WO2021063498A1

WO2021063498A1 - System and method for stabilizing an electrical grid

Info

Publication number: WO2021063498A1
Application number: PCT/EP2019/076720
Authority: WO
Inventors: Ervin SPAHIC; Richy Antrio JULIUS GUNASEKARAN
Original assignee: Siemens Energy Global GmbH & Co. KG
Priority date: 2019-10-02
Filing date: 2019-10-02
Publication date: 2021-04-08
Also published as: EP4022733A1

Abstract

The invention relates to a method for the control-based stabilization of an electrical grid (11), in which a setpoint value parameter (P) for the control is adapted on the basis of a further control parameter (f) by using a control characteristic curve (20) that has a first and/or a second control limit value (fmin, fmax) of the further control parameter. The method according to the invention is distinguished in that the first and/or the second control limit value is/are stipulated or dynamically adapted in temporally dynamic fashion on the basis of instantaneous values of a predetermined grid variable. The invention also relates to a grid stabilization apparatus (10) that can be used to perform the method according to the invention.

Description

System and method for stabilizing an electrical network

The invention relates to a method for control-based stabilization of an electrical network, in which a control characteristic is used to adapt or define a setpoint parameter of the control as a function of a further control parameter, which has a first and / or a second control limit value of the further control parameter having. The control limit values represent a control limitation in the sense that the control characteristic curve has a constant profile below the first control limit value, i.e. for values smaller than the corresponding limit value, or above the second control limit value, i.e. for larger values.

Such a method can be used, for example, when, in the event of a frequency deviation in the electrical network, active power is fed into the network or taken from the network in order to stabilize the network frequency. The exchange of the active power with the network can be achieved, for example, by means of a suitable stabilization device with energy stores for temporarily storing the energy. The use of the control characteristic is usually referred to as droop control.

An example of a control characteristic that is usually used is shown in a schematic representation in FIG. A control characteristic 1 represents the dependency of a setpoint parameter, in the example shown, the power P, depending on a further control parameter, here the frequency f. In a region 2 of positive power, a power feed is initiated up to a maximum power Pmax In a range 3 of negative power, up to a power Pmin, a power is drawn from the network. In the origin of the diagram, the power exchange with the network is P = 0 and the frequency corresponds to a nominal frequency. sequence fnom of the electrical network. The control characteristic curve 1 usually has a dead band area 4 in a certain value range around the origin, in which no power exchange with the network is initiated (P = 0). The control characteristic 1 also has a first control limit value fmin and a second control limit value fmax. Below the first and above the second control limit value fmin or fmax, the course of control characteristic 1 is constant in relation to power P. The control characteristic shows between the first control limit value fmin and the dead band and between the dead band and the second control limit fmax 1 shows a linearly falling course. The power consumption or power output to be initiated depends on a frequency deviation from the nominal frequency of the network.

In addition, EP 3392 994 A1 discloses a control method with a control characteristic which in some cases has a non-linear profile. By using the non-linear control characteristic, in particular the transition between the area of the dead band and the outer area outside the dead band area can be designed in such a way that sudden or even oscillating behavior at the transition can advantageously be minimized or avoided.

The object of the invention is to provide a method of the type that allows the most efficient and reliable possible stabilization of the electrical network.

In a method according to the invention, the object is achieved in that the first and / or the second control limit value is determined or dynamically adapted in a time-dynamic manner as a function of instantaneous values of a predetermined network variable. The instantaneous values of the network size can suitably be measured or determined in some other way. The rule limit value or the rule limit values are therefore not statically defined, but are instead adapted to the current network status during control. If the control limit values are changed, the entire control characteristic or its course is generally changed or adapted. The instantaneous values can be direct measured variables or variables derived therefrom.

Thanks to the adaptive adjustment of the control limit values, (faults) incidents occurring in the network can be taken into account in the control in order to achieve the most effective and reliable stabilization of the network possible. For example, failures in the network (for example a failure of an energy generating device such as a generator) can have different effects on the network, for example depending on the number and size of the remaining rotating machines connected to the network. They can also vary greatly over the course of a day. The same failure can therefore lead to different frequency deviations in the network. This fact can be taken into account in the control by means of the dynamic adjustment of the control limit values. The increase in the flexibility of the regulation also has advantageous effects on the suitably used network stabilization device or its energy store. According to our own investigations, adaptive control results in overall reduced electrical losses when exchanging power with the network. This has positive effects on the efficiency of the power exchange and the permitted design of the network stabilization device.

The control characteristic, expediently above the first, below the second or between the first and the second control limiting value, preferably has a non-linear profile, at least in sections. A non-linear control characteristic has some advantages in the context of the present invention. In contrast to the linear characteristic curve known from the state of the art, it can be avoided that the maximum power Pmax (or Pmin) is not included until the frequency deviation is equal to the control limit value the network is exchanged. Instead, high power can only be exchanged with the network in the event of very large frequency deviations. In the case of small frequency deviations, on the other hand, only a relatively small amount of power (compared to a linear characteristic curve) is exchanged with the network. Overall, this advantageously leads to a particularly efficient use of the available energy.

The course of the control characteristic preferably corresponds, at least in sections, to the course of a quadratic function. The quadratic curve advantageously allows a relatively simple implementation of the control algorithm. A quadratic function can generally be given by the formula y = a * x ^ 2 + b * x + c, where x, y are the variables and a, b, c are real function parameters.

The setpoint parameter is expediently a power that is suitably exchanged or to be exchanged between a network stabilization device and the electrical network, in particular a reactive and / or active power. This means that the exchange of power with the network can be controlled directly via the setpoint specification. Alternatively, for example, current or voltage are also conceivable as setpoint values.

The further control parameter can be a frequency of the electrical network. This is particularly useful when using the frequency stabilization of the network.

The predetermined network size is suitably a network frequency of the electrical network. The dependency of the control limit values on the network frequency is indicated to be particularly easy to implement if the further control parameter is also the frequency of the network.

It is considered advantageous if the determination of the first and / or second control limit value is dependent occurs from a temporal change in the network frequency. In this way, the change over time is first derived from the instantaneous values of the network frequency. The adjustment of the rule limit values is then carried out taking the change into account. In this way, the control can react quickly, especially in the event of rapid changes in the network frequency.

It can be advantageous if the instantaneous values are filtered by means of a low-pass filter, in particular a moving average filter. In this way, frequency deviations that are insignificant for the control, which are caused, for example, by operational switching events, such as the connection of lines and / or loads, can advantageously be filtered out.

The control characteristic preferably has a dead band range. For example, it can be a frequency dead band, that is, a value range around the nominal frequency, so that no power exchange with the network is initiated for network frequencies in this value range. In this way, small changes in the frequency are advantageously masked out and the load on a stabilizing device that is used is thus relieved.

The invention also relates to a network stabilization device for stabilizing the electrical network, which comprises a control device.

The network stabilization device is connected to the network during operation and is set up to carry out suitable measures for network stabilization.

The object of the invention is to propose such a network stabilization device that enables the most efficient and reliable possible stabilization of the connected electrical network. In the case of a network stabilization device of this type, the object is achieved in that the control device is set up to carry out the method according to the invention. The control device can expediently comprise a separate controller or a separate control module, by means of which the time-dynamic adaptation of the control limit values is carried out. The advantages of the network stabilization device according to the invention result in particular from the advantages described above in connection with the method according to the invention.

According to one embodiment of the invention, the network stabilization device comprises a converter, which has an AC voltage side for connecting to the electrical network and a DC voltage side, as well as an energy storage device that can be connected to the DC voltage side of the converter, so that by means of the network - stabilization device reactive and active power can be exchanged with the electrical network. For this purpose, the energy storage device suitably comprises at least one energy store for storing electrical energy, for example in the form of one or more batteries and / or SuperCaps.

By using the network stabilization device according to the invention, the available storage energy can be used efficiently. In this way, the service life of the energy storage device or the energy storage device can be advantageously extended. In addition, the operating losses in the storage and power converter can be advantageously reduced.

Furthermore, a better design of the energy storage device is made possible. In particular, the energy store can be designed to be smaller for the same output, which enables a cost advantage.

The invention is explained further below with reference to the exemplary embodiments of FIGS. 2 to 5. FIG. 2 shows an exemplary embodiment of a network stabilization device according to the invention in a schematic representation;

FIG. 3 shows an exemplary embodiment of a control characteristic for a method according to the invention;

FIG. 4 shows a schematic flow diagram of a method according to the invention;

FIG. 5 shows a further flow chart of a method according to the invention.

FIG. 2 shows a network stabilization device 10 which is set up to stabilize an electrical network 11, which in the example shown is a three-phase supply network and is connected to it. The network stabilization device 10 comprises a converter 12, which in the example shown is a self-commutated converter, the converter 12 including converter arms which are connected to one another in a double star circuit. It should be noted here that other converter configurations are also possible, for example a triangular connection of the converter arms. The converter 12 has an AC voltage side 13 for connection to the network 11 and a DC voltage side 14. An energy storage device 15 is connected to the DC voltage side 14 of the converter 12 and comprises energy storage devices in the form of one or more batteries and / or SuperCaps . Electrical energy taken from the network 11 can be stored by means of the energy storage device. Energy stored there can also be fed into the network 11 by means of the energy storage device 15. A reactive power can also be exchanged with the network 11 by means of the converter 12. Overall, both active and reactive power can be achieved by means of the network stabilization device 10 be exchanged with the electrical network 11. The exchange of power can, for example, influence a frequency in the network 11 and thus stabilize the network 11 as a whole. Furthermore, for example, a voltage in the network 11 can be influenced and the network 11 as a whole can thus be stabilized. For this purpose, the network stabilization device 10 comprises a control device 16 which, using instantaneous values of network parameters of the network 11 measured by means of a measuring device 17, in particular a network frequency, carries out the corresponding regulation of the converter 12 and the energy storage device 15, suitably there The controllable components used, such as controllable semiconductor switches, are to be controlled accordingly.

FIG. 3 shows a control characteristic 20 for a control-based stabilization according to the invention of an electrical network, for example the network 11 of FIG.

The control characteristic 20 represents the dependency of a setpoint parameter, in the example shown the power P, as a function of a further control parameter, here the frequency f of the network. In the area 21 of positive power, power is fed in up to a maximum power Pmax, in the area 22 of negative power, up to a power Pmin, power is taken from the network. In the origin of the diagram, the power exchange with the network is P = 0 and the frequency corresponds to a nominal frequency fnom of the electrical network. The control characteristic curve 20 has a dead band region 23 in a certain value range around the origin, in which no power exchange with the network is initiated (P = 0). The control characteristic curve 20 also has a first control limit value fmin and a second control limit value fmax. Below the first and above the second control limit value fmin and fmax, the course of the control characteristic 20 is constant with respect to the power P. The control characteristic 20 a non-linear curve, in the example shown, a square curve. The power consumption or power output to be initiated depends on the frequency deviation from the nominal frequency of the network.

The control limit values fmin and fmax are set adaptively and dynamically in time during the control as a function of a network variable, in the illustrated embodiment the measured current values of the network frequency. For example, at a point in time t1, the value of the lower control limit value fmin is reduced so that it is at fmin '. The value of the upper control limit value fmax is changed accordingly to fmax '. The entire course of the control characteristic is adapted accordingly, the course always corresponding to a quadratic function, only with changed function parameters. In a further case, the lower control limit value can be set to one

The value fmin ″ and the upper control limit value can be set to a value fmax ″, the course of the entire control characteristic curve being adapted accordingly, as indicated in FIG. 3 by means of dotted lines 24 and 25.

In FIG. 4, an example of the sequence of the method is illustrated on a flow chart 30. In a first step 31, predefined rule limit values fmin and fmax are assumed. In a second step, a measured instantaneous value of the network frequency is provided (at a nominal frequency of 50 Hz, for example). In a third step 33, a query is made regarding the frequency deviation from the nominal frequency and the sequence is assigned to one of the three states 33a-33c as a function of the result. The first state 33a is present when the measured frequency is below 49.9 Hz, for example. The second state 33b is present when the instantaneous value of the frequency is between, for example, 49.9 Hz and 50.1 Hz. The third state 33c is present when the current frequency is above 50.1 Hz, for example. In this case the current frequency lies in a frequency dead band of the control.

Starting from the first state 33a, the change in the network frequency over time is calculated in a fourth step 34 using frequency values that have already been provided beforehand. The calculated change in the network frequency over time is filtered in a fifth step 35 by means of a time delay moving average filter. On the basis of the filtered values (for example using a linear dependency of the rule limit values on the respective filtered value), a new lower rule limit value fmin 'is calculated in a sixth step 36.

Starting from the second state 33b, the control limit values fmin and fmax are left unchanged according to a seventh step 37.

Starting from the third state 33c, the change in the network frequency over time is calculated in an eighth step 38 using frequency values that have already been provided beforehand. The calculated change in the network frequency over time is filtered in a ninth step 39 by means of a time delay moving average filter. On the basis of the filtered values (for example using a linear dependency of the rule limit values on the respective filtered value), a new upper rule limit value fmax 'is calculated in a tenth step 40.

The respective result of steps 36, 37 or 40 is made available in an eleventh step 41 for further processing of the regulation.

Based on the frequency deviation over time (df / dt), it can be determined, for example, how serious a fault that has occurred in the network is. The rule limit value can be adjusted accordingly. A possible implementation of the method according to the invention is shown in a flow chart 50 in FIG. In a first (regulation) block 51, a measured frequency value of the network frequency is provided (measured for example at a point of common coupling of a network system). In a second block 52, a predetermined nominal frequency of the electrical network is provided. A lower control limit value fmin is provided in a third block 53. The value fmin can result from the determination according to FIG. 4, for example. The deviation of the instantaneous frequency from the nominal frequency determined by means of a difference generator 54 is then checked to see whether it lies within the dead band range. If this is the case, this is forwarded directly via a fifth block 55 to determine the control setpoint. If the measured frequency is outside the dead band, the course of the control characteristic is determined in blocks 56-58 as a function of fmin, the control characteristic corresponding in sections to a course of a quadratic function (see FIG. 3). Finally, in a ninth block 59, the setpoint value of the power to be exchanged with the network is determined from the course of the control characteristic and the instantaneous value of the frequency.

Claims

1. A method for control-based stabilization of an electrical network (11), in which a control characteristic (20) is used to adapt a setpoint parameter of the control (P) as a function of a further control parameter (f), which has a first and / or or a second control limit value (fmin, fmax) of the further control parameter (f), d ad urchgekenn ze i ch net that the first and / or the second control limit value (fmin, fmax) is time-dynamically determined as a function of instantaneous values of a predetermined network variable becomes.

2. The method according to claim 1, wherein the control characteristic (20) has a non-linear profile at least in sections.

3. The method according to claim 2, wherein the course of the control characteristic (20) corresponds at least in sections to the course of a quadratic function.

4. The method according to any one of the preceding claims, wherein the setpoint parameter is a power, in particular a reactive and / or active power.

5. The method according to any one of the preceding claims, wherein the further control parameter is a frequency.

6. The method according to any one of the preceding claims, wherein the predetermined network size is a network frequency of the electrical network (11).

7. The method according to claim 6, wherein the determination of the first and / or second control limit value (fmin, fmax) depends on The possibility of a temporal change in the network frequency takes place.

8. The method according to claim 7, wherein the instantaneous values are filtered by means of a low-pass filter, in particular a moving average filter.

9. The method according to any one of the preceding claims, wherein the control characteristic (20) has a dead band region (23).

10. Network stabilization device (10) for stabilizing an electrical network (11) connected to the network stabilization device (10), comprising a control device (16) which is set up to carry out a method according to one of claims 1 to 9.

11. Network stabilization device (10) according to claim 10, wherein the network stabilization device (10) comprises a converter (12) which has an AC voltage side (13) for connection to the electrical network (11) and a DC voltage side (14) comprises, an energy storage device (15) being provided which can be connected to the DC voltage side (14) of the converter (12) so that reactive and active power can be connected to the electrical network (11 ) can be exchanged.