reached the set time Ts1.

  Before the timer count stable_cnt reaches the set time Ts1, the average power generation amount Ppv_avg calculated this time is an increase from the previously calculated average power generation amount Ppv_avg (= the maximum average power generation amount Ppv_max so far). It is determined whether it is present or decreased.

  If it is increased, the average power generation amount Ppv_avg calculated this time is the previous average power generation amount Ppv_avg (= the maximum average so far, while maintaining the direction of adjustment with respect to the output of the boost chopper 5 at that time. It is updated and registered as the amount of generated power (Ppv_max).

  If it is a decrease, it is determined whether or not the decrease amount is equal to or greater than a predetermined amount (for example, about 2% to 5%, which is a predetermined ratio of the previous average generated power amount Ppv_avg). That is, the coefficient DirThras (for example, 98% to 95%) is added to the previously calculated average generated power amount Ppv_avg, and is the calculated average generated power amount Ppv_avg smaller than the integrated value (update direction determination threshold value)? Please judge.

  When the decrease amount is equal to or larger than the predetermined amount, the previously calculated average generated power amount Ppv_avg (= the maximum average generated power amount Ppv_max so far) is cleared, and the adjustment direction with respect to the output of the boost chopper 5 is reversed. When the reduction amount is less than the predetermined amount, the adjustment amount Width with respect to the output of the boost chopper 5 is reduced to a predetermined minimum adjustment amount Width_min.

  If the average power generation amount Ppv_avg calculated this time is within the predetermined range between the stable allowable upper limit value Ppv_Hi and the stable allowable lower limit value Ppv_Li, and the timer count stable_cnt reaches the set time Ts1 as it is, the average generated power calculated this time Based on the determination that the amount Ppv_avg is in a stable state near the maximum generated power amount Ppv_max, the adjustment amount Width with respect to the output of the boost chopper 5 is adjusted by a set amount in the decreasing direction, and the coefficient DirThras is increased. The predetermined amount (2% to 5%), which serves as a criterion for determining the decrease amount, is adjusted by a set amount in the decreasing direction.

If the average power generation amount Ppv_avg calculated this time is outside the predetermined range between the stable allowable upper limit value Ppv_Hi and the stable allowable lower limit value Ppv_Li, the stable allowable upper limit value Ppv_Hi and the stable allowable lower limit value Ppv_Li are the average generated power calculated this time. It is updated and set by the following equation based on the amount Ppv_avg, and the timer count (power generation amount stabilization detection counter count) stable_cnt is cleared.
Ppv_Hi = Ppv_avg × 1.1
Ppv_Li = Ppv_avg × 0.9
By the MPPT control described above, the average generated power amount Ppv_avg of the solar cell 10 increases at an accelerated rate toward the maximum average generated power amount Ppv_max at first, and eventually reaches the maximum average generated power amount Ppv_max. The increase / decrease is repeated in small increments around the amount Ppv_max, and the amount of increase / decrease is gradually reduced while quickly converging to the maximum average generated power amount Ppv_max.

  In the flowchart of FIG. 2, the block Sa corresponds to the processing of (4) adjustment means, and the block Sb corresponds to the processing of (2) determination means and (3) adjustment direction control means.

[2] A second embodiment will be described.
In the MPPT control of the MCU 61, the following first adjustment means (4a) and second adjustment means (4b) are employed instead of the adjustment means (4) of the first embodiment.
(4a) When the average generated power amount Ppv_avg detected by the detection means is within the predetermined range over the first set time Ts1, it is determined that the average generated power amount Ppv_avg is in a stable state near the maximum average generated power amount Ppv_max. Below, a first adjustment means for adjusting a predetermined amount (2% to 5%) of the adjustment direction control means and an adjustment amount Width with respect to the output of the step-up chopper 5 by a set amount in a decreasing direction.

  (4b) Under the judgment that the stable state of the average power generation amount Ppv_avg has increased when the average power generation amount Ppv_avg detected by the detection means is within the predetermined range over the first set time Ts2 (> Ts1), Second adjustment means for further adjusting a predetermined amount (2% to 5%) of the adjustment direction control means and the adjustment amount Width with respect to the output of the step-up chopper 5 in a decreasing direction by a set amount.

  In the flowchart of FIG. 6, the block Sa ′ corresponds to (4a) processing of the first adjusting means and (4b) processing of the second adjusting means.

  That is, when the average power generation amount Ppv_avg calculated this time is within the predetermined range between the allowable upper limit value Ppv_Hi and the allowable lower limit value Ppv_Li, and the timer count stable_cnt reaches the first set time Ts1 as it is, Based on the determination that the average power generation amount Ppv_avg is in the stable state near the maximum average power generation amount Ppv_max, the adjustment amount Width for the output of the boost chopper 5 is adjusted by the set amount in the decreasing direction, and the coefficient DirThras increases. Thus, the predetermined amount serving as a reference for the decrease amount determination is adjusted by a set amount in the decrease direction.

  Moreover, the timer count stable_cnt exceeds the first set time Ts1 and reaches the second set time Ts2 while the average power generation amount Ppv_avg calculated this time remains within the predetermined range between the allowable upper limit value Ppv_Hi and the allowable lower limit value Ppv_Li. When it reaches, under the judgment that the stable state of the average generated power amount Ppv_avg has increased, the adjustment amount Width for the output of the boost chopper 5 is further adjusted by the set amount in the decreasing direction, and the coefficient DirThras is further increased, A predetermined amount (2% to 5%) serving as a reference for determining the amount of decrease is further adjusted by a set amount in the decreasing direction.

In this way, by using a plurality of set times having different lengths as time elements for determining the stable state of the average generated power amount Ppv_avg, the longer the stable state, the higher the average generated power amount Ppv_avg becomes the maximum average generated power amount Ppv_max. It converges quickly to the maximum average generated electric energy Ppv_max while repeating the increase and decrease in small increments.
Other configurations, operations, and effects are the same as those in the first embodiment. Therefore, the description is omitted.

[3] A third embodiment will be described.
In the MPPT control of the MCU 61, in addition to the adoption of the first adjustment means (4a) and the second adjustment means (4b) of the second embodiment, the following protection means (5) and average power generation (6) The voltage detection means, the first correction means (7), and the second correction means (8) are employed.
(5) When the power generation voltage Vpv_ad of the solar cell 10 falls below the allowable lower limit value, for example, less than 100 V, for safety, all the relay contact points 43, 44, 48 for output are opened and the boost chopper 5 and the single-phase inverter Protection means for stopping the operation of 20 and setting a standby mode.

  (6) Average generated voltage detection means for detecting the average generated voltage Vpv_avg of the solar cell 10 at a time interval shorter than the detection of the average generated power amount Ppv_avg, for example, at an interval of 1 msec.

  (7) First correction for reducing the adjustment amount Width with respect to the output of the boost chopper 5 when the generated voltage Vpv_ad of the solar cell 10 is lower than the average generated voltage Vpv_avg detected by the average generated voltage detecting means by a certain value ΔV or more. means.

  (8) When the adjustment to the output of the boost chopper 5 is increased, and the generated voltage Vpv_ad of the solar cell 10 is larger than the average generated voltage Vpv_avg detected by the average generated voltage detection means, the adjustment amount for the output of the boost chopper 5 Second correction means for increasing Width.

  In the flowchart of FIG. 7, the block Sc corresponds to the processing of the protection means (5), and the block Sd corresponds to the processing of the first correction means (7) and the second correction means (8).

  That is, when the power generation voltage Vpv_ad of the solar cell 10 falls below the allowable lower limit value of 100 V, for safety, all the relay contact points 43, 44, 48 for output are opened and the boost chopper 5 and the single-phase inverter 20 are operated. The standby mode to stop the operation is set.

  Further, the average power generation voltage Vpv_avg of the solar cell 10 is detected at a time interval of 1 msec shorter than the detection of the average power generation amount Ppv_avg. When the power generation voltage Vpv_ad of the solar cell 10 decreases by a certain value ΔV or more with respect to the average power generation voltage Vpv_avg, it is determined that the power is taken out more than the power generation amount of the solar cell 10 or the solar cell 10 On the basis of the determination that the amount of solar radiation has decreased rapidly, the adjustment amount Width with respect to the output of the boost chopper 5 is reduced by the set amount regardless of the adjustment direction. Due to this reduction, a further decrease in the generated voltage Vpv_ad is suppressed.

As a result, even when abrupt fluctuations in the amount of solar radiation occur, the average generated power amount Ppv_avg can be quickly converged to the maximum average generated power amount Ppv_max.
Further, in spite of the increase in the adjustment to the output of the boost chopper 5, when the power generation voltage Vpv_ad of the solar cell 10 is larger than the average power generation voltage Vpv_avg, the control cannot follow the increase in the power generation amount of the solar cell 10. As a result, the adjustment amount Width with respect to the output of the boost chopper 5 is increased by a set amount.

As a result, even when the amount of solar radiation increases rapidly, the average generated power amount Ppv_avg can be quickly converged to the maximum average generated power amount Ppv_max.
Other configurations, operations, and effects are the same as those of the second embodiment. Therefore, the description is omitted.

[4] Modification
In the above embodiments, the control in consideration of the power generation voltage Vpv_ad and the average power generation amount Ppv_avg of the solar cell 10 has been described. However, control in consideration of the power generation current Ipv_ad of the solar cell 10 may be added thereto.

  For example, when the generated voltage Vpv_ad is high and the average generated power amount Ppv_avg is reasonably large. On the other hand, when the generated current Ipv_ad is small, the adjustment amount Width with respect to the output of the boost chopper 5 is suppressed and the coefficient DirThras is increased. A predetermined amount (2% to 5%) serving as a criterion for judging the adjustment direction inversion for the output of 5 is adjusted in the decreasing direction. Conversely, when the generated voltage Vpv_ad is low and the generated current Ipv_ad is large, the adjustment amount Width for the output of the boost chopper 5 is increased, the coefficient DirThras is decreased, and the determination of reversal of the adjustment direction for the output of the boost chopper 5 is made. A predetermined amount (2% to 5%) serving as a reference is adjusted in the increasing direction.

  Moreover, although each said embodiment demonstrated the case where the solar cell 10 was used as an electric power generating apparatus to the example, it can implement similarly not only when using a solar cell but when using a biomass, a fuel cell, etc.

  In addition, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments.

The figure which shows the structure of each embodiment. The flowchart which shows control of MCU in 1st Embodiment. The figure which shows the relationship between the change of the electric power generation amount in each embodiment, the change of MPPT command value, and the direction and quantity of adjustment. The figure which shows a mode that the electric power generated of the solar cell in each embodiment increases toward the optimal operating point (maximum electric power generation) of MPPT control. The figure which shows a mode that the electric power generation of the solar cell in each embodiment repeats an increase / decrease little by little near the optimal operating point of MPPT control. The flowchart for demonstrating the effect | action of 2nd Embodiment. The flowchart for demonstrating the effect | action of 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Solar cell (power generation device), 5 ... Boost chopper (converter), 20 ... Single phase inverter, 47 ... Commercial power supply system (single-phase three-wire AC200V), 50 ... Commercial power supply system for independent operation (single-phase single wire) AC 100V), 60 ... control unit, 61 ... MCU

Claims (5)

A converter that converts the generated power of the power generator into a DC voltage; an inverter that converts the output of the converter into an AC; and an MPPT control means that adjusts the output of the converter so that the generated power of the power generator is maximized. In the grid-connected inverter that outputs the output of the inverter to the commercial power system,
The MPPT control means includes
Detecting means for detecting an average amount of generated power per unit time of the power generation device;
A determination unit for determining whether the current average generated power amount detected by the detection unit is an increase or a decrease with respect to the previous average generated power amount detected by the detection unit;
An adjustment direction control means for maintaining the adjustment direction as it is when the determination result of the determination means is increased, and reversing the adjustment direction when the determination result is decreased and the decrease amount is a predetermined amount or more ;
An adjustment means for adjusting the adjustment amount for the output of the converter in a decreasing direction when the average generated power amount detected by the detection means is within a predetermined range over a set time;
including,
A grid-connected inverter characterized by that. The adjustment means adjusts the predetermined amount of the adjustment direction control means and the adjustment amount with respect to the output of the converter in a decreasing direction when the average generated power amount detected by the detection means is within a predetermined range over a set time. The grid interconnection inverter according to claim 1 . The adjusting means includes
When the change in the average amount of generated power detected by the detection means is within a predetermined range over a first set time, the predetermined amount of the adjustment direction control means and the adjustment amount for the output of the converter are reduced by a set amount in the decreasing direction. First adjusting means for adjusting;
When the change in the average power generation amount detected by the detection means is within a predetermined range over a second set time (> first set time), the adjustment amount for the predetermined amount of the adjustment direction control means and the output of the converter A second adjusting means for further adjusting the amount by a set amount in a decreasing direction;
The grid interconnection inverter according to claim 1 , comprising: The MPPT control means includes
Average power generation voltage detection means for detecting an average power generation voltage of the power generation device at a shorter time interval than detection of the average power generation amount;
Correction means for reducing an adjustment amount with respect to the output of the converter when the power generation voltage of the power generation device is lowered by a certain value or more than the average power generation voltage detected by the average power generation voltage detection means;
The grid interconnection inverter according to any one of claims 1 to 3 , further comprising: The MPPT control means includes
Correction means for increasing the amount of adjustment to the output of the converter when adjustment to the output of the converter is increased and when the generated voltage of the power generator is greater than the average generated voltage detected by the average voltage detecting means;
The grid interconnection inverter according to claim 4 , further comprising:

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