Harmonic suppression method of power conversion system, related device and storage medium

Abstract

The application discloses a harmonic suppression method of a power conversion system, related devices and a storage medium. The harmonic suppression method of the power conversion system comprises the following steps: determining whether a harmonic component in an output electrical signal of the power conversion system is greater than a preset threshold; and in response to the harmonic component in the output electrical signal of the power conversion system being greater than the preset threshold, adjusting an output impedance of at least one power converter according to the harmonic component, so that the harmonic component is transmitted into the at least one power converter. The method makes the harmonic component in the power conversion system exist in the at least one power converter in the form of circulating current, so as to suppress the harmonic in the remaining power converters of the power conversion system except the at least one power converter. The method not only can reduce the harmonic component of the output electrical signal of the power conversion system, but also does not need to additionally increase hardware and change the overall external characteristics of the power conversion system, thereby reducing the cost and computation amount and improving the stability of the power conversion system.

Description

Technical Field

[0001] This application relates to the field of harmonic suppression technology, and more specifically, to a harmonic suppression method, related apparatus and storage medium for a power conversion system. Background Technology

[0002] Power conversion systems are primarily used to convert direct current (DC) to alternating current (AC) for use by connected AC circuits. However, during operation, harmonics are introduced into the output signal of the power conversion system. Harmonics increase losses in AC circuit components, reducing their lifespan and decreasing the reliability and accuracy of relay protection and metering devices. Therefore, harmonic suppression in power conversion systems is crucial. Summary of the Invention

[0003] This application provides a harmonic suppression method, related apparatus, and storage medium for a power conversion system. The various aspects involved in this application's embodiments are described below.

[0004] In a first aspect, a harmonic suppression method for a power conversion system is provided, the power conversion system including multiple power converters connected in parallel through a common coupling point, the method including: determining whether a harmonic component in the output electrical signal of the power conversion system is greater than a preset threshold; in response to the harmonic component in the output electrical signal of the power conversion system being greater than the preset threshold, adjusting the output impedance of at least one power converter according to the harmonic component, so that the harmonic component is transmitted to the at least one power converter.

[0005] As one possible implementation, the method further includes: in response to the harmonic component in the output electrical signal of the power conversion system being greater than a preset threshold, reducing the power setpoint of the at least one power converter and increasing the power setpoint of the remaining power converters, so that the total output power of the power conversion system remains unchanged, wherein the remaining power converters are power converters other than the at least one power converter among the plurality of power converters.

[0006] As one possible implementation, the output electrical signal of the power conversion system is the output electrical signal of the power conversion system after the first harmonic suppression processing. The method further includes: determining whether the first harmonic component is greater than the preset threshold, wherein the first harmonic component is the harmonic component in the output electrical signal of the power conversion system before the first harmonic suppression processing; and in response to the first harmonic component being greater than the preset threshold, performing the first harmonic suppression processing on the first harmonic component using virtual impedance.

[0007] As one possible implementation, the method further includes: after adjusting the output impedance of at least one power converter according to the harmonic components, determining whether the output harmonics of the at least one power converter are less than the preset threshold; in response to the output harmonics of the at least one power converter being less than the preset threshold, restoring the power setpoints of the plurality of power converters and the output impedance of the at least one power converter; and in response to the output harmonics of the at least one power converter being greater than or equal to the preset threshold, maintaining the power setpoints of the plurality of power converters and the output impedance of the at least one power converter unchanged.

[0008] As one possible implementation, the power conversion system is a grid-type power conversion system, and the adjustment of the output impedance of the at least one power converter according to the harmonic components includes: determining the desired output impedance according to the frequency of the harmonic components; and performing feedforward control on the load current of the at least one power converter according to the desired output impedance to adjust the output impedance of the at least one power converter.

[0009] As one possible implementation, the feedforward control of the load current of the at least one power converter based on the desired output impedance to adjust the output impedance of the at least one power converter includes: determining the desired output voltage of the at least one power converter based on the desired output impedance and the load current of the at least one power converter; determining a reference voltage adjustment value based on a reference voltage, the desired output voltage, and the actual output voltage of the at least one power converter; determining a reference current using a voltage regulator based on the reference voltage adjustment value; and controlling the at least one power converter based on the reference current.

[0010] As one possible implementation, the power conversion system is a grid-type power conversion system, and the adjustment of the output impedance of the at least one power converter according to the harmonic components includes: determining the desired output admittance according to the frequency of the harmonic components; and performing feedforward control on the voltage of the common coupling point according to the desired output admittance to adjust the output impedance of the at least one power converter.

[0011] As one possible implementation, the step of feedforward control of the voltage at the common coupling point based on the desired output admittance to adjust the output impedance of the at least one power converter includes: determining a desired output current based on the desired output admittance and the voltage at the common coupling point; determining a reference current adjustment value based on a reference current, the desired output current, and the actual output current of the at least one power converter; determining a modulation voltage using a current loop regulator based on the reference current adjustment value; and controlling the at least one power converter based on the modulation voltage.

[0012] As one possible implementation, the adjusted output impedance of the at least one power converter at a predetermined subharmonic is lower than the output impedance of the remaining power converters at the predetermined subharmonic.

[0013] In a second aspect, a control device is provided, comprising: a memory for storing code; and a processor for executing the code stored in the memory to perform the method as described in the first aspect.

[0014] Thirdly, a power conversion system is provided, comprising: a plurality of power converters connected in parallel via a common coupling point; and a control device as described in the second aspect.

[0015] Fourthly, a computer-readable storage medium is provided, having stored thereon information for performing the method as described in the first aspect.

[0016] The harmonic suppression method for power conversion systems provided in this application can adjust the output impedance of at least one power converter in the power converter control system according to the harmonic components when the harmonic components in the output electrical signal of the power conversion system exceed a preset threshold. This allows the harmonic components to be transmitted to the at least one power converter with adjusted output impedance. By dedicating the harmonic components to the at least one power converter with adjusted output impedance, the harmonic components in the system mainly exist in the form of circulating current in the selected at least one power converter. This suppresses harmonics in the remaining power converters in the power conversion system, reducing the harmonic components in the output electrical signal of the power conversion system. This method does not require additional hardware or changes to the overall external characteristics of the power conversion system, thereby reducing cost and computational load while improving the stability of the power conversion system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the architecture of a power conversion system provided in an embodiment of this application.

[0018] Figure 2 This is a schematic diagram of the architecture of a power conversion system provided in another embodiment of this application.

[0019] Figure 3 This is a schematic flowchart of a harmonic suppression method for a power conversion system provided in an embodiment of this application.

[0020] Figure 4 This is a schematic diagram of a control block diagram for adjusting output impedance provided in an embodiment of this application.

[0021] Figure 5This is a schematic diagram of a control block diagram for adjusting output impedance, provided in another embodiment of this application.

[0022] Figure 6 This is a schematic flowchart of a harmonic suppression method for a power conversion system provided in another embodiment of this application.

[0023] Figure 7 This is a schematic diagram of the control device provided in the embodiments of this application. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application should fall within the scope of protection of the present application.

[0025] Power conversion systems are primarily used to convert direct current (DC) into alternating current (AC) for use by AC circuits connected to the power conversion system. This application does not specifically limit the AC circuit; any circuit that requires AC power can be used. For example, the AC circuit can be the power grid, and a power conversion system connected to the power grid can also be called a grid-connected power conversion system.

[0026] Power conversion systems typically include multiple power converters connected in parallel, and these parallel power converters are connected to the AC circuit through a point of common coupling (PCC). For ease of understanding, the following section will explain... Figure 1 and Figure 2 The power conversion system provided in the embodiments of this application will be described.

[0027] like Figure 1 The power conversion system shown is a grid-type power conversion system. See details. Figure 1 The grid-type power conversion system 10 includes power converters 1 to N connected in parallel. All power converters 1 to N in the grid-type power conversion system 10 are grid-type power converters. Among them, power converter K in power converters 1 to N can be equivalently represented as an equivalent voltage source e. k and power converter output impedance Z ok In the form of a series, k = 1, 2, ..., n.

[0028] like Figure 2 The power conversion system shown is a grid-type power conversion system. See details. Figure 2The grid-connected power conversion system 10 includes power converters 1 to N connected in parallel. All power converters 1 to N in the grid-connected power conversion system 10 are grid-connected power converters. Specifically, power converter K in power converters 1 to N can be equivalently represented as an equivalent electrical signal source i. sk and power converter output admittance Y ok In parallel configuration, k = 1, 2, ..., n. The output admittance of the power converter and the output impedance of the power converter are reciprocals of each other.

[0029] in, Figure 1 and Figure 2 The AC circuits 20 shown are all power grids. A power grid can typically be considered equivalent to an ideal voltage source v. g and grid impedance Z g In series. Figure 1 and Figure 2 In the power conversion system 10 shown, each power converter is connected to the power grid via a PCC. Therefore, it can be assumed that each power converter is grid-connected via the PCC. The power converter can be, for example, an inverter or a power conversion system (PCS).

[0030] In some embodiments, the power converter may be connected to the AC circuit via a transformer, and the impedance of this part of the transformer can be considered to have been included in the output impedance of the power converter.

[0031] During the use of power conversion systems, harmonics often appear in the output electrical signal due to various reasons. According to current research and analysis, the main causes of harmonic generation related to power converters are as follows:

[0032] First, the PWM modulation of the power converter has a dead zone, which causes the output of the inverter bridge to contain low-order harmonic components, and these harmonics cannot be completely filtered out by the power converter's filter.

[0033] Second, under load switching or other conditions, the steady-state operating point of the power converter will change. At this time, the impedance characteristics of the AC circuit side and the power converter will change. The overall loop gain of the system has a low stability margin at the predetermined harmonic, and harmonic components at the predetermined harmonic may be generated.

[0034] Harmonics increase losses in AC circuits (especially when the AC circuit is connected to the power grid), thereby reducing the lifespan and utilization rate of components in the AC circuit. Examples of components in AC circuits include transmission lines, rotating electrical machines, and transformers. Furthermore, harmonics reduce the reliability and accuracy of relay protection and metering devices. Therefore, harmonic suppression in power conversion systems is crucial, as it affects the quality of the electrical signals provided by the power conversion system to the AC circuit and the lifespan of components in the AC circuit.

[0035] As mentioned earlier, the causes of harmonics can be broadly categorized into two types. For harmonics caused by the first type, dead-zone compensation and other methods can be used to reduce the harmonics generated by the dead zone. Therefore, how to suppress harmonics caused by the second type becomes a pressing issue.

[0036] One possible approach is to add additional harmonic suppression devices to the power conversion system. For example, these devices could be filters. However, this increases the construction cost of the power conversion system, and the design of the capacity and location of the added devices needs to be considered for different power conversion systems, making it quite complex.

[0037] As another possible implementation, harmonic source tracing can be performed on the harmonics generated by the power conversion system based on the control strategy. This involves analyzing the participation factor of each power converter in the generation of the harmonic under the current operating state and temporarily disconnecting the power converter with the high participation factor. However, this method requires obtaining the real-time parameters of each power converter. In application scenarios with large power conversion system capacity and a large number of power converter units, the computational load of this method is large, making it impractical for real-world applications.

[0038] To avoid increasing the construction cost and computational burden of power conversion systems, one possible approach is to use virtual impedance or virtual admittance to increase the gain of the power converter at the corresponding frequency after detecting excessive harmonics, thereby suppressing harmonics in the output signal of the power conversion system. However, the suppression methods based on virtual impedance or virtual admittance provided by related technologies may not completely suppress harmonics from the power converter, and this method requires consideration of the overall external characteristics of the power station. Therefore, the adjustment of the power converter's output impedance should not be excessive; otherwise, it may lead to stability problems under other fault conditions. In other words, existing control strategies for harmonic suppression based on virtual impedance or virtual admittance rely on the overall external characteristics of the power station, thus affecting the stability of the power conversion system.

[0039] In summary, the relevant technologies for suppressing harmonics caused by the second reason mentioned above are not ideal, and have problems such as high construction cost of power conversion systems, large amount of computation, or affecting the stability of power conversion systems.

[0040] In view of this, embodiments of this application provide a harmonic suppression method for a power conversion system. When the harmonic components in the output electrical signal of the power conversion system exceed a preset threshold, the output impedance of at least one power converter in the power converter control system is adjusted according to the harmonic components, so that the harmonic components are transmitted to the at least one power converter with adjusted output impedance. By dedicating the harmonic components to the at least one power converter with adjusted output impedance, the harmonic components in the system mainly exist in the form of circulating current in the selected at least one power converter. This suppresses harmonics in the remaining power converters in the power conversion system, reducing the harmonic components in the output electrical signal of the power conversion system. This method does not require additional hardware or changes to the overall external characteristics of the power conversion system, thereby reducing cost and computational load while improving the stability of the power conversion system.

[0041] To facilitate understanding of this application, the following is combined with... Figures 3-6 The harmonic suppression method for the power conversion system provided in the embodiments of this application will be described in detail.

[0042] like Figure 3 As shown, the harmonic suppression method 300 for a power conversion system provided in this application includes steps S310-S320.

[0043] In step S310, it is determined whether the harmonic components in the output electrical signal of the power conversion system are greater than a preset threshold.

[0044] The output electrical signal of a power conversion system can be the original output electrical signal of the power conversion system (which can be understood as the first output electrical signal). That is, the output electrical signal output by the power converter without any harmonic suppression processing. Alternatively, the output electrical signal of the power conversion system can be the output electrical signal after the first harmonic suppression processing (which can be understood as the second output electrical signal). That is, the output electrical signal of the power conversion system is the output electrical signal after the first harmonic suppression processing of the original output electrical signal. The output electrical signal can be, for example, output voltage and / or output current.

[0045] Harmonic components are the sinusoidal components in the output electrical signal of a power conversion system other than the fundamental frequency. In some embodiments, harmonic components are predetermined harmonic components. Predetermined harmonics are typically odd-numbered harmonics below the 40th order, with the 5th, 7th, 9th, 11th, and 13th harmonics being dominant. For example, harmonic components may be those resulting from the second type of harmonics mentioned above.

[0046] In step S320, in response to the harmonic component in the output electrical signal of the power conversion system being greater than a preset threshold, the output impedance of at least one power converter is adjusted according to the harmonic component so that the harmonic component is transmitted to at least one power converter.

[0047] At least one power converter is a portion of the multiple parallel-connected power converters forming the power conversion system as described above. The multiple parallel-connected power converters in the power conversion system can be divided into two parts: one part is the at least one power converter, and the other part is the remaining power converters. That is, the remaining power converters are the power converters in the power conversion system excluding the at least one power converter. The at least one power converter can be pre-defined.

[0048] To distinguish between at least one power converter and the remaining power converters, in some embodiments, the power converter in the at least one power converter is referred to as the second power converter, and the power converter in the remaining power converters is referred to as the first power converter.

[0049] For example, at least one power converter (i.e., the second power converter) is a pre-designed redundant (or standby) power converter in the power conversion system. A redundant power converter is an additional power converter configured during the design phase of the power conversion system to improve system reliability and fault tolerance. The main function of the second power converter is to provide additional support when the first power converter in the power conversion system fails or requires maintenance, ensuring the continuity and reliability of the entire system. The first power converter is a non-redundant power converter in the power conversion system used for normal grid-connected operation. The first power converter is the fundamental component for the operation of the power conversion system, responsible for maintaining grid stability and meeting user electricity demands. The first power converter undertakes the main power conversion task, stably converting DC to AC in daily operation and feeding it into the AC circuit. The first power converter is usually optimally configured according to the load demand of the power conversion system and grid conditions to ensure efficient and reliable power supply.

[0050] For example, at least one power converter and the remaining power converters are power converters in a power conversion system used for normal grid-connected operation. At least one power converter is one of several power converters in a power conversion system that are artificially designated. At least one power converter and the remaining power converters together enable the power conversion system to provide an additional power margin beyond the target power, so that the target electrical signal can be provided to the AC circuit using only the remaining power converters in the power conversion system, excluding the designated at least one power converter.

[0051] In this embodiment of the application, after the processing in step S320, the output impedance of at least one power converter is adjusted (or reshaped) to be an output impedance that facilitates the transmission of harmonic components. Based on this, the harmonic components in the remaining power converters will be transmitted to at least one power converter, so that at least one power converter becomes a power converter dedicated to transmitting harmonic components when the occurrence of harmonic components exceeds a preset threshold.

[0052] By assigning the harmonic components to at least one power converter with adjusted output impedance, harmonics in the remaining power converters in the power conversion system can be suppressed. This method does not require additional hardware or changes to the overall external characteristics of the power conversion system, thereby reducing cost and computation while improving the stability of the power conversion system.

[0053] As previously mentioned, the harmonic components may be, for example, predetermined harmonic components. To adjust the output impedance of at least one power converter so that it more readily transmits the predetermined harmonic components than other power converters, thereby transferring the predetermined harmonic components from the remaining power converters to at least one power converter for suppression. In some embodiments, after performing step S320, the output impedance of the adjusted at least one power converter at the predetermined harmonic is lower than the output impedance of the remaining power converters at the predetermined harmonic.

[0054] In essence, harmonic currents tend to flow along paths with lower impedance. By adjusting the output impedance of at least one power converter to be less than that of the others, at least one power converter can become a device that attracts harmonic current flow more easily than the others.

[0055] In some embodiments, the number of power converters in at least one power converter can be two or more. Since at least two power converters are used to adjust the output impedance, and both of these power converters are connected via a PCC, the at least two power converters with adjusted output impedance can jointly form a loop path for diverting harmonic components. This loop path can introduce harmonic components that would otherwise flow in the other power converters from the PCC point into the loop path, thereby causing at least two power converters to take over the harmonic components from the other power converters, suppressing the harmonic components in the other power converters, and achieving harmonic suppression of the output current of the power conversion system.

[0056] In addition, according to Figure 1 and Figure 2 As can be seen from the equivalent circuit, in a multi-machine parallel system, multiple power converters are connected in parallel to supply power to the load / grid. When the output impedance of some selected power converters (some selected units are at least one power converter in the embodiments of this application) at a predetermined harmonic frequency is small, the harmonics will mainly exist in the selected power converters in the form of circulating current, while the unselected power converters (i.e., the remaining power converters in the embodiments of this application) will have no or very few harmonics, thereby improving the quality of the output current of the power conversion system formed by the unselected power converters.

[0057] By forming a ring path dedicated to transmitting harmonic currents with at least one power converter, the harmonic suppression effect on the output current of the remaining power converters in the power conversion system is improved.

[0058] To prevent at least one power converter from overcurrent when transmitting harmonic components and to further ensure that the overall external characteristics of the power conversion system remain unchanged, thereby improving the stability of the power conversion system, in some embodiments, the harmonic suppression method for the power conversion system further includes: in response to the harmonic components in the output electrical signal of the power conversion system exceeding a preset threshold, reducing the power setpoint of at least one power converter and increasing the power setpoint of the remaining power converters, so that the total output power of the power conversion system remains unchanged.

[0059] In other words, before adjusting the output impedance of at least one power converter, the power input of at least one power converter can be reduced to prevent overcurrent caused by harmonic components flowing through it, thus avoiding circuit damage. Furthermore, since the power inputs of the remaining power converters are increased simultaneously to keep the total output power of the power conversion system constant, the overall external characteristics of the power conversion system remain unchanged, thereby improving the stability of the power conversion system.

[0060] This application does not specifically limit the method for reducing the power setpoint of at least one power converter. As one implementation, the power setpoint of at least one power converter can be reduced according to preset conditions. These preset conditions may include, for example, the mapping relationship between harmonic components and the power setpoint of at least one power converter. Based on this, reducing the power setpoint of at least one power converter according to preset conditions includes: determining the power setpoint of at least one power converter based on the preset conditions and harmonic components, and reducing the power of at least one power converter to its preset power setpoint. Then, based on the principle that the total output power of the power conversion system remains unchanged, the power setpoints of the remaining power converters are simultaneously increased.

[0061] As mentioned above, in some embodiments, the output electrical signal of the power conversion system is the output electrical signal of the power conversion system after the first harmonic suppression processing. Therefore, the harmonic suppression method of the power conversion system may further include the method of the first harmonic suppression processing.

[0062] Specifically, the harmonic suppression method for the power conversion system may further include: determining whether a first harmonic component is greater than the preset threshold, wherein the first harmonic component is a harmonic component in the output electrical signal of the power conversion system before the first harmonic suppression processing; and, in response to the first harmonic component being greater than the preset threshold, performing first harmonic suppression processing on the first harmonic component using virtual impedance. The output electrical signal of the power conversion system before the first harmonic suppression processing can be understood as the original output electrical signal of the power conversion system described above.

[0063] This application does not specifically limit the method of using virtual impedance to perform first harmonic suppression processing on the harmonic components in the first output electrical signal, as long as the harmonics in the power conversion system can be pre-suppressed before the harmonic components are transmitted to at least one power converter. As one implementation, a virtual resistor and inductor (or capacitor) can be added to the controller to give the multiple power converters in the power conversion system higher impedance to harmonics at predetermined frequencies, thereby reducing harmonic currents at these frequencies.

[0064] This application embodiment first uses virtual impedance to perform first harmonic suppression processing on the original output signal of the power conversion system, and then adjusts the output impedance of at least one power converter to perform second harmonic suppression processing on the harmonic components in the output electrical signals of the remaining power converters. This achieves dual harmonic suppression processing, thereby further improving the harmonic suppression effect, improving the quality of the output electrical signal of the power conversion system and the lifespan of the devices in the AC circuit.

[0065] It should be understood that the harmonic components in the output current of a power conversion system will not remain above the preset threshold for an extended period. The harmonic components will only exceed the preset threshold during short periods of time, such as under load changes or at specific moments (i.e., during periods when the power conversion system's output is unstable). Therefore, the time during which the harmonic current exceeds the preset threshold is finite.

[0066] In view of this, after adjusting the output impedance of at least one power converter based on the harmonic components in the output electrical signal of the power conversion system, it can be determined whether the power conversion system has entered a stable output state based on the output harmonics of at least one power converter. Based on the determination result, the working strategy of at least one power converter can be flexibly adjusted to improve the working efficiency of the power conversion system while ensuring the harmonic suppression effect.

[0067] As one possible implementation, the harmonic suppression method further includes: after adjusting the output impedance of at least one power converter according to the harmonic components, determining whether the output harmonics of at least one power converter are less than a preset threshold; in response to the output harmonics of at least one power converter being less than the preset threshold, restoring the power setpoints of the multiple power converters and the output impedance of at least one power converter in the power conversion system; and in response to the output harmonics of at least one power converter being greater than or equal to the preset threshold, maintaining the power setpoints of the multiple power converters and the output impedance of at least one power converter unchanged.

[0068] Specifically, the power setpoints of multiple power converters and the output impedance of at least one power converter are kept constant. That is, the power setpoints of multiple power converters are maintained at the adjusted power setpoints, and the output impedance of at least one power converter is maintained at the adjusted output impedance. Both the adjusted power setpoints and the adjusted output impedances are obtained by adjusting the power setpoints of the multiple power converters and the output impedance of at least one power converter respectively in response to a harmonic component in the output electrical signal of the power conversion system exceeding a preset threshold. It should be noted that maintaining the power setpoints of multiple power converters constant includes maintaining the power setpoint of at least one power converter at the adjusted power setpoint, and maintaining the power setpoints of the remaining power converters at the adjusted power setpoints.

[0069] In this embodiment, when the output harmonics of at least one power converter are less than a preset threshold, it can be understood that the power conversion system has restored output stability. At this time, restoring the power setpoints of the multiple power converters and the output impedance of at least one power converter allows the operating role of at least one power converter to shift from bearing harmonic components to participating in power conversion, thereby improving the operating efficiency of the power conversion system. It should be noted that restoring the power setpoints of the multiple power converters in this case includes: restoring the power setpoint of at least one power converter to the power setpoint of at least one power converter when the power setpoint was not reduced, and restoring the power setpoints of the remaining power converters to the power setpoints of the remaining power converters when the power setpoint was not increased.

[0070] In this embodiment, if the output harmonics of at least one power converter are greater than or equal to a preset threshold, it can be understood that the power conversion system has not recovered output stability. At this time, keeping the power input of multiple power converters and the output impedance of at least one power converter unchanged is equivalent to making at least one power converter continue to play the role of harmonic components, thereby ensuring the efficiency and quality of harmonic suppression.

[0071] This application does not specifically limit the method of adjusting the output impedance of at least one power converter according to harmonic components, as long as the output impedance of the adjusted at least one power converter is more conducive to the flow of harmonic components compared with the output impedance of the other power converters.

[0072] As one possible implementation, the power conversion system is a grid-type power conversion system. For this grid-type power conversion system, adjusting the output impedance of at least one power converter based on harmonic components includes: determining the desired output impedance based on the frequency of the harmonic components; and performing feedforward control on the load current of at least one power converter based on the desired output impedance to adjust the output impedance of at least one power converter.

[0073] Determining the desired output impedance based on the frequency of the harmonic components can be achieved by using a function related to the frequency of the harmonic components. For example, the function related to the frequency of the harmonic components could be a quasi-resonant term R(s). In some embodiments, the desired output impedance can be represented by Z. h_desire The specific method for determining the desired output impedance is as follows: Z h_desire =|Z|*R(s), where |Z| is the preset amplitude.

[0074] Feedforward control of the load current of at least one power converter based on the desired output impedance to adjust the output impedance of at least one power converter can be understood as feedforward control of the load current of each of the at least one power converter based on the desired output impedance to adjust the output impedance of each power converter.

[0075] As one implementation, feedforward control of the load current of at least one power converter based on the desired output impedance to adjust the output impedance of at least one power converter may include: based on the desired output impedance Z h_desire and the load current i of at least one power converter o Determine the desired output voltage of at least one power converter; based on the reference voltage u ref The desired output voltage and the actual output voltage u of at least one power converter. o Determine the reference voltage adjustment value; use the voltage regulator to determine the reference current i based on the reference voltage adjustment value. ref Based on reference current i ref At least one power converter is controlled. The reference voltage u is... ref This can be provided by the power outer loop. Based on the reference current i ref Controlling at least one power converter can be understood as adjusting the output impedance of at least one power converter.

[0076] The control block diagram of the above method for adjusting the output impedance of a single power converter in at least one power converter can be shown as follows: Figure 4 As shown. In Figure 4 in,i o u is the load current of a single power converter in at least one power converter. o u represents the actual output voltage of a single power converter in at least one power converter. ref The reference voltage provided for the power outer loop, i ref This is the reference current output after adjustment by the voltage regulator. Where, for example... Figure 4 As shown, at Figure 4 The desired output voltage of a single power converter (which can be denoted as u) desire ) = i o *Z h_desire Reference voltage adjustment value = u desire +u ref -u o .

[0077] As another possible implementation, the power conversion system is a grid-based power conversion system. For this grid-based power conversion system, adjusting the output impedance of at least one power converter based on harmonic components includes: determining the desired output admittance based on the frequency of the harmonic components; and performing feedforward control on the voltage of the common coupling point based on the desired output admittance to adjust the output impedance of at least one power converter.

[0078] Determining the desired output admittance based on the frequency of the harmonic components can be achieved by determining the desired output admittance based on a function related to the frequency of the harmonic components. For example, the function related to the frequency of the harmonic components is a quasi-resonant term R(s). In some embodiments, the desired output admittance can be represented by Y. h_desire The specific method for determining the expected output admittance is as follows: Y h_desire =|Y|*R(s), where |Y| is the preset amplitude.

[0079] Feedforward control of the voltage at the common coupling point based on the desired output admittance to adjust the output impedance of at least one power converter can be understood as feedforward control of the voltage at the common coupling point based on the desired output admittance to adjust the output impedance of each power converter in at least one power converter.

[0080] As one implementation, feedforward control of the voltage at the common coupling point based on the desired output admittance to adjust the output impedance of at least one power converter may include: based on the desired output admittance Y h_desire Voltage V at the common coupling point PCC Determine the desired output current; based on the reference current i g_ref The desired output current and the actual output current i of at least one power converter. o Determine the reference current adjustment value; use the current loop regulator to determine the modulation voltage V based on the reference current adjustment value. M Based on modulation voltage V M At least one power converter is controlled. The reference current i... g_ref It can be provided by the power outer loop. Based on the modulation voltage V M Controlling at least one power converter can be understood as adjusting the output impedance of at least one power converter.

[0081] The control block diagram of the above method for adjusting the output impedance of a single power converter in at least one power converter can be shown as follows: Figure 5 As shown. See details. Figure 5 G i It is a current loop regulator; i o i represents the actual output current of a single power converter in at least one power converter. g_refReference current provided for the power outer loop; Y h_desire V is the desired output admittance; PCC V is the voltage at the common coupling point. M This is the modulated voltage output after adjustment by the current loop regulator. For example, Figure 5 As shown, at Figure 5 The expected output current of a single power converter (which can be denoted as i) desire ) = Y h_desire *V PCC Reference voltage adjustment value = i desire +i g_ref -i o .

[0082] In the embodiments of this application, the quasi-resonant term R(s) can be determined based on the following formula.

[0083]

[0084] Among them, R k (s) represents the quasi-resonant term at the kth harmonic frequency, K rk It is the harmonic coefficient, ω ik It is the bandwidth of the resonant term, ω rk This is the characteristic angular frequency. It should be noted that when the AC circuit is a power grid, the distribution of background harmonics in the power grid voltage indicates that k ≤ 40 and is generally an odd number. k can be selected based on the harmonic frequencies to be suppressed. The resonant term bandwidth ω... ik In the design process, it is usually necessary to ensure the complementary influence between adjacent resonant terms, and based on this, the ω can be adjusted. ik The design.

[0085] To make it easier to understand, the following will be combined with... Figure 6 This application provides a specific example of a harmonic suppression method for a power conversion system. It should be noted that... Figure 6 The flowchart illustrating the harmonic suppression method for the power conversion system is illustrative and intended only to facilitate understanding of the present application's solution. It should not be construed as limiting the scope of the present application. The present application can also reasonably recombine the solutions described above, and such recombination should also be included within the protection scope of the present application.

[0086] See details Figure 6 The harmonic suppression method 600 for a power conversion system provided in this application includes steps S610-S670.

[0087] In step S610, the first output electrical signal of the power conversion system is acquired and the harmonic components in the first output electrical signal are calculated.

[0088] For example, the first output electrical signal of the power conversion system is the original total output current i of the power conversion system. 总 By analyzing the original total output current i 总 Analysis shows that the original total output current i 总 In addition to the fundamental frequency component, it also contains multiple harmonic components.

[0089] In step S620, it is determined whether the predetermined harmonic component in the first output electrical signal is greater than a preset threshold.

[0090] If yes, proceed to step S630; otherwise, proceed to step S610.

[0091] In step S630, a virtual impedance is used to suppress the predetermined harmonic components.

[0092] After suppressing the predetermined harmonics using virtual impedance, the electrical signal output by the power conversion system is the second output electrical signal.

[0093] In step S640, it is determined whether the predetermined harmonic in the second output electrical signal exceeds a set threshold.

[0094] If yes, proceed to step S650; otherwise, end.

[0095] In step S650, the power setpoint of at least one power converter is reduced, the power setpoint of the remaining power converters is increased, and the output impedance of at least one power converter is adjusted according to a predetermined subharmonic component.

[0096] At least one power converter is part of a plurality of power converters forming a power conversion system. The specific number of at least one power converter can be greater than or equal to two. The adjustment method is detailed in the preceding description.

[0097] Preferably, while reducing the power setpoint of at least one power converter, the power setpoint of the remaining power converters in the power conversion system is increased simultaneously to ensure that the total output power of the power conversion system remains unchanged.

[0098] The output impedance of at least one power converter at the predetermined harmonic is less than the output impedance of the other power converters at the predetermined harmonic. Furthermore, the amplitude of the output impedance of at least one power converter at the predetermined harmonic should be as low as possible to ensure that the harmonic circulating current component flows between at least one power converter as much as possible, but it is necessary to ensure that, under the same harmonic voltage conditions, the amplitude of the corresponding current harmonic component does not exceed the protection value of at least one power converter.

[0099] In step S660, it is determined whether the output harmonics of at least one power converter are less than a preset threshold.

[0100] If yes, proceed to step S670; otherwise, proceed to step S680.

[0101] In step S670, the power setpoints of the multiple power converters and the output impedance of at least one power converter are restored.

[0102] In step S680, the power input of the plurality of power converters and the output impedance of at least one power converter are kept constant.

[0103] After completing step S680, continue with step S660.

[0104] The process ends after step S670 is completed.

[0105] This method modifies the output impedance of a selected power converter through control, causing predetermined harmonics in the power conversion system to exist primarily as circulating currents within the selected power converter, thereby reducing harmonic components in the output current. This method does not alter the overall external characteristics of multiple power converters, requires no additional equipment, is low-cost, and easy to implement in practice.

[0106] The above text combined Figures 1 to 6 The method embodiments of this application have been described in detail below, in conjunction with... Figure 7 The apparatus embodiments of this application are described in detail below. It should be understood that the descriptions of the method embodiments correspond to the descriptions of the apparatus embodiments; therefore, any parts not described in detail can be referred to the foregoing method embodiments.

[0107] The following is combined Figure 7 This application describes a control device 700 according to an embodiment of the present application. The control device 700 can be used to implement the methods described in the above method embodiments. As an example, the control device 700 is a controller in the power conversion system described above.

[0108] The control device 700 may include one or more processors 710. The processor 710 may enable the control device 700 to implement the methods described in the preceding method embodiments.

[0109] The processor 710 can be a general-purpose processor or a special-purpose processor. For example, the processor can be a central processing unit (CPU). Alternatively, the processor can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor.

[0110] The control device 700 may further include one or more memories 720. The memories 720 store a program that can be executed by the processor 710 to control the control device 700 to perform the methods described in the preceding method embodiments. The memories 720 may be independent of the processor 710 or integrated within the processor 710.

[0111] The control device 700 may also include a transceiver 730. The processor 710 can communicate with other devices via the transceiver 730. For example, the processor 710 can send and receive data with other devices via the transceiver 730.

[0112] This application also provides a chip, including a processor, which can be used to call and run a computer program from memory, causing a power conversion system on which the chip is installed to perform the methods described in the above method embodiments. It is understood that the processor can be any type of processor mentioned above. It is also understood that the memory can be independent of the chip or integrated into the chip.

[0113] This application also provides a power conversion system, including multiple power converters connected in parallel as described above, and a control device as described above.

[0114] This application also provides a machine-readable storage medium for storing a program. This program causes a computer to execute the methods described in the various embodiments of this application.

[0115] This application also provides a computer program product. The computer program product includes a program. The program causes a computer to perform the methods described in various embodiments of this application.

[0116] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any other combination. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this disclosure are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a machine-readable storage medium or transmitted from one machine-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another via wired (e.g., coaxial cable, fiber optic, Digital Subscriber Line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The machine-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available media can be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., digital video discs (DVDs)), or semiconductor media (e.g., solid-state drives (SSDs)).

[0117] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments of this disclosure can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the intended application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each intended application, but such implementation should not be considered beyond the scope of this disclosure.

[0118] In the several embodiments provided in this disclosure, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0119] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0120] In addition, the functional units in the various embodiments of this disclosure can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0121] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A harmonic suppression method for a power conversion system, characterized in that, The power conversion system includes multiple power converters connected in parallel through a common coupling point, and the method includes: Determine whether the harmonic components in the output electrical signal of the power conversion system are greater than a preset threshold; In response to the harmonic component in the output electrical signal of the power conversion system being greater than a preset threshold, the output impedance of at least one power converter is adjusted according to the harmonic component so that the harmonic component is transmitted to the at least one power converter.

2. The method according to claim 1, characterized in that, The method further includes: In response to the harmonic component in the output electrical signal of the power conversion system being greater than a preset threshold, the power setpoint of the at least one power converter is reduced and the power setpoint of the remaining power converters is increased, so that the total output power of the power conversion system remains unchanged. The remaining power converters are the power converters other than the at least one power converter among the plurality of power converters.

3. The method according to claim 1, characterized in that, The output electrical signal of the power conversion system is the output electrical signal of the power conversion system after first harmonic suppression processing, and the method further includes: Determine whether the first harmonic component is greater than the preset threshold. The first harmonic component is the harmonic component in the output electrical signal of the power conversion system before the first harmonic suppression processing. In response to the first harmonic component being greater than the preset threshold, the first harmonic component is subjected to first harmonic suppression processing using virtual impedance.

4. The method according to claim 2, characterized in that, The method further includes: After adjusting the output impedance of at least one power converter according to the harmonic components, it is determined whether the output harmonics of the at least one power converter are less than the preset threshold. In response to the output harmonics of the at least one power converter being less than the preset threshold, the power setpoint of the plurality of power converters and the output impedance of the at least one power converter are restored; In response to the output harmonics of the at least one power converter being greater than or equal to the preset threshold, the power input of the plurality of power converters and the output impedance of the at least one power converter are kept constant.

5. The method according to any one of claims 1-4, characterized in that, The power conversion system is a grid-type power conversion system, and adjusting the output impedance of the at least one power converter according to the harmonic components includes: The desired output impedance is determined based on the frequency of the harmonic components. Feedforward control is performed on the load current of the at least one power converter based on the desired output impedance to adjust the output impedance of the at least one power converter.

6. The method according to claim 5, characterized in that, The step of feeding forward control of the load current of the at least one power converter based on the desired output impedance to adjust the output impedance of the at least one power converter includes: The desired output voltage of the at least one power converter is determined based on the desired output impedance and the load current of the at least one power converter. The reference voltage adjustment value is determined based on the reference voltage, the desired output voltage, and the actual output voltage of the at least one power converter. The reference current is determined using a voltage regulator based on the reference voltage adjustment value; The at least one power converter is controlled based on the reference current.

7. The method according to any one of claims 1-4, characterized in that, The power conversion system is a grid-type power conversion system, and the adjustment of the output impedance of the at least one power converter according to the harmonic components includes: The desired output admittance is determined based on the frequency of the harmonic components. Feedforward control is performed on the voltage at the common coupling point based on the desired output admittance to adjust the output impedance of the at least one power converter.

8. The method according to claim 7, characterized in that, The step of feeding forward control of the voltage at the common coupling point based on the desired output admittance to adjust the output impedance of the at least one power converter includes: The desired output current is determined based on the desired output admittance and the voltage at the common coupling point. The reference current adjustment value is determined based on the reference current, the desired output current, and the actual output current of the at least one power converter. The modulation voltage is determined using a current loop regulator based on the reference current adjustment value; The at least one power converter is controlled based on the modulation voltage.

9. The method according to any one of claims 1-4, characterized in that, The adjusted output impedance of the at least one power converter at a predetermined harmonic is lower than the output impedance of the other power converters at the predetermined harmonic.

10. A control device, characterized in that, include: Memory, used to store code; A processor for executing code stored in the memory to perform the method as described in any one of claims 1 to 9.

11. A power conversion system, characterized in that, include: Multiple power converters are connected in parallel through a common coupling point; as well as The control device as described in claim 10.

12. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer-executable instructions for causing a computer to perform the method as described in any one of claims 1 to 9.

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