Operation control method and system of self-synchronizing voltage source centralized photovoltaic inverter

Abstract

The invention provides a stable operation control method and system for a self-synchronizing voltage source centralized photovoltaic inverter, and the method comprises the steps: detecting the change rate of the DC voltage of the centralized photovoltaic inverter and the output active power of a photovoltaic panel in real time, and when the ratio of the change rate of the DC voltage to the change rate of the output active power of the photovoltaic panel exceeds a threshold value, starting the control of the stable operation of the photovoltaic inverter. A system working mode is converted from a power control mode to a voltage control mode, and a power given value and a direct-current voltage given value of a control system are adjusted in real time. A synchronous angular frequency is obtained by adding an output value of the deviation of the active power through a proportional controller and a power grid frequency value, and the phase of an output modulation voltage of a grid-connected converter is obtained after integration, so that the grid-connected power of the photovoltaic inverter is adjusted. The working points of the photovoltaic inverter can stably operate on all the working points of the photovoltaic power-voltage characteristic curve, it is ensured that the photovoltaic inverter is located at the maximum power point all the time, and then stable operation control over the self-synchronizing voltage source centralized photovoltaic inverter is achieved.

Description

Technical Field

[0001] The present invention relates to the technical fields of wind power generation technology and power electronic converter control technology in a power system, and specifically, to a stable operation control method and system for a self-synchronized voltage source centralized photovoltaic inverter. Background Art

[0002] In recent years, new energy power sources such as wind power and photovoltaic power have developed rapidly, and the installed capacity has been increasing year by year. However, currently, most new wind and photovoltaic energy sources exhibit a grid-following characteristic of a current source nature and do not exhibit inertia in the power grid, resulting in a serious shortage of the equivalent inertia of the power system and posing a serious threat to its safety and stability.

[0003] The self-synchronized voltage source photovoltaic technology can achieve automatic synchronization of the power grid and real-time control of active power by adopting a virtual synchronous control method that simulates the rotor motion equation of a synchronous generator for the grid-connected inverter; by adopting a virtual excitation control method that simulates the excitation regulator of a synchronous generator, it can automatically adjust the voltage and real-time control of reactive power, showing an active frequency modulation - reactive power voltage regulation external characteristic similar to that of a synchronous generator at the output port and having the ability to independently support the grid frequency and voltage.

[0004] However, the centralized photovoltaic inverter adopts a first-stage converter and lacks a front-stage DC boost converter, which makes the grid-connected converter not only have to undertake the power generation task but also execute the maximum power tracking control. Especially after adopting the virtual synchronous machine control method, the power control response speed of the centralized photovoltaic inverter has decreased. At the same time, the power-voltage curve characteristic makes the operating point easily shift to the left area of the curve during maximum power tracking, thereby triggering an instability problem and causing the photovoltaic inverter to malfunction.

[0005] Currently, in the industrial community, to solve this problem, the operating point of the centralized photovoltaic inverter is often set at a position slightly less than the maximum power point. However, this method will reduce the power generation of the photovoltaic inverter and cause a loss in power generation economic benefits.

[0006] Through the retrieval of patent documents, it is found that the invention patent with the publication number CN115313510A discloses a control method and system for a photovoltaic inverter with adaptive reactive power compensation. Among them, the electrical part is connected by a photovoltaic array through a cable to a photovoltaic DC-AC converter, and the photovoltaic DC-AC converter converts the direct current output by the photovoltaic array into alternating current and transmits it to the AC bus; the control part communicates with the environmental data detection system through a self-learning optimization controller to obtain the environmental irradiance and environmental temperature data collected in real time by the environmental detection system; obtains the current and voltage data output by the photovoltaic array through current and voltage transformers; obtains the voltage data of the AC bus through a voltage transformer; the self-learning optimization controller uses the voltage and power information communicated with the data acquisition device of the adjacent network node as the calculation input data of the self-learning optimization controller, and sends the calculation result to the photovoltaic DC-AC converter to control its operation. This patent focuses on the control method of an adaptive reactive power compensation photovoltaic inverter based on a graph convolutional neural network model, and does not involve switching the system working mode, and cannot achieve the stable operation of the photovoltaic inverter at all working points of the characteristic curve, and ensure the technical effect of always working at the maximum power point.

[0007] In summary, aiming at the problems of the above-mentioned existing technologies, it has become a key task to be solved urgently at present to study a stable operation control method and system for a self-synchronous voltage source centralized photovoltaic inverter. Summary of the Invention

[0008] Aiming at the defects in the existing technologies, the purpose of the present invention is to provide a stable operation control method and system for a self-synchronous voltage source centralized photovoltaic inverter. This method monitors the change rates of the DC voltage of the centralized photovoltaic inverter and the active power output of the photovoltaic panel in real time. When the ratio of the change rate of the DC voltage to the change rate of the active power output of the photovoltaic panel exceeds the threshold, the system working mode is changed from the power control mode to the voltage control mode, and at the same time, the power given value and the DC voltage given value of the control system are corrected in real time. Using the deviation of the active power, the output value of the proportional controller is superimposed with the power grid frequency value to obtain the synchronous angular frequency of the grid-connected converter. After integrating the synchronous angular frequency, the phase of the modulated voltage output by the grid-connected converter is obtained, and then the grid-connected power of the photovoltaic inverter is adjusted to realize the stable operation of the working point of the photovoltaic inverter at all working points of the photovoltaic power-voltage characteristic curve, ensure that the photovoltaic inverter always works at the maximum power point, and achieve the stable control of the maximum power tracking of the self-synchronous voltage source centralized photovoltaic inverter.

[0009] A stable operation control method for a self-synchronous voltage source centralized photovoltaic inverter provided by the present invention includes the following steps:

[0010] Step S1, through the stable control of the maximum power tracking of the self-synchronous voltage source centralized photovoltaic inverter, generate the active power given value, determine the DC voltage given value, and judge the system control mode;

[0011] Step S2: According to the system control mode, select the power control mode or the voltage control mode, and generate the angle for modulating the voltage output by the arm of the self - synchronous voltage - source centralized photovoltaic inverter.

[0012] Step S3: Control the voltage amplitude of the arm of the self - synchronous voltage - source centralized photovoltaic inverter by generating the desired amplitude of the modulating voltage of the grid - connected converter.

[0013] Step S4: Based on the angle of the modulating voltage and the desired amplitude of the modulating voltage of the grid - connected converter, generate the real - time values of the three - phase modulating voltages of the grid - connected converter to control the modulating voltage of the self - synchronous voltage - source centralized photovoltaic inverter.

[0014] Preferably, the maximum power tracking and stable control in Step S1 includes the following sub - steps:

[0015] Step S1.1: According to the active power scheduling command value, generate the active power reference value at a fixed time step ΔTP, and the expression is:

[0016]

[0017] where P ref0 [k] is the active power command value in the k - th control period; P ref0 [k - 1] is the active power command value in the (k - 1) - th control period; ΔP s is the active power increment in each control period; P cmd is the scheduling power command value of the photovoltaic inverter.

[0018] Step S1.2: Sample the active power and DC voltage output by the photovoltaic panel at a fixed sampling period T S . Every m sampling periods form a calculation period T C . In each calculation period, perform mean filtering on the active power and DC voltage to obtain the filtered values of the active power and DC voltage, and the expression is:

[0019]

[0020] where P pv [i] is the i - th sampling value of the active power of the photovoltaic panel in the n - th calculation period; U dc [i] is the i - th sampling value of the DC voltage of the photovoltaic panel in the n - th calculation period; P pvavg [n] is the average value of the active power output by the photovoltaic panel in the n - th calculation period; U dcavg [n] is the average value of the DC voltage of the photovoltaic panel in the n - th calculation period.

[0021] Step S1.3, record the minimum value of the active power and the maximum value of the DC voltage in each calculation period, and the expression is:

[0022]

[0023] where, P pvmin is the minimum value of the active power of the photovoltaic panel in the nth calculation period; U dcmax is the maximum value of the DC voltage of the photovoltaic panel in the nth calculation period; min() is the function to take the minimum value; max() is the function to take the maximum value;

[0024] Step S1.4, calculate the change in the active power and the change in the DC voltage of the photovoltaic panel in each calculation period, and the expression is:

[0025]

[0026] where, ΔP pv [n] is the change in the active power of the photovoltaic panel in the nth calculation period; ΔU dc [n] is the change in the DC voltage of the photovoltaic panel in the nth calculation period; P pvavg [n - 1] is the average value of the active power output by the photovoltaic panel in the (n - 1)th calculation period; U dcavg [n - 1] is the average value of the DC voltage of the photovoltaic panel in the (n - 1)th calculation period;

[0027] Step S1.5, calculate the rate of change of the DC voltage, the rate of change of the active power of the photovoltaic panel, and the ratio of the change in the DC voltage to the change in the active power of the photovoltaic panel in each calculation period, and the expression is:

[0028]

[0029] where, dU / dT is the rate of change of the DC voltage; dP / dT is the rate of change of the active power of the photovoltaic panel; dU / dP is the ratio of the change in the DC voltage to the change in the active power of the photovoltaic panel;

[0030] Step S1.6, revise the given value of the active power according to the three characteristic quantities of the rate of change of the DC voltage, the rate of change of the active power of the photovoltaic panel, and the ratio of the change in the DC voltage to the change in the active power of the photovoltaic panel, and the expression is:

[0031]

[0032] where, K1 is the set threshold of the rate of change of the DC voltage; K2 is the set threshold of the rate of change of the active power of the photovoltaic panel; K3 is the set threshold of the ratio of the change in the DC voltage to the change in the active power of the photovoltaic panel;

[0033] Step S1.7, set the system control mode according to three characteristic quantities: the change rate of the DC voltage, the change rate of the active power of the photovoltaic panel, and the ratio of the change amount of the DC voltage to the change amount of the active power of the photovoltaic panel. The expression is:

[0034]

[0035] Step S1.8, set the DC voltage set value according to the system control mode. The expression is:

[0036]

[0037] Preferably, step S2 includes the following sub-steps:

[0038] Step S2.1, in the power control mode, generate a compensation angular frequency reflecting the change in active power by controlling the deviation of the active power.

[0039] Step S2.2, in the voltage control mode, generate a compensation angular frequency reflecting the change in DC voltage by controlling the deviation of the DC voltage.

[0040] Step S2.3, based on the compensation angular frequency in the power control mode, the compensation angular frequency in the voltage control mode, and the system control mode, generate the angle of the modulation voltage output by the arm of the self-synchronous voltage source centralized photovoltaic inverter.

[0041] Preferably, the calculation formula for step S2.1 is:

[0042]

[0043] where, Δω p is the compensation angular frequency reflecting the change in active power output by the power control loop in the power control mode; G P (s) is the transfer function of the power controller of the power control loop; P ref is the set value of the active power of the grid-connected converter; P fdbk is the feedback value of the active power of the grid-connected converter; P g is the instantaneous value of the active power of the grid-connected converter; F P (s) is the transfer function of the active power filter of the grid-connected converter.

[0044] The expression of the transfer function of the power controller of the power control loop is:

[0045]

[0046] where, J is the equivalent inertia time constant of the photovoltaic inverter in the power control mode; D is the damping coefficient of the photovoltaic inverter in the power control mode.

[0047] The feedback value of the active power of the grid-connected converter is obtained by low-pass filtering the actual value of the reactive power of the grid-connected converter. The expression of the transfer function of the active power filter is:

[0048]

[0049] Among them, T p is the filtering time constant of the active power filter.

[0050] Preferably, the calculation formula in step S2.2 is:

[0051]

[0052] Among them, Δω u is the compensation angular frequency reflecting the change of the DC voltage output by the voltage control loop in the voltage control mode; G u (s) is the transfer function of the voltage controller of the voltage control loop; U ref is the set value of the DC voltage of the grid-connected converter; U fdbk is the feedback value of the DC voltage of the grid-connected converter; U dc is the instantaneous value of the DC voltage of the grid-connected converter; F u (s) is the transfer function of the DC voltage filter of the grid-connected converter.

[0053] The expression of the transfer function of the voltage controller of the voltage control loop is:

[0054]

[0055] Among them, K T is the DC voltage tracking coefficient of the voltage controller; K J is the inertia coefficient of the voltage controller; K D is the damping coefficient of the voltage controller.

[0056] The feedback value of the DC voltage of the grid-connected converter is obtained by low-pass filtering the actual value of the DC voltage of the grid-connected converter. The expression of the transfer function of the DC voltage filter is:

[0057]

[0058] Among them, T u is the filtering time constant of the DC voltage filter.

[0059] Preferably, the calculation formula in step S2.3 is:

[0060]

[0061] Among them, ω g is the grid angular frequency; Δω vsg is the compensation angular frequency; ωvsg is the angular frequency of the output voltage of the arm of the self-synchronous voltage source centralized photovoltaic inverter; θ vsg is the phase angle of the output voltage of the arm of the self-synchronous voltage source centralized photovoltaic inverter.

[0062] The compensation angular frequency is obtained from the power control mode compensation angular frequency and the voltage control mode compensation angular frequency according to the control mode, and the calculation formula is:

[0063]

[0064] wherein, CMD is the system control mode of the self-synchronous voltage source centralized photovoltaic inverter; =0 indicates that the self-synchronous voltage source centralized photovoltaic inverter operates in the power control mode; =1 indicates that the self-synchronous voltage source centralized photovoltaic inverter operates in the voltage control mode.

[0065] Preferably, step S3 includes the following sub-steps:

[0066] Step S3.1, obtaining the reactive power command deviation value through the difference between the grid voltage set value and the actual grid voltage value by a proportional controller;

[0067] Step S3.2, adding the reactive power scheduling command value and the reactive power command deviation value to obtain the reactive power set value;

[0068] Step S3.3, adding the output value obtained by the proportional controller from the difference between the reactive power set value and the actual grid voltage value to the grid voltage set value to obtain the desired amplitude of the modulation voltage of the grid-connected converter.

[0069] Preferably, the calculation formula of step S3.3 is:

[0070]

[0071] wherein, U s is the amplitude of the arm voltage of the grid-connected converter; V ref is the grid voltage set value; V fdbk is the feedback value of the grid phase voltage amplitude; K V is the droop coefficient of the AC voltage; Q sref0 is the reactive power scheduling command value of the grid-connected converter; Q sref is the reactive power set value of the grid-connected converter; Q fdbk is the feedback value of the reactive power of the grid-connected converter; G q (s) is the transfer function of the reactive power controller; V sn is the rated value of the grid voltage.

[0072] The expression of the transfer function of the reactive power controller in the reactive power control loop is:

[0073]

[0074] Among them, K Pq is the proportional coefficient of the reactive power controller; K Iq is the integral coefficient of the reactive power controller.

[0075] The feedback value Q of the reactive power of the grid-connected converter fdbk is obtained by low-pass filtering the actual value of the reactive power of the grid-connected converter, and the expression is:

[0076]

[0077] Among them, Q g is the instantaneous value of the reactive power of the grid-connected converter; T q is the filtering time constant of the reactive power filter.

[0078] The feedback value U of the grid-connected point phase voltage of the grid-connected converter fdbk is obtained by filtering the instantaneous value U sm of the amplitude of the grid-connected point phase voltage of the grid-connected converter through a low-pass filter, and the expression is:

[0079]

[0080] Among them, V sm is the instantaneous value of the amplitude of the grid-connected point phase voltage of the grid-connected converter; T v is the filtering time constant of the grid phase voltage filter.

[0081] Preferably, step S4 includes:

[0082] Using the mathematical relationship between the AC voltage amplitude-phase and the instantaneous value, based on the angle of the modulation voltage and the expected amplitude of the modulation voltage of the grid-connected converter, the modulation voltage of the photovoltaic inverter is calculated in real time, and the calculation formula is:

[0083]

[0084] Among them, U ma , U mb and U mc are the real-time values of the three-phase modulation voltages of the grid-connected converter.

[0085] The present invention also provides a stable operation control system for a self-synchronous voltage source centralized photovoltaic inverter, including:

[0086] A maximum power tracking control module, through the maximum power tracking and stable control of the self-synchronous voltage source centralized photovoltaic inverter, generates an active power set value, determines a DC voltage set value, and judges the system control mode;

[0087] The synchronization angle control module selects a power control mode or a voltage control mode according to the system control mode, and generates an angle for modulating the voltage output by the bridge arm of the self-synchronizing voltage source centralized photovoltaic inverter;

[0088] The AC voltage amplitude control module realizes the control of the bridge arm voltage amplitude of the self-synchronizing voltage source centralized photovoltaic inverter by generating the desired amplitude of the modulation voltage of the grid-connected converter;

[0089] The modulation voltage control module generates the real-time value of the three-phase modulation voltage of the grid-connected converter based on the angle of the modulation voltage and the desired amplitude of the modulation voltage of the grid-connected converter, and realizes the control of the modulation voltage of the self-synchronizing voltage source centralized photovoltaic inverter.

[0090] Compared with the prior art, the present invention has the following beneficial effects:

[0091] 1. The present invention realizes the stable control of maximum power tracking of the self-synchronizing voltage source centralized photovoltaic inverter in the power control mode. While maintaining the inertia response function of the photovoltaic inverter, it ensures the stable power control of the grid-connected converter at each operating point on the photovoltaic power-voltage characteristic curve.

[0092] 2. The present invention extracts the instability characteristic value of the photovoltaic inverter grid-connected system by detecting the changes in the DC voltage of the self-synchronizing voltage source centralized inverter and the output power of the photovoltaic panel in real time, and modulates the power and voltage commands and the system operation mode according to the changes in the characteristic value, so as to realize the stable control of tracking the maximum power point on the entire photovoltaic power-voltage characteristic curve of the grid-connected inverter, and ensure that the photovoltaic inverter always operates at the maximum power point.

[0093] 3. Compared with the traditional control method that requires complex switching operations, the present invention greatly simplifies the control algorithm of the converter, reduces the requirements for the control performance of the digital controller, and effectively improves the power generation efficiency of the photovoltaic power generation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects, and advantages of the present invention will become more apparent:

[0095] Figure 1 It is a schematic diagram of the stable operation control method for a self-synchronizing voltage source centralized photovoltaic inverter;

[0096] Figure 2 It is a schematic diagram of the maximum power tracking control method for a self-synchronizing voltage source centralized photovoltaic inverter;

[0097] Figure 3 It is a schematic diagram of the phase angle control strategy for a self-synchronizing voltage source centralized photovoltaic inverter;

[0098] Figure 4 Schematic diagram of the amplitude control strategy for a self - synchronous voltage - source centralized photovoltaic inverter;

[0099] Figure 5 Effect diagram of the maximum power tracking stable control before the self - synchronous voltage - source centralized photovoltaic inverter adopts the method of the present invention;

[0100] Figure 6 Effect diagram of the maximum power tracking stable control after the self - synchronous voltage - source centralized photovoltaic inverter adopts the method of the present invention. Specific implementation manners

[0101] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all belong to the protection scope of the present invention.

[0102] The present invention discloses a stable operation control method and system for a self - synchronous voltage - source centralized photovoltaic inverter. This method is applied to a centralized photovoltaic inverter grid - connected power generation system. The core of the present invention is to detect in real - time the change rate of the DC voltage of the centralized photovoltaic inverter and the active power output of the photovoltaic panel. When the ratio of the change rate of the DC voltage to the change rate of the active power output of the photovoltaic panel exceeds a threshold, the system working mode is switched from the power control mode to the voltage control mode, and the power reference value and the DC voltage reference value of the control system are adjusted in real - time. By adding the output value of the proportional controller of the active power deviation to the grid frequency value, the synchronous angular frequency of the grid - connected converter is obtained. After integrating the synchronous angular frequency, the phase of the modulation voltage output by the grid - connected converter is obtained, so as to adjust the grid - connected power of the photovoltaic inverter, make the operating point of the photovoltaic inverter stable at all operating points on the photovoltaic power - voltage characteristic curve, ensure that the photovoltaic inverter is always at the maximum power point, and further realize the stable operation control of the self - synchronous voltage - source centralized photovoltaic inverter.

[0103] Embodiment 1:

[0104] This embodiment provides a stable operation control method for a self - synchronous voltage - source centralized photovoltaic inverter. This method is applied to a centralized photovoltaic inverter grid - connected power generation system. The centralized photovoltaic inverter grid - connected power generation system includes a front - end photovoltaic panel, a DC capacitor bank, a grid - connected converter, and an AC filter circuit; among them, the grid - connected converter can be a two - level converter or a three - level converter.

[0105] Figure 1 Schematic diagram of the stable operation control method for a self - synchronous voltage - source centralized photovoltaic inverter.

[0106] AsFigure 1 As shown in the figure, the stable operation control method of the self-synchronous voltage source centralized photovoltaic inverter includes the following steps:

[0107] Step S1: Generate the active power reference value, determine the DC voltage reference value, and judge the system control mode through the maximum power tracking and stable control of the self-synchronous voltage source centralized photovoltaic inverter.

[0108] Figure 2 It is a schematic diagram of the maximum power tracking control method for the self-synchronous voltage source centralized photovoltaic inverter.

[0109] As Figure 2 shown, the maximum power tracking and stable control in step S1 includes the following sub-steps:

[0110] Step S1.1: Generate the active power reference value at a fixed time step ΔTP according to the active power scheduling command value, and the expression is:

[0111]

[0112] where, P ref0 [k] is the active power command value of the kth control period; P ref0 [k - 1] is the active power command value of the (k - 1)th control period; ΔP s is the active power increment of each control period; P cmd is the scheduling power command value of the photovoltaic inverter;

[0113] Step S1.2: Sample the active power and DC voltage output by the photovoltaic panel at a fixed sampling period T S . Every m sampling periods form a calculation period T C . In each calculation period, perform mean filtering on the active power and DC voltage to obtain the filtered values of the active power and DC voltage, and the expression is:

[0114]

[0115] where, P pv [i] is the ith sampling value of the active power of the photovoltaic panel in the nth calculation period; U dc [i] is the ith sampling value of the DC voltage of the photovoltaic panel in the nth calculation period; P pvavg [n] is the average value of the active power output by the photovoltaic panel in the nth calculation period; U dcavg [n] is the average value of the DC voltage of the photovoltaic panel in the nth calculation period;

[0116] Step S1.3: Record the minimum value of the active power and the maximum value of the DC voltage in each calculation period, and the expression is:

[0117]

[0118] Among them, P pvmin is the minimum value of the active power of the photovoltaic panel in the nth calculation period; U dcmax is the maximum value of the DC voltage of the photovoltaic panel in the nth calculation period; min() is the minimum value function; max() is the maximum value function;

[0119] Step S1.4, calculate the change in the active power of the photovoltaic panel and the change in the DC voltage in each calculation period. The expressions are as follows:

[0120]

[0121] Among them, ΔP pv [n] is the change in the active power of the photovoltaic panel in the nth calculation period; ΔU dc [n] is the change in the DC voltage of the photovoltaic panel in the nth calculation period; P pvavg [n - 1] is the average value of the active power output by the photovoltaic panel in the (n - 1)th calculation period; U dcavg [n - 1] is the average value of the DC voltage of the photovoltaic panel in the (n - 1)th calculation period;

[0122] Step S1.5, calculate the rate of change of the DC voltage, the rate of change of the active power of the photovoltaic panel, and the ratio of the change in the DC voltage to the change in the active power of the photovoltaic panel in each calculation period. The expressions are as follows:

[0123]

[0124] Among them, dU / dT is the rate of change of the DC voltage; dP / dT is the rate of change of the active power of the photovoltaic panel; dU / dP is the ratio of the change in the DC voltage to the change in the active power of the photovoltaic panel;

[0125] Step S1.6, revise the given value of the active power according to the three characteristic quantities of the rate of change of the DC voltage, the rate of change of the active power of the photovoltaic panel, and the ratio of the change in the DC voltage to the change in the active power of the photovoltaic panel. The expression is as follows:

[0126]

[0127] Among them, K1 is the set threshold of the rate of change of the DC voltage; K2 is the set threshold of the rate of change of the active power of the photovoltaic panel; K3 is the set threshold of the ratio of the change in the DC voltage to the change in the active power of the photovoltaic panel;

[0128] Step S1.7, set the system control mode according to the three characteristic quantities of the rate of change of the DC voltage, the rate of change of the active power of the photovoltaic panel, and the ratio of the change in the DC voltage to the change in the active power of the photovoltaic panel. The expression is as follows:

[0129]

[0130] Step S1.8, set the DC voltage given value according to the system control mode, and the expression is:

[0131]

[0132] Step S2, select the power control mode or the voltage control mode according to the system control mode, and generate the angle of the modulation voltage output by the arm of the self-synchronous voltage source centralized photovoltaic inverter.

[0133] Figure 3 It is a schematic diagram of the phase angle control strategy of the self-synchronous voltage source centralized photovoltaic inverter.

[0134] As Figure 3 shown, step S2 includes the following sub-steps:

[0135] Step S2.1, in the power control mode, control the deviation of the active power to generate a compensation angular frequency reflecting the change of the active power.

[0136] Furthermore, the calculation formula of step S2.1 is:

[0137]

[0138] where, Δω p is the compensation angular frequency reflecting the change of the active power output by the power control loop in the power control mode; G P (s) is the transfer function of the power controller of the power control loop; P ref is the set value of the active power of the grid-connected converter; P fdbk is the feedback value of the active power of the grid-connected converter; P g is the instantaneous value of the active power of the grid-connected converter; F P (s) is the transfer function of the active power filter of the grid-connected converter.

[0139] The expression of the transfer function of the power controller of the power control loop is:

[0140]

[0141] where, J is the equivalent inertia time constant of the photovoltaic inverter in the power control mode; D is the damping coefficient of the photovoltaic inverter in the power control mode.

[0142] The feedback value of the active power of the grid-connected converter is obtained by low-pass filtering the actual value of the reactive power of the grid-connected converter, and the expression of the transfer function of the active power filter is:

[0143]

[0144] Among them, T p is the filtering time constant of the active power filter.

[0145] Step S2.2, in the voltage control mode, by controlling the deviation of the DC voltage, a compensation angular frequency reflecting the change of the DC voltage is generated.

[0146] Furthermore, the calculation formula of step S2.2 is:

[0147]

[0148] Among them, Δω u is the compensation angular frequency reflecting the change of the DC voltage output by the voltage control loop in the voltage control mode; G u (s) is the transfer function of the voltage controller of the voltage control loop; U ref is the DC voltage set value of the grid-connected converter; U fdbk is the feedback value of the DC voltage of the grid-connected converter; U dc is the instantaneous value of the DC voltage of the grid-connected converter; F u (s) is the transfer function of the DC voltage filter of the grid-connected converter.

[0149] The expression of the transfer function of the voltage controller of the voltage control loop is:

[0150]

[0151] Among them, K T is the DC voltage tracking coefficient of the voltage controller; K J is the inertia coefficient of the voltage controller; K D is the damping coefficient of the voltage controller.

[0152] The feedback value of the DC voltage of the grid-connected converter is obtained by low-pass filtering the actual value of the DC voltage of the grid-connected converter. The expression of the transfer function of the DC voltage filter is:

[0153]

[0154] Among them, T u is the filtering time constant of the DC voltage filter.

[0155] Step S2.3, based on the compensation angular frequency in the power control mode, the compensation angular frequency in the voltage control mode and the system control mode, generate the angle of the modulation voltage output by the bridge arm of the self-synchronous voltage source centralized photovoltaic inverter.

[0156] Furthermore, the calculation formula of step S2.3 is:

[0157]

[0158] Among them, ω g is the grid angular frequency; Δω vsg is the compensation angular frequency; ω vsg is the angular frequency of the output voltage of the arm of the self-synchronous voltage source centralized photovoltaic inverter; θ vsg is the phase angle of the output voltage of the arm of the self-synchronous voltage source centralized photovoltaic inverter.

[0159] The compensation angular frequency is obtained from the power control mode compensation angular frequency and the voltage control mode compensation angular frequency according to the control mode, and the calculation formula is:

[0160]

[0161] Among them, CMD is the system control mode of the self-synchronous voltage source centralized photovoltaic inverter; = 0 indicates that the self-synchronous voltage source centralized photovoltaic inverter operates in the power control mode; = 1 indicates that the self-synchronous voltage source centralized photovoltaic inverter operates in the voltage control mode.

[0162] Step S3, by generating the desired amplitude of the grid-connected converter modulation voltage, the control of the arm voltage amplitude of the self-synchronous voltage source centralized photovoltaic inverter is realized.

[0163] Figure 4 is a schematic diagram of the amplitude control strategy of the self-synchronous voltage source centralized photovoltaic inverter.

[0164] As Figure 4 shown, step S3 includes the following sub-steps:

[0165] Step S3.1, by taking the difference between the grid voltage set value and the actual grid voltage value, and passing it through a proportional controller to obtain the reactive power command deviation value;

[0166] Step S3.2, adding the reactive power scheduling command value to the reactive power command deviation value to obtain the reactive power set value;

[0167] Step S3.3, adding the output value obtained by taking the difference between the reactive power set value and the actual grid voltage value through a proportional controller to the grid voltage set value to obtain the desired amplitude of the grid-connected converter modulation voltage.

[0168] Furthermore, the calculation formula of step S3.3 is:

[0169]

[0170] Among them, U s is the amplitude of the grid-connected converter arm voltage; V ref is the grid voltage set value; V fdbk is the feedback value of the grid phase voltage amplitude; K Vis the droop coefficient of the AC voltage; Q sref0 is the reactive power scheduling command value of the grid-connected converter; Q sref is the reactive power set value of the grid-connected converter; Q fdbk is the feedback value of the reactive power of the grid-connected converter; G q (s) is the transfer function of the reactive power controller; V sn is the rated value of the grid voltage.

[0171] The expression of the transfer function of the reactive power controller in the reactive power control loop is:

[0172]

[0173] Among them, K Pq is the proportional coefficient of the reactive power controller; K Iq is the integral coefficient of the reactive power controller.

[0174] The feedback value Q of the reactive power of the grid-connected converter fdbk is obtained by low-pass filtering the actual value of the reactive power of the grid-connected converter, and the expression is:

[0175]

[0176] Among them, Q g is the instantaneous value of the reactive power of the grid-connected converter; T q is the filtering time constant of the reactive power filter.

[0177] The feedback value U of the phase voltage at the grid connection point of the grid-connected converter fdbk is obtained by filtering the instantaneous value U of the amplitude of the phase voltage at the grid connection point of the grid-connected converter sm through a low-pass filter, and the expression is:

[0178]

[0179] Among them, V sm is the instantaneous value of the amplitude of the phase voltage at the grid connection point of the grid-connected converter; T v is the filtering time constant of the grid phase voltage filter.

[0180] Step S4, based on the angle of the modulation voltage and the desired amplitude of the modulation voltage of the grid-connected converter, generate the real-time value of the three-phase modulation voltage of the grid-connected converter to realize the control of the modulation voltage of the self-synchronous voltage source centralized photovoltaic inverter.

[0181] Specifically, step S4 includes:

[0182] Using the mathematical relationship between the amplitude-phase and instantaneous value of the AC voltage, based on the angle of the modulation voltage and the desired amplitude of the modulation voltage of the grid-connected converter, calculate the modulation voltage of the photovoltaic inverter in real time, and the calculation formula is:

[0183]

[0184] Among them, U ma 、U mb and U mc are the real-time values of the three-phase modulation voltages of the grid-connected converter.

[0185] Embodiment 2:

[0186] The present invention also provides a stable operation control system for a self-synchronous voltage source centralized photovoltaic inverter. The stable operation control system for a self-synchronous voltage source centralized photovoltaic inverter can be implemented by executing the process steps of the stable operation control method for a self-synchronous voltage source centralized photovoltaic inverter. That is, those skilled in the art can understand the stable operation control method for a self-synchronous voltage source centralized photovoltaic inverter as a preferred implementation manner of the stable operation control system for a self-synchronous voltage source centralized photovoltaic inverter.

[0187] Specifically, the stable operation control system for a self-synchronous voltage source centralized photovoltaic inverter includes:

[0188] A maximum power tracking control module, which generates an active power reference value, determines a DC voltage reference value, and judges the system control mode through the maximum power tracking and stable control of the self-synchronous voltage source centralized photovoltaic inverter;

[0189] A synchronization angle control module, which selects a power control mode or a voltage control mode according to the system control mode and generates the angle of the modulation voltage output by the bridge arm of the self-synchronous voltage source centralized photovoltaic inverter;

[0190] An AC voltage amplitude control module, which realizes the control of the bridge arm voltage amplitude of the self-synchronous voltage source centralized photovoltaic inverter by generating the desired amplitude of the modulation voltage of the grid-connected converter;

[0191] A modulation voltage control module, which generates the real-time values of the three-phase modulation voltages of the grid-connected converter based on the angle of the modulation voltage and the desired amplitude of the modulation voltage of the grid-connected converter, and realizes the control of the modulation voltage of the self-synchronous voltage source centralized photovoltaic inverter.

[0192] Figure 5 is the effect diagram of the maximum power tracking and stable control of the self-synchronous voltage source centralized photovoltaic inverter before adopting the method of the present invention. It can be seen from Figure 5 that without adopting the method proposed by the present invention, the waveforms of the three-phase current, active power, and reactive power output by the self-synchronous voltage source centralized photovoltaic inverter show serious oscillation phenomena after reaching the maximum power point, indicating that the self-synchronous voltage source centralized photovoltaic inverter has a serious instability phenomenon; Figure 6The figure shows the maximum power tracking stability control effect diagram of the self-synchronous voltage source centralized photovoltaic inverter after adopting the method of the present invention. It can be seen from Figure 6 that after the self-synchronous voltage source centralized photovoltaic inverter reaches the maximum power point by adopting the method proposed by the present invention, after about 160 ms of adjustment time, the three-phase current output by the inverter remains sinusoidal, and the active power and reactive power remain constant, indicating that the self-synchronous voltage source centralized photovoltaic inverter can operate stably. The effectiveness of the control method proposed in the invention patent is verified by comparing the simulation results.

[0193] Those skilled in the art know that in addition to implementing the system and its various devices, modules, and units provided by the present invention in the form of pure computer-readable program code, the method steps can be logically programmed to enable the system and its various devices, modules, and units provided by the present invention to be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers to achieve the same functions. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be regarded as the structure within the hardware component; the devices, modules, and units for implementing various functions can also be regarded as both software modules for implementing the method and the structure within the hardware component.

[0194] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be combined arbitrarily with each other.

Claims

1. A stable operation control method for a self-synchronized voltage source centralized photovoltaic inverter, characterized in that, It includes the following steps: Step S1, through the maximum power tracking and stable control of the self-synchronous voltage source centralized photovoltaic inverter, generate the active power reference value, determine the DC voltage reference value, and judge the system control mode; Step S2, according to the system control mode, select the power control mode or the voltage control mode, and generate the angle of the modulated voltage output by the bridge arm of the self-synchronous voltage source centralized photovoltaic inverter; Step S3, by generating the desired amplitude of the modulated voltage of the grid-connected converter, realize the control of the bridge arm voltage amplitude of the self-synchronous voltage source centralized photovoltaic inverter; Step S4, based on the angle of the modulated voltage and the desired amplitude of the modulated voltage of the grid-connected converter, generate the real-time value of the three-phase modulated voltage of the grid-connected converter, and realize the control of the modulated voltage of the self-synchronous voltage source centralized photovoltaic inverter.

2. The stable operation control method of a self-synchronous voltage source centralized photovoltaic inverter according to claim 1, characterized in that The maximum power tracking and stable control in the step S1 includes the following sub-steps: Step S1.1, according to the active power scheduling command value, generate the active power reference value at a fixed time step ΔTP, and the expression is: Among them, P ref0 [k] is the active power command value for the k-th control period; P ref0 [k - 1] is the active power command value for the (k - 1)-th control period; ΔP s is the active power increment for each control period; P cmd is the scheduling power command value of the photovoltaic inverter; Step S1.2, according to a fixed sampling period T S Sample the active power and DC voltage output by the photovoltaic panel. Every m sampling periods form a calculation period T C , in each calculation period, perform mean filtering on the active power and DC voltage to obtain the filtered values of the active power and DC voltage. The expression is as follows: Among them, P pv [i] is the i-th sampling value of the active power of the photovoltaic panel in the n-th calculation period; U dc [i] is the i-th sampling value of the DC voltage of the photovoltaic panel in the n-th calculation period; P pvavg [n] is the average value of the active power output by the photovoltaic panel in the n-th calculation period; U dcavg [n] is the average value of the DC voltage of the photovoltaic panel in the n-th calculation period; Step S1.3, record the minimum value of the active power and the maximum value of the DC voltage in each calculation period, and the expression is: Among them, P pvmin is the minimum value of the active power of the photovoltaic panel in the nth calculation period; U dcmax is the maximum value of the DC voltage of the photovoltaic panel in the nth calculation period; min() is the minimum value function; max() is the maximum value function; Step S1.4, calculate the change amount of the photovoltaic panel active power and the change amount of the DC voltage in each calculation period, and the expression is: Among them, ΔP pv [n] is the change in the active power of the photovoltaic panel in the nth calculation cycle; ΔU dc [n] is the change in the DC voltage of the photovoltaic panel in the nth calculation cycle; P pvavg [n - 1] is the average value of the active power output by the photovoltaic panel in the (n - 1)th calculation cycle; U dcavg [n - 1] is the average value of the DC voltage of the photovoltaic panel in the (n - 1)th calculation cycle; Step S1.5, calculate the change rate of the DC voltage, the change rate of the photovoltaic panel active power, and the ratio of the change amount of the DC voltage to the change amount of the photovoltaic panel active power in each calculation period, and the expression is: Among them, dU / dT is the change rate of the DC voltage; dP / dT is the change rate of the photovoltaic panel active power; dU / dP is the ratio of the change amount of the DC voltage to the change amount of the photovoltaic panel active power; Step S1.6, according to the three characteristic quantities of the change rate of the DC voltage, the change rate of the photovoltaic panel active power, and the ratio of the change amount of the DC voltage to the change amount of the photovoltaic panel active power, revise the active power reference value, and the expression is: Among them, K1 is the set threshold of the DC voltage change rate; K2 is the set threshold of the photovoltaic panel active power change rate; K3 is the set threshold of the ratio of the change amount of the DC voltage to the change amount of the photovoltaic panel active power; Step S1.7, according to the three characteristic quantities of the change rate of the DC voltage, the change rate of the photovoltaic panel active power, and the ratio of the change amount of the DC voltage to the change amount of the photovoltaic panel active power, set the system control mode, and the expression is: Step S1.8, set the DC voltage reference value according to the system control mode, and the expression is:

3. The stable operation control method of a self - synchronous voltage - source centralized photovoltaic inverter according to claim 2, characterized in that, The step S2 includes the following sub-steps: Step S2.1, in the power control mode, generate the compensation angular frequency reflecting the change of the active power by controlling the deviation of the active power; Step S2.2, in the voltage control mode, generate the compensation angular frequency reflecting the change of the DC voltage by controlling the deviation of the DC voltage; Step S2.3, based on the compensation angular frequency in the power control mode, the compensation angular frequency in the voltage control mode, and the system control mode, generate the angle of the modulated voltage output by the bridge arm of the self-synchronous voltage source centralized photovoltaic inverter.

4. The stable operation control method of a self-synchronous voltage source centralized photovoltaic inverter according to claim 3, characterized in that The calculation formula of the step S2.1 is: Among them, Δω p is the compensation angular frequency reflecting the change in active power output by the power control loop in the power control mode; G P (s) is the transfer function of the power controller of the power control loop; P ref is the set value of the active power of the grid-connected converter; P fdbk is the feedback value of the active power of the grid-connected converter; P g is the instantaneous value of the active power of the grid-connected converter; F P (s) is the transfer function of the active power filter of the grid-connected converter; The expression of the transfer function of the power controller in the power control loop is as follows: Where, J is the equivalent inertia time constant of the PV inverter in the power control mode; D is the damping coefficient of the PV inverter in the power control mode; The feedback value of the active power of the grid-connected converter is obtained by low-pass filtering the actual value of the reactive power of the grid-connected converter. The expression of the transfer function of the active power filter is as follows: Among them, T p is the filtering time constant of the active power filter.

5. The stable operation control method of a self-synchronous voltage source centralized photovoltaic inverter according to claim 4, characterized in that The calculation formula of the step S2.2 is as follows: Among them, Δω u is the compensation angular frequency reflecting the DC voltage change output by the voltage control loop in the voltage control mode; G u (s) is the transfer function of the voltage controller of the voltage control loop; U ref is the DC voltage set value of the grid-connected converter; U fdbk is the feedback value of the DC voltage of the grid-connected converter; U dc is the instantaneous value of the DC voltage of the grid-connected converter; F u (s) is the transfer function of the DC voltage filter of the grid-connected converter; The expression of the transfer function of the voltage controller in the voltage control loop is as follows: Among them, K T is the DC voltage tracking coefficient of the voltage controller; K J is the inertia coefficient of the voltage controller; K D is the damping coefficient of the voltage controller; The feedback value of the DC voltage of the grid-connected converter is obtained by low-pass filtering the actual value of the DC voltage of the grid-connected converter. The expression of the transfer function of the DC voltage filter is as follows: Among them, T u is the filtering time constant of the DC voltage filter.

6. The stable operation control method of a self-synchronous voltage source centralized photovoltaic inverter according to claim 5, characterized in that The calculation formula of the step S2.3 is as follows: where, ω g is the grid angular frequency; Δω vsg is the compensation angular frequency; ω vsg is the angular frequency of the output voltage of the arm of the self - synchronous voltage - source centralized photovoltaic inverter; θ vsg is the phase angle of the output voltage of the arm of the self - synchronous voltage - source centralized photovoltaic inverter; The compensation angular frequency is obtained from the compensation angular frequency in the power control mode and the compensation angular frequency in the voltage control mode according to the control mode. The calculation formula is as follows: Where, CMD is the system control mode of the centralized PV inverter with a self-synchronous voltage source; = 0 indicates that the centralized PV inverter with a self-synchronous voltage source operates in the power control mode; = 1 indicates that the centralized PV inverter with a self-synchronous voltage source operates in the voltage control mode.

7. The stable operation control method of a self - synchronous voltage - source centralized photovoltaic inverter according to claim 6, characterized in that, The step S3 includes the following sub-steps: Step S3.1, obtaining the reactive power command deviation value by passing the difference between the grid voltage set value and the actual grid voltage through a proportional controller; Step S3.2, adding the reactive power scheduling command value to the reactive power command deviation value to obtain the reactive power set value; Step S3.3, adding the output value obtained by passing the difference between the reactive power set value and the actual grid voltage through a proportional controller to the grid voltage set value to obtain the desired amplitude of the modulation voltage of the grid-connected converter.

8. The stable operation control method of a self-synchronous voltage source centralized photovoltaic inverter according to claim 7, characterized in that The calculation formula of the step S3.3 is as follows: Among them, U s is the amplitude of the grid-connected converter arm voltage; V ref is the grid voltage set value; V fdbk is the feedback value of the grid phase voltage amplitude; K V is the droop coefficient of the AC voltage; Q sref0 is the reactive power scheduling command value of the grid-connected converter; Q sref is the reactive power set value of the grid-connected converter; Q fdbk is the feedback value of the reactive power of the grid-connected converter; G q (s) is the transfer function of the reactive power controller; V sn is the rated value of the grid voltage; The expression of the transfer function of the reactive power controller in the reactive power control loop is as follows: Among them, K Pq is the proportional coefficient of the reactive power controller; K Iq is the integral coefficient of the reactive power controller; Feedback value Q of the reactive power of the grid-connected converter fdbk It is obtained by low-pass filtering the actual value of the reactive power of the grid-connected converter, and the expression is: Among them, Q g is the instantaneous reactive power of the grid-connected converter; T q is the filtering time constant of the reactive power filter; Feedback value U of the grid-connected converter's grid connection point phase voltage fdbk Obtained by filtering the instantaneous value U of the grid-connected converter's grid connection point phase voltage amplitude sm through a low-pass filter, and the expression is: Among them, V sm is the instantaneous value of the phase voltage amplitude at the grid connection point of the grid-connected converter; T v is the filtering time constant of the grid phase voltage filter.

9. The stable operation control method of a self-synchronous voltage source centralized photovoltaic inverter according to claim 8, characterized in that, The step S4 includes: Using the mathematical relationship between the AC voltage amplitude-phase and instantaneous value, and based on the angle of the modulation voltage and the desired amplitude of the modulation voltage of the grid-connected converter, calculating the modulation voltage of the PV inverter in real time. The calculation formula is as follows: Among them, U ma , U mb and U mc are the real-time values of the three-phase modulation voltages of the grid-connected converter.

10. A stable operation control system for a self - synchronous voltage - source centralized photovoltaic inverter, characterized in that, Including: The maximum power tracking control module generates the active power set value, determines the DC voltage set value, and judges the system control mode through the maximum power tracking and stable control of the centralized PV inverter with a self-synchronous voltage source; The synchronization angle control module selects the power control mode or the voltage control mode according to the system control mode, and generates the angle of the modulation voltage output by the bridge arm of the centralized PV inverter with a self-synchronous voltage source; The AC voltage amplitude control module realizes the control of the bridge arm voltage amplitude of the centralized PV inverter with a self-synchronous voltage source by generating the desired amplitude of the modulation voltage of the grid-connected converter; The modulation voltage control module generates the real-time value of the three-phase modulation voltage of the grid-connected converter based on the angle of the modulation voltage and the desired amplitude of the modulation voltage of the grid-connected converter, and realizes the control of the modulation voltage of the centralized PV inverter with a self-synchronous voltage source.

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