JP2021035279A - Power converter and control method of power converter - Google Patents

Abstract

To provide a power converter capable of preventing the occurrence of inverse load flow during communication abnormality.SOLUTION: A power converter (1) converts DC power by photovoltaic generation into AC power, and its AC side receives power from a power system and is connected to a bus (80) connected to a load (70). The power converter includes a control device (100) that sets an upper limit of output power of the power converter (1) based on information acquired by communication and controls the output power of the power converter. When communication abnormality occurs, the control device (100) switches the upper limit of the output power to a predetermined value larger than zero set according to the load (70) and suppresses the output power.SELECTED DRAWING: Figure 1

Description

The present invention relates to a power converter for a photovoltaic power generation system and a control method thereof.

In recent years, photovoltaic power generation systems have become widespread all over the world due to the feed-in tariff system (hereinafter referred to as FIT) and tax incentives. Due to mass diffusion and the principle of market competition, the cost per kW of the photovoltaic power generation system is reduced, and in areas with good solar radiation conditions, the power generation cost by the photovoltaic power generation system is higher than the power generation cost by the conventional power generation system such as thermal power generation. So-called grid parity, which is cheaper, is beginning to be established.

On the other hand, due to the spread of solar power generation, the amount of electricity purchased at FIT has decreased or has been abolished in some areas. In response to this, the number of cases of introducing self-consumed photovoltaic power generation, which consumes the electricity generated by solar power in its own equipment, is increasing, not for the purpose of selling electricity.

When power generation equipment is installed in a customer, the power system operator may request the customer to install a reverse power flow prevention relay that prevents reverse power flow in the system for stable operation of the system. This relay detects the power receiving point of the consumer, and when it detects the occurrence of reverse power flow based on the power receiving point, it opens the circuit breaker at the receiving point. Therefore, when reverse power flow occurs, the consumer side will have a power outage. Therefore, in a self-consumption type photovoltaic power generation system, a means for preventing the occurrence of reverse power flow is required.

As a conventional technique for preventing reverse power flow, the techniques described in Patent Document 1 and Patent Document 2 are known.

In the technique described in Patent Document 1 (paragraphs 0142 to 0150), the centralized control device sets a suppression index and a charge / discharge index for suppressing reverse power flow based on the interconnection point power and the reverse power flow avoidance target value. It is calculated, and the calculated suppression index and charge / discharge index are transmitted to a plurality of power conditioners. The plurality of power conditioners are controlled in a decentralized manner according to these received indicators.

In the technique described in Patent Document 2 (abstract, etc.), a power measuring unit that measures the received power from the grid transmits data on the received power and a signal regarding the presence or absence of reverse power flow to the power conditioner. The power conditioner controls the output power based on these received data and signals.

Japanese Unexamined Patent Publication No. 2018-182847 Japanese Unexamined Patent Publication No. 2013-179748

In the above-mentioned conventional technique, when a communication abnormality occurs between the power converter and the control means, reverse power flow may occur due to a decrease in the load in the equipment or an increase in solar radiation.

Therefore, the present invention provides a power converter capable of preventing the occurrence of reverse power flow at the time of communication abnormality and a control method thereof.

In order to solve the above problems, the power converter according to the present invention converts DC power generated by solar power generation into AC power, and the AC side of the power converter receives power from the power system and loads the power. Is connected to the bus to which is connected, and is equipped with a control device that controls the output power of the power converter by setting the upper limit of the output power of the power converter based on the information acquired by the communication. When an abnormality occurs, the upper limit of the output power is switched to a predetermined value larger than zero, which is set according to the load, and the output power is suppressed.

Further, in order to solve the above problems, the power converter control method according to the present invention is a power converter control method for converting DC power generated by solar power generation into AC power, and the AC side of the power converter is used. It receives power from the power system and is connected to the bus to which the load is connected, sets the upper limit of the output power of the power converter based on the information acquired by communication, controls the output power of the power converter, and communicates. When the abnormality occurs, the upper limit of the output power is switched to a predetermined value larger than zero set according to the load, and the output power is suppressed.

According to the present invention, it is possible to prevent reverse power flow while avoiding the stoppage of the power converter when a communication abnormality occurs.

Issues, configurations and effects other than those described above will be clarified by the description of the following embodiments.

It is an overall block diagram of the photovoltaic power generation system which is Example 1. FIG. It is a control block diagram which shows the structure of a converter control device. It is a flowchart which shows the communication state determination process which a communication state determination device executes. It is a graph which shows the operation state example of the solar power generation system of Example 1. FIG. It is a control block diagram which shows the structure of the converter control device in the solar power generation system which is Example 2. FIG. It is a control block diagram which shows the structure of the converter control device in the photovoltaic power generation system which is the modification of Example 2. FIG. It is a control block diagram which shows the structure of the converter control device in the solar power generation system which is Example 3. FIG. It is a control block diagram which shows the structure of the converter control device in the photovoltaic power generation system which is Example 4. FIG. It is a control block diagram which shows the structure of the converter control device in the photovoltaic power generation system which is Example 5. FIG. It is a circuit block diagram of the IGBT assembly. An example of the display screen of the liquid crystal display included in the power converter 1 in the first embodiment is shown.

Hereinafter, embodiments of the present invention will be described with reference to the following Examples 1 to 5 with reference to the drawings. In each figure, those having the same reference number indicate the same constituent requirements or constituent requirements having similar functions.

FIG. 1 is an overall configuration diagram of a photovoltaic power generation system according to a first embodiment of the present invention. The photovoltaic power generation system of the first embodiment is for self-consumption (the same applies to the other embodiments).

In the distribution system to which power is supplied from the photovoltaic power generation system, the AC side of the power converter 1 that converts the DC power generated by the solar panel 90 into AC power and the load 70 are connected to the bus 80. The AC side of the power converter 1 is connected to the bus 80 via the transformer 60. Such a distribution system is connected to a power system (for example, a commercial AC power supply system) (for example, a commercial AC power supply system) (for example, a commercial AC power supply system) not shown via a circuit breaker 20. Therefore, the photovoltaic power generation system including the power converter 1 is connected to the power system via the circuit breaker 20.

The power flow at the interconnection point is detected using the voltage detector 10 and the current detector 11. Each detection value by the voltage detector 10 and the current detector 11 is output to the reverse power flow prevention relay 5000 and the monitoring control device 30. The reverse power flow prevention relay 5000 prevents the reverse power flow from the photovoltaic power generation system by opening the circuit breaker 20 when the reverse power flow exceeding the predetermined value continues for a predetermined time or longer.

In this embodiment, the reverse power flow prevention relay 5000 opens the circuit breaker 20 when the reverse power flow detection condition is satisfied, but it may be configured to transmit a stop command to the power converter 1.

The monitoring control device 30 sets the generated power upper limit value (Plim) and the invalid power command value (Qref) to the power converter 1 via the communication line 40 based on the respective detection values by the voltage detector 10 and the current detector 11. Send. The power converter 1 transmits each value of the active power Pac and the ineffective power Qac output by the power converter 1 to the transformer 60 to the monitoring control device 30 via the communication line 40.

A solar cell panel 90 is connected to the DC side of the main circuit of the power converter 1. The power converter 1 controls the DC input voltage so as to maximize the amount of power generated from the solar panel 90 within a range not exceeding the generated power upper limit value (Plim). That is, in the power converter 1, so-called MPPT (Maximum Power Point Tracking) control is executed.

The power converter 1 includes an IGBT assembly 50, a filter reactor 55, voltage detectors 12 and 15, current detectors 13 and 14, and a converter control device 100.

The IGBT assembly 50 constitutes the main circuit of the power converter 1. In this embodiment, as shown in FIG. 10 (circuit configuration diagram of the IGBT assembly 50), the IGBT assembly 50 is a 3-phase 2-level voltage type power converter assembly, and is an IGBT (Insulated Gate) which is a semiconductor switching element. The Bipolar Transistor) includes an IGBT module IGBT_UP, IGBT_UN, IGBT_VP, IGBT_VN, IGBT_WP and IGBT_WN, and a DC capacitor Cdc, which comprises an arm in which a recirculation diode is connected in antiparallel. The IGBT modules IGBT_UP, IGBT_UN, IGBT_VP, IGBT_VN, IGBT_WP and IGBT_WN form a three-phase full bridge circuit, and a DC capacitor Cdc is connected to the DC side of the three-phase full bridge circuit.

In FIG. 10, one arm is shown for each IGBT module, but each IGBT module has one or a plurality of arms connected in parallel to each other depending on the power capacity of the power converter 1. Be prepared. Further, each IGBT module may be composed of a group of IGBT modules in which a plurality of unit IGBT modules are connected in parallel.

The IGBT assembly 50 is not limited to the two-level power converter assembly, but may be a three-level power converter assembly or the like.

As shown in FIG. 1, the filter reactor 55 is connected between the AC side of the IGBT assembly 50 and the transformer 60. The filter reactor 55 functions as a harmonic filter. Instead of the filter reactor 55, a harmonic filter such as an LC filter or an LCL filter may be applied.

The voltage detector 12 and the current detector 13 detect the current and voltage on the AC side of the IGBT assembly 50, respectively, via the filter reactor 55. Further, the voltage detector 15 and the current detector 14 detect the current and the voltage on the DC side of the IGBT assembly 50, respectively.

The converter control device 100 receives the detection values of the voltage detectors 12 and 15 and the current detectors 13 and 14 and the information received via the communication line 40 (power generation upper limit value (Plim) and invalid power command value (Qref)). ), The gate signal GateSign of the IGBT assembly 50 is calculated and output. As a result, the converter control device 100 executes the generated power limit and the invalid power control as described later.

FIG. 2 is a control block diagram showing the configuration of the converter control device 100.

The converter control device 100 includes a communication interface 1008, an interface 1009 for analog sensors (current detectors 13, 14, voltage detectors 12, 15), and a PWM interface 1011 that outputs a gate signal to the IGBT assembly 50.

The communication interface 1008 is connected to the monitoring control device 30 via the communication line 40, receives the output power upper limit value Plim and the invalid power command value Quref from the monitoring control device 30, and the active power Pac output by the power converter 1. And each value of the ineffective power Qac is transmitted to the monitoring control device 30.

The output power upper limit value Plim is input to the changeover switch 1007 described later, and the output of the changeover switch 1007 is input to the MPPT1002 with a limiter as the power generation upper limit value Plim2.

The MPPT1002 with a limiter creates and outputs an input DC voltage command value Vdc_ref so that the active power output by the power converter 1 to the transformer 60 does not exceed the power generation upper limit value Plim2.

The active power and reactive power control means of the power converter 1 will be described below.

The system voltage of the distribution system to which the power converter 1 is connected is detected by the voltage detector 12, and the current output by the power converter 1 to the distribution system is detected by the current detector 13. The converter interconnection point voltage Vs, which is the detection value of the voltage detector 12, and the AC output current detection value Is, which is the detection value of the current detector 13, are input to the power calculator 1001. The power calculator 1001 calculates the active power Pac and the ineffective power Qac output by the power converter 1 based on the converter interconnection point voltage Vs and the AC output current detection value Is. The active power Pac is input to the MPPT1002 with a limiter and the communication interface 1008, and the invalid power Qac is input to the invalid power controller 1004 and the communication interface 1008.

In addition to the power generation upper limit value Plim2 and the active power Pac, the DC input voltage Vdc detected by the voltage detector 15 and the DC input current Idc detected by the current detector 14 are input to the MPPT1002 with a limiter.

The MPPT1002 with a limiter searches for a DC input voltage command value Vdc_ref that maximizes the input DC power, which is the product of the DC input voltage Vdc and the DC input current Idc, within the range where the active power Pac does not exceed the power generation upper limit value Plim2. When the active power Pac exceeds the power generation upper limit value Plim2, the MPPT1002 with a limiter raises and corrects the DC input voltage command value Vdc_ref.

The DC voltage controller 1003 calculates an effective current command value Id_ref that reduces the difference between Vdc_ref and Vdc based on the DC input voltage command value Vdc_ref and the DC input voltage Vdc.

The ineffective power Qac and the ineffective power command value Quref are input to the ineffective power controller 1004. The reactive power controller 1004 calculates the reactive current command value Iq_ref that reduces the difference between the Qref and the Qac based on the reactive power command value Qref and the reactive power Qac.

The active current command value Id_ref, the reactive current command value Iq_ref, and the AC output current detection value Is are input to the current controller 1005. The current controller 1005 calculates the AC output voltage command value V_ref of the IGBT assembly 50 so that the AC output current detection value Is follows the current command value (Id_ref, Iq_ref), and outputs the AC output voltage command value V_ref to the PWM interface 1011. Here, so-called vector control is used, and V_ref is calculated so that the d-axis current component (Isd) and the q-axis current component (Isq) of Is in the rotating coordinate system match Id_ref and Iq_ref, respectively.

The PWM interface 1011 creates and outputs a gate signal GateSign to each IGBT in the IGBT assembly by so-called PWM (Pulse Width Modulation) control so that the instantaneous average value of the AC output voltage of the IGBT assembly 50 matches V_ref. .. That is, the PWM interface 1011 creates a gate signal GateSign by using V_ref as a modulated wave and comparing a carrier wave (for example, a triangular wave) having a predetermined frequency (fc) with V_ref.

By the converter control device 100 as described above, the power converter 1 outputs the active power in which the generated power is suppressed to the power generation upper limit value or less, and follows the invalid power command value QRef transmitted from the monitoring control device 30. Output the invalid power.

Next, the communication state determination function and the active power upper limit value switching function in this embodiment will be described.

The information (Plim, Quref) received by the communication interface 1008 is input to the communication processing calculation unit 1010 and the communication state determination unit 1006.

The communication state determination device 1006 executes the communication state determination process described later in a predetermined time cycle. The communication status determination device 1006 measures the transmission information start interval (communication interval) transmitted from the monitoring control device 30, and changes the communication status flag C_Status from 1 to 0 when the communication interval becomes longer than the predetermined time, and communicates. When the interval becomes shorter than the predetermined time, C_Status is returned to 1.

FIG. 3 is a flowchart showing a communication state determination process executed by the communication state determination device 1006.

When the processing is started (step S1), the communication state determination device 1006 initializes the counter Tcount for measuring the communication interval and the communication state flag C_Status to 0 (zero) and 1 (step S2), respectively.

Next, the communication state determination device 1006 increments the counter Tcount by 1 (step S3).

Next, the communication state determination device 1006 determines whether or not an interrupt for starting communication has occurred (step S4). The communication state determination device 1006 executes step S5 next when an interrupt occurs (Yes in step S4), and then executes step S6 when an interrupt does not occur (No in step S4).

In step S5, the communication state determination device 1006 sets the counter Tcount to 0 and the communication state flag C_Status to 1. The communication state determination device 1006 executes step S5, and then executes step S6.

In step S6, the communication state determination device 1006 determines whether the counter Tcount is larger than Max_count, which is a predetermined value. The communication state determination device 1006 executes step S7 next when the Tcount is larger than Max_count (Yes in step S6), and executes step S3 again when the Tcount is less than or equal to Max_count (No in step S7). The Max_count is set to be larger than a value corresponding to twice the communication cycle between the monitoring control device 30 and the power converter 1 and shorter than the operating time of the reverse power flow prevention relay 5000 in order to avoid erroneous detection of a communication abnormality. To do.

In step S7, the communication status determination device 1006 determines that a communication abnormality has occurred because the communication start interval is long, and sets the communication status flag C_Status to 0. The communication state determination device 1006 executes step S7 and then executes step S3 again.

As described above, in the present embodiment, the communication failure is determined based on the interrupt generation interval at the start of communication, but the present invention is not limited to this, and the communication failure may be determined based on the number of consecutive times in which the parity bit of communication is not established. In this case, C_Status is set to 0 when the number of consecutive times that the parity bit is not established is greater than a predetermined value.

As shown in FIG. 2, the communication state determination device 1006 outputs the communication state flag C_Status set by the above processing to the changeover switch 1007.

When C_Status is 1, that is, when the communication state determination device 1006 determines that the communication state is normal, the changeover switch 1007 is extracted from the reception information of the communication interface 1008 and output by the communication processing calculation unit 1010. The photovoltaic power generation output upper limit value Plim to be output is output to the MPPT1002 with a limiter as the corrected photovoltaic power generation output upper limit value Plim2. Further, when C_Status is 0, that is, when the communication state determination device 1006 determines that the communication is abnormal, the changeover switch 1007 sets the predetermined output power upper limit value P0 as the corrected photovoltaic power generation upper limit value Plim2. Output to MPPT1002 with limiter.

Here, P0 is set to a power value equal to or less than the minimum power consumption of the load 70 (FIG. 1). As a result, when communication is abnormal, the upper limit of the amount of power generated by the photovoltaic power generation system is lower than the power consumption of the load 70, so that the occurrence of reverse power flow can be prevented. Further, by setting P0 to a power value larger than 0 (zero), the photovoltaic power generation system can supply power to the load while preventing reverse power flow even when a communication abnormality occurs. Further, since it is not necessary to excessively increase the reliability of communication between the monitoring control device 30 and the power converter 1 by making the communication network redundant or multiplexing, it is possible to avoid an increase in communication cost. ..

FIG. 4 is a graph showing an example of an operating state of the photovoltaic power generation system of the first embodiment. The vertical and horizontal axes of the graph indicate electric power and time, respectively.

Note that FIG. 4 shows the power consumption PL of the load 70, the output power Ppv of the solar cell panel 90, the corrected output upper limit value Plim2, and the active power Pac output by the power converter 1.

The sun rises from time t1 and Ppv increases.

The power converter 1 suppresses Pac to Plim 2 or less so that Pac does not exceed PL, that is, reverse power flow does not occur.

The communication abnormality is determined by the communication state determination device 1006 at time t2, and then the communication abnormality continues until time t3. Between time t2 and time t3, the correction output upper limit value Plim2 is switched to P0 (≦ the minimum power consumption of the load), but P0> 0 and the power converter 1 continuously outputs the active power Pac (= P0). To do.

At time t3, the communication state determination device 1006 determines that the communication is normal, and the power converter 1 increases the output (Pac).

As shown in FIG. 4, the active power Pac output by the power converter 1 is lower than the minimum power consumption of the load at the time of communication abnormality. Therefore, even if a communication abnormality occurs, the occurrence of reverse power flow is prevented.

From time t2 to time t3, the state of the photovoltaic power generation system including the power converter 1 should be grasped by the monitoring control device 30 due to a communication abnormality between the power converter 1 and the monitoring control device 30. Is difficult. Therefore, in the first embodiment, the state of the photovoltaic power generation system is displayed on the power converter 1 side.

FIG. 11 shows an example of the display screen of the liquid crystal display included in the power converter 1 in the first embodiment.

The liquid crystal display 2000 includes the status of the switch around the power converter 1 and the power generation status (“Generated Power”, “Reactive Power”), as well as the communication status (“Communication status”) and communication failure with the monitoring control device 30. Display the duration (“Duration”).

In an example of the display screen of FIG. 11, a communication abnormality has occurred with the display of the communication status (“Communication status”) set to “ERROR” in response to the above-mentioned communication status flag C_Status being 0 (zero). Is shown. Further, the communication failure duration (“Duration”) is displayed as “1000 sec” according to the above-mentioned Tcount value. As described above, in the first embodiment, the converter control device 100 determines the communication abnormality and further counts up the duration of the communication abnormality, so that the communication status can be displayed on the power converter 1 side.

With such a display device, the system operator can grasp the cause of the unintended decrease in the generated power, and can confirm the reset of the monitoring control device 30 and the soundness of the communication line 40 from the communication failure duration.

FIG. 5 is a control block diagram showing a configuration of a converter control device in the photovoltaic power generation system according to the second embodiment of the present invention.

The overall configuration of the photovoltaic power generation system of the second embodiment is the same as that of the first embodiment (FIG. 1). Hereinafter, the converter control device will be mainly described as being different from the first embodiment.

In the second embodiment, unlike the first embodiment, the upper limit value P0 of the photovoltaic power generation when the communication state determining device 1006 determines that the communication is abnormal is changed depending on the time zone and the day of the week.

When a photovoltaic power generation system is installed in a building or factory, the minimum value of power consumption changes depending on the number of people in the building or factory and the production plan in the factory. On the other hand, in the second embodiment, by providing a means for changing P0 depending on the time zone and the day of the week, the upper limit value P0 of the generated power at the time of communication abnormality is set to the minimum power consumption assumed at the time when the communication abnormality is determined. Set to a smaller value. As a result, the upper limit of the amount of power generated by the photovoltaic power generation system in the event of a communication abnormality can be changed according to the fluctuation of the minimum power consumption. Therefore, it is possible to secure a power generation amount commensurate with the magnitude of the minimum power consumption at the time when the communication abnormality occurs while preventing the occurrence of reverse power flow at the time of the communication abnormality.

The specific configuration of the second embodiment will be described below. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted (the same applies to FIGS. 6 to 9).

As shown in FIG. 5, the converter control device 100A stores the information of the clock 1020 that outputs the date and time information and the output power upper limit value P0 according to the minimum power consumption that fluctuates according to the day and time. It includes a database 1021. The output power upper limit value database 1021 stores a value smaller than the assumed minimum power consumption for each hour of the load 70 (FIG. 1) as P0, and the time indicated by the output according to the output (time) of the clock 1020. P0 corresponding to is output to the changeover switch 1007.

Further, the converter control device 100A includes an interface 1023 with a maintenance device for changing the output power upper limit value database 1021 from the outside. As a result, the information of P0 is accurately stored in the output power upper limit database 1021 according to various fluctuation patterns of the minimum power consumption of the load 70 and the fluctuation pattern of the minimum power consumption due to the change of the load device. Can be set or changed.

FIG. 6 is a control block diagram showing a configuration of a converter control device in a photovoltaic power generation system, which is a modification of the second embodiment.

In this modification, the above-mentioned clock (“1020” in FIG. 5) and the output power upper limit database (“1021” in FIG. 5) are provided by the monitoring control device 30 (FIG. 1). Therefore, the converter control device 100B receives the information of P0 from the monitoring control device 30 via the communication line 40. In this case, the communication processing calculator 1022 outputs the information of P0 received and held at the time of normal communication immediately before the occurrence of the communication abnormality to the changeover switch 1007 at the time of communication abnormality.

According to the second embodiment, as in the first embodiment, it is possible to supply electric power from the photovoltaic power generation system to the load while preventing reverse power flow even when a communication abnormality occurs. Further, as in the first embodiment, it is possible to avoid an increase in communication cost. Further, according to the second embodiment, even if the minimum power consumption of the load fluctuates depending on the day and time, the minimum power consumption at the time when the communication abnormality occurs while preventing the occurrence of reverse power flow at the time of the minimum power consumption communication abnormality. It is possible to secure the amount of power generation commensurate with the amount of power consumption.

FIG. 7 is a control block diagram showing a configuration of a converter control device in the photovoltaic power generation system according to the third embodiment of the present invention.

The overall configuration of the photovoltaic power generation system of the third embodiment is the same as that of the first embodiment (FIG. 1). Hereinafter, the converter control device will be mainly described as being different from the first embodiment.

In the third embodiment, unlike the first embodiment, when the communication status flag C_Status is 1, the invalid power command value Qref received from the monitoring control device 30 (FIG. 1) is set as the corrected invalid power command value Qref2, and the invalid power controller is used. When input to 1004 and C_Status changes from 1 to 0, the invalid power command value Qref at the last time when C_Status was 1 is retained, and the retained invalid power command value Qref is corrected. It is input to the invalid power controller 1004 as Qref2. As a result, it is possible to prevent fluctuations in the reactive power output by the power converter 1 in the event of a communication abnormality and reduce fluctuations in the voltage of the bus 80 (FIG. 1).

The specific configuration of the third embodiment will be described below. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. As shown in FIG. 7, the communication processing calculator 1010 receives the converter control device 100C from the monitoring control device 30. It is provided with a sample hold 1040 for inputting the invalid power command value Quref which is extracted from the collected information and is output, and the communication state flag C_Status which is output by the communication state determination device 1006. When C_Status is 1, the sample hold 1040 outputs the input Qref as it is as the correction invalid power command value Quref2. Further, the sample hold 1040 has a recording means (for example, a memory) for holding the QRef input when C_Status is 1.

When C_Status changes from 1 to 0, the sample hold 1040 reads the Qref held from the recording means, outputs the read Qref as the correction invalid power command value Qref2, and prohibits overwriting of the recording means.

According to the third embodiment, as in the first embodiment, it is possible to supply electric power from the photovoltaic power generation system to the load while preventing reverse power flow even when a communication abnormality occurs. Further, as in the first embodiment, it is possible to avoid an increase in communication cost. Further, according to the third embodiment, when the communication is abnormal, the invalid power output by the power converter 1 can be controlled according to the invalid power command value acquired at the time of normal communication, so that the fluctuation of the bus voltage can be reduced.

FIG. 8 is a control block diagram showing a configuration of a converter control device in the photovoltaic power generation system according to the fourth embodiment of the present invention.

The overall configuration of the photovoltaic power generation system of the fourth embodiment is the same as that of the first embodiment (FIG. 1). Hereinafter, the converter control device will be mainly described as being different from the first embodiment.

In the fourth embodiment, unlike the first embodiment, the invalid power command value is switched to the predetermined value Q0 at a predetermined rate of change when a communication abnormality occurs.

If the output power of the power converter 1 is limited in order to avoid reverse power flow when the communication between the monitoring control device 30 and the power converter 1 is abnormal, the power received from the power system increases and the received voltage of the load equipment increases. May decrease. On the other hand, by setting the invalid power command value Q0 set at the time of communication abnormality to the polarity that the operating state of the power converter 1 becomes the capacitor operation, the decrease in the receiving point voltage can be alleviated. Further, by limiting the rate of change of the reactive power command value, it is possible to avoid a sudden change in the bus voltage.

The specific configuration of the fourth embodiment will be described below. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. As shown in FIG. 8, the converter control device 100D has an invalid power command value QReff output by the communication processing calculator 1010. A changeover switch 1030 for switching between the fixed value and the invalid power command value Q0 according to C_Status is provided, and when C_Status changes to 0, the change rate of the output of the changeover switch 1030 is limited to limit the change rate. A change rate limiter 1031 that outputs a value as a correction invalid power command value Qref2 to the invalid power controller 1004 is provided. Q0 has a polarity value at which the power converter 1 operates as a capacitor.

According to the fourth embodiment, as in the first embodiment, it is possible to supply electric power from the photovoltaic power generation system to the load while preventing reverse power flow even when a communication abnormality occurs. Further, as in the first embodiment, it is possible to avoid an increase in communication cost. Further, according to the fourth embodiment, since the power converter 1 can output the reactive power having the polarity of the capacitor operation when the communication is abnormal, the decrease of the bus voltage can be suppressed. Further, since the rate of change of the reactive power output from the power converter 1 can be suppressed when a communication abnormality occurs, a sudden change in the bus voltage can be avoided.

FIG. 9 is a control block diagram showing a configuration of a converter control device in the photovoltaic power generation system according to the fifth embodiment of the present invention.

The overall configuration of the photovoltaic power generation system of the fifth embodiment is the same as that of the first embodiment (FIG. 1). Hereinafter, the converter control device will be mainly described as being different from the first embodiment.

In the fifth embodiment, unlike the first embodiment, when the duration of the communication abnormality continues longer than a predetermined time, the operation of the power converter 1 is performed after the current output by the power converter 1 is reduced in a lamp shape. Is stopped. Further, when the output current is reduced like a lamp, the rate of change of the reactive current is slower than that of the active current.

As a result, when the communication abnormality between the monitoring control device 30 and the power converter 1 continues for a long time, the reverse power flow can be reliably prevented by stopping the power generation by the photovoltaic power generation system. Further, by narrowing the output current in a lamp shape, it is possible to avoid a sudden change in the bus voltage. Further, by reducing the reactive current more gently than the active current, the voltage control on the power system side can follow the voltage fluctuation, and the fluctuation of the bus voltage can be suppressed.

The specific configuration of the fifth embodiment will be described below. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted (however, for “1040” in FIG. 9, see FIG. 7).

As shown in FIG. 9, the converter control device 100E has a communication abnormality time determination device 1050 that measures the period during which C-Status continues to be 0 (zero), and an effective current based on the outputs of the communication abnormality time determination device 1050. For the output of the current command value limiter 1053 and the current command value limiter 1054 that reduce the command value Id_ref and the invalid current command value Iq_ref, respectively, the delay device 1051 that delays the output of the communication abnormality time determination device 1050, and the output of the delay device 1051. Correspondingly, the PWM interface 1052 for turning off all the gate signals output to the IGBT assembly 50 is provided.

Hereinafter, the operation of the fifth embodiment will be described.

The communication abnormality time determination device 1050 measures the time for which the communication state flag C_Status output by the communication state determination device 1006 is maintained at 0 (that is, the communication abnormality duration). Further, the communication abnormality time determining device 1050 determines whether or not the time for maintaining 0 of C_Status exceeds a predetermined time, and if it exceeds the predetermined time, the self-output is changed from 1 to 0.

Here, the predetermined time to be compared with the communication abnormality duration in the communication abnormality time determination device 1050 is set as follows, for example.

Communication is interrupted when noise is mixed in the communication path, or when an interrupt having a higher priority than communication occurs on the monitoring control device 30 side or the power converter 1 side. In order to recover from such a single communication abnormality, a retry function is generally implemented in the communication system. However, if the communication fails despite a large number of retries, that is, if the communication abnormality duration becomes long, the communication line may be disconnected or the monitoring / control device 30 may hang. Therefore, the monitoring / control device 30 controls the communication. It is desirable to stop the equipment to be used safely. Since the allowable number of communication retries is set according to the time during which the system can safely continue operation, the above-mentioned predetermined time, which is a criterion for the communication abnormality time determination device 1050 to change the output to 0, is reverse power flow. It is preferable to set the operation time of the prevention relay 5000 longer than the time corresponding to the allowable number of communication retries.

The output of the communication abnormality time determination device 1050 is input to the current command value limiter 1053, the current command value limiter 1054, and the delay device 1051.

The current command value limiter 1053 and the current command value limiter 1054 set the magnitudes of the active current command value Id_ref and the reactive current command value Iq_ref, respectively, at the time when the output of the communication abnormality time determiner 1050 changes from 1 to 0. It is reduced at a predetermined rate of change from to 0 (zero). Then, the output of the current command value limiter 1053 and the output of the current command value limiter 1054 are input to the current controller 1005 as new effective current command values and invalid current command values, respectively.

Here, since the power converter 1 is a device controlled by the monitoring control device 30 to prevent reverse power flow, it can be safely stopped when the communication abnormality duration becomes long as described above. desirable. However, a sudden change in the output current when the power converter 1 is stopped may cause a sudden change in the voltage of the bus 80, which may lead to unnecessary stop of the load 70 connected to the bus 80. Therefore, in the fifth embodiment, the output current is reduced to 0 (zero) by the current command value limiter 1053, 1054 while suppressing the rate of change. As a result, the power converter 1 can be stopped while suppressing a sudden change in the voltage of the bus 80.

The reactive current causes a large voltage change as compared with the active current. Therefore, in the fifth embodiment, the current command value limiter 1054 limits the reactive current command value at a gradual rate of change as compared with the current command value limiter 1053. In order to stabilize the bus voltage, it is preferable to limit the reactive current more gently than the operating time of the voltage control device installed on the power system side.

The delay device 1051 delays the output signal of the communication abnormality time determination device 1050 by the time until the current command value limiter 1054 limits the invalid current command value to 0 (zero), and outputs the output signal to the PWM interface 1052. The PWM interface 1052 turns off the gate signal GateSig output to the IGBT assembly 50 when the output of the delay device 1051 changes from 1 to 0. That is, when the output current is reduced to 0 (zero) by the current command value limiter 1053 and the current command value limiter 1054 while suppressing the magnitude of the change, the gate signal GateSig is turned off. At this time, the gate signals to all the IGBT modules shown in FIG. 10 are turned off, that is, the power converter 1 is gate-blocked and the power converter 1 is stopped.

According to the fifth embodiment, as in the first embodiment, it is possible to supply electric power from the photovoltaic power generation system to the load while preventing reverse power flow even when a communication abnormality occurs. Further, as in the first embodiment, it is possible to avoid an increase in communication cost. Further, according to the fifth embodiment, when the communication abnormality continues, the output current of the power converter 1 can be suppressed while alleviating the fluctuation of the bus voltage, and the operation of the power converter 1 can be stopped stably. it can.

The present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described examples have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations. Further, it is possible to add / delete / replace a part of the configuration of each embodiment with another configuration.

1 ... Power converter, 10 ... Voltage detector, 11 ... Current detector, 12 ... Voltage detector,
13 ... current detector, 14 ... current detector, 15 ... voltage detector, 20 ... circuit breaker,
30 ... monitoring control device, 40 ... communication line, 50 ... IGBT assembly,
55 ... filter reactor, 60 ... transformer, 70 ... load, 80 ... bus,
90 ... Solar panel,
100, 100A, 100B, 100C, 100D, 100E ... Converter control device,
1001 ... Power calculator, 1002 ... MPPT calculator with limiter,
1003 ... DC voltage controller, 1004 ... Reactive power controller, 1005 ... Current controller,
1006 ... Communication status judge, 1007 ... Changeover switch,
1008 ... Communication interface, 1009 ... Analog sensor interface,
1010 ... Communication processing calculator, 1011 ... PWM interface, 1020 ... Clock,
1021 ... Output power upper limit database, 1022 ... Communication processing calculator,
1023 ... Interface, 1030 ... Changeover switch, 1031 ... Change rate limiter,
1040 ... Sample hold, 1050 ... Communication abnormality time judge, 1051 ... Delayer,
1052 ... PWM interface, 1053 ... Current command value limiter,
1053 ... Current command value limiter

Claims (11)

In a power converter that converts DC power generated by photovoltaic power generation into AC power
The AC side of the power converter is connected to a bus that receives power from the power system and is connected to a load.
The power converter includes a control device that controls the output power of the power converter by setting an upper limit of the output power of the power converter based on information acquired by communication.
The control device is a power converter characterized in that when an abnormality in the communication occurs, the upper limit is switched to a predetermined value larger than zero set according to the load, and the output power is suppressed. In the power converter according to claim 1,
A power converter characterized in that the predetermined value is a power value equal to or less than the minimum power consumption of the load. In the power converter according to claim 1,
The control device is a power converter including a communication state determining device for determining the occurrence of the abnormality in the communication. In the power converter according to claim 3,
The communication state determining device is a power converter characterized in that the occurrence of the abnormality in the communication is determined in a time shorter than the operating time of the reverse power flow prevention relay provided between the bus and the power system. In the power converter according to claim 1,
The power converter, characterized in that the predetermined value is changed according to the date and time when the abnormality of the communication occurs. In the power converter according to claim 1,
The control device sets a first invalid power command value based on the information acquired by the communication, and controls the invalid power output by the power converter according to the first invalid power command value. A power converter characterized by In the power converter according to claim 6,
When the abnormality of the communication occurs, the control device outputs the invalid power output by the power converter according to the first invalid power command value held at the last time point in the normal state of the communication. A power converter characterized by being controlled. In the power converter according to claim 6,
The control device is characterized in that when the abnormality of the communication occurs, the invalid power command value used for controlling the reactive power is switched from the first reactive power command value to a predetermined second reactive power command value. Power converter. In the power converter according to claim 1,
The control device is a power converter that stops the operation of the power converter when the duration of the abnormality of the communication is longer than a predetermined time. In the power converter according to claim 1,
A power converter including a display device that displays information on the communication status. In the control method of the power converter that converts DC power generated by photovoltaic power generation into AC power,
The AC side of the power converter is connected to a bus that receives power from the power system and is connected to a load.
Based on the information acquired by communication, the upper limit of the output power of the power converter is set to control the output power of the power converter.
A method for controlling a power converter, which comprises switching the upper limit to a predetermined value larger than zero set according to the load when an abnormality of the communication occurs, and suppressing the output power.

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