EP2769447A2

EP2769447A2 - Method for stabilizing a voltage supply network

Info

Publication number: EP2769447A2
Application number: EP13702771.0A
Authority: EP
Inventors: Jens-Uwe Busser
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2012-01-31
Filing date: 2013-01-25
Publication date: 2014-08-27
Also published as: JP5940173B2; JP2015505661A; DE102012201315A1; CN104067474A; WO2013113629A2; US20140379161A1; CN104067474B; WO2013113629A3

Abstract

In conventional voltage supply networks, the balance between the power fed in by the generators and the power drawn by the loads is controlled by means of the frequency of the alternating voltage. In future intelligent voltage supply networks (smart grids) having many small decentralized plants, such control by means of the network frequency will become more and more difficult. Instead, a central electronic control signal is transmitted in a separate communication network to devices in order to control the decentralized generators and also loads. However, there is a risk of network instability if many decentralized plants are simultaneously switched upon reaching a preset threshold value. Therefore, according to the invention, preset threshold values are not directly used as threshold values, but rather suitable effective threshold values are derived therefrom. Thus, the threshold values assume different values for different devices in the smart grid, and an undesired simultaneous reaction of all control devices in the smart grid is prevented.

Description

description

The invention relates to a method and a gateway for stabilizing a power supply network of a distribution system operator.

In conventional networks for the transmission and distribution of electrical energy by means of alternating voltage (hereinafter referred to as "power grids"), the equilibrium between the power fed in by the generators and the power consumed by the consumers is controlled by the frequency of the AC voltage.

In Central Europe this is 50 Hz or in the USA 60 Hz. If more power is taken from the power grid than the generators feed in, the rotors in the electric generators are braked more strongly. As a result of this slowdown, the frequency of the alternating voltage generated in the power grid drops. If, on the other hand, less power is drawn than generated, the rotors accelerate and the grid frequency increases. The inertia of the rotating masses

The rotors have a stabilizing effect on the power grid, since they can release and absorb energy by changing their rotational frequency (primary control).

By controlling the AC voltage in the power grid, it is thus easy to balance generation and consumption:

If the frequency drops, new generators are activated. In the event of a very sharp drop, consumers can also be forcibly switched off (load shedding). Increases

the frequency, producers are shut down or possibly other consumers are switched on (secondary and tertiary control). In the long-term average, the mains frequency, which is also used as a clock for clocks (clock radio, etc.), can be kept very stable between 49.990 and 50.010 Hz. Power from renewable sources is increasingly being fed into the European interconnected grid, for example from mostly small, decentralized photovoltaic systems. These do not have any rotating masses. Instead, the generated direct current of the PV cells by means of a

power electronic inverter transformed into alternating current. This will be synchronous in the

fed into local low-voltage grid. In order to avoid large deviations from the desired network frequency, these systems - which are responsible for a considerable part of the locally generated power in some specific network segments - and their infeed must also be used

is usually strongly correlated due to locally very similar solar radiation - be frequency-dependent controllable.

According to [1], generating systems with mains frequencies greater than 50.2 Hz must disconnect from the low-voltage grid within 200 ms. However, due to the strong expansion of photovoltaics in Europe, there is now the danger that several GW feed-in power will be suddenly disconnected from the power grid when it reaches 50.2 Hz on sunny days

Stability of the European interconnected network can be significantly jeopardized [2,3].

Therefore, a transitional regulation was already adopted at short notice, which is a gradual reduction

the feed-in [3,4]:

1. Instead of a fixed overfrequency cutoff at 50.2 Hz, which is the same for all systems

Manufacturers and installers of PV systems use different frequencies between 50.3 and 51.5 Hz as shutdown frequencies of their systems. These should be distributed equally.

2. Systems reduce their feed-in power frequency dependent according to a defined characteristic [5]. If overfrequencies occur more frequently, operators of a low-cut-off system in accordance with Figure 1 may be economically disadvantaged as their systems shut down sooner and more often, allowing them to sell less solar power. You may therefore be tempted to increase the cut-off frequency by manipulating the setting of your system. If such manipulations occur frequently, the effectiveness of the stabilization control is reduced.

Further regulation is possible via the mains voltage measured locally at the feed-in point: as soon as this exceeds a certain value (overvoltage), the feed-in must be switched off or at least reduced.

If producers with rotating masses in future smart grids are increasingly displaced by small, decentralized systems without rotating masses, regulation via the mains frequency becomes more and more difficult. Instead, for example, a

electronic control signal (price signal, generation consumption quotient, or the like) in one

Separate communication network to devices (personal energy agent PEA, energy gateway, control unit, etc.) for controlling the decentralized producers and consumers are used. Here, too, care must be taken to ensure that there are no abrupt changes in feed-in and consumption so as not to jeopardize grid stability. This will happen, for example, when the control signal reaches a value that is for many

(or all) smart grid gateways are a threshold at which they change their behavior. This can be, for example, a threshold for a comfort level that sets the conditions under which controllable consumers (freezer, air conditioning, etc.) are supplied with electrical energy: • Comfort level "low" = electricity purchase for controllable consumers only if price is below 15c / kWh

• Comfort level "high" = electricity purchase also for controllable

Consumers always, regardless of the current price

If this threshold is the same for many gateways in the local smart grid, they would (if low comfort level is switched on) all turn on their local consumers when they fall below this threshold. Such a strong increase in consumption can then

easily lead to a risk of grid stability, similar to when reaching a grid frequency of 50.2 Hz and the associated shutdown of the PV systems. Causes of identical thresholds of gateways can be, for example:

• Legal requirements (as with PV systems)

• Same manufacturer or even same device series: The devices are preconfigured with identical threshold values. · Threshold values are set by the central control point

• Set thresholds by installer / user when it is expected that the same values will often be set, for example:

o By frequently using rounded values (like 50 instead of 49 or 51), or

o Values that are easy to adjust (for example, by keystrokes), or

o if the number of possible positions is very limited (10 instead of 10, 7).

It is therefore the object of the present invention to provide a method and a device which enables network stabilization in a smart grid power supply network.

This object is achieved by a method and a gateway with the specified in claim 1 and 9 Characteristics solved. Advantageous developments of the invention are specified in the dependent claims.

The inventive method for stabilizing a voltage supply network comprises the steps of: receiving a control signal through a gateway of at least one subscriber; Generating local control commands for connecting or disconnecting energy consumption or energy generation devices connected to the gateway by the gateway of the subscriber in dependence on the received control signal; and

Transmitting the generated local control command over a local area network to at least one energy or power generation device connected to the gateway. The gateway has an effective threshold; when the effective threshold value is exceeded or fallen below by a value transmitted with the control signal, the local control commands for switching on or off are generated; the effective threshold is formed from a preset threshold and a correction parameter.

The control signal is transmitted, for example, from a central control unit of a distribution system operator. The control signal can also be measured locally and transmitted to the gateway or be determined with a measurement by the gateway itself (voltage, frequency). Furthermore, the control signal can arise locally and / or distributed decentrally. The gateway responds appropriately to control signals from multiply occurring or decentralized units (substation controllers, local electricity market platforms) or to locally measured parameters (grid frequency, local voltage).

Advantageously, the adjusted parameters (preset thresholds) are not directly used as thresholds but effective thresholds derived therefrom. As a result, the threshold values for different devices in the smart grid assume different values, and a lower The desired simultaneous response of all control devices (gateways) in the Smart Grid is prevented.

According to a development of the present invention, the correction parameter is a random number and the effective threshold value is formed by a multiplication of the preset threshold value with the random number. If the random number is generated randomly, for example, based on internal random number start numbers ("seeds") for the various gateways, as they are also required for cryptographic operations, and a probability distribution (uniform distribution) that is constant over the desired range, Thus, for stochastic reasons, even without central coordination, an approximate equal distribution of the effective threshold values is obtained.

According to a further embodiment of the present invention, the random number and the effective threshold will be redetermined at predeterminable time intervals. Advantageously, this effectively prevents a gateway operator from being permanently disadvantaged by an unfavorable value.

According to a further embodiment of the present invention, the correction parameter is a time-varying function and the effective threshold is formed time-dependently by a link, such as a multiplication, of the preset threshold with the time-varying function. Advantageously, a distribution of the effective threshold values, which is as even as possible, is achieved both between the different gateways and also for the individual gateway over time.

According to a further embodiment of the present invention, the period is large in comparison with a change frequency of the control signal. This is advantageous since the number of affected gateways is as proportional as possible to this change when the control signal is changed. In accordance with a further embodiment of the present invention, the control signal has information about a mains voltage or a mains frequency and / or information about an electricity price or a generation-consumption quotient.

The gateway according to the invention for network stabilization of a power supply network of a distribution network operator generates in response to a received control signal local control commands for switching on or off of energy and power generation equipment and transmits them via a local network to the energy and power generation equipment. The gateway has an effective threshold. If the effective threshold value is exceeded or undershot by a value transmitted with the control signal, the local control commands for switching on or off are generated. The effective threshold is formed from a preset threshold and a correction parameter.

In the following, embodiments of the gateway according to the invention and of the method according to the invention for network stabilization of a power supply network will be described with reference to the attached figures.

Show it:

FIG. 1 shows a flow diagram of a possible embodiment of the method according to the invention for stabilizing a voltage supply network.

FIG. 2 a representation of various correction functions for determining an effective threshold value according to the invention,

3 shows a representation of a time course of

Control signal and correction functions in comparison. FIG. 1 shows a flow chart of a possible embodiment of the method according to the invention for stabilizing a voltage supply network of a distribution network operator.

In a first step 101, a control signal is transmitted from a central control unit of the distribution system operator to at least one gateway of a subscriber.

In a second step 102, the gateway compares a value transmitted with the control signal with a local effective threshold. If the effective threshold is exceeded 103 by the transmitted value, the affected gateway generates one or more local control commands for turning on or off the power and power generation devices 105 connected to the gateway.

Alternatively, the gateway generates one or more local control commands for switching on or switching off the energy consumption and energy generation devices connected to the gateway when the effective threshold value is undershot by the transmitted value.

However, if the threshold is undershot (or exceeded in the alternative embodiment) by the transmitted value, the gateway receives a next control signal 104 and no control commands are generated.

In a further step 106, the generated local control command-for example via a local power-line-based network or a local IP (Internet Protocol) -based network-is transmitted to the energy and power generation devices connected to the gateway. In the following, exemplary embodiments for determining the effective threshold values are described. These gateway internal effective thresholds should be different from the set thresholds. By choosing suitable parameters for the determination of the effective threshold values, even with an identical configuration of gateways (PEAs and similar control devices), it is then possible to prevent the problems described above from being simultaneously switched on or off, for example, by entire device classes.

The measures described below enable this without central coordination: 1st variant: Constant correction factor

It must be ensured that not all gateways have the same effective thresholds because

Otherwise they would all react at the same time. Therefore, when setting a (new) threshold value S_set and, of course, during initial startup when accepting a factory-set initial value, the gateway should multiply this value by a random number Z in the interval [1-P%, 1 + P%]. P is dependent on the granularity of the transmitted control signal (e.g.

Price signal). The effective threshold S_eff is then

S_eff = Z * S_set and can not be read or influenced directly from the outside to avoid manipulation.

Z is randomly generated based on internal, different seed numbers for the various gateways, as they are also needed for cryptographic operations, and a constant probability distribution over the desired range (Uniform distribution), we obtain for stochastic reasons, even without central coordination, an approximate uniform distribution of the effective threshold values. 2nd variant: Regularly newly defined correction factor

Preferably, the random multiplication factor at certain time intervals (e.g.

a few days) automatically or at the request of a control center again and again randomly calculated so that no gateway operator is permanently disadvantaged by a once fixed, unfavorable value.

Alternatively, the correction factor can also be calculated in the control center and then distributed.

3rd variant: temporally varying correction function

Particularly advantageous is the use of a time-dependent correction function Z (t), which changes the correction factor virtually continuously:

S_eff (t) = Z (t-t_0) * S_set This is shown in Figure 2 on some functions. For better comparison, all functions shown are drawn over two periods; the amplitude (2P) is 0.05. The frequency distribution of their values obtained in this way is shown in the right part of FIG. 2; the areas of the frequency distribution are the same for all functions.

It is important that the frequency distributions of the assumed values 202 are as low as possible over the entire possible value range. Due to the constant total area, therefore, a broad, constant distribution is ideal.

Especially suitable are therefore very periodic functions such as sawtooth curves 203 or zigzag curves 205. These should preferably be relatively smooth (continuous). This will make one over the entire area as possible

uniform and low distribution achieved. The relative frequency of the values is constant in the example about 50 (arbitrary units - these depend on the "binning", ie the division of the data channels).

The zigzag curve 205 also has the advantage over the sawtooth curve 203 that it avoids the unsteady jump at t = (n + 0.5) * T.

Stepped functions 204, 206 are also well-suited if the step height is low enough to allow enough different values. Here, the step height for demonstration purposes was a little too high. As a result, the range available for possible values is not uniformly used. This results in gaps in the frequency distribution, which - due to the constancy of the total area - leads to higher frequencies of about 100 (arbitrary units).

Sinusoidal functions 207 are less well suited because of their non-constant frequency distribution, since particularly large and especially small values occur more frequently here. Here are especially at the edge particularly high frequencies of almost

150 (arbitrary units) reached. However, even a sinusoidal distribution is, of course, still better than concentrating on a single fixed value. For the period of the functions used, note the following:

• If period durations differ significantly for different gateways, with enough gateways, it is extremely rare for many gateways to simultaneously reach the maximum (or minimum) of their correction function. • If the gateways are synchronized in time and they also have the same period duration of their function, then a random, as even as possible distribution of the start times (t_ 0)

important. The time of the (first) commissioning alone is not suitable as a start time, because this usually in the time 9:00 to 17:00 falls - here should at least one random, evenly distributed time from 0 to 24h (better: 0 to 7 * 24h) are added.

• The periods are to be chosen long enough (hours, days), ie. H. significantly larger than the typical changes in the control signal in the smart grid. This is necessary so that when a change in the control signal, the number of affected gateways is proportional to this change as possible.

This is illustrated in FIG. Shown in two examples 301 and 302 is the time variation of a control signal 303a, 303b in comparison to the temporal variation of the correction function Z (t) 304a-307a and 304b-307b of different gateways.

In the first example 301, the correction functions Z (t) 304a-307a vary only slowly compared to the control signal 303a. Depending on the magnitude of the change of the control signal 303a comparatively few gateways are activated. In the example shown, the two gateways 304a and 305a. In the second example 302, the correction functions Z (t) 304b-307b vary rapidly compared to the control signal 303b. In this case, the threshold values of all gateways 304b-307b coincide with the control signal 303b in a short time (maximum one period), and all gateways are activated-at least for a short time. This would lead to frequent switching on and off of the associated consumers or producers or - if a rapid re-switching is not feasible - too an activation of a large number of consumers or producers. Both are not desired.

• Periods (and their multiples) should not coincide with typical rhythms (exactly 1 day or exactly 1/8 week) in the energy grid, but should be slightly different to avoid that e.g. a certain gateway has a particularly high threshold value at lunchtime (or every Sunday lunchtime) over a longer period of time, thereby purchasing particularly expensive electricity.

Advantageously, it is provided that different, but interdependent threshold values are modified within a gateway in a suitable manner. If e.g. If the effective threshold value for "switching on" is reduced by 3% as a result of the measures described above, then the corresponding threshold for "switching off" must be corrected accordingly in the same way. In the case of continuous changes of the control signal for balancing between generation and consumption, when reaching a threshold value, advantageously not many gateways switch simultaneously, but one after the other when a different threshold value is reached

Bandwidth of the control signal.

If the correction factor is also varied, each gateway receives "favorable" and sometimes "unfavorable" thresholds. Therefore, in terms of time, no gateway is permanently disadvantaged by the awarding of "unfavorable" thresholds.

The present invention increases network stability in the smart grid, in particular when using many similar devices. Furthermore, the solution according to the invention is compatible with a regulatory measure (similar to the transitional regulation for the PV systems at 50.2 Hz), if or as soon as such is decided. literature

[1] BDEW: Technical Guideline "Generation Plants on the Medium Voltage Grid - Guideline for

Connection and parallel operation of generation plants in the medium voltage grid, issue June 2008,

BDEW Bundesverband der Energie- und Wasserwirtschaft e.V. [2] http: / / www. sfv. en / article / das_502_hertz ~ roblem. htm

[3] Forum Netztechnik / Netzbetrieb im VDE: Framework conditions for a transitional control for the frequency-dependent active power control of PV systems in the LV network [4] EON: Transition control for PV systems - Active power supply for overfrequency

[5] BDEW guideline "Generating units on the medium voltage network", Chap. 2.5.3 and Figure 2.5.3-1

Claims

claims

1. Method for stabilizing a power supply network with the steps:

Receiving a control signal through a gateway of at least one subscriber;

Generating local control commands for connecting or disconnecting energy consumption or energy generation devices connected to the gateway by the gateway of the subscriber in dependence on the received control signal; and

Transmitting the generated local control command via a local area network to at least one energy or power generation device connected to the gateway, characterized in that

the gateway has an effective threshold,

when the effective threshold value is exceeded or fallen below by a value transmitted with the control signal, the local control commands for switching on or off are generated, the effective threshold value being from a preset value

Threshold and a correction parameter is formed.

2. The method of claim 1, wherein

the correction parameter is a random number,

the effective threshold is formed by combining the preset threshold with the random number.

3. The method of claim 2, wherein

the random number and the effective threshold are re-determined at predeterminable time intervals.

4. The method of claim 1, wherein

the correction parameter is a temporally variable function,

the effective threshold is time-dependent formed by multiplying the preset threshold by the time varying function.

5. The method of claim 4, wherein

the time-varying function is periodic with a period duration.

6. The method of claim 5, wherein

the period is large compared to a change frequency of the control signal.

7. The method of claim 1, wherein

the control signal comprises information about a mains voltage or a mains frequency.

8. The method of claim 1, wherein

the control signal comprises information about an electricity price or a generation-consumption quotient.

9. Gateway for network stabilization of a power supply network,

wherein the gateway generates, in response to a received control signal, local control commands for turning on or off power consumption and power generation devices and transmits them to the energy and power generation devices via a local area network,

characterized in that

the gateway has an effective threshold,

Threshold and a correction parameter is formed.