Control method of power supply system and power supply system

Abstract

The application discloses a control method of a power supply system and the power supply system. The power supply system comprises a generator and an inverter in parallel connection, and is connected with a load. The method comprises the following steps: determining that a load sudden drop event of the power supply system occurs according to a first frequency change rate of an output frequency of the generator; determining compensation power corresponding to the load sudden drop event according to the first frequency change rate and a preset target virtual inertia constant, and controlling a direct current side device of the inverter to absorb the compensation power, wherein the target virtual inertia constant is determined according to an equivalent inertia time constant of the generator. Based on the technical scheme, the probability of damage of the generator can be effectively reduced in the case of load power sudden drop, so that the maintenance cost is reduced.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a control method and power supply system for a power supply system. Background Technology

[0002] In off-grid or microgrid power supply systems, parallel operation of diesel generators (hereinafter referred to as diesel generators) and energy storage inverters is a common configuration, aiming to balance the continuous power supply capability of diesel generators with the fast and clean response characteristics of inverters. In the above power supply systems, when the load power undergoes sudden changes (especially sudden drops), existing control strategies mainly employ independent droop control strategies and communication-based coordinated control strategies. In the independent droop control strategy, both the diesel generator and the inverter use traditional active power-to-frequency droop control, independently adjusting their own power output based on local frequency measurements. In the communication-based coordinated control strategy, a warning signal is sent via a communication link before load switching, enabling the diesel generator and inverter to adjust their output in advance.

[0003] However, during a sudden drop in load power, the inverter's power control loop response speed (typically tens to hundreds of milliseconds) is much slower than the actual disconnection speed of the load (milliseconds). During this period, the total generating power of the power supply system momentarily exceeds the total load power. The excess power flows into the generator with the lowest impedance within the power supply system, causing the generator to be dragged backward and its rotor to be accelerated. This can lead to mechanical stress impact, shaft torsional vibration, and even damage to the generator's mechanical components. Therefore, existing technology has a relatively high probability of causing generator damage under conditions of a sudden drop in load power. Summary of the Invention

[0004] This application provides a control method and power supply system for a power supply system, which can effectively reduce the probability of generator damage in the event of a sudden drop in load power, thereby reducing maintenance costs.

[0005] In a first aspect, embodiments of this application provide a control method for a power supply system, the power supply system including a generator and an inverter connected in parallel, the power supply system being connected to a load, the method comprising: Based on the first frequency change rate of the generator's output frequency, it is determined that a load drop event has occurred in the power supply system; Based on the first frequency change rate and the preset target virtual inertia constant, the compensation power corresponding to the load drop event is determined, wherein the target virtual inertia constant is determined based on the equivalent inertia time constant of the generator; The inverter's DC-side device is controlled to absorb the compensation power, wherein after the DC-side device absorbs the compensation power, the generator's output power is greater than a preset set power, wherein the set power is greater than 0.

[0006] In some embodiments, determining the compensation power corresponding to the load drop event based on the first frequency change rate and a preset target virtual inertial constant includes: Obtain the ratio of the rated capacity of the generator to the rated frequency of the generator; The compensation power is determined based on the first frequency change rate, the target virtual inertial constant, and the ratio.

[0007] In some embodiments, determining that the power supply system has experienced a load drop event based on a first rate of change of the generator's output frequency includes: By comparing the first frequency change rate with a preset first threshold, if the first frequency change rate exceeds the first preset threshold, it is determined that the power supply system has experienced the load drop event, wherein the first preset threshold is greater than 0.

[0008] In some embodiments, the step of obtaining the target virtual inertial constant includes: When the output frequency of the generator is at the rated frequency of the generator, multiple load reduction operations are applied to the power supply system, and for each load reduction operation, the total time taken for the output frequency of the generator to rise from the rated frequency to the peak frequency is obtained; For each load reduction operation, a candidate inertial time constant is determined based on the total duration, the power reduction of the load reduction operation, and the rated capacity of the generator. The equivalent inertial time constant of the generator is determined based on the candidate inertial time constant corresponding to each load reduction operation. The target virtual inertial constant is determined based on the equivalent inertial time constant.

[0009] In some embodiments, the target virtual inertial constant is the equivalent inertial time constant ranging from a first set multiple to a second set multiple, wherein the second set multiple is greater than the first set multiple, and the first set multiple is greater than 0.

[0010] In some embodiments, determining the target virtual inertial constant based on the equivalent inertial time constant includes: Choose a value from the range of values ​​as the initial virtual inertial constant; Within the specified value range, by applying a load reduction operation to the power supply system, iterative experiments are conducted on the initial virtual inertial constant until the frequency change rate of the generator's output frequency does not exceed the first preset threshold, and the generator's output frequency is in a non-oscillating state. At this point, the virtual inertial constant corresponding to the current iteration is determined as the target virtual inertial constant. During the iterative experiment, if the frequency change rate of the output frequency exceeds the first preset threshold, the current virtual inertial constant is increased; if the output frequency is in an oscillating state, the current virtual inertial constant is decreased.

[0011] In some embodiments, the DC-side equipment of the inverter includes a DC bus capacitor and / or energy storage devices.

[0012] In some embodiments, the DC-side device controlling the inverter absorbs the compensation power, including: According to the compensation power generation control command; In response to the control command, the inverter controls the DC-side equipment to absorb the compensation power.

[0013] In some embodiments, after controlling the DC-side devices of the inverter to absorb the compensation power, the method further includes: The second frequency change rate of the generator's output frequency is obtained, and it is detected whether the second frequency change rate is less than a preset second preset threshold, wherein the second preset threshold is less than the first preset threshold. If the second frequency change rate is less than the second preset threshold, then the generation of the control command will stop, so that the DC-side device will no longer absorb the compensation power.

[0014] Secondly, embodiments of this application also provide a power supply system, including: A generator is used to provide electrical energy to a load. An inverter, connected in parallel with the generator, is used to provide electrical energy to the load and determine a load drop event in the power supply system based on a first frequency change rate of the generator's output frequency; it determines the compensation power corresponding to the load drop event based on the first frequency change rate and a preset target virtual inertia constant, wherein the target virtual inertia constant is determined based on the generator's equivalent inertia time constant; it controls the DC-side device of the inverter to absorb the compensation power, and after the DC-side device absorbs the compensation power, the generator's output power is greater than a preset set power, wherein the set power is greater than 0.

[0015] In the power supply system control method provided in this application embodiment, a load drop event is determined based on a first frequency change rate of the generator's output frequency; the compensation power corresponding to the load drop event is determined based on the first frequency change rate and a preset target virtual inertia constant; and the DC-side device of the inverter is controlled to absorb the compensation power. After the DC-side device absorbs the compensation power, the generator's output power is greater than a preset set power, wherein the set power is greater than 0. Through the above technical solution, by detecting the first frequency change rate of the generator's output frequency, once a load drop event is determined, the inverter is immediately controlled to perform power compensation, diverting the compensation power that might flow back to the generator to the inverter's DC-side device for absorption. This effectively reduces the probability of the generator entering a reverse power state, which increases the probability of generator damage. Thus, by reducing the probability of the generator entering a reverse power state, the probability of generator damage under load drop can be effectively reduced, maintenance costs can be reduced, and the continuity of power supply can be ensured. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0018] Figure 1 This is a schematic diagram of the power supply system provided in an exemplary embodiment of the present disclosure; Figure 2 A flowchart illustrating a control method for a power supply system provided in an exemplary embodiment of this disclosure; Figure 3 A schematic diagram of the connection between an inverter and an energy storage device provided as an exemplary embodiment of this disclosure; Figure 4 A schematic diagram of the process for obtaining the target virtual inertial constant provided as an exemplary embodiment of this disclosure; Figure 5 This is a control logic diagram for obtaining the target virtual inertial constant provided in an exemplary embodiment of this disclosure.

[0019] Explanation of reference numerals in the attached figures: 10. Generator; 20. Inverter; 21. DC / DC converter circuit; 22. DC / AC converter circuit; 23. Energy storage device; 24. DC bus capacitor; 30. Load. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0021] In the embodiments of this application, "at least one" refers to one or more; "multiple" refers to two or more. In the description of this application, the terms "first," "second," etc., are used only for the purpose of distinguishing descriptions and should not be construed as indicating or implying relative importance, nor should they be construed as indicating or implying order.

[0022] References such as “one embodiment” or “some embodiments” as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the terms “comprising,” “including,” “having,” and variations thereof, as used in this specification, mean “including, but not limited to,” unless otherwise specifically emphasized.

[0023] It should be noted that in the embodiments of this application, "and / or" describes the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. In addition, the character " / ", unless otherwise specified, generally indicates that the associated objects before and after it are in an "or" relationship.

[0024] It should be noted that in the embodiments of this application, "connection" can be understood as electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0025] See Figure 1 This application provides a power supply system including a generator 10 and an inverter 20, which are connected in parallel. The power supply system is connected to a load 30. The generator 10 can be a diesel generator or a gasoline generator, etc., used to provide electrical energy to the load 30. The inverter 20 and the generator 10 are connected in parallel via an AC bus.

[0026] Specifically, the AC side of the inverter 20 is connected to the AC bus, and the generator 10 is mounted on the AC bus. The positive side of the load 30 is connected to the positive side of the AC bus, and the negative side of the load 30 is connected to the negative side of the AC bus.

[0027] In some embodiments, the inverter 20 may employ a single-stage power conversion architecture or a two-stage power conversion architecture. When employing a single-stage power conversion architecture, the inverter 20 may include a DC / AC conversion circuit; when employing a two-stage power conversion architecture, the inverter 20 may include a DC / DC conversion circuit and a DC / AC conversion circuit. The following description uses a power supply system as the implementing entity.

[0028] In some embodiments, the power supply system described above may be an off-grid system or a microgrid system, etc.

[0029] See Figure 2 The control method for the power supply system provided in this application embodiment, applied to the aforementioned power supply system, includes steps S201-S203, wherein... Step S201: Determine whether a load drop event has occurred in the power supply system based on the first frequency change rate of the generator's output frequency.

[0030] In some embodiments, the entity executing steps S201-S203 may be a controller in an inverter or an independent controller in a power supply system.

[0031] In some implementation examples, see Figure 1 Since generator 10 is directly connected in parallel to the AC bus, the voltage frequency of the AC bus is synchronized with the output frequency of generator 10. Therefore, the voltage frequency of the AC bus is the output frequency of generator 10. Thus, a voltage sampling unit installed on the AC bus (…) Figure 1 (Not shown in the image) The voltage signal on the AC bus is acquired in real time, and then the acquired voltage signal is processed using the zero-crossing detection method or the phase-locked loop method to obtain the voltage frequency of the AC bus. The voltage frequency of the AC bus is then used as the output frequency of the generator 10. In this way, by acquiring the voltage frequency of the AC bus in real time, the output frequency of the generator 10 can be acquired in real time.

[0032] In some embodiments, when obtaining the generator's output frequency, a potential transformer (PT) can also be provided at the generator's output terminal. One side of the voltage transformer is connected to the generator's output terminal, and the other side is connected to a frequency detection unit. In this way, the frequency detection unit is used to collect the generator's output voltage signal in real time, and the generator's output frequency is obtained in real time based on the output voltage signal.

[0033] Specifically, based on the real-time output frequency of the generator, the frequency value is read according to a preset sampling period, and the first frequency change rate is obtained by calculating the frequency change per unit sampling time. The sampling period can be set according to the actual situation. The sampling period can be a fixed value or a variable value. Taking a fixed sampling period as an example, the sampling period can be 10 milliseconds (ms), 50 ms, and 100 ms, etc.

[0034] In some embodiments, taking the current frequency value read at the current sampling time as f(t) and the historical frequency value at the previous sampling time as f(t-1) as an example, if the sampling period is Δt, then the frequency change per unit sampling time is Δf = f(t) - f(t-1), and the first frequency change rate is P1 = Δf / Δt = (f(t) - f(t-1)]) / Δt. At this time, the first frequency change rate is the ratio of the frequency change in the current sampling period to the sampling period.

[0035] In some embodiments, the sampling period can be preset according to the actual application scenario and stored in the internal register of the frequency detection unit. Additionally, the frequency detection unit can also have a buffer to store the historical frequency value from the previous sampling moment. At each sampling moment, the frequency detection unit reads the current frequency value and the historical frequency value from the buffer, calculates the difference, and divides it by the sampling period to obtain the first frequency change rate.

[0036] In some embodiments, to reduce the impact of measurement noise on the accuracy of frequency change rate calculation, the frequency detection unit may further filter the calculated first frequency change rate. For example, the frequency detection unit uses a first-order low-pass filter or a moving average filter to filter the first frequency change rate, obtaining a filtered first frequency change rate. The frequency detection unit can be, for example, any of a frequency transmitter, a digital frequency meter, or a smart power transmitter. The above sampling, calculation, and filtering processes are continuously performed within each sampling period, thereby achieving real-time monitoring of the generator's frequency change rate and providing a reliable data foundation for the rapid determination of load drop events.

[0037] In some embodiments, after obtaining the first frequency change rate, it can be determined whether a load drop event has occurred in the power supply system based on the first frequency change rate and a preset first threshold.

[0038] Specifically, after obtaining the first frequency change rate, it can be compared with a preset first threshold. If the first frequency change rate exceeds the first preset threshold, it is determined that a load drop event has occurred in the power supply system, wherein the first preset threshold is greater than 0. If the first frequency change rate does not exceed the first preset threshold, it is determined that no load drop event has occurred in the power supply system.

[0039] Specifically, the first frequency change rate and the first preset threshold can be compared in real time to obtain the comparison result. If the comparison result indicates that the first frequency change rate exceeds the first preset threshold, it is determined that a load drop event has occurred in the power supply system. If the comparison result indicates that the first frequency change rate does not exceed the first preset threshold, it is determined that no load drop event has occurred in the power supply system.

[0040] In some embodiments, the first preset threshold is pre-calibrated. The first preset threshold is greater than the maximum frequency change rate of the generator's output frequency when the power supply system is in normal operation. After obtaining the maximum frequency change rate, the sum of the maximum frequency change rate and a set value, or the product of a set coefficient, can be used as the first preset threshold, where the set coefficient is greater than 1. When calibrating the first preset threshold, the minimum frequency change rate or average frequency change rate of the generator's output frequency obtained by applying a load reduction operation to the power supply system can be used as the first preset threshold. Thus, the first preset threshold can be used to accurately determine whether a load drop event has occurred in the power supply system.

[0041] The above comparison process is carried out continuously in each sampling period, thereby realizing the real-time detection of load drop events. Since the response speed of the frequency change rate is much faster than that of the power amplitude change, the power supply system can detect the power imbalance at the moment the load is disconnected (within the millisecond time window), thus gaining valuable response time for subsequent power compensation.

[0042] Since the rate of frequency change is the most direct electrical indicator of system power imbalance, and its rate of change is much faster than the change in power amplitude, detecting the rate of frequency change allows for the immediate detection of power imbalance within a millisecond-level time window after the load is disconnected. Compared to traditional methods that rely on power amplitude changes for detection or communication-based early warning, this significantly reduces response time. By utilizing the rate of frequency change as the most direct electrical indicator of power imbalance, rapid and accurate identification of load drop events is achieved, providing a reliable triggering condition for the inverter to absorb compensation power in a timely manner and preventing power backflow to the generator.

[0043] Step S202: Determine the compensation power corresponding to the load drop event based on the first frequency change rate and the preset target virtual inertia constant, wherein the target virtual inertia constant is determined based on the equivalent inertia time constant of the generator.

[0044] In some embodiments, if a load drop event is determined to have occurred in the power supply system through step S201, the target virtual inertial constant is read from the storage device that stores the target virtual inertial constant in advance, and the compensation power corresponding to the load drop event is determined based on the first frequency change rate and the target virtual inertial constant.

[0045] Step S203: Control the DC side equipment of the inverter to absorb compensation power.

[0046] Wherein, after the DC-side equipment absorbs the compensation power, the output power of the generator is greater than a preset set power, wherein the set power is greater than 0.

[0047] In some embodiments, after the compensation power is determined in step S202, the DC-side device is controlled to absorb the compensation power.

[0048] In some embodiments, after the DC-side equipment absorbs the compensation power, the output power of the generator is greater than a preset set power, wherein the set power is greater than 0.

[0049] Specifically, the power setting can be set according to actual needs. For example, the power setting can be a preset percentage of the generator's rated power, such as 5% to 10%. By setting the power setting, it is ensured that the generator has sufficient power margin throughout the entire period of a load drop event, and the generator will not enter a reverse power state even if there are measurement errors and control delays.

[0050] In some embodiments, after determining the compensation power, the DC-side equipment can be controlled to absorb the compensation power, so that when a load drop event occurs, the DC-side equipment can be controlled to absorb the compensation power in a timely manner, avoiding the complete backflow of the drop power corresponding to the load drop event to the generator. This can effectively reduce the probability of the generator entering the reverse power state, which will increase the probability of generator damage. Thus, by reducing the probability of the generator entering the reverse power state, the probability of generator damage under load drop can be effectively reduced, maintenance costs can be reduced, and the continuity of power supply can be ensured.

[0051] In some embodiments, the DC-side equipment of the inverter includes DC bus capacitors and / or energy storage devices, etc.

[0052] Specifically, energy storage devices include one or more of the following: energy storage batteries (such as lithium batteries, lead-acid batteries, flow batteries, etc.), supercapacitors, flywheel energy storage devices, and superconducting magnetic energy storage devices.

[0053] In some embodiments, if the inverter is configured with only a DC bus capacitor and no energy storage device, the DC bus capacitor absorbs compensation power, and the DC bus voltage will rise accordingly after the DC bus capacitor absorbs compensation power. When the compensation power is small or the duration is extremely short, the capacitor alone can meet the requirements. If the DC-side equipment also includes an energy storage device, when the DC bus voltage rises to the charging threshold of the energy storage device, the DC / D conversion circuit in the inverter is activated, transferring the electrical energy on the DC bus capacitor to the energy storage device for storage. The energy storage device has a large energy storage capacity and can continuously absorb compensation power, preventing the DC bus voltage from continuously rising beyond the safe range. Of course, if the DC-side equipment only includes an energy storage device, then only the energy storage device can absorb the compensation power.

[0054] In some embodiments, when controlling the DC-side equipment of the inverter to absorb compensation power, a control command can be generated based on the compensation power; in response to the control command, the DC-side equipment is controlled by the inverter to absorb compensation power.

[0055] Specifically, after determining the compensation power, a control command corresponding to the compensation power is generated and sent to the inverter. The inverter responds to the control command and controls the DC-side equipment to absorb the compensation power.

[0056] Specifically, taking an inverter that includes both DC / DC conversion circuits and DC / AC conversion circuits as an example, such as... Figure 3 As shown, the inverter 20 includes a DC / DC conversion circuit 21 and a DC / AC conversion circuit 22. The first terminal of the DC / DC conversion circuit 21 is connected to the energy storage device 23, and the second terminal is connected to the DC bus. This allows the DC side of the inverter 20 to be connected to the DC bus capacitor 24 and the energy storage device 23 via the DC bus. The DC bus capacitor 24 is directly connected in parallel between the positive (bus+) and negative (bus-) terminals of the DC bus for voltage regulation and power balancing. Thus, after determining that a load drop event has occurred in the power supply system and determining the compensation power, a control command to absorb the compensation power can be sent to the inverter 20. In response to the control command, the inverter 20 controls the DC bus capacitor 24 to absorb the compensation power from the AC side when the compensation power does not exceed the power that the DC bus capacitor 24 can absorb; when the compensation power exceeds the power that the DC bus capacitor 24 can absorb, the compensation power can be absorbed together by the DC bus capacitor 24 and the energy storage device 23. In this way, through the coordinated action of the instantaneous absorption by the DC bus capacitor and the continuous absorption by the energy storage device, rapid and continuous absorption of the compensation power is achieved.

[0057] Specifically, since the DC bus capacitor 24 is directly connected between the positive and negative terminals of the DC bus, its charging and discharging response time is in the microsecond to millisecond range. Without the need for an additional power conversion stage, it can absorb the compensation power instantly when the inverter 20 returns the compensation power to the DC side. This can improve the timeliness of absorbing the compensation power and ensure that the impact power of the load drop is quickly captured, preventing the compensation power from accumulating on the AC side and flowing back to the generator.

[0058] In some embodiments, when determining the compensation power in step S202, the ratio of the generator's rated capacity to the generator's rated frequency can be obtained; then, the compensation power is determined based on the first frequency change rate, the target virtual inertia constant, and the ratio.

[0059] Specifically, the rated capacity of the generator will be pre-stored in the storage devices of the power supply system. With the generator's rated frequency In this way, the rated capacity can be read directly from the storage device. With rated frequency Then read the rated capacity With rated frequency Divide the values ​​to obtain the ratio. Then, obtain the product of the first frequency change rate, the target virtual inertial constant, and the ratio. Based on this product, obtain the compensation power. At this point, the product can be multiplied by a set coefficient to obtain the compensation power. The set coefficient can be set according to the implementation situation and is greater than 1, for example, it can be 1.5, 2, or 3, etc. Of course, the sum of the product and a set threshold can also be used as the compensation power.

[0060] In some embodiments, the target virtual inertial constant is pre-stored in a storage device, so that when determining the compensation power, it is denoted as the compensation power. Taking a set coefficient of 2 as an example, the compensation power can be calculated using the following formula (1), as follows: (1) In formula (1) Represents the target's virtual inertial constant. This represents the first frequency change rate. Thus, by using formula (1), when a load drop event occurs in the power supply system, the power imbalance can be instantly detected within a millisecond-level time window of load disconnection by detecting the frequency change rate. This allows the first frequency change rate to be obtained within the millisecond-level time window of load disconnection. Based on timely acquisition of the first frequency change rate, the target virtual inertia constant, rated capacity, and rated frequency can be read from the storage device, further improving the timeliness of obtaining compensation power. Therefore, it can be ensured that within a shorter time window (millisecond-level time window) of a load drop event, the compensation power can be absorbed by the DC-side equipment in a timely manner, thereby reducing the probability of the compensation power generator entering a reverse power state.

[0061] In some embodiments, after controlling the DC-side device of the inverter to absorb compensation power, a second frequency change rate of the generator output frequency can be obtained, and it can be detected whether the second frequency change rate is less than a preset second preset threshold, wherein the second preset threshold is less than a first preset threshold; if the second frequency change rate is less than the second preset threshold, then the generation of control commands is stopped so that the DC-side device no longer absorbs compensation power.

[0062] Specifically, after the DC-side equipment absorbs the compensation power, the frequency change rate of the generator's output frequency can be obtained in real time as the second frequency change rate. The specific steps for obtaining the second frequency change rate can be referred to the description of the first frequency change rate. For the sake of brevity, they will not be repeated here.

[0063] In some embodiments, the second preset threshold can be set according to actual needs. The second preset threshold is less than the first preset threshold. For example, the second preset threshold can be a value that approaches zero, such as 0.1, 0.08 or 0.15.

[0064] In some embodiments, when the second frequency change rate is detected to be less than a second preset threshold, it is determined that the load is close to rebalancing. Therefore, the generation of control commands can be stopped, thereby controlling the withdrawal of compensation power. Since no control commands are generated, the inverter does not need to respond to control commands, and thus the DC-side equipment no longer absorbs compensation power. In this way, when the generator's output frequency tends to stabilize, power compensation automatically stops without manual operation or other external signal triggering, achieving fully automatic control and avoiding power backtiling caused by overcompensation.

[0065] Specifically, after the initial compensation power is determined and absorbed by the DC-side equipment, the normal power absorbed by the DC-side equipment gradually increases from its initial value, while the compensation power gradually decreases. Thus, during the compensation power withdrawal process, the normal power absorbed by the DC-side equipment gradually increases from its initial low value to the first steady-state value and then remains stable. At this point, the compensation power is withdrawn, and the DC-side equipment no longer absorbs supplementary power but maintains its normal power absorption, i.e., the first steady-state value. Simultaneously, the generator's speed governor responds to the frequency change, gradually adjusting the mechanical power input, and the generator's output power synchronously adjusts from its initial value to the second steady-state value. Under the combined action of the virtual synchronous machine algorithm and the generator speed governor, the generator's output frequency gradually recovers from its peak frequency to its rated frequency. The power supply system ultimately establishes a new power balance, with the generator's output frequency remaining at its rated frequency, and the generator and inverter continuing to supply power to the load under the new power conditions.

[0066] In some embodiments, before performing step S202, it is necessary to obtain the target virtual inertial constant in advance and store the obtained target virtual inertial constant in a storage device, wherein, for example, Figure 4 As shown, the steps for obtaining the target virtual inertial constant include steps S401-S404, wherein, Step S401: When the generator's output frequency is at the rated frequency, apply multiple load reduction operations to the power supply system, and for each load reduction operation, obtain the total time it takes for the generator's output frequency to rise from the rated frequency to the peak frequency.

[0067] Specifically, this can be achieved by detecting whether the generator's output frequency is stable at a stable frequency. If the output frequency is confirmed to be stable at the rated frequency, then the generator's output frequency is considered to be at the rated frequency. Multiple load reduction operations can then be applied to the power supply system. These load reduction operations can be achieved by stopping power to some of the electrical equipment corresponding to the load or by shutting down some of the equipment.

[0068] In some embodiments, the power reduction corresponding to each load reduction operation can be preset, and then the load reduction operation is performed according to the power reduction. For each load reduction operation, the generator's output frequency can be detected in real time, and the total time Δt taken for the output frequency to rise from the rated frequency to the peak frequency can be recorded. Repeating the load reduction operation multiple times (e.g., 5 to 10 times), with the power reduction for each operation being the same or different, and recording the corresponding total time for each operation, can eliminate the influence of random errors in a single measurement by repeating the operation multiple times.

[0069] In some embodiments, the peak frequency may be calibrated at the time of manufacture of the generator or calibrated by testing after manufacture.

[0070] Step S402: For each load reduction operation, determine the candidate inertial time constant corresponding to each load reduction operation based on the total duration, the power reduction of the load reduction operation, and the rated capacity of the generator.

[0071] Specifically, the candidate inertia time constant is directly proportional to the power reduction, rated frequency, and total duration, and inversely proportional to the generator's rated capacity and the product of the peak frequency and the difference between the peak and rated frequencies. For a given load reduction operation, the greater the power reduction, the longer the time required for the generator's output frequency to rise from the rated frequency to the peak frequency, resulting in a larger candidate inertia time constant; conversely, the larger the generator's rated capacity and the greater the increase in output frequency, the smaller the candidate inertia time constant. This proportional relationship reflects the physical nature of generator rotor inertia. A generator with greater inertia experiences a slower frequency change under the same power impact, resulting in a longer time required for the output frequency to reach the peak frequency after a load reduction operation.

[0072] Taking the power reduction during a load reduction operation as ΔP, and the total time taken for the generator's output frequency to rise from the rated frequency to the peak frequency as Δt, the power reduction ΔP can be calculated using the following formula (2): (2) In formula (1), H represents the candidate inertial time constant. This represents the rate of change of the generator's output frequency from its rated frequency to its peak frequency. Indicates the rated capacity of the generator , This indicates the rated frequency. If the generator's peak frequency is... ,but = .

[0073] Thus, according to formula (2) and = The candidate inertial time constant can be calculated using the following formula (3), as follows: (3) As can be seen from formula (3), the candidate inertial time constant H is directly proportional to the power reduction, rated frequency, and total duration, and inversely proportional to the product of the generator's rated capacity and the difference between the peak frequency and the rated frequency. Thus, for each load reduction operation, the candidate inertial time constant corresponding to each load reduction operation can be obtained through formula (3).

[0074] Step S403: Determine the equivalent inertial time constant of the generator based on the candidate inertial time constant corresponding to each load reduction operation.

[0075] Specifically, after obtaining the candidate inertial time constants corresponding to each load reduction operation, the average value of all candidate inertial time constants corresponding to load reduction operations can be calculated as the equivalent inertial time constant. Alternatively, after obtaining the average value, the product of the average value and a weight, or the sum or difference of the average value and a set value, can be used as the equivalent inertial time constant. In this way, by taking the average of multiple measurements, the impact of voltage sampling errors, frequency measurement errors, and random disturbances during load switching on the accuracy of inertial time constant identification can be effectively reduced, improving the accuracy and reliability of the obtained equivalent inertial time constant.

[0076] In some embodiments, outlier removal can be performed on multiple candidate inertial time constants before averaging. Specifically, the standard deviation of all candidate inertial time constants can be calculated, and candidate values ​​that deviate from the average by more than three times the standard deviation can be identified as outliers and removed. Then, the average of the remaining candidate values ​​can be taken. This method can avoid identification bias caused by abnormal disturbances (such as transient oscillations during load switching) during a load reduction operation.

[0077] Step S404: Determine the target virtual inertial constant based on the equivalent inertial time constant.

[0078] In some embodiments, after determining the equivalent inertial time constant of the generator, the range of values ​​for the target virtual inertial constant is determined based on the equivalent inertial time constant. The range of values ​​for the target virtual inertial constant is the equivalent inertial time constant from a first set multiple to a second set multiple, wherein the second set multiple is greater than the first set multiple, and the first set multiple is greater than 0.

[0079] Specifically, the first set multiple can be, for example, 0.1, 0.2 or 0.3, and the second set multiple can be, for example, 0.9, 1 or 1.1, etc. Both the first set multiple and the second set multiple can be set according to actual needs.

[0080] In some embodiments, after determining the range of values ​​for the target virtual inertial constant, the target virtual inertial constant can be determined from the range of values. The step of determining the target virtual inertial constant includes steps S501 and S502, wherein... Step S501: Determine a value from the range of values ​​as the initial virtual inertia constant.

[0081] Specifically, a value can be randomly selected from the range as the initial virtual inertial constant. Of course, to reduce the number of iterative experiments described below, an intermediate value can also be selected from the range as the initial virtual inertial constant. The initial virtual inertial constant can be, for example, 0.5 or 0.6 times the equivalent inertial time constant.

[0082] Step S502: Within the range of values, apply a load reduction operation to the power supply system to conduct iterative tests on the initial virtual inertial constant until the frequency change rate of the generator's output frequency does not exceed a preset first preset threshold, and the generator's output frequency is in a non-oscillating state. Then, determine the virtual inertial constant corresponding to the current iteration as the target virtual inertial constant. During the iterative test, if the frequency change rate of the output frequency exceeds the first preset threshold, increase the current virtual inertial constant; if the output frequency is in an oscillating state, decrease the current virtual inertial constant.

[0083] In some embodiments, during each iteration test, a load reduction operation is first applied to the power supply system, and the compensation power corresponding to the iteration test is determined based on the virtual inertia constant corresponding to the iteration test. The DC-side equipment is then controlled to absorb the compensation power corresponding to the iteration test. Furthermore, the frequency change rate of the generator's output frequency is acquired in real time during the iteration test. If the frequency change rate exceeds a first preset threshold, the virtual inertia constant corresponding to the iteration test is increased to proceed to the next iteration test. If the frequency change does not exceed the first preset threshold, the output frequency is checked for oscillation. If the output frequency is detected to be oscillating, the virtual inertia constant corresponding to the iteration test is decreased to proceed to the next iteration test. This process continues until the frequency change rate of the output frequency does not exceed the first preset threshold and the output frequency is not oscillating. At this point, the current virtual inertia constant corresponding to the iteration test is determined to have met the convergence condition, the iteration ends, and the current virtual inertia constant corresponding to the iteration test is used as the target virtual inertia constant.

[0084] Taking the first iteration test as an example, a load reduction operation is applied to the power supply system, and the compensation power T1 corresponding to the initial virtual inertia constant H0 is determined according to the initial virtual inertia constant. The DC side equipment is controlled to absorb T1, and the frequency change rate of the generator's output frequency is recorded. If the frequency change rate is detected to be greater than the first preset threshold γ, H0 is increased. At this time, H0 can be increased according to a preset step size B1, that is, the virtual inertia constant of the next iteration is H0+B1. B1+H0 is used as the virtual inertia constant of the next iteration test. Then the above steps are executed until the frequency change rate of the output frequency is not exceeded by the first preset threshold and the output frequency is not in an oscillating state. Then it is determined that the current virtual inertia constant corresponding to the iteration test has met the convergence condition, the iteration ends, and the current virtual inertia constant corresponding to the iteration test is used as the target virtual inertia constant. The target virtual inertia constant is written into the storage device. When needed, the target virtual inertia constant can be directly read from the storage device, which can reduce the calculation time of calculating the compensation power based on the target virtual inertia constant.

[0085] See Figure 5This is the control logic diagram for obtaining the target virtual inertia constant in this embodiment of the application. See also... Figure 5 First, step 501 is executed to set the initial virtual inertia constant. Specifically, the initial virtual inertia constant can be 0.5 times the equivalent inertia time constant. Next, step 502 is executed to apply a load reduction operation. The power reduction corresponding to each load reduction operation is a fixed value. After applying the load reduction operation, the frequency change rate of the generator's output frequency is recorded. Then, step 503 is executed to determine whether the frequency change rate is greater than a first preset threshold. If the frequency change rate is greater than the first preset threshold, step 504 is executed to increase the virtual inertia constant, and steps 502 and 503 are repeated after step 504. If the frequency change rate is not greater than the first preset threshold, step 505 is executed to determine whether the output frequency is in an oscillating state. Specifically, if the output frequency is in an oscillating state, step 506 is executed to decrease the virtual inertia constant, and step 502 is returned to be executed after step 504. Furthermore, if the output frequency is not in an oscillating state, the process of obtaining the target virtual inertial constant ends, and the virtual inertial constant corresponding to the output frequency not being in an oscillating state is taken as the target virtual inertial constant.

[0086] Thus, through iterative experiments, the optimal virtual inertia constant value for the dynamic response of the power supply system can be found within the range of values. This optimal balance point, where the frequency change rate does not exceed the threshold and oscillations do not occur, ensures a higher degree of matching between the inverter's target virtual inertia constant and the generator's equivalent inertia time constant. Furthermore, the virtual inertia constant is increased to enhance absorption capacity when the frequency change rate is too large, and decreased to avoid resonance when the output frequency is oscillating. Through this bidirectional adjustment mechanism, resonance conflicts between the virtual synchronous machine's inertia response and the generator's speed governor's mechanical adjustment can be avoided, resulting in a monotonic decay characteristic of the generator's output frequency and preventing underdamped oscillations.

[0087] In some embodiments, the determination of the compensation power is also based on the constraint of the maximum backflow energy allowed by the generator.

[0088] Specifically, the maximum backflow energy that the generator can allow. It can be determined based on the equivalent inertial time constant H and the generator's rated capacity. Rated frequency and peak frequency With rated frequency The difference is determined, and the maximum backflow energy can be calculated using the following formula (4), as follows: (4) In formula (4) Indicates decreasing power. This indicates the total time elapsed from the rated frequency to the peak frequency of the generator's output frequency.

[0089] And compensation power Based on the target virtual inertial constant, rated capacity S_N, rated frequency f0, and the first frequency change rate. It is determined that the compensation power can be calculated using the following formula (5), as follows: (5) In formula (5) This represents the target's virtual inertial constant.

[0090] Thus, according to formulas (4) and (5), during the transient process following a load drop event, the inverter compensates for the power loss. Excess power is absorbed, limiting the actual backflow to the generator to a safe range. Because the target virtual inertia constant is limited to a multiple of H between the first and second set multiples, the generator maintains a positive output throughout the transient process, and the actual backflow energy it experiences is always less than the generator's maximum allowable backflow energy. This ensures that the generator 10 is not damaged by energy surges.

[0091] Taking a diesel generator as an example, the diesel generator and the inverter jointly supply power to the load. Let the initial output power of the diesel generator be P_D0, the output power of the inverter be P_I0, and the total load power be P_L0 = P_D0 + P_I0. The output frequency of the generator is stable at the rated value f0. At time t0, the power supply system experiences a sudden drop, and the total load power decreases instantaneously by ΔP_L. The disconnection of the load causes an instantaneous power imbalance in the power supply system. The rotor of the generator is accelerated by the excess power, and the output frequency of the diesel generator begins to rise. The frequency change rate df / dt increases sharply. The inverter 20 detects in real time whether df / dt exceeds the first preset threshold γ. If df / dt > γ is detected, it is determined that a load drop event has occurred. The inverter controller can calculate the compensation power according to the current frequency change rate df / dt and the preset target virtual inertia constant through formula (5). and generate The corresponding instantaneous power correction command is then issued. The inverter responds to this command by controlling the DC-side equipment to absorb compensation power. After the DC-side equipment absorbs compensation power, the second frequency change rate of the generator's output frequency can be obtained in real time. When this second frequency change rate is detected to be less than a preset second threshold, it can be determined that the frequency change rate df / dt has fallen and tends to zero. At this point, control command generation stops, and the DC-side equipment is no longer controlled to absorb compensation power. Furthermore, under the combined action of the virtual synchronous machine algorithm and the diesel generator's speed governor, the diesel generator's output frequency recovers from the peak frequency to the rated frequency f0. During the gradual withdrawal of compensation power, the normal power absorbed by the DC-side equipment gradually adjusts from an initial smaller value to the first steady-state value P_I1. After the DC-side equipment no longer compensates for power, the normal power absorbed by the DC-side equipment remains unchanged at P_I1, and the diesel generator's output power is also adjusted accordingly to the second steady-state value P_D1. The power supply system ultimately establishes a new power balance: P_D1 + P_I1 = P_L0 ΔP_L, and the output frequency of the diesel generator is stable at the rated frequency.

[0092] Thus, throughout the entire transient process corresponding to the load drop event, the diesel generator's output power remains positive and does not enter a reverse power state, thereby preventing the generator's reverse power protection from being triggered and ensuring complete power supply continuity. Simultaneously, since the diesel generator does not experience abnormal mechanical stress impacts, the risk of shaft torsional vibration and mechanical component damage is effectively avoided, significantly reducing the probability of generator damage. Furthermore, by detecting the frequency change rate and triggering power compensation when it exceeds a first preset threshold, the inverter can instantly perceive power imbalance within a millisecond-level time window of load disconnection, without relying on communication or waiting for power amplitude changes. This enables rapid identification of load drop events. Moreover, since the target virtual inertia constant is predetermined based on the generator's equivalent inertia time constant, the compensation power is coordinated and matched with the diesel generator's dynamic characteristics, avoiding both undercompensation (leading to power backflow) and overcompensation (causing frequency oscillations).

[0093] See Figure 1This application discloses a power supply system including a generator 10 for providing electrical energy to a load 30; an inverter 20 connected in parallel with the generator 10 for providing electrical energy to the load 30, and determining a load drop event in the power supply system based on a first frequency change rate of the generator 10's output frequency; determining the compensation power corresponding to the load drop event based on the first frequency change rate and a preset target virtual inertia constant, wherein the target virtual inertia constant is determined based on the generator's equivalent inertia time constant; controlling the DC-side equipment of the inverter 20 to absorb the compensation power, wherein after the DC-side equipment absorbs the compensation power, the generator's output power is greater than a preset set power, wherein the set power is greater than 0.

[0094] In some embodiments, the inverter 20 is configured to obtain the ratio of the generator's rated capacity to the generator's rated frequency; and to determine the compensation power based on a first frequency change rate, a target virtual inertia constant, and the ratio.

[0095] In some embodiments, the inverter 20 is used to compare a first frequency change rate with a preset first preset threshold. If the first frequency change rate exceeds the first preset threshold, it is determined that a load drop event has occurred in the power supply system, wherein the first preset threshold is greater than 0.

[0096] In some embodiments, if the first frequency change rate does not exceed a first preset threshold, it is determined that no load drop event has occurred in the power supply system.

[0097] In some embodiments, the target virtual inertial constant can also be obtained through a control terminal connected to the power supply system. Specifically, the control terminal is configured to apply multiple load reduction operations to the power supply system when the generator's output frequency is at the rated frequency, and for each load reduction operation, obtain the total time taken for the generator's output frequency to rise from the rated frequency to the peak frequency; for each load reduction operation, determine a candidate inertial time constant corresponding to each load reduction operation based on the total time, the power reduction of the load reduction operation, and the generator's rated capacity; determine the equivalent inertial time constant of the generator based on the candidate inertial time constant corresponding to each load reduction operation; and determine the target virtual inertial constant based on the equivalent inertial time constant.

[0098] In some embodiments, the target virtual inertial constant ranges from a first set multiple to a second set multiple of the equivalent inertial time constant, wherein the second set multiple is greater than the first set multiple, and the first set multiple is greater than 0.

[0099] In some embodiments, the control terminal is configured to determine a value from a range of values ​​as an initial virtual inertial constant; within the range of values, by applying a load reduction operation to the power supply system, iterative tests are conducted on the initial virtual inertial constant until the frequency change rate of the generator's output frequency does not exceed a preset first preset threshold, and the generator's output frequency is in a non-oscillating state. At this point, the virtual inertial constant corresponding to the current iteration is determined as the target virtual inertial constant. During the iterative test, if the frequency change rate of the output frequency exceeds the first preset threshold, the current virtual inertial constant is increased; if the output frequency is in an oscillating state, the current virtual inertial constant is decreased.

[0100] In some embodiments, the DC-side devices of the inverter 20 include a DC bus capacitor and / or energy storage devices.

[0101] In some embodiments, the inverter 20 is configured to generate control commands based on the compensation power; in response to the control commands, the DC-side devices of the inverter 20 are controlled to absorb the compensation power.

[0102] In some embodiments, the inverter 20 is configured to, after controlling the DC-side device of the inverter to absorb compensation power, obtain a second frequency change rate of the generator output frequency and detect whether the second frequency change rate is less than a preset second preset threshold, wherein the second preset threshold is less than a first preset threshold; if the second frequency change rate is less than the second preset threshold, then stop generating control commands so that the DC-side device no longer absorbs compensation power.

[0103] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0104] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Although this application has disclosed preferred embodiments as above, it is not intended to limit this application. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the technical solution of this application. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A control method for a power supply system, characterized in that, The power supply system includes a generator and an inverter connected in parallel, the power supply system is connected to a load, and the method includes: Based on the first frequency change rate of the generator's output frequency, it is determined that a load drop event has occurred in the power supply system; Based on the first frequency change rate and the preset target virtual inertia constant, the compensation power corresponding to the load drop event is determined, wherein the target virtual inertia constant is determined based on the equivalent inertia time constant of the generator; The inverter's DC-side device is controlled to absorb the compensation power, wherein after the DC-side device absorbs the compensation power, the generator's output power is greater than a preset set power, wherein the set power is greater than 0.

2. The control method according to claim 1, characterized in that, The step of determining the compensation power corresponding to the load drop event based on the first frequency change rate and the preset target virtual inertia constant includes: Obtain the ratio of the rated capacity of the generator to the rated frequency of the generator; The compensation power is determined based on the first frequency change rate, the target virtual inertial constant, and the ratio.

3. The control method according to claim 1 or 2, characterized in that, The step of determining a load drop event in the power supply system based on a first frequency change rate of the generator's output frequency includes: By comparing the first frequency change rate with a preset first threshold, if the first frequency change rate exceeds the first preset threshold, it is determined that the power supply system has experienced the load drop event, wherein the first preset threshold is greater than 0.

4. The control method according to claim 3, characterized in that, The steps for obtaining the target virtual inertial constant include: When the output frequency of the generator is at the rated frequency of the generator, multiple load reduction operations are applied to the power supply system, and for each load reduction operation, the total time taken for the output frequency of the generator to rise from the rated frequency to the peak frequency is obtained; For each load reduction operation, a candidate inertial time constant is determined based on the total duration, the power reduction of the load reduction operation, and the rated capacity of the generator. The equivalent inertial time constant of the generator is determined based on the candidate inertial time constant corresponding to each load reduction operation. The target virtual inertial constant is determined based on the equivalent inertial time constant.

5. The control method according to claim 4, characterized in that, The target virtual inertial constant is the equivalent inertial time constant ranging from a first set multiple to a second set multiple, wherein the second set multiple is greater than the first set multiple, and the first set multiple is greater than 0.

6. The control method according to claim 5, characterized in that, Determining the target virtual inertial constant based on the equivalent inertial time constant includes: Choose a value from the range of values ​​as the initial virtual inertial constant; Within the specified value range, by applying a load reduction operation to the power supply system, iterative experiments are conducted on the initial virtual inertial constant until the frequency change rate of the generator's output frequency does not exceed the first preset threshold, and the generator's output frequency is in a non-oscillating state. At this point, the virtual inertial constant corresponding to the current iteration is determined as the target virtual inertial constant. During the iterative experiment, if the frequency change rate of the output frequency exceeds the first preset threshold, the current virtual inertial constant is increased; if the output frequency is in an oscillating state, the current virtual inertial constant is decreased.

7. The control method according to claim 3, characterized in that, The DC-side equipment of the inverter includes a DC bus capacitor and / or energy storage equipment.

8. The control method according to claim 7, characterized in that, The DC-side device controlling the inverter absorbs the compensation power, including: According to the compensation power generation control command; In response to the control command, the inverter controls the DC-side equipment to absorb the compensation power.

9. The control method according to claim 8, characterized in that, The method further includes: The second frequency change rate of the generator's output frequency is obtained, and it is detected whether the second frequency change rate is less than a preset second preset threshold, wherein the second preset threshold is less than the first preset threshold. If the second frequency change rate is less than the second preset threshold, then the generation of the control command will stop, so that the DC-side device will no longer absorb the compensation power.

10. A power supply system, characterized in that, include: A generator is used to provide electrical energy to a load. An inverter, connected in parallel with the generator, is used to provide electrical energy to the load and determine a load drop event in the power supply system based on a first frequency change rate of the generator's output frequency; it determines the compensation power corresponding to the load drop event based on the first frequency change rate and a preset target virtual inertia constant, wherein the target virtual inertia constant is determined based on the generator's equivalent inertia time constant; it controls the DC-side device of the inverter to absorb the compensation power, and after the DC-side device absorbs the compensation power, the generator's output power is greater than a preset set power, wherein the set power is greater than 0.

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