JP7135927B2 - POWER SUPPLY SYSTEM, POWER CONVERTER, AND CONTROL METHOD OF POWER CONVERTER - Google Patents

Description

The present invention relates to a power supply system, a power conversion device, and a control method for a power conversion device.

In a power generation system that is connected to a commercial power system, if simultaneous disconnection or continuous output drop occurs due to momentary voltage drop, etc., it may have a large impact on maintaining the voltage and frequency of the entire system. It is required to satisfy a Fault Ride Through (FRT) requirement (hereinafter also referred to as an FRT requirement) (for example, see Non-Patent Document 1).

"Japan Electrotechnical Standards Committee Grid Interconnection Regulations JEAC 9701-2012 [2013 Supplement (Part 1)]", Japan Electric Association Grid Interconnection Expert Subcommittee

FIG. 8 is a diagram showing part of the contents of the FRT requirements.
For photovoltaic power generation systems, storage battery systems, etc., the FRT requirement is to continue operation for a voltage drop with a residual voltage of 20% or more (voltage drop duration of 1.0 seconds or less), and to restore the voltage after the voltage is restored. It stipulates that the output should return to 80% or more of the output before the drop.
Furthermore, in this case, the time (output recovery time) for recovering the output to 80% or more after the voltage recovery is stipulated to be within 0.1 second.

In this way, after a power drop lasting 1.0 seconds or less (hereinafter also referred to as an instantaneous power drop or momentary drop) occurs, when the voltage recovers, it is necessary to quickly restore the output of the power generation system. There is

Here, in the photovoltaic power generation system, it may be difficult to quickly restore the output to the extent that the FRT requirements are satisfied after the voltage drop is restored.
In a photovoltaic power generation system controlled by MPPT (Maximum Power Point Tracking) control, when an attempt is made to output more power than the power corresponding to the amount of solar radiation, the photovoltaic power generation system is controlled near the short-circuit current, and the operation is interrupted. become unstable.

For this reason, for example, if there is a drop in solar radiation at the timing when the momentary sag is to be restored, the operation of the photovoltaic power generation system that is about to output power becomes unstable, and the output cannot be quickly restored. There is As a result, there is a possibility that the output cannot be stably restored.
The above problem is not limited to solar cell panels, but is a problem that occurs in power generation systems that use natural energy.
Therefore, in a power generation system using natural energy, there is a demand for a technology that can stably restore output quickly after restoration from a voltage drop.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a technique capable of stably restoring the output quickly after the instantaneous voltage drop is restored.

A power supply system in one embodiment is a power supply system interconnected to a commercial power system, comprising a first DC power supply, a second DC power supply comprising a storage battery, a DC bus, the first DC power supply and the DC bus. a first DC/DC converter provided between, a second DC/DC converter provided between the second DC power supply and the DC bus, and a DC bus provided between the commercial power system and a control section that controls the first DC/DC converter, the second DC/DC converter, and the inverter, and the control section controls, after an instantaneous power drop occurs in the commercial power system, and causing at least the second DC/DC converter to discharge the power of the second DC power supply for a predetermined first period from the detection of the recovery when recovery from the instantaneous power drop is detected, and the inverter Of the power output by the first DC / DC converter and the second DC, the proportion of power borne by the second DC power supply is greater than the proportion of power borne by the first DC power supply. /DC converter.

A power conversion device according to another embodiment is a power conversion device that performs power conversion between a first DC power source and a second DC power source composed of a storage battery and a commercial power system, the power conversion device comprising: a DC bus; a first DC/DC converter provided between one DC power supply and the DC bus; a second DC/DC converter provided between the second DC power supply and the DC bus; the DC bus and the commercial power supply; An inverter provided between a power system and a control unit that controls the first DC/DC converter, the second DC/DC converter, and the inverter, and the control unit is provided in the commercial power system After an instantaneous power drop occurs, when recovery from the instantaneous power drop is detected, the power of the second DC power supply is supplied to at least the second DC/DC converter for a predetermined first period after the recovery is detected. The first DC power supply is discharged, and the first DC power supply is discharged so that the proportion of power borne by the second DC power supply in the power output by the inverter is greater than the proportion of power borne by the first DC power supply. /DC converter and the second DC/DC converter.

Still another embodiment of a control method for a power conversion device includes a DC bus, a first DC/DC converter provided between a first DC power supply and the DC bus, a second DC power supply comprising a storage battery, and the a second DC/DC converter provided between the DC bus and an inverter provided between the DC bus and the commercial power system, the first DC power supply and the second DC power supply; A control method for a power conversion device that performs power conversion between a commercial power system and a commercial power system, wherein after an instantaneous power drop occurs in the commercial power system, detecting a recovery from the instantaneous power drop, detecting the recovery. for a predetermined first period thereafter, causing at least the second DC/DC converter to discharge the power of the second DC power supply, and of the power output by the inverter, the power borne by the second DC power supply The first DC/DC converter and the second DC/DC converter are controlled such that the share of the power is greater than the share of the power borne by the first DC power supply.

The characteristic processing performed by the power supply system according to the above embodiment can be realized not only as the power supply system, but also as a program for causing a computer to execute the processing by each unit.

ADVANTAGE OF THE INVENTION According to this invention, the rapid restoration of the output after a voltage drop restoration can be performed stably.

FIG. 1 is a block diagram showing an example of the configuration of a power supply system. FIG. 2 is a flow chart showing the control operation executed by the control unit 21 of the power converter of this embodiment. FIG. 3 is a diagram showing an example of temporal changes in the values of the respective units when the control unit performs an instantaneous voltage sag. FIG. 4 is a diagram showing an example of each mode executed by the control unit. FIG. 5 is a diagram showing an example of temporal changes in power of each part in the power supply system of the present embodiment. FIG. 6 is a diagram showing another example of temporal changes in the power of each unit in the power supply system of this embodiment. FIG. 7 is a diagram showing still another example of temporal changes in power of each unit in the power supply system of the present embodiment. FIG. 8 is a diagram showing part of the contents of the FRT requirements.

[Description of Embodiments of the Present Invention]
First, the contents of the embodiments will be listed and explained.
(1) A power supply system according to one embodiment is a power supply system interconnected to a commercial power system, comprising a first DC power supply, a second DC power supply comprising a storage battery, a DC bus, and the first DC power supply. A first DC/DC converter provided between the DC bus, a second DC/DC converter provided between the second DC power supply and the DC bus, and a DC bus and the commercial power system. and an inverter provided between the When recovery from the instantaneous power drop is detected after the occurrence, causing at least the second DC/DC converter to discharge the power of the second DC power supply for a predetermined first period after the recovery is detected, and , the first DC/DC converter and the controlling the second DC/DC converter;

According to the power supply system having the above configuration, for example, even if the first DC power supply is a power generation system that uses natural energy, the second DC power supply, which is a storage battery, is responsible for the second DC power supply, which is a storage battery, out of the power output by the inverter after recovery from the voltage drop. Since the load is made larger than the load of one DC power supply, it is possible to suppress the operation of the first DC power supply from becoming unstable. As a result, the power output from the inverter can be quickly restored stably.

(2) In the above power supply system, it is preferable that the control section controls the second DC/DC converter so that the power output from the inverter is preferentially borne by the second DC power supply.
In this case, by controlling so that the output of the inverter is preferentially borne by the second DC power supply and the shortfall is borne by the first DC power supply, the dependence on the first DC power supply can be further reduced, and the inverter can make the quick recovery of the output power more stable.

(3) In the above power supply system, the control unit may further direct the power supply from the second DC/DC converter to the DC bus during a period from after the predetermined first period to a predetermined second period. The second DC/DC converter may be controlled such that the power output by the inverter is less than or equal to the power consumed by a load connected between the inverter and the commercial power system.
In this case, the discharge power of the second DC power supply, for which reverse power flow is not permitted, can be controlled to be prevented from flowing backward to the commercial power system before the predetermined second period elapses.

(4) In addition, a power conversion device according to another embodiment is a power conversion device that performs power conversion between a first DC power source and a second DC power source composed of a storage battery and a commercial power system, a bus, a first DC/DC converter provided between the first DC power supply and the DC bus, a second DC/DC converter provided between the second DC power supply and the DC bus, and an inverter provided between the DC bus and the commercial power system; and a control section that controls the first DC/DC converter, the second DC/DC converter, and the inverter, wherein the control section After an instantaneous power drop occurs in the commercial power system, when recovery from the instantaneous power drop is detected, at least the second DC/DC converter is switched to the second DC/DC converter for a predetermined first period after the recovery is detected. The power of the DC power supply is discharged, and the proportion of power borne by the second DC power supply in the power output by the inverter is set to be greater than the proportion of power borne by the first DC power supply. and controlling the first DC/DC converter and the second DC/DC converter.

(5) In another embodiment, a control method for a power conversion device includes a DC bus, a first DC/DC converter provided between a first DC power supply and the DC bus, and a second DC/DC converter comprising a storage battery. a second DC/DC converter provided between the DC power supply and the DC bus; and an inverter provided between the DC bus and the commercial power system, wherein the first DC power supply and the second A control method for a power conversion device that performs power conversion between a DC power supply and a commercial power system, wherein after an instantaneous power drop occurs in the commercial power system, when recovery from the instantaneous power drop is detected, Discharging the power of the second DC power supply to at least the second DC/DC converter for a predetermined first period after the detection of the return, and of the power output by the inverter, the second DC power supply The first DC/DC converter and the second DC/DC converter are controlled such that a power share ratio borne by is greater than a power share ratio borne by the first DC power supply.

[Details of the embodiment of the present invention]
Preferred embodiments are described below with reference to the drawings.
At least part of the embodiments described below may be combined arbitrarily.

[Regarding the overall system configuration]
FIG. 1 is a block diagram showing an example of the configuration of a power supply system. This power supply system 1 includes a photovoltaic panel 2 , a storage battery 4 , and a power conversion device 6 .
The photovoltaic panel 2 and the storage battery 4 are connected to the power converter 6 . A commercial power system 8 is also connected to the power converter 6 .
The power conversion device 6 and the commercial power system 8 are connected via an AC electric line 10 . A consumer's load 12 is connected to the AC electric line 10 . The two wires of the AC electric circuit 10 are usually single-phase three-wire voltage wires (U wire and W wire).

The power conversion device 6 is interconnected with the commercial power system 8 . The power conversion device 6 is supplied with the outputs of the photovoltaic panel 2 and the storage battery 4, and has a function of converting the supplied DC power into AC power and outputting the AC power.
The power conversion device 6 includes a first DC/DC converter 16 , a second DC/DC converter 18 , an inverter 20 and a control section 21 .

A power output from the photovoltaic panel 2 is provided to the first DC/DC converter 16 via the DC side capacitor 22 . The first DC/DC converter 16 is configured by connecting a DC reactor 24, a low-side switching element Q1, and a high-side switching element Q2 as shown. Diodes d1 and d2 are connected in anti-parallel to the switching elements Q1 and Q2, respectively. The first DC/DC converter 16 operates as a boost chopper and performs MPPT control on the power generation output.

The illustrated switching elements Q1 and Q2 are IGBTs (Insulated Gate Bipolar Transistors). The same applies to other switching elements Q3 to Q8, which will be described later. However, instead of IGBTs, semiconductor elements such as MOS-FETs (Metal-Oxide-Semiconductor Field-Effect Transistors) can also be used.

The storage battery 4 is, for example, a lithium ion battery, and is connected to the second DC/DC converter 18 via a DC side capacitor 26 . The second DC/DC converter 18 is configured by connecting a DC reactor 28, a low-side switching element Q3, and a high-side switching element Q4 as shown. Diodes d3 and d4 are connected in anti-parallel to the switching elements Q3 and Q4, respectively. The second DC/DC converter 18 can operate bidirectionally as a step-down chopper when charging the storage battery 4 and as a step-up chopper when discharging the storage battery 4 .

Two DC/DC converters 16 , 18 are connected to DC bus 30 . An intermediate capacitor 32 is provided between the two lines of the DC bus 30 . An inverter 20 is connected to the DC bus 30 .
The inverter 20 includes switching elements Q5, Q6, Q7, and Q8 that form a bridge circuit, an AC reactor 34, and an AC side capacitor 36. Diodes d5, d6, d7 and d8 are connected in anti-parallel to the switching elements Q5, Q6, Q7 and Q8, respectively.

The power conversion device 6 further includes an interconnection switch 38 . The interconnection switch 38 is provided between the inverter 20 and the AC electric line 10 . The interconnection switch 38 is closed during system interconnection and opened during a power failure or the like.

Next, elements related to measurement and control in the power conversion device 6 will be described. First, the voltage sensors 40 and 42 respectively detect the voltage across the DC side capacitors 22 and 26 and give the detection output to the controller 21 . Current sensors 44 and 46 respectively detect currents flowing through DC/DC converters 16 and 18 and provide detection outputs to control section 21 . Voltage sensor 48 detects the voltage between the two lines of DC bus 30 and provides the detected output to control section 21 . Current sensor 50 detects the current flowing through AC reactor 34 and provides a detection output to control unit 21 . The voltage sensor 52 detects the voltage between the two voltage lines of the AC electric circuit 10 and gives the detection output to the control section 21 . Further, current sensors 54 and 56 outside the power conversion device 6 detect currents in the two voltage lines flowing between them and the commercial power system 8 and provide detection outputs to the control unit 21 .

The control unit 21 controls the switching elements Q1 to Q8 based on the detection output from each sensor. The control unit 21 includes, for example, a computer having a processor and storage units such as ROM and RAM. Various computer programs for realizing the functions of the control unit 21 are stored in the storage unit. By causing the processor to execute these computer programs, the control unit 21 realizes the processing described later and the control functions necessary for the control unit 21 .

[Regarding the operation at the time of the momentary sag]
FIG. 2 is a flow chart showing the control operation executed by the control unit 21 of the power conversion device 6 of the present embodiment, and shows a flow chart showing the control for the voltage sag that occurs in the commercial power system 8 .

First, the control unit 21 executes steady control in step S1 (step S1). In steady state control, the control unit 21 controls the first DC/DC converter 16 to perform MPPT control. The control unit 21 also controls the voltage between the two lines of the DC bus 30 (hereinafter also referred to as the DC bus voltage) by the inverter 20 to control the output of the system. Further, the control unit 21 controls the second DC/DC converter 18 so that the output corresponds to the DC bus voltage.

Control unit 21 that executes steady control acquires the charge/discharge power of both converters 16 and 18 in step S2 (step S2).
Next, the control unit 21 determines whether or not a voltage drop has been detected in the commercial power system 8 (step S3).
The control unit 21 constantly detects the occurrence of voltage sag in the commercial power system 8 . Further, when detecting the occurrence of the voltage sag, the control unit 21 detects recovery from the voltage sag. The detection of the voltage sag and the detection of recovery from the voltage sag are detected by the voltage between the two voltage lines of the AC electric circuit 10, which is the detection output from the voltage sensor 52, or the voltage of the DC bus 30, which is the detection output from the voltage sensor 48. It is determined using the voltage between the two lines.

If it is determined in step S3 that an instantaneous sag is not detected, the control unit 21 returns to step S1 and executes steps S1, S2, and S3 again. Therefore, the control unit 21 executes steady control until the momentary sag is detected.

If it is determined in step S3 that the voltage sag has been detected, the control unit 21 proceeds to step S4 and executes the voltage sag mode (step S4).
The voltage sag mode is a control mode executed by the control unit 21 from detection of the voltage sag to recovery. The contents of the voltage sag mode will be described later.

After executing the voltage sag mode, the control unit 21 proceeds to step S5 and determines whether recovery from the voltage sag is detected in the commercial power system 8 (step S5).
When it is determined in step S5 that recovery from the voltage sag is not detected, the control unit 21 returns to step S4 and executes steps S4 and S5 again. Therefore, the control unit 21 executes the voltage sag mode until recovery from the voltage sag is detected.

When it is determined in step S5 that recovery from the voltage drop has been detected, the control unit 21 proceeds to step S6 and executes the first recovery mode (step S6).
The first recovery mode is a control mode executed by the control unit 21 for a first predetermined period (here, 0.1 seconds) after recovery from the instantaneous sag is detected. The contents of the first return mode will be described later.

After executing the first recovery mode, the control unit 21 proceeds to step S7 and determines whether or not 0.1 seconds have elapsed since recovery from the momentary sag (step S7).
If it is determined in step S7 that 0.1 second has not passed after recovery from the voltage drop, the control unit 21 returns to step S6 and executes steps S6 and S7 again. Therefore, the control unit 21 executes the first recovery mode until 0.1 second elapses after recovery from the momentary sag.

When it is determined in step S7 that 0.1 seconds have elapsed after recovery from the instantaneous sag, the control unit 21 proceeds to step S8 and executes the second recovery mode (step S8).
The second return mode is after the end of the first return mode, and the control executed by the control unit 21 for a second predetermined period (here, 0.5 seconds) after detecting the return from the voltage drop. mode. The contents of the second return mode will be described later.

After executing the second recovery mode, the control unit 21 proceeds to step S9 and determines whether or not 0.5 seconds have elapsed since recovery from the momentary sag (step S9).
If it is determined in step S9 that 0.5 seconds have not passed after recovery from the voltage drop, the control unit 21 returns to step S8 and executes steps S8 and S9 again. Therefore, the control unit 21 executes the second recovery mode after 0.1 seconds have elapsed since recovery from the instantaneous sag and until 0.5 seconds have elapsed since recovery from the instantaneous sag.

When it is determined in step S9 that 0.5 seconds have elapsed after recovery from the instantaneous sag, the control unit 21 returns to step S1 and executes steady control (step S1).

FIG. 3 is a diagram showing an example of changes over time in the values of each part when the control part 21 performs an instantaneous sag.
In FIG. 3, the horizontal axis indicates time, and the horizontal axes (time) of each graph shown in FIG. 3 are associated with each other.
In FIG. 3 , the uppermost stage shows changes over time in the voltage (system voltage) of the commercial power system 8 . In the lower part of the system voltage, the output power (AC output power) of the inverter 20, which is the output of the system 1, the DC bus voltage, the charge/discharge power of the storage battery 4 (output power of the second DC/DC converter 18), and the solar power It shows changes over time in the power generated by the photovoltaic panel 2 (output power of the first DC/DC converter 16).

In FIG. 3, during a period P1 when the system voltage (effective value) is approximately 100%, the control unit 21 performs steady control (step S1 in FIG. 2). In this case, control unit 21 causes inverter 20 to control the DC bus voltage and causes first DC/DC converter 16 to perform MPPT control, as described above.
Assume that in period P1, the AC output power is 10 kW, the charge/discharge power of the storage battery 4 is 5 kW, and the power generated by the photovoltaic panel 2 is 5 kW.

As shown in FIG. 3, it is assumed that a voltage drop occurs in the commercial power system 8 while the control unit 21 is executing steady state control. Here, it is assumed that a voltage drop of 20% of residual voltage has occurred.
When a voltage sag occurs in the commercial power system 8, the control unit 21 detects the voltage sag and executes the voltage sag mode (steps S3 and S4 in FIG. 2).

When a voltage sag occurs, as shown in FIG. 3, the DC bus voltage rises from the value before the voltage sag. The control unit 21 can detect a voltage sag by detecting a drop in the system voltage, and can also detect a voltage sag by detecting a rise in the DC bus voltage.
In FIG. 3, the control unit 21 detects the voltage sag at timing T1, and executes the voltage sag mode during period P2 after timing T1.

FIG. 4 is a diagram showing an example of each mode executed by the control unit 21. As shown in FIG.
Control unit 21 controls inverter 20, first DC/DC converter 16, and second DC/DC converter 18 so that the operation shown in FIG. 4 is performed in each mode.
In the sag mode, the inverter 20 is controlled to cease controlling the DC bus voltage. Moreover, the inverter 20 is controlled to continue the minimum operation according to the remaining voltage.
The first DC/DC converter 16 is controlled so as to maintain MPPT control from steady state control.
Also, the second DC/DC converter 18 is controlled instead of the inverter 20 to control the DC bus voltage. At this time, the second DC/DC converter 18 controls the DC bus voltage to be higher than the steady state control state.

In FIG. 3, the control unit 21 maintains the voltage sag mode during the period P2 in which the voltage sag state continues.
In the voltage sag mode, the first DC/DC converter 16 maintains MPPT control. Therefore, the power generated by the photovoltaic panel 2 in FIG. 3 maintains the output power of 5 kW during the period P2. The second DC/DC converter 18 also causes the storage battery 4 to charge during the period P2 in order to control the DC bus voltage to be constant.

After that, it is assumed that the commercial power system 8 recovers from the voltage drop.
When the commercial power system 8 recovers from the voltage sag, the control unit 21 detects recovery from the voltage sag and executes the first recovery mode instead of the voltage sag mode (steps S5 and S6 in FIG. 2). .
As shown in FIG. 3, when the DC bus voltage recovers from the momentary sag, it drops relative to the time of the momentary sag. The control unit 21 can detect recovery from a voltage sag by detecting a rise in the system voltage, and can also detect recovery from a voltage sag by detecting a drop in the DC bus voltage.
In FIG. 3, the control unit 21 detects recovery from the voltage drop at timing T2, and executes the first recovery mode during period P3 after timing T2.

As shown in FIG. 4, in the first recovery mode, the inverter 20 resumes control of the DC bus voltage instead of the second DC/DC converter 18 .
The second DC/DC converter 18 is controlled to cease controlling the DC bus voltage. The control unit 21 sets 80% of the total power obtained by summing the outputs of the converters 16 and 18 (the power generated by the photovoltaic power generation panel 2 and the charge/discharge power of the storage battery 4) immediately before the voltage drop as the target value of the AC output power. do. The second DC/DC converter 18 is controlled to output power within the range of the rated output and discharge the power from the storage battery 4 so as to achieve the set target value. When the target value exceeds the rated output of the second DC/DC converter 18, the second DC/DC converter 18 outputs power at the rated output, which is the maximum power that can be output.
Further, when the output power of the second DC/DC converter 18 is insufficient for the target value, the first DC/DC converter 16 is controlled to output the same power as the shortage. However, the first DC/DC converter 16 outputs power in a range smaller than the output power of the second DC/DC converter 18 .

The outputs of both converters 16 and 18 immediately before the voltage sag are values obtained immediately before the voltage sag is detected (step S2 in FIG. 2).

In this way, the control unit 21 causes the storage battery 4 to bear the AC output power preferentially, and causes the photovoltaic power generation panel 2 to bear the shortfall with respect to the target value. 18.

In FIG. 3, the control unit 21 maintains the first recovery mode for a period P3 (predetermined first period) from timing T2 when recovery from the voltage drop is detected to timing T3.
That is, when the control unit 21 detects the recovery from the voltage sag, the control unit 21 discharges the electric power of the storage battery 4 to the second DC/DC converter 18 until 0.1 seconds have elapsed since the recovery from the voltage sag was detected. In addition, control is performed so that the share of the power borne by the storage battery 4 in the power output by the inverter 20 is higher than the share of the power borne by the photovoltaic panel 2 .
Thereby, the control unit 21 restores the output power of the inverter 20 mainly by the discharged power of the storage battery 4 .
Note that the period P3 is, for example, 0.1 second.

In FIG. 3, during period P3, the first DC/DC converter 16 reduces the output from 5 kW to 3 kW.
Further, in order to restore the AC output power mainly by the discharge power of the storage battery 4, the control unit 21 increases the output of the second DC/DC converter 18 with the rated output of 5 kW as a target in the period P3. As a result, the control unit 21 increases the total power of the power generated by the photovoltaic power generation panel 2 and the discharged power of the storage battery 4 to 8 kW within the period P3, and the alternating current output by the inverter 20 before the instantaneous voltage drop. Restore to 80% of output power.
In this way, the control unit 21 can quickly restore the power output by the inverter 20 by performing control so as to relatively increase the burden ratio of the storage battery 4 that can quickly provide an output.

Since the control unit 21 performs control so as to relatively reduce the share of the power borne by the photovoltaic power generation panel 2, for example, even if the solar radiation decreases during the period P3, the power corresponding to the solar radiation It is possible to suppress the occurrence of a situation where the photovoltaic power generation panel 2 must output the above electric power.
That is, even if the solar radiation decreases and the power corresponding to the solar radiation drops to 3 kW during the period P3 in FIG.
As a result, during the period P3, it is possible to prevent the operation of the photovoltaic panel 2 from becoming unstable, and to stably restore the power output by the inverter 20 quickly.

In addition, since the control unit 21 preferentially causes the storage battery 4 to bear the output power of the inverter 20, the dependency on the photovoltaic panel 2 can be further reduced, and the power output by the inverter 20 can be quickly restored. can be made more stable.

When 0.1 seconds have passed since the recovery from the instantaneous sag was detected (when the period P3 ends), the control unit 21 executes the second recovery mode instead of the first recovery mode at timing T3 (Fig. 2, steps S7 and S8).

As shown in FIG. 4, in the second recovery mode, inverter 20 is controlled to continue to control the DC bus voltage.
The output power of the second DC/DC converter 18 is controlled to be 80% of the output of the second DC/DC converter 18 immediately before the voltage drop.
Further, the output power of the first DC/DC converter 16 is controlled so as to be 80% of the output of the first DC/DC converter 16 immediately before the voltage drop. It should be noted that the first DC/DC converter 16 is controlled so as not to output more than the electric power corresponding to the solar radiation.

In the second recovery mode, the output of the inverter 20 may be controlled to be 80% or more of the output immediately before the voltage sag. , the output of the first DC/DC converter 16 may be lower than 80%.

In FIG. 3, the control unit 21 maintains the second return mode during a period P4 from timing T3 to timing T4.
Therefore, the second DC/DC converter 18 is controlled to target the discharge power of 4 kW during the period P4. The first DC/DC converter 16 is also controlled to target an output of 4 kW during the period P4.
As a result, the control unit 21 restores the outputs of the converters 16 and 18 (the power generated by the photovoltaic panel 2 and the charge/discharge power of the storage battery 4) within the period P4 to the state before the voltage drop occurred. can be restored.
Note that the period P4 is, for example, 0.4 seconds. Therefore, the timing T4 indicates the timing when 0.5 seconds have passed after the momentary sag recovery.

Here, the power supply system 1 of this embodiment includes a storage battery 4 . Therefore, the control unit 21 controls the discharge power output from the second DC/DC converter 18 toward the DC bus 30 to be equal to or less than the power consumption of the load 12 . As a result, the control unit 21 prevents the discharged power from the storage battery 4 from flowing backward to the commercial power system 8 .
That is, the control unit 21 controls the power output from the second DC/DC converter 18 to the DC bus 30 to be equal to or less than the power consumption of the load 12 before the momentary sag occurs.

As described above, the control unit 21 restores the output of the second DC/DC converter 18 to the state before the momentary sag by maintaining the second return mode during the period P4. Therefore, the control unit 21 maintains the second recovery mode during the period P4 (predetermined second period), so that the power output from the second DC/DC converter 18 to the DC bus 30 is reduced to the load 12 control so that the power consumption is less than or equal to
As a result, it is possible to control the discharge power of the storage battery 4, for which reverse power flow is not allowed, from flowing backward to the commercial power system 8 before the period P4 elapses.

For example, assume that the power supply system 1 is equipped with a reverse power protection relay, and that the period from the detection of the reverse power flow of the discharged power of the storage battery 4 to the opening of the reverse power protection relay is 0.5 seconds. In this case, since the total period of the period P3 and the period P4 is 0.5 seconds, the control unit 21 can suppress the reverse power flow of the discharged power of the storage battery 4 before the reverse power protection relay is opened. can. Therefore, even if a reverse power flow occurs in the discharged power of the storage battery 4, it is possible to prevent the reverse power protection relay from opening.

Note that the power consumption of the load 12 in this embodiment is 5 kW, and no reverse power flow to the commercial power system 8 occurs in FIG. Therefore, the second DC/DC converter 18 is controlled to continuously output power of 4 kW.

In FIG. 3, after the timing T4, the control unit 21 executes the steady control instead of the second return mode, and maintains the steady control during the period P5. Therefore, in period P5, the output power of both DC/DC converters 16 and 18 is also 5 kW. As a result, the output power of the inverter 20 returns to 10 kW before the voltage drop occurred.

[Regarding a specific example of the operation at the moment of voltage sag]
Below, when the power conversion device 6 (power supply system 1) has a plurality of modes (hereinafter referred to as "operation modes") in the operation operation, the operation at the moment of voltage sag in each operation mode will be described. Here, it is assumed that the power converter 6 has three operation modes (for example, "single power generation mode", "double power generation mode", and "green mode"). Selection of the operation mode is performed by a user's operation, for example.

FIG. 5 is a diagram showing an example of temporal changes in the power of each unit in the power supply system 1 of the present embodiment.
FIG. 5 schematically shows each element constituting the power supply system 1, and shows the entire power supply system 1 arranged in chronological order. In FIG. 5, "PV" is the photovoltaic panel 2, "BS" is the storage battery 4, "1stCNV" is the first DC/DC converter 16, "2ndCNV" is the second DC/DC converter 18, "INV" is the inverter 20, “G” indicates the utility grid 8 and “L” indicates the load 12 . Also, the numbers shown adjacent to "1stCNV", "2ndCNV", "INV", "G", and "L" indicate the power flowing to the adjacent elements, and the arrows indicate the direction of the power flowing to the adjacent elements. is shown.

In the power supply system 1 shown in FIG. 5, the first DC/DC converter 16 (photovoltaic panel 2) is assumed to be capable of outputting 2 kW of generated power. It is assumed that the second DC/DC converter 18 (storage battery 4) is capable of charging and discharging 1.5 kW of power. It is also assumed that the power consumption of the load 12 is 1 kW. It is also assumed that the power conversion efficiency of each device that performs power conversion is 100%.
Furthermore, it is assumed that the power supply system 1 has a reverse power protection relay, and that the period from the detection of the reverse power flow of the discharged power of the storage battery 4 to the opening of the reverse power protection relay is 0.5 seconds.

It is also assumed that the power supply system 1 shown in FIG. 5 operates in the single power generation mode. In addition, single power generation is a power generation mode in which only the photovoltaic panel 2 or only the storage battery 4 is operated. In this mode, in principle, the storage battery 4 is not charged or discharged while the photovoltaic panel 2 is generating power.

As shown in FIG. 5, in the steady state (before the voltage drop), the first DC/DC converter 16 outputs 2 kW of electric power, and the second DC/DC converter 18 does not charge or discharge. The inverter 20 is supplied with 2 kW of power from the first DC/DC converter 16 , of which 1 kW is supplied to the commercial power system 8 and the remaining 1 kW is supplied to the load 12 .

Thereafter, after the voltage sag occurs and after the voltage sag is recovered, the control unit 21 executes the first recovery mode. In the first recovery mode, control unit 21 sets the output power target value of inverter 20 to 80% of the total power obtained by summing the outputs of both converters 16 and 18 immediately before the momentary sag. In FIG. 5 the target value is set at 1.6 kW. Furthermore, in the first return mode, the second DC/DC converter 18 is controlled to output power within the rated output range and discharge the power from the storage battery 4 so as to achieve the set target value. The first DC/DC converter 16 bears the shortfall that cannot be covered by the power output by the second DC/DC converter 18 with respect to the target value.

Therefore, as shown in FIG. 5, at the stage of 0.1 seconds after the momentary sag recovery, the second DC/DC converter 18 discharges 1.5 kW, which is the maximum value that can be output, and the first DC/DC converter 16 discharges the target 0.1 kW, which is insufficient for the value, is output. Inverter 20 is supplied with 1.6 kW of power from both DC/DC converters 16 and 18 , of which 0.6 kW is supplied to commercial power system 8 and the remaining 1 kW is supplied to load 12 .

In this way, in this example, the control unit 21 controls to relatively increase the burden ratio of the storage battery 4, so that the power output from the inverter 20 can be quickly restored. At the 0.1 second step, control that meets the FRT requirements is achieved.
In this example, the single power generation mode is selected, but the control unit 21 exceptionally allows power to be output simultaneously from both the converters 16 and 18 in the first return mode.

When 0.1 second has elapsed after the momentary sag recovery, the control unit 21 executes the second recovery mode. In the second recovery mode, the output power of the first DC/DC converter 16 is controlled to be 80% of the output just before the voltage sag. The input/output power of the second DC/DC converter 18 is controlled to be 80% of the input/output power immediately before the voltage drop.

Therefore, when 0.1 seconds have passed after the recovery from the voltage sag, the output power of the first DC/DC converter 16 is adjusted to 1.6 kW, which is 80% of the output immediately before the voltage sag. Also, the output power of the second DC/DC converter 18 is adjusted to 0 kW.
As a result, as shown in FIG. 5, the first DC/DC converter 16 outputs 1.6 kW and the second DC/DC converter 18 does not charge or discharge at the stage of 0.5 seconds after recovery from the voltage drop. Inverter 20 is supplied with 1.6 kW of power from both DC/DC converters 16 and 18 , of which 0.6 kW is supplied to commercial power system 8 and the remaining 1 kW is supplied to load 12 .

Here, at the stage of 0.1 seconds after the momentary sag recovery, the second DC/DC converter 18 discharges 1.5 kW, which is larger than the power consumption of the load 12. Therefore, the discharge of the storage battery 4 in which reverse power flow is not allowed. Power is flowing in reverse. However, the second DC/DC converter 18 is not charging/discharging at the stage of 0.5 seconds after recovery from the voltage drop.
Therefore, in this example, even if a reverse power flow occurs in the discharged power of the storage battery 4 at the stage of 0.1 seconds after the momentary sag recovery, it is possible to suppress the reverse power protection relay from opening and maintain the operating state. can do.

FIG. 6 is a diagram showing another example of temporal changes in the power of each unit in the power supply system 1 of this embodiment.
The power supply system 1 shown in FIG. 6 has the same conditions as those of the power supply system 1 shown in FIG. 5 except that it operates in the double power generation mode. Note that double power generation is a power generation mode that allows discharge of the storage battery 4 while the photovoltaic power generation panel 2 is generating power.

As shown in FIG. 6, in the steady state (before the voltage drop), the first DC/DC converter 16 outputs 2 kW of power, and the second DC/DC converter 18 discharges 1 kW. Inverter 20 is supplied with 3 kW of power from both DC/DC converters 16 and 18 , of which 2 kW is supplied to commercial power system 8 and the remaining 1 kW is supplied to load 12 .

Thereafter, after the voltage sag occurs and after the voltage sag is recovered, the control unit 21 executes the first recovery mode. In the first recovery mode, the target value of the output power of inverter 20 is set to 2.4 kW.
Therefore, as shown in FIG. 6, at the stage of 0.1 seconds after the momentary sag recovery, the second DC/DC converter 18 discharges power of 1.5 kW, which is the maximum value that can be output, and the first DC/DC converter 16 outputs a power of 0.9 kW, which is insufficient for the target value. Inverter 20 is supplied with 2.4 kW of power from both DC/DC converters 16 and 18 , of which 1.4 kW is supplied to commercial power system 8 and the remaining 1 kW is supplied to load 12 .

In this way, also in the present example, the control unit 21 controls to relatively increase the burden ratio of the storage battery 4, so that the power output from the inverter 20 can be quickly restored, and the voltage drop can be restored. At the stage of 0.1 seconds after, the control satisfying the FRT requirement is realized.

When 0.1 second has elapsed after the momentary sag recovery, the control unit 21 executes the second recovery mode.
Therefore, when 0.1 seconds have passed after the recovery from the voltage sag, the output power of the first DC/DC converter 16 is adjusted to 1.6 kW, which is 80% of the output immediately before the voltage sag. Also, the output power of the second DC/DC converter 18 is adjusted to 0.8 kW, which is 80% of the output just before the voltage sag.
As a result, as shown in FIG. 6, the first DC/DC converter 16 outputs power of 1.6 kW and the second DC/DC converter 18 outputs power of 0.8 kW at the stage of 0.5 seconds after the recovery from the voltage drop. to output Inverter 20 is supplied with 2.4 kW of power from both DC/DC converters 16 and 18 , of which 1.4 kW is supplied to commercial power system 8 and the remaining 1 kW is supplied to load 12 .

In this example as well, the discharged power of the storage battery 4 reversely flows at the stage of 0.1 seconds after the momentary sag recovery. However, the second DC/DC converter 18 outputs power of 0.8 kW, which is less than the power consumption of the load 12, at the stage of 0.5 seconds after recovery from the voltage drop.
Therefore, even in this example, even if a reverse power flow occurs in the discharged power of the storage battery 4 at the stage of 0.1 seconds after the momentary sag recovery, it is possible to suppress the reverse power protection relay from opening, thereby preventing the operating state from being reversed. can be maintained.

FIG. 7 is a diagram showing still another example of temporal changes in the power of each unit in the power supply system 1 of this embodiment.
The power supply system 1 shown in FIG. 7 has the same conditions as those of the power supply system 1 shown in FIGS. 5 and 6 except that it operates in the green mode.
Note that the green mode stores the surplus power of the power generated by the photovoltaic panel 2 during the day and uses the stored power during other time periods, thereby reducing power purchases from the power company. It is a mode aiming at self-sufficiency of electric power.

As shown in FIG. 7, in the steady state (before the voltage drop), the first DC/DC converter 16 outputs 2 kW of electric power, and the second DC/DC converter 18 charges the storage battery 4 with 1 kW. 1 kW of power is applied to the inverter 20 , and the 1 kW of power applied to the inverter 20 is applied to the load 12 .

Thereafter, after the voltage sag occurs and after the voltage sag is recovered, the control unit 21 executes the first recovery mode. In the first return mode, the target value of the output power of inverter 20 is set to 0.8 kW.
Therefore, as shown in FIG. 7, the second DC/DC converter 18 discharges power of 0.8 kW at the stage of 0.1 seconds after recovery from the voltage drop. Since there is no shortage of the target value, the first DC/DC converter 16 does not output power. The inverter 20 is supplied with 0.8 kW of power from the second DC/DC converter 18 . Load 12 is supplied with 0.8 kW of output power from inverter 20 and 0.2 kW of power from commercial power system 8 .

In this way, also in the present example, the control unit 21 controls to relatively increase the burden ratio of the storage battery 4, so that the power output from the inverter 20 can be quickly restored, and the voltage drop can be restored. At the stage of 0.1 seconds after, the control satisfying the FRT requirement is realized.

When 0.1 second has elapsed after the momentary sag recovery, the control unit 21 executes the second recovery mode.
At this time, the output power of the first DC/DC converter 16 is adjusted to 1.6 kW, which is 80% of the output just before the momentary sag. Also, the output power of the second DC/DC converter 18 is adjusted so as to charge the 0.8 kW storage battery 4, which is 80% of the output just before the voltage drop.
As a result, as shown in FIG. 7, the first DC/DC converter 16 outputs power of 1.6 kW and the second DC/DC converter 18 outputs power of 0.8 kW at the stage of 0.5 seconds after the recovery from the voltage drop. is charged to the storage battery 4. Inverter 20 is supplied with 0.8 kW of power from both DC/DC converters 16 and 18, and load 12 receives 0.8 kW of output power from inverter 20 and 0.2 kW of power from commercial power system 8. Given.

〔others〕
It should be noted that the embodiments disclosed this time should be considered as examples in all respects and not restrictive.
In the above embodiment, the period P3 is set to 0.1 seconds, but the period P3 may be shorter as long as the FRT requirements are satisfied, and can be changed as appropriate.
In the above embodiment, the period from the detection of the reverse power flow of the discharged power of the storage battery 4 to the opening of the reverse power protection relay is 0.5 seconds, and accordingly, the period P4 is set to 0.4 seconds. Although the case where the reverse power flow is detected has been exemplified, the period P4 may be shortened because the reverse power flow may be prevented during the period from the detection of the reverse power flow to the opening of the reverse power protection relay.

Further, in the above-described embodiment, the case of the configuration including one photovoltaic power generation panel 2 and one storage battery 4, which are power generation systems using natural energy, was exemplified. A configuration in which they are connected in parallel may be used.
Further, instead of the photovoltaic power generation panel 2, a power generation system using other natural energy other than photovoltaic power generation, such as wind power generation, may be used.

The scope of the present invention is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope of equivalence to the scope of claims.

1 power supply system 2 photovoltaic panel 4 storage battery 6 power conversion device 8 commercial power system 10 AC electric circuit 12 load 16 first DC/DC converter 18 second DC/DC converter 20 inverter 21 control section 22 DC side capacitor 24 DC reactor 26 DC side Capacitor 28 DC reactor 30 DC bus 32 Intermediate capacitor 34 AC reactor 36 AC side capacitor 38 Interconnection switch 40, 42, 48, 52 Voltage sensor 44, 46, 50, 54, 56 Current sensor d1-d8 Diode Q1-Q8 Switching element P1-P5 Period T1-T4 Timing

Claims (5)

A power supply system interconnected to a commercial power system,
a first DC power supply;
a second DC power supply comprising a storage battery;
a DC bus;
a first DC/DC converter provided between the first DC power supply and the DC bus;
a second DC/DC converter provided between the second DC power supply and the DC bus;
an inverter provided between the DC bus and the commercial power system;
A control unit that controls the first DC/DC converter, the second DC/DC converter, and the inverter,
After an instantaneous power drop occurs in the commercial power system, the control unit, when detecting a recovery from the instantaneous power drop, maintains at least the second DC/DC power supply during a predetermined first period after detecting the recovery. The converter discharges the power of the second DC power supply, and the share of power borne by the second DC power supply in the power output by the inverter is the share of power borne by the first DC power supply. A power supply system that controls the first DC/DC converter and the second DC/DC converter to be greater than. 2. The control unit according to claim 1, wherein the control unit controls the second DC/DC converter so that the power output from the inverter is preferentially borne by the second DC power supply during the predetermined first period. power system. The control unit further controls the power output from the second DC/DC converter to the DC bus for a period from the elapse of the predetermined first period until the predetermined second period to be equal to that of the inverter. 3. The power supply system according to claim 1, wherein the power consumption of the second DC/DC converter is controlled so as to be less than or equal to the power consumed by a load connected to the commercial power system. A power conversion device that performs power conversion between a first DC power supply and a second DC power supply composed of a storage battery and a commercial power system,
a DC bus;
a first DC/DC converter provided between the first DC power supply and the DC bus;
a second DC/DC converter provided between the second DC power supply and the DC bus;
an inverter provided between the DC bus and the commercial power system;
A control unit that controls the first DC/DC converter, the second DC/DC converter, and the inverter,
After an instantaneous power drop occurs in the commercial power system, the control unit, when detecting a recovery from the instantaneous power drop, maintains at least the second DC/DC power supply during a predetermined first period after detecting the recovery. The converter discharges the power of the second DC power supply, and the share of power borne by the second DC power supply in the power output by the inverter is the share of power borne by the first DC power supply. A power conversion device that controls the first DC/DC converter and the second DC/DC converter to be greater than. a DC bus;
a first DC/DC converter provided between a first DC power supply and the DC bus;
a second DC/DC converter provided between a second DC power supply made up of a storage battery and the DC bus;
an inverter provided between the DC bus and a commercial power system,
A control method for a power conversion device that performs power conversion between the first DC power supply, the second DC power supply, and a commercial power system,
After an instantaneous power drop occurs in the commercial power system, when recovery from the instantaneous power drop is detected, at least the second DC/DC converter is switched to the second DC/DC converter for a predetermined first period after the recovery is detected. The power of the DC power supply is discharged, and the proportion of power borne by the second DC power supply in the power output by the inverter is set to be greater than the proportion of power borne by the first DC power supply. 2. A control method for a power converter that controls the first DC/DC converter and the second DC/DC converter.

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