A control method for an energy storage inverter coupled to a diesel generator

Abstract

This invention discloses a control method for an energy storage inverter coupled to a diesel generator, including a harmonic suppression step, a reactive power compensation step, and a bus adjustment step. The harmonic suppression step includes: dynamically adjusting the proportional control parameters of the current loop control based on the diesel generator voltage, and introducing a filtering module in the feedforward signal processing. The reactive power compensation step includes: actively outputting reactive power compensation based on load characteristics to offset the influence of capacitive loads on the diesel generator power factor. The bus adjustment step includes: real-time detection of whether the AC side voltage exhibits characteristics of the diesel generator; if so, adjusting the bus reference voltage value to a safe range close to the overvoltage protection value. This invention's control method for an energy storage inverter coupled to a diesel generator improves the adaptability of the energy storage inverter to different diesel generators.

Description

Technical Field

[0001] This invention relates to the field of energy storage system technology, and in particular to a control method for an energy storage inverter coupled to a diesel generator. Background Technology

[0002] With the increasing popularity of residential energy storage inverters, consumers are demanding more and more applications for them. The combination of a residential energy storage inverter and a diesel generator is gaining popularity. However, current technologies often suffer from poor compatibility between diesel generators and residential energy storage inverters.

[0003] The above background information is provided only to aid in understanding the concept and technical solution of this invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above information was disclosed on the filing date of this patent application, the above background information should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a control method for an energy storage inverter coupled with a diesel generator, thereby improving the adaptability of the energy storage inverter to different diesel generators.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention discloses a control method for an energy storage inverter coupled to a diesel generator, comprising a harmonic suppression step, a reactive power compensation step, and a bus adjustment step, wherein...

[0007] The harmonic suppression step includes: dynamically adjusting the proportional control parameters of the current loop control according to the voltage of the diesel generator, and introducing a filtering module in the feedforward signal processing;

[0008] The reactive power compensation step includes: actively outputting reactive power compensation amount according to load characteristics to offset the influence of capacitive load on the power factor of diesel generator;

[0009] The bus adjustment steps include: real-time detection of whether the voltage on the AC side has the characteristics of a diesel generator; if so, adjusting the bus reference voltage value to a safe range close to the overvoltage protection value.

[0010] Furthermore, the harmonic suppression step specifically includes periodically performing the following steps:

[0011] A1: Collect the voltage phase signal of the diesel generator and adjust the proportional control parameters of the current loop control based on the voltage phase signal of the diesel generator;

[0012] A2: In the feedforward signal processing, a bandpass filter module is introduced, wherein the cutoff frequency of the bandpass filter module is set to ±5Hz of the rated power of the diesel generator.

[0013] Further, step A1 specifically includes: acquiring the voltage phase signal of the diesel generator, determining whether the voltage phase of the diesel generator is within a first preset range, and if it is within the first preset range, adjusting the proportional control parameter of the current loop control to the first preset multiple of the default value; if it is not within the first preset range, the proportional control parameter of the current loop control is the default value.

[0014] Furthermore, the first preset range includes [π / 3, 2π / 3] and [-2π / 3, -π / 3], and the first preset multiple is 1.2 to 1.8 times.

[0015] Furthermore, the harmonic suppression step specifically includes periodically determining whether the first condition, the second condition, and the third condition are met to determine the load characteristics; when the first condition, the second condition, and the third condition are all met, the reactive power compensation is actively output to offset the capacitive load.

[0016] The steps for determining whether the first condition is met include: obtaining the phase of the load current and the phase of the diesel engine voltage, and calculating the phase difference between the load current and the diesel generator voltage = load current phase - diesel engine voltage phase, and determining whether the phase difference between the load current and the diesel generator voltage is within a second preset range. If it is, then the first condition is met.

[0017] The steps for determining whether the second condition is met include: determining whether the effective value of the load current is greater than a second preset multiple of the rated current of the energy storage inverter; if so, the second condition is met.

[0018] The step of determining whether the third condition is met includes: determining whether the absolute value of the instantaneous peak value of the diesel generator voltage is greater than a third preset multiple of its normal theoretical peak value in multiple consecutive cycles; if so, the third condition is met.

[0019] Furthermore, the second preset range is greater than 15° and less than 180°, the second preset multiple is 10%~20%, and the third preset multiple is 1.1~1.3 times.

[0020] Furthermore, in the harmonic suppression step, when actively outputting reactive power compensation, the reactive power compensation is output at a preset rate, wherein the preset rate of increase is 100-500 var / s.

[0021] Furthermore, the busbar adjustment step specifically includes:

[0022] The effective value and instantaneous peak value of the AC voltage are periodically acquired, and the absolute value of the instantaneous peak value is compared with that of the effective value. Is the ratio of the multiples greater than or equal to the first threshold?

[0023] When the absolute value of the instantaneous voltage peak is detected at least three times consecutively, the voltage RMS value is equal to the absolute value of the voltage peak. If the ratio is greater than or equal to the first threshold, the bus reference voltage value is set to the smaller of the first value and the second value, wherein the first value is equal to the sum of the absolute value of the instantaneous peak voltage of the diesel generator and the second threshold, and the second value is equal to the difference between the overvoltage protection value of the diesel generator and the third threshold.

[0024] Furthermore, the first threshold is 1.1~1.3, the second threshold is 2V~4V, and the third threshold is 5V~15V.

[0025] In a second aspect, the present invention discloses a computer-readable storage medium storing a computer program, wherein the computer program is configured to be run by a processor to perform the control method of the energy storage inverter described in the first aspect.

[0026] Compared with existing technologies, the beneficial effects of this invention are as follows: The control method for the energy storage inverter coupled with a diesel generator proposed in this invention systematically solves the instability problem during the coupled operation of the diesel generator and the energy storage inverter through the synergistic effect of "active current loop optimization" and "DC bus adaptive adjustment". Specifically, it effectively suppresses current harmonics through dynamic parameter variation and optimized feedforward control, offsets the capacitive reactive component of the load by actively outputting inductive reactive power, and effectively avoids the problem of uncontrollable current distortion caused by excessively high AC side voltage in residential energy storage inverters through automatic bus adjustment. The synergistic integration of the above control methods not only effectively suppresses the problem of diesel generator voltage rise in special scenarios, but also improves the adaptability of residential energy storage inverters to different diesel generators.

[0027] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0028] Figure 1 This is a flowchart of the control method for an energy storage inverter coupled to a diesel generator according to a preferred embodiment of the present invention;

[0029] Figure 2 This is a coupling diagram of a residential energy storage inverter and a diesel generator according to a specific embodiment of the present invention;

[0030] Figure 3 This is the current loop control structure diagram of the residential energy storage inverter in diesel generator mode;

[0031] Figure 4 It is a dynamic parameter variable flowchart;

[0032] Figure 5a This is a flowchart illustrating the process of using a bandpass filter;

[0033] Figure 5b This is a diagram showing the effect of using a bandpass filter;

[0034] Figure 6a This is a schematic diagram of a purely resistive load, with inverter charging PF=1.0;

[0035] Figure 6b This is a schematic diagram of a capacitive load being charged by an inverter with PF=1.0.

[0036] Figure 6c This is a schematic diagram of a capacitive load diesel generator with PF=1.0;

[0037] Figure 7 This is the flowchart for automatic bus adjustment. Detailed Implementation

[0038] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0039] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as "connected to" another component, it can be directly connected to or indirectly connected to that other component. Furthermore, a connection can be used for both fixing and circuit / signal connectivity.

[0040] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0042] Based on the existing technology, there is often a problem of poor compatibility between diesel generators and residential energy storage inverters. Through research, it was found that there are two problems in the coupling process between residential energy storage inverters and diesel generators: (1) Capacitive loads and high-frequency harmonics of residential energy storage inverters will reduce the excitation of diesel generators and increase the output voltage. The higher voltage is easy to trigger overvoltage protection. On the other hand, when the voltage peak exceeds the DC bus of the residential energy storage inverter, an uncontrollable rectifier circuit will be formed, resulting in uncontrollable charging current and severe current distortion; (2) System-level resonance will occur during the coupling process, which is manifested as voltage and frequency fluctuating and changing slowly in a periodic manner. The greater the charging power of the diesel generator to the residential energy storage inverter, the more obvious the above problems are. If, in order to address the above problems, only diesel generators with larger quotas or diesel generators of a specific brand are selected to achieve a better match with the residential energy storage inverter, it will limit consumers' freedom of choice of diesel generators and is not conducive to the market promotion of residential energy storage inverter products. If the compatibility issue in the control of residential energy storage inverters is addressed by increasing the bus voltage or limiting the charging current, there will still be issues such as insufficient improvement in current harmonics, failure to resolve the problem of increased output voltage due to capacitive loads during the charging process of residential energy storage inverters, and limitation of diesel generator output power; thus, the compatibility between diesel generators and energy storage inverters remains poor.

[0043] Based on the above research, such as Figure 1 As shown, a preferred embodiment of the present invention discloses a control method for an energy storage inverter coupled to a diesel generator, including a harmonic suppression step, a reactive power compensation step, and a bus adjustment step. These steps are not sequential and can all be executed synchronously and periodically. Each step is described below.

[0044] A: Harmonic suppression steps

[0045] Step A includes: dynamically adjusting the proportional control parameters of the current loop control based on the voltage of the diesel generator, and introducing a filtering module in the feedforward signal processing.

[0046] Specifically, step A includes:

[0047] A1: Dynamic variable parameters: Collect the voltage phase signal of the diesel generator and adjust the proportional control parameters of the current loop control according to the voltage phase signal of the diesel generator.

[0048] Specifically, this step involves: acquiring the voltage phase signal of the diesel generator, determining whether the voltage phase of the diesel generator is within a first preset range, and if it is within the first preset range, adjusting the proportional control parameter of the current loop control to a first preset multiple of the default value; otherwise, the proportional control parameter of the current loop control remains at the default value. Specifically, the first preset range includes [π / 3, 2π / 3] and [-2π / 3, -π / 3], and the first preset multiple is 1.2 to 1.8 times.

[0049] A2: Optimize feedforward control: Introduce a bandpass filter module in the feedforward signal processing, where the cutoff frequency of the bandpass filter module is set to ±5Hz of the rated power of the diesel generator.

[0050] To address the high voltage harmonics characteristic of diesel generators, a dedicated bandpass filter with extremely small phase deviation near the rated frequency (e.g., ±5Hz) was designed. Unlike typical low-pass filters, this filter removes high-frequency harmonics while preserving the original power frequency signal to the greatest extent possible, and ensures the fastness of the power frequency feedforward signal. The sampled AC side voltage is filtered before being used as the feedforward signal, significantly reducing secondary interference to the generator excitation caused by harmonics introduced by the feedforward.

[0051] B: Reactive power compensation steps

[0052] Step B includes: actively outputting reactive power compensation based on load characteristics to offset the impact of capacitive load on the diesel generator power factor. Further, the capacitive characteristics of the load are determined based on the phase difference between the load current and the diesel generator voltage, and the energy storage inverter is controlled to actively output corresponding reactive power compensation based on these characteristics to offset the impact of capacitive load on the diesel generator power factor.

[0053] Specifically, step B includes periodically determining whether the first, second, and third conditions are met to determine the load characteristics. When all three conditions are met, reactive power compensation is actively output to offset the capacitive load.

[0054] The steps for determining whether the first condition is met (load capacitive characteristic criterion) include: obtaining the phase of the load current and the phase of the diesel engine voltage, and calculating the phase difference between the load current and the diesel generator voltage = load current phase - diesel engine voltage phase; determining whether the phase difference between the load current and the diesel generator voltage is within a second preset range; if so, the first condition is met; wherein, the second preset range is greater than 15° and less than 180°; this range indicates that the load current leads the voltage, exhibiting a clear capacitive characteristic, which may have an adverse effect on the generator excitation. If the angle is negative, it indicates that it is inductive and does not require compensation.

[0055] The steps for determining whether the second condition is met (load validity criterion) include: determining whether the effective value of the load current is greater than a second preset multiple of the rated current of the energy storage inverter; if so, the second condition is met. The second preset multiple is 10%~20%, and the rated current of the energy storage inverter refers to the value of the inverter's nominal rated power / rated voltage. This condition is used to filter out small capacitive components caused by light loads or noise, avoiding unnecessary system responses to insignificant loads and ensuring that compensation actions are meaningful.

[0056] The steps for determining whether the third condition (voltage anomaly criterion) is met include: determining whether the instantaneous absolute peak value of the diesel generator's output voltage continuously exceeds a third preset multiple of its normal theoretical peak value for multiple consecutive cycles (e.g., 3 cycles). If so, the third condition is met. The third preset multiple is 1.1 to 1.3 times. This condition is a crucial "result verification" criterion, directly indicating that the capacitive load has actually caused an abnormal increase in the diesel generator's output voltage, requiring intervention.

[0057] When the first, second, and third conditions mentioned above are all met, the controllable inductive reactive power compensation is output by the energy storage inverter. This inductive reactive power is out of phase with the capacitive reactive power of the load. The superposition of the two can significantly reduce the total reactive power demand at the diesel generator port, thereby compensating its power factor to close to 1.0, effectively avoiding the problems of generator excitation weakening and abnormal output voltage rise caused by capacitive load.

[0058] According to the formula Q inv = i_rms load * u_rms grid *sin The amount of reactive power that needs to be compensated according to the calculation theory. Among them, Q_ inv This is the theoretical reactive power compensation amount. i_rms_load For load current, u_rms_grid This represents the effective voltage value of the diesel generator. This represents the phase difference between the load current and the diesel generator voltage.

[0059] To accommodate load fluctuations and avoid overcompensation, the actual output compensation is usually set as a percentage of the theoretical value, preferably 0.4-0.6 (e.g., 0.5 times).

[0060] In this step, when actively outputting reactive power compensation, the reactive power compensation is output at a preset rate, where the preset rate of increase is 100-500 var / s.

[0061] After reactive power compensation is implemented, the energy storage system continuously monitors the above conditions. If any condition is no longer met due to compensation taking effect or load changes, the system automatically exits the reactive power compensation state. This mechanism ensures the accuracy and economy of compensation, avoiding unnecessary energy consumption.

[0062] C: Busbar Adjustment Steps

[0063] Step C includes: real-time detection of whether the AC side voltage has the characteristics of a diesel generator; if so, adjusting the bus reference voltage value to a safe range close to the overvoltage protection value.

[0064] The AC side voltage characteristics are detected in real time. When the voltage is identified as having the typical high peak distortion characteristics of a diesel generator, the reference value of the DC bus voltage is automatically increased to prevent uncontrolled rectification and current distortion caused by the instantaneous value of AC voltage exceeding the DC bus voltage.

[0065] Specifically, step B includes:

[0066] The effective value and instantaneous peak value of the AC voltage are periodically acquired, and the absolute value of the instantaneous peak value is compared with that of the effective value. Whether the ratio of times is greater than or equal to the first threshold; where the first threshold is 1.1 to 1.3.

[0067] When the absolute value of the instantaneous voltage peak is detected at least three times consecutively, the voltage RMS value is equal to the absolute value of the voltage peak. If the ratio is greater than or equal to the first threshold, it indicates that a diesel generator is currently connected to the AC side. Therefore, the bus reference voltage value is set to the smaller of the first and second values. The first value is equal to the sum of the absolute value of the instantaneous peak voltage of the diesel generator and the second threshold, and the second value is equal to the difference between the overvoltage protection value of the diesel generator and the third threshold. The second threshold is 2V~4V, and the third threshold is 5V~15V.

[0068] The control method for the energy storage inverter coupled to the diesel generator in the preferred embodiment of the present invention is applied to... Figure 2The diagram shows the coupling connection circuit between the residential energy storage inverter and the diesel generator. The residential energy storage inverter 10 includes a bidirectional DC / DC circuit 11 (DC / DC section) and a DC / AC circuit 12 (DC / AC section). The battery 40 is boosted / buckled through the bidirectional DC / DC circuit 11 to establish a stable bus voltage on the DC bus (BUS). This bus voltage is then converted to AC voltage by the DC / AC circuit 12 and output from the AC output port; alternatively, the DC / AC circuit 12 converts the AC voltage on the AC side to DC voltage, which is then converted back to DC voltage by the bidirectional DC / DC circuit 11 and used to charge the battery 40. When the diesel generator 20 is connected to the AC output port of the residential energy storage inverter 10, the two are coupled once the inverter 10 detects that the voltage frequency of the diesel generator 20 is normal. If the AC output port of the residential energy storage inverter 10 is simultaneously connected to the load 30, the relationship between the inverter current i_inv, the load current i_load, and the diesel generator current i_gen at the AC output port is as follows: Figure 2 As shown.

[0069] The following combination Figure 2 The coupling circuit between the residential energy storage inverter and the diesel generator shown provides a further detailed explanation of the control method for the energy storage inverter coupled to the diesel generator.

[0070] The control method for the energy storage inverter coupled with the diesel generator addresses the problem that the capacitive load of the diesel generator and the high-frequency harmonics of the residential energy storage inverter can lead to a decrease in the excitation of the diesel generator and an increase in the output voltage. It proposes a multi-method fusion strategy that automatically adjusts the DC bus (i.e., the bus adjustment step) while optimizing the current control (including harmonic suppression steps and reactive power compensation steps).

[0071] The optimized current control section will be introduced first.

[0072] In this specific embodiment, the optimized current control includes current harmonic suppression and current reference angle control. The harmonic suppression scheme includes a PI controller and a PR controller with dynamic parameter variation, as well as a second-order bandpass filter added to the feedforward. The current reference angle control is achieved by actively outputting reactive power Qinv to calculate the current reference phase offset θ and finally applying it to the current reference.

[0073] like Figure 3 The diagram shows the current loop control structure of a residential energy storage inverter in diesel generator mode. This current loop control includes PI (Proportional-Integral) control, PR (Proportional-Resonant) control, and feedforward control. Through the combined action of harmonic suppression and reactive power compensation steps, effective current improvement in diesel generator mode is achieved. (Reference) Figure 3 The voltage phase of the diesel generator is φ. The reactive power to be compensated, Qinv, is calculated by actively inputting reactive power. The current reference phase offset executed by the actual current control is θ. Then, the actual current reference Iref is the current reference amplitude Id multiplied by sin(θ+φ), and finally applied to the PI controller and PR controller. The instantaneous voltage value of the diesel generator is used as FW (Feedforward). However, the voltage of the diesel generator usually has large harmonics. If FW is used directly for current control, current harmonics will be introduced. After adding a second-order bandpass filter after the feedforward, the harmonic signal can be effectively filtered out, greatly reducing the current harmonics introduced by the feedforward control.

[0074] Optimized current control comprises three parts: dynamic parameter variation, optimized feedforward control, and active reactive power output. Dynamic parameter variation and optimized feedforward control can achieve harmonic suppression, while active reactive power output enables current reference angle control. The following sections will describe each of these three parts in detail.

[0075] (1) Dynamic variable parameters

[0076] Based on the waveform characteristics, the current changes rapidly at the peaks and troughs; therefore, in actual control, the parameters should be increased at these points. The proportional control coefficient kp parameter of the PI and PR controllers is adjusted according to the voltage phase, as detailed in the following process: Figure 4 As shown. Given that the voltage phase ψ of the diesel generator is between -π and π, when the angle of the voltage phase ψ is between π / 3 and 2π / 3 or between -2π / 3 and -π / 3, the kp parameter reaches its maximum at the peak and valley, with a maximum value of 1.3 to 1.8 times kp_set. In this embodiment, it is taken as 1.5 times kp_set. When the angle of the voltage phase ψ of the diesel generator is in other ranges, the kp parameter is directly taken as kp_set; where kp_set is the default proportional coefficient of the PI controller and the PR controller.

[0077] (2) Optimize feedforward control

[0078] The grid-connected current loop control of a residential energy storage inverter consists of three parts: PI control, PR control, and feedforward control. The feedforward is the sampled AC side voltage, which in this scheme is the diesel generator voltage. The most significant characteristic of feedforward is its ability to accelerate current response. However, based on the waveform characteristics of the diesel generator voltage, it contains significant harmonics. Directly using this voltage for feedforward control would generate substantial current harmonics, and the high-frequency harmonics in the residential energy storage inverter would reduce the excitation of the diesel generator. Therefore, the voltage feedforward needs to be optimized to reduce the harmonics introduced by the feedforward.

[0079] In this embodiment, a well-designed filter effectively removes high-frequency components and exhibits no phase deviation within ±5Hz of the diesel generator's rated frequency. The specific filter design method includes:

[0080] A21: Use MATLAB filter design tools to design a second-order bandpass filter: set the upper and lower limits of the cutoff frequency, select the filter type, and finally obtain the parameters of the second-order bandpass filter.

[0081] A22: Verify the filtering effect using circuit simulation software. In the PSIM environment, replace the filter coefficients with those designed in MATLAB, and set the PSIM environment's running step size to match the step size of the residential energy storage inverter control chip. Observe the simulation effect. If the filtered waveform is distorted or has a phase delay, return to step A21 to fine-tune the parameters to obtain the optimal filtering parameters.

[0082] like Figure 5a and Figure 5b The diagram shows the effect of using the optimal filtering parameters in the PSIM environment. This not only effectively filters out high-frequency interference components but also ensures that the filtered signal is in phase with the original signal, with virtually no phase delay. In the waveform diagram, the red line corresponds to Vinit, the voltage waveform without high-frequency harmonics; the blue line corresponds to Vo, the voltage waveform after adding a 20kHz high-frequency harmonic; and the green line corresponds to Vo_Filter, the voltage waveform after filtering using a second-order bandpass filter.

[0083] A23: Transplant the verified filter parameters into the control chip of the residential energy storage inverter.

[0084] By optimizing the feedforward signal, the introduction of high-order harmonic signals into the current loop of the residential energy storage inverter can be significantly reduced, thereby improving the current harmonics of the diesel generator. This also alleviates the problem of generator rotor excitation being affected and output voltage rising due to high-order harmonics from the residential energy storage inverter.

[0085] (3) Actively output reactive power

[0086] When a diesel generator is simultaneously operating under load and charging a residential energy storage inverter, its structure is as follows: Figure 2 As shown. According to Kirchhoff's Current Law (KCL), the inverter current at the grid port of the residential energy storage inverter... Load current and diesel generator current The relationship satisfies the following equation:

[0087]

[0088] When the load is purely resistive, the inverter maintains a charging power factor of 1.0, and the diesel generator's discharging power factor is also 1.0, with voltage and current in phase. Figure 6a As shown, where , , These are the representations of i_inv, i_load, and i_gen in the complex plane, respectively. When the load is capacitive, if the inverter maintains a charging power factor of 1.0, the diesel generator's output current will lead the voltage. Figure 6b As shown, the diesel generator exhibits a capacitive load at this point, ultimately affecting the generator rotor excitation and increasing the output voltage. When the load is capacitive, actively outputting reactive power within the inverter's allowable range to offset the capacitive load changes the inverter's charging power factor, thus ensuring that the diesel generator's discharging power factor is also 1.0, preventing current lead. Figure 6c As shown, this can greatly reduce the voltage rise problem caused by capacitance.

[0089] Residential energy storage inverters are powered by batteries, and continuous reactive power output also consumes electrical energy. Therefore, determining when and how much reactive power compensation is appropriate is a challenge in this embodiment. This embodiment specifically adopts the following scheme: sampling the instantaneous value of the load current. Diesel generator voltage The phase of the load current can be obtained through phase-locked loop. Diesel generator voltage phase The effective value of the load current can be obtained through sampling and calculation. Effective value of diesel generator voltage The phase difference between the load current and the diesel generator is denoted as... , Active reactive power output is triggered when the following conditions are met simultaneously: (a) (1) The angle is greater than 15° and less than 180°. This indicates that there is a capacitive load, and the inverter needs to actively output reactive power to offset it; (2) The effective value of the load current (c) The absolute value of the instantaneous peak voltage of the diesel generator, VAC_INS_MAX, is greater than 15% of the rated current for three consecutive cycles. 1.2 times that.

[0090] Adding the above conditions can prevent false triggering or unnecessary triggering of the residential energy storage inverter to actively output reactive power due to very small reactive power. When the conditions are met, actively outputting reactive power can reduce voltage rise caused by capacitive loads. Theoretically, the required reactive power output should be... *sin .

[0091] To adapt to load fluctuations and avoid overcompensation, the actual output compensation is usually set as a percentage of the theoretical value, preferably 0.4-0.6 (e.g., 0.5 times). Considering the real-time fluctuations in load, the actual output reactive power is sampled and increased slowly, by 200 var per second. If the above conditions are no longer met during the increase, reactive power compensation can be stopped, thus saving energy by avoiding excessive reactive power output due to load fluctuations.

[0092] In summary, in specific embodiments of the present invention, current harmonics are effectively suppressed through dynamic parameter variation and optimized feedforward control. Current harmonics affect the excitation of the diesel generator; by optimizing current control to reduce current harmonics, their impact on the generator's excitation can be minimized, ultimately suppressing the increase in output voltage caused by reduced excitation. On the other hand, capacitive reactive power is reduced through active reactive power output. When the capacitive load is large, it also leads to reduced generator excitation and increased output voltage. By adjusting the current reference angle, active reactive power output can be achieved, offsetting some of the impact of reduced capacitive reactive power on the generator's excitation, thereby reducing the increase in output voltage.

[0093] Then, the automatic adjustment DC bus section will be introduced.

[0094] For grid-connected inverters, when the instantaneous voltage on the grid side exceeds the bus voltage, the grid voltage and the body diode of the inverter's switching transistors will form an uncontrollable rectifier circuit, resulting in uncontrollable current distortion and large current distortion. Although the aforementioned method of optimizing the current control section effectively reduces the problem of output voltage rise caused by the influence of diesel generator rotor excitation, the performance of diesel generators on the market varies, and this effect will increase with the increase of diesel generator power. Therefore, in this specific embodiment, the adaptability to diesel generators is improved by appropriately adjusting the DC bus of the residential energy storage inverter.

[0095] Automatic bus adjustment strategy Figure 7 As shown, when the generator mode is identified or set during grid connection, the DC bus will raise or lower the closed-loop reference value of the bus according to the peak voltage on the grid side.

[0096] refer to Figure 7 The process is executed periodically, with the execution cycle being the same as the control cycle. For example, in this specific embodiment, both the execution cycle and the control cycle are 50 μs. Figure 7 The process shown includes the following steps:

[0097] C1: Calculate the effective value of the output voltage (voltage of the diesel generator), VAC_RMS, and continue to step C2;

[0098] C2: Record the instantaneous peak value of the output voltage (diesel generator voltage) VAC_INS_MAX, and continue to execute step C3;

[0099] C3: Judgment .2. If true, proceed to step C5; otherwise, proceed to step C4.

[0100] Among them, this step determines .2 Whether it is successful depends on whether the current grid voltage has the characteristics of a diesel generator;

[0101] C4: Set the bus reference voltage Vbus_Ref = VBUS_RATE, clear the counter to zero (i.e., set Trip_cnt = 0), and continue to step C9;

[0102] Here, VBUS_RATE is the default value of the bus reference voltage. In this step, the bus reference is set according to the default value VBUS_RATE, which is equivalent to no adjustment.

[0103] C5: Increment the trigger counter by 1, i.e., Trip_cnt++;

[0104] C6: Determine if Trip_cnt≥3 is true. If it is, proceed to step C7; otherwise, proceed to step C8.

[0105] C7: Set the bus reference voltage Vbus_Ref = min{|VAC_INS_MAX|+3, BUS_OV-10}, and continue to step C9;

[0106] C8: Set the bus reference voltage Vbus_Ref = VBUS_RATE, and continue to step C9;

[0107] C9: Execute bus adjustment command.

[0108] In summary, this specific embodiment selects the effective value of the output voltage VAC_RMS and the maximum instantaneous absolute value of the output voltage |VAC_INS_MAX| for judgment. If this characteristic is present, the counter Trip_cnt is incremented by one, and the bus reference value is adjusted only after at least three consecutive satisfactions, which can reduce false judgments. The bus reference voltage cannot be too large, and the ripple size and overvoltage protection point must be considered. In this specific implementation, it is designed as the overvoltage protection value BUS_OV minus 10V. If the condition is not met, the bus reference voltage executes the default value VBUS_RATE.

[0109] By automatically adjusting the bus, the problem of uncontrollable current and large current distortion caused by excessive grid voltage in residential energy storage inverters can be effectively avoided.

[0110] The control method for an energy storage inverter coupled to a diesel generator, provided by a preferred embodiment of the present invention, was applied to several diesel generators for testing. Through the fusion strategy of the two parts (optimized current control and automatic DC bus adjustment), significant improvements were made to the voltage rise and large current harmonics issues. Especially in scenarios where the diesel generator is simultaneously charging a residential energy storage inverter and operating a capacitive load, if the inverter does not actively output reactive power to improve the power factor of the diesel generator, the output voltage of the diesel generator rises significantly. When the above method is used to actively output reactive power, the output voltage of the diesel generator no longer rises and can be stabilized within a certain range, and the power is not limited. Table 1 below shows the data obtained from testing on one diesel generator.

[0111] Table 1. Data obtained from tests on a diesel generator.

[0112] In summary, this invention integrates multiple control methods (including dynamic parameter variation, optimized feedforward control, active reactive power compensation based on load characteristics, and automatic bus adjustment) to identify the characteristics of diesel generators and execute this integrated strategy. This not only effectively suppresses the problem of diesel generator voltage rise in special scenarios, but also improves the adaptability of residential energy storage inverters to different diesel generators.

[0113] Another preferred embodiment of the present invention discloses a computer-readable storage medium storing a computer program, wherein the computer program is configured to be run by a processor to perform the steps of the control method for an energy storage inverter coupled to a diesel generator in Embodiment 1 described above.

[0114] Optionally, the aforementioned computer-readable storage media may include, but are not limited to, various media capable of storing computer programs, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0115] The background section of this invention may include background information about the problems or circumstances surrounding the invention, rather than a description of prior art by others. Therefore, the content included in the background section is not an admission of prior art by the applicant.

[0116] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate different embodiments or examples and features of different embodiments or examples described in this specification without contradiction. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope defined by the appended claims.

Claims

1. A control method of an energy storage inverter coupled with a diesel generator, characterized by, It includes harmonic suppression steps, reactive power compensation steps, and bus adjustment steps, among which, The harmonic suppression step includes: dynamically adjusting the proportional control parameters of the current loop control according to the voltage of the diesel generator, and introducing a filtering module in the feedforward signal processing; The reactive power compensation step includes: actively outputting reactive power compensation amount according to load characteristics to offset the influence of capacitive load on the power factor of diesel generator; The bus adjustment steps include: real-time detection of whether the AC side voltage has the characteristics of a diesel generator; if so, adjusting the bus reference voltage value to a safe range close to the overvoltage protection value. The harmonic suppression step specifically includes periodically determining whether the first, second, and third conditions are met to determine the load characteristics, and actively outputting reactive power compensation to offset the capacitive load when the first, second, and third conditions are all met. The steps for determining whether the first condition is met include: obtaining the phase of the load current and the phase of the diesel engine voltage, and calculating the phase difference between the load current and the diesel generator voltage = load current phase - diesel engine voltage phase, and determining whether the phase difference between the load current and the diesel generator voltage is within a second preset range. If it is, then the first condition is met. The steps for determining whether the second condition is met include: determining whether the effective value of the load current is greater than a second preset multiple of the rated current of the energy storage inverter; if so, the second condition is met. The step of determining whether the third condition is met includes: determining whether the absolute value of the instantaneous peak value of the diesel generator voltage is greater than a third preset multiple of its normal theoretical peak value in multiple consecutive cycles; if so, the third condition is met.

2. The control method of the energy storage inverter according to claim 1, characterized by, The harmonic suppression step specifically includes periodically performing the following steps: A1: Collect the voltage phase signal of the diesel generator and adjust the proportional control parameters of the current loop control based on the voltage phase signal of the diesel generator; A2: In the feedforward signal processing, a bandpass filter module is introduced, wherein the cutoff frequency of the bandpass filter module is set to ±5Hz of the rated power of the diesel generator.

3. The control method of the energy storage inverter according to claim 2, characterized by, Step A1 specifically includes: acquiring the voltage phase signal of the diesel generator, determining whether the voltage phase of the diesel generator is within the first preset range, and if it is within the first preset range, adjusting the proportional control parameter of the current loop control to the first preset multiple of the default value; if it is not within the first preset range, the proportional control parameter of the current loop control is the default value.

4. The control method of the energy storage inverter according to claim 3, characterized by, The first preset range includes [π / 3, 2π / 3] and [-2π / 3, -π / 3], and the first preset multiple is 1.2 to 1.8 times.

5. The control method of the energy storage inverter according to claim 1, wherein The second preset range is greater than 15° and less than 180°, the second preset multiple is 10% to 20%, and the third preset multiple is 1.1 to 1.3 times.

6. The control method of the energy storage inverter according to claim 1 or 5, characterized by, When actively outputting reactive power compensation in the harmonic suppression step, the reactive power compensation is output at a preset rate, wherein the preset rate of increase is 100-500 var / s.

7. The control method for the energy storage inverter according to claim 1, characterized in that, The busbar adjustment steps specifically include: The effective value and instantaneous peak value of the AC voltage are periodically acquired, and the absolute value of the instantaneous peak value is compared with that of the effective value. Is the ratio of the multiples greater than or equal to the first threshold? When the absolute value of the instantaneous voltage peak is detected at least three times consecutively, the voltage RMS value is equal to the absolute value of the voltage peak. If the ratio is greater than or equal to the first threshold, the bus reference voltage value is set to the smaller of the first value and the second value, wherein the first value is equal to the sum of the absolute value of the instantaneous peak voltage of the diesel generator and the second threshold, and the second value is equal to the difference between the overvoltage protection value of the diesel generator and the third threshold.

8. The control method for the energy storage inverter according to claim 7, characterized in that, The first threshold is 1.1~1.3, the second threshold is 2V~4V, and the third threshold is 5V~15V.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, wherein the computer program is configured to be run by a processor to perform the control method of the energy storage inverter according to any one of claims 1 to 8.

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