A double-channel anti-hunting current sampling system suitable for zero-feed control

Abstract

The present application relates to photovoltaic energy storage technology field, especially to a kind of double-channel anti-hunting current sampling system suitable for zero feed control.The system includes double turns ratio current transformer, which contains primary winding N1 and two secondary windings mutually induced with primary winding N1, and the two secondary windings form different turns ratio with primary winding N1 respectively;Sampling module, which contains two sampling channels, two sampling channels correspond to two secondary windings respectively, for transmitting the induced voltage of secondary winding to ADC module;ADC module is used to map the induced voltage of secondary winding as digital quantity and send to processing module;Processing module is used to execute current value calculation step and control channel selection, and also used to eliminate channel switching hunting based on hysteresis algorithm, and execute transition zone weighted fusion algorithm to obtain the measured grid current corresponding to transition zone.The system can eliminate channel switching hunting, reduce transition zone sampling error, and improve the sampling accuracy of double turns ratio current transformer.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic energy storage technology, and in particular to a zero-feed dual-channel anti-oscillation current sampling system suitable for photovoltaic inverters. Background Technology

[0002] In the field of photovoltaic energy storage, the zero-feed function of inverters places stringent requirements on the accuracy of grid current sampling. Traditional single-turn current transformer (CT) solutions (such as 100A / 0.5% accuracy) have a fundamental flaw: the contradiction between their range and accuracy leads to a sharp increase in error to 1%–2% under low-current conditions (e.g., less than 5A). For example, the sampling error of a 5A static current in a 230V grid reaches 0.5A, causing a significant power error and exceeding the threshold required for zero-feed. This can potentially cause the DSP to misjudge "electricity selling behavior," triggering a circuit breaker trip.

[0003] To address the challenges of high-precision sampling with low current and wide sampling range with high current, existing technologies have proposed a dual-turns current transformer scheme. A dual-turns current transformer comprises one primary winding and two secondary windings with different numbers of turns. One secondary winding has a large turns ratio with the primary winding, while the other has a small turns ratio. The former has a larger measurement range but lower accuracy, and is responsible for high-current sampling, while the latter has a smaller measurement range but higher sampling accuracy within the usable range.

[0004] While the above-mentioned solutions can achieve selective measurement under high / low current conditions by enabling different secondary windings to a certain extent, thus initially solving the problems of wide-range current sampling and high-precision low-current sampling, when the grid current fluctuates around the switching threshold (e.g., 5A), the limitations of the fixed threshold switching logic can easily lead to channel oscillation, error jumps, and decreased system stability. For example, when the current fluctuates in the range of 5A±0.5A, the traditional solution relies on a single threshold comparator, and the large and small range channels will switch frequently, reducing the sampling accuracy of the dual-turn current transformer in zero-feed scenarios. Summary of the Invention

[0005] The purpose of this invention is to provide a dual-channel anti-oscillation current sampling system suitable for zero-feed control. This system can eliminate channel switching oscillation, reduce sampling error in the transition zone, and systematically improve the sampling accuracy of dual-turn ratio current transformers in zero-feed scenarios.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] This application provides a dual-channel anti-oscillation current sampling system suitable for zero-feed control, the system comprising:

[0008] A dual-turn ratio current transformer, comprising a primary winding and two secondary windings inducted with the primary winding, wherein the two secondary windings form different turns ratios with the primary winding respectively;

[0009] The sampling module includes two sampling channels, which correspond to two secondary windings respectively, and are used to transmit the induced voltage of the secondary windings to the ADC module.

[0010] The ADC module is used to map the induced voltage of the secondary winding into a digital quantity and send it to the processing module.

[0011] The processing module is used to perform current value calculation steps and control channel selection. It is also used to eliminate channel switching oscillations based on hysteresis algorithm and to perform transition zone weighted fusion algorithm to calculate and obtain the measured grid current corresponding to the transition zone.

[0012] As a preferred embodiment of the present invention, the dual-turns-ratio current transformer includes a high-turns-ratio winding N2 and a low-turns-ratio winding N3 that are mutually inducted with the primary winding N1; the sampling module includes a low-level channel connected to the output terminal of the high-turns-ratio winding N2 and a high-level channel connected to the output terminal of the low-turns-ratio winding N3.

[0013] As a preferred embodiment of the present invention, the processing module monitors the output voltages of the low-turns-ratio winding N3 and the high-turns-ratio winding N2 in real time, and switches the sampling channel based on a hysteresis algorithm, wherein the hysteresis algorithm includes a first switching logic and a second switching logic.

[0014] As a preferred embodiment of the present invention, the transition region weighted fusion algorithm is specifically as follows:

[0015] I 网 =(1-w)* (V1–V bias ) / G1 + w*(V2 - V bias ) / G2

[0016] Among them, I 网 V is the measured grid current value, w is the fusion weight, V1 is the output voltage of the low turns ratio winding, and V2 is the output voltage of the high turns ratio winding; V bias G1 is the average bias voltage, G2 is the low turns ratio winding gain, and G2 is the high turns ratio winding gain.

[0017] As a preferred embodiment of the present invention, the first switching logic specifically involves determining whether the absolute value of the output voltage V1 of the low-turns-ratio winding N3 is greater than the saturation voltage V. sat With the first voltage margin ΔV a If the calculated value is greater than 0, the processing module will switch the sampling channel of the ADC module from the high-order channel to the low-order channel; if it is not greater than 0, the current sampling channel will be maintained.

[0018] As a preferred embodiment of the present invention, the second switching logic specifically involves determining whether the absolute value of the output voltage V2 of the high turns ratio winding is less than the saturation voltage V. sat Subtract the second voltage margin ΔV b If the calculated value is less than 0, the processing module will switch the sampling channel of the ADC module from the low-order channel to the high-order channel; if it is not less than 0, the current sampling channel will be maintained.

[0019] As a preferred embodiment of the present invention, the first voltage margin ΔV a Less than the second voltage margin ΔV b .

[0020] As a preferred embodiment of the present invention, the first voltage margin ΔV a The absolute value of the second voltage margin ΔV b The absolute values ​​of the differences are all less than or equal to 0.1 times the saturation voltage.

[0021] As a preferred embodiment of the present invention, this dual-channel anti-oscillation current sampling system further includes an error calculation module. The error calculation module calculates the total error of the measured grid current value acquisition based on an error propagation algorithm, specifically as follows:

[0022] δ=sqrt((δ _1 *(1-w) 2 ) + (δ _2 *w) 2 )

[0023] Where δ is the total error value, sqrt() is the formula for calculating the square root, and δ _1 For the high-level channel sampling error, δ _2 This represents the sampling error of the low-level channel.

[0024] In summary, the present invention has the following beneficial effects:

[0025] 1. The technical solution provided in this application uses a dual-turn ratio transformer design (the high-turn ratio winding N2 is responsible for high-current sampling, and the low-turn ratio winding N3 is responsible for high-precision low-current sampling), which enables the low-turn ratio winding N3 to provide high-precision current detection results under low current range, reducing the error under low current conditions to within 0.2%, meeting the requirement of zero-feed power error ≤10W; while the high-turn ratio winding N2 covers the high current range, meeting the wide range of application requirements in multiple scenarios.

[0026] 2. This application solves the problem of frequent channel oscillation caused by fixed threshold switching by introducing a hysteresis algorithm, and performs current sampling calculation in the transition region based on a transition region weighted fusion algorithm, so that the saturation voltage V... satWhen the sampled values ​​are near the source, the dual-channel data can be fused, avoiding jumps in the sampled values ​​and successfully reducing the error in the transition zone, thus achieving a system-level accuracy improvement.

[0027] 3. In this application, the dual secondary windings are integrated into the same magnetic core, eliminating the need for additional sensor costs; both weighted fusion and error calculation can be run in real time in the existing DSP without requiring additional computing resources; the technical solution provided by this application can provide a reliable guarantee for high-precision zero-feed control and promote the intelligent development of photovoltaic grid-connected technology. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this specification, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a block diagram of the dual-channel anti-oscillation current sampling system;

[0030] Figure 2 This is a circuit diagram of the dual-channel anti-oscillation current sampling system in this embodiment;

[0031] Figure 3 This is a schematic diagram of the dual-turn ratio current transformer in this invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be explained and described below with reference to the accompanying drawings. However, the following embodiments are only preferred embodiments of the present invention and not all of them. Based on the embodiments in the implementation,

[0033] Other embodiments obtained by those skilled in the art without inventive effort are all within the scope of protection of this invention. The terms "first," "second," etc., in the specification, claims, and accompanying drawings are used to distinguish different objects, not to describe a specific order. Furthermore, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0034] According to Faraday's law of electromagnetic induction and the power conservation principle of an ideal transformer (P1=P2), the current and the number of turns satisfy the following relationship: I1:I2=N2:N1 (ampere-turn balance); that is, the larger the turns ratio, the lower the detection sensitivity; the smaller the turns ratio, the higher the detection sensitivity.

[0035] Although a small turns ratio has better sensitivity detection, it is not suitable for current sampling across the entire range. When the power grid is under high current, the magnetic flux density increases dramatically. Since the magnetic flux density B∝I1:N1, when I1 approaches the threshold current, the magnetic flux density of the iron core will rapidly approach the saturation point. Therefore, in order to solve the above problem, the existing technology usually uses current transformers with a large turns ratio. However, current transformers with a large turns ratio have the problem of insufficient sampling accuracy at small currents, that is, a balance point needs to be found.

[0036] In this embodiment, as Figure 1 As shown, a dual-channel anti-oscillation current sampling system suitable for zero-feed control is provided. The system includes:

[0037] Two-turn current transformers, such as Figure 3 As shown, the dual-turn ratio current transformer includes a primary winding N1 and two secondary windings that are mutually inducted with the primary winding N1. The two secondary windings form different turns ratios with the primary winding N1.

[0038] Among them, the primary winding N1 is connected in series to the power grid conductor, and the current value I of the power grid being measured flows through it. The output terminals of the high-turn ratio winding N2 and the low-turn ratio winding N3, which are mutually inducted with the primary winding N1, are respectively connected to the low-level channel and the high-level channel.

[0039] The low-level channel is used to collect voltage information of the high-turns-ratio winding N2, while the high-level channel is used to collect voltage information of the low-turns-ratio winding N3. The high-level channel can be compatible with more bit acquisition signals and is suitable for high-precision scenarios, but it has weak anti-saturation capability and small range, so it is not suitable for high-turns-ratio windings.

[0040] The two sampling channels correspond to the two secondary windings respectively, and are used to transmit the induced voltage of the secondary windings to the ADC module; the ADC module is used to map the induced voltage of the secondary windings into digital quantities and send them to the processing module.

[0041] Specifically, dual-channel shared single-channel 12-bit ADC (such as STM32F407) switches the input source through an analog switch (such as ADG1412), so that the input to the processing module only needs to occupy one ADC port; the ADC (analog-to-digital converter) module is the core component of the electronic system, responsible for converting continuously changing analog signals (such as voltage and current) into discrete digital signals so that the processing module can analyze, store or control them.

[0042] The processing module is used to perform the current value calculation steps and control the channel selection. It is also used to execute the transition zone weighted fusion algorithm to eliminate channel switching oscillations and calculate the measured grid current corresponding to the transition zone.

[0043] The processing module can be implemented based on a DSP (Digital Signal Processor) or an MCU. Taking a DSP as an example, it has a built-in hardware multiply-accumulate unit (MAC) that can perform multiplication and addition operations and efficiently execute the transition zone weighted fusion algorithm. In addition, it can adopt a Harvard architecture (separate instruction / data bus) and pipeline technology to ensure that tasks such as current sampling, channel switching, and fusion calculation are completed in microseconds, meeting the real-time requirements of the power system. The DSP can manage task scheduling through a real-time operating system (such as FreeRTOS) and accurately control the high and low channel switching thresholds. Specifically, for the dual-turn ratio current transformer system in this embodiment, a TI TMS320F28379D DSP can be used. It has a built-in dual-core C28x + CLA, a main frequency of 200MHz, and an integrated 16-channel 12-bit ADC that supports synchronous sampling and can calculate the transition zone current value in real time to control the photovoltaic inverter to zero feed.

[0044] The following examples are combined Figure 2 For the measured grid current I 网 When the measured grid current I is in the non-transition zone or in the transition zone 网 The calculation method will be explained.

[0045] The primary winding N1 is set to have 20 turns, and the high-turn-ratio winding N2 is set to have 40,000 turns, with a turns ratio of 1:2000; the low-turn-ratio winding N3 is set to have 2,000 turns, with a turns ratio of 1:100. For example... Figure 2 As shown, resistor R1 is connected in parallel across the high-turns-ratio winding N2, and resistor R2 is connected in parallel across the low-turns-ratio winding N3. Both are used to convert the induced current into an induced voltage; that is, the voltage across the high-turns-ratio winding N2 is U1 = I / 2000*R1, while the voltage across the low-turns-ratio winding N3 is U2 = I / 100*R2. In accordance with safety regulations, the external CT is electrically isolated from the internal sampling circuit, and a linear isolation capacitor is set.

[0046] Then, operational amplifiers U3 and U4 are connected respectively, which is a conventional signal processing method. Next, chip select chip U5 and ADC chip are connected. Chip select chip U5 is used for channel selection. Finally, the core processing MCU (or DSP) U6 is connected.

[0047] Set saturation voltage V sat The voltage is 3.3V, resistors R1 and R2 are 1Ω, and the first voltage margin is ΔV. a The second voltage margin is 0.2V, ΔV. b Since the voltage is 0.3V, the gain G1 of the low turns ratio winding is 100, and the gain G2 of the high turns ratio winding is 2000.

[0048] Then, based on the first voltage margin ΔV a Second voltage margin ΔV bHysteresis algorithm is used to determine the current sampling system. When the initial grid current is less than 3.1A (e.g., 2.8A), the current sampling system continuously uses the low-turns-ratio winding N3 and the high-level channel to provide high-precision current sampling data (actually converted into sampling voltage and sent to the processing module). As the grid current gradually increases, to avoid the core flux density approaching the saturation point, the high-turns-ratio winding N2 and the low-level channel need to be activated in a timely manner to ensure a large-range sampling capability. At this time, the saturation voltage V is determined. sat With the first voltage margin ΔV a The difference in voltage between the two values ​​is compared to the absolute value of the output voltage V1 of the low-turns-ratio winding N3. If the latter is greater than the former, the processing module will switch the sampling channel of the ADC module from the high-level channel to the low-level channel. For example, when the grid current increases from 2.5A to 3.15A, V1 increases from 2.5V to 3.15V. Since V... sat -△V a =3.1V, V1>(V sat -△V a Therefore, the switching action is executed, and the switching point is 3.1V.

[0049] When the initial grid current is greater than 3.1A (e.g., 4A), the current sampling system continuously uses the high-turns-ratio winding N2 and the low-level channel to ensure that the core magnetic flux density does not reach saturation and that a large sampling range is available. However, as the grid current gradually decreases, the sampling accuracy of the high-turns-ratio winding N2 gradually declines, and the error gradually increases. Therefore, it is necessary to activate the low-turns-ratio winding N3 and the high-level channel at specific switching points to provide high-precision current sampling data. At this point, the saturation voltage V is determined. sat With the second voltage margin ΔV b The difference in values ​​is compared with the absolute value of the output voltage V2 of the high-turns-ratio winding N2. When the latter is less than the former, the processing module switches the sampling channel of the ADC module from the low-level channel to the high-level channel. For example, when the grid current decreases from 4A to 2.95A, V1 decreases from 4V to 2.95V. Since V sat -△V b =3V, V2<(V sat -△V b Therefore, the switching action is performed, and the switching point is 3V.

[0050] As can be seen above, the first voltage margin ΔV a Greater than the second voltage margin ΔV b In this embodiment, the difference between the two voltage margins creates a hysteresis range (3A~3.1A) at the switching point, which can avoid repeated switching at 3.3A due to noise.

[0051] Then, the transition zone weighted fusion algorithm is executed. First, the weight factor w is calculated. For example, the weight factor can be calculated as follows:

[0052] w = (|V1| - (V sat - △V a )) / △V a It is set that when w falls within the range [0, 1], it is considered that the transition zone weighted fusion algorithm needs to be executed to calculate the new grid current I. 网 At this time, the grid current I 网 The calculation result is based on the composite data of the two secondary windings and the two sampling channels. The chip select chip will enable the two channels at an extremely fast interval (less than 1μs), which can be regarded as V1 and V2 being available at the same time to ensure that the phase deviation is minimal and the data calculation is not affected.

[0053] I 网 =(1-w)* (V1–V bias ) / G1 + w*(V2 - V bias ) / G2

[0054] Among them, I 网 V is the measured grid current value, w is the fusion weight, V1 is the output voltage of the low turns ratio winding, and V2 is the output voltage of the high turns ratio winding; V bias G1 is the average bias voltage, G2 is the low turns ratio winding gain, and G2 is the high turns ratio winding gain.

[0055] From this, we can obtain the weighted and fused measured grid current I. 网 .

[0056] In addition, this dual-channel anti-oscillation current sampling system also includes an error calculation module. The error calculation module calculates the total error of the measured power grid current value acquisition based on the error propagation algorithm, specifically:

[0057] δ=sqrt((δ_1*(1-w) 2 ) + (δ_2*w) 2 )

[0058] Where δ is the total error value, sqrt() is the square root calculation formula, δ_1 is the sampling error of the high-level channel, and δ_2 is the sampling error of the low-level channel.

[0059] Based on the above error calculation method, the total error value corresponding to the transition zone weighted fusion algorithm can be obtained. This value can be used to calculate the measured grid current I based on existing technology. 网 Parameter correction can also be used to retain data for subsequent data analysis and verification.

[0060] In addition, the first voltage margin ΔV a The absolute value and the second voltage margin ΔV bThe absolute values ​​of the differences are all less than or equal to 0.1 times the saturation voltage. This ensures the numerical difference between the saturation voltage and the voltage margin.

[0061] The above description is merely a preferred embodiment disclosed in this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of protection involved in this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-disclosed concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this disclosure.

[0062] Furthermore, while several specific implementation details are included in the foregoing discussion, these should not be construed as limiting the scope of this disclosure. Certain features described in the context of individual embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments.

Claims

1. A dual-channel anti-oscillation current sampling system suitable for zero-feed control, characterized in that, The system includes: A dual-turn ratio current transformer, the dual-turn ratio current transformer comprising a primary winding and a high-turn ratio winding and a low-turn ratio winding mutually inducted with the primary winding; The sampling module includes a low-level channel connected to the output terminal of the high-turns-ratio winding and a high-level channel connected to the output terminal of the low-turns-ratio winding, for transmitting the induced voltage of the high-turns-ratio winding and the low-turns-ratio winding to the ADC module. The ADC module is used to map the induced voltages of the high-turns-ratio winding and the low-turns-ratio winding into digital quantities and send them to the processing module. The processing module is used to perform current value calculation steps and control channel selection. It is also used to eliminate channel switching oscillations based on a hysteresis algorithm and to calculate the measured grid current corresponding to the transition zone using a transition zone weighted fusion algorithm. The processing module monitors the output voltages of the low-turns-ratio winding and the high-turns-ratio winding in real time and switches the sampling channel based on a hysteresis algorithm. The hysteresis algorithm includes a first switching logic and a second switching logic. Specifically, the first switching logic determines whether the absolute value of the low-turns-ratio winding output voltage is greater than the calculated value of the saturation voltage and the first voltage margin. If it is greater, the processing module switches the sampling channel connected to the ADC module from a high-level channel to a low-level channel; if it is not greater, the current sampling channel is maintained. Specifically, the second switching logic determines whether the absolute value of the high-turns-ratio winding output voltage is less than the calculated value of the saturation voltage minus the second voltage margin. If it is less, the processing module switches the sampling channel connected to the ADC module from a low-level channel to a high-level channel; if it is not less, the current sampling channel is maintained. The first voltage margin is less than the second voltage margin.

2. The dual-channel anti-oscillation current sampling system suitable for zero-feed control according to claim 1, characterized in that, The transition zone weighted fusion algorithm is specifically as follows: I 网 =(1-w)* (V1–V bias ) / G1 + w*(V2 - V bias ) / G2 Among them, I 网 V is the measured grid current value, w is the fusion weight, V1 is the output voltage of the low turns ratio winding, and V2 is the output voltage of the high turns ratio winding; V bias G1 is the average bias voltage, G2 is the low turns ratio winding gain, and G2 is the high turns ratio winding gain.

3. A dual-channel anti-oscillation current sampling system suitable for zero-feed control according to claim 2, characterized in that, The difference between the absolute value of the first voltage margin and the absolute value of the second voltage margin is less than or equal to 0.1 times the saturation voltage.

4. A dual-channel anti-oscillation current sampling system suitable for zero-feed control according to claim 3, characterized in that, This dual-channel anti-oscillation current sampling system also includes an error calculation module. The error calculation module calculates the total error of the measured grid current value acquisition based on an error propagation algorithm. Specifically: δ=sqrt((δ _1 *(1-w) 2 ) + (d _2 *w) 2 ) Where δ is the total error value, sqrt() is the formula for calculating the square root, and δ _1 For the high-level channel sampling error, δ _2 This represents the sampling error of the low-level channel.

Images