CN102496964B - Method for controlling output power of microgrid - Google Patents

Abstract

The present invention provides a method for controlling the output power of a microgrid, which includes: collecting multiple output power values of a first distributed power supply within a first predetermined time period; performing smoothing filtering on the multiple output power values to obtain a relationship with multiple output power values. Multiple active expected values corresponding to one-to-one output power values; calculate the difference between each output power value in the multiple output power values and the corresponding active expected value in the multiple active expected values to obtain multiple power control values; according to the Modify multiple power control values based on the limit power of the second distributed power source to obtain multiple corrected power control values; determine whether the second distributed power source can be charged and/or discharged based on the state of charge of the second distributed power source; The second distributed power source is controlled to charge or discharge within a second predetermined time period based on the plurality of corrected power control values and the result of determining whether the second distributed power source can be charged and/or discharged. This method can effectively suppress the fluctuation of output power.

Description

Method for controlling output power of microgrid

technical field

The invention relates to the field of power grids. More specifically, the present invention relates to a method for controlling output power of a microgrid.

Background technique

With the gradual depletion of conventional energy and the increasingly serious environmental pollution, renewable energy and distributed power generation technologies have received more and more attention and development worldwide in recent years. At present, distributed power generation generally refers to a small power generation system connected to the power distribution system that is miniaturized, modularized, decentralized, and arranged near the user to supply power for the user with a generating power of several thousand watts to 50 MW. The existing research and practice have shown that connecting the distributed generation energy supply system to the large grid in the form of a microgrid (MicroGrid, hereinafter referred to as the microgrid) and running in parallel, and supporting each other with the large grid, is the best way to play the role of distributed generation. The most efficient way to provide energy system performance.

As one of the important components of distributed power generation, the microgrid is usually a small power generation and distribution system composed of distributed power sources, energy storage devices, energy conversion devices, related loads, monitoring systems, protection systems, and power transmission equipment. It is an autonomous system capable of self-control, protection and management. Because the microgrid can operate in parallel with the large power grid through the distribution network to form a joint operation system of the large power grid and the small power grid, and can also independently provide power demand for the local load, and its flexible operation mode greatly improves the reliability of power supply at the load side. At the same time, the microgrid can reduce the impact on the traditional grid after a large number of small-power distributed power sources are connected to the grid through a single point of access to the grid. In addition, the microgrid combines scattered and different types of small power generation sources (distributed power sources) to supply power, which can make small power sources obtain higher utilization efficiency. In the normal state of the large power grid, the microgrid needs to run stably for a long time; and when the large power grid is disturbed, the microgrid must quickly separate from the large power grid, enter and maintain an island operation state, and automatically re-connect to the grid after the large power grid is eliminated. The above functions are summarized as: peak shaving, power smoothing, mode switching, etc. The control method required to realize these functions is the difficulty of microgrid technology, and research teams from various countries are constantly developing better control methods and hardware components.

The output power of renewable energy such as wind power and photovoltaic power generation is highly intermittent and random, and the power curve fluctuates violently, which causes the output power of the microgrid to fluctuate accordingly. Therefore, in the system control of the microgrid, smoothing the output power curve of renewable energy is one of the most important control purposes.

Fig. 1 shows an existing microgrid topology.

As shown in FIG. 1 , the microgrid includes a distributed power source 101 and a microgrid load 103 .

The distributed power supply 101 and the microgrid load 103 are connected to the bus BUS1. The bus BUS1 is generally a low-voltage AC bus with a voltage between 220V and 35KV, and is connected to the bus BUS2 through a transformer 104 . The bus BUS2 is generally a high-voltage AC bus, which can be regarded as a large power grid, and the voltage is usually between 10KV and 220KV.

The distributed power source 101 is a power source whose output power curve fluctuates violently (for example, renewable energy sources such as wind power generation and photovoltaic power generation). In order to eliminate the power fluctuation of the distributed power supply 101 , a filter circuit is usually used to filter out the short-term abrupt change of the power curve of the distributed power supply 101 .

However, the above-mentioned microgrid output power control method has the following problems: the overall response speed is slow (less than a second), which is not suitable for practical engineering applications; DC power smooth control can only be performed in DC systems, but not in AC systems. Therefore, it is difficult to adapt to the AC micro-grid system; the coordination effect with a variety of renewable energy generation is poor.

Contents of the invention

The purpose of the present invention is to provide a microgrid output power control method, thereby effectively reducing the fluctuation of the output power of the microgrid.

One aspect of the present invention provides a method for controlling the output power of a microgrid, wherein the microgrid includes a first distributed power supply and a second distributed power supply, and the method includes: (a) collecting the first distributed power supply within a first predetermined time period A plurality of output power values of a distributed power supply; (b) smoothing and filtering the plurality of output power values to obtain a plurality of expected active values corresponding to the plurality of output power values; (c) calculating the The difference between each output power value in the multiple output power values and the corresponding active power expected value in the multiple active power expected values to obtain multiple power control values; (d) according to the limit power of the second distributed power supply modifying the plurality of power control values to obtain a plurality of revised power control values; (e) determining whether the second distributed power source can be charged and/or discharged according to the state of charge of the second distributed power source; (f) Control the second distributed power supply to charge or discharge according to the plurality of modified power control values and the result of determining whether the second distributed power supply can be charged and/or discharged within the second predetermined time period.

Optionally, when the second distributed power supply is capable of charging and the modified power control value is greater than zero, the second distributed power supply is charged, and the charging power is the modified power control value.

Optionally, when the second distributed power source is capable of discharging and the modified power control value is less than zero, the second distributed power source is discharged, and the discharge power is the modified power control value.

Optionally, step (d) includes: when the power control value is greater than the maximum charging power value of the second distributed power supply, correcting the power control value to the maximum charging power value; when the power control value is less than the second distributed power supply When the maximum discharge power value is the maximum discharge power value, the power control value is corrected to the maximum discharge power value; in other cases, the power control value remains unchanged.

Optionally, step (e) includes: when the state of charge of the second distributed power source is greater than the first threshold, determining that the second distributed power source can only discharge; when the state of charge of the second distributed power source is less than the second When the threshold is reached, it is determined that the second distributed power supply can only be charged; when the state of charge of the second distributed power supply is less than or equal to the first threshold and greater than or equal to the second threshold, it is determined that the second distributed power supply can be charged and discharged.

Optionally, in step (f), when controlling the second distributed power supply to discharge or charge according to a modified power control value and the result, before reaching the timing of the next modified power control value, the discharge power or Charging power remains unchanged.

Optionally, step (a) is performed while performing step (f) within the second predetermined time period.

Optionally, the second predetermined time period is after the first predetermined time period.

Optionally, when the output power of the microgrid needs to be controlled in units of predetermined time lengths, the lengths of the first predetermined time period and the second predetermined time period are less than half of the predetermined time length.

Optionally, the second distributed power source is an energy storage element.

Optionally, the energy storage element is a supercapacitor or a flywheel energy storage device.

The microgrid output power control method according to the present invention can effectively suppress the fluctuation of the microgrid output power. In addition, the microgrid output power control method according to the present invention can greatly delay the life of the energy storage elements used.

Description of drawings

The above-mentioned and other objects, features and advantages of the present invention will become more clear through the following detailed description in conjunction with the accompanying drawings, wherein:

Figure 1 shows an existing microgrid topology;

Figure 2 shows a microgrid topology according to the present invention;

Fig. 3 shows a flow chart of the microgrid output power control method according to the present invention.

Detailed ways

Exemplary embodiments of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. Example embodiments may, however, be embodied in many different forms, and the invention should not be construed as limited to the example embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the example embodiments to those skilled in the art.

Fig. 2 shows a microgrid topology according to the present invention.

As shown in FIG. 2 , the microgrid includes a first distributed power source 101 , a second distributed power source 102 , and a microgrid load 103 . It can be seen that, compared with the microgrid topology shown in FIG. 1 , the microgrid according to the present invention further includes a second distributed power source 102 .

The first distributed power source 101 is a power source whose output power fluctuates violently (for example, renewable energy sources such as wind power generation and photovoltaic power generation). The second distributed power source 102 is an energy storage element (eg, supercapacitor, flywheel energy storage).

The first distributed power source 101, the second distributed power source 102, and the microgrid load 103 are connected to the bus BUS1. The bus BUS1 is connected to the bus BUS2 through the transformer 104 so as to be connected to the large power grid. The macrogrid refers to a grid having a voltage higher than that of the microgrid.

Fig. 3 shows a flow chart of the microgrid output power control method according to the present invention.

In step 301, a plurality of output power values P1 of the first distributed power source 101 are collected at a predetermined frequency within a predetermined time period T1. It should be understood that the predetermined frequency may be understood as a constant frequency or a varying frequency.

In step 302, smoothing and filtering are performed on the multiple output power values collected in step 301 to obtain multiple expected active power values P2 corresponding to the multiple output power values one-to-one.

In step 303, the difference between each of the multiple output power values and the corresponding expected active value is calculated to obtain multiple power control values P3.

In step 304, the multiple power control values P3 are corrected according to the limit power of the second distributed power source 102 to obtain multiple corrected power control values P4.

Specifically, when the power control value P3 is greater than the maximum charging power value (positive value), the power control value is corrected to the maximum charging power value; when the power control value P3 is smaller than the maximum discharging power value (negative value) , the power control value is corrected to the maximum discharge power value; in other cases, the power control value P3 remains unchanged.

When the modified power control value P4 is a positive value, it means that the second distributed power source 102 is being charged, and the charging power is the power control value. When the modified power control value P4 is a negative value, it means that the second distributed power source 102 is discharged, and the discharge power is the power control value. When the modified power control value P4 is zero, the second distributed power source 102 is neither charged nor discharged.

In step 305 , it is determined according to the state of charge (SOC) of the second distributed power source 102 which states among the charging state and the discharging state are opened by the second distributed power source 102 .

The charging state indicates that the second distributed power source 102 can be charged. The discharge state indicates that the second distributed power source 102 can be discharged.

When the state of charge of the second distributed power source 102 is greater than the first threshold, it means that the second distributed power source 102 is only in the discharge state and can only discharge.

When the state of charge of the second distributed power supply 102 is less than the second threshold, it means that the second distributed power supply 102 has only opened the charging state and can only be charged.

When the state of charge of the second distributed power supply 102 is less than or equal to the first threshold and greater than or equal to the second threshold, it means that the second distributed power supply 102 has opened the charging state and discharging state, and can perform charging and discharging.

It should be understood that the first threshold is greater than the second threshold.

In step 306, within the next predetermined time period T2 after the predetermined time period T1, control the second The distributed power source 102 performs charging or discharging.

According to the previous description of the power control value and state, it can be seen that when the second distributed power source 102 opens the charging state and the modified power control value P4 is greater than zero, the second distributed power source 102 is controlled to charge, and the second distributed power source 102 is controlled to charge. The input power of the formula power source 102 is the modified power control value P4; when the second distributed power source 102 opens the discharge state, and when the modified power control value P4 is less than zero, the second distributed power source 102 is controlled to discharge, and the second distributed power source 102 is controlled to discharge. The output power of the two distributed power sources 102 is the modified power control value P4.

It should be understood that the time sequence of each corrected power control value P4 is the corresponding time sequence of the output power value P1 collected in step 301 . In addition, it should be understood that when the second distributed power source 102 is controlled to discharge or charge according to a modified power control value P4, the discharging or charging power remains unchanged until the next modified power control value P4 is reached.

When it is necessary to perform output power control within a plurality of predetermined time periods, while performing step 306 within the next predetermined time period T2, step 301 may be simultaneously performed within the next predetermined time period T2, so that The next predetermined time period T3 after the predetermined time period T2 controls the second distributed power source 102 to perform charging and discharging. In this way, steps 301-306 are repeatedly executed for each predetermined time period to control the output power.

In addition, there may be a need to smooth the output power of the first distributed power source 101 with a predetermined period of time (also referred to as an evaluation period, for example, 0.5 minutes to 5 minutes) (that is, with the predetermined period of time as a unit, In the case of suppressing sudden changes in the output power of the first distributed power supply 101), the length of the above-mentioned predetermined period of time (also referred to as a control period) should be less than half of the predetermined period of time.

According to the power control method of the present invention, although the control of the output power has a certain hysteresis, the control period is only a part of the evaluation period (for example, the output power in two adjacent control periods is all in a sudden increase) , so effective smoothing of the power is still possible overall.

Preferably, the length of the evaluation period is an integer multiple of the length of the control period.

In the present invention, since the charge state and the discharge state are actively opened according to the state of charge of the energy storage element, power can only be absorbed in the charge state, and power can only be emitted in the discharge state, so that the energy storage element works at a higher performance. The best range, and will not switch frequently between charging and discharging, thus prolonging the life of the energy storage element. For example, in the test of a microgrid system containing a 200kW×10s supercapacitor and 500kW solar photovoltaic power generation, when the control period is 1 second and the evaluation period is 60 seconds, the maximum life of the supercapacitor is extended by 30 times.

Preferably, the second distributed power source 102 according to the present invention is a supercapacitor or a flywheel accumulator. Compared with other types of energy storage elements, a supercapacitor and a flywheel accumulator have the advantages of large instantaneous power and short charging and discharging time . In the prior art, supercapacitors and flywheel accumulators can realize charging and discharging of DC or AC electric energy by setting power controllers and/or inverters, and can control the size of charging and discharging power.

The micro-grid output power control method according to the present invention can effectively suppress the fluctuation of the micro-grid output power, and can delay the life of the used energy storage elements.

While the invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that changes may be made in form and detail without departing from the spirit and scope of the invention as defined by the claims. various changes.

Claims (9)

1. A method of controlling the output power of a microgrid, wherein the microgrid includes a first distributed power supply and a second distributed power supply, the method comprising: (a) collecting a plurality of output power values of the first distributed power source with a constant frequency or a variable frequency within a first predetermined period of time; (b) smoothing and filtering the plurality of output power values to obtain a plurality of expected active values corresponding to the plurality of output power values; (c) calculating the difference between each output power value of the plurality of output power values and a corresponding expected value of active power in the plurality of expected values of active power to obtain a plurality of power control values; (d) modifying the plurality of power control values according to the limit power of the second distributed power source to obtain a plurality of modified power control values; (e) determining whether the second distributed power supply can be charged and/or discharged according to the state of charge of the second distributed power supply; (f) controlling the second distributed power supply to charge or discharge according to the plurality of modified power control values and the result of determining whether the second distributed power supply can be charged and/or discharged within a second predetermined time period, Wherein, the second predetermined time period is after the first predetermined time period, Wherein, step (d) comprises: When the power control value is greater than the maximum charging power value of the second distributed power supply, correcting the power control value to the maximum charging power value, When the power control value is less than the maximum discharge power value of the second distributed power supply, the power control value is corrected to the maximum discharge power value, In other cases, the power control value is unchanged. 2. The method according to claim 1, wherein, when the second distributed power supply is capable of charging and the modified power control value is greater than zero, the second distributed power supply is charged, and the charging power is the modified power control value. 3. The method according to claim 1, wherein, when the second distributed power source is capable of discharging and the modified power control value is less than zero, the second distributed power source is discharged, and the discharge power is the modified power control value. 4. The method of claim 1, wherein step (e) comprises: When the state of charge of the second distributed power supply is greater than the first threshold, it is determined that the second distributed power supply can only discharge; When the state of charge of the second distributed power supply is less than the second threshold, it is determined that the second distributed power supply can only be charged; When the state of charge of the second distributed power supply is less than or equal to the first threshold and greater than or equal to the second threshold, it is determined that the second distributed power supply can perform charging and discharging. 5. The method according to claim 1, wherein, in step (f), when the second distributed power source is controlled to discharge or charge according to a modified power control value and the result, when the next modified power control value is reached Keep the discharge power or charge power constant until the timing of the value. 6. The method of claim 1, wherein step (a) is performed while step (f) is performed within a second predetermined time period. 7. The method according to claim 1, wherein, when the output power of the microgrid needs to be controlled in units of a predetermined duration, the lengths of the first predetermined time period and the second predetermined time period are less than half of the predetermined duration one. 8. The method of claim 1, wherein the second distributed power source is an energy storage element. 9. The method of claim 8, wherein the energy storage element is a supercapacitor or a flywheel energy storage.