Frequency stabilization system and frequency stabilization method

Abstract

A frequency stabilization system according to one aspect of the present invention comprises: a power conversion unit that converts, into AC power, DC power output by a solar panel and / or a storage battery, and outputs the AC power to a power grid; a bidirectional DC converter that is connected in series to the storage battery, and controls, on the basis of an effective power command value, the charging and discharging of the power conversion unit by the storage battery; a grid frequency detection unit that detects the grid frequency of AC power output to the power grid by the power conversion unit; a required power calculation unit that calculates the required power for the power grid on the basis of the detected grid frequency; a command value calculation unit that calculates the effective power command value for the bidirectional DC converter on the basis of the calculated required power; and an output control unit that, on the basis of the calculated effective power command value, controls charging and discharging outputs to the power conversion unit of the storage battery by the bidirectional DC converter.

Description

[Technical Field]

[0001] The present invention relates to a frequency stabilization system and a frequency stabilization method. [Background technology]

[0002] For example, in a grid-connected system in which DC power generated by a solar cell panel (PV panel) is converted into AC power by a PCS (power conditioning system) and connected to a power grid, a configuration including a storage battery for charging the generated power is commonly known.

[0003] The system frequency in a power system fluctuates due to various conditions, such as fluctuations in the amount of power generated by solar panels.

[0004] For example, when multiple remote islands equipped with power generation facilities and power storage devices that utilize renewable energy are interconnected by transmission lines to form a small-scale power grid, a frequency control method is known that controls the grid frequency while taking into account fluctuations in the amount of renewable energy power generation due to the influence of natural conditions (see, for example, Patent Document 1).

[0005] Furthermore, an output control device is known that includes a conversion unit that converts power generated by a solar power generation device into AC power of a predetermined first range of frequency when the power can be supplied to the power grid, and converts stored power accumulated in a storage battery into AC power of a second range of frequency that is equal to or lower than the lower limit of the first range of frequency when the generated power cannot be supplied to the power grid, and an output unit that outputs the AC power whose frequency has been converted by the conversion unit to the power grid, and controls the output of power generated by the power generation device and power discharged from the storage battery to the power grid (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-178736 [Patent Document 2] Japanese Patent Publication No. 2022-025226 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the solar cell panel and the storage battery are connected in parallel to the power system so as to be interconnected on the DC side, there is a problem in that the system frequency of the power system cannot be stabilized.

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a frequency stabilization system and a frequency stabilization method that make it possible to convert DC power generated by a solar panel into AC power stabilized within a predetermined frequency range. [Means for solving the problem]

[0009] a bidirectional DC converter connected in series to the storage battery and configured to control charging and discharging of the storage battery to the power conversion unit based on an active power command value; a system frequency detection unit detecting a system frequency of the AC power output by the power conversion unit to the power grid; a required power calculation unit calculating required power for the power grid based on the system frequency detected by the system frequency detection unit; a command value calculation unit calculating an active power command value for the bidirectional DC converter based on the required power calculated by the required power calculation unit; and an output control unit controlling charging and discharging output of the storage battery to the power conversion unit by the bidirectional DC converter based on the active power command value calculated by the command value calculation unit.

[0010] Moreover, a frequency stabilization system according to an aspect of the present invention further includes a frequency determination unit that determines whether the grid frequency detected by the grid frequency detection unit is higher than a predetermined frequency range, lower than the frequency range, or within the frequency range, and when the frequency determination unit determines that the grid frequency detected by the grid frequency detection unit is higher than the frequency range, the command value calculation unit calculates an active power command value such that the power output from the solar cell panel to the power conversion unit approaches zero and the bidirectional DC converter charges and discharges the storage battery with power of the same magnitude as the required power calculated by the required power calculation unit.

[0011] Furthermore, in a frequency stabilization system according to an aspect of the present invention, when the frequency determination unit determines that the grid frequency detected by the grid frequency detection unit is a frequency lower than the frequency range, the command value calculation unit calculates an active power command value so that the power output from the solar cell panel to the power conversion unit approaches the required power calculated by the required power calculation unit and the storage battery discharges the power that is insufficient for the required power calculated by the required power calculation unit to the power conversion unit.

[0012] Furthermore, in a frequency stabilization system according to an aspect of the present invention, when the frequency determination unit determines that the grid frequency detected by the grid frequency detection unit is within the frequency range, the command value calculation unit calculates an active power command value so as to maximize the power output from the solar cell panel to the power conversion unit.

[0013] Furthermore, according to one aspect of the present invention, there is provided a frequency stabilization method for controlling a frequency stabilization system including: a solar cell panel and a storage battery connected in parallel to be interconnected to an electric power grid; a power conversion unit that converts DC power output by at least one of the solar cell panel and the storage battery into AC power and outputs the AC power to the electric power grid; and a bidirectional DC converter connected in series to the storage battery and that controls charging and discharging of the storage battery to the power conversion unit based on an active power command value, the method comprising the steps of: a system frequency detection step of detecting a system frequency of the AC power output by the power conversion unit to the electric power grid; a required power calculation step of calculating required power for the electric power grid based on the system frequency detected in the system frequency detection step; a command value calculation step of calculating an active power command value for the bidirectional DC converter based on the required power calculated in the required power calculation step; and an output control step of controlling charging and discharging output of the storage battery to the power conversion unit by the bidirectional DC converter based on the active power command value calculated in the command value calculation step.

[0014] Moreover, the frequency stabilization method according to one aspect of the present invention further includes a frequency determination step of determining whether the system frequency detected in the system frequency detection step is higher than a predetermined frequency range, lower than the frequency range, or within the frequency range, and in the command value calculation step, when it is determined in the frequency determination step that the system frequency detected in the system frequency detection step is higher than the frequency range, calculates an active power command value so that the power output from the solar cell panel to the power conversion unit approaches zero and the bidirectional DC converter charges and discharges the storage battery with power of the same magnitude as the required power calculated in the required power calculation step.

[0015] In addition, in a frequency stabilization method according to one aspect of the present invention, when it is determined in the frequency determination step that the system frequency detected in the system frequency detection step is a frequency lower than the frequency range, the command value calculation step calculates an active power command value so that the power output from the solar cell panel to the power conversion unit approaches the required power calculated in the required power calculation step, and the storage battery discharges power that is insufficient for the required power calculated in the required power calculation step to the power conversion unit.

[0016] In addition, in the frequency stabilization method according to one aspect of the present invention, when it is determined in the frequency determination step that the grid frequency detected in the grid frequency detection step is within the frequency range, the command value calculation step calculates an active power command value so as to maximize the power output from the solar cell panel to the power conversion unit. [Effects of the Invention]

[0017] According to the present invention, it is possible to convert DC power generated by a solar panel into AC power stabilized within a predetermined frequency range. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram illustrating a configuration example of a frequency stabilization system according to an embodiment. [Figure 2] FIG. 2 is a functional block diagram illustrating the functions of a PCS. [Figure 3] FIG. 2 is a functional block diagram illustrating functions of a bidirectional DC converter. [Figure 4] 1 is a graph showing an overview of the dfdP function. [Figure 5] FIG. 10 is a diagram illustrating an example of the operation of the frequency stabilization system when the system frequency is higher than a predetermined frequency range. [Figure 6] FIG. 10 is a diagram illustrating an example of the operation of the frequency stabilization system when the system frequency is lower than a predetermined frequency range. DETAILED DESCRIPTION OF THE INVENTION

[0019] A frequency stabilization system according to an embodiment will be described below with reference to the drawings. Fig. 1 is a diagram showing an example of the configuration of a frequency stabilization system 1 according to an embodiment.

[0020] As shown in Fig. 1, the frequency stabilization system 1 is a grid-connected system having, for example, a solar cell panel 2 and a storage battery 3 connected in parallel to be connected to a power grid 100, a PCS (power conditioner) 4, a bidirectional DC / DC converter 5, and a diode 6. The frequency stabilization system 1 is also configured to include a control unit 47 (see Fig. 2) and a control unit 53 (see Fig. 3).

[0021] For example, in order to stabilize the system frequency of the power system 100, the frequency stabilization system 1 controls the power output by the PCS 4 to the power system 100 in accordance with fluctuations in the system frequency.

[0022] The solar panel 2 generates DC power from sunlight and is capable of supplying the power to the power grid 100 via the PCS 4. The storage battery 3 is capable of being charged with the DC power generated by the solar panel 2.

[0023] The PCS 4 has a function of converting DC power output by at least one of the solar cell panel 2 and the storage battery 3 into AC power and supplying it to the power system 100. The PCS 4 will be described in more detail later with reference to FIG. 2.

[0024] The bidirectional DC converter 5 is connected in series to the storage battery 3 and controls charging and discharging of the storage battery 3 to the PCS 4 based on an active power command value Pref (described later) output by the PCS 4. For example, the bidirectional DC converter 5 and the storage battery 3 constitute an ESS (Energy Storage System).

[0025] The diode 6 is a protection circuit that prevents current from flowing toward the solar panel 2. Here, as shown in Fig. 1, a configuration in which the solar panel 2 and the storage battery 3, which are provided in parallel with the power grid 100, are directly linked via the diode 6, is referred to as a DC link type grid-connected system.

[0026] The frequency stabilization system 1 is also provided with nodes A to F shown in FIG. 1, and the PCS 4 is able to detect parameters such as frequency, power, and voltage in the frequency stabilization system 1.

[0027] Next, a more detailed description will be given of the functions of the PCS 4. Fig. 2 is a functional block diagram illustrating the functions of the PCS 4. As shown in Fig. 2, the PCS 4 includes, for example, a grid frequency detector 41, a supply power detector 42, a DC link voltage detector 43, a PV power detector 44, a controller 47, and a power converter 48.

[0028] At node A (see FIG. 1 ), which is the interconnection point of PCS 4 to power system 100, system frequency detection unit 41 detects system frequency f of AC power output by PCS 4 to power system 100, and outputs the system frequency f to control unit 47. More specifically, system frequency detection unit 41 detects the system frequency of AC power output by power conversion unit 48, which will be described later, to power system 100, and outputs the system frequency f to frequency determination unit 471, which will be described later.

[0029] The supply power detection unit 42 detects the power P (or the power command value P*) that the PCS 4 supplies to the power system 100 at the node B, and outputs it to the control unit 47.

[0030] The DC link voltage detection unit 43 detects the voltage (DC link voltage) applied to the PCS 4 from at least one of the solar cell panel 2 and the storage battery 3 at the node C, and outputs the detected voltage to the control unit 47.

[0031] The PV power detection unit 44 detects the power output by the solar cell panel 2 (PV power: Ppv) at node D and outputs it to the control unit 47.

[0032] The control unit 47 has a frequency determination unit 471, a required power calculation unit 472, an MPPT control unit 473, a PWM 474, a command value calculation unit 475, and an output control unit 476, and is capable of realizing a dfdP function (Frequency-Watt function) for the power system 100.

[0033] The dfdP function, as shown in Figure 4, for example, keeps the charging and discharging of the storage battery constant when the frequency of the output power is within a predetermined frequency range, controls the storage battery in the charging direction when the frequency of the output power is higher than the predetermined frequency range, and controls the storage battery in the discharging direction when the frequency of the output power is lower than the predetermined frequency range.

[0034] The frequency determination unit 471 determines whether the system frequency f detected by the system frequency detection unit 41 is a frequency higher than a predetermined frequency range, a frequency lower than the frequency range, or within the frequency range. Here, the predetermined frequency range is a range of the system frequency f that is predetermined for the frequency stabilization system 1 to perform normal operation, such as a range of the rated frequency ±0.2 Hz.

[0035] The required power calculation unit 472 acquires the system frequency f detected by the system frequency detection unit 41, and calculates the required power P for the power system 100 (power to support the power system 100: equivalent to the power command P*) based on the system frequency f.

[0036] The MPPT control unit 473 performs MPPT (Maximum Power Point Tracking) and controls the power conversion unit 48 via the PWM 474 .

[0037] The command value calculation unit 475 calculates an active power command value (Pref) for the bidirectional DC converter 5 based on the system frequency f or the required power calculated by the required power calculation unit 472.

[0038] For example, when the frequency determination unit 471 determines that the system frequency f detected by the system frequency detection unit 41 is a frequency higher than the above-mentioned frequency range, the command value calculation unit 475 calculates an active power command value (Pref) so that the power output by the solar cell panel 2 approaches zero and the bidirectional DC converter 5 charges the storage battery 3 with power of the same magnitude as the required power P (equivalent to the power command P*) calculated by the required power calculation unit 472.

[0039] Furthermore, when the frequency determination unit 471 determines that the system frequency f detected by the system frequency detection unit 41 is a frequency lower than the above-mentioned frequency range, the command value calculation unit 475 calculates an active power command value (Pref) so that the power output by the solar cell panel 2 approaches the required power P (equivalent to the power command P*) calculated by the required power calculation unit 472, and so that the storage battery 3 discharges the power that is insufficient for the required power P calculated by the required power calculation unit 472 to the power conversion unit 48.

[0040] Furthermore, when the frequency determination unit 471 determines that the system frequency f detected by the system frequency detection unit 41 is within the above-mentioned frequency range, the command value calculation unit 475 calculates an active power command value (Pref) so as to maximize the power output by the solar cell panel 2 (to bring it closer to the required power P (equivalent to the power command P*)).

[0041] The output control unit 476 outputs the active power command value (Pref) calculated by the command value calculation unit 475 to the bidirectional DC converter 5. Then, the output control unit 476 controls the charging / discharging output of the storage battery 3 to the power conversion unit 48 by the bidirectional DC converter 5 based on the active power command value (Pref) calculated by the command value calculation unit 475.

[0042] The power conversion unit 48 converts DC power output from at least one of the solar cell panel 2 and the storage battery 3 into AC power, and outputs the AC power to the power grid 100.

[0043] Next, the functions of the bidirectional DC converter 5 will be described in more detail. Fig. 3 is a functional block diagram illustrating the functions of the bidirectional DC converter 5. As shown in Fig. 3, the bidirectional DC converter 5 has a battery power detection unit 51, a battery voltage detection unit 52, and a control unit 53, which control a power conversion unit (not shown) provided in the bidirectional DC converter 5.

[0044] The battery power detection unit 51 detects at the node E the power supplied from the bidirectional DC converter 5 to the PCS 4 (battery power Pbatt).

[0045] The battery voltage detection unit 52 detects the output voltage (Vbatt) of the storage battery 3 at node F. The battery voltage detection unit 52 may be configured to detect the state of charge (SOC) of the storage battery 3.

[0046] The control unit 53 includes a power control unit 530 and a PWM 532 , and controls the bidirectional DC converter 5 .

[0047] Next, we will explain an example of the operation of the frequency stabilization system 1. When the system frequency f detected by the system frequency detection unit 41 is within the above-mentioned frequency range, the frequency stabilization system 1 causes the solar cell panel 2 to discharge to the power system 100, and the PCS 4 controls the bidirectional DC converter 5 so that the state of charge (SOC) of the storage battery 3 falls within a predetermined range (see FIG. 1).

[0048] For example, when the battery voltage detection unit 52 detects the SOC, the command value calculation unit 475 of the PCS 4 calculates the active power command value Pref so that the SOC is within a predetermined range (for example, the SOC is within a range of 20% to 80%).

[0049] In PCS4, the command value calculation unit 475 may calculate the active power command value Pref so that the battery voltage Vbatt detected by the battery voltage detection unit 52 is within a predetermined range (Vbatt = Vmin to Vmax), or so that the battery power Pbatt detected by the battery power detection unit 51 is within a predetermined range.

[0050] Furthermore, when the system frequency f detected by the system frequency detection unit 41 is within the above-mentioned frequency range, the PCS 4 controls the DC link voltage so as to maximize the output power Ppv of the solar cell panel 2, giving top priority to discharging (selling power) from the power system 100 (MPPT control: Maximum Power Point Tracking control).

[0051] Furthermore, in the frequency stabilization system 1, when the frequency determination unit 471 determines that the grid frequency f detected by the grid frequency detection unit 41 is a frequency higher than the above-mentioned frequency range, the PCS 4 performs control as shown in Fig. 5. That is, the PCS 4 performs control so that the solar cell panel 2 and the storage battery 3 do not discharge electricity to the power grid 100.

[0052] More specifically, the required power calculation unit 472 calculates the power required for the power system 100 (P* required to support the power system 100) according to the system frequency f detected by the system frequency detection unit 41.

[0053] Then, the PCS 4 controls the output power to the power system 100 by the dfdP function using P* based on the system frequency f detected by the frequency determination unit 471.

[0054] At this time, the PCS 4 controls the DC link voltage so as to set the output power Ppv of the solar cell panel 2 to zero. For example, the PCS 4 sets the active power command value Pref for the bidirectional DC converter 5 to Pref=-P* as a charge command value, and controls the storage battery 3 to charge.

[0055] In other words, when the grid frequency f is higher than the above-mentioned frequency range, the frequency stabilization system 1 controls the output power of the solar panel 2 to approach zero, and charges the storage battery 3 using Pref=-P* calculated according to the grid frequency f.

[0056] Furthermore, in the frequency stabilization system 1, when the frequency determination unit 471 determines that the system frequency f detected by the system frequency detection unit 41 is lower than the above-mentioned frequency range, the PCS 4 performs control as shown in Fig. 6. That is, the PCS 4 performs control so that the solar cell panel 2, or the solar cell panel 2 and the storage battery 3, output the required power to the power system 100.

[0057] More specifically, the required power calculation unit 472 calculates the power required for the power system 100 (P* required to support the power system 100) according to the system frequency f detected by the system frequency detection unit 41.

[0058] Then, the PCS 4 controls the output power to the power grid 100 by the dfdP function using P* based on the grid frequency f detected by the frequency determination unit 471. At this time, the PCS 4 controls the DC link voltage so that the output power Ppv of the solar cell panel 2 corresponds to P*. For example, the PCS 4 sets the active power command value Pref for the bidirectional DC converter 5 to Pref=abs(P*-Ppv) as a discharge command value, and controls the storage battery 3 to discharge.

[0059] That is, when the system frequency f is lower than the above-mentioned frequency range, the frequency stabilization system 1 outputs power to the power system 100 according to P* calculated according to the system frequency f. At this time, the PCS 4 controls the solar cell panel 2 to output as much power as possible corresponding to P*, but if the output power Ppv of the solar cell panel 2 is insufficient for the required power, the PCS 4 controls the storage battery 3 to discharge to make up for it.

[0060] In this way, the frequency stabilization system 1 detects the system frequency f of the AC power output to the power system 100, and calculates the required power based on the detected system frequency f and the active power command value (Pref) for the bidirectional DC converter 5 based on the required power. Therefore, the frequency stabilization system 1 can convert the DC power generated by the solar cell panel 2 into AC power stabilized within a predetermined frequency range.

[0061] The functions of the PCS 4 and the bidirectional DC converter 5 may be partially or entirely configured by hardware such as a programmable logic device (PLD) or a field programmable gate array (FPGA), or may be configured as a program executed by a processor such as a CPU. [Explanation of symbols]

[0062] 1 Frequency stabilization system, 2 Solar panel, 3 Storage battery, 4 PCS, 5 Bidirectional DC converter, 6 Diode, 41 System frequency detection unit, 42 Supply power detection unit, 43 DC link voltage detection unit, 44 PV power detection unit, 47 Control unit, 48 Power conversion unit, 51 Battery power detection unit, 52 Battery voltage detection unit, 53 Control unit, 100 Power system, 471 Frequency determination unit, 472 Required power calculation unit, 473 MPPT control unit, 474 PWM, 475 Command value calculation unit, 476 Output control unit, 530 Power control unit, 532 PWM

Claims

1. A frequency stabilization system having solar panels and a storage battery connected in parallel to an electric power grid, a power conversion unit that converts DC power output from at least one of the solar cell panel and the storage battery into AC power and outputs the AC power to the power grid; a bidirectional DC converter connected in series to the storage battery and controlling charging and discharging of the storage battery to the power conversion unit based on an active power command value; a system frequency detection unit that detects a system frequency of AC power output from the power conversion unit to the power system; a required power calculation unit that calculates required power for the power grid based on the grid frequency detected by the grid frequency detection unit; a command value calculation unit that calculates an active power command value for the bidirectional DC converter based on the required power calculated by the required power calculation unit; an output control unit that controls the charge / discharge output of the storage battery to the power conversion unit by the bidirectional DC converter based on the active power command value calculated by the command value calculation unit; a frequency determination unit that determines whether the system frequency detected by the system frequency detection unit is a frequency higher than a predetermined frequency range, a frequency lower than the frequency range, or within the frequency range; and The command value calculation unit When the frequency determination unit determines that the system frequency detected by the system frequency detection unit is a frequency higher than the frequency range, the power determination unit calculates an active power command value so that the power output from the solar cell panel to the power conversion unit approaches zero and the bidirectional DC converter charges and discharges the storage battery with power of the same magnitude as the required power calculated by the required power calculation unit. A frequency stabilization system featuring:

2. The command value calculation unit When the frequency determination unit determines that the system frequency detected by the system frequency detection unit is a frequency lower than the frequency range, an active power command value is calculated so that the power output from the solar cell panel to the power conversion unit approaches the required power calculated by the required power calculation unit, and the storage battery discharges the power that is insufficient for the required power calculated by the required power calculation unit to the power conversion unit.

2. The frequency stabilization system according to claim 1,

3. The command value calculation unit When the frequency determination unit determines that the system frequency detected by the system frequency detection unit is within the frequency range, an active power command value is calculated so as to maximize the power output from the solar cell panel to the power conversion unit.

3. The frequency stabilization system according to claim 1 or 2,

4. A frequency stabilization method for controlling a frequency stabilization system including a solar cell panel and a storage battery connected in parallel to be interconnected to an electric power grid, a power conversion unit that converts DC power output from at least one of the solar cell panel and the storage battery into AC power and outputs the AC power to the electric power grid, and a bidirectional DC converter that is connected in series to the storage battery and controls charging and discharging of the storage battery to the power conversion unit based on an active power command value, a system frequency detection step of detecting a system frequency of AC power output from the power conversion unit to the power system; a required power calculation step of calculating required power for the power grid based on the grid frequency detected in the grid frequency detection step; a command value calculation step of calculating an active power command value for the bidirectional DC converter based on the required power calculated in the required power calculation step; an output control step of controlling a charge / discharge output of the storage battery to the power conversion unit by the bidirectional DC converter based on the active power command value calculated in the command value calculation step; a frequency determination step of determining whether the system frequency detected in the system frequency detection step is a frequency higher than a predetermined frequency range, a frequency lower than the frequency range, or within the frequency range; Including, In the command value calculation step, When it is determined in the frequency determination step that the system frequency detected in the system frequency detection step is a frequency higher than the frequency range, an active power command value is calculated so that the power output from the solar cell panel to the power conversion unit approaches zero and the bidirectional DC converter charges and discharges the storage battery with power of the same magnitude as the required power calculated in the required power calculation step. A frequency stabilization method comprising:

5. In the command value calculation step, When it is determined in the frequency determination step that the system frequency detected in the system frequency detection step is a frequency lower than the frequency range, an active power command value is calculated so that the power output from the solar cell panel to the power conversion unit approaches the required power calculated in the required power calculation step, and the storage battery discharges the power that is insufficient for the required power calculated in the required power calculation step to the power conversion unit.

5. The method for stabilizing a frequency according to claim 4, wherein:

6. In the command value calculation step, When it is determined in the frequency determination step that the grid frequency detected in the grid frequency detection step is within the frequency range, an active power command value is calculated so as to maximize the power output from the solar cell panel to the power conversion unit.

6. The frequency stabilization method according to claim 4 or 5,

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