CN111864800B - Converter grid-connected equipment-based multi-scale inertia control method and additional controller - Google Patents

Abstract

The invention discloses a multi-scale inertia control method and an additional controller based on converter grid-connected equipment, including: according to the time response speed during disturbance, the control module of the converter grid-connected equipment is divided into DC voltage control scale and AC voltage control scale. Current control scale module; pass the terminal voltage q-axis components in the phase-locked coordinate system through filters and signal conversion modules of different frequency bands respectively, and output control signals corresponding to the different time scale control modules; control the low frequency band and high frequency band The signals are respectively attached to the active branch of the DC voltage control standard module and the reactive branch of the AC current control standard module, so as to make full use of the different response degrees of the active/reactive branches of the converter grid-connected equipment to the signals at different time scales of the system. Efficiently and coordinated to provide inertia support for different time scales of the system. Furthermore, the present invention does not additionally increase the number of sensors and change the active/reactive power injected into the grid by the converter grid-connected equipment in steady state.

Description

Multi-scale inertia control method and additional controller based on inverter grid-connected equipment

technical field

The invention belongs to the technical field of frequency stability control of power systems, and more particularly, relates to a multi-scale inertia control method and an additional controller based on converter grid-connected equipment.

Background technique

With the rapid and continuous development of power electronics technology, the penetration rate of voltage source converters in the power system is getting higher and higher, and its influence on the voltage amplitude/frequency dynamic process concerned by the power system is also increasing. In order to output constant active/reactive power, the voltage amplitude/frequency output by the grid-connected equipment of the converter will change rapidly with the change of the grid voltage amplitude/frequency, so it is difficult to provide effective inertia support for the power system. In recent years, there have been many power outages due to insufficient power grid inertia support capacity, such as the "9.28" blackout in South Australia and the "8.9" blackout in the United Kingdom. Therefore, how to improve the inertia support capacity of the power system with large-scale converter grid-connected equipment has become an important issue for the safe and stable operation of the power system.

At present, academia and industry have carried out a lot of research on the inertia control of inverter grid-connected equipment. Among them, the most widely used is the virtual synchronous machine control principle, that is, the control of the converter grid-connected equipment is designed according to the process of the synchronous generator rotor movement, so that the converter grid-connected equipment is similar to the synchronous generator with inertia support capability, but this This kind of control and method needs to upgrade and transform the control of the entire equipment, and cannot be applied to the existing grid-connected converter equipment on a large scale. Another way is to design a corresponding additional controller according to the frequency change rate of the grid to improve the inertia support capability of the inverter grid-connected equipment. However, these studies do not deeply consider the influence of the speed of the grid frequency change rate on the relationship between the active/reactive power and the amplitude/frequency of the system, so there is no more efficient grid connection equipment for the grid frequency change rate of different speeds. Inertia control method.

Due to the existence of energy storage elements with different capacities and controllers with different response times in power electronic equipment such as converters, the system dynamic process caused by them presents the characteristics of multiple time scales. In order to ensure the safe and stable operation of the power system, the power system needs to have sufficient inertia support at different time scales. Therefore, increasing and improving the multi-time-scale inertia support capability of grid-connected converter equipment is of great strategic significance for the safe and stable operation of the power system at multi-time scales.

SUMMARY OF THE INVENTION

In view of the defects of the prior art, the purpose of the present invention is to provide a multi-scale inertia control method and an additional controller based on inverter grid-connected equipment, aiming to solve the problem that the existing additional inertia control method does not consider the frequency change rate of the grid. The influence of speed on the relationship between active/reactive power and amplitude/frequency of the system leads to the problem that multi-scale inertia support cannot be provided for the power system in an efficient and coordinated manner.

In order to achieve the above purpose, the present invention provides a multi-scale inertia control method based on converter grid-connected equipment, comprising the following steps:

(1) According to the size of the energy storage element inside the converter grid-connected equipment and the response speed of the controller, the control module of the converter grid-connected equipment is divided into control modules of different time scales;

(2) filtering the q-axis components of the terminal voltage in the phase-locked coordinate system at different frequency bands to obtain different frequency band signals corresponding to the different time scale control modules;

(3) After processing the signals of different frequency bands, the control signals of the corresponding time scale control modules are obtained;

(4) By adding the control signal corresponding to the low frequency band to the active branch of the DC voltage control standard module, and adding the control signal corresponding to the high frequency band to the reactive branch of the AC current control standard module, the grid-connected equipment of the converter is realized. The multi-scale inertia control of the inverter enables grid-connected converter equipment to efficiently and coordinately respond to system frequency changes on different time scales, providing multi-scale inertia support for the system.

Further, in step (1), according to the size of the internal energy storage element and the response speed of the controller in the grid-connected converter equipment, the different time scale control modules of the grid-connected converter equipment include a DC voltage control scale module and an AC current control scale. module.

Among them, the response speed of the DC voltage control standard module is 100ms level; the response speed of the AC current control standard module is 10ms level. The DC voltage control scale corresponds to the low frequency band with a bandwidth of 10 Hz; the AC current control scale corresponds to the high frequency band with a bandwidth of 100 Hz.

Further, in step (2), the q-axis component of the terminal voltage in the phase-locked coordinate system is used to reflect the rate of change of the system frequency.

Further, in step (2), low-pass filtering and high-pass filtering are performed on the q-axis components of the terminal voltage in the phase-locked coordinate system, respectively, and low-frequency and high-frequency signals are obtained.

Further, the active branch of the grid-connected converter equipped with the DC voltage control standard module is the DC voltage control branch; the reactive power branch of the grid-connected converter equipped with the AC current control standard module is the q-axis current control branch.

The present invention also provides a multi-scale inertia additional controller for the grid-connected equipment of the converter, comprising: a filter and a signal conversion module; the filter is used for outputting and direct current voltage according to the q-axis component of the lower end voltage of the phase-locked coordinate system The low-frequency frequency change rate signal corresponding to the control scale and the high-frequency frequency change rate signal corresponding to the AC current control scale; the input end of the signal conversion module is connected to the output end of the filter, and the output end of the signal conversion module The terminal is used for connecting to the input terminal of the corresponding time scale control branch, and the signal conversion module is used for converting the frequency change rate signals of different frequency bands into additional control signals corresponding to the different time scale control modules.

Further, the signal conversion module includes: a low-frequency signal conversion unit and a high-frequency signal conversion unit; the low-frequency signal conversion unit is used to convert the low-frequency signal into a first control signal for controlling the DC voltage control scale module; the high-frequency signal The conversion unit is used for converting the high frequency band signal into a second control signal for controlling the AC current control scale module.

Preferably, the signal conversion module can be a PID controller; the PID controller includes a proportional controller, an integral controller, a differential controller and an adder; the proportional controller can fast track; the integral controller can eliminate steady-state errors, but may increase Overshoot: The differential controller can speed up the response speed of the large inertia system and reduce the tendency of overshoot. The output signal with good control effect can be obtained by adding the signals output by the proportional controller, the integral controller and the differential controller through the adder.

Further, the filter includes: a low-pass filter and a high-pass filter; the low-pass filter is used to low-pass filter the q-axis component of the terminal voltage in the phase-locked coordinate system and obtain a low-frequency signal; the high-pass filter is used to The q-axis components of the terminal voltage in the phase-locked coordinate system are subjected to high-pass filtering to obtain high-frequency signals.

Preferably, the filter may be a Butterworth filter. The frequency response curve in the passband of the Butterworth filter is as flat as possible without fluctuations, while it gradually drops to zero in the stopband, which has excellent filtering performance.

The present invention also provides a converter grid-connected equipment, which includes the above-mentioned multi-scale inertia additional controller. Compared with the prior art, the converter grid-connected equipment has added a multi-scale inertia additional controller, so that the converter grid-connected equipment can efficiently and coordinately respond to system frequency changes on different time scales, and provide multi-scale inertia support for the system. .

Preferably, the converter grid-connected equipment with different time scale control modules includes: a DC voltage control scale module and an AC current control scale module; wherein, the active power branch of the converter grid-connected equipment DC voltage control scale module is a DC voltage control branch; The reactive power branch of the converter grid-connected equipment AC current control standard module is the q-axis current control branch.

The low-frequency control signal output by the low-frequency signal conversion unit is added to the DC voltage control branch of the DC voltage control scale module, and the high-frequency control signal output by the high-frequency signal conversion unit is added to the q-axis current control branch of the AC current control scale module. .

Among them, the DC voltage control scale module is used to realize an efficient response to the slow (100ms level) system frequency change rate under the control of the first control signal, and provide inertia support for the DC voltage control scale for the system; the AC current control scale module Under the control of the second control signal, it is used to realize an efficient response to a faster (10ms level) system frequency change rate, and to provide the system with an inertia support of the AC current control scale.

Through the above technical solutions conceived by the present invention, compared with the prior art, the following beneficial effects can be achieved:

(1) The present invention utilizes the multi-time scale flexible control characteristics of the grid-connected equipment of the converter to process the low-frequency (about 10Hz) signal in the frequency change rate signal and attach it to the active power of the DC voltage control scale module of the grid-connected equipment of the converter. In the branch, the high-frequency (about 100Hz) signal in the frequency change rate signal is processed and added to the reactive branch of the AC current control standard module of the converter grid-connected equipment, which can make full use of the converter grid-connected equipment active power / The reactive power branch has different response degrees to the signals of different time scales of the system. On the basis of not changing the actual converter control, the above additional control can realize the multi-scale coordination and efficient provision of inertia of the converter grid-connected equipment.

(2) In the present invention, the q-axis component of the terminal voltage in the phase-locked coordinate system is processed by the filter and the signal conversion module to obtain a corresponding additional control signal. Since the q-axis component of the terminal voltage is 0 in the steady state, the The proposed control method neither increases the number of additional sensors nor changes the active/reactive power injected into the grid by the converter grid-connected equipment in steady state.

Description of drawings

FIG. 1 is an implementation flowchart of a multi-scale inertia control method based on converter grid-connected equipment provided by an embodiment of the present invention.

FIG. 2 is a block diagram of a control structure of a grid-connected equipment for a converter and a time scale division thereof provided by an embodiment of the present invention.

FIG. 3 is a schematic structural diagram of a multi-scale inertia additional controller based on inverter grid-connected equipment provided by an embodiment of the present invention.

In FIG. 4, (a) is a schematic diagram of a low-pass filter provided by an embodiment of the present invention, and (b) is a schematic diagram of a high-pass filter provided by an embodiment of the present invention.

5 is a schematic diagram of a PID control structure adopted by a signal conversion module in a multi-scale inertia additional controller provided by an embodiment of the present invention.

6 is a comparison diagram of the control results between the multi-scale inertia additional controller based on the inverter grid-connected equipment and the conventional additional inertia control provided by the embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The invention provides a multi-scale inertia control method and an additional controller based on converter grid-connected equipment, which solves the problem that the existing additional inertia control method does not take into account the speed of the grid frequency change rate and affects the system active/reactive power and amplitude. Therefore, additional controls are not designed for different time-scale control modules based on the speed of frequency change rate, resulting in the inability to efficiently and coordinately provide multi-scale inertia support for the power system.

In order to further illustrate the multi-scale inertia control method based on the converter grid-connected equipment provided by the embodiments of the present invention, the following is now described in detail with reference to the accompanying drawings and in conjunction with specific examples:

As shown in FIG. 1, the present invention provides a multi-scale inertia control method based on converter grid-connected equipment, comprising the following steps:

(1) According to the size of the energy storage element inside the converter grid-connected equipment and the response speed of the controller, the control module of the converter grid-connected equipment is divided into control modules of different time scales;

(2) filtering the q-axis components of the terminal voltage in the phase-locked coordinate system at different frequency bands to obtain different frequency band signals corresponding to the different time scale control modules;

(3) After processing the signals of different frequency bands, the control signals of the corresponding time scale control modules are obtained;

(4) By adding the control signal corresponding to the low frequency band to the active branch of the DC voltage control standard module, and adding the control signal corresponding to the high frequency band to the reactive branch of the AC current control standard module, the grid-connected equipment of the converter is realized. The multi-scale inertia control of the inverter enables grid-connected converter equipment to efficiently and coordinately respond to system frequency changes on different time scales, providing multi-scale inertia support for the system.

In the embodiment of the present invention, the control module of the grid-connected equipment of the converter is divided according to the size of the internal energy storage element and the response speed of the controller, as shown in FIG.

Figure 2 shows the control structure and time scale division diagram of the converter grid-connected equipment, where P _m is the input active power of the converter grid-connected equipment, e _abc is the internal potential vector, v _tabc is the terminal voltage vector, i _abc is the converter side filter inductor current vector, i _fabc is the filter capacitor current vector, i _gabc is the grid side inductor current vector, and v _gabc is the voltage vector of the three-phase ideal voltage source. T1~T6 are switch tubes of each bridge arm of the converter. C _dc is the DC bus capacitor, V _dc is the DC bus capacitor voltage, L ₁ is the filter inductance, C _f is the filter capacitor, R _c is the damping resistance, and L _g is the grid equivalent inductance. Variables in a phase-locked coordinate system are denoted by the superscript 'p'. The subscripts 'd' and 'q' represent the components of the 'd' axis and the 'q' axis in the phase-locked coordinate system, respectively; the subscripts 'α' and 'β' represent the 'α' axis and 'β' axis component; subscript 'ref' indicates command value. Vectors are in bold italics and scalars are in italics. The inverter grid-connected equipment contains energy storage elements of different carrier forms and different capacities, such as DC bus capacitors and AC inductors. In order to ensure that the state of each energy storage element operates in a safe and stable range, controllers with different response speeds, such as a DC voltage controller (~100ms) and an AC current controller (~10ms), are designed in the grid-connected equipment of the converter. When the grid-connected equipment of the converter is disturbed, since the energy storage capacity of the AC inductor is smaller than that of the DC capacitor, after about 10ms, its state quantity (AC current) will change and drive the current controller to act; when the disturbance continues When the time is further extended to about 100ms, the DC capacitance state quantity (DC voltage) changes and drives the DC voltage controller to act. Therefore, according to the size of the internal energy storage element and the response speed of the controller, the time scale of the inverter grid-connected equipment control module includes: DC voltage control time scale (100ms level), AC current control time scale (10ms level); among them, The control module 100 corresponding to the DC voltage control time scale mainly includes terminal voltage control and DC voltage control; the control module 200 corresponding to the AC current control time scale mainly includes a current control unit, as shown by the dotted line frame and the single-dot-chain line frame in FIG. 2 , respectively. Show. The structure of the phase-locked loop 201 is shown in the double-dot chain line frame in FIG. 2 , and is used to track the position of the terminal voltage in real time.

FIG. 3 is a schematic structural diagram of a multi-scale inertia additional controller based on converter grid-connected equipment provided by an embodiment of the present invention, including: a filter and a signal conversion module; The component outputs the low frequency frequency change rate signal corresponding to the DC voltage control scale and the high frequency frequency change rate signal corresponding to the AC current control scale; the input end of the signal conversion module is connected to the output end of the filter, and the output end of the signal conversion module It is used to connect to the input end of the corresponding time scale control branch, and the signal conversion module is used to convert the frequency change rate signals of different frequency bands into additional control signals corresponding to the different time scale control modules.

In the embodiment of the present invention, the filter includes: a low-pass filter and a high-pass filter, the low-pass filter is used to receive the q-axis component of the lower end voltage of the phase-locked coordinate system, and output the low-frequency frequency change rate corresponding to the DC voltage control scale signal, and output the additional control signal of low frequency band through the low frequency band signal conversion unit. The high-pass filter is used to receive the q-axis component of the voltage at the lower end of the phase-locked coordinate system, and output the high-frequency frequency change rate signal corresponding to the AC current control scale, and output the high-frequency additional control signal through the high-frequency signal conversion unit.

There are various implementation schemes for low-pass filter and high-pass filter. In this embodiment, a commonly used Butterworth filter can be selected. As shown in Figure 4, the frequency response curve in the passband is as flat as possible without fluctuations. In the stop band, it gradually drops to zero, which is mainly used to obtain the low-frequency and high-frequency signal components in the frequency change rate signal. The Butterworth low-pass filter and high-pass filter can be represented by the transfer function in Figure 4. The frequency response curve of the low-pass filter is maximally flat in the passband below the cutoff frequency, while the stopband above the cutoff frequency is gradually drops to zero; the frequency response curve of a high-pass filter is maximally flat in the passband above the cutoff frequency, and gradually drops to zero in the stopband below the cutoff frequency.

In the embodiment of the present invention, the signal conversion module includes a low-frequency signal conversion unit and a high-frequency signal conversion unit, wherein the low-frequency signal conversion unit is used to convert the low-frequency signal into a first control signal for controlling the DC voltage control scale module; The frequency band signal converting unit is used for converting the high frequency band signal into a second control signal for controlling the AC current control scale module.

Among them, the low-frequency signal conversion unit and the high-frequency signal conversion unit are implemented in the same manner, and there are various control schemes to choose from. In this embodiment, a commonly used PID controller is selected as an example for illustration, as shown in FIG. 5 . The frequency change rate information of different frequency bands is output through the PID controller, including proportional controller, integral controller, differential controller and adder; the proportional controller can fast track; the integral controller can eliminate the steady-state error, but may increase the overshoot ; The differential controller can speed up the response speed of the large inertia system and reduce the tendency of overshoot. The output signal is obtained by adding the signals output by the proportional controller, the integral controller and the differential controller through the adder.

In the present invention, the low frequency (about 10Hz) components in the frequency change rate signal are used to control the active branch of the DC voltage control scale module, and the high frequency (about 100Hz) components in the frequency change rate signal are used to control the AC current control scale module The theoretical reasons for the reactive branch are as follows:

The three-phase inductor excitation-response relationship is as follows:

为同步旋转坐标系下流过电感的电流响应，E为电压激励的幅值，θ_e为电压激励的相位，ω_e为电压激励的频率。where e _αβ and i _αβ are the voltage excitation on the inductor and the current response flowing through the inductor in the static coordinate system, respectively, L is the inductance value,

is the current response flowing through the inductor in the synchronous rotating coordinate system, E is the amplitude of the voltage excitation, θ _e is the phase of the voltage excitation, and ω _e is the frequency of the voltage excitation.

After differentiating and sorting (1), the following expression can be obtained:

After linearizing and arranging (2), the following expression can be obtained:

和

为稳态时同步旋转坐标系下流过电感的电流响应。where the prefix Δ represents the small deviation, s is the differential operator, E ₀ and ω ₀ are the amplitude and frequency of the voltage excitation at steady state,

and

is the current response flowing through the inductor in a synchronous rotating frame at steady state.

From the expressions (2) and (3), it can be obtained that in the steady state, there is only reactive current but no active current in the inductor. In the dynamic process, both active current and reactive current exist in the inductor. In addition, the influence laws of different amplitude/frequency change rate on the active/reactive current on the inductor are different. When the amplitude and frequency change rate is slow, LsΔE and LsΔω _e are much smaller than ω ₀ LΔE and ω ₀ LΔω _e , which means that the change of amplitude is more likely to affect the reactive current on the inductor, while the change of frequency is more likely to affect Active current on the inductor. When the rate of change of amplitude and frequency is fast, LsΔE and LsΔω _e are much larger than ω ₀ LΔE and ω ₀ LΔω _e , which means that the change of amplitude is more likely to affect the active current on the inductor, while the change of frequency is more likely to affect Reactive current on the inductor.

This means that the DC voltage control scale active branch in the converter grid-connected equipment is more likely to respond to the slower component of the frequency change rate, while the AC current control time scale reactive branch is more likely to respond to the faster frequency change component. . Therefore, the present invention can make full use of the different response degrees of the active/reactive branches of the converter grid-connected equipment to signals of different time scales in the system, and realize the converter grid-connected equipment with the above additional control on the basis of not changing the actual converter control. Scale coordination efficiently provides inertia.

FIG. 6 is a comparison diagram of control results between the multi-scale inertia additional controller provided by the embodiment of the present invention and the existing additional inertia controller. The simulation scenario is that a single converter connected to the grid is connected to an infinite system, and the system is connected to an additional load at 3s. Under the same disturbance, when the multi-scale inertia is attached to the controller, the fluctuation range of the system frequency on both short time scale and long time scale is smaller, and the fluctuation speed is slower. The system inertia on short time scale and long time scale is significantly higher than the existing Additional inertia control.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (8)

1. a multi-scale inertia control method based on converter grid-connected equipment, is characterized in that, comprises the following steps: (1) According to the size of the internal energy storage element of the converter grid-connected equipment and the response speed of the controller, the control module of the converter grid-connected equipment is divided into control modules of different time scales; (2) Filtering the q-axis components of the terminal voltage in the phase-locked coordinate system in different frequency bands to obtain signals in different frequency bands corresponding to the different time scale control modules; (3) After processing the signals of different frequency bands, the control signal of the corresponding time scale control module is obtained; (4) By adding the control signal corresponding to the low frequency band to the active branch of the DC voltage control standard module, and adding the control signal corresponding to the high frequency band to the reactive branch of the AC current control standard module, the converter grid-connected equipment is realized. The multi-scale inertia control enables the grid-connected equipment of the converter to efficiently and coordinately respond to system frequency changes on different time scales, providing multi-scale inertia support for the system; In step (1), the control module of the grid-connected equipment of the converter is divided into a DC voltage control scale module and an AC current control scale module; the response speed of the DC voltage control scale is 100ms, and the AC current control scale The response speed of the scale is 10ms level. 2 . The multi-scale inertia control method according to claim 1 , wherein, in step (2), the q-axis component of the terminal voltage in the phase-locked coordinate system is used to reflect the rate of change of the system frequency. 3 . 3 . The multi-scale inertia control method according to claim 2 , wherein in step (2), the q-axis components of the terminal voltage in the phase-locked coordinate system are respectively subjected to low-pass filtering and high-pass filtering, and a low-pass filter is obtained. 4 . band signal and high band signal. 4. The multi-scale inertia control method according to any one of claims 1-3, wherein the active branch of the grid-connected converter equipped with a DC voltage control scale module is a DC voltage control branch; the conversion The reactive power branch of the grid-connected AC current control standard module is the q-axis current control branch. 5. A multi-scale inertia additional controller for converter grid-connected equipment, characterized in that, comprising: a filter and a signal conversion module; The filter is used to output a low-frequency frequency change rate signal corresponding to the DC voltage control scale and a high-frequency frequency change rate signal corresponding to the AC current control scale according to the q-axis component of the lower end voltage of the phase-locked coordinate system; The input end of the signal conversion module is connected to the output end of the filter, the output end of the signal conversion module is used to connect to the input end of the corresponding time scale control branch, and the signal conversion module is used to convert different frequency bands. The frequency change rate signal is converted into additional control signals corresponding to different time scale control modules; The signal conversion module includes: a low-frequency signal conversion unit and a high-frequency signal conversion unit; The low-frequency signal conversion unit is configured to convert the low-frequency signal into a first control signal that is attached to the active branch of the DC voltage control scale module and controls the DC voltage control scale module; The high-frequency signal conversion unit is used for converting the high-frequency signal into a second control signal that is attached to the reactive power branch of the AC current control scale module and controls the AC current control scale module. 6. The multi-scale inertia additional controller according to claim 5, wherein the filter comprises: a low-pass filter and a high-pass filter; The low-pass filter is used to low-pass filter the q-axis component of the terminal voltage in the phase-locked coordinate system and obtain a low-frequency signal; The high-pass filter is used for high-pass filtering the q-axis component of the terminal voltage in the phase-locked coordinate system to obtain a high-frequency signal. 7. A converter grid-connected equipment, characterized by comprising the multi-scale inertia additional controller according to claim 5 or 6. 8. The converter grid-connected device according to claim 7, wherein the converter grid-connected device further comprises: a DC voltage control standard module and an AC current control standard module; The DC voltage control scale module is used to realize an efficient response to a slower system frequency change rate under the control of the first control signal, and provide inertia support for the DC voltage control scale for the system; The AC current control scale module is used to realize an efficient response to a faster system frequency change rate under the control of the second control signal, and provide inertia support for the AC current control scale for the system.

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