A multi-unit parallel frequency modulation method for a diesel-storage hybrid system

Abstract

This invention discloses a multi-unit parallel frequency regulation method for a diesel-storage hybrid system, relating to the fields of microgrid and diesel-storage hybrid control technology. By dynamically adjusting a second reference frequency, the invention enables the system to gradually withdraw from frequency support after the load increases and reaches a steady state. This ensures that the battery state-of-charge management and power distribution strategies remain undisturbed, while allowing the energy storage converter to release more power reserves to cope with subsequent load fluctuations. Furthermore, by dynamically generating a third reference frequency for inertia determination, the invention ensures both rapid frequency recovery and effective suppression of frequency oscillations when the load decreases. During periods of significant load drop, it prompts the converter to provide inertia support earlier, thereby more promptly and effectively preventing reverse power generation from the generator, comprehensively improving the system's power supply quality and safety.

Description

Technical Field

[0001] This invention belongs to the field of microgrid and diesel-storage hybrid control technology, and specifically relates to a multi-unit parallel frequency regulation method for a diesel-storage hybrid system. Background Technology

[0002] To meet the power supply demands of high loads and enhance the flexibility of generator unit configuration, microgrids typically require the parallel operation of multiple generator units to simultaneously supply power to the loads. When multiple diesel generator sets operate in parallel, the system will operate in frequency droop mode, meaning that under stable operating conditions, the system frequency will deviate from the rated frequency. In scenarios with significant load fluctuations, to improve power quality, avoid frequency and voltage fluctuations caused by load surges, and rationally configure generator unit capacity, a diesel-storage hybrid system equipped with an energy storage system is typically used for power supply.

[0003] In the parallel frequency regulation process of traditional diesel-electric hybrid systems, when the system is in frequency droop mode, once the energy storage converter detects a continuous frequency deviation, it will continuously output active power to provide support. This not only directly affects the battery's state of charge management but also seriously interferes with the power distribution strategy of the control system. On the other hand, if active frequency support occupies the power reserve of the energy storage converter for a long time, the converter will not be able to provide sufficient subsequent support when the load suddenly increases again. In addition, due to the mechanical adjustment delay of the diesel generator, when the load suddenly decreases, the system will not only face the problems of slow frequency recovery and frequency oscillation, but under conditions of significant load reduction, it may even trigger the generator reverse power hazard, seriously threatening power supply security. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a multi-unit parallel frequency modulation method for diesel-storage hybrid systems, thereby solving the aforementioned technical problems.

[0005] A method for multi-unit parallel frequency regulation of a diesel-storage hybrid system is proposed, comprising the following steps: Obtain the actual frequency of the parallel system during operation; The actual frequency is filtered to obtain the second reference frequency; The third reference frequency is calculated based on the set first reference frequency and the second reference frequency; Based on the difference logic between the actual frequency and the frequency reference value, the first frequency deviation for frequency support is calculated, and the first active power change of the energy storage converter is calculated based on the first frequency deviation. Calculate the second frequency deviation between the third reference frequency and the actual frequency. Based on the directional relationship between the second frequency deviation and the actual frequency change rate, calculate the second active power change of the energy storage converter to provide inertia support. The first active power change and the second active power change are superimposed on the active power command of the energy storage converter to control the active power output of the energy storage converter.

[0006] Preferably, in the step of filtering the actual frequency to obtain the second reference frequency, the filtering process is a second-order low-pass filter, and its complex frequency domain transfer function model is:

[0007] in, The complex frequency domain expression for the second reference frequency. The complex frequency domain expression for the actual frequency. For the Laplace operator, The set natural angular frequency of the filter. is the damping ratio of the filter.

[0008] Preferably, the step of calculating the first frequency deviation for frequency support has the following difference logic: Set the frequency dead zone; When the actual frequency is greater than the sum of the first reference frequency and the frequency modulation dead zone, the first frequency deviation is the sum of the first reference frequency and the frequency modulation dead zone minus the actual frequency. When the actual frequency is less than the difference between the second reference frequency and the frequency modulation dead zone, the first frequency deviation is the second reference frequency minus the frequency modulation dead zone minus the actual frequency. When the actual frequency is between the difference between the second reference frequency and the frequency modulation dead zone and the sum of the first reference frequency and the frequency modulation dead zone, the first frequency deviation is zero.

[0009] Preferably, the calculation of the first active power change of the energy storage converter based on the first frequency deviation specifically includes the following steps: The first change in active power is the product of the preset frequency modulation coefficient and the first frequency deviation.

[0010] Preferably, the calculation of the third reference frequency specifically includes the following steps: The arithmetic mean of the first reference frequency and the second reference frequency is used as the third reference frequency.

[0011] Preferably, when calculating the second active power change of the energy storage converter to provide inertia support, the process further includes calculating the initial active power change of inertia, specifically including the following steps: The difference between the third reference frequency and the actual frequency is taken as the second frequency deviation; Determine the sign and direction relationship between the actual rate of change of frequency and the second frequency deviation; When the second frequency deviation and the actual frequency change rate have the same sign and their product is greater than zero, the initial inertia active change is the product of the set inertia coefficient and the actual frequency change rate. When the second frequency deviation has the opposite sign to the actual frequency change rate, or when at least one of them is zero, the active change in the initial inertia is zero.

[0012] Preferably, after calculating the initial change in inertia, a smoothing process is also included, specifically comprising the following: The initial change in active power is processed by a first-order low-pass filter to obtain the final change in the second active power. Its complex frequency domain transfer function model is:

[0013] in, This is the complex frequency domain expression for the change in the second active power. This is the complex frequency domain expression for the active change of the initial inertia. For the Laplace operator, This is the set filter time constant.

[0014] Preferably, the method also includes a reactive power support determination step based on the actual voltage: Obtain the actual AC side voltage during the operation of the parallel system; Set the reference voltage and voltage regulation dead zone; When the absolute value of the difference between the actual AC side voltage and the reference voltage is greater than the voltage regulation dead zone, the voltage deviation is the difference between the reference voltage and the actual AC side voltage. The voltage deviation is zero when the absolute value of the difference between the actual AC side voltage and the reference voltage is not greater than the voltage regulation dead zone.

[0015] Preferably, after obtaining the voltage deviation, the method further includes the following steps: The reactive power change of the energy storage converter is controlled to be the product of the set voltage regulation coefficient and the voltage deviation.

[0016] Preferably, controlling the active power output of the energy storage converter specifically includes the following steps: The active power reference command issued by the upper control system, the first active power change, and the second active power change are added together to obtain the composite active power command. The reactive power reference command issued by the upper control system is added to the reactive power change to obtain the composite reactive power command; The output of the energy storage converter is controlled by the synthesized active power command and the synthesized reactive power command; and the synthesized active power command is limited to the current allowed active power limit of the energy storage converter and the synthesized reactive power command is limited to the current allowed reactive power limit of the energy storage converter at the control layer.

[0017] The beneficial effects of this invention are as follows: By dynamically adjusting the second reference frequency, the system gradually withdraws from frequency support after the load increases and reaches a steady state. This ensures that the battery state-of-charge management and power distribution strategy are not disturbed, and allows the energy storage converter to release more power reserves to cope with subsequent load fluctuations. On the other hand, by dynamically generating a third reference frequency for inertia determination, when the load decreases, it ensures both rapid frequency recovery and effective suppression of frequency oscillations; when the load drops sharply, it prompts the converter to provide inertia support earlier, thereby more timely and effectively preventing reverse power phenomena from the generator, and comprehensively improving the power supply quality and safety of the system. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0019] Figure 1 The present invention provides a flowchart of the steps of a multi-unit parallel frequency modulation method for a diesel-storage hybrid system. Detailed Implementation

[0020] The following disclosure provides many different embodiments or examples for implementing various embodiments of the invention. To simplify the disclosure, specific embodiments are described below. Of course, these are merely examples and are not intended to limit the scope of the invention.

[0021] The embodiments of the invention will now be described in detail with reference to the accompanying drawings.

[0022] like Figure 1 As shown, a multi-unit parallel frequency regulation method for a diesel-storage hybrid system includes the following steps: Obtain the actual frequency of the parallel system during operation; The actual frequency is filtered to obtain the second reference frequency; The third reference frequency is calculated based on the set first reference frequency and the second reference frequency; Based on the difference logic between the actual frequency and the frequency reference value, the first frequency deviation for frequency support is calculated, and the first active power change of the energy storage converter is calculated based on the first frequency deviation. Calculate the second frequency deviation between the third reference frequency and the actual frequency. Based on the directional relationship between the second frequency deviation and the actual frequency change rate, calculate the second active power change of the energy storage converter to provide inertia support. The first active power change and the second active power change are superimposed on the active power command of the energy storage converter to control the active power output of the energy storage converter.

[0023] To address the shortcomings of existing technologies, such as the lag in response of diesel generator sets in diesel-storage hybrid systems under load step conditions, and the tendency of traditional fixed reference frequency regulation to cause depletion of the state of charge of energy storage batteries and reverse power of generators, the core principle of this invention is to decouple the transient high-frequency fluctuations and steady-state low-frequency drift of the actual frequency at the control level by using a low-pass filtering algorithm, and to reconstruct the active power command of the energy storage converter using dynamic reference frequencies at different time scales.

[0024] In a specific implementation case, taking the parallel operation of the system and a sudden increase in load as an example, the actual frequency of the system drops. At this time, due to the hysteresis characteristic of the filtering process, the extracted second reference frequency maintains the level before the drop for a short period of time. The control system quickly generates the first active power change based on the difference between the actual frequency and the higher reference frequency, driving the energy storage converter to perform transient discharge to compensate for the power deficit of the generator set. As the generator set completes mechanical speed regulation and enters a new steady state, the second reference frequency gradually approaches the actual frequency, causing the first frequency deviation to fall into the dead zone, and the energy storage converter automatically withdraws from the first active power output. During this process, the system uses the third reference frequency synthesized from the first and second reference frequencies, combined with the actual frequency change rate, to determine the direction. When the determined frequency recovers or the load suddenly decreases, the system outputs the second active power change in the opposite direction in a timely manner to provide inertial damping.

[0025] Compared to existing technologies, this solution not only leverages the rapid response advantage of energy storage converters, effectively suppressing the depth and rate of frequency drop during sudden load increases, and completely avoiding the ineffective consumption of energy storage battery state of charge, but also uses direction determination logic to precisely prevent reverse power phenomena caused by excessive energy storage support during the frequency recovery phase of the generator set, significantly improving the self-healing capability and overall operational stability of the microgrid system.

[0026] More specifically, in the step of filtering the actual frequency to obtain the second reference frequency, the filtering process is a second-order low-pass filter, and its complex frequency domain transfer function model is:

[0027] in, The complex frequency domain expression for the second reference frequency. The complex frequency domain expression for the actual frequency. For the Laplace operator, The set natural angular frequency of the filter. is the damping ratio of the filter.

[0028] In the specific implementation process, the system first acquires the actual frequency of the parallel system during operation, and then filters the actual frequency using a second-order low-pass filter to obtain a dynamically tracked second reference frequency. Based on the pre-set first reference frequency and the second reference frequency, the system calculates a third reference frequency. When the system load suddenly increases, causing the frequency to drop, due to the delay in the dynamic tracking of the second reference frequency, the actual frequency will be less than the difference between the second reference frequency and the frequency regulation dead zone. The system determines and calculates the first frequency deviation based on this, and then generates a first active power change to provide frequency support. At the same time, the system calculates the second frequency deviation between the third reference frequency and the actual frequency, and combines it with the directional relationship of the frequency change rate to generate a second active power change to provide inertia support. As the diesel generator gradually adjusts to restore the system frequency to a stable state, the second reference frequency gradually approaches the actual frequency. When the actual frequency is greater than or equal to the difference between the second reference frequency and the frequency regulation dead zone, the first frequency deviation returns to zero, the system automatically stops frequency support, and releases the power reserve of the energy storage converter. The design principle utilizes the dynamic characteristics of a second-order low-pass filter to cause the second reference frequency to lag behind the actual frequency during transients to trigger support, while gradually tracking the actual frequency in steady state to achieve automatic support deactivation. This not only solves the problem of charge imbalance caused by continuous active power output in traditional energy storage systems, but also effectively releases the power reserves of the energy storage converter to cope with subsequent load fluctuations while maintaining system frequency stability. Furthermore, the inertia determination mechanism of the third reference frequency significantly suppresses frequency overshoot and generator reverse power risk during sudden load reductions.

[0029] More specifically, the step of calculating the first frequency deviation used for frequency support has the following difference logic: Set the frequency dead zone; When the actual frequency is greater than the sum of the first reference frequency and the frequency modulation dead zone, the first frequency deviation is the sum of the first reference frequency and the frequency modulation dead zone minus the actual frequency. When the actual frequency is less than the difference between the second reference frequency and the frequency modulation dead zone, the first frequency deviation is the second reference frequency minus the frequency modulation dead zone minus the actual frequency. When the actual frequency is between the difference between the second reference frequency and the frequency modulation dead zone and the sum of the first reference frequency and the frequency modulation dead zone, the first frequency deviation is zero.

[0030] This frequency deviation calculation logic aims to address the technical shortcoming of traditional diesel-storage hybrid systems, which cannot autonomously withdraw from frequency support. Its design principle involves constructing a dynamic dead zone boundary using dual reference frequencies, enabling the energy storage converter to automatically switch support strategies based on the system's operational phase.

[0031] In one specific implementation, the system first sets 50Hz as the first reference frequency and sets a frequency dead zone of 0.2Hz. When the load suddenly increases, causing the frequency to drop, due to the low-pass filtering effect, the second reference frequency temporarily remains at a higher level, and the actual frequency quickly falls below the threshold of the difference between the second reference frequency and the dead zone. Based on this, the system calculates the positive first frequency deviation and drives the energy storage converter to output compensated power. As the diesel generator set gradually increases its output and enters a new steady state, the filtered second reference frequency slowly follows the actual frequency as it decreases. When the actual frequency rises back to above the difference between the second reference frequency and the dead zone, the first frequency deviation is forcibly returned to zero, and the energy storage converter automatically withdraws from active power support.

[0032] This dynamic dead-zone mechanism offers significant advantages: firstly, it avoids ineffective power output from the energy storage unit during steady-state system operation, effectively improving the controllability of battery state-of-charge management; secondly, it provides ample power regulation margin for potential load fluctuations. Simultaneously, it eliminates the power oscillation problem caused by frequent switching in traditional fixed-threshold control, fundamentally resolving the power coordination conflict between energy storage and generators in multi-unit parallel systems.

[0033] More specifically, the calculation of the first active power change of the energy storage converter based on the first frequency deviation includes the following steps: The first change in active power is the product of the preset frequency modulation coefficient and the first frequency deviation.

[0034] In practical implementation, the system first determines the first frequency deviation based on the interval between the actual frequency and the reference frequency. When the actual frequency is lower than the difference between the second reference frequency and the frequency regulation dead zone, the first frequency deviation is equal to the second reference frequency minus the frequency regulation dead zone and then minus the actual frequency. This first frequency deviation is multiplied in real time by a pre-tuned frequency regulation coefficient in the controller to generate the first active power change. This frequency regulation coefficient is set based on the rated capacity of the energy storage converter, the system inertia time constant, and the frequency regulation requirements to ensure that the energy storage converter can output compensating power proportionally when the frequency drops.

[0035] Under conditions of sudden load increases, the frequency deviation increases. The product operation automatically increases the change in the first active power, driving the energy storage converter to discharge rapidly, thereby suppressing frequency drops. When the system enters steady state and the second reference frequency tracks close to the actual frequency, the first frequency deviation approaches zero, and the product result naturally decays to zero, causing the energy storage converter to automatically withdraw from frequency support. This design principle is based on proportional control theory, directly mapping the frequency deviation to a power adjustment amount through a linear relationship. This not only achieves adaptive adjustment of the frequency support strength, avoiding excessive intervention caused by traditional fixed power support, but also eliminates the need for additional exit judgment logic during frequency recovery. The natural decay of the product relationship ensures a smooth exit from the support process. This effectively solves the problem of state-of-charge imbalance caused by continuous active power output from energy storage in existing technologies, while reserving sufficient power reserve space for subsequent load fluctuations, significantly improving the operational stability and adjustment continuity of the diesel-energy storage hybrid system under multiple operating conditions.

[0036] More specifically, the calculation of the third reference frequency includes the following steps: The arithmetic mean of the first reference frequency and the second reference frequency is used as the third reference frequency.

[0037] The third reference frequency calculation method mentioned in this claim aims to solve the frequency recovery overshoot and generator reverse power problems that occur in traditional diesel-storage hybrid systems when the load suddenly decreases. Its design principle is to provide a precise switching threshold for inertia support by dynamically balancing the steady-state and transient frequency characteristics.

[0038] In one specific implementation, the system sets a rated 50Hz as the first reference frequency, and simultaneously extracts a dynamic second reference frequency from the actual frequency using a second-order low-pass filter. When the multi-unit parallel system encounters a sudden load reduction, the actual frequency rises rapidly, while the second reference frequency remains at a low level due to filtering lag. At this time, the system performs an arithmetic average of the first and second reference frequencies to generate a third reference frequency between the two. When the actual frequency exceeds this third reference frequency and shows an upward trend, the energy storage converter immediately outputs a negative change in active power to suppress frequency overshoot.

[0039] The beneficial effects of this arithmetic averaging mechanism are as follows: it effectively balances the difference between the steady-state frequency setting and the dynamically tracked frequency. In the initial stage of frequency recovery, the diesel generator is allowed to dominate the regulation process; while when the frequency approaches the overshoot threshold, the damping effect of the energy storage system is activated in a timely manner. This not only significantly reduces frequency overshoot and avoids reverse power protection actions triggered by the generator set due to frequency overshoot, but also reduces the number of invalid actions of the energy storage system through dynamic threshold determination, extending the service life of the energy storage equipment, while maintaining the frequency stability of the system under both transient and steady-state conditions.

[0040] More specifically, when calculating the second active power change of the energy storage converter to provide inertia support, the process also includes calculating the initial active power change of inertia, specifically including the following steps: The difference between the third reference frequency and the actual frequency is taken as the second frequency deviation; Determine the sign and direction relationship between the actual rate of change of frequency and the second frequency deviation; When the second frequency deviation and the actual frequency change rate have the same sign and their product is greater than zero, the initial inertia active change is the product of the set inertia coefficient and the actual frequency change rate. When the second frequency deviation has the opposite sign to the actual frequency change rate, or when at least one of them is zero, the active change in the initial inertia is zero.

[0041] In a specific implementation, the system first calculates the difference between the third reference frequency and the actual frequency, using this as the second frequency deviation, while simultaneously acquiring the real-time rate of change of the actual frequency. During a sudden load reduction, the actual frequency begins to rise. Since the third reference frequency is lower than the rising actual frequency, the second frequency deviation is negative, while the rate of change of frequency is positive, indicating opposite signs. The system determines that the initial inertial active power change is zero. When the frequency rises above the third reference frequency, the second frequency deviation becomes positive, matching the sign of the positive rate of change of frequency. The system immediately activates inertia support, calculating the product of the inertia coefficient and the rate of change of frequency as the initial inertial active power change, driving the energy storage converter to absorb power and suppress frequency overshoot. This design principle is based on the energy balance theory of electromechanical transient processes. By judging the consistency of the signs of the second frequency deviation and the rate of change of frequency, it determines the system's energy surplus state, providing reverse power support only when the frequency accelerates in the direction deviating from the third reference frequency. Compared with existing technologies, this solution can not only accurately identify the critical transient stages that require inertia support, avoiding the ineffective power exchange of traditional fixed inertia control in steady state, but also suppress overshoot in a timely manner during frequency recovery, effectively preventing the reverse power condition of diesel generator sets due to rapid frequency recovery. At the same time, the sign direction determination mechanism significantly reduces the number of ineffective actions of the energy storage system, significantly improving the frequency regulation accuracy and equipment operation safety of the diesel-energy storage hybrid system under variable operating conditions.

[0042] More specifically, after calculating the initial change in inertia's active power, a smoothing process is also included, specifically comprising the following: The initial change in active power is processed by a first-order low-pass filter to obtain the final change in the second active power. Its complex frequency domain transfer function model is:

[0043] in, This is the complex frequency domain expression for the change in the second active power. This is the complex frequency domain expression for the active change of the initial inertia. For the Laplace operator, This is the set filter time constant.

[0044] This first-order filtering and smoothing process aims to address the technical shortcomings of traditional diesel-storage hybrid systems, which suffer from equipment stress and frequency oscillations caused by sudden power command changes during inertia support. Its design principle involves using a low-pass filter to smooth the initial inertia active power change in the time domain, thereby making the power output of the energy storage converter more closely match the dynamic response characteristics of the physical inertia system. In specific implementation, when the system determines that the second frequency deviation has the same sign as the actual frequency change rate, it first calculates the initial inertia active power change and then uses a first-order low-pass filter for smoothing. Under conditions where a sudden load reduction causes a rapid frequency increase, this filtering mechanism ensures that the negative active power change output by the energy storage converter exhibits a smooth upward trend, rather than a step change, thus effectively suppressing the system's damped oscillations. The beneficial effects of this design are: firstly, it significantly reduces the current stress and heat loss of the energy storage converter's power devices, extending the equipment's service life; secondly, by simulating the inertia response characteristics of a traditional synchronous generator, the frequency recovery process is made smoother, avoiding secondary frequency fluctuations caused by sudden power changes. Meanwhile, during the frequency overshoot suppression process, it can maintain sufficient dynamic response speed, resolve the contradiction between inertia support and system stability in existing technologies, and significantly improve the frequency regulation quality and operational reliability of the diesel-storage hybrid system under complex operating conditions.

[0045] More specifically, it also includes a reactive power support determination step based on actual voltage: Obtain the actual AC side voltage during the operation of the parallel system; Set the reference voltage and voltage regulation dead zone; When the absolute value of the difference between the actual AC side voltage and the reference voltage is greater than the voltage regulation dead zone, the voltage deviation is the difference between the reference voltage and the actual AC side voltage. The voltage deviation is zero when the absolute value of the difference between the actual AC side voltage and the reference voltage is not greater than the voltage regulation dead zone.

[0046] In practice, the system collects the actual voltage values ​​of the AC bus in the parallel system in real time and sets the nominal voltage as the reference voltage value, while also configuring a reasonable voltage regulation dead zone. When the system faces a sudden increase in load, the actual AC voltage will drop instantaneously, and the absolute value of the difference between it and the reference voltage will exceed the preset voltage regulation dead zone. At this time, the control unit will immediately calculate the voltage deviation, which is the reference voltage minus the actual voltage. This deviation is amplified by the reactive power regulation coefficient to generate a reactive power command, driving the energy storage converter to output capacitive reactive power to support voltage recovery. When the system enters the steady-state operation phase, the actual voltage rises back to near the reference voltage, and the absolute value of the deviation is less than the voltage regulation dead zone, the voltage deviation will be forcibly returned to zero, and the energy storage converter will automatically withdraw from reactive power support.

[0047] Based on the theory of static voltage stability in power systems, this design utilizes a dead-zone mechanism to achieve threshold control of reactive power regulation. This design not only avoids the frequent actions and power oscillations caused by small voltage fluctuations in traditional continuous regulation strategies, but also ensures that the energy storage converter can provide precise reactive power compensation during critical transient phases when voltage support is truly needed. Simultaneously, this design, in coordination with active power frequency support, effectively solves the power distribution imbalance problem caused by voltage fluctuations in multi-unit parallel systems. It significantly improves the voltage quality and dynamic response capability of the system under drastic load changes, extends the service life of the energy storage equipment, and creates more stable operating conditions for the diesel generator sets.

[0048] More specifically, after obtaining the voltage deviation, the following steps are also included: The reactive power change of the energy storage converter is controlled to be the product of the set voltage regulation coefficient and the voltage deviation.

[0049] In practical implementation, the system monitors the bus voltage of the parallel system in real time and compares it with the rated voltage to determine the voltage deviation. When the system load increases sharply, causing a voltage drop, this voltage deviation enters the positive range. The control system multiplies the voltage deviation by a pre-set voltage regulation coefficient, generating a positive reactive power change command. This command drives the energy storage converter to output capacitive reactive power, thereby supporting the voltage. When the load decreases sharply, causing a voltage rise, the voltage deviation becomes negative. The multiplication operation automatically generates a negative reactive power change, prompting the energy storage converter to absorb reactive power and suppress voltage overshoot. This design principle is based on the static characteristic relationship between reactive power and voltage in the power system. By using linear proportional control, the reactive power output strictly corresponds to the voltage deviation, avoiding voltage fluctuations caused by dead zones and hysteresis effects in traditional hierarchical control.

[0050] The change in reactive power is obtained by the following formula:

[0051]

[0052]

[0053] in, This represents the change in reactive power of the energy storage converter. This is the voltage regulation coefficient; For the AC port voltage deviation of the energy storage converter; The set reference voltage; For AC voltage measurement; This is the voltage regulation dead zone; when the voltage deviation is within the set dead zone, the reactive power change of the energy storage converter is 0.

[0054] Compared with existing technologies, this solution not only achieves rapid response and smooth transition in voltage regulation, effectively suppressing voltage flicker caused by load fluctuations, but also separates reactive power regulation from the diesel generator set, reducing the regulation burden on the generator excitation system and extending the service life of the equipment. Simultaneously, this voltage regulation mechanism works in conjunction with the frequency regulation strategy described above, enabling the energy storage converter to comprehensively improve the system's power quality under active-reactive power decoupling control.

[0055] More specifically, controlling the active power output of the energy storage converter includes the following steps: The active power reference command issued by the upper control system, the first active power change, and the second active power change are added together to obtain the composite active power command. The reactive power reference command issued by the upper control system is added to the reactive power change to obtain the composite reactive power command; The output of the energy storage converter is controlled by the synthesized active power command and the synthesized reactive power command; and the synthesized active power command is limited to the current allowed active power limit of the energy storage converter and the synthesized reactive power command is limited to the current allowed reactive power limit of the energy storage converter at the control layer.

[0056] In the implementation process, the upper-level control system comprehensively evaluates the current state of charge of the energy storage battery and the fuel economy curve of the diesel generator set, and issues active power reference commands to the lower level to maintain the long-term energy balance of the system. At the same time, it issues reactive power reference commands for steady-state voltage compensation based on line losses or network topology. When the multi-unit parallel system faces sudden load disturbances, the lower-level controller of the energy storage converter, with the help of locally acquired electrical quantities, quickly and autonomously calculates the first active power change to suppress frequency drops, the second active power change to prevent generator reverse power and provide inertia support, and the reactive power change to actively respond to bus voltage fluctuations. The system directly superimposes the upper-level steady-state reference commands with the lower-level transient changes to generate real-time composite active power commands and composite reactive power commands. Before execution, physical safety boundary constraints are introduced to forcibly limit the composite commands that exceed the current dynamic and static limit capacity of the converter to within the allowable range.

[0057] Compared to the response delays caused by relying entirely on upper-level communication scheduling in existing technologies, or the system energy distribution imbalances caused by simply using local control, the beneficial effects of this composite command mechanism are as follows: it leverages the advantages of high bandwidth and zero delay in local transient regulation to promptly curb the deterioration of frequency and voltage, while ensuring global state of charge balance and unit operation economy through the introduction of reference commands; coupled with strict underlying power limiting logic, it not only effectively resolves the command conflicts and equipment overload risks that may occur in multi-objective optimization control, but also fundamentally solves the technical problem of balancing regulation quality and system safety in diesel-storage hybrid systems under complex grid conditions.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for multi-unit parallel frequency modulation of a diesel-storage hybrid system, characterized in that, Includes the following steps: Obtain the actual frequency of the parallel system during operation; The actual frequency is filtered to obtain the second reference frequency; The third reference frequency is calculated based on the set first reference frequency and the second reference frequency; Based on the difference logic between the actual frequency and the frequency reference value, the first frequency deviation for frequency support is calculated, and the first active power change of the energy storage converter is calculated based on the first frequency deviation. Calculate the second frequency deviation between the third reference frequency and the actual frequency. Based on the directional relationship between the second frequency deviation and the actual frequency change rate, calculate the second active power change of the energy storage converter to provide inertia support. The first active power change and the second active power change are superimposed on the active power command of the energy storage converter to control the active power output of the energy storage converter.

2. The multi-unit parallel frequency modulation method for a diesel-storage hybrid system according to claim 1, characterized in that, In the step of filtering the actual frequency to obtain the second reference frequency, the filtering process is a second-order low-pass filter, and its complex frequency domain transfer function model is: ； in, The complex frequency domain expression for the second reference frequency. The complex frequency domain expression for the actual frequency. For the Laplace operator, The set natural angular frequency of the filter. is the damping ratio of the filter.

3. The multi-unit parallel frequency modulation method for a diesel-storage hybrid system according to claim 1, characterized in that, The step of calculating the first frequency deviation used for frequency support has the following difference logic: Set the frequency dead zone; When the actual frequency is greater than the sum of the first reference frequency and the frequency modulation dead zone, the first frequency deviation is the sum of the first reference frequency and the frequency modulation dead zone minus the actual frequency. When the actual frequency is less than the difference between the second reference frequency and the frequency modulation dead zone, the first frequency deviation is the second reference frequency minus the frequency modulation dead zone minus the actual frequency. When the actual frequency is between the difference between the second reference frequency and the frequency modulation dead zone and the sum of the first reference frequency and the frequency modulation dead zone, the first frequency deviation is zero.

4. The multi-unit parallel frequency modulation method for a diesel-storage hybrid system according to claim 3, characterized in that, The calculation of the first active power change of the energy storage converter based on the first frequency deviation specifically includes the following steps: The first change in active power is the product of the preset frequency modulation coefficient and the first frequency deviation.

5. The multi-unit parallel frequency modulation method for a diesel-storage hybrid system according to claim 1, characterized in that, The calculation of the third reference frequency specifically includes the following steps: The arithmetic mean of the first reference frequency and the second reference frequency is used as the third reference frequency.

6. The multi-unit parallel frequency modulation method for a diesel-storage hybrid system according to claim 5, characterized in that, When calculating the second active power change of the energy storage converter to provide inertia support, the process also includes calculating the initial active power change of inertia, specifically including the following steps: The difference between the third reference frequency and the actual frequency is taken as the second frequency deviation; Determine the sign and direction relationship between the actual rate of change of frequency and the second frequency deviation; When the second frequency deviation and the actual frequency change rate have the same sign and their product is greater than zero, the initial inertia active change is the product of the set inertia coefficient and the actual frequency change rate. When the second frequency deviation has the opposite sign to the actual frequency change rate, or when at least one of them is zero, the active change in the initial inertia is zero.

7. The multi-unit parallel frequency modulation method for a diesel-storage hybrid system according to claim 6, characterized in that, After calculating the initial change in inertia, a smoothing process is also included, specifically comprising the following: The initial change in active power is processed by a first-order low-pass filter to obtain the final change in the second active power. Its complex frequency domain transfer function model is: ； in, This is the complex frequency domain expression for the change in the second active power. This is the complex frequency domain expression for the active change of the initial inertia. For the Laplace operator, This is the set filter time constant.

8. The multi-unit parallel frequency modulation method for a diesel-storage hybrid system according to claim 1, characterized in that, It also includes a reactive power support determination step based on actual voltage: Obtain the actual AC side voltage during the operation of the parallel system; Set the reference voltage and voltage regulation dead zone; When the absolute value of the difference between the actual AC side voltage and the reference voltage is greater than the voltage regulation dead zone, the voltage deviation is the difference between the reference voltage and the actual AC side voltage. The voltage deviation is zero when the absolute value of the difference between the actual AC side voltage and the reference voltage is not greater than the voltage regulation dead zone.

9. The multi-unit parallel frequency modulation method for a diesel-storage hybrid system according to claim 8, characterized in that, After obtaining the voltage deviation, Includes the following steps: The reactive power change of the energy storage converter is controlled to be the product of the set voltage regulation coefficient and the voltage deviation.

10. The multi-unit parallel frequency modulation method for a diesel-storage hybrid system according to claim 9, characterized in that, The control of the active power output of the energy storage converter specifically includes the following steps: The active power reference command issued by the upper control system, the first active power change, and the second active power change are added together to obtain the composite active power command. The reactive power reference command issued by the upper control system is added to the reactive power change to obtain the composite reactive power command; The output of the energy storage converter is controlled by the synthesized active power command and the synthesized reactive power command; and the synthesized active power command is limited to the current allowed active power limit of the energy storage converter and the synthesized reactive power command is limited to the current allowed reactive power limit of the energy storage converter at the control layer.

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