Grid-connected circuit and grid-connected control method and device thereof

Abstract

The invention discloses a grid-connected circuit and a grid-connected control method and a grid-connected control device thereof. The grid-connected circuit comprises a grid-connected inverter, a relay and a power grid, and the grid-connected inverter is connected with the power grid through the relay. The grid-connected control method comprises the following steps: collecting electric signals of a power grid voltage and an inversion voltage; obtaining amplitude and phase angle information of the power grid voltage according to the electric signal of the power grid voltage; obtaining the amplitude and phase angle information of the inversion voltage according to the electric signal of the inversion voltage; respectively comparing the amplitudes and phase angles of the power grid voltage and the inverter voltage to obtain an amplitude deviation and a phase angle deviation; if the amplitude deviation is smaller than the first set value and the phase angle deviation is smaller than the second set value, the relay is controlled to be switched on. According to the grid-connected control method, it can be guaranteed that the amplitude, frequency and phase of the inverter voltage and the amplitude, frequency and phase of the power grid voltage are basically consistent before the relay is switched on, the impact current generated when the relay is switched on is reduced, and the service life of circuit elements such as the relay in a grid-connected circuit is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter grid-connected power generation, and in particular to a grid-connected circuit and a grid-connected control method and a grid-connected control device. Background Art

[0002] As the world's energy crisis and environmental pollution worsen, the large-scale development and utilization of new energy represented by wind energy and solar energy has become an urgent need to alleviate the energy and environmental crisis. With the development of power electronics technology, the grid-connected access of new energy mostly adopts pulse width modulation grid-connected converter (Pulse Width Modulation Grid-Connected Converter), whose DC side uses DC support capacitors to stabilize the DC bus voltage, and the AC side mostly uses LCL filters to suppress high-frequency harmonic currents, so that the energy fed into the grid meets the power quality requirements.

[0003] As the key link between new energy and the power grid, the grid-connected inverter is the key equipment for network-source coordination in the construction of smart grids. Impact-free grid connection and seamless access to the power grid have become the inevitable requirements for grid-friendly grid-connected converters. During the closing process, the relay between the grid-connected inverter and the power grid has an impact current phenomenon, which will affect the life of circuit components such as relays. Summary of the invention

[0004] In view of this, the present invention aims to solve one of the problems in the related art at least to a certain extent. To this end, the object of the present invention is to provide a grid-connected circuit and a grid-connected control method and a grid-connected control device thereof.

[0005] The present application provides a grid-connected control method for a grid-connected circuit. The grid-connected circuit includes a grid-connected inverter, a relay, and a grid. The grid-connected inverter is connected to the grid through the relay. The grid-connected control method includes: collecting electrical signals of grid voltage and inverter voltage; obtaining the amplitude and phase angle information of the grid voltage according to the electrical signal of the grid voltage; obtaining the amplitude and phase angle information of the inverter voltage according to the electrical signal of the inverter voltage; respectively comparing the amplitude and phase angle of the grid voltage and the inverter voltage to obtain the amplitude deviation and the phase angle deviation; if the amplitude deviation is less than a first set value and the phase angle deviation is less than a second set value, controlling the relay to close.

[0006] In some embodiments, the grid-connected control method includes: if the amplitude deviation is greater than or equal to a first set value, modulating the amplitude of the inverter voltage according to the amplitude of the grid voltage so that the amplitude deviation between the inverter voltage and the grid voltage is less than the first set value.

[0007] In some embodiments, if the amplitude deviation is greater than or equal to a first set value, the amplitude of the inverter voltage is modulated according to the amplitude of the grid voltage so that the amplitude deviation between the inverter voltage and the grid voltage is less than the first set value, including: calculating the effective amplitude of the grid voltage and the effective amplitude of the inverter voltage respectively according to a voltage effective value strategy; and performing closed-loop control on the effective amplitude of the inverter voltage according to the effective amplitude of the grid voltage and a preset control algorithm.

[0008] In some embodiments, the preset control algorithm includes a proportional-integral control algorithm, and the closed-loop control of the effective amplitude of the inverter voltage based on the effective amplitude of the grid voltage and the preset control algorithm includes: calculating the effective amplitude of the inverter voltage modulation wave based on the effective amplitude of the grid voltage, the effective amplitude of the inverter voltage and the proportional-integral control algorithm; and performing closed-loop control on the effective amplitude of the inverter voltage based on the effective amplitude of the inverter voltage modulation wave.

[0009] In some embodiments, the grid-connected control method includes: if the phase angle deviation is greater than or equal to a second set value, modulating the phase angle of the inverter voltage according to the phase angle of the grid voltage so that the phase angle deviation between the inverter voltage and the grid voltage is less than the second set value.

[0010] In some embodiments, if the phase angle deviation is greater than or equal to a second set value, modulating the phase angle of the inverter voltage according to the phase angle of the grid voltage so that the phase angle deviation between the inverter voltage and the grid voltage is less than the second set value includes: calculating a compensation phase angle according to the phase angle of the grid voltage and the phase angle of the inverter voltage; and compensating the phase angle of the inverter voltage according to the compensation phase angle.

[0011] In certain embodiments, the calculation of the compensating phase angle based on the phase angle of the grid voltage and the phase angle of the inverter voltage includes: obtaining the frequency of the grid voltage through a phase-locked loop strategy based on the electrical signal of the grid voltage; periodically detecting the zero crossing points of the grid voltage and the inverter voltage according to a preset period; calculating the zero crossing time difference between the grid voltage and the inverter voltage; and calculating the compensating phase angle between the grid voltage and the inverter voltage based on the preset period, frequency and the zero crossing time difference.

[0012] In some embodiments, the grid-connected control method includes: obtaining the amplitude and phase angle information of the grid voltage through a phase-locked loop strategy based on the electrical signal of the grid voltage; and obtaining the amplitude and phase angle information of the inverter voltage through a phase-locked loop strategy based on the electrical signal of the inverter voltage.

[0013] The present application also provides a grid-connected control device for a grid-connected circuit. The grid-connected circuit includes a grid-connected inverter, a relay and a grid. The grid-connected inverter is connected to the grid through a relay. The grid-connected control device includes: a voltage acquisition module, an acquisition module, a comparison module and a control module. The voltage acquisition module is used to collect electrical signals of the grid voltage and the inverter voltage; the acquisition module is used to obtain the amplitude and phase angle information of the grid voltage according to the electrical signal of the grid voltage; and obtain the amplitude and phase angle information of the inverter voltage according to the electrical signal of the inverter voltage; the comparison module is used to compare the amplitude deviation and phase angle deviation of the grid voltage and the inverter voltage; the control module is used to control the relay to close if the amplitude deviation is less than a first set value and the phase angle deviation is less than a second set value.

[0014] The present application also provides a grid-connected circuit. The grid-connected circuit is used to implement the grid-connected control method of the grid-connected circuit described in any one of the above embodiments and the grid-connected control device including the grid-connected circuit described in the above embodiments, the grid-connected circuit includes a grid-connected inverter, a relay and a power grid, and the grid-connected inverter is connected to the power grid through the relay.

[0015] In this way, the grid-connected control method of the grid-connected circuit of the present application compares the amplitude deviation and phase angle deviation of the grid voltage and the inverter voltage. When the amplitude deviation between the two is less than the first set value and the phase angle deviation is less than the second set value, the relay is controlled to close. This can ensure that before the relay is closed, the inverter voltage and the grid voltage amplitude, frequency and phase are within a reasonable deviation range, that is, the inverter voltage and the grid voltage amplitude, frequency and phase are basically consistent, thereby reducing the impact current and increasing the life of circuit components such as relays in the grid-connected circuit.

[0016] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0018] Figure 1 is a schematic diagram of the structure of a grid-connected circuit of certain embodiments of the present application;

[0019] Figure 2 is a flow chart of a grid-connected control method of a grid-connected circuit in certain embodiments of the present application;

[0020] Figure 3 is a structural schematic diagram of a grid-connected control device of a grid-connected circuit in certain embodiments of the present application;

[0021] Figure 4 It is a schematic diagram of electrical signals of an inverter voltage and a grid voltage in a grid-connected control method of a grid-connected circuit in certain embodiments of the present application;

[0022] Figure 5 is a structural schematic diagram of a grid-connected control device of a grid-connected circuit in certain embodiments of the present application;

[0023] Figure 6 is a flow chart of a grid-connected control method of a grid-connected circuit in certain embodiments of the present application;

[0024] Figure 7 is a flow chart of a grid-connected control method of a grid-connected circuit in certain embodiments of the present application;

[0025] Figure 8 is a flow chart of a grid-connected control method of a grid-connected circuit in certain embodiments of the present application;

[0026] Fig. 9 is a flow chart of a grid-connected control method of a grid-connected circuit in certain embodiments of the present application;

[0027] Fig.10 It is a flow chart of a grid-connected control method of a grid-connected circuit in certain embodiments of the present application. DETAILED DESCRIPTION

[0028] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0029] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance, or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0030] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense, and may refer to fixed connection, detachable connection, or integral connection; mechanical connection, electrical connection, or mutual communication; direct connection, indirect connection through an intermediate medium, internal connection between two elements, or interaction between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] The disclosure below provides many different embodiments or examples to implement different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed.

[0032] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0033] See also Figure 1 and Figure 2 The present application provides a grid-connected control method of a grid-connected circuit 100. The grid-connected circuit 100 includes a grid-connected inverter 20, a relay 30, and a grid 40, and the grid-connected inverter 20 is connected to the grid 40 via the relay 30. The grid-connected control method includes:

[0034] 01: Collect electrical signals of grid voltage and inverter voltage;

[0035] 02: Obtain the amplitude and phase angle information of the grid voltage according to the electrical signal of the grid voltage;

[0036] 03: Obtain the amplitude and phase angle information of the inverter voltage according to the electrical signal of the inverter voltage;

[0037] 04: Compare the amplitude and phase angle of the grid voltage and inverter voltage respectively to obtain the amplitude deviation and phase angle deviation;

[0038] 05: If the amplitude deviation is less than the first set value and the phase angle deviation is less than the second set value, the control relay is closed.

[0039] See also Figure 3The present application also provides a grid-connected control device 10 for a grid-connected circuit. The grid-connected control device 10 includes: a voltage acquisition module 11, an acquisition module 12, a comparison module 13 and a control module 14. The voltage acquisition module 11 is used to collect grid voltage and inverter voltage; the acquisition module 12 is used to obtain the amplitude and phase angle information of the grid voltage according to the electrical signal of the grid voltage; and obtain the amplitude and phase angle information of the inverter voltage according to the electrical signal of the inverter voltage; the comparison module 13 is used to compare the amplitude and phase angle of the grid voltage and the inverter voltage respectively, and obtain the amplitude deviation and phase angle deviation; the control module 14 is used to control the relay to close if the amplitude deviation is less than the first set value and the phase angle deviation is less than the second set value.

[0040] Specifically, the electrical signals of the grid voltage and the inverter voltage are collected. It can be understood that since the grid-connected inverter is a power conversion device, it is mainly used to convert the direct current generated by renewable energy equipment (such as solar panels, small wind turbines) into alternating current compatible with the grid and allow the electrical energy to be transmitted to the grid. Therefore, Figure 4 As shown, the electrical signal of the inverter voltage Uinv corresponding to the grid-connected inverter end can be a sinusoidal wave signal obtained by converting direct current into alternating current through the inverter, T1 is the period of the inverter voltage Uinv, and the electrical signal of the grid voltage Ug corresponding to the grid segment is also a sinusoidal wave signal corresponding to the alternating current at the grid input end, and T0 is the period of the grid voltage Ug.

[0041] After collecting the electrical signals of the grid voltage and the inverter voltage, the amplitude and phase angle information of the grid voltage can be obtained according to the electrical signal of the grid voltage, and the amplitude and phase angle information of the inverter voltage can be obtained according to the electrical signal of the inverter voltage.

[0042] Among them, the amplitude and phase angle information of the grid voltage can be obtained through the phase-locked loop strategy according to the electrical signal of the grid voltage. The phase-locked loop (PLL) strategy is a frequency and phase synchronization technology realized by the feedback control principle. The phase-locked loop is mainly composed of three parts: phase detector (FPD), loop filter (LF) and voltage controlled oscillator (VCO). The working principle of the phase-locked loop is as follows: the phase detector compares the frequency and phase of the input reference signal and the signal of the feedback loop, and outputs a signal representing the difference between the two to the loop filter; the loop filter filters the signal output by the phase detector to eliminate high-frequency components and noise, and then sends it to the voltage-controlled oscillator; the voltage-controlled oscillator adjusts the frequency and phase of its output signal according to the control voltage output by the loop filter to synchronize it with the reference signal. Understandably, when there is fluctuation or interference in the grid voltage, the phase-locked loop can still maintain phase synchronization, thereby ensuring that the acquired grid voltage information has high accuracy and stability. The present application obtains accurate grid voltage information through the phase-locked loop, which helps the grid-connected inverter to achieve accurate grid-connected control.

[0043] In addition, the amplitude of the inverter voltage can be obtained by a direct measurement method according to the electrical signal of the inverter voltage. That is, due to the electrical signal of the inverter voltage at the output end of the grid-connected inverter, the peak value or effective value of the output voltage can be directly measured by using a measuring tool such as a voltmeter or a multimeter, which is directly connected to the output end of the inverter, to obtain the amplitude of the inverter voltage.

[0044] In addition, the phase angle of the inverter voltage can be obtained by an indirect calculation method or a phase-locked loop strategy according to the electrical signal of the inverter voltage. The phase angle of the inverter voltage can also be indirectly calculated by detecting the time point of the inverter voltage signal crossing the zero point and comparing it with a known reference signal (such as a grid voltage signal). That is, compared with the control scheme of the relay closing in the related art, the grid-connected control method of the present application does not require a pre-charge resistor, and can avoid the scheme of directly closing the switch through the AC pre-charge resistor. Due to the instant of closing, there is a voltage difference between the two ends of the relay. Although the current-limiting resistor is suppressed, the drawback of the impact current cannot be eliminated, and a better effect of reducing the impact current is achieved. The grid-connected control method of the present application also does not need to perform a phase-locked loop calculation on the inverter voltage, and will not occupy too much controller resources.

[0045] After obtaining the amplitude and phase angle information of the grid voltage and the amplitude and phase angle information of the inverter voltage, the amplitude and phase angle of the grid voltage and the inverter voltage can be compared respectively to obtain the amplitude deviation and the phase angle deviation. If the amplitude deviation is less than the first set value and the phase angle deviation is less than the second set value, the relay 30 is controlled to close. Among them, the first set value can be 3% of the rated voltage at the grid end, or other values, which are not limited here. The second set value can be 0.02*π, or other phase angle values, which are not limited here. The setting principle of the first set value and the second set value is to meet the requirement that the inrush current is small when the relay is closed.

[0046] That is, the grid-connected control method of the grid-connected circuit of the present application can ensure that before the relay 30 is closed, the inverter voltage and the grid voltage amplitude, frequency and phase are within a reasonable deviation range, that is, the inverter voltage and the grid voltage amplitude, frequency and phase are basically consistent, thereby reducing the impact current when the relay 30 is closed and improving the life of circuit components such as the relay 30 in the grid-connected circuit 100.

[0047] In this way, the grid-connected control method of the grid-connected circuit of the present application compares the amplitude deviation and phase angle deviation of the grid voltage and the inverter voltage. When the amplitude deviation between the two is less than the first set value and the phase angle deviation is less than the second set value, the relay 30 is controlled to close. This can ensure that before the relay 30 is closed, the inverter voltage and the grid voltage amplitude, frequency and phase are within a reasonable deviation range, that is, the inverter voltage and the grid voltage amplitude, frequency and phase are basically consistent, thereby reducing the impact current when the relay 30 is closed and improving the life of the circuit components such as the relay 30 in the grid-connected circuit 100.

[0048] In some embodiments, the grid-connected control method includes:

[0049] 06: If the amplitude deviation is greater than or equal to the first set value, the amplitude of the inverter voltage is modulated according to the amplitude of the grid voltage so that the amplitude deviation between the inverter voltage and the grid voltage is less than the first set value.

[0050] See also Figure 5 The grid-connected control device 10 further includes a modulation module 16. The modulation module 16 is used to modulate the amplitude of the inverter voltage according to the amplitude of the grid voltage if the amplitude deviation is greater than or equal to the first set value, so that the amplitude deviation between the inverter voltage and the grid voltage is less than the first set value.

[0051] That is, in the grid-connected control method of the present application, when the deviation between the amplitude of the inverter voltage and the amplitude of the grid voltage is large and greater than or equal to the first set value, the amplitude of the inverter voltage can be modulated according to the amplitude of the grid voltage, so that the amplitude deviation between the modulated inverter voltage amplitude and the grid voltage amplitude is less than the first set value, and the amplitude of the grid voltage is used as the inverter voltage target amplitude for closed-loop output, ensuring that the amplitude deviation between the inverter voltage and the grid voltage is less than the first set value, ensuring that the inverter voltage and the grid voltage amplitudes are basically consistent.

[0052] Specifically, see Figure 6 , step 06 includes:

[0053] 061: Calculate the effective amplitude of the grid voltage and the effective amplitude of the inverter voltage respectively according to the voltage effective value strategy;

[0054] 062: Perform closed-loop control on the effective amplitude of the inverter voltage according to the effective amplitude of the grid voltage and a preset control algorithm.

[0055] See also Figure 5 The modulation module 16 is used to calculate the effective amplitude of the grid voltage and the effective amplitude of the inverter voltage according to the voltage effective value strategy; and perform closed-loop control on the effective amplitude of the inverter voltage according to the effective amplitude of the grid voltage and a preset control algorithm.

[0056] Understandably, in an AC circuit, the direction and magnitude of the voltage are constantly changing, and using the average value directly cannot accurately describe the actual effect of the voltage. The effective value can more truly reflect the actual effect of the AC voltage in the circuit and is an important parameter in circuit analysis and design.

[0057] The grid-connected control method of the present application calculates the effective amplitudes of the grid voltage and the inverter voltage respectively according to the voltage effective value strategy, and can more realistically calculate the amplitudes of the grid voltage and the inverter voltage, so as to more accurately perform closed-loop control on the effective amplitude of the inverter voltage according to the effective amplitude of the grid voltage, thereby more accurately ensuring that the amplitude deviation between the inverter voltage and the grid voltage is less than the first set value.

[0058] Then, the effective amplitude of the inverter voltage is closed-loop controlled according to the effective amplitude of the grid voltage and the preset control algorithm. Among them, closed-loop control is the process of continuously measuring a controlled quantity (controlled variable) in a closed loop, comparing it with another quantity (reference variable), and then making corresponding adjustments based on the comparison results. The output variable of the closed-loop control will affect the control variable through feedback, that is, the actual value of the output is fed back to the controller, and corresponding adjustments are made taking into account the interference factors, so that the system can continue to approach and maintain the desired state. Closed-loop control has the advantages of strong anti-interference ability and high control accuracy.

[0059] The preset control algorithm of the present application can be to compare the effective amplitude of the inverter voltage with the reference effective amplitude of the set grid voltage, and then adjust the control strategy according to the comparison result, so that the effective amplitude of the output inverter voltage can be stabilized near the reference effective amplitude of the grid voltage, thereby realizing closed-loop control of the effective amplitude of the inverter voltage.

[0060] In this way, the grid-connected control method of the present application can perform closed-loop control on the effective amplitude of the inverter voltage according to the effective amplitude of the grid voltage and a preset control algorithm, thereby realizing closed-loop control of the amplitude of the inverter voltage.

[0061] See also Figure 7 In some embodiments, the preset control algorithm includes a proportional-integral control algorithm, and step 062 includes:

[0062] 0621: According to the effective amplitude of the grid voltage, the effective amplitude of the inverter voltage and the proportional integral control algorithm, the effective amplitude of the inverter voltage modulation wave is calculated;

[0063] 0622: The effective amplitude of the inverter voltage is closed-loop controlled according to the effective amplitude of the inverter voltage modulation wave.

[0064] See also Figure 5 The modulation module 16 is used to calculate the effective amplitude of the inverter voltage modulation wave according to the effective amplitude of the grid voltage and the inverter voltage and the proportional integral control algorithm; and perform closed-loop control on the effective amplitude of the inverter voltage according to the effective amplitude of the inverter voltage modulation wave.

[0065] Specifically, the proportional integral control (PI) algorithm is a control method commonly used in amplitude closed-loop control. That is, a PI controller may be provided in the grid-connected circuit of the present application, and the effective amplitude of the grid voltage may be used as the input reference signal of the PI controller, and the effective amplitude of the inverter voltage may be used as the feedback signal. The error between the reference signal and the feedback signal is calculated, and the PI control algorithm is applied for adjustment, so as to control the output voltage amplitude of the inverter. In addition, the present application can achieve high-precision control of the output voltage amplitude by reasonably setting the parameters of the PI controller.

[0066] In one embodiment, Ugrms is defined as the effective amplitude of the grid voltage, Uinvrms is defined as the effective amplitude of the inverter voltage, Uref is defined as the effective amplitude of the inverter voltage modulation wave (i.e., the control target), Kp is defined as the proportional coefficient, Ki is defined as the integral coefficient, e(t) is defined as the error signal, and e(t)=Ugrms-Uinvrms. ∫e(t)dt is defined as the integral of the error signal. The error signal e(t) is the difference between the effective amplitude of the grid voltage Ugrms and the effective amplitude of the inverter voltage Uinvrms. e(t)=Ugrms-Uinvrms. The output Uref of the PI controller is the sum of the proportion and integral of the error signal, i.e., Uref=Kp·e(t)+Ki·∫e(t)dt.

[0067] In order to simplify the calculation, the cumulative error E[n] is usually used, E[n] = E[n-1] + e[n] Ts, then Uref[n] = Kp e[n] + Ki E[n]. Before the control algorithm starts, the cumulative error E[n] needs to be initialized: E[-1] = 0. E[-1] = 0 means that before the control algorithm starts (that is, before n = 0), the cumulative error is set to 0. This ensures that when the algorithm starts running, the cumulative error starts from a known and determined state.

[0068] At each sampling time n, update the error signal e[n] and the cumulative error E[n], and then calculate Uref[n]: Calculate the error signal: e[n] = Ugrms[n] - Uinvrms[n]. Update the cumulative error: E[n] = E[n-1] + e[n]·Ts.

[0069] Finally, calculate the effective amplitude of the inverter voltage modulation wave: Uref[n]=Kp·e[n]+Ki·E[n]. Figure 1 As shown, the inverter voltage modulation wave finally output to the grid-connected inverter is Where U is the effective amplitude of the inverter voltage modulation wave.

[0070] This application uses the calculated Uref[n] as the modulation wave signal of the inverter, and generates the switching signal of the grid-connected inverter through pulse width modulation and other methods, thereby controlling the inverter voltage to track the grid voltage. Among them, by adjusting the proportional coefficient Kp and the integral coefficient Ki, the response speed and stability of the control system can be optimized.

[0071] In this way, the present application can calculate the effective amplitude of the inverter voltage modulation wave according to the effective amplitude of the grid voltage and the inverter voltage and the proportional-integral control algorithm, thereby realizing closed-loop control of the effective amplitude of the inverter voltage and making the inverter voltage.

[0072] The above implementation is a detailed scheme for modulating the amplitude of the inverter voltage according to the amplitude of the grid voltage when the amplitude deviation between the inverter voltage and the grid voltage is large. The following introduces a detailed scheme for modulating the phase angle of the inverter voltage according to the phase angle of the grid voltage when the phase angle deviation between the inverter voltage and the grid voltage is large.

[0073] Specifically, in some embodiments, the grid connection control method includes:

[0074] 07: If the phase angle deviation is greater than or equal to the second set value, the phase angle of the inverter voltage is modulated according to the phase angle of the grid voltage so that the phase angle deviation between the inverter voltage and the grid voltage is less than the second set value.

[0075] See also Figure 5 The modulation module 16 is also used to modulate the phase angle of the inverter voltage according to the phase angle of the grid voltage if the phase angle deviation is greater than or equal to the second set value, so that the phase angle deviation between the inverter voltage and the grid voltage is less than the second set value.

[0076] That is, in the grid-connected control method of the present application, when the deviation between the phase angle of the inverter voltage and the phase angle of the grid voltage is large and greater than or equal to two set values, the phase angle of the inverter voltage can be modulated according to the phase angle of the grid voltage, so that the phase angle deviation between the inverter voltage and the grid voltage is less than the second set value, and the phase angle of the grid voltage is used as the inverter voltage target phase angle for closed-loop output, ensuring that the phase angle deviation between the inverter voltage and the grid voltage is less than the second set value, ensuring that the phase angles of the inverter voltage and the grid voltage are basically consistent.

[0077] See also Figure 8 In some embodiments, step 07 includes:

[0078] 071: Calculate the compensation phase angle according to the phase angle of the grid voltage and the phase angle of the inverter voltage;

[0079] 072: Compensate the phase angle of the inverter voltage according to the compensation phase angle.

[0080] See also Figure 5 The modulation module 16 is also used to calculate a compensation phase angle according to the phase angle of the grid voltage and the phase angle of the inverter voltage; and compensate the phase angle of the inverter voltage according to the compensation phase angle.

[0081] It can be understood that if the phase angle of the grid voltage calculated by the phase-locked loop strategy based on the electrical signal of the grid voltage is directly used as the phase angle of the modulation wave of the inverter voltage for modulation output, the voltage on the inverter filter capacitor at the grid-connected inverter end in the grid-connected circuit will have a phase lag, such as Figure 1 and Figure 4As shown in Figure 1, the phase lag of the voltage on the inverter filter capacitor is caused by the software control delay and line impedance. Therefore, if you want to reduce the impact current when the relay is closed, you need to compensate for the lag phase angle of the inverter voltage.

[0082] Correspondingly, the grid-connected control method of the present application can calculate the compensation phase angle based on the phase angle of the grid voltage and the phase angle of the inverter voltage, and compensate the phase angle of the inverter voltage based on the compensation phase angle, so that the phase angle deviation between the inverter voltage and the grid voltage is less than a second set value, thereby reducing the impact current when the relay is closed.

[0083] See also Fig. 9 In some embodiments, step 071 includes:

[0084] 0711: Obtain the frequency of the grid voltage through a phase-locked loop strategy according to the electrical signal of the grid voltage;

[0085] 0712: Regularly detect the zero-crossing points of the grid voltage and inverter voltage according to a preset cycle;

[0086] 0713: Calculate the zero-crossing time difference between the grid voltage and the inverter voltage;

[0087] 0714: Calculate the compensation phase angle between the grid voltage and the inverter voltage based on the preset period, frequency and zero-crossing time difference.

[0088] See also Figure 5 The modulation module 16 is also used to obtain the frequency of the grid voltage through a phase-locked loop strategy according to the electrical signal of the grid voltage; regularly detect the zero-crossing points of the grid voltage and the inverter voltage according to a preset period; calculate the zero-crossing time difference between the grid voltage and the inverter voltage; and calculate the compensation phase angle between the grid voltage and the inverter voltage according to the preset period, frequency and zero-crossing time difference.

[0089] It can be understood that the grid-connected control method of the present application can not only obtain the amplitude and phase angle information of the grid voltage through a phase-locked loop strategy based on the electrical signal of the grid voltage, but also obtain the frequency f of the grid voltage through a phase-locked loop strategy based on the electrical signal of the grid voltage.

[0090] Assume that the preset period is Ts, that is, every Ts time, the instantaneous value of the grid voltage and the instantaneous value of the inverter voltage are detected respectively. When the zero crossing point of the grid voltage is detected for the first time, the time corresponding to the first change of the grid voltage from negative to positive is taken as the timing zero point. Every Ts time, the timer is incremented by 1. When the zero crossing point of the inverter voltage is detected, the inverter voltage changes from negative to positive, and the counter value N at this time is recorded. Then the zero crossing time difference between the grid voltage and the inverter voltage is N*Ts.

[0091] Afterwards, the compensation phase angle θ between the grid voltage and the inverter voltage is calculated as N*Ts*2*π*f according to the preset period Ts, the frequency f and the zero-crossing time difference N*Ts.

[0092] By compensating the compensation phase angle θ to the phase angle information of the inverter voltage modulation wave, the voltages at both ends of the relay can be phase synchronized.

[0093] See also Fig.10 In some embodiments, the grid-connected control method includes:

[0094] 021: Obtaining the amplitude and phase angle information of the grid voltage through a phase-locked loop strategy according to the electrical signal of the grid voltage; and

[0095] 031: The amplitude and phase angle information of the inverter voltage are obtained through a phase-locked loop strategy according to the electrical signal of the inverter voltage.

[0096] Please combine Figure 3 The acquisition module 12 is used to obtain the amplitude and phase angle information of the grid voltage through a phase-locked loop strategy according to the electrical signal of the grid voltage; and to obtain the amplitude and phase angle information of the inverter voltage through a phase-locked loop strategy according to the electrical signal of the inverter voltage.

[0097] That is to say, the grid-connected control method of the present application can simultaneously calculate the electrical signals of the grid voltage and the inverter voltage through the phase-locked loop strategy, accurately obtain the amplitude and phase information of the grid voltage and the inverter voltage, and help the grid-connected inverter to achieve precise grid-connected control.

[0098] In this embodiment, the amplitude of the inverter voltage modulation wave can be directly obtained by performing an amplitude closed-loop calculation on the inverter voltage according to the amplitude of the grid voltage, that is, the compensation phase angle of the inverter voltage modulation wave can be obtained by performing a phase closed-loop calculation on the inverter voltage according to the phase information of the grid voltage.

[0099] Afterwards, the amplitude of the inverter voltage is controlled in an amplitude closed-loop according to the amplitude of the inverter voltage modulation wave, and the phase angle of the inverter voltage is controlled in a phase closed-loop according to the compensation phase angle of the inverter voltage modulation wave.

[0100] In this way, this embodiment can also ensure that the amplitude deviation between the grid voltage and the inverter voltage is less than the first set value and the phase angle deviation between the grid voltage and the inverter voltage is less than the second set value, and then control the relay to close, thereby reducing the impact current when the relay is closed and improving the life of circuit components such as relays in the grid-connected circuit.

[0101] See also Figure 1The present application also provides a grid-connected circuit 100. The grid-connected circuit 100 is used to implement the grid-connected control method of the grid-connected circuit described in any one of the above embodiments and the grid-connected control device 10 including the grid-connected circuit described in the above embodiments. The grid-connected circuit 100 also includes a grid-connected inverter 20, a relay 30 and a power grid 40, and the grid-connected inverter 20 is connected to the power grid 40 through the relay 30.

[0102] In this way, the grid-connected circuit 100 of the present application applies the grid-connected control method of the above-mentioned grid-connected circuit to compare the amplitude deviation and phase angle deviation of the grid voltage and the inverter voltage. When the amplitude deviation between the two is less than the first set value and the phase angle deviation is less than the second set value, the relay 30 is controlled to close. This can ensure that before the relay 30 is closed, the inverter voltage and the grid voltage amplitude, frequency and phase are within a reasonable deviation range, that is, the inverter voltage and the grid voltage amplitude, frequency and phase are basically consistent, thereby reducing the impact current when the relay 30 is closed and improving the life of circuit components such as the relay 30 in the grid-connected circuit 100.

[0103] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. A grid-connected control method for a grid-connected circuit, characterized in that: The grid-connected circuit includes a grid-connected inverter, a relay and a power grid, the grid-connected inverter and the power grid are connected via the relay, and the grid-connected control method includes: Collect electrical signals of grid voltage and inverter voltage; Obtaining the amplitude and phase angle information of the grid voltage according to the electrical signal of the grid voltage; Obtaining the amplitude and phase angle information of the inverter voltage according to the electrical signal of the inverter voltage; Respectively comparing the amplitudes and phase angles of the grid voltage and the inverter voltage to obtain an amplitude deviation and a phase angle deviation; If the amplitude deviation is smaller than the first set value and the phase angle deviation is smaller than the second set value, the relay is controlled to close.

2. The grid connection control method according to claim 1, characterized in that: The grid-connected control method comprises: If the amplitude deviation is greater than or equal to a first set value, the amplitude of the inverter voltage is modulated according to the amplitude of the grid voltage so that the amplitude deviation between the inverter voltage and the grid voltage is less than the first set value.

3. The grid connection control method according to claim 2, characterized in that: If the amplitude deviation is greater than or equal to a first set value, modulating the amplitude of the inverter voltage according to the amplitude of the grid voltage so that the amplitude deviation between the inverter voltage and the grid voltage is less than the first set value comprises: Calculate the effective amplitude of the grid voltage and the effective amplitude of the inverter voltage respectively according to the voltage effective value strategy; The effective amplitude of the inverter voltage is closed-loop controlled according to the effective amplitude of the grid voltage and a preset control algorithm.

4. The grid connection control method according to claim 3, characterized in that: The preset control algorithm includes a proportional-integral control algorithm, and the closed-loop control of the effective amplitude of the inverter voltage according to the effective amplitude of the grid voltage and the preset control algorithm includes: Calculating the effective amplitude of the inverter voltage modulation wave according to the effective amplitude of the grid voltage, the effective amplitude of the inverter voltage and the proportional-integral control algorithm; The effective amplitude of the inverter voltage is controlled in a closed loop according to the effective amplitude of the inverter voltage modulation wave.

5. The grid connection control method according to claim 1, characterized in that: The grid-connected control method comprises: If the phase angle deviation is greater than or equal to a second set value, the phase angle of the inverter voltage is modulated according to the phase angle of the grid voltage so that the phase angle deviation between the inverter voltage and the grid voltage is less than the second set value.

6. The grid connection control method according to claim 5, characterized in that: If the phase angle deviation is greater than or equal to a second set value, modulating the phase angle of the inverter voltage according to the phase angle of the grid voltage so that the phase angle deviation between the inverter voltage and the grid voltage is less than the second set value includes: Calculating a compensation phase angle according to the phase angle of the grid voltage and the phase angle of the inverter voltage; The phase angle of the inverter voltage is compensated according to the compensation phase angle.

7. The grid connection control method according to claim 6, characterized in that: The step of calculating the compensation phase angle according to the phase angle of the grid voltage and the phase angle of the inverter voltage comprises: Obtaining the frequency of the grid voltage through a phase-locked loop strategy according to the electrical signal of the grid voltage; Regularly detecting the zero-crossing points of the grid voltage and the inverter voltage according to a preset period; Calculating a zero-crossing time difference between the grid voltage and the inverter voltage; The compensation phase angle between the grid voltage and the inverter voltage is calculated according to the preset period, frequency and the zero-crossing time difference.

8. The grid connection control method according to claim 1, characterized in that: The grid-connected control method comprises: Obtaining the amplitude and phase angle information of the grid voltage through a phase-locked loop strategy according to the electrical signal of the grid voltage; and The amplitude and phase angle information of the inverter voltage are obtained through a phase-locked loop strategy according to the electrical signal of the inverter voltage.

9. A grid-connected control device for a grid-connected circuit, characterized in that: The grid-connected circuit includes a grid-connected inverter, a relay and a grid, the grid-connected inverter and the grid are connected via a relay, and the grid-connected control device includes: Voltage acquisition module, used to collect electrical signals of grid voltage and inverter voltage; An acquisition module, configured to obtain the amplitude and phase angle information of the grid voltage according to the electrical signal of the grid voltage; and to obtain the amplitude and phase angle information of the inverter voltage according to the electrical signal of the inverter voltage; A comparison module, used for comparing the amplitude deviation and phase angle deviation of the grid voltage and the inverter voltage; and The control module is used to control the relay to close if the amplitude deviation is less than a first set value and the phase angle deviation is less than a second set value.

10. A grid-connected circuit, characterized in that: The grid-connected circuit is used to implement the grid-connected control method of the grid-connected circuit described in claims 1 to 8 and the grid-connected control device including the grid-connected circuit described in claim 9. The grid-connected circuit includes a grid-connected inverter, a relay and a power grid. The grid-connected inverter and the power grid are connected through the relay.

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