CN116545018A - Self-synchronization voltage source grid-connected stability improving method based on current control loop reshaping - Google Patents

Abstract

The invention discloses a self-synchronization voltage source grid-connected stability improving method based on current control loop reshaping, and belongs to the technical field of grid-connected inverter control. The method comprises the following steps: measuring the port voltage and the output current of the grid-connected inverter and calculating and outputting active power and reactive power; respectively obtaining the amplitude value and the phase angle reference of the port voltage to generate a port voltage reference value; then, taking the port voltage as a feedback value of the voltage regulator; the port voltage reference value is then subtracted from the feedback value as an input to the voltage regulator. The voltage regulator outputs a current reference value, the sum of the output current and the output value of the current control loop reshaping branch is subtracted, the current reference value is input into the current regulator, finally, the output value of the current regulator is added with the feedforward quantity of the grid voltage to obtain a modulation signal, and the modulation signal is used for generating a driving signal through SVPWM so as to control the inverter. The method of the invention improves the stable operation capability of the self-synchronous voltage source under the strong network working condition on the premise of not increasing the hardware cost.

Description

Method for improving grid-connected stability of self-synchronized voltage source based on current control loop reshaping

technical field

The invention relates to the technical field of grid-connected inverter control, in particular to a method for improving the grid-connected stability of a self-synchronized voltage source based on current control loop reshaping.

Background technique

The current source grid-connected inverter belongs to the grid-connected inverter, which has the advantages of fast power regulation and high utilization rate of renewable energy, but it generally takes maximizing active power output as its main operating goal, and cannot generate synchronously as traditional The machine supports the grid voltage and frequency stability. With the continuous improvement of the penetration rate of new energy power generation, the power grid is gradually changing from a strong grid to a weak grid. In order to enhance the adaptability of grid-connected inverters under complex working conditions, grid-connected inverters have emerged as the times require.

The self-synchronizing voltage source belongs to the grid-constructed inverter, which has the potential to simulate the damping and inertia of the traditional synchronous generator. Although it can provide frequency and voltage support for the grid, the self-synchronizing voltage source generally adopts a voltage and current double inner loop control structure. , there is a risk of oscillation in the case of a strong network, and the existing virtual impedance method relies on differential operations. In order to avoid the influence of high-frequency noise, it is necessary to introduce a low-pass filter. The hysteresis of the low-pass filter will make the self-synchronizing voltage source The dynamic characteristics deteriorate.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention provides a self-synchronizing voltage source grid-connected stability improvement method based on current control loop reshaping, the purpose of which is to suppress grid-connected current oscillation and improve its performance without additional hardware cost. Operational stability under strong network conditions.

The purpose of the present invention can be achieved through the following technical solutions:

A self-synchronous voltage source grid-connected stability improvement method based on current control loop reshaping, the topology of the self-synchronous voltage source includes: a DC side power supply, a three-phase inverter, a three-phase grid impedance, and a three-phase grid;

The self-synchronizing voltage source grid-connected stability improvement method includes the following steps:

Collect inverter port voltage and port current;

Calculate the output active power and reactive power of the inverter according to the inverter port voltage and port current;

The phase of the potential reference value in the bridge arm and the amplitude of the potential reference value in the bridge arm are calculated according to the active power loop and the reactive power loop respectively, and then the internal potential reference value is obtained through the internal potential calculation formula;

The voltage control loop generates a reference value for the current control loop;

Reshape the current control loop and add grid voltage feed-forward control to generate modulation waves;

The modulated wave is subjected to space vector modulation to generate a driving signal.

Optionally, the calculation of the inverter output active power and reactive power includes the following steps:

Convert the inverter port voltage and port current from the three-phase stationary coordinate system to the two-phase stationary coordinate system;

The transformation formula for converting the voltage of the three-phase stationary coordinate system to the voltage of the two-phase stationary coordinate system is:

The transformation formula for converting the current in the three-phase stationary coordinate system to the current in the two-phase stationary coordinate system is:

The inverter output active power p and reactive power q are obtained through the instantaneous power calculation formula; the instantaneous power calculation formula is:

p=1.5×(v _α i _α +v _β i _β )

q＝1.5×(v _β i _α -v _α i _β )

Optionally, the phase of the internal potential reference value, the amplitude of the internal potential reference value of the bridge arm and the calculation method of the internal potential include the following steps:

According to the active power loop calculation formula, the phase θ of the potential reference value in the bridge arm is calculated, and the active power loop calculation formula is:

In the formula, P _set is the reference value of the active power output by the three-phase inverter, ω _n is the rated angular frequency of the three-phase power grid, D _p is the active damping coefficient, J is the virtual moment of inertia, and s is the Laplacian operator;

The amplitude U of the potential reference value in the bridge arm is calculated according to the reactive power loop calculation formula, and the reactive power loop calculation formula is:

In the formula, Q _set is the reference value of the reactive power output by the three-phase inverter, V _n is the rated voltage amplitude of the three-phase grid, D _q is the reactive damping coefficient, K is the reactive inertia coefficient, and s is the Laplace operator;

According to the internal potential phase angle reference θ and the internal potential amplitude reference U, the internal potential reference value u _φ-ref is obtained through the internal potential calculation formula. The internal potential calculation formula is:

Optionally, the voltage control loop generating the reference value of the current control loop includes the following steps:

Use the internal potential reference value as the reference value of the voltage control loop;

Use the port voltage as the feedback value of the voltage control loop;

The reference value of the voltage control loop minus the feedback value of the voltage control loop is used as the input of the voltage control loop, and the voltage control loop outputs the reference value of the current control loop, and the transfer function of the voltage control loop is H _v (s).

Optionally, said reshaping the current control loop and adding grid voltage feed-forward control to generate a modulation wave includes the following steps:

The output current i _abc of the self-synchronous voltage source is the feedback value 1 of the current control loop, denoted as i _fb1 ;

Design the reshaping branch of the current control loop, the input of the reshaping branch of the current control loop is the output value of the current control loop, and the output is the feedback value 2 of the current control loop, denoted as _ifb2 ; the reshaping branch of the current control loop is The transfer function is H _ires = H _v (s);

Calculate the feedback quantity i _fb of the current control loop, the calculation formula is i _fb =i _fb1 +i _fb2 ;

The input of the current control loop is the reference value i _ref of the current control loop minus the feedback value i _fb of the current control loop;

The output modulation wave component 1 of the current control loop is denoted as v _mabc1 ;

The grid voltage feed-forward component v _ff is the modulation wave component 2, denoted as v _mabc2 , and the modulation wave is calculated with the formula v _mabc =v _mabc1 +v _mabc2 .

Optionally, performing space vector modulation on the modulated wave to generate a drive signal includes the following steps:

The modulated wave is sent to the PWM module to generate a drive signal to control the inverter; the modulated wave is compared with the three-phase triangular carrier, and the drive signal is generated by the space vector modulation method.

Optionally, the three-phase inverter includes a three-phase inverter circuit, a three-phase LC filter, a three-phase voltage sensor, a three-phase current sensor and a three-phase inverter controller.

The three-phase inverter circuit is connected to the three-phase LC filter, the three-phase voltage sensor and the three-phase current sensor respectively sample the three-phase voltage of the filter capacitor and the three-phase current of the filter inductor in the three-phase LC filter, and transmit the sampled signal to the three phases Inverter controller; the three-phase inverter controller outputs a drive signal to control the three-phase inverter circuit after calculation.

Beneficial effects of the present invention:

1. The method of the present invention realizes reshaping the impedance of the self-synchronizing voltage source by reshaping the current control loop. Compared with the current voltage and current double closed-loop control self-synchronizing voltage source, the output current oscillation can be avoided, and it can be realized under strong network conditions. run stably.

2. The method of the present invention reshapes the impedance of the self-synchronizing voltage source by optimizing the control loop. Compared with the scheme of adding actual impedance, the hardware cost can be saved.

3. The method of the present invention realizes reshaping the impedance of the self-synchronizing voltage source by reshaping the current control loop. Compared with the traditional virtual impedance method, it can avoid low-pass filtering and differential operation, and does not need to know the filter inductance value. Simple to implement.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Fig. 1 is the circuit topological diagram of the three-phase grid-connected inverter of the application embodiment of the present invention;

Fig. 2 is a schematic diagram of form 1 of the self-synchronizing voltage source grid-connected stability improvement method based on current control loop reshaping in the present invention;

Fig. 3 is a schematic diagram of form 2 of the self-synchronizing voltage source grid-connected stability improvement method based on current control loop reshaping in the present invention;

Fig. 4 is before adopting the inventive method and after adopting the inventive method the inverter A phase port voltage and the output current waveform figure;

Fig. 5 is a waveform diagram of active power and reactive power output by the inverter before and after adopting the method of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

In some embodiments of the present invention, a self-synchronous voltage source grid-connected stability improvement method based on current control loop reshaping is disclosed. The grid-connected inverter topology using this control method includes: DC side power supply, three-phase Inverter, three-phase grid impedance, and three-phase grid; where, the three-phase inverter includes a three-phase inverter circuit, a three-phase LC filter, a three-phase voltage sensor, a three-phase current sensor, and a three-phase inverter controller ;

In the three-phase inverter: the three-phase inverter circuit is connected to the three-phase LC filter, the three-phase voltage sensor and the three-phase current sensor respectively sample the three-phase voltage of the filter capacitor and the three-phase current of the filter inductor in the three-phase LC filter, and The sampling signal is transmitted to the three-phase inverter controller; the three-phase inverter controller outputs the driving signal to control the three-phase inverter circuit after calculation;

The method for improving the grid-connected stability of the self-synchronizing voltage source in this embodiment includes the following steps:

S1, collecting inverter port voltage v _abc and output current i _abc , the specific process includes:

S11, use the three-phase voltage sensor to collect the three-phase voltage of the filter capacitor of the three-phase LC filter as the inverter port voltage v _abc , and use the three-phase current sensor to collect the three-phase current of the filter inductor of the three-phase LC filter as the inverter output current i _abc ;

S12, converting the inverter port voltage v _abc and output current i _abc from analog to digital and transmitting them to the three-phase inverter controller.

S2, calculate the active power and reactive power output by the inverter, the specific process includes:

S21, converting the inverter port voltage v _abc and port current i _abc from a three-phase stationary coordinate system to a two-phase stationary coordinate system;

The transformation formula for converting the voltage of the three-phase stationary coordinate system to the voltage of the two-phase stationary coordinate system is:

The transformation formula for converting the current in the three-phase stationary coordinate system to the current in the two-phase stationary coordinate system is:

S22. Obtain the active power p and reactive power q output by the inverter through the instantaneous power calculation formula; the instantaneous power calculation formula is:

p=1.5×(v _α i _α +v _β i _β )

q＝1.5×(v _β i _α -v _α i _β )

S3, calculating the internal potential amplitude U and the phase θ reference value and calculating the internal potential reference value;

S31, calculate the phase θ of the potential reference value in the bridge arm according to the calculation formula of the active power loop, and the calculation formula of the active power loop is:

In the formula, P _set is the reference value of the active power output by the three-phase inverter, ω _n is the rated angular frequency of the three-phase power grid, D _p is the active damping coefficient, J is the virtual moment of inertia, and s is the Laplacian operator;

S32. Calculate the amplitude U of the potential reference value in the bridge arm according to the reactive power loop calculation formula, and the reactive power loop calculation formula is:

In the formula, Q _set is the reference value of the reactive power output by the three-phase inverter, V _n is the rated voltage amplitude of the three-phase grid, D _q is the reactive damping coefficient, K is the reactive inertia coefficient, and s is the Laplace operator.

S33, according to the internal potential phase angle reference θ and the internal potential amplitude reference U, the internal potential reference value u _φ-ref is obtained through the internal potential calculation formula, and the internal potential calculation formula is:

The steps for the S4 voltage control loop to generate a current reference include:

S41, using the internal potential reference value u _φ-ref obtained in step S33 as the reference value u _ref of the voltage control loop;

S42, using the port voltage v _abc as the feedback value u _fb of the voltage control loop;

S43, the reference value u _φ-ref of the voltage control loop minus the feedback value u _fb of the voltage control loop is used as the input of the voltage control loop, and the voltage control loop outputs the reference value i _ref of the current control loop, and the transfer function of the voltage control loop is H _v (s).

S5 steps to reshape the current control loop and add grid voltage feed-forward control to generate modulation waves include:

S51, the output current _iabc from the synchronous voltage source is the feedback value 1 of the current control loop, denoted as _ifb1 ;

S52, design the remodeling branch of the current control loop, the input of the remodeling branch of the current control loop is the output value of the current control loop, and the output is the feedback value 2 of the current control loop, denoted as _ifb2 ; the remodeling branch of the current control loop The transfer function of the circuit is Hi _ires =H _v (s), which corresponds to Form 1 of the self-synchronous voltage source grid-connected stability improvement method based on current control loop reshaping shown in FIG. 2 .

S53, calculate the feedback value i _fb of the current control loop, the calculation formula is i _fb =i _fb1 +i _fb2 ;

S54, the input of the current control loop is the reference value i _ref of the current control loop obtained in step S43 minus the feedback value _ifb of the current control loop.

In other examples of the present invention, according to the principle of equivalent transformation of the transfer function block diagram, the comparison point of the current control loop reshaping branch in the above step S53 can also be moved forward to obtain the self-current control loop reshaping based on the current control loop shown in Figure 3. Form 2 of the synchronous voltage source grid-connected stability improvement method, the transfer function of the corresponding current control loop reshaping branch is H _ires =H _v (s)/H _v (s)=1.

Correspondingly, the port voltage v _abc in step S42 is used as the voltage control loop feedback value 1, denoted as u _fb1 , the output value of the current control loop reshaping branch is the voltage control loop feedback value 2, denoted as u _fb2 , the voltage control loop feedback value u _fb =u _fb1 +u _fb2 .

Correspondingly, in step S53, the feedback quantity of the current control loop _ifb = _ifb1 = _iabc .

S55, output modulation wave component 1 of the current control loop, denoted as v _mabc1 ;

S56, the grid voltage feedforward component v _ff is the modulation wave component 2, which is recorded as v _mabc2 , and the modulation wave is calculated, and the calculation formula is v _mabc = v _mabc1 + v _mabc2 ;

S6, the space vector modulation generates a driving signal. The specific process is: send the modulated wave v _mabc obtained by S5 into the PWM module to generate a driving signal and control the inverter; compare the modulated wave v _mabc with the three-phase triangular carrier, and generate a driving signal through the space vector modulation (SVPWM) method.

Application example:

The following further discloses the embodiments of the methods in the foregoing embodiments in specific application scenarios. Specifically, the main circuit and inverter control method of a typical grid-connected system are shown in FIG. 1 . Among them, the DC side of the main circuit part can be regarded as a DC source with constant voltage. The DC-AC conversion part is realized by a three-phase full-bridge inverter circuit composed of 6 IGBTs. The current output by the bridge arm is connected to the power grid after being filtered by LC. The sampling part obtains the port voltage and output current of the inverter through the sampling device. In the inverter control part, the inverter port voltage and output current are input to the power calculation module to obtain the instantaneous output active power and reactive power of the inverter, and the instantaneous output active power of the inverter is input to the active power/frequency (P/f) The adjustment module obtains the phase of the reference internal potential, and the instantaneous output reactive power of the inverter is input to the reactive power/voltage (Q/u) adjustment module to obtain the amplitude of the reference internal potential. The reference value of the voltage control loop is calculated according to the phase and amplitude of the internal potential, and the port voltage is used as the feedback value of the voltage control loop. The difference between the reference value and the feedback value of the voltage control loop is input to the voltage regulation module, and the voltage regulation module outputs the current reference value. Further, the feedback value of the current control loop is calculated according to the output current and the reshaping branch of the current control loop, and the difference between the reference value and the feedback value of the current control loop is input to the current control module. Then, the output value of the current control module is added to the grid voltage feed-forward to obtain the modulated wave. Finally, the modulated wave undergoes space vector modulation SVPWM to generate a drive signal to drive the IGBT.

The main parameter values of this embodiment are as follows: main circuit parameters, DC side voltage V _dc = 700V, inverter side filter inductance L = 150uH, filter inductance branch circuit 0.01Ω, filter capacitor C = 600uF, damping resistance R _d = 0.2 Ω, the effective value of the AC bus voltage is 315V, the AC bus voltage frequency f ₀ =50Hz, the line resistance is 0Ω, the line inductance is 0Ω, the rated capacity of the inverter is 500kW, and the switching frequency of the inverter is 3.2kHz. Controller parameters, active power given P _set ＝500kW, reactive power given Q _set ＝0kVar, virtual moment of inertia J＝0.3, reactive inertia coefficient K＝318, active damping coefficient D _p ＝252.87, reactive damping coefficient D _q =2000, virtual resistance is 0.01Ω, virtual inductance is 150uH, voltage controller proportional coefficient K _pv =50, voltage controller integral coefficient K _iv =0, current controller proportional coefficient K _pi =0.64, current controller integral Coefficient K _ii =100.

In order to verify the effectiveness of the self-synchronous voltage source grid-connected stability improvement method based on the reshaping of the current control loop in the present invention, a simulation model is built in MATLAB/Simulink to verify the effectiveness of the control method. The inverter operates off-grid during 0-0.1s, connects to the grid at 0.1s, sets active power P _set =500kW, sets reactive power as 0kVar, and adopts the method of the present invention at 0.4s.

Figure 4 shows the A-phase port voltage and output current waveforms of the self-synchronizing voltage source before and after the method is adopted. The time period of 0-0.1s is off-grid operation, the time period of 0.1s is connected to the grid, and the time period of 0.1s-0.4s does not use the method of the present invention, because the line impedance is 0, so the port voltage does not fluctuate, but the output current oscillates. At 0.4s, by adopting the method of the present invention, the output current oscillation decays rapidly, and at 0.8s, the output current oscillation is completely suppressed.

Figure 5 shows the waveforms of active power and reactive power output from the synchronous voltage source before and after adopting the method. The time period of 0-0.1s is off-grid operation, the time period of 0.1s is connected to the grid, and the time period of 0.1s-0.4s, if the method of the present invention is not used, the output active power and reactive power both oscillate. At 0.4s, using the method of the present invention, the output active power and reactive power are rapidly attenuated, and at 0.8s the output active power and reactive power oscillations are completely suppressed, the active power reaches a given value of 500kW, and the reactive power reaches a given value of 0kVar .

In the description of this specification, descriptions with reference to the terms "one embodiment", "example", "specific example" and the like mean that specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment of the present invention. In an embodiment or example. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Variations and improvements are possible, which fall within the scope of the claimed invention.

Claims (7)

1. A self-synchronous voltage source grid-connected stability improvement method based on current control loop reshaping, characterized in that, the topology of the self-synchronous voltage source includes: a DC side power supply, a three-phase inverter, and a three-phase power grid Impedance and three-phase grid; The self-synchronizing voltage source grid-connected stability improvement method includes the following steps: Collect inverter port voltage and port current; Calculate the output active power and reactive power of the inverter according to the inverter port voltage and port current; The phase of the potential reference value in the bridge arm and the amplitude of the potential reference value in the bridge arm are calculated according to the active power loop and the reactive power loop respectively, and then the internal potential reference value is obtained through the internal potential calculation formula; The voltage control loop generates a reference value for the current control loop; Reshape the current control loop and add grid voltage feed-forward control to generate modulation waves; The modulated wave is subjected to space vector modulation to generate a drive signal. 2. The self-synchronizing voltage source grid-connected stability improvement method based on current control loop reshaping according to claim 1, wherein said calculating the inverter output active power and reactive power comprises the following steps: Convert the inverter port voltage and port current from the three-phase stationary coordinate system to the two-phase stationary coordinate system; The conversion formula of the three-phase stationary coordinate system voltage to the two-phase stationary coordinate system voltage is: The transformation formula for converting the current in the three-phase stationary coordinate system to the current in the two-phase stationary coordinate system is: The inverter output active power p and reactive power q are obtained through the instantaneous power calculation formula; the instantaneous power calculation formula is: 3. The self-synchronous voltage source grid-connected stability promotion method based on current control loop reshaping according to claim 1, characterized in that, the phase of the internal potential reference value, the amplitude of the potential reference value in the bridge arm and The internal potential calculation method includes the following steps: According to the active power loop calculation formula, the phase θ of the potential reference value in the bridge arm is calculated, and the active power loop calculation formula is: In the formula, P _set is the reference value of the active power output by the three-phase inverter, ω _n is the rated angular frequency of the three-phase power grid, D _p is the active damping coefficient, J is the virtual moment of inertia, and s is the Laplacian operator; The amplitude U of the potential reference value in the bridge arm is calculated according to the reactive power loop calculation formula, and the reactive power loop calculation formula is: In the formula, Q _set is the reference value of the reactive power output by the three-phase inverter, V _n is the rated voltage amplitude of the three-phase grid, D _q is the reactive damping coefficient, K is the reactive inertia coefficient, and s is the Laplace operator; According to the internal potential phase angle reference θ and the internal potential amplitude reference U, the internal potential reference value u _φ-ref is obtained through the internal potential calculation formula. The internal potential calculation formula is: 4. The self-synchronizing voltage source grid-connected stability improvement method based on current control loop remodeling according to claim 1, wherein the voltage control loop generates the reference value of the current control loop comprising the following steps: Use the internal potential reference value as the reference value of the voltage control loop; Use the port voltage as the feedback value of the voltage control loop; The reference value of the voltage control loop minus the feedback value of the voltage control loop is used as the input of the voltage control loop, and the voltage control loop outputs the reference value of the current control loop, and the transfer function of the voltage control loop is H _v (s). 5. The self-synchronous voltage source grid-connected stability improvement method based on current control loop reshaping according to claim 1, characterized in that, said reshaping the current control loop and adding grid voltage feed-forward control generates modulation waves, Include the following steps: The output current i _abc of the self-synchronous voltage source is the feedback value 1 of the current control loop, denoted as i _fb1 ; Design the reshaping branch of the current control loop, the input of the reshaping branch of the current control loop is the output value of the current control loop, and the output is the feedback value 2 of the current control loop, denoted as _ifb2 ; the reshaping branch of the current control loop is The transfer function is H _ires = H _v (s); Calculate the feedback quantity i _fb of the current control loop, the calculation formula is i _fb =i _fb1 +i _fb2 ; The input of the current control loop is the reference value i _ref of the current control loop minus the feedback value i _fb of the current control loop; The output modulation wave component 1 of the current control loop is denoted as v _mabc1 ; The grid voltage feed-forward component v _ff is the modulation wave component 2, denoted as v _mabc2 , and the modulation wave is calculated with the formula v _mabc =v _mabc1 +v _mabc2 . 6. The self-synchronous voltage source grid-connected stability improvement method based on current control loop reshaping according to claim 1, wherein said carrying out space vector modulation of said modulated wave to generate a drive signal comprises the following steps: The modulated wave is sent to the PWM module to generate a drive signal to control the inverter; the modulated wave is compared with the three-phase triangular carrier, and the drive signal is generated by the space vector modulation method. 7. The self-synchronous voltage source grid-connected stability improvement method based on current control loop reshaping according to claim 1, wherein the three-phase inverter comprises a three-phase inverter circuit and a three-phase LC filter , three-phase voltage sensor, three-phase current sensor and three-phase inverter controller; The three-phase inverter circuit is connected to the three-phase LC filter, the three-phase voltage sensor and the three-phase current sensor respectively sample the three-phase voltage of the filter capacitor and the three-phase current of the filter inductor in the three-phase LC filter, and transmit the sampled signal to the three phases Inverter controller; the three-phase inverter controller outputs a drive signal to control the three-phase inverter circuit after calculation.