A method and system for directly controlling the potential in the bridge arm of a new energy grid-connected inverter

Abstract

The invention discloses a method and system for directly controlling the internal potential of a bridge arm of a new energy grid-connected inverter, belonging to the technical field of grid-connected inverter control. The control method comprises the following steps: obtaining measured values ​​by measuring the port voltage and current of the grid-connected inverter, and calculating instantaneous active and reactive values; obtaining the phase angle reference and amplitude reference of the internal potential of the bridge arm of the grid-connected inverter respectively, and then generating the internal potential reference of the bridge arm; at the same time, estimating the internal potential of the bridge arm of the grid-connected inverter based on the port voltage and current measured values ​​and the grid-connected inverter model by using an observer; finally, using the estimated internal potential as a feedback signal of the closed-loop feedback control of the internal potential, comparing it with the generated internal potential reference of the bridge arm, and sending it to the internal potential controller, thereby obtaining a modulation signal and sending it to the PWM module, so as to realize direct control of the internal potential of the bridge arm of the grid-connected inverter; compared with the existing control method of the grid-connected inverter, the method of the invention improves the dynamic performance of the grid-connected inverter and improves the power quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of grid-connected inverter control, and in particular relates to a method and system for directly controlling the potential in a bridge arm of a new energy grid-connected inverter. Background Art

[0002] Grid-connected inverters have the advantages of fast power regulation and high utilization of renewable energy, but they generally take maximizing active power output as their main operating goal and cannot support grid voltage and frequency stability like traditional synchronous generators. With the continuous increase in the penetration rate of new energy power generation, the power grid has gradually changed from a strong grid to a weak grid state. In order to enhance the adaptability of grid-connected inverters under complex working conditions, grid-connected inverters came into being.

[0003] Grid-connected inverters have the potential to simulate the damping and inertia of traditional synchronous generators and provide frequency and voltage support for the grid. However, grid-connected inverters have the risk of oscillation under strong grid conditions, which can lead to instability of the grid-connected system.

[0004] Existing grid-connected inverters generally use a voltage and current dual inner loop control structure, which has the risk of oscillation under strong grid conditions. In order to achieve stable operation under strong grid conditions, virtual inductance is generally required. Virtual inductance requires differential operation of the sampled current, so the sampled current needs to be low-pass filtered, but adding low-pass filtering will deteriorate the dynamic characteristics. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method and system for directly controlling the potential in the bridge arm of a new energy grid-connected inverter, so as to enhance the dynamic performance of the grid-connected inverter and improve the power quality.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for directly controlling the potential in a bridge arm of a new energy grid-connected inverter, wherein the grid-connected inverter topology structure includes: a DC side power supply, a three-phase inverter, a three-phase grid impedance and a three-phase grid; wherein 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;

[0008] The method comprises:

[0009] The three-phase voltage sensor and the three-phase current sensor are used to collect the three-phase voltage of the three-phase LC filter capacitor and the three-phase current of the three-phase LC filter inductor respectively, and use them as the inverter port voltage v abc and the inverter port current i abc ;

[0010] According to the inverter port voltage vabc and the port current i abc , calculate the inverter output active power p and reactive power q;

[0011] The inverter port voltage v abc and the port current i abc As input, the observer is used to estimate the potential u' in the inverter bridge arm φ ;

[0012] According to the active power p and the reactive power q, the potential phase angle reference θ and the amplitude reference U in the bridge arm are generated;

[0013] According to the internal potential phase angle reference θ and the internal potential amplitude reference U, the internal potential reference value u is obtained by the internal potential calculation formula φ-ref ;

[0014] The internal potential reference value u φ-ref and the estimated value of the internal potential u' φ After comparison, the modulation wave v is obtained mabc ;

[0015] Modulation wave v mabc Send it to the PWM module to generate a drive signal to control the inverter.

[0016] Furthermore, the inverter port voltage v is collected abc and the port current i abc After that, the analog quantity of the collected signal is converted into digital quantity and transmitted to the three-phase inverter controller.

[0017] Further, the steps of calculating the inverter output active power p and reactive power q include:

[0018] S21, the inverter port voltage v abc and the port current i abc Convert from a three-phase stationary coordinate system to a two-phase stationary coordinate system;

[0019] The conversion formula of the three-phase stationary reference system voltage to the two-phase stationary reference system voltage is:

[0020]

[0021] The transformation formula for converting the three-phase stationary coordinate system current to the two-phase stationary coordinate system current is:

[0022]

[0023] S22, the inverter output active power p and reactive power q are obtained by instantaneous power calculation formula; the instantaneous power calculation formula is:

[0024] p=1.5×(v α iα +v β i β )

[0025] q=1.5×(v β i α -v α i β ).

[0026] Furthermore, the observer estimates the potential u' in the inverter bridge arm φ The specific process includes:

[0027] S31, establish the potential u in the inverter bridge arm according to Kirchhoff’s voltage law and Kirchhoff’s current law φ , inverter port voltage v abc , inverter port current i abc Equation of state:

[0028]

[0029] in, C = [1 0], y = i L , u=v, R L is the resistance value of the filter inductor branch, L is the filter inductor value, i L is the inductor current on the inverter side, u φ is the base value of the potential in the inverter bridge arm;

[0030] S32, establish an observer equation according to the observer theory, determine the eigenvalue of the observed system according to the mathematical model of the inverter, and further design the eigenvalue of the observer according to the state observer theory so that it is much more negative than the eigenvalue of the observed system, so that the state of the observer converges to the state of the observed system;

[0031] S33, using an observer to observe the potential in the inverter bridge arm, with the inverter port voltage and port current as inputs of the observer, and the potential in the inverter bridge arm as output of the observer.

[0032] Furthermore, the observer equation is:

[0033]

[0034] in, is the state observation of the observer, is the output observation of the observer, H=[h1 h2] T is the feedback gain matrix of the state observer;

[0035] The characteristic equation of the observer is:

[0036]

[0037] Assuming that both characteristic roots are negative real numbers k, the feedback gain matrix is:

[0038]

[0039] The larger the corresponding k is, the farther the negative real root is from the real axis, and the faster the convergence speed is.

[0040] Further, the step of generating the potential phase angle reference θ and the amplitude reference U in the bridge arm includes:

[0041] S41, calculate the phase angle reference θ of the potential reference value in the bridge arm according to the active power loop calculation formula, the active power loop calculation formula is:

[0042]

[0043] Where P set is the active power reference value 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 Laplace operator;

[0044] S42, calculate the potential amplitude reference U in the bridge arm according to the reactive power loop calculation formula, the reactive power loop calculation formula is:

[0045]

[0046] In the formula, Q set is the reactive power reference value output by the three-phase inverter, v n is the rated voltage amplitude of the three-phase power grid, D q is the reactive damping coefficient, K is the reactive inertia coefficient, and s is the Laplace operator.

[0047] Furthermore, the internal potential calculation formula is:

[0048]

[0049] Furthermore, we get the modulation wave v mabc The specific process is: the internal potential reference value u φ-ref Subtract the estimated internal potential u' φ The deviation is obtained and input into the proportional-integral regulator to obtain the modulation wave.

[0050] Furthermore, the specific process of generating the driving signal is as follows: the modulation wave v mabc Compared with the three-phase triangle carrier, the driving signal is generated by the space vector modulation method.

[0051] A direct control system for the potential in the bridge arm of a new energy grid-connected inverter, comprising:

[0052] Signal acquisition module: Use three-phase voltage sensor and three-phase current sensor to collect three-phase voltage of three-phase LC filter capacitor and three-phase current of three-phase LC filter inductor respectively, and use them as inverter port voltage v abc and the inverter port current i abc ;

[0053] Power calculation module: According to the inverter port voltage v abc and the port current i abc , calculate the inverter output active power p and reactive power q;

[0054] State observer module: based on the inverter port voltage v abc and the port current i abc As input, the observer is used to estimate the potential u' in the inverter bridge arm φ ;

[0055] Power control module: Generates the potential phase angle reference θ and amplitude reference U in the bridge arm according to the active power p and reactive power q;

[0056] Internal potential reference production module: According to the internal potential phase angle reference θ and the internal potential amplitude reference U, the internal potential reference value u is obtained through the internal potential calculation formula φ-ref ;

[0057] Internal potential adjustment module: the internal potential reference value u φ-ref and the estimated value of the internal potential u' φ After comparison, the modulation wave v is obtained mabc ;

[0058] PWM module: modulation wave v mabc Send it to the PWM module to generate a drive signal to control the inverter.

[0059] Beneficial effects of the present invention: The present invention observes the internal potential of the bridge arm of the three-phase inverter through an observer, thereby realizing direct control of the internal potential of the bridge arm of the grid-connected inverter. Compared with the current method for calculating the internal potential of the bridge arm, the phase delay is smaller, and the dynamic performance of the grid-connected inverter can be improved. At the same time, compared with the current method for calculating the internal potential of the bridge arm, the high-frequency characteristics of the internal potential are retained, and the inverter output current has less harmonic content, which can improve the power quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0061] Figure 1 A schematic diagram of a circuit topology and a control method of a three-phase grid-connected inverter of the present invention;

[0062] Figure 2 It is a schematic diagram of the state observer model of the present invention;

[0063] Figure 3 It is a schematic diagram of the potential observer model in the bridge arm of the three-phase grid-connected inverter of the present invention;

[0064] Figure 4 This is a diagram showing the effect of observing the potential in the bridge arm of a three-phase grid-connected inverter according to an application embodiment of the present invention;

[0065] Figure 5 A comparison diagram of the dynamic response of the inverter port current when the method of the present invention is adopted and when the method of the present invention is not adopted;

[0066] Figure 6 A comparison diagram of inverter port current quality using the method of the present invention and not using the method of the present invention;

[0067] Figure 7 When the grid frequency suddenly increases from 50 Hz to 50.5 Hz, the inverter port voltage, port current and active power waveforms using the method of the present invention and not using the method of the present invention;

[0068] Figure 8 The waveforms of the inverter port voltage, port current and active power when the grid frequency suddenly drops from 50 Hz to 49.5 Hz using the method of the present invention and not using the method of the present invention;

[0069] Fig. 9 When the grid voltage suddenly increases from the rated voltage to 1.1 times the rated voltage, the inverter port voltage, port current and reactive power waveforms using the method of the present invention and not using the method of the present invention;

[0070] Fig.10 When the grid voltage suddenly drops from the rated voltage to 0.9 times the rated voltage, the waveforms of the inverter port voltage, the port current and the reactive power using the method of the present invention and not using the method of the present invention are shown. DETAILED DESCRIPTION

[0071] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0072] like Figure 1 A method for directly controlling the potential in the bridge arm of a new energy grid-connected inverter is shown. The grid-connected inverter topology structure to which the control method is applied includes: a DC side power supply, a three-phase inverter, a three-phase grid impedance and a three-phase grid; wherein 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;

[0073] 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 transmit the sampled signals to the three-phase inverter controller; after calculation, the three-phase inverter controller outputs a drive signal to control the three-phase inverter circuit;

[0074] A method for directly controlling the potential in a bridge arm of a new energy grid-connected inverter comprises the following steps:

[0075] S1, collects the inverter port voltage v abc and current i abc The specific process includes:

[0076] S11, use the three-phase voltage sensor to collect the three-phase voltage of the three-phase LC filter capacitor as the inverter port voltage v abc , use the three-phase current sensor to collect the three-phase current of the three-phase LC filter inductor as the inverter port current i abc ;

[0077] S12, the inverter port voltage v abc and the port current i abc The analog quantity is converted into digital quantity and transmitted to the three-phase inverter controller.

[0078] S2, using the inverter port voltage v abc and the port current i abc , calculate the inverter output active power p and reactive power q, the specific process includes:

[0079] S21, the inverter port voltage v abc and the port current i abc Convert from a three-phase stationary coordinate system to a two-phase stationary coordinate system;

[0080] The conversion formula of the three-phase stationary reference system voltage to the two-phase stationary reference system voltage is:

[0081]

[0082] The transformation formula for converting the three-phase stationary coordinate system current to the two-phase stationary coordinate system current is:

[0083]

[0084] S22, the inverter output active power p and reactive power q are obtained by instantaneous power calculation formula; the instantaneous power calculation formula is:

[0085] p=1.5×(v α i α +v β i β )

[0086] q=1.5×(v β i α -v α i β ).

[0087] S3, with the inverter port voltage v abc and the port current i abc As input, the observer is used to estimate the potential u' in the inverter bridge arm φ The specific process includes:

[0088] S31, establishing a mathematical model of the inverter;

[0089] According to Kirchhoff's voltage law and Kirchhoff's current law, the potential u in the inverter bridge arm is established. φ , inverter port voltage v abc , inverter port current i abc Equation of state:

[0090]

[0091] in, C = [1 0], y = i L , u=v, R L is the resistance value of the filter inductor branch, L is the filter inductor value, i L is the inductor current on the inverter side, u φ is the base value of the potential in the inverter bridge arm;

[0092] S32, designing observer parameters according to the physical parameters and mathematical model of the inverter;

[0093] First, the observer equation is established according to the observer theory, and the eigenvalue of the observed system (i.e., the inverter system) is further determined according to the mathematical model of the inverter. Then, according to the state observer theory, the eigenvalue of the observer is designed so that it is much more negative than the eigenvalue of the observed system, and the state of the observer converges to the state of the observed system.

[0094] The observer equation is:

[0095]

[0096] in, is the state observation of the observer, is the output observation of the observer, H=[h1 h2] T is the feedback gain matrix of the state observer, h1 is the feedback gain from the terminal voltage to the inductor current, and h2 is the feedback gain from the terminal voltage to the internal potential; the observer model is as follows: Figure 2 As shown;

[0097] According to the observer equation, the internal potential observer model is obtained as follows: Figure 3 As shown; the characteristic equation of the observer is:

[0098]

[0099] Assuming that both characteristic roots are negative real numbers k, the feedback gain matrix is:

[0100]

[0101] The larger the corresponding k is, the farther the negative real root is from the real axis, and the faster the convergence speed is;

[0102] S33, using an observer to observe the potential in the inverter bridge arm, with the inverter port voltage and port current as inputs of the observer, and the potential in the inverter bridge arm as output of the observer.

[0103] S4, based on the active power p and reactive power q obtained in S2, generates the potential phase angle reference θ and amplitude reference U in the bridge arm by adjusting the power. The specific process includes:

[0104] S41, calculate the phase θ of the potential reference value in the bridge arm according to the active power loop calculation formula, the active power loop calculation formula is:

[0105]

[0106] Where P set is the active power reference value 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 Laplace operator;

[0107] S42, calculate the amplitude U of the potential reference value in the bridge arm according to the reactive power loop calculation formula, the reactive power loop calculation formula is:

[0108]

[0109] In the formula, Q set is the reactive power reference value output by the three-phase inverter, v n is the rated voltage amplitude of the three-phase power grid, D q is the reactive damping coefficient, K is the reactive inertia coefficient, and s is the Laplace operator.

[0110] S5, according to the internal potential phase angle reference θ and the internal potential amplitude reference U, the internal potential reference value u is obtained by the internal potential calculation formula φ-ref , the internal potential calculation formula is:

[0111]

[0112] S6, the internal potential reference value u obtained in S5 φ-ref The estimated internal potential u' obtained with S3 φ After comparison, the modulation wave v is obtained through the internal potential adjustment module. mabc ; The specific process is: internal potential reference value u φ-ref Subtract the estimated internal potential u' φ The deviation is obtained and input into the proportional-integral regulator to obtain the modulation wave.

[0113] S7, the modulation wave v obtained by S6 mabc The PWM module generates a drive signal to control the inverter. The specific process is as follows: the modulation wave v mabc Compared with the three-phase triangle carrier, the driving signal is generated by the space vector modulation (SVPWM) method.

[0114] Application examples:

[0115] The main circuit and inverter control method of a typical grid-connected system are as follows: Figure 1As shown. 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 LC filtering. In the sampling part, the inverter port voltage and port current are obtained through the sampling device. In the inverter control part, the inverter port voltage and port current are input into the power calculation module to obtain the instantaneous output active power and reactive power of the inverter. The instantaneous output active power of the inverter is input into the active power / frequency (P / f) regulation module to obtain the reference internal potential phase, and the instantaneous output reactive power of the inverter is input into the reactive power / voltage (Q / u) regulation module to obtain the reference internal potential amplitude. The inverter port voltage and port current are input into the internal potential observer module to obtain the internal potential of the inverter bridge arm. Further, the modulation wave is obtained through the internal potential regulation module, and the drive signal is generated through space vector modulation SVPWM to drive the IGBT.

[0116] The main parameter values ​​of this embodiment are as follows: main circuit parameters, DC side voltage V dc =700V, inverter side filter inductor L = 150uH, filter inductor branch circuit 0.01Ω, filter capacitor C = 600uF, damping resistor R d =0.2Ω, AC bus voltage effective value 315V, AC bus voltage frequency f0 = 50Hz, inverter rated capacity 500kW, inverter switching frequency is 3.2kHz. Controller parameters, active power given P set =500kW, reactive power given by 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, internal potential controller proportional coefficient K pe =150, internal potential controller integral coefficient K ie =200, current controller proportional coefficient K pi 0.64, current controller integral coefficient K ii =100; state observer part h1 = 127933, h2 = 614400, k a =-6667, k b =-614400, k c =127933.

[0117] In order to verify the effectiveness of the direct control technology of the potential in the bridge arm of the new energy grid-connected inverter of the present invention, a simulation model was built in MATLAB / Simulink to verify the effectiveness of the control method. The inverter was off-grid in the 0-0.1s period and connected to the grid at 0.1s. The active power was given as Pset=500kW and the reactive power was given as 0kVar.

[0118] First, the effectiveness of the internal potential observer is verified by sampling the bridge arm midpoint voltage and filtering it with a first-order low-pass filter with a cutoff frequency of 1kHz. In order to eliminate the lag effect caused by the low-pass filter, the internal potential observed by the internal potential observer is also filtered with a first-order low-pass filter with a cutoff frequency of 1kHz. Figure 4 The figure shows the effect of observing the potential in the bridge arm of a three-phase grid-connected inverter. The solid line is the fundamental component of the potential in the bridge arm (reference), and the dotted line is based on Calculated, the dotted line is observed by the observer. Figure 4 It can be seen that the internal potential observer can accurately observe the internal potential of the inverter bridge arm. Compared with the internal potential calculated according to the formula, it does not have the disadvantage of phase lag and can restore some high-frequency characteristics of the internal potential of the bridge arm.

[0119] Figure 5 The figure shows a comparison of the dynamic response of the inverter port current using the method of the present invention and not using the method of the present invention. Among them, the solid line is the inverter port current waveform corresponding to the method of the present invention, and the dotted line is the inverter port current waveform corresponding to the method of the present invention. By comparison, it can be found that under the same control parameters, the inverter port current without the method of the present invention has an overshoot of 8.32%, and the time to stabilize to the rated current is 0.1s longer than that of the inverter port current using the method of the present invention. It can be seen that the dynamic response of the inverter using the method of the present invention is better.

[0120] Figure 6 The figure shows a comparison of the inverter steady-state port current waveforms under the same control parameters, wherein the solid line is the inverter port current waveform corresponding to the method of the present invention, and the dotted line is the inverter port current waveform corresponding to the method of the present invention not being used. By comparison, it can be found that the inverter port current using the method of the present invention contains less high-frequency harmonic content, that is, the power quality is better.

[0121] Figure 7 The figure shows the comparison of the inverter port voltage, port current and output active power when the grid frequency suddenly rises from 50Hz to 50.5Hz under the same control parameters using the method of the present invention and not using the method of the present invention. The solid line and the dotted line are the inverter port voltage, port current and output active power waveforms corresponding to the method of the present invention and not using the method of the present invention, respectively. The comparison shows that the method of the present invention can provide frequency support for the grid, and there is no overshoot during the adjustment process, and the dynamic response is good.

[0122] Figure 8The figure shows the comparison of the inverter port voltage, port current and output active power when the grid frequency drops suddenly from 50Hz to 49.5Hz under the same control parameters using the method of the present invention and not using the method of the present invention. The solid line and the dotted line are the inverter port voltage, port current and output active power waveforms corresponding to the method of the present invention and not using the method of the present invention, respectively. The comparison shows that the method of the present invention can provide frequency support for the grid, and there is no overshoot during the adjustment process, and the dynamic response is good.

[0123] Fig. 9 The figure shows the comparison of the inverter port voltage, port current and output active power when the grid voltage suddenly rises from the rated voltage to 1.1 times the rated voltage under the same control parameters using the method of the present invention and not using the method of the present invention. The solid line and the dotted line are the inverter port voltage, port current and output active power waveforms corresponding to the method of the present invention and not using the method of the present invention, respectively. The comparison shows that the method of the present invention can provide voltage support for the grid, and there is no overshoot during the adjustment process, and the dynamic response is good.

[0124] Fig.10 The figure shows the comparison of the inverter port voltage, port current and output active power when the grid voltage drops from the rated voltage to 0.9 times the rated voltage under the same control parameters using the method of the present invention and not using the method of the present invention. The solid line and the dotted line are the inverter port voltage, port current and output active power waveforms corresponding to the method of the present invention and not using the method of the present invention, respectively. The comparison shows that the method of the present invention can provide voltage support for the grid, and there is no overshoot during the adjustment process, and the dynamic response is good.

[0125] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0126] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for directly controlling the potential in the bridge arm of a new energy grid-connected inverter, characterized in that: The grid-connected inverter topology structure includes: a DC side power supply, a three-phase inverter, a three-phase grid impedance and a three-phase grid; wherein 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 method comprises: The three-phase voltage sensor and the three-phase current sensor are used to collect the three-phase voltage of the three-phase LC filter capacitor and the three-phase current of the three-phase LC filter inductor respectively, and use them as the inverter port voltage v abc and the inverter port current i abc ; According to the inverter port voltage v abc and the port current i abc , calculate the inverter output active power p and reactive power q; The inverter port voltage v abc and the port current i abc As input, the observer is used to estimate the potential u' in the inverter bridge arm φ ; According to the active power p and the reactive power q, the potential phase angle reference θ and the amplitude reference U in the bridge arm are generated; According to the internal potential phase angle reference θ and the internal potential amplitude reference U, the internal potential reference value u is obtained by the internal potential calculation formula φ-ref ; The internal potential reference value u φ-ref and the estimated value of the internal potential u' φ After comparison, the modulation wave v is obtained mabc ; Modulation wave v mabc Send it to the PWM module to generate a drive signal to control the inverter.

2. The method for directly controlling the potential in the bridge arm of a new energy grid-connected inverter according to claim 1, characterized in that: The inverter port voltage v is collected abc and the port current i abc After that, the analog quantity of the collected signal is converted into digital quantity and transmitted to the three-phase inverter controller.

3. The method for directly controlling the potential in the bridge arm of a new energy grid-connected inverter according to claim 1, characterized in that: The steps for calculating the inverter output active power p and reactive power q include: S21, the inverter port voltage v abc and the port current i abc Convert from a three-phase stationary coordinate system to a two-phase stationary coordinate system; The conversion formula of the three-phase stationary reference system voltage to the two-phase stationary reference system voltage is: The transformation formula for converting the three-phase stationary coordinate system current to the two-phase stationary coordinate system current is: S22, the inverter output active power p and reactive power q are obtained by 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 )。 4. The method for directly controlling the potential in the bridge arm of a new energy grid-connected inverter according to claim 1, characterized in that: The observer estimates the potential u' in the inverter bridge arm φ The specific process includes: S31, establish the potential u in the inverter bridge arm according to Kirchhoff’s voltage law and Kirchhoff’s current law φ , inverter port voltage v abc , inverter port current i abc Equation of state: in, C = [1 0], y = i L , u=v, R L is the resistance value of the filter inductor branch, L is the filter inductor value, i L is the inductor current on the inverter side, u φ is the base value of the potential in the inverter bridge arm; S32, establish an observer equation according to the observer theory, determine the eigenvalue of the observed system according to the mathematical model of the inverter, and further design the eigenvalue of the observer according to the state observer theory so that it is much more negative than the eigenvalue of the observed system, so that the state of the observer converges to the state of the observed system; S33, using an observer to observe the potential in the inverter bridge arm, with the inverter port voltage and port current as inputs of the observer, and the potential in the inverter bridge arm as output of the observer.

5. The method for directly controlling the potential in the bridge arm of a new energy grid-connected inverter according to claim 4, characterized in that: The observer equation is: in, is the state observation of the observer, is the output observation of the observer, H=[h1 h2] T is the feedback gain matrix of the state observer; The characteristic equation of the observer is: Assuming that both characteristic roots are negative real numbers k, the feedback gain matrix is: The larger the corresponding k is, the farther the negative real root is from the real axis, and the faster the convergence speed is.

6. The method for directly controlling the potential in the bridge arm of a new energy grid-connected inverter according to claim 1, characterized in that: The steps of generating the potential phase angle reference θ and amplitude reference U in the bridge arm include: S41, calculate the phase angle reference θ of the potential reference value in the bridge arm according to the active power loop calculation formula, the active power loop calculation formula is: Where P set is the active power reference value 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 Laplace operator; S42, calculate the potential amplitude reference U in the bridge arm according to the reactive power loop calculation formula, the reactive power loop calculation formula is: In the formula, Q set is the reactive power reference value output by the three-phase inverter, v n is the rated voltage amplitude of the three-phase power grid, D q is the reactive damping coefficient, K is the reactive inertia coefficient, and s is the Laplace operator.

7. The method for directly controlling the potential in the bridge arm of a new energy grid-connected inverter according to claim 1, characterized in that: The internal potential calculation formula is:

8. The method for directly controlling the potential in the bridge arm of a new energy grid-connected inverter according to claim 1, characterized in that: Get the modulation wave v mabc The specific process is: the internal potential reference value u φ-ref Subtract the estimated internal potential u' φ The deviation is obtained and input into the proportional-integral regulator to obtain the modulation wave.

9. The method for directly controlling the potential in the bridge arm of a new energy grid-connected inverter according to claim 1, characterized in that: The specific process of generating the driving signal is as follows: the modulation wave v mabc Compared with the three-phase triangle carrier, the driving signal is generated by the space vector modulation method.

10. A direct control system for the potential in the bridge arm of a new energy grid-connected inverter, characterized in that: include: Signal acquisition module: Use three-phase voltage sensor and three-phase current sensor to collect three-phase voltage of three-phase LC filter capacitor and three-phase current of three-phase LC filter inductor respectively, and use them as inverter port voltage v abc and the inverter port current i abc ; Power calculation module: According to the inverter port voltage v abc and the port current i abc , calculate the inverter output active power p and reactive power q; State observer module: based on the inverter port voltage v abc and the port current i abc As input, the observer is used to estimate the potential u' in the inverter bridge arm φ ; Power control module: Generates the potential phase angle reference θ and amplitude reference U in the bridge arm according to the active power p and reactive power q; Internal potential reference production module: According to the internal potential phase angle reference θ and the internal potential amplitude reference U, the internal potential reference value u is obtained through the internal potential calculation formula φ-ref ; Internal potential adjustment module: the internal potential reference value u φ-ref and the estimated value of the internal potential u' φ After comparison, the modulation wave v is obtained mabc ; PWM module: modulation wave v mabc Send it to the PWM module to generate a drive signal to control the inverter.

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