CN102624010A - A Dynamic Reactive Power Compensation Control Method Applicable to AC-DC Hybrid External Transmission Grid - Google Patents

Abstract

The invention discloses a dynamic reactive compensation control method applied to an alternating current and direct current hybrid transmission power grid. For a dynamic reactive compensation device in the alternating current-direct current hybrid transmission power grid, important alternating current section line power is selected as a wide area input signal of an additional controller, parameters of the additional controller are set according to a control aim, an output signal of the additional controller is superposed with an output signal of a master controller to generate a dynamic reactive power signal, and the dynamic reactive power signal is output to a low-voltage bus of a transformation substation to enhance the transient stability and dynamic damping level of first oscillation of a system. Actual requirements on reactive power when the system has an alternating current failure and a direct current failure can be truly reflected, and the transient and dynamic stability of the system after an alternating current failure and a direct current locking failure of the alternating current-direct current hybrid transmission power grid can be improved.

Description

A Dynamic Reactive Power Compensation Control Method Applicable to AC-DC Hybrid External Transmission Grid

technical field

The invention relates to a dynamic reactive power compensation method of an electric power system, in particular to a dynamic reactive power compensation method of an AC/DC hybrid external transmission network.

Background technique

Technical terms used in the present invention:

Dynamic reactive power compensation device: based on high-power power electronic component technology, it realizes the setting of dynamic reactive power compensation in the transient process of the power system, such as static var compensator SVC (Static Var Compensator) and static synchronous compensator STATCOM (Static Synchronous Compensator) ).

AC-DC hybrid power grid: When the AC grid contains the converter station of the DC project, it can realize the mixed transmission mode of the AC grid and the DC grid.

Wide Area Measurement System (WAMS): Based on synchrophasor measurement technology, it is a real-time monitoring system aimed at monitoring, analyzing and controlling the dynamic process of power systems.

At present, the traditional control strategy of the reactive power compensation device in the power system is to use the bus voltage on the high-voltage side of the substation at the installation point as the input control signal, or to introduce additional control signals such as adjacent line power to provide reactive power compensation to the system in time and improve the system stability. At the same time, it meets the reactive power demand of the system for AC faults and DC blocking faults of the AC/DC hybrid grid.

Taking SVC as an example, the bus voltage on the high-voltage side of the substation at the installation point is used as the control input signal, and after the sampling filter (time constant T _r1 ) link (that is, the unit or device, the same below), the lead-lag link (time constant T ₂ , T ₃ , After T ₄ , T ₅ ) and the output link (thyristor output time constant T _s ), the dynamic reactive power is output to the low-voltage busbar of the substation. When dynamic reactive power compensation devices such as SVC need to provide dynamic damping, additional control signals such as line power can be considered to be added to the V _ref signal (additional point 1) or to the final controller output link ( Additional point 2). In order to give full play to the fast compensation characteristics of SVC, the controller adds a transient compensation function, that is, when the voltage drop at the control point exceeds Δu, and the active power drop of the line exceeds ΔP, the SVC outputs the maximum capacitive reactive power for t seconds. The functional block diagram is shown in Figure 1.

Since the traditional control strategies of reactive power compensation devices refer to local voltage and line power as input signals, the control goal is to maintain a constant high-voltage bus voltage at the local site. However, the demand forms of dynamic reactive power compensation for AC fault and DC blocking in AC/DC hybrid power grid are different, so the traditional strategy of reactive power compensation device cannot meet the requirements of reactive power compensation for AC fault and DC blocking fault at the same time.

When an AC fault occurs in the power grid, the traditional control strategy of dynamic devices such as SVC can improve the stable operation level of the system, regardless of whether there is a lead-lag link in the reactive power output. If there is no lead-lag link in the reactive power output, the reactive power compensation device will provide dynamic reactive power in the first swing of the system power angle to improve the temporary stability of the system. If the reactive power output contains a lead-lag link, the dynamic stability level of the system can be improved without affecting the first swing angle of the system.

However, the situation when DC blocking occurs in the power grid is different from that of AC faults. When the DC is blocked, due to the delay exit of the DC filter capacitor and the redistribution of the power flow, the voltage of the DC near-area grid generally increases. Therefore, after the DC is blocked, the dynamic reactive power equipment will not only have no transient compensatory power, but will also release part of the inductive reactive power, which reduces the transient stability of the system.

Contents of the invention

The purpose of the present invention is to provide a dynamic reactive power compensation control method suitable for AC/DC hybrid external transmission grid that can take into account both the transient state and dynamic stability of the system after DC and AC faults.

The purpose of the present invention is achieved in this way: a dynamic reactive power compensation control method suitable for AC-DC hybrid external transmission grid, comprising the following steps:

1) The bus voltage on the high-voltage side of the substation at the installation point is used as the input control signal of the main controller of the dynamic reactive power compensation device. output signal;

2) Select the AC section power of important lines or the generator speed as the wide-area input signal of the additional controller of the dynamic reactive power compensation device;

3) Set the parameters of the above additional controller:

$\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="6"\; label="T"\; filenames="HDA0000155079000000021.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="6"\; label="T"\; filenames="HDA0000155079000000021.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="8"\; label="T"\; filenames="HDA0000155079000000011.png,HDA0000155079000000014.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}<span\; class="notranslate">\; ;</span>$

T ₇ =T ₉ =αT ₆ ;

Wherein, φ is the lead-lag compensation phase angle, α is the ratio between zero and pole, ω is the dominant frequency T ₆ , T ₇ , T ₈ , and T ₉ are the time constants of the lead-lag unit; and,

Select the amplification factor K _P =1~10 according to the size of the DC power transmission;

4) Input the wide-area input signal selected in step 2) and the corresponding parameters set in step 3) to the additional controller of the dynamic reactive power compensation device, and the wide-area input signal passes through the sampling unit and DC blocking unit of the additional controller in sequence , a lead-lag unit and an amplifying unit, thereby obtaining an additional voltage control signal, which is superimposed with the output signal of the main controller in step 1) as a dynamic reactive power signal and output to the substation low-voltage busbar; the above-mentioned dynamic reactive power compensation device It is a static var compensator or a static synchronous compensator.

The AC section power of the above-mentioned important lines is the power of inter-area tie lines.

The beneficial effects of the present invention are:

The control strategy of the dynamic reactive power compensation device (composed of main controller and additional controller) proposed by the present invention introduces important AC section power to truly reflect the actual demand for reactive power when AC faults and DC faults occur in the system , to improve the transient and dynamic stability of the system after the AC fault and DC blocking fault of the AC-DC hybrid grid.

In order to meet the system stability requirements after the AC and DC faults in the hybrid external transmission grid, the wide-area measurement signals, such as the generator speed or the AC section power of important lines, are introduced into the control of dynamic reactive devices such as SVC/STATCOM, which can simultaneously Taking into account the transient and dynamic stability of the system after DC and AC faults. It should be noted that the introduction of AC section power as an additional control signal such as SVC has been proposed in many literatures, and the output amplitude of the additional controller is relatively small, and its fundamental purpose is to improve the system damping. The primary purpose of the present invention to introduce signals such as important AC section power into the AC/DC hybrid system is to enhance the stability of the first pendulum of the system, and the second is to enhance the system damping. The control strategies and controller parameters of the two are not consistent.

Taking the existing 890Mvar SVC capacity in Sichuan as an example, the reactive power control strategy of the present invention has limited effect on improving the transient stability of the AC system after a fault, but it can further improve the system damping by more than 4%; The pendulum power angle is more than 5 degrees, and the system damping can be increased by 8%, so that the maximum voltage increase of the controlled bus voltage is less than 5kV.

Description of drawings

Fig. 1 is a typical existing SVC control block diagram.

Fig. 2 is a block diagram of SVC control using wide-area signals in the present invention.

Figure 3 and Figure 4 are the open-loop transfer function block diagram and closed-loop transfer function block diagram of the system respectively.

Figure 5 is a graph of the power angle difference between Sichuan and Central China with or without STATCOM wide-area control when the AC fault occurs.

Figure 6 is a graph of the power angle difference between Sichuan and Central China with or without STATCOM wide-area control during a DC fault.

Detailed ways

In Fig. 1, VC is the voltage of the control point, and P _l is the active power of the local line.

In Fig. 2, VC is the control point voltage, and P _l is the AC section power of important lines.

Working principle of the present invention:

The core idea of the present invention is to introduce the generator speed or the AC section power of important lines into the control method of the dynamic reactive power compensation device, so as to truly reflect the actual demand of the system for reactive power, and adapt to AC faults and DC blocking failure.

After a serious AC fault, the active power of the important AC sending section increases rapidly due to the acceleration of the unit; after a DC blocking fault, the active power of the important AC sending section also increases rapidly because the DC power is transferred to the AC channel. Take Q _s =Kh(s)P _l (s) (K is the magnification factor, P _l (s) is the AC section power, h(s) is the lead-lag correction, s is the complex frequency) as SVC/STATCOM reactive power addition Control quantity, regardless of AC fault or DC fault, SVC/STATCOM can output capacitive reactive power after the fault, and the transient stability of the system is improved. The block diagram of SVC reactive power compensation control using wide-area signals is shown in Figure 2.

Embodiments of the present invention:

(1) Introduce line power of important AC section:

Using the small-signal analysis method, inject reactive power step disturbance ΔQ(t) at the installation point of SVC or STATCOM, and use the transient simulation analysis method to obtain the active power response ΔP _i (t) of each important AC line, i=1, ..., N. According to the dominant frequency ω that exists in the large interval, select the power ΔP _l (t), (l∈1,...,N) of the line l with the dominant frequency ω (i.e. the low-frequency oscillation frequency) and the maximum observability as the reactive power Compensation device wide area input signal. Generally, the power of the inter-area tie line can be directly selected as the wide-area input signal.

(2) Additional (wide area) controller parameter setting:

According to the input and output responses ΔQ(t) and ΔP _l (t) obtained by the small signal analysis method, the open-loop transfer function G ₀ (s)=ΔP _l (s)/ΔQ(s) is obtained, as shown in Figure 3.

ΔP _l (s) is introduced as the feedback variable, and the closed-loop transfer function block diagram of the system is shown in Figure 4. The closed-loop transfer function of the system is:

${\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;Q</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

T_r2为广域信号采样延时时间常数Where: G(s) = G ₀ (s) G ₁ (s),

T _r2 is the wide-area signal sampling delay time constant

According to formula (1), the characteristic equation of the closed-loop system is:

1-G(s)H(s)＝0

Assume that after adding the feedback compensation link, the new dominant pole of the closed-loop system is s _d , which satisfies the system characteristic equation

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The lead-lag compensation phase angle of the feedback compensation link H(s) at s=s _d is:

φ=arg(H(s _d ))=-arg(G(s _d )) (4)

According to the obtained results, the second-order lead-lag compensation link can be designed, and the corresponding parameters can be adjusted according to formula (5).

$\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="6"\; label="T"\; filenames="HDA0000155079000000021.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}$

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="6"\; label="T"\; filenames="HDA0000155079000000021.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="8"\; label="T"\; filenames="HDA0000155079000000011.png,HDA0000155079000000014.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

T ₇ =T ₉ =αT ₆

In Figure 2, _Kv and _Kp are local voltage control weights and wide-area additional control weight coefficients respectively, which need to be properly selected according to the actual AC and DC operation of the power grid. K _v is generally selected from 100 to 300, and K _P is selected from 1 to 10 according to the DC transmission power.

(3) Case analysis:

Taking the installation of 150MVA STATCOM in a station in Sichuan as an example, the voltage signal of the control point is taken from the local bus voltage signal, and the active power of the double circuit line on the flood plate in the Sichuan-Chongqing section is introduced as an additional control signal for wide-area control.

Local voltage signal sampling and filtering time constant T _r1 = 0.02s, wide-area signal sampling and filtering time constant T _r2 = 0.2s, DC blocking time constant T _w1 = T _w2 = 6s, STATCOM controller output time constant T _s = 0.02s, I _max = 2.4, I _min = -0.6. The specific parameters of the controller are shown in Table 1.

Table 1 Controller parameters using wide-area control

When the AC fault occurs, the maximum power angle difference of the STATCOM first pendulum when using wide-area control is basically the same as when using local signal control, but it has better dynamic stability, as shown in Figure 5. When DC fault occurs, the first swing power angle of STATCOM has the best stability when wide-area control is adopted, and the dynamic stability is far better than that of local bus voltage control mode, as shown in Figure 6. It can be seen that in the AC/DC hybrid system, after wide-area control is adopted and the weight of the additional controller is increased, a unified controller can simultaneously meet the regulation requirements of the system for DC faults and dynamic reactive power after AC.

The steps of the present invention are as follows:

1) For the dynamic reactive power compensation device under the AC-DC hybrid grid, first select the line power of the important AC section as the wide-area input signal;

2) Set additional wide area controller parameters. Use the formula (5) to set the parameters T ₆ , T ₇ , T ₈ and T ₉ of _the additional controller in the lead-lag link. The filter time constant T _r2 is determined by the collector itself. The magnification K _P is selected from 1 to 10 according to the size of the DC power transmission;

3) Set the controller according to the obtained additional wide-area controller parameters, and superimpose it in the control strategy of the dynamic reactive power compensation device as shown in Figure 2;

4) The wide-area power signal is introduced into the additional controller of the dynamic reactive power compensation device through the wide-area measurement system (WAMS system). And the amplification link, so as to obtain the additional voltage control signal, this signal is superimposed on the control signal of the dynamic reactive power compensation device itself, and jointly determines the dynamic reactive power output value of the compensation setting, so as to complete the reactive power compensation under the AC-DC hybrid grid. purpose of the requirement.

Claims (2)

1. A dynamic reactive power compensation control method applicable to the AC/DC hybrid external transmission grid, characterized in that it comprises the following steps: 1) The bus voltage on the high-voltage side of the substation at the installation point is used as the input control signal of the main controller of the dynamic reactive power compensation device. output signal; 2) In order to enhance the stability of the first pendulum of the system and at the same time enhance the damping of the system, the AC section power of important lines or the generator speed are selected as the wide-area input signal of the additional controller of the dynamic reactive power compensation device; 3) Set the parameters of the above additional controller: $\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}}{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}<span\; class="notranslate">\; ;</span>$ T ₇ =T ₉ =αT ₆ ; where φ is the lead-lag compensation phase angle, α is the ratio between zero and pole, ω is the dominant frequency, T ₆ , T ₇ , T ₈ , T ₉ are the time constants of the lead-lag unit; and, Select the amplification factor K _P =1~10 according to the size of the DC power transmission; 4) Input the wide-area input signal selected in step 2) and the corresponding parameters set in step 3) to the additional controller of the dynamic reactive power compensation device, and the wide-area input signal passes through the sampling unit and DC blocking unit of the additional controller in sequence , a lead-lag unit and an amplifying unit, thereby obtaining an additional voltage control signal, which is superimposed with the output signal of the main controller in step 1) as a dynamic reactive power signal and output to the substation low-voltage busbar; the above-mentioned dynamic reactive power compensation device It is static var compensator or static synchronous compensator. 2. A dynamic reactive power compensation control method suitable for AC/DC hybrid transmission power grid according to claim 1, characterized in that the power of the AC section of the important line is the power of the inter-regional tie line.

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