CN107332282B - Micro-grid pre-synchronization grid-connected control system and control method thereof - Google Patents

Abstract

A micro-grid pre-synchronization grid-connected control system comprises a frequency adjusting module, an SPLL phase-locked loop module, a voltage adjusting module, a phase generating module, a phase adjusting module and a PWM signal generator module; the presynchronization control method mainly comprises the steps of recording the working state in the grid-connected operation stage, controlling the mode in a proportional-integral mode during mode switching, adjusting the phase based on linear gradual approximation, and completing the adjustment of the voltage amplitude, the frequency and the phase of the microgrid; the advantages are that the stability of power supply quality is improved; realizing rapid error-free control; the speed of the phase ramp-up can be adjusted.

Description

A micro-grid pre-synchronization grid-connected control system and its control method

(1) Technical field:

The invention relates to the field of microgrids or distributed power generation systems, in particular to a microgrid pre-synchronization grid-connected control system and a working method thereof.

(two) background technology:

Distributed power generation technology has developed rapidly in recent years, because of its low pollution, high energy utilization rate, flexible application and other characteristics, it has attracted more and more attention. Distributed power generation is connected to the main power grid in the form of a micro-grid, combining various distributed power sources, energy storage units, power loads, management and control systems, etc. It will play an increasingly important role in the smart grid system. However, it is precisely because the idea of distributed generation is gradually ingrained in the power system that the impact of distributed generation on the system cannot be ignored.

The ability to operate in both grid-connected and islanded states is the key for the microgrid to give full play to its advantages. Stable operation in dual modes, especially the smooth switching between the two modes, is the key to ensuring that the microgrid can operate in both grid-connected and islanded states. One of the primary techniques for a smooth transition between modes. If smooth switching cannot be achieved, it may seriously affect the power supply quality of both the microgrid and the main grid.

Regarding the control strategy in the switching process of the working mode, it is difficult to achieve good results simply by using a certain control strategy. Therefore, some new control strategies or control techniques must be applied in the actual process. At present, the research on this part of the working process has achieved a lot of results, but most of the work is still in the experimental research stage, especially the phase synchronization problem before grid connection has not been well resolved.

(3) Contents of the invention:

The object of the present invention is to provide a microgrid pre-synchronization grid-connected control system and its working method, which can overcome the deficiencies of the prior art, and is a pre-synchronization control and its working method with simple structure, easy implementation and strong operability.

The technical solution of the present invention: a micro-grid pre-synchronization grid-connected control system, including the main power grid, is characterized in that it includes a frequency adjustment module, an SPLL (Software Phase-Locked Loop—software phase-locked loop) phase-locked loop module, a voltage An adjustment module, a phase generation module, a phase adjustment module, and a PWM (Pulse Width Modulation——pulse width modulation) signal generator module; wherein, the input end of the frequency adjustment module is connected to the main power grid, and the active power at the grid-connected point of the microgrid is collected The reference value signal of the active power of the power and control system, its output terminal is connected with the input terminal of the phase generation module; the input terminal of the voltage regulation module is connected with the main power grid, and the reactive power and control system The reference value signal of reactive power, its output end is connected with the input end of PWM signal generator module; The input end of described SPLL phase-locked loop module is connected with main grid, collects the voltage signal, frequency signal and phase signal of main grid , its output end is respectively connected to the input end of phase generation module, phase adjustment module and PWM signal generator module; The output end of described phase generation module is respectively connected to the input end of phase adjustment module and PWM signal generator module; Described phase adjustment The output end of the module is connected to the input end of the PWM signal generator module; the output end of the PWM signal generator module outputs a PWM signal to control the on-off of the power electronic switch at the grid-connected place.

The frequency adjustment module is composed of a proportional amplifier I, an integral regulator I, a control switch K1 and two accumulators; the one accumulator is a reference to the input signal of the frequency adjustment module, that is, the active power and the active power of the control system. The input terminal of the proportional amplifier receives the superimposed signal, and its output terminal outputs an amplified signal to an input terminal of another accumulator; the input terminal of the integral regulator receives the active power and controls the active power through the control switch K1 The superposition signal of the reference value signal of the active power of the system, its output end is connected to the second input end of another accumulator; The output end of the second accumulator is connected with the input end of the phase generation module and the PWM signal generator module connect.

The voltage regulation module is composed of a proportional amplifier II, an integral regulator II, a control switch K2 and two accumulators; the one accumulator converts the input signal of the frequency regulation module, that is, the reactive power and the reactive power of the control system The reference value signal is superimposed; the input terminal of the proportional amplifier II receives the superimposed signal, and its output terminal outputs an amplified signal to an input terminal of another accumulator; the input terminal of the integral regulator II is received by the control switch K2 The superposition signal of reactive power and the reference value signal of reactive power of the control system, its output terminal is connected to the second input terminal of another accumulator; the output terminal of the second accumulator is connected with the phase generation module and the PWM signal Input connection of the generator block.

The phase adjustment module is composed of a linear gradual approximation phase unit, a phase limiting unit, a control switch K3 and 2 accumulators; the two input ends of the accumulator collect the phase output signal of the phase generation module through the control switch respectively and the main grid phase signal collected by the SPLL phase-locked loop module, its output terminal is connected with the input terminal of the linear gradual approximation phase unit; the two input terminals of the second accumulator receive the phase output signal and the phase generation module of the second accumulator respectively The output signal of the linear gradual approximation phase unit is connected to the input terminal of the phase limiting unit; the output terminal of the phase limiting unit is connected to the input terminal of the PWM signal generator module.

The linear gradual approximation phase unit is a step signal generator.

A pre-synchronization control method for a micro-grid pre-synchronization grid-connected control system, characterized in that it comprises the following steps:

(1) During the grid-connected operation stage, the microgrid works in droop control mode. At this stage, the SPLL phase-locked loop module is used to collect the frequency, phase and voltage amplitude signals of the main grid at any time, and the micro-grid pre-synchronization grid-connected control system judges the current working status. If the working status at this time meets the grid-connected stable work If required, save the current voltage, frequency and phase;

(2) When the "grid-connected-island" mode switching occurs, the microgrid no longer collects the voltage, frequency, and phase of the main grid, but uses the previously saved values as the reference value of the microgrid in the island operation mode; At the same time, the droop control strategy is changed. On the basis of P-f and Q-V control, an integral link is added to reduce the deviation between the frequency and voltage in the microgrid and the reference value, so as to realize the power supply quality of the microgrid within a small range. fluctuation;

(3) K1 and K2 are control switches. When the mode switch of "grid-connected to island" occurs, the control signal of the mode switch controls K1 and K2 to close, and the integral link is connected to the control system, so that the original proportional control The method is changed to the proportional-integral control method, namely:

In the formula, f and U are frequency and voltage in droop control respectively, P and Q are system output active power and reactive power, f ₀ , U ₀ , P ₀ , Q ₀ are corresponding control reference values, m and n are respectively is the droop coefficient, m=K _pf , n=K _pu , using the integral control to eliminate the static error of the system, keep the frequency and amplitude of the microgrid as much as possible in the grid-connected state, or in a small fluctuation Improve the stability of the power supply quality of the microgrid system within the range;

(4) Through steps (1)-(3) by the frequency adjustment module and the voltage adjustment module, obtain the frequency signal and the voltage amplitude signal after the mediation, these two signals are respectively combined with the main signal collected by the SPLL phase-locked loop module The grid frequency signal and the voltage amplitude signal are superimposed to generate the frequency signal f ₁ required by the phase generation module and the voltage amplitude signal U ₁ required by the PWM signal generator module;

(5) Convert the frequency signal f obtained in step (4) into _a phase signal θ by the phase generation module, and give the phase adjustment module as an input signal;

(6) The phase adjustment module closes the switch K3 by the grid-connected control signal before the grid-connection, and collects and saves the phase θ and θ ₀ of the micro-grid and the main grid at the same time when closing K3, calculates the phase difference, and converts the obtained in step (5) The phase signal θ and the main grid phase signal θ ₀ collected by the SPLL phase-locked loop module are adjusted according to the following relationship;

θ ₂ ＝θ+kt(θ ₀ -θ)

kt is a linear function of the time series, k is the time coefficient;

(7) Limit θ ₂ between θ and θ ₀ to get θ ₃ , which is the output value of the linear gradual approximation correction algorithm; the key to the linear gradual approximation phase correction algorithm is to use the time series linear function kt to combine the microgrid and The phase difference between the main power grids is converted into a function that gradually increases with time. By adjusting the time coefficient k, the purpose of adjusting the speed of the phase approach can be achieved; there is this θ ₃ and θ superposition to generate the phase required by the PWM signal generator module signal θ ₁ ;

(8) Combine the obtained voltage amplitude signal U ₁ , frequency signal f ₁ , and phase signal θ ₁ to jointly control the PWM signal generator module to complete the adjustment of the microgrid voltage amplitude, frequency, and phase.

In described step (5), be converted into phase signal θ by frequency signal f ₁ , be made of following steps:

① Multiply the frequency signal f ₁ by 2π to obtain the angular frequency ω ₁ ;

② The angular frequency ω ₁ is transformed into a phase signal θ through an integral link.

The advantages of the present invention: the addition of the integral link improves the stability when the microgrid grid-connected mode and the island mode are switched to each other; the integral control can eliminate the static error of the system, and keep the frequency and amplitude of the microgrid as close as possible Same as in the grid-connected state, or within a small fluctuation range, improve the stability of the power supply quality of the micro-grid system; by adding a phase feed-forward compensation link, realize fast and seamless control of the phase between the micro-grid and the main grid; linear The key of the gradually approaching phase correction algorithm is to use the time series linear function to adjust the speed of the gradually approaching phase by adjusting the time coefficient k.

(4) Description of drawings:

Fig. 1 is a block diagram of the overall structure of a micro-grid pre-synchronization grid-connected control system according to the present invention.

Fig. 2 is a structural block diagram of a frequency regulation module and a voltage regulation module in a microgrid pre-synchronization grid-connected control system according to the present invention.

Fig. 3 is a structural block diagram of a phase adjustment module in a micro-grid pre-synchronization grid-connected control system according to the present invention.

FIG. 4 is a schematic diagram of a control flow of a pre-synchronization control method of a microgrid pre-synchronization grid-connected control system according to the present invention.

Fig. 5 is a schematic flowchart of frequency adjustment and voltage adjustment in a pre-synchronization control method of a microgrid pre-synchronization grid-connected control system according to the present invention.

FIG. 6 is a schematic flowchart of phase adjustment in a pre-synchronization control method of a microgrid pre-synchronization grid-connected control system according to the present invention.

(5) Specific implementation methods:

Embodiment: a kind of micro-grid pre-synchronization grid-connected control system (see Fig. 1), comprises main grid, is characterized in that it comprises frequency adjustment module, SPLL phase-locked loop module, voltage adjustment module, phase generation module, phase adjustment module and PWM signal generator module; wherein, the input end of described frequency regulation module is connected with main power grid, collects the reference value signal of the active power of grid-connected point place of micro-grid and the active power of control system, and its output end and the input of phase generation module terminal connection; the input terminal of the voltage regulation module is connected with the main grid, and the reference value signal of the reactive power at the grid-connected point of the microgrid and the control system is collected, and its output terminal is connected with the input terminal of the PWM signal generator module Connect; the input end of the SPLL phase-locked loop module is connected to the main grid, and the voltage signal, frequency signal and phase signal of the main grid are collected, and its output end is respectively connected to the input of the phase generation module, the phase adjustment module and the PWM signal generator module end; the output end of the phase generation module is connected to the input end of the phase adjustment module and the PWM signal generator module respectively; the output end of the phase adjustment module is connected to the input end of the PWM signal generator module; the PWM signal generator module The output end of the output terminal outputs a PWM signal to control the on-off of the power electronic switch at the grid-connected place.

Described frequency adjustment module (seeing Fig. 2) is made of proportional amplifier I, integral regulator I, control switch K1 and 2 accumulators; The reference value signal of the active power is superimposed; the input terminal of the proportional amplifier receives the superimposed signal, and its output terminal outputs an amplified signal to an input terminal of another accumulator; the input terminal of the integral regulator controls the switch K1 Receive the active power and the superposition signal of the active power reference value signal of the control system, and its output end is connected to the second input end of another accumulator; the output end of the second accumulator is connected with the phase generation module and the PWM signal to generate The input terminal connection of the converter module.

Described voltage regulation module (see Fig. 2) is made up of proportional amplifier II, integral regulator II, control switch K2 and 2 accumulators; Described one accumulator is the input signal of frequency regulation module, namely reactive power and control The reference value signal of the reactive power of the system is superimposed; the input terminal of the proportional amplifier II receives the superimposed signal, and its output terminal outputs an amplified signal to an input terminal of another accumulator; the input terminal of the integral regulator II The superposition signal of the reference value signal of reactive power and reactive power of the control system is received by controlling the switch K2, and its output terminal is connected to the second input terminal of another accumulator; the output terminal of the second accumulator is connected with the phase The input terminals of the generation module and the PWM signal generator module are connected.

Described phase adjustment module (seeing Fig. 3) is made up of linear gradual approximation phase unit, phase limiting unit, control switch K3 and 2 accumulators; The phase output signal of the generation module and the main grid phase signal collected by the SPLL phase-locked loop module, its output terminal is connected to the input terminal of the linear gradual approximation phase unit; the two input terminals of the second accumulator respectively receive the phase generation The phase output signal of the module and the output signal of the linear gradual approximation phase unit are connected with the input terminal of the phase limiting unit; the output terminal of the phase limiting unit is connected with the input terminal of the PWM signal generator module.

The linear gradual approximation phase unit is a step signal generator.

A pre-synchronization control method for a micro-grid pre-synchronization grid-connected control system, characterized in that it comprises the following steps:

(1) During the grid-connected operation stage, the microgrid works in droop control mode. At this stage, the SPLL phase-locked loop module is used to collect the frequency, phase and voltage amplitude signals of the main grid at any time, and the micro-grid pre-synchronization grid-connected control system judges the current working status. If the working status at this time meets the grid-connected stable work requirements, save the current voltage, frequency, phase (see Figure 4);

(2) When the "grid-connected-island" mode switching occurs, the microgrid no longer collects the voltage, frequency, and phase of the main grid, but uses the previously saved values as the reference value of the microgrid in the island operation mode; At the same time, the droop control strategy is changed. On the basis of P-f and Q-V control, an integral link is added to reduce the deviation between the frequency and voltage in the microgrid and the reference value, so as to realize the power supply quality of the microgrid within a small range. fluctuation;

(3) K1 and K2 are control switches. When the mode switch of "grid-connected to island" occurs, the control signal of the mode switch controls K1 and K2 to close, and the integral link is connected to the control system, so that the original proportional control The method is changed to the proportional-integral control method, namely:

In the formula, f and U are frequency and voltage in droop control respectively, P and Q are system output active power and reactive power, f ₀ , U ₀ , P ₀ , Q ₀ are corresponding control reference values, m and n are respectively is the droop coefficient, m=K _pf , n=K _pu , using the integral control to eliminate the static error of the system, keep the frequency and amplitude of the microgrid as much as possible in the grid-connected state, or in a small fluctuation Within the range, improve the stability of the power supply quality of the microgrid system (see Figure 4, Figure 5);

(4) Through steps (1)-(3) by the frequency adjustment module and the voltage adjustment module, obtain the frequency signal and the voltage amplitude signal after the mediation, these two signals are respectively combined with the main signal collected by the SPLL phase-locked loop module The power grid frequency signal and the voltage amplitude signal are superimposed to generate the frequency signal _f1 required by the phase generation module and the voltage amplitude signal _U1 required by the PWM signal generator module (see Fig. 4 and Fig. 5);

(5) Convert the frequency signal f obtained in step (4) into _a phase signal θ by the phase generation module, and give the phase adjustment module (seeing Fig. 4 and Fig. 5) as an input signal;

(6) The phase adjustment module closes the switch K3 by the grid-connected control signal before the grid-connection, and collects and saves the phase θ and θ ₀ of the micro-grid and the main grid at the same time when closing K3, calculates the phase difference, and converts the obtained in step (5) Phase signal θ is adjusted according to the following relationship with the main grid phase signal θ ₀ that the SPLL phase-locked loop module gathers (seeing Fig. 4, Fig. 6);

θ ₂ ＝θ+kt(θ ₀ -θ)

kt is a linear function of the time series, k is the time coefficient;

(7) Limit θ ₂ between θ and θ ₀ to get θ ₃ , which is the output value of the linear gradual approximation correction algorithm; the key to the linear gradual approximation phase correction algorithm is to use the time series linear function kt to combine the microgrid and The phase difference between the main power grids is converted into a function that gradually increases with time. By adjusting the time coefficient k, the purpose of adjusting the speed of the phase approach can be achieved; there is this θ ₃ and θ superposition to generate the phase required by the PWM signal generator module Signal θ ₁ (see Fig. 4, Fig. 6);

(8) Combine the obtained voltage amplitude signal U ₁ , frequency signal f ₁ , and phase signal θ ₁ to jointly control the PWM signal generator module to complete the adjustment of the microgrid voltage amplitude, frequency, and phase (see Figure 4).

In described step (5), be converted into phase signal θ by frequency signal f ₁ , be made of following steps (see Fig. 4):

① Multiply the frequency signal f ₁ by 2π to obtain the angular frequency ω ₁ ;

② The angular frequency ω ₁ is transformed into a phase signal θ through an integral link.

Claims (4)

1. A micro-grid pre-synchronization grid-connected control system, comprising a main grid, is characterized in that it includes a frequency adjustment module, an SPLL phase-locked loop module, a voltage adjustment module, a phase generation module, a phase adjustment module and a PWM signal generator module; Wherein, the SPLL phase-locked loop module is connected with the main grid for collecting the voltage signal, phase signal and frequency signal of the main grid; the input terminal of the frequency adjustment module is connected with the main grid for collecting the active power The reference value signal of the active power of the power and control system, the output signal of the output terminal and the frequency signal output by the output terminal of the SPLL phase-locked loop module are superimposed by the accumulator I and sent to the input terminal of the phase generation module and the PWM signal is generated The input terminal of the voltage regulator module; the input terminal of the voltage regulation module is connected to the main grid, and the reference value signal of the reactive power at the grid-connected point of the micro-grid and the reactive power of the control system is collected, and the output signal of the output terminal is phase-locked with the SPLL The voltage signal output by the output terminal of the ring module is sent to the input terminal of the PWM signal generator module after being superimposed by the accumulator II; the output terminal of the phase generation module is connected to the phase adjustment module; the input terminals of the phase adjustment module are respectively It is connected with the output end of the phase generation module and the output end of the SPLL phase-locked loop module, and its output end is connected with the input end of the PWM signal generator module; the output end of the PWM signal generator module outputs a PWM signal to control the grid-connected power electronics switch on and off; The frequency adjustment module is composed of a proportional amplifier I, an integral regulator I, a control switch K1, an accumulator III and an accumulator IV; The reference value signal of the power is superimposed; the input terminal of the proportional amplifier receives the superimposed signal, and its output terminal outputs an amplified signal to an input terminal of the accumulator IV; the input terminal of the integral regulator receives active power through the control switch K1 And the superposition signal of the reference value signal of the active power of control system, its output end connects the second input end of accumulator IV; The output end of described accumulator IV is connected with the input end of phase generation module and PWM signal generator module ;When the mode switching of "grid-connected to island" occurs, the control switch K1 is closed; The voltage regulation module is composed of a proportional amplifier II, an integral regulator II, a control switch K2, an accumulator V and an accumulator VI; the accumulator V converts the input signal of the frequency regulation module, that is, reactive power and control system The reference value signal of reactive power is superimposed; the input terminal of the proportional amplifier II receives the superimposed signal, and its output terminal outputs an amplified signal to an input terminal of the accumulator VI; the input terminal of the integral regulator II passes through the control switch K2 receives the superposition signal of reactive power and the reference value signal of the reactive power of the control system, and its output end is connected to the second input end of the accumulator VI; the output end of the accumulator VI is connected to the phase generation module and the PWM signal to generate The input terminal of the switch module is connected; when the mode switching of "grid-connected to island" occurs, the control switch K2 is closed; The phase adjustment module is composed of a linear gradual approximation phase unit, a phase limiting unit, a control switch K3, an accumulator VII and an accumulator VIII; The main grid phase signal collected by the phase output signal and the SPLL phase-locked loop module, its output terminal is connected with the input terminal of the linear gradual approximation phase unit; the two input terminals of the accumulator VIII respectively receive the phase output signal of the phase generation module and the output signal of the linear gradually approaching phase unit, its output terminal is connected with the input terminal of the phase limiting unit; the output terminal of the phase limiting unit is connected with the input terminal of the PWM signal generator module; when grid-connected, the The control switch K3 is closed. 2. A micro-grid pre-synchronization grid-connected control system according to claim 1, characterized in that the linear gradual approximation phase unit is a step signal generator. 3. A pre-synchronization control method applied to the micro-grid pre-synchronization grid-connected control system according to claim 1, characterized in that it comprises the following steps: (1) In the grid-connected operation stage, the microgrid works in the droop control mode; at this stage, the frequency, phase and voltage amplitude signals of the main grid are collected at any time by using the SPLL phase-locked loop module, and the microgrid is pre-synchronized and grid-connected The control system judges the current working state, if the working state meets the requirements of grid-connected and stable work at this time, then save the current voltage, frequency and phase; (2) When the "grid-connected-island" mode switching occurs, the microgrid no longer collects the voltage, frequency, and phase of the main grid, but uses the previously saved values as the reference value of the microgrid in the island operation mode; At the same time, the droop control strategy is changed. On the basis of P-f and Q-V control, an integral link is added to reduce the deviation between the frequency and voltage in the microgrid and the reference value, so as to realize the power supply quality of the microgrid within a small range. fluctuation; (3) K1 and K2 are control switches. When the mode switch of "grid-connected to island" occurs, the control signal of the mode switch controls K1 and K2 to close, and the integral link is connected to the control system, so that the original proportional control The method is changed to the proportional-integral control method, namely:

In the formula, f and U are frequency and voltage in droop control respectively, P and Q are system output active power and reactive power, f ₀ , U ₀ , P ₀ , Q ₀ are corresponding control reference values, m and n are respectively is the droop coefficient, m=K _pf , n=K _pu , using the integral control to eliminate the static error of the system, keep the frequency and amplitude of the microgrid as much as possible in the grid-connected state, or in a small fluctuation Improve the stability of the power supply quality of the microgrid system within the range; (4) Through steps (1)-(3) by the frequency adjustment module and the voltage adjustment module, obtain the frequency signal and the voltage amplitude signal after the mediation, these two signals are respectively combined with the main signal collected by the SPLL phase-locked loop module The grid frequency signal and the voltage amplitude signal are superimposed to generate the frequency signal f ₁ required by the phase generation module and the voltage amplitude signal U ₁ required by the PWM signal generator module; (5) Convert the frequency signal f obtained in step (4) into _a phase signal θ by the phase generation module, and give the phase adjustment module as an input signal; (6) The phase adjustment module closes the switch K3 by the grid-connected control signal before the grid-connection, and collects and saves the phase θ and θ ₀ of the micro-grid and the main grid at the same time when closing K3, calculates the phase difference, and converts the obtained in step (5) The phase signal θ and the main grid phase signal θ ₀ collected by the SPLL phase-locked loop module are adjusted according to the following relationship; θ ₂ ＝θ+kt(θ ₀ -θ) kt is a linear function of the time series, k is the time coefficient; (7) Limit θ ₂ between θ and θ ₀ to get θ ₃ , which is the output value of the linear gradual approximation correction algorithm; the key to the linear gradual approximation phase correction algorithm is to use the time series linear function kt to combine the microgrid and The phase difference between the main power grids is converted into a function that gradually increases with time. By adjusting the time coefficient k, the purpose of adjusting the speed of the phase approach can be achieved; there is this θ ₃ and θ superposition to generate the phase required by the PWM signal generator module signal θ ₁ ; (8) Combine the obtained voltage amplitude signal U ₁ , frequency signal f ₁ , and phase signal θ ₁ to jointly control the PWM signal generator module to complete the adjustment of the microgrid voltage amplitude, frequency, and phase. 4. according to the pre-synchronization control method of a kind of microgrid pre-synchronization grid-connected control system according to claim 3, it is characterized in that in described step (5) by frequency signal f ₁ is converted into phase signal θ, is made of following steps : ① Multiply the frequency signal f ₁ by 2Π to obtain the angular frequency ω ₁ ; ② The angular frequency ω ₁ is transformed into a phase signal θ through an integral link.

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