Method and apparatus for harmonic compensation

Abstract

Embodiments of the present disclosure relate to methods and arrangements for harmonic compensation. A method and arrangement for harmonic compensation in an electrical system, the electrical system comprising an alternating current network, at least one load entity (10) comprising at least a first electrical power converter (11, 12) connected to the alternating current network, and a harmonic compensation entity (20) connected to the alternating current network, the method comprising estimating at least one harmonic current component caused by the at least one load entity (10) in the alternating current network based on at least data indicative of an operating point of the at least one load entity (10), and performing, by the harmonic compensation entity (20), at least partial harmonic compensation in the alternating current network based on the estimated at least one harmonic current component caused by the at least one load entity (10).

Description

Technical Field

[0001] This invention relates to a method and apparatus for harmonic compensation in an electrical system. Background Technology

[0002] As an example, an electric drive, such as a motor drive, may have an uncontrolled AC-to-DC diode rectifier (or line-commutated thyristor rectifier), which may cause low-order current harmonics to flow into the AC power grid to which it is connected. Since the impedance of the AC system is not zero, such current harmonics can also cause AC voltage harmonics and distortion, potentially leading to several consequences, such as additional heating in cables and transformers, and resonance. A typical rectifier in an electric drive is a three-phase full-bridge diode (or thyristor) rectifier that draws 6 pulses of current from the AC power grid and can be referred to as a 6-pulse rectifier. For example, such a rectifier may produce characteristic current harmonic components at the 5th, 7th, 11th, 13th… harmonic frequencies. Alternatively, the electric drive may be equipped with different multi-pulse rectifiers (such as 12-pulse or 18-pulse rectifiers), which may have different but still identifiable characteristic harmonic spectra.

[0003] Electric drives can forgo uncontrolled (or line-commutated) rectifiers and instead feature pulse-width modulation (PWM) active front-end (AFE) rectifiers for AC-to-DC conversion, significantly reducing the amplitude of low-order harmonic current components flowing to the AC grid. Furthermore, using an AFE rectifier, the grid (input) current to the drive can be nearly sinusoidal. However, for example, a typical AFE rectifier may introduce more power losses in an electric drive compared to a drive with a 6-pulse diode rectifier, and increase the cost and size of the drive. Moreover, active rectifiers are generally more expensive than uncontrolled rectifiers.

[0004] One possible way to reduce harmonic current distortion caused by the diode rectifier of an electric drive is to install a passive harmonic filter, i.e., an inductor and capacitor, in parallel with the drive's rectifier. For example, the inductor and capacitor of the filter can be chosen such that they provide a low-impedance path for selected current harmonic components, thus reducing the corresponding current component flowing to the AC grid. Besides simplicity, this can be a cost-effective solution in some cases. However, passive filters can be bulky, and for example, they are not easily adapted to changing grid or load conditions. They can also cause system-level electrical resonance, for example.

[0005] As an alternative to such filters composed of passive components, various active harmonic filters are available. Typically, they may have a PWM bridge (as in an AFE rectifier) ​​and additional passive filtering elements for high-frequency PWM ripple. Active harmonic filters can be more flexible because they can adapt to different load and network conditions and provide multiple functions, such as harmonic cancellation, imbalance compensation, and reactive power compensation. Disadvantages of active filters may include cost (at least in simple systems) and the potential need for additional current measurement equipment (such as current transformers) to be installed in the AC system for operation. In particular, the installation of such current transformers or corresponding equipment may not be straightforward, for example, due to wiring and / or a lack of suitable space in existing AC system installations, resulting in high installation costs. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a method and an apparatus for implementing the method, to overcome or at least mitigate the aforementioned problems. This object is achieved by a method and an apparatus, the features of which are defined by the statements in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.

[0007] The present invention is based on the concept of estimating at least one harmonic current component caused by at least one load entity based at least on data indicating the operating point of at least one load entity in an AC network, and performing at least partial harmonic compensation in the AC network by a harmonic compensation entity based on the estimated at least one harmonic current component caused by at least one load entity.

[0008] The advantage of the solution of the present invention is that harmonic compensation can be achieved without the need to install additional current measuring equipment. Attached Figure Description

[0009] In the following, the invention will be described in more detail with reference to the accompanying drawings, in which:

[0010] Figure 1 An example of an electrical system according to an embodiment is shown;

[0011] Figure 2 An example of an electrical system according to an embodiment is shown;

[0012] Figure 3 An example of an electrical system according to an embodiment is shown;

[0013] Figure 4 An example of an electrical system according to an embodiment is shown;

[0014] Figure 5A schematic diagram illustrating the representation of harmonic components according to an embodiment is shown;

[0015] Figure 6 A schematic diagram of a harmonic component estimator according to an embodiment is shown;

[0016] Figure 7 A schematic diagram illustrating a model for harmonic components according to an embodiment is shown;

[0017] Figure 8 A schematic diagram of a parallel harmonic component estimator according to an embodiment is shown;

[0018] Figure 9 A load entity according to an embodiment is shown;

[0019] Figure 10 A block diagram according to an embodiment is shown;

[0020] Figure 11 A flowchart according to an embodiment is shown;

[0021] Figure 12 A flowchart according to an embodiment is shown;

[0022] Figure 13 A flowchart according to an embodiment is shown;

[0023] Figure 14 A flowchart according to an embodiment is shown;

[0024] Figure 15 A flowchart according to an embodiment is shown;

[0025] Figure 16 An example of a harmonic compensation entity according to an embodiment is shown;

[0026] Figure 17 A schematic diagram according to an embodiment is shown;

[0027] Figure 18 A schematic diagram illustrating an example of the amplitude and phase of harmonic components according to an embodiment is shown;

[0028] Figure 19 A schematic diagram illustrating an example of the current of a rectifier according to an embodiment is shown;

[0029] Figure 20 A schematic diagram illustrating an example of the amplitude of harmonic components according to an embodiment is shown;

[0030] Figure 21 A schematic diagram illustrating an example of current THD according to an embodiment is shown;

[0031] Figure 22A schematic diagram illustrating an example of the current of a rectifier according to an embodiment is shown; and

[0032] Figure 23 A block diagram according to an embodiment is shown. Detailed Implementation

[0033] The following embodiments are exemplary. The embodiments described herein may be implemented in ways other than those described below. Although the description may refer to "an," "a," or "some" (or more) embodiments in several places, this does not necessarily mean that each such reference points to the same (or more) embodiments, or, for example, that the feature applies only to a single embodiment. Individual features of different embodiments may also be combined to provide other embodiments. When a particular feature, structure, or characteristic is described in conjunction with an embodiment, it should be understood that, whether explicitly described or not, its influence in conjunction with other embodiments affects such feature, structure, or characteristic within the knowledge of those skilled in the art.

[0034] Furthermore, terms such as “comprises / comprising / includes / including” and “has / having” should be understood not to limit the described embodiments to consisting only of those features, elements, components, and / or combinations thereof that have been mentioned, and such embodiments may also include features, elements, components, and / or combinations thereof not specifically mentioned. Additionally, terms such as “connected” and “coupled” are used to mean directly or indirectly (i.e., via one or more elements) connected or coupled.

[0035] Reference numerals in the specification and / or claims are used to illustrate embodiments with reference to the accompanying drawings, but not to limit the embodiments to these examples only. Generally, all terms and expressions used should be interpreted broadly, and they are intended to illustrate rather than limit the embodiments. The drawings only show the components necessary for understanding the various embodiments. The number, shape, and / or configuration of the various elements, and generally their implementation, may differ from the examples shown in the drawings.

[0036] Furthermore, it should be understood that although terms such as “first” and “second” may be used herein to describe various elements, these elements should not be limited by these terms. Such terms are used only to distinguish one element from another. For example, without departing from the scope of the exemplary embodiments, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. As used herein, the expression “and / or” includes any and all combinations of one or more of the listed terms.

[0037] Unless otherwise stated, the embodiments described herein are not limited to any particular system, but can be applied to a variety of electrical power systems, such as electrical power converter systems. Furthermore, the use of the embodiments described herein is not limited to, for example, any system utilizing a specific base frequency or any specific voltage level.

[0038] According to an embodiment, a method for harmonic compensation in an electrical system is provided, wherein the electrical system includes an AC network, at least one load entity, and a harmonic compensation entity connected to the AC network, the at least one load entity including at least a first electrical power converter connected to the AC network. According to an embodiment, the method includes: estimating at least one harmonic current component induced by the at least one load entity in the AC network based at least on data indicating the operating point of the at least one load entity; and the harmonic compensation entity performing at least partial harmonic compensation in the AC network based on the estimated at least one harmonic current component induced by the at least one load entity. According to an embodiment, the at least one harmonic current component to be estimated and / or compensated can be appropriately selected, for example, pre-selected or pre-determined, for example, according to system characteristics and / or requirements. For example, the at least one harmonic current component may include one or more odd-order harmonic current components and / or one or more even-order harmonic current components.

[0039] Figure 1 , Figure 2 , Figure 3 and Figure 4 Some possible examples of electrical systems according to embodiments are shown.

[0040] Figure 1 Examples include alternating current (AC) networks, i.e., AC power grids, which can be single-phase or multi-phase networks, such as three-phase networks. An AC network can be a public power grid or another AC network configured to supply power to one or more loads. Figure 1The example also illustrates a load entity 10. Such a load entity 10 can typically be or include any type of load (unit, device, apparatus, system, or combination thereof), the load comprising at least a (first) electrical power converter 11 connected to an AC network (connected to its common coupling point PCC in this example). Load entity 10 can typically be or represent a nonlinear load, i.e., it can have nonlinear characteristics at least occasionally and / or periodically. Thus, for example, load entity 10 can induce one or more harmonic current components in the AC network, and thus cause harmonic distortion, the level of which can vary over time. The terms electrical power converter and electrical power converter unit as used herein generally refer to any type of device, apparatus, circuit, or typical configuration capable of (being configured to) perform electrical power conversion. An electrical power converter can include one or more electrical power converter units (modules). For example, such one or more electrical power converter units can be physical units or logical units. Typically, such electrical power converter units can be implemented using (a plurality of) controllable and / or uncontrollable semiconductors, which can be configured as, for example, one or more semiconductor bridges. For example, in the case of (multiple) controllable semiconductors, they can be controlled by appropriate control methods or schemes, such as pulse width modulation (PWM). A non-limiting list of examples of electrical power converters and / or electrical power converter units includes, for example, AC-to-DC converters, such as controllable or uncontrollable rectifiers; DC-to-AC converters, such as inverters; AC-to-AC converters; and DC-to-DC converters; and any combination of two or more of such converters and / or converter units. As an example, a combination of a rectifier and an inverter constitutes a frequency converter. Typically, such electrical power converters and / or electrical power converter units can be unidirectional, i.e., capable of transmitting electrical power only in a single direction. For example, such electrical power converters and / or electrical power converter units can also be bidirectional, i.e., capable of transmitting electrical power in two opposite directions, thus achieving bidirectional power flow between two sources. Figure 1In the example, the example power converter 11 includes two power converter units 11A and 11B. The first power converter unit 11A is configured to operate at least as a rectifier, and the second power converter unit 11B is configured to operate at least as an inverter. The two power converter units 11A and 11B of the power converter 11 can be connected in a manner known in the art via a DC link (not shown separately). For example, such a DC link (intermediate circuit) may include a capacitor (capacitive circuit), which may include one or more capacitors. Alternatively, or additionally, such a DC link may include an inductor (inductive circuit), which may include one or more inductors. However, for example, the (first) power converter 11 connected to a load entity 10 of an AC network may include, for example, a power converter unit 11A configured, only (or at least) to operate at least as a rectifier or another type of converter unit. Figure 1 In the example, load entity 10 also includes motor 13, which represents the load for the electrical power converter 11 of load entity 10. Therefore, by way of example, load entity 10 may include an electric drive, such as a motor drive. However, the electrical power converter 11 of load entity 10 may supply power to one or more other types of loads, rather than motor 13 or a typical electric motor. Figure 1 The example also illustrates a harmonic compensation entity 20 connected to an AC network, in this example also connected to its common coupling point PCC. For example, the harmonic compensation entity 20 can typically be or include any type of unit, device, apparatus, system, or combination thereof, capable of (being configured to) at least partially compensate for one or more harmonic current components in the AC network. According to an embodiment, the harmonic compensation entity 20 may include a (second) electrical power converter 21 connected to the AC network, such as... Figure 1 As illustrated in the example. Figure 1 In this example, the power converter 21 includes at least one power converter unit 21A, which can be configured to operate bidirectionally, i.e., acting as both a rectifier and an inverter, thus enabling power flow in both directions through the power converter unit 21A. Furthermore, in this example, the harmonic compensation entity 20 also includes a capacitor C (or typically an energy storage device) connected to the power converter 21, which may include one or more capacitors. Alternatively, or additionally, such an energy storage device may include an inductor, which may include one or more inductors. This combination of the power converter 21 and the capacitor C can therefore constitute a so-called active filter capable of providing harmonic compensation to an AC network. Figure 1The example also illustrates a communication connection between load entity 10 and harmonic compensation entity 20. For instance, such a communication connection can typically be implemented using one or more suitable communication protocols in a wired and / or wireless manner. Figure 1 The connections shown are logical connections, and the corresponding actual physical connections may differ. At least one load entity 10 and harmonic compensation entity 20 can be (e.g., physically) different (independent) entities, i.e., entities distinct from each other. However, such different entities can still be connected, for example, via one or more communication connections and / or via one or more power connections.

[0041] Figure 2 This illustrates another example, with other aspects corresponding to Figure 1 Examples, but Figure 2 In the example, the harmonic compensation entity 20 includes a (second) power converter 21, which in this example includes two power converter units 21A and 21B. The two power converter units 21A and 21B of the power converter 21 can be connected via a DC link (not shown separately). The first power converter unit 21A can be configured to operate bidirectionally, i.e., acting as both a rectifier and an inverter, thus enabling power flow in both directions through the power converter unit 21A, for example, at least between the AC network and the DC link of the power converter 21. Furthermore, the second power converter unit 21B can also be configured to operate bidirectionally, i.e., acting as both an inverter and a rectifier, thus enabling power flow in both directions through the power converter unit 21B. Alternatively, the first and second power converter units 21A and 21B can be configured to operate unidirectionally. In this case, the first power converter unit 21A can be configured to control its input current waveform. An example of such a unidirectional converter capable of controlling its input current waveform is the so-called Vienna rectifier. Therefore, the power converter 21 can operate as a frequency converter. Furthermore, the harmonic compensation entity 20 in the example includes a load 23, in this example a motor M, to which the power converter 21 can supply power. The power converter 21 of the harmonic compensation entity 20 can supply power to one or more other types of loads besides the motor 23 or a typical electric motor. In this example, the power converter 21 is also capable of (being configured to) providing harmonic compensation to the AC network.

[0042] Figure 3 Another example is shown, corresponding in a different way. Figure 2 Examples, but Figure 3 In the example, there are two (or more) parallel load entities 10 connected to the AC network. In this case, as shown, all load entities 10 may have a communication connection to the harmonic compensation entity 20. Figure 4 Yet another example is shown, corresponding in other ways. Figure 2 Examples, but Figure 4 In the examples, there exists an additional entity 30, or control entity, capable of implementing one or more control-related functions of the various embodiments described herein. According to embodiments, control entity 30 is different (independent) from at least one load entity 10 and different from harmonic compensation entity 20. In other words, control entity 30 can be an entity that is (e.g., physically) different from both at least one load entity 10 and harmonic compensation entity 20. However, although they are different entities, control entity 30 can be connected to one or more load entities 10 and / or harmonic compensation entities 20 at least via one or more communication connections to enable data communication, such as... Figure 4 As illustrated in the example. Such a control entity 30 can be or includes any suitable control device, such as a computing device, gateway device, industrial PC, computer / server in a network and / or cloud, programmable logic controller (PLC), microcontroller, and / or a mini / single-board computer that can communicate directly or indirectly with one or more load entities 10 and harmonic compensation entities 20 via, for example, gateways (multiple)

[0043] For example, to avoid the need for multiple additional AC current sensors for implementing harmonic filtering or compensation, a substantially open-loop harmonic compensation solution can be provided according to the various embodiments described herein. The solutions according to the various embodiments described herein can be implemented without a mains current sensor. According to the embodiments, harmonic current estimation can be performed, and data communication implementing the estimation and / or the estimation results can be performed between at least one load entity 10, harmonic compensation entity 20, and / or control entity 30.

[0044] Typically, the harmonic angular frequency is The harmonic current components at the location (where h It is the harmonic order (such as or ), It is the fundamental angular frequency (such as Hz or (Hz) can be determined by its amplitude and phase Characterized as Phase It can be relative to the zero phase to be defined. For example, the grid voltage component with zero phase equal to the fundamental frequency (i.e., the first harmonic) at PCC can be selected. phase ,like Figure 5As shown. Therefore, the phase of the harmonic current component is relative to the phase of the fundamental voltage component and can be propagated from one entity to another in both global and shared coordinate systems. Harmonic components can be viewed as or represented as phasors, or essentially equivalently as complex numbers, and in addition to polar coordinates, there are alternative ways to represent them, such as two-dimensional vectors. , or as the real part and the imaginary part and (or in) Figure 5 (The x and y components in the Cartesian coordinate system illustrated in the example). Furthermore, for this type of alternative labeling, the following equation holds. (1) in It is the imaginary unit. and These are the real and imaginary parts of the harmonic components, respectively, and they can also be represented as vectors. Therefore, as alternatives to amplitude and phase, harmonic components can be characterized substantially equivalently by their real and imaginary parts, or by using complex numbers or vectors combining these. However, it is worth noting that the specific notation used is irrelevant. According to embodiments, for example, at least one harmonic current component can be defined by the amplitude and phase of the harmonic current component, or by any equivalent method as described above.

[0045] In a three-phase (three-wire) system, all three phases (e.g., phase a, phase b, and phase c) are typically at harmonic frequencies. It has its own harmonic current component. , and The subscripts a, b, and c represent three phases. These harmonic components of each phase are combined into a single vector harmonic component. It is possible to describe all three phases simultaneously, for example, using space vectors. Complexity can also be reduced by assuming equal amplitudes for each harmonic component and a typical 120-degree phase shift. In this case, for example, the information can be packaged into a single complex value (phasor) for each harmonic component. Furthermore, each phase harmonic component can be obtained through phase shifting.

[0046] Estimating at least one harmonic current component induced by at least one load entity 10 in an AC network, based at least on data indicating the operating point of at least one load entity 10, can be accomplished in various ways. According to an embodiment, for example, the operating point of at least one load entity 10 can be determined by the load state of a first electrical power converter 11 within the load entity 10.

[0047] According to embodiments, data indicating the operating point of at least one load entity 10 may include one or more of the following: the operating power of the first power converter 11, the DC link voltage of the first power converter 11, and / or the DC link current of the first power converter 11. For example, the operating power of the first power converter 11 may be used alone to indicate the operating point of at least one load entity 10. For example, data indicating the operating point of at least one load entity 10 may alternatively or additionally include one or more quantities or combinations thereof that indicate and / or have a known relationship with the operating power of the first power converter 11 and / or the DC link voltage of the first power converter 11 and / or the DC link current of the first power converter 11. Some examples of such quantities include, for example, current, voltage, and energy. The term "operating power of the first power converter 11" herein may generally refer to any power quantity, for example, indicating the power drawn by the first power converter 11 from the AC network and / or the power flowing from the AC network through the first power converter 11 to a load powered by the AC network. For example, such power quantities can be or are represented as AC power or DC power. Furthermore, for example, any energy quantity corresponding to such power quantities can be used instead of the power quantity. According to embodiments, the (operating) power quantity is the active (operating) power quantity. As an example, the operating power of the first electrical power converter 11 can be determined directly from one or more quantities of the first electrical power converter 11 itself or from one or more quantities of its components (such as the first electrical power converter unit 11A and / or the second electrical power converter unit 11B). As another example, for example, the operating power of the first electrical power converter 11 can be determined at least partially indirectly from one or more quantities of the load 13. Such one or more quantities of the load 13 can, for example, include, in the case where the load 13 includes a motor, the estimated or measured torque of the motor and / or the estimated or measured (rotational) speed of the motor and / or any similar quantity of the load 13. Generally, any one or more quantities of the load 13 that have any known relationship with the operating power of the first electrical power converter 11 can be used, for example, to determine the operating power of the first electrical power converter 11. Additionally or alternatively, data indicating the operating point of at least one load entity 10 may include one or more such quantities of load 13. Furthermore, for example, power quantities and / or DC link voltage quantities and / or DC link current quantities may be instantaneous values, filtered values, or time averages over selected time periods (e.g., 10 ms, 20 ms, 100 ms, 200 ms, 1 s, ...). Power quantities can be determined using current and voltage measured within the first power converter 11, for example within the first power converter unit 11A and / or its second power converter unit 11B.

[0048] According to an embodiment, the estimation of at least one harmonic current component caused by at least one load entity 10 may be performed additionally based on characteristic data of the AC network. According to an embodiment, such characteristic data of the AC network may include, for example, one or more of the following: the voltage of the AC network, the impedance of the AC network, the short-circuit current of the AC network, and / or the short-circuit power of the AC network. For example, the voltage of the AC network may be indicated by the voltage of one phase or by the voltages of two or more phases of the AC network. For example, the voltage(s) may be or be based on instantaneous values ​​or root mean square (RMS) values(s). Furthermore, for example, such values(s) may be, for example, filtered values(s) or time-averaged values(s) of sampled values ​​over a selected time period (e.g., 10 ms, 20 ms, 100 ms, 200 ms, 1 s, ...). The characteristic data of the AC network may alternatively or additionally include one or more quantities or combinations of quantities indicating the voltage of the AC network, the impedance of the AC network, the short-circuit current of the AC network, and / or the short-circuit power of the AC network.

[0049] According to embodiments, for example, the estimation of at least one harmonic current component caused by at least one load entity 10 can be performed substantially continuously or periodically at predetermined intervals. As an example, the estimation can be performed at (predetermined) time intervals from 1 ms to 10 s, such as 1 ms, 10 mms, 100 ms, ... 1 s, or any suitable system-specific time interval. Additionally or alternatively, the estimation of at least one harmonic current component caused by at least one load entity 10 can be performed when one or more predetermined conditions are met and / or in response to a received query or command. According to embodiments, the estimation of at least one harmonic current component caused by at least one load entity 10 can be performed using a predetermined static model or by simulating a model of the load entity 10. Some possible examples are disclosed below.

[0050] In a simple form, the estimator used to perform the estimation can be based on a statically pre-calculated, predicted, or otherwise predefined harmonic current model that takes the operating point data of at least one load entity 10 as input and outputs one or more estimated harmonic components. Figure 6 An example of such a simple estimator 100 is illustrated, wherein the running point data includes active power flowing to a load 13 (e.g., to a motor) connected to an electrical power converter 11 connected to a load entity 10. ,and The second harmonic current component (its amplitude) and phase It is modeled as a function of power, for example, it is modeled as In the following text, for simplicity, harmonic components are presented in their polar coordinate form (using amplitude and phase), but the embodiments described herein are also applicable to alternative equivalent representations of harmonic components as previously described.

[0051] To provide an example (see...) Figure 7 The function used in harmonic estimation It can be piecewise linear, such as (2) (3) in and These are the harmonic current amplitudes at switching points c1 and c2, respectively. and These are the harmonic current phases at switching points c1 and c2, respectively. and It is the active power at these switching points. It is the third power point (such as the rated power point) The harmonic current amplitude at point ) It is the phase of the harmonic current at the third power point. and These are the amplitude and phase at zero power. For example, these example piecewise linear functions (2) and (3) have three parts, but the function can alternatively consist of one, two, three, or more parts. In such functions, the parameters of the function (e.g., active power, and harmonic amplitude and phase at the switching point, zero point, and rated point) need to be predefined (e.g., using measured, calculated, and / or simulated data from load entity 10 or a portion thereof). Then, during operation, the estimator can simply input the active (running) power into the function and select the amplitude and angle of the (multiple) harmonic components based on the function's (multiple) outputs. For example, alternatives to the piecewise linear function that can be used in the estimator are polynomial functions or combinations of piecewise linear and polynomial functions. Generally, any real function that can describe the characteristics of harmonic currents as a function of power can be applied.

[0052] For example, instead of analytical functions (e.g., linear, piecewise linear, polynomial, or combinations thereof), harmonic estimation can be implemented numerically using, for example, lookup tables, arrays, and / or other suitable data structures. This can be achieved at different active power levels. Below The (predicted) harmonic current amplitude and phase It can be stored in (multiple) lookup tables and / or (multiple) arrays. Then, the estimator 100 can retrieve the output value from the lookup table or array via array indexing operations. The index corresponds to the run-point data (e.g., power) that serves as input to the function. Since lookup tables or arrays only give output for discrete input values ​​(indexes or keys), linear interpolation can be used between discrete input values ​​(indexes or keys), and / or, for example, output values ​​corresponding to the most recent discrete input value can be selected.

[0053] As described above, the estimation of at least one harmonic current component caused by at least one load entity 10 can be additionally performed based on characteristic data of the AC network. Examples of such characteristic data of the AC network may include one or more of the following: the voltage of the AC network (i.e., the grid voltage), the impedance of the AC network (i.e., the grid impedance), the short-circuit current of the AC network, and / or the short-circuit power of the AC network. As an example, to enhance the single-input single-output model structure, the input data may typically include more than one signal associated with the harmonic component estimation. The estimated harmonic component can then typically be represented as... ,in These are the inputs to the model. We will first explain an example case where the model and estimator have two inputs.

[0054] Figure 7 This illustrates the methods used to model, for example, the 5th and 7th harmonic current components ( and As for different grid voltages Active power at horizontal level This is a representative example of a function. However, it should be noted that the 5th and 7th harmonic current components are selected only as examples in this example, and any one or more harmonic current components (h = 2, 3, 4, 5, …) can be selected (e.g., pre-selected) for this purpose, depending on, for example, system characteristics. Furthermore, in the example, different exemplary predefined grid voltages (h = 2, 3, 4, 5, …) are used. level pu、 pu, and pu) generated three different function sets , ,and 。 Let's generalize this example to have M predefined grid voltage levels. (x=1, 2, 3, ...M) and its corresponding harmonic model function (x=1, 2, 3, ...M). In actual power grid voltage... Match one of the predefined grid voltage levels In the case of function-based estimators Simplified to In the case of, right Modeling the harmonics at the location. Otherwise, a function-based estimator. For example, two closest predefined voltage levels can be used. (x=1, 2, 3,...M) and (y=1, 2, 3, ...M) and the corresponding model and From the model and The output is interpolated (or extrapolated) to estimate harmonic currents. For example, an alternative to interpolation could be to use the most recent voltage level and its predefined model in the estimation.

[0055] Above, by using a single-input function set In harmonic estimation, the case with two input signals is simplified to a single-input case. This is because, for example, the analytical function can directly model the harmonics for estimation. If not, this is not necessary. Alternatively, numerical methods using two-dimensional lookup tables, arrays, or other suitable data structures can be employed, similar to those explained above.

[0056] In the case of a nonlinear load, such as an electric driver equipped with a 6-pulse (or multi-pulse) diode rectifier, estimate the grid voltage in the above function. DC link voltage can be used Instead, it is used because it is known that the average DC link voltage and the grid voltage in the rectifier are closely related. For example, when When the line-to-line voltage is the root mean square (RMS) value, the average DC link voltage of the 6-pulse rectifier is Therefore, the model-based estimate can then be written as And it can be similarly as described above. It was formulated and implemented in accordance with the circumstances. (Usage) The advantage is that it is typically measured or estimated within the electric drive, or more specifically within the electrical power converter 11 therein. Other variations for the input can be formulated by writing the active power as the product of voltage and current, such as... ,in This refers to the current flowing through the DC link. In other words, for example, essentially the same harmonic estimation target can be utilized. and To be realized.

[0057] Furthermore, estimation accuracy can be improved by increasing the number of inputs or parameters in the static model and estimator. One parameter that can benefit the estimator to give more accurate results is the AC grid impedance. (or short-circuit current) / power For example, this can be seen from the common coupling point PCC. For instance, an estimator that takes these as input parameters can have the following form: , , , , , , , ,or Naturally, the power equation This can be used to create more alternative input signal scenarios. The grid impedance (or short-circuit current / power) or any similar parameter can be predetermined and therefore can be provided to the estimator, for example, during system commissioning and / or after estimation / measurement / updating during operation. Furthermore, for example, in the model described above, instead of the AC grid impedance... The input describing conductivity or grid strength may also be or include reactance, resistance, admittance, conductance and / or susceptance or any other suitable quantity for this purpose.

[0058] Another input that can further improve the estimation results is the grid voltage and / or its (multiple) harmonics. In addition to the inputs previously described, or as alternatives to one or more of the previously described inputs, other inputs can be added to the model. This includes the selection of (multiple) grid voltage harmonics (which may include the fundamental frequency component).

[0059] The estimation of a single harmonic component was discussed in the embodiments and examples described above. According to the embodiments, the same method can be extended to multiple (two or more) harmonic current components. In the case of estimating multiple harmonic components, the estimator can, for example, be implemented in parallel, such as... Figure 8 The example shown illustrates parallel estimators 100-1, 100-2, ..., 100-n. It is worth noting that the harmonic component estimation in this case is not limited to the 5th and 7th harmonic components (h=5 and h=7) (given only as an example), because the same method can be used for any harmonic component (h=2, 3, 4, 5, ...) caused by the load entity 10.

[0060] According to an embodiment, alternatively or additionally, the estimator and estimator may be based on a simulation (such as a real-time simulation) of a system model of the load entity 10 or at least a portion thereof, and calculate harmonic components from the real-time simulated grid current. Figure 9 An example of a 6-pulse rectifier system is depicted, comprising an AC choke, a DC capacitor bank, and a variable load powered by the rectifier (through the current of the variable load). i L= p L / u dc The system is first modeled using an equivalent circuit. The phase-to-phase input voltage of the system is... u ab , u bc .like Figure 10 As shown in the example, such a circuit model can then be written, for example, as a system of nonlinear differential / difference equations (or, for example, it can be written as computer code), and finally the system of differential equations (or computer code) can be solved step by step to obtain an estimated grid current for load entity 10 in block 110. i a , i b , i c The system. The estimated harmonic components can then be calculated from the estimated grid current in block 120, for example, using Fourier transform or digital filtering or some other suitable method. It is worth noting that, for example, rectifiers and / or other electrical power converters and their components or the circuit topology connected to them are not limited to... Figure 9 and 10 The example shown. As an example, in Figure 9 In example rectifier systems, there may be a DC choke instead of an AC choke (or in addition to an AC choke) and / or a 6-pulse rectifier may be a multi-pulse rectifier bridge, such as a 12-pulse, 18-pulse, or 24-pulse diode rectifier, or another type of rectifier, such as a thyristor rectifier.

[0061] For example, the estimation of at least one harmonic current component caused by at least one load entity 10 can be performed within the load entity 10 itself, or it can be performed within the harmonic compensation entity 20. Furthermore, the estimation of at least one harmonic current component caused by at least one load entity 10 may also be performed in, for example... Figure 4 The estimation is performed in the illustrated control entity 30. Depending on which entity the estimation is performed in, data communication implementing the estimation and / or the estimation results can then be appropriately performed between at least one load entity 10, harmonic compensation entity 20, and / or control entity 30. Some possible alternatives and examples are disclosed below, but the implementation is not limited to these examples.

[0062] According to an embodiment, the estimation of at least one harmonic current component caused by at least one load entity 10 can be performed in a harmonic compensation entity 20, wherein the method includes transmitting data indicating the operating point of at least one load entity 10 from at least one load entity 10 to the harmonic compensation entity 20. Therefore, as Figure 11As shown, 1001 selects one or more harmonic components to be compensated. Selection 1001 can be pre-executed, i.e., the selected one or more harmonic components to be compensated can be predetermined. Alternatively, selection 1001 can be (re)executed, for example, each time or at a lower frequency, when performing estimation. Selection 1001 may also be executed in response to one or more predetermined conditions being met and / or in response to a received query or command. Data indicating the operating point of at least one load entity 10 is transmitted 1002 from at least one load entity 10 to the harmonic compensation entity 20, and in the harmonic compensation entity 20, at least one harmonic current component caused by at least one load entity 10 is estimated 1003 based at least on the transmitted data indicating the operating point of the load entity 10. The harmonic component to be compensated can then be determined and injected from the compensation device 1004 into the AC power grid to obtain at least partial harmonic compensation in the AC network. Thus, in, for example... Figure 1 and 2 In the example shown, load entity 10 (such as an electric drive equipped with diode rectifier 11) can transmit its operating point data (sufficient for harmonic estimation) to harmonic compensation entity 20 (such as an electric drive equipped with controlled rectifier 21), and harmonic compensation entity 20 can estimate (a plurality of) selected harmonic current components (caused by) load entity 10 based on the transmitted operating point data. Harmonic compensation entity 20 can then determine (a plurality of) compensated harmonic current components based on (a plurality of) the estimated harmonic current components and inject (a plurality of) compensated current components into the AC grid to achieve partial harmonic current cancellation at PCC.

[0063] According to another embodiment, the estimation of at least one harmonic current component caused by at least one load entity 10 is performed in the same at least one load entity 10, wherein the method includes transmitting the estimated at least one harmonic current component from the at least one load entity 10 to a harmonic compensation entity 20. Therefore, as Figure 12 As shown, 2001 one or more harmonic components to be compensated are selected, for example, similar to step 1001 described above. 2002 At least one harmonic current component caused by at least one load entity 10 is estimated in the involved load entity 10 based at least on data indicating the operating point of the involved load entity 10. One or more estimated harmonic components are conveyed from the load entity 10 to the harmonic compensation entity 20, 2003 whereby the compensation harmonic component can be determined and 2004 injected from the compensation device into the AC power grid to achieve at least partial harmonic compensation in the AC network. Therefore, in, for example... Figure 1 and 2In the example shown, load entity 10 (such as an electric driver equipped with diode rectifier 11) can estimate its harmonic current components based on operating point data and transmit the estimated harmonic current components to harmonic compensation entity 20 (such as an electric driver equipped with controlled rectifier 21). Harmonic compensation entity 20 can then determine compensated harmonic current components based on the estimated harmonic current components and inject the compensated current components into the AC grid to achieve partial harmonic current cancellation at the PCC.

[0064] According to another embodiment, the estimation of at least one harmonic current component caused by at least one load entity 10 is performed in a control entity 30 that is different from both the at least one load entity 10 and the harmonic compensation entity 20. The method includes transmitting data indicating the operating point of the at least one load entity 10 from the at least one load entity 10 to the control entity 30, and transmitting the estimated at least one harmonic current component from the control entity 30 to the harmonic compensation entity 20. Therefore, as... Figure 13 As shown, 3001 one or more harmonic components to be compensated are selected, for example, similar to step 1001 described above. Data indicating the operating point of at least one load entity 10 is transmitted from at least one load entity 10 to control entity 30, and at least one harmonic current component caused by at least one load entity 10 is estimated in control entity 30 based at least on the transmitted data indicating the operating point of load entity 10. One or more estimated harmonic components are transmitted from control entity 30 to harmonic compensation entity 20, whereby the harmonic components to be compensated can be determined and 3005 injected from the compensation device into the AC power grid to achieve at least partial harmonic compensation in the AC network.

[0065] According to another embodiment, the estimation of at least one harmonic current component caused by at least one load entity 10 is performed in a control entity 30 that is different from both the at least one load entity 10 and the harmonic compensation entity 20. The method includes transmitting an operating point command from the control entity 30 to the at least one load entity 10, and transmitting the estimated at least one harmonic current component from the control entity 30 to the harmonic compensation entity 20. Therefore, as Figure 14As shown, 4001 one or more harmonic components to be compensated are selected, for example, similar to step 1001 described above. An operating point command is transmitted 4002 from control entity 30 to at least one load entity 10 to set the operating point of load entity 10 to the operating point of the command. Furthermore, at least one harmonic current component caused by at least one load entity 10 is estimated 4002 in control entity 30 based at least on data indicating the operating point of load entity 10, which corresponds to the operating point in the operating point command. One or more estimated harmonic components are transmitted 4003 from control entity 30 to harmonic compensation entity 20, whereby the harmonic components to be compensated can be determined and 4004 injected from the compensation device into the AC power grid to achieve at least partial harmonic compensation in the AC network.

[0066] According to another embodiment, the estimation of at least one harmonic current component caused by at least one load entity 10 is performed in a harmonic compensation entity 20, wherein the method includes transmitting an operating point command from a control entity 30, which is different from and different from the at least one load entity 10 and the harmonic compensation entity 20, to the at least one load entity 10, and transmitting data indicating the operating point of the at least one load entity 10 from the control entity 30 to the harmonic compensation entity 20. Therefore, as Figure 15 As shown, 5001 one or more harmonic components to be compensated are selected, for example, similar to step 1001 described above. An operating point command is transmitted 5002 from control entity 30 to at least one load entity 10 to set the operating point of load entity 10 to the operating point of the command, and data indicating the operating point of at least one load entity 10 (corresponding to the operating point in the operating point command) is transmitted 5002 from control entity 30 to harmonic compensation entity 20. Then, in harmonic compensation entity 20, at least one harmonic current component caused by at least one load entity 10 is estimated 5003 based at least on the transmitted data indicating the operating point of load entity 10. The harmonic component to be compensated can then be determined and 5004 injected from the compensation device into the AC power grid to achieve at least partial harmonic compensation in the AC network.

[0067] In embodiments involving an additional control entity 30, this control entity 30 may further utilize additional input data for estimation, such as measured or estimated grid voltage, as described above. Furthermore, for example in an electric drive system, the electric drive may obtain operating point commands (references) from an external control entity (such as a PLC) via a communication bus, such as... Figure 4As depicted. Therefore, as described in the embodiments above, the operating point data required for harmonic estimation can be derived from such operating point commands (references) commanded by the external control entity 30. In this case, the control entity 30 is aware of its commands and can also formulate operating point data for estimation tasks performed by itself or by the harmonic compensation entity 20, or directly calculate the harmonic current reference required for compensation. The external control entity 30 can further convey the information required by the harmonic compensation entity 20. Then, for example, based on the conveyed information, the harmonic compensation entity 20 can perform only the compensation task (conveying the estimated harmonic or harmonic current reference), or perform the estimation task in addition to the compensation task based on the received operating point data.

[0068] According to an embodiment, for example, there may be two (or more) such control entities 30, which may be different entities, i.e., different from each other, such that one control entity gives an operating point command (reference), while the other control entity is configured to estimate harmonics based on the received operating point data or operating point command (reference).

[0069] The estimation and / or communication and / or any other functions according to the various embodiments described herein can be implemented by appropriate software or firmware in the controller(s) (units, devices, systems) (the respective entities perform the functions). For example, a load entity 10 including at least one electric power converter and / or a harmonic compensation entity 20 may include a controller for the electric power converter or a controller for the electric power converter, which may be configured to perform estimation and / or communication functions according to the various embodiments described herein, such as receiving and / or sending data (information) to be conveyed. As an example, the electric power converter 11 of the load entity 10, or its first electric power converter unit 11A and / or second electric power converter unit 11B, and / or the electric power converter 21 of the harmonic compensation entity 20, or its first electric power converter unit 21A and / or second electric power converter unit 21B, may include a controller(s) (in the respective entities perform the functions) (the ... Figures 1 to 4 (Not shown separately), the controller can be configured to perform any function according to the various embodiments described herein. Similarly, the possible control entity 30 can also be readily configured, for example, by appropriate software or firmware, to implement estimation and / or communication functions according to the various embodiments described herein. Simulations of predetermined static models and / or models of the load entity 10 involved can also be stored and / or implemented in the corresponding entity performing the function. As an example, for instance, Figure 9 The example model shown, or any similar model of the load entity 10 involved, can be conveniently simulated in the harmonic compensation entity 20 because the line-to-line voltage of the AC power grid can be readily known in the harmonic compensation entity 20. Furthermore, it can acquire power flowing to nonlinear loads via appropriate communication connections. .

[0070] Data indicating the operating point of at least one load entity 10 (i.e., operating point data), and / or estimated harmonic components and / or any other data to be conveyed, can be communicated via any suitable communication device. Typically, there are no high requirements for communication; any known communication method and / or protocol suitable for this purpose can be used. Communication can be conducted wirelessly and / or via wired means, for example, using fieldbus, Ethernet, or any similar solution, and / or utilizing other relevant means. The harmonic compensation entity 20 can also communicate information back to the load entity 10 (e.g., to an electric drive). This allows the load entity 10 to use more input signals to improve the estimation results, if the estimation is performed within the load entity. For example, potentially useful information shared from the harmonic compensation entity 20 to one or more load entities 10 may include measured or estimated grid voltage and / or measured or estimated grid impedance. For example, operating point data, harmonic components, and / or other relevant information for harmonic compensation can be communicated in various ways, such as synchronously, asynchronously, at predefined constant communication intervals, and / or at varying communication intervals. If the operating point data or estimated harmonic components are communicated periodically, for example at time intervals from 1 ms to 10 s, such as 1 ms, 10 ms, 100 ms, ... 1 s, or any suitable system-specific time interval, then a longer communication interval simply means a slower response to changes in the operating point of the load entity 10. Even a slower response time for harmonic compensation can be considered feasible because harmonic currents can primarily cause additional heat in AC systems, and the system's thermal time constant can be much longer than the previously mentioned example of a communication interval. Therefore, it can be recognized that even using simple communication methods, the proposed solution is achievable in its basic form, while increasing the data exchange frequency or adding more information to the communication between devices can improve the accuracy and speed of harmonic estimation and compensation.

[0071] According to an embodiment, performing at least partial harmonic compensation in an AC network by the harmonic compensation entity 20 based on at least one estimated harmonic current component includes: providing at least one compensated harmonic current component to the AC network, wherein the at least one compensated harmonic current component is configured to at least partially compensate the estimated at least one harmonic current component. For this purpose, the harmonic compensation entity 20 (e.g., an electric driver having a controllable rectifier 21) can be equipped with a suitable controller (unit, device, system) configured to generate commands to the pulse width modulation (PWM) rectifier / inverter semiconductor bridge such that the harmonic compensation entity 20 can inject the desired compensated harmonic current components(s) into the AC grid. As an example, when the positive direction of the current in load entity 10 is defined as from the AC grid toward load entity 10, and similarly defined (from the AC grid toward harmonic compensation entity 20) for the harmonic compensation entity 20, Kirchhoff's current law gives, for The harmonic components are compensated, and the harmonic current components become That is, it is the opposite phase.

[0072] Figure 16 A simplified example high-level diagram of an electrical power converter 21 (such as a rectifier / inverter 21) is shown, including an electrical power converter unit 21A equipped with a grid-side L, LC, or LCL filter 40 and a DC-side capacitor bank C connected between DC and AC voltage ports. For example, the grid-side filter 40 and / or the DC-side capacitor bank C may be separate components or included in the electrical power converter unit 21A or typically within the electrical power converter 21. Furthermore, additional components and / or assemblies (such as one or more input and / or output filters or switching devices) may be included in the electrical power converter unit 21A or typically within or connected to the electrical power converter 21. Figure 16 Also shown separately is the controller 210 of the power converter unit 21A, which is capable of (being configured to) use (multiple) harmonic current components as reference signals and generate switching commands to the PWM rectifier / inverter bridge 200 of the power converter unit 21A as outputs. For example, the power converter 21 can internally measure its own current (from the AC side) and voltage (from the DC side). It can also have internal / external AC (grid) voltage measurement, or it can estimate it. From the measured or estimated grid voltage, the harmonic compensation entity 20 can extract the fundamental frequency (first harmonic) grid voltage component. phase And without loss of generality, the phase of this phasor It can be set to zero in the coordinate system of the harmonic compensation entity 20.

[0073] exist Figure 2 , Figure 3 and Figure 4 In the examples shown, the harmonic compensation entity 20 may be or include another electric driver equipped with a controllable (e.g., active front end, AFE) rectifier. In these examples, the first electrical power converter unit 21A may correspond to Figure 16 The electric power converter unit 21A is shown. In this case, another (second) electric power converter unit 21B may be connected to the DC voltage port to supply power to the motor 23 or another load. If the harmonic compensation entity 20 is or includes an electric drive, the compensation can be performed in parallel with its normal operation and the task of rotating the motor or feeding another type of load. Preferably, the sizing and / or design ensures that these two tasks can be performed simultaneously. Naturally, if the electric drive is not operating at its full power capacity, its controlled rectifier has at least some power and current capacity available for the parallel compensation task. Alternatively, the harmonic compensation entity 20 may be or include a grid converter module (such as a PWM inverter bridge), possibly equipped with an AC-side L, LC, or LCL filter and / or a DC-side capacitor bank, and substantially corresponds to... Figure 16 The depicted device. Similarly, in this case, for example, compensation can be performed in parallel with its normal operation to regulate DC voltage and / or follow active and reactive power commands. It is also possible that the harmonic compensation entity 20 is dedicated to harmonic current and reactive power compensation. In this case, it can be similar to a typical active harmonic filter, possibly differing in the absence of any additional AC current measurements.

[0074] In order to inject multiple compensated harmonic current components with desired amplitude and phase, for example, the harmonic compensation entity 20 should preferably know how zero phase is defined in the harmonic estimation. This is to handle the estimated and compensated harmonic current components in a common reference frame. One possible alternative is to use zero phase... Defined as equal to the phase of the fundamental (first harmonic) PCC voltage component in the AC power grid. ,like Figure 5 As illustrated, since the harmonic compensation entities 20 can measure or at least estimate the AC grid voltage (as they typically do in their normal operation under any circumstances), they can track the angle of the fundamental voltage component, and in this practical example, the phase of the tracked grid voltage phasor is set to zero. Clearly, the harmonic compensation entity 20 can then interpret the estimated harmonic current components(s) in a common reference frame. To create (multiple) compensated (anti-phase) harmonic current components. This uses zero phase as... The actual choice is merely one possible way to ensure that the estimated harmonic components can be correctly interpreted in the compensation device. It will be apparent to those skilled in the art that, for example, zero phase can also be fixed to some other orientation (such as...). or This is possible, provided it can be understood both during the estimation process and within the harmonic compensation entity 20. How to control the current or its harmonic components (e.g., the PWM rectifier / inverter) is considered inherently known in a reference frame (or other reference frame) closely connected to the fundamental component of the grid voltage. Any suitable known control technique can be applied to the harmonic compensation entity 20 to achieve (at least approximately or partially) matching of the injected compensated harmonic components to (at least approximately or partially) the desired (selected) harmonic components, such that they are at least partially compensated. For tracking the grid voltage angle, a possible approach is to use, for example, a phase-locked loop (PLL), but any other known technique can also be utilized.

[0075] Due to the open-loop nature of the proposed harmonic compensation solution, any error in harmonic current estimation can lead to errors in harmonic current compensation. However, the harmonic compensation entity 20 can use one or more correction coefficients as additional inputs (but this is not required) and adjust the reference values ​​of the harmonic current components provided to the control system to fine-tune the compensation current components, resulting in smaller harmonic components in the PCC of the AC power grid. The basic principle is as follows: Figure 17 The described method involves several possible ways to adjust (multiple) correction coefficients. Input is given to harmonic compensation entity 20. One or more such correction factors can be given as user-defined parameters, for example, during system commissioning or in any other suitable manner. Alternatively, they can be obtained from another entity, monitoring equipment, and / or a control system using a communication bus. Such correction factors(s) can also be calculated in harmonic compensation entity 20 if information related to fine-tuning can be obtained from user parameters in a different form or conveyed by other devices or entities.

[0076] According to an embodiment, the electrical system may include two or more load entities, wherein estimation of at least one harmonic current component caused by at least one load entity 10 can be performed individually for each of the load entities. The proposed solution can be derived from... Figure 1 , Figure 2 and Figure 4 The system shown has only one load entity 10. Figure 3 The example shows a system with two or more load entities 10. In this system or configuration, there is typically more than one. A load entity 10 and at least one harmonic compensation entity 20. Harmonic estimation, communication, and compensation can be performed in a manner similar to the previously described embodiments. Alternatively, where the harmonic compensation entity 20 estimates harmonic current components based on operating point data communicated by the load entity 10, it may use multiple estimator groups (see [link to previous embodiments]). Figure 8 For example, a group is formed for each load entity 10 to obtain estimated harmonic currents generated by multiple load entities 10. In another alternative, where load entities 10 estimate their own harmonic current components and transmit them to a harmonic compensation entity 20, multiple estimators can be distributed to the controllers of the load entities 10. The sum of the effective harmonic currents seen at the PCC without compensation can be calculated using Kirchhoff's current law. ,in These are the estimated harmonic components for each load. The harmonic compensation entity 20 can use this law when aggregating harmonic components generated by multiple estimators. For example, in the case of multiple load entities 10, the harmonic compensation entity 20 can compensate for the sum of harmonic currents within its current and power capabilities. Multiple harmonic compensation entities 20 may exist within the same AC system or connected to the same AC system.

[0077] The feasibility of the proposed compensation method was tested using time-domain simulation and frequency-domain analysis. The simulation examples considered below basically correspond to... Figure 2 The example shown illustrates this. In the example configuration, there is a 50 kW, three-phase, 6-pulse, diode rectifier equipped with a DC choke and connected to a 400 V, 50 Hz AC grid, supplying a varying DC load. The AC grid is modeled with a configurable power supply transformer with a reactance of 5% (in transformer-based units) to test different network strengths. Three different power supply transformer sizes (1000 kVA, 500 kVA, and 100 kVA) are considered. A 50 kVA AFE rectifier equipped with an LCL filter is present in parallel with the 6-pulse rectifier; this AFE rectifier can be loaded and selected (compensated) harmonic components can be injected. Simulations are performed using the PLECS circuit simulator, and the simulation parameters are given in Table I below. Table I: Electrical Parameters of the Simulation System

[0078] first, Figure 18The example 6 pulse rectifier displays the 1st (left), 5th (middle), and 7th (right) harmonic AC current components (amplitude and phase) under an example DC load variation from 0 to 1.2 pu, and the test case was repeated using transformers of different sizes to power the rectifier: a 1000 kVA transformer, a 500 kVA transformer, and a 100 kVA transformer. It can be noted that when the power supply transformer is smaller, the harmonic component amplitude is smaller due to the increased transformer leakage inductance (absolute value), which effectively connects the transformer in series with the diode rectifier. Figure 18 The example also shows, in dashed lines, the model used for the 5th and 7th harmonic components (h=5 and h=7). .Model Here it is essentially a piecewise linear function, where active power is the input, and they attempt to follow the analog harmonic components in the case of a 500 kVA power supply transformer.

[0079] Figure 18 The example model shown (black dashed line) was also used in the next step to estimate harmonic components, where the AFE rectifier was commanded to inject 5th and 7th order compensated harmonic current components based on the estimator output. Figure 19 The time-domain waveforms of the 6-pulse rectifier AC current (top), AFE rectifier current (middle), and PCC current (bottom) are shown when the 6-pulse rectifier is fully loaded (50 kW) and the AFE rectifier begins injecting 5th and 7th harmonic compensation components based on estimated harmonic components at t = 0.2 s. It can be clearly seen that after enabling open-loop compensation, the typical three-phase diode rectifier current waveform at the PCC becomes somewhat more sinusoidal. Figure 20 The diagram shows the 5th and 7th current components at the PCC when open-loop compensation in the AFE is enabled. A model for harmonic component estimation is also shown. Marked with a dashed line, it is similar to Figure 18 The lines shown are the same. When comparing... Figure 18 (No compensation) and Figure 20 When considering the 5th and 7th harmonic components (with compensation), it is clear that their amplitudes are significantly reduced to approximately one-quarter, and the compensation is effective across the entire power range. It is also noteworthy that the proposed open-loop compensation is effective regardless of the size of the power transformer (1000 kVA, 500 kVA, 100 kVA), i.e., the network strength. This can be explained by the impedance shaping effect of the harmonic compensator at the 5th and 7th harmonic frequencies, meaning that from the perspective of a 6-pulse rectifier, the power transformer is connected in parallel with the harmonic compensator. The impedance shaping effect can also be seen in… Figure 19 As seen in the 6-pulse rectifier current, when the AFE begins to inject compensating harmonic components, the peak value of the pulse current is higher and the valley value is deeper.

[0080] also, Figure 21 The effect of partial harmonic compensation on the THD of the current at the PCC is described. Under the condition of no compensation, i.e., only a 6-pulse rectifier operating, such as... Figure 21 As shown in alternative scheme a), the THD caused by the 6-pulse rectifier is approximately 40% at full load and higher at partial load. When open-loop compensation is enabled and the AFE compensates for the 5th and 7th harmonic components of the 6-pulse rectifier, as... Figure 21 As shown in alternative b), the THD at the PCC is reduced to half or less (approximately 20%) over a wide power range. If the AFE rectifier is used to power its own load while compensating for harmonic components, the THD at the PCC can be further reduced (by close to 10%). This is as follows... Figure 21 As shown in alternative c), the further reduction in THD at PCC is due to the increased fundamental frequency current component drawn by the AFE rectifier. Figure 22 The diagram illustrates the AC current at the 6-pulse rectifier (top), the AFE rectifier (middle), and the current at the PCC (bottom) when the 6-pulse rectifier is fully loaded (50kW) and the AFE rectifier is loaded with 25kW, and the estimated harmonic components of the 5th and 7th harmonics are injected at t = 0.2s. Figure 22 The time-domain current waveforms at the 6-pulse rectifier, AFE rectifier, and PCC are shown when the AFE rectifier first powers its own 25 kW load and then begins injecting compensating harmonic components after t=0.2s. The PCC current after t=0.2s now has a clearly discernible fundamental component, although some harmonics are still present in the waveform.

[0081] According to an embodiment, an apparatus for harmonic compensation in an electrical system is provided, wherein the electrical system includes an AC network and at least one load entity 10, the at least one load entity 10 including at least a first electrical power converter 11 connected to the AC network. According to an embodiment, the apparatus includes: an estimation component configured to estimate at least one harmonic current component in the AC network caused by the at least one load entity 10, based at least on data indicating the operating point of the at least one load entity 10; and a harmonic compensation entity 20 configured to be connected to the AC network and to perform at least partial harmonic compensation in the AC network based on the estimated at least one harmonic current component caused by the at least one load entity 10.

[0082] According to an embodiment, the harmonic compensation entity 20 includes an estimation component (or is configured to perform estimation) and is configured to receive data indicating the operating point of at least one load entity 10. The harmonic compensation entity 20 may be configured to receive data indicating the operating point of at least one load entity 10 (directly or indirectly) from at least one load entity 10 or from some other entities. Furthermore, at least one load entity 10 may be configured to transmit data indicating the operating point of at least one load entity 10 to the harmonic compensation entity 20.

[0083] According to another embodiment, the estimation component is located in at least one load entity 10 (or the load entity is configured to perform estimation) and is configured to transmit at least one harmonic current component estimated by the estimation component to a harmonic compensation entity.

[0084] According to another embodiment, the apparatus further includes a control entity 30, which is different from at least one load entity 10 and different from the harmonic compensation entity 20. The control entity 30 includes an estimation component, and is configured to receive data indicating the operating point of at least one load entity 10, and to transmit the estimated at least one harmonic current component to the harmonic compensation entity 20. The control entity 30 may be configured to receive data indicating the operating point of at least one load entity 10 (directly or indirectly) from at least one load entity 10. Furthermore, at least one load entity 10 may be configured to transmit data indicating the operating point of at least one load entity 10 to the control entity 30.

[0085] According to another embodiment, the apparatus further includes a control entity 30 that is different from at least one load entity 10 and different from the harmonic compensation entity 20, wherein the control entity 30 includes an estimation component (or is configured to perform estimation), wherein the control entity 30 is configured to transmit an operating point command to at least one load entity 10 and to transmit the estimated at least one harmonic current component to the harmonic compensation entity 20. Furthermore, at least one load entity 10 may be configured to set its operating point according to the operating point command received from the control entity 30.

[0086] According to another embodiment, the apparatus further includes a control entity 30 that is different from at least one load entity 10 and different from the harmonic compensation entity 20, wherein the harmonic compensation entity 20 includes an estimation component (or is configured to perform estimation), wherein the control entity 30 is configured to transmit an operating point command to at least one load entity 10 and transmit data indicating the operating point of at least one load entity 10 to the harmonic compensation entity 20. Furthermore, at least one load entity 10 may be configured to set its operating point according to the operating point command received from the control entity 30.

[0087] According to another embodiment, the harmonic compensation entity 20 is configured to perform at least partial harmonic compensation in the AC network based on at least one estimated harmonic current component by providing at least one compensated harmonic current component to the AC network, wherein the at least one compensated harmonic current component is configured to at least partially compensate the at least one estimated harmonic current component.

[0088] According to an embodiment, an electrical system is provided, comprising: an AC network; at least one load entity 10 including a first electrical power converter 11 connected to the AC network; and means according to any embodiment described herein, wherein a harmonic compensation entity 20 is connected to the AC network. According to an embodiment, an electrical power converter is provided, configured to be connected to the AC network, and estimates at least one harmonic current component induced in the AC network by the at least one load entity 10 based at least on data indicating the operating point of the at least one load entity 10 connected to the AC network.

[0089] The controller (control device, unit, system) of any entity described herein and / or any other component used to implement at least a portion of the functionality of any embodiment according to the embodiments herein may be implemented as a single physical unit or as two or more separate physical units configured to implement one or more functionalities. The term "unit" as used herein generally refers to a physical or logical entity, such as a physical device or a portion thereof, or a software routine. Figure 23This is a simplified block diagram illustrating some units for a device (apparatus, apparatus, system) 300 configured to perform at least some functions of a controller. In the illustrated example, device 300 includes one or more interface (IF) entities 301, such as one or more user interfaces and / or data interfaces, and one or more processing entities 302 connected to the various interface entities 301 and one or more memories 303. The one or more interface entities 301 may be entities for receiving and / or sending information, such as communication interfaces including hardware and / or software for implementing: establishing communication connections according to one or more communication protocols, or for storing and retrieving data (e.g., measurement or operational data), and / or for providing user interaction via one or more user interfaces. Processing entities 302 are capable of performing calculations using corresponding algorithms 304 stored in memory 303 and are configured to implement at least a portion of the aforementioned functions and / or operations. Processing entities 302 may include one or more processors, controllers, control units, microcontrollers, etc., configured to perform, for example, the embodiments, examples, implementations, and / or operations described above. Typically, the processor can be a central processing unit, but processor entity 302 can be, for example, an additional operating processor, a multi-core processor, or a microprocessor. Memory 303 can be used to store the computer program code required for one or more of the aforementioned functions / operations, i.e., the algorithm 304 for implementing the aforementioned functions / operations. Memory 303 can also be used to at least temporarily store other possible information required for one or more of the aforementioned functions / operations. Memory 303 may include a data buffer, which can at least temporarily store, for example, measurement and / or operational data and / or information received as user input and / or from another entity. Components including those used to provide any embodiment described herein can be at least partially provided by, as... Figure 23 The illustrated device 300 implements this.

[0090] Typically, for example, such a controller 300 and / or any other components used to implement at least a portion of the functionality of any of the embodiments described herein can be implemented at least partially by one or more computers or corresponding digital signal processing (DSP) devices (provided with suitable software). Such computers or DSP devices preferably include at least a working memory (RAM) providing storage areas for arithmetic operations and a central processing unit (CPU), such as a general-purpose digital signal processor. The CPU may include a register set, an arithmetic logic unit, and a control unit. The CPU control unit is controlled by a series of program instructions transferred from RAM to the CPU. The CPU control unit may contain numerous microinstructions for basic operations. The implementation of the microinstructions can vary depending on the CPU design. The program instructions can be encoded using a programming language, which can be a high-level programming language such as C, Java, etc., or a low-level programming language such as machine language or assembly language. The computer may also have an operating system that provides system services to computer programs written using the program instructions. Computers or other devices implementing various embodiments or parts thereof may also include suitable input components for receiving, for example, measurement data and / or control data, and output components for outputting, for example, control data or any other data. One or more specific integrated circuits, such as application-specific integrated circuits (ASICs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), and / or discrete electrical components and devices, may also be used to implement the functionality according to any of the embodiments.

[0091] The various embodiments described herein can be implemented, at least in part, in existing system elements (such as various electrical power converter devices or similar devices) and / or in a centralized or distributed manner using separate dedicated elements or devices. Such existing devices may include processors and memory that can be used for the functionality of the various embodiments described herein. Typically, many electrical devices (such as electrical power systems) and their components (such as intelligent electronic devices) may include processors and memory that can also be used to implement at least a portion of the functionality of the various embodiments described herein. Therefore, at least some modifications and configurations that may be needed to implement the embodiments can be executed as software routines, which can be implemented as added or updated software routines. If at least a portion of the functionality of any embodiment is implemented by software, such software can be provided as a computer program product comprising computer program code that, when run on a computer, causes the computer or corresponding device to perform the functionality of the embodiments described herein. Such computer program code can be stored or generally embodied on a computer-readable medium, such as suitable memory, e.g., flash memory or optical disc, from which it can be loaded onto one or more units that execute the program code. Furthermore, for example, such computer program code implementing any embodiment can be loaded onto one or more units executing the computer program code via a suitable data network, and it can replace or update any existing program code. Embodiments can provide a computer program embodied on any client-readable distributed / data storage medium or (multiple) memory units or (multiple) artifacts, including program instructions executable by one or more processors / computers, which, when loaded into a device, constitute a control device, or any corresponding unit or entity providing corresponding functionality or at least a portion thereof. Programs including software routines, program fragments constituting a "program library," applets, and macros (also referred to as program products) can be stored on any medium and can be downloaded into a device. In other words, for each or some or one possible unit / subunit and / or algorithm (e.g., via...) for one or more of the above-described functions / operations... Figures 1 to 23 Any diagram (and any combination thereof) can be an element comprising one or more arithmetic logic units, multiple special registers, and control circuitry.

[0092] It will be apparent to those skilled in the art that the inventive concept can be implemented in various ways as technology advances. The present invention and its embodiments are not limited to the examples described above, but can be varied within the scope of the claims.

Claims

1. A method for harmonic compensation in an electrical system, the electrical system comprising an AC network, at least one load entity, and a harmonic compensation entity connected to the AC network, the at least one load entity comprising at least a first electrical power converter connected to the AC network, the method comprising: At least one harmonic current component induced by the at least one load entity in the AC network is estimated based on data indicating the operating point of the at least one load entity; as well as The harmonic compensation entity performs at least partial harmonic compensation in the AC network based on the estimated harmonic current component caused by the at least one load entity.

2. The method of claim 1, wherein the data indicating the operating point of the at least one load entity includes one or more of the following: the operating power of the first power converter, the DC link voltage of the first power converter, and / or the DC link current of the first power converter, and / or wherein the data indicating the operating point of the at least one load entity includes one or more quantities indicating the following: the operating power of the first power converter and / or the DC link voltage of the first power converter and / or the DC link current of the first power converter.

3. The method according to claim 1 or 2, wherein the estimation of the at least one harmonic current component caused by the at least one load entity is further performed based on characteristic data of the AC network.

4. The method according to claim 3, wherein the characteristic data of the AC network includes one or more of the following: the voltage of the AC network, the impedance of the AC network, the short-circuit current of the AC network, and / or the short-circuit power of the AC network.

5. The method of claim 1 or 2, wherein the estimation of the at least one harmonic current component caused by the at least one load entity is performed by using a predetermined static model or by simulating a model of the load entity.

6. The method of claim 1 or 2, wherein the electrical system comprises two or more load entities, wherein the estimation of the at least one harmonic current component caused by the at least one load entity is performed individually for each of the load entities.

7. The method of claim 1 or 2, wherein the estimation of the at least one harmonic current component caused by the at least one load entity is performed in the harmonic compensation entity, wherein the method includes transmitting the data indicating the operating point of the at least one load entity from the at least one load entity to the harmonic compensation entity.

8. The method of claim 1 or 2, wherein the estimation of the at least one harmonic current component caused by the at least one load entity is performed in the same at least one load entity, wherein the method includes transmitting the estimated at least one harmonic current component from the at least one load entity to the harmonic compensation entity.

9. The method of claim 1 or 2, wherein the estimation of the at least one harmonic current component caused by the at least one load entity is performed in a control entity that is different from the at least one load entity and different from the harmonic compensation entity, wherein the method includes transmitting data indicating the operating point of the at least one load entity from the at least one load entity to the control entity, and transmitting the estimated at least one harmonic current component from the control entity to the harmonic compensation entity.

10. The method of claim 1 or 2, wherein the at least partial harmonic compensation performed by the harmonic compensation entity in the AC network based on the estimated at least one harmonic current component comprises: At least one compensated harmonic current component is provided to the AC network, wherein the at least one compensated harmonic current component is configured to at least partially compensate the estimated at least one harmonic current component.

11. The method according to claim 1 or 2, wherein the harmonic compensation entity comprises a second electrical power converter connected to the AC network.

12. An apparatus for harmonic compensation in an electrical system, the electrical system including an AC network and at least one load entity, the at least one load entity including at least a first electrical power converter connected to the AC network, the apparatus comprising: The estimation component is configured to estimate at least one harmonic current component induced by the at least one load entity in the AC network, based at least on data indicating the operating point of the at least one load entity. as well as A harmonic compensation entity is configured to be connected to the AC network and to perform at least partial harmonic compensation in the AC network based on the estimated harmonic current component caused by the at least one load entity.

13. The apparatus of claim 12, wherein the harmonic compensation entity includes the estimation component and is configured to receive the data indicating the operating point of the at least one load entity.

14. The apparatus of claim 12, wherein the estimation component is located in the at least one load entity and is configured to transmit the at least one harmonic current component estimated by the estimation component to the harmonic compensation entity.

15. The apparatus of claim 12, wherein the apparatus further comprises a control entity, the control entity being different from the at least one load entity and different from the harmonic compensation entity, wherein the control entity includes the estimation component, and wherein the control entity is configured to receive the data indicating the operating point of the at least one load entity, and is configured to transmit the estimated at least one harmonic current component to the harmonic compensation entity.

16. The apparatus of any one of claims 12 to 15, wherein the harmonic compensation entity is configured to perform the at least partial harmonic compensation in the AC network based on the estimated at least one harmonic current component by providing at least one compensated harmonic current component to the AC network, wherein the at least one compensated harmonic current component is configured to at least partially compensate the estimated at least one harmonic current component.

17. The apparatus according to any one of claims 12 to 15, wherein the harmonic compensation entity includes a second electrical power converter configured to be connected to the AC network.

18. An electrical system comprising: Communication network; At least one load entity, the at least one load entity including a first electrical power converter connected to the AC network; as well as The apparatus according to any one of claims 12 to 17, wherein the harmonic compensation entity is connected to the AC network.

19. An electrical power converter configured to be connected to an AC network and to estimate at least one harmonic current component in the AC network caused by at least one load entity, based at least on data indicating the operating point of at least one load entity connected to the AC network.

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