Voltage over-limit judgment and adjustment method for DC microgrid

Abstract

The present invention provides a method for judging and adjusting the voltage over-limit of a DC microgrid. 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 a 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 a 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 actual load power value of the DC microgrid voltage; and judges whether the actual load power value exceeds the load power range: if not, it indicates that the voltage of the DC microgrid is not over-limit; if so, it indicates that the voltage of the DC microgrid is over-limit. Compared with the prior art, the present invention can judge whether the bus voltage of the DC microgrid is over-limit through simple calculation and make effective adjustments.

Description

Technical Field

[0001] The present invention is applicable to the field of power grid technology, and in particular relates to a method for determining and adjusting voltage over-limit in a DC microgrid. Background Art

[0002] In a DC microgrid, bus voltage affects the operation of all system components. Therefore, the bus voltage of a DC microgrid must operate within an allowable deviation range. Different regions have different voltage deviation requirements for microgrids, with some regions setting the range within ±10% Un or ±5% Un of the rated voltage. However, factors influencing the bus voltage of a DC microgrid include the droop factor, the size and type of load carried by the system, and other factors. The droop factor is a control parameter that may vary during system operation, and load power consumption can exhibit a certain degree of randomness. Therefore, a simple and effective method is needed to determine whether the bus voltage exceeds the limit, taking into account the droop factor and load factors. If the bus voltage exceeds the allowable range, a convenient adjustment method suitable for engineering applications should be provided.

[0003] There are two types of loads in DC microgrids: constant power loads and resistive loads. Constant power loads are connected to the grid via converters and tend to consume constant power, exhibiting a negative impedance characteristic. DC microgrid systems generally incorporate both constant power and resistive loads, resulting in a combined load exhibiting a nonlinear volt-ampere characteristic. Existing techniques for DC microgrid analysis only consider resistive or constant power loads, resulting in inaccurate bus voltage limit determinations. These methods are complex and have limited applicability. The impact of these combined loads should be fully considered when determining and adjusting voltage.

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

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

[0006] The present invention provides a method for determining and adjusting voltage over-limit in 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 using a first preset rule to obtain an equivalent droop coefficient;

[0009] S3. Calculate 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 using 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 indicates that the voltage of the DC microgrid is within the limit; if so, it indicates 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 busbar 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. Determine whether the actual load power value 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: Adjust 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 coefficient according to the multiple droop coefficients using a first preset rule; calculates 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 using a second preset rule to obtain the load power range; calculates the actual load power value of the DC microgrid voltage; and determines whether the actual load power value exceeds the load power range: if not, it indicates that the DC microgrid voltage is within the limit; if so, it indicates that the DC microgrid voltage is within the limit. In this way, the present invention can determine whether the DC microgrid bus voltage is beyond the limit through simple calculation. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0032] Figure 1 1 is a structural diagram of a DC microgrid according to an embodiment of the present invention;

[0033] Figure 2 This is a block diagram of a constant power load structure of a method for determining and adjusting voltage over-limit in a DC microgrid provided by an embodiment of the present invention;

[0034] Figure 3 This is a block diagram of a constant power supply structure of a method for determining and adjusting voltage over-limit in a DC microgrid provided by an embodiment of the present invention;

[0035] Figure 4 This is a structural block diagram of a converter droop controller for a method for determining and adjusting voltage over-limit in a DC microgrid provided by an embodiment of the present invention;

[0036] Figure 5 This is a simplified diagram of the equivalent structure of a DC microgrid according to the method for determining and adjusting the voltage over-limit of a DC microgrid provided by an embodiment of the present invention;

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

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

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

[0040] Figure 9 1 is a schematic diagram of simulation waveforms of Case 1 of the method for determining and adjusting voltage over-limit in a DC microgrid provided by an embodiment of the present invention;

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

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

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

[0044] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to 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 Figures 1-12 The present invention provides a method for determining 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 using a first preset rule to obtain an equivalent droop coefficient;

[0048] S3. Calculate 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 using 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 indicates that the voltage of the DC microgrid is within the limit; if so, it indicates 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 grid area where the microgrid is located; U N Indicates the busbar rated voltage, P ∑.limit1 , P ∑.limit2 Respectively represent the load power upper limit and the load power lower limit.

[0057] In this 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 this embodiment of the present invention, the bus voltage satisfies the following rules:

[0061]

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

[0063] S51. Determine whether the actual load power value 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: Adjust 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, a DC microgrid with multiple DC power sources and loads can be operated independently, such as Figure 1 As shown in Figure 1, a DC microgrid typically consists of a distributed power supply (DGS), an energy storage device, a constant power load, a resistive load, bus cables, and bus-side capacitors. The DGS, energy storage device, and constant power load are connected to the DC bus via 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 the 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 the 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 equivalent constant power load current after combination is:

[0073]

[0074] Equivalent modeling of energy storage. In DC microgrids, the converter control of energy storage equipment 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 According to the droop control algorithm, 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 command, i is the converter output current to the bus, r is the line resistance between the energy storage device and the load point, and k is the virtual resistance for droop control. Generally, r<<k, so related art generally ignores the line resistance and considers only the droop coefficient. In this invention, the virtual resistance and line resistance are combined into a virtual resistance k, which is the droop coefficient of the energy storage converter.

[0077] The distributed power supply using droop control adds a feedback link of the distributed power supply output current to the voltage and current dual-loop control to achieve output current regulation. Therefore, the design of the droop controller parameters must first ensure the stability of the dual closed-loop control, and then 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 with multiple energy storage converters running in parallel, the converters can be further equivalent. Assume that 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 inductor 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 running in parallel 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, to prevent the smaller energy storage unit from reaching an overcharge or undercharge state first, causing the energy storage device to stop operating, 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 using droop control when operating in parallel can be rewritten as

[69] :

[0090]

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

[0092]

[0093] Equivalent modeling of DC microgrids: Single-bus DC microgrid systems usually cover a small geographical area, so their connecting cables are 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. Its power and current can be expressed as:

[0102]

[0103] The volt-ampere characteristic of the integrated load can be obtained from formula (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, showing the 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, the load curve P cpl >0 represents 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 represents the stable operating point of the DC microgrid system. The steady-state operating point of a DC microgrid system with a constant power load can be divided into two categories. The first category is acceptable, while the second category is generally not used because it deviates significantly from the rated voltage and can easily lead to instability when the DC microgrid is operating at the second category. Therefore, the subsequent discussion of steady-state operating points refers to the first category.

[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 all system components of the DC microgrid. 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 a DC microgrid: constant power load and resistive 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 operating point (13) into the equation, eliminate the resistance value R of the resistive load, and obtain the bus voltage U bus and P R and P cpl The expression is as follows, which can be simplified to get:

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

[0109] By further sorting out the above formula, we can get the expression of bus voltage as follows:

[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 of the load power P 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 operating standard of the 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 state of charge of the energy storage battery. N This 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 value U of the DC microgrid. NS ;U Nnew The original steady-state operating point a1 has a low voltage, but after adjustment, the new operating point a2 can make the system bus voltage run at the rated voltage 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] For example, a simulation model is established by 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 k1 = 1 and k2 = 0.6 respectively, so the equivalent droop coefficient is 0.375; the rated voltage of the two drooping power supplies is U N = 200V. A photovoltaic power station uses maximum power point tracking (MPPT) control. Since output power is primarily affected by sunlight intensity and not bus voltage, it is equivalent to a constant power supply. The loads include constant power loads and resistive loads. The simulation parameters are shown in the table below. The voltage conditions determined by the voltage determination process are:

[0121]

Table 1

[0122]

[0123] In the three sets of data in the table above, according to the voltage judgment process proposed in this patent, the bus voltage values ​​of the first and second sets of data are within the allowable range, and 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 Figure 9 As shown in the figure, at time 0.3s, the constant power load and resistive load shown in the table above are applied. At time 0.3s, the bus voltage shows a significant drop. The bus voltage is 191.3V, consistent with the calculated value and within the normal voltage deviation range. The output power of converters 1 and 2 is inversely proportional to the droop factor, PDC1:PDC2 = k2:k1, consistent with the power distribution principle of droop control.

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

[0126] The simulation waveform of Case 3 is as follows Figure 10 As shown, at a time of 0.3s, the constant power load and resistive 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 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 coefficient according to the multiple droop coefficients using a first preset rule; calculates 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 using a second preset rule to obtain the load power range; calculates the actual load power value of the DC microgrid voltage; and determines whether the actual load power value exceeds the load power range: if not, it indicates that the DC microgrid voltage is within the limit; if so, it indicates that the DC microgrid voltage is within the limit. In this way, the present invention can determine whether the DC microgrid bus voltage is beyond the limit through simple calculation.

[0128] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0129] The embodiments of the present invention are described above in conjunction with the accompanying drawings. What is disclosed is only a preferred embodiment of the present invention. However, the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance 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, which are all within the protection of the present invention.

Claims

1. A method for judging and adjusting voltage over-limit in 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 using a first preset rule to obtain an equivalent droop coefficient; S3. Calculate 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 using 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 load power value exceeds the load power range: if not, it indicates that the voltage of the DC microgrid is within the limit; if so, it indicates that the voltage of the DC microgrid has exceeded the limit, and adjust the voltage of the DC microgrid; Step S5 further includes the following sub-steps: S51. Determine whether the actual load power value 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; Define the droop reference voltage as , the droop reference voltage satisfies the following rules: ； in, represents the equivalent droop coefficient or virtual resistance, represents the resistance value of the resistive load of the DC microgrid, Indicates the busbar rated voltage, represents the equivalent constant power load of the DC microgrid.

2. The method for determining and adjusting voltage over-limit in a DC microgrid according to claim 1, wherein: The first preset rule is to make the plurality of droop coefficients satisfy the following relationship: ； in, represents the equivalent droop coefficient or virtual resistance, represents the control coefficient of the nth droop controller in the DC microgrid, m represents the total number of droop controllers in the DC microgrid.

3. The method for determining and adjusting voltage over-limit in a DC microgrid according to claim 2, wherein: 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: ； in, represents the bus voltage deviation coefficient; U N Indicates the busbar rated voltage, , Respectively represent the load power upper limit and the load power lower limit.

4. The method for determining and adjusting voltage over-limit in a DC microgrid according to claim 3, wherein: The actual load power value meets the following rules: ； in, represents the actual value of the load power of the voltage of the DC microgrid, represents the equivalent constant power load of the DC microgrid, represents the resistive load power of the DC microgrid, represents the bus voltage of the DC microgrid, R Indicates the resistance value of the resistive load of the DC microgrid.

5. The method for determining and adjusting voltage over-limit in a DC microgrid according to claim 4, wherein: The bus voltage satisfies the following rules: 。

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