CN103023058A - Control method for high-voltage direct-current flexible system for supplying power to passive network - Google Patents

Abstract

A control method for a flexible direct current transmission system that supplies power to a passive network. It sets a rectifier controller at the head end of the direct current transmission line of the flexible direct current transmission system, and performs constant direct current voltage control on the VSC-rectifier on the side of the alternating current system. The end of the direct current transmission line Set the VSC-inverter controller to control the VSC-inverter at a constant AC voltage. The constant DC voltage control of the VSC-rectifier adopts a double closed-loop vector control strategy, wherein the outer voltage loop adopts fuzzy PI control, and the inner loop adopts current Decoupling control to achieve independent control of active power and reactive power. The method avoids the cumbersome off-line parameter adjustment of the traditional PI regulator, and can perform online PI parameter adjustment according to the change of the system operating state. The self-adaptive adjustment ability is strong, and the system has faster response speed and better High control precision improves the anti-interference ability and dynamic stability performance of the system.

Description

A control method for a flexible direct current transmission system that supplies power to a passive network

technical field

The invention relates to the technical field of direct current transmission, in particular to a control method for a flexible direct current transmission system that supplies power to a passive network.

Background technique

Since the world's first high-voltage direct current transmission (HVDC) line was put into commercial operation in 1954, HVDC has been widely used in long-distance high-power transmission due to its superior performance, such as long-distance large-capacity transmission power, asynchronous networking between AC grids, etc. , Submarine cable power transmission, power supply to high-density cities with cables, asynchronous communication between AC systems, etc. However, since traditional HVDC uses semi-controlled thyristors as commutation devices, the AC grid is required to provide commutation current during commutation, which requires that the converter must be connected to an active network. At the same time, when HVDC is running in reverse, Faults such as commutation failure are prone to occur.

With the development of power electronics technology, high-voltage direct current transmission (VSC-HVDC) based on voltage source converters (VSC-HVDC), that is, flexible direct current transmission, has become a research hotspot. VSC-HVDC not only fundamentally solves the defects of traditional HVDC, but also has the advantages of traditional HVDC Incomparable advantages. The VSC-HVDC system adopts PWM technology and fully-controlled power electronic devices represented by insulated gate bipolar transistors (IGBTs). Due to the current self-shutdown capability of VSC, the most notable feature of VSC-HVDC is that it can work in passive The inverter mode does not require an external commutation voltage, and the receiving end system can be a passive network, which overcomes the defect that the traditional HVDC receiving end system must be an active network, and can transmit power to long-distance isolated loads. At the same time, the PWM technology is used to realize the decoupling control of active power and reactive power, which can stabilize the AC bus voltage, and can even reverse the power from the other side when one side of the AC system fails, providing emergency support for power, thereby improving power supply. reliability and power quality.

As a new type of power transmission, the VSC-HVDC system has broad application prospects in the fields of connecting scattered small power plants (such as wind power, solar power, etc.) to the grid, and supplying power to long-distance isolated loads. the

The inverter side of the VSC-HVDC system that supplies power to the passive network adopts constant AC voltage control to stabilize the load voltage and improve the quality of the power supply voltage; the rectifier side adopts constant DC voltage control to stabilize the DC voltage and provide voltage support for the VSCs on both sides . The constant DC voltage control strategy usually adopts double closed-loop vector control based on PI regulator, and the inner loop adopts current feed-forward decoupling control, so that the active current and reactive current track the output values of the outer loop voltage regulator and reactive power regulator respectively. . At present, most VSC-HVDC projects use the trial and error method or experience method to select the PI regulator parameters, which requires high skills and experience in the system debugging process, and the obtained regulator may not be able to make the system performance reach the optimal state , PI control has poor anti-interference ability, large overshoot, and it is inconvenient to adjust. For a multivariable, strongly coupled and nonlinear system like VSC-HVDC, it is difficult for the PI regulator to meet the requirements of the actual system under different working conditions.

Contents of the invention

The purpose of the present invention is to aim at the drawbacks of the prior art, to provide a control method for a flexible direct current transmission system that can supply power to a passive network that can perform online PI parameter adjustment according to changes in the system operating state, so as to improve the anti-interference ability and Dynamic and steady state performance.

Problem described in the present invention is realized with following technical scheme:

A control method for a flexible direct current transmission system that supplies power to a passive network. The method sets a rectifier controller at the head end of the direct current transmission line of the flexible direct current transmission system, and performs constant direct current voltage control on the VSC-rectifier on the side of the alternating current system, and direct current transmission A VSC-inverter controller is installed at the end of the line to control the constant AC voltage of the VSC-inverter. The constant DC voltage control of the VSC-rectifier adopts a double closed-loop vector control strategy, wherein the outer voltage loop adopts fuzzy PI control, and the inner loop Adopt current decoupling control to realize independent control of active power and reactive power.

In the control method of the flexible direct current transmission system for supplying power to the passive network, the specific steps of the constant direct current voltage control of the VSC-rectifier are as follows:

测量模块对柔性直流输电线路的直流电压进行实时检测，得到直流电压实际值，并与直流电压给定值

相比较，得到直流电压误差信号； a.

The measurement module detects the DC voltage of the flexible DC transmission line in real time to obtain the actual value of the DC voltage , and with a DC voltage setpoint

By comparison, a DC voltage error signal is obtained;

； b. The DC voltage error signal passes through the DC voltage fuzzy PI controller and the subsequent current limiting circuit, and outputs the d-axis AC current reference value

;

，与无功功率给定值

相比较，得到无功误差信号； c. The instantaneous reactive power calculation module calculates the actual value of reactive power according to the current system AC voltage and AC current

, and reactive power given value

Comparing to obtain reactive power error signal;

； d. The reactive power error signal passes through the reactive power PI controller and the current limiting circuit to obtain the q-axis AC current reference value

;

和

经过内环电流解耦控制电路输出d轴交流电压参考值

和q轴交流电压参考值

； e.

and

Output the d-axis AC voltage reference value through the inner loop current decoupling control circuit

and q-axis AC voltage reference

;

和

经过两相旋转坐标系到两相静止坐标系的坐标变换（2r/2s）输出两相静止坐标系（

坐标系）下

和

； f.

and

After the coordinate transformation (2r/2s) from the two-phase rotating coordinate system to the two-phase stationary coordinate system, the two-phase stationary coordinate system (

coordinate system)

and

;

进行调制，所得到的6路PWM信号分别控制VSC-整流器的6个IGBT运行。 g. Use the voltage space vector modulation (SVPWM) method to and

After modulation, the obtained 6 PWM signals respectively control the operation of 6 IGBTs of the VSC-rectifier.

，模糊PI控制器的具体工作步骤如下： In the above-mentioned flexible direct current transmission system control method for supplying power to a passive network, the direct current voltage fuzzy PI controller adopts a second-order fuzzy controller, and its input signal is a direct current voltage error signal and its rate-of-change signal

, the specific working steps of the fuzzy PI controller are as follows:

The working principle of the fuzzy PI controller is as follows:

和

进行模糊化处理，分别得到模糊量

和

； ① According to the membership function, the input language variables

and

Perform fuzzy processing to obtain the fuzzy amount

and

;

② According to the established fuzzy control rules and Carry out fuzzy reasoning and decide the output fuzzy amount;

③ Complete the transformation from fuzzy quantity to precise quantity through the defuzzification method, and output the PI parameters of the DC voltage error , to adjust the parameters of the PI regulator online.

In the control method of the flexible direct current transmission system for supplying power to the passive network, the defuzzification method adopts a weighted average method.

In the control method of the flexible direct current transmission system for supplying power to the passive network, the membership function used in the fuzzification and defuzzification process of the direct current voltage error signal and its rate of change signal all selects a triangular membership function.

The invention adopts a double-closed-loop vector control strategy to control the constant DC voltage of the rectifier, wherein the outer voltage loop adopts fuzzy PI control, and the inner loop adopts current decoupling control, thereby realizing independent control of active power and reactive power. The method avoids the cumbersome off-line parameter adjustment of the traditional PI regulator, and can perform online PI parameter adjustment according to the change of the system operating state. The self-adaptive adjustment ability is strong, so that the system has a faster response speed and Higher control precision improves the anti-interference ability and dynamic stability performance of the system.

Description of drawings

Fig. 1 is a structural block diagram of a flexible direct current transmission system for supplying power to a passive network and a rectifier control principle provided by the present invention;

Fig. 2 is the schematic diagram of the DC voltage fuzzy PI control principle provided by the present invention;

Fig. 3 is a schematic diagram of a triangle membership function provided by the present invention;

Fig. 4 is a schematic circuit diagram of the hardware realization circuit of the control system of the rectifier of the flexible direct current transmission system provided by the present invention;

The list of symbols used in the drawings or text is:

HVDC: High Voltage Direct Current Transmission, VSC-HVDC: Flexible Direct Current Transmission,

：柔性直流输电线路的直流电压，      

：直流电压给定值，

: DC voltage of the flexible HVDC line,

: DC voltage given value,

：无功功率实际值，                  

：无功功率给定值，

: actual value of reactive power,

: Reactive power given value,

：d轴交流电流参考值，             

：q轴交流电流参考值，

: d-axis AC current reference value,

: q-axis AC current reference value,

：d轴交流电压参考值，            ：q轴交流电压参考值，

: d-axis AC voltage reference value, : q-axis AC voltage reference value,

: α-axis AC voltage reference value in the static coordinate system,

：静止坐标系下β轴交流电压参考值，

: β-axis AC voltage reference value in the static coordinate system,

：直流电压误差信号变化率， : DC voltage error signal,

: rate of change of DC voltage error signal,

：

的模糊量，                   ：

的模糊量，

:

the amount of blur, :

the amount of blur,

：PI调节器参数，              

：交流系统电压，

: PI regulator parameters,

: AC system voltage,

：VSC-整流器交流侧电压；

: VSC- rectifier AC side voltage;

1. AC system, 2. AC filter, 3. Commutation reactor, 4. VSC-rectifier, 5. Capacitor, 6. Ground electrode, 7. DC transmission line, 8. Capacitor, 9. VSC-inverter , 10, commutation reactor, 11, AC filter, 12, remote load.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Referring to Fig. 1, the flexible direct current transmission system of the present invention includes:

AC system 1, connected to the AC filter.

The AC filter 2 is connected with the AC system 1 and the commutation reactor 3, and is used for filtering out harmonics on the AC side.

The commutation reactor 3, connected with the AC filter 2 and the VSC-rectifier 4, is the link between the AC side and the converter for energy exchange, and also plays a certain filtering role.

The VSC-rectifier 4 is connected with the commutation reactor 3 and the capacitor 5 . The VSC operates in a rectification state and is used to convert the AC power of the AC system 1 into DC power and transmit it to the DC transmission line 7 .

The capacitor 5 is connected with the VSC-rectifier 4 and the DC transmission line 7, provides DC voltage support for the VSC at both ends, and at the same time buffers the impact current when the bridge arm of the converter is turned off, and can also play a certain role in filtering.

The ground electrode 6 is used to provide a reference zero potential for the DC voltage, and the DC power transmission system adopts bipolar operation.

The direct current transmission line 7 is connected with the VSC-rectifier 4, the capacitor 5, the capacitor 8 and the VSC-inverter 9, and connects both ends of the VSC for direct current power transmission.

VSC-inverter 9 is connected with capacitor 8, DC transmission line 7 and commutation reactor 10. The VSC operates in an inverter state and is used to convert DC power on the DC transmission line into AC power for supplying remote isolated loads .

The remote load, connected to the AC filter 11, is an AC power load.

Referring to Fig. 1, the VSC-rectifier fixed DC voltage fuzzy PI control method provided by the present invention adopts a double closed-loop vector control strategy, including the following steps:

，并与直流电压给定值

相比较，得到直流电压误差信号； first step: The measuring circuit detects the DC voltage in real time and obtains the actual value of the DC voltage

, and with a DC voltage setpoint

By comparison, a DC voltage error signal is obtained;

； Step 2: The DC voltage error signal passes through the DC voltage fuzzy PI control and the subsequent current limiting circuit, and outputs the d-axis AC current reference value

;

，与无功功率给定值

相比较，得到无功误差信号； Step 3: The instantaneous reactive power calculation module calculates the actual value of reactive power according to the current system AC voltage and AC current

, and reactive power given value

Comparing to obtain reactive power error signal;

； Step 4: The reactive power error signal passes through the reactive power PI control and current limiting circuit to obtain the q-axis AC current reference value

;

和

经过内环电流解耦控制输出d轴交流电压参考值

和q轴交流电压参考值

； the fifth step:

and

Output d-axis AC voltage reference value through inner loop current decoupling control

and q-axis AC voltage reference

;

和经过两相旋转坐标系到两相静止坐标系的坐标变换（2r/2s）输出两相静止坐标系（坐标系）下

和

； Step six:

and After the coordinate transformation (2r/2s) from the two-phase rotating coordinate system to the two-phase stationary coordinate system, the two-phase stationary coordinate system ( coordinate system)

and

;

和

采用电压空间矢量调制（SVPWM）方法，输出6路PWM控制VSC-整流器6个IGBT运行。 Step seven:

and

Using the voltage space vector modulation (SVPWM) method, output 6 PWMs to control the operation of 6 IGBTs of the VSC-rectifier.

The DC voltage fuzzy PI control can adjust PI parameters online according to different operating conditions of the system, which ensures the control accuracy and control effect of the DC voltage, and improves the system response speed and anti-interference ability.

The current limiting circuit mentioned above may generate a high instantaneous current due to external interference, which will cause the VSC at both ends to be overloaded, thereby destroying the power electronic device. Therefore, a current limiting circuit is required. When a very high instantaneous current is generated Limit it to the current upper limit value.

The adoption of the SVPWM method ensures that the switching frequency of the VSC-rectifier is constant and the generated harmonics are smaller.

The fuzzy PI control of the above-mentioned seven-step constant DC voltage is realized through software programming and executed by a digital signal processor (DSP).

Referring to FIG. 2 , it is a schematic diagram of the DC voltage fuzzy PI control principle.

的实时在线调节。本发明采用二阶模糊控制器，故其输入信号为直流电压误差信号

及其变化率信号

，这种结构反映了模糊控制器具有非线性PD控制规律，从而有利于保证系统的稳定性，并可减小响应过程的超调量以及消弱其振荡现象。

和经过模糊化、模糊推理及解模糊三个过程，最终输出调节此时直流电压误差的PI参数

，对PI调节器参数进行在线调节。 The part framed by the dotted line in Fig. 2 is the internal structure of the DC voltage fuzzy PI controller. Realize the parameters of the PI regulator

real-time online adjustment. The present invention uses a second-order fuzzy controller, so its input signal is a DC voltage error signal

and its rate-of-change signal

, this structure reflects that the fuzzy controller has nonlinear PD control law, which is beneficial to ensure the stability of the system, and can reduce the overshoot of the response process and weaken its oscillation phenomenon.

and After three processes of fuzzification, fuzzy reasoning and defuzzification, the PI parameters that adjust the DC voltage error at this time are finally output

, to adjust the parameters of the PI regulator online.

和，输出语言变量是

。语言变量的语言值越多，则制定控制规则越方便，但模糊控制规则相应变得更复杂；语言值过少，使得描述变量变得粗糙，导致控制器的性能变坏。所以，本发明对于输入语言变量

,

和输出变量

均选取七个语言值，分别为：“负大、负中、负小、零、正小、正中、正大”。 It should be noted that the input language variables of the fuzzy controller are

and , the output linguistic variable is

. The more linguistic values of linguistic variables, the more convenient it is to formulate control rules, but the fuzzy control rules become correspondingly more complicated; too few linguistic values make the description variables rough and cause the performance of the controller to deteriorate. Therefore, the present invention for the input language variable

,

and the output variable

Seven language values are selected, which are: "negative big, negative middle, negative small, zero, positive small, positive middle, positive large".

的隶属度。所选取的七个语言值“负大、负中、负小、零、正小、正中、正大”在图3中分别对应于“NB、NM、NS、ZE、PS、PM、PB”。 Referring to FIG. 3 , the membership functions used in the fuzzification and defuzzification processes of the present invention are triangular membership functions. In Figure 3, the ordinate is the exact value

degree of membership. The selected seven language values "negative large, negative medium, negative small, zero, positive small, positive medium, positive large" respectively correspond to "NB, NM, NS, ZE, PS, PM, PB" in Fig. 3 .

The working principle of the fuzzy PI controller is as follows:

根据隶属度函数进行模糊化处理后分别得到模糊量

和； Step 1: Enter Linguistic Variables and

Fuzzy quantities are obtained after fuzzy processing according to the membership function

and ;

和

进行模糊推理，即根据制定的模糊控制规则进行模糊推理，并决策出输出的模糊量； Step two: add

and

Carry out fuzzy reasoning, that is, carry out fuzzy reasoning according to the established fuzzy control rules, and determine the output fuzzy quantity;

下，模糊控制规则设定的原则为： What needs to be explained is that the establishment of fuzzy control rules and fuzzy reasoning and decision-making are the key parts of fuzzy controller design, which directly affect the quality of the control system. In the present invention, in different

Next, the principles set by the fuzzy control rules are:

较大，为使系统具有较好的快速跟踪性能，应取较大的

，同时为了避免系统响应出现较大的超调，应对积分作用加以限制，通常取。 (1) when

Larger, in order to make the system have better fast tracking performance, a larger

, and at the same time, in order to avoid a large overshoot in the system response, the integral action should be limited, usually take .

处于中等大小时，为使系统具有较小的超调，应取较小的

和适当的

。 (2) when

At a medium size, in order to make the system have a small overshoot, a small

and appropriate

.

较小时，为使系统具有较好的稳态性能，应取较大的

和。 (3) when

When is small, in order to make the system have better steady-state performance, a larger

and .

Step 3: Defuzzify the output fuzzy quantity, that is, complete the conversion from fuzzy quantity to precise quantity through the defuzzification method, and output parameters , to adjust the parameters of the PI regulator online. The defuzzification method of the present invention adopts the weighted average method.

Referring to FIG. 4 , it is a schematic diagram of a hardware realization circuit of a control system of a rectifier of a flexible direct current transmission system. include:

以及直流电压

。

和

用于无功功率计算。 Voltage detection, used to detect AC system voltage , VSC- rectifier AC side voltage

and DC voltage

.

and

Used for reactive power calculations.

The voltage conditioning circuit converts the voltage value output by the voltage detection module to the voltage range (0~3V) acceptable to the DSP.

，用于无功功率计算。 Current detection, used to detect the three-phase current of the AC system

, for reactive power calculations.

The voltage conditioning circuit converts the voltage value output by the current detection module to the voltage range (0~3V) acceptable to the DSP.

The present invention adopts DSP TMS320F2812 as the control chip, which has ADC module, EV module and so on inside. Using DSP internal ADC module to realize the conversion from analog signal to digital signal.

VSC- rectifier constant DC voltage fuzzy PI control strategy is implemented by general software programming, and the programmed program is executed by DSP. The DSP finally outputs 6-way PWM through the EV module. Since the power supply voltage of the DSP chip is 0~3V, the 6-way PWM cannot directly drive the VSC-rectifier.

The drive isolation circuit is used to raise the level of the 6-channel PWM output by the DSP to drive the VSC-rectifier; at the same time, it plays the role of isolating the weak current signal from the strong current to avoid the strong current from affecting the weak current signal.

In summary, compared with the prior art, the constant DC voltage control of the rectifier provided by the present invention adopts a double closed-loop vector control strategy, in which the outer voltage loop adopts fuzzy PI control, and the inner loop adopts current decoupling control, realizing active power and independent control of reactive power, the method avoids the cumbersome off-line parameter adjustment of traditional PI regulators, and can perform online PI parameter adjustment according to changes in system operating status. All have faster response speed and higher control precision, which improves the anti-interference ability and dynamic stability performance of the system.

Claims (5)

1. flexible DC power transmission system control method to passive network power supply, it is characterized in that, described method arranges rectifier controller at the DC power transmission line head end of flexible DC power transmission system, VSC-rectifier to the AC system side carries out constant DC voltage control, the DC power transmission line end arranges circuit control device, the VSC-inverter is carried out deciding alternating voltage control, described VSC-rectifier constant DC voltage control adopts two closed-loop vector control strategies, wherein outer voltage adopts fuzzy PI hybrid control, interior ring adopts Current Decoupling control, thereby realizes the independent control of active power and reactive power.

2. a kind of flexible DC power transmission system control method to passive network power supply according to claim 1 is characterized in that the concrete steps of described VSC-rectifier constant DC voltage control are as follows:

A. the direct voltage of flexible DC power transmission circuit detected in real time, obtained the direct voltage actual value

, and with the direct voltage set-point

Compare, obtain the direct current voltage error signal;

B. the direct current voltage error signal is exported d axis AC current reference value through direct voltage Fuzzy PI Controller and follow-up current limit circuit

C. calculate according to current system alternating voltage, alternating current and obtain the reactive power actual value

, with the reactive power set-point

Compare, obtain idle error signal;

D. idle error signal obtains q axis AC current reference value through reactive power PI controller and current limit circuit

E.

With Through interior circular current decoupling zero control circuit output d axis AC voltage reference value

With q axis AC voltage reference value

F. With

Through the two-phase rotational coordinates be tied to the two-phase rest frame coordinate transform (2r/2s) output two-phase rest frame (

Coordinate system) under

With

G. adopt based on SVPWM (SVPWM) method pair

With

Modulate, resulting 6 road pwm signals are controlled respectively 6 IGBT operations of VSC-rectifier.

3. a kind of flexible DC power transmission system control method to the passive network power supply according to claim 2 is characterized in that described direct voltage Fuzzy PI Controller adopts the second order mode fuzzy controllers, and its input signal is the direct current voltage error signal And rate of change signal

4. a kind of flexible DC power transmission system control method to the passive network power supply according to claim 3 is characterized in that described ambiguity solution method adopts weighted mean method.

5. a kind of flexible DC power transmission system control method to passive network power supply according to claim 4, it is characterized in that the obfuscation of direct current voltage error signal and rate of change signal thereof is conciliate the used membership function of blurring process and all chosen Triangleshape grade of membership function.

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