Cycle conversion device control method, inverter system and storage medium

Abstract

The embodiment of the invention provides a control method of a cyclic wave conversion device, an inversion system and a storage medium, and belongs to the technical field of power electronics. The method comprises the following steps: acquiring a sampling alternating-current voltage corresponding to an alternating-current voltage output by a cyclic wave conversion device at the current moment and a zero-crossover interval; determining a first switch element and a second switch element of the cyclic wave conversion device under the condition that the sampled alternating current voltage is in the zero-crossover interval, each first switch element is in a high-frequency complementary switching state, each second switch element is controlled to perform high-frequency switching, and the high-frequency switching phase of the second switch element is the same as the high-frequency switching phase of the first switch element in one-to-one correspondence; the duty cycle of each second switching element is greater than the duty cycle of the first switching element. And the first switch element is a switch element for performing high-frequency complementation in a time interval except a zero-crossover interval in an alternating current half cycle. Through the method, the output reliability of the cyclic wave conversion device can be improved.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a control method, an inverter system, and a storage medium for a cycloconverter. Background Art

[0002] When a cycloconverter is used in grid-connected control technology, different switching strategies must be adopted during the positive and negative half-cycles of the AC power cycle. Using a switching strategy for the negative half-cycle during the positive half-cycle of the AC voltage cycle can cause an AC grid short circuit, resulting in output current distortion and even damage to power devices (and vice versa). To avoid misjudging the positive and negative half-cycles, existing technologies typically use a comparator circuit or microcontroller unit (MCU) to determine whether the AC voltage output of the cycloconverter is within the positive or negative half-cycle. However, this approach can still misjudge the positive or negative half-cycle of the AC voltage due to noise interference or component errors, resulting in reduced reliability of the cycloconverter output and distorted AC grid output current. Therefore, improving the reliability of the cycloconverter output is a technical problem that needs to be addressed urgently. Summary of the Invention

[0003] The main purpose of the embodiments of the present application is to provide a control method, an inverter system and a storage medium for a cycloconverter, which can improve the output reliability of the cycloconverter.

[0004] To achieve the above-mentioned objectives, a first aspect of an embodiment of the present application provides a control method for a cycloconverter, the method comprising: Obtaining a sampled AC voltage corresponding to the AC voltage output by the cycloconverter at the current moment and a preset zero-crossing interval; When the sampled AC voltage is within the zero-crossing interval, determining a first switching element and a second switching element of the cycloconverter; the first switching element and the second switching element correspond one to one; When the sampled AC voltage is within the zero-crossing interval, executing a target switching strategy on the first switching element and the second switching element includes: placing each of the first switching elements in a high-frequency complementary switching state; Controlling each of the second switching elements to perform high-frequency switching, wherein the high-frequency switching phase of the second switching element is the same as the high-frequency switching phase of the one-to-one corresponding first switching element; wherein the duty cycle of each of the second switching elements is greater than the duty cycle of the first switching element; Among them, the first switching element is a switching element that needs to perform high-frequency complementation within the half cycle corresponding to the sampled AC voltage when the target switching strategy is not executed; the second switching element is a switching element that needs to remain normally on within the same half cycle as the corresponding first switching element when the target switching strategy is not executed.

[0005] To achieve the above-mentioned object, a second aspect of an embodiment of the present application provides an inverter system, comprising: Frequency conversion device; an AC voltage sampling unit, configured to sample the AC voltage output by the cycloconverter to obtain a sampled AC voltage; A control unit is communicatively connected to the frequency conversion device, and the control unit executes the control method of the frequency conversion device as described in any one of the first aspects.

[0006] To achieve the above-mentioned purpose, the third aspect of the embodiment of the present application proposes a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it implements the control method of the frequency conversion device described in any one of the first aspects.

[0007] The control method, inverter system, and storage medium for a cycloconverter proposed in the present application maintain high-frequency complementarity of the first switching element within a zero-crossover interval; and ensure that the high-frequency switching phase of the second switching element is consistent with that of the corresponding first switching element within the zero-crossover interval, and the duty cycle is greater than the duty cycle of the first switching element. As a result, in the event of a positive or negative misjudgment of an AC half-cycle, only the overlapping portion of the second switching elements generates a short-circuit path. This overlapping portion is often relatively short due to the setting of the duty cycle, thereby shortening the short-circuit path sent by the AC power grid connected to the cycloconverter and shortening the duration of AC power grid current distortion. Therefore, compared with related technologies, the embodiments of the present application can improve the output reliability of the cycloconverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a schematic diagram of PWM control signals for each switching element of a cycloconverter in the prior art; Figure 2 This is a module diagram of an embodiment of the inverter system provided by the present application; Figure 3 This is a schematic structural diagram of a total control unit of an embodiment of an inverter system provided by the present application; Figure 4 This is a schematic diagram of the circuit principle of an embodiment of the inverter system provided by the present application; Figure 5 This is a flow chart of an embodiment of a control method for a frequency conversion device provided by the present application; Figure 6 This is a schematic diagram of PWM control signals for each switching element in an embodiment of a control method for a cycloconverter provided by the present application; Figure 7 This is a control flow diagram of an embodiment of a control method for a cycloconverter provided by the present application; Figure 8 It is a structural diagram of the hardware structure corresponding to the control method of the frequency conversion device provided in this application.

[0009] Reference numerals: The power conversion unit 100 , the frequency conversion device 200 , the control unit 300 , the AC voltage sampling unit 400 , the AC power grid 500 , the EMI unit 600 , and the resonance unit 700 . DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0011] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein are for the purpose of describing the embodiments of this application only and are not intended to limit this application.

[0012] The following is an explanation of the terms involved in the embodiments of this application: PWM, short for Pulse Width Modulation, is essentially a digital signal defined primarily by its duty cycle and frequency. The duty cycle is the percentage of the total cycle time that the signal is high. The frequency represents the speed at which PWM completes a cycle and determines how quickly the signal switches between high and low states.

[0013] AC half-cycle: An AC half-cycle consists of two half-cycles. The time when the instantaneous value of the AC voltage is greater than the center voltage and the time when it is less than the center voltage each occupy half a cycle. The half-cycle when the instantaneous value of the AC voltage is greater than the center voltage is called the positive half-cycle, and the half-cycle when the instantaneous value of the AC voltage is less than the center voltage is called the negative half-cycle.

[0014] AC cycle: An AC cycle is the time it takes from one state to the next. For example, in a sinusoidal AC waveform, the time it takes for the voltage or current to reach its maximum positive value, complete a complete sinusoidal waveform change, and then return to its maximum positive value is the AC cycle.

[0015] Duty cycle refers to the duty cycle of the duration that the signal is in a high-frequency state within one AC cycle.

[0016] Zero crossings: Also known as zero crossings, these are the points in time when a signal changes from positive to negative or vice versa. These are the moments when the signal changes from positive to negative or vice versa, not just when the signal is exactly zero.

[0017] When a cycloconverter is used in grid-connected control technology, different switching strategies need to be adopted during the positive and negative half-cycles of the AC half-cycle. For example, the input of the cycloconverter is coupled directly to a high-frequency transformer or through a resonant unit, and the output of the cycloconverter is coupled directly to the AC grid or through an EMI unit. The switching strategy of the cycloconverter needs to be determined according to the voltage polarity of the AC grid, such as Figure 1 For example, when the AC grid voltage is in the positive half-cycle, S6 and S8 of the cycloconverter remain on, while S5 and S7 perform high-frequency complementary switching. When the AC grid voltage is in the negative half-cycle, S5 and S7 of the cycloconverter remain on, while S6 and S8 perform high-frequency complementary switching. However, based on the above switching strategy, if the negative half-cycle switching strategy is used during the positive half-cycle of the AC voltage cycle, a short circuit path will be generated in the AC grid, causing output current distortion and even the risk of damage to power devices (and vice versa). In the prior art, in order to avoid misjudging the positive and negative half-cycles corresponding to the AC voltage output by the frequency converter, a comparator circuit or a microcontroller unit (MCU) is usually used to determine whether the AC voltage output by the frequency converter is in the positive half-cycle or the negative half-cycle. However, this method may still cause errors in the zero-crossing judgment due to noise interference or component errors. As a result, if a switching strategy for the negative half-cycle is adopted when the AC voltage is in the positive half-cycle, a short-circuit path will occur in the AC grid voltage, and current surges are likely to occur at the moment the switching strategy changes, resulting in reduced reliability of the frequency converter and distortion of the AC grid output current. Therefore, how to improve the reliability of the frequency converter is a technical problem that needs to be solved urgently. Based on this, the embodiments of the present application provide a control method, an inverter system, and a storage medium for a frequency converter, which can improve the reliability of the output of the frequency converter.

[0018] It is understandable that, referring to Figures 2 to 4 As shown, according to an embodiment of the present application, an inverter system is provided, and the inverter system includes: Frequency conversion device 200; The AC voltage sampling unit 400 is used to sample the AC voltage output by the frequency conversion device 200 to obtain a sampled AC voltage; The control unit 300 is in communication with the frequency conversion device 200 and performs the following steps: Obtaining a sampled AC voltage and a preset zero-crossing interval; When the sampled AC voltage is in the zero-crossing interval, the first switching element and the second switching element of the frequency conversion device 200 are determined; the first switching element and the second switching element have a one-to-one correspondence; When the sampled AC voltage is in a zero-crossing interval, executing a target switching strategy on the first switching element and the second switching element includes: placing each first switching element in a high-frequency complementary switching state; Controlling each second switching element to perform high-frequency switching, wherein the high-frequency switching phase of the second switching element is the same as the high-frequency switching phase of the one-to-one corresponding first switching element; wherein the duty cycle of each second switching element is greater than the duty cycle of the first switching element; Among them, the first switching element is a switching element that needs to perform high-frequency complementation within the half cycle corresponding to the sampled AC voltage when the target switching strategy is not executed; the second switching element is a switching element that needs to remain normally on within the same half cycle as the corresponding first switching element when the target switching strategy is not executed.

[0019] The first switching element and the second switching element are both logical definitions of the switching elements in the frequency conversion device 200. A half-cycle is the positive or negative half-cycle of the AC half-cycle. When the sampled AC voltage is determined to be within the positive half-cycle of the current AC half-cycle, the first group of switching elements that require high-frequency complementation during the positive half-cycle, if no misjudgment occurs in the sampled AC voltage half-cycle, are used as the first switching elements, and the second group of switching elements that require constant on during the positive half-cycle, if no misjudgment occurs, are used as the second switching elements. When the sampled AC voltage is determined to be within the negative half-cycle of the current AC half-cycle, the second group of switching elements that require high-frequency complementation during the negative half-cycle, if no misjudgment occurs, are used as the first switching elements, and the first group of switching elements that require constant on during the negative half-cycle, if no misjudgment occurs, are used as the second switching elements. The switching elements in the frequency conversion device 200 are used to convert the input voltage into the voltage required by the AC power grid 500.

[0020] The sampled AC voltage represents the sampled value of the AC voltage provided by the frequency conversion device 200 to the AC power grid 500. If the frequency conversion device 200 is directly connected to the AC power grid 500, the sampled AC voltage is a direct sample of the AC voltage output by the frequency conversion device 200. Figure 2As shown, the frequency conversion device 200 is connected to the AC power grid 500 through the EMI unit 600, and the sampling of the AC voltage is an indirect sampling of the AC voltage output by the frequency conversion device 200, and a direct sampling of the AC voltage filtered by the EMI unit 600.

[0021] The zero-crossing interval is a voltage interval covering the zero crossing point. The zero-crossing interval may include only the zero crossing point and part of the negative half-cycle period, or only the zero crossing point and part of the positive half-cycle period, or part of the positive half-cycle period, the zero crossing point, and part of the negative half-cycle period. This embodiment of the present application does not limit this, and those skilled in the art can selectively set the zero-crossing interval based on the interval where the misjudgment exists.

[0022] The present application embodiment does not limit the structure of the frequency conversion device 200. In some embodiments, such as Figure 4 As shown, the frequency conversion device 200 includes a first group of switching elements and a second group of switching elements, each switching element in the first group of switching elements corresponds to each switching element in the second group of switching elements one by one, and each switching element in the first group of switching elements and each switching element in the second group of switching elements are arranged in series; and the source of each switching element in the first group of switching elements is connected to the source of the corresponding switching element in the second group of switching elements. Taking the example that the first group of switching elements and the second group of switching elements are each provided with 2 switching elements, assuming that S5 and S7 in the first group of switching elements are high-frequency complementary switching elements in the positive half-cycle period, and S6 and S8 in the second group of switching elements are high-frequency complementary switching elements in the negative half-cycle period, then the elements in the first group of switching elements or the second group of switching elements can be used as the first switching element or the second switching element according to the positive and negative properties of the half-cycle corresponding to the sampled AC voltage. The embodiment of the present application does not limit the type of switching elements and the selection of specific types. For example, Figure 4 As shown, each switching element of the frequency conversion device 200 is configured as a MOS transistor.

[0023] It is understandable that in the positive half cycle, due to the high frequency switching of the two switches (S5, S7), a dead band is required to ensure that all switching elements are turned on at the same time at the zero crossing point and achieve zero voltage switching. Figure 1 When S5 and S7 in the positive half cycle are complementary at high frequency, the duty cycle of S5 and S7 will be less than 50%. Similarly, in the negative half cycle, Figure 1 When S6 and S8 in the circuit are complementary at high frequency, the duty cycles of the two switches (S6 and S8) switching at high frequency are both less than 50%.

[0024] For example, refer to Figure 2As shown, the AC grid 500 is coupled to the frequency converter 200, and its frequency and phase are the same as those of the frequency converter 200; the AC voltage sampling unit 400 converts the AC voltage input to the AC grid 500 into an AC voltage sampling signal that can be received by the control unit 300; the control unit 300 receives the AC voltage sampling signal and determines the level of the sampled AC voltage corresponding to the AC voltage sampling signal, thereby controlling the PWM switching mode of the frequency converter 200.

[0025] It is understandable that, referring to Figure 4 As shown, the inverter system further includes an EMI unit 600 , and an input end of the EMI unit 600 is connected to an output end of the cycloconverter 200 .

[0026] The main functions of the EMI unit 600 include preventing harmonic interference, protecting the AC grid 500 equipment from external interference, improving the output quality of the frequency conversion device 200, and ensuring the stable operation of the AC grid 500 equipment.

[0027] The embodiments of the present application do not limit the specific structure of EMI, and those skilled in the art can selectively set it according to actual conditions.

[0028] It is understandable that, referring to Figure 4 As shown, the inverter system further includes a power conversion unit 100 and a resonance unit 700 . The output end of the power conversion unit 100 is connected to the input end of the resonance unit 700 , and the output end of the resonance unit 700 is connected to the input end of the frequency conversion device 200 .

[0029] The power conversion unit 100 is a device that converts input DC power into high-frequency AC power. In some embodiments, the power conversion unit 100 may include a high-frequency transformer, the output of which is coupled to the frequency conversion device 200 via the resonance unit 700 .

[0030] The embodiment of the present application does not limit the composition of the resonance unit 700. The resonance unit 700 is used to make the current between the power conversion unit 100 and the frequency conversion device 200 more stable. In some embodiments, the resonance unit 700 is composed of an inductor. In some embodiments, the resonance unit 700 is composed of multiple inductors or a combination of inductors and capacitors.

[0031] It is understandable that, referring to Figure 3 As shown, the control unit 300 includes a full-bridge conversion control module and a frequency conversion device 200 control module. The full-bridge conversion control module is used to control the output high-frequency AC power of the power conversion unit 100; the frequency conversion device 200 control module is used to control the frequency conversion device 200 to output low-frequency AC power.

[0032] By controlling the current conversion unit and the cycloconverter 200 separately through a control unit 300 , centralized management of the inverter system can be achieved.

[0033] For example, refer to Figure 3 As shown, the full-bridge converter control module controls the switching elements (S1-S4) of the power converter unit 100 based on the input power command and the sampled DC voltage of the input DC power, thereby converting DC to high-frequency AC. Similarly, the oscillator control module controls the switching elements of the frequency converter 200 based on the output power command and the sampled AC voltage, thereby converting high-frequency AC to low-frequency AC.

[0034] For example, refer to Figure 3 and 4 The inverter system of the present invention is described. The input of the power conversion unit 100 of the inverter system is a DC voltage source. The power conversion unit 100 includes a full-bridge converter (S1-S4) and a high-frequency transformer. The full-bridge converter and the high-frequency transformer convert the input DC voltage source into a high-frequency (e.g., 70kHz-200kHz) AC power. The power conversion unit 100 is coupled to the frequency conversion device 200 through the resonant unit 700. Figure 4 As shown, the resonant unit 700 is an inductor; the frequency conversion device 200 is used to convert high-frequency AC power into low-frequency (such as 50Hz) AC power, and the frequency conversion device 200 is coupled to the AC grid 500 through the EMI unit 600; at this time Figure 3 As shown, the control unit 300 receives the sampled DC voltage Vdc of the DC voltage source, the sampled AC voltage Vac corresponding to the AC voltage output by the cycloconverter 200, the input power command of the power conversion unit 100, and the output power command of the cycloconverter 200. The control unit 300 generates a full-bridge converter PWM control signal through the full-bridge conversion control module to control the on-off of S1-S4, and generates a PWM control signal of the cycloconverter 200 through the control program of the cycloconverter 200 to control the on-off of S5-S8, thereby implementing the execution of the target switching strategy when the sampled AC voltage is in the zero-crossing interval within each AC half-cycle and the on-off control in the non-zero-crossing interval.

[0035] It is understandable that, referring to Figures 5 to 7 As shown, according to an embodiment of the present application, a control method for a frequency conversion device is provided, the method comprising: Step S100, obtaining a sampled AC voltage corresponding to the AC voltage output by the cycloconverter at the current moment and a preset zero-crossing interval; Step S200: When the sampled AC voltage is in a zero-crossing interval, determining a first switching element and a second switching element of a cycloconverter; the first switching element and the second switching element have a one-to-one correspondence; Step S300: When the sampled AC voltage is in a zero-crossing interval, executing a target switching strategy on the first switching element and the second switching element, including: Step S310, placing each first switching element in a high-frequency complementary switching state; Step S320 , controlling each second switching element to perform high-frequency switching, and the high-frequency switching phase of the second switching element is the same as the high-frequency switching phase of the one-to-one corresponding first switching element; wherein the duty cycle of each second switching element is greater than the duty cycle of the first switching element.

[0036] Among them, the first switching element is a switching element that needs to perform high-frequency complementation within the half cycle corresponding to the sampled AC voltage when the target switching strategy is not executed; the second switching element is a switching element that needs to remain normally on within the same half cycle as the corresponding first switching element when the target switching strategy is not executed.

[0037] Therefore, by maintaining the high-frequency complementarity of the first switching element within the zero-crossing interval, and by making the high-frequency switching phase of the second switching element consistent with the corresponding first switching element within the zero-crossing interval, and the duty cycle being greater than the duty cycle of the first switching element, in the case of a positive and negative misjudgment of the AC half-cycle, the short-circuit path is only the overlapping part of the second switching elements, and the overlapping part is often relatively short due to the setting of the duty cycle, thereby shortening the short-circuit path sent by the AC power grid connected to the frequency conversion device and shortening the duration of the AC power grid current distortion. Therefore, the embodiment of the present application can improve the reliability of the output of the frequency conversion device.

[0038] Sampling AC voltage is direct sampling or indirect sampling of AC voltage, representing the input voltage of the AC power grid.

[0039] The zero-crossing interval indicates that there is a misjudgment of the positive or negative half-cycle of the AC power at the current moment within the zero-crossing interval. The zero-crossing interval covers the zero crossing point and can include part of the negative half-cycle interval as well as part of the positive half-cycle interval.

[0040] The first switching element and the second switching element are logical divisions of the switching elements involved in the AC voltage conversion process in the cycloconverter.

[0041] The target switching strategy is a control strategy for controlling the on-off of each switching element of the cycloconverter within the zero-crossing interval.

[0042] The target switching strategy can be pre-set or dynamically configured.

[0043] It can be understood that the zero-crossing interval consists of a positive half-cycle transition interval and a negative half-cycle transition interval; when the sampled AC voltage is in the zero-crossing interval, determining the first switching element and the second switching element of the frequency conversion device includes: When the sampled AC voltage is in the positive half-cycle transition interval, each switching element in the first group of switching elements of the cycloconverter is used as a first switching element, and each switching element in the second group of switching elements of the cycloconverter is used as a second switching element; When the sampled AC voltage is in the negative half-cycle transition interval, each switching element in the second group of switching elements of the cycloconverter is used as a first switching element, and each switching element in the first group of switching elements of the cycloconverter is used as a second switching element.

[0044] For example, refer to Figure 4 As shown, assuming that each switching element S5 and S7 in the first group of switching elements are continuously high-frequency complementary in the positive half cycle, and each switching element S6 and S8 in the second group of switching elements are continuously high-frequency complementary in the negative half cycle, then when the sampled AC voltage is in the positive half cycle transition interval, S5 and S7 are the first switching elements, S8 and S6 are the first switching elements, when S6 corresponds to S5, and S7 corresponds to S8, then refer to Figure 6 As shown, in the positive half-cycle transition interval, S5 switches from high frequency to low frequency first, and the phase of the high frequency is the same; S6 also switches from high frequency to low frequency first. Similarly, in the negative half-cycle, S8 and S7 are both started at low frequency; at high frequency, the phase of S8 and S7 is the same.

[0045] It is understood that the duty cycle can be adjusted by adjusting the duration of the high frequency of PWM.

[0046] It is understood that this application does not impose any restrictions on the specific duty cycle of the second switching element during the zero-crossing interval. For example, during the positive half-cycle transition interval, the more the duty cycle of second switching elements S6 and S8 exceeds 50%, the longer S6 and S8 remain normally on during the dead time of the first switching element, making it easier to achieve zero-voltage switching. However, this increases the duration of the short-circuit path when a misjudgment occurs. Therefore, it is necessary to shorten the duty cycle of the second switching elements as much as possible while ensuring zero-voltage switching. For example, in one embodiment, the duty cycle of S6 and S8 is 51%. Similarly, during the negative half-cycle transition interval, the more the duty cycle of second switching elements S5 and S7 exceeds 50%, the easier it is to achieve zero-voltage switching. However, the longer the short-circuit path when a misjudgment occurs, the shorter the duty cycle as much as possible while ensuring zero-voltage switching. For example, in one embodiment, the duty cycle of S5 and S7 is 51%. The duty cycles of the second switching elements during different positive and negative half-cycles can be the same or different. Those skilled in the art can determine the duty cycle of each second switch through simulation and debugging.

[0047] It is understood that the zero crossing interval is determined by the following steps: Obtaining the peak voltage and error proportional factor output by the cycloconverter; Determine the positive half-cycle threshold value and the negative half-cycle threshold value according to the peak voltage and the error proportional factor; The positive half-cycle threshold value and the negative half-cycle threshold value are used as boundary values ​​to determine the zero crossing interval.

[0048] The error proportional factor can be determined by collecting data or performing simulation on an actual network, and the embodiments of the present application do not impose too many restrictions on this.

[0049] The positive half-cycle threshold value indicates the voltage value that is closest to the zero crossing point in the positive half-cycle and may cause misjudgment.

[0050] The negative half-cycle threshold value indicates the voltage value that is closest to the zero crossing point in the negative half-cycle and may cause misjudgment.

[0051] It is understood that the error proportional factor includes the sampling element error proportional factor and the AC center offset error proportional factor. According to the peak voltage and the error proportional factor, the positive half-cycle threshold value and the negative half-cycle threshold value are determined, including: Performing weighted calculation on the sampling element error proportional factor and the peak voltage to obtain a first error value; Performing weighted calculation on the AC center bias error proportional factor and the peak voltage to obtain a second error value; A positive half-cycle threshold value and a negative half-cycle threshold value are determined according to the first error value and the second error value.

[0052] It is understandable that the positive half-cycle threshold value and the negative half-cycle threshold value are determined according to the peak voltage and the error proportional factor, including: Get the redundant error ratio; A positive half-cycle threshold value and a negative half-cycle threshold value are determined according to the peak voltage, the redundancy error ratio and the error ratio factor.

[0053] By introducing a redundant error ratio, the error range can be further expanded, thereby increasing the probability of misjudging the zero-crossing interval.

[0054] For example, take the zero crossing judgment error coming from the AC voltage sampling element error and the AC center offset error as an example, that is, the error proportional factor includes the sampling element error proportional factor and the AC center offset error proportional factor. Assuming that the sampling element error proportional factor is ±1%, the AC center offset error proportional factor is ±1%, and the sampling target voltage is 240RMS, then the peak voltage = 240 *2=678.72V. At this time, the total component error is 678.72*1% (sampling component error proportional factor) + 678.72*1% (AC center offset error proportional factor) = 13.57V. Assuming that there is a redundant error ratio used as a design factor and it is set to 1.5, the total cycle error value ≒20V. In this case, the positive half-cycle threshold value is set as the total cycle error value, and the positive half-cycle threshold value = 20V. The negative half-cycle threshold value is set as the complex number of the total cycle error value, and the negative half-cycle threshold value = -20V.

[0055] Reference Figure 6 and Figure 7 , describes the control method of the frequency conversion device of the embodiment of the present application, such as Figure 6 As shown, the zero crossing interval and the zero crossing point divide the AC half cycle into four control intervals, namely the first control interval on the left side of the positive half cycle threshold, the second control interval between the positive half cycle threshold and the zero crossing point (also known as the positive half cycle transition interval), the third control interval between the zero crossing point and the negative half cycle threshold (also known as the negative half cycle transition interval), and the fourth control interval on the right side of the negative half cycle threshold. Figure 7 As shown, the specific steps of the control method are as follows: S1. Determine in which control range the sampled AC voltage Vac is? S2.1. When Vac>positive half-cycle threshold, that is, it is in the first control interval, the positive half-cycle control strategy is executed, specifically controlling S5 and S7 to complement each other at high frequency, and S6 and S8 to be always on.

[0056] S2.2 When Vac is less than the positive half-cycle threshold and greater than the zero-crossing point, the positive half-cycle zero-crossing control strategy is adopted. The positive half-cycle zero-crossing control strategy is specifically that S5 and S7 remain consistent with the positive half-cycle control strategy (and high-frequency complementarity and a duty cycle of less than 50%), and S6 and S8 adopt high-frequency switching, wherein the phase of the high-frequency switching signal of S6 is the same as that of S5, and the duty cycle is greater than 50%, and the phase of the high-frequency switching signal of S8 is the same as that of S7, and the duty cycle is greater than 50%. At this time, if the control unit mistakenly judges this control interval as a negative half-cycle due to sampling error or noise factors, then the current short-circuit path in this control interval is only the overlapping part of S6 and S8. At this time, because the overlapping time is short, the current distortion duration can be shortened, and the reliability of the output of the frequency conversion device can be improved. In some embodiments, an EMI unit can also be provided so that the short-circuit current can be suppressed by the EMI unit, thereby avoiding current distortion and improving system reliability.

[0057] S2.3 When Vac is less than the zero crossing point and greater than the negative half-cycle threshold, the negative half-cycle zero crossing control strategy is adopted, such as Figure 6As shown, the negative half-cycle zero-crossing control strategy is specifically that S6 and S8 maintain the same period as the negative half-cycle (that is, maintain high-frequency complementarity and the duty cycle is less than 50%), and S5 and S7 adopt high-frequency switching, wherein the high-frequency switching signal phase of S5 is the same as that of S6, and the duty cycle is greater than 50%, and the high-frequency switching signal phase of S7 is the same as that of S8, and the duty cycle is greater than 50%; at this time, if the control unit mistakenly judges this control interval as a positive half-cycle due to sampling error or noise factors, then the short-circuit path of the current in this control interval is only the overlapping part of S5 and S7. Since the overlapping time is short, the current distortion duration can be shortened, and the reliability of the output of the frequency conversion device can be improved. In some embodiments, an EMI unit can also be provided so that the short-circuit current can be suppressed by the EMI unit, thereby avoiding current distortion and improving system reliability.

[0058] S2.4 When Vac is less than the negative half-cycle threshold, the negative half-cycle control strategy is adopted. Figure 6 As shown, the negative half-cycle control strategy is that S6 and S8 complement each other at high frequency, and S5 and S7 remain normally on.

[0059] S3. Outputting a PWM control signal through the PWM controller to implement the corresponding control strategy.

[0060] At this time, through the positive half-cycle zero-crossing control strategy of the above-mentioned embodiment of the present application, it is possible to correctly judge it as a positive half-cycle to ensure the normal operation of the frequency conversion device. If it is mistakenly judged as a negative half-cycle, since S6 and S8 are not kept in a normally on state, the short-circuit current of the AC power grid is limited, which greatly reduces the risk of damage to components of the frequency conversion device.

[0061] Similarly, through the negative half-cycle zero-crossing control strategy of the above embodiment of the present application, it is possible to correctly judge it as a negative half-cycle to ensure the normal operation of the frequency conversion device. If it is mistakenly judged as a positive half-cycle, the short-circuit current of the AC power grid is limited because S5 and S7 are not kept in a normally on state.

[0062] Secondly, since there is a smooth transition between the positive half-cycle control strategy and the positive half-cycle zero-crossing control strategy, and a smooth transition between the positive half-cycle zero-crossing control strategy and the negative half-cycle control strategy, switching the control strategy in different control intervals will not cause current surges and output current distortion.

[0063] Similarly, when the negative half-cycle control strategy is switched to the negative half-cycle zero-crossing control strategy or when the negative half-cycle zero-crossing control strategy is switched to the negative half-cycle control strategy, the transition is smooth and will not cause current surges to cause output current distortion.

[0064] Therefore, the control method of the embodiment of the present application makes the reliability of the frequency conversion device higher.

[0065] The present application also provides an electronic device comprising a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the control method of the frequency conversion device. The electronic device can be any smart terminal, such as a tablet computer or an in-vehicle computer.

[0066] See also Figure 8 , Figure 8 The hardware structure of an electronic device according to another embodiment is shown. The electronic device includes: The processor 801 may be implemented as a general-purpose CPU (Central Processing Unit), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of the present application. The memory 802 may be a NAND flash. The relevant program code is stored in the memory 802 and is called by the processor 801 to execute the control method of the frequency conversion device according to the embodiment of the present application. Input / output interface 803, used to implement information input and output; Communication interface 804, used to implement communication interaction between this device and other devices, which can be achieved through wired means (such as USB, network cable, etc.) or wireless means (such as mobile network, WiFi, Bluetooth, etc.); Bus 805 , which transmits information between various components of the device (e.g., processor 801 , memory 802 , input / output interface 803 , and communication interface 804 ); The processor 801 , the memory 802 , the input / output interface 803 and the communication interface 804 are connected to each other in communication within the device via a bus 805 .

[0067] It is understandable that an embodiment of the present application also provides a computer-readable storage medium, which is a computer-readable storage medium that stores a computer program. When the computer program is executed by a processor, it implements the control method of the above-mentioned frequency conversion device.

[0068] The memory, as a non-transient computer-readable storage medium, can be used to store non-transient software programs and non-transient computer executable programs. In addition, the memory may include a high-speed random access memory and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some embodiments, the memory may optionally include a memory remotely arranged relative to the processor, and these remote memories may be connected to the processor via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0069] The embodiments described in the embodiments of this application are intended to more clearly illustrate the technical solutions of the embodiments of this application and do not constitute a limitation on the technical solutions provided by the embodiments of this application. Those skilled in the art will appreciate that with the evolution of technology and the emergence of new application scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical problems.

[0070] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of the present application, and may include more or fewer steps than shown in the figures, or a combination of certain steps, or different steps.

[0071] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, i.e., they may be located in one place or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of this embodiment.

[0072] Those skilled in the art will appreciate that all or some of the steps in the methods, systems, and functional modules / units in the devices disclosed above may be implemented as software, firmware, hardware, or appropriate combinations thereof.

[0073] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0074] It should be understood that in this application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "At least one of the following items" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0075] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the above-mentioned units is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0076] The units described above as separate components may or may not be physically separate, and 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 these units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0077] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0078] If the integrated unit is implemented in the form of 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, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes multiple instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of various embodiments of the present application. The aforementioned storage medium includes: various media that can store programs, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0079] The preferred embodiments of the present invention are described above with reference to the accompanying drawings, but are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and essence of the present invention should be within the scope of the present invention.

Claims

1. A control method for a frequency conversion device, characterized in that: The method comprises: Obtaining a sampled AC voltage corresponding to the AC voltage output by the cycloconverter at the current moment and a preset zero-crossing interval; When the sampled AC voltage is within the zero-crossing interval, determining a first switching element and a second switching element of the cycloconverter; the first switching element and the second switching element correspond one to one; When the sampled AC voltage is within the zero-crossing interval, executing a target switching strategy on the first switching element and the second switching element includes: placing each of the first switching elements in a high-frequency complementary switching state; Controlling each of the second switching elements to perform high-frequency switching, wherein the high-frequency switching phase of the second switching element is the same as the high-frequency switching phase of the one-to-one corresponding first switching element; wherein the duty cycle of each of the second switching elements is greater than the duty cycle of the first switching element; Among them, the first switching element is a switching element that needs to perform high-frequency complementation within the half cycle corresponding to the sampled AC voltage when the target switching strategy is not executed; the second switching element is a switching element that needs to remain normally on within the same half cycle as the corresponding first switching element when the target switching strategy is not executed.

2. The control method of the frequency conversion device according to claim 1, characterized in that: The zero-crossing interval consists of a positive half-cycle transition interval and a negative half-cycle transition interval; when the sampled AC voltage is located in the zero-crossing interval, determining the first switching element and the second switching element of the cyclic conversion device includes: When the sampled AC voltage is within the positive half-cycle transition interval, each switching element in the first group of switching elements of the cycloconverter is used as a first switching element, and each switching element in the second group of switching elements of the cycloconverter is used as a second switching element; When the sampled AC voltage is within the negative half-cycle transition interval, each switching element in the second group of switching elements of the cyclotron converter is used as a first switching element, and each switching element in the first group of switching elements of the cyclotron converter is used as a second switching element.

3. The control method of the frequency conversion device according to claim 2, characterized in that: The zero crossing interval is determined by the following steps: Obtaining a peak voltage and an error proportional factor output by the cyclic conversion device; Determining a positive half-cycle threshold value and a negative half-cycle threshold value according to the peak voltage and the error proportional factor; The positive half-cycle threshold value and the negative half-cycle threshold value are used as boundary values ​​to determine the zero crossing interval.

4. The control method of the frequency conversion device according to claim 3, characterized in that: The error proportional factor includes a sampling element error proportional factor and an AC center offset error proportional factor, and determining a positive half-cycle threshold value and a negative half-cycle threshold value according to the peak voltage and the error proportional factor includes: Performing weighted calculation on the sampling element error proportional factor and the peak voltage to obtain a first error value; Performing weighted calculation on the AC center bias error proportional factor and the peak voltage to obtain a second error value; The positive half-cycle threshold value and the negative half-cycle threshold value are determined according to the first error value and the second error value.

5. The control method of the frequency conversion device according to claim 3, characterized in that: The determining of the positive half-cycle threshold value and the negative half-cycle threshold value according to the peak voltage and the error proportional factor includes: Get the redundant error ratio; A positive half-cycle threshold value and a negative half-cycle threshold value are determined according to the peak voltage, the redundancy error ratio, and the error proportional factor.

6. An inverter system, characterized in that: The inverter system includes: Frequency conversion device; an AC voltage sampling unit, configured to sample the AC voltage output by the cyclic conversion device to obtain a sampled AC voltage; A control unit is communicatively connected to the frequency conversion device, and the control unit executes the control method of the frequency conversion device according to any one of claims 1 to 5.

7. The inverter system according to claim 6, characterized in that: The inverter system further includes an EMI unit, an input end of the EMI unit being connected to an output end of the cycloconverter.

8. The inverter system according to claim 6, characterized in that: The inverter system further includes a power conversion unit and a resonance unit. The output end of the power conversion unit is connected to the input end of the resonance unit, and the output end of the resonance unit is connected to the input end of the cyclotron converter.

9. The inverter system according to claim 8, characterized in that: The control unit includes a full-bridge conversion control module and a cyclic conversion device control module. The full-bridge conversion control module is used to control the output high-frequency alternating current of the power conversion unit; the cyclic conversion device control module is used to control the output low-frequency alternating current of the cyclic conversion device.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the control method of the frequency converter according to any one of claims 1 to 5 is implemented.

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