CN104701886A - Presynchronization control method based on virtual synchronous generator - Google Patents

Abstract

The invention relates to a presynchronization control method based on a virtual synchronous generator. The method comprises the steps that a three-phase network voltage amplitude value Vg, a three-phase network voltage frequency omega g and a three-phase network voltage phase angle theta g are obtained; a voltage amplitude value Vo output by an inverter, voltage frequency omega o output by the inverter and a voltage phase angle theta o output by the inverter are obtained; a frequency feedback integration element is cut in; a voltage feedback integration element is cut in; a proportional integral adjuster III is cut in; and a grid connection switch is closed, so that the synchronous generator is connected into a power grid. According to the technical scheme, the fact that before virtual synchronous generator grid connection, the frequency, the amplitude, the phase and the grid voltage output by the virtual synchronous generator are the same can be guaranteed, accordingly small grid connection instant impact current is achieve, and inverter smooth friendly grid connection is guaranteed.

Description

A Pre-synchronization Control Method Based on Virtual Synchronous Generator

technical field

The invention relates to a control method, in particular to a pre-synchronization control method based on a virtual synchronous generator.

Background technique

With the depletion of fossil energy and the improvement of environmental protection awareness, distributed power generation systems based on renewable energy have developed rapidly. However, as the proportion of distributed generation in the power system gradually increases, the impact of distributed generation on the power system cannot be ignored. In order to improve the acceptance capacity of the grid for distributed energy, a virtual synchronous generator technology can be used, that is, through control, the grid-connected inverter can simulate the inertia, primary frequency regulation, primary voltage regulation and excitation regulation characteristics of the synchronous generator, so that the distributed The power supply, like the synchronous generator, can actively participate in the power regulation of the grid, thereby improving the stability of the entire grid.

Fig. 1 is a structural diagram of a virtual synchronous generator, which includes a DC input power supply V _in , a three-phase inverter bridge, and an LC filter. Where v _Ca , v _Cb , and v _Cc are the three-phase output voltages of the inverter, i _La , i _Lb , and i _Lc are the inductor currents on the three-phase inverter side, and i _ga , i _gb , and i _gc are the three-phase inverter Incoming grid current, v _ga , v _gb , and v _gc are three-phase grid voltages. Sampling the three-phase output voltage v _C and the three-phase grid current i _g for power calculation to obtain the active power and reactive power output by the inverter, and send the calculated active power and reactive power to the virtual synchronous generator controller Among them, the three-phase modulation waves e _a , _eb , e _c are obtained by the virtual synchronous generator controller, and the three-phase modulation waves are sent to the PWM modulator to obtain the drive signals of each power switch tube of the inverter.

Fig. 2 is a specific control block diagram of the virtual synchronous generator controller in Fig. 1 . The upper part of Figure 2 is the control of active power, where P _set is the given active power, P _e is the actual active power of the virtual synchronous generator, and ω _n is the rated frequency. The active power control loop simulates the primary frequency modulation and inertia link of the synchronous generator, including active power (frequency droop control (D _p in Figure 2 and below represents the frequency droop coefficient) and virtual inertia control (J represents the virtual moment of inertia). The lower part of Figure 2 Half part is the control of reactive power, where Q _set is the given reactive power, Q _e is the actual reactive power of the virtual synchronous generator. _{V n} is the rated voltage amplitude. The reactive power control loop simulates the synchronous generator The primary voltage regulation and electromagnetic relationship, including reactive power (voltage droop control (voltage droop coefficient is D _q ) and excitation regulation control (excitation integral gain is 1/K). The modulation wave e obtained by active power control and reactive power control The frequency reference ω, the amplitude reference E and the phase reference θ. The modulation wave e controls the on-off of each switch tube in Figure 1 through the PWM link to make the inverter output three-phase symmetrical voltage.

However, Figure 2 only shows the control block diagram of the steady-state operation of the virtual synchronous generator after it is integrated into the grid, and does not illustrate the switching process of the virtual synchronous generator from off-grid to grid-connected. It should be pointed out that the control block diagram shown in Figure 2 only makes the virtual synchronous generator simulate the external characteristics of the synchronous generator in control, and its main circuit is still composed of fragile power electronic devices, which are similar to the actual synchronous generator. Compared with it, its ability to resist overvoltage and overcurrent is weak. If the virtual synchronous generator is connected to the power grid using the traditional method of dragging the synchronous generator into synchronization, the inrush current will be too large at the moment of grid connection, which will cause damage to the switching devices and magnetic components of the inverter. Therefore, it is necessary to provide a pre-synchronization control strategy so that the virtual synchronous generator can be grid-friendly.

Contents of the invention

In order to solve the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a pre-synchronization control method based on a virtual synchronous generator, and the technical solution provided by the present invention can ensure the frequency of the output voltage of the virtual synchronous generator before grid connection , amplitude, and phase are the same as the grid voltage, so that the instantaneous impact current of the grid connection is small, and the virtual synchronous generator inverter is smooth and friendly to the grid.

In order to provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is presented below. This summary is not an overview, nor is it intended to identify key/critical elements or delineate the scope of these embodiments. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

The object of the present invention is to adopt following technical scheme to realize:

The present invention provides a pre-synchronization control method based on a virtual synchronous generator, characterized in that the method comprises the following steps:

(1) Obtain the three-phase grid voltage amplitude V _g , the three-phase grid voltage frequency ω _g and the three-phase grid voltage phase angle θ _g ;

(2) Obtain the inverter output voltage amplitude V _o , the inverter output voltage frequency ω _o and the inverter output voltage phase angle θ _o ;

(3) Cut into the frequency feedback integration link;

(4) Cut into the voltage feedback integration link;

(5) cut into the proportional integral regulator III;

(6) Close the grid-connected switch to connect the virtual synchronous generator to the grid;

(7) Cut out the frequency feedback integral link, the voltage feedback integral link and the phase regulator; slowly increase the active power reference value P _{set of} the virtual synchronous generator, and control the slow increase of the output power of the virtual synchronous generator;

(8) After the active power reference value P _{set of} the virtual synchronous generator increases to the rated value, the frequency reference is switched from the grid voltage frequency ω _g to the rated frequency ω _n of the virtual generator, and the voltage reference is switched from V _g to the rated Voltage amplitude V _n .

Further, in the step (1), the three-phase grid voltage v _ga , v _gb and v _gc are obtained through the voltage sensor, and the phase-locked loop algorithm is used to obtain the three-phase grid voltage amplitude V _g and the three-phase grid voltage frequency ω _g and three-phase grid voltage phase angle θ _g ;

In the step (2), the inverter output voltages v _Ca , v _Cb and v _Cc are obtained through the voltage sensor, and the inverter output voltage amplitude V _o and the inverter output voltage frequency ω _o are obtained by using the phase-locked loop algorithm And inverter output voltage phase angle θ _o .

Further, in the step (3), the frequency reference of the virtual synchronous generator is replaced by the rated frequency ω _n to the three-phase grid voltage frequency ω _g , and at the same time, a frequency feedback integration link is added to the active frequency drooping link, and the frequency Feedback points link;

The frequency feedback integral link is the integral link of gain K ₁ , which is used as the integral part of the regulator, and uses _Dp as the proportional part of the regulator to form a proportional-integral regulator I, so that the frequency ω of the virtual synchronous generator can have no static poorly track the voltage frequency ω _g of the upper three-phase grid; the proportional-integral control regulator I is a voltage regulator.

Further, in the step (4), the voltage amplitude reference of the virtual synchronous generator is replaced by the rated voltage amplitude V _n by the grid voltage amplitude V _g , and the voltage feedback integration is added to the reactive voltage droop link link, and cut into the voltage feedback integration link;

The integral part of the voltage feedback is the integral part of the gain _K2 , which is used as the integral part of the regulator, and _Dq is used as the proportional part of the regulator to form a proportional-integral regulator II, so that the output voltage amplitude of the virtual synchronous generator is E It can track the voltage amplitude V _g of the upper voltage grid without static error; the proportional-integral control regulator II is a voltage regulator.

Further, in the step (5), the phase angle θ _g of the grid voltage is different from the phase angle θ _o of the inverter output voltage to obtain the phase angle difference Δθ, and the Δθ is input into the proportional-integral regulator III, and the The output of the proportional-integral regulator is added to the output frequency of the virtual synchronous generator;

The proportional-integral regulator III is a phase regulator, and the sum of the output of the phase regulator and the output frequency of the frequency regulator is integrated to obtain the phase of the virtual synchronous generator, so as to ensure that the phase of the output voltage of the virtual synchronous generator has no static Poorly tracks the phase of the grid voltage.

Further, in the step (6), after ensuring that the output voltage of the virtual synchronous generator is equal in frequency, amplitude and phase to the grid voltage, the grid-connected switch is closed and connected to the grid.

Further, the initial state of the virtual synchronous generator is P _set =0, Q _set =0, ω _r =ω _n , V _r =V _n , and the grid-connected switch is off; when performing the pre-synchronization control, and The grid switch is closed, and the virtual synchronous generator is switched from off-grid to grid-connected; where: P _set represents the active power reference value of the virtual synchronous generator, Q _set represents the reactive power reference value of the virtual synchronous generator = 0, ω _r represents the virtual synchronous Generator frequency reference value, V _r represents the virtual synchronous generator voltage amplitude reference value.

Compared with the closest prior art, the excellent effect that the technical solution provided by the present invention has is:

On the basis of the original virtual synchronous generator control structure, the present invention embeds a pre-synchronization control algorithm to realize the pre-synchronization function, which can ensure that the frequency, amplitude, and phase of the output voltage of the virtual synchronous generator before grid connection are the same as the grid voltage , so as to realize the small impulse current at the moment of grid connection, and realize the pre-synchronization quickly and accurately, so as to realize the smooth and friendly grid connection of virtual synchronous generators.

To the above and related ends, one or more embodiments comprise the features hereinafter specified and particularly pointed out in the claims. The following description and drawings detail certain exemplary aspects and are indicative of but a few of the various ways in which the principles of various embodiments may be employed. Other benefits and novel features will become apparent upon consideration of the following detailed description in conjunction with the accompanying drawings, and the disclosed embodiments are intended to include all such aspects and their equivalents.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the description, and are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention. In the attached picture:

Fig. 1 is a structural diagram of a virtual synchronous generator in the prior art;

Fig. 2 is the control block diagram of virtual synchronous generation controller of prior art;

Fig. 3 is a phase-locked loop control block diagram provided by the present invention;

Fig. 4 is a control block diagram of a virtual synchronous power generation controller after adding a pre-synchronization control strategy provided by the present invention.

Detailed ways

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

The following description and drawings illustrate specific embodiments of the invention sufficiently to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Individual components and functions are optional unless explicitly required, and the order of operations may vary. Portions and features of some embodiments may be included in or substituted for those of other embodiments. The scope of embodiments of the present invention includes the full scope of the claims, and all available equivalents of the claims. These embodiments of the present invention may be referred to herein, individually or collectively, by the term "invention", which is for convenience only and is not intended to automatically limit the application if in fact more than one invention is disclosed The scope is any individual invention or inventive concept.

The present invention provides a pre-synchronization control method based on a virtual synchronous generator. The pre-synchronization control method based on a virtual synchronous generator can ensure that the frequency, amplitude, and phase of the output voltage of the virtual synchronous generator before grid connection are the same as the grid voltage. In this way, the instantaneous impact current of the grid connection is small, and the inverter is smooth and friendly to the grid. The hardware circuit adopted by the present invention is the same as the hardware part of the existing virtual synchronous generator, as shown in FIG. 1 . However, the control method has been improved, and pre-synchronization control is added on the basis of the existing virtual synchronous generator control structure, as shown in Figure 4. The specific improvements are as follows:

(1) For frequency adjustment, since the original virtual synchronous generator control structure uses the frequency droop coefficient D _p as the proportional regulator, the low-frequency band gain of the frequency regulation loop is not high enough, and the frequency ω of the virtual synchronous generator cannot be static poorly tracks the upper grid frequency ω _g . Therefore, as an improvement, now add an integrator whose gain is K ₁ (the present invention is referred to as a frequency feedback integration link) as the integral part of the regulator, and use _Dp as the proportional part of the regulator to form a proportional integral (proportionintegration, PI) Regulator I, so that the frequency ω of the virtual synchronous generator can track the grid frequency ω _g without static error.

(2) For the adjustment of voltage amplitude, since the original virtual synchronous generator control structure uses the voltage amplitude droop coefficient D _q as the proportional regulator, the low-frequency band gain of the voltage amplitude adjustment loop is not high enough, and the virtual synchronous generator The amplitude E of the output voltage cannot track the amplitude V _g of the grid voltage without static error. Therefore, as an improvement, an integrator with a gain of K ₂ (the present invention is called a voltage feedback integral link) is added as the integral part of the regulator, and D _q is used as the proportional part of the regulator to form a proportional-integral regulator II (PI regulator), so that the output voltage amplitude E of the virtual synchronous generator can track the grid voltage amplitude V _g without static error.

(3) For the adjustment of the phase, the improvement of the present invention is as follows: subtract the virtual synchronous generator output voltage phase θ _o from the grid voltage phase θ _g , and send the difference to the proportional-integral regulator III (PI regulator, the present invention is called The phase regulator), the output of the PI regulator is added to the output frequency of the frequency regulator, and the sum is integrated to obtain the phase of the virtual synchronous generator. In this way, it can be ensured that the phase of the output voltage of the virtual synchronous generator can track the phase of the grid voltage without static difference.

(4) At the same time, since the improved control structure requires grid voltage information (including grid voltage amplitude V _g , grid voltage frequency ω _g , grid voltage phase angle θ _g ) and inverter output voltage information ( Including the amplitude V _o of the inverter output voltage, the frequency ω _o of the inverter output voltage, and the phase angle θ _o of the inverter output voltage), so a phase-locked loop is further added to the control, and the control of the phase-locked loop The block diagram is shown in Figure 3. Among them, T _dq / _abc is the transformation matrix of the three-phase voltage from the abc coordinate system to the dq coordinate system, and G _c (s) is the phase-locked loop regulator. Generally, the PI regulator is selected. Since the phase-locked loop is a relatively mature technology, it is only used here to provide the necessary information for the pre-synchronization of the virtual synchronous generator. Therefore, the specific implementation of the phase-locked loop control will not be repeated here.

The method comprises the steps of:

(1) Obtain the three-phase grid voltage v _ga , v _gb , v _gc through the voltage sensor, and use the phase-locked loop algorithm to obtain the amplitude V _g of the three-phase grid voltage, the frequency ω _g of the three-phase grid voltage and the three-phase grid voltage phase angle θ _g ;

(2) Obtain the inverter output voltage v _Ca , v _Cb , v _Cc through the voltage sensor, use the phase-locked loop algorithm to obtain the amplitude V _o of the inverter output voltage, the frequency ω _o of the inverter output voltage and the inverter The phase angle θ _o of the device output voltage;

Using the pre-synchronization control shown in Figure 4, when the synchronous generator is from off-grid to grid-connected, the initial state of the virtual synchronous generator is P _set =0, Q _set =0, ω _r =ω _n , V _r =V _n , and The network switch is disconnected, where: P _set represents the active power reference value of the virtual synchronous generator, Q _set represents the reactive power reference value of the virtual synchronous generator = 0, ω _r represents the frequency reference value of the virtual synchronous generator, V _r represents the virtual synchronous Generator voltage amplitude reference value; the specific implementation steps are as follows:

(3) Cut into the frequency feedback integration link (that is, throw switch SW ₄ to the ω _g side and close SW ₁ ): replace the frequency reference of the virtual synchronous generator from the rated frequency ω _n to the grid voltage frequency ω _g , and at the same time droop at the active frequency Integral links are added to the link;

(4) Cut into the voltage feedback integration link (that is, throw SW ₅ on the V _g side and close SW ₂ ): the voltage amplitude reference of the virtual synchronous generator is replaced by the rated voltage amplitude V _n by the grid voltage amplitude V _g , and at the same time Integral links are added to reactive voltage droop links;

The purpose of the above steps (3) and (4) is to control the output voltage frequency of the virtual synchronous generator to be equal to the grid voltage frequency (to prepare for the reduction of the phase difference in the following control), and to control the output voltage amplitude of the virtual synchronous generator to be equal to the grid voltage amplitude. The values are equal.

(5) Cut into the proportional-integral regulator III (that is, close SW ₃ ): make a difference between the phase angle θ _g of the grid voltage and the phase angle θ _o of the inverter output voltage to obtain the phase angle difference Δθ, and input Δθ to the proportional-integral In the regulator, the output of the proportional-integral regulator is added to the output frequency of the virtual synchronous generator;

The purpose of this step is to control the voltage phase of the virtual synchronous generator and the three-phase grid to be the same.

(6) Ensure that the output voltage of the virtual synchronous generator is equal to the frequency, amplitude, and phase of the grid voltage, then close the grid-connected switch and connect to the grid.

(7) Cut out the frequency feedback integral link, the voltage feedback integral link and the phase regulator (that is, disconnect SW ₁ , SW ₂ and SW ₃ ). Slowly increase P _set to control the output power of the virtual synchronous generator to increase slowly.

(8) After P _set increases to the rated value, switch the frequency reference from ω _g to ω _n , and switch the voltage reference from V _g to V _n (throw SW ₄ to ω _n side, and SW ₅ to V _n side). The purpose of this step is to realize frequency droop control and voltage droop control, so that the virtual synchronous generator can be completely integrated into the grid.

It is understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged without departing from the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy described.

In the foregoing Detailed Description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are expressly recited in each claim. Rather, as the following claims reflect, the invention lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby expressly incorporated into the Detailed Description, with each claim standing on its own as a separate preferred embodiment of this invention.

Those skilled in the art should also understand that various illustrative logical blocks, modules, circuits and algorithm steps described in conjunction with the embodiments herein may be implemented as electronic hardware, computer software or a combination thereof. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

The foregoing description includes illustrations of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods to describe the above-mentioned embodiments, but those skilled in the art should recognize that various embodiments can be further combined and permuted. Accordingly, the embodiments described herein are intended to embrace all such alterations, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent that the term "comprises" is used in the specification or claims, the word is encompassed in a manner similar to the term "comprises" as interpreted when "comprises" is used as a link in the claims. Furthermore, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or".

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art can still implement the present invention Any modification or equivalent replacement that does not deviate from the spirit and scope of the present invention is within the protection scope of the claims of the pending application of the present invention.

Claims (7)

1. based on a presynchronization control method for virtual synchronous generator, it is characterized in that, described method comprises the steps:

(1) three-phase power grid voltage amplitude V is obtained _g, three-phase power grid voltage frequencies omega _gwith three-phase power grid voltage phase angle theta _g;

(2) inverter output voltage amplitude V is obtained _o, inverter output voltage frequencies omega _owith inverter output voltage phase angle theta _o;

(3) frequency feedback integral element is cut;

(4) cut-in voltage feedback score link;

(5) proportional and integral controller III is cut;

(6) closed grid-connected switch, makes virtual synchronous generator access electrical network;

(7) frequency feedback integral element, Voltage Feedback integral element and phase regulator is cut out; Slow increase virtual synchronous generator active power reference value P _set, controlling virtual synchronous output of a generator slowly increases;

(8) virtual synchronous generator active power reference value P is treated _setafter being increased to rated value, by frequency reference benchmark from line voltage frequencies omega _gswitch to the rated frequency ω of virtual synchronous generator _n, voltage reference is from V _gswitch to rated voltage amplitude V _n.

2. presynchronization control method as claimed in claim 1, is characterized in that, in described step (1), obtain three-phase power grid voltage v by voltage sensor _ga, v _gband v _gc, utilize phase-lock-loop algorithm to obtain three-phase power grid voltage amplitude V _g, three-phase power grid voltage frequencies omega _gwith three-phase power grid voltage phase angle theta _g;

In described step (2), obtain inverter output voltage v by voltage sensor _ca, v _cband v _cc, utilize phase-lock-loop algorithm to obtain inverter output voltage amplitude V _o, inverter output voltage frequencies omega _owith inverter output voltage phase angle theta _o.

3. presynchronization control method as claimed in claim 1, is characterized in that, in described step (3), by the frequency reference of virtual synchronous generator by rated frequency ω _nreplace with three-phase power grid voltage frequencies omega _g, in meritorious frequency droop link, add frequency feedback integral element simultaneously, and cut frequency feedback integral element;

Described frequency feedback integral element is gain K ₁integral element, it, as the integral part of adjuster, utilizes D _pas the proportional parts of adjuster, proportion of composing integral controller I, makes the frequencies omega of virtual synchronous generator can follow the tracks of three-phase power grid voltage frequencies omega to floating _g; Described proportional plus integral control adjuster I is voltage regulator.

4. presynchronization control method as claimed in claim 1, is characterized in that, in described step (4), by the voltage magnitude reference of virtual synchronous generator by rated voltage amplitude V _nreplace with the amplitude V of line voltage _g, in the sagging link of reactive voltage, add Voltage Feedback integral element simultaneously, and cut-in voltage feedback score link;

Described Voltage Feedback integral element is gain K ₂integral element, it, as the integral part of adjuster, utilizes D _qas the proportional parts of adjuster, proportion of composing integral controller II, makes the output voltage amplitude E of virtual synchronous generator can follow the tracks of to floating voltage Grid voltage magnitude V _g; Described proportional plus integral control adjuster II is voltage regulator.

5. presynchronization control method as claimed in claim 1, is characterized in that, in described step (5), by the phase angle theta of line voltage _gwith inverter output voltage phase angle theta _odo difference, obtain phase angle difference Δ θ, Δ θ is input in proportional and integral controller III, the output of proportional and integral controller is added in the output frequency of virtual synchronous generator;

Described proportional and integral controller III is phase regulator, the output of described phase regulator and the output frequency sum of frequency regulator obtain the phase place of virtual synchronous generator by integration, to follow the tracks of the phase place of line voltage with ensureing the phase place floating of virtual synchronous generator output voltage.

6. presynchronization control method as claimed in claim 1, it is characterized in that, in described step (6), ensure that virtual synchronous generator output voltage is equal with voltage Grid electric voltage frequency, amplitude is equal, the identical rear closed grid-connected switch of phase place, access electrical network.

7. presynchronization control method as claimed in claim 1, it is characterized in that, described virtual synchronous generator initial conditions is P _set=0, Q _set=0, ω _r=ω _n, V _r=V _n, grid-connected switch disconnects; When carrying out described presynchronization and controlling, grid-connected switch closes, and virtual synchronous generator is grid-connected from switching to from net; Wherein: P _setrepresent virtual synchronous generator active power reference value, Q _setrepresent virtual synchronous generator reactive power reference value=0, ω _rrepresent virtual synchronous generator frequency reference value, V _rrepresent virtual synchronous generator voltage amplitude reference value.