Carrier synchronization method and system for multiple inverters, and readable storage medium

Abstract

Disclosed in the present application are a carrier synchronization method and system for multiple inverters, and a readable storage medium. The method comprises the following steps: sampling the grid voltage, and, on the basis of the frequency of the grid voltage, performing frequency modulation on a triangular carrier, such that one power frequency cycle of the grid voltage corresponds to an integer multiple of the triangular carrier; on the basis of a zero-crossing point of the grid voltage, performing phase modulation on the triangular carrier, such that the absolute value of the phase of the phase-modulated triangular carrier is consistent with the absolute value of the phase of the grid voltage; and executing the described steps on each inverter, thus achieving carrier synchronization of multiple inverters. The readable storage medium is used for implementing the described method, and the system comprises the readable storage medium. The beneficial effects of the present application are that: compared with traditional carrier synchronization solutions that rely on external communication devices for high-speed information interaction to achieve information interaction between inverters, the solution of the present application does not need any external communication device, thus saving cost and achieving convenient implementation.

Description

A carrier synchronization method, system, and readable storage medium for multiple inverters Technical Field

[0001] This application relates to the field of new energy power generation technology, and in particular to a carrier synchronization method, system and readable storage medium for multiple inverters. Background Technology

[0002] With the rapid development of new energy sources, photovoltaic grid-connected inverters are increasingly being used in ground-mounted power plants. Ground-mounted power plants are characterized by large capacity and multiple inverters per transformer. Parallel operation of multiple inverters can easily generate circulating currents at the switching frequency. Therefore, a carrier synchronization solution can effectively avoid this problem. Currently, most carrier synchronization solutions rely on external high-speed communication equipment to enable multiple inverters to synchronize after receiving the carrier synchronization signal from the main inverter. However, using external communication for carrier synchronization is complex in terms of wiring, costly in implementation, and requires pre-setting communication interfaces during the initial design phase. If this is not done initially, implementation becomes quite difficult. Therefore, there is an urgent need for a software-based multi-inverter carrier synchronization method. Summary of the Invention

[0003] One objective of this application is to provide a carrier synchronization method for multi-inverters that can solve at least one of the defects in the aforementioned background art.

[0004] Another objective of this application is to provide a carrier synchronization system for multi-inverters that can solve at least one of the defects in the above-mentioned background art.

[0005] Another object of this application is to provide a readable storage medium capable of implementing a carrier synchronization method for multiple inverters.

[0006] To achieve at least one of the above objectives, the technical solution adopted in this application is: a carrier synchronization method for multiple inverters, comprising the following specific steps:

[0007] Sample the grid voltage;

[0008] Frequency modulation of the triangular carrier wave is performed based on the frequency of the grid voltage, so that one power frequency cycle of the grid voltage corresponds to an integer multiple of the triangular carrier wave.

[0009] Phase modulation of the triangular carrier wave is performed based on the zero-crossing point of the grid voltage, so that the phase of the phase-modulated triangular carrier wave is consistent with the absolute value of the phase of the grid voltage.

[0010] Perform the above steps for each inverter to achieve carrier synchronization of multiple inverters.

[0011] Preferably, frequency modulation of the triangular carrier wave based on the grid voltage frequency includes the following process:

[0012] Based on the frequency of the grid voltage, calculate the switching frequency when the triangular carrier wave is an integer multiple of one power frequency cycle.

[0013] The period value T0 of the triangular carrier is calculated by using the obtained switching frequency f.

[0014] The period value T′ of the current triangular carrier wave is adjusted to T′=T0.

[0015] Preferably, phase modulation of the triangular carrier wave based on the zero-crossing point of the grid voltage includes the following process:

[0016] Read the grid voltage sampling values ​​U1 and U2 before and after the grid voltage crosses zero;

[0017] Determine whether the midpoint of two grid voltage sample values ​​is the zero-crossing point of the grid voltage;

[0018] If the midpoint of the sampled values ​​of the two grid voltages is the zero-crossing point of the non-grid voltage, the phase synchronization value DeltaT of the triangular carrier is calculated based on the sampled values ​​of the two grid voltages and synchronization adjustment is performed.

[0019] Preferably, the absolute average of the two grid voltage samples is calculated, along with an offset value DeltaV from one of the grid voltage samples. Based on the value of DeltaV, it is determined whether the midpoint of the two grid voltage samples is a zero-crossing point of the grid voltage.

[0020] Preferably, the formula for calculating the offset value DeltaV is: DeltaV = |U1| - (|U1| + |U2|) / 2; if the value of DeltaV is zero, it is determined that the midpoint of the two grid voltage sample values ​​coincides with the zero-crossing point of the grid voltage; if the value of DeltaV is negative, it is determined that the midpoint of the two grid voltage sample values ​​is located to the right of the zero-crossing point of the grid voltage, and the triangular carrier needs to be shifted to the left for synchronization; if the value of DeltaV is positive, it is determined that the midpoint of the two grid voltage sample values ​​is located to the left of the zero-crossing point of the grid voltage, and the triangular carrier needs to be shifted to the right for synchronization.

[0021] Preferably, the formula for calculating the offset value DeltaV is: DeltaV = |U2| - (|U1| + |U2|) / 2; if the value of DeltaV is zero, it is determined that the midpoint of the two grid voltage sample values ​​coincides with the zero-crossing point of the grid voltage; if the value of DeltaV is negative, it is determined that the midpoint of the two grid voltage sample values ​​is located to the left of the zero-crossing point of the grid voltage, and the triangular carrier needs to be shifted to the right for synchronization; if the value of DeltaV is positive, it is determined that the midpoint of the two grid voltage sample values ​​is located to the right of the zero-crossing point of the grid voltage, and the triangular carrier needs to be shifted to the left for synchronization.

[0022] Preferably, the formula for calculating the phase synchronization value DeltaT of the triangular carrier is as follows:

[0023] or,

[0024] Wherein, TBPRD is the period value of the current triangular carrier.

[0025] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described carrier synchronization method for multiple inverters.

[0026] A carrier synchronization system for multiple inverters includes the aforementioned computer-readable storage medium and an EPWM module; at the zero-crossing point of the grid voltage, the phase value of TBPHS in the EPWM module is adjusted based on the phase adjustment signal of the triangular carrier output by the computer-readable storage medium, thereby software-triggered SWFSYNC within one power frequency cycle.

[0027] Preferably, during carrier synchronization, it is necessary to determine the timing of phase shift adjustment. The specific determination process is as follows: During the synchronization adjustment, the value of software phase shifting is compared with the value of CMPA in the EPWM module. If the current value of CMPA is between the period values ​​of the triangular carrier before and after phase shift, then wait; if the current value of CMPA is equal to the period value of the triangular carrier after phase shift, then execute the phase shifting program.

[0028] Compared with the prior art, the beneficial effects of this application are as follows:

[0029] (1) Compared with the traditional carrier synchronization scheme that relies on external communication equipment for high-speed information exchange between inverters, the scheme of this application does not require external communication equipment, which has the effect of saving costs and being easy to implement.

[0030] (2) Compared with the traditional carrier synchronization scheme, which requires setting up master and slave inverters and the slave inverter relies on the master inverter information to achieve carrier synchronization, the scheme of this application only relies on grid voltage information to achieve synchronization. There is no need to distinguish between master and slave inverters. The carrier synchronization function can be achieved when there is grid voltage sampling.

[0031] (3) The solution of this application can adjust the phase in a timely manner according to the relative position of the triangular carrier and the grid voltage, which can effectively avoid the situation where the phase shift cannot be recovered when there are errors in the crystal oscillators of each control chip. Attached Figure Description

[0032] Figure 1 is a schematic diagram of the topology circuit structure of two single cameras connected in parallel in the prior art.

[0033] Figure 2 is a schematic diagram of the equivalent circuit of the topology circuit shown in Figure 1.

[0034] Figure 3 is a schematic diagram of carrier modeling in this invention.

[0035] Figure 4 is a schematic diagram of the overall workflow of the present invention.

[0036] Figure 5 is a schematic diagram of the grid voltage sampling before and after the grid voltage zero crossing point in this invention.

[0037] Figure 6 is a schematic diagram of the experimental results of grid current and inductor current without carrier synchronization.

[0038] Figure 7 is a schematic diagram of the experimental structure of the grid current and inductor current after carrier synchronization according to the present invention. Detailed Implementation

[0039] The present application will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0040] In the description of this application, it should be noted that the directional terms such as "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this application.

[0041] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0042] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0043] To facilitate understanding of the technical solution of this application, we can first analyze the case where the carrier is not synchronized. As shown in Figure 1, taking a system of two single-phase parallel inverters as an example, the two inverters are labeled #1 and #2 respectively; wherein, the output voltage of inverter #1 is u n1 The output voltage of inverter #2 is u n2The output impedances of the two inverters are assumed to be the same and both are Z. L The impedance on the grid side is Z. s Based on the topology shown in Figure 1, the equivalent circuit shown in Figure 2 can be obtained; the two inverter circuits in the equivalent circuit can be regarded as two modules connected in parallel to the power grid. The analysis method based on the parallel system of two single-phase inverters can be extended to the parallel system of any number of inverters.

[0044] Assuming we ignore the power grid V for now g Considering only the equivalent output voltage U of the two inverters n1 and U n2 Due to the high-frequency current components I1 and I2 caused by carrier asynchrony, the following expression can be obtained (1).

[0045]

[0046] Among them, I s I represents the grid-side current. s =I1+I2.

[0047] To facilitate a clear expression of the high-frequency current components I1 and I2, I1 and I2 can be simplified, resulting in the following hypothetical expression (2).

[0048]

[0049] Based on expression (2), the high-frequency current components I1 and I2 in expression (1) can be transformed to obtain the following expression (3).

[0050]

[0051] As can be seen from the above expression (3), the high-frequency current components I1 and I2 are both composed of two parts. The first part is only related to the equivalent output voltage U of each of the two modules. n1 and U n2 Related, i.e., I 11 and I 22 This portion of the current flows into the power grid. The voltage difference between the second portion and the second portion is ΔU = U. n1 –U n2 Related, i.e., I 12 and I 21 This current is the circulating current. The following analysis will examine the magnitude of this circulating current component under carrier asynchrony.

[0052] As shown in Figure 3, the carrier wave is first modeled, with reference wave u. s The expression for can be taken as the following formula (4).

[0053]

[0054] Among them, U m ω represents the peak voltage of the triangular carrier wave. c The frequency of the high-frequency carrier. Indicates phase.

[0055] Based on the intersection of the reference wave and the triangular carrier wave in Figure 3, bipolar modulation can be used to obtain the expression (5) of the modulated wave signal u as shown below.

[0056]

[0057] Among them, U dc / 2 represents the peak value of the modulated wave.

[0058] Expanding the above expression (5) into a Fourier series yields u = A + B; where the specific expressions for parts A and B are shown in the following equation.

[0059]

[0060]

[0061] From the above expression, it can be seen that part A is the modulating wave, which is a low-frequency signal; part B is the high-frequency component, which is related not only to the modulating wave but also to the frequency ω of the high-frequency carrier. c related.

[0062] Assume that the SPWM carrier corresponding to inverter #2 lags behind the phase of inverter #1 by . Based on the Fourier series expansion of the modulated wave signal u, the equivalent high-frequency component voltage difference can be obtained as Δu. n =u n1 -u n2 ;Δu n The corresponding Fourier series expansion expression is shown below.

[0063]

[0064] The high-frequency component voltage difference Δu n This will cause a high-frequency circulating current, the magnitude of which is:

[0065] The above analysis shows that high-frequency circulating currents occur when the carriers are not synchronized. To suppress these high-frequency circulating currents, one aspect of this application provides a carrier synchronization method for multiple inverters, used to achieve carrier synchronization and suppress high-frequency circulating currents. As shown in Figure 1, a preferred embodiment includes the following specific steps:

[0066] Sample the grid voltage.

[0067] Frequency modulation of the triangular carrier wave is performed based on the frequency of the grid voltage, so that one power frequency cycle of the grid voltage corresponds to an integer multiple of the triangular carrier wave.

[0068] Phase modulation of the triangular carrier wave is performed based on the zero-crossing point of the grid voltage, so that the phase of the phase-modulated triangular carrier wave is consistent with the absolute value of the phase of the grid voltage.

[0069] Perform the above steps for each inverter to achieve carrier synchronization of multiple inverters.

[0070] It is understandable that carrier synchronization for multiple inverters can be viewed as a set of carrier synchronization operations performed on each individual inverter. That is, the method for carrier synchronization of each individual inverter is the same. After all inverters have completed their respective carrier synchronization, since the grid voltages corresponding to multiple inverters are the same, the waveform structures of the triangular carriers corresponding to each inverter are also the same.

[0071] The basic working principle of inverter carrier synchronization is to use the zero-crossing point of the grid voltage as a reference for multiple inverters to achieve carrier synchronization. This can be divided into two processes: frequency modulation and phase modulation. Frequency modulation aims to ensure that one power frequency cycle corresponds to an integer multiple of the triangular carrier wave length. This ensures that the triangular carrier waves, after synchronization, can be aligned with the grid voltage waveform in a relatively neat manner. Phase modulation, based on frequency modulation, unifies the position of the triangular carrier waves from different inverters relative to the zero-crossing point of the grid voltage. In other words, after phase modulation, the phase of the first triangular carrier wave is kept absolutely consistent with the phase of the grid voltage, thus achieving carrier synchronization.

[0072] It should be understood that the reference selection for inverter carrier synchronization includes, but is not limited to, the zero-crossing point of the grid voltage; for example, the peak point of the grid voltage, including positive and negative peak points, can also be selected. Generally speaking, the grid voltage is at a zero level at the zero-crossing point, which has the least impact on the system. Therefore, in this embodiment, the zero-crossing point of the grid voltage is preferably used as the reference for carrier synchronization.

[0073] As can be seen from the above, compared to traditional carrier synchronization schemes that rely on external communication equipment for high-speed information exchange between inverters, the scheme in this application does not require external communication equipment, thus saving costs and being easier to implement.

[0074] Furthermore, compared to traditional carrier synchronization schemes that require setting up master and slave inverters, with the slave inverter relying on the master inverter's information for carrier synchronization, the scheme in this application only relies on grid voltage information to achieve synchronization. It does not require distinguishing between master and slave inverters; carrier synchronization can be achieved as long as grid voltage sampling is available.

[0075] The solution proposed in this application can also adjust the phase in a timely manner according to the relative position of the triangular carrier and the grid voltage, which can effectively avoid the situation where the phase shift caused by the error of the crystal oscillator of each control chip cannot be recovered.

[0076] In this embodiment, there are multiple ways to perform triangular carrier frequency modulation, one of which includes the following process:

[0077] Calculate the switching frequency corresponding to an integer multiple of the triangular carrier wave within one power frequency cycle, based on the frequency of the grid voltage.

[0078] The period value T0 of the triangular carrier is calculated by using the obtained switching frequency f.

[0079] The period value T′ of the current triangular carrier wave is adjusted to T′=T0.

[0080] It should be understood that since carrier synchronization is performed separately in each inverter, to ensure accurate carrier synchronization across multiple inverters, it is necessary to sample the grid voltage of the same phase within a certain error margin. After sampling the grid voltage, the frequency of the grid voltage can be calculated using a specific algorithm. The specific number of triangular carriers corresponding to one power frequency cycle can be determined by those skilled in the art based on their actual needs.

[0081] For ease of understanding, this can be represented by parameters; the frequency of the grid voltage is f. By calculating the switching frequency of the triangular carriers, which are integer multiples of the frequency within one power frequency cycle, the number N of triangular carriers corresponding to one power frequency cycle can be obtained. Then, the theoretically calculated period value of the triangular carrier is T0 = 1 / (fN). After obtaining the theoretically calculated period value of the triangular carrier, it can be compared with the current period value T′. If T′ = T0, it is determined that the current triangular carrier meets the carrier synchronization requirements; if T′ ≠ T0, it is determined that the current triangular carrier does not meet the carrier synchronization requirements, and the frequency of the current triangular carrier needs to be adjusted to T′ = T0. Frequency adjustment is achieved by fine-tuning the current period value of the triangular carrier. After frequency adjustment, the length of each power frequency cycle is an integer multiple of the period length of the triangular carrier. This ensures that when the initial phase of the triangular carrier at the zero-crossing point within one power frequency cycle is fixed relative to the absolute position of the grid voltage, the phase of the triangular carrier relative to the grid voltage in each subsequent power frequency cycle is unified.

[0082] In this embodiment, the zero-crossing point and the initial triangular carrier phase of different inverters after only triangular carrier frequency modulation are not necessarily unified, which makes carrier synchronization of multiple inverters impossible. Therefore, after completing the triangular carrier frequency modulation, phase modulation of the triangular carrier is also required; as shown in Figure 5, triangular carrier phase modulation includes the following specific process:

[0083] Read the grid voltage sampling values ​​U1 and U2 before and after the grid voltage crosses zero.

[0084] Determine whether the midpoint of two grid voltage sample values ​​is the zero-crossing point of the grid voltage.

[0085] If the midpoint of the sampled values ​​of the two grid voltages is the zero-crossing point of the non-grid voltage, the phase synchronization value DeltaT of the triangular carrier is calculated based on the sampled values ​​of the two grid voltages and synchronization adjustment is performed.

[0086] It is understandable that the zero-crossing point of the grid voltage can be directly identified by algorithms or software, or it can be identified by the sign of two consecutive grid voltage sampling values; that is, when two consecutive grid voltage sampling values ​​are one negative and one positive, it can be determined that the zero-crossing point of the grid voltage is located between the two consecutive grid voltage sampling values; these two grid voltage sampling values ​​are the two grid voltage sampling values ​​U1 and U2 before and after the grid voltage zero-crossing point.

[0087] It should be understood that, since the grid voltage is a sinusoidal waveform, if the grid voltage is in carrier synchronization, theoretically, the absolute values ​​of the two sampled grid voltage values ​​U1 and U2 before and after the zero-crossing point are equal. That is, the midpoint of the sampled grid voltage values ​​U1 and U2 corresponds to the zero-crossing point. Therefore, in subsequent processes, whether the grid voltage is in carrier synchronization can be determined by whether the midpoint of the sampled grid voltage values ​​U1 and U2 coincides with the zero-crossing point. If the grid voltage is not in carrier synchronization, the phase difference between the triangular carrier and the grid voltage can be calculated using the sampled grid voltage values ​​U1 and U2. Finally, the phase of the triangular carrier is adjusted based on the calculated phase difference to ultimately achieve carrier synchronization.

[0088] In this embodiment, there are multiple ways to determine whether the midpoint of the sampled values ​​U1 and U2 of the grid voltage coincides with the zero-crossing point of the grid voltage; including but not limited to the two examples below.

[0089] Example 1: As shown in Figure 5, the absolute values ​​of the sampled values ​​U1 and U2 of the two grid voltages can be calculated to determine whether the midpoint of the sampled values ​​U1 and U2 of the two grid voltages coincides with the zero-crossing point of the grid voltage.

[0090] Specifically, if the absolute value of sampled value U1 equals the absolute value of sampled value U2, it can be determined that the midpoint of the two grid voltage sampled values ​​coincides with the zero-crossing point of the grid voltage. If the absolute value of sampled value U1 is less than the absolute value of sampled value U2, it can be determined that the midpoint of the two grid voltage sampled values ​​does not coincide with the zero-crossing point of the grid voltage, and the midpoint is located to the right of the zero-crossing point of the grid voltage. In this case, the triangular carrier wave needs to be shifted to the left to achieve synchronization. If the absolute value of sampled value U1 is greater than the absolute value of sampled value U2, it can be determined that the midpoint of the two grid voltage sampled values ​​does not coincide with the zero-crossing point of the grid voltage, and the midpoint is located to the left of the zero-crossing point of the grid voltage. In this case, the triangular carrier wave needs to be shifted to the right to achieve synchronization.

[0091] Example 2: As shown in Figure 5, the absolute average of two grid voltage sample values ​​and the offset value DeltaV of one of the grid voltage sample values ​​can be calculated. Based on the value of the offset value DeltaV, it can be determined whether the midpoint of the two grid voltage sample values ​​is the zero-crossing point of the grid voltage.

[0092] Specifically, if the average of the sum of the absolute values ​​of sampled values ​​U1 and U2 is equal to the absolute value of one of the grid voltage sampled values, it can be determined that the midpoint of the two grid voltage sampled values ​​coincides with the zero-crossing point of the grid voltage. If the average of the sum of the absolute values ​​of sampled values ​​U1 and U2 is not equal to the absolute value of one of the grid voltage sampled values, it can be determined that the midpoint of the two grid voltage sampled values ​​does not coincide with the zero-crossing point of the grid voltage. The specific offset direction depends on the selected grid voltage sampled value, which will be analyzed in detail below.

[0093] If the absolute value of the grid voltage sample value U1 is compared with the average of the sum of the absolute values ​​of U1 and U2, the offset value DeltaV is calculated using the formula: DeltaV = |U1| - (|U1| + |U2|) / 2. If DeltaV is zero, the midpoint of the two grid voltage sample values ​​coincides with the zero-crossing point of the grid voltage. If DeltaV is negative, the midpoint of the two grid voltage sample values ​​is to the right of the zero-crossing point, and the triangular carrier wave needs to be shifted to the left for synchronization. If DeltaV is positive, the midpoint of the two grid voltage sample values ​​is to the left of the zero-crossing point, and the triangular carrier wave needs to be shifted to the right for synchronization.

[0094] If the absolute value of the grid voltage sample value U2 is compared with the average of the sum of the absolute values ​​of sample values ​​U1 and U2, the formula for calculating the offset value DeltaV is: DeltaV = |U2| - (|U1| + |U2|) / 2. If the value of DeltaV is zero, the midpoint of the two grid voltage sample values ​​coincides with the zero-crossing point of the grid voltage. If the value of DeltaV is negative, the midpoint of the two grid voltage sample values ​​is to the left of the zero-crossing point of the grid voltage, and the triangular carrier wave needs to be shifted to the right to achieve synchronization. If the value of DeltaV is positive, the midpoint of the two grid voltage sample values ​​is to the right of the zero-crossing point of the grid voltage, and the triangular carrier wave needs to be shifted to the left to achieve synchronization.

[0095] It should be understood that both of the above examples can meet the requirements of this application; at the same time, in order to facilitate the calculation of the phase adjustment amount required for subsequent triangular carrier synchronization, the determination of whether the midpoint of the sampled values ​​U1 and U2 of the grid voltage coincides with the zero-crossing point of the grid voltage adopts the above example two.

[0096] In this embodiment, the formula for calculating the phase synchronization value DeltaT of the triangular carrier is as follows:

[0097] DeltaT=TBBPRD×2×DeltaV / (|U1|+|U2|).

[0098] Where TBPRD is the period value of the current triangular carrier; depending on the specific formula for the offset value DeltaV, the formula for calculating the phase synchronization value DeltaT of the triangular carrier can be expanded as follows:

[0099] or,

[0100] It is understood that both of the above formulas can meet the requirements of this application. The calculation results of the two formulas based on the same grid voltage sampling values ​​U1 and U2 only have a positive and negative relationship, that is, the absolute values ​​of the phase synchronization value DeltaT of the triangular carrier calculated by the two formulas are the same.

[0101] To facilitate understanding, experiments can be conducted on the carrier synchronization method provided in this application. Based on the experimental results, carrier synchronization between multiple inverters can be effectively achieved. Taking two inverters as an example, the specific experimental results are shown in Figures 6 and 7. A comparison of the two figures shows that, without the carrier synchronization scheme of this application, as shown in Figure 6, the grid current (red waveform) has a large switching circulating current; simultaneously, the inductor currents (green and blue waveforms) of the two inverters are not overlapping. However, after adopting the carrier synchronization scheme of this application, as shown in Figure 7, the switching circulating current of the grid current (red waveform) is significantly improved, and the inductor currents (green and blue waveforms) of the two inverters are basically overlapping.

[0102] Another aspect of this application provides a computer-readable storage medium having a computer program stored thereon, wherein a preferred embodiment is provided in which the above-described carrier synchronization method for multiple inverters can be implemented when the computer program is executed by a processor.

[0103] Another aspect of this application provides a carrier synchronization system for multiple inverters, one preferred embodiment of which includes the aforementioned computer-readable storage medium and an EPWM module. At the zero-crossing point of the grid voltage, based on the phase adjustment signal of the triangular carrier output by the computer-readable storage medium, the phase value of the TBPHS (phase register) in the EPWM module is adjusted, thereby software-triggered SWFSYNC (software forced synchronization pulse) within one power frequency cycle.

[0104] In this embodiment, during carrier synchronization, it is necessary to determine the timing of phase shift adjustment. The specific determination process is as follows: During synchronization adjustment, the value of software phase shifting is compared with the value of CMPA (Comparison Register A) in the EPWM module. If the current CMPA value is between the period values ​​of the triangular carrier before and after phase shift, the process waits. The phase shifting procedure is executed to perform carrier synchronization only when the current CMPA value equals the period value of the triangular carrier after phase shift. This ensures that the CMPA value before and after phase shift does not become invalid due to phase shift, allowing the EPWM module to continue operating normally and preventing changes in the waveform generated during the phase shift switching cycle.

[0105] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A multi-inverter carrier synchronization method based on zero-crossing grid voltage sampling, characterized in that, Includes the following steps: Sample the grid voltage; Frequency modulation of the triangular carrier wave is performed based on the frequency of the grid voltage, so that one power frequency cycle of the grid voltage corresponds to an integer multiple of the triangular carrier wave. Phase modulation of the triangular carrier wave is performed based on the zero-crossing point of the grid voltage, so that the phase of the phase-modulated triangular carrier wave is consistent with the absolute value of the phase of the grid voltage. Perform the above steps for each inverter to achieve carrier synchronization of multiple inverters.

2. The multi-inverter carrier synchronization method based on zero-crossing grid voltage sampling as described in claim 1, characterized in that, Frequency modulation of a triangular carrier wave based on the grid voltage frequency includes the following process: Based on the frequency of the grid voltage, calculate the switching frequency when the triangular carrier wave is an integer multiple of the power frequency cycle; The period value T0 of the triangular carrier is calculated based on the calculated switching frequency f; The period value T′ of the current triangular carrier wave is adjusted to T′=T0.

3. The multi-inverter carrier synchronization method based on zero-crossing grid voltage sampling as described in claim 1, characterized in that, Phase modulation of the triangular carrier wave based on the zero-crossing point of the grid voltage includes the following process: Read the grid voltage sampling values ​​U1 and U2 before and after the grid voltage crosses zero; Determine whether the midpoint of two grid voltage sample values ​​is the zero-crossing point of the grid voltage; If the midpoint of the sampled values ​​of the two grid voltages is the zero-crossing point of the non-grid voltage, the phase synchronization value DeltaT of the triangular carrier is calculated based on the sampled values ​​of the two grid voltages and synchronization adjustment is performed.

4. The multi-inverter carrier synchronization method based on zero-crossing grid voltage sampling as described in claim 3, characterized in that, Calculate the absolute average of two grid voltage samples and the offset value DeltaV of one of the grid voltage samples. Based on the value of the offset value DeltaV, determine whether the midpoint of the two grid voltage samples is the zero-crossing point of the grid voltage.

5. The multi-inverter carrier synchronization method based on zero-crossing grid voltage sampling as described in claim 4, characterized in that, The formula for calculating the offset value DeltaV is: DeltaV = |U1| - (|U1| + |U2|) / 2; If the value of DeltaV is zero, determine that the midpoint of the sampled values ​​of the two grid voltages coincides with the zero-crossing point of the grid voltage; If the value of DeltaV is negative, it is determined that the midpoint of the two grid voltage sample values ​​is located to the right of the zero-crossing point of the grid voltage, and the triangular carrier needs to be shifted to the left for synchronization; If the value of DeltaV is positive, it is determined that the midpoint of the two grid voltage sample values ​​is located to the left of the zero-crossing point of the grid voltage, and the triangular carrier needs to be shifted to the right for synchronization.

6. The multi-inverter carrier synchronization method based on zero-crossing grid voltage sampling as described in claim 4, characterized in that, The formula for calculating the offset value DeltaV is: DeltaV = |U2| - (|U1| + |U2|) / 2; If the value of DeltaV is zero, determine that the midpoint of the sampled values ​​of the two grid voltages coincides with the zero-crossing point of the grid voltage; If the value of DeltaV is negative, it is determined that the midpoint of the two grid voltage sample values ​​is located to the left of the zero-crossing point of the grid voltage, and the triangular carrier needs to be shifted to the right for synchronization. If the value of DeltaV is positive, it is determined that the midpoint of the two grid voltage sample values ​​is located to the right of the zero-crossing point of the grid voltage, and the triangular carrier needs to be shifted to the left for synchronization.

7. The multi-inverter carrier synchronization method based on zero-crossing grid voltage sampling as described in any one of claims 3-6, characterized in that, The formula for calculating the phase synchronization value DeltaT of the triangular carrier wave is as follows: or, Wherein, TBPRD is the period value of the current triangular carrier.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the carrier synchronization method for multiple inverters as described in any one of claims 1-7.

9. A carrier synchronization system for multiple inverters, characterized in that, Includes the computer-readable storage medium as described in claim 8 and the EPWM module; at the zero-crossing point of the mains voltage, based on the phase adjustment signal of the triangular carrier output by the computer-readable storage medium, the phase value of TBPHS in the EPWM module is adjusted, thereby software-triggered SWFSYNC within one power frequency cycle.

10. The carrier synchronization system for multiple inverters as described in claim 9, characterized in that, During carrier synchronization, it is necessary to determine the timing of phase shift adjustment. The specific determination process is as follows: During the synchronization adjustment process, the software phase modulation value is compared with the CMPA value in the EPWM module; If the current CMPA value is between the period values ​​of the triangular carrier before and after phase shift, then wait; If the current CMPA value is equal to the period value of the phase-shifted triangular carrier, then the phase-shifting procedure is executed.

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