CN107994603A - One kind is based on virtual synchronous generator failure traversing control method and system - Google Patents

Abstract

The present invention provides a fault ride-through control method and system based on a virtual synchronous generator. When the power grid fails, the DC/DC converter of the virtual synchronous machine switches from the constant voltage control mode to the constant voltage plus feedforward control mode, and the voltage command The first current command value is obtained by subtracting the value from the voltage feedback value and adjusted by PI, and the first voltage value is obtained by subtracting the first current command value from the current feedback value and adjusted by PI to control the DC/DC converter; and the virtual Synchronous machine DC/AC converter switches from VSG control mode to constant current control mode, obtains reactive current through reactive voltage regulation control, and calculates active current according to reactive current, according to the calculated reactive current and active current. The virtual synchronous machine DC/AC converter is controlled. The invention realizes fault ride-through of the power station type virtual synchronous generator through mode conversion and control strategy optimization of the virtual synchronous generator system, and ensures the stability of the power system.

Description

Fault ride-through control method and system based on virtual synchronous generator

technical field

The invention belongs to the technical field of virtual synchronous generators, in particular to a fault ride-through control method and system based on virtual synchronous generators.

Background technique

With the contradiction between the development of the national economy and the depletion of fossil energy becoming more and more obvious, the distributed power generation system featuring renewable energy quickly occupies a key position in future power research. The grid-connected capacity of renewable energy is also increasing, and its impact on the large power grid is getting deeper and deeper. The micro-grid provides a way for the application of distributed wind power generation systems. The grid-connected inverter is used as a link between the micro-grid and the large grid. The ties have an important impact on the operation of the microgrid. The grid-connected inverter is mainly composed of power electronic devices, which brings a series of shortcomings, including low system output impedance, lack of inertia, insufficient power distribution capacity during grid-connected operation, and difficulty in integrating with existing power system regulation strategies. Cooperate. Therefore, the virtual synchronous generator system with the ontology model of the simulated synchronous generator and the characteristics of active power frequency regulation and reactive power voltage regulation is gradually adopted, but the virtual synchronous generator fault ride-through problem caused by it is becoming more and more prominent.

For the research on virtual synchronous generator fault ride-through control technology, the existing methods usually only consider the grid connection and topology, but do not fully consider the characteristics of the virtual synchronous machine. The virtual synchronous generator has no demagnetization characteristics, and the internal potential will not follow the The terminal voltage of the machine decreases. When the power grid fails, the current generated by the voltage difference between the terminal voltage and the internal potential on the damping stator impedance far exceeds the current that the virtual synchronous generator device can withstand. Therefore, the existing methods cannot fundamentally solve the problem of power station type Control problems of virtual synchronous generators.

Contents of the invention

The purpose of the present invention is to provide a virtual synchronous generator based fault ride-through control method and system, which is used to solve the problem in the prior art that the characteristics of the virtual synchronous generator are not fully considered when dealing with the grid fault ride-through problem.

For realizing the above object, technical scheme of the present invention is:

A fault ride-through control method based on a virtual synchronous generator, comprising the steps of:

When the power grid fails, the DC/DC converter of the virtual synchronous generator switches from the constant voltage control mode to adding the current feedback value in the constant voltage control mode. The current feedback value is obtained by dividing the active power of the grid by the DC voltage. For DC /DC converter for control;

Switch the DC/AC converter of the virtual synchronous generator from the VSG control mode to the constant current control mode. The constant current control mode means that the reactive current is obtained through reactive voltage regulation control, and the active current is calculated according to the reactive current. According to The calculated reactive current and active current control the DC/AC converter of the virtual synchronous generator.

Further, the judgment condition when the power grid is faulty is: when it is detected that the grid voltage is less than 0.9 pu or greater than 1.1 pu, it is judged as a power grid fault.

Further, the step of obtaining reactive current through reactive voltage regulation control is: subtracting the rated voltage of the grid from the terminal voltage of the virtual synchronous generator to obtain a difference, multiplying the difference by the voltage regulation coefficient and adding the reactive power The feedback value obtains a reactive power command value, and the reactive current is obtained by dividing the reactive power command value by the grid rated voltage.

Further, the calculation formula of the active current is: Among them, _id is the active current, and i _q is the reactive current.

Further, when it is detected that the grid voltage is greater than 0.9pu or less than 1.1pu, and lasts for the first set time, it is judged that the grid fault has recovered, and when it lasts for the second set time, the constant current control mode is switched to VSG control mode.

The present invention also provides a fault ride-through control system based on a virtual synchronous generator, including a controller that controls the DC/DC converter of the virtual synchronous generator to switch from the constant voltage control mode to In the constant voltage control mode, the current feedback value is added, and the current feedback value is obtained by dividing the active power of the grid by the DC voltage to control the DC/DC converter; and control the DC/AC converter of the virtual synchronous generator from The VSG control mode is switched to the constant current control mode. The constant current control mode means that the reactive current is obtained through reactive voltage regulation control, and the active current is calculated according to the reactive current. The virtual synchronization is performed according to the calculated reactive current and active current. Generator DC/AC converter for control.

Further, the judgment condition when the power grid is faulty is: when it is detected that the grid voltage is less than 0.9 pu or greater than 1.1 pu, it is judged as a power grid fault.

Further, the step of obtaining reactive current through reactive voltage regulation control is: subtracting the rated voltage of the grid from the terminal voltage of the virtual synchronous generator to obtain a difference, multiplying the difference by the voltage regulation coefficient and adding the reactive power The feedback value obtains a reactive power command value, and the reactive current is obtained by dividing the reactive power command value by the grid rated voltage.

Further, the calculation formula of the active current is: Among them, _id is the active current, and i _q is the reactive current.

Further, when it is detected that the grid voltage is greater than 0.9pu or less than 1.1pu, and lasts for the first set time, it is judged that the grid fault has recovered, and when it lasts for the second set time, the constant current control mode is switched to VSG control mode.

The beneficial effects of the present invention are:

Based on the virtual synchronous generator fault ride-through control method provided by the present invention, when the power grid fails, the DC/DC converter of the virtual synchronous generator switches from the constant voltage control mode to adding the current feedback value in the constant voltage control mode. The DC converter is controlled; the DC/AC converter of the virtual synchronous generator is switched from the VSG control mode to the constant current control mode. The active current is calculated by the active current, and the DC/AC converter of the virtual synchronous generator is controlled according to the calculated reactive current and active current. The invention realizes fault ride-through of the power station type virtual synchronous generator through mode conversion and control strategy optimization of the virtual synchronous generator system, and ensures the stability of the power system.

Description of drawings

Figure 1 is a structural block diagram of a power station virtual synchronous generator system;

Figure 2 is a block diagram of current command switching when the power grid is faulty;

Fig. 3 is a virtual synchronous generator active/reactive loop control block diagram when the power grid is faulty;

Figure 4 is a block diagram of the DC/DC side control of the virtual synchronous generator.

Detailed ways

The specific embodiment of the present invention will be further described below in conjunction with accompanying drawing:

A fault ride-through control system based on a virtual synchronous generator, as shown in Figure 1, includes a controller, a virtual synchronous generator DC/DC converter and a virtual synchronous generator DC/AC converter; wherein, the DC/DC converter The converter and the DC/AC converter respectively include power modules, and each power module is composed of an insulated gate bipolar transistor (IGBT). The controller controls and connects the DC/DC converter of the virtual synchronous generator and the DC/AC converter of the virtual synchronous generator. When the controller judges the failure of the power grid, it controls the DC/DC conversion of the virtual synchronous generator when the power grid fails. Switch from constant voltage control mode to add current feedback value in constant voltage control mode to control DC/DC converter; and control virtual synchronous generator DC/AC converter to switch from VSG control mode to constant current Control mode, constant current control mode refers to obtaining reactive current through reactive voltage regulation control, calculating active current according to the reactive current, and controlling the DC/AC converter according to the calculated reactive current and active current.

A fault ride-through control method based on a virtual synchronous generator, comprising the steps of:

1) Collect the grid voltage and detect the collected grid voltage. When the grid voltage is detected to be normal, the DC/DC converter adopts the constant voltage control mode, and the DC/AC converter adopts the virtual synchronous generator VSG control mode , VSG control mode refers to the operating state in which the virtual synchronous generator system automatically participates in the frequency regulation, voltage regulation and virtual inertia response of the grid, as shown in Figure 3 when the grid fault flag is 0, the control mode of the active loop and the control mode of the reactive loop , since the control mode of the active loop and the control mode of the reactive loop are the control methods based on the virtual synchronous generator in the prior art when the grid fault flag is 0, it will not be repeated here; when the grid voltage is detected to be less than 0.9pu or When it is greater than 1.1pu, it is judged that the power grid is faulty.

2) When a grid fault is detected, the DC/DC converter of the virtual synchronous generator switches from the constant voltage control mode to the constant voltage plus feedforward control mode, the grid fault flag is 1, and the voltage command value is compared with the voltage feedback value Subtract the first current command value through PI adjustment, subtract the first current command value and the current feedback value to obtain the first voltage value through PI adjustment, and control the DC/DC converter. The current feedback value i _{dc_fdb} passes through the active power of the grid The power is obtained by dividing the DC voltage, and the expression is: i _{dc_fdb} = P/V _dc , where P is the active power of the grid, and V _dc is the DC voltage; the specific control process is shown in Figure 4, that is, the voltage command value Vdc _ref and the voltage The feedback value Vdc _fdb is subtracted, and then the first current command value i _ref is obtained through PI adjustment, the first current command value i _ref is subtracted from the current feedback value i _{dc_fdb} , and the first voltage value is obtained through PI adjustment, and the first voltage value is then Compared with the carrier wave, the PWM modulation wave is obtained, so as to control the DC/DC converter. The control process adopts PWM modulation wave, which can effectively improve the voltage utilization rate.

3) When a grid fault is detected, at this time, the DC/AC converter of the virtual synchronous generator switches from VSG control mode to constant current control mode, the grid fault flag is 0, and the reactive current is obtained through reactive voltage regulation control, and The active current is calculated according to the reactive current, and the DC/AC converter of the virtual synchronous generator is controlled according to the calculated reactive current and active current.

Among them, the step of obtaining reactive current through reactive voltage regulation control is as follows: subtracting the rated grid voltage U ₀ (the size of U ₀ is 1pu) from the terminal voltage of the virtual synchronous generator to obtain a difference, and multiplying the difference by the regulation Voltage coefficient Kv plus reactive power scheduling value Q ₀ to get reactive power command value Qu _u , reactive power command value divided by grid rated voltage to get reactive current, further, reactive power command value _Qu and virtual synchronous The reactive power Q _e of the generator is added, and the virtual synchronous generator body is controlled by the adjustment coefficient K/S, where E is the virtual potential command, and E0 is the no-load potential of the virtual synchronous machine, as shown in Figure 3. The power loop control block diagram also needs to limit the reactive current and active current, and the reactive current and active current must satisfy the following relationship: Among them, i _d is the active current, i _q is the reactive current, the active current is calculated according to the relationship between the reactive current and the active current, and the virtual synchronous generator is controlled by the constant current method, as shown in Figure 2, Wherein, i _d corresponds to i _d0 in Fig. 2, and i _q corresponds to i _q0 in Fig. 2 .

4) When it is detected that the grid voltage is greater than 0.9pu or less than 1.1pu, and it continues for the set time, the set time in this embodiment is 1s, as other implementations, it can also be set to other time that meets the set requirements , it is judged that the power grid has returned to normal from a fault, the power grid fault flag is cleared, active power control resumes at a speed of 0.5pu/s, 2s after the power grid fault flag is cleared, the constant current flag is cleared, and the inner loop current command is switched to VSG control Mode output command, that is, the generation of current command is based on the control block diagram in the upper part of Figure 2, that is, the three-phase internal potential e _abc is subtracted from the machine terminal voltage u _abc , and a current value i is obtained by adjusting the adjustment coefficient 1/LS _abc , the current value is fed back to the difference between the three-phase internal potential and the machine terminal voltage through the adjustment coefficient R to obtain the voltage value; the current value i _abc is combined with the phase angle θ to generate the d-axis positive sequence current i _dp and the q-axis positive sequence current i _qp , so as to carry out current inner loop control; the process of active loop control in Figure 3 is to subtract the rated frequency f ₀ of the power grid from the terminal frequency f of the virtual synchronous generator, and the obtained difference is obtained through the frequency modulation coefficient k _f to obtain active power Power value, add the obtained active power value and the active power dispatching instruction value P _dis to obtain the mechanical power P _m , divide the mechanical power P _m by the angular velocity ω of the virtual synchronous generator to obtain the mechanical torque Tm, and perform the virtual synchronous generator body control; and the reactive loop control in Fig. 3 no longer has the participation of adjustment coefficient 1/LS.

Specific implementations have been given above, but the present invention is not limited to the above-described implementations. The basic idea of the present invention lies in the above-mentioned basic scheme. For those of ordinary skill in the art, according to the teaching of the present invention, it does not need to spend creative labor to design various deformation models, formulas, and parameters. Changes, modifications, substitutions and variations to the implementations without departing from the principle and spirit of the present invention still fall within the protection scope of the present invention.

Claims (10)

1. one kind is based on virtual synchronous generator failure traversing control method, it is characterised in that includes the following steps：

During electric network fault, virtual synchronous generator DC/DC current transformers are from Isobarically Control pattern switching in Isobarically Control pattern Plus current feedback values, the current feedback values are obtained by network re-active power divided by DC voltage, to DC/DC current transformers into Row control；

From VSG control mode switchs it is current constant control pattern by virtual synchronous generator DC/AC current transformers, current constant control pattern refers to Reactive current is obtained by idle Regulation Control, and watt current is calculated according to the reactive current, according to the nothing being calculated Work(electric current and watt current are controlled virtual synchronous generator DC/AC current transformers.

2. according to claim 1 be based on virtual synchronous generator failure traversing control method, it is characterised in that power grid event Rule of judgment during barrier is：When detecting network voltage less than 0.9pu or more than 1.1pu, it is judged as electric network fault.

3. according to claim 1 be based on virtual synchronous generator failure traversing control method, it is characterised in that passes through nothing The step of work(Regulation Control obtains reactive current be：Power grid rated voltage and virtual synchronous generator terminal voltage are subtracted each other to obtain Difference, is multiplied by pressure regulation coefficient by the difference and is worth to reactive power command value, the reactive current plus reactive power feedback Obtained by the reactive power command value divided by power grid rated voltage.

4. according to claim 1 be based on virtual synchronous generator failure traversing control method, it is characterised in that described to have The calculation formula of work(electric current is：Wherein, i_dFor watt current, i_qFor reactive current.

5. according to claim 1 be based on virtual synchronous generator failure traversing control method, it is characterised in that works as detection During to network voltage more than 0.9pu or less than 1.1pu, and continue the time of the first setting, be then judged as that electric network fault recovers, when It is VSG control models by current constant control pattern switching when continuing the time of the second setting.

6. one kind passes through control system based on virtual synchronous generator failure, it is characterised in that including controller, the controller When judging grid collapses, control virtual synchronous generator DC/DC current transformers from Isobarically Control pattern switching in constant pressure Current feedback values are added in control model, the current feedback values are obtained by network re-active power divided by DC voltage, to DC/ DC current transformers are controlled；And control virtual synchronous generator DC/AC current transformers from VSG control mode switchs be current constant control mould Formula, current constant control pattern refers to obtains reactive current by idle Regulation Control, and calculates watt current according to the reactive current, Virtual synchronous generator DC/AC current transformers are controlled according to the reactive current and watt current being calculated.

7. according to claim 6 pass through control system based on virtual synchronous generator failure, it is characterised in that power grid event Rule of judgment during barrier is：When detecting network voltage less than 0.9pu or more than 1.1pu, it is judged as electric network fault.

8. according to claim 6 pass through control system based on virtual synchronous generator failure, it is characterised in that passes through nothing The step of work(Regulation Control obtains reactive current be：Power grid rated voltage and virtual synchronous generator terminal voltage are subtracted each other to obtain Difference, is multiplied by pressure regulation coefficient by the difference and is worth to reactive power command value, the reactive current plus reactive power feedback Obtained by the reactive power command value divided by power grid rated voltage.

9. according to claim 6 pass through control system based on virtual synchronous generator failure, it is characterised in that described to have The calculation formula of work(electric current is：Wherein, i_dFor watt current, i_qFor reactive current.

10. according to claim 6 pass through control system based on virtual synchronous generator failure, it is characterised in that works as inspection When measuring network voltage more than 0.9pu or less than 1.1pu, and continue the time of the first setting, be then judged as that electric network fault recovers, It is VSG control models by current constant control pattern switching when continuing the time of the second setting.