DE102011122580A1 - Method for operating electrical supply network in e.g. larger photovoltaic system, involves controlling line voltage changing unit depending on power available in electrical supply network to influence energy consumption - Google Patents

Abstract

The method involves providing a voltage of an upper voltage level with a nominal voltage by transformers (Ta-Tc). The nominal voltage is extended up to an associated maximum voltage to be stepped down to a voltage of a lower voltage level with another nominal voltage and another associated maximum voltage. A line voltage changing unit is provided for changing a line voltage to upper and/or lower voltage level within the maximum voltages. The changing unit is controlled depending on power available in an electrical supply network (1) to influence energy consumption. An independent claim is also included for a controlling-and regulating device.

Description

The invention relates to a method for operating an electrical supply network, which has a transformer, wherein the transformer, the voltage of an upper voltage level with a first rated voltage whose exceeding in the network operation is allowed up to a maximum allowable voltage, down-converted to the voltage of a lower voltage level having a second rated voltage and an associated second maximum voltage, and means for varying an operating voltage at the upper and / or lower voltage levels within the maximum allowable voltage (s). The invention further relates to a control and regulating unit for carrying out the method.

A device that realizes such method steps is, for example, a larger photovoltaic system, whose photovoltaic generator can generate several MW of power, which is fed via one or more inverters in a medium voltage level. The medium voltage level is here the upper voltage level with the first rated voltage, the z. B. 20 KV should be. The photovoltaically generated electrical power is transported through the supply network to various locations where one or more transformers are connected to lower the medium voltage to a low voltage. The low voltage is to be assumed here as an example 400/230 volts as the second rated voltage, depending on whether the voltage between the phases or against earth is considered. As a means for changing the operating voltage is in such a photovoltaic generator, the associated inverter

The low voltage is kept by the grid operator within a desired range, which has a lower limit, at the level of which the electrical appliances fail or are no longer working properly, and which has an upper limit beyond which the electrical appliances are endangered. Analogously, the grid operator also provides for a maximum permissible maximum voltage for the main network with 20 kV here, which is usually 10% higher than the nominal voltage due to the technical design of the building components involved, ie 22 kV in the numerical example.

Plants for generating regenerative energy are widely known. Each photovoltaic system, also referred to below as the PV system, generates a direct current which is converted into an alternating current by means of an inverter. As inverters, both purely electronic devices and electromechanical converters can be used. Under inverter while all devices are to be considered, which can generate an AC voltage from a DC voltage. Although wind turbines generate directly an alternating current, but which is to be adapted via a frequency converter to the conditions of the public supply network. These frequency converters also include inverters.

The electronic components of an inverter, as well as the combination of a DC machine with a synchronous generator as a mechanical inverter, allow setting a desired cos phi value in relation to the power. In many PV systems, this is done by a cos phi pointer, which can be used to set a fixed ratio of injected power to injected or referenced reactive power. If no active power is present or not desired, an inverter can also be used as a pure reactive power supplier.

Recently, with the emergence of offshore wind farms and other site-based regenerative energy producers another aspect is current, namely that the existing transmission networks are not sufficient to transport the temporarily uneven and quantitatively unpredictable, generated electrical energy to the demand centers. This goes so far as to give away generated electrical energy across national borders, possibly to buy it back later or the next day, when regenerative energy is not sufficiently available. Alternatively, it comes to switching off wind turbines and the possibility of generating energy itself is not even used.

The invention is based on the initially contradictory consideration that a waste of electrically generated energy can be advantageous from an economic point of view.

Based on this consideration, the present invention has the object to better utilize an existing, currently available amount of energy.

This object is achieved in a first variant according to the invention in that the means for changing the operating voltage are controlled in dependence on the available energy in the supply network. According to a second embodiment, the object is achieved according to the invention by controlling the means for variation as a function of a current measurement on the transformer in order to influence the consumption of energy. Finally, the object is achieved according to a third embodiment in that the means for changing depending on a current measurement on a line piece between two grid connection points to transformers is controlled to affect the consumption of energy.

With respect to the control unit, the object is provided by an input for detecting the amount of energy available in the supply network, by calculating means for calculating a reactive power supply or a reactive power supply from or into the supply network depending on the available amount of energy or as a function of the transformer current or in dependence of the line current , and solved by an output, via which a control signal according to the calculation result to a reactive power supplier is deliverable.

In order to increase the amount of energy consumed, the operating voltage in the supply network has to be increased via a targeted reactive power feed-in. Conversely, by a targeted reactive power reference from the supply network whose operating voltage is lowered.

Under the available power in the context of the present invention, the sum of all individual services is understood, which is applied by the power generators located on the grid and currently fed into the supply network. In this case, a limit value can also be taken into account, for which it applies that energy producers whose power falls below the limit value are not used to calculate the reactive power management (supply or feed-in). So z. B. smaller photovoltaic systems that provide no significant contribution to the provision of services are left out in the calculation. In this respect, the sum of all individual services then refers to all above the predefinable limit value.

When measuring the current on the transformer, it is advantageous to measure the temperature prevailing at a suitable point on or in the transformer. So z. For example, the temperature at internal windings can be included in the calculation of the amount of reactive power feed or reference. In a warm transformer, the operating voltage must be lowered or more than a cold transformer, the remaining available heat capacity for the higher operating voltage associated with higher currents with correspondingly higher heat generation.

In the means for modifying the operating voltage to be used in accordance with the present invention, in a first alternative, the property of inverters is used to provide any reactive power reference from the grid or any reactive power feed into the grid as part of its nominal power and thus lower the operating voltage in the grid or lift. Another alternative with which the operating voltage can be changed is the use of a step transformer, in which the transmission ratio can be changed in predetermined levels, resulting in different voltage conditions on the secondary side. There are also known infinitely variable, electronic transformers, which can be used in the present case as means for changing the operating voltage.

The invention has the advantage that a current, good supply situation can be used with electrical energy by the energy is introduced by a voltage increase in the supply network, and beyond, what for a safe operation of the settled at the consumers, electrical equipment would be necessary. If the mains or operating voltage z. B. increased by 5%, the consumption or the power consumption of the consumer will increase according to the relationship P = U ² / R by 10.25% (assuming a constant electrical resistance at the consumer) and the electrical work as power times time (P × t) is also correspondingly larger. This means for some consumers a rather pointless increase in consumption, such. As for street lighting, running ventilation fans, etc. and for other consumers, this means a faster achievement of their target, such. For example, in the production of renewable energy through a wind turbine, a photovoltaic system or the like, no reliable prediction on the short to medium term accumulating amount of energy generated is possible, it is Advantageous ever "in stock" to consume energy to possibly better later, in case of a failure or a reduction of available energy to better stand there, because then a voltage reduction can be envisaged, the result of the consumer then a slightly lowered operating voltage can be supplied with less energy. This then coincides with a supply situation in which less energy is available.

It is advantageous to use the already existing inverter an existing plant for the production of renewable energy for this purpose. If, for example, a voltage increase of 10% is carried out at a first rated voltage of 20 kV, according to the known relationship, power P is equal to the product of voltage U and current I (or also P = U ² / R) more electrical energy over the existing cable or cable to be transported to consumers. Then z. B. the wind turbine inherent inverter for Voltage boost via reactive power delivery used. The IGBTs installed in modern inverters are controlled accordingly.

A particularly advantageous embodiment of the invention is when at least one active network stabilizer is provided at the lower voltage level, which in particular comprises at least one further inverter, with the aid of its reactive power reference, the voltage at the lower voltage level below a predetermined value, for example, at 110% the second rated voltage is maintained. The network stabilizer can be classically composed of coils and capacitances or, as is preferred, formed by further inverters that are part of smaller solar generators or wind turbines that are connected to the lower voltage level. It also makes sense to provide an inverter arrangement alone, ie without an associated DC voltage source. In keeping with the above numerical example, the voltage of the upper voltage level of 20 KV can be increased by 10% to 22 KV in order to correspondingly provoke an increase in consumed power in the consumers.

Without the use of active voltage stabilizers on a lower network level, the height of the reactive power supply to an upper network must be such that a maximum permissible voltage value is established at the lower voltage level on the secondary side of the transformer, as a rule exceeding the aforementioned value of 10% the second rated voltage. For this purpose, it makes sense that a voltage sensor is arranged on the lower voltage level and that the reactive power supply to the upper network is limited depending on the voltage measured in the sub-network voltage in that the measured voltage is at most 10% above the second rated voltage.

It is particularly advantageous if a control and regulating unit is provided, to which the measured voltages at the secondary side of the transformer and / or at the feed-in point of the inverter are fed to the upper voltage level, and the height or the voltage (s) measured a voltage increase or a voltage reduction as a function of the available amount of energy calculated and initiated. This may result in reactive power sourcing or reactive power input from the inverter and / or the other inverter to set a desired voltage level in the 400 volt side utility power grid. This measure makes it possible to juggle with the reactive power supply and the reactive power reference in the supply network in such a way that situations with high energy availability are exploited in order to be able to better respond to a later situation with low energy availability.

It is also advantageous if in relation to the feed point of the alternative energy generator more distant consumers such. B. a 10 km away locality, preferably with a voltage boost with good energy availability is considered as lying directly at the feed point consumer. Due to the inevitably associated with the power transmission line losses then those consumers are already considered with an energy supply, which are present at a low energy supply situation anyway lower voltage level than it is present at the feed point, which is even further deliberately lowered. Such a deliberate reduction is possible due to the previously stored energy by means of an increase in operating voltage.

Further advantages and embodiments of the invention will become apparent from the description of an embodiment with reference to FIGS. Show it:

1 a schematically drawn supply network with voltage control according to a first embodiment;

2 a schematically drawn supply network with voltage control according to a second embodiment; and

3 a schematically drawn supply network with voltage control according to a third embodiment

In the 1 is a section of a supply network 1 shown by an energy supplier 3 is supplied with electrical energy on the 20 kV voltage level. The energy provider 3 may be a coal power plant, a wind farm or the like, or even a substation, which is supplied by an overhead line in the high voltage range of a large power plant, eg a nuclear power plant. The energy provider 3 feeds at a starting point 4 on a 20 KV line 5 or a 20 kV cable having a length of z. B. 20 km has. Along the line 5 Several localities, three of which are shown A, B, C shown, connected via respective associated transformers T _A , T _B , T _C , which stretch the 20 kV to the local voltage level of 400 volts down. In the village A is a solar system 7 present, which feeds the generated solar power directly into the local network A via their inherent inverter. At the end of the 20 km long line 5 is located the village C, in the vicinity of a larger photovoltaic generator 9 located. The photovoltaic generator 9 is to an inverter 11 connected, via which the generated solar energy directly into the 20 kV level at an end point 6 the line 5 is fed. The village C has a community own solar system 13 , their associated inverter 15 also has a variable cos phi setting.

On the secondary side of the transformer T _C is a first voltage measuring device 17 provided, which is the prevailing on the 400 volt side voltage to a control unit 19 transmitted. A second voltmeter 21 measures the at the entry point 6 of the inverter 11 on the 20 kV line 5 present voltage, their value also to a signal input 27 the control and control unit 19 is transmitted. Further, dashed lines shown control lines lead from a signal output 29 the control and control unit 19 to the inverter 11 and the other inverter 15 to set their cos phi, ie their ratio of active power to referenced or fed reactive power. For non-existent active power, which z. B. in the case of a solar generator at night is the case, only pure reactive power can be purchased or fed. The control and control unit 19 can be connected to one or more additional, measuring value giving bodies, the z. B. the voltage curve along the line 5 replicate.

As already mentioned, the available power in the sense of the present invention is understood to be the sum of all individual powers which are applied by the energy producers located on the network and are currently fed into the supply network. It is also possible to use only selected energy producers which make a certain contribution to the power supply. This is at the 1 through further signal lines 25a and 25b shown leading to the inverter 7 or to the energy producer 3 lead, and about the generated power to the control unit 19 is reported.

The inventive method runs z. As follows: It is cloud-free and the photovoltaic generator 9 generates a high amount of energy that is the supply network 1 can be made available. The control and control unit 19 detects this situation via the at the output of the inverter 11 with the help of the voltage measuring device 21 measured voltage and the current flowing at the output. It also makes sense, the control and control unit 19 on the DC side at the output of the photovoltaic generator 9 prevailing current and voltage values via a signal line 25 as an input to determine the available amount of energy. Due to the good supply situation, ie the good energy availability, provides the control unit 19 the drive values for the inverter 11 so that a high reactive power share with in the line 5 is fed. This high reactive power component leads to a voltage increase, which may be on the secondary side of the transformer T _C maximum up to the maximum voltage, usually up to 10% above the rated voltage, if there is not another, voltage-reducing measure such as a targeted reactive power reference to a another network site is made.

The deliberately high operating voltage leads to a desired additional consumption of energy in the locality C. This additional consumption is partly useless depending on the consumer or causes an accelerated achievement of a functionally expected target by the consumer. Such a goal can z. B. the cooling of a refrigerator to a lower temperature, or, if the consumer is a heater, reaching the set upper limit of the room temperature.

In the afternoon, when the sun is lower, the functional goals associated with the electrical consumers (freezer temperature at the minimum allowed, room temperature at the preselected maximum, etc.) are reached or planned. Did the sun go down and do not feed other energy sources, such as As wind turbines, biomass plants or the like, high amounts of energy in the supply network, the supply network can be relieved that its operating voltage is lowered, resulting in a reduced consumption of electrical equipment. The reduced voltage is not critical for some consumers, such. B. at a street lighting, which then sheds slightly weaker, and leads to other consumers, such. As the said cooling or heating device, to a reduced cooling capacity or heating power. This reduction can be readily accepted, because previously due to the increased operating voltage, an energy cushion in the form of the lowered cooling temperature to its lower control temperature or in the form of the raised room temperature was carried out to its upper control temperature.

The reactive power feed of the alternative energy generator 9 not necessarily at the end of the line 5 respectively. She can be anywhere along the line 5 take place as long as the maximum voltage is not exceeded.

The used line components and transformers T _A , T _B , T _C are designed to their maximum voltage. About a reactive power reference on the secondary side of the transformers T _A , T _B , T _C. it is ensured that the voltage in the local network remains below the maximum permissible voltage of 440 volts. The reference to reactive power becomes the example of the locality C then over the municipality own photovoltaic plant 13 with her other inverter 15 causes. Depending on requirements, the voltage on the secondary side of the transformers T _A , T _B , T _C can be adjusted up or down by adjusting the cos phi, as indicated by the two voltage arrows 23 is indicated. This possibility brings with it the particular advantage that a simply constructed component with a fixed transmission ratio can be used as the transformer T. But there are also other transformers T _A , T _B , T _C possible z. B. via tap-changer or other means allow adjustment of the transmission ratio.

Exceeding the maximum stress is to be avoided under all circumstances. Accordingly, the reactive power supply on the 20 kV side must always be matched with the reactive power reference on the 400 volt side.

In the 2 is the schematically drawn supply network 1 around a maximum stress level 31 adds to which primary side a transformer transformer 33 whose secondary side is connected to the 20 kV line 5 connected is. In or on the transformer transformer 33 is a temperature sensor 35 appropriate. The measured temperature is sent via a signal line to the control unit 19a directed.

Furthermore, the current flowing on the primary or the secondary side of the transformer transformer is measured via a current sensor (not shown). This value is also the control and control unit 19a provided by means of a further signal line, which is shown as dashed lines like all other signal lines. The control and control unit 19a still has a signal output 29 to which a signal line is connected, leading to the inverter 11 the photovoltaic system 9 leads.

In this embodiment, the method according to the invention runs such that the current value through the transformer transformer 33 is permanently evaluated. If the current value is at its upper allowable limit, this means that the transformer transformer 33 to the limit of its supply capability for the 20 kV cable 5 has arrived, so must the supply network 1 be relieved on the 20 kV level, so that the connection of other consumers does not lead to an overcurrent at the transformer transformer and possibly to a subsequent breakdown of the network. This relief is achieved by a targeted reactive power extraction by means of the inverter 11 performed by the control unit 19a via a control signal S to the inverter 11 is initiated. In the inverter 11 are then there inherently existing electronic components such as IGBT's driven so that reactive power from the supply network is taken out of the inverter. This leads to a voltage reduction at the feed point 6 , The reduced voltage leads to a correspondingly reduced voltage at the primary side of the local transformers T, which leads to a smaller secondary voltage at a fixed transmission ratio. The localities A, B and C will take correspondingly smaller amounts of energy (electrical work), which leads to a relief of the supply situation. As an alternative or in addition to driving the inverter 11 can achieve a lower voltage on the 20 kV line 5 also by changing the transmission ratio at the transformer transformer 33 achieved when he z. B. is equipped with a Stufenanwählvorrichtung over which its translation ratio is changeable.

Is the measured current at the transformer transformer 33 on the other hand, it can be low, via a reactive power supply by the inverter and / or a change of the transmission ratio at the transformer transformer 33 the voltage on the 20 kV line 5 be raised to force the consumption of electrical energy. The timing of an intervention in the supply network via reactive power supply or reference can be determined by specifying certain limit values for the transformer current.

A third variant, on the basis of which procedure the means for varying the operating voltage on one of the voltage levels is activated, is disclosed in US Pat 3 shown. There is a current sensor 37 at a basically arbitrary point of the 20 kV cable 5 intended. Advantageously, a critical location is chosen where the flow conditions can change rapidly and / or significantly. This can be z. B. on the connecting line 5 between two closely spaced villages. The operational procedure corresponds to the previously in connection with the 1 and 2 described. Instead of the current value at the transformer transformer 33 like in the 2 becomes that of the current sensor 37 measured value for the line current to the input 27 the control and control unit 19b given. In the further process sequence, the line current is then used to decide whether and, if so, by how much, the voltage on the 20 kV line 5 to change.

LIST OF REFERENCE NUMBERS

1

supply network

3

energy producers

5

20 kV line / cable

6

entry point

7

inverter

9

photovoltaic generator

11

inverter

13

Community own photovoltaic generator

15

another inverter

17

first voltmeter

19, 19a, 19b

Control unit

21

second voltmeter

23

voltage arrows

25, 25a, 25b

signal line

27

signal input

29

signal output

31

High voltage level

33

Umspanntransformator

35

temperature sensor

37

current sensor

S

control signal

Claims (10)

Method for operating an electrical supply network ( 1 ), which has a transformer (T), wherein the transformer, the voltage of an upper voltage level with a first rated voltage (U1 _nenn ), the exceeding of which is permissible in network operation up to a maximum allowable voltage, downconverted to the voltage of a lower voltage level with a second nominal voltage (U2 _nenn ) and associated second maximum voltage, and means for varying an operating voltage at the upper and / or lower voltage level within the maximum permissible voltage (s), characterized in that the means for altering depending on the power available in the supply network is controlled to influence the consumption of energy. Method for operating an electrical supply network ( 1 ), which has a transformer (T), wherein the transformer, the voltage of an upper voltage level with a first rated voltage (U1 _nenn ), the exceeding of which is permissible in network operation up to a maximum allowable voltage, downconverted to the voltage of a lower voltage level with a second nominal voltage (U2 _nenn ) and associated second maximum voltage, and means for varying an operating voltage at the upper and / or the lower voltage level within the maximum permissible voltage (s), characterized in that the means for changing depending on a current measurement is controlled on the transformer, to influence the consumption of energy. Method for operating an electrical supply network ( 1 ), which has a transformer (T), wherein the transformer, the voltage of an upper voltage level with a first rated voltage (U1 _nenn ), the exceeding of which is permissible in network operation up to a maximum allowable voltage, downconverted to the voltage of a lower voltage level with a second nominal voltage (U2 _nenn ) and assigned second maximum voltage, and having means for varying an operating voltage at the upper and / or lower voltage level within the maximum permissible voltage (s), characterized in that the means for changing depending on a current measurement on a line piece between two Grid connection points to transformers is controlled to affect the consumption of energy. Method according to one of claims 1 to 3, characterized in that at an available power above a first limit value, the operating voltage in the supply network is raised and lowered in the presence of an available power below a second limit value. Method according to one of claims 1 to 4, characterized in that the available power in the supply network via a current and voltage measurement takes place at a high-voltage transformer, which spans from a maximum voltage level to the upper voltage level. Method according to one of claims 1 to 5, characterized in that the means comprises an inverter, which optionally includes a transformer. Control unit ( 19 ) for carrying out the method according to claim 1, characterized in that it receives a signal input ( 27 ) for detecting the power available in the supply network, that it has calculation means for calculating a reactive power supply or a reactive power supply from or into the supply network depending on the available power, and that it has a signal output ( 29 ), via which a control signal (S) according to the calculation result to a reactive power supplier ( 11 ) is deliverable. ( 1 ) Control unit ( 19a ) for carrying out the method according to claim 2, characterized in that it receives a signal input ( 27 ) for detecting the on the transformer ( 33 ) current flow means, that it has calculation means for calculating a reactive power reference or a reactive power feed from or into the supply network ( 5 ) depending on the current flowing, and that they have a signal output ( 29 ), via which a control signal (S) in accordance with the calculation result to a reactive power supplier ( 11 ) is deliverable. ( 2 ) Control unit ( 19a ) according to claim 8, characterized in that it has an input for the measured value of the transformer temperature (T) and that the transformer temperature is included in the calculation. Control unit ( 19b ) for carrying out the method according to claim 3, characterized in that it has a signal input ( 27 ) for detecting the current flowing in a line section, that it has computing means for calculating a reactive power reference or a reactive power feed from the supply network in dependence of the flowing current, and that it has a signal output ( 29 ), via which a control signal (S) can be delivered to a reactive power supplier in accordance with the result of the calculation. ( 3 )

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