Adjustment of parameter values of control rules of a generator

Abstract

A method for controlling a generator (1) comprising an inverter (2) and an electric energy source (3), the generator (1) being configured to deliver an output electrical value (V S ) to an electricity distribution grid, the inverter (2) being controlled by a control law (5) comprising a set of fixed values of parameters (p ref ) used to model the operation of a synchronous virtual generator, such that the control law (5) is configured to determine at least one target output value (V S,target ) that must be delivered by said generator (1) to the electricity distribution grid.

Description

Technical Field

[0001] This invention relates to a method for controlling a generator.

[0002] The present invention also relates to a generator using this method. Background Technology

[0003] Microgrids are typically local grids used to produce and distribute electricity in areas that are usually isolated from and far from major power production centers.

[0004] Such isolated areas are, for example, islands, mountainous regions, or desert areas.

[0005] The principle of microgrids can also be applied when a building or group of buildings, or any other entity connected to a large distribution network, wishes to at least partially manage its own power production.

[0006] Therefore, the main advantage of microgrids is that they operate autonomously and are located near consumption areas (also known as "loads"). Consequently, the inherent losses in long-distance distribution networks are limited.

[0007] The power capacity of a microgrid is typically guaranteed by one or more different types of electrical energy, including renewable energy sources such as solar or wind power.

[0008] In order to supply power to a microgrid, a generator includes at least an electrical power source and an inverter.

[0009] The power source generates electrical power by producing DC voltage and current. The DC voltage and current are then converted into AC voltage and current by an inverter.

[0010] Inverters can be controlled using static control laws to simulate generator behavior. Then, let's discuss virtual generators. Therefore, virtual generators can be connected in parallel with other generators on the microgrid.

[0011] However, under certain conditions, this virtual generator may face instability, especially in the event of a short circuit or low current cycle on a microgrid.

[0012] In particular, such short circuits can occur when several events affect the microgrid, such as when maintenance work causes an unexpected breakage of a cable on the microgrid.

[0013] The control law may not be sufficient to effectively control the electrical values ​​at the generator output.

[0014] To overcome this problem, document WO 2012 / 116559 A1 and Rahmani et al., in their presentation “Virtual synchronous generators for microgrid stabilization: Modeling, implementation and experimental validation on a microgrid laboratory” at the IEEE 2017 Asian Conference on Energy, Power and Transport Electrification, provided, for example, an impedance referred to as virtual impedance, to ensure better inverter stability.

[0015] According to another example, the control law provided in document FR 1858434 includes integral and correction loops to adjust the electrical values ​​at the inverter output.

[0016] However, while these methods have proven satisfactory in general, they may prove insufficient, especially when instability on the power grid is shown to be of particularly short duration and / or excessive magnitude.

[0017] Therefore, the resulting overvoltage or overcurrent can easily degrade generator performance, especially inverter performance.

[0018] When instability occurs, and in order to protect the generator, one solution currently implemented is to temporarily disconnect the inverter from the microgrid.

[0019] However, a drawback of this disconnection is that it prevents the distribution of electricity from the source. This necessitates restarting the generator. Furthermore, especially in the case of microgrids, this disconnection can further destabilize the microgrid, creating new instabilities that may be detrimental to other generators connected to it.

[0020] Therefore, one of the objectives of this invention is to find a method for controlling a generator, and a simple, reliable and economical generator that improves the solution to problems related to instability. Summary of the Invention

[0021] This invention improves upon this situation.

[0022] A method is proposed for controlling a generator comprising an inverter and electrical energy, the generator being configured to deliver an output electrical value to a distribution network. The generator is controlled by a control law comprising a set of fixed values ​​for a set of parameters used to model the operation of a virtual generator, such that the control law is configured to determine at least one target output value that must be delivered by the generator to the distribution network. The method includes:

[0023] At least one target output value is determined by a control law;

[0024] Compare the target output value with at least one of the generator's maximum allowable values;

[0025] If the target output value is higher than the maximum allowable value, then determine the correction value for at least one parameter of the control law.

[0026] These configurations improve generator performance compared to generators controlled by static control laws. In particular, the generator can achieve satisfactory electrical output values, especially under unstable distribution network conditions.

[0027] The features disclosed in the following paragraphs may be used optionally. They may be used independently or in combination:

[0028] According to one embodiment, if the target output value is lower than or equal to the maximum allowable value, the parameters of the control law are kept at a fixed value.

[0029] According to another embodiment, the steps of the method are repeated periodically, and during the next iteration k+1 of the method, the control law includes the parameter values ​​determined during the previous iteration k.

[0030] According to another embodiment, the steps of the method are repeated at a frequency greater than 1 kHz or even greater than 5 kHz.

[0031] According to another embodiment, the generator simulates a synchronous generator that transmits current, the frequency of which is determined by the rotor speed relative to the stator. The parameters of the control law are selected from the stator resistance, transient inductance, permanent inductance, and transient open-loop time of the stator of the synchronous virtual generator.

[0032] According to another embodiment, a target output value is determined by a control law based on at least one electrical output value measured at the generator terminals.

[0033] According to another embodiment, a correction value for the parameter is determined in order to minimize the difference between the correction value and the fixed value of the parameter.

[0034] According to another embodiment, a correction value for the parameter is determined in order to minimize the difference between the correction values ​​of the parameter obtained during two consecutive iterations k, k+1 of the method step.

[0035] According to another embodiment, the output electrical value is selected from the current value, voltage value, and frequency value.

[0036] According to another embodiment, the method is configured to control the output electrical value of a generator when instability occurs on the power distribution network.

[0037] According to another aspect, a computer program comprising instructions is proposed, which, when executed by a processor, causes the method according to the invention to be implemented.

[0038] According to another aspect, a non-temporary recording medium readable by a processor is proposed, on which a program for implementing the method according to the invention is recorded.

[0039] According to another aspect, a generator comprising an inverter and electrical energy is proposed, the generator being configured to deliver an output electrical value to a distribution network. The generator is controlled by a control law comprising a set of fixed values ​​for a set of parameters used to model the operation of a virtual generator, such that the control law is configured to determine at least one target output value that must be delivered by the generator to the distribution network. The generator includes a processor configured to:

[0040] At least one target output value is determined by a control law;

[0041] Compare the target output value with at least one of the generator's maximum allowable values;

[0042] If the target output value is higher than the maximum allowable value, then determine the correction value for at least one parameter of the control law.

[0043] According to one embodiment, the generator is configured to deliver output electrical values ​​to the microgrid.

[0044] According to another embodiment, the electrical energy is a renewable energy source. Attached Figure Description

[0045] Other features, details, and advantages will become apparent from the following detailed description and analysis of the accompanying drawings:

[0046] Figure 1

[0047] Figure 1 It is a schematic representation of a virtual generator known in the prior art.

[0048] Figure 2

[0049] Figure 2 It is a representation of the equivalent circuit diagram of the connection between the inverter and the power distribution network.

[0050] Figure 3

[0051] Figure 3 This is a schematic representation of the control method according to the present invention.

[0052] Figure 4

[0053] Figure 4It is a representation of the voltage value of a three-phase virtual generator after a short circuit on a distribution network (on the left) as known in the prior art and the voltage value of a three-phase virtual generator after the same short circuit on a distribution network according to the present invention (on the right).

[0054] Figure 5

[0055] Figure 5 It is a representation of the current value of a three-phase virtual generator after a short circuit in a distribution network (on the left) as known in the prior art and the current value of a three-phase virtual generator after the same short circuit in a distribution network according to the present invention (on the right). Detailed Implementation

[0056] The accompanying drawings and the following description primarily contain elements of certain characteristics. Therefore, they can be used not only to better understand this disclosure, but also to aid in its definition where necessary.

[0057] dynamo

[0058] Figure 1 A virtual generator according to the present invention, particularly a synchronous virtual generator, is illustrated schematically.

[0059] "Virtual generator" refers to a generator that appears as an autonomous device capable of generating electricity.

[0060] This virtual generator is Figure 1 As shown in the document EP 3208907, the contents of which are incorporated herein by reference.

[0061] Although described in the context of a specific virtual generator, the invention is not to be limited to this aspect. In particular, any generator for transmitting current and voltage (especially alternating current and voltage) on a distribution network can be contemplated.

[0062] The distribution network can be a microgrid or a traditional distribution network. Generator 1 is then configured for grid formation.

[0063] Generator 1 includes at least one inverter 2 and electrical energy source 3.

[0064] Inverter 2 is configured to connect to the distribution network and supply the output electrical value V to the distribution network. S Output electrical value V S Specifically, AC voltage V abc and alternating current I abc Both of these have a frequency f abc Output electrical value V S It can also include active power P abc and reactive power Q abc .

[0065] Output electrical value V S Inverter 2 is the input electrical value V E The result of the conversion. Input electrical value V E In particular, the DC voltage V generated by electrical energy source 3 c and DC current I c .

[0066] Inverter 2 is equipped with an electronic switch based on what is known as the instantaneous duty cycle α. abc The duty cycle is used for control, so that the output electrical value V can be controlled. S It is transmitted to the power distribution network.

[0067] Electronic switches may include, for example, insulated-gate bipolar transistors (IGBTs).

[0068] Electric energy source 3 can be a renewable energy source, including, for example, photovoltaic panels, wind turbines, marine turbines, or thermal engines. Other types of renewable electric energy sources are also possible.

[0069] Renewable energy source 3 is susceptible to unpredictable weather events, and is therefore an unstable and intermittent energy source.

[0070] The generator 1 may also include an electrical and / or energy accumulation system 4, such as a battery.

[0071] Control Law

[0072] In order to adjust and optimize the output electrical value V transmitted to the distribution network S Generator 1, and especially inverter 2, are driven by control law 5.

[0073] Control law 5 is implemented by a data processing device such as a computer, calculator, processor, or control card.

[0074] Control law 5 is configured to provide a match between the electrical power generated by electrical energy source 3 and the power consumed by the distribution network.

[0075] Control law 5 is also configured to enable generator 1 to respond to load demands on the distribution network and / or fluctuations in the power generation of electrical energy 3.

[0076] "Load demand" specifically refers to the change in power consumed by loads on a distribution network. As a non-limiting example, loads can be industrial equipment (such as factories and their machinery), household appliances, street facilities in a distribution network, charging terminals, or others.

[0077] According to one embodiment, control law 5 is thus configured to cause generator 1 to simulate the behavior of a synchronous generator.

[0078] A "synchronous generator" refers to a generator that produces an electric current whose frequency is determined by the rotational speed of the movable part (rotor) relative to the stationary part (stator).

[0079] Therefore, refer to Figure 1 (Document EP 3208907) Figure 1 a) Control law 5 may include various blocks. In particular, control law 5 includes control block 100.

[0080] Control block 100 is configured to determine the control values ​​used to control inverter 2, such that the output electrical value V S Equal to or close to the target output value V S,target Therefore, the target output value V S,target It can be the electrical value of inverter 2.

[0081] Inverter 2 can therefore deliver an output electrical value V adapted to the distribution network. S .

[0082] method

[0083] Control Law 5 involves solving the electromechanical differential equations used to model the operation of the virtual generator and its connection to the distribution network. Using Control Law 5 requires the development of computer programs (or algorithms) based on these differential equations.

[0084] For illustrative purposes only, the following describes the equations for modeling the operation of a synchronous virtual generator based on a specific modeling known to those skilled in the art. Naturally, the invention is not limited to this model, and other known models can also be used to establish control law 5.

[0085] In the following text, the symbols shown in the table below are used to model synchronous virtual generators:

[0086] [Table 1]

[0087]

[0088]

[0089] The modeling uses the transformation dq0 associated with the synchronous motor and three-phase inverter. Based on this modeling, the magnetic flux on the synchronous generator shafts d and q can be described as follows:

[0090] [Mathematical Expression 1]

[0091]

[0092]

[0093]

[0094] Furthermore, the output currents on axes d and q of the synchronous virtual generator can be described as follows:

[0095] [Mathematical Expression 2]

[0096]

[0097]

[0098] Modeling can also specifically utilize the characteristics of the distribution network and inverter 2. These characteristics of the distribution network are imposed and cannot be corrected. Then, the symbols shown in the table below are... Figure 2 Relevant use:

[0099] [Table 2]

[0100] variable definition <![CDATA[V c ]]> Voltage of a filtered single-wire power grid <![CDATA[V r ]]> Voltage of a single-wire power grid <![CDATA[L L and R L ]]> Inverter impedance and resistance <![CDATA[L r and R r ]]> Impedance and resistance of the power grid <![CDATA[C f and R f ]]> Capacitors and resistors of the output filter

[0101] In this way, parameters are obtained for modeling the synchronous virtual generator and its connection to the distribution network.

[0102] As shown in the equation above, the control law typically includes a fixed value p for the parameters used to model the virtual generator. ref , here corresponding to R α L' d L d L q 、T' do Next, let's talk about static control laws. The number of parameters in a control law can certainly be more or less, because there are models available with greater or less complexity.

[0103] "Fixed values ​​of parameters of static control law" means values ​​determined when the control law is established and which remain unchanged over time, especially when the generator is running.

[0104] As is known in the prior art, such a control law 5 thus allows us to obtain an equation that can be simplified as follows:

[0105] [Mathematical Expression 3]

[0106] V S,target (k+1)=M[p ref V S (k)]

[0107] M corresponds to modeling, which specifically corresponds to solving the differential equation under consideration, p ref The fixed value of the parameter corresponding to the static control law, V S This corresponds to the output electrical value of inverter 2 at time k.

[0108] Of course, control law 5 can also consider other values, especially electrical values ​​that are not described here for simplicity. For example, control law 5 can also consider the DC voltage value V of electrical energy source 3. c and DC current value I c Or any other value.

[0109] Therefore, it can be based on the fixed value p of the parameter. ref and the output electrical value V measured at time k S Determine the target output value V for controlling the inverter at time k+1. S,target .

[0110] Therefore, considering the output electrical value V S This allows for continuous detection of fluctuations in the distribution network and, based on the target output value V S,target These values ​​are adjusted in real time, with the target output value V. S,target The setpoint value is determined by the control law and used as the setpoint value for inverter 2.

[0111] However, when controlling generator 1 during certain unstable periods (especially during short durations and / or high amplitudes), this fixed value p is appropriate. ref The static control law can be proven to be unsatisfactory.

[0112] "Short-duration instability" refers to a temporary divergent mode that results in an unstable state that differs from the acceptable and usual stable state of generator 1. Instability can, in particular, have a duration of less than 20 milliseconds, or even less than 10 seconds, or even less than 5 milliseconds.

[0113] For example, instability is particularly likely to occur when generator 1, which does not generate any current, reaches its maximum power output very quickly. Instability can also occur during short circuits, causing the nominal voltage V to drop. abc It drops to 0 (or close to 0) within seconds.

[0114] Therefore, the control method according to the present invention allows the parameter values ​​of control law 5 to be adjusted over time. Next, let's discuss the dynamic control law, which differs from the static control law. The parameter values ​​are no longer necessarily equal to the fixed value p of the static control law. ref .

[0115] Therefore, when instability occurs in the distribution network, the parameter values ​​of the modified control law 5 allow the acceptable electrical output value V to be determined by eliminating the inherent limitations in modeling the operation of the virtual generator. S .

[0116] refer to Figure 3 The control method according to the present invention will be described in more detail.

[0117] According to step 101, control law 5 is implemented. Control law 5 specifically considers the output electrical value V of generator 1. S The measured value of (k). More specifically, these output electrical values ​​V S (k) is measured at the output of inverter 2 at time k.

[0118] According to step 102, inverter 2 must actually deliver the target output value V to the distribution network at time k+1. S,target (k+1) is determined according to control law 5.

[0119] These target output electrical values ​​V S,target It is not permissible to cause any overvoltage or overcurrent in generator 1, otherwise it may easily cause its operation to degrade.

[0120] Therefore, according to step 103, the target output value V is determined. S,target Is it easy to exceed the maximum allowable value V? S,max More specifically, the maximum allowed value V is... S,max In particular, the maximum operating value of generator 1 (especially inverter 2) is inherent to its design and operating electrical characteristics.

[0121] According to one embodiment, the target output value V S,target Therefore, in step 103, the acceptable maximum value V is... S,max Compare them.

[0122] According to the embodiment described in more detail below, the target output value V S,target It can include AC voltage V abc (corresponding to the values ​​e along the axes d and q of the transformation dq0) d and e q Alternating current I abc (corresponding to the values ​​i along the axes d and q of the transformation dq0) d and i q and duty cycle α abc (corresponding to the values ​​α of axes d and q along the transformation dq0) d and α q ).

[0123] According to this embodiment, a maximum value V is allowed. S,max This may specifically include the maximum allowable output current value I of the inverter. max The allowable duty cycle α of the inverter max The maximum output value and / or the maximum allowable output voltage value e of the inverter max .

[0124] By calculating, for example, the target output value VS,target and maximum value V S,max The difference between the absolute values ​​can determine the value exceeding the case V. e V i V α As shown below:

[0125] [Mathematical Expression 4]

[0126]

[0127]

[0128]

[0129] Other methods for calculating out-of-value cases are also possible; it should be understood that the term refers to the mathematical distance between the compared values.

[0130] In step 104, the target output value V is determined. S,target And the maximum allowable value V S,max Case V of exceeding the value between e V i V α Whether at least one of them is greater than or less than 0.

[0131] If all calculated out-of-range cases are less than or equal to 0, this means there is no electrical output value V. S Easy to exceed the maximum allowable value V S,max .

[0132] Therefore, in step 105, the parameter is fixed at a value p. ref At time k+1, parameter p(k+1) is assigned. This is because the static control law is sufficient to ensure the satisfactory behavior of generator 1, which conforms to its electrical operating limits.

[0133] Conversely, if at least one of the out-of-value cases is greater than 0, this means that at least one electrical output value V S It is easy not to keep at the maximum allowable value V S,max Within the restrictions.

[0134] If this target output value V S,target In practice, if used to control inverter 2 (as is typically the case according to static control laws), generator 1 will be at risk of being subjected to overcurrent or overvoltage conditions, leading to operational degradation. Static control laws are insufficient to ensure that generator 1 behaves satisfactorily within its electrical operating limits.

[0135] Therefore, it is necessary to optimize the value of parameter p(k+1) at time k+1 (step 106).

[0136] Therefore, according to step 107, the parameter values ​​of control law 5 are corrected. Then, the correction value p of the parameters of control law 5 is determined. optim .

[0137] Correction value p optim First, by setting the correction value p optim Relative to the fixed value p of the static control law ref Minimize the changes, and then limit the maximum allowable value V. S,max Any excess thereof is advantageously determined.

[0138] According to one embodiment, the correction value p optim It can be determined, for example, by a quadratic solution.

[0139] According to this embodiment, the goal is to minimize the cost function, for example, such that:

[0140] [Mathematical Expression 5]

[0141]

[0142] Furthermore, the aim is to limit the maximum allowable value V. S,max Any condition exceeding this can be written as:

[0143] [Mathematical Expression 6]

[0144]

[0145] μ and β are fixed values. M allows us to consider the acceptable error ε for each output value to ensure convergence to a possible solution is minimized. β aims to ensure the correction value p at time k+1. optim k+1 Keep close to the correction value p obtained at the previous time k. optim k .

[0146] According to the specific described embodiments, ε E ,ε i ,ε α Corresponding to the case of exceeding the value V e V i V α The acceptable error. These errors ε E ,ε i ,ε α It is advantageously smaller, or even equal to 0. This represents a three-row, one-column vector with zero values.

[0147] Once the correction value p has been obtained optim Control law 5 can include these correction values ​​p optim And it enables the determination of the target output value V that provides suitable control for generator 1.S,target .

[0148] The steps of the control method can be repeated, particularly periodically. More specifically, the steps of the method are repeated at regular time intervals, for example, at frequencies greater than 1 kHz, or even 5 kHz, or even approximately 6.66 kHz.

[0149] In one variant, the control method considers a time window at each iteration and then offsets the time window by sliding during each consecutive iteration.

[0150] Experimental results

[0151] Figure 4 and Figure 5 The results obtained according to the method of the invention (on the right) are presented after a short circuit on the distribution network, compared with a virtual generator using only the control law statically (on the left).

[0152] Clearly, the method according to the invention makes it possible to prevent overvoltage or overcurrent exceeding the generator's permissible maximum value.

[0153] Obviously, the present invention is not limited to the embodiments described above, and the embodiments described above are provided only as examples. It covers various modifications, alternatives or other variations that can be conceived by those skilled in the art in the context of the present invention, in particular all combinations of the various operating modes described above, which can be used alone or in combination.

Claims

1. A method for controlling a generator (1) comprising an inverter (2) and an electric energy source (3), the generator (1) being configured to deliver an output electrical value (V S ) to an electricity distribution grid, the generator (1) being controlled by a control law (5) comprising a set of fixed values (p ref ) of parameters used to model the operation of a virtual generator, such that the control law (5) is configured to determine at least one target output value (V S,target ) that must be delivered by the generator (1) to the electricity distribution grid, the method comprising: At least one target output value (V) is determined by control law (5). S,target ); Set the target output value (V) S,target At least one of the allowable maximum values ​​(V) of the generator (1) S,max ) for comparison; If the target output value (V) S,target ) higher than the maximum allowable value (V) S,max Then determine the correction value (p) of at least one parameter of the control law (5). optim ), The generator (1) simulates a synchronous generator transmitting current, the frequency of which is determined by the rotor speed relative to the stator. The parameters of the control law (5) are derived from the stator resistance (R) of the synchronous virtual generator. α Transient inductance on the stator shaft d (L') d ), permanent inductance on the stator shaft d (L d ), permanent inductance on the stator shaft q (L q ) and transient open-loop time (T' do Choose from ).

2. The method according to claim 1, further comprising: if the target output value (V) S,target ) less than or equal to the maximum allowable value (V) S,max ), then the parameters of control law (5) are kept at a fixed value (p ref ).

3. The method according to any one of claims 1-2, wherein the steps of the method are repeated periodically, and during the next iteration k+1 of the method, the control law (5) includes the parameter values ​​(p) determined during the previous iteration k. optim ).

4. The method according to any one of claims 1-2, wherein the steps of the method are repeated at a frequency greater than 1 kHz or even 5 kHz.

5. The method according to any one of claims 1-2, wherein the target output value (V) S,target By means of control law (5) based on at least one output electrical value (V) measured at the terminals of generator (1), S To determine.

6. The method according to any one of claims 1-2, wherein the correction value of the parameter (p) is determined. optim ) so that the correction value of the parameter (p) optim ) and fixed value (p) ref Minimize the difference between them.

7. The method according to any one of claims 1-2, wherein the correction value of the parameter (p) is determined. optim This is done so that the difference between the corrected values ​​of the parameters obtained during two consecutive iterations k, k+1 of the steps in the method is minimized.

8. The method according to any one of claims 1-2, wherein the output electrical value (V) S ) is from the current value (I abc ), voltage value (V) abc ) and frequency value (f abc Selected from ).

9. The method according to any one of claims 1-2, configured to control the output electrical value (V) of generator (1) when instability occurs on the distribution network. abc ).

10. A computer program product comprising instructions that, when executed by a processor, cause the implementation of the method according to any one of claims 1 to 9.

11. A non-temporary recording medium readable by a processor, having thereon recorded a program for implementing the method according to any one of claims 1 to 9.

12. A generator (1) comprising an inverter (2) and electrical energy (3), the generator (1) being configured to supply an output electrical value (V) to a distribution network. S The generator (1) is controlled by a control law (5), which includes a set of fixed values ​​(p) of parameters used to model the operation of the virtual generator. ref ), so that the control law (5) is configured to determine at least one target output value (V) that the generator (1) must deliver to the distribution network. S,target The generator (1) includes a processor configured to: At least one target output value (V) is determined by control law (5). S,target ); Set the target output value (V) S,target At least one of the allowable maximum values ​​(V) of the generator (1) S,max ) for comparison; If the target output value (V) S,target ) higher than the maximum allowable value (V) S,max Then determine the correction value (p) of at least one parameter of the control law (5). optim ), The generator (1) simulates a synchronous generator transmitting current, the frequency of which is determined by the rotor speed relative to the stator. The parameters of the control law (5) are derived from the stator resistance (R) of the synchronous virtual generator. α Transient inductance on the stator shaft d (L') d ), permanent inductance on the stator shaft d (L d ), permanent inductance on the stator shaft q (L q ) and transient open-loop time (T' do Choose from ).

13. The generator (1) according to claim 12, configured to supply an output electrical value (V) to a microgrid. S ).

14. The generator (1) according to claim 12 or 13, wherein the electrical energy (3) is a renewable energy source.

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