A grid-connected inverter active and reactive power quasi-closed loop control method
By employing a fitting formula and a quasi-closed-loop method of PID control in the inverter, the problem of insufficient active and reactive power correction accuracy in traditional inverters under miniaturization and cost control is solved, achieving high-precision power compensation and cost savings.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-27
- Publication Date
- 2026-03-24
AI Technical Summary
Traditional inverters struggle to achieve high-precision active and reactive power correction under miniaturization and cost control, especially when grid-connected current is not sampled. Existing technologies rely on grid-connected current sampling and complex software correction, resulting in insufficient inverter output power accuracy.
A quasi-closed-loop control method for the active and reactive power of a grid-connected inverter is adopted. By measuring the actual output power of the inverter, discrete sampling data is obtained, and a fitting formula is used for correction. A Lissajous figure is formed using the grid voltage and inverter current, and the reactive power is calculated by combining Green's formula and then compensated by PID control.
It achieves an inverter output power accuracy of less than 2% of the rated power without the need for a grid-connected current sensor, reducing the chip computing power and storage space requirements and simplifying the mass production process.
Smart Images
Figure CN119253775B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a kind of grid-connected inverter active and reactive power quasi-closed loop control method, belong to the technical field of inverter active and reactive power compensation correction. BACKGROUND
[0002] Inverter filter output circuit generally uses LC or LCL circuit, and system modulation frequency is generally between 5k~100k.In the discrete sampling of the inverter current flowing through inverter inductance, such as Figure 7 Indisputable, there is phase difference between the phase of the fundamental component of the discrete sampling inverter current and the actual fundamental component, which is mainly caused by the influence of ADC sampling delay, filter circuit delay, sampling noise, sampling trigger time, PWM modulation strategy and other factors.The phenomenon will affect the accuracy of the active and reactive power output by inverter, according to the laboratory test results, when opening the reactive power output function, such as Figure 8 And Figure 9 The maximum deviation of the reactive power output by the device and the expected reactive power output is more than 8% of the rated power, and at the same time, the calculation deviation of the phase angle of the inverter current is more than 6°, so it is necessary to correct the active and reactive power output by inverter in a convenient and efficient way.
[0003] The traditional inverter corrects active and reactive power by sampling grid-connected current, i.e. using grid-connected current sensor, and needs to cooperate with correction software for corresponding correction operation.The traditional correction software contains many complex operation items, occupies more chip computing power and storage space, and with the miniaturization and cost control of inverter, the grid-connected output current sampling of inverter is omitted, so it is difficult to realize compensation correction, and it is also not conducive to the debugging of batch inverter. SUMMARY
[0004] The present application aims to solve the above-mentioned problems of the prior art, and proposes a kind of grid-connected inverter active and reactive power quasi-closed loop control method to solve the problems of traditional dependence on grid-connected current sampling and correction software.
[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:
[0006] A kind of grid-connected inverter active and reactive power quasi-closed loop control method, characterized in that it comprises the following steps:
[0007] S1: measuring the active power And reactive power output by inverter
[0008] S2: obtaining the active power reactive power ;
[0009] S3: fitting the data obtained in S1 and S2 respectively, obtaining the fitting formula of to , to ;
[0010] S4: substituting and into the fitting formula respectively, obtaining the active power and the reactive power output by the inverter at present;
[0011] S5: taking and as feedback, forming a quasi-closed loop control with the active power reference and the reactive power reference to compensate the output power of the inverter.
[0012] Preferably, in the step S2, let the grid voltage and the fundamental component of the inverter current , where is the grid angular frequency, and is the phase difference between the grid voltage and the inverter current, to form a Lissajous figure with the grid voltage as the horizontal axis and the inverter current as the vertical axis.
[0013] According to Green's theorem:
[0014] ,
[0015] If , in the above formula, then:
[0016] ,
[0017] According to the above formula, the area enclosed by the closed curve of the Lissajous figure is calculated by:
[0018] ,
[0019] Convert the above formula to the integral of time within a whole period ( , ) time period, and substitute , :
[0020] ,
[0021] In the above formula, For the reactive power, there is:
[0022] ,
[0023] For discrete data, let the number of sampling times in one power frequency period be The above formula can be discretized as:
[0024] ,
[0025] Where is the difference between the current value calculated at the discrete sampling time and the last sampling time.
[0026] Preferably, in the step S3, the abstraction is a mathematical expression:
[0027] ,
[0028] The Taylor expansion is performed on the above formula, and the high-order terms are ignored:
[0029] ,
[0030] Where , ( , , ) are polynomial fitting coefficients.
[0031] The beneficial effects of the present application mainly include:
[0032] 1. The fitting formula does not contain complex operation items, and the chip computing power and storage space occupied are very small;
[0033] 2. No grid-connected current sensor is needed, saving the production and design cost of the inverter;
[0034] 3. For batch-produced inverters, there is no need to repeat the complex fitting process for each device, and only linear proportional fine-tuning of the fitting formula is needed. BRIEF DESCRIPTION OF DRAWINGS
[0035] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments made with reference to the following drawings:
[0036] Figure 1 is a flowchart of the control method of the present application.
[0037] Figure 2 is the Lissajous figure of the grid voltage and the inverter current in the control method of the present application.
[0038] Figure 3is a discrete signal pattern with Gaussian white noise in the control method of the application.
[0039] Figure 4 is a diagram showing the deviation of the actual output of the reactive power of the inverter after the quasi-closed loop control from the reference value.
[0040] Figure 5 is a diagram showing the deviation of the actual output of the apparent power of the inverter after the quasi-closed loop control from the reference value.
[0041] Figure 6 is a system structure diagram of the control method of the grid-connected inverter of the application.
[0042] Figure 7 is a diagram showing the discrete sampling points of the current of the conventional inverter.
[0043] Figure 8 is a diagram showing the variation of the fundamental phase error of the inverter current with the voltage-current phase difference and the apparent power under the condition of the grid voltage of 180V in the prior art.
[0044] Figure 9 is a diagram showing the variation of the fundamental phase error of the inverter current with the voltage-current phase difference and the apparent power under the condition of the grid voltage of 260V in the prior art. DETAILED DESCRIPTION
[0045] In order to make the objectives, technical solutions and advantages of the embodiments of the application clearer, the technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only some but not all of the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.
[0046] The application will be described in further detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application and not to limit the application. In addition, it should be noted that, for the convenience of description, only the parts related to the application are shown in the drawings. It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict.
[0047] In the prior art, due to cost considerations, the grid-connected output current of some inverters is not sampled, and in this case, the phase correction of the fundamental wave of the inverter current calculated by sampling is particularly important. From the perspective of the user side, the phase correction of the fundamental wave of the inverter current is equivalent to the correction of the phase of the grid-connected current.
[0048] Inverters can calculate the active and reactive power output in real time by sampling. However, the power output of the inverter may deviate due to the influence of sampling phase deviation. If the inverter can accurately calculate the actual output power in a certain way, the active and reactive power can be compensated by automatic control.
[0049] This invention proposes a method for software correction of the active and reactive power output of an inverter without relying on grid current sampling. Without using a grid current sensor, the inverter can use a fitting method to estimate the actual output power in real time using the currently calculated power, thereby completing quasi-closed-loop control. The deviation of the actual output active and reactive power of the inverter can be limited to within 2% of the rated power.
[0050] Specifically, refer to Figures 1 to 6 As shown, a quasi-closed-loop control method for active and reactive power of a grid-connected inverter is adopted, and the steps are as follows:
[0051] Measure the actual active power output of the inverter. With reactive power ;
[0052] Obtain the active power calculated by discrete sampling of the inverter. With reactive power ;
[0053] The acquired data were fitted separately to obtain... right , right The fitting formula;
[0054] The inverter and Substitute the values into the fitting formula to estimate the current active power output of the inverter. and reactive power ;
[0055] Will and As a feedback quantity, it is related to the active power reference. and reactive power reference Formation as Figure 6 The quasi-closed-loop control shown compensates for the inverter's output power.
[0056] In one specific embodiment, the active and reactive power data output by the grid-connected inverter can be collected in a laboratory using a power analyzer. This data acquisition method is existing technology and will not be described in detail here.
[0057] In one specific embodiment, reactive power The calculation employs the following method:
[0058] Taking single-phase electricity as an example, ignoring high-order harmonics, let the grid voltage , the fundamental component of the inverter current , where is the grid angular frequency, is the phase difference between the grid voltage and the inverter current, and the Lissajous figure is formed with the grid voltage as the horizontal axis and the inverter current as the vertical axis, as shown in FIG. 1. Figure 2
[0059] According to Green's formula:
[0060] ;
[0061] If , in the above formula, then:
[0062] ;
[0063] According to the above formula, Figure 1 the area enclosed by the closed curve in can be calculated in the following way:
[0064] ;
[0065] The above formula is converted into an integral with respect to time within an integral period (0, , ), and , is substituted into the formula:
[0066]
[0067] In the above formula, is the reactive power, so:
[0068]
[0069] For discrete data, let the number of sampling times in one power frequency period be , and the above formula can be discretized as:
[0070]
[0071] where is the difference between the current value calculated at the time and the previous sampling time.
[0072] In a specific embodiment, through analysis of the collected data, it is found that for , for The correspondence is not entirely linear. Using a sliding filter to remove random high-frequency fluctuations caused by discrete ADC sampling, it was found that the correspondence exhibits stable nonlinear time-invariant characteristics. The main influencing factor can be summarized as grid voltage. Active power and reactive power Abstracted into a mathematical expression, this is:
[0073]
[0074] Performing a Taylor expansion on the above equation, ignoring higher-order terms:
[0075]
[0076] in , ( , , ) represents the polynomial fitting coefficients.
[0077] In the process of compensating for the inverter output power, such as Figure 6 As shown, its active power and reactive power have reference data, which is obtained by... and As a feedback quantity, the control compensation output is performed by increasing or decreasing the PID controller. The compensation calculation between two reference data is an existing technology and will not be elaborated here. The main purpose of this case is to obtain effective feedback information without sampling data, so as to meet the requirements of quasi-closed-loop control.
[0078] The above fitting process often results in different polynomial coefficients due to varying initial values, which may lead to the fitting result entering a locally optimal solution with a large error. Therefore, during the fitting process, terms in the polynomial coefficients that infinitely approach 0 can be assigned 0 and the process can be iterated again. Through the collection of a large amount of data for fitting, the analysis results show that the polynomial fitting error can be controlled within 2%, with reactive power within -60% to 60% and active power within 20% to 100%, and the error controlled within 1.5%.
[0079] To fully verify the feasibility of this method, the actual output power of the inverter was tested under different apparent output power ranges at AC180V, AC220V, and AC260V conditions. The test data are as follows: Figure 4 and Figure 5As shown, the deviation of the actual reactive power output of the inverter does not exceed 1% of the rated output power 16.5kVA, and the actual apparent power output is within 1.5% of the rated output power, which exceeds the target of 2% of the expected power control accuracy, verifying that the method can meet the requirements of the inverter for output power control accuracy.
[0080] Since the ADC inverter current sampling can be corrected by zero and proportional methods, and the inverter current fundamental phase error caused by factors such as filter circuit, ADC sampling delay, and PWM modulation strategy can be summarized in the fitting formula, the same fitting formula can be used for linear proportional fine tuning of the same type of inverters in mass production to correct the active and reactive power output of the inverters.
[0081] As can be seen from the above description, the fitting formula does not contain complex operation items, and occupies very little chip computing power and storage space; it does not need to use grid-connected current sensors, saving the production and design cost of the inverter; for mass-produced inverters, there is no need to repeat the complex fitting process for each device, only linear proportional fine tuning of the fitting formula is needed.
[0082] The term "comprising" or any other similar word is intended to encompass non-exclusive inclusion, so that a process, method, article or device / apparatus including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to the process, method, article or device / apparatus.
[0083] So far, the technical solutions of the present application have been described in combination with the preferred embodiments shown in the drawings, but those skilled in the art can easily understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to related technical features without departing from the principles of the present application, and the technical solutions after the changes or replacements will fall within the protection scope of the present application.
Claims
1. A quasi-closed-loop control method for active and reactive power of a grid-connected inverter, characterized in that... Includes the following steps: S1: Measure the actual active power output of the inverter. With reactive power ; S2: Obtain the active power calculated by discrete sampling of the inverter. With reactive power ; S3: Fit the data obtained in steps S1 and S2 respectively to obtain... right , right The fitting formula; S4: Obtain the inverter's output and Substituting the values into the fitting formula, we obtain the current active power output of the inverter. and reactive power ; S5: Will and As a feedback quantity, it is related to the active power reference. and reactive power reference Quasi-closed-loop control is formed to compensate for the inverter output power; In step S2, let the grid voltage Inverter current fundamental frequency component ,in The angular frequency of the power grid. The phase difference between the grid voltage and the inverter current is represented by a Lissajous figure with the grid voltage on the horizontal axis and the inverter current on the vertical axis. According to Green's theorem: ， If we let the above formula , Then we have: ， According to the above formula, the area enclosed by the closed curve of a Lissajous figure is... Calculated as follows: ， Convert the above formula to the whole cycle ( , Integrating time over a given period of time, and... , Substitute: ， In the above formula Since it is reactive power, we have: ， For discrete data, let the number of samples per power frequency cycle be... The above equation can be discretized as: ， in For discrete sampling The difference between the current value calculated at the current time and the previous sampling time.
2. The quasi-closed-loop control method for active and reactive power of a grid-connected inverter according to claim 1, characterized in that: In step S3, the abstract is expressed as a mathematical expression: ， Performing a Taylor expansion on the above equation, ignoring higher-order terms: ， in , ( , , ) represents the polynomial fitting coefficients.