A carrier synchronization method and related device for a parallel energy storage converter system with constant switching frequency at any grid frequency

Abstract

This invention provides a communication-free carrier synchronization method and related apparatus for a parallel energy storage converter system with a constant switching frequency under any grid frequency, belonging to the field of pulse width modulation technology. The method determines whether carrier synchronization of the energy storage converter is required based on the actual reference value of the carrier phase at the current moment and a preset minimum phase error resolution. When carrier synchronization is required, the actual carrier synchronization cycle count and the number of carrier synchronization adjustments are updated according to the current actual carrier phase reference value and the preset minimum phase error resolution until the number of iterations equals the number of carrier synchronization adjustments. The actual carrier synchronization cycle count is then restored, and carrier synchronization of the energy storage converter is completed. Compared with existing technologies, this invention solves the problems of phase time delay and high cost caused by the need for communication lines.

Description

Technical Field

[0001] This invention belongs to the field of pulse width modulation technology, specifically relating to a communication-free carrier synchronization method and related devices for a parallel energy storage converter system with a constant switching frequency under any power grid frequency. Background Technology

[0002] With the increasing installed capacity of new energy sources, some problems (such as power fluctuations) have arisen. Energy storage systems, as one solution, can address power fluctuation issues to some extent. As the core of an energy storage system, the energy storage converter connects the battery system and the power grid. The performance of the energy storage converter not only affects output characteristics and waveform quality but also the lifespan of the battery system.

[0003] Today, large-scale energy storage converters are widely used. Based on their application scenarios, energy storage converters can be divided into residential energy storage converters and commercial energy storage converters. The main difference between the two lies in their power rating. Residential energy storage converters have a power rating below 10kW and are typically powered by an independent DC source. However, commercial energy storage converters usually have a power rating greater than 250kW. A single energy storage converter cannot meet such high power requirements; therefore, commercial energy storage converters often adopt a parallel structure with a common DC bus and a common AC bus to meet the system's high power requirements.

[0004] Parallel operation of energy storage converters offers several advantages. First, it can meet the requirements of high-power levels. Second, modular parallel operation of multiple energy storage converters not only reduces system design costs but also facilitates expansion. However, due to the inconsistency in hardware parameters of the converter systems, parallel operation of energy storage converters also introduces some problems. Even assuming the modulation waves of each converter are the same, their carrier frequencies and phases may differ. This inconsistency in carrier frequency and phase leads to inconsistent switching actions, resulting in differences in the common-mode voltage output of each converter, and this difference varies with the carrier phase angle difference. In a parallel energy storage converter system with both DC and AC connections, the presence of a common-mode loop can generate a large zero-sequence circulating current even with a small common-mode voltage difference. This circulating current can adversely affect the system, such as increasing system losses, reducing system efficiency, and hindering the safe and stable operation of the parallel energy storage converter system.

[0005] Fortunately, carrier synchronization technology can effectively solve this problem. By ensuring that the carriers are completely in phase and frequency, the switching states of corresponding phases among the energy storage converters are kept consistent, thus eliminating the problem of fluctuating common-mode circulating currents at the source.

[0006] However, current carrier synchronization technology has some problems. Compared to parallel converters using a centralized controller, where all converters' PWM carriers are generated by the same controller and have identical frequencies, multiple carriers can be easily synchronized within a single controller without asynchronous issues, and the phase shift angle between carriers can be easily adjusted. However, for parallel converter groups using independent controllers, each converter's clock reference is provided by its own crystal oscillator, resulting in a lack of a unified clock source. Therefore, in parallel energy storage converter systems controlled by independent controllers, the carriers of multiple converters are asynchronous.

[0007] Some literature proposes a master-slave synchronization technique, which achieves carrier synchronization among multiple parallel converters by sending carrier signals through independent synchronization units. While this method is simple in principle and can achieve carrier synchronization to a certain extent, the synchronization units have high requirements for the transmission bandwidth of the communication channel. When the master controller synchronization unit fails, the parallel converters cannot achieve carrier synchronization. Furthermore, for parallel converter groups distributed over long distances, long-distance communication lines need to be laid, which is costly and difficult to apply.

[0008] Recent literature has proposed using local information for carrier synchronization, while other literature has proposed using virtual oscillators and zero-sequence current components. This latter method, compared to the previous methods, can achieve carrier synchronization without any communication tools and can be applied to parallel converter clusters located over long distances. However, this method employs nonlinear control algorithms, resulting in high implementation complexity and limiting its applicability.

[0009] Some literature proposes using a phase-locked loop (PLL) to obtain the phase information of the AC bus and calculate the carrier frequency for the current switching cycle when the carrier ratio is a constant integer. Since the AC bus information is common, the calculated carrier frequency for the current moment is also the same, thus achieving carrier synchronization. However, when the AC bus frequency changes, the switching frequency will change to a non-integer value to maintain a constant carrier ratio. Implementing a non-constant switching frequency in a digital controller becomes more complex and difficult. Furthermore, there may be errors between the sampled values ​​of each converter, and even small errors can affect carrier synchronization.

[0010] Furthermore, the existing parallel energy storage converter system requires communication lines for carrier synchronization, which leads to phase time delay and high cost. Summary of the Invention

[0011] The purpose of this invention is to provide a communication-free carrier synchronization method and related apparatus for a parallel energy storage converter system with a constant switching frequency under any grid frequency, in order to solve the problems of phase time delay and high cost caused by the need for communication lines in the prior art.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] In a first aspect, the present invention provides a communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any power grid frequency, comprising the following steps:

[0014] Connect the DC input terminals and AC output terminals of all energy storage converters in parallel.

[0015] Obtain the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency for each energy storage converter;

[0016] Determine the time when the power grid phase crosses zero based on the current power grid phase value and the previous power grid phase value;

[0017] Based on the grid frequency and constant switching frequency, calculate the carrier ratio at the zero-crossing moment of the grid phase, and based on the carrier ratio at the zero-crossing moment of the grid phase, calculate the largest integer not greater than the carrier ratio at the current moment;

[0018] Based on the carrier ratio at the zero-crossing moment of the power grid phase and the largest integer not greater than the carrier ratio at the current moment, calculate the non-integer part of the carrier phase at the current moment, and based on the non-integer part of the carrier phase at the current moment, calculate the difference between the complete carrier period and the carrier phase at the current moment;

[0019] Based on the ideal carrier phase reference value of the previous moment and the difference between the complete carrier period and the carrier phase of the current moment, the ideal carrier phase reference value of the current moment is calculated iteratively. The ideal carrier phase reference value of the previous moment is obtained by updating the ideal carrier phase reference value of the current moment obtained by iterative calculation of the previous moment, and the default initial value is 0.

[0020] Based on the current power grid phase value, determine the current sampling error value, and sum the current ideal reference value of the carrier phase with the current sampling error value to obtain the current actual reference value of the carrier phase.

[0021] Based on the actual reference value of the carrier phase at the current moment and the preset minimum phase error resolution, determine whether to perform carrier synchronization on the energy storage converter;

[0022] When performing carrier synchronization on the energy storage converter, the actual carrier synchronization cycle count and the number of carrier synchronization adjustments are updated based on the current actual carrier phase reference value and the preset minimum phase error resolution until the number of iterations equals the number of carrier synchronization adjustments. Then, the actual carrier synchronization cycle count is restored, and the carrier synchronization of the energy storage converter is completed.

[0023] A further improvement of the present invention is that, in the step of obtaining the current grid phase value, the previous grid phase value, the grid frequency and the constant switching frequency of each energy storage converter, the current grid phase value, the previous grid phase value, the grid frequency and the constant switching frequency of each energy storage converter are specifically obtained through a phase-locked loop.

[0024] A further improvement of this invention is that, in the steps of calculating the carrier ratio at the zero-crossing moment of the power grid phase based on the power grid frequency and the constant switching frequency, and calculating the largest integer not greater than the carrier ratio at the current moment based on the carrier ratio at the zero-crossing moment of the power grid phase, the formula for calculating the carrier ratio at the zero-crossing moment of the power grid phase is as follows:

[0025]

[0026] Where R(k) is the carrier ratio at the zero-crossing moment of the power grid phase, f g f is the power grid frequency. s For constant switching frequency;

[0027] The formula for calculating the largest integer not greater than the carrier ratio at the current time is:

[0028]

[0029] in, f represents the floor function. g f is the power grid frequency. s The switching frequency is constant, and R(k) is the carrier ratio at the zero-crossing point of the grid phase.

[0030] A further improvement of this invention is that, in the step of calculating the non-integer part of the carrier phase at the current moment based on the carrier ratio at the zero-crossing point of the power grid phase and the largest integer not greater than the carrier ratio at the current moment, and calculating the difference between the complete carrier period and the carrier phase at the current moment based on the non-integer part of the carrier phase at the current moment, the formula for calculating the non-integer part of the carrier phase at the current moment is as follows:

[0031]

[0032] Where, θ non-integer The non-integer part of the carrier phase at the current moment, 2π is the complete carrier period, R(k) is the carrier ratio at the zero-crossing moment of the grid phase, and T fFor the fundamental period, T s For switching cycles;

[0033] The formula for calculating the difference between the complete carrier period and the carrier phase at the current moment is:

[0034]

[0035] Where, δ q θ is the difference between the complete carrier period and the carrier phase at the current moment. non-integer R(k) represents the non-integer part of the carrier phase at the current moment, and R(k) represents the carrier ratio at the moment when the grid phase crosses zero.

[0036] A further improvement of this invention is that, in the step of iteratively calculating the ideal reference value of the carrier phase at the current moment based on the ideal reference value of the carrier phase at the previous moment and the difference between the complete carrier period and the carrier phase at the current moment, the formula for calculating the ideal reference value of the carrier phase at the current moment is:

[0037] θ ide (k)=θ ide (k-1)-δ q

[0038] Where, θ ide (k) represents the ideal reference value of the carrier phase at the current moment, θ ide (k-1) is the ideal reference value of the carrier phase at the previous moment, δ q It is the difference between the complete carrier cycle and the carrier phase at the current moment.

[0039] A further improvement of this invention is that, in the step of determining the sampling error value at the current time based on the current power grid phase value, and summing the ideal reference value of the carrier phase at the current time with the sampling error value at the current time to obtain the actual reference value of the carrier phase at the current time, the calculation formula for the actual reference value of the carrier phase at the current time is as follows:

[0040] θ ref (k)=θ ide (k)+θ samp (k)

[0041] Where, θ ref (k) represents the actual reference value of the carrier phase at the current moment, θ ide [k] represents the ideal reference value for the carrier phase at the current moment, θ samp (k) represents the sampling error value at the current time.

[0042] A further improvement of the present invention is that, in the step of determining whether to perform carrier synchronization on the energy storage converter based on the actual reference value of the carrier phase at the current moment and the preset minimum phase error resolution, the specific determination process is as follows: if the actual reference value of the carrier phase at the current moment is greater than the preset minimum phase error resolution, then carrier synchronization is performed on the energy storage converter; otherwise, carrier synchronization is not performed on the energy storage converter.

[0043] In a second aspect, the present invention provides a communication-free carrier synchronization system for a parallel energy storage converter system with a constant switching frequency under any grid frequency, comprising several energy storage converters, a grid frequency phase acquisition module, a carrier reference iterative calculation module, a sampling phase error calculation module, a carrier actual phase reference calculation module, a carrier synchronization decision submodule, and a carrier adjustment system;

[0044] Several energy storage converters, with the DC input terminal and AC output terminal of all energy storage converters connected in parallel;

[0045] The grid frequency phase acquisition module is used to acquire the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency for each energy storage converter.

[0046] The power grid frequency phase acquisition module is also used to determine the time when the power grid phase crosses zero based on the current power grid phase value and the previous power grid phase value;

[0047] The power grid frequency phase acquisition module is also used to calculate the carrier ratio at the zero-crossing time of the power grid phase based on the power grid frequency and the constant switching frequency;

[0048] The carrier reference iterative calculation module is used to calculate the largest integer not greater than the carrier ratio at the current time, based on the carrier ratio at the time when the power grid phase crosses zero.

[0049] The carrier reference iterative calculation module is also used to calculate the non-integer part of the carrier phase at the current time based on the carrier ratio at the time the power grid phase crosses zero and the largest integer not greater than the carrier ratio at the current time, and to calculate the difference between the complete carrier period and the carrier phase at the current time based on the non-integer part of the carrier phase at the current time.

[0050] The carrier reference iterative calculation module is also used to iteratively calculate the ideal carrier phase reference value at the current moment based on the ideal carrier phase reference value at the previous moment and the difference between the complete carrier period and the carrier phase at the current moment. The ideal carrier phase reference value at the previous moment is obtained by updating the ideal carrier phase reference value at the current moment obtained by iterative calculation at the previous moment, and the default initial value is 0.

[0051] The sampling phase error calculation module is used to determine the sampling error value at the current time based on the current power grid phase value;

[0052] The carrier actual phase reference calculation module is used to sum the ideal reference value of the carrier phase at the current moment with the sampling error value at the current moment to obtain the actual reference value of the carrier phase at the current moment;

[0053] The carrier synchronization decision submodule is used to determine whether to perform carrier synchronization on the energy storage converter based on the actual reference value of the carrier phase at the current moment and the preset minimum phase error resolution.

[0054] The carrier adjustment system is used to update the actual carrier synchronization cycle count and the number of carrier synchronization adjustments based on the current actual carrier phase reference value and the preset minimum phase error resolution when performing carrier synchronization on the energy storage converter, until the number of iterations equals the number of carrier synchronization adjustments, then restores the actual carrier synchronization cycle count value, and the carrier synchronization of the energy storage converter is completed.

[0055] Thirdly, the present invention provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency described above.

[0056] Fourthly, the present invention provides a storage medium storing a computer program thereon, wherein when the computer program is executed by a processor, it implements the steps of the above-described carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency without communication.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] This invention is an improved version. Compared with existing carrier synchronization methods for parallel energy storage converter systems with constant switching frequency under arbitrary grid frequencies, this invention, on the one hand, determines the zero-crossing time of the grid phase based on the current and previous grid phase values; and on the other hand, calculates the carrier ratio at the zero-crossing time based on the grid frequency and constant switching frequency. This demonstrates that this invention considers not only arbitrary grid frequencies but also maintaining a constant switching frequency, rather than solely adjusting the actual carrier count based on a carrier reference. This consideration of diverse factors improves the accuracy of subsequent carrier synchronization. On the other hand, by calculating the non-integer part of the current carrier phase, this invention enables fine control of the carrier phase, further improving synchronization accuracy. Moreover, this invention iteratively calculates the ideal reference value of the current carrier phase based on the ideal reference value of the carrier phase from the previous moment and the difference between the complete carrier period and the current carrier phase. This allows the invention to adjust the carrier phase reference value based on the carrier ratio, providing direction for carrier adjustment. Furthermore, this invention eliminates the need for communication lines, effectively solving the problems of phase time delay and high cost associated with existing technologies that require communication lines. Attached Figure Description

[0059] Figure 1 This is a flowchart of the communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency, according to the present invention.

[0060] Figure 2 This is a schematic diagram of a communication-free carrier synchronization system for a parallel energy storage converter system with a constant switching frequency under any grid frequency, as described in this invention.

[0061] Figure 3 This is a flowchart of the communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any power grid frequency in Embodiment 3 of the present invention;

[0062] Figure 4 This is a flowchart illustrating the calculation of the corresponding reference carrier phase based on the detected power grid phase in Embodiment 3 of the present invention.

[0063] Figure 5 This is a schematic diagram illustrating the specific operation of Embodiment 3 of the present invention;

[0064] Figure 6 The simulation waveform diagram for the AC side shows that the three-phase voltage contains the 3rd, 5th, and 7th harmonics.

[0065] Figure 7 The following are simulation waveforms of the carrier wave and time base counter of two converters under the carrier synchronization method proposed in this invention; from top to bottom: the carrier wave waveform of the two converters and the difference between the time base counters of the two converters;

[0066] Figure 8 The simulation waveform diagram of carrier phase synchronization when the power grid contains multiple harmonics under the carrier synchronization method proposed in this invention; from top to bottom, they are: power grid phase value, carrier phase difference between the two converters, and carrier phase synchronization count value;

[0067] Figure 9 , Figure 10 and Figure 11 The diagram shows the results of carrier synchronization and carrier phase synchronization under the carrier synchronization method proposed in this invention, when the power grid frequency is 50.05Hz.

[0068] Figure 12 , Figure 13 and Figure 14 The diagram shows the results of carrier synchronization and carrier phase synchronization under the carrier synchronization method proposed in this invention, when the power grid frequency is 50.00Hz.

[0069] Figure 15 This is a schematic diagram of the structure of the electronic device of the present invention. Detailed Implementation

[0070] To further understand the content of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0071] This invention proposes a communication-free carrier synchronization method for parallel energy storage converter systems with constant switching frequency under arbitrary grid frequencies. The method determines whether carrier synchronization is required for the energy storage converter based on the current actual carrier phase reference value and a preset minimum phase error resolution. When carrier synchronization is needed, the actual carrier synchronization cycle count and the number of carrier synchronization adjustments are updated based on the current actual carrier phase reference value and the preset minimum phase error resolution until the number of iterations equals the number of carrier synchronization adjustments. The actual carrier synchronization cycle count is then restored, and carrier synchronization of the energy storage converter is complete. Compared to existing technologies, this invention effectively solves the problems of phase time delay and high cost caused by the need for communication lines.

[0072] Example 1:

[0073] The flowchart of the communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency according to the present invention is as follows: Figure 1 As shown, the communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency according to the present invention includes the following steps:

[0074] S1. Connect the DC input terminals and AC output terminals of all energy storage converters in parallel.

[0075] S2. Obtain the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency for each energy storage converter.

[0076] S3. Determine the time when the grid phase crosses zero based on the current grid phase value and the previous grid phase value.

[0077] S4. Based on the grid frequency and constant switching frequency, calculate the carrier ratio at the time when the grid phase crosses zero, and based on the carrier ratio at the time when the grid phase crosses zero, calculate the largest integer not greater than the carrier ratio at the current time.

[0078] S5. Based on the carrier ratio at the zero-crossing moment of the power grid phase and the largest integer not greater than the carrier ratio at the current moment, calculate the non-integer part of the carrier phase at the current moment, and based on the non-integer part of the carrier phase at the current moment, calculate the difference between the complete carrier period and the carrier phase at the current moment.

[0079] S6. Based on the ideal reference value of the carrier phase at the previous moment and the difference between the complete carrier period and the carrier phase at the current moment, the ideal reference value of the carrier phase at the current moment is calculated iteratively. The ideal reference value of the carrier phase at the previous moment is obtained by updating the ideal reference value of the carrier phase at the current moment obtained by iterative calculation at the previous moment, and the default initial value is 0.

[0080] S7. Based on the current power grid phase value, determine the current sampling error value, and sum the current ideal reference value of the carrier phase with the current sampling error value to obtain the current actual reference value of the carrier phase.

[0081] S8. Based on the actual reference value of the carrier phase at the current moment and the preset minimum phase error resolution, determine whether to perform carrier synchronization on the energy storage converter.

[0082] S9. When performing carrier synchronization on the energy storage converter, update the actual carrier synchronization cycle count and the number of carrier synchronization adjustments based on the current actual carrier phase reference value and the preset minimum phase error resolution, until the number of iterations equals the number of carrier synchronization adjustments, restore the actual carrier synchronization cycle count, and complete the carrier synchronization of the energy storage converter.

[0083] Example 2:

[0084] A schematic diagram of the communication-free carrier synchronization system for a parallel energy storage converter system with a constant switching frequency under any power grid frequency according to the present invention is shown below. Figure 2As shown, the communication-free carrier synchronization system of the parallel energy storage converter system with constant switching frequency under any grid frequency of the present invention includes several energy storage converters, a grid frequency phase acquisition module, a carrier reference iterative calculation module, a sampling phase error calculation module, a carrier actual phase reference calculation module, a carrier synchronization decision submodule, and a carrier adjustment system.

[0085] Several energy storage converters (also called converters, this embodiment includes two converters, converter 1 and converter 2) are connected in parallel with the DC side input and AC side output of all energy storage converters.

[0086] The grid frequency and phase acquisition module is used to acquire the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency for each energy storage converter.

[0087] The power grid frequency and phase acquisition module is also used to determine the time when the power grid phase crosses zero based on the current power grid phase value and the previous power grid phase value.

[0088] The power grid frequency and phase acquisition module is also used to calculate the carrier ratio at the zero-crossing moment of the power grid phase based on the power grid frequency and the constant switching frequency.

[0089] The carrier reference iterative calculation module is used to calculate the largest integer not greater than the carrier ratio at the current time, based on the carrier ratio at the time when the power grid phase crosses zero.

[0090] The carrier reference iteration calculation module is also used to calculate the non-integer part of the carrier phase at the current time based on the carrier ratio at the zero-crossing moment of the power grid phase and the largest integer not greater than the carrier ratio at the current time, and to calculate the difference between the complete carrier period and the carrier phase at the current time based on the non-integer part of the carrier phase at the current time.

[0091] The carrier reference iterative calculation module is also used to iteratively calculate the ideal carrier phase reference value at the current moment based on the ideal carrier phase reference value at the previous moment and the difference between the complete carrier period and the carrier phase at the current moment. The ideal carrier phase reference value at the previous moment is obtained by updating the ideal carrier phase reference value at the current moment obtained from the iterative calculation at the previous moment, and the default initial value is 0.

[0092] The sampling phase error calculation module is used to determine the sampling error value at the current moment based on the current power grid phase value.

[0093] The carrier actual phase reference calculation module is used to sum the ideal reference value of the carrier phase at the current moment with the sampling error value at the current moment to obtain the actual reference value of the carrier phase at the current moment.

[0094] The carrier synchronization decision submodule is used to determine whether to perform carrier synchronization on the energy storage converter based on the actual reference value of the carrier phase at the current moment and the preset minimum phase error resolution.

[0095] The carrier adjustment system is used to update the actual carrier synchronization cycle count and the number of carrier synchronization adjustments when performing carrier synchronization on the energy storage converter, based on the current actual carrier phase reference value and the preset minimum phase error resolution, until the number of iterations equals the number of carrier synchronization adjustments, then restores the actual carrier synchronization cycle count value, and the carrier synchronization of the energy storage converter is completed.

[0096] Example 3:

[0097] The flowchart of the communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency according to the present invention is as follows: Figure 3 As shown, the process of calculating the corresponding reference carrier phase based on the detected power grid phase in this invention is as follows: Figure 4 As shown, the communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency according to the present invention includes the following steps:

[0098] S1. Connect the DC input terminals and AC output terminals of all energy storage converters in parallel.

[0099] In this step, all energy storage converters adopt a "common DC, common AC bus" structure. Each energy storage converter has an independent controller, and there are no communication lines connecting the energy storage converters.

[0100] S2. Obtain the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency for each energy storage converter.

[0101] In this step, the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency of each energy storage converter are obtained through a phase-locked loop (in this embodiment, a second-order generalized integral phase-locked loop is used).

[0102] S3. Determine the time when the grid phase crosses zero based on the current grid phase value and the previous grid phase value.

[0103] The specific calculation formula for determining the zero-crossing time of the power grid phase in this step is as follows:

[0104]

[0105] in, This represents the current phase value of the power grid. This represents the power grid phase value at the previous moment.

[0106] S4. Based on the grid frequency and constant switching frequency, calculate the carrier ratio at the time when the grid phase crosses zero, and based on the carrier ratio at the time when the grid phase crosses zero, calculate the largest integer not greater than the carrier ratio at the current time.

[0107] The formula for calculating the carrier ratio at the zero-crossing moment of the power grid phase in this step is:

[0108]

[0109] Where R(k) is the carrier ratio at the zero-crossing moment of the power grid phase, f g f is the power grid frequency. s For constant switching frequency;

[0110] The formula for calculating the largest integer not greater than the carrier ratio at the current time is:

[0111]

[0112] in, f represents the floor function. g f is the power grid frequency. s The switching frequency is constant, and R(k) is the carrier ratio at the zero-crossing point of the grid phase.

[0113] S5. Based on the carrier ratio at the zero-crossing moment of the power grid phase and the largest integer not greater than the carrier ratio at the current moment, calculate the non-integer part of the carrier phase at the current moment, and based on the non-integer part of the carrier phase at the current moment, calculate the difference between the complete carrier period and the carrier phase at the current moment.

[0114] The formula for calculating the non-integer part of the carrier phase at the current moment in this step is:

[0115]

[0116] Where, θ non-integer The non-integer part of the carrier phase at the current moment, 2π is the complete carrier period, R(k) is the carrier ratio at the zero-crossing moment of the grid phase, and T f For the fundamental period, T s For switching cycles;

[0117] The formula for calculating the difference between the complete carrier period and the carrier phase at the current moment is:

[0118]

[0119] Where, δ q θ is the difference between the complete carrier period and the carrier phase at the current moment. non-integer R(k) represents the non-integer part of the carrier phase at the current moment, and R(k) represents the carrier ratio at the moment when the grid phase crosses zero.

[0120] S6. Based on the ideal reference value of the carrier phase at the previous moment and the difference between the complete carrier period and the carrier phase at the current moment, the ideal reference value of the carrier phase at the current moment is calculated iteratively.

[0121] In this step, the ideal carrier phase reference value of the previous moment is obtained by updating the ideal carrier phase reference value of the current moment obtained by iterative calculation of the previous moment, and the default initial value is 0.

[0122] The formula for calculating the ideal reference value of the carrier phase at the current moment in this step is:

[0123] θ ide (k)=θ ide (k-1)-δ q

[0124] Where, θ ide (k) represents the ideal reference value of the carrier phase at the current moment, θ ide (k-1) is the ideal reference value of the carrier phase at the previous moment, δ q It is the difference between the complete carrier cycle and the carrier phase at the current moment.

[0125] S7. Based on the current power grid phase value, determine the current sampling error value, and sum the current ideal reference value of the carrier phase with the current sampling error value to obtain the current actual reference value of the carrier phase.

[0126] The formula for calculating the sampling error value at the current time in this step is:

[0127]

[0128] Where, θ samp (k) represents the sampling error value at the current moment, and R(k) represents the carrier ratio at the moment the grid phase crosses zero. This represents the current phase value of the power grid.

[0129] The formula for calculating the actual reference value of the carrier phase at the current moment is:

[0130] θ ref (k)=θ ide (k)+θ samp (k)

[0131] Where, θ ref (k) represents the actual reference value of the carrier phase at the current moment, θ ide [k] represents the ideal reference value for the carrier phase at the current moment, θ samp (k) represents the sampling error value at the current time.

[0132] S8. Based on the actual reference value of the carrier phase at the current moment and the preset minimum phase error resolution, determine whether to perform carrier synchronization on the energy storage converter.

[0133] The specific process for determining whether to perform carrier synchronization on the energy storage converter in this step is as follows: If the actual reference value of the carrier phase at the current moment is greater than the preset minimum phase error resolution, then carrier synchronization is performed on the energy storage converter; otherwise, carrier synchronization is not performed on the energy storage converter. The specific calculation formula for this determination is as follows:

[0134] θ ref [k]>θ LSB

[0135] Where, θ LSB θ is the preset minimum phase error resolution. ref (k) represents the actual reference value of the carrier phase at the current moment.

[0136] S9. When performing carrier synchronization on the energy storage converter, update the actual carrier synchronization cycle count and the number of carrier synchronization adjustments based on the current actual carrier phase reference value and the preset minimum phase error resolution, until the number of iterations equals the number of carrier synchronization adjustments, restore the actual carrier synchronization cycle count, and complete the carrier synchronization of the energy storage converter.

[0137] The formulas for calculating the actual carrier period count and the number of carrier synchronization adjustments are as follows:

[0138]

[0139] Among them, C act C is the actual carrier period count value. ref The reference carrier period count value is ΔC, which is the carrier period count adjustment value, and θ is the reference carrier period count value. LSB θref is the preset minimum phase error resolution, θref is the actual reference value of the carrier phase, and N is the number of carrier synchronization adjustments.

[0140] A schematic diagram of the specific operation of this invention is shown below. Figure 5 As shown, from top to bottom, they are the grid phase, reference carrier, reference carrier phase, actual carrier, and actual carrier phase. Figure 5 As can be seen, in order to achieve synchronization with the reference carrier, the actual carrier performs a judgment at the zero-crossing point of the grid voltage. At this point, the zero-crossing condition is met, and the carrier phase adjustment value and count value are finally obtained through conversion iteration within the system. Fine-tuning is then performed, and after several switching cycles, synchronization between the actual carrier and the reference carrier is achieved.

[0141] To verify the effectiveness of the communication-free carrier synchronization method for parallel energy storage converter systems with constant switching frequency under arbitrary grid frequencies proposed in this invention, this embodiment builds a simulation model of the three-phase converter controller connected to the grid in the simulation software Matlab / Simulink. An experimental platform is constructed using two MWINV-9R144 converters, line impedance, and a Chroma 61860 grid simulator for hardware experiments. Specific descriptions of the simulation model and experimental platform are as follows:

[0142] The simulation model consists of a system composed of two converters directly connected to a power grid simulator. Figure 6 , Figure 7 and Figure 8 This is a set of simulation waveforms, which illustrate the carrier synchronization phenomenon in a communication-free parallel energy storage converter system using the method proposed in this invention when the grid voltage contains various harmonics. Figure 6 For the three-phase voltage waveform under grid voltage distortion conditions, according to the principle that the harmonic order is inversely proportional to the amplitude, the third harmonic component is injected into the three-phase sine wave. Figure 8 The three graphs, from top to bottom, show the AC side phase-locked loop results, the PWM carrier phase difference between the two converters, and the carrier synchronization count value. Figure 8 As can be seen from this, after several switching cycles, parallel energy storage converters without signal interconnection lines can achieve carrier synchronization without communication. Figure 7 The two graphs, from top to bottom, show the PWM carrier waveforms output by each of the two converters and the waveform of the difference in their count values. After several switching cycles, the PWM carriers output by the two converters achieve phase synchronization and overlap. From... Figure 7 As can be seen from this, the carrier phase synchronization method proposed in this invention can achieve carrier synchronization between multiple energy storage converters without the aid of communication lines.

[0143] The experimental platform consists of two three-phase converters (MWINV-9R144) connected to a three-phase power grid simulator (Chroma 61860) via line impedance and solid-state relays. Figure 9 , Figure 10 , Figure 11 , Figure 12 , Figure 13 and Figure 14 Experimental waveforms of the carrier phase and the converter's PWM output with a constant duty cycle before and after applying the carrier synchronization method proposed in this invention are presented at any grid frequency. The experimental waveforms show that, using the carrier synchronization method proposed in this invention, the two converters quickly achieve carrier phase synchronization.

[0144] In summary, both simulation and experimental results demonstrate that the method of this invention can effectively achieve communication-free carrier synchronization of parallel energy storage converters with constant switching frequency under any grid frequency. This method is correct and reliable, providing valuable reference for engineering applications.

[0145] Example 4:

[0146] Please see Figure 15 As shown, the present invention also provides an electronic device 100 for a communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency; the electronic device 100 includes a memory 101, at least one processor 102, a computer program 103 stored in the memory 101 and executable on the at least one processor 102, and at least one communication bus 104.

[0147] The memory 101 can be used to store the computer program 103. The processor 102 implements the communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency as described in Embodiment 1 by running or executing the computer program stored in the memory 101 and calling the data stored in the memory 101. The memory 101 may mainly include a program storage area and a data storage area. The program storage area may store the operating system, at least one application program required for a function (such as sound playback function, image playback function, etc.), etc.; the data storage area may store data created according to the use of the electronic device 100 (such as audio data), etc. In addition, the memory 101 may include non-volatile memory, such as hard disk, memory, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one disk storage device, flash memory device, or other non-volatile solid-state storage device.

[0148] The at least one processor 102 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The processor 102 may be a microprocessor or any conventional processor. The processor 102 is the control center of the electronic device 100, connecting various parts of the electronic device 100 via various interfaces and lines.

[0149] The memory 101 in the electronic device 100 stores multiple instructions to implement a communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency. The processor 102 can execute the multiple instructions to achieve the following:

[0150] Connect the DC input terminals and AC output terminals of all energy storage converters in parallel.

[0151] Obtain the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency for each energy storage converter;

[0152] Determine the time when the power grid phase crosses zero based on the current power grid phase value and the previous power grid phase value;

[0153] Based on the grid frequency and constant switching frequency, calculate the carrier ratio at the zero-crossing moment of the grid phase, and based on the carrier ratio at the zero-crossing moment of the grid phase, calculate the largest integer not greater than the carrier ratio at the current moment;

[0154] Based on the carrier ratio at the zero-crossing moment of the power grid phase and the largest integer not greater than the carrier ratio at the current moment, calculate the non-integer part of the carrier phase at the current moment, and based on the non-integer part of the carrier phase at the current moment, calculate the difference between the complete carrier period and the carrier phase at the current moment;

[0155] Based on the ideal carrier phase reference value of the previous moment and the difference between the complete carrier period and the carrier phase of the current moment, the ideal carrier phase reference value of the current moment is calculated iteratively. The ideal carrier phase reference value of the previous moment is obtained by updating the ideal carrier phase reference value of the current moment obtained by iterative calculation of the previous moment, and the default initial value is 0.

[0156] Based on the current power grid phase value, determine the current sampling error value, and sum the current ideal reference value of the carrier phase with the current sampling error value to obtain the current actual reference value of the carrier phase.

[0157] Based on the actual reference value of the carrier phase at the current moment and the preset minimum phase error resolution, determine whether to perform carrier synchronization on the energy storage converter;

[0158] When performing carrier synchronization on the energy storage converter, the actual carrier synchronization cycle count and the number of carrier synchronization adjustments are updated based on the current actual carrier phase reference value and the preset minimum phase error resolution until the number of iterations equals the number of carrier synchronization adjustments. Then, the actual carrier synchronization cycle count is restored, and the carrier synchronization of the energy storage converter is completed.

[0159] Example 5:

[0160] If the modules / units integrated in the electronic device 100 are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, and a read-only memory (ROM).

[0161] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0162] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0163] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0164] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0165] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under arbitrary grid frequencies, characterized in that, Includes the following steps: Connect the DC input terminals and AC output terminals of all energy storage converters in parallel. Obtain the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency for each energy storage converter; Determine the time when the power grid phase crosses zero based on the current power grid phase value and the previous power grid phase value; Based on the grid frequency and constant switching frequency, calculate the carrier ratio at the zero-crossing moment of the grid phase, and based on the carrier ratio at the zero-crossing moment of the grid phase, calculate the largest integer not greater than the carrier ratio at the current moment; Based on the carrier ratio at the zero-crossing moment of the power grid phase and the largest integer not greater than the carrier ratio at the current moment, calculate the non-integer part of the carrier phase at the current moment, and based on the non-integer part of the carrier phase at the current moment, calculate the difference between the complete carrier period and the carrier phase at the current moment; Based on the ideal carrier phase reference value of the previous moment and the difference between the complete carrier period and the carrier phase of the current moment, the ideal carrier phase reference value of the current moment is calculated iteratively. The ideal carrier phase reference value of the previous moment is obtained by updating the ideal carrier phase reference value of the current moment obtained by iterative calculation of the previous moment, and the default initial value is 0. Based on the current power grid phase value, determine the current sampling error value, and sum the current ideal reference value of the carrier phase with the current sampling error value to obtain the current actual reference value of the carrier phase. Based on the actual reference value of the carrier phase at the current moment and the preset minimum phase error resolution, determine whether to perform carrier synchronization on the energy storage converter; When performing carrier synchronization on the energy storage converter, the actual carrier synchronization cycle count and the number of carrier synchronization adjustments are updated based on the current actual carrier phase reference value and the preset minimum phase error resolution until the number of iterations equals the number of carrier synchronization adjustments. Then, the actual carrier synchronization cycle count is restored, and the carrier synchronization of the energy storage converter is completed.

2. The communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency as described in claim 1, characterized in that, In the step of obtaining the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency of each energy storage converter, the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency of each energy storage converter are specifically obtained through a phase-locked loop.

3. The communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency as described in claim 1, characterized in that, In the steps of calculating the carrier ratio at the zero-crossing moment of the power grid phase based on the power grid frequency and the constant switching frequency, and calculating the largest integer not greater than the carrier ratio at the current moment based on the carrier ratio at the zero-crossing moment of the power grid phase, the formula for calculating the carrier ratio at the zero-crossing moment of the power grid phase is as follows: Where R(k) is the carrier ratio at the zero-crossing moment of the power grid phase, f g f is the power grid frequency. s For constant switching frequency; The formula for calculating the largest integer not greater than the carrier ratio at the current time is: in, f represents the floor function. g f is the power grid frequency. s The switching frequency is constant, and R(k) is the carrier ratio at the zero-crossing point of the grid phase.

4. The communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency as described in claim 1, characterized in that, In the step of calculating the non-integer part of the carrier phase at the current moment based on the carrier ratio at the zero-crossing point of the power grid phase and the largest integer not greater than the carrier ratio at the current moment, and calculating the difference between the complete carrier period and the carrier phase at the current moment based on the non-integer part of the carrier phase at the current moment, the formula for calculating the non-integer part of the carrier phase at the current moment is as follows: Where, θ non-integer The non-integer part of the carrier phase at the current moment, 2π is the complete carrier period, R(k) is the carrier ratio at the zero-crossing moment of the grid phase, and T f For the fundamental period, T s For switching cycles; The formula for calculating the difference between the complete carrier period and the carrier phase at the current moment is: Where, δ q θ is the difference between the complete carrier period and the carrier phase at the current moment. non-integer R(k) represents the non-integer part of the carrier phase at the current moment, and R(k) represents the carrier ratio at the moment when the grid phase crosses zero.

5. The communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency as described in claim 1, characterized in that, In the step of iteratively calculating the ideal reference value of the carrier phase at the current moment based on the ideal reference value of the carrier phase at the previous moment and the difference between the complete carrier period and the carrier phase at the current moment, the formula for calculating the ideal reference value of the carrier phase at the current moment is: i ide (k)=θ ide (k-1)-d q Where, θ ide (k) represents the ideal reference value of the carrier phase at the current moment, θ ide (k-1) is the ideal reference value of the carrier phase at the previous moment, δ q It is the difference between the complete carrier cycle and the carrier phase at the current moment.

6. The carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency, as described in claim 1, is characterized in that... In the step of determining the sampling error value at the current time based on the current power grid phase value, and summing the ideal reference value of the carrier phase at the current time with the sampling error value to obtain the actual reference value of the carrier phase at the current time, the formula for calculating the actual reference value of the carrier phase at the current time is as follows: i ref (k)=θ ide (k)+θ samp (k) Where, θ ref (k) represents the actual reference value of the carrier phase at the current moment, θ ide [k] represents the ideal reference value for the carrier phase at the current moment, θ samp (k) represents the sampling error value at the current time.

7. The communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency under any grid frequency as described in claim 1, characterized in that, In the step of determining whether to perform carrier synchronization on the energy storage converter based on the actual reference value of the carrier phase at the current moment and the preset minimum phase error resolution, the specific determination process is as follows: if the actual reference value of the carrier phase at the current moment is greater than the preset minimum phase error resolution, then carrier synchronization is performed on the energy storage converter; otherwise, carrier synchronization is not performed on the energy storage converter.

8. A communication-free carrier synchronization system for a parallel energy storage converter system with a constant switching frequency under any grid frequency, characterized in that, It includes several energy storage converters, a grid frequency phase acquisition module, a carrier reference iterative calculation module, a sampling phase error calculation module, a carrier actual phase reference calculation module, a carrier synchronization decision submodule, and a carrier adjustment system; Several energy storage converters, with the DC input terminal and AC output terminal of all energy storage converters connected in parallel; The grid frequency phase acquisition module is used to acquire the current grid phase value, the previous grid phase value, the grid frequency, and the constant switching frequency for each energy storage converter. The power grid frequency phase acquisition module is also used to determine the time when the power grid phase crosses zero based on the current power grid phase value and the previous power grid phase value; The power grid frequency phase acquisition module is also used to calculate the carrier ratio at the zero-crossing time of the power grid phase based on the power grid frequency and the constant switching frequency; The carrier reference iterative calculation module is used to calculate the largest integer not greater than the carrier ratio at the current time, based on the carrier ratio at the time when the power grid phase crosses zero. The carrier reference iterative calculation module is also used to calculate the non-integer part of the carrier phase at the current time based on the carrier ratio at the time the power grid phase crosses zero and the largest integer not greater than the carrier ratio at the current time, and to calculate the difference between the complete carrier period and the carrier phase at the current time based on the non-integer part of the carrier phase at the current time. The carrier reference iterative calculation module is also used to iteratively calculate the ideal carrier phase reference value at the current moment based on the ideal carrier phase reference value at the previous moment and the difference between the complete carrier period and the carrier phase at the current moment. The ideal carrier phase reference value at the previous moment is obtained by updating the ideal carrier phase reference value at the current moment obtained by iterative calculation at the previous moment, and the default initial value is 0. The sampling phase error calculation module is used to determine the sampling error value at the current time based on the current power grid phase value; The carrier actual phase reference calculation module is used to sum the ideal reference value of the carrier phase at the current moment with the sampling error value at the current moment to obtain the actual reference value of the carrier phase at the current moment; The carrier synchronization decision submodule is used to determine whether to perform carrier synchronization on the energy storage converter based on the actual reference value of the carrier phase at the current moment and the preset minimum phase error resolution. The carrier adjustment system is used to update the actual carrier synchronization cycle count and the number of carrier synchronization adjustments based on the current actual carrier phase reference value and the preset minimum phase error resolution when performing carrier synchronization on the energy storage converter, until the number of iterations equals the number of carrier synchronization adjustments, then restores the actual carrier synchronization cycle count value, and the carrier synchronization of the energy storage converter is completed.

9. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency at any grid frequency as described in any one of claims 1 to 7.

10. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the communication-free carrier synchronization method for a parallel energy storage converter system with a constant switching frequency at any grid frequency as described in any one of claims 1 to 7.

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