Voltage out-of-limit judgment and adjustment method for direct-current micro-grid

Abstract

The invention provides a voltage out-of-limit judgment and adjustment method for a direct-current micro-grid. The method comprises the following steps: acquiring a bus rated voltage and a bus voltage deviation coefficient of the DC micro-grid; obtaining droop coefficients of a plurality of droop controllers in the DC micro-grid, and performing calculation through a first preset rule according to the plurality of droop coefficients to obtain an equivalent droop coefficient; according to the bus rated voltage, the bus voltage deviation coefficient and the equivalent droop coefficient, a load power upper limit and a load power lower limit of the DC micro-grid are calculated through a second preset rule, and a load power range is obtained; calculating a load power actual value of the voltage of the DC micro-grid; judging whether the actual load power value exceeds the load power range or not: if not, indicating that the voltage of the direct-current micro-grid does not exceed the limit; and if yes, indicating that the voltage of the DC micro-grid is out of limit. Compared with the prior art, whether the bus voltage of the direct current micro-grid is out of limit or not can be judged through simple and convenient calculation, and effective adjustment is carried out.

Description

Technical Field

[0001] The present invention is applicable to the technical field of power grids, and in particular relates to a method for judging and adjusting voltage over-limit of a direct current microgrid. Background Art

[0002] In a DC microgrid, the bus voltage affects the operation of the entire system components. Therefore, the bus voltage of a DC microgrid needs to operate within the allowable deviation range. The requirements for the voltage deviation of the microgrid in different regions are different. Some regions are set to ±10%Un or ±5%Un of the rated voltage value. However, the factors affecting the bus voltage of a DC microgrid include the droop coefficient, the load size and load type of the system, etc. The droop coefficient is a control parameter, which may change during the operation of the system, and the load power consumption may have a certain degree of randomness. Therefore, a method is needed to take into account the droop coefficient and load factors, and to simply and effectively determine whether the bus voltage is out of limit. If the bus voltage exceeds the allowable range, a convenient adjustment method suitable for engineering applications should be given.

[0003] There are two types of loads in DC microgrids: constant power loads and resistive loads. Constant power loads are connected to the grid by converters, tend to consume constant power, and exhibit negative impedance characteristics. DC microgrid systems generally have two types of loads connected: constant power loads and resistive loads. The combined load exhibits nonlinear volt-ampere characteristics. In the existing related technologies, when performing relevant analysis of DC microgrids, only a single load type of resistive load or constant power load is considered. It is not accurate to judge whether the bus voltage exceeds the limit. It has high complexity and a small scope of application. The impact of the comprehensive load should be fully considered when making voltage judgments and voltage adjustments.

[0004] Therefore, a new voltage over-limit judgment and adjustment method for DC microgrid is urgently needed to solve the above technical problems. Summary of the invention

[0005] The present invention provides a method for judging and adjusting voltage over-limit of a DC microgrid, aiming to provide a method for judging whether the bus voltage of a DC microgrid is over-limit, which is simple and effective and has a wide application range.

[0006] The present invention provides a method for judging and adjusting voltage over-limit of a DC microgrid, comprising the following steps:

[0007] S1. Obtain the bus rated voltage and bus voltage deviation coefficient of the DC microgrid;

[0008] S2, obtaining a droop coefficient of the DC microgrid, and calculating according to the droop coefficient by a first preset rule to obtain an equivalent droop coefficient;

[0009] S3, calculating the load power upper limit and load power lower limit of the DC microgrid according to the bus rated voltage, the bus voltage deviation coefficient and the equivalent droop coefficient through a second preset rule to obtain a load power range;

[0010] S4. Calculate the actual load power value of the voltage of the DC microgrid;

[0011] S5. Determine whether the actual value of the load power exceeds the load power range: if not, it means that the voltage of the DC microgrid has not exceeded the limit; if so, it means that the voltage of the DC microgrid has exceeded the limit, and the voltage of the DC microgrid is adjusted.

[0012] Preferably, the first preset rule is to make the plurality of droop coefficients satisfy the following relationship:

[0013]

[0014] Among them, k eq represents the equivalent droop coefficient, k represents the control coefficient of the nth droop controller in the DC microgrid, and m represents the total number of droop controllers in the DC microgrid.

[0015] Preferably, the second preset rule is to make the bus rated voltage, the bus voltage deviation coefficient and the equivalent droop coefficient satisfy the following relationship:

[0016]

[0017] Wherein, δ represents the bus voltage deviation coefficient; U N Indicates the bus rated voltage, P ∑.limit1 , P ∑.limit2 Respectively represent the load power upper limit and the load power lower limit.

[0018] Preferably, the actual value of the load power satisfies the following rules:

[0019]

[0020] Wherein, P represents the actual value of the load power of the voltage of the DC microgrid, P cpl represents the equivalent constant power load of the DC microgrid, P R represents the resistive load power of the DC microgrid, U bus represents the bus voltage of the DC microgrid, and R represents the resistance value of the resistive load of the DC microgrid.

[0021] Preferably, the bus voltage satisfies the following rules:

[0022]

[0023] Preferably, step S5 further includes the following sub-steps:

[0024] S51, judging whether the actual value of the load power is less than the lower limit of the load power:

[0025] If yes, it means that the bus voltage of the DC microgrid is too high;

[0026] If not, it means that the bus voltage of the DC microgrid is too low;

[0027] S52: adjusting the bus voltage of the DC microgrid according to the droop reference voltage.

[0028] Preferably, the droop reference voltage is defined as U Nnew , the droop reference voltage satisfies the following rules:

[0029]

[0030] Compared with the prior art, the present invention obtains the bus rated voltage and bus voltage deviation coefficient of the DC microgrid; obtains the droop coefficients of multiple droop controllers in the DC microgrid, and calculates the equivalent droop coefficients according to the first preset rule based on the multiple droop coefficients; calculates the load power upper limit and load power lower limit of the DC microgrid according to the second preset rule based on the bus rated voltage, the bus voltage deviation coefficient and the equivalent droop coefficient to obtain the load power range; calculates the load power actual value of the voltage of the DC microgrid; determines whether the load power actual value exceeds the load power range: if not, it means that the voltage of the DC microgrid has not exceeded the limit; if so, it means that the voltage of the DC microgrid has exceeded the limit. In this way, the present invention can determine whether the bus voltage of the DC microgrid has exceeded the limit through simple calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be described in detail below in conjunction with the accompanying drawings. The above and other aspects of the present invention will become clearer and easier to understand through the detailed description made in conjunction with the following drawings. In the accompanying drawings:

[0032] Figure 1 It is a structural diagram of a DC microgrid of a method for determining and adjusting a voltage over-limit of a DC microgrid provided by an embodiment of the present invention;

[0033] Figure 2 It is a constant power load structure block diagram of the voltage over-limit judgment and adjustment method of the DC microgrid provided by an embodiment of the present invention;

[0034] Figure 3 It is a constant power supply structure block diagram of the voltage over-limit judgment and adjustment method of the DC microgrid provided by an embodiment of the present invention;

[0035] Figure 4 It is a structural block diagram of a converter droop controller of a voltage over-limit judgment and adjustment method of a DC microgrid provided by an embodiment of the present invention;

[0036] Figure 5 It is a simplified diagram of the equivalent structure of a DC microgrid of the voltage over-limit judgment and adjustment method of the DC microgrid provided by an embodiment of the present invention;

[0037] Figure 6 It is a schematic diagram of a balance point analysis of a DC microgrid of comprehensive load types according to a method for judging and adjusting a voltage over-limit of a DC microgrid provided by an embodiment of the present invention;

[0038] Figure 7 It is a schematic diagram of the voltage adjustment principle of a DC microgrid according to a method for judging and adjusting the voltage over-limit of a DC microgrid provided by an embodiment of the present invention;

[0039] Figure 8 1 is a schematic diagram of the structure of a DC microgrid equivalent to the method for determining and adjusting the voltage over-limit of a DC microgrid provided by an embodiment of the present invention;

[0040] Fig. 9 It is a schematic diagram of simulation waveforms of Case 1 of the voltage over-limit judgment and adjustment method of a DC microgrid provided by an embodiment of the present invention;

[0041] Fig.10 1 is a schematic diagram of simulation waveforms of Case 2 of the method for determining and adjusting voltage over-limit of a DC microgrid provided by an embodiment of the present invention;

[0042] Fig.11 1 is a schematic diagram of simulation waveforms of Case 3 of the method for determining and adjusting voltage over-limit of a DC microgrid provided by an embodiment of the present invention;

[0043] Fig.12 It is a flowchart of a method for determining and adjusting voltage over-limit of a DC microgrid provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0045] Please refer to Figure 1-Figure 12 The present invention provides a method for judging and adjusting voltage over-limit of a DC microgrid, comprising the following steps:

[0046] S1. Obtain the bus rated voltage and bus voltage deviation coefficient of the DC microgrid;

[0047] S2, obtaining a droop coefficient of the DC microgrid, and calculating according to the droop coefficient by a first preset rule to obtain an equivalent droop coefficient;

[0048] S3, calculating the load power upper limit and load power lower limit of the DC microgrid according to the bus rated voltage, the bus voltage deviation coefficient and the equivalent droop coefficient through a second preset rule to obtain a load power range;

[0049] S4. Calculate the actual load power value of the voltage of the DC microgrid;

[0050] S5. Determine whether the actual value of the load power exceeds the load power range: if not, it means that the voltage of the DC microgrid has not exceeded the limit; if so, it means that the voltage of the DC microgrid has exceeded the limit, and the voltage of the DC microgrid is adjusted.

[0051] In an embodiment of the present invention, the first preset rule is to make the plurality of droop coefficients satisfy the following relationship:

[0052]

[0053] Among them, k eq represents the equivalent droop coefficient, k represents the control coefficient of the nth droop controller in the DC microgrid, and m represents the total number of droop controllers in the DC microgrid.

[0054] In an embodiment of the present invention, the second preset rule is to make the bus rated voltage, the bus voltage deviation coefficient and the equivalent droop coefficient satisfy the following relationship:

[0055]

[0056] Wherein, δ represents the bus voltage deviation coefficient, which is usually determined by the operation standard of the power grid area where the microgrid is located; U N Indicates the bus rated voltage, P ∑.limit1 , P ∑.limit2 Respectively represent the load power upper limit and the load power lower limit.

[0057] In the embodiment of the present invention, the actual value of the load power satisfies the following rules:

[0058]

[0059] Wherein, P represents the actual value of the load power of the voltage of the DC microgrid, P cpl represents the equivalent constant power load of the DC microgrid, P R represents the resistive load power of the DC microgrid, U busrepresents the bus voltage of the DC microgrid, and R represents the resistance value of the resistive load of the DC microgrid.

[0060] In the embodiment of the present invention, the bus voltage satisfies the following rules:

[0061]

[0062] In the embodiment of the present invention, step S5 further includes the following sub-steps:

[0063] S51, judging whether the actual value of the load power is less than the lower limit of the load power:

[0064] If yes, it means that the bus voltage of the DC microgrid is too high;

[0065] If not, it means that the bus voltage of the DC microgrid is too low.

[0066] S52: adjusting the bus voltage of the DC microgrid according to the droop reference voltage.

[0067] Define the droop reference voltage as U Nnew , the droop reference voltage satisfies the following rules:

[0068]

[0069] Specifically, an independently operated DC microgrid with multiple DC power sources and loads is Figure 1 As shown in Figure 1. A DC microgrid is usually composed of a distributed power source, an energy storage device, a constant power load, a resistive load, a bus cable, and a bus side capacitor. The distributed power source, the energy storage device, and the constant power load are connected to the DC bus through a converter.

[0070] The present invention calculates the load power range of the DC microgrid better and determines whether the voltage of the DC microgrid exceeds the limit by respectively performing equivalent modeling of the load of the DC microgrid, equivalent modeling of energy storage and equivalent modeling of the DC microgrid system.

[0071] Equivalent modeling of loads. In order to maximize the utilization of renewable energy, distributed power sources such as photovoltaic power generation and wind power generation usually adopt maximum power point tracking technology. The control method of their grid-connected converters is to track the maximum power. The output power fluctuates with the natural environment and can be regarded as a constant power power supply. The output power of a constant power power supply is mainly affected by the natural environment rather than the bus voltage. Therefore, distributed power sources and constant power loads have similar characteristics. A constant power power supply can be regarded as a constant power load with a negative output current. When simplifying the mathematical model of a DC microgrid, it can be simplified into an equivalent constant power load with bidirectional power flow. It is combined with existing loads such as resistors to form a comprehensive load of a DC microgrid. The constant power load structure is as follows: Figure 2 As shown, the constant power supply is Figure 3 shown.

[0072] The constant power load and constant power source connected to the same bus can be simplified into an equivalent load. The output current of the jth constant power source is recorded as I cps.j , which is equivalent to a load current of -I cps.j Assuming that there are m1 constant power loads and m2 constant power sources in the DC microgrid system, the combined equivalent constant power load current is:

[0073]

[0074] Equivalent modeling of energy storage,In the DC microgrid, the converter control of the energy storage device adopts voltage-current droop control. In steady-state operation, the output end is equivalent to a series connection of an ideal voltage source and a resistor, such as Figure 4 As shown. The reference value u of the voltage loop in the above figure is ref It is obtained from the droop control algorithm that when droop control is adopted, the operating characteristics of the energy storage system can be expressed as.

[0075] u ref =U N -(k+r)i; (2)

[0076] Among them U N is the bus rated voltage of the DC microgrid system, u ref is the bus voltage control instruction, i is the current output from the converter to the bus, r is the line resistance between the energy storage device and the load point, and k is the virtual resistance of the droop control. Usually r<<k, so the line resistance is generally ignored in the related art and only the droop coefficient is considered. In the present invention, the virtual resistance and the line resistance are combined into a virtual resistance k, that is, the droop coefficient of the energy storage converter.

[0077] The distributed power source using droop control adds a feedback link of the output current of the distributed power source on the basis of the voltage and current dual-loop control to achieve output current regulation. Therefore, the parameter design of the droop controller must first ensure the stability of the dual closed-loop control, and on this basis, use current feedback to achieve autonomous distribution of load power. The energy storage converters running in parallel are all in the droop control working area, and the bus voltage changes with the load power according to the droop control. In a DC microgrid system where multiple energy storage converters run in parallel, the converter can be further equivalent. Suppose the mathematical model of the nth droop control converter running in parallel is:

[0078]

[0079] Among them, i n is the bus output current, L n is the inductance connected in series on the output side, k n is the droop coefficient (or virtual resistance). eq is the equivalent output current of the energy storage system of the entire DC microgrid, which can be expressed as:

[0080]

[0081] Therefore, the equivalent droop coefficient k of multiple droop converters in parallel operation in the energy storage system is eq It can be expressed as:

[0082]

[0083] When n energy storage devices using droop control are operated in parallel, in order to prevent the energy storage unit with small capacity from reaching a state of too high or too low charge first and causing the energy storage device to exit operation, the droop coefficient of the grid-connected converter of the energy storage device is usually set to meet the following requirements:

[0084] k1i1=k2i2=…=k n i n ; (6)

[0085] In practice, the filter inductance and droop coefficient of the converter usually have the following relationship:

[0086]

[0087] Therefore, the equivalent inductance of the energy storage device can be written as:

[0088]

[0089] In summary, the equivalent output current of energy storage devices in parallel operation with droop control can be rewritten as

[69] :

[0090]

[0091] The equivalent model of energy storage devices operating in parallel can be summarized as:

[0092]

[0093] Equivalent modeling of DC microgrids, single-bus DC microgrid systems usually cover a small geographical area, so the length of the connecting cables is short, and the impedance of the connecting wires is small and can be ignored. The DC bus capacitance and resistance load can be equivalently expressed as:

[0094]

[0095] Where C is the total capacitance of the DC bus of the DC microgrid, and R is the total resistive load of the DC microgrid.

[0096]

[0097] Combining the above equivalent models, the equivalent circuit model of the DC microgrid can be obtained. The simplified DC microgrid model consists of a DC power supply, a DC bus capacitor, a resistive load RL and a constant power load P cpl Composition, such as Figure 5 shown.

[0098] After equivalent simplification of the DC microgrid, the current and voltage expressions of the DC microgrid in steady state can be obtained:

[0099]

[0100] Among them, U bus is the bus voltage, I dc is the output current of the droop control power supply, P cpl is the equivalent constant power load power value, R is the equivalent resistive load resistance value, C is the equivalent bus capacitance, and L is the equivalent inductance of the droop power supply.

[0101] Among them, I dc Indicates the droop power supply output current. If I dc A positive value indicates that the energy storage device is in a discharging state and outputs power to the bus. Correspondingly, I dc If it is a negative value, it means that the energy storage device is in a charging state and absorbs power from the bus. The comprehensive load of the DC microgrid consists of a constant power load CPL and a resistance load RL, and its power and current can be expressed as:

[0102]

[0103] The volt-ampere characteristic of the integrated load can be obtained from equation (14). The relationship between the voltage and current of the integrated load can be obtained by Figure 6In the equivalent DC microgrid model, if the total load of the constant power source is less than the total constant power source, the equivalent constant power load P cpl is a positive value, which indicates power consumption. On the contrary, the equivalent constant power load P cpl It is a negative value, which represents the system output power of the DC microgrid.

[0104] The load curve P in the figure cpl <0 is the volt-ampere characteristic curve when the constant power load is negative, and the load curve P cpl >0 is the volt-ampere characteristic curve when the constant power load is positive. The intersection of the droop curve and the load volt-ampere characteristic curve is the stable operating point of the DC microgrid system. The steady-state operating point of the DC microgrid system with a constant power load can be divided into two types of operating points. The first type of operating point is a steady-state operating point that can be used, and the second type of operating point is usually not used because the second type of operating point deviates too much from the rated voltage, and when the DC microgrid system operates at the second type of operating point, it will easily become unstable after being disturbed. Therefore, the subsequent discussion on the steady-state operating point refers to the first type of operating point.

[0105] The size and type of the combined loads in a DC microgrid system usually vary. Figure 6 This is a typical combined load.

[0106] In a DC microgrid, the bus voltage affects the operation of the entire DC microgrid system components. Therefore, the bus voltage of the DC microgrid needs to operate within the allowable deviation range, which is usually set to ±10% of the rated value. n Or ±5%U n There are two types of loads in the DC microgrid: constant power load and resistance load. Therefore, it is necessary to analyze which type of load plays a major role in generating bus voltage deviation.

[0107] In order to analyze the influence of constant power load and resistance load on bus voltage, the resistance value R of the resistance load is converted into the power P of the resistance load. R .Will Substitute the voltage expression of the DC microgrid system steady-state operation point into formula (13), eliminate the resistance value R of the resistive load, and obtain the bus voltage U bus and P R and P cpl The expression of is as follows, which can be simplified to obtain:

[0108] U bus 2 -U N U bus +k(P cpl +P R )=0;(15)

[0109] Further rearrangement of the above formula can give the expression of bus voltage:

[0110]

[0111] From the above formula, it can be seen that the influence of constant power load and resistance load on bus voltage is the same, that is, when the total load power P = P cpl +P R When it remains unchanged, no matter what the proportion of constant power load and resistive load in the total power is, the impact on the bus voltage remains unchanged.

[0112] Assume that the operating range of bus voltage is (1-δ)U N <U bus <(1+δ)U N , then the actual value P of the load power of the DC microgrid should be within the following range:

[0113]

[0114] Wherein, δ represents the bus voltage deviation coefficient, which is usually determined by the operation standard of the power grid area where the microgrid is located; k represents the equivalent droop coefficient, P ∑.limit1 , P ∑.limit2 Respectively represent the load power upper limit and the load power lower limit.

[0115] If the bus voltage exceeds the limit, the bus voltage can be adjusted by adjusting the droop parameters. The droop parameters include the rated voltage U N And the equivalent droop coefficient k eq , in multiple droop power supplies operating in parallel, the equivalent droop coefficient k of droop control eq Usually, the value is determined by considering factors such as current sharing accuracy and the charge state of the energy storage battery. N is a better method. Taking Pcpl>0 as an example, the principle of shifting the droop curve upward to adjust the voltage is demonstrated. The specific adjustment method is as follows Figure 7 As shown. N It is the reference voltage of the original droop curve, and its value is equal to the rated bus voltage U of the DC microgrid. NS ; U Nnew is the reference voltage of the droop curve after translation. The original voltage of the steady-state operation point a1 is too low, but after adjustment, the new operation point a2 can make the bus voltage of the system run at the rated voltage value U NS .

[0116] The operating point of the new equivalent droop coefficient can be derived from the bus voltage expression in equation (13).

[0117]

[0118] In the above formula, k eq is the equivalent droop coefficient, Pcpl is the equivalent constant power load, and R is the equivalent resistance load.

[0119] Exemplarily, a simulation model is established through PSCAD to demonstrate the voltage judgment method and the voltage adjustment method.

[0120] The bus rated voltage U of the DC microgrid case used in the simulation SN =200V, the allowable operating range of voltage is (190V, 210V), and the allowable deviation coefficient δ = ±5%. The power grid contains two energy storage power supplies, both of which use droop control, with droop coefficients of k1 = 1 and k2 = 0.6, respectively, then the equivalent droop coefficient is 0.375; the rated voltage of the two droop power supplies is U N =200V. A photovoltaic power station adopts maximum power point tracking control, referred to as MPPT control. Since the output power is mainly affected by the light intensity and not affected by the bus voltage, it is equivalent to an equal power supply. The load includes constant power load and resistance load. The simulation parameters are shown in the following table. The voltage situation determined by the voltage judgment process is.

[0121]

Table 1

[0122]

[0123] According to the voltage judgment process proposed in this patent, the bus voltage values ​​of the first and second sets of data in the above table are within the allowable range, while the voltage of the third set of data is too low and needs to be adjusted. According to the method of this patent, the adjusted droop control parameter U should be calculated according to formula (18). N , the adjusted droop control parameter is U Nnew , its value is 213.125V. The structure of the simulation model is as follows Figure 8 shown.

[0124] The simulation waveform of Case 1 is as follows Fig. 9 As shown in the figure, at the time of 0.3s, the constant power load and resistance load in the above table are applied. At the time of 0.3s, the bus voltage drops significantly. The bus voltage value is 191.3V, which is consistent with the calculated value and belongs to the normal voltage deviation range. The output power of converters 1 and 2 is inversely proportional to the droop coefficient, PDC1:PDC2=k2:k1, which is consistent with the power distribution principle of droop control.

[0125] The simulation waveform of Case 2 is as follows Fig.10As shown in the figure, at the time of 0.3s, the constant power load and resistance load in the above table are applied. It can be seen that at the time of 0.3s, the bus voltage drops significantly. The bus voltage value is 201.9V, which is consistent with the calculated value and belongs to the normal voltage deviation range. The absorbed power of converters 1 and 2 is inversely proportional to the droop coefficient, PDC1:PDC2=k2:k1, which is consistent with the power distribution principle of droop control.

[0126] The simulation waveform of Case 3 is as follows Fig.10 As shown, at a time of 0.3s, the constant power load and resistance load in the above table are applied. It can be seen that at 0.3s, the bus voltage drops significantly. The bus voltage value is 186.4V, which is consistent with the calculated value. The voltage is too low and exceeds the normal voltage deviation range. The absorbed power of converters 1 and 2 is inversely proportional to the droop coefficient, PDC1:PDC2=k2:k1, which is consistent with the power distribution principle of droop control. At 1.5s, the reference voltage value of the droop parameter is adjusted to 213.125, and it can be seen that the bus voltage returns to the system rated value of 200V. This illustrates the feasibility of the method of the present invention.

[0127] Compared with the prior art, the present invention obtains the bus rated voltage and bus voltage deviation coefficient of the DC microgrid; obtains the droop coefficients of multiple droop controllers in the DC microgrid, and calculates the equivalent droop coefficients according to the first preset rule based on the multiple droop coefficients; calculates the load power upper limit and load power lower limit of the DC microgrid according to the second preset rule based on the bus rated voltage, the bus voltage deviation coefficient and the equivalent droop coefficient to obtain the load power range; calculates the load power actual value of the voltage of the DC microgrid; determines whether the load power actual value exceeds the load power range: if not, it means that the voltage of the DC microgrid has not exceeded the limit; if so, it means that the voltage of the DC microgrid has exceeded the limit. In this way, the present invention can determine whether the bus voltage of the DC microgrid has exceeded the limit through simple calculation.

[0128] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0129] The embodiments of the present invention are described above in conjunction with the accompanying drawings. What is disclosed is only the preferred embodiment of the present invention. However, the present invention is not limited to the above-mentioned specific implementation manner. The above-mentioned specific implementation manner is only illustrative rather than restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms and equivalent changes without departing from the scope of protection of the purpose of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for judging and adjusting voltage over-limit of a DC microgrid, characterized in that: The following steps are involved: S1. Obtain the bus rated voltage and bus voltage deviation coefficient of the DC microgrid; S2, obtaining droop coefficients of multiple droop controllers in the DC microgrid, and calculating according to the multiple droop coefficients by a first preset rule to obtain an equivalent droop coefficient; S3, calculating the load power upper limit and load power lower limit of the DC microgrid according to the bus rated voltage, the bus voltage deviation coefficient and the equivalent droop coefficient through a second preset rule to obtain a load power range; S4. Calculate the actual load power value of the voltage of the DC microgrid; S5. Determine whether the actual value of the load power exceeds the load power range: if not, it means that the voltage of the DC microgrid has not exceeded the limit; if so, it means that the voltage of the DC microgrid has exceeded the limit, and the voltage of the DC microgrid is adjusted.

2. The voltage over-limit judgment and adjustment method of a DC microgrid as claimed in claim 1, characterized in that: The first preset rule is to make the plurality of droop coefficients satisfy the following relationship: Among them, k eq represents the equivalent droop coefficient, k represents the control coefficient of the nth droop controller in the DC microgrid, and m represents the total number of droop controllers in the DC microgrid.

3. The voltage over-limit judgment and adjustment method of the DC microgrid as claimed in claim 2, characterized in that: The second preset rule is to make the bus rated voltage, the bus voltage deviation coefficient and the equivalent droop coefficient satisfy the following relationship: Wherein, δ represents the bus voltage deviation coefficient; U N Indicates the bus rated voltage, P ∑.limit1 , P ∑.limit2 Respectively represent the load power upper limit and the load power lower limit.

4. The voltage over-limit judgment and adjustment method of a DC microgrid as claimed in claim 3, characterized in that: The actual value of the load power meets the following rules: Wherein, P represents the actual value of the load power of the voltage of the DC microgrid, P cpl represents the equivalent constant power load of the DC microgrid, P R represents the resistive load power of the DC microgrid, U bus represents the bus voltage of the DC microgrid, and R represents the resistance value of the resistive load of the DC microgrid.

5. The voltage over-limit judgment and adjustment method of a DC microgrid as claimed in claim 4, characterized in that: The bus voltage satisfies the following rules:

6. The voltage over-limit judgment and adjustment method of a DC microgrid as claimed in claim 5, characterized in that: Step S5 also includes the following sub-steps: S51, judging whether the actual value of the load power is less than the lower limit of the load power: If yes, it means that the bus voltage of the DC microgrid is too high; If not, it means that the bus voltage of the DC microgrid is too low; S52: adjusting the bus voltage of the DC microgrid according to the droop reference voltage.

7. The method for determining and adjusting voltage over-limit of a DC microgrid according to claim 6, characterized in that: Define the droop reference voltage as U Nnew , the droop reference voltage satisfies the following rules:

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