CN109066814B - Control method and system for secondary frequency modulation of thermal power unit assisted by energy storage device - Google Patents

Abstract

The invention discloses a control method and a system for using an energy storage device to assist the secondary frequency regulation of a thermal power unit. The control system adopted in the present invention includes a power control module based on the state of charge of the energy storage device and a time delay compensation module based on the Smith predictor. The control system accepts the secondary frequency modulation command from the power grid, the active power feedback of the thermal power unit, the state of charge of the energy storage device and the feedback of the output active power; according to the feedback data, the control system adopts the method based on the state of charge of the energy storage device to determine the output required by the energy storage device After using the Smith predictor to compensate for the time delay in the auxiliary frequency modulation system, the control system obtains the command power, and the command is sent to the energy storage device through the communication equipment, and the thermal power generation power of the thermal power unit is calculated by the fast response characteristics of the energy storage device. Compensation; auxiliary frequency regulation system includes control system and energy storage device. The invention can improve the dynamic performance of the thermal power unit participating in the frequency regulation of the power system, and obtain higher frequency regulation benefits.

Description

Control method and system for secondary frequency modulation of thermal power unit assisted by energy storage device

technical field

The invention belongs to the field of energy storage control, and relates to the control of an energy storage device, in particular to a control method and a system for the secondary frequency modulation of an energy storage device to assist a thermal power unit.

Background technique

In recent years, with the large-scale connection of renewable energy to the power grid, the uncertainty in the power grid is increasing, which puts forward higher requirements for frequency regulation of the power system. The frequency regulation capability of traditional thermal power units is weak, and the ramp rate is generally only 2% of the rated capacity of the unit per minute. At the same time, frequent and rapid adjustment will increase the wear and coal consumption of thermal power units, and endanger the safety of the unit itself and the power grid.

Compared with thermal power units, energy storage devices have the capability of millisecond-level full power output and fast response speed, so they can be used as auxiliary components to improve the ability of thermal power units to participate in secondary frequency regulation of the power grid, and at the same time obtain higher frequency regulation benefits. In recent years, energy storage devices assist thermal power units to participate in the secondary frequency regulation of the power grid, and many projects have been implemented.

The energy storage auxiliary frequency regulation system needs to focus on two issues: 1) It is necessary to keep the state of charge of the energy storage device within a reasonable range to avoid deep charging and deep discharging of the energy storage device; 2) When the auxiliary frequency regulation system of the energy storage device contains many components Delay links, such as signal measurement, control execution, data transmission, etc., the accumulation of time delays in these links will have an important impact on the performance of the auxiliary frequency modulation system. Therefore, it is necessary to design a control strategy to reduce the impact of time delay on system performance.

SUMMARY OF THE INVENTION

In order to improve the performance of the secondary frequency regulation of the existing energy storage device auxiliary thermal power unit, the present invention provides a control method and system for the secondary frequency regulation of the energy storage device auxiliary thermal power unit, so as to reduce the influence of time delay on the system performance and improve the auxiliary frequency regulation system dynamic performance, and obtain higher FM income.

For this reason, the present invention adopts the following technical scheme: a control method and system for secondary frequency regulation of an auxiliary thermal power unit by an energy storage device, and the control system includes a power control module based on the state of charge of the energy storage device and a Smith predictor-based power control module. Time delay compensation module, the control method includes the following steps:

1) The described control system accepts the AGC secondary frequency modulation command from the power grid through the data acquisition device, the output active power feedback of the thermal power unit, the state of charge of the energy storage device and the output active power feedback, respectively denoted as P _AGC , P _GEN , SOC , P _ESS ; according to the feedback data, the control system adopts the method based on the state of charge of the energy storage device to determine the active power P _cmd,0 that the energy storage needs to output;

2) Using Smith predictor to compensate the time delay of the auxiliary frequency modulation system, the control system obtains the command power P _cmd , and sends it to the energy storage device through the data transmission device, and the energy storage device outputs the command power;

The auxiliary frequency regulation system includes a control system and an energy storage device.

As a supplement to the above technical solution, in the step 1), the process of determining the active power P _cmd,0 that the energy storage device needs to output by using a method based on the state of charge of the energy storage device is as follows: first, obtain its intermediate power:

P _cmd,1 =P _AGC -P _GEN ,

Then, continue to use the limit operation on P _cmd,1 to obtain P _cmd,0 , the limit interval of which is related to the state of charge of the energy storage device.

As a supplement to the above technical solution, the state of charge of the energy storage device is divided into three intervals, namely a low interval [SOC _low1 , SOC _up1 ], a middle interval [SOC _low2 , SOC _up2 ] and a high interval [SOC _low3 , SOC _{up3 ]} ], the output active power limit interval of the energy storage device in the low interval is [-P _max , P _max /k ₁ ], and the output active power limit interval of the energy storage device in the middle interval is [-P _max , P _max ], in the The output active power limit interval of the energy storage device in the high interval is [-P _max /k ₂ ,P _max ]; among them, SOC _low1 <SOC _up1 <SOC _low2 <SOC _up2 <SOC _low3 <SOC _up3 is the interval for judging the state of charge parameters, P _max is the maximum charge and discharge power of the energy storage, k ₁ is the charge and discharge limit control coefficient in the low range, and k ₂ is the charge and discharge limit control coefficient in the high range.

As a supplement to the above technical solutions, k ₁ and k ₂ are obtained by adopting heuristic algorithm optimization and calculation according to the objective of maximizing the benefit of auxiliary frequency modulation.

As a supplement to the above technical solution, the control system adopts a hysteresis control method when switching between different charge states.

As a supplement to the above technical solution, the hysteresis control method is:

The default SOC of the control system is in the middle range. After the auxiliary frequency modulation system is started, the control system will determine the range of the SOC of the energy storage device in a hysteretic manner, that is, when the SOC is in the middle range and SOC<SOC _up1 , it will switch from the middle range to the low range. In the interval, when the SOC is in the middle interval and SOC>SOC _low3 , it switches from the middle interval to the high interval. When the SOC is in the low interval and SOC>SOC _low2 , it switches from the low interval to the middle interval. When the SOC is in the high interval and SOC< Switch from high range to middle range when SOC _up2 .

As a supplement to the above technical solution, the Smith predictor is used to compensate the time delay of the auxiliary frequency modulation system, and the power command P _cmd for the energy storage device is obtained:

Among them, s is the Laplacian operator, K _P and K _I are the proportional and integral parameters of the proportional-integral controller, P _feedback is the power feedback with compensation, τ is the equivalent time delay of the auxiliary frequency modulation system, H(s ) is the equivalent transfer function of the auxiliary FM system.

The present invention has the beneficial effects that: by dividing the state of charge of the energy storage device into three intervals, the energy storage device can perform different charging and discharging amplitude limiting values in different intervals, and not only can the state of charge of the energy storage device be kept within the Reasonable range, at the same time, the maximum frequency modulation benefit can be obtained by optimizing the k ₁ and k ₂ parameters. By introducing the time delay compensation module based on the Smith predictor, the invention can improve the dynamic performance of the auxiliary frequency modulation system and obtain higher frequency modulation income.

Description of drawings

1 is a schematic structural diagram of an auxiliary frequency regulation system (including an energy storage device and a control system) in an embodiment of the present invention;

2 is a schematic diagram of power control based on the state of charge of an energy storage device in an embodiment of the present invention;

3 is a schematic diagram of the principle of a time delay compensation module based on a Smith predictor in an embodiment of the present invention;

Fig. 4 is a comparison diagram of the simulation results of the secondary frequency modulation of the thermal power unit without the auxiliary frequency modulation of the energy storage device and the thermal power unit with the frequency modulation of the energy storage device in the embodiment of the present invention (the above figure is the simulation result of the secondary frequency modulation of the thermal power unit without the auxiliary frequency modulation of the energy storage device, The dotted line is the AGC command, the solid line is the active power output of the thermal power unit; the figure below is the simulation result of the secondary frequency modulation of the thermal power unit with frequency modulation of the energy storage device, the dotted line is the AGC command, and the solid line is the combined active power output of the thermal power unit and the energy storage device );

FIG. 5 is a graph of SOC changes of the energy storage device in one day in the embodiment of the present invention.

Detailed ways

The technical solutions in this embodiment will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of examples of the present invention, rather than all examples. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The complete structure of the auxiliary frequency modulation system is shown in Figure 1, including the energy storage device and the control system. The energy storage device is mainly composed of an energy storage battery and an inverter. The control system includes two parts: the power control module based on the state of charge of the energy storage device and the time delay compensation module based on the Smith _predictor . _GEN , SOC, _PESS . The difference between the secondary frequency modulation command and the output active power of the thermal power unit is the active power that the energy storage device needs to output, which is denoted as P _cmd,1 .

P _cmd,1 =P _AGC -P _GEN ,

After obtaining P _cmd,1 , it is necessary to limit the energy storage device according to the state of charge.

Table 1 Symbol definitions and descriptions of some system variables in the accompanying drawings of the present invention

symbol Definition and Explanation P_AGC Power grid secondary frequency regulation command P_GEN Thermal power unit output active power feedback P_ESS Energy storage device output active power feedback SOC State-of-charge feedback of energy storage devices SOC_low1,SOC_up1 The upper and lower range of the SOC low interval of the energy storage device SOC_low2,SOC_up2 The upper and lower ranges of the middle interval of the SOC of the energy storage device SOC_low3,SOC_up3 The upper and lower range of the SOC high interval of the energy storage device P_cmd,0 Intermediate value of power command of energy storage device P_cmd Energy storage device power command P_max Maximum charge and discharge power of energy storage device P_feedback With compensation power feedback H(s) Equivalent Transfer Function of Auxiliary Frequency Modulation System τ Equivalent Time Delay of Auxiliary Frequency Modulation System s Laplace operator

The power control based on the state of charge of the energy storage device is shown in Figure 2. The state of charge of the energy storage device is divided into three intervals, namely the low interval [SOC _low1 , SOC _up1 ], the middle interval [SOC _low2 , SOC _up2 ] and the high interval [SOC _low3 , SOC _up3 ]. The output active power limit interval is [-P _max , P _max /k ₁ ], in the middle interval the output active power limit interval of the energy storage device is [-P _max , P _max ], in the high interval the energy storage device outputs active power The clipping interval is [-P _max /k ₂ , P _max ]. Among them, SOC _low1 <SOC _up1 <SOC _low2 <SOC _up2 <SOC _low3 <SOC _up3 , is a parameter for judging the state of charge interval, P _max is the maximum charge and discharge power of the energy storage device, and k ₁ is the low interval charge and discharge limit control coefficient , k ₂ is the high-range charge-discharge limiting control coefficient, k ₁ and k ₂ are obtained by heuristic algorithm optimization according to the maximization goal of auxiliary frequency modulation revenue.

The default SOC of the control system is in the middle range. After the auxiliary frequency modulation system is started, the control system will determine the range of the SOC of the energy storage device in a hysteretic manner, that is, when the SOC is in the middle range and SOC<SOC _up1 , it will switch from the middle range to the low range. In the interval, when the SOC is in the middle interval and SOC>SOC _low3 , switch from the middle interval to the high interval, when the SOC is in the low interval and SOC>SOC _low2 , switch from the low interval to the middle interval, when the SOC is in the high interval and SOC< Switch from high range to middle range when SOC _up2 . k ₁ and k ₂ are charge and discharge limit control coefficients (greater than or equal to 1), the physical meaning of which is that when the SOC is in the low range, the maximum charging power remains unchanged and the maximum discharge power is reduced, so that the energy storage device has the auxiliary frequency regulation capability At the same time, its SOC can be restored to the middle range; when the SOC is in the high range, the maximum discharge power remains unchanged, and its maximum charging power is reduced, so that the energy storage device has the auxiliary frequency regulation capability and can restore its SOC to the middle range.

After getting P _cmd,0 , the Smith predictor is used to compensate the time delay of the auxiliary frequency modulation system, so that the system can obtain better dynamic performance. Its structure is shown in Figure 3. The command P _cmd is obtained in the following way:

Among them, s is the Laplacian operator, K _P and K _I are the proportional and integral parameters of the controller, P _feedback is the power feedback with compensation, τ is the equivalent time delay of the auxiliary frequency modulation system, and H(s) is Auxiliary FM system transfer function.

Taking the secondary frequency regulation of a thermal power unit with an installed capacity of 300MW as an example, the energy storage device is simulated and verified, and the energy storage configuration is 9MW/4.5MWh. Other parameters required for the simulation are listed in Table 2.

Table 2 Values of parameters required for simulation of the present invention

parameter value SOC_low1,SOC_up1 0,40% SOC_low2,SOC_up2 50%, 70% SOC_low3,SOC_up3 80%, 100% k₁,k₂ 30,15 Proportional-integral controller, K_P,K_I 0.001,10 H(s) 1 τ 3s

Figure 4 is a comparison diagram of the simulation results of secondary frequency modulation of thermal power units without auxiliary frequency modulation of energy storage devices and auxiliary frequency modulation of energy storage devices. The dotted line in the upper figure is the AGC command, and the solid line is the active power output of the thermal power unit; AGC command, the solid line is the combined active power output of the thermal power unit and the energy storage device. It can be clearly seen that the combined response speed, steady-state accuracy and response time of the thermal power unit and the energy storage device are better than those of the simple thermal power unit after using the energy storage device-assisted secondary frequency modulation control method for the thermal power unit proposed by the present invention. marked improvement. Figure 5 shows the SOC change of the energy storage device in one day, and it can be seen that the SOC can be within a reasonable range, which verifies the effectiveness of the power control method based on the state of charge of the energy storage device of the present invention.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (5)

1. The control method for assisting secondary frequency modulation of the thermal power generating unit by the energy storage device is characterized in that a control system adopted by the method comprises a power control module based on the charge state of the energy storage device and a time lag compensation module based on a Smith predictor, and the control method comprises the following steps:

1) the control system receives AGC secondary frequency modulation instructions from a power grid, thermal power unit output active power feedback, energy storage device charge state and output active power feedback through a data acquisition device, and the AGC secondary frequency modulation instructions, the thermal power unit output active power feedback and the energy storage device charge state and output active power feedback are respectively recorded as P_AGC，P_GEN，SOC，P_ESS(ii) a According to the feedback data, the control system determines the active power P required to be output by energy storage by adopting a method based on the state of charge of the energy storage device_cmd,0；

2) When using Smith predictor to auxiliary frequency modulation systemThe hysteresis is compensated, and the control system obtains the instruction power P_cmdThe command power is sent to the energy storage device through the data transmission device, and the command power is output by the energy storage device; the auxiliary frequency modulation system comprises a control system and an energy storage device;

in the step 1), the active power P required to be output by the energy storage device is determined by adopting a method based on the state of charge of the energy storage device_cmd,0The process of (2) is as follows: first, its intermediate power is obtained:

P_cmd,1＝P_AGC-P_GEN，

then, continue to P_cmd,1Obtaining P by amplitude limiting operation_cmd,0The amplitude limiting interval is related to the charge state of the energy storage device;

compensating the time lag of the auxiliary frequency modulation system by adopting a Smith predictor to obtain a power instruction P of the energy storage device_cmd：

Wherein s is Laplace operator, K_PAnd K_IProportional and integral parameters, P, for proportional-integral controllers_feedbackIn order to contain the compensation power feedback quantity, tau is the equivalent time lag of the auxiliary frequency modulation system, and H(s) is the equivalent transfer function of the auxiliary frequency modulation system.

2. The control method of claim 1, wherein the energy storage device state of charge is divided into three intervals, each interval being a low interval [ SOC [ ]_low1,SOC_up1]Middle zone [ SOC ]_low2,SOC_up2]And high interval [ SOC_low3,SOC_up3]The amplitude limiting interval of the active power output by the low interval energy storage device is [ -P ]_max,P_max/k₁]In the middle area, the output active power amplitude limit of the energy storage deviceThe interval is [ -P_max,P_max]The amplitude limiting interval of the active power output by the high interval energy storage device is [ -P ]_max/k₂,P_max](ii) a Therein, SOC_low1<SOC_up1<SOC_low2<SOC_up2<SOC_low3<SOC_up3To determine the parameters of the state-of-charge interval, P_maxFor storing maximum charge-discharge power, k₁Is a low range charge-discharge amplitude limit control coefficient, k₂And the high interval charging and discharging amplitude limiting control coefficient.

3. The control method of claim 2, wherein k is₁And k₂And according to the auxiliary frequency modulation profit maximization target, optimizing and calculating by adopting a heuristic algorithm.

4. The control method of claim 2, wherein the control system employs a hysteresis control method when switching between different states of charge.

5. The control method according to claim 4, wherein the hysteresis control method is:

the control system defaults that the SOC is in a middle interval, after the auxiliary frequency modulation system is started, the control system can determine the interval where the SOC of the energy storage device is in a hysteresis mode, namely when the condition that the SOC is in the middle interval and the SOC is in the middle interval is met<SOC_up1When the SOC is in the middle interval and the SOC is in the low interval>SOC_low3When the SOC is in the low interval and the SOC is in the high interval>SOC_low2When the SOC is in the high interval and the SOC is in the low interval, the low interval is switched to the middle interval, and when the SOC is in the high interval and the SOC is satisfied<SOC_up2It switches from the high interval to the middle interval.

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