CN105743107A - Control method for frequency regulation of electric power isolated network system - Google Patents

Abstract

The invention discloses a control method for frequency regulation of an isolated power grid system, which is characterized in that it includes the following steps: Step 1. According to the requirements of the power grid, set the permanent slip coefficient bp, PID parameters, frequency modulation dead zone 0.05Hz and call The frequency range of the frequency modulation module is ±0.05Hz to ±θHz, where θ is a positive number greater than 0.05; step 2, the governor detects the current unit frequency; step 3, calculate the difference between the detected current unit frequency and the rated frequency of 50Hz value Δf; step 4, adjust according to the value range of the frequency difference Δf. Solve the problems of large frequency control error, poor precision and instability in the power system, especially the isolated grid system, so as to achieve precise and stable control of the power grid frequency, ensure the power quality of the power system, prevent the expansion of power grid accidents, and realize the rapid recovery of the power grid after the accident .

Description

A control method for frequency regulation of power isolated grid system

technical field

The invention relates to a control method for frequency regulation of an electric isolated grid system.

Background technique

In the domestic power system, regardless of large grid, small grid or isolated grid, there are usually two conventional methods for power grid frequency regulation: one is to detect frequency fluctuations, with the help of power load statistics with large data volumes, and through a dedicated frequency regulation model, power dispatching is used for each The power plant sets the load, and each power plant adjusts the active power according to the set load curve (data), so as to adjust the frequency of the system, but this adjustment method alone cannot meet the frequency control requirements; the second is for small frequency fluctuation adjustment, In the generator set governor, the control link adopts the difference adjustment formula to adjust the frequency. This formula is the change relationship between the frequency and the unit opening (active power), but this formula cannot overcome the inherent static frequency difference and cannot achieve precise control of the frequency. It will cause the oscillation of the system frequency.

For the isolated grid system, the fluctuation range of voltage and frequency is relatively large, and the influence of load operation is more obvious. Due to its small capacity and the small kinetic energy stored in the rotational inertia, the speed control system of the unit is required to have higher sensitivity, smaller sluggish rate and faster dynamic response.

At present, the power system frequency adjustment method adopts the difference adjustment formula, which is simplified as follows: In the formula, the numerator Δf/50 is the percentage (%) of the frequency difference, and the denominator bp is the permanent slip coefficient. Δy is the guide vane opening (%), which determines the input energy of the water turbine (or steam turbine).

In the industry, the bp of the governor is set between 3% and 8%, generally set at 4% or 6%. It can be seen from the formula: the larger the bp is set, the smaller the adjustment of the guide vane opening to the frequency change, the less obvious the frequency modulation effect, and the greater the static error; if the bp is set too small, the adjustment of the guide vane opening to the frequency change The larger the amount, but it is easy to cause frequency oscillation. It is difficult to determine the accuracy and correctness of bp setting, and it is not easy to be verified.

The difference adjustment formula, for the control device of the water turbine (or steam turbine), is to detect the frequency deviation, and then perform a simple linear calculation on the frequency difference. or steam turbine) energy, reduce frequency; low frequency produces a positive opening, increase energy, and increase speed. When the frequency of the machine is within the dead zone, the opening of the guide vane returns to the original given value, the frequency will fluctuate twice, and the regulator will cycle again to adjust as above. It has following deficiencies:

First, the frequency adjustment formula is used in China. This formula is only a simple proportional relationship between the frequency and the opening of the guide vane. The internal connection between the frequency and the guide vane is not reflected, and the precise control of the frequency cannot be achieved;

Second, the domestic bp is generally set at 4% or 6%. This value has not been rigorously derived mathematically, but an empirical parameter. It is only based on the former Soviet Union, which is unscientific, and this parameter is not corresponding to different grid structures. The frequency optimal control of the system cannot be realized by using this parameter;

Third, the industry adopts the differential adjustment formula to adjust, and the frequency returns to the dead zone. After the power system is stable, due to the negative feedback of bp, the opening of the guide vane will return to the opening before the action. This return will cause the frequency to change. The secondary oscillation and the secondary adjustment of the regulator, if there is no human intervention, will be cyclically adjusted, and the system frequency stability is poor.

Contents of the invention

In view of the above-mentioned problems, the present invention provides a control method for frequency adjustment of the power isolated grid system, which solves the problems of large frequency control errors, poor precision and instability in the power system, especially the isolated grid system, so as to achieve precise and stable control of the grid frequency. The power quality of the power system is guaranteed, the expansion of the power grid accident is prevented, and the rapid recovery of the power grid after the accident is realized.

Name explanation:

Isolated grid system: a small grid operating in isolation, a local power system or several local power systems are connected through a common connection point, and a grid operation state that is electrically separated from the rest of the power system, including special cases: several units Parallel operation, single machine with load and load shedding with plant power.

Turbine regulator: detect the speed of the water turbine, generate a signal proportional to the speed deviation, and generate corresponding hydraulic control output to the main servomotor of the water turbine.

No-load opening: the opening of the guide vane at the moment when the unit reaches the rated speed and is put into the grid.

Perpetual slip coefficient bp: The slip coefficient at steady state after the buffer device attenuates. The slip coefficient is the negative number of the slope at a specified operating point on the static characteristic curve of the speed control system.

In order to achieve the above-mentioned technical purpose and achieve the above-mentioned technical effect, the present invention is realized through the following technical solutions:

A control method for frequency regulation of an isolated power grid system, characterized in that it includes the following steps:

Step 1. According to the requirements of the power grid, set the permanent slip coefficient bp, PID parameters, frequency modulation dead zone 0.05Hz and the frequency range of the frequency modulation module ±0.05Hz-±θHz, where θ is a positive number greater than 0.05;

Step 2, the governor detects the current unit frequency;

Step 3. Calculate the difference Δf between the detected current unit frequency and the rated frequency of 50 Hz;

Step 4. Adjust according to the numerical range of the frequency difference Δf, as follows:

A. If the absolute value of the frequency difference Δf is greater than 0.05Hz and less than θHz, the governor will call the frequency modulation module and use the frequency modulation formula Adjust the unit output;

In the formula, Δa is the variation of the guide vane opening, a is the no-load opening of the guide vane, f ₀ is the corresponding system frequency under the no-load opening of the guide vane a, and f ₁ is the changed frequency;

B. If the absolute value of the frequency difference Δf is greater than θHz, the governor adopts PID control and difference adjustment formula Adjust the unit output;

In the formula, Δy is the opening of the guide vane, and Δf/50 is the percentage of frequency difference;

C. If the absolute value of the frequency difference Δf is less than 0.05Hz in the frequency modulation dead zone, the governor will exit the frequency modulation mode.

Preferably, θ=0.1. In practical applications, θ is adjustable according to the actual operating conditions of different power stations, not necessarily 0.1 Hz.

Among them, if the absolute value of the frequency difference Δf is greater than 0.1Hz, the governor adopts PID control and difference adjustment formula Adjust the output of the unit. When the absolute value of the frequency difference Δf gradually decreases to 0.05Hz-0.1Hz, the governor will call the frequency modulation module and use the frequency modulation formula Adjust unit output.

Based on the output characteristics of the generator set combined with the principle of fixed axis rotation energy, a frequency regulation method suitable for isolated grid systems was invented. The main core is to use a new frequency regulation formula internally through the regulator of the water turbine (or steam turbine) In order to achieve precise control of frequency, this formula reveals the relationship between frequency and unit guide vane opening, and has been verified in the operation of on-site hydropower generating units.

The beneficial effects of the present invention are:

1. The new frequency modulation formula of the present invention characterizes the internal relationship between frequency and guide vane opening;

2. This formula is simple and clear, and it is easy to embed it into the control model of the prime mover regulator by means of programming, and it is very difficult to convert theory into application.

3. The prime mover regulator with this formula can detect the frequency fluctuation, and then calculate according to the formula to obtain the corresponding guide vane opening (or nozzle) change, and the variable will act on the generator set through the actuator Input energy to achieve the purpose of precisely controlling the frequency of the system.

4. Realize the precise and stable control of the frequency of the power grid, guarantee the power quality of the power system, prevent the expansion of the power grid accident, and realize the rapid recovery of the power grid after the accident.

Description of drawings

Fig. 1 is the schematic diagram of the governor frequency control strategy of the present invention;

Fig. 2 is the schematic diagram of the torque balance of the rotating body of the generating set of the present invention;

Fig. 3 is the 50Hz-52Hz regulating disturbance curve diagram of the 2# unit of the Xiaowan Hydropower Station of the present invention;

Fig. 4 is a 52Hz-50Hz regulation disturbance curve of the 2# unit of the Xiaowan Hydropower Station according to the present invention.

detailed description

The technical scheme of the present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the examples given are not intended to limit the present invention.

A control method for frequency regulation of an isolated power grid system, comprising the following steps:

Step 1. According to the requirements of the power grid, set the permanent slip coefficient bp, PID parameters, frequency modulation dead zone 0.05Hz and the frequency range of the frequency modulation module ±0.05Hz-±θHz, where θ is a positive number greater than 0.05;

Step 2. The governor detects the current unit frequency, and the unit frequency value is equal to the power grid frequency value in the power generation mode of the isolated grid system;

Step 3. Calculate the difference Δf between the detected current unit frequency and the rated frequency of 50 Hz;

Step 4. Adjust according to the numerical range of the frequency difference Δf, as follows:

A. If the absolute value of the frequency difference Δf is greater than 0.05Hz and less than θHz, the governor will call the frequency modulation module and use the frequency modulation formula Adjust the output of the unit, balance the active power and load of the system, and then adjust the grid frequency to stabilize it to the rated frequency of 50Hz;

In the formula, Δa is the variation of the guide vane opening, a is the no-load opening of the guide vane, f ₀ is the corresponding system frequency under the no-load opening of the guide vane a, and f ₁ is the changed frequency;

B. If the absolute value of the frequency difference Δf is greater than θHz, the governor adopts PID control and difference adjustment formula Adjust the unit output;

In the formula, Δy is the opening of the guide vane, and Δf/50 is the percentage of frequency difference;

C. If the absolute value of the frequency difference Δf is less than 0.05Hz in the frequency modulation dead zone, the governor will exit the frequency modulation mode.

Preferably, θ=0.1. Among them, if the absolute value of the frequency difference Δf is greater than 0.1Hz, the governor adopts PID control and difference adjustment formula Adjust the output of the unit. When the absolute value of the frequency difference Δf gradually decreases to 0.05Hz-0.1Hz, the governor will call the frequency modulation module and use the frequency modulation formula Adjust unit output. In practical application, according to the actual operating conditions of different power stations, θ is adjustable, not necessarily 0.1Hz.

As shown in Figure 1, the speed governor is the core equipment of power system frequency control. The speed control system consists of three parts, the electrical control part, the hydraulic execution part and the generator set frequency feedback unit. This model has the function of conventional frequency PID control. By detecting the deviation of frequency reference (50Hz) and frequency feedback, and then performing PID calculation on the deviation, outputting the given guide vane opening, and then controlling the guide vane opening to change In this way, the balance relationship between the active power generated in the power system and the power load will be adjusted, so that the system frequency can be maintained within a reasonable range.

In order to achieve precise control of the frequency, a new frequency modulation module is added. This module uses the new frequency modulation formula as a means, abandons the conventional PID closed-loop calculation, but adopts the method of directly calculating the frequency itself, theoretically, accurately calculates the required Adjust the opening of the guide vane, so as to move the guide vane in a targeted manner. Since the opening of the guide vane and the frequency have a certain internal relationship, the precise and rapid control of the frequency can be achieved. The model is transferred in the frequency range of ±0.05Hz-±0.1Hz, and the conventional difference adjustment method is adopted outside ±0.1Hz.

FM formula The derivation process is as follows:

The power generation operation of the hydroelectric generating set can be considered as a rigid body rotating with a fixed axis under the inertial system, and its rotational kinetic energy can be expressed as:

$\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; J\&omega;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, J is the moment of inertia of the unit, and its value depends on the structure and quality of the unit, which is a fixed value; ω is the angular velocity of the unit, ω=2πn, and n is the rotational speed.

According to the analysis of the principle of energy conservation, if the frequency of the entire power system decreases, it means that the generating set does not generate enough active power. If the prime mover regulator in the system does not adjust, the self-balancing ability of the system will reduce the rotating speed of the generating set and save energy to make up for the power load gap. If each unit timely and accurately compensates the reduced rotational kinetic energy of the unit through its own regulator input energy (proportional to the guide vane opening, equivalent driving torque TP), the system frequency can be quickly restored. The calculation derivation below is also based on this fundamental idea.

According to Thevenin's theorem, all generating units in the power grid are equivalent to one unit. At this time, the power system can be considered as a single unit with load. The rotational kinetic energy and input energy of the unit present an isolated balance, which means a stable The energy input corresponds to a steady unit speed. As shown in Figure 2, the output of the unit directly affects the system frequency. It can be seen that each unit has a "no-load opening" a, ignoring the electromagnetic connection between units and the electromagnetic active power of the unit, that is to say, the opening makes the unit maintain a 50Hz speed. If the electromagnetic torque of the generator set (electromagnetic active power, equivalent resistance torque TE) is considered, the "load opening" b of the governor (the opening above the no-load opening a, which is used to do work) can be used to perform equivalent work. Offset, the following specific analysis:

According to the principle of equal power, the equivalent rotational speed torque T _K = prime mover torque T _P - electromagnetic torque T _E ;

Among them, T _P ∝(a+b), T _E ∝(b), thus we can get T _K ∝(a), that is, T _K ＝f(a). In this way, the equivalent torque can be simplified as a proportional function of the guide vane opening (a). According to the operating characteristics of the turbine, the equivalent torque is proportional to the input water flow of the turbine, and the input water flow is proportional to the guide vane opening. Therefore, it can be Get T _K ∝ Q = ka, k is a fixed value, and Q is the input water flow of the turbine. According to basic physics, power multiplied by time t equals energy, which is the balance relation:

Pt=E (2)

It can also be seen that the output formula of the water turbine is:

P=9.8QHη (3)

In the formula, H is the working water head in meters, and η is the efficiency of the water turbine;

Put the formulas (1) and (3) into the above formula (2) to get:

$\mathrm{<span\; class="notranslate">\; 9.8</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; \&eta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; J\&omega;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

It is known that ω=2πn; n=60f/p, p is the pole logarithm of the unit, and ω=120πf/p can be obtained, which can be brought into the formula (4) to obtain:

$\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 7243</span>}\mathrm{<span\; class="notranslate">\; J</span>}}{{\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; \&eta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$

Simplify the fixed parameter in the above formula to K:

$\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Kf</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ;</span>$

Similarly, it can be seen that the relationship between the opening position of the second guide vane and the frequency is, a ₁ =Kf ₁ ² ;

Compare the two formulas:

translates to: which is

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

f ₀ is the system frequency corresponding to the no-load opening of the guide vane a, f ₁ is the changed frequency, and Δa is the amount of change in the guide vane opening that needs to be operated. It can be known from formula (5) that if the frequency of the equivalent isolated system fluctuates, the opening variation Δa is related to the no-load opening a at the action moment, and also related to the square of the front and rear frequencies.

Assuming that the no-load opening when maintaining the system at 50Hz (f ₀ =50Hz) is a = 20%, if the frequency is to be adjusted to 51Hz (f ₁ =51Hz), the opening of the guide vane Similarly, reverse analysis shows that the stable rated frequency of my country's power system is 50Hz. If the network frequency fluctuates to 51Hz, the turbine regulator should reduce the guide vane opening by 0.81%. Therefore, if this formula is to stabilize the power system frequency and keep the rated frequency f ₀ unchanged, a negative sign needs to be added to formula (5). which is If the system frequency is raised to a certain frequency, the formula (5) is used, and the essence is the same.

The above is an analysis of the simplification of the power system. If each machine in the real power system is adjusted in this way to pull the unit speed to the rated speed, it can theoretically achieve precise frequency control. From an overall point of view, the frequency stability of this kind of system is a kind of dynamic stability formed by the continuous adjustment of the water turbine (or steam turbine) regulator (with the characteristic of position maintenance).

In the large network system, since there are many suppliers of turbine regulators and the control models are different, it will take a certain amount of cognition and time to apply the invented formula widely. In the isolated grid system, there are few units and the regulator is relatively single, so it is easier to adopt the principle of this formula.

Correctness verification:

In order to verify the present invention, technicians have carried out the frequency disturbance test under the isolated grid operation mode in Liyuan Hydropower Station and Xiaowan Hydropower Station in Yunnan. By recording the change data of the guide vane opening before and after the frequency disturbance, the analysis found that the measured results and theoretical values It fit very well.

Table 1 and Table 2 are the frequency disturbance test data of Liyuan Hydropower Station and Xiaowan Hydropower Station in isolated grid operation mode respectively. The method is: by manually increasing and decreasing the frequency slowly, keep the unit running at 50Hz, 52Hz, and 48Hz respectively, and record the corresponding measured values of the guide vane opening respectively. (Under manual control conditions, the measured value of the guide vane opening may have a slight error.) At the same time, using the formula of the present invention Enter the frequency value to calculate the change of theoretical guide vane opening. By comparing the theoretical value and the measured value of the guide vane opening change, it is found that the two values are relatively close.

Table 1

Table 2

Figure 3 and Figure 4 are the wave recording curves of the no-load state frequency disturbance test in Xiaowan, which adopts the conventional method of frequency PID control. Change the frequency target value, after a period of adjustment, the unit runs stably at the frequency target value, and the curve records the actual measured value of the unit frequency and guide vane opening during the whole process. Read the unit frequency and the guide vane opening degree of unit steady state in the curve, bring into the formula of the present invention It is found that its change law is basically consistent with the formula, which proves the correctness of the formula.

From the application point of view, we can bring the frequency target value required to be adjusted into the formula, and directly calculate the change amount of the guide vane, so that the frequency can be adjusted quickly and accurately.

This invention adopts a new formula in the precise control of frequency. This formula clearly reveals the internal relationship between the frequency of the controlled object and the opening of the guide vane of the actuator. The stable and precise control of the frequency is achieved by changing the opening of the guide vane. Through this formula, the theoretical calculation is performed in advance, and then the direct output is obtained. Accurate control of frequency can be achieved, frequency fluctuation can be quickly suppressed, and precise and stable control can be achieved. Abandoning the method of permanent slip coefficient used in conventional system frequency control combined with PID adjustment method.

Using the principle of frequency division control, the new frequency regulation formula is combined with the conventional differential adjustment method to control the output of the unit and balance the relationship between active power and load in the system, thereby adjusting the frequency of the isolated grid system.

The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technical fields , are all included in the scope of patent protection of the present invention in the same way.

Claims (3)

1. the control method of an electric power Isolated Network System frequency regulation, it is characterised in that comprise the steps:

Step 1, according to grid requirements, the coefficient bp of state slip forever, pid parameter, Regulation dead-band 0.05Hz are set and transfer frequency modulation mould The frequency range of block ± 0.05Hz-± θ Hz, θ are the positive number more than 0.05；

Step 2, speed regulator detect current machine class frequency；

Step 3, difference DELTA f asked between the current machine class frequency and rated frequency 50Hz that detect；

Step 4, numerical range according to frequency difference Δ f are adjusted, specific as follows:

If the absolute value of A frequency difference Δ f is more than Regulation dead-band 0.05Hz and less than θ Hz, then FM module transferred by speed regulator, uses Frequency modulation formulaUnit output is adjusted；

In formula, Δ a is guide vane opening variable quantity, and a is stator no-load opening, f₀For system frequency corresponding under stator no-load opening a Rate, f₁For the frequency after variation；

If the absolute value of B frequency difference Δ f is more than θ Hz, then speed regulator uses PID to control and adjusts difference formulaRight Unit output is adjusted；

In formula, Δ y is guide vane opening, and Δ f/50 is the percentage ratio of frequency difference；

If the absolute value of C frequency difference Δ f is less than Regulation dead-band 0.05Hz, then speed regulator exits hopping pattern.

The control method of a kind of electric power Isolated Network System frequency the most according to claim 1 regulation, it is characterised in that θ= 0.1。

The control method of a kind of electric power Isolated Network System frequency the most according to claim 2 regulation, it is characterised in that if frequency difference The absolute value of Δ f is more than 0.1Hz, then speed regulator uses PID to control and adjusts difference formulaUnit output is entered Row regulation, when the absolute value of frequency difference Δ f tapers into 0.05Hz-0.1Hz, then FM module transferred by speed regulator, uses and adjusts Frequently formulaUnit output is adjusted.