CN105743116A - Subsynchronous oscillation evaluation method of alternating-current/direct-current hybrid power system - Google Patents

Abstract

The invention discloses a subsynchronous oscillation evaluation method of an AC/DC hybrid power system, belonging to the technical field of power system planning and operation. The method includes: S1. Establishing a model for subsynchronous oscillation research of the HVDC unit HVDC; S2. Analyzing the HVDC and each unit in the grid according to the position of the HVDC in the power grid and the trend of the HVDC during actual operation. Determine the coupling strength of the generator set to determine the power unit to be developed; S3, simplify the AC-DC hybrid power system according to the equivalent boundary of the system composed of HVDC and the power unit to be developed, and obtain the equivalent simplification of the AC-DC hybrid power system system; S4. According to the equivalent simplified system, calculate the electrical damping and subsynchronous oscillation evaluation indexes at each natural torsional vibration frequency of the motor unit to be developed. The invention also discloses a planning and design method for an AC/DC hybrid power system. The invention can accurately evaluate and predict the subsynchronous oscillation behavior of the AC/DC hybrid power system including HVDC.

Description

Subsynchronous Oscillation Evaluation Method for AC/DC Hybrid Power Systems

technical field

The invention relates to the technical field of power system planning and operation, in particular to a subsynchronous oscillation evaluation method of an AC/DC hybrid power system.

Background technique

Due to the flexible operation mode of AC-DC hybrid transmission, HVDC transmission is widely used in actual power grids. While bringing huge economic benefits, it also brings new challenges to the power system. Improper DC transmission control may cause subsynchronous oscillation, which will lead to serious damage to the rotor shafting of the AC system generator set on the rectification side.

High voltage direct current transmission technology (HVDC) is the earliest application of power electronics technology in the field of power system transmission, and it is also a relatively mature technology. The high-voltage direct current transmission unit is composed of three parts: a rectifier that converts alternating current to direct current, a high-voltage direct current transmission line, and an inverter that converts direct current into alternating current. From a structural point of view, it is an AC-DC-AC form of power electronic commutation circuit . The cost and operation cost of HVDC transmission lines are lower than those of AC transmission. For the same transmission capacity, the longer the transmission distance, the better the economic performance of DC than AC. Moreover, there is no problem of power angle stability in DC transmission, and the power grids on both sides of the connection do not need to run synchronously. Therefore, DC transmission can realize the asynchronous interconnection of the grid and play the role of a frequency converter. Large-capacity transmission of electric power within a certain range. In addition, DC transmission has the characteristics of fast and controllable power flow, which can be used for the stability and frequency control of the connected AC system. The converter of DC transmission is a power control circuit based on power electronic devices, which controls the power flow quickly and accurately. For double-terminal DC transmission, the reversal of power flow can be realized quickly.

The rationality and practicability of HVDC means are clearly reflected in long-distance and large-capacity power transmission. With the development of power electronics technology, this advantage is more significant. However, DC transmission is a complex system involving a large number of various components and equipment. Its control system is very complex and its control strategies are diversified. Improper control strategies and control parameters may lead to subsynchronous oscillations. It is not conducive to the interconnection between AC and DC systems. Therefore, it is very necessary to conduct sufficient research on the interaction between AC and DC systems and coordinated control, and to establish models and evaluate and analyze the influence of HVDC control strategies and control parameter changes on subsynchronous oscillations, so as to analyze the impact of power transmission. Provide guidance for the planning and operation of the system.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a subsynchronous oscillation evaluation method of an AC/DC hybrid power system, which can accurately evaluate and predict the subsynchronous oscillation behavior of an AC/DC hybrid power system including HVDC, And then provide guidance for the planning and operation of the power system.

The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems:

A subsynchronous oscillation evaluation method of an AC-DC hybrid power system, the AC-DC hybrid power system includes a high-voltage direct-current transmission unit and several generator sets; the evaluation method includes the following steps:

Step 1. Establishing a model for subsynchronous oscillation research of the HVDC unit;

Step 2. According to the position of the HVDC power transmission unit in the power grid and the power flow trend of the HVDC power transmission unit during actual operation, analyze the coupling strength between the HVDC power transmission unit and each generator set in the power grid, and determine the power to be developed. unit;

Step 3. Simplify the AC/DC hybrid power system according to the equivalent boundary of the system formed by the HVDC power transmission unit and the motor unit to be developed, to obtain an equivalent simplified system of the AC/DC hybrid power system;

Step 4. According to the equivalent simplified system, calculate the electrical damping and subsynchronous oscillation evaluation indexes at each natural torsional vibration frequency of the motor unit to be developed. The specific steps are as follows:

Step 4-1, performing linearization on the subsynchronous oscillation research model of the HVDC unit to obtain the state equation of the HVDC unit;

Step 4-2, determining the common coordinate system xy of the equivalent simplified system, and decomposing the voltage across the HVDC unit into the xy coordinate system;

Step 4-3, perform calculation to eliminate intermediate variables, and use the complex torque coefficient method to obtain the electrical damping expression of the motor unit to be developed;

Step 4-4. According to the obtained electrical damping expression, analyze the equivalent impedance of the system at each natural torsional vibration frequency of the motor unit to be developed, and calculate the corresponding subsynchronous oscillation evaluation index Index according to the following formula, and the subsynchronous oscillation evaluation index Index The smaller the value of , the greater the risk of subsynchronous oscillation in the AC/DC hybrid power system:

$\mathrm{<span\; class="notranslate">\; I</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 8</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>$

In the formula, R and X are the equivalent resistance and equivalent reactance of the system at the natural torsional vibration frequency f _n of the motor unit to be developed respectively, f is the synchronous frequency of the system, H _n is the The constant associated with the frequency f _n .

Preferably, the model for subsynchronous oscillation research established in step 1 is a quasi-steady-state model.

Preferably, said step 3 specifically includes the following sub-steps:

Step 3-1. With the HVDC unit and the motor unit to be developed as the center, reserve a substation area with a voltage level of the backbone grid outward as the equivalent boundary of the system composed of the HVDC unit and the motor unit to be developed ;

Step 3-2, based on the equivalent boundary, calculate the equivalent impedance of each AC branch of the system composed of the HVDC unit and the motor unit to be developed;

Step 3-3, based on the stable operating state and power flow of the AC-DC hybrid power system, and in combination with the equivalent impedance of the equivalent boundary point, the external network outside the equivalent boundary is equivalent to a power supply or load, and Determine the parameters of the source or load.

Preferably, in step 2, the unit action coefficient method is used to determine the electrical unit to be developed.

According to the same inventive idea, the following technical solutions can also be obtained:

A planning and design method for an AC-DC hybrid power system, the AC-DC hybrid power system includes a high-voltage direct current transmission unit and several generator sets; when the high-voltage direct current transmission unit adopts different control methods and parameters, use any one of the above The method described in the technical solution evaluates the subsynchronous oscillation of the AC/DC hybrid power system, and selects the control mode and parameters with the least risk of subsynchronous oscillation for the HVDC power transmission unit according to the evaluation result.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

The invention realizes the accurate evaluation of whether subsynchronous oscillation occurs in the power system and the strength of subsynchronous oscillation under the consideration of high-voltage direct current transmission, and can effectively analyze the degree of influence of high-voltage direct current transmission on subsynchronous oscillation and the planning and operation of the actual power grid. has important practical significance.

Description of drawings

Figure 1 is a schematic diagram of the structure of HVDC.

detailed description

The technical scheme of the present invention is described in detail below in conjunction with accompanying drawing:

The planning and design method of the present invention is aimed at the AC-DC hybrid power system including the high-voltage direct current transmission unit (HVDC), and first evaluates the subsynchronous oscillation to obtain the electrical damping and subsynchronous oscillation evaluation indexes at each natural torsional vibration frequency of the motor unit to be developed ; Then adjust the control mode and parameters of the HVDC, and repeat the subsynchronous oscillation assessment, and finally select the control mode and parameters with the least risk of subsynchronous oscillation according to the subsynchronous oscillation assessment results. The basic process is as follows:

Step 1. Obtain grid data of the AC/DC hybrid power system, generator set data in the system, and HVDC operation data (including control methods and parameters).

Step 2, establishing a model for subsynchronous oscillation research of the HVDC unit;

The HVDC subsynchronous oscillation research model preferably adopted in the present invention is a quasi-steady-state model. The subsynchronous oscillation research model established in this embodiment is specifically as follows:

For the HVDC structure shown in Figure 1, assume that the two ends of the HVDC are connected to any two nodes k and m of the AC transmission system respectively, and the voltage phasors of the two nodes are respectively and The current phasors are and n′ is the conversion ratio of the rectifier side converter transformer, n″ is the conversion ratio of the inverter side converter transformer, α is the firing angle of the rectifier, β is the leading firing angle of the inverter, γ is the arc-extinguishing angle of the inverter, L _d Respectively, the sum of the reactance and flat reactance on the HVDC line, R _d is the resistance value of the HVDC line, C _d is the capacitance value of the HVDC line to ground, X′ and X″ are the commutation values of the rectifier and inverter respectively Reactance, I′ _d is the output current of the rectifier, I″ _d is the input current of the inverter, V′ _d0 is the ideal no-load voltage of the rectifier, V′ _d is the actual rectified voltage, V″ _d0 is the ideal no-load voltage of the inverter, V ″ _d is the actual inverter voltage, V _d1 is the HVDC line-to-ground voltage, and are the power factors of the two nodes k and m respectively, and p is the differential operator. K _r , T _d , T _r , K _i , T _i are parameters of various fixed-value control adjustment modes, and Δα ₀ and Δβ ₀ are the adjustment differences of fixed-value control on the rectifier side and inverter side, respectively.

On the rectifier side there are:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The equation of DC transmission line is:

L _d pI' _d = -R _d I' _d +V' _d -V _d1 (8)

C _d pV _d1 ＝I′ _d −I″ _d (9)

L _d pI″ _d ＝-R _d I″ _d +V _d1 -V″ _d (10)

On the inverter side there are:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

Step 3. According to the position of the HVDC power transmission unit in the power grid and the power flow trend of the HVDC power transmission unit during actual operation, analyze the coupling strength between the HVDC power transmission unit and each generator set in the power grid, and determine the power to be developed. Unit: The present invention preferably adopts the unit action coefficient method to determine the electrical unit to be developed.

Step 4. Simplify the AC/DC hybrid power system according to the equivalent boundary of the system composed of the HVDC power transmission unit and the motor unit to be developed, to obtain an equivalent simplified system of the AC/DC hybrid power system; in this embodiment The system simplification process is as follows:

Step 4-1. With the HVDC unit and the motor unit to be developed as the center, reserve a substation area with a voltage level of the backbone grid outward as the equivalent boundary of the system composed of the HVDC unit and the motor unit to be developed ;

Step 4-2, based on the equivalent boundary, calculate the equivalent impedance of each AC branch of the system composed of the HVDC unit and the motor unit to be developed;

Step 4-3, based on the stable operating state and power flow of the AC-DC hybrid power system, and in combination with the equivalent impedance of the equivalent boundary point, the external network outside the equivalent boundary is equivalent to a power supply or load, and Determine the parameters of the source or load.

Step 5. According to the equivalent simplified system, calculate the electrical damping and subsynchronous oscillation evaluation indexes at each natural torsional vibration frequency of the motor unit to be developed. The specific steps are as follows:

Step 5-1. Linearize the model for subsynchronous oscillation research of the HVDC unit to obtain the state equation of the HVDC unit; linearize the subsynchronous oscillation research model used in this embodiment

Personalization, take the state variable as:

X _DC ＝[Δα ₀ ,ΔI′ _d ,ΔV _d1 ,ΔI″ _d ,Δβ ₀ ] ^T (17)

The HVDC state equation is obtained as:

B _D pX _DC = C _D X _DC + D _k V _kDC + D _m V _mDC (18)

R _k ·I _kDC ＝S _k X _DC +T _k V _kDC (19)

R _m I _mDC = S _m X _DC + T _m V _mDC (20)

Step 5-2. Determine the common coordinate system xy of the equivalent simplified system, and decompose the voltages V _k and V _m across the HVDC unit into the xy coordinate system:

V _k =E _k ·V _kDC , I _k =F _k ·I _kDC (21)

V _m =E _m ·V _mDC , I _m =F _m ·I _mDC (22)

Step 5-3, perform calculation to eliminate the intermediate variable, and use the complex torque coefficient method to obtain the electrical damping expression of the motor unit to be developed; after eliminating the intermediate variable X _DC in this embodiment, it can be obtained:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\\ {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; three</span>}<span\; class="notranslate">\; )</span>$

Combining Equation (23) with other parts of the system, the electrical damping expression of the motor unit to be developed can be obtained by using the complex torque coefficient method.

Step 5-4. According to the obtained electrical damping expression, analyze the equivalent impedance of the system at each natural torsional vibration frequency of the motor unit to be developed, and calculate the corresponding subsynchronous oscillation evaluation index Index according to the following formula, and the subsynchronous oscillation evaluation index Index The smaller the value of , the greater the risk of subsynchronous oscillation in the AC/DC hybrid power system:

$\mathrm{<span\; class="notranslate">\; I</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 8</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; four</span>}<span\; class="notranslate">\; )</span>$

In the formula, R and X are the equivalent resistance and equivalent reactance of the system at the natural torsional vibration frequency f _n of the motor unit to be developed respectively, f is the synchronous frequency of the system, H _n is the The constant associated with the frequency f _n .

Step 6. Adjust the control mode and parameters of the HVDC, and repeat the above steps 1 to 5 to obtain the subsynchronous oscillation evaluation index of the HVDC AC-DC hybrid power system under different control modes and parameters, and by comparing these subsynchronous oscillation evaluation indices, Select the control mode and parameters with the least risk of subsynchronous oscillation for HVDC.

In order to guide the planning and design of the AC/DC hybrid power system quickly and conveniently, according to the subsynchronous oscillation evaluation method of the present invention, a subsynchronous oscillation evaluation simulation model of the AC/DC hybrid power system can be established in MATLAB or SIMULINK, by adjusting the HVDC in the simulation model The evaluation results of subsynchronous oscillation under different control methods and parameter combinations of HVDC can be obtained conveniently and quickly, and then guide the planning and design of the AC-DC hybrid power system.

Claims (5)

1. A subsynchronous oscillation evaluation method of an AC-DC hybrid power system, the AC-DC hybrid power system comprising a HVDC power transmission unit and some generator sets; it is characterized in that the evaluation method comprises the following steps: Step 1. Establishing a model for subsynchronous oscillation research of the HVDC unit; Step 2. According to the position of the HVDC power transmission unit in the power grid and the power flow trend of the HVDC power transmission unit during actual operation, analyze the coupling strength between the HVDC power transmission unit and each generator set in the power grid, and determine the power to be developed. unit; Step 3. Simplify the AC/DC hybrid power system according to the equivalent boundary of the system formed by the HVDC power transmission unit and the motor unit to be developed, to obtain an equivalent simplified system of the AC/DC hybrid power system; Step 4. According to the equivalent simplified system, calculate the electrical damping and subsynchronous oscillation evaluation indexes at each natural torsional vibration frequency of the motor unit to be developed. The specific steps are as follows: Step 4-1, performing linearization on the subsynchronous oscillation research model of the HVDC unit to obtain the state equation of the HVDC unit; Step 4-2, determining the common coordinate system xy of the equivalent simplified system, and decomposing the voltage across the HVDC unit into the xy coordinate system; Step 4-3, perform calculation to eliminate intermediate variables, and use the complex torque coefficient method to obtain the electrical damping expression of the motor unit to be developed; Step 4-4. According to the obtained electrical damping expression, analyze the equivalent impedance of the system at each natural torsional vibration frequency of the motor unit to be developed, and calculate the corresponding subsynchronous oscillation evaluation index Index according to the following formula, and the subsynchronous oscillation evaluation index Index The smaller the value of , the greater the risk of subsynchronous oscillation in the AC/DC hybrid power system: $\mathrm{<span\; class="notranslate">\; I</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 8</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>$ In the formula, R and X are the equivalent resistance and equivalent reactance of the system at the natural torsional vibration frequency f _n of the motor unit to be developed respectively, f is the synchronous frequency of the system, H _n is the The constant associated with the frequency f _n . 2. The subsynchronous oscillation evaluation method as claimed in claim 1, characterized in that, the subsynchronous oscillation research model established in step 1 is a quasi-steady-state model. 3. The subsynchronous oscillation evaluation method according to claim 1, wherein said step 3 specifically comprises the following sub-steps: Step 3-1. With the HVDC unit and the motor unit to be developed as the center, reserve a substation area with a voltage level of the backbone grid outward as the equivalent boundary of the system composed of the HVDC unit and the motor unit to be developed ; Step 3-2, based on the equivalent boundary, calculate the equivalent impedance of each AC branch of the system composed of the HVDC unit and the motor unit to be developed; Step 3-3, based on the stable operating state and power flow of the AC-DC hybrid power system, and in combination with the equivalent impedance of the equivalent boundary point, the external network outside the equivalent boundary is equivalent to a power supply or load, and Determine the parameters of the source or load. 4. The subsynchronous oscillation evaluation method according to claim 1, characterized in that in step 2, the unit action coefficient method is used to determine the electrical unit to be developed. 5. A planning and design method for an AC-DC hybrid power system, the AC-DC hybrid power system includes a high-voltage direct-current transmission unit and several generator sets; it is characterized in that, when the high-voltage direct-current transmission unit adopts different control methods and parameters , using the method according to any one of claims 1 to 4 to evaluate the subsynchronous oscillation of the AC/DC hybrid power system, and select the control mode with the least risk of subsynchronous oscillation for the HVDC power transmission unit according to the evaluation results and parameter.