阅读说明：本技术 多模态无缝切换光伏逆变器控制器和光伏逆变器系统 (Multi-modal seamless switching photovoltaic inverter controller and photovoltaic inverter system ) 是由 梁纪峰 李铁成 曾四鸣 范辉 罗蓬 易皓 周文 王振雄 陈二松 于 2021-08-06 设计创作，主要内容包括：本发明实施例涉及配电网逆变器技术领域,公开了一种多模态无缝切换光伏逆变器控制器和光伏逆变器系统。上述多模态无缝切换光伏逆变器控制器包括：控制器用于控制光伏逆变器运行以及控制光伏逆变器切换工作模式,光伏逆变器工作模式包括并网模式和离网模式；由并网模式切换至离网模式时,控制器对离网时检测到的相位进行锁定,并生成连续变化的相位,以及将并网模式的电流指令发送给离网模式的电压外环PI调节器；由离网模式切换至并网模式时,控制器控制光伏逆变器切换前后的相位输出连续变化。(The embodiment of the invention relates to the technical field of power distribution network inverters, and discloses a multi-mode seamless switching photovoltaic inverter controller and a photovoltaic inverter system. The above-mentioned multimode seamless switching photovoltaic inverter controller includes: the controller is used for controlling the photovoltaic inverter to operate and controlling the photovoltaic inverter to switch the working mode, and the working mode of the photovoltaic inverter comprises a grid-connected mode and an off-grid mode; when the grid-connected mode is switched to the off-grid mode, the controller locks the phase detected in the off-grid mode, generates a continuously-changed phase, and sends a current instruction of the grid-connected mode to the voltage outer ring PI regulator of the off-grid mode; when the off-grid mode is switched to the grid-connected mode, the controller controls the phase output of the photovoltaic inverter to continuously change before and after switching.)

1. The controller for the multi-mode seamless switching photovoltaic inverter is characterized in that the controller is used for controlling the photovoltaic inverter to operate and controlling the photovoltaic inverter to switch the working modes, and the working modes of the photovoltaic inverter comprise a grid-connected mode and an off-grid mode;

when the grid-connected mode is switched to the off-grid mode, the controller locks the phase detected in the off-grid mode, generates a continuously-changed phase, and sends a current instruction of the grid-connected mode to the voltage outer ring PI regulator of the off-grid mode;

when the off-grid mode is switched to the grid-connected mode, the controller controls the phase output of the photovoltaic inverter to continuously change before and after switching.

2. The controller of a multimodal seamless switching photovoltaic inverter of claim 1, wherein the controller comprises an operation control module and a switching control module, the operation control module is configured to control the operation of the photovoltaic inverter, and the switching control module is configured to control the switching operation mode of the photovoltaic inverter;

the switching control module comprises a power grid instantaneous phase detection module, a phase pre-synchronization module and a reference phase generation module, wherein the power grid instantaneous phase detection module is used for detecting the phase of a power grid in real time, the reference phase generation module is used for generating a continuously-changed phase when the grid-connected mode is switched to the grid-disconnected mode, and the phase pre-synchronization module is used for controlling the phase output of the photovoltaic inverter before and after switching to be continuously changed when the grid-disconnected mode is switched to the grid-connected mode.

3. The controller of a multimodal seamless switching photovoltaic inverter of claim 1, wherein the photovoltaic inverter comprises a front stage Boost converter, a back stage inverter, and a filter;

the operation control module is specifically used for controlling the constant voltage of the capacitor through the preceding stage Boost converter, and the process is as follows:

obtaining capacitor voltage u output by Boost converter_dc；

Calculating the capacitor voltage u_dcAnd a predetermined DC capacitor voltage reference u_dcrefA first difference of (a);

performing PI regulation on the first difference value to generate a modulation wave, wherein a PI regulation formula is as follows:

in the formula u_{dc_pwm}For modulating signals for Boost switching tubes, k_{p_dc}Is the value of the proportional controller of the PI regulator, k_{i_dc}Integrating the value of the controller for the PI regulator, u_dcrefIs a reference value of the DC side capacitor voltage u_dcThe PWM waveform modulates the duty ratio of a switch in a Boost booster circuit for the voltage of a direct-current side capacitor.

4. The controller of a multimodal seamless switching photovoltaic inverter of claim 1, wherein the photovoltaic inverter comprises a front stage Boost converter, a back stage inverter, and a filter;

the operation control module is specifically used for controlling the rear-stage inverter to output constant power, and the process is as follows:

carrying out abc/dq conversion on the voltage and the current of a system bus to obtain a voltage component and a current component under a dq coordinate system;

calculating a current reference signal from the voltage component;

calculating a second difference value between the current reference signal and the current component, and generating a voltage modulation signal according to the second difference value;

and carrying out dq/abc transformation on the voltage modulation signal.

5. The controller of a multimodal seamless switching photovoltaic inverter of claim 4, wherein the abc/dq transformation expression is:

in the formula i_a、i_b、i_cRespectively the value i of the inverter output current in the abc three-phase stationary coordinate system_d、i_qFor the value of the inverter output current in dq synchronous rotating coordinate system, u_a、u_b、u_cRespectively, the value u of the output voltage of the inverter in an abc three-phase static coordinate system_d、u_qFor the value of the inverter output voltage in the dq synchronous rotation coordinate system, theta₁Is the included angle between the d axis and the phase reference axis;

the dq/abc transform is the inverse of the abc/dq transform, and the expression is:

6. the controller of a multimodal seamless switching pv inverter according to claim 4, wherein in the grid-tie mode, the current reference signal is calculated by the formula:

the current reference signal comprises a current active component reference value and a current reactive component reference value, wherein i_{d_ref}And i_{q_ref}Respectively a current active component reference value and a current reactive component reference value, P_refIs an active power command value, Q_refIs a reactive power command value, u_dAnd u_qRespectively an active component and a reactive component of the output voltage;

in the off-grid mode, the calculation formula of the current reference signal is as follows:

in the formula i_{d_ref}And i_{q_ref}Are respectively asReference value of active component and reference value of reactive component of output current of inverter, k_{p_du}Value, k, of proportional controller for the active component of the output voltage of the inverter PI regulator_{i_du}Value, k, of integral controller for the output voltage active component PI regulator of an inverter_{p_qu}Value, k, of proportional controller for output voltage reactive component PI regulator of inverter_{i_qu}Integrating controller value, u, for an inverter output voltage reactive component PI regulator_{d_ref}For the reference value of the active component of the output voltage of the inverter, u_dcIs a real component of the output voltage of the inverter u_{q_ref}For the output of a reference value of the reactive component of the voltage, u, of the inverter_qAnd outputting a voltage reactive component for the inverter.

7. The controller for a multimodal seamless switching photovoltaic inverter according to claim 4, wherein said calculating a second difference between said current reference signal and said current component, and generating a voltage modulation signal based on said second difference comprises:

calculating a current reference signal i_{d_ref}And i_{q_ref}And i_d、i_qThe second difference value is used for generating a voltage modulation signal m through a PI regulator_dAnd m_qVoltage modulation signal m_dAnd m_qThe calculation formula of (2) is as follows:

in the formula, m_d、m_qD-axis modulation quantity of inverter output voltage and q-axis modulation quantity, k of inverter output voltage_{p_di}Value, k, of proportional controller for the output current active component of an inverter PI regulator_{i_di}Value, k, of integral controller for the output current active component PI regulator of an inverter_{p_qi}Value, k, of proportional controller for output current reactive component PI regulator of inverter_{i_qi}Value of integral controller for output current reactive component PI regulator of inverter_{d_ref}Reference value for active component of output current of inverter，i_dFor the active component of the output current of the inverter i_{q_ref}For the reference value of the reactive component of the output current of the inverter, i_qAnd outputting reactive components of current for the inverter.

8. The controller of a multimodal seamless switching photovoltaic inverter of claim 2, wherein the grid instantaneous phase detection module is specifically configured to:

real-time detection of three-phase voltage u of an electrical network_ga、u_gbAnd u_gcPerforming abc/dq conversion to obtain a voltage component u of a q axis_q；

Calculating the voltage component u_qA third difference from the preset reference value;

performing PI regulation on the third difference value to obtain the instantaneous angular frequency omega of the power grid voltage_g；

For the angular frequency ω_gThe instantaneous phase theta of the power grid is obtained by integration_g；

Wherein the angular frequency ω_gThe calculation formula of (2) is as follows:

in the formula, ω_gFor grid voltage angular frequency, k_pValue of proportional element of PI regulator, k_iValue of the integral element of the PI regulator, u_qFor the q-axis component, omega, of the mains voltage₀Is the initial frequency.

9. The controller of a multimodal seamless switching photovoltaic inverter of claim 2, wherein the phase pre-synchronization module is specifically configured to:

obtaining a grid phase θ_gWith microgrid phase theta_invThe phase difference Δ θ between;

performing PI adjustment on the phase difference delta theta to obtain a frequency compensation signal delta f;

calculating a frequency compensation signal delta f and a rated frequency f in the off-grid mode_refIs a fourth difference of；

Determining a frequency reference value f of the inverter according to the fourth difference value, wherein a calculation formula is as follows:

where f is the inverter output frequency, f_refFor the grid frequency, f is the frequency compensation signal, k_pIs the value of the proportional controller of the PI regulator, k_iIntegrating the value of the controller for the PI regulator, theta_gFor the phase of the mains voltage, theta_invThe inverter is output with a voltage phase.

10. A multimodal seamless switching pv inverter system comprising a pv inverter and a controller of a multimodal seamless switching pv inverter as claimed in any of claims 1 to 9.

Technical Field

The invention relates to the technical field of power distribution network inverters, in particular to a multi-mode seamless switching photovoltaic inverter controller and a photovoltaic inverter system.

Background

With the development of social economy, the modern power industry has stepped into the era of a large power grid with large units, ultrahigh voltage and alternating current and direct current mixed, but as fossil fuels are gradually exhausted and the environmental pressure is gradually increased, the traditional power system pattern is gradually challenged by the distributed power generation technology based on renewable energy, and the permeability of a microgrid containing green new energy such as photovoltaic energy, wind power energy and the like in a power distribution network is higher and higher. When the new energy power generation is connected to the power distribution network in a large scale, the requirement of a user on the electric energy quality is met while the safe and stable operation of the power distribution network is realized. The mutual supplement of the micro-grid mainly based on the distributed micro-source and the traditional large power grid is an ideal way of giving full play to the advantages of new energy and providing reliable and high-quality electric energy. Photovoltaic power generation is mainly applied to distributed grid connection at present as a main renewable energy source. When the distributed photovoltaic system is connected to a power distribution network to work, the distributed photovoltaic system is possibly separated from the external power grid support after the power grid side breaks down, and enters an off-grid mode. At the moment, the distributed photovoltaic power generation system needs to be switched from a grid-connected mode to an off-grid operation state, and emergency power supply under an extreme mode is provided for users.

In the current research, a current mode control technology is generally adopted in a traditional photovoltaic inverter in a grid-connected mode, when a large power grid fails, the power grid is directly cut off from the power grid and enters an independent off-grid state, grid connection is carried out again after the failure is repaired, multi-mode smooth switching is difficult to achieve, a grid-connected static switch lags behind control program switching and sudden change occurs to control instructions before and after switching, voltage and current distortion is easily generated before and after switching, and power supply safety is damaged.

Disclosure of Invention

In view of this, embodiments of the present invention provide a multi-mode seamless switching photovoltaic inverter controller and a photovoltaic inverter system, so that the photovoltaic inverter can implement smooth switching between multiple control modes.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, an embodiment of the present invention provides a controller for a multi-modal seamless switching photovoltaic inverter, including: the controller is used for controlling the photovoltaic inverter to operate and controlling the photovoltaic inverter to switch working modes, and the working modes of the photovoltaic inverter comprise a grid-connected mode and an off-grid mode; when the grid-connected mode is switched to the off-grid mode, the controller locks the phase detected in the off-grid mode, generates a continuously-changed phase, and sends a current instruction of the grid-connected mode to the voltage outer ring PI regulator of the off-grid mode; when the off-grid mode is switched to the grid-connected mode, the controller controls the phase output of the photovoltaic inverter to continuously change before and after switching.

Based on the first aspect, in some embodiments, the controller includes an operation control module and a switching control module, the operation control module is configured to control the operation of the photovoltaic inverter, and the switching control module is configured to control the switching operation mode of the photovoltaic inverter; the switching control module comprises a power grid instantaneous phase detection module, a phase pre-synchronization module and a reference phase generation module, wherein the power grid instantaneous phase detection module is used for detecting the phase of a power grid in real time, the reference phase generation module is used for generating a continuously-changed phase when the grid-connected mode is switched to the grid-disconnected mode, and the phase pre-synchronization module is used for controlling the phase output of the photovoltaic inverter before and after switching to be continuously changed when the grid-disconnected mode is switched to the grid-connected mode.

Based on the first aspect, in some embodiments, the photovoltaic inverter includes a front stage Boost converter, a rear stage inverter, and a filter; the operation control module is specifically used for controlling the constant voltage of the capacitor through the preceding stage Boost converter, and the process is as follows: obtaining capacitor voltage u output by Boost converter_dc(ii) a Calculating the capacitor voltage u_dcAnd a predetermined DC capacitor voltage reference u_dcrefA first difference of (a); performing PI regulation on the first difference value to generate a modulation wave, wherein a PI regulation formula is as follows:

in the formula u_{dc_pwm}For modulating signals for Boost switching tubes, k_{p_dc}Is the value of the proportional controller of the PI regulator, k_{i_dc}Integrating the value of the controller for the PI regulator, u_dcrefIs a reference value of the DC side capacitor voltage u_dcThe PWM waveform modulates the duty ratio of a switch in a Boost booster circuit for the voltage of a direct-current side capacitor.

Based on the first aspect, in some embodiments, the photovoltaic inverter includes a front stage Boost converter, a rear stage inverter, and a filter; the operation control module is specifically used for controlling the rear-stage inverter to output constant power, and the process is as follows: carrying out abc/dq conversion on the voltage and the current of a system bus to obtain a voltage component and a current component under a dq coordinate system; calculating a current reference signal from the voltage component; calculating a second difference value between the current reference signal and the current component, and generating a voltage modulation signal according to the second difference value; and carrying out dq/abc transformation on the voltage modulation signal.

Based on the first aspect, in some embodiments, the abc/dq transformation expression is:

in the formula i_a、i_b、i_cRespectively the value i of the inverter output current in the abc three-phase stationary coordinate system_d、i_qFor the value of the inverter output current in dq synchronous rotating coordinate system, u_a、u_b、u_cRespectively, the value u of the output voltage of the inverter in an abc three-phase static coordinate system_d、u_qFor the value of the inverter output voltage in the dq synchronous rotation coordinate system, theta₁Is the included angle between the d axis and the phase reference axis; the dq/abc transform is the inverse of the abc/dq transform, and the expression is:

based on the first aspect, in some embodiments, in the grid-connected mode, the calculation formula of the current reference signal is:

the current reference signal comprises a current active component reference value and a current reactive component reference value, wherein i_{d_ref}And i_{q_ref}Respectively a current active component reference value and a current reactive component reference value, P_refIs an active power command value, Q_refIs a reactive power command value, u_dAnd u_qRespectively an active component and a reactive component of the output voltage; in the off-grid mode, the calculation formula of the current reference signal is as follows:

in the formula i_{d_ref}And i_{q_ref}Respectively outputting a reference value of active component and a reference value of reactive component, k_{p_du}Value, k, of proportional controller for the active component of the output voltage of the inverter PI regulator_{i_du}Value, k, of integral controller for the output voltage active component PI regulator of an inverter_{p_qu}Value, k, of proportional controller for output voltage reactive component PI regulator of inverter_{i_qu}Integrating controller value, u, for an inverter output voltage reactive component PI regulator_{d_ref}For the reference value of the active component of the output voltage of the inverter, u_dcIs a real component of the output voltage of the inverter u_{q_ref}For the output of a reference value of the reactive component of the voltage, u, of the inverter_qAnd outputting a voltage reactive component for the inverter.

Based on the first aspect, in some embodiments, the calculating a second difference between the current reference signal and the current component, and generating a voltage modulation signal according to the second difference comprises: calculating a current reference signal i_{d_ref}And i_{q_ref}And i_d、i_qThe second difference value is used for generating a voltage modulation signal m through a PI regulator_dAnd m_qVoltage modulation signal m_dAnd m_qThe calculation formula of (2) is as follows:

in the formula, m_d、m_qRespectively an inverter output voltage d-axis modulation quantity and an inverter output voltage q-axis modulation quantity,

k_{p_di}value, k, of proportional controller for the output current active component of an inverter PI regulator_{i_di}Value, k, of integral controller for the output current active component PI regulator of an inverter_{p_qi}Value of proportional controller for output current reactive component PI regulator of inverter，k_{i_qi}Value of integral controller for output current reactive component PI regulator of inverter_{d_ref}Reference value of active component for output current of inverter i_dFor the active component of the output current of the inverter i_{q_ref}For the reference value of the reactive component of the output current of the inverter, i_qAnd outputting reactive components of current for the inverter.

Based on the first aspect, in some embodiments, the grid instantaneous phase detection module is specifically configured to: real-time detection of three-phase voltage u of an electrical network_ga、u_gbAnd u_gcPerforming abc/dq conversion to obtain a voltage component u of a q axis_q(ii) a Calculating the voltage component u_qA third difference from the preset reference value; performing PI regulation on the third difference value to obtain the instantaneous angular frequency omega of the power grid voltage_g(ii) a For the angular frequency ω_gThe instantaneous phase theta of the power grid is obtained by integration_g(ii) a Wherein the angular frequency ω_gThe calculation formula of (2) is as follows:

in the formula, ω_gFor grid voltage angular frequency, k_pValue of proportional element of PI regulator, k_iValue of the integral element of the PI regulator, u_qFor the q-axis component, omega, of the mains voltage₀Is the initial frequency.

Based on the first aspect, in some embodiments, the phase pre-synchronization module is specifically configured to: obtaining a grid phase θ_gWith microgrid phase theta_invThe phase difference Δ θ between; performing PI adjustment on the phase difference delta theta to obtain a frequency compensation signal delta f; calculating a frequency compensation signal delta f and a rated frequency f in the off-grid mode_refA fourth difference of (d); determining a frequency reference value f of the inverter according to the fourth difference value, wherein a calculation formula is as follows:

wherein f is the inverter outputFrequency, f_refFor the grid frequency, f is the frequency compensation signal, k_pIs the value of the proportional controller of the PI regulator, k_iIntegrating the value of the controller for the PI regulator, theta_gFor the phase of the mains voltage, theta_invThe inverter is output with a voltage phase.

In a second aspect, embodiments of the present invention provide a multi-modal seamless switching pv inverter system, including a pv inverter and a controller of the pv inverter as described in the first aspect above.

In the embodiment of the invention, the controller of the multimode seamless switching photovoltaic inverter can meet the power requirement of a load during grid-connected operation and off-grid operation, maintain the stability of the voltage and the frequency of a power grid, realize seamless smooth switching of a grid-connected mode and an off-grid mode, detect the phase of the power grid in real time during grid-connected and off-grid switching, ensure the seamless switching of the inverter by the phase pre-synchronization module and the reference phase generation module, and avoid generating impulse voltage current.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.

Fig. 1 is a schematic structural diagram of a multi-modal seamless switching photovoltaic inverter system according to an embodiment of the present invention;

fig. 2 is a control block diagram of a grid-connected mode of a photovoltaic inverter system according to an embodiment of the present invention;

fig. 3 is a block diagram of an off-grid mode control of a photovoltaic inverter system according to an embodiment of the present invention;

fig. 4 is a structure diagram of a piconet in parallel and off-grid switching according to an embodiment of the present invention;

fig. 5 is a control block diagram of a power grid instantaneous phase detection module according to an embodiment of the present invention;

fig. 6 is a control block diagram of a phase pre-synchronization module according to an embodiment of the present invention;

FIG. 7 is a control block diagram of a reference phase generation module according to an embodiment of the present invention;

fig. 8 is a voltage waveform diagram of a dc side capacitor simulated when the photovoltaic inverter switches from the off-grid mode to the grid-connected mode according to the embodiment of the present invention;

fig. 9 is a graph of an output voltage waveform of a photovoltaic inverter simulated by switching the photovoltaic inverter from an off-grid mode to a grid-connected mode according to an embodiment of the present invention;

fig. 10 is a graph of output current waveforms of a photovoltaic inverter simulated when the photovoltaic inverter is switched from an off-grid mode to a grid-connected mode according to an embodiment of the present invention;

fig. 11 is a waveform diagram of output power of a photovoltaic inverter simulated by switching the photovoltaic inverter from an off-grid mode to a grid-connected mode according to an embodiment of the present invention;

fig. 12 is a voltage waveform diagram of a dc side capacitor for simulating switching of a photovoltaic inverter from a grid-connected mode to an off-grid mode according to an embodiment of the present invention;

fig. 13 is a graph of an output voltage waveform of a photovoltaic inverter simulated when the photovoltaic inverter switches from a grid-connected mode to an off-grid mode according to an embodiment of the present invention;

fig. 14 is a graph of output current waveforms of a photovoltaic inverter simulated when the photovoltaic inverter is switched from a grid-connected mode to an off-grid mode according to an embodiment of the present invention;

fig. 15 is a waveform diagram of output power of a photovoltaic inverter simulated when the photovoltaic inverter is switched from a grid-connected mode to an off-grid mode according to an embodiment of the present invention;

fig. 16 is a schematic diagram of a terminal device according to an embodiment of the present invention.

Detailed Description

The present invention will be more clearly described below with reference to specific examples. The following examples will assist those skilled in the art in further understanding the role of the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the following description is made by way of specific embodiments with reference to the accompanying drawings.

The photovoltaic inverter is controlled in a current mode in a grid-connected mode, and constant power is output; and voltage type control is adopted in an off-grid mode, so that the voltage frequency of the power grid is maintained to be stable. The photovoltaic inverter system capable of realizing multi-mode seamless switching is provided for solving the problem that the current and voltage waveform distortion is easily generated when the traditional photovoltaic inverter is switched in a grid-connected and off-grid working mode.

The multi-mode seamless switching photovoltaic inverter system provided by the invention is shown in fig. 1 and comprises a photovoltaic inverter and a controller of the photovoltaic inverter. The photovoltaic array is connected with a photovoltaic inverter, the photovoltaic inverter is connected with a power grid and a load, and the photovoltaic inverter comprises a front-stage Boost converter, a rear-stage inverter and an LC filter. The photovoltaic array is electrically connected with the front-stage Boost converter, the front-stage Boost converter is electrically connected with the rear-stage inverter, the rear-stage inverter is electrically connected with the LC filter, the LC filter is connected with the load after being connected with the switch S in series, and the power grid is connected with the load in parallel.

The controller of the photovoltaic inverter comprises an operation control module and a switching control module; the operation control module is used for controlling the operation of the photovoltaic inverter, the switching control module is used for controlling the photovoltaic inverter to switch working modes, and the working modes of the photovoltaic inverter comprise a grid-connected mode and an off-grid mode; the switching control module comprises a power grid instantaneous phase detection module, a phase pre-synchronization module and a reference phase generation module; the power grid instantaneous phase detection module is used for detecting the phase of a power grid in real time; when the grid-connected mode is switched to the off-grid mode, the phase detected in the off-grid mode is locked, the reference phase generation module is used for generating continuous phase change, and a current instruction of the grid-connected mode is sent to the voltage outer ring PI regulator of the off-grid mode; when the off-grid mode is switched to the grid-connected mode, the phase output changes continuously before and after the photovoltaic inverter is switched through the phase pre-synchronization module.

The grid-connected mode control block diagram of the photovoltaic inverter system is shown as 2, and the operation process of the grid-connected mode comprises steps 101 to 102.

Step 101: and the operation control module controls the voltage of the capacitor to be constant through the preceding stage Boost converter.

Obtaining output capacitor voltage u of Boost converter_dcAnd a given DC capacitor voltage reference u_dcrefComparing and making difference, carrying out PI regulation on the generated difference value to generate a modulation wave, wherein the calculation formula is as follows:

in the formula u_{dc_pwm}For modulating signals for Boost switching tubes, k_{p_dc}Is the value of the proportional controller of the PI regulator, k_{i_dc}Integrating the value of the controller for the PI regulator, u_dcrefIs a reference value of the DC side capacitor voltage u_dcThe PWM waveform modulates the duty ratio of a switch in a Boost booster circuit for the voltage of a direct-current side capacitor.

Step 102: the operation control module controls the rear-stage inverter so that the photovoltaic inverter outputs constant power.

Step 1021: and carrying out abc/dq transformation on the system bus voltage and current to obtain a voltage component and a current component in a dq coordinate system.

The system bus voltage u_abcObtaining a component u under a dq coordinate system after abc/dq transformation_d、u_qSystem bus current i_abcObtaining a component i under a dq coordinate system after abc/dq transformation_d、i_q. The formula for the abc/dq transformation is:

in the formula i_a、i_b、i_cRespectively the value i of the inverter output current in the abc three-phase stationary coordinate system_d、i_qFor the value of the inverter output current in dq synchronous rotating coordinate system, u_a、u_b、u_cRespectively, the value u of the output voltage of the inverter in an abc three-phase static coordinate system_d、u_qFor the inverter to output voltage atValue theta in dq synchronous rotation coordinate system₁Is the angle between the d-axis and the phase reference axis.

Step 1022: a current reference signal is calculated from the voltage component.

The current reference signal is calculated as follows:

in the formula i_{d_ref}And i_{q_ref}Respectively a current active component reference value and a current reactive component reference value, P_refIs an active power command value, Q_refIs a reactive power command value, u_dAnd u_qThe active component and the reactive component of the output voltage are respectively.

Step 1023: the current reference signal is subtracted from the current component to generate a voltage modulated signal.

Current reference signal i to be generated_{d_ref}And i_{q_ref}And i_d、i_qAfter comparison and difference, the difference is controlled by a PI regulator to generate a voltage modulation signal m_d、m_qThe calculation formula is as follows:

in the formula, m_d、m_qD-axis modulation quantity of inverter output voltage and q-axis modulation quantity, k of inverter output voltage_{p_di}Value, k, of proportional controller for the output current active component of an inverter PI regulator_{i_di}Value, k, of integral controller for the output current active component PI regulator of an inverter_{p_qi}Value, k, of proportional controller for output current reactive component PI regulator of inverter_{i_qi}Value of integral controller for output current reactive component PI regulator of inverter_{d_ref}Reference value of active component for output current of inverter i_dFor the active component of the output current of the inverter i_{q_ref}For the reference value of the reactive component of the output current of the inverter, i_qTo be invertedThe output current of the converter is a reactive component.

Step 1024: the voltage modulated signal is dq/abc transformed.

Voltage modulation signal m_d、m_qAnd obtaining a modulation signal of the rear-stage inverter through a dq/abc conversion module, wherein the calculation formula of the dq/abc conversion module is as follows:

in the formula i_a、i_b、i_cRespectively the value i of the inverter output current in the abc three-phase stationary coordinate system_d、i_qFor the value of the inverter output current in dq synchronous rotating coordinate system, u_a、u_b、u_cRespectively, the value u of the output voltage of the inverter in an abc three-phase static coordinate system_d、u_qValue theta of output voltage of inverter under dq synchronous rotation coordinate system₁Is the angle between the d-axis and the phase reference axis.

The off-grid mode control block diagram of the photovoltaic inverter system provided by the invention is shown as 3, and comprises steps 201 to 202:

step 201: the operation control module controls the voltage of the capacitor to be constant through the preceding stage Boost converter, and power balance between source loads is achieved.

Obtaining output capacitor voltage u of Boost converter_dcAnd a given DC capacitor voltage reference u_dcrefComparing and making difference, carrying out PI regulation on the generated difference value to generate a modulation wave, wherein the calculation formula is as follows:

in the formula u_{dc_pwm}For modulating signals for Boost switching tubes, k_{p_dc}Is the value of the proportional controller of the PI regulator, k_{i_dc}Integrating the value of the controller for the PI regulator, u_dcrefIs a reference value of the DC side capacitor voltage u_dcFor DC side capacitor voltage, PWM waveform modulates the switch in Boost booster circuitThe duty cycle is off.

Step 202: and the voltage frequency support of the alternating current bus is realized by adopting V/f control by a rear-stage inverter.

Step 2021: and carrying out abc/dq transformation on the system bus voltage and current to obtain a voltage component and a current component in a dq coordinate system.

The system bus voltage u_abcObtaining a component u under a dq coordinate system after abc/dq transformation_d、u_qSystem bus current i_abcObtaining a component i under a dq coordinate system after abc/dq transformation_d、i_q。

Step 2022: a current reference signal is calculated from the voltage component.

Will u_d、u_qWith a given voltage reference value U_drefAnd U_qrefComparing and making difference, making PI regulation on the difference value to produce current inner loop reference signal i_drefAnd i_qrefThe calculation formula is as follows:

in the formula i_{d_ref}And i_{q_ref}Respectively outputting a reference value of active component and a reference value of reactive component, k_{p_du}Value, k, of proportional controller for the active component of the output voltage of the inverter PI regulator_{i_du}Value, k, of integral controller for the output voltage active component PI regulator of an inverter_{p_qu}Value, k, of proportional controller for output voltage reactive component PI regulator of inverter_{i_qu}Integrating controller value, u, for an inverter output voltage reactive component PI regulator_{d_ref}For the reference value of the active component of the output voltage of the inverter, u_dcIs a real component of the output voltage of the inverter u_{q_ref}For the output of a reference value of the reactive component of the voltage, u, of the inverter_qAnd outputting a voltage reactive component for the inverter.

Step 2023: the current reference signal is subtracted from the current component to generate a voltage modulated signal. Current reference signal i_dref、i_qrefAre respectively connected with i_d、i_qAfter comparison and difference, the difference is input into a current inner ring, and a voltage modulation signal m is generated through PI regulation_d、m_q。

Step 2024: the voltage modulated signal is dq/abc transformed.

Voltage modulation signal m_d、m_qAnd obtaining a modulation signal of the rear-stage inverter through a dq/abc conversion module.

The structure diagram of the microgrid with grid-connected and off-grid switching provided by the invention is shown in fig. 4, the inverter output voltage phase is continuously changed when the mode switching is realized through the switching control module, and the switching control module comprises the following three parts:

1) a power grid instantaneous phase detection module;

2) a phase pre-synchronization module;

3) a reference phase generation module.

The control block diagram of the grid instantaneous phase detection module is shown in fig. 5, and the control block diagram comprises steps a1 to a 2.

Step A1: real-time detection of three-phase voltage u of an electrical network_ga、u_gb、u_gcPerforming abc/dq conversion to obtain a voltage component u of a q axis_q。

The expression is as follows:

u_q＝Vsin(θ-θ_g) (7)

in the formula u_qIs a component of the q-axis voltage, representing the phase angle theta obtained by phase locking_gAnd the phase angle theta of the actual grid voltage, V being the voltage amplitude, theta_gTo phase lock the resulting phase angle, θ is the phase angle of the actual grid voltage.

Step A2: and calculating the instantaneous phase of the power grid according to the voltage component.

Specifically, u is_qComparing with a given reference value 0 to obtain a difference value, and obtaining the tracked instantaneous angular frequency omega of the grid voltage through a PI regulator_gDiagonal frequency omega_gThe instantaneous phase theta of the power grid is obtained by integration_g。

Calculating angular frequency omega_gThe formula of (1) is:

in the formula, ω_gFor grid voltage angular frequency, k_pValue of proportional element of PI regulator, k_iValue of the integral element of the PI regulator, u_qFor the q-axis component, omega, of the mains voltage₀Is the initial frequency.

The phase pre-synchronization module control block diagram is shown in fig. 6, and includes steps B1 to B3:

step B1: obtaining a grid phase θ_gWith microgrid phase theta_invThe phase difference between Δ θ.

Step B2: PI regulating the delta theta to obtain a frequency compensation signal delta f, and comparing the frequency compensation signal delta f with a rated frequency f in an off-grid mode_refAnd obtaining a frequency reference value of the inverter by taking the difference, wherein the calculation formula is as follows:

where f is the inverter output frequency, f_refFor the grid frequency, f is the frequency compensation signal, k_pIs the value of the proportional controller of the PI regulator, k_iIntegrating the value of the controller for the PI regulator, theta_gFor the phase of the mains voltage, theta_invThe inverter is output with a voltage phase.

Step B3: the voltage frequency of the inverter is changed to approach the grid phase.

The control block diagram of the reference phase generation module is shown in fig. 7, and includes steps C1 through C2.

Step C1: when the photovoltaic inverter is in grid-connected operation, Ctrl is 1, the selection switch S is switched on 2 channels, and theta_inv＝θ_g. When the upper power supply is suddenly cut off, Ctrl is equal to 0, the selection switch S is switched on the channel 1 to lock the off-line phase, and theta_invAt an angular frequency of 2 pi f_refAnd continuing to operate.

Step C2: when the inverter is switched from the off-grid mode to the grid-connected operation, the phase pre-synchronization is completed before the conversion due to the existence of the phase pre-synchronization module,i.e. theta_inv＝θ_g。

The method for controlling the photovoltaic inverter to smoothly switch in the grid-connected mode and the off-grid mode through the switching control module comprises the following steps 301 to 302.

Step 301: and the photovoltaic inverter is smoothly switched from the off-grid mode to the grid-connected mode.

After the photovoltaic inverter is switched to a grid-connected presynchronization signal, starting a presynchronization program; the microgrid phase-locked angle tracks the phase of the power grid step by step, and after synchronization is realized, a grid-connected control signal Ctrl is set to be 1; and switching the inverter current inner loop command from the off-grid mode to the grid-connected mode.

Step 302: and the photovoltaic inverter is smoothly switched from a grid-connected mode to an off-grid mode.

Setting the control signal Ctrl to 0, and locking the off-line phase; tracking off-line phase of reference frequency of master control inverter, and working angular frequency theta of inverter_invAt 2 pi f_refContinuing to operate; endowing the working value of the inverter outer ring PI regulator in the grid-connected mode to the off-grid mode inverter outer ring PI regulator, wherein the specific value is as follows:

I_{dq_ref_2_initial}＝I_{dq_ref_1_final} (10)

in the formula I_{dq_ref_2_initial}Initial output value, I, of voltage outer loop PI regulator in off-grid mode_{dq_ref_1_final}The current command value is in the grid-connected mode.

Example 1 to test the invention, a simulation of a photovoltaic inverter was built in MATLAB/Simulink.

Fig. 8, fig. 11, and the simulation waveform diagrams of switching the pv inverter from the off-grid mode to the on-grid mode are respectively a dc-side capacitor voltage waveform, a pv inverter output current waveform, and a pv inverter output power waveform. The three-phase output voltage, the three-phase output current and the voltage waveform of the direct-current side capacitor of the photovoltaic inverter can be smoothly transited. After the grid-connected mode is switched to, the internal power of the micro-grid is balanced by the stored energy, and the power of the photovoltaic inverter is changed from 10kW output power to 5kW output constant power in the off-grid state.

As shown in fig. 12, 13, 14, and 15, the simulated waveforms of the switching of the pv inverter from the grid-connected mode to the off-grid mode are a dc-side capacitor voltage waveform, a pv inverter output current waveform, and a pv inverter output power waveform, respectively. The photovoltaic mode is changed from grid connection to off-grid mode, the frequency and phase change of output voltage is smooth in the conversion process, and voltage and current are continuous and have no impact; the output power of the photovoltaic inverter is changed from 8kW which is constantly output during grid connection to 10kW which is balanced with load power during grid disconnection.

Fig. 16 is a schematic diagram of a terminal device according to an embodiment of the present invention. As shown in fig. 16, the terminal device 4 of this embodiment includes: a processor 40, a memory 41, and a computer program 42, such as a multi-modal seamless switching photovoltaic inverter controller control program, stored in the memory 41 and executable on the processor 40.

Illustratively, the computer program 42 may be partitioned into one or more modules/units that are stored in the memory 41 and executed by the processor 40 to implement the present invention. The one or more modules/units may be a series of computer program instruction segments capable of performing specific functions, which are used to describe the execution process of the computer program 42 in the terminal device 4.

The terminal device 4 may be a desktop computer, a notebook, a palm computer, a cloud server, or other computing devices. The terminal device may include, but is not limited to, a processor 40, a memory 41. Those skilled in the art will appreciate that fig. 16 is merely an example of terminal device 4 and does not constitute a limitation of terminal device 4 and may include more or fewer components than shown, or some components may be combined, or different components, e.g., the terminal device may also include input-output devices, network access devices, buses, etc.

The Processor 40 may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf Programmable Gate Array (FPGA) or other Programmable logic device, discrete Gate or transistor logic, discrete hardware components, etc. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.

The memory 41 may be an internal storage unit of the terminal device 4, such as a hard disk or a memory of the terminal device 4. The memory 41 may also be an external storage device of the terminal device 4, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), and the like, which are provided on the terminal device 4. Further, the memory 41 may also include both an internal storage unit and an external storage device of the terminal device 4. The memory 41 is used for storing the computer program and other programs and data required by the terminal device. The memory 41 may also be used to temporarily store data that has been output or is to be output.

It will be apparent to those skilled in the art that, for convenience and brevity of description, only the above-mentioned division of the functional units and modules is illustrated, and in practical applications, the above-mentioned function distribution may be performed by different functional units and modules according to needs, that is, the internal structure of the apparatus is divided into different functional units or modules to perform all or part of the above-mentioned functions. Each functional unit and module in the embodiments may be integrated in one processing unit, or each unit may exist alone physically, or two or more units are integrated in one unit, and the integrated unit may be implemented in a form of hardware, or in a form of software functional unit. In addition, specific names of the functional units and modules are only for convenience of distinguishing from each other, and are not used for limiting the protection scope of the present invention. The specific working processes of the units and modules in the system may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.

In the above embodiments, the descriptions of the respective embodiments have respective emphasis, and reference may be made to the related descriptions of other embodiments for parts that are not described or illustrated in a certain embodiment.

Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

In the embodiments provided in the present invention, it should be understood that the disclosed apparatus/terminal device and method may be implemented in other ways. For example, the above-described embodiments of the apparatus/terminal device are merely illustrative, and for example, the division of the modules or units is only one logical division, and there may be other divisions when actually implemented, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.

The integrated modules/units, if implemented in the form of software functional units and sold or used as separate products, may be stored in a computer readable storage medium. Based on such understanding, all or part of the flow of the method according to the embodiments of the present invention may also be implemented by a computer program, which may be stored in a computer-readable storage medium, and when the computer program is executed by a processor, the steps of the method embodiments may be implemented. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an executable file or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, usb disk, removable hard disk, magnetic disk, optical disk, computer Memory, Read-Only Memory (ROM), Random Access Memory (RAM), electrical carrier wave signals, telecommunications signals, software distribution medium, and the like. It should be noted that the computer readable medium may contain content that is subject to appropriate increase or decrease as required by legislation and patent practice in jurisdictions, for example, in some jurisdictions, computer readable media does not include electrical carrier signals and telecommunications signals as is required by legislation and patent practice.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present invention, and are intended to be included within the scope of the present invention.