CN111900710B - Grid-connected direct-current micro-grid coordination control method - Google Patents
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Abstract
The invention relates to a grid-connected direct current micro-grid coordination control method, which comprises a photovoltaic power generation unit, a networking unit, an energy storage unit, an alternating current/direct current load unit and a working mode controller, wherein the networking unit, the energy storage unit, the alternating current/direct current load unit and the working mode controller are connected with an alternating current main network, the working mode controller is used for setting a plurality of voltage levels to divide direct current bus voltage into a plurality of voltage layers, the voltage layers execute corresponding working modes, the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating current/direct current load unit execute corresponding control modes in the working modes, the units do not interfere with each other, the working mode controller is used for judging the voltage layer according to the voltage value of the locally collected direct current bus voltage, and controlling the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating current/direct current load unit to be adjusted to the corresponding control modes. Compared with the prior art, the invention has the advantages of avoiding the influence of micro-source output fluctuation or load change on the bus voltage, having good system expansibility and the like.
Description
Technical Field
The invention relates to the technical field of energy management and coordination control of a direct-current micro-grid, in particular to a grid-connected direct-current micro-grid coordination control method.
Background
Solar energy is used as a renewable energy source which is widely distributed and pollution-free, so that the photovoltaic is a power generation scheme which is favored by countries around the world, but the photovoltaic has the characteristics of small inertia, large output randomness and easiness in being influenced by factors such as illumination intensity and temperature, the centralized power generation scheme is not suitable, and the clean energy source can be obviously better utilized by distributed power generation, so that the energy utilization rate is greatly improved. In this context, the concept of micro-grids has grown. Because the photovoltaic power generation unit outputs direct current, direct current loads such as electric automobiles are more and more, and the problems of frequency and phase are not needed to be considered in the direct current micro-grid, the direct current micro-grid has unique application advantages compared with the alternating current micro-grid.
Because a large number of power electronic devices are connected into the micro-grid, the inertia of the system is low, and when the micro-source output fluctuates or the load changes, the bus voltage may severely fluctuate, so that the stable operation of the direct-current micro-grid is affected, and therefore, the research on energy coordination and voltage control of the direct-current micro-grid becomes a key technical drive for affecting the development of the direct-current micro-grid.
Disclosure of Invention
The invention aims to overcome the defect that the bus voltage seriously fluctuates due to the fluctuation of micro-source output or load change in the prior art, and provides a grid-connected direct-current micro-grid coordinated control method.
The aim of the invention can be achieved by the following technical scheme:
The grid-connected direct current micro-grid coordination control method comprises a photovoltaic power generation unit, a networking unit, an energy storage unit, an alternating current-direct current load unit and a working mode controller, wherein the networking unit, the energy storage unit, the alternating current-direct current load unit and the working mode controller are connected with an alternating current main network, the working mode controller is used for setting a plurality of voltage levels to divide direct current bus voltage into a plurality of voltage layers, the voltage layers execute corresponding working modes, the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating current-direct current load unit execute corresponding control modes in the working modes, the units are not interfered with each other, the working mode controller is used for judging the voltage layer where the direct current bus voltage is located according to the voltage value of the locally collected direct current bus voltage, and controlling the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating current-direct current load unit to be adjusted to the corresponding control modes.
The number of the voltage levels is 6, and the voltage levels specifically comprise a third low voltage, a second low voltage, a first high voltage, a second high voltage and a third high voltage.
Further, the 6 voltage levels are ordered according to the magnitude of the voltage values, and the voltage levels are a third low voltage, a second low voltage, a first high voltage, a second high voltage and a third high voltage in sequence from small to large.
Further, the number of the working modes is 4, and the working modes specifically comprise a first working mode, a second working mode, a third working mode and a fourth working module.
Further, when the voltage value of the direct current bus voltage is between the first low voltage and the first high voltage, the corresponding working mode is the first working mode, the networking unit controls power fluctuation in the balance system and controls bus voltage, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit is in a charging state, the energy storage unit is kept in a full-power standby state if the electric quantity of the energy storage unit is full, the storage battery is not discharged, and the alternating current/direct current load unit is in a normal operation state.
Further, when the voltage value of the direct current bus voltage is between the second low voltage and the first low voltage or between the first high voltage and the second high voltage, the corresponding working mode is the second working mode, the power transmission quantity of the networking unit reaches the limit capacity or is in a disconnection state, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit adjusts unbalanced power and controls the bus voltage, and the alternating current/direct current load unit is in a normal operation state.
Further, when the voltage value of the direct current bus voltage is between the second high voltage and the third high voltage, the corresponding working mode is the third working mode, the networking unit absorbs electric energy from the direct current micro-grid by the limit power capacity or is in a disconnection state, the photovoltaic power generation unit is switched to a voltage sag control mode, the energy storage unit charges according to the maximum power, if the electric quantity of the energy storage unit is full, the full-power standby state is maintained, the storage battery does not discharge, and the alternating current/direct current load unit is in a normal operation state.
Further, when the voltage value of the direct current bus voltage is between the third low voltage and the second low voltage, the corresponding working mode is a fourth working mode, the networking unit transmits electric energy to the direct current micro-grid by the limit power capacity or is in a disconnection state, the photovoltaic power generation unit operates in an MPPT control mode, the energy storage unit discharges by the maximum power, the idle power standby state is kept if the electric quantity of the energy storage unit is discharged, the storage battery is not charged, and the alternating current/direct current load unit cuts off the internal load according to the proportion.
The networking unit is internally provided with a bidirectional DC/AC converter, the bidirectional DC/AC converter adopts a double closed-loop structure, the double closed-loop structure is specifically a voltage outer ring and a current inner ring, the voltage outer ring maintains stable voltage of a direct current bus, and the current inner ring controls network side current.
The photovoltaic power generation unit adopts a three-section type maximum power point tracking control mode and a voltage droop control mode based on a working point, and the energy storage unit adopts a self-repairing positive voltage droop control mode based on an SOC droop coefficient.
Compared with the prior art, the invention has the following beneficial effects:
According to the invention, the direct current bus voltage is divided into a plurality of voltage layers by setting a plurality of voltage levels, the voltage layers execute corresponding working modes, only the direct current bus voltage is used as a unique signal to complete control of each micro source and load and switching of the working modes, meanwhile, no communication coordination of a photovoltaic power generation unit, a networking unit, an energy storage unit and an alternating current/direct current load unit is realized by selecting peer-to-peer control, and all units are not influenced by each other in 'plug and play', so that the system expansibility is good.
Drawings
FIG. 1 is a schematic diagram of the structure of the present invention;
FIG. 2 is a graph of the output characteristics of the photovoltaic power generation unit of the present invention;
FIG. 3 is a schematic flow chart of a three-stage maximum power point tracking control of the photovoltaic power generation unit of the present invention;
FIG. 4 is a schematic diagram of an analysis of operating point stability of a photovoltaic power unit of the present invention;
FIG. 5 is a schematic diagram of the derating voltage regulation control of the photovoltaic power generation unit of the present invention;
FIG. 6 is a graph showing sagging characteristic curves of the energy storage unit according to the present invention;
Fig. 7 is a schematic diagram of a networked converter control structure according to the present invention;
FIG. 8 is a schematic diagram of DC bus voltage stratification according to the present invention;
Fig. 9 is a simulation effect diagram of a dc micro-grid networking regulation mode according to the present invention, in which fig. 9 (a) is a graph of illumination intensity variation, fig. 9 (b) is a graph of networking unit output power variation, and fig. 9 (c) is a graph of dc bus voltage variation;
fig. 10 is a simulation effect diagram of an energy storage regulation mode of the direct current micro-grid according to the present invention, wherein fig. 10 (a) is a graph of illumination intensity variation, fig. 10 (b) is a graph of discharge power variation of a storage battery of an energy storage unit, and fig. 10 (c) is a graph of direct current bus voltage variation;
Fig. 11 is a simulation effect diagram of a photovoltaic derating operation mode of a direct current micro-grid according to the present invention, wherein fig. 11 (a) is a graph of illumination intensity variation, fig. 11 (b) is a graph of power variation of a photovoltaic power generation unit, and fig. 11 (c) is a graph of direct current bus voltage variation;
Fig. 12 is a simulation effect diagram of an active load shedding mode of the dc micro-grid according to the present invention, wherein fig. 12 (a) is a graph of illumination intensity variation, fig. 12 (b) is a graph of ac/dc load unit power variation, and fig. 12 (c) is a graph of dc bus voltage variation.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical scheme of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following examples.
As shown in fig. 1, a grid-connected direct current micro-grid coordination control method is provided, the direct current micro-grid comprises a photovoltaic power generation unit, a networking unit, an energy storage unit, an alternating current/direct current load unit and a working mode controller, wherein the networking unit, the energy storage unit, the alternating current/direct current load unit and the working mode controller are connected with an alternating current main network, the working mode controller sets a plurality of voltage levels to divide direct current bus voltage into a plurality of voltage layers, the voltage layers execute corresponding working modes, the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating current/direct current load unit execute corresponding control modes in the working modes, the units do not interfere with each other, the working mode controller judges the voltage layer where the voltage value of the locally collected direct current bus voltage is located according to the voltage value of the locally collected direct current bus voltage, and controls the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating current/direct current load unit to be adjusted to the corresponding control modes.
The dc bus voltage rating U dc_n is 380V and the amount of change in the dc bus voltage is Δu.
The number of voltage classes is6, and specifically includes a third low voltage, a second low voltage, a first high voltage, a second high voltage, and a third high voltage.
The 6 voltage levels are ordered according to the voltage values, and the voltage levels are a third low voltage, a second low voltage, a first high voltage, a second high voltage and a third high voltage in sequence from small to large.
The number of the working modes is 4, and the working modes specifically comprise a first working mode, a second working mode, a third working mode and a fourth working module.
When the fluctuation range of the direct current bus voltage |delta U| < 7.6V, namely the direct current bus voltage meets U L1＜Udc＜UH1, the corresponding working mode is a first working mode, the networking unit controls the power fluctuation in the balance system and the bus voltage, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit is in a charging state, if the electric quantity of the energy storage unit is full, the energy storage unit is kept in a full-power standby state, the alternating current/direct current load unit is in a normal operation state, the output of the micro-grid and the main grid is in a state of power surplus except for meeting the load requirement, the storage battery is preferably charged, and then the storage battery is fed to the alternating current main grid through the networking unit and is only charged and not discharged, and if the storage battery is in a state of voltage reduction under the condition of full charge, the storage battery is kept in a non-discharging state so as to ensure the regulation capability of the storage battery.
When the fluctuation range of the direct current bus voltage |delta U| < 19V, namely the bus voltage meets U H1＜Udc＜UH2 or U L2＜Udc＜UL1, the corresponding working mode is a second working mode, the power transmission quantity of the networking unit reaches the limit capacity or is in a disconnected state, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit adjusts unbalanced power and controls the bus voltage, and the alternating current/direct current load unit is in a normal operation state.
When the voltage of the direct current bus meets U dc＞UH2, the corresponding working mode is a third working mode, the networking unit absorbs electric energy from the direct current micro-grid by the limit power capacity or is in a disconnected state, the photovoltaic power generation unit is switched to a voltage sag control mode, the energy storage unit charges according to the maximum power, the full-power standby state is kept if the electric quantity of the energy storage unit is full, the storage battery does not discharge, and the alternating current-direct current load unit is in a normal running state.
When the voltage value of the direct current bus meets U dc＜UL2, the corresponding working mode is a fourth working mode, the networking unit transmits electric energy to the direct current micro-grid by the limit power capacity or is in a disconnected state, the photovoltaic power generation unit operates in an MPPT control mode, the energy storage unit discharges by the maximum power, the idle power standby state is kept if the electric quantity of the energy storage unit is discharged, the storage battery is not charged, and the alternating current load unit cuts off the internal load according to the proportion.
The photovoltaic power generation units are connected through unidirectional DC/DC converters, the energy storage units for balancing power when the system power fluctuates are connected through bidirectional DC/DC converters, and the alternating current/direct current load units are connected to the direct current bus voltage through corresponding unidirectional DC/AC or DC/DC.
As shown in fig. 2, the photovoltaic power generation unit adopts a three-section Maximum Power Point Tracking (MPPT) control combined with a voltage sag control mode based on a working point, the photovoltaic power generation unit is divided into three sections of non-MPP, MPP-like and MPP according to the slope of an output characteristic curve of the photovoltaic power generation unit, and corresponding MPPT strategies are respectively adopted to accelerate the tracking speed and improve the optimizing precision, and the flow of the MPPT strategies is shown in fig. 3.
The sections a-B and E-F of fig. 2 are non-MPP sections, the absolute value of the slope of the two curves is larger and is far away from the maximum power point, and the two sections are skipped by adopting a fixed voltage method (constant voltage tracking, CVT) to increase the tracking speed, wherein U n1、Un2 can be respectively taken as 0.65U oc、0.9Uoc;
The B-C section and the D-E section of the graph in FIG. 2 are MPP-like sections, the absolute value of the slope of the two sections of curves is smaller and is closer to the maximum power point, a variable-step disturbance observation method (Perturbation and Observation Method, P & O) is adopted to further approach the maximum power point, disturbance oscillation is not easy to occur, and the judging conditions are as follows:
Wherein, Is the absolute value of the slope of the curve, ε is the critical slope into the CD segment;
The C-D segment of FIG. 2 is the MPP segment, the slope is near 0, and the slope satisfies The length is shorter, and the maximum power point is on the section of curve, so that Particle Swarm Optimization (PSO) is adopted for optimizing, the tracking precision is improved, and the oscillation about the maximum power point can not be generated like the conventional algorithm.
Based on the output characteristic curve of the photovoltaic power generation unit, voltage droop control based on a stable operating point is adopted. As can be seen from the P-U characteristic curve of the photovoltaic cell, when the photovoltaic power generation unit operates at a reduced power, there are two operating points satisfying the power condition, which are located at the left and right sides of the maximum power point, respectively, as shown at points B and C in fig. 4.
If the photovoltaic cell currently works at the point B and keeps the voltage U pv of the photovoltaic power generation unit stable, when the illumination intensity suddenly decreases, the current I pv of the photovoltaic power generation unit is instantaneously reduced, the output power of the photovoltaic cell is smaller than the power required by a load, but U pv is reduced, and then the output power of the photovoltaic cell is gradually increased, so that negative feedback is formed, and the photovoltaic cell finally reaches a new stable working point. Therefore, the point located at the right side of the maximum power point is a stable operating point, and the reduction of U pv can further reduce the output power of the photovoltaic cell, so that positive feedback is formed, the system cannot be stabilized, and therefore, the point C is an unstable operating point.
The control block diagram of the photovoltaic power generation unit for stabilizing the voltage of the direct current bus is shown in fig. 5: the double-loop control of the direct-current bus voltage outer loop and the inductance current inner loop is adopted, and PI regulators are used for both the inner loop and the outer loop. In order to meet the requirement that the photovoltaic cell works in the right area of the maximum power point, an amplitude limiting link is added after the output of the PI regulator of the outer ring, the inductance current is limited not to exceed the current I m corresponding to the maximum power point of the photovoltaic cell, and the stability of the working point is ensured.
The droop control method is adopted to improve the voltage stabilizing control of the photovoltaic power generation unit, and the droop control expression is as follows:
Wherein, The reference value of the voltage of the direct current bus in closed loop control is K pv、Idc_pv, the sagging coefficient of the photovoltaic power generation unit and the bus side current of the converter, and U H3 is the third high voltage.
And determining a reference value of the DC bus voltage according to the sagging control method, and performing closed-loop control on the DC bus voltage by adopting a double-loop control system of an outer ring of the DC bus voltage and an inner ring of the inductance current. The voltage outer ring is used for regulating and stabilizing the voltage of the direct current bus, the PI regulator is adopted to realize no static difference control, meanwhile, the current inner ring is introduced, on one hand, the dynamic performance is improved, on the other hand, the control current does not damage the power electronic device, the PI regulator is also used for the current inner ring, and the specific control structure is shown in figure 5.
As shown in fig. 6, the energy storage unit adopts a droop control mode of self-repairing positive voltage based on the droop coefficient of the SOC, and adopts a method of droop control of charge-discharge current-bus voltage to control the bidirectional energy storage converter, so that a current sharing effect is realized when multiple groups of equipment of the energy storage unit are operated in parallel.
As shown in fig. 6, U H1、UH2、UL1 and U L2 are threshold voltages for switching the working modes, which are a first high voltage, a second high voltage, a first low voltage and a second low voltage, respectively, U dcn is a dc bus reference voltage, I B is a battery charging and discharging current, I B >0 corresponds to battery discharging, and I B <0 corresponds to battery charging.
The voltage regulating capability of the storage battery is distributed by applying the following sagging control method, and the method is concretely as follows:
Wherein, As a reference value of the dc bus voltage to be controlled, K Bi、Idc_Bi is the sag factor of battery B i and the current on the bus side of the converter.
In general, the sagging control coefficient of the energy storage unit only considers the capacity of the energy storage device, and the state of charge (SOC) of the storage battery is a key parameter of the working of the storage battery, and because the SOC is always changed when the storage battery works, the SOC values of the devices are also different, so that in the storage battery parallel energy storage system, the SOC of each storage battery tends to be consistent through a control strategy, and the consistency of the parallel working state is ensured. For this purpose, α i is defined as the ratio of the SOC of the battery to the average SOC of all devices, specifically as follows:
The original sagging coefficient K Bi of the storage battery is corrected according to alpha i, and the method is concretely as follows:
Wherein, K' Bi is a sagging coefficient after the correction of the battery Bi, and if the SOC of the battery Bi is higher than the average value, the application of the sagging coefficient after the correction will lead to the decrease of the charging current, slow down the charging speed, or increase the discharging current, and speed up the discharging speed. Therefore, the sagging control is performed according to the correction coefficient so that the final state of charge of each battery tends to be uniform.
The frequent overcharge and overdischarge of the storage battery are extremely unfavorable for the safe operation of the storage battery during the working, and in order to protect the storage battery, the charge state of the storage battery needs to satisfy that the SOC is less than 90 percent and the storage battery is in an idle standby state when the storage battery is out of range.
As shown in fig. 7, a bidirectional DC/AC converter is disposed in the networking unit, and the bidirectional DC/AC converter adopts a double closed-loop structure, and the double closed-loop structure is specifically a voltage outer loop and a current inner loop, wherein:
The voltage outer ring maintains the voltage stability of the direct current bus, a feedback U dc is introduced, the result is sent to the PI regulator, and the output of the PI regulator is set as a reference value i d * of the active current inner ring, so that the static difference-free control of U dc is realized;
The current of the current inner loop control network side is provided with a reference value i q * =0 of the reactive current inner loop, the active current i d and the reactive current i q are obtained by converting the three-phase current of the main network through abc/dq, the current is used as corresponding feedback of the current inner loop, after the adder result is sent into the PI regulator, the output u dr * and u qr * are combined with decoupling compensation quantity to obtain control quantity ud and uq, and the control quantity is modulated through SVPWM to generate PWM driving signals, so that the control of the converter is realized.
Example 1
The direct current micro-grid comprises a photovoltaic power generation unit, a networking unit, an energy storage unit and an alternating current-direct current load unit, and the third low voltage, the second low voltage, the first high voltage, the second high voltage and the third high voltage are specifically shown in table 1:
table 1 dc bus voltage layering interval table
As shown in fig. 8, the first operation mode is a networking adjustment mode, the second operation mode is an energy storage adjustment mode, the third operation mode is a photovoltaic derating mode, and the fourth operation mode is an active load shedding mode.
The system simulation is performed according to the simulation conditions shown in table 2, the working condition of the system in the networking regulation mode is verified, the simulation result is shown in fig. 9, and table 2 specifically comprises the following steps:
Table 2 networking regulatory mode simulation condition table
As shown in fig. 9 (a), 9 (b) and 9 (c), in the networking regulation mode, as the environment and load use conditions change, the power demand of the system changes, the power demand of the system is met by the networking unit, and the direct current bus voltage is stabilized between 0.98 and 1.02 per unit value according to droop control; and the photovoltaic power generation unit operates in an MPPT control mode, the alternating current/direct current load unit is in a normal operation state, and if the electric quantity of the energy storage unit is unsaturated and the networking converter has residual power, the energy storage equipment is charged.
System simulation is performed according to the simulation conditions shown in table 3, and the working condition of the system in the energy storage regulation mode is verified, wherein the simulation result is shown in fig. 10, and table 3 specifically includes the following steps:
TABLE 3 energy storage adjustment mode simulation Condition Table
As shown in fig. 10 (a), 10 (b) and 10 (c), when the power of the network converter reaches the limit due to the fault of the ac main network, the network unit loses the capacity of balancing the system power, the dc bus voltage changes, and the energy storage unit bears the power balance node, so that the switching from the network regulation mode to the energy storage regulation mode is realized. The energy storage unit is used as a power balance node, the voltage of the direct current bus is stabilized at 0.95 to 0.98 per unit value or 1.02 to 1.05 per unit value under the sagging control, the energy storage unit is discharged at 0.95 to 0.98 per unit value, and the energy storage unit is charged at 1.02 to 1.05 per unit value.
System simulation was performed according to the simulation conditions shown in table 4, and the operation conditions of the system in the derating mode of the photovoltaic power generation unit were verified, and the simulation results are shown in fig. 11, and table 4 specifically includes:
table 4 photovoltaic derate mode simulation condition table
As shown in fig. 11 (a), 11 (b) and 11 (c), when the power of the distributed power supply is greater than the load power and the networking unit and the energy storage unit cannot absorb the residual power, the dc bus voltage rises to enter a distributed power supply derating operation mode, so as to realize switching from the energy storage regulation mode to the photovoltaic derating mode. The photovoltaic power generation unit reduces the power generation power and meets the load demand. Under the sagging control of the photovoltaic power generation unit, the voltage of the direct-current bus is stabilized at a value of 1.05 to 1.1 per unit. When the photovoltaic power generation power is smaller than the load power, the voltage of the direct-current bus is changed, and the direct-current micro-grid system is switched from a photovoltaic derating mode to an energy storage adjusting mode.
The system simulation is performed according to the simulation conditions shown in table 5, the working condition of the system in the active load shedding mode is verified, the simulation result is shown in fig. 12, and table 5 specifically includes:
TABLE 5 active load shedding mode simulation condition table
As shown in fig. 12 (a), 12 (b) and 12 (c), when the power supply is smaller than the load power and the energy storage unit and the networking unit cannot provide the shortage power, the voltage of the dc bus is reduced, and when the ac/dc load unit captures that the voltage of the bus is reduced to below 0.95 per unit value, the load with low priority is actively cut off, so that reliable power supply of the load with high priority is ensured. After the busbar voltage rises, when the load control unit calculates that the power which can be provided by the direct current micro-grid system meets the load demand of excision, the excision load is put into use again independently.
Furthermore, the particular embodiments described herein may vary from one embodiment to another, and the above description is merely illustrative of the structure of the present invention. Equivalent or simple changes of the structure, characteristics and principle of the present invention are included in the protection scope of the present invention. Various modifications or additions to the described embodiments or similar methods may be made by those skilled in the art without departing from the structure of the invention or exceeding the scope of the invention as defined in the accompanying claims.
Claims (9)
1. The grid-connected direct current micro-grid coordination control method is characterized in that the direct current micro-grid comprises a photovoltaic power generation unit, a networking unit, an energy storage unit, an alternating current/direct current load unit and a working mode controller, wherein the networking unit, the energy storage unit, the alternating current/direct current load unit and the working mode controller are connected with an alternating current main network, the working mode controller is used for setting a plurality of voltage levels to divide direct current bus voltage into a plurality of voltage layers, the voltage layers execute corresponding working modes, the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating current/direct current load unit execute corresponding control modes in the working modes, the units do not interfere with each other, the working mode controller judges the voltage layer where the direct current bus voltage is located according to the voltage value of the locally collected direct current bus voltage, and controls the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating current/direct current load unit to be adjusted to the corresponding control modes;
the number of the voltage levels is 6, and the voltage levels specifically comprise a third low voltage, a second low voltage, a first high voltage, a second high voltage and a third high voltage; the photovoltaic power generation unit judges a voltage layer based on the voltage value, and selects a three-section type maximum power point tracking control mode or a voltage droop control mode based on a working point;
The photovoltaic power generation unit adopts a mode of combining three-section type maximum power point tracking control with voltage droop control based on a working point;
The three-section type maximum power point tracking control is characterized in that the three sections of non-MPP, MPP-like and MPP-like are divided according to the slope of an output characteristic curve of the photovoltaic power generation unit; the non-MPP section is skipped by adopting a fixed voltage method, the MPP-like section is subjected to a variable step disturbance observation method to further approach a maximum power point, and the MPP section is subjected to optimization by adopting a particle swarm algorithm;
The photovoltaic power generation unit adopts a sagging control method to perform voltage stabilizing control on the photovoltaic power generation unit, and a reference value of the voltage of the direct current bus in closed loop control is obtained
Wherein K pv、Idc_pv is the sagging coefficient of the photovoltaic power generation unit and the current of the bus side of the converter, and U H3 is the third high voltage;
According to the reference value of the DC bus voltage in the closed-loop control determined by the sagging control method, adopting a double-loop control system of a DC bus voltage outer loop and an inductance current inner loop to carry out closed-loop control on the DC bus voltage; the voltage outer ring is used for regulating and stabilizing the voltage of the direct current bus, and the PI regulator is adopted to realize the dead-error-free control; the current inner loop adopts a PI regulator to control the current without damaging power electronic devices; setting an amplitude limiting link after the output of the outer ring, and limiting the current of the inductor not to exceed the current corresponding to the maximum power point of the photovoltaic cell;
the energy storage unit adopts a droop control mode based on self-repairing positive voltage of a droop coefficient of the SOC, and distributes voltage regulation capacity of the storage battery, and the energy storage unit is specifically as follows:
Wherein, As a reference value of the dc bus voltage to be controlled, U H1 is a first high voltage, U L1 is a first low voltage, I dc_Bi is a current on the bus side of the converter, I Bi is a charge-discharge current of the battery Bi, K Bi is a sagging coefficient of the battery Bi, and the original sagging coefficient K Bi of the battery is corrected according to a ratio α i of the SOC of the battery to the average SOC of all devices:
Wherein K' Bi is the sagging coefficient of the storage battery Bi after correction.
2. The grid-connected direct current micro grid coordinated control method according to claim 1, wherein the 6 voltage levels are ordered according to the magnitude of voltage values, and the voltage levels are sequentially from small to large, namely a third low voltage, a second low voltage, a first high voltage, a second high voltage and a third high voltage.
3. The grid-connected direct current micro grid coordination control method according to claim 2, wherein the number of the working modes is 4, and specifically comprises a first working mode, a second working mode, a third working mode and a fourth working module.
4. The grid-connected direct-current micro-grid coordinated control method according to claim 3, wherein when the voltage value of the direct-current bus voltage is between a first low voltage and a first high voltage, the corresponding working mode is the first working mode, the networking unit controls power fluctuation in a balance system and controls bus voltage, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit is in a charging state, the energy storage unit is kept in a full-power standby state if the electric quantity of the energy storage unit is full, the storage battery is not discharged, and the alternating-current and direct-current load unit is in a normal operation state.
5. The grid-connected direct-current micro-grid coordinated control method according to claim 3, wherein when the voltage value of the direct-current bus voltage is between the second low voltage and the first low voltage or between the first high voltage and the second high voltage, the corresponding working mode is the second working mode, the power transmission quantity of the networking unit reaches the limit capacity or is in a disconnected state, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit adjusts unbalanced power and controls the bus voltage, and the alternating-current/direct-current load unit is in a normal operation state.
6. The grid-connected direct-current micro-grid coordinated control method according to claim 3, wherein when the voltage value of the direct-current bus voltage is between the second high voltage and the third high voltage, the corresponding working mode is the third working mode, the networking unit absorbs electric energy from the direct-current micro-grid by the limit power capacity or is in a disconnection state, the photovoltaic power generation unit is switched to a voltage sag control mode, the energy storage unit is charged according to the maximum power, the full-power standby state is maintained if the electric quantity of the energy storage unit is full, the storage battery is not discharged, and the alternating-current/direct-current load unit is in a normal running state.
7. The grid-connected direct-current micro-grid coordinated control method according to claim 3, wherein when the voltage value of the direct-current bus voltage is between the third low voltage and the second low voltage, the corresponding working mode is a fourth working mode, the networking unit transmits electric energy to the direct-current micro-grid by the limit power capacity or is in a disconnection state, the photovoltaic power generation unit operates in an MPPT control mode, the energy storage unit discharges by the maximum power, the idle state is kept if the electric quantity of the energy storage unit is discharged, the storage battery is not charged, and the alternating-current/direct-current load unit cuts off the internal load according to the proportion.
8. The grid-connected direct-current micro-grid coordinated control method according to claim 1, wherein a bidirectional DC/AC converter is arranged in the networking unit, the bidirectional DC/AC converter adopts a double closed-loop structure, and the double closed-loop structure is specifically a voltage outer loop and a current inner loop.
9. The grid-connected direct-current micro-grid coordinated control method according to claim 1, wherein the energy storage unit adopts a self-repairing positive voltage droop control mode based on a droop coefficient of an SOC.
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