A method and device for detecting the resonant frequency of an inverter

Abstract

The present invention discloses a method and device for detecting the resonant frequency of an inverter, which collect the voltage values of the input voltage, output voltage and drain-source voltage and input them into the ADC pins of a DSP; calculate the value ranges of the turn-on time and resonant duration of the flyback MOS transistor under each phase, and in the flyback switching algorithm, limit the turn-on time through a power control function to control the switching frequency, calculate the optimal turn-on time of the flyback MOS transistor within the current switching period, perform resonant voltage sampling for one switching period at one phase, enter the next power frequency period after completing several switching periods, and increase the acquisition delay to change the position of the sampling point. After several power frequency periods, perform the acquisition of the next phase, obtain the resonant period corresponding to each phase and average it as the equivalent average resonant time, and obtain the resonant frequency. The present invention can accurately obtain the resonant frequency only by using a simple signal acquisition circuit, and enhances the noise immunity ability.

Description

Technical Field

[0001] The present invention relates to the field of soft switching of inverters, and particularly to a method and device for detecting the resonant frequency of an inverter. Background Art

[0002] In the prior art, the detection of the resonant frequency generally requires an external analog acquisition chip, and the resonant frequency is detected by the change rate of the analog quantity. Although this method is relatively accurate, its anti-interference performance is relatively poor. Under high-power working conditions, the noise of the system will affect the acquisition of the analog quantity, resulting in the inability to accurately find the change rate of the desired waveform, and the use of the analog acquisition chip will increase the complexity of the system circuit. Summary of the Invention

[0003] The purpose of the present invention is to propose a method and device for detecting the resonant frequency of an inverter in view of the deficiencies of the prior art.

[0004] The purpose of the present invention is achieved by the following technical solutions: A method for detecting the resonant frequency of an inverter, the method comprising the following steps:

[0005] S1. Synchronize the phase of the DSP and the power grid to obtain different output voltage phase angles; collect the input and output voltages through a signal acquisition circuit;

[0006] S2. Calculate the thresholds of the turn-on time and the resonant duration of the flyback MOS transistor at each phase according to the peak value of the primary current;

[0007] S3. Set the desired output current value and the resonant duration, and calculate the optimal turn-on time of the flyback MOS transistor within the current switching period through the output voltage, the desired output current value, the resonant duration, and the power control function;

[0008] S4. According to the obtained optimal turn-on time of the flyback MOS transistor, sample the resonant voltage for one switching period at one of the phases;

[0009] S5. Repeat the process of S3-S4. After completing several switching periods, enter the next power frequency period, and increase the acquisition delay so that the position of the sampling point starts to change. After several power frequency periods, perform the acquisition of the next phase;

[0010] S6. According to the resonant voltage at the acquisition point, draw the resonant waveforms of each phase, obtain the resonant period corresponding to each phase, and calculate the average value as the equivalent average resonant time, so as to obtain the resonant frequency.

[0011] Further, the signal acquisition circuit specifically includes: a main power circuit, a sampling circuit, and a control module;

[0012] Main power circuit: The input capacitor, the primary side of the flyback transformer, and the flyback switching MOS transistor are connected in series. The secondary side of the flyback transformer, the secondary side freewheeling diode, and the output capacitor are connected in series. The inverter module is connected in parallel across the output capacitor.

[0013] Sampling circuit: It includes an input voltage sampling circuit and a drain-source voltage sampling circuit.

[0014] The input terminal of the input voltage sampling circuit is connected in parallel across the input capacitor, and the output terminal is connected to the DSP.

[0015] The input terminal of the drain-source voltage sampling circuit is connected in parallel to the drain and source of the flyback switching MOS transistor, and the output terminal is connected to the DSP. The input terminal of the drain-source voltage sampling circuit is connected in parallel across the output ports of the inverter module, and the output terminal is connected to the DSP.

[0016] The control module is composed of a DSP and outputs a MOS transistor control signal connected to the gate of the MOS transistor.

[0017] Further, the threshold value of the turn-on time of the flyback MOS transistor in S2 is specifically selected as follows: Select the current value of 20% - 80% of the magnetic saturation current of the flyback transformer, and inversely deduce the maximum time and minimum time of the required turn-on time of the flyback MOS transistor, that is: and the minimum time , that is:

[0018] ,

[0019] where is the maximum peak value of the primary side current, Vin is the input voltage, and Lp is the excitation inductance of the transformer.

[0020] Further, the threshold value of the resonance duration in S2 is specifically selected as follows: According to the turn-on time of the flyback MOS transistor and the value range of the instantaneous reference value of the output current, obtain the value range of the resonance duration.

[0021] Further, the set expected resonance duration in S3 is specifically: Select the maximum resonance duration that does not cause the transformer to saturate within the value range.

[0022] Further, the power control function in S3 is specifically:

[0023] T on

[0024] where, T on is the turn-on time of the flyback MOS transistor, V in is the input voltage obtained by sampling, V outis the sampled output voltage, n is the transformer turns ratio, and Lp is the transformer exciting inductance. is the expected output current value, and Tm is the resonance duration.

[0025] Further, the setting of the acquisition delay in S5 includes: the delay increases sequentially with the power frequency cycle, and after setting 5 power frequency cycles, the resonance voltage acquisition under one phase is completed.

[0026] Further, S6 specifically includes:

[0027] The acquired resonance waveform minus V in , to obtain a series of oscillating voltage values with 0V as the zero point. After performing double power frequency filtering on the series of voltage values, the time between two adjacent zero crossing points is denoted as T r_θ / 2, where is the currently detected phase angle; the resonance times of different phases are averaged to obtain the equivalent average resonance time.

[0028] According to another aspect of the specification, there is also provided an inverter resonance frequency detection device, including a memory and one or more processors. An executable code is stored in the memory, and when the processor executes the executable code, the described inverter resonance frequency detection method is implemented.

[0029] According to another aspect of the specification, there is also provided a computer-readable storage medium, on which a program is stored. When the program is executed by a processor, the described inverter resonance frequency detection method is implemented.

[0030] Advantages of the present invention: The present invention uses a general signal acquisition circuit. Compared with discrete and multiple acquisitions, discrete acquisitions are less sensitive to noise, and the algorithm uses the data acquired multiple times to ensure accuracy; the present invention calculates the resonance frequency through simple signal acquisition and uses software algorithms. With this set of resonance detection algorithms, accurate resonance frequency can be obtained only by using a simple signal acquisition circuit; the complexity of the system is greatly simplified, and the anti-interference ability to noise is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of a signal acquisition circuit provided by an embodiment of the present invention;

[0032] Figure 2 is a schematic diagram of the phase points to be acquired provided by an embodiment of the present invention;

[0033] Figure 3 is the waveform diagram of each phase expansion provided by an embodiment of the present invention;

[0034] Figure 4Schematic diagram of an inverter resonant frequency detection device provided by an embodiment of the present invention. Detailed implementation manners

[0035] The following further describes the detailed implementation manners of the present invention with reference to the accompanying drawings.

[0036] As Figure 1 shown, a method for detecting the resonant frequency of an inverter provided by the present invention includes:

[0037] According to the voltage values of the voltage V ds across the drain and source of the MOS transistor, the input voltage V in and the output voltage V out collected by the signal acquisition circuit, input to the ADC pin of the DSP; in the flyback switching algorithm, the switching frequency is controlled by the function T on (i ref ,V in ,V out ,L p ,n,T m ). In the function, i ref is the desired output current value, V in is the input voltage, V out is the output voltage, L p is the primary excitation inductance of the flyback transformer, n is the turn ratio of the primary and secondary sides of the flyback transformer, T m is the parameter for controlling the resonant oscillation time. Increasing T m can extend the resonant oscillation time, where T m =T d +T c , T d is the delay before sampling; T c is the sampling time. Sampling starts after the delay ends and ends when the next switching cycle starts; when a power is given, a T on is calculated within each switching cycle, and there will be a corresponding T off , T off =(n*V in / V out )* T on . Sampling starts after a delay of T off after T d ends. T c is the time for collecting data points of the resonant waveform; the accurate resonant time T r is calculated through the resonant waveform and the input voltage value;

[0038] Specifically, the method includes the following steps:

[0039] S1. Use a DSP and the power grid to perform phase synchronization to obtain different output voltage phase angles; collect the input and output voltages through a signal acquisition circuit;

[0040] The signal acquisition circuit specifically includes: a main power circuit, a sampling circuit, and a control module;

[0041] Main power circuit: The input capacitor C1, the primary side of the flyback transformer T1, and the flyback switch MOS transistor Q1 are connected in series. The secondary side of the flyback transformer T1, the secondary side freewheeling diode D1, and the output capacitor C2 are connected in series. The inverter module is connected in parallel across the output capacitor; Sampling circuit: V in The input end of the sampling circuit is connected in parallel across the input capacitor, and the output end is connected to the DSP; V ds The input end of the sampling circuit is connected in parallel to the drain (D) and source (S) of the flyback switch MOS transistor Q1, and the output end is connected to the DSP; V out The input end of the sampling circuit is connected in parallel across the output ports of the inverter module, and the output end is connected to the DSP; The control algorithm module is mainly composed of a DSP to output a MOS transistor control signal connected to the gate (G) of the MOS transistor;

[0042] S2. Calculate the thresholds of the turn-on time and resonance duration of the flyback MOS transistor at each phase according to the peak value of the primary current; specifically including: T on selection of and setting of T m , the peak value of the primary current (V in and L p are determined, the larger T on is, the larger i pp is), Excessive will cause magnetic saturation of the flyback transformer. To prevent magnetic saturation of the flyback transformer, a T that does not exceed the peak current limit is set on , T on Too small will cause distortion of the resonance waveform or no resonance waveform; Therefore, select a current value of 20% - 80% of the magnetic saturation current of the flyback transformer and deduce the required T on_min , T on_max , that is , , so control T on during the process cannot exceed T on_max this value and cannot be lower than T on_min this value; We actually use T m and to control T on . According to the transformer turns ratio n, at phase , , so , ;

[0043] Parameter T m For the setting of parameter T, first set different values of T m , the longer the time T m is, the longer the resonance time will be, and the more points will be collected. When V in , V out , is determined, if T m is too large, it will cause the switching frequency to decrease (i.e., the calculated T on is too large), and it must be less than ; then deduce the function T m ( , ), where , . Calculate the range of T m as [T m_min , T m_max . Select a value of T within this range that can prevent the transformer from saturating as much as possible m for use in the algorithm;

[0044] S3. Set the desired output current value and the resonance duration. Calculate the optimal turn-on time of the flyback MOSFET within the current switching period through the output voltage, the desired output current value, the resonance duration, and the power control function. Specifically, according to the sampled input voltage V in , the output voltage V out ( , V out is the instantaneous value of the output voltage, is the phase angle of the output voltage), set the transformer turns ratio n and the transformer magnetizing inductance Lp. According to different systems, set a suitable iref and resonance duration Tm. Calculate the appropriate turn-on time Ton of the MOSFET and the switching period Ts of the MOSFET based on the above parameters. In this embodiment, iref is selected as 0.1 A and the resonance duration Tm is 10 us.

[0045] Among them, the function for controlling the power magnitude is T on (denoted as function T on ([[]] , ))). By changing ([[]] , is the target value of the effective value of the output current, is the phase angle of the output current) and the magnitude of T m , the magnitude of T on can be controlled, and thus the magnitude of the flyback input peak current can be changed (that is, the output power magnitude is changed). In addition, T m is a parameter for controlling the resonance time;

[0046] S4. According to the obtained optimal turn-on time of the flyback MOS transistor, sample the resonant voltage for one switching cycle at one of the phases; in this embodiment, At the turn-on of the flyback MOS transistor for time T on Time T on is the turn-on time calculated for the current situation, and after the turn-off time T off duration, delay for time T d_1 duration and then start collecting the resonant voltage. After several switching cycles, enter the collection operation of the resonant voltage at the current phase of the next power frequency cycle. Repeat the collection of the current phase for several power frequency cycles and then end the collection of the current phase, and enter the collection operation of the resonant voltage at the next phase, and so on;

[0047] S5. Repeat the process of S3 - S4. After completing several switching cycles, enter the next power frequency cycle, and increase the collection delay so that the position of the sampling point starts to change. After several power frequency cycles, perform the collection of the next phase;

[0048] Specifically set the collection delay. Under the condition of the same phase T m being determined, because the sampling frequency of the DSP is fixed at f c , so the number of points sampled at this time is also fixed. The number and position of sampling points within each resonant cycle are also fixed and limited. In order to accurately draw the actual resonant waveform in the software, it is necessary to extend T d . In this way, although the number of sampling points within each resonant cycle is still fixed, the position of the sampled points will change. After several power frequency cycles, the DSP can draw the resonant waveform under the current working condition through the sampled points; since T m = T d + T c , what can be controlled is the time from the end of T off to the start of collection, that is, the delay T d . Therefore, in the algorithm, set T d to increase sequentially with the power frequency cycle. The first power frequency collection delay is T d_1 = 0 us. Since the standard resonant cycle is generally 2 us, it is set to increase the delay by 0.5 us each time. After setting 5 power frequency cycles, complete the collection of the resonant voltage at one phase; according to T on and T off calculated in Step 2 and Step 3, plus the set T m , the switching cycle T s of the MOS transistor can be obtained. T s = T on + T off + T m ;

[0049] S6. Draw the resonance waveforms of each phase according to the resonance voltage at the acquisition points, as Figure 2 shown in the schematic diagram of the phase points to be acquired provided by the embodiment of the present invention. Obtain the resonance period corresponding to each phase and calculate the average value as the equivalent average resonance time, so as to obtain the resonance frequency.

[0050] In this embodiment, as Figure 3 shown, subtract V in from the acquired resonance waveform to obtain a series of oscillating voltage values with 0V as the zero point. After filtering this series of voltage values by twice the power frequency, record the time between two adjacent zero-crossing points as T r_θ / 2 ( is the phase angle currently detected); because the resonance voltage vibrates up and down with V in as the zero point, subtracting V in from the acquired resonance voltage can obtain a resonance waveform that vibrates up and down with 0V as the zero point, and the time between two adjacent zero-crossing points is half of the resonance period T r / 2; average the resonance times of different phases to obtain the equivalent average resonance time Tr.

[0051] After considering the specification and the practice disclosed herein, those skilled in the art will readily think of other implementation schemes of the present application. The present application aims to cover any variations, uses or adaptations of the present application, and these variations, uses or adaptations follow the general principles of the present application and include the common general knowledge or conventional technical means in the technical field not disclosed in the present application. The specification and the embodiments are only regarded as exemplary, and the true scope and spirit of the present application are pointed out by the claims.

[0052] Corresponding to the embodiment of the above-mentioned method for detecting the resonance frequency of an inverter, the present invention also provides an embodiment of a device for detecting the resonance frequency of an inverter.

[0053] Refer to Figure 4 , a device for detecting the resonance frequency of an inverter provided by the embodiment of the present invention includes a memory and one or more processors. An executable code is stored in the memory. When the processor executes the executable code, it is used to implement the method for detecting the resonance frequency of an inverter in the above-mentioned embodiment.

[0054] An embodiment of the inverter resonant frequency detection device provided by the present invention can be applied to any device with data processing capabilities. Such a device with data processing capabilities can be a device or apparatus such as a computer. The device embodiment can be implemented through software, or through hardware, or a combination of software and hardware. Taking software implementation as an example, as a logically meaningful device, it is formed by the processor of any device with data processing capabilities reading the corresponding computer program instructions in the non-volatile memory into the memory for operation. At the hardware level, as Figure 4 shown, it is a hardware structure diagram of any device with data processing capabilities where the inverter resonant frequency detection device provided by the present invention is located. In addition to Figure 4 the processor, memory, network interface, and non-volatile memory shown, usually according to the actual functions of the device with data processing capabilities where the embodiment device is located, other hardware may also be included, which will not be elaborated here.

[0055] The implementation processes of the functions and roles of each unit in the above device are specifically described in detail in the implementation processes of the corresponding steps in the above method, which will not be elaborated here.

[0056] For the device embodiment, since it basically corresponds to the method embodiment, the relevant parts can refer to the partial description of the method embodiment. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they can be located in one place, or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the present invention solution. Those of ordinary skill in the art can understand and implement it without creative efforts.

[0057] The embodiment of the present invention also provides a computer-readable storage medium, on which a program is stored. When the program is executed by a processor, it implements an inverter resonant frequency detection method in the above embodiment.

[0058] The computer-readable storage medium may be an internal storage unit of any device with data processing capabilities described in any of the foregoing embodiments, such as a hard disk or a memory. The computer-readable storage medium may also be an external storage device of any device with data processing capabilities, such as a plug-in hard disk, a Smart Media Card (SMC), an SD card, a Flash Card, etc. equipped on the device. Further, the computer-readable storage medium may also include both an internal storage unit and an external storage device of any device with data processing capabilities. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capabilities, and may also be used to temporarily store the data that has been output or is to be output.

[0059] The present invention also provides a computer program product, including a computer program, which when executed by a processor, implements the inverter resonance frequency detection method described above.

[0060] After considering the specification and practicing the content disclosed herein, those skilled in the art will readily conceive of other embodiments of the present application. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include the common general knowledge or conventional technical means in the technical field not disclosed in the present application. The specification and the embodiments are only regarded as exemplary, and the true scope and spirit of the present application are pointed out by the claims.

[0061] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. The present application is not limited to the exact structure described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present application is only limited by the appended claims.

Claims

1. A method for detecting the resonant frequency of an inverter, characterized in that, The method includes the following steps: S1. Use a DSP to synchronize the phase with the power grid to obtain different output voltage phase angles; collect the input voltage, output voltage, and drain-source voltage through a signal acquisition circuit; S2. Calculate the value range of the turn-on time and resonance duration of the flyback MOS transistor at each phase according to the peak value of the primary current; S3. Set the desired output current value and resonance duration, and calculate the optimal turn-on time of the flyback MOS transistor within the current switching period through the output voltage, desired output current value, resonance duration, and power control function; The specific power control function is: T on ； Among them, T on is the turn-on time of the flyback MOSFET, V in is the input voltage obtained by sampling, V out is the output voltage obtained by sampling, n is the transformer turns ratio, Lp is the transformer magnetizing inductance, is the desired output current value, is the resonance duration; S4. According to the obtained optimal turn-on time of the flyback MOS transistor, sample the resonance voltage for one switching period at one of the phases; S5. Repeat the process of S3 - S4. After completing several switching periods, enter the next power frequency period, and increase the acquisition delay so that the position of the sampling point starts to change. After several power frequency periods, perform the acquisition of the next phase; S6. According to the resonance voltage at the acquisition point, draw the resonance waveform of each phase, obtain the resonance period corresponding to each phase, and calculate the average value as the equivalent average resonance time, so as to obtain the resonance frequency.

2. The method for detecting the resonant frequency of an inverter according to claim 1, wherein The signal acquisition circuit specifically includes: a main power circuit, a sampling circuit, and a control module; Main power circuit: The input capacitor, the primary side of the flyback transformer, and the flyback switching MOS transistor are connected in series. The secondary side of the flyback transformer, the secondary side freewheeling diode, and the output capacitor are connected in series. The inverter module is connected in parallel across the output capacitor; Sampling circuit: It includes an input voltage sampling circuit, an output voltage sampling circuit, and a drain-source voltage sampling circuit; The input terminal of the input voltage sampling circuit is connected in parallel across the input capacitor, and the output terminal is connected to the DSP; The input terminal of the drain-source voltage sampling circuit is connected in parallel to the drain and source of the flyback switching MOS transistor, and the output terminal is connected to the DSP; the input terminal of the output voltage sampling circuit is connected in parallel across both ends of the output port of the inverter module, and the output terminal is connected to the DSP; The control module is composed of a DSP, and outputs a MOS transistor control signal connected to the gate of the MOS transistor.

3. A method for detecting the resonance frequency of an inverter according to claim 1, characterized in that, The threshold selection of the turn-on time of the flyback MOSFET in S2 is specifically as follows: Select a current value of 20% to 80% of the magnetic saturation current of the flyback transformer, and inversely deduce the maximum time and minimum time of the required turn-on time of the flyback MOSFET, that is and the minimum time , namely ， ； where is the maximum peak value of the primary side current, Vin is the input voltage, and Lp is the excitation inductance of the transformer.

4. A method for detecting the resonant frequency of an inverter according to claim 3, characterized in that, The selection of the threshold value of the resonance duration in S2 is specifically: According to the value range of the turn-on time of the flyback MOS transistor and the desired output current value, obtain the value range of the resonance duration.

5. A method for detecting the resonant frequency of an inverter according to claim 4, characterized in that, The setting of the resonance duration in S3 is specifically: Select the maximum resonance duration that does not cause the transformer to saturate within the value range.

6. A method for detecting the resonance frequency of an inverter according to claim 1, characterized in that, The setting of the acquisition delay in S5 includes: The delay increases sequentially with the power frequency period, and after setting 5 power frequency periods, the acquisition of the resonance voltage at one phase is completed.

7. A method for detecting the resonance frequency of an inverter according to claim 1, characterized in that S6 specifically includes: The collected resonant waveform is subtracted from V in , obtaining a series of oscillating voltage values with 0V as the zero point. After filtering the series of voltage values with twice the power frequency, the time between two adjacent zero-crossing points is recorded as T r_θ / 2, where is the phase angle detected currently; the resonant times at different phases are averaged to obtain the equivalent average resonant time.

8. An inverter resonant frequency detection device, comprising a memory and one or more processors, wherein executable code is stored in the memory, characterized in that, When the processor executes the executable code, it implements an inverter resonance frequency detection method as described in any one of claims 1 - 7.

9. A computer-readable storage medium having a program stored thereon, characterized in that, When the program is executed by the processor, it implements an inverter resonance frequency detection method as described in any one of claims 1 - 7.

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