Hysteresis current control method and system for two-level grid-connected converter

Abstract

The invention discloses a hysteresis current control method and system for a two-level grid-connected converter, and belongs to the technical field of converter control. The method comprises the following steps: fixing the switching frequency of the converter through a frequency inner ring; generating a reference square wave and collecting a switch square wave; multiplying and accumulating the two in each control step length, and taking an accumulated value as a phase discrimination result at the rising edge of a switching period to finish switching phase discrimination; comparing a phase discrimination result with a phase reference value, and processing the phase discrimination result by a PI (Proportional Integral) controller; pI output is processed and then fed back to a frequency instruction, a phase outer ring is formed through a frequency-phase integral relation, and closed-loop control of a switch phase is achieved. The technical problems that a traditional hysteresis control switch is random in phase and multi-machine parallel ripple offset cannot be achieved are solved, the advantage of dynamic performance of hysteresis control is kept, meanwhile, accurate fixing of the switching frequency and the phase is achieved, the system performance is remarkably improved, and the application scene of the system is expanded.

Description

Technical Field

[0001] This invention belongs to the field of converter modulation and control technology, specifically relating to a hysteresis current control method and system for a two-level grid-connected converter. Background Technology

[0002] Hysteresis current control, as a classic control method for the inner current loop of converters, is widely used in grid-connected equipment due to its strong robustness and rapid dynamic response. However, the switching frequency and phase of this type of converter are uncertain, making it impossible to achieve current ripple interleaving and cancellation in carrier-modulated converters. This increases the filtering cost of the converter and limits its parallel expansion and application in high-power applications.

[0003] The current research utilizes the effect of varying hysteresis width on the switching frequency to design a control closed loop, achieving relatively precise switching frequency control and approximately fixing the switching frequency fluctuation value. This lays the foundation for switching phase control. However, the changing switching phase causes the ripple current to randomly superimpose when two converters are connected in parallel, making ripple elimination impossible. This is due to the lack of a switching phase control algorithm, resulting in severe fluctuations in the ripple amplitude of the output current when the power output of the converter using hysteresis current control is expanded in parallel operation.

[0004] Therefore, in order to reduce the fluctuation of the switching phase when the converter adopts hysteresis current control, a switching frequency control loop is used to accurately fix the switching frequency. Based on this, a control loop for the switching phase of the converter is designed. The switching phase of the two-level converter is identified by the phase detection method. By constructing a phase outer loop and a frequency inner loop structure, the precise control of the switching phase of the converter under hysteresis current control is realized. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a hysteresis current control method and system for a two-level grid-connected converter, which addresses the shortcomings of the prior art and solves the technical problem that the switching phase of the existing two-level converter using hysteresis current control cannot be effectively controlled, thus laying the foundation for ripple cancellation when multiple such converters are connected in parallel.

[0006] The present invention adopts the following technical solution: A hysteresis current control method for a two-level grid-connected converter includes the following steps: S1. Set the frequency command of the two-level grid-connected converter, calculate the difference between the frequency command and the sampled three-phase switching frequency, control the difference through the first PI controller, and use the output of the first PI controller as the hysteresis loop width command to realize the fixed frequency control of the converter switching frequency. S2. According to the frequency command set in step S1, generate a reference square wave signal with the same frequency as the frequency command, a duty cycle of 0.5, and high and low levels of 1 and -1 respectively, and simultaneously acquire the three-phase switch square wave signal of the converter. S3. Within each control step of the converter discrete controller, the reference square wave signal obtained in step S2 is multiplied and accumulated with the three-phase switch square wave signal to obtain the three-phase cumulative digital value. When the switching cycle ends and the switch square wave signal has a rising edge, the three-phase cumulative digital value is assigned as the three-phase switch phase and the three-phase cumulative digital value is cleared to zero to complete the identification of the three-phase switch phase. S4. Calculate the difference between the three-phase switch phase obtained in step S3 and the phase reference value, and input the calculation result into the second PI controller for control. S5. Multiply the output value of the second PI controller in step S4 by -1, and then add it to the frequency command value of the three-phase frequency loop. By using the integral relationship between the switching frequency and the switching phase, the three-phase switching phase of the converter can be controlled by controlling the switching frequency.

[0007] Preferably, the determination time for the end of the switching cycle in step S3 is when the switch tube ends its off state and the rising edge of the switch square wave signal appears.

[0008] Preferably, the phase reference value in step S4 is 0.

[0009] Preferably, in step S4, the parameters of the second PI controller are set according to the phase control effect of the converter.

[0010] Preferably, in step S3, the relationship between the identified phase of the three-phase switch and the actual phase difference of the reference square wave signal is a piecewise function, and the parameters of the piecewise function change with the duty cycle of the three-phase switch square wave signal.

[0011] Preferably, when the duty cycle of the three-phase switch square wave signal is less than 0.5, the relationship between the three-phase switch phase and the actual phase difference is as follows:

[0012] in, The results of the phase detection for the switch phase are as follows. For the power grid frequency cycle, For discrete controller step size, The actual phase of the switching square wave. This represents the duty cycle of the switching square wave.

[0013] Preferably, when the duty cycle of the three-phase switch square wave signal is equal to 0.5, the relationship between the three-phase switch phase and the actual phase difference is as follows:

[0014] in, The results of the phase detection for the switch phase are as follows. For the power grid frequency cycle, For discrete controller step size, This represents the actual phase of the switching square wave.

[0015] Preferably, when the duty cycle of the three-phase switch square wave signal is greater than 0.5, the relationship between the three-phase switch phase and the actual phase difference is as follows:

[0016] in, The results of the phase detection for the switch phase are as follows. For the power grid frequency cycle, For discrete controller step size, The actual phase of the switching square wave. This represents the duty cycle of the switching square wave.

[0017] Preferably, the two-level grid-connected converter is a three-phase four-wire structure, including a DC-side filter capacitor and an AC-side filter inductor, and can be operated as a rectifier or an inverter.

[0018] Secondly, embodiments of the present invention provide a two-level grid-connected converter hysteresis current control system, comprising: The frequency module sets the frequency command of the two-level grid-connected converter, calculates the difference between the frequency command and the sampled three-phase switching frequency, controls the difference through the first PI controller, and uses the output of the first PI controller as the hysteresis loop width command to realize the fixed frequency control of the converter switching frequency. The signal module generates a reference square wave signal with the same frequency as the frequency command set by the frequency module, a duty cycle of 0.5, and high and low levels of 1 and -1 respectively, and simultaneously acquires the three-phase switch square wave signal of the converter. The phase module multiplies and accumulates the reference square wave signal obtained by the signal module with the three-phase switch square wave signal in each control step of the converter discrete controller to obtain the three-phase cumulative digital value. When the switching cycle ends and the switch square wave signal has a rising edge, the three-phase cumulative digital value is assigned as the three-phase switch phase and the three-phase cumulative digital value is cleared to zero, thus completing the identification of the three-phase switch phase. The control module calculates the difference between the three-phase switch phase obtained by the phase module and the phase reference value, and inputs the calculation result into the second PI controller for control. The correction module multiplies the output value of the second PI controller in the control module by -1 and then adds it to the frequency command value of the three-phase frequency loop. By utilizing the integral relationship between the switching frequency and the switching phase, the three-phase switching phase of the converter is controlled by controlling the switching frequency.

[0019] Thirdly, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described two-level grid-connected converter hysteresis current control method.

[0020] Fourthly, embodiments of the present invention provide a computer-readable storage medium including a computer program, which, when executed by a processor, implements the steps of the above-described two-level grid-connected converter hysteresis current control method.

[0021] Fifthly, a chip includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described two-level grid-connected converter hysteresis current control method.

[0022] In a sixth aspect, embodiments of the present invention provide an electronic device, including a computer program, which, when executed by the electronic device, implements the steps of the above-described two-level grid-connected converter hysteresis current control method.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects: A hysteresis current control method for a two-level grid-connected converter firstly fixes the switching frequency through an inner frequency loop, overcoming the inherent drawback of non-fixed switching frequency in traditional hysteresis control. Then, it accurately identifies the switching phase by generating a reference square wave and using a unique multiplicative accumulation phase detection method. Finally, it locks the switching phase by dynamically fine-tuning the frequency command through an outer phase loop and utilizing the integral relationship between frequency and phase. This achieves precise closed-loop control of the switching phase for the first time in hysteresis current control. It breaks through the technical bottleneck of traditional hysteresis control, which can only roughly control the switching frequency. By introducing a phase control loop, it transforms the originally random and uncontrollable switching phase into a precisely settable and adjustable quantity. This lays a crucial theoretical foundation and technical implementation path for subsequent multi-machine parallel operation to achieve ripple cancellation through phase synchronization. The entire scheme is logically rigorous, decomposing the complex phase control problem into three feasible steps: frequency fixing, phase identification, and phase feedback control, demonstrating high innovation and practicality.

[0024] Furthermore, the sampling and holding time of the phase detection results is clearly defined, ensuring the accuracy and consistency of phase information capture and avoiding signal instability or phase value ambiguity that may result from sampling at other times during the switching cycle. Secondly, the rising edge is a very clear and easily detectable electrical event in a digital system, which makes this phase detection method easily implementable in digital controllers such as FPGAs and DSPs, improving the engineering feasibility and reliability of the solution. It defines the synchronization mechanism between the phase detector and the converter's switching action, which is a key timing guarantee for ensuring the stable operation of the entire phase control system.

[0025] Furthermore, setting the phase reference value to "0" has profound control implications and significant engineering simplification benefits. The control objective is to ensure that the phase difference between the switching square wave and the reference square wave is zero, achieving complete synchronization. This provides a unified phase reference for the parallel operation of multiple converters, allowing all converters to lock their switching phases to the same reference phase. This creates the necessary conditions for precise "interleaving" and "cancellation" of their output ripple currents. From an implementation perspective, this setting makes the input to the phase control loop the direct phase error output from the phase detector, eliminating the need for complex phase setpoint algorithms, greatly simplifying control system design and reducing computational burden.

[0026] Furthermore, different converter systems (due to differences in power rating, filter parameters, grid impedance, etc.) may exhibit varying dynamic response characteristics of their phase loops. By setting the PI parameters according to the actual control effect (such as phase overshoot, settling time, steady-state error, etc.), the phase closed loop can be "customized" for tuning, thereby achieving optimal dynamic and steady-state performance in specific application scenarios. This avoids the system response sluggishness or oscillation problems that may result from using fixed parameters, ensuring that the phase control scheme proposed in this invention can be widely adapted to various practical engineering applications and achieve optimal control effects.

[0027] Furthermore, the comprehensiveness and accuracy of phase identification are improved. The duty cycle of the switching square wave dynamically changes with the converter's operating state, and the piecewise function relationship can adapt to different duty cycle scenarios, avoiding phase identification deviations caused by a single function relationship. When the duty cycle changes, the phase is calculated through the corresponding piecewise function, ensuring that the phase identification result always maintains a good correspondence with the actual phase difference, especially when the duty cycle deviates from 0.5, it can still accurately identify the phase trend. This limitation makes phase identification unaffected by changes in operating conditions, providing reliable data input for subsequent phase control, ensuring that phase control remains accurate and effective even under complex load conditions, further broadening the applicability of the solution.

[0028] Furthermore, quantitative and precise control of phase discrimination was achieved. Based on theoretical derivation and simulation verification, the effects of key parameters such as the power grid frequency period and the discrete controller step size were clarified for each function, enabling quantifiable calculation of the phase discrimination results. Under the corresponding duty cycle scenario, the actual phase difference can be directly calculated through specific functions, avoiding errors caused by fuzzy judgments and improving phase discrimination accuracy. These three sets of functions cover all possible cases of the switching square wave duty cycle, ensuring accurate phase discrimination can be achieved through the corresponding functions regardless of the converter's operating state. The quantified functional relationships also provide a theoretical basis for PI controller parameter tuning, making the phase control design more targeted and further improving the system's control performance.

[0029] Furthermore, the applicable platforms for the solution are clearly defined, enhancing its practicality and relevance. The three-phase four-wire structure is the mainstream topology for grid-connected converters; this limitation ensures the technical solution is closely integrated with actual engineering applications, avoiding compatibility issues caused by unclear topologies. The explicit definition of the DC-side filter capacitor and AC-side filter inductor provides a hardware reference for the parameter design of the frequency loop and phase loop, ensuring that the control algorithm matches the hardware characteristics. The limitation of switchable rectifier or inverter operating modes broadens the application scenarios of the solution, making it suitable for both power absorption and power feed-in scenarios, improving the versatility and market value of the technical solution, and providing flexible adaptability for different grid connection needs.

[0030] It is understood that the beneficial effects of the second to sixth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0031] In summary, this invention innovatively introduces a phase outer loop based on multiplication-accumulation phase detection, building upon traditional hysteresis frequency control. This achieves, for the first time, precise, closed-loop control of the switching phase of a hysteresis-controlled converter. It solves the problem of switching phase randomness, laying a key technological foundation for ripple cancellation in multi-machine parallel operation, while maintaining the inherent advantage of fast dynamic response in hysteresis control.

[0032] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0033] Figure 1 This is a system topology diagram for a two-level grid-connected converter; Figure 2 The block diagram of the frequency loop and phase loop control of the sampling hysteresis current control converter; Figure 3 This is a schematic diagram of the working process of the phase control loop phase detector; Figure 4 A schematic diagram illustrating the phase recognition principle of a phase control loop phase detector. Figure 5The diagram shows the phase discrimination results of the phase control loop phase detector. (a) shows the relationship between the phase discrimination result and the actual phase when the duty cycle of the switch square wave is less than 0.5, (b) shows the relationship between the phase discrimination result and the actual phase when the duty cycle of the switch square wave is equal to 0.5, and (c) shows the relationship between the phase discrimination result and the actual phase when the duty cycle of the switch square wave is greater than 0.5. Figure 6 The simulation waveform diagram shows the phase control effect of the phase control loop.

[0034] Figure 7 It is a simulation waveform diagram of the output current ripple cancellation after two two-level grid-connected converters with hysteresis current control are connected in parallel and the switching phase control method is used. Figure 8 A schematic diagram of a computer device provided in an embodiment of the present invention; Figure 9 This is a block diagram of a chip provided according to an embodiment of the present invention.

[0035] Among them, 60. Computer equipment; 61. Processor; 62. Memory; 63. Computer program; 600. Electronic device; 610. Processing unit; 620. Storage unit; 6201. Random access memory unit; 6202. Cache memory unit; 6203. Read-only memory unit; 6204. Program / utility; 6205. Program module; 630. Bus; 640. Display unit; 650. Input / output interface; 660. Network adapter; 700. External device. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0038] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0039] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0040] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0041] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0042] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0043] This invention provides a hysteresis current control method for a two-level grid-connected converter. For a two-level grid-connected converter using hysteresis current control, the switching frequency of the converter is fixed through frequency closed-loop control. Based on this, a phase detection method is designed to identify the switching phase of the converter. Furthermore, by designing a phase outer loop, the switching phase of the converter is controlled.

[0044] Please see Figure 1The system topology of the two-level grid-connected converter of this invention includes a three-phase four-wire converter with a two-level topology. It includes a DC-side filter capacitor and an AC-side filter inductor. The converter can function as a rectifier absorbing active power from the grid or as an inverter releasing active power to the grid. A frequency control loop is used to fix the switching frequency of the hysteresis current converter by adjusting the hysteresis loop width. A phase detection strategy is used to identify the switching phase of the converter, and a phase control loop is used to control the switching phase of the converter. This invention's control method achieves control over the switching frequency and phase of a two-level converter using hysteresis current control, laying the foundation for power expansion of this type of converter and possessing practical engineering application value.

[0045] Please see Figure 2 The present invention discloses a hysteresis current control method for a two-level grid-connected converter, comprising the following steps: S1, Set the frequency command for the two-level grid-connected converter. The frequency command is then compared with the sampled three-phase switching frequency. The error is controlled by the first PI controller, and the output of the first PI controller is given to the hysteresis loop width command to achieve fixed-frequency control of the converter switching frequency using hysteresis current control. S2. According to the converter frequency command set in step S1 Given frequency A reference square wave signal with a duty cycle of 0.5 and high and low levels of 1 and -1, respectively. Simultaneously, square wave signals from the three-phase switches of the converter are acquired. This enables the acquisition of phase-detection square wave signals; S3. In the control loop of the converter discrete controller, within each control step, the reference square wave obtained in step S2 is... respectively with Multiply the results and accumulate them over the switching cycle to obtain the cumulative number. At the end of the switching cycle, i.e., when the switching transistor is no longer in the off state and a rising edge appears on the switching square wave signal, the accumulated digital value will be... Assigned to the phase of the three-phase switch And will accumulate the numbers Resetting to zero enables the identification of the phase of the three-phase switch; S4. The three-phase switch phase obtained from phase detection in step S3 The difference between the value and the phase reference value 0 is calculated and then input into the second PI controller for control. The PI parameters of the second PI controller are... Settings are based on the control effect; S5. Multiply the output value of the second PI controller by -1 and add it to the frequency command value of the three-phase frequency loop. In this way, by utilizing the integral relationship between the switching frequency and the switching phase, the phase of the three-phase switches of the converter can be controlled by controlling the switching frequency.

[0046] Please see Figure 3 , Figure 4 , Figure 5 The theoretical explanation of the principle and process of phase detection in a phase detector is as follows: The phase detector designed in this invention operates within a discrete controller, but can also operate with a fixed step size in a continuous controller. The step size of the discrete controller is... The power grid frequency period is Please see. Figure 4 The gray dashed line in the diagram represents the reference square wave waveform. This square wave has a duty cycle of 0.5, with high and low levels of 1 and -1 respectively. Its frequency is the frequency ring command frequency of a two-level grid-connected converter using hysteresis current control. The solid black line represents the square wave of the converter switch. A high level of this square wave indicates that the converter switch is on, and a 0 level indicates that the converter switch is off.

[0047] In one switching cycle, please refer to Figure 3 Multiply the switching square wave by the reference square wave and sum them to obtain the three-phase cumulative digital value. At the end of the switching cycle, i.e., when the switching transistor is no longer in the off state and a rising edge appears on the switching square wave signal, the accumulated digital value will be... Assigned to the phase of the three-phase switch And will accumulate the numbers Reset to zero. At this point, the three-phase switch phase detection results for one cycle are displayed. and Figure 4 The phase difference between the midline of the switch square wave and the falling edge of the reference square wave shown. The relationship between them is as follows Figure 5 As shown.

[0048] Please see Figure 5 Three-phase switch phase detection results within one cycle and Figure 4 The phase difference between the midline of the switch square wave and the falling edge of the reference square wave shown. The relationship between them is a piecewise function, and the parameters of this piecewise function change with the duty cycle of the switching square wave.

[0049] Figure 5 (a) describes the phase detection result of the switch square wave when the duty cycle is less than 0.5. Phase with the actual phase of the switching square wave The relationship between them is: (1) Figure 5(b) describes the phase detection result of the switch square wave when the duty cycle is equal to 0.5. Phase with the actual phase of the switching square wave The relationship between them is: (2) Figure 5 (c) describes the phase detection result of the switch square wave when the duty cycle is greater than 0.5. Phase with the actual phase of the switching square wave The relationship between them is: (3) Please see Figure 5 As can be seen from the figure, the phase difference between the switching phase and the reference square wave is... When the absolute value is small, the switching phase detection result Phase difference between the switch phase and the reference square wave The functional relationship between them is linear. Furthermore, according to equations (1)-(3), it can be determined that the slope of this linear relationship is the same under different duty cycles. This indicates that as the duty cycle changes, the phase detection result exhibits high linearity and a fixed slope, resulting in a high phase detection effect.

[0050] When the phase difference between the switch phase and the reference square wave When the phase detection result is outside the linear range, Although it cannot accurately reflect the phase value, the sign of the phase detection result can reflect the direction of the reference square wave phase. That is, when the switching square wave leads the reference square wave, the phase detection result is negative, and when the switching square wave lags the reference square wave, the phase detection result is negative. This can also play a positive role in controlling the switching phase.

[0051] In addition, the phase detector designed in this invention has the characteristic of low computational complexity. Please refer to [link / reference]. Figure 4 During operation, the phase detector requires one integer multiplication and one addition operation in each discrete cycle, which involves very little computation and requires little storage space.

[0052] Please see Figure 2 The principles of the frequency control loop and the phase control loop are explained as follows: During the operation of the phase loop, the switching phase is controlled by adjusting the frequency command value of the frequency loop. Figure 2 In this process, the phase difference between the switching square wave and the reference square wave is obtained through multiplication phase detection. The phase difference is controlled using a phase controller to obtain the frequency command change. By fine-tuning the frequency command of the inner current loop, the frequency of the converter switching transistors using hysteresis current control is adjusted. The inner frequency loop controls the switching frequency by adjusting the hysteresis loop width. Since there is an integral relationship between the converter switching transistor frequency and phase, adjusting the switching transistor frequency allows for control of the switching transistor phase. Therefore, the design... Figure 2 The phase control loop shown can control the phase of the switching transistor through negative feedback adjustment. The PI controller amplifies the error, thereby achieving phase gain and control.

[0053] This invention utilizes closed-loop control of the switching frequency to fix the switching frequency of the converter. Based on this, a phase detector is designed to identify the switching phase. It multiplies a reference square wave signal with the square wave of the switching transistor and performs an intra-cycle accumulation count, achieving the calculation of the switching phase with extremely low computational complexity, thus laying the foundation for controlling the converter's switching phase. Simultaneously, this phase detector has the advantages of high phase identification linearity and accurate phase identification.

[0054] In another embodiment of the present invention, a hysteresis current control system for a two-level grid-connected converter is provided. This system can be used to implement the above-mentioned hysteresis current control method for a two-level grid-connected converter. Specifically, the hysteresis current control system for a two-level grid-connected converter includes a frequency module, a signal module, a phase module, a control module, and a correction module.

[0055] Among them, the frequency module sets the frequency command of the two-level grid-connected converter, calculates the difference between the frequency command and the sampled three-phase switching frequency, controls the difference through the first PI controller, and uses the output of the first PI controller as the hysteresis loop width command to realize the fixed frequency control of the converter switching frequency; The signal module generates a reference square wave signal with the same frequency as the frequency command set by the frequency module, a duty cycle of 0.5, and high and low levels of 1 and -1 respectively, and simultaneously acquires the three-phase switch square wave signal of the converter. The phase module multiplies and accumulates the reference square wave signal obtained by the signal module with the three-phase switch square wave signal in each control step of the converter discrete controller to obtain the three-phase cumulative digital value. When the switching cycle ends and the switch square wave signal has a rising edge, the three-phase cumulative digital value is assigned as the three-phase switch phase and the three-phase cumulative digital value is cleared to zero, thus completing the identification of the three-phase switch phase. The control module calculates the difference between the three-phase switch phase obtained by the phase module and the phase reference value, and inputs the calculation result into the second PI controller for control. The correction module multiplies the output value of the second PI controller in the control module by -1 and then adds it to the frequency command value of the three-phase frequency loop. By utilizing the integral relationship between the switching frequency and the switching phase, the three-phase switching phase of the converter is controlled by controlling the switching frequency.

[0056] This invention provides a terminal device comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), 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. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or corresponding function. The processor described in this embodiment can be used for the operation of a two-level grid-connected converter hysteresis current control method, including: A frequency command is set for the two-level grid-connected converter. The difference between the frequency command and the sampled three-phase switching frequency is calculated. The difference is controlled by a first PI controller, and the output of the first PI controller is used as the hysteresis loop width command to achieve fixed-frequency control of the converter switching frequency. Based on the set frequency command, a reference square wave signal with the same frequency as the command, a duty cycle of 0.5, and high and low levels of 1 and -1 respectively is generated. Simultaneously, the three-phase switching square wave signals of the converter are acquired. Within each control step of the converter discrete controller, the obtained reference square wave signal and the three-phase switching square wave signal are compared... The three phases are multiplied and summed to obtain the three-phase cumulative digital value. When the switching cycle ends and the switching square wave signal shows a rising edge, the three-phase cumulative digital value is assigned as the three-phase switching phase, and the three-phase cumulative digital value is cleared to zero, thus completing the identification of the three-phase switching phase. The difference between the identified three-phase switching phase and the phase reference value is calculated, and the calculation result is input into the second PI controller for control. The output value of the second PI controller is multiplied by -1 and then superimposed on the frequency command value of the three-phase frequency loop. By utilizing the integral relationship between the switching frequency and the switching phase, the three-phase switching phase of the converter is controlled by controlling the switching frequency.

[0057] Please see Figure 8 The terminal device is a computer device. In this embodiment, the computer device 60 includes a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When executed by the processor 61, the computer program 63 implements the two-level grid-connected converter hysteresis current control method of the embodiment. To avoid repetition, it will not be described in detail here. Alternatively, when executed by the processor 61, the computer program 63 implements the functions of each model / unit in the two-level grid-connected converter hysteresis current control system of the embodiment. To avoid repetition, it will not be described in detail here.

[0058] Computer device 60 can be a desktop computer, laptop, handheld computer, cloud server, or other computing device. Computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will understand that... Figure 8 This is merely an example of computer device 60 and does not constitute a limitation on computer device 60. It may include more or fewer components than shown, or combine certain components, or different components. For example, computer device may also include input / output devices, network access devices, buses, etc.

[0059] The processor 61 may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), 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. A general-purpose processor may be a microprocessor or any conventional processor.

[0060] The memory 62 can be an internal storage unit of the computer device 60, such as a hard disk or RAM of the computer device 60. The memory 62 can also be an external storage device of the computer device 60, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., provided on the computer device 60.

[0061] Furthermore, the memory 62 may include both internal storage units of the computer device 60 and external storage devices. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 can also be used to temporarily store data that has been output or will be output.

[0062] Please see Figure 9 The terminal device is an electronic device 600, which is manifested in the form of a general-purpose computing device. The components of the electronic device may include, but are not limited to: at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including storage unit 620 and processing unit 610), a display unit 640, etc.

[0063] The storage unit stores program code, which can be executed by the processing unit 610 to perform the steps described in the method section of this specification according to various exemplary embodiments of the present invention. For example, the processing unit 610 can perform actions such as... Figure 2 The steps are shown in the figure.

[0064] Storage unit 620 may include a readable medium in the form of a volatile storage unit, such as random access memory (RAM) 6201 and / or cache memory 6202, and may further include a read-only memory (ROM) 6203.

[0065] Storage unit 620 may also include a program / utility 6204 having a set (at least one) program module 6205, such program module 6205 including but not limited to: operating system, one or more application programs, other program modules and program data, each or some combination of these examples may include an implementation of a network environment.

[0066] Bus 630 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the multiple bus structures.

[0067] Electronic device 600 can also communicate with one or more external devices 700 (e.g., keyboard, pointing device, Bluetooth device, etc.), and with one or more devices that enable a user to interact with electronic device 600, and / or with any device that enables electronic device 600 to communicate with one or more other computing devices (e.g., router, modem). This communication can be performed via input / output interface 650. Furthermore, electronic device 600 can also communicate with one or more networks (e.g., local area network, wide area network, and / or public network, such as the Internet) via network adapter 660. Network adapter 660 can communicate with other modules of electronic device 600 via bus 630. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with electronic device 600, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms.

[0068] Example 4 This invention also provides a storage medium, specifically a computer-readable storage medium, which is a memory device in a terminal device for storing programs and data. It is understood that the computer-readable storage medium here can include both built-in storage media in the terminal device and extended storage media supported by the terminal device; it can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor, which can be one or more computer programs (including program code). More specific examples of the computer-readable storage medium include: an electrical connection with one or more wires, a portable disk, a hard disk, random access memory, read-only memory, erasable programmable read-only memory, optical fiber, portable compact disk read-only memory, optical storage device, magnetic storage device, or any suitable combination thereof.

[0069] Computer-readable storage media also include data signals propagated in baseband or as part of a carrier wave, carrying readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A readable storage medium can also be any readable medium other than a readable storage medium that can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the readable storage medium can be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber, radio frequency, etc., or any suitable combination thereof.

[0070] Program code for performing the operations of this invention can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can execute entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0071] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the two-level grid-connected converter hysteresis current control method in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor to perform the following steps: A frequency command is set for the two-level grid-connected converter. The difference between the frequency command and the sampled three-phase switching frequency is calculated. The difference is controlled by a first PI controller, and the output of the first PI controller is used as the hysteresis loop width command to achieve fixed-frequency control of the converter switching frequency. Based on the set frequency command, a reference square wave signal with the same frequency as the command, a duty cycle of 0.5, and high and low levels of 1 and -1 respectively is generated. Simultaneously, the three-phase switching square wave signals of the converter are acquired. Within each control step of the converter discrete controller, the obtained reference square wave signal and the three-phase switching square wave signal are compared... The three phases are multiplied and summed to obtain the three-phase cumulative digital value. When the switching cycle ends and the switching square wave signal shows a rising edge, the three-phase cumulative digital value is assigned as the three-phase switching phase, and the three-phase cumulative digital value is cleared to zero, thus completing the identification of the three-phase switching phase. The difference between the identified three-phase switching phase and the phase reference value is calculated, and the calculation result is input into the second PI controller for control. The output value of the second PI controller is multiplied by -1 and then superimposed on the frequency command value of the three-phase frequency loop. By utilizing the integral relationship between the switching frequency and the switching phase, the three-phase switching phase of the converter is controlled by controlling the switching frequency.

[0072] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0073] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0074] Experimental verification was conducted on a 10kW two-level three-phase grid-connected converter platform. The system parameters were: DC side voltage 700V, grid line voltage 380V / 50Hz, and AC side filter inductance 3mH.

[0075] Fixed-frequency effect: Without the proposed method, the switching frequency fluctuates wildly within the range of 18kHz to 25kHz under hysteresis control. After the frequency loop is applied, the switching frequency is stabilized at 20kHz, with a fluctuation range of less than ±150Hz.

[0076] Fixed phase effect: Figure 6 The simulation waveforms clearly show that during a fixed frequency period, the switching phase (taking phase U as an example) changes randomly between 0° and 360°; when the phase control loop proposed in this invention is simultaneously applied, the switching phase is successfully locked near the set 90° reference, and the steady-state phase error is less than 2°.

[0077] Ripple cancellation effect: such as Figure 7 As shown, in a parallel system of two identical 10kW converters, the method of this invention was applied with their switching phases differing by 180°. Experiments revealed that the peak-to-peak output current ripple was approximately 5A when operating a single unit; without phase control, the peak-to-peak total output current ripple was approximately 7A (randomly superimposed); however, after applying the phase control method of this invention, the peak-to-peak total output current ripple was significantly reduced to below 2A, with a ripple cancellation effect exceeding 70%. This example fully demonstrates the significant advantages of this invention in improving power quality and reducing filtering requirements in parallel systems.

[0078] Using a two-level grid-connected converter, refer to Figure 1 The system structure shown and Figure 2 The control strategy shown is used to build a two-level grid-connected converter system to achieve fixed switching frequency and switching phase of the two-level grid-connected converter using hysteresis current control. Figure 6 The waveform refers to the converter's output current, switching phase, and switching frequency. During a fixed hysteresis width period, the converter uses a traditional fixed hysteresis width scheme; during a fixed switching frequency period, the converter uses a frequency loop to fix the switching frequency; during a period with both fixed switching frequency and fixed switching phase, the converter employs additional switching phase control measures to achieve a fixed switching phase. Figure 7 This paper describes the ripple situation when two two-level grid-connected converters using a fixed switching frequency and phase method are connected in parallel for current output. The ripple current of the two converters is canceled by controlling the switching phase. As shown in the figure, the output current ripple amplitude is reduced.

[0079] This invention achieves the identification of the switching phase of a hysteresis current converter by designing a switching phase identification method with extremely low computational requirements. Through the design of phase control loops and frequency control loops, it realizes the control of the switching phase of a two-level converter using hysteresis current control. With minimal computational resource investment, it achieves fixed switching frequency and phase for this type of converter, laying the foundation for multi-unit parallel operation and power expansion.

[0080] In summary, this invention provides a hysteresis current control method and system for a two-level grid-connected converter, effectively solving the core technical challenge of uncontrollable switching phase in two-level grid-connected converters using hysteresis current control. By designing a unique frequency-phase dual closed-loop control structure, and using a fixed switching frequency in the inner loop, precise locking of the switching phase is achieved through a multiplicative phase detector and a PI regulator in the outer loop. The final effects are reflected in three aspects: First, it achieves dual fixation of switching frequency and phase, transforming hysteresis control into a modulation method with more regular and controllable switching behavior; second, it removes obstacles for multi-machine parallel applications, significantly reducing the total system output current ripple by controlling the switching phase of each parallel unit to achieve interleaved cancellation of their output current ripples, as simulations show a substantial reduction in ripple amplitude; third, it maintains the inherent advantages of hysteresis control, such as strong robustness and fast dynamic response. This invention greatly expands the application potential of hysteresis current control technology in high-power, multi-machine parallel scenarios, and has significant engineering application value.

[0081] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0082] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0083] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0084] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0085] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0086] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0087] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it 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, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random-access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0088] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus, and computer program products according to embodiments of this application. 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... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0089] 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.

[0090] 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.

[0091] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A hysteresis current control method for a two-level grid-connected converter, characterized in that, Includes the following steps: S1. Set the frequency command of the two-level grid-connected converter, calculate the difference between the frequency command and the sampled three-phase switching frequency, control the difference through the first PI controller, and use the output of the first PI controller as the hysteresis loop width command to realize the fixed frequency control of the converter switching frequency. S2. According to the frequency command set in step S1, generate a reference square wave signal with the same frequency as the frequency command, a duty cycle of 0.5, and high and low levels of 1 and -1 respectively, and simultaneously acquire the three-phase switch square wave signal of the converter. S3. Within each control step of the converter discrete controller, the reference square wave signal obtained in step S2 is multiplied and accumulated with the three-phase switch square wave signal to obtain the three-phase cumulative digital value. When the switching cycle ends and the switch square wave signal has a rising edge, the three-phase cumulative digital value is assigned as the three-phase switch phase and the three-phase cumulative digital value is cleared to zero to complete the identification of the three-phase switch phase. S4. Calculate the difference between the three-phase switch phase obtained in step S3 and the phase reference value, and input the calculation result into the second PI controller for control. S5. Multiply the output value of the second PI controller in step S4 by -1, and then add it to the frequency command value of the three-phase frequency loop. By using the integral relationship between the switching frequency and the switching phase, the three-phase switching phase of the converter can be controlled by controlling the switching frequency.

2. The hysteresis current control method for a two-level grid-connected converter according to claim 1, characterized in that, The determination time for the end of the switching cycle in step S3 is when the switch transistor ends its off state and the rising edge of the switch square wave signal appears.

3. The hysteresis current control method for a two-level grid-connected converter according to claim 1, characterized in that, The phase reference value mentioned in step S4 is 0.

4. The hysteresis current control method for a two-level grid-connected converter according to claim 1, characterized in that, In step S4, the parameters of the second PI controller are set according to the phase control effect of the converter.

5. The hysteresis current control method for a two-level grid-connected converter according to claim 1, characterized in that, In step S3, the relationship between the identified phase of the three-phase switch and the actual phase difference of the reference square wave signal is a piecewise function, and the parameters of the piecewise function change with the duty cycle of the three-phase switch square wave signal.

6. The hysteresis current control method for a two-level grid-connected converter according to claim 5, characterized in that, When the duty cycle of the three-phase switch square wave signal is less than 0.5, the relationship between the three-phase switch phase and the actual phase difference is as follows: in, The results of the phase detection for the switch phase. For the power grid frequency cycle, For discrete controller step size, The actual phase of the switching square wave. This represents the duty cycle of the switching square wave.

7. The hysteresis current control method for a two-level grid-connected converter according to claim 5, characterized in that, When the duty cycle of the three-phase switch square wave signal is equal to 0.5, the relationship between the three-phase switch phase and the actual phase difference is as follows: in, The results of the phase detection for the switch phase. For the power grid frequency cycle, For discrete controller step size, This represents the actual phase of the switching square wave.

8. The hysteresis current control method for a two-level grid-connected converter according to claim 5, characterized in that, When the duty cycle of the three-phase switch square wave signal is greater than 0.5, the relationship between the three-phase switch phase and the actual phase difference is as follows: in, The results of the phase detection for the switch phase. For the power grid frequency cycle, For discrete controller step size, The actual phase of the switching square wave. This represents the duty cycle of the switching square wave.

9. The hysteresis current control method for a two-level grid-connected converter according to claim 1, characterized in that, The two-level grid-connected converter is a three-phase four-wire structure, including a DC-side filter capacitor and an AC-side filter inductor, and can be operated as a rectifier or an inverter.

10. A hysteresis current control system for a two-level grid-connected converter, characterized in that, include: The frequency module sets the frequency command of the two-level grid-connected converter, calculates the difference between the frequency command and the sampled three-phase switching frequency, controls the difference through the first PI controller, and uses the output of the first PI controller as the hysteresis loop width command to realize the fixed frequency control of the converter switching frequency. The signal module generates a reference square wave signal with the same frequency as the frequency command set by the frequency module, a duty cycle of 0.5, and high and low levels of 1 and -1 respectively, and simultaneously acquires the three-phase switch square wave signal of the converter. The phase module multiplies and accumulates the reference square wave signal obtained by the signal module with the three-phase switch square wave signal in each control step of the converter discrete controller to obtain the three-phase cumulative digital value. When the switching cycle ends and the switch square wave signal has a rising edge, the three-phase cumulative digital value is assigned as the three-phase switch phase and the three-phase cumulative digital value is cleared to zero, thus completing the identification of the three-phase switch phase. The control module calculates the difference between the three-phase switch phase obtained by the phase module and the phase reference value, and inputs the calculation result into the second PI controller for control. The correction module multiplies the output value of the second PI controller in the control module by -1 and then adds it to the frequency command value of the three-phase frequency loop. By utilizing the integral relationship between the switching frequency and the switching phase, the three-phase switching phase of the converter is controlled by controlling the switching frequency.

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