CN108599199B - Improved microgrid internal frequency partition control method based on droop method control - Google Patents
Improved microgrid internal frequency partition control method based on droop method control Download PDFInfo
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Abstract
The embodiment of the invention discloses a method for detecting the bus frequency of a micro-grid system; determining the region where the bus frequency is located according to a preset frequency division standard; and controlling internal equipment of the micro-grid system according to the region where the bus frequency is located. By implementing the embodiment of the invention, the frequency in different areas can be controlled in a non-passing way, the system frequency can be stabilized within the range (49.5 Hz-50.5 Hz) required by the national standard (GB/T12325), and the stability of the system is ensured.
Description
Technical Field
The invention relates to the technical field of micro-grids, in particular to an improved micro-grid internal frequency partition control method based on droop method control.
Background
Compared with the traditional large power grid, the micro power grid has larger differences in structure, power supply and load. This makes the conventional large grid control methods no longer adaptable to the control requirements of the microgrid.
In view of the situation of the micro-grid system, when energy in the system fluctuates, the voltage and frequency of the system often fluctuate. When the frequency of the system changes, an appropriate control strategy needs to be adopted to ensure the stability of the system.
Disclosure of Invention
The embodiment of the invention aims to provide an improved method for controlling the internal frequency partition of a microgrid based on droop method control, so that the frequency of different areas is controlled in an unqualified control strategy, the system frequency is stabilized within a national standard requirement range, and the stability of the system is ensured.
In order to achieve the above object, an embodiment of the present invention provides an improved method for controlling an internal frequency partition of a microgrid based on droop method control, including:
detecting the bus frequency of the microgrid system;
determining a region where the bus frequency is located according to a preset frequency division standard, wherein the frequency division standard comprises an AH region, an AL region, a BH region, a BL region, a CH region and a CL region;
and controlling internal equipment of the micro-grid system according to the region where the bus frequency is located.
In a preferred embodiment of the present invention, when the bus frequency is in the AH zone or the AL zone, the charging control, the discharging control, and the balancing control are performed on the storage battery of the microgrid system.
Specifically, the discharge control of the storage battery of the microgrid system specifically comprises the following steps:
(1) carrying out state evaluation on the storage battery, reporting to an upper computer and changing a control mode into a balance control mode if the storage battery finishes discharging, and turning to the step (2) if the storage battery does not finish discharging;
(2) performing state evaluation on the storage battery again, and if the storage battery is in a non-discharge state, turning to the step (3);
(3) if the diesel engine is in a closed state, sequentially reducing the power of the distributed power supply according to the ascending power sequence of the priority; and if the diesel engine is in an open state and the storage battery cannot bear the load of the diesel engine, sequentially reducing the power of the distributed power supply according to the ascending power order of the priority.
4. The method as claimed in claim 2 or 3, wherein the balancing control of the storage battery of the microgrid system specifically comprises:
(1) evaluating the current state of the load, and if the current state of the load is in a relatively stable state, turning to the step (2);
(2) evaluating the current state of the distributed generator, and if the distributed generator is in a stable state, turning to the step (3);
(3) acquiring the current state of the diesel engine, and if the diesel engine is in a shutdown state, turning to the step (4);
(4) if the situation that the non-sensitive load is not accessed exists in the micro-grid system and the non-sensitive load is allowed to be accessed by the current power generation plan, accessing the non-sensitive load according to the ascending power sequence of the load priority; if the non-sensitive loads of the micro-grid system are all accessed or the current power generation plan does not allow the non-sensitive loads to be accessed, the step (5) is carried out;
(5) and sequentially reducing the power of the distributed power supplies according to the ascending power order of the priority.
Specifically, if the bus frequency is in the BH zone, controlling the internal devices of the microgrid system specifically includes:
(1) estimating the state of charge of the storage battery, if the storage battery is in an unfilled state, turning to the step (2), and if the storage battery is in a filled state, turning to the step (3);
(2) performing charging control on the storage battery;
(3) if the disturbance time is more than 30 minutes and the diesel engine is in a starting state, turning to the step (4); if the disturbance time is more than 30 minutes and the diesel engine is in a shutdown state, turning to the step (5);
(4) evaluating the current generating power of the diesel engine, and closing the diesel engine or reducing the generating power of the distributed generator according to the ascending power of the priority level according to the evaluation result;
(5) and if the micro-grid system has the condition that no load is not accessed, sequentially accessing the non-sensitive loads in an ascending power sequence, and if the micro-grid system does not have the condition that no load is accessed, reducing the generating power of the distributed generator in an ascending power according to the priority.
Specifically, if the bus frequency is in the BL region, controlling the internal device of the microgrid system specifically includes:
(1) if the distributed power supply is 100% of the maximum output, turning to the step (2), and if the distributed power supply is not 100% of the maximum output, adjusting the distributed power supply;
(2) performing state evaluation on the storage battery, if the storage battery can be discharged, performing discharge control on the storage battery, and otherwise, turning to the step (3);
(3) if the disturbance time is less than 30 minutes, maintaining the discharge state of the storage battery, otherwise, turning to the step (4);
(4) if the diesel engine is in an open state and the non-sensitive load of the micro-grid system is not cut off, cutting off the non-sensitive load according to a power lowering sequence; if the non-sensitive load is completely removed, reporting the energy shortage of the micro-grid system in the BL area to the monitoring system, and maintaining the current situation.
Specifically, if the bus frequency is in the CH region, controlling the internal devices of the microgrid system specifically includes:
(1) if the diesel engine is in a closed state, checking whether the distributed power supplies have faults one by one;
(2) if the fault occurs, cutting off the distributed power supply, otherwise, turning to the step (3);
(3) cutting off the distributed power supplies one by one according to the power reduction times of the priority of the distributed generator, and reporting the power generation times to a micro-grid system of an upper layer monitoring system to generate a CH area fault;
(4) and if the disturbance time of the CH area is greater than the preset time, stopping the micro-grid system and reporting the system fault of the upper computer.
Specifically, if the bus frequency is in the CL region, controlling the internal device of the microgrid system specifically includes:
(1) discharging control is carried out on the storage battery, the state of the diesel engine is detected, and if the diesel engine is in the opening state, the step (2) is carried out;
(2) checking whether the distributed power supply is in a 100% output state, if so, adjusting to the 100% output state, and if not, turning to the step (3);
(3) detecting whether a non-sensitive load is accessed into the microgrid system, if so, cutting off all the non-sensitive loads, and if not, turning to the step (4);
(4) if the distributed generator and the primary load have faults, the operation of cutting system equipment is adopted;
(5) and predicting the stability of the micro-grid system, and reporting the fault of the frequency CL region of the micro-grid system of the upper monitoring system or carrying out shutdown operation on the system according to the prediction result.
By implementing the embodiment of the invention, the bus frequency of the microgrid system is detected, the region where the bus frequency is located is determined according to the preset frequency division standard, and finally the internal equipment of the microgrid system is controlled according to the region where the bus frequency is located; namely, the embodiment of the invention can adopt a non-passing control strategy for the frequencies in different regions, can realize the stabilization of the system frequency within the national standard (GB/T12325) requirement range (49.5 Hz-50.5 Hz), and ensures the stability of the system.
Drawings
In order to more clearly illustrate the detailed description of the invention or the technical solutions in the prior art, the drawings that are needed in the detailed description of the invention or the prior art will be briefly described below. Throughout the drawings, like elements or portions are generally identified by like reference numerals. In the drawings, elements or portions are not necessarily drawn to scale.
Fig. 1 is a schematic flow chart of an improved method for controlling partition of internal frequency of a microgrid based on droop method control according to a first embodiment of the present invention;
FIG. 2 is a flow chart of the control of the charging of the battery with the frequency in zone A;
FIG. 3 is a flow chart of discharge control for the battery with the frequency in zone A;
FIG. 4 is a control flow diagram of the case of additional charging of the floating power of the battery with the frequency in zone A;
FIG. 5 is a control flow chart of the case of extra discharge of the floating power of the storage battery when the frequency is in the region A;
FIG. 6 is a flow chart of frequency control when the frequency is in the BH region;
FIG. 7 is a flow chart of frequency control when the frequency is in the BL region;
fig. 8 is a flowchart of frequency control when the frequency is in the CH region;
fig. 9 is a flowchart of frequency control when the frequency is in the CL region.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.
As used in this specification and the appended claims, the term "if" may be interpreted contextually as "when", "upon" or "in response to a determination" or "in response to a detection". Similarly, the phrase "if it is determined" or "if a [ described condition or event ] is detected" may be interpreted contextually to mean "upon determining" or "in response to determining" or "upon detecting [ described condition or event ]" or "in response to detecting [ described condition or event ]".
For a better understanding of the embodiments of the present invention, the following description is made:
the final purpose of the microgrid control strategy designed in this embodiment is to achieve energy balance in the microgrid, that is, the sum of the generated energy of each distributed generator is equal to the sum of the power consumption of the load, and at the same time, to achieve stabilization of the internal voltage and frequency of the microgrid, as shown in formulas 3-1 to 3-3
Vmin≤V(t)≤Vmax(3-1)
fmin≤f(t)≤fmax(3-2)
∑PDG(t)＝∑Pload(t) (3-3)
Where V (t) is the system bus voltage at the present moment, which should be between the upper limit VmaxAnd a lower limit VminIn the meantime. f (t) is the frequency of the busbar at the present moment, which should be between a defined upper limit fmaxWith a lower limit fminIn the meantime. According to the requirements of national electricity quality safety standard GB/T12325 [54]In this embodiment, the system voltage index is Vmax235.4V and Vmin198V, considering that the installed power of the micro-grid is small, the micro-grid has a small capacity according to the requirement of national standard GB/T15945, and considering that the micro-grid has a small capacity, so the design frequency index of the embodiment is fmax50.5Hz and fmin＝49.5Hz。∑PDGAnd (t) is the sum of the power of each distributed power supply in the microgrid at the current moment. Each distributed power supply comprises a diesel engine, a storage battery, a photovoltaic generator and a wind driven generator, and the specific expression is shown in formulas 3-4:
∑PDG＝Pbat(t)+Pwind(t)kMTTP_wind+Psolar(t)kMTTP_solar+Pengine(t)kMTTP_engine(3-4)
wherein P isbat(t) is the current charge and discharge power of the storage battery, the charge and discharge of the storage battery are controlled by the bidirectional energy storage inverter PCS, and P is preferably controlled from the optimal consideration of the system stabilitybat(t) is within the optimum balance range, and the current state of charge (SOC) of the secondary battery is controlled to be within the normal discharge range. Pwind(t) is the current power generated by the fan, kMTTP_windThe maximum MTTP power factor of the fan grid-connected inverter is 0-100%. Psolar(t) is the current generated power of the photovoltaic generator, kMTTP_solarThe maximum MTTP power factor of the photovoltaic grid-connected inverter is 0-100%. Pengine(t) is the real-time generated power of the diesel generator, kMTTP_engineThe maximum MTTP power factor is provided for the diesel generator.
∑Pload(t) is the load value in the system at the current moment, and the specific expression is shown as the formula (3-5):
∑Pload(t)＝∑Psensitive(t)+∑PNon-sensitive(t)+∑PEquipment(t) (3-5)
where ∑ PEquipment(t) is the self power consumption of the devices in the system, such as the inverter, etc., at the present moment. Sigma Psensitive(t) and ∑ PNon-sensitive(t) is the load summation condition of the sensitive load and the non-sensitive load in the system at the current moment. The control strategy designed in this chapter adopts a hierarchical control strategy for the load, and the specific hierarchical strategy is shown in table 1:
table 1: load priority order criteria
Similarly, the embodiment of the invention also performs priority evaluation on the power generation sequence of the power generator, and the specific evaluation criteria are as shown in table 2:
table 2: generator prioritization criteria
As shown in table 2, the priority of power generation mainly considers stability and economic performance, and the diesel engine is used as the most stable power generator, and when daily wind and light energy storage meets daily power consumption requirements of the microgrid, no power generation plan is put into consideration due to economic factors. When partial gaps of electric energy provided by daily wind and solar energy storage occur or faults such as frequency deviation occur in a system, the electric energy needs to be input, and the diesel engine is used for generating electricity. The deployment of the diesel engine is mainly used for continuous haze and steady weather, weather with insufficient windless illumination intensity, low photovoltaic power generation efficiency in winter and other conditions.
Referring to fig. 1, a schematic flow chart of an improved method for controlling an internal frequency partition of a microgrid based on droop method control according to a first embodiment of the present invention is shown, where the method may include the following steps:
s101, detecting the bus frequency of the microgrid system.
S102, determining the region where the bus frequency is located according to a preset frequency division standard.
The frequency division standard includes an AH region, an AL region, a BH region, a BL region, a CH region, and a CL region, and the corresponding values are shown in table 3.
| Section name | Frequency range |
| CH region | Above 52Hz |
| BH region | 50.5Hz—52Hz |
| AH area | 50Hz—50.5Hz |
| Region AL | 49.5Hz—50Hz |
| BL region | 48Hz—49.5Hz |
| CL region | Below 48Hz |
Table 3: frequency division standard
And S103, controlling internal equipment of the micro-grid system according to the region where the bus frequency is located.
As shown in table 3, when the frequency interval is within the range of AH or AL, the microgrid system does not need to intervene, and only the energy balance allocation implementation formula (3-6) is needed
ΣPload(t)＝ΣPDG(t),PBAT＝0 (3-6)
The system does not need excessive interference when the frequency is in the AH region or the AL region, and the specific control strategy thereof will be detailed later.
When the frequency is in the BH region or BL region, it is generally caused by system disturbance factors, and at this time, it needs to be adjusted according to the P-f droop method, and its specific control strategy will be described in detail later.
When the frequency is in the CL region or the CH region, generally caused by equipment failure or severe load imbalance, emergency control of the system is required, and a specific control strategy thereof will be described in detail later.
Frequency control strategy for bus frequency in A zone
When the frequency is in the A region, the system does not need excessive interference, and the charging control, the discharging control and the balance control of the storage battery can be carried out on the system in the A region. The storage battery is maintained in an optimal state so as to deal with various upcoming situations, such as continuous energy supply of the storage battery in haze weather, continuous energy supply of the storage battery in night, balance maintenance of an extreme wind weather system and the like. Meanwhile, the storage battery is periodically operated to be fully charged and discharged, so that the service life of the storage battery is prolonged, and the polarization in the storage battery is reduced.
The charging, discharging and balancing control strategies for the battery will be described in detail below.
1. Battery charging control
The specific measures adopted for controlling the charging of the storage battery are to increase the generated power of the system in the stable time period of the microgrid system and store the extra generated energy into the storage battery. The specific control flow is shown in fig. 2:
(1) estimating the state of the storage battery, reporting to an upper monitoring system that the system finishes the charging of the storage battery if the storage battery finishes the charging, and switching a control mode into a storage battery balance control mode; and (4) if the charging is not finished, jumping to the step (2).
(2) And (5) evaluating the current state of the storage battery, if the current storage battery is in a charging state, turning to the step (3), and if the storage battery is still in a non-charging state at the moment, turning to the step (5).
(3) And (4) at the moment, the system is in a charging state, whether the current state of the distributed generators is 100% output is checked, if the current state is 100% output, the step is carried out, otherwise, the MTTP control coefficient of each distributed generator is adjusted to be 100%, the control period is ended, and the data of the next period are waited for judgment.
(4) If the state of the diesel engine is started, the system is not interfered, the control period is ended, and the next period of data is waited for judgment. And if the state of the diesel engine is not started, checking the current power generation plan, if the current power generation plan allows the diesel engine to be started, starting the diesel engine to generate power, and controlling the total power of the system to perform charging control within the maximum charging power of the storage battery. If the authority does not exist, the system is not interfered, the control period is ended, and the data of the next period are waited for judgment.
(5) And (3) at the moment, the system is in a discharging state, whether the current state of the distributed generators is 100% output is checked, if the current state is 100% output, the step (6) is carried out, otherwise, the MTTP control coefficient of each distributed generator is adjusted to be 100%, the control period is ended, and the data of the next period are waited for judgment.
(6) And (5) checking the current state of the diesel engine, and if the diesel engine is in an opening state, turning to the step (7). And if the diesel engine is in a shutdown state, checking the current power generation plan, and if the current power generation plan allows the diesel engine to be started to generate power. And finishing the control period and waiting for the next period of data to judge. And (5) if the current power generation plan does not allow the diesel engine to be started, reporting to an upper monitoring system, requesting the diesel engine to start the authority, and turning to the step (7).
(7) And checking the condition that the current non-sensitive load is accessed into the system, if the current system has the non-sensitive load accessed, and if the current power generation plan allows to cut off the sensitive load, sequentially cutting off the non-sensitive load according to the descending order of the load priority within the range of the non-sensitive load which is allowed to be cut off by the current power generation plan. And ending the current control period and waiting for the data of the next period for judgment. And (4) if the current system has no non-sensitive load access or the power generation plan does not allow the non-sensitive load to be cut off, then the step (8) is carried out.
(8) And reporting that the system charging power of the upper monitoring system is insufficient, starting a storage battery to perform discharging control, and maintaining the stability of the system. And waiting for the control instruction of the upper monitoring system. And ending the current control period and waiting for the data of the next period for judgment.
2. Battery discharge control
The discharge control of the storage battery is realized by reducing the power generation power of the system in the stable period of the system and discharging and supplying energy to partial load by the storage battery. While maintaining the discharge power of the battery within a certain suitable range. The specific control flow is shown in fig. 3:
(1) and evaluating the state of the storage battery, reporting that the storage battery of the upper computer finishes discharging if the storage battery finishes discharging, and changing the control mode into storage battery balance control. And ending the current control period and waiting for the data of the next period for judgment. And (4) if the storage battery does not finish discharging, then the step (2) is carried out.
(2) And (4) evaluating the state of the storage battery, and if the storage battery is in a non-discharge state, turning to the step (3). If the storage battery is in a discharging state, the starting condition of the diesel engine is checked, if the current state of the diesel engine is closed, the system is not interfered, the current control period is ended, and the next period of data is waited for control. If the diesel engine is in the on state and satisfies the formula 3-28
PBAT(t)+Pengine(t)<PBAT_Discharge_MAX(3-28)
Wherein, PBAT_Discharge_MAXIs the maximum allowable discharge power of the storage battery
At the moment, the diesel engine is turned off, the storage battery supplies power to the load, and the electric energy of the storage battery is consumed. And finishing the control period and waiting for the next period of data to judge. If the formula does not satisfy the formulas 3-28, the system is not intervened, the current control period is ended, and the data of the next period is waited for judgment.
(3) And in the discharging state, checking the starting condition of the diesel engine, if the diesel engine is in the starting state and the current data meets the formula 3-28, closing the diesel engine, ending the current control period and waiting for the data of the next period for judgment. And (4) if the diesel engine is in a shutdown state or does not meet the formulas 3-28, turning to the step (4).
(4) And sequentially reducing MTTP control coefficients of the distributed generators according to the ascending power sequence of the priority of the generators, and maintaining the discharge power of the storage battery in an optimal interval. And finishing the control period and waiting for the next period of data to judge.
3. Battery balance control
When the system is in the interval with relatively stable voltage and frequency, the load balance in the system is controlled by charging the storage battery preferentially. Because the reaction speed of the storage battery is optimal and the charging and discharging power required by the system is not too large. When the charging and discharging power of the storage battery is within a certain range, the range is a normal storage battery charge floating space, and no intervention is needed. When the charging power of the storage battery exceeds the floating range, the specific control flow is shown in fig. 4:
(1) the load condition is evaluated and if the power of the load is in a fluctuating state, no intervention is performed. And ending the current control period and waiting for the data of the next period for judgment. And (4) if the load is in a relatively stable state, turning to the step (2).
(2) And evaluating the state of the distributed generator, if the fan and the photovoltaic are in an unstable state, performing corresponding operation according to a corresponding evaluation result, for example, if the fan is in a high-level energy unstable state, performing generator tripping processing, and if the photovoltaic is in a state of not generating power at night, performing generator tripping processing. If the fan generates large energy impact due to extreme weather, the storage battery is adopted to absorb the energy impact so as to maintain the relative stability of the system. And finishing the control period and waiting for the next period of data to judge. And (4) if the distributed generator is in a stable state, turning to the step (3).
(3) And (5) checking the current state of the diesel engine, if the diesel engine is in the starting state, turning to the step (4), and if the diesel engine is in the shutdown state, turning to the step (5).
(4) If the current system satisfies the formula 3-29
PBAT+Pengine<PBAT_Blance_Discharge_Limit(3-29)
Wherein P isBAT_Blance_Discharge_LimitThe maximum charging power of the floating power of the storage battery.
The diesel engine is closed, the control period is ended, and the next period of data is waited for judgment. If the formula 3-29 is not satisfied, the process proceeds to step (5).
(5) And if the system still has the non-sensitive load which is not accessed into the system and the current power generation plan allows the non-sensitive load to be accessed into the system, accessing the non-sensitive load according to the ascending power order of the load priority. And (4) if all the non-sensitive loads of the system are accessed to the system or the power generation plan does not allow the non-sensitive loads to be accessed to the system, then the step (6) is carried out.
(6) Adjusting the MTTP control coefficient of the generator according to the ascending power order of the priority until the formula (3-30) is satisfied
And ending the current control period and waiting for the data of the next period for judgment.
If the discharging power of the storage battery exceeds the floating range, the control flow is shown in fig. 5:
(1) and evaluating the state of the storage battery, reporting that the storage battery of the upper computer finishes discharging if the storage battery finishes discharging, and changing the control mode into storage battery balance control. And ending the current control period and waiting for the data of the next period for judgment. And (4) if the storage battery does not finish discharging, then the step (2) is carried out.
(2) And evaluating the state of the distributed generator, if the fan and the photovoltaic are in an unstable state, performing corresponding operation according to a corresponding evaluation result, for example, if the fan is in a high-level energy unstable state, performing generator tripping processing, and if the photovoltaic is in a state of not generating power at night, performing generator tripping processing. If the fan generates large energy impact due to extreme weather, the storage battery is adopted to absorb the energy impact so as to maintain the relative stability of the system. And finishing the control period and waiting for the next period of data to judge. And (4) if the distributed generator is in a stable state, turning to the step (3).
(3) And (4) if the diesel engine is in an opening state, switching to the step (4), and if the diesel engine is in a closing state, switching to the step (6).
(4) And (5) if the distributed power supply is in a 100% output state, increasing the MTTP control coefficient of the distributed power supply according to the ascending power sequence of the priority of the generator if the distributed power supply is not in the 100% output state, stopping 100% or meeting the formula 3-30, ending the current control period and waiting for the data of the next period for judgment.
(5) If the system is accessed with non-sensitive loads and the power generation plan allows to cut off the sensitive loads, cutting off the loads according to the priority descending order of the loads, ending the control period and waiting for the data of the next period for judgment. If the system has no non-sensitive load or the power generation plan does not allow the non-sensitive load to be cut off, reporting that the energy of the system A area is insufficient in the upper monitoring system, controlling the storage battery to continue discharging, and maintaining the current situation of the system. And finishing the control period and waiting for the next period of data to judge.
(6) And (4) if the distributed power supply is in a 100% output state, turning to the step (7), if the distributed power supply is not in the 100% output state, increasing the MTTP control coefficient of the distributed power supply according to the ascending power sequence of the priority of the generator until the MTTP control coefficient is 100% or meets the formula 3-30, ending the current control period and waiting for the data of the next period for judgment.
(7) If the current parameters of the system meet the requirements of the formulas 3-31
PBAT+Pengine_full>PBAT_Blance_Charge_Limit(3-31)
Wherein P isBAT_Blance_Charge_LimitThe maximum allowable charging power is the floating power of the storage battery, and the maximum allowable charging power is a negative value.
And if the power generation plan allows the diesel engine to be used, the diesel engine is started to generate power, and the system finishes the current control period and waits for the data of the next period to judge. And (4) if the system does not meet the requirements of the formulas 3-31, then the step (8) is carried out. If the system meets the requirements of the formulas 3-31 but the power generation plan does not allow the generator to be put into use, the step (8) is also carried out.
(8) If the system is accessed with non-sensitive loads and the power generation plan allows to cut off the sensitive loads, cutting off the loads according to the priority descending order of the loads, ending the control period and waiting for the data of the next period for judgment. If the system has no non-sensitive load or the power generation plan does not allow the non-sensitive load to be cut off, reporting that the energy of the system A area is insufficient in the upper monitoring system, controlling the storage battery to continue discharging, and maintaining the current situation of the system. And finishing the control period and waiting for the next period of data to judge.
Second, frequency control strategy for bus frequency in BH area
When the bus frequency is in the BH region, it is generally caused by excessive active power in the system, but this disturbance may be transient. When the bus frequency is detected to enter the BH area, the operation should not be carried out immediately, and system oscillation is possibly caused, so that the robustness of the system is reduced. Therefore, when the bus frequency enters into the BH zone, the specific control flow is as shown in fig. 6:
(1) and (4) estimating the charge state of the storage battery, and if the storage battery is in a chargeable and unfilled state, skipping to the step (2). And (4) if the storage battery is in a fully charged and non-chargeable state, skipping to the step (3).
(2) And (4) performing charging control on the control storage battery, absorbing redundant active power, and skipping to the step (3).
(3) If the perturbation lasts more than 30 minutes, jump to step (4). Otherwise, ending the control of the period and waiting for the data of the next period to judge.
(4) And (5) if the diesel engine is in the starting state at the moment, jumping to the step (5), otherwise, jumping to the step (6).
(5) Simply evaluating the generated power of the diesel engine at the moment, if the formula (3-17) is met, jumping to the step (6), otherwise, jumping to the step (8),
PBAT_MIN<PBAT(t)+Pengine(t)<PBAT_MAX(3-17)
wherein P isBAT_MINIs the limit of the charging power, P, that the battery can withstandBAT_MAXIs the limit of discharge power that the battery can withstand.
(6) And (4) turning off the diesel engine, controlling the charging and discharging of the storage battery, and properly reducing the discharging power of the storage battery. And finishing the control of the period and waiting for the data of the next period for judgment.
(7) And reducing the generated power of the distributed generators one by one according to the ascending order of the priority of the distributed generators. And finishing the control of the period and waiting for the data of the next period for judgment.
(8) And (4) if the load which is not accessed exists in the system, jumping to the step (9), otherwise, jumping to the step (7).
(9) And accessing the loads into the system one by one according to the ascending power priority order of the loads. And finishing the control of the period and waiting for the data of the next period for judgment.
Frequency control strategy for bus frequency in BL region
When the bus frequency is in the BL region, the specific control flow is as shown in fig. 7:
(1) if the system frequency falls to the BL area, firstly checking whether the distributed power supplies in the system, such as photovoltaic, fan and the like, have 100% maximum output, if not, adjusting to gradually increase the output coefficient to 100%, ending the period control and waiting for the next period data for judgment, otherwise, jumping to the step (2).
(2) And (4) judging the state of the storage battery if the BL region disturbance occurs, and skipping to the step (3) if the storage battery can be discharged without reaching the lower discharge limit, or skipping to the step (4).
(3) And (5) controlling the storage battery to discharge, keeping the frequency stable for the system function, and skipping to the step (5).
(4) And if the disturbance is less than 30 minutes, maintaining the discharge state of the storage battery, finishing the period control and waiting for the data of the next period for judgment. Otherwise, jumping to step (5)
(5) And (6) if the diesel engine is in the starting state, skipping to the step (6), otherwise, starting the diesel engine, ending the period control and waiting for the next period data for judgment.
(6) And judging the load condition in the system, and if the non-sensitive load still has access, successively cutting off the non-sensitive load according to the load power lowering sequence. And finishing the period control and waiting for the next period data for judgment. And (5) if the non-sensitive load is completely cut off, jumping to the step (7).
(7) And reporting the energy shortage of the system in the BL area to an upper monitoring system, maintaining the output maximization of all distributed generators in the system, and waiting for a control instruction of an upper control system. And finishing the period control and waiting for the next period data for judgment.
Frequency control strategy for bus frequency in CH region
When the system frequency is in the CH region, it is a dangerous state, and it is necessary to change the region in a short time, otherwise, the system is in danger of breakdown. Therefore, the state of the distributed power supplies needs to be evaluated one by one, and the fault load needs to be eliminated, and a specific control flow is shown in fig. 8:
(1) when the system detects that the frequency enters the CH area, the state of the diesel engine is checked firstly, and if the diesel engine is in the opening state, the diesel engine is shut down. And finishing the period control and waiting for the next period data for judgment. Otherwise, jumping to the step (2).
(2) And checking whether each distributed power supply fails or not successively, and if so, cutting off the distributed power supply. And finishing the period control and waiting for the next period data for judgment. Otherwise, jumping to the step (3).
(3) According to the power-down sequence of the priority of the generators, the distributed power supplies are cut off one by one and reported to an upper monitoring system, namely 'the system has a CH area fault'. And jumping to the step (4).
(4) Checking whether the CH region disturbance exceeds a specified time, and if not, maintaining the current state of the system and keeping the frequency of the system stable as much as possible. And finishing the period control and waiting for the next period data for judgment. And (5) if the specified time is exceeded, jumping to the step.
(5) And the micro-grid system stops working so as to protect the safety of important equipment and the equipment of the generator in the micro-grid. And evaluating the electric quantity of the storage battery, and preparing a black start plan. And reporting the 'system has serious fault and is shut down' of the upper monitoring system, and waiting for a black start instruction of the upper monitoring system.
Frequency control strategy for bus frequency in CL region
When the system frequency is in the CL region, particularly in a dangerous state, the region must be changed out in a short time, otherwise, the failure of the system may cause the damage of the internal equipment of the microgrid, and the island protection shutdown of the distributed power supply is started, which may cause more serious consequences. Therefore, the control strategy in this interval takes the core idea of rapidly improving the internal power supply of the system, cutting off all unnecessary loads, and rapidly evaluating the fault state of the distributed power supply as follows, and the specific control flow is shown in fig. 9:
(1) when the system detects that the system is in the CL area, the discharging control is immediately carried out on the storage battery, because the starting speed and the reaction speed of the storage battery are the fastest. And then, the step (2) is carried out.
(2) And detecting the state of the diesel generator, and if the state is a shutdown state, starting the diesel engine to charge the system. And finishing the control period and waiting for the next period of data to judge. And (4) if the diesel engine is in the opening state, turning to the step (3).
(3) And detecting whether other distributed power supplies are in a 100% output state, and if not, immediately adjusting the MTTP coefficient to be 100%. And finishing the control period and waiting for the next period of data to judge. And (4) if the output is in a 100% output state, switching to the step (4).
(4) And detecting whether the non-sensitive load is accessed to the micro-grid system. If so, all non-sensitive loads are immediately removed. And finishing the control period and waiting for the next period of data to judge. And (5) if no non-sensitive load is accessed into the system, jumping to the step (5).
(5) And detecting whether the distributed generator of the system fails or not and whether the primary load fails or not. And taking the operation of cutting off the system for the corresponding fault. And proceeds to step (6).
(6) Estimating the stability of the system if equations 3-18 and 3-19 are satisfied
Δf(n)＝f(t)-f(t-1) (3-18)
If the system frequency is still in the offset state and the situation is worsened, the step (7) should be carried out, otherwise, the upper monitoring system reports the system frequency CL area fault, and tries to maintain the system stable state to wait for the instruction of the upper monitoring system. And finishing the cycle operation and waiting for the next cycle data to judge.
(7) If the system frequency is in a continuously deteriorated state, the micro-grid system is stopped in order to protect system equipment and not to damage loads in the system. And reporting the upper computer that the system is stopped and is in the CL region frequency fault. And evaluating the state of the storage battery, and making a black start plan. And waiting for a starting instruction of the upper monitoring system.
By implementing the embodiment of the invention, the bus frequency of the microgrid system is detected, the region where the bus frequency is located is determined according to the preset frequency division standard, and finally the internal equipment of the microgrid system is controlled according to the region where the bus frequency is located; namely, the embodiment of the invention can adopt a non-passing control strategy for the frequencies in different regions, can realize the stabilization of the system frequency within the national standard (GB/T12325) requirement range (49.5 Hz-50.5 Hz), and ensures the stability of the system.
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications and substitutions can be easily made by those skilled in the art within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (5)
1. An improved method for controlling the internal frequency partition of a microgrid based on droop method control is characterized by comprising the following steps:
detecting the bus frequency of the microgrid system;
determining a region where the bus frequency is located according to a preset frequency division standard, wherein the frequency division standard comprises an AH region, an AL region, a BH region, a BL region, a CH region and a CL region;
controlling internal equipment of the micro-grid system according to the region where the bus frequency is located;
if the bus frequency is in the AH area or the AL area, performing charge control, discharge control and balance control on a storage battery of the microgrid system;
the discharge control specifically includes:
(A1) performing state evaluation on the storage battery, reporting to an upper computer and changing a control mode into a balance control mode if the storage battery finishes discharging, and turning to the step (A2) if the storage battery does not finish discharging;
(A2) performing state evaluation on the storage battery again, and if the storage battery is in a non-discharge state, turning to the step (A3);
(A3) if the diesel engine is in a closed state, sequentially reducing the power of the distributed power supply according to the ascending power sequence of the priority; if the diesel engine is in a starting state and the storage battery cannot bear the load of the diesel engine, sequentially reducing the power of the distributed power supply according to the ascending power order of the priority;
the balance control specifically includes:
(1) evaluating the current state of the load, and if the current state of the load is in a relatively stable state, turning to the step (2);
(2) evaluating the current state of the distributed generator, and if the distributed generator is in a stable state, turning to the step (3);
(3) acquiring the current state of the diesel engine, and if the diesel engine is in a shutdown state, turning to the step (4);
(4) if the situation that the non-sensitive load is not accessed exists in the micro-grid system and the non-sensitive load is allowed to be accessed by the current power generation plan, accessing the non-sensitive load according to the ascending power sequence of the load priority; if the non-sensitive loads of the micro-grid system are all accessed or the current power generation plan does not allow the non-sensitive loads to be accessed, the step (5) is carried out;
(5) and sequentially reducing the power of the distributed power supplies according to the ascending power order of the priority.
2. The method of claim 1, wherein if the bus frequency is in the BH region, controlling the internal devices of the microgrid system specifically comprises:
(B1) estimating the state of charge of the storage battery, if the storage battery is in an unfilled state, then turning to the step (B2), and if the storage battery is in a filled state, then turning to the step (B3);
(B2) performing charging control on the storage battery;
(B3) if the disturbance time is more than 30 minutes and the diesel engine is in a starting state, the step (B4) is carried out; if the disturbance time is more than 30 minutes and the diesel engine is in a shutdown state, the step (B5) is carried out;
(B4) evaluating the current generating power of the diesel engine, and closing the diesel engine or reducing the generating power of the distributed generator according to the ascending power of the priority level according to the evaluation result;
(B5) and if the micro-grid system has the condition that no load is not accessed, sequentially accessing the non-sensitive loads in an ascending power sequence, and if the micro-grid system does not have the condition that no load is accessed, reducing the generating power of the distributed generator in an ascending power according to the priority.
3. The method of claim 1, wherein if the bus frequency is in the BL region, controlling internal devices of the microgrid system specifically comprises:
(C1) if the distributed power supply is 100% of maximum output, the step (C2) is carried out, and if the distributed power supply is not 100% of maximum output, the distributed power supply is adjusted;
(C2) evaluating the state of the storage battery, if the storage battery can be discharged, performing discharge control on the storage battery, and otherwise, turning to a step (C3);
(C3) if the disturbance time is less than 30 minutes, maintaining the discharge state of the storage battery, otherwise, turning to the step (C4);
(C4) if the diesel engine is in an open state and the non-sensitive load of the micro-grid system is not cut off, cutting off the non-sensitive load according to a power lowering sequence; if the non-sensitive load is completely removed, reporting the energy shortage of the micro-grid system in the BL area to the monitoring system, and maintaining the current situation.
4. The method of claim 1, wherein if the bus frequency is in the CH region, controlling internal devices of the microgrid system specifically comprises:
(D1) if the diesel engine is in a closed state, checking whether the distributed power supplies have faults one by one;
(D2) if the fault occurs, cutting off the distributed power supply, otherwise, turning to the step (D3);
(D3) cutting off the distributed power supplies one by one according to the power reduction times of the priority of the distributed generator, and reporting the power generation times to a micro-grid system of an upper layer monitoring system to generate a CH area fault;
(D4) and if the disturbance time of the CH area is greater than the preset time, stopping the micro-grid system and reporting the system fault of the upper computer.
5. The method of claim 1, wherein if the bus frequency is in the CL zone, controlling internal devices of the microgrid system specifically comprises:
(E1) discharging control is carried out on the storage battery, the state of the diesel engine is detected, and if the diesel engine generator is in an opening state, the step (E2) is carried out;
(E2) checking whether the distributed power supply is in a 100% output state, if so, adjusting to the 100% output state, and if not, turning to the step (E3);
(E3) detecting whether a non-sensitive load is accessed to the microgrid system, if so, cutting off all the non-sensitive loads, and if not, turning to the step (E4);
(E4) if the distributed generator and the primary load have faults, the operation of cutting system equipment is adopted;
(E5) and predicting the stability of the micro-grid system, and reporting the fault of the frequency CL region of the micro-grid system of the upper monitoring system or carrying out shutdown operation on the system according to the prediction result.
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