Grid-connected control method for micro-grid comprising diesel generator

Abstract

The invention discloses a grid-connected control method for a micro-grid comprising a diesel generator. The grid-connected control method comprises the following steps: establishing simulation models of a photovoltaic power generation system, an energy storage system and the diesel generator, and setting power parameters; dC output is obtained through a DC / DC booster; the output direct current is converted into alternating current through a DC / AC converter, and three-phase alternating current high voltage matched with a power grid is obtained; and enabling the amplitude, phase and frequency of the output voltage to be consistent with the power grid by adopting a pre-synchronization system, and completing the grid connection of the micro-grid. According to the method, power conservation law analysis is carried out on the light-storage complementary micro-grid containing the diesel generator, power flow direction analysis is continued after the large power grid is accessed, the effectiveness of the diesel-storage complementary micro-grid model is finally obtained, and the grid-connected control effect of the micro-grid is improved.

Description

Technical Field

[0001] The present invention belongs to the field of power grids and relates to microgrid grid-connected technology, and in particular to a microgrid grid-connected control method including a diesel generator. Background Art

[0002] The data center power supply system is the most critical subsystem within its infrastructure. Failures in the system can cause power outages to servers, switches, and other equipment, leading to data loss and disruption to data services, resulting in significant economic losses. Ensuring a continuous and uninterrupted power supply has become essential for modern data center power supply systems. To ensure reliable power supply, companies often deploy backup diesel generators in a 1:1.2 ratio and maintain a constant reserve of diesel.

[0003] In the context of global energy transformation, microgrids, as an important carrier for distributed energy consumption, have become a key technology to solve power supply problems in remote areas and improve grid resilience. However, the intermittent nature of renewable energy (such as photovoltaic and wind power) challenges the stability of microgrids, and diesel generators are often used as backup power or main power sources for microgrids because of their fast response speed and high reliability. The grid-connected control technology of data centers containing diesel generator microgrids needs to take into account economy, stability and environmental protection, which is a hot topic of current research.

[0004] Amidst the current intensifying energy crisis, distributed generation technology, particularly renewable energy-based applications, can easily disrupt centralized power grids. However, due to restrictive management policies for distributed energy access, this strategy is seen as a core trend in energy development for the foreseeable future. This has resulted in a low level of commercialization of distributed power, significantly limiting its development and hindering its large-scale operation. The advent of microgrid technology offers significant improvements to the current state of distributed generation technology by ensuring stable frequency and voltage output, thereby reducing the impact on the larger power grid. Furthermore, in the event of a large power grid failure, microgrids can operate in an isolated mode while fully utilizing renewable energy, ensuring the supply of internal baseload power and increasing power reliability. As a power system integrating distributed power sources and loads, microgrids can operate in both grid-connected and islanded modes. Their hallmark is their high reliability and stability in both modes. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the deficiencies in the prior art, a method for controlling the grid connection of a microgrid containing a diesel generator in a data center is provided.

[0006] Technical solution: To achieve the above-mentioned purpose, the present invention provides a microgrid grid connection control method including a diesel generator, comprising the following steps:

[0007] S1: Establish simulation models of photovoltaic power generation, energy storage system and diesel generator and set power parameters;

[0008] S2: obtains DC output through the DC / DC booster;

[0009] S3: Converts the output from DC to AC through a DC / AC converter to obtain a three-phase AC high voltage that matches the power grid;

[0010] S4: Use the pre-synchronization system to make the output voltage amplitude, phase and frequency consistent with the grid, completing the microgrid grid connection.

[0011] Furthermore, the establishment of the photovoltaic power generation simulation model in step S1 includes:

[0012] Use MPPT maximum power point tracking to set up photovoltaic modules;

[0013] After in-depth analysis, the equivalent input impedance expression of the Boost converter is deduced as follows:

[0014]

[0015] In order to match the output equivalent impedance of the photovoltaic array with the equivalent input impedance of the Boost circuit, it can be seen from the above formula that the duty cycle D of the Boost converter is adjusted to ensure that the photovoltaic array maintains the maximum output power.

[0016] Furthermore, in step S2, the photovoltaic power generation is regulated by the DC / DC converter based on the MPPT control strategy, including: adopting a voltage and current double closed-loop regulation mechanism to generate a PWM control signal to drive the photovoltaic DC / DC converter. The voltage reference value U is calculated by the admittance increment algorithm. ref At the same time, the actual output voltage of the photovoltaic array U PV With the output current I PV By comparing the voltage and current closed-loop control, the voltage reference value determined by the MPPT algorithm can be tracked more accurately.

[0017] Furthermore, in step S2, the DC / DC interface of the energy storage system is subjected to droop control, and the control method includes: U oc *、I b They are the reference value and actual value of lithium battery charge and discharge current respectively; D boost and D buck are the converter step-up and step-down PWM control signals respectively; R b is the internal resistance of the lithium battery; L bis the inductance at the lithium battery outlet; C is the DC side capacitance;

[0018] The DC bus voltage measurement value Udc is used to generate the input reference value I of the current control loop through the battery IV droop control algorithm. b *, then after passing through the PI controller, the trigger pulse is generated through PWM.

[0019] Furthermore, in step S2, a control to prevent the battery from being overcharged and over-discharged is set in the controller, including: when the battery charge and discharge reaches the limit, the current reference value I is forced to b * is 0. When the battery does not work as a voltage regulator but works in a constant current charging state, the battery charging current I b Able to maintain the reference value I b *Nearby; the rated operating voltage of the DC bus is set to U dc *=380V, the critical value of battery charging voltage is U H1 =1.05U dc *, when the discharge voltage critical value is U L1 =0.95U dc *, the critical voltage of the grid-side bidirectional DC / AC converter in the working and rectification states is U H2 =1.1U dc *, the critical voltage working in the inverter state is U L2 =0.9U dc *; DC bus voltage at U H1 and U L1 The battery enters the standby working state, the bus voltage is within the allowable working range and is greater than U H1 Charge the battery, less than U L1 This indicates that the system energy is insufficient. At this time, the battery is working in a discharge state to increase the DC bus voltage.

[0020] Furthermore, in step S3, after the energy storage battery generates a DC voltage, it passes through a bidirectional boost circuit, and then stabilizes the voltage through a filter circuit. The signals G1 and G2 of the driving diodes are used to drive the IGBT tube through the DC bus voltage outer loop and the battery current inner loop, thereby outputting the voltage. The real-time state of energy (SOC) of the energy storage battery is defined as the ratio between the current stored energy of the battery and its maximum stored energy.

[0021] Furthermore, the operation of the pre-synchronization system in step S4 includes: inputting the three-phase voltage signal Vgabc into a phase-locked loop (PLL) module; the PLL module processes the input three-phase voltage signal to separate two orthogonal components Vd and Vq, and a frequency signal Freq, wherein the Freq signal is labeled as Freq_g output and connected to a display module for monitoring, and also participates in subsequent calculations;

[0022] Vd and Vq enter the multiplication module (×) for square operation, then add them together and perform square root operation through the \sqrt u module to obtain the voltage amplitude Vgm, which is also connected to the display module for monitoring;

[0023] Calculate and control the frequency difference and voltage amplitude difference;

[0024] The outputs of the last two switch modules enter the OR logic module for operation. When both switches are 0 at the same time, the output is 0, indicating that the pre-synchronization step is completed.

[0025] Furthermore, the calculation and control of the frequency difference in step S4 includes:

[0026] The calculated output frequency is subtracted from the rated frequency of 50 Hz to obtain a frequency difference signal. This difference signal passes through the absolute value operation module |u| to convert the difference into a positive value. The feedback link composed of an integrator and a virtual damping coefficient PD gradually narrows the gap between the two frequencies until the two frequencies are consistent in size. Finally, it enters a switch module with two inputs, 1 and 0. When the difference is less than 0.1 Hz, the output is 0.

[0027] Furthermore, the calculation and control of the voltage amplitude difference in step S4 includes:

[0028] The calculated voltage amplitude Vgm is subtracted from the rated voltage 311V to obtain a voltage amplitude difference signal. This difference signal also passes through the absolute value operation module |u| to convert the difference into a positive value. The difference is then gradually reduced through a feedback link consisting of an integrator and a reactive voltage regulation coefficient. Finally, it enters a switch module with two inputs, 1 and 0. If the difference is less than the allowable value (±5%), the output is 0.

[0029] In synchronous networked operation, this invention implements a power feedback control strategy from a cybernetics perspective, ensuring that the diesel generator can output the desired power. A corresponding diesel generator model is constructed, and a power feedback control system is employed to achieve precise control under networked operation conditions.

[0030] Finally, the phase-locked loop measures the voltage, frequency, and phase of the power grid, and compares them with the output voltage, frequency, and phase of the inverter. The comparison result is added to the feedback link to optimize the output value of the inverter. Finally, the two are gradually synchronized, completing the pre-synchronization operation.

[0031] Beneficial effects: Compared with the existing technology, the present invention establishes a detailed mathematical model for photovoltaic power supply, diesel power generation and battery energy storage based on the development characteristics of the diesel-powered light-storage-compensated microgrid. The corresponding model is built with the help of Simulink, and the entire wind-solar-storage complementary microgrid simulink model is run. Island operation is performed from 0s to 0.5s, and it is connected to the large power grid and grid-side loads from 0.5s to 1.5s. The power conservation law of the photovoltaic-storage complementary microgrid containing diesel generators is analyzed, and the power flow analysis is continued after connecting to the large power grid. Finally, the effectiveness of the diesel-powered light-storage complementary microgrid model is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a grid-connected operation flow chart;

[0033] Figure 2 This is the MPPT mode control block diagram;

[0034] Figure 3 This is the model diagram of the diesel generator speed regulator when running on the grid;

[0035] Figure 4 It is the control diagram of energy storage converter;

[0036] Figure 5 This is the simulink block diagram of the diesel generator;

[0037] Figure 6 This is the simulink block diagram of the photovoltaic PV module;

[0038] Figure 7 This is the simulink diagram of the energy storage battery module;

[0039] Figure 8 This is the result diagram of amplitude and phase adjustment of the pre-synchronization system;

[0040] Figure 9 It is the frequency difference waveform. DETAILED DESCRIPTION

[0041] The present invention is further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, modifications of various equivalent forms of the present invention made by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0042] like Figure 1 As shown, the present invention provides a microgrid grid connection control method including a diesel generator, comprising the following steps:

[0043] S1: Establish simulation models of photovoltaic power generation, energy storage system and diesel generator and set power parameters;

[0044] S2: obtains DC output through the DC / DC booster;

[0045] S3: Converts the output from DC to AC through a DC / AC converter to obtain a three-phase AC high voltage that matches the power grid;

[0046] S4: Use the pre-synchronization system to make the output voltage amplitude, phase and frequency consistent with the grid, completing the microgrid grid connection.

[0047] The present invention designs microgrids for both isolated and grid-connected operation. In the microgrid system's islanded operation mode, the difference between the energy generated by the photovoltaic system and diesel generator set and the power consumed by the load determines the battery's charge and discharge. When there's surplus energy, the battery charges; when energy is insufficient, the battery discharges. The battery's charge and discharge capacities are both within the permitted range, preventing overcharge and overdischarge. When the battery charge capacity exceeds the maximum permitted value, the photovoltaic system operates in a voltage-stabilized state, reducing energy output. When the battery discharge capacity exceeds the maximum permitted value, islanded operation ends, the grid-side DC / AC converter is activated, and the system enters grid-connected operation, with energy supplied from the main grid to the DC microgrid system. The entire DC microgrid system aims to achieve "self-sufficiency" while minimizing energy flow with the main grid. Only when the energy generated by the photovoltaic system is greater than the sum of the maximum storage energy of the energy storage system and the DC side load, the system will operate and be connected to the grid, transmitting energy to the large power grid; when the power consumed by the DC side load is greater than the sum of the maximum power generated by the photovoltaic system and the energy of the energy storage system, the DC microgrid system will be short of energy and will need to absorb energy from the large power grid to maintain the stability of the microgrid system.

[0048] The establishment of the photovoltaic power generation simulation model in step S1 includes:

[0049] Use MPPT maximum power point tracking to set up photovoltaic modules;

[0050] like Figure 2 As shown, after in-depth analysis, the equivalent input impedance expression of the Boost converter is deduced as follows:

[0051]

[0052] In order to match the output equivalent impedance of the photovoltaic array with the equivalent input impedance of the Boost circuit, it can be seen from the above formula that the duty cycle D of the Boost converter is adjusted to ensure that the photovoltaic array maintains the maximum output power.

[0053] In step S2, the DC / DC converter of photovoltaic power generation is regulated based on the MPPT control strategy, including: using a dual closed-loop regulation mechanism of voltage and current to generate a PWM control signal to drive the photovoltaic DC / DC converter. The voltage reference value U is calculated by the admittance increment algorithm.ref At the same time, the actual output voltage of the photovoltaic array U PV With the output current I PV By comparing the voltage and current closed-loop control, the voltage reference value determined by the MPPT algorithm can be tracked more accurately.

[0054] like Figure 4 As shown, in step S2, the DC / DC interface of the energy storage system adopts droop control, and the control method includes: U oc *、I b They are the reference value and actual value of lithium battery charge and discharge current respectively; D boost and D buck are the converter step-up and step-down PWM control signals respectively; R b is the internal resistance of the lithium battery; L b is the inductance at the lithium battery outlet; C is the DC side capacitance;

[0055] The DC bus voltage measurement value Udc is used to generate the input reference value I of the current control loop through the battery IV droop control algorithm. b *, then after passing through the PI controller, the trigger pulse is generated through PWM.

[0056] The controller is equipped with a control system to prevent the battery from overcharging and over-discharging, including: when the battery charge and discharge reaches the limit, the current reference value I is forced to b * is 0. When the battery does not work as a voltage regulator but works in a constant current charging state, the battery charging current I b Able to maintain the reference value I b *Nearby; the rated operating voltage of the DC bus is set to U dc *=380V, the critical value of battery charging voltage is U H1 =1.05U dc *, when the discharge voltage critical value is U L1 =0.95U dc *, the critical voltage of the grid-side bidirectional DC / AC converter in the working and rectification states is U H2 =1.1U dc *, the critical voltage working in the inverter state is U L2 =0.9U dc *; DC bus voltage at U H1 and U L1 The battery enters the standby working state, the bus voltage is within the allowable working range and is greater than U H1 Charge the battery, less than U L1 This indicates that the system energy is insufficient. At this time, the battery is working in a discharge state to increase the DC bus voltage.

[0057] Reference Figure 3and Figure 5 The diesel generator outputs DC voltage, which is converted into three-phase AC through the DC / AC inverter module and connected to the grid side for power supply.

[0058] In step S3, after the energy storage battery generates a DC voltage, it passes through a bidirectional boost circuit and then a filtering circuit to stabilize the voltage. The signals G1 and G2 of the driving diodes are used to drive the IGBT tube through the DC bus voltage outer loop and the battery current inner loop to output the voltage. The real-time state of energy (SOC) of the energy storage battery is defined as the ratio between the current stored energy of the battery and its maximum stored energy.

[0059] Reference Figure 6 The leftmost part of the photovoltaic PV module is the photovoltaic PV model. The area and temperature of the photovoltaic panel are input, and the radiation intensity S is output: the photovoltaic intensity from 0 to 0.75s is 795W / m2, and the photovoltaic intensity rises to 1000W / m2 after 0.75s. The temperature is defined as 25℃. The photovoltaic output voltage is obtained through the PV model, and then boosted by the Boost circuit and sent out of the system. Maximum power point tracking (MPPT) is applied to achieve the maximum power output of the photovoltaic panel. The light step is achieved in 0.75s, and the photovoltaic MPPT outputs the maximum power, with an output power of 50kW to 60kW.

[0060] Reference Figure 4 and Figure 7 After the energy storage battery generates DC voltage, it passes through a bidirectional boost circuit and then a filter circuit to stabilize the voltage. The signals driving the diodes G1 and G2 drive the IGBTs through the DC bus voltage outer loop and the battery current inner loop, thereby outputting the voltage. The real-time state of energy (SOC) of the energy storage battery is defined as the ratio between the battery's current stored energy and its maximum stored energy.

[0061] The operation of the pre-synchronization system in step S4 includes: the three-phase voltage signal Vgabc is input to the phase-locked loop (PLL) module; the PLL module processes the input three-phase voltage signal to separate two orthogonal components Vd and Vq, and the frequency signal Freq, where the Freq signal is output as Freq_g and connected to the display module for monitoring and also participates in subsequent calculations;

[0062] Vd and Vq enter the multiplication module (×) for square operation, then add them together and perform square root operation through the \sqrt u module to obtain the voltage amplitude Vgm, which is also connected to the display module for monitoring;

[0063] Calculate and control the frequency difference and voltage amplitude difference;

[0064] The outputs of the last two switch modules enter the OR logic module for operation. When both switches are 0 at the same time, the output is 0, indicating that the pre-synchronization step is completed.

[0065] The calculation and control of frequency difference include:

[0066] The calculated output frequency is subtracted from the rated frequency of 50 Hz to obtain a frequency difference signal. This difference signal passes through the absolute value operation module |u| to convert the difference into a positive value. The feedback link composed of an integrator and a virtual damping coefficient PD gradually narrows the gap between the two frequencies until the two frequencies are consistent in size. Finally, it enters a switch module with two inputs, 1 and 0. When the difference is less than 0.1 Hz, the output is 0.

[0067] The calculation and control of the voltage amplitude difference include:

[0068] The calculated voltage amplitude Vgm is subtracted from the rated voltage 311V to obtain a voltage amplitude difference signal. This difference signal also passes through the absolute value operation module |u| to convert the difference into a positive value. The difference is then gradually reduced through a feedback link consisting of an integrator and a reactive voltage regulation coefficient. Finally, it enters a switch module with two inputs, 1 and 0. If the difference is less than the allowable value (±5%), the output is 0.

[0069] In synchronous networked operation, this invention implements a power feedback control strategy from a cybernetics perspective, ensuring that the diesel generator can output the desired power. A corresponding diesel generator model is constructed, and a power feedback control system is employed to achieve precise control under networked operation conditions.

[0070] Finally, the phase-locked loop measures the voltage, frequency, and phase of the power grid, and compares them with the output voltage, frequency, and phase of the inverter. The comparison result is added to the feedback link to optimize the output value of the inverter. Finally, the two are gradually synchronized, completing the pre-synchronization operation.

[0071] Result analysis: The entire diesel-to-photovoltaic-storage hybrid microgrid simuink model was run, with island operation performed from 0s to 0.5s, and integration into the main grid and grid-side loads from 0.5s to 1.5s. The power output image was observed and analyzed, and the law of conservation of energy was satisfied in the microgrid mode.

[0072] like Figure 8 As shown in the figure, at the beginning, there are differences in amplitude and phase between the output voltage and the grid voltage. After adjustment, the output phase waveform basically coincides with the grid before 0.5 seconds of grid connection. Figure 9 As shown in Figure 1, the frequency difference between the output end and the grid quickly becomes 0, thereby reducing the inrush current.

[0073] Finally, by observing the output voltage and current waveforms of the diesel generator, as well as the voltage and current waveforms on the grid side, they are all standard sine waves, indicating that the grid connection effect is good.

Claims

1. A microgrid grid connection control method including a diesel generator, characterized in that: The steps include: S1: Establish simulation models of photovoltaic power generation, energy storage system and diesel generator and set power parameters; S2: obtains DC output through the DC / DC booster; S3: Converts the output from DC to AC through a DC / AC converter to obtain a three-phase AC high voltage that matches the power grid; S4: Use the pre-synchronization system to make the output voltage amplitude, phase and frequency consistent with the grid, completing the microgrid grid connection.

2. A microgrid grid connection control method including a diesel generator according to claim 1, characterized in that: The establishment of the photovoltaic power generation simulation model in step S1 includes: Use MPPT maximum power point tracking to set up photovoltaic modules; After in-depth analysis, the equivalent input impedance expression of the Boost converter is deduced as follows: In order to match the output equivalent impedance of the photovoltaic array with the equivalent input impedance of the Boost circuit, it can be seen from the above formula that the duty cycle D of the Boost converter is adjusted to ensure that the photovoltaic array maintains the maximum output power.

3. A microgrid grid connection control method including a diesel generator according to claim 1, characterized in that: In step S2, the photovoltaic power generation is regulated by the DC / DC converter based on the MPPT control strategy, including: using a voltage and current double closed-loop regulation mechanism to generate a PWM control signal to drive the photovoltaic DC / DC converter. The voltage reference value U is calculated by the admittance increment algorithm. ref At the same time, the actual output voltage of the photovoltaic array U PV With the output current I PV Comparison after voltage and current closed-loop control.

4. A microgrid grid connection control method including a diesel generator according to claim 1, characterized in that: In step S2, the DC / DC interface of the energy storage system is subjected to droop control, and the control method includes: oc *、I b They are the reference value and actual value of lithium battery charge and discharge current respectively; D boost and D buck are the converter step-up and step-down PWM control signals respectively; R b is the internal resistance of the lithium battery; L b is the inductance at the lithium battery outlet; C is the DC side capacitance; The DC bus voltage measurement value Udc is used to generate the input reference value I of the current control loop through the battery IV droop control algorithm. b *, then after passing through the PI controller, the trigger pulse is generated through PWM.

5. A microgrid grid connection control method including a diesel generator according to claim 4, characterized in that: In step S2, the controller is provided with a control to prevent the battery from being overcharged and over-discharged, including: when the battery charge and discharge reaches the limit, the current reference value I is forced to b * is 0. When the battery does not work as a voltage regulator but works in a constant current charging state, the battery charging current I b Able to maintain the reference value I b *Nearby; DC bus voltage is U H1 and U L1 The battery enters the standby working state, and the bus voltage is within the allowable working range and is greater than U H1 Charge the battery, less than U L1 This indicates that the system energy is insufficient. At this time, the battery is working in a discharge state to increase the DC bus voltage.

6. A microgrid grid connection control method including a diesel generator according to claim 1, characterized in that: In step S3, after the energy storage battery generates a DC voltage, it passes through a bidirectional boost circuit, and then stabilizes the voltage through a filtering circuit. The signals G1 and G2 of the driving diodes are used to drive the IGBT tube through the DC bus voltage outer loop and the battery current inner loop, thereby outputting the voltage. The real-time state of energy (SOC) of the energy storage battery is defined as the ratio between the current stored energy of the battery and its maximum stored energy.

7. A microgrid grid connection control method including a diesel generator according to claim 1, characterized in that: The operation of the pre-synchronization system in step S4 includes: inputting the three-phase voltage signal Vgabc into a phase-locked loop (PLL) module; the PLL module processes the input three-phase voltage signal to separate two orthogonal components Vd and Vq, and a frequency signal Freq, wherein the Freq signal is output as Freq_g and connected to a display module for monitoring, and also participates in subsequent calculations; Vd and Vq enter the multiplication module (×) for square operation, then add them together and perform square root operation through the \sqrt u module to obtain the voltage amplitude Vgm, which is also connected to the display module for monitoring; Calculate and control the frequency difference and voltage amplitude difference; The outputs of the last two switch modules enter the OR logic module for operation. When both switches are 0 at the same time, the output is 0, indicating that the pre-synchronization step is completed.

8. A microgrid grid connection control method including a diesel generator according to claim 7, characterized in that: The calculation and control of the frequency difference in step S4 includes: The calculated output frequency is subtracted from the rated frequency of 50 Hz to obtain a frequency difference signal. This difference signal passes through the absolute value operation module |u| to convert the difference into a positive value. The feedback link composed of an integrator and a virtual damping coefficient PD gradually narrows the gap between the two frequencies until the two frequencies are consistent in size. Finally, it enters a switch module with two inputs, 1 and 0. When the difference is less than 0.1 Hz, the output is 0.

9. A microgrid grid connection control method including a diesel generator according to claim 7, characterized in that: The calculation and control of the voltage amplitude difference in step S4 includes: The calculated voltage amplitude Vgm is subtracted from the rated voltage 311V to obtain a voltage amplitude difference signal. This difference signal also passes through the absolute value operation module |u| to convert the difference into a positive value. The difference is then gradually reduced through a feedback link consisting of an integrator and a reactive voltage adjustment coefficient. Finally, it enters a switch module with two inputs, 1 and 0. If the difference is less than the allowable value, the output is 0.

Images