A droop control method for isolated island microgrid based on logistic exponential function

Abstract

The invention discloses a droop control method for an isolated microgrid based on a Logistic exponential function, comprising the following steps: Step 1, establishing an isolated microgrid three-phase inverter system, including a main circuit, a measurement system, a power calculation module, a droop control module, and a voltage and current double closed-loop module; Step 2, measuring the output voltage and output current of the isolated microgrid three-phase inverter by the measurement system; Step 3, inputting the power calculation module to calculate the real-time active power and reactive power output by the inverter; Step 4, inputting the droop control module to obtain the frequency value and reference voltage value of the isolated microgrid three-phase inverter system. Step 5, subtracting the reference voltage value from the output voltage value to obtain a voltage offset, inputting the voltage and current double closed-loop module, and obtaining a space vector pulse width modulation modulation wave SVPWM after processing; Step 6, the SVPWM controls the switch of the system power tube, thereby controlling the output voltage of the system and realizing overall precise control.

Description

Technical Field

[0001] The present invention relates to the field of microgrids, and in particular to a droop control method for an island microgrid based on a Logistic exponential function. Background Art

[0002] Driven by the growing demand for energy and the urgent need to protect the environment, distributed generation has become a hot topic of concern in various countries due to its advantages of environmental protection, high efficiency and flexibility. However, distributed power sources are often limited by environmental conditions, and the penetration of a large number of distributed generation also has an adverse impact on traditional large power grids. Microgrids can effectively solve these problems. In microgrids, in order to meet the demand for electric energy from loads, it is necessary to control the output voltage and frequency within the allowable range. Distributed power sources in isolated microgrids are usually networked and operated with inverter parallel technology based on droop control. Droop control is to adjust the voltage and frequency by measuring local active power and reactive power and according to the droop gain. Since droop control does not require communication, it has high reliability and good flexibility and has been widely used. However, the disadvantages of droop control are also very obvious. The droop controller reduces the frequency and voltage amplitude to simulate the power regulation of synchronous generators, which will lead to poor system stability, deviation in the frequency and amplitude of the output voltage, and inability to reasonably distribute active power or reactive power, affecting the power quality of the microgrid system. In addition, in traditional droop control, when loads are switched on or off, the frequency fluctuation of the system will cause a mismatch with the grid frequency.

[0003] Therefore, those skilled in the art are motivated to develop a droop control method for an island microgrid based on a Logistic exponential function to solve the technical problems existing in the prior art. Summary of the invention

[0004] The present invention is made to solve the above-mentioned problem, and aims to provide an island microgrid droop control method based on Logistic exponential function.

[0005] The present invention provides a droop control method for an isolated microgrid based on a Logistic exponential function, which has the following characteristics and comprises the following steps: Step 1, establishing an isolated microgrid three-phase inverter system, wherein the isolated microgrid three-phase inverter system comprises a main circuit, a measurement system, a power calculation module, a droop control module and a voltage and current double closed-loop module; Step 2, measuring the output voltage and output current output by the isolated microgrid three-phase inverter by the measurement system to obtain the output voltage value and the output current value; Step 3, inputting the output voltage value and the output current value into the power calculation module to calculate the active power and reactive power output by the inverter in real time; Step 4, inputting the active power and the reactive power into the droop control module to obtain the frequency value and the reference voltage value of the isolated microgrid three-phase inverter system. Step 5, subtract the reference voltage value from the output voltage value to obtain a voltage offset, input the voltage offset into the voltage-current dual closed-loop module, and obtain a space vector pulse width modulation modulation wave SVPWM after processing; Step 6, the space vector pulse width modulation modulation wave SVPWM controls the switch of the power tube of the three-phase inverter system of the isolated microgrid, thereby controlling the output voltage from the three-phase inverter system of the isolated microgrid to achieve overall precise control.

[0006] The island microgrid droop control method based on the Logistic exponential function provided by the present invention may also have the following characteristics: wherein, in step 2, the output voltage value and the output current value are transformed from AC quantities to DC quantities through abc-dq coordinate transformation.

[0007] In the droop control method of the isolated microgrid based on the Logistic exponential function provided by the present invention, it can also have the following characteristics: wherein, in step 4, the specific process of obtaining the frequency value and the reference voltage value of the three-phase inverter system of the isolated microgrid is: in the droop control module, after the real-time active power is input into the Pf droop characteristic model, the frequency value of the isolated microgrid system is obtained, and after the real-time reactive power is input into the QV droop characteristic model, the reference voltage value of the isolated microgrid system is obtained.

[0008] In the droop control method of the isolated island microgrid based on the Logistic exponential function provided by the present invention, it can also have the following characteristics: wherein the Pf droop characteristic model is:

[0009]

[0010] Where, f is the frequency of the output voltage, P is the output active power, and f n is the frequency reference value, P n is the active power rating and m is the coefficient of the model.

[0011] In the droop control method of the isolated island microgrid based on the Logistic exponential function provided by the present invention, it can also have the following characteristics: wherein the QV droop characteristic model is:

[0012]

[0013] Where U is the amplitude of the output voltage, Q is the output reactive power, and U n is the voltage reference value, Q n is the reactive power rating and n is the coefficient of the model.

[0014] In the droop control method of the isolated microgrid based on the Logistic exponential function provided by the present invention, it can also have the following characteristics: wherein, in step 5, the specific processing process is: the voltage offset is used as the current signal reference value in the voltage and current dual closed-loop module after passing through the proportional integral link, the current signal reference value and the measured output voltage value are subtracted to obtain the offset current, and the offset current value is input into the proportional integral link to output the space vector pulse width modulation modulation wave SVPWM.

[0015] Functions and Effects of the Invention

[0016] According to the droop control method of the isolated island microgrid based on the Logistic exponential function involved in the present invention, the specific process is as follows: Step 1, establish an isolated island microgrid three-phase inverter system, the isolated island microgrid three-phase inverter system includes a main circuit, a measurement system, a power calculation module, a droop control module and a voltage and current dual closed-loop module; Step 2, the measurement system measures the output voltage and output current of the isolated island microgrid three-phase inverter output to obtain the output voltage value and the output current value; Step 3, input the output voltage value and the output current value into the power calculation module, and calculate the active power and reactive power output by the inverter in real time; Step 4, input the active power and the reactive power into the droop control module to obtain the frequency value and the reference voltage value of the isolated island microgrid three-phase inverter system. Step 5, subtract the reference voltage value from the output voltage value to obtain a voltage offset, input the voltage offset into the voltage-current dual closed-loop module, and obtain a space vector pulse width modulation modulation wave SVPWM after processing; Step 6, the space vector pulse width modulation modulation wave SVPWM controls the switch of the power tube of the three-phase inverter system of the isolated microgrid, thereby controlling the output voltage from the three-phase inverter system of the isolated microgrid to achieve overall precise control.

[0017] Therefore, the droop control method for an island microgrid based on a Logistic exponential function provided by the present invention improves the droop control equation, and can ensure frequency stability and improve power control accuracy.

[0018] In addition, the droop control method of the isolated microgrid based on the Logistic exponential function provided by the present invention can achieve better power distribution when switching loads, meet the needs of load changes, and maintain the stability of system voltage and frequency.

[0019] Finally, the droop control method of an island microgrid based on a Logistic exponential function provided by the present invention can realize power distribution for different distributed power sources according to their capacities. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of a three-phase inverter system of an isolated island microgrid in Embodiment 1 of the present invention;

[0021] Figure 2 is a comparison diagram of the microgrid output frequency waveforms under different droop control methods in Example 1 of the present invention;

[0022] Figure 3 is a comparison diagram of the active power waveforms output by the microgrid under different droop control methods in Example 1 of the present invention;

[0023] Figure 4 is a comparison diagram of reactive power waveforms output by a microgrid under different droop control methods in Example 1 of the present invention;

[0024] Figure 5 is a comparison diagram of the waveforms of the microgrid output voltage amplitudes under different droop control methods in Example 1 of the present invention;

[0025] Figure 6 is an output load current waveform diagram of DG1 in Embodiment 2 of the present invention;

[0026] Figure 7 is an output load current waveform diagram of DG2 in Embodiment 2 of the present invention;

[0027] Figure 8 is an output active power waveform diagram of different distributed power sources in embodiment 2 of the present invention;

[0028] Fig. 9 1 is a waveform diagram of output reactive power of different distributed power sources in Example 2 of the present invention. DETAILED DESCRIPTION

[0029] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following embodiments and the accompanying drawings specifically illustrate the droop control method of an island microgrid based on a Logistic exponential function of the present invention.

[0030] Example 1

[0031] In this embodiment, a droop control method for an island microgrid based on a Logistic exponential function is provided.

[0032] Figure 1 It is a schematic diagram of the three-phase inverter system of the isolated island microgrid in Example 1 of the present invention.

[0033] like Figure 1 As shown, the droop control method of the isolated island microgrid based on the Logistic exponential function involved in this embodiment includes the following steps:

[0034] Step S1, establishing an island microgrid three-phase inverter system, the island microgrid three-phase inverter system includes a main circuit, a measurement system, a power calculation module, a droop control module, and a voltage and current double closed loop module.

[0035] In step S2, the output voltage and output current of the three-phase inverter of the isolated microgrid are measured by the measurement system. After abc-dq coordinate transformation, the measured output voltage value and output current value are transformed from AC quantity to DC quantity.

[0036] Step S3, inputting the output voltage value and the output current value into a power calculation module to calculate the active power and reactive power output by the inverter in real time.

[0037] Step S4, the real-time active power and reactive power calculated by the power calculation module are input into the droop control module. In the droop control module, after the real-time active power is input into the Pf droop characteristic model, the frequency value of the isolated island microgrid system is obtained; after the real-time reactive power is input into the QV droop characteristic model, the reference voltage value of the isolated island microgrid system is obtained.

[0038] In this embodiment, the Pf droop characteristic model is:

[0039]

[0040] The QV droop characteristic model is:

[0041]

[0042] Step S5, the reference voltage value output by the droop control module is subtracted from the measured output voltage value to obtain a voltage offset. The voltage offset is used as a current signal reference value in the voltage-current dual closed-loop module after passing through a proportional-integral link. The current signal reference value is subtracted from the measured output voltage value to obtain an offset current, and the offset current value is input into a proportional-integral link to output a modulation signal.

[0043] Step S6, using the space vector pulse width modulation wave SVPWM output by the voltage and current dual closed-loop module to control the switch of the power tube of the three-phase full-bridge inverter, thereby controlling the output voltage from the system to achieve overall precise control.

[0044] Figure 2 It is a comparison diagram of the microgrid output frequency waveforms under different droop control methods in Example 1 of the present invention.

[0045] like Figure 2 As shown in the figure, compared with the traditional droop control method, the system load frequency of the improved droop control can quickly transition from transient to steady state.

[0046] Figure 3 It is a comparison diagram of the active power waveforms output by the microgrid under different droop control methods in Example 1 of the present invention.

[0047] Figure 4 It is a comparison diagram of the reactive power waveforms output by the microgrid under different droop control methods in Example 1 of the present invention.

[0048] like Figure 3 and Figure 4 As shown, it can be observed that within (0~0.2s), since the DG system is in no-load operation, the output power is 0. At 0.2s, the first group of loads is put into operation. After the transient process, compared with the input load, the active power and reactive power output by the traditional droop control fluctuate at ΔP=170W and ΔQ=1320Var respectively. The active power and reactive power output by the improved droop control are ΔP=14W and ΔQ=60Var respectively. At 0.5s, the second group of loads is put into operation. After the transient process, compared with the input load, the active power and reactive power output by the traditional droop control fluctuate at ΔP=364W and ΔQ=1907Var respectively, and the active power and reactive power output by the improved droop control are ΔP=23W and ΔQ=101Var respectively. By comparing with the increase of load, the improved droop control improves the control accuracy of active power and reactive power, and the waveform is more stable, which is conducive to system stability.

[0049] Figure 5 It is a comparison diagram of the microgrid output voltage amplitude waveforms under different droop control methods in Example 1 of the present invention.

[0050] like Figure 5 As shown, compared with the traditional method, the output voltage amplitude of the improved method drops less and the waveform changes more gently.

[0051] Example 2

[0052] In this embodiment, a specific application of an isolated island microgrid droop control method based on a Logistic exponential function is provided. The isolated island microgrid droop control method based on a Logistic exponential function in this embodiment is specifically described for two distributed power sources.

[0053] The capacity of distributed power source 1 (DG1) is 10kw+8kVar, and the capacity of distributed power source 2 (DG2) is 20kw+16kVar. The microgrid system runs for 1s. The entire microgrid is in no-load operation from 0 to 0.2s. At 0.2s, the first group of loads 7.5kw+6kVar is put into operation, at 0.5s, the second group of loads 10.5kw+12kVar is put into operation, and at 0.8s, the first group of loads is cut off.

[0054] Figure 6 is a waveform diagram of the output load current of DG1 in Embodiment 2 of the present invention.

[0055] like Figure 6 As shown, when DG1 puts the first set of loads into the system at 0.2s, the amplitude of the output load current is 1.5A; when the second set of loads is put into the system at 0.5s, the amplitude of the output load current is 4.0A; when the first set of loads is removed at 0.8s, the amplitude of the output load current is 2.5A.

[0056] Figure 7 is a waveform diagram of the output load current of DG2 in Embodiment 2 of the present invention.

[0057] like Figure 7 As shown, when DG2 puts the first set of loads into the system at 0.2s, the amplitude of the output load current is 3.0A; when the second set of loads is put into the system at 0.5s, the amplitude of the output load current is 8.0A; when the first set of loads is removed at 0.8s, the amplitude of the output load current is 5.0A.

[0058] Figure 8 1 is a waveform diagram of output active power of different distributed power sources in Example 2 of the present invention.

[0059] like Figure 8 As shown in the figure, when the first set of loads is put into operation at 0.2s, the output active power of DG1 is 2500W, and the output active power of DG2 is 5000W; when the second set of loads is put into operation at 0.5s, the output active power of DG1 is 6000W, and the output active power of DG2 is 12000W; when the first set of loads is removed at 0.8s, the output active power of DG1 is 3500W, and the output active power of DG2 is 7000W.

[0060] Fig. 91 is a waveform diagram of output reactive power of different distributed power sources in Example 2 of the present invention.

[0061] like Fig. 9 As shown in the figure, when the first set of loads is put into operation at 0.2s, the output reactive power of DG1 is 2000Var, and the output reactive power of DG2 is 4000Var; when the second set of loads is put into operation at 0.5s, the output active power of DG1 is 6000Var, and the output active power of DG2 is 12000Var; when the first set of loads is removed at 0.8s, the output active power of DG1 is 4000Var, and the output active power of DG2 is 8000Var. The above results show that the power distribution between DG1 and DG2 is 1:2.

[0062] Functions and Effects of the Embodiments

[0063] According to the droop control method of the isolated island microgrid based on the Logistic exponential function involved in this embodiment, the specific process is as follows: Step 1, establish an isolated island microgrid three-phase inverter system, the isolated island microgrid three-phase inverter system includes a main circuit, a measurement system, a power calculation module, a droop control module and a voltage and current dual closed-loop module; Step 2, the output voltage and output current output by the isolated island microgrid three-phase inverter are measured by the measurement system to obtain the output voltage value and the output current value; Step 3, the output voltage value and the output current value are input into the power calculation module to calculate the active power and reactive power output by the inverter in real time; Step 4, the active power and the reactive power are input into the droop control module to obtain the frequency value and the reference voltage value of the isolated island microgrid three-phase inverter system. Step 5, subtract the reference voltage value from the output voltage value to obtain a voltage offset, input the voltage offset into the voltage-current dual closed-loop module, and obtain a space vector pulse width modulation modulation wave SVPWM after processing; Step 6, the space vector pulse width modulation modulation wave SVPWM controls the switch of the power tube of the three-phase inverter system of the isolated microgrid, thereby controlling the output voltage from the three-phase inverter system of the isolated microgrid to achieve overall precise control.

[0064] Therefore, the above-mentioned embodiment provides a droop control method for an island microgrid based on a Logistic exponential function, which improves the droop control equation and can ensure frequency stability and improve power control accuracy.

[0065] In addition, the above-mentioned embodiment provides an island microgrid droop control method based on a Logistic exponential function, which can achieve better power distribution when switching loads, meet the needs of load changes, and maintain the stability of system voltage and frequency.

[0066] Finally, the above embodiment provides a droop control method for an isolated microgrid based on a Logistic exponential function, which can realize power allocation for different distributed power sources according to their capacities. The above implementation is a preferred case of the present invention and is not intended to limit the protection scope of the present invention.

Claims

1. A droop control method for an island microgrid based on a Logistic exponential function, characterized in that: The following steps are involved: Step 1, establishing an isolated island microgrid three-phase inverter system, wherein the isolated island microgrid three-phase inverter system includes a main circuit, a measurement system, a power calculation module, a droop control module, and a voltage and current dual closed-loop module; Step 2, measuring the output voltage and output current of the three-phase inverter of the isolated island microgrid by the measurement system to obtain the output voltage value and the output current value; Step 3, inputting the output voltage value and the output current value into the power calculation module to calculate the active power and reactive power output by the inverter in real time; Step 4, inputting the active power and the reactive power into the droop control module to obtain the frequency value and the reference voltage value of the three-phase inverter system of the isolated island microgrid; Step 5, subtracting the reference voltage value from the output voltage value to obtain a voltage offset, inputting the voltage offset into the voltage-current dual closed-loop module, and obtaining a space vector pulse width modulation modulation wave SVPWM after processing; Step 6, the space vector pulse width modulation modulation wave SVPWM controls the switch of the power tube of the three-phase inverter system of the isolated microgrid, thereby controlling the output voltage from the three-phase inverter system of the isolated microgrid to achieve overall precise control. Among them, in step 4, the specific process of obtaining the frequency value and the reference voltage value of the three-phase inverter system of the isolated microgrid is: In the droop control module, after the real-time active power is input into the Pf droop characteristic model, the frequency value of the isolated island microgrid system is obtained. After the real-time reactive power is input into the QV droop characteristic model, the reference voltage value of the island microgrid system is obtained. The Pf droop characteristic model is: Where, f is the frequency of the output voltage, P is the output active power, and f n is the frequency reference value, P n is the active power rating, m is the coefficient of the model, The QV droop characteristic model is: In the formula, U is the amplitude of the output voltage, Q is the output reactive power, and U n is the voltage reference value, Q n is the reactive power rating and n is the coefficient of the model.

2. The droop control method of an isolated island microgrid based on a Logistic exponential function according to claim 1, characterized in that: in, In step 2, the output voltage value and the output current value are transformed from AC quantities to DC quantities through abc-dq coordinate transformation.

3. The droop control method of an isolated island microgrid based on a Logistic exponential function according to claim 1, characterized in that: in, In step 5, the specific process of the processing is: The voltage offset is used as the current signal reference value in the voltage-current dual closed-loop module after passing through the proportional-integral link. The current signal reference value and the measured output voltage value are subtracted to obtain the offset current. The offset current value is input into the proportional-integral link to output the space vector pulse width modulation modulation wave SVPWM.

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