Non-transient control method for three-phase grid-connected inverter based on VOC

Abstract

The invention discloses a non-transient control method for a three-phase grid-connected inverter based on virtual oscillator control (VOC), which comprises the following steps of: sampling grid-connected three-phase current of the inverter, and performing three-phase / two-phase static coordinate transformation. And calculating a grid-connected current two-phase instruction value according to the active power instruction value and the reactive power instruction value. And an inductor-capacitor second-order oscillator circuit is adopted to obtain inverter control modulation waves. Calculating a steady-state operation point approximately obtained by the system according to the power instruction value, the filter inductance and the equivalent resistance; calculating to obtain a voltage output signal of the inverter in the next period; an oscillator operating at an ideal steady-state point is used to couple and synchronize modulation waves output by the VOC; calculating a superposed voltage; and adding the voltage output signal of the inverter in the next period and the superposed voltage to obtain a voltage instruction signal, and generating a switching tube on-off signal to drive a switching tube after PWM modulation. According to the method, the transient process after the working condition is changed can be effectively reduced, the transient current waveform is improved, and the universality is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of three-phase grid-connected inverter control, and in particular is a VOC-based three-phase grid-connected inverter non-transient control method. Background Art

[0002] The stability of traditional power grids and the synchronization between inverters rely on synchronous generators. The inverter is controlled in a "grid following" mode to adjust the current injected into the grid to track the power command value. However, in a pure inverter grid without synchronous generators, the inverter under this control strategy will not be able to maintain stability and global synchronization. Virtual oscillation control (VOC) is a new control method for inverters in recent years. In this control, the inverter can not only realize the power dispatch function, but also act as a controllable voltage source, which is suitable for grid-connected and island modes. VOC includes traditional droop control characteristics, and does not require a phase-locked loop. It only requires grid-connected current information and can achieve completely non-communication control. It has broad application prospects in the field of inverters.

[0003] However, traditional VOC control is difficult to balance the contradiction between transient process and steady-state performance, and it is difficult to have both a faster power command tracking speed and a smaller steady-state frequency error. Summary of the invention

[0004] The object of the present invention is to provide a transient-free control method for a three-phase grid-connected inverter based on VOC.

[0005] A VOC-based three-phase grid-connected inverter non-transient control method according to the present invention includes:

[0006] The three-phase current of the inverter grid is sampled and abc / αβ transformation is performed to obtain the three-phase current of the grid;

[0007] Calculating a grid-connected current command value according to an active power command value and a reactive power command value;

[0008] The virtual oscillator is controlled according to the grid-connected current command value, and the capacitor voltage and inductor current of the virtual oscillator are collected and amplified as the inverter grid-connected voltage;

[0009] Calculate the phase angle difference between the inverter output voltage and the grid voltage according to the active power command value, the reactive power command value and the parameters of the three-phase grid-connected inverter;

[0010] According to the calculated steady-state data, an oscillator running at an ideal steady-state point is virtualized so that it couples the VOC output modulation wave, thereby realizing rapid switching of the controller output state;

[0011] The zero-crossing point of the current after the working condition changes is selected as the updating time of the voltage signal to start applying the coupling effect;

[0012] Select the superimposed voltage amplitude according to the DC power supply margin and calculate the superimposed voltage application time;

[0013] The voltage command signal is obtained by adding the inverter voltage output signal and the superimposed voltage in the next cycle, and the switch tube on-off signal is generated after PWM modulation to drive the switch tube.

[0014] Preferably, the inverter grid-connected three-phase current i abc The coordinate transformation matrix for sampling and abc / αβ transformation is:

[0015]

[0016] Preferably, the grid-connected current command value is calculated according to the active power command value and the reactive power command value, and the specific formula is:

[0017]

[0018] Among them, v α and v β Indicates the inverter grid-connected voltage, P * is the active power command value, Q * is the reactive power command value.

[0019] Preferably, the virtual oscillator comprises an inductor L, a capacitor C, a controlled voltage source v m , controlled voltage source v u , controlled current source i m , controlled current source i u .

[0020] Inductor L is connected in series with a controlled voltage source v m and a controlled voltage source v u Then connect a capacitor C and a controlled current source i in parallel. m A controlled current source i u .

[0021] Preferably, the specific method of controlling the virtual oscillator according to the grid-connected current command value, collecting the capacitor voltage and inductor current of the virtual oscillator and amplifying them as the inverter grid-connected voltage is:

[0022] The three-phase current i α 、i β and grid-connected current command value and By comparison, the error is amplified by K after the rotation matrix. i times to get u1 and u2, u1 as the controlled current source i u The current u2 is used as the controlled voltage source v after passing the coefficient εu Voltage;

[0023] Collect the capacitor C voltage u of the LC second-order oscillator C and the inductor current i L As state variables x1 and x2, the controlled voltage source v is calculated according to the state variables m and the controlled current source i m Signal, state variable amplified to a fixed amplitude V n As the inverter voltage command v α 、v β .

[0024] Preferably, the coefficient ε, the controlled voltage source v m and the controlled current source i m Specifically:

[0025]

[0026] Among them, k i represents the amplification factor, ω is the grid power frequency angular frequency, x1 and x2 are state variables, X n is the nominal value of the state variable, ||x|| is the modulus of the state variable, and ξ is a constant.

[0027] Preferably, the active power command value P * and reactive power command value Q * The phase angle difference between the inverter output voltage and the grid voltage is obtained by approximate calculation of the circuit parameters. The specific formula is:

[0028]

[0029] Among them, V g is the grid voltage amplitude, R is the circuit equivalent resistance, L eq It is the sum of the filter inductance and the grid-side inductance.

[0030] Preferably, the inverter voltage output signal v′ of the next cycle is calculated αβ , the corresponding formula is:

[0031]

[0032] v' αβ =V n sin(wt+δ * );

[0033] Among them, δ * represents the next steady-state phase angle difference, δ0 represents the current steady-state phase angle difference, P * represents the next steady-state power instruction, and P0 represents the current steady-state power instruction.

[0034] Preferably, the feedback applied by the ideal steady-state oscillator to the output modulation wave is calculated according to the Kuramoto model, and the corresponding formula is:

[0035]

[0036] Where θ1 is the phase of the oscillator in AHO, θ2 is the phase of the oscillator running in the desired state. K represents the coupling coefficient, Wnom is the rated frequency, ΔV' α and ΔV' β They respectively represent the coupling effect exerted by the ideal oscillator on the output modulation wave.

[0037] Preferably, the superimposed voltage duration Δt is calculated based on the instantaneous current value at the time of updating the voltage signal in each cycle, and the corresponding formula is:

[0038]

[0039] Among them, u add is the superimposed voltage amplitude, I0 is the instantaneous current value at the time of voltage signal update, L f is the filter inductor, R f is the filter resistor.

[0040] Compared with the prior art, the present invention has the following significant advantages: the present invention calculates the ideal steady-state value and uses coupling to quickly make the modulation wave approach the ideal steady state, and then accurately controls the time when the modulation wave changes and applies a superimposed voltage of appropriate intensity and time, which can effectively reduce the transient process, increase the current response speed, and has strong versatility.

[0041] The present invention is further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The invention discloses a three-phase grid-connected inverter topology structure based on VOC.

[0043] Figure 2 This is the control block diagram of VOC.

[0044] Figure 3 This is a schematic diagram of the coupling effect of an ideal oscillator.

[0045] Figure 4 This is a control block diagram without transient VOC.

[0046] Figure 5 This is a comparison chart of active power waveforms without and with the addition of the non-transient control algorithm.

[0047] Figure 6 This is a comparison of the current waveforms without and with the non-transient control algorithm. DETAILED DESCRIPTION

[0048] The present invention is described in detail below with reference to specific examples.

[0049] In order to more clearly describe the purpose, technical solutions and advantages of the present invention, the specific implementation methods are illustrated by examples and drawings. Obviously, the described embodiments are only used to explain the present invention and are not limited to the present invention.

[0050] A VOC-based three-phase grid-connected inverter non-transient control method, the method specifically comprising:

[0051] Step 1: Sample the three-phase current of the inverter grid and perform abc / αβ transformation, that is, the three-phase current signal i abc After αβ transformation, the grid-connected three-phase current value i is obtained α and i β ,;

[0052] In a further embodiment, coordinate transformation: the inverter grid-connected three-phase current i abc Sampling, and abc / αβ transformation, the coordinate transformation matrix is:

[0053]

[0054] Step 2: Calculate the grid-connected current command value according to the active power command value and the reactive power command value;

[0055] According to the active power command value P * and reactive power command value Q * Calculate the grid-connected current command value, the corresponding formula is:

[0056] Among them, v α and v β Indicates the inverter grid-connected voltage,

[0057] Step 3: Control the virtual oscillator according to the grid-connected current command value, collect the capacitor voltage and inductor current of the virtual oscillator and amplify them as the inverter grid-connected voltage;

[0058] The virtual oscillator includes an inductor L, a capacitor C, a controlled voltage source v m , controlled voltage source v u , controlled current source i m , controlled current source i u .

[0059] Inductor L is connected in series with a controlled voltage source v m and a controlled voltage source v uThen connect a capacitor C and a controlled current source i in parallel. m A controlled current source i u .

[0060] Control of virtual oscillator: The three-phase current i α 、i β and grid-connected current command value and By comparison, the error is amplified by K after the rotation matrix. i times to get u1 and u2, u1 as the controlled current source i u The current u2 is used as the controlled voltage source v after passing the coefficient ε u The voltage of capacitor C of LC second-order oscillator is collected. C and the inductor current i L As state variables x1 and x2, the controlled voltage source v is calculated according to the state variables m and the controlled current source i m Signal, state variable amplified to a fixed amplitude V n As the inverter voltage command v α 、v β .

[0061] In a further embodiment, the coefficient ε, the controlled voltage source v m and the controlled current source i m Given by:

[0062]

[0063] where k i represents the amplification factor, ω is the grid power frequency angular frequency, x1 and x2 are state variables, X n is the nominal value of the state variable, ||x|| is the modulus of the state variable, and ξ is a constant.

[0064] Step 4: Calculate the approximate steady-state value of the system: through the power command P * , Q * The phase angle difference between the inverter output voltage and the grid voltage is obtained by approximate calculation of the circuit parameters. The corresponding formula is:

[0065]

[0066] Where V g is the grid voltage amplitude, R is the circuit equivalent resistance, L eq It is the sum of the filter inductance and the grid-side inductance.

[0067] Step 5: Select the same zero-crossing point of the current in each cycle as the update time of the voltage signal, and compare the actual active power P with the active power command P * By comparison, the error goes through the proportional link Kp Then the voltage phase angle θ of the next cycle is obtained. According to the voltage phase angle θ of the next cycle, the inverter voltage output signal v' of the next cycle is calculated. αβ , the specific formula is:

[0068] v' αβ =V n sin(wt+δ * );

[0069] In a further embodiment, the proportion link is determined by the approximate steady-state value of the phase angle difference, and the specific formula is:

[0070]

[0071] where δ * represents the next steady-state phase angle difference, δ0 represents the current steady-state phase angle difference, P * represents the next steady-state power instruction, and P0 represents the current steady-state power instruction.

[0072] Step 6: Use an oscillator running in an ideal steady state to apply coupled feedback to the output modulation wave. The corresponding formula is:

[0073]

[0074] Where θ1 is the phase of the oscillator in AHO, θ2 is the phase of the oscillator running in the desired state. K represents the coupling coefficient, Wnom is the rated frequency, ΔV' α and ΔV' β They respectively represent the coupling effect exerted by the ideal oscillator on the output modulation wave.

[0075] Step 7: Superimposed voltage calculation: Select the superimposed voltage amplitude U according to the DC power supply margin add The superimposed voltage duration Δt is calculated based on the instantaneous current value at the time when the voltage signal is updated in each cycle. The corresponding formula is:

[0076]

[0077] Among them, u add is the superimposed voltage amplitude, I0 is the instantaneous current value at the time of voltage signal update, L f is the filter inductor, R f is the filter resistor.

[0078] Step 8: PWM modulation module: the inverter voltage output signal v' of the next cycle αβ The voltage command signal is added to the superimposed voltage, and after PWM modulation, a switch tube on-off signal is generated to drive the switch tube.

[0079] Example

[0080] like Figure 1 FIG. 1 is a schematic diagram of a hardware circuit of a three-phase grid-connected inverter without transient control method based on VOC provided by an example of the present invention, including a DC power supply, a three-phase IGBT full bridge, a filter inductor L f , circuit equivalent resistance R, grid side inductance L g , three-phase AC power grid, current sensor, control main board and drive module.

[0081] like Figure 2 FIG. 1 is a schematic diagram of a VOC control method provided by an example of the present invention. The control part includes: calculating the command current, converting the sampled current i abc After coordinate transformation and comparison with the command current, the error is sent to the virtual oscillation controller to finally obtain the voltage signal v αβ .

[0082] like Figure 3 The figure shows a schematic diagram of an ideal oscillator coupling provided by an example of the present invention. The coupling application process includes: detecting whether the power command value changes, maintaining normal VOC operation when it does not change, starting the coupling after the change, and then applying coupling and synchronization to the controller through the ideal oscillator.

[0083] like Figure 4 As shown, it is a schematic diagram of the control part of a three-phase grid-connected inverter non-transient control method based on VOC provided by an example of the present invention. The main process includes: the normal VOC part, calculating the ideal steady-state phase angle difference when the power command value changes, performing non-transient control when the current crosses zero, using formula 1 to calculate and apply coupling to the control signal, calculating and applying the superimposed voltage signal, and adding it to the inverter voltage to obtain the switch tube on-off signal through PWM modulation.

[0084] In order to illustrate the correctness and effectiveness of the control strategy proposed by the present invention, according to Figure 1 Figure 2 Figure 4 A simulation model is established, and the active power instruction changes from 500W to 2000W at 0.5s.

[0085] Figure 5 The active power waveforms of the traditional virtual oscillation control (AHO) and the non-transient control (NT-VOC) proposed by the present invention are compared. From the simulation results, it can be seen that under the traditional virtual oscillation control, the new steady state is reached 0.2s after the active power instruction, and the dynamic response is slow. The active power of the method proposed by the present invention reaches the active power instruction in about 0.02s, and can quickly reach the new steady state. It can be seen that the control method proposed by the present invention can quickly track the power instruction and effectively reduce the transient process between the two steady states.

[0086] Figure 6Comparing the grid-side current waveforms of the traditional virtual oscillation control and the non-transient control proposed in the present invention, it can be seen that the non-transient control proposed in the present invention has a fast current response and no obvious transient, which is significantly superior to the traditional virtual oscillator control.

Claims

1. A VOC-based three-phase grid-connected inverter non-transient control method, characterized in that: include: The three-phase current of the inverter grid is sampled and abc / αβ transformation is performed to obtain the three-phase current of the grid; Calculating a grid-connected current command value according to an active power command value and a reactive power command value; The virtual oscillator is controlled according to the grid-connected current command value, and the capacitor voltage and inductor current of the virtual oscillator are collected and amplified as the inverter grid-connected voltage; Calculate the phase angle difference between the inverter output voltage and the grid voltage in a steady state according to the active power command value, the reactive power command value and the parameters of the three-phase grid-connected inverter; According to the calculated steady-state data, an oscillator running at the set steady-state point is virtualized, and the oscillator is coupled and synchronized with the VOC output modulation wave at the set time to achieve rapid switching of the controller output state; The zero-crossing point of the current after the working condition changes is selected as the updating time of the voltage signal to start applying the coupling effect; Select the superimposed voltage amplitude according to the DC power supply margin and calculate the superimposed voltage application time; The voltage command signal is obtained by adding the inverter voltage output signal and the superimposed voltage in the next cycle, and the switch tube on-off signal is generated after PWM modulation to drive the switch tube.

2. The VOC-based three-phase grid-connected inverter non-transient control method according to claim 1, characterized in that: The three-phase current i of the inverter grid abc The coordinate transformation matrix for sampling and abc / αβ transformation is:

3. The VOC-based three-phase grid-connected inverter non-transient control method according to claim 1, characterized in that: The grid-connected current command value is calculated based on the active power command value and the reactive power command value. The specific formula is: Among them, v α and v β Indicates the inverter grid-connected voltage, P * is the active power command value, Q * is the reactive power command value.

4. The VOC-based three-phase grid-connected inverter non-transient control method according to claim 1, characterized in that: The virtual oscillator includes an inductor L, a capacitor C, a controlled voltage source v m , controlled voltage source v u , controlled current source i m , controlled current source i u , the inductor L is connected in series with a controlled voltage source v m and a controlled voltage source v u Then connect a capacitor C and a controlled current source i in parallel. m A controlled current source i u .

5. The VOC-based three-phase grid-connected inverter non-transient control method according to claim 1, characterized in that: The specific method of controlling the virtual oscillator according to the grid-connected current command value, collecting the capacitor voltage and inductor current of the virtual oscillator and amplifying them as the inverter grid-connected voltage is as follows: The three-phase current i α 、i β and grid-connected current command value and By comparison, the error is amplified by K after the rotation matrix. i times to get u1 and u2, u1 as the controlled current source i u The current u2 is used as the controlled voltage source v after passing the coefficient ε u Voltage; Collect the voltage u on the capacitor C of the LC second-order oscillator C and the inductor current i L As state variables x1 and x2, the controlled voltage source v is calculated according to the state variables m and the controlled current source i m Signal, state variable amplified to a fixed amplitude V n As the inverter voltage command v α 、v β .

6. The VOC-based three-phase grid-connected inverter non-transient control method according to claim 5, characterized in that: Coefficient ε, controlled voltage source v m and the controlled current source i m Specifically: Among them, k i represents the amplification factor, ω is the grid power frequency angular frequency, x1 and x2 are state variables, X n is the nominal value of the state variable, ||x|| is the modulus of the state variable, and ξ is a constant.

7. The VOC-based three-phase grid-connected inverter non-transient control method according to claim 1, characterized in that: Through the active power command value P * and reactive power command value Q * The phase angle difference between the inverter output voltage and the grid voltage is obtained by approximate calculation of the circuit parameters. The specific formula is: Among them, V g is the grid voltage amplitude, R is the circuit equivalent resistance, L eq It is the sum of the filter inductance and the grid-side inductance.

8. The VOC-based three-phase grid-connected inverter non-transient control method according to claim 1, characterized in that: Calculate the inverter voltage output signal v' for the next cycle αβ , the corresponding formula is: v' αβ NV n sin(wt+δ * )4 Among them, δ * represents the next steady-state phase angle difference, δ0 represents the current steady-state phase angle difference, P * represents the next steady-state power instruction, and P0 represents the current steady-state power instruction.

9. The VOC-based three-phase grid-connected inverter non-transient control method according to claim 1, characterized in that: According to the Kuramoto model, an oscillator operating in an ideal steady state is used to apply coupled feedback to the output modulation wave. The corresponding formula is: Where θ1 is the phase of the oscillator in AHO, θ2 is the phase of the oscillator running in the desired state, K represents the coupling coefficient, and W nom is the rated frequency, ΔV' α and ΔV' β They respectively represent the coupling effect exerted by the ideal oscillator on the output modulation wave.

10. The VOC-based three-phase grid-connected inverter non-transient control method according to claim 1, characterized in that: The superimposed voltage duration Δt is calculated based on the instantaneous current value at the time when the voltage signal is updated in each cycle. The corresponding formula is: Among them, u add is the superimposed voltage amplitude, I0 is the instantaneous current value at the time of voltage signal update, L f is the filter inductor, R f is the filter resistor.

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