JP7796604B2 - Grid stabilizer - Google Patents

Description

This disclosure relates to a power grid stabilization device.

Grid stabilization systems designed to maintain frequency detect events that cause frequency fluctuations (e.g., power source failures, route cutoff accidents on heavy current lines, etc.) and shut off generators and load shedding to maintain frequency (e.g., Non-Patent Document 1).

Kina, A., Yamazato, K., Kinjo, F., Shima, W., Owada, Y., Nishino, H., Maeda, T., Oshida, S., Development and Application of a Centralized Stabilization Control System (SSC) for Small-Scale and Isolated Power Systems, IEEJ Power and Energy Conference 2011, 19-1, 2011.

Short-term fluctuations and frequency characteristics of loads in power systems, as well as short-term output fluctuations and frequency characteristics of renewable energy sources (e.g., solar power generation, wind power generation, etc.), the amount of which has been rapidly increasing in recent years, are uncertain factors in the control performed by power system stabilization systems. In such situations, there is a need for a method to appropriately set control variables (e.g., load control variables, generator control variables) so that the power system frequency does not deviate from the target frequency even when system disturbances occur.

An object of one aspect of the present disclosure is to provide a power system stabilization device that can maintain the frequency of a power system within a target frequency range after a system disturbance.

According to one embodiment, a system stabilization device for a power system connected to multiple generators and multiple loads is provided. The system stabilization device includes a frequency prediction unit that predicts the system frequency of the power system, and a controlled variable setting unit that sets a controlled variable to be disconnected from the power system. The frequency prediction unit predicts a second system frequency at a second timing, which occurs a specified time after the first timing, based on a first system frequency at a first timing. The controlled variable setting unit calculates a first total mechanical input value to the multiple generators at the first timing based on a first total output value of the multiple generators at the first timing and an equation of motion for the multiple generators. It calculates a second total output value of the multiple generators at the second timing based on the first and second system frequencies, the first total output value, and load frequency characteristic coefficients for the multiple loads. It sets the controlled variable based on the second total mechanical input value to the multiple generators at the second timing, which is estimated from the first total mechanical input value, and the second total output value.

According to this disclosure, the frequency of the power grid can be maintained within a target frequency range after a grid disturbance.

1 is a diagram showing an overall configuration of a power grid stabilization system according to a first embodiment. FIG. 2 is a block diagram showing an example of a hardware configuration of an accident detection terminal device. FIG. 10 is an image diagram for explaining an example of the effect of embodiment 1. FIG. 10 is an image diagram for explaining another example of the effect according to the first embodiment. 1 is a block diagram showing an example of a functional configuration of a power system stabilizing device according to a first embodiment; FIG. 10 is a diagram showing an overall configuration of a power grid stabilization system according to a second embodiment. FIG. 10 is a diagram for explaining an equivalent load model. FIG. 10 is a diagram for explaining the frequency characteristics of the total output value of renewable energy power sources. FIG. 11 is a block diagram showing an example of a functional configuration of a power system stabilizing device according to a second embodiment.

Embodiments of the present disclosure will be described below with reference to the drawings. In the following description, identical components are designated by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated.

Embodiment 1.
<Overall structure>
Fig. 1 is a diagram showing the overall configuration of a power system stabilization system 1000 according to a first embodiment. Referring to Fig. 1, the power system stabilization system 1000 includes a fault detection terminal device 10, a power system stabilization device 15, and load control terminal devices 21 to 2n (hereinafter also referred to as "load control terminal device 20"). When the plant is operating normally, the plant control devices GA1C to GAnC control the input amounts of the generators GA1 to GAn in a direction such that the output of the generators GA1 to GAn is increased when the frequency of the power system 120 (hereinafter also referred to as "power system frequency") decreases, and the output of the generators GA1 to GAn is decreased when the power system frequency increases.

The multiple generators GA1 to GAn installed in the power plant 100 are connected to the power grid 120 via a bus BA and a transmission line 80. Electric power from the multiple generators GA1 to GAn is supplied to the power grid 120.

The power plant 100 is equipped with multiple generators GA1 to GAn (hereinafter collectively referred to as "generators GA") whose output is individually controlled by corresponding plant control devices. Specifically, the output of generator GA1 is controlled by plant control device GA1C, and the output of generator GAn is controlled by plant control device GAnC.

Each of the generators GA1 to GAn is connected to the bus BA via a corresponding transformer and a corresponding circuit breaker. Specifically, the generator GA1 is connected to the bus BA via the transformer MTr1 and the circuit breaker CB1. The generator GAn is connected to the bus BA via the transformer MTrn and the circuit breaker CBn.

A plurality of loads L1, L2, ... Ln (hereinafter collectively referred to as "loads L") are connected to the power system 120. Each load L is disconnected from the power system 120 under the control of a corresponding load control terminal device. Specifically, load L1 is disconnected from the power system 120 under the control of load control terminal device 21, load L2 under the control of load control terminal device 22, and load Ln under the control of load control terminal device 2n. Note that each load L may also be connected to the power system 120 under the control of a corresponding load control terminal device.

The grid stabilization device 15 is configured to be able to communicate with each load control terminal device 20 and receives the load amount of the corresponding load L from each load control terminal device 20 as measurement information. The grid stabilization device 15 transmits a command signal to the load control terminal device 20 to disconnect the load from the power grid 120.

A current transformer that measures current is provided at the sending end of each transformer corresponding to generators GA1 to GAn. Specifically, a current transformer CT1 that measures the sending end output current of generator GA1 is provided at the sending end of transformer MTr1 corresponding to generator GA1. A current transformer CTn that measures the sending end output current of generator GAn is provided at the sending end of transformer MTrn corresponding to generator GAn. In addition, a voltage transformer PT that measures the bus voltage is provided at bus BA.

The power plant 100 is equipped with a fault detection terminal device 10. The outputs of the current transformers CT1 to CTn and the output of the potential transformer PT are individually input to the fault detection terminal device 10. The fault detection terminal device 10 also individually receives signals indicating the open/closed state of the circuit breakers CB1 to CBn (hereinafter also referred to as "open/close signals").

Each plant control device detects plant faults (e.g., failures in the boiler, turbine, multiple valves, etc. in the plant control device, or generator failures). If each plant control device detects a plant fault, it outputs a tripping command (i.e., an opening command) to the corresponding circuit breaker.

Alternatively, a transmission line protection relay (not shown) installed on the transmission line 80 outputs a tripping command to each circuit breaker when it detects a fault on the transmission line 80 based on the current value detected by the current detector (for example, when the current value is equal to or greater than a specified value).

When a circuit breaker opens due to a power line accident, plant failure, etc., the corresponding generator is disconnected from the power grid 120. In the following description, disconnecting a generator from the power grid 120 is also referred to as "the generator dropping out." For example, when circuit breaker CB1 opens, generator GA1 is disconnected from the power grid 120 (i.e., generator GA1 drops out).

Signals indicating the open/closed state of circuit breakers CB1 to CBn are transmitted from the fault detection terminal device 10 to the grid stabilization device 15 at predetermined intervals. Based on the open/close signals of circuit breakers CB1 to CBn, the grid stabilization device 15 determines whether generators GA1 to GAn have tripped. Specifically, if circuit breaker CB1 is open, the grid stabilization device 15 determines that generator GA1 has tripped, and if circuit breaker CB1 is closed, it determines that generator GA1 has not tripped.

The fault detection terminal device 10 calculates the active power values output from each of the generators GA1-GAn based on the current values from the current transformers CT1-CTn and the voltage value from the voltage transformer PT. The calculated active power values are transmitted to the grid stabilization device 15 at predetermined intervals. This allows the grid stabilization device 15 to constantly monitor the active power values output from each generator. The fault detection terminal device 10 may also transmit electrical quantity (e.g., current, voltage) information input from the current transformers CT1-CTn and the voltage transformer PT to the grid stabilization device 15 as measurement information.

The system stabilization device 15 receives the output active power value of each generator GA1 to GAn as measurement information from the fault detection terminal device 10, and also receives tripping information indicating whether each generator GA has tripped. Note that the mechanical input value to each generator GA1 to GAn corresponds to the output active power value when each generator GA has not tripped and the system is not fluctuating. Typically, the tripping information is an opening/closing signal for each circuit breaker CB.

The system stabilization device 15 also receives from each of the load control terminal devices 21-2n measurement information indicating the load amount of the corresponding load and drop information indicating whether the corresponding load has dropped. Typically, the drop information is a signal indicating the connection status between each load monitored by each load control terminal device 21-2n and the power system 120. The system stabilization device 15 determines whether loads L1-Ln have dropped based on each drop information. For example, when the system stabilization device 15 receives drop information from the load control terminal device 21 indicating that load L1 has been disconnected, it determines that load L1 has dropped.

When a system disturbance occurs in the power system 120, the system frequency fluctuates. For example, if a generator trips from the power system 120, the system frequency drops. In this case, the system stabilization device 15 sets the load control amount to be disconnected (i.e., shedding) from the power system 120 so that the minimum value of the frequency of the power system 120 after the generator trips (hereinafter also referred to as the "bottom frequency") falls within the target frequency range.

Specifically, the grid stabilization device 15 predicts the grid frequency after a generator trips. Then, the grid stabilization device 15 sets the load control amount so that the predicted grid frequency falls within the target frequency range.

Typically, the grid stabilization device 15 selects a load corresponding to the load control amount from among the loads L1 to Ln based on a preset priority order, and outputs a command signal to the corresponding load control terminal device 21 to 2n to shedding that load. Note that this is one example of a method for setting the load control target in the grid stabilization device 15, and other methods may also be used to select the load.

After a generator trips, the grid stabilization device 15 constantly performs grid frequency prediction processing, allowing it to set an appropriate load control amount according to the grid frequency. As a result, when a frequency drop occurs after a grid disturbance, the grid frequency is maintained within the target frequency range. In other words, grid stabilization is achieved.

On the other hand, if a load is dropped from the power grid 120, the system frequency will rise. In this case, the power grid stabilization device 15 sets the generator control amount to be disconnected (i.e., shut off) from the power grid 120 so that the maximum frequency of the power grid 120 after the load drop (hereinafter also referred to as the "top frequency") falls within the target frequency range.

Specifically, the grid stabilization device 15 predicts the grid frequency after load drop. Then, the grid stabilization device 15 sets the generator control variable so that the predicted grid frequency falls within the target frequency range.

Typically, the grid stabilization device 15 selects a generator from among the generators GA1 to GAn corresponding to the generator control amount based on a preset priority order, and outputs a command signal to shut off that generator to the fault detection terminal device 10. Note that this is one example of a method for setting the generator control target in the grid stabilization device 15, and generators may be selected using other methods. The fault detection terminal device 10 outputs a shutoff command to the circuit breaker CB in accordance with the command signal.

The grid stabilization device 15 constantly performs grid frequency prediction processing after load drop, allowing it to set appropriate generator control variables according to the grid frequency. As a result, when the frequency increases after a grid disturbance, the grid frequency is maintained within the target frequency range. In other words, grid stabilization is achieved.

<Hardware configuration>
(Accident detection terminal device)
Fig. 2 is a block diagram showing an example of the hardware configuration of the accident detection terminal device 10. Referring to Fig. 2, the accident detection terminal device 10 includes an auxiliary transformer 32, an A/D conversion unit 35, an arithmetic processing unit 40, a communication circuit 50, a digital output circuit (D/O: Digital Output) 55, and a digital input circuit (D/I: Digital Input) 56.

The auxiliary transformer 32 takes in electrical quantities from the current transformer and voltage transformer, converts them into voltages suitable for signal processing in the relay's internal circuitry, and outputs them. The A/D conversion unit 35 takes in the voltage output from the auxiliary transformer 32 and converts it into digital data. Specifically, the A/D conversion unit 35 includes an analog filter, a sample-and-hold circuit, a multiplexer, and an A/D converter.

The analog filter removes high-frequency noise components from the current waveform signal output from the auxiliary transformer 32. The sample-and-hold circuit samples the current waveform signal output from the analog filter at a sampling period. Based on a timing signal input from the arithmetic processing unit 40, the multiplexer sequentially switches the waveform signals input from the sample-and-hold circuit in time series and inputs them to the A/D converter. The A/D converter converts the waveform signals input from the multiplexer from analog data to digital data. The A/D converter outputs the digitally converted waveform signals to the arithmetic processing unit 40.

The arithmetic processing unit 40 includes a CPU (Central Processing Unit) 41, a RAM (Random Access Memory) 42, and a ROM (Read Only Memory) 43. These elements are interconnected via a bus 44. The arithmetic processing unit 40 may also include electrically rewritable non-volatile memory such as flash memory or hardware.

The communication circuit 50 communicates with an external device (e.g., the power system stabilization device 15). The communication circuit 50 communicates with the external device in accordance with a specified protocol.

The digital output circuit 55 is an interface circuit for outputting signals to external devices. For example, the digital output circuit 55 may output a breaker command to a circuit breaker in accordance with a command from the CPU 41. The digital input circuit 56 receives, for example, an open/close signal from the circuit breaker indicating the open/close state of the circuit breaker.

(System stabilization device, load control terminal device)
The hardware configuration of the power system stabilizing device 15 and the load control terminal device 20 may be the same as that of the fault detection terminal device 10. Alternatively, the power system stabilizing device 15 and the load control terminal device 20 may have a configuration including hardware equivalent to the arithmetic processing unit 40 and the communication circuit 50 in FIG.

<Load control amount setting process>
A description will now be given of the load control amount setting process executed by the grid stabilization device 15. Here, it is assumed that at time t0, the generator trips and the grid frequency drops.

At time t1 after the generator trips, the grid stabilization device 15 executes a process to predict the grid frequency at time t2, a specified time after time t1. Here, time t1 is the timing when the control calculation for setting the load control amount begins. Time t2 is the timing when load control is performed using the set load control amount (i.e., the load corresponding to the load control amount is shedding).

Typically, the frequency deviation between the reference frequency Fn [Hz] and the system frequency F(t1) [Hz] at time t1 is defined as ΔF(t1), and the system stabilization device 15 calculates ΔF EST (t2), which is an estimate of the frequency deviation between the reference frequency Fn and the system frequency F(t2) at time t2, using _{the following equation} (1):

The system frequency F(t1) is calculated, for example, from the voltage of the bus BA detected by the potential transformer PT at time t1. F(t1) = Fn + ΔF(t1) holds. The system stabilization device 15 can predict the system frequency F(t2) (i.e., F(t2) = Fn + ΔF _EST (t2)) using the frequency deviation ΔF _EST (t2) calculated from equation (1).

The rate of change of the frequency deviation used in equation (1) may be simply estimated from time-series data of the grid frequency. Furthermore, although equation (1) calculates the estimated value of the frequency deviation (i.e., ΔF _EST (t2)) as a linear function of time, it may be configured to calculate the estimated value as a more complex function, including a quadratic function, by using more time-series data.

The total inertia constant of the multiple generators GA1 to GAn connected to the power system 120 is M [s], the total output value of each generator GA1 to GAn (i.e., the total value of the output active power values) is P _E [pu], and the total mechanical input value to each generator GA1 to GAn is P _M [pu]. The total inertia constant M is an equivalent inertia constant when the multiple generators GA1 to GAn are considered as a single generator. In this case, from the equation of motion of the multiple generators GA1 to GAn (for example, the equation of motion when the multiple generators GA1 to GAn are considered as a single generator), the total mechanical input value P _M (t1) at time t1 is calculated using the total output value P _E (t1) according to the following equation (2): The total output value P _E (t1) is the total value of the active power values output from each generator at time t1.

If one of the multiple generators GA1 to GAn (for example, generator GAx) trips, the remaining generators will increase their output power due to the characteristics of their governors. However, because the governors have a control system delay, there is a time delay before the output power from the generators changes even when the frequency changes.

Here, it is assumed that the time from time t1, which is the control calculation timing, to time t2, which is the control implementation timing, is short, and therefore changes due to governor control of the generator GA can be ignored. In this case, the total mechanical input value _PM (t1) at time t1 is equal to the total mechanical input value _PM (t2) at time t2, and therefore the following equation (3) holds.

If losses in the lines, etc. are ignored, the total output value P _E and the total load value P _L of each load L are balanced. Furthermore, since the losses are sufficiently small compared to the total output value, it can be assumed that "P _E = P _L ". Furthermore, the frequency deviation between the reference frequency Fn of the power system 120 and the system frequency F (i.e., ΔF = F - Fn) is defined as ΔF, and the initial value of the total load value P _L is defined as P _L0 [pu]. In this case, the total load value P _L is expressed as "P _L0 (1 + K _L ΔF)" using ΔF, P _L0 , and the load frequency characteristic coefficient K _L [pu/Hz]. Therefore, the relationship between the total output value P _E (t1) and the total output value P _E (t2) is expressed as shown in the following equation (4). The load frequency characteristic coefficient K _L is an equivalent frequency characteristic coefficient when a plurality of loads L are regarded as one load, and is stored in advance in the memory of the power system stabilization device 15 .

Then, when the load control amount for eliminating the imbalance between supply and demand at time t2 is P _LCS [pu], the load control amount P _LCS is calculated using the following equation (5).

_kv is an adjustment coefficient for avoiding insufficient control due to voltage changes or the like during load control, and is stored in advance in the memory of the power system stabilization device 15.

The system stabilizing device 15 outputs a command signal to the corresponding load control terminal device 20 to shed the load corresponding to the load control amount P _LCS calculated by the formula (5).

Figure 3 is an image diagram illustrating an example of the effect of embodiment 1. Referring to Figure 3, graph 301 shows the change in frequency over time when control corresponding to the load control amount set based on the series of processes described above is implemented (i.e., the load control amount is blocked). Graph 302 shows the change in frequency over time when this control is not implemented.

Referring to graph 301, the generator trips at time t0, causing the grid frequency to drop. At time t1 after the generator trips, the grid stabilization device 15 predicts the grid frequency F(t2) at time t2, a specified time after time t1.

Here, it is assumed that the power system stabilizing device 15 determines that the power system frequency F(t2) is less than the threshold value Fth1. In this case, the power system stabilizing device 15 executes a process of calculating a total mechanical input value _PM (t1) using equation (1), a process of calculating a total output value _PE (t2) using equation (4), and a process of setting a load control amount _PLCS using equation (5). The power system stabilizing device 15 outputs a command signal to the corresponding load control terminal device 20 to shed a load equivalent to the load control amount _PLCS calculated by equation (5). At time t2, the shed of the load equivalent to the load control amount _PLCS is executed.

From this, it can be seen from graph 301 that the bottom frequency Fsbt after the generator trips is within the target frequency range (i.e., greater than or equal to Fth1 and less than or equal to Fn). Similarly, the finishing frequency Fse is also within the target frequency range.

On the other hand, looking at graph 302, which shows the case where the load control variable was not shut off, the finished frequency Fce after the generator tripped is within the target frequency range, but the bottom frequency Fcbt is not within the target frequency range.

In this way, the grid stabilization device 15 according to embodiment 1 can keep the grid frequency within the target frequency range after a generator trip by shedding the load corresponding to the appropriate load control amount at the appropriate timing.

<Generator control variable setting process>
A description will be given of the process for setting the generator control amount executed by the system stabilization device 15. Here, it is assumed that the load drops at time t0 and the system frequency increases.

The processing flow for equations (1) to (4) described in <Load control amount setting process> is basically the same.

Specifically, at time t1 after load drop, the grid stabilization device 15 executes a process to predict the grid frequency at time t2, a specified time after time t1. Here, time t1 is the timing for executing a control calculation to set the generator control variable, and time t2 is the timing for implementing control using the set generator control variable (i.e., for shutting off the generator corresponding to the generator control variable).

The grid stabilization device 15 calculates an estimated value ΔF _EST (t2) of the frequency deviation at time t2 using equation (1). The grid stabilization device 15 calculates a total mechanical input value P _M (t1) at time t1 using equation (2). Even in the case of load drop, if it is assumed that changes due to governor control of the generator GA can be ignored, equation (3) holds. The grid stabilization device 15 calculates a total output value P _E (t2) using equation (4).

Then, when the generator control amount for eliminating the supply and demand imbalance at time t2 is P _GCS [pu], the generator control amount P _GCS is calculated using the following equation (6).

Figure 4 is an image diagram illustrating another example of the effect according to embodiment 1. Referring to Figure 4, graph 401 shows the change in frequency over time when control corresponding to the generator control amount set based on the series of processes described above is implemented (i.e., the generator control amount is shut off). Graph 402 shows the change in frequency over time when this control is not implemented.

Referring to graph 401, the load is dropped at time t0, causing the system frequency to increase. At time t1 after the load is dropped, the system stabilization device 15 predicts the system frequency F(t2) at time t2, a specified time after time t1.

Here, it is assumed that the system stabilization device 15 determines that the system frequency F(t2) is greater than the threshold value Fth2. In this case, the system stabilization device 15 executes a process of calculating a total mechanical input value _PM (t1) using equation (1), a process of calculating a total output value _PE (t2) using equation (4), and a process of setting a generator control amount _PGCS using equation (6). The system stabilization device 15 outputs a command signal to shut off the generator corresponding to the generator control amount _PGCS calculated by equation (6) to the fault detection terminal device 10. At time t2, the shutdown of the generator corresponding to the generator control amount _PGCS is executed.

From this, it can be seen from graph 401 that the top frequency Fstp after load drop is within the target frequency range (i.e., above Fn and below Fth2). Similarly, the finishing frequency Fse is also within the target frequency range.

On the other hand, looking at graph 402, which shows the case where the generator control variable was not shut off, the finished frequency Fce after load drop is within the target frequency range, but the top frequency Fctp is not within the target frequency range.

In this way, the grid stabilization device 15 according to embodiment 1 can keep the grid frequency within the target frequency range after load drop by shutting off the generator corresponding to the appropriate generator control variable at the appropriate timing.

<Functional configuration>
Fig. 5 is a block diagram showing an example of a functional configuration of the power grid stabilizing device according to the first embodiment. Referring to Fig. 5, the power grid stabilizing device 15 includes an information receiving unit 201, a frequency predicting unit 203, a controlled variable setting unit 205, and a command transmitting unit 207. Typically, these functions are realized by a CPU of the power grid stabilizing device 15 executing a program, but may also be realized by a dedicated hardware circuit.

The information receiving unit 201 receives various types of information from the fault detection terminal device 10 and the load control terminal device 20. For example, the information receiving unit 201 receives from the fault detection terminal device 10 electrical quantity information detected by the current transformers CT1 to CTn and the voltage transformer PT, the output active power values of each generator GA1 to GAn, and dropout information. The information receiving unit 201 also receives the load quantity and dropout information of the corresponding load L from each load control terminal device 20.

The frequency prediction unit 203 predicts a future system frequency based on a system frequency calculated from the voltage of the bus BA. Specifically, the frequency prediction unit 203 predicts a second system frequency (e.g., system frequency F(t2)) at a second timing (e.g., time t2) after a specified time has elapsed from a first timing (e.g., time t1) based on a first system frequency (e.g., system frequency F(t1)) at a first timing (e.g., time t1) using equation (1). For example, the frequency prediction unit 203 predicts the system frequency F(t2) (=Fn+ΔF _ES (t2)) using equation (1).

The controlled variable setting unit 205 receives input of measurement information, setting information, and the prediction result of the frequency prediction unit 203, and sets the controlled variable to be disconnected from the power grid 120. The setting information includes the total inertia constant M of the multiple generators GA, the reference frequency Fn, the load frequency characteristic coefficient _KL , and the adjustment coefficient _kv . The setting information is pre-stored in the memory of the power grid stabilization device 15. The controlled variable setting unit 205 may also receive input of dropout information.

The control amount setting unit 205 calculates a total mechanical input value _PM (t1) at time t1 based on the total output value _PE (t1) of the multiple generators GA at time t1 and the equation of motion of the multiple generators GA. For example, the control amount setting unit 205 calculates the total mechanical input value _PM (t1) using equation (2).

The controlled variable setting unit 205 calculates the total output value P _E (t2) of the multiple generators GA at time t2 based on the system frequencies F(t1) and F(t2), the total output value P _E (t1), and the load frequency characteristic coefficient K _L. For example, the controlled variable setting unit 205 calculates the total output value P _E (t2) using equation (4).

The control variable setting unit 205 sets the control variable based on the total mechanical input value _PM (t2) at time t2 estimated from the total mechanical input value _PM (t1) and the total output value _PE (t2). For example, the control variable setting unit 205 sets the load control variable _PLCS using equation (5). Alternatively, the control variable setting unit 205 sets the generator control variable _PGCS using equation (6). Typically, the total mechanical input value _PM (t1) and the total mechanical input value _PM (t2) are equal, as shown in equation (3).

In one aspect, when the system frequency F(t2) is less than a first threshold (e.g., threshold Fth1), the controlled variable setting unit 205 executes a series of processes including a first process of calculating a total machine input value P _M (t1), a second process of calculating a total output value P _E (t2), and a third process of setting a load controlled variable P _LCS to be disconnected from the power grid 120. The specified time from the first timing to the second timing is set to be equal to or longer than the time from the start of the series of processes to the time when the load corresponding to the load controlled variable is disconnected from the power grid 120. As a result, the load corresponding to the load controlled variable is in a disconnected state at the second timing.

In another aspect, when the grid frequency F(t2) is greater than a second threshold value (e.g., threshold value Fth2), the controlled variable setting unit 205 executes a series of processes including a first process of calculating a total machine input value _PM (t1), a second process of calculating a total output value _PE (t2), and a third process of setting a generator controlled variable _PGCS to be disconnected from the power grid 120. In this case, the specified time is set to be equal to or longer than the time from the start of the series of processes until the generator corresponding to the generator controlled variable is disconnected from the power grid 120. As a result, the generator corresponding to the generator controlled variable is shut off at the second timing.

The command transmission unit 207 transmits a command signal to the load control terminal device 20 to disconnect a load corresponding to the set load control amount from the power grid 120. The load control terminal device 20 disconnects the corresponding load L from the power grid 120 in accordance with the command signal. In another aspect, the command transmission unit 207 transmits a command signal to the fault detection terminal device 10 to disconnect a generator corresponding to the set generator control amount from the power grid 120. The fault detection terminal device 10 disconnects the corresponding generator GA from the power grid 120 in accordance with the command signal.

Embodiment 2.
In the above-described first embodiment, a configuration has been described in which a plurality of generators and a plurality of loads are connected to the power system 120. In the second embodiment, a configuration will be described in which a plurality of renewable energy power sources are further connected to the power system 120.

Figure 6 is a diagram showing the overall configuration of a grid stabilization system 1000A according to embodiment 2. Referring to Figure 6, the grid stabilization system 1000A differs from the grid stabilization system 1000 of Figure 1 in that renewable energy power sources ER1 to ERn are further connected to the power grid 120. The differences from the grid stabilization system 1000 are described below.

A plurality of renewable energy power sources ER1, ER2, ... ERn (hereinafter collectively referred to as "renewable energy power sources ER") are connected to the power grid 120. In embodiment 2, each renewable energy power source ER is disconnected from the power grid 120 by control of the corresponding load control terminal device.

Specifically, renewable energy power source ERn is disconnected from the power grid 120 under the control of load control terminal device 2n. Furthermore, the power grid stabilization device 15 receives the output amount (e.g., active power value) of the corresponding renewable energy power source ER from each load control terminal device 20 as measurement information. Each renewable energy power source ER may be connected to the power grid 120 under the control of the corresponding load control terminal device. Furthermore, the load control terminal device 20 may be configured to be able to individually control the connection and disconnection between each of the load L and renewable energy power source ER and the power grid 120.

The grid stabilization device 15 also receives disconnection information from each of the load control terminal devices 21-2n, indicating whether the corresponding renewable energy power source ER has disconnected. Based on each disconnection information, the grid stabilization device 15 determines whether the renewable energy power sources ER1-ERn have disconnected.

Note that each renewable energy power source ER may be disconnected from or connected to the power grid 120 under the control of a corresponding power control terminal device (not shown). In this case, the power grid stabilization device 15 is configured to be able to communicate with each power control terminal device.

In embodiment 2, we consider an equivalent load model that combines a load L and a renewable energy power source ER.

7 is a diagram illustrating an equivalent load model. Referring to FIG. 7, the equivalent load amount P _LE of the equivalent load LE, which is a combination of each load L and each renewable energy power source ER, corresponds to the sum of the load amounts P _L of each load L minus the total output value P _ER of the renewable energy power sources ER (i.e., P _LE = P _L - P _ER ). In the second embodiment, the equivalent load amount P _LE is assumed to be positive. In other words, the total load amount P _L is assumed to be greater than the total output value P _ER .

Referring again to FIG. 6, the grid stabilization device 15 replaces the load in embodiment 1 with an "equivalent load" and performs various processes. For example, if a generator drops out of the power grid 120, the grid frequency drops. Therefore, the grid stabilization device 15 sets a control amount for the equivalent load LE (e.g., equivalent to the load reduction amount of the equivalent load) so that the bottom frequency of the power grid 120 after the generator drops out is within the target frequency range.

Based on a preset priority order, the grid stabilization device 15 selects a load corresponding to the equivalent load control amount from among the loads L1 to Ln and outputs a command signal to the corresponding load control terminal device 21 to 2n to shedding that load. Alternatively, the grid stabilization device 15 may select a renewable energy power source corresponding to the equivalent load control amount from among multiple renewable energy power sources ER1 to ERn based on a preset priority order and output a command signal to that renewable energy power source to cause that renewable energy power source to perform a discharge operation (e.g., an operation to control power in the discharge direction). Alternatively, the grid stabilization device 15 may be configured to select a load and renewable energy power source corresponding to the equivalent load control amount, shedding that load, and causing that renewable energy power source to perform a discharge operation.

On the other hand, for example, when a part of the equivalent load LE (for example, equivalent load LEx) is dropped from the power grid 120, the system frequency increases. In the second embodiment, the dropout of the equivalent load LEx means that the equivalent load LEx having a positive equivalent load amount P _LEX is dropped. When the equivalent load amount P _LEX is positive, the load amount of the load L at the equivalent load LEx is greater than the output amount of the renewable energy power source ER at the equivalent load LEx.

The grid stabilization device 15 sets the generator control variable to be disconnected from the grid 120 so that the top frequency of the grid 120 after equivalent load drop falls within the target frequency range. Based on a preset priority, the grid stabilization device 15 selects a generator from generators GA1 to GAn that corresponds to the generator control variable, and outputs a command signal to shut off that generator to the fault detection terminal device 10. The fault detection terminal device 10 outputs a shutoff command to circuit breaker CB in accordance with the command signal.

<Equivalent Load Control Amount Setting Process>
The flow of the process of setting the equivalent load control amount when a system disturbance occurs (for example, when a generator trips) is basically the same as the process flow described in <Load control amount setting process> in embodiment 1. First, in the process of setting the equivalent load control amount, the process flow of equations (1) to (3) is the same.

As described above, the equivalent load is a combination of multiple loads L and multiple renewable energy power sources ER. Therefore, in the process of setting the equivalent load control amount, the load frequency characteristic coefficient _KL in equation (4) is replaced with the equivalent load frequency characteristic coefficient _KLE [pu/Hz] for the equivalent load, and the load control amount _PLCS in equation (5) is replaced with the equivalent load control amount _PLECS [pu]. A method for calculating the equivalent load frequency characteristic coefficient _KLE will be described below.

Let P _LE (t) be the change over time in the equivalent load amount P _LE [pu], P _LE0 [pu] be the initial value of the equivalent load amount P _LE , P _L (t) be the change over time in the total load amount of each load L (i.e., the total load amount P _L [pu]), P _L0 [pu] be the initial value of the total load amount P _L , P _ER (t) be the change over time in the total output amount of each renewable energy power source ER (i.e., the total output amount P _ER [pu]), and ΔF(t) be the change over time in the frequency deviation ΔF [Hz]. In this case, the following equation (7) holds:

P _LE0 is calculated based on the load amount of each load L and the output amount of each renewable energy power source ER as measurement information in an initial state (for example, before the occurrence of a grid disturbance and when ΔF is 0). The frequency deviation ΔF is the frequency deviation between the reference frequency Fn of the power grid 120 and the grid frequency F (i.e., ΔF = F - Fn).

Here, assume that the total output value P _ER does not have frequency characteristics. In this case, the total output value P _ER (t) becomes P _ER0 , which is the initial value of the total output value P _ER . That is, P _ER (t) = P _ER0 holds. Furthermore, as explained in FIG. 7, the equivalent load P _LE corresponds to the total load value P _L minus the total output value P _ER , so the following equation (8) holds.

Therefore, when the relational expression "P _ER (t)=P _ER0 " and the expression (8) are used in the expression (7), the equivalent load frequency characteristic coefficient K _LE is calculated by the following expression (9).

Next, it is assumed that the total output value P _ER has frequency characteristics _, for example, as shown in FIG.

8 is a diagram illustrating the frequency characteristics of the total output value of renewable energy power sources. Referring to FIG. 8, the horizontal axis represents the frequency deviation ΔF. The vertical axis represents the deviation ΔP _ER between the total output value P _ER and its initial value P _ER0 (i.e., ΔP _ER =P _ER -P _ER0 ).

It can be understood that when the frequency deviation ΔF is within a reference range (for example, -ΔF _X ≦ ΔF ≦ ΔF _X ), the deviation ΔP _ER is 0, and therefore the total output value P _ER does not change. The reference range corresponds to a dead band in which the total output value P _ER does not change. From this, the total output value P _ER does not have frequency characteristics when the frequency deviation ΔF is within the reference range, and has frequency characteristics when the frequency deviation ΔF is outside the reference range.

Therefore, when the frequency deviation ΔF is within the reference range, the output total value P _ER does not change (i.e., P _ER =P _ER0 holds), and therefore the equivalent load frequency characteristic coefficient K _LE is expressed as in the above-mentioned equation (9).

On the other hand, when the frequency deviation ΔF is larger than "ΔF _X ", P _ER (t) is expressed by the following equation (10), and when the frequency deviation ΔF is smaller than "-ΔF _X ", P _ER (t) is expressed by the following equation (11). K _ER is an equivalent frequency characteristic coefficient when multiple renewable energy power sources ER are regarded as one renewable energy power source, and is stored in advance in the memory of the power system stabilization device 15.

Therefore, by substituting equations (8) and (10) into equation (7), the equivalent load frequency characteristic coefficient K _LE when the frequency deviation ΔF is larger than “ΔF _X ” is expressed by the following equation (12).

Similarly, when equations (8) and (11) are applied to equation (7), the equivalent load frequency characteristic coefficient K _LE when the frequency deviation ΔF is smaller than "-ΔF _X " is expressed by the following equation (13).

By using the equivalent load frequency characteristic coefficient _KLE calculated by equations (9), (12), and (13) in the following equation (14), which is a modification of equation (4), an appropriate total output value P _E (t2) is calculated that takes into account the frequency characteristics of the equivalent load including the load and renewable energy power source. K _LE (t1) in equation (14) is _{KLE calculated when ΔF in equations (12) and (13) is replaced with "ΔF(t1)". K LE (} t2) in equation (14) is _KLE calculated when ΔF in equations (12) and (13) is replaced with "ΔF(t2)".

By applying the output total value P _E (t2) obtained by equation (14) to the equation in which "P _LCS " in equation (5) is replaced with "P _LECS ", it is possible to obtain the equivalent load control amount P _LECS required to keep the system frequency within the target frequency range after the tripping of the generator.

<Generator control variable setting process>
The flow of the process for setting the generator control variables when a system disturbance occurs (for example, when an equivalent load drops) is basically the same as the process flow described in <Generator Control Variable Setting Process> in Embodiment 1. First, in the process for setting the generator control variables, the flow of the processes of equations (1) to (3) is the same. Second, the method for calculating the equivalent load frequency characteristic coefficient K _LE and the use of equation (14) to calculate the output total value P _E (t2) are also the same.

Therefore, by applying the total output value P _E (t2) obtained by equation (14) to equation (6), it is possible to obtain the generator control amount P _GCS required to keep the system frequency within the target frequency range after the equivalent load drop (for example, after the equivalent load LEx drops).

<Functional configuration>
Fig. 9 is a block diagram showing an example of a functional configuration of a power system stabilizing device according to embodiment 2. Referring to Fig. 9, the power system stabilizing device 15 according to embodiment 2 corresponds to a configuration in which a coefficient calculation unit 209 is added to the power system stabilizing device 15 according to embodiment 1. The functions of the information receiving unit 201 and the frequency predicting unit 203 are similar to the functions described in Fig. 5.

The coefficient calculation unit 209 accepts input of measurement information and setting information and calculates an equivalent load frequency characteristic coefficient _KLE for the equivalent load LE. The setting information includes a reference frequency Fn, frequency characteristic coefficients _KG , _KL , _KER , etc. Specifically, the coefficient calculation unit 209 calculates the equivalent load frequency characteristic coefficient KLE based on the load amount total value _PLO of the multiple loads L and the output total value _PER0 of the multiple renewable energy power sources ER at an initial point in time before the first timing, and the load frequency characteristic coefficient _{KL .} The initial point in time is a point in time before a grid disturbance, such as a point in time before the generator GAx drops out of the power grid 120 or a point in time before the equivalent load LEx drops out of the power grid 120.

In one aspect, when the total output value P _ER does not have a frequency characteristic, the coefficient calculation unit 209 calculates the equivalent load frequency characteristic coefficient K _LE using equation (9). Alternatively, when the total output value P _ER has a frequency deviation ΔF within a reference range (e.g., −ΔF _X ≦ ΔF ≦ ΔF _X ), the coefficient calculation unit 209 calculates the equivalent load frequency characteristic coefficient K _LE using equation (9).

In another aspect, the coefficient calculation unit 209 calculates an equivalent load frequency characteristic coefficient K LE based on the total load value P _L0 and the total output value P _ER0 at the initial point in time, a load frequency characteristic coefficient K _L , frequency characteristic coefficients K _ER for the plurality of renewable energy power sources _ER , the frequency deviation ΔF, and the reference range.

Specifically, when the frequency deviation ΔF is larger than the upper limit value "ΔF _X " of the reference range, the coefficient calculation unit 209 calculates the equivalent load frequency characteristic coefficient K _LE using equation (12). When the frequency deviation ΔF is smaller than the lower limit value "-ΔF _X " of the reference range, the coefficient calculation unit 209 calculates the equivalent load frequency characteristic coefficient K _LE using equation (13).

The controlled variable setting unit 205 calculates the total output value P _E (t2) based on the system frequency F(t1), the system frequency F(t2), the total output value P _E (t1), and the equivalent load frequency characteristic coefficient K _LE . For example, the controlled variable setting unit 205 calculates the total output value P _E (t2) using equation (14).

The command transmission unit 207 transmits a command signal to the load control terminal device 20 to disconnect a load corresponding to the set equivalent load control amount from the power grid 120. The command transmission unit 207 may also transmit a command signal to the load control terminal device 20 to instruct a renewable energy power source corresponding to the set equivalent load control amount to perform a discharge operation. Furthermore, the command transmission unit 207 may select a load and renewable energy power source corresponding to the equivalent load control amount, and transmit a command signal to the corresponding load control terminal device 20 to disconnect the load and cause the renewable energy power source to perform a discharge operation.

In another aspect, the command transmission unit 207 transmits a command signal to the fault detection terminal device 10 to disconnect the generator corresponding to the set generator control amount from the power grid 120.

Other embodiments.
(1) In the above-described embodiment, the power system stabilizing device 15 is configured to receive various pieces of information from the fault detection terminal device 10 and the load control terminal device 20, but is not limited to this configuration. For example, the power system stabilizing device 15 may be configured to store the various pieces of information received from the fault detection terminal device 10 and the load control terminal device 20 in a memory in advance, and to execute the above-described frequency prediction process by using simulation software that can change the various pieces of information as appropriate.

(2) The configurations exemplified as the above-described embodiments are merely examples of the configuration of the present invention, and may be combined with other known technologies. They may also be modified, such as by omitting some parts, without departing from the spirit of the present invention. Furthermore, the above-described embodiments may also be implemented by appropriately adopting the processes and configurations described in other embodiments.

The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications that are equivalent in meaning to and within the scope of the claims.

Various aspects of the present disclosure are summarized below as appendices.
(Appendix 1)
a first system frequency at a first timing based on the first system frequency at the first timing; a second system frequency at a second timing at which a specified time has elapsed since the first timing; a first total mechanical input value to the plurality of generators at the first timing based on a first total output value of the plurality of generators at the first timing and an equation of motion of the plurality of generators; a second total mechanical input value to the plurality of generators at the second timing based on the first system frequency, the second system frequency, the first total output value, and a load frequency characteristic coefficient for the plurality of loads; and a second total mechanical input value to the plurality of generators at the second timing estimated from the first total mechanical input value and the second total output value.

(Appendix 2)
2. The power system stabilization device according to claim 1, wherein, when the second power system frequency is less than a first threshold, the controlled variable setting unit executes a series of processes including a first process of calculating the first mechanical input sum value, a second process of calculating the second output sum value, and a third process of setting the controlled variable, and the controlled variable is a load controlled variable to be disconnected from the power system.

(Appendix 3)
3. The power system stabilization device according to claim 2, wherein the specified time is equal to or longer than the time from the start of the series of processes to the time when the load corresponding to the load control amount is disconnected from the power system.

(Appendix 4)
2. The power grid stabilization device according to claim 1, wherein, when the second power grid frequency is greater than a second threshold value, the controlled variable setting unit executes a series of processes including a first process of calculating the first mechanical input sum value, a second process of calculating the second mechanical output sum value, and a third process of setting the controlled variable, and the controlled variable is a generator controlled variable to be disconnected from the power grid.

(Appendix 5)
5. The grid stabilization device according to claim 4, wherein the specified time is equal to or longer than the time from the start of the series of processes to the time when the generator corresponding to the generator control amount is disconnected from the power grid.

(Appendix 6)
6. The power system stabilization device according to any one of claims 1 to 5, wherein the first mechanical input sum value and the second mechanical input sum value are equal.

(Appendix 7)
The system stabilization device according to any one of Supplementary notes 1 to 6, wherein the control variable setting unit _calculates the second total output value by using the above formula (4), where _ΔF (t1) is a deviation between a reference frequency of the power system and the first system frequency, ΔF _EST (t2) is a deviation between the reference frequency and the second system frequency, K L is the load frequency characteristic coefficient, P _E (t1) is the first total output value, and P E (t2) is the second total output value.

(Appendix 8)
the power grid stabilization device according to any one of Supplementary note 1 to Supplementary note 7, wherein a plurality of renewable energy power sources are further connected to the power grid, and the device further comprises a coefficient calculation unit that calculates an equivalent load frequency characteristic coefficient for an equivalent load that is a combination of the plurality of loads and the plurality of renewable energy power sources, wherein the coefficient calculation unit calculates the equivalent load frequency characteristic coefficient based on a total load amount value of the plurality of loads and a total output value of the plurality of renewable energy power sources at an initial point in time that is before the first timing, and the load frequency characteristic coefficient, and the controlled variable setting unit calculates the second total output value based on the first system frequency and the second system frequency, the first total output value, and the equivalent load frequency characteristic coefficient.

(Appendix 9)
The power system stabilization device according to Supplementary Note 8, wherein when the total output value of the plurality of renewable energy power sources does not have frequency characteristics, and when the load frequency characteristic coefficient is _KL , the coefficient calculation unit calculates the equivalent load frequency characteristic coefficient using the above formula (9).

(Appendix 10)
Supplementary note 9. The power system stabilization device according to Supplementary note 8, wherein the total output value of the plurality of renewable energy power sources does not have frequency characteristics when a frequency deviation between a reference frequency of the power system and the first system frequency is within a reference range, and has frequency characteristics when the frequency deviation is outside the reference range, and the coefficient calculation unit calculates the equivalent load frequency characteristic coefficient based on the total load value and the total output value at the initial point in time, the load frequency characteristic coefficient, frequency characteristic coefficients for the plurality of renewable energy power sources, the frequency deviation, and the reference range.

(Appendix 11)
The power system stabilization device according to Supplementary Note 10, wherein when the load frequency characteristic coefficient is K _L , the frequency characteristic coefficient for the plurality of renewable energy power sources is K _ER , and an upper limit value of the reference range is ΔF _X , if the frequency deviation is larger than the upper limit value of the reference range, the coefficient calculation unit calculates the equivalent load frequency characteristic coefficient using the above formula (12), and when the lower limit value of the reference range is −ΔF _X , if the frequency deviation is smaller than the lower limit value of the reference range, the coefficient calculation unit calculates the equivalent load frequency characteristic coefficient using the above formula (13).

21, 22, 2n Load control terminal device, 10 Fault detection terminal device, 15 System stabilization device, 32 Auxiliary transformer, 35 A/D conversion unit, 40 Arithmetic processing unit, 41 CPU, 44 Bus, 50 Communication circuit, 55 Digital output circuit, 56 Digital input circuit, 80 Transmission line, 100 Power plant, 120 Power system, 201 Information receiving unit, 203 Frequency prediction unit, 205 Control variable setting unit, 207 Command transmission unit, 209 Coefficient calculation unit, 1000, 1000A System stabilization system.

Claims (11)

A system stabilization device for a power system to which a plurality of generators and a plurality of loads are connected,
a frequency prediction unit that predicts a system frequency of the power system;
a control amount setting unit that sets a control amount to be disconnected from the power grid,
the frequency predicting unit predicts a second system frequency at a second timing after a specified time has elapsed from the first timing, based on the first system frequency at the first timing;
The control amount setting unit
calculating a first total mechanical input value to the plurality of generators at the first timing based on a first total output value of the plurality of generators at the first timing and an equation of motion of the plurality of generators;
calculating a second output sum of the plurality of generators at the second timing based on the first system frequency, the second system frequency, the first output sum, and load frequency characteristic coefficients for the plurality of loads;
a power system stabilization device that sets the controlled variable based on a second sum of mechanical inputs to the plurality of generators at the second timing, the second sum of outputs being estimated from the first sum of mechanical inputs. when the second system frequency is less than a first threshold value, the controlled variable setting unit executes a series of processes including a first process of calculating the first mechanical input sum value, a second process of calculating the second mechanical output sum value, and a third process of setting the controlled variable;
The grid stabilization device according to claim 1 , wherein the controlled variable is a load controlled variable that is disconnected from the power grid. The grid stabilization device of claim 2, wherein the specified time is equal to or longer than the time from the start of the series of processes to the time when the load corresponding to the load control amount is disconnected from the power grid. when the second system frequency is greater than a second threshold value, the controlled variable setting unit executes a series of processes including a first process of calculating the first mechanical input sum value, a second process of calculating the second mechanical output sum value, and a third process of setting the controlled variable;
The grid stabilization device according to claim 1 , wherein the controlled variable is a generator controlled variable for disconnecting from the power grid. The grid stabilization device of claim 4, wherein the specified time is equal to or longer than the time from the start of the series of processes to the time when the generator corresponding to the generator control variable is disconnected from the power grid. The power system stabilization device according to any one of claims 1 to 5, wherein the first mechanical input total value and the second mechanical input total value are equal. When the deviation between the reference frequency of the power system and the first system frequency is ΔF(t1), the deviation between the reference frequency and the second system frequency is ΔF _EST (t2), the load frequency characteristic coefficient is K _L , the first output total value is P _E (t1), and the second output total value is P _E (t2), the controlled variable setting unit calculates the second output total value using the following equation (1):

The system stabilization device according to any one of claims 1 to 5. a plurality of renewable energy power sources are further connected to the power grid;
Further provided is a coefficient calculation unit that calculates an equivalent load frequency characteristic coefficient for an equivalent load that combines the plurality of loads and the plurality of renewable energy power sources,
The coefficient calculation unit calculates the equivalent load frequency characteristic coefficient based on a total load amount value of the plurality of loads and a total output value of the plurality of renewable energy power sources at an initial point in time before the first timing, and the load frequency characteristic coefficient;
6. The system stabilization device according to claim 1, wherein the control variable setting unit calculates the second total output value based on the first system frequency, the second system frequency, the first total output value, and the equivalent load frequency characteristic coefficient. When the total output value of the plurality of renewable energy power sources does not have frequency characteristics, when the load frequency characteristic coefficient is _KL , the coefficient calculation unit calculates the equivalent load frequency characteristic coefficient using the following equation (2):

The power system stabilization device according to claim 8. The output total value of the plurality of renewable energy power sources does not have frequency characteristics when a frequency deviation between a reference frequency of the power grid and the first system frequency is within a reference range, and has frequency characteristics when the frequency deviation is outside the reference range,
The coefficient calculation unit
9. The system stabilization device according to claim 8, wherein the equivalent load frequency characteristic coefficient is calculated based on the load total value and the output total value at the initial point in time, the load frequency characteristic coefficient, frequency characteristic coefficients for the plurality of renewable energy power sources, the frequency deviation, and the reference range. When the load frequency characteristic coefficient is K _L , the frequency characteristic coefficient for the plurality of renewable energy power sources is K _ER , and the upper limit value of the reference range is ΔF _X , if the frequency deviation is greater than the upper limit value of the reference range, the coefficient calculation unit calculates the equivalent load frequency characteristic coefficient using the following formula (3):

When the lower limit value of the reference range is −ΔF _X , if the frequency deviation is smaller than the lower limit value of the reference range, the coefficient calculation unit calculates the equivalent load frequency characteristic coefficient by using the following equation (4):

The power system stabilization device according to claim 10.