Vima inverter and voltage network

Abstract

The utility model relates to a VISA inverter having a synchronization event input, a connection point for voltage connection to an intermediate circuit for power supply of the inverter, an output for connection to a load and at least one further output of a further VISA inverter, the load requiring more power than the inverter alone can provide, and the inverter having a synchronization event input, a connection point for voltage connection to the intermediate circuit for power supply of the inverter, an output for connection to the load and at least one further output of the further VISA inverter, the VISA inverter is designed in such a way that: a. A VISA regulation of the output AC voltage is constructed at the output of the VISA inverter on the basis of a predefined target network voltage; b. Synchronizing the phase of the output AC voltage to a first synchronization event received at the synchronization event input; and c. Constructing the network voltage from the voltage applied at the connection point for the voltage connection to the intermediate circuit after the synchronization of the phase has been completed. The utility model also relates to a voltage network, which is provided with a plurality of VISA inverters.

Description

Technical Field

[0001] The invention relates to a method for building up a grid voltage from a plurality of independently regulated VISMA inverters which are connected together to a load, wherein the load requires more power than can be provided by a single one of the inverters. The invention also relates to an inverter and a voltage grid. Background Art

[0002] According to the definition at http: / / www.iee.tu-clausthal.de / en / visma / , a virtual synchronous machine (VISMA for short) is a special inverter that is primarily intended for feeding regeneratively generated electrical energy into decentralized and weak-current networks. The design features of this inverter are similar to those of a synchronous machine for electric machines, whose static and dynamic operating behavior is largely reflected in this inverter.

[0003] Therefore, the VISMA inverter has a regulator which enables the VISMA inverter to function for other network participants such as synchronous machines. Further information on the VISMA inverter can be found in Hesse et al., "Microgrid stabilization using the Virtual Synchronos Machine (VISMA)", International Conference on Renewable Energy and Power Quality (ICREPQ'09), Valencia (Spain), April 15-17, 2009, and Chen et al., "Comparison of methods for implementing virtual synchronos machine on in-verters", RE&PQJ, Vol. 1, No. 10, April 10, 2012, pp. 734-739.

[0004] VISMA inverters have not yet been accepted by the market on a wider basis. Especially for the power of 1kW to 500kW, such inverters are still very rare. However, with the increasing number of inverters in renewable energy and the replacement of mechanical rotating energy, it is becoming more and more important to use such inverters so that the power grid can be kept stable, especially in the case of short-term power grid fluctuations. Determined by the principle, VISMA inverters are connected to the existing connection network without any problems and work in support of the network at the same time. These advantages should also be available in small networks, especially independent power supply networks. Therefore, preferably, the same VISMA inverter with the same regulator is also used in such a power grid. Here, if multiple VISMA inverters must be connected simultaneously to supply the load in order to supply the load, especially if there is no power grid voltage in advance, problems may occur. This is a typical case of starting a power grid that is turned off and must be started (Hochfahren). This start is also called black start. In independent power supply networks, especially in very small independent power supply networks, this is a frequent situation.

[0005] DE 10 2013 102 603 B4 discloses a method for black starting a power plant having a plurality of inverters connectable to a local AC power grid, wherein an AC voltage is built up in the AC power grid using a first inverter, the AC power grid is connected after a second inverter is synchronized with the AC voltage, a first AC voltage built up by the first inverter is reduced by at least one quarter relative to a nominal voltage of the AC power grid, and after the second inverter is connected, a second AC voltage increased relative to the first AC voltage is built up in the AC power grid. Summary of the invention

[0006] The object of the present invention is to provide a method and an inverter with which a network structure is achieved for operating loads which require more power than can be provided by each individual inverter.

[0007] According to the invention, this object is achieved by a method for building up a grid voltage from a plurality of independently controlled VISMA inverters, which are connected jointly to a load, wherein the load requires a greater power than can be provided by a single one of the VISMA inverters, the method comprising the following method steps:

[0008] a. Supply power to each inverter;

[0009] b. starting VISMA control in each VISMA inverter by predefining a target grid voltage, in particular on a control model of the VISMA inverter, in order to generate a virtual target grid voltage in each VISMA inverter,

[0010] c. Send synchronization events to all VISMA inverters so that the virtual target grid voltages of the VISMA inverters are phase matched to each other,

[0011] d. constructing an output AC voltage with an adjusted phase position in each VISMA inverter according to the target grid voltage and the synchronization event,

[0012] e. The grid voltage is built up simultaneously by all VISMA inverters with output AC voltage.

[0013] Since all independently regulated VISMA inverters are connected together to one load, it is clear that

[0014] a) The grid voltage can only be built up during the construction of a single output AC voltage, so the two steps d and e are carried out simultaneously, and

[0015] b) The grid voltage refers to the voltage across the connected load.

[0016] Here, “predetermining the target grid voltage” refers to predetermining at least the voltage amplitude and the frequency. Thus, each VISMA inverter can construct its own virtual target grid voltage.

[0017] Thus, for example, a black start of an independent power supply network or a joint power grid is possible by a plurality of independently regulated VISMA inverters, which simulate the behavior of a virtual synchronous machine (VISMA), wherein the required power of the load to be supplied exceeds the power of a single inverter. This can be understood as follows: before the output AC voltage is built up, the phase position of the VISMA inverter is adjusted by means of a synchronization event, and then the VISMA inverters continue to operate independently of each other according to their VISMA automatic regulators, and when the output AC voltage is built up, the phase position of the output AC voltage is further fully adjusted, i.e., the phase position differs only slightly between these two steps. This method has the advantage that when the grid voltage is built up, the load does not have to be separated from the VISMA inverter and must be connected via a power switch. The load can be coupled all the time. This saves expensive power switches (so-called contactors), as they are necessary in other arrangements.

[0018] For ease of understanding, it should be mentioned again that conventional VISMA inverters behave like virtual synchronous machines in terms of regulation technology, which can automatically support existing power grids or independent power supply networks and can be connected in parallel as arbitrarily as normal synchronous machines after synchronization has been completed. Here, a single conventional VISMA inverter can also build an independent power supply network to which other inverters can be synchronized. For the black start of an independent power supply network with multiple VISMA-based inverters at the same time, it is necessary that all inverters start voltage construction at the same time point as accurately as possible and with the same phase position. For this purpose, the inverters must be synchronized in advance. That is, synchronization refers to the adjustment of the phase position. The problem is that the existing system cannot be used during synchronization. This problem is solved by the described method.

[0019] The power used to supply the inverter may come from a DC source, in particular a battery.

[0020] Method steps b and c can be carried out simultaneously or successively in any order.

[0021] A simultaneous build-up of the mains voltage is understood to mean a time interval of typically less than one cycle (50 Hz→20 ms), preferably 5 ms or less, in particular 1 ms or less.

[0022] The target grid voltage can be specified as a function of a virtual target grid voltage at a specified grid frequency, which is in particular transmitted to a control model of the VISMA inverter.

[0023] Typically, the controller of the VISMA inverter uses the actual measured grid voltage for regulation. Since such a measured grid voltage does not exist, for example in the case of a black start, a stored or predefined value of such a grid voltage can be used. These values ​​form a "virtual target grid voltage". This virtual target grid voltage preferably has an amplitude, preferably a frequency and preferably a phase position.

[0024] Each inverter can generate a virtual target grid voltage itself. This has the advantage that the virtual target grid voltage does not have to be centrally specified and transmitted.

[0025] The phase position can be adjusted in the inverter by adjusting the phase position of the virtual target grid voltage. Thus, the output AC voltage can be synchronized before it is used to build the grid voltage.

[0026] Furthermore, the phase position can be adjusted by means of a synchronization event, in particular an edge, preferably a rising edge, of a synchronization pulse. Thus, a synchronization event can trigger an adjustment of the phase position of the virtual grid voltage and thus lead to an adjustment of the phase position of the output AC voltage.

[0027] The generation of the mains voltage can be triggered by a second synchronization event, in particular an edge, preferably a falling edge, of a synchronization pulse. This ensures that a mains voltage is generated that is suitable for supplying power to a load.

[0028] With or after the grid voltage is built up, the pre-determination of the target grid voltage can be changed from the dependency on the virtual target grid voltage to the dependency on the measured grid voltage. This change can be carried out in particular with or after the second synchronization event. Thus, the virtual target grid voltage can only be used to build up the grid voltage, and then the measured grid voltage can be used.

[0029] The load to be supplied can be evenly distributed on the inverters, in particular triggered by the second synchronization event. The even load distribution can be performed automatically based on the VISMA control.

[0030] A virtual current target value may be determined for each inverter, and the virtual current may be regulated to the virtual current target value.

[0031] The current target value can be determined by the VISMA inverter based on the measured grid voltage. As long as the target grid voltage is still a virtual target grid voltage, the current target value is also a virtual current target value. When switching from the virtual target grid voltage to the actual measured grid voltage, the presetting of the current value can also be changed in the same way.

[0032] However, if the actual grid voltage is measured on the existing grid before the inverter is connected to the existing grid, regulation can also be performed based on a virtual current target value. Here, synchronization on the existing grid can be performed by measuring the grid voltage applied externally, which is transferred to the regulation model of the inverter. Then, the model calculates a virtual current target value based on the measured grid voltage, which is returned to the model as an actual value. In this way, the virtual current is regulated to such a value: the value may appear on the existing grid during actual operation. Once the model adjusts the virtual current to a constant value, the inverter can be connected to the grid and switched to the actual value of the actual grid voltage of the existing grid for real regulation.

[0033] For black starts with multiple inverters, according to the invention, the synchronization mechanism described above is used, in addition to virtually generating the externally measured grid voltage in the individual inverters. The phase position of the virtual target grid voltage on all inverters can be adjusted precisely to a few μs, for example 4 μs or less, in particular by the rising edge of the synchronization pulse sent by the controller to all inverters. Then, the synchronization process described for parallel operation of the grid can be started by the control model.

[0034] The grid voltage can be built up after the virtual current regulation time has expired. After the virtual current regulation time has expired, the controller can output the falling edge of the synchronization pulse, and then all inverters can switch to regulation with the actual measured voltage simultaneously within a few μs and can build up the grid voltage together. In this way, large loads are evenly distributed to the inverters from the beginning.

[0035] Typically, the adjustment time can be 1 to 10 grid cycles. This means typically 20 ms to 200 ms. The adjustment time can be predetermined. Too large a value can be disadvantageous, since the phase position synchronization can again change to such a large extent that it is no longer sufficient for simultaneous starting. This is because each inverter usually has its own time base, which can be inaccurate.

[0036] It is conceivable to implement the default values ​​for the inverter in a standardized form for the control time.

[0037] Furthermore, it is conceivable that no adjustment time is predefined, but that it is recognized as expired when all inverters are adjusted. For this purpose, an additional communication channel must exist between the inverters, on which the inverters can communicate that they are adjusted.

[0038] Furthermore, it is conceivable that no control time is predefined, but rather the grid voltage is built up when the deviation of the virtual current target value from the virtual current actual value in all inverters lies below a reference value.

[0039] During or after the control time, the specification of the target grid voltage can be changed from a dependence on a virtual target grid voltage to a dependence on a measured grid voltage.

[0040] The grid voltage can be built up by a defined ramp. The duration of the defined ramp can typically be half, the entire ramp or a maximum of 5 cycles. Overcurrents can be avoided by gradually building up the grid voltage on a defined ramp, in particular when supplying capacitive and / or inductive loads. For example, the ramp can be implemented by intentionally overlapping the regulation, in particular the regulation in each inverter, with the calibration operation by the duration of the ramp and not exceeding the determined maximum values ​​for the voltage and / or current. Alternatively, the regulation can be performed by a reduced regulation value.

[0041] The inverter can be connected to the intermediate circuit (DC link) to supply it with power. This can be done, for example, by switching switches.

[0042] Furthermore, a VISMA inverter is also within the scope of the present invention, the VISMA inverter having a synchronization event input and being configured for

[0043] a. establishing a VISMA control of an output AC voltage at its output in accordance with a predetermined target grid voltage, which can in particular be predetermined for a control model of the VISMA inverter, and the VISMA inverter is configured to generate a virtual target grid voltage in accordance with the predetermined target grid voltage and further configured to synchronize the virtual target grid voltage based on a first synchronization event received at a synchronization event input, and thus

[0044] b. synchronizing the phase position of the output AC voltage based on the first synchronization event received on the synchronization event input, and

[0045] c. Build up the grid voltage after completing the synchronization of the phase positions.

[0046] Furthermore, a set of at least two such inverters also falls within the scope of the present invention.

[0047] Such inverters are particularly suitable for building up a grid voltage, in particular a grid voltage for supplying power to a load, in conjunction with other similar inverters, wherein each individual inverter is not designed to provide the power required by the load.

[0048] In this case, the inverter can further be designed to build up the grid voltage synchronously with the second synchronization event.

[0049] The invention further relates to a voltage network having a plurality of independently regulated VISMA inverters according to the invention, having a synchronization event generator connected to each synchronization event input of the inverter, wherein the inverters are designed to synchronize the phase position of their output AC voltages with one another. For this purpose, each inverter can have a CPU, an embedded controller, an FPGA or a combination of some of the above mentioned.

[0050] The grid voltage in such a voltage grid can be built up in particular in a black start manner.

[0051] The inverter can be connected to a system controller. In this case, the system controller can be a higher-level controller, which is operated, for example, by a grid supplier.

[0052] The system controller can be designed to output a synchronization signal to the inverter. The synchronization signal can be an electrical pulse supplied via a line. The synchronization signal can also be supplied wirelessly. It can also be a data exchange, through which all inverters are informed to synchronize at a certain synchronization time. For this purpose, the inverter must have a synchronized clock. For example, this can be done by a GPS time signal, a DCF77 time signal or other synchronization signals (for example, based on WIFI or a mobile phone network, such as 5G).

[0053] A control model can be stored in the inverter or, in the case of a voltage grid, in at least one inverter, which control model is designed to calculate a virtual current that is fed back to the control model as a virtual current target value. This results in the advantages described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Further advantages of the invention are apparent from the description and the drawings. Likewise, according to the invention, the above-mentioned and still further explained features can be used individually or in multiples in any combination. The embodiments shown and described are not to be understood as a final enumeration, but rather have an exemplary character for the description of the invention.

[0055] Figure 1 A diagram showing a voltage network with a plurality of inverters;

[0056] Figure 2 showing synchronization of phase positions of multiple AC voltages;

[0057] Figure 3 shows a virtual current;

[0058] Figure 4 shows synchronization for building up the grid voltage;

[0059] Figure 5 A flow chart of the method according to the invention is shown. DETAILED DESCRIPTION

[0060] Figure 1 A voltage grid 10 is shown with a plurality of independently regulated VISMA inverters 12, 14, 16. The inverters 12, 14, 16 are connected to an intermediate circuit voltage 18, whereby the inverters 12, 14, 16 are supplied with a DC voltage. On the output side, the inverters 12, 14, 16 are connected to a load 20, wherein the load 20 requires more power than each individual inverter 12, 14, 16 can provide.

[0061] The inverters 12, 14, 16 are connected to a synchronization event generator 22, which may be arranged in a central controller 24. In particular, the synchronization event generator 22 is connected to each synchronization event input 26, 28, 30 of the inverters 12, 14, 16. The inverters 12, 14, 16 are designed to synchronize the phase positions of their output AC voltages with each other.

[0062] In particular, the inverters 12, 14, 16 are configured to establish VISMA regulation of the output AC voltage at their respective output terminals 32, 34, 36 according to a predetermined target grid voltage. In addition, they are configured to synchronize the phase position of the output AC voltage based on the first synchronization event received at the synchronization event input terminals 26, 28, 30, and to establish the grid voltage to supply the load 20 after the synchronization of the phase position is completed.

[0063] If the system controller 24 receives a switch-on command, the inverters 12, 14, 16 are connected to the intermediate circuit voltage 18, for example, by operating corresponding switches, so that the inverters 12, 14, 16 are supplied with power. Next, the inverters 12, 14, 16 wait for the first synchronization event from the synchronization event generator 22, such as the rising edge 40 of the synchronization pulse, see Figure 2 .

[0064] Figure 2-4 The situation is shown for one of the inverters 12 , 14 , 16 , respectively.

[0065] When a synchronization event is detected, each inverter 12, 14, 16 can form a three-phase internal virtual target grid voltage 42, 44, 46 corresponding to a predetermined target grid voltage. In this case, each inverter 12, 14, 16 is connected to the same phase position (in Figure 2It is also conceivable that an internal virtual target grid voltage is first generated according to a predetermined target grid voltage and then the phase position is synchronized according to a synchronization event. The virtual target grid voltages 42, 44, 46 are introduced into the VISMA control model, which calculates the virtual current 50 ( Figure 3 ), which in turn is fed back into the control model as a virtual current target value.

[0066] The output AC voltage is built up with an adjusted phase position as a function of the (virtual) target grid voltage and a first synchronization event in each inverter 12 , 14 , 16 .

[0067] The synchronization pulse remains high for such a long time until the virtual current 50 is adjusted to a constant value (see Figure 3 If the virtual current 50 is set, the inverters 12, 14, 16 receive a second synchronization event 54, in particular a falling edge of a synchronization pulse (see Figure 4 ).

[0068] Figure 4 First, a virtual grid voltage 55 is shown. After the second synchronization event 54, they remain constant. When the second synchronization event 54 occurs, a switch is made from the control model to control with the actual value of the actual grid voltage of the existing grid. The inverters 12, 14, 16 then build up the grid voltage 56 via a defined ramp.

[0069] Figure 5 The method steps of the method according to the invention are given.

[0070] In step 100 , each inverter 12 , 14 , 16 is supplied with power, for example with a DC voltage power, for example with an intermediate circuit voltage power.

[0071] In step 102, VISMA control is started by predefining a target grid voltage (for example a virtual target grid voltage) in each inverter 12, 14, 16. In this case, the target grid voltage can be predefined, in particular, on the basis of a control model of the VISMA inverters 12, 14, 16 in order to generate a virtual target grid voltage 42, 44, 46 in each VISMA inverter 12, 14, 16.

[0072] In step 104 , a synchronization event is sent to all VISMA inverters 12 , 14 , 16 . The sending is used to phase-match the virtual target grid voltages 42 , 44 , 46 of the VISMA inverters 12 , 14 , 16 .

[0073] Steps 104 (sending of a synchronization event) and 102 (activation of VISMA regulation in each inverter) may be performed simultaneously or in any order.

[0074] In step 106, an output AC voltage with an adjusted phase position is built up in each VISMA inverter 12, 14, 16 according to the target grid voltage and the synchronization event. In this case, the VISMA inverters 12, 14, 16 are regulated independently of one another according to their own VISMA control algorithms.

[0075] In step 108 , the grid voltage 56 is simultaneously built up by all inverters 12 , 14 , 16 having an output AC voltage.

[0076] Since all independently controlled VISMA inverters 12 , 14 , 16 are connected jointly to the load 20 , it is clear that, here,

[0077] a) the grid voltage 56 can only be built up during the construction of a single output AC voltage, so that the two steps 106 and 108 are carried out simultaneously, and

[0078] b) The grid voltage 56 refers to the voltage across the connected load 20 .

Claims

1. A VISMA inverter (12), comprising: Synchronous event input terminal (26), a connection point for connection to an intermediate circuit voltage (18) for supplying power to the inverter (12), An output (32) for connection to a load (20) and at least one further output (34, 36) of a further VISMA inverter (14, 16), wherein the load (20) requires more power than the inverter (12) alone can provide, Wherein, the VISMA inverter is constructed as follows: a. constructing a VISMA regulation of the output AC voltage at the output end (32) of the VISMA inverter according to a predetermined target grid voltage, b. synchronizing the phase of the output AC voltage to a first synchronization event received at the synchronization event input (26, 28, 30) and c. After the phase synchronization has been completed, the VISMA inverter builds up the grid voltage (56) from the voltage present at the connection point for connection to the intermediate circuit voltage (18).

2. The VISMA inverter (12, 14, 16) according to claim 1, characterized in that The VISMA inverter is further designed as a VISMA inverter that builds up the grid voltage (56) synchronously with a second synchronization event.

3. The VISMA inverter (12, 14, 16) according to claim 1 or 2, characterized in that: A control model is stored in the inverter (12, 14, 16), which is designed to calculate a virtual current (50) which is returned to the control model as a virtual target value.

4. A voltage network (10) having a plurality of independently regulated VISMA inverters (12, 14, 16) according to any one of claims 1 to 3, the voltage network having a synchronization event generator (22) connected to each synchronization event input (26, 28, 30) of the inverters (12, 14, 16), wherein: The inverters (12, 14, 16) are configured as inverters in which the phase positions of the output AC voltages of the inverters are synchronized with each other.

5. The voltage network according to claim 4, characterized in that: The inverter (12, 14, 16) is connected to a system controller (24).

6. The voltage network according to claim 4 or 5, characterized in that: The system controller (24) is designed to output a synchronization signal to the inverters (12, 14, 16).

7. The voltage network according to claim 4 or 5, characterized in that: A control model is stored in the inverter (12, 14, 16), which is designed to calculate a virtual current (50) which is returned to the control model as a virtual target value.

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