Inverter and control method thereof

Abstract

The invention provides an inverter and a control method thereof. A controller generates a first PWM signal used for controlling a first switch tube in a direct current conversion circuit and a second PWM signal used for controlling a second switch tube in an inverter circuit. The first PWM signal takes the second PWM signal as a reference, the first PWM signal and the second PWM signal have a plurality of frequencies in a power frequency period of a power grid, and the jittering frequency period of the first PWM signal and the jittering frequency period of the second PWM signal are the same and are one integral multiple of the power frequency period of the power grid. As the jitter frequency periods of the first PWM signal and the second PWM signal are consistent, the EMI of the whole system can be suppressed without introducing extra hardware cost in the high-frequency process of product hardware. Meanwhile, due to the fact that the phase difference of a plurality of frequency changing curves along with time in the jittering frequency period of the first PWM signal and the second PWM signal is a fixed value, direct-current bus ripples can be reduced.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular, to an inverter and a control method thereof. Background Art

[0002] With the continuous maturity of photovoltaic systems, photovoltaic systems are currently more and more widely used in the market. As a core component in a photovoltaic system, the switching devices in an inverter perform switching actions at a fixed frequency, which will cause electromagnetic interference problems. Moreover, with the high-frequencyization of the switching action frequency, the electromagnetic interference (EMI) problems will be aggravated. Although the electromagnetic interference in the photovoltaic system can be suppressed by increasing the electromagnetic compatibility (EMC) filter capacitors or electromagnetic rings, it inevitably increases the hardware cost and the occupied area of the circuit board. By changing the switching action frequency of the switching devices, that is, adopting a frequency dithering scheme, the distribution of energy in the frequency spectrum can be changed, electromagnetic interference can be reduced, and the high-frequency realization of the product hardware can be supported.

[0003] For a two-stage inverter composed of a DC conversion circuit and an inverter circuit, there will be two EMI signal sources, namely the DC conversion circuit and the inverter circuit. Currently, only the DC conversion circuit is frequency-dithered to ensure the EMC performance of the PV port and the BAT port of the photovoltaic module connected to the DC conversion circuit, or only the inverter circuit is frequency-dithered to ensure the EMC performance of the AC port connected to the inverter circuit. It is impossible to take into account the overall EMC performance of multiple ports, namely the PV port, the BAT port, and the AC port, and at the same time, it is impossible to suppress the DC bus ripple. Therefore, in the process of high-frequencyizing the product hardware, how to suppress the overall EMI of the system and reduce the DC bus ripple without introducing additional hardware costs is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] An inverter and a control method thereof provided by the present application are used to suppress the overall EMI of the system and reduce the DC bus ripple at the same time.

[0005] In a first aspect, the present application provides an inverter, comprising: a DC conversion circuit DC / DC, an inverter circuit DC / AC, and a controller. The DC / DC is used to be connected between a DC power source and the DC / AC. The DC / DC is used to implement the conversion between direct current and direct current, specifically converting the first direct current provided by the DC power source into a second direct current and outputting it to the DC / AC. The DC / AC is used to be connected between the power grid and the DC / DC. The DC / AC is used to implement the conversion of direct current into alternating current, specifically converting the second direct current into alternating current and outputting it to the power grid. The dual-stage inverter provided by the present application can be applied to a photovoltaic system, and the DC power source can specifically be a photovoltaic module or a storage battery. The DC / DC includes at least one first switching tube, and the DC / AC includes at least one second switching tube. The controller is used to generate a first pulse-width modulation (PWM) signal and a second PWM signal. The first PWM signal is used to control the first switching tube in the DC / DC to continuously switch between conduction and cutoff, and the second PWM signal is used to control the second switching tube in the DC / AC to continuously switch between conduction and cutoff. The second PWM signal generated by the controller has multiple frequencies within a power grid power frequency period, and the frequency hopping period of the second PWM signal is one over an integer multiple of the power grid power frequency period. The controller generates the first PWM signal based on the generated second PWM signal. The first PWM signal generated by the controller has multiple frequencies within a power grid power frequency period, and the frequency hopping period of the first PWM signal is the same as that of the second PWM signal. The curve of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curve of multiple frequencies changing with time in the frequency hopping period of the second PWM signal have a fixed phase difference.

[0006] In the present application, since the controller generates the first PWM signal based on the second PWM signal, the calculation amount of frequency hopping can be reduced. The frequency hopping periods of the first PWM signal and the second PWM signal are consistent, and synchronous frequency hopping in the dual-stage inverter can be achieved. Therefore, during the process of high-frequency operation of the product hardware, without introducing additional hardware costs, the overall EMI of the system can be suppressed. At the same time, since the curve of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curve of multiple frequencies changing with time in the frequency hopping period of the second PWM signal have a fixed phase difference, the fixed phase difference means that when the types of curves of the frequencies of the two PWM signals changing with time are the same, that is, the frequency hopping rules are the same, the two curves have a fixed phase difference, making the frequency hopping rules of the two PWM signals relatively fixed, and the DC bus ripple can be reduced.

[0007] In some embodiments of the present application, within a dithering frequency period, the multiple frequencies of the first PWM signal and the second PWM signal can be controlled to change in a stepped manner, so as to facilitate the controller to calculate and control the frequencies of the first PWM signal and the second PWM signal. Exemplarily, within a dithering frequency period, the controller can control the first PWM signal and the second PWM signal to start the dithering frequency period from their respective corresponding reference frequencies (the reference frequency of the first PWM signal is the DC reference frequency, and the reference frequency of the second PWM signal is the AC reference frequency), that is, their respective corresponding reference frequencies serve as the starting point of a dithering frequency period. Specifically, the multiple frequencies of the first PWM signal changing in a stepped manner can control the first PWM signal to be the DC reference frequency at the start of the dithering frequency period and last for a set duration, then increase the set frequency on the basis of the DC reference frequency and adjust the first PWM signal to the first DC frequency and last for a set duration, then increase the set frequency on the basis of the first DC frequency and adjust the first PWM signal to the second DC frequency and last for a set duration, and so on, until the first PWM signal is adjusted to the DC maximum frequency and lasts for a set duration, then decrease the set frequency on the basis of the DC maximum frequency and adjust the first PWM signal to the third DC frequency and last for a set duration, and so on, until the first PWM signal is adjusted to the DC minimum frequency and lasts for a set duration, then increase the set frequency on the basis of the DC minimum frequency and adjust the first PWM signal to the fourth DC frequency and last for a set duration, and so on, until the first PWM signal is adjusted to the DC reference frequency. Specifically, the multiple frequencies of the second PWM signal changing in a stepped manner can control the second PWM signal to be the AC reference frequency at the start of the dithering frequency period and last for a set duration, then increase the set frequency on the basis of the AC reference frequency and adjust the second PWM signal to the first AC frequency and last for a set duration, then increase the set frequency on the basis of the first AC frequency and adjust the second PWM signal to the second AC frequency and last for a set duration, and so on, until the second PWM signal is adjusted to the AC maximum frequency and lasts for a set duration, then decrease the set frequency on the basis of the AC maximum frequency and adjust the second PWM signal to the third AC frequency and last for a set duration, and so on, until the second PWM signal is adjusted to the AC minimum frequency and lasts for a set duration, then increase the set frequency on the basis of the AC minimum frequency and adjust the second PWM signal to the fourth AC frequency and last for a set duration, and so on, until the second PWM signal is adjusted to the AC reference frequency.

[0008] In some other embodiments of the present application, within a dither frequency period, the first PWM signal or the second PWM signal may also start from their respective corresponding minimum frequencies (the minimum frequency of the first PWM signal is the DC minimum frequency, and the minimum frequency of the second PWM signal is the AC minimum frequency) or maximum frequencies (the maximum frequency of the first PWM signal is the DC maximum frequency, and the maximum frequency of the second PWM signal is the AC maximum frequency), etc. Moreover, the frequency change within a dither frequency period is not limited to the above rules and will not be exhaustively listed here.

[0009] In some embodiments of the present application, for the convenience of adjustment and control, the controller may control the frequency difference between two adjacent frequencies of the first PWM signal and the second PWM signal to be the same within a dither frequency period. For example, the first PWM signal takes 130 kHz as the DC reference frequency, 140 kHz as the DC maximum frequency, 120 kHz as the DC minimum frequency, and 200 Hz as the frequency step for increase or decrease, and sets the frequencies within the dither frequency period; the second PWM signal takes 65 kHz as the AC reference frequency, 68 kHz as the AC maximum frequency, 62 kHz as the AC minimum frequency, and 100 Hz as the frequency step for increase or decrease, and sets the frequencies within the dither frequency period. Moreover, the frequency step can be set according to the difference between the reference frequency and the peak frequencies (including the maximum frequency and the minimum frequency). Generally, the greater the difference, the larger the frequency step.

[0010] In some embodiments of the present application, after the controller fixes the frequencies of the first PWM signal (or the second PWM signal) within a dither frequency period, it can maintain a fixed number of carrier signals at each frequency. Different frequencies may maintain different numbers of carrier signals or the same number of carrier signals, which is not limited here. This can ensure that within different dither frequency periods, at the same frequency, the number of pulses of the first PWM signal (or the second PWM signal) generated according to the carrier signals is the same. Ensure that within different power frequency periods of the power grid, the number of pulses of the first PWM signal (or the second PWM signal) at the same frequency is the same, so that each grid-connected inverter can set the phase of the first PWM signal (or the second PWM signal) at different frequencies using a unified standard without communication, and achieve a fixed phase difference between the frequency-time change curves of the first PWM signal and the second PWM signal.

[0011] In some embodiments of the present application, for the convenience of adjustment and control, the controller may control the duration of multiple frequencies of the first PWM signal and the second PWM signal to be the same within a dither frequency period.

[0012] In some other embodiments of the present application, within a dithering frequency period, the controller can also control the durations of the DC maximum frequency and the DC minimum frequency among the multiple frequencies of the first PWM signal to be the same, and the durations of the DC maximum frequency and the DC minimum frequency are longer than those of other frequencies. Similarly, within a dithering frequency period, the controller can also control the durations of the AC maximum frequency and the AC minimum frequency among the multiple frequencies of the second PWM signal to be the same, and the durations of the AC maximum frequency and the AC minimum frequency are longer than those of other frequencies. Since the dithering frequency scheme presents a more ideal effect in the medium and high frequencies (generally referring to the frequency band greater than 1 MHz in the EMI test), the performance in the low frequencies (generally referring to the frequency band less than 1 MHz in the EMI test) becomes the main factor restricting the EMC design. Therefore, by increasing the durations of the maximum frequency and the minimum frequency within the dithering frequency period, the electromagnetic interference in the low frequencies can be improved, and the low-frequency EMC benefit can be enhanced. Moreover, by comparing the different durations of the maximum frequency and the minimum frequency within the dithering frequency period, it can be known that the greater the durations of the maximum frequency and the minimum frequency within the dithering frequency period, the higher the low-frequency EMC benefit. In specific implementation, the proportion of the durations of the maximum frequency and the minimum frequency within the dithering frequency period can be controlled between 0.1 and 0.4.

[0013] In some embodiments of the present application, by connecting the multiple frequencies in the dithering frequency period of the PWM signal according to the starting points of their durations, a frequency-versus-time curve can be established, obtaining the frequency-versus-time curve of the multiple frequencies in the dithering frequency period of the first PWM signal and the frequency-versus-time curve of the multiple frequencies in the dithering frequency period of the second PWM signal.

[0014] In some embodiments of the present application, when the frequency difference between two adjacent frequencies of the first PWM signal and the second PWM signal is the same, and the durations of the multiple frequencies of the first PWM signal and the second PWM signal are the same, the frequency-versus-time curves of the multiple frequencies in the dithering frequency periods of the first PWM signal and the second PWM signal change in a triangular wave pattern, that is, the dithering rule is the triangular wave mode in this case.

[0015] In some other embodiments of the present application, when the frequency difference between two adjacent frequencies of the first PWM signal and the second PWM signal is the same, and the durations of the maximum frequency and the minimum frequency of the first PWM signal and the second PWM signal are longer, the frequency-versus-time curves of the multiple frequencies in the dithering frequency periods of the first PWM signal and the second PWM signal change in a trapezoidal wave pattern, that is, the dithering rule is the trapezoidal wave mode in this case.

[0016] In some other embodiments of the present application, when the frequency difference between two adjacent frequencies of the first PWM signal and the second PWM signal is different, and the durations of the maximum frequency and the minimum frequency of the first PWM signal and the second PWM signal are relatively long, the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the second PWM signal can change in a sine wave, that is, in this case, the frequency hopping rule is a sine wave mode.

[0017] In some embodiments of the present application, the controller controls the phase difference between the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal to be a fixed value. Specifically, it can be controlled that the phase difference between the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal is 0 degree, 90 degrees, 180 degrees or 270 degrees.

[0018] In some embodiments of the present application, since the circuit structure and control timing of DC / DC are simpler than those of DC / AC, the controller can set the DC reference frequency of the first PWM signal to be higher than the AC reference frequency of the second PWM signal. And, for the convenience of calculation and control, the DC reference frequency can also be set to an integer multiple of the AC reference frequency. For example, the DC reference frequency is 130 kHz and the AC reference frequency is 65 kHz.

[0019] In some embodiments of the present application, for the convenience of calculation and control, the first PWM signal and the second PWM signal can change their frequencies according to a fixed ratio within each frequency hopping period. For example, the maximum frequency and the minimum frequency are both set at ±5% of the reference frequency. Based on this, since the DC reference frequency of the first PWM signal is set to be higher than the AC reference frequency of the second PWM signal, generally, the difference between the DC minimum frequency and the DC maximum frequency of the first PWM signal will also be greater than the difference between the AC minimum frequency and the AC maximum frequency of the second PWM signal.

[0020] Second aspect, the present application provides a control method for an inverter, including: generating a first pulse width modulation (PWM) signal and a second PWM signal, where the first PWM signal is used to control a first switch tube in a DC conversion circuit of the inverter to switch between conduction and cutoff, and the second PWM signal is used to control a second switch tube in an inverter circuit of the inverter to switch between conduction and cutoff. Among them, the first PWM signal has multiple frequencies within a power grid power frequency cycle, and the frequency hopping period of the first PWM signal is one over an integer multiple of the power frequency cycle; the second PWM signal has multiple frequencies within a power grid power frequency cycle, and the frequency hopping period of the second PWM signal is the same as that of the first PWM signal; the phase difference between the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal is a fixed value.

[0021] In the present application, generating the first PWM signal based on the second PWM signal can reduce the calculation amount of frequency hopping. The frequency hopping periods of the first PWM signal and the second PWM signal are consistent, which can achieve synchronous frequency hopping in a two-stage inverter. Therefore, during the process of high-frequency operation of the product hardware, without introducing additional hardware costs, the overall EMI of the system can be suppressed. At the same time, since the phase difference between the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal is a fixed value, the fixed phase difference means that when the types of the curves of the frequencies of the two PWM signals changing with time are the same, that is, the frequency hopping rules are the same, the two curves have a fixed phase difference, making the frequency hopping rules of the two PWM signals relatively fixed, and the DC bus ripple can be reduced.

[0022] In some embodiments of the present application, within a dithering frequency period, the multiple frequencies of the first PWM signal and the second PWM signal can be controlled to change in a stepped manner, so as to facilitate the frequency calculation and control of the first PWM signal and the second PWM signal. Exemplarily, within a dithering frequency period, the first PWM signal and the second PWM signal can be controlled to start the dithering frequency period from their respective reference frequencies (the reference frequency of the first PWM signal is the DC reference frequency, and the reference frequency of the second PWM signal is the AC reference frequency), that is, their respective reference frequencies serve as the starting point of a dithering frequency period. Specifically, for the multiple frequencies of the first PWM signal to change in a stepped manner, at the start of the dithering frequency period, the first PWM signal can be controlled to be the DC reference frequency and last for a set duration, then after increasing the set frequency on the basis of the DC reference frequency, the first PWM signal is adjusted to the first DC frequency and lasts for a set duration, then after increasing the set frequency on the basis of the first DC frequency, the first PWM signal is adjusted to the second DC frequency and lasts for a set duration, and so on, until the first PWM signal is adjusted to the DC maximum frequency and lasts for a set duration, then after decreasing the set frequency on the basis of the DC maximum frequency, the first PWM signal is adjusted to the third DC frequency and lasts for a set duration, and so on, until the first PWM signal is adjusted to the DC minimum frequency and lasts for a set duration, then after increasing the set frequency on the basis of the DC minimum frequency, the first PWM signal is adjusted to the fourth DC frequency and lasts for a set duration, and so on, until the first PWM signal is adjusted to the DC reference frequency. Specifically, for the multiple frequencies of the second PWM signal to change in a stepped manner, at the start of the dithering frequency period, the second PWM signal can be controlled to be the AC reference frequency and last for a set duration, then after increasing the set frequency on the basis of the AC reference frequency, the second PWM signal is adjusted to the first AC frequency and lasts for a set duration, then after increasing the set frequency on the basis of the first AC frequency, the second PWM signal is adjusted to the second AC frequency and lasts for a set duration, and so on, until the second PWM signal is adjusted to the AC maximum frequency and lasts for a set duration, then after decreasing the set frequency on the basis of the AC maximum frequency, the second PWM signal is adjusted to the third AC frequency and lasts for a set duration, and so on, until the second PWM signal is adjusted to the AC minimum frequency and lasts for a set duration, then after increasing the set frequency on the basis of the AC minimum frequency, the second PWM signal is adjusted to the fourth AC frequency and lasts for a set duration, and so on, until the second PWM signal is adjusted to the AC reference frequency.

[0023] In some other embodiments of the present application, within a dithering frequency period, the first PWM signal or the second PWM signal may also start with their respective corresponding minimum frequencies (the minimum frequency of the first PWM signal is the DC minimum frequency, and the minimum frequency of the second PWM signal is the AC minimum frequency) or maximum frequencies (the maximum frequency of the first PWM signal is the DC maximum frequency, and the maximum frequency of the second PWM signal is the AC maximum frequency), etc. Moreover, the frequency change within a dithering frequency period is not limited to the above rules, and no exhaustive listing is provided here.

[0024] In some embodiments of the present application, for the convenience of adjustment and control, within a dithering frequency period, the frequency difference between two adjacent frequencies of the first PWM signal and the second PWM signal can be controlled to be the same. For example, the first PWM signal uses 130 kHz as the DC reference frequency, 140 kHz as the DC maximum frequency, 120 kHz as the DC minimum frequency, and 200 Hz as the frequency step for increase or decrease to set the frequencies within the dithering frequency period; the second PWM signal uses 65 kHz as the AC reference frequency, 68 kHz as the AC maximum frequency, 62 kHz as the AC minimum frequency, and 100 Hz as the frequency step for increase or decrease to set the frequencies within the dithering frequency period. Moreover, the frequency step can be set according to the difference between the reference frequency and the peak frequency (including the maximum frequency and the minimum frequency). Generally, the larger the difference, the larger the frequency step.

[0025] In some embodiments of the present application, for the convenience of adjustment and control, within a dithering frequency period, the duration of multiple frequencies of the first PWM signal and the second PWM signal can be controlled to be the same.

[0026] In some other embodiments of the present application, within a dither frequency period, it is also possible to control the durations of the DC maximum frequency and the DC minimum frequency among the multiple frequencies of the first PWM signal to be the same, and the durations of the DC maximum frequency and the DC minimum frequency are longer than those of other frequencies. Similarly, within a dither frequency period, it is also possible to control the durations of the AC maximum frequency and the AC minimum frequency among the multiple frequencies of the second PWM signal to be the same, and the durations of the AC maximum frequency and the AC minimum frequency are longer than those of other frequencies. Since the dither frequency scheme presents a more ideal effect in the medium and high frequencies (generally referring to the frequency band greater than 1 MHz in the EMI test), the performance in the low frequencies (generally referring to the frequency band less than 1 MHz in the EMI test) becomes the main factor restricting the EMC design. Therefore, by increasing the durations of the maximum frequency and the minimum frequency within the dither frequency period, the electromagnetic interference in the low frequencies can be improved, and the low-frequency EMC benefit can be enhanced. Moreover, by comparing the different durations of the maximum frequency and the minimum frequency within the dither frequency period, it can be known that the greater the durations of the maximum frequency and the minimum frequency within the dither frequency period, the higher the low-frequency EMC benefit. In specific implementation, the duration ratio of the maximum frequency and the minimum frequency within the dither frequency period can be controlled between 0.1 and 0.4.

[0027] In some embodiments of the present application, by connecting the multiple frequencies in the dither frequency period of the PWM signal according to the starting points of their durations, a frequency-versus-time curve can be established, obtaining the frequency-versus-time curves of the multiple frequencies in the dither frequency period of the first PWM signal and the frequency-versus-time curves of the multiple frequencies in the dither frequency period of the second PWM signal.

[0028] In some embodiments of the present application, when the frequency differences between adjacent two frequencies of the first PWM signal and the second PWM signal are the same, and the durations of the multiple frequencies of the first PWM signal and the second PWM signal are the same, the frequency-versus-time curves of the multiple frequencies in the dither frequency periods of the first PWM signal and the second PWM signal change in a triangular wave pattern, that is, the dither frequency rule is the triangular wave mode in this case.

[0029] In some other embodiments of the present application, when the frequency differences between adjacent two frequencies of the first PWM signal and the second PWM signal are the same, and the durations of the maximum frequency and the minimum frequency of the first PWM signal and the second PWM signal are longer, the frequency-versus-time curves of the multiple frequencies in the dither frequency periods of the first PWM signal and the second PWM signal change in a trapezoidal wave pattern, that is, the dither frequency rule is the trapezoidal wave mode in this case.

[0030] In some other embodiments of the present application, when the frequency difference between two adjacent frequencies of the first PWM signal and the second PWM signal is different, and the duration of the maximum frequency and the minimum frequency of the first PWM signal and the second PWM signal is relatively long, the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the second PWM signal can vary in a sine wave pattern, that is, in this case, the frequency hopping rule is a sine wave mode.

[0031] In some embodiments of the present application, the phase difference between the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal is controlled to be a fixed value. Specifically, the phase difference between the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal can be 0 degree, 90 degrees, 180 degrees or 270 degrees.

[0032] In some embodiments of the present application, since the circuit structure and control timing of DC / DC are simpler than those of DC / AC, the DC reference frequency of the first PWM signal can be set higher than the AC reference frequency of the second PWM signal. And, for the convenience of calculation and control, the DC reference frequency can also be set as an integer multiple of the AC reference frequency. For example, the DC reference frequency is 130 kHz and the AC reference frequency is 65 kHz.

[0033] In some embodiments of the present application, for the convenience of calculation and control, the frequencies of the first PWM signal and the second PWM signal can change according to a fixed ratio within each frequency hopping period. For example, the maximum frequency and the minimum frequency are both set at ±5% of the reference frequency. Based on this, since the DC reference frequency of the first PWM signal is set higher than the AC reference frequency of the second PWM signal, generally, the difference between the DC minimum frequency and the DC maximum frequency of the first PWM signal is also greater than the difference between the AC minimum frequency and the AC maximum frequency of the second PWM signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic structural diagram of an inverter applied to a photovoltaic system provided by an embodiment of the present application;

[0035] Figure 2 It is a schematic diagram of an inverter generating a frequency hopping period provided by an embodiment of the present application;

[0036] Figure 3 It is another schematic diagram of an inverter generating a frequency hopping period provided by an embodiment of the present application;

[0037] Figure 4 It is a schematic diagram of an inverter generating a PWM signal provided by an embodiment of the present application;

[0038] Figure 5 Another schematic diagram of the inverter provided by the embodiment of the present application for generating a dither frequency period;

[0039] Figure 6 Another schematic diagram of the inverter provided by the embodiment of the present application for generating a dither frequency period;

[0040] Figure 7 Another schematic diagram of the inverter provided by the embodiment of the present application for generating a dither frequency period;

[0041] Figure 8 Another schematic diagram of the inverter provided by the embodiment of the present application for generating a dither frequency period;

[0042] Figure 9 Another schematic diagram of the inverter provided by the embodiment of the present application for generating a dither frequency period;

[0043] Figure 10 Another schematic diagram of the inverter provided by the embodiment of the present application for generating a dither frequency period. Detailed implementation manners

[0044] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings. However, the exemplary embodiments can be implemented in various forms and should not be construed as limited to the embodiments described herein; on the contrary, these embodiments are provided to make the present application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and thus their repeated description will be omitted. The words expressing positions and directions described in the present application are illustrative with reference to the drawings, but can be changed according to needs, and all changes are included in the protection scope of the present application. The drawings of the present application are only used to illustrate the relative positional relationship and do not represent the true proportion.

[0045] It should be noted that specific details are set forth in the following description to facilitate a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present application. Therefore, the present application is not limited by the specific implementation manners disclosed below. The subsequent description in the specification is the preferred implementation manner for implementing the present application, but the description is for the purpose of illustrating the general principles of the present application and is not intended to limit the scope of the present application. The protection scope of the present application shall be defined by the appended claims.

[0046] To facilitate an understanding of the embodiments of the present application, the related technologies involved in the embodiments of the present application will be introduced first below.

[0047] The terms used in the following embodiments are for the purpose of describing specific embodiments only and are not intended to limit the present application. As used in the specification and appended claims of the present application, the singular forms "a", "an", and "the" are intended to include the forms such as "one or more" as well, unless the context clearly indicates otherwise. It should also be understood that in the following embodiments of the present application, "at least one" means one, two or more than two.

[0048] Reference to "one embodiment" etc. described in this specification means that a specific feature, structure or characteristic described in connection with the embodiment is included in one or more embodiments of the present application. Thus, statements such as "in one embodiment", "in some embodiments", "in other embodiments" etc. that appear in different places in this specification do not necessarily all refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "comprising", "having" and their variants mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0049] The embodiments of the present application provide an inverter and its control method. The frequency dithering in the DC conversion circuit is based on the frequency dithering in the inverter circuit. By adjusting the dithering period of the DC conversion circuit to be the same as that of the inverter circuit, and the two dithering periods are adjusted to have a fixed phase difference, synchronous frequency dithering in the two-stage inverter is achieved. In this way, during the process of high-frequency of the product hardware, without introducing additional hardware costs, the overall EMI of the system is suppressed, and at the same time, the DC bus ripple is reduced.

[0050] Refer to Figure 1, the inverter provided by the embodiment of the present application is a two-stage inverter, which may specifically include: a DC-DC conversion circuit, an inverter circuit DC / AC, and a controller. The DC-DC is used to connect between the DC power source and the DC / AC. The DC-DC is used to realize the conversion between direct current and direct current, specifically converting the first direct current provided by the DC power source into a second direct current and outputting it to the DC / AC. The DC / AC is used to connect between the power grid and the DC-DC. The DC / AC is used to realize the conversion of direct current into alternating current, specifically converting the second direct current into alternating current and outputting it to the power grid. The two-stage inverter provided by the present application can be applied to a photovoltaic system, and the DC power source may specifically be a photovoltaic module or a storage battery. The DC-DC includes at least one first switching tube, and the DC / AC includes at least one second switching tube. The controller is used to generate a first pulse-width modulation (PWM) signal and a second PWM signal. The first PWM signal is used to control the first switching tube in the DC-DC to continuously switch between conduction and cutoff, and the second PWM signal is used to control the second switching tube in the DC / AC to continuously switch between conduction and cutoff. The second PWM signal generated by the controller has multiple frequencies within a power grid power frequency cycle, and the frequency hopping period of the second PWM signal is one over an integer multiple of the power grid power frequency cycle. The controller generates the first PWM signal based on the generated second PWM signal. The first PWM signal generated by the controller has multiple frequencies within a power grid power frequency cycle, and the frequency hopping period of the first PWM signal is the same as the frequency hopping period of the second PWM signal. The curve of multiple frequencies changing with time in the frequency hopping period of the first PWM signal has a fixed phase difference from the curve of multiple frequencies changing with time in the frequency hopping period of the second PWM signal.

[0051] In the present application, since the controller generates the first PWM signal based on the second PWM signal, the calculation amount of frequency hopping can be reduced. The frequency hopping periods of the first PWM signal and the second PWM signal are consistent, and synchronous frequency hopping in the two-stage inverter can be realized. Therefore, during the process of high-frequency operation of the product hardware, without introducing additional hardware costs, the overall EMI of the system can be suppressed. At the same time, since the curve of multiple frequencies changing with time in the frequency hopping period of the first PWM signal has a fixed phase difference from the curve of multiple frequencies changing with time in the frequency hopping period of the second PWM signal, the fixed phase difference means that when the types of curves of the frequencies of the two PWM signals changing with time are the same, that is, the frequency hopping rules are the same, the two curves have a fixed phase difference, making the frequency hopping rules of the two PWM signals relatively fixed, and the DC bus ripple can be reduced.

[0052] In this application, when the controller generates the second PWM signal, the grid angle can be used as a unified reference. The phase of the grid ranges from 0 degrees to 360 degrees in one power frequency cycle. The frequency hopping period of the first PWM signal and the second PWM signal is one over an integer multiple of the power frequency cycle of the grid, that is, a fixed number of frequency hopping periods are executed within each power frequency cycle, enabling each grid-connected inverter to set the frequency hopping period using a unified standard without communication and achieving frequency hopping synchronization. Specifically, the first PWM signal and the second PWM signal can execute N frequency hopping periods within one power frequency cycle of the grid, where N is a positive integer. For example, one frequency hopping period can be executed within one power frequency cycle, or two frequency hopping periods can be executed within one power frequency cycle.

[0053] Referring to Figure 2 and Figure 3 , in some embodiments of this application, the controller can control the first PWM signal and the second PWM signal to enter a new frequency hopping period when the voltage of the grid is zero. Specifically, within one power frequency cycle of the grid, the voltage of the grid is zero at a phase of 0 degrees and also zero at a phase of 180 degrees. Therefore, to facilitate the synchronization of the frequency hopping periods of each inverter, the zero voltage of the grid can be used as a reference, serving as the starting point of each frequency hopping period of the first PWM signal and the second PWM signal within each power frequency cycle, that is, two frequency hopping periods are set within one power frequency cycle. In some other embodiments of this application, other phase angles of the grid can also be used as a reference. For example, within one power frequency cycle, every 60 degrees is set as the starting point of the frequency hopping period of the first PWM signal and the second PWM signal. That is, when the phase of the grid is 0 degrees, 60 degrees, 120 degrees, 180 degrees, 240 degrees, and 300 degrees, they are respectively used as the starting points of each frequency hopping period of the first PWM signal or the second PWM signal.

[0054] Referring to Figure 2 and Figure 3, in some embodiments of the present application, within a dithering frequency period, the multiple frequencies of the first PWM signal and the second PWM signal can be controlled to change in a stepped manner, so as to facilitate the controller to calculate and control the frequencies of the first PWM signal and the second PWM signal. Exemplarily, the controller can, within a dithering frequency period, control the first PWM signal and the second PWM signal to start the dithering frequency period from their respective corresponding reference frequencies (the reference frequency of the first PWM signal is the DC reference frequency, and the reference frequency of the second PWM signal is the AC reference frequency), that is, their respective corresponding reference frequencies serve as the starting point of a dithering frequency period. Specifically, the multiple frequencies of the first PWM signal changing in a stepped manner can control the first PWM signal to be the DC reference frequency at the start of the dithering frequency period and last for a set duration, then increase the set frequency based on the DC reference frequency and adjust the first PWM signal to the first DC frequency and last for a set duration, then increase the set frequency based on the first DC frequency and adjust the first PWM signal to the second DC frequency and last for a set duration, and so on, until the first PWM signal is adjusted to the DC maximum frequency and lasts for a set duration, then decrease the set frequency based on the DC maximum frequency and adjust the first PWM signal to the third DC frequency and last for a set duration, and so on, until the first PWM signal is adjusted to the DC minimum frequency and lasts for a set duration, then increase the set frequency based on the DC minimum frequency and adjust the first PWM signal to the fourth DC frequency and last for a set duration, and so on, until the first PWM signal is adjusted to the DC reference frequency and lasts for a set duration. Specifically, the multiple frequencies of the second PWM signal changing in a stepped manner can control the second PWM signal to be the AC reference frequency at the start of the dithering frequency period and last for a set duration, then increase the set frequency based on the AC reference frequency and adjust the second PWM signal to the first AC frequency and last for a set duration, then increase the set frequency based on the first AC frequency and adjust the second PWM signal to the second AC frequency and last for a set duration, and so on, until the second PWM signal is adjusted to the AC maximum frequency and lasts for a set duration, then decrease the set frequency based on the AC maximum frequency and adjust the second PWM signal to the third AC frequency and last for a set duration, and so on, until the second PWM signal is adjusted to the AC minimum frequency and lasts for a set duration, then increase the set frequency based on the AC minimum frequency and adjust the second PWM signal to the fourth AC frequency and last for a set duration, and so on, until the second PWM signal is adjusted to the AC reference frequency.In some other embodiments of the present application, within a dither frequency period, the first PWM signal or the second PWM signal may also start with their respective corresponding minimum frequencies (the minimum frequency of the first PWM signal is the DC minimum frequency, and the minimum frequency of the second PWM signal is the AC minimum frequency) or maximum frequencies (the maximum frequency of the first PWM signal is the DC maximum frequency, and the maximum frequency of the second PWM signal is the AC maximum frequency), etc. Moreover, the frequency change within a dither frequency period is not limited to the above rules and will not be exhaustively listed here.

[0055] In some embodiments of the present application, since the circuit structure and control timing of DC / DC are simpler than those of DC / AC, the controller can set the DC reference frequency of the first PWM signal to be higher than the AC reference frequency of the second PWM signal. And, for the convenience of calculation and control, the DC reference frequency can also be set to an integer multiple of the AC reference frequency. For example, the DC reference frequency is 130 kHz and the AC reference frequency is 65 kHz.

[0056] In some embodiments of the present application, for the convenience of calculation and control, the first PWM signal and the second PWM signal can change their frequencies in a fixed ratio within each dither frequency period. For example, both set the maximum frequency and the minimum frequency at ±5% of the reference frequency. Based on this, since the DC reference frequency of the first PWM signal is set to be higher than the AC reference frequency of the second PWM signal, generally, the difference between the DC minimum frequency and the DC maximum frequency of the first PWM signal will also be greater than the difference between the AC minimum frequency and the AC maximum frequency of the second PWM signal.

[0057] Refer to Figure 2 and Figure 3 , in some embodiments of the present application, for the convenience of adjustment and control, the controller can control the frequency differences Δf1 and Δf2 between two adjacent frequencies of the first PWM signal and the second PWM signal to be the same within a dither frequency period. For example, the first PWM signal uses 130 kHz as the DC reference frequency, 140 kHz as the DC maximum frequency, 120 kHz as the DC minimum frequency, and 200 Hz as the frequency step size for increase or decrease, i.e., the frequency difference Δf1, to set the frequencies within the dither frequency period. The second PWM signal uses 65 kHz as the AC reference frequency, 68 kHz as the AC maximum frequency, 62 kHz as the AC minimum frequency, and 100 Hz as the frequency step size for increase or decrease, i.e., the frequency difference Δf2, to set the frequencies within the dither frequency period. And, the frequency step size can be set according to the difference between the reference frequency and the peak frequencies (including the maximum frequency and the minimum frequency). Generally, the larger the difference, the larger the frequency step size. For example, Figure 2 and Figure 3The difference between the DC reference frequency and the DC maximum frequency (or DC minimum frequency) of the first PWM signal shown is greater than the difference between the AC reference frequency and the AC maximum frequency (or AC minimum frequency) of the second PWM signal, and the frequency difference Δf1 is greater than the frequency difference Δf2.

[0058] Referring to Figure 4 , in some embodiments of the present application, after the controller fixes the frequencies of the first PWM signal (or the second PWM signal) within the frequency hopping period, it can maintain a fixed number of carrier signals at each frequency, and different frequencies can maintain different numbers of carrier signals or the same number of carrier signals, which is not limited herein. This can ensure that within different frequency hopping periods, at the same frequency, the number of pulses of the first PWM signal (or the second PWM signal) generated according to the carrier signals is the same. Ensure that within different power frequency periods of the power grid, the number of pulses of the first PWM signal (or the second PWM signal) at the same frequency is the same, so that each inverter connected to the grid can set the phase of the first PWM signal (or the second PWM signal) at different frequencies using a unified standard without communication, and realize that the phases of the frequency-time change curves of the first PWM signal and the second PWM signal differ by a fixed value. Figure 4 shows an example for illustration with four carrier signals maintained at each frequency. The period X1 of each carrier signal corresponding to the maximum frequency is the shortest, and the period X2 of each carrier signal corresponding to the minimum frequency is the longest.

[0059] Referring to Figure 2 , in some embodiments of the present application, for the convenience of adjustment and control, within one frequency hopping period, the controller can control the duration of multiple frequencies of the first PWM signal and the second PWM signal to be the same. Exemplarily, the duration T13 of the first PWM signal at the DC reference frequency is the same as the duration T11 at the DC maximum frequency and the duration T12 at the DC minimum frequency; the duration T23 of the second PWM signal at the AC reference frequency is the same as the duration T21 at the AC maximum frequency and the duration T22 at the AC minimum frequency.

[0060] Referring to Figure 3, in some other embodiments of the present application, within a dithering frequency period, the controller can also control the duration T11 of the DC maximum frequency and the duration T12 of the DC minimum frequency among the multiple frequencies of the first PWM signal to be the same, and the duration T11 of the DC maximum frequency and the duration T12 of the DC minimum frequency are longer than the durations of other frequencies, such as the duration T13 of the DC reference frequency. Similarly, within a dithering frequency period, the controller can also control the duration T21 of the AC maximum frequency and the duration T22 of the AC minimum frequency among the multiple frequencies of the second PWM signal to be the same, and the duration T21 of the AC maximum frequency and the duration T22 of the AC minimum frequency are longer than the durations of other frequencies, such as the duration T23 of the AC reference frequency. Since the dithering frequency scheme presents a more ideal effect in the medium and high frequencies (generally referring to the frequency band greater than 1 MHz in the EMI test), the performance in the low frequencies (generally referring to the frequency band less than 1 MHz in the EMI test) becomes the main factor restricting the EMC design. Therefore, by increasing the durations of the maximum frequency and the minimum frequency within the dithering frequency period, the electromagnetic interference in the low frequencies can be improved, and the low-frequency EMC benefit can be enhanced. Moreover, by comparing the different durations of the maximum frequency and the minimum frequency within the dithering frequency period, it can be known that the greater the durations of the maximum frequency and the minimum frequency within the dithering frequency period, the higher the low-frequency EMC benefit. In specific implementation, the duration ratio of the maximum frequency and the minimum frequency within the dithering frequency period can be controlled between 0.1 and 0.4.

[0061] Referring to Figures 5 to 7 , in some embodiments of the present application, by connecting the multiple frequencies in the dithering frequency period of the PWM signal according to the starting points of their durations, a frequency-versus-time curve can be established, obtaining the frequency-versus-time curve of the multiple frequencies in the dithering frequency period of the first PWM signal and the frequency-versus-time curve of the multiple frequencies in the dithering frequency period of the second PWM signal.

[0062] Referring to Figure 5 , when the frequency differences Δf1 and Δf2 between two adjacent frequencies of the first PWM signal and the second PWM signal are the same, and the durations of the multiple frequencies of the first PWM signal and the second PWM signal are the same, the frequency-versus-time curves of the multiple frequencies in the dithering frequency periods of the first PWM signal and the second PWM signal change in a triangular wave pattern, that is, in this case, the dithering rule is the triangular wave mode. Exemplarily, the duration T13 of the first PWM signal at the DC reference frequency is the same as the duration T11 at the DC maximum frequency and the duration T12 at the DC minimum frequency; the duration T23 of the second PWM signal at the AC reference frequency is the same as the duration T21 at the AC maximum frequency and the duration T22 at the AC minimum frequency. By connecting the multiple frequencies in the dithering frequency periods of the first PWM signal and the second PWM signal according to the starting points of their durations, the obtained frequency-versus-time curve changes in a triangular wave pattern.

[0063] Referring to Figure 6 , when the frequency differences Δf1 and Δf2 between two adjacent frequencies of the first PWM signal and the second PWM signal are the same, and the durations of the maximum frequency and the minimum frequency of the first PWM signal and the second PWM signal are relatively long, the curves of multiple frequencies with time in the dithering frequency period of the first PWM signal and the second PWM signal change in a trapezoidal wave, that is, in this case, the dithering frequency rule is the trapezoidal wave mode. Exemplarily, the duration T13 of the first PWM signal at the DC reference frequency is less than the duration T11 at the DC maximum frequency and the duration T12 at the DC minimum frequency; the duration T23 of the second PWM signal at the AC reference frequency is less than the duration T21 at the AC maximum frequency and the duration T22 at the AC minimum frequency. Connecting the multiple frequencies in the dithering frequency period of the first PWM signal and the second PWM signal according to the starting points of their durations, the curve of the frequency with time obtained changes in a trapezoidal wave.

[0064] Referring to Figure 7 , when the frequency differences Δf1 and Δf2 between two adjacent frequencies of the first PWM signal and the second PWM signal are different, and the durations of the maximum frequency and the minimum frequency of the first PWM signal and the second PWM signal are relatively long, the curves of multiple frequencies with time in the dithering frequency period of the first PWM signal and the second PWM signal can change in a sine wave, that is, in this case, the dithering frequency rule is the sine wave mode. Exemplarily, the duration T13 of the first PWM signal at the DC reference frequency is less than the duration T11 at the DC maximum frequency and the duration T12 at the DC minimum frequency, and the frequency difference Δf1 is set to change; the duration T23 of the second PWM signal at the AC reference frequency is less than the duration T21 at the AC maximum frequency and the duration T22 at the AC minimum frequency, and the frequency difference Δf2 is set to change. Connecting the multiple frequencies in the dithering frequency period of the first PWM signal and the second PWM signal according to the starting points of their durations, the curve of the frequency with time obtained changes in a sine wave.

[0065] Referring to Figures 5 to 7, in some embodiments of the present application, the controller controls the phase difference between the curves of multiple frequencies varying with time in the dithering period of the first PWM signal and the curves of multiple frequencies varying with time in the dithering period of the second PWM signal to be a fixed value. Specifically, it can be to control the phases of the curves of multiple frequencies varying with time in the dithering period of the first PWM signal and the curves of multiple frequencies varying with time in the dithering period of the second PWM signal to be the same, that is, within one dithering period, the dithering rules of the first PWM signal and the second PWM signal are the same. For example, at the first moment t1, the first PWM signal is controlled to be the DC reference frequency and the second PWM signal is controlled to be the AC reference frequency; at the second moment t2, the first PWM signal is controlled to be the DC maximum frequency and the second PWM signal is controlled to be the AC maximum frequency; at the third moment t3, the first PWM signal is controlled to be the DC minimum frequency and the second PWM signal is controlled to be the AC minimum frequency, so as to synchronously dither to reduce the DC bus ripple.

[0066] Referring to Figures 8 to 10 , in some other embodiments of the present application, the controller controls the phase difference between the curves of multiple frequencies varying with time in the dithering period of the first PWM signal and the curves of multiple frequencies varying with time in the dithering period of the second PWM signal to be a fixed value other than 0. Exemplarily, referring to Figure 8 , the phase difference between the curves of multiple frequencies varying with time in the dithering period of the first PWM signal and the curves of multiple frequencies varying with time in the dithering period of the second PWM signal is 180 degrees. For example, at the first moment t1, the first PWM signal is controlled to be the DC reference frequency and the second PWM signal is controlled to be the AC reference frequency; at the second moment t2, the first PWM signal is controlled to be the DC minimum frequency and the second PWM signal is controlled to be the AC maximum frequency; at the third moment t3, the first PWM signal is controlled to be the DC maximum frequency and the second PWM signal is controlled to be the AC minimum frequency, that is, the DC maximum frequency of the first PWM signal and the AC maximum frequency of the second PWM signal have a phase difference of 180 degrees within one dithering period, and the DC minimum frequency of the first PWM signal and the AC minimum frequency of the second PWM signal have a phase difference of 180 degrees within one dithering period.

[0067] Referring to Figure 9 and Figure 10 , the phases of the curves of multiple frequencies varying with time in the dithering period of the first PWM signal and the curves of multiple frequencies varying with time in the dithering period of the second PWM signal are orthogonal. Referring to Figure 9, the phase difference between the phase of the curves of multiple frequencies varying with time in the frequency hopping period of the first PWM signal and the phase of the curves of multiple frequencies varying with time in the frequency hopping period of the second PWM signal is 90 degrees. For example, at the first moment t1, the first PWM signal is controlled to be the DC minimum frequency and the second PWM signal is controlled to be the AC reference frequency; at the second moment t2, the first PWM signal is controlled to be the DC reference frequency and the second PWM signal is controlled to be the AC maximum frequency; at the third moment t3, the first PWM signal is controlled to be the DC reference frequency and the second PWM signal is controlled to be the AC minimum frequency, that is, the phase difference between the DC reference frequency of the first PWM signal and the DC reference frequency of the second PWM signal is 90 degrees within one frequency hopping period. Refer to Figure 10 , the phase difference between the phase of the curves of multiple frequencies varying with time in the frequency hopping period of the first PWM signal and the phase of the curves of multiple frequencies varying with time in the frequency hopping period of the second PWM signal is 270 degrees. For example, at the first moment t1, the first PWM signal is controlled to be the DC maximum frequency and the second PWM signal is controlled to be the AC reference frequency; at the second moment t2, the first PWM signal is controlled to be the DC reference frequency and the second PWM signal is controlled to be the AC maximum frequency; at the third moment t3, the first PWM signal is controlled to be the DC reference frequency and the second PWM signal is controlled to be the AC minimum frequency, that is, the phase difference between the DC reference frequency of the first PWM signal and the DC reference frequency of the second PWM signal is 270 degrees within one frequency hopping period.

[0068] Based on the same inventive concept, an embodiment of the present application further provides a control method for an inverter, including:

[0069] Generating a first pulse width modulation (PWM) signal and a second PWM signal, where the first PWM signal is used to control the first switching tube in the DC conversion circuit of the inverter to switch between conduction and cutoff, and the second PWM signal is used to control the second switching tube in the inverter circuit of the inverter to switch between conduction and cutoff. Among them, the first PWM signal has multiple frequencies within one power grid power frequency period, and the frequency hopping period of the first PWM signal is one integer multiple of the power frequency period; the second PWM signal has multiple frequencies within one power grid power frequency period, and the frequency hopping period of the second PWM signal is the same as that of the first PWM signal; the phase difference between the curves of multiple frequencies varying with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies varying with time in the frequency hopping period of the second PWM signal is a fixed value.

[0070] In this application, generating the first PWM signal based on the second PWM signal can reduce the computational complexity of frequency dithering. The frequency dithering periods of the first PWM signal and the second PWM signal are the same, enabling synchronous frequency dithering in a two-stage inverter. Therefore, during the process of high-frequency product hardware, without introducing additional hardware costs, the overall EMI of the system can be suppressed. At the same time, since the phases of the multiple frequency-versus-time curves in the frequency dithering period of the first PWM signal and the multiple frequency-versus-time curves in the frequency dithering period of the second PWM signal differ by a fixed value. The fixed phase difference means that when the types of the frequency-versus-time curves of the two PWM signals are the same, i.e., the frequency dithering rules are the same, the two curves have a fixed phase difference, making the frequency dithering rules of the two PWM signals relatively fixed and reducing the DC bus ripple.

[0071] In this application, when generating the second PWM signal, the grid angle can be used as a unified reference. The phase of the grid ranges from 0 degrees to 360 degrees in one power frequency cycle. The frequency dithering periods of the first PWM signal and the second PWM signal are one over an integer multiple of the power frequency cycle of the grid, that is, a fixed number of frequency dithering periods are executed within each power frequency cycle, enabling each grid-connected inverter to set the frequency dithering period using a unified standard without communication and achieving frequency dithering synchronization. Specifically, the first PWM signal and the second PWM signal can execute N frequency dithering periods within one power frequency cycle of the grid, where N is a positive integer. For example, one frequency dithering period can be executed within one power frequency cycle, or two frequency dithering periods can be executed within one power frequency cycle.

[0072] In some embodiments of this application, when the voltage of the grid is zero, the first PWM signal and the second PWM signal can be controlled to enter a new frequency dithering period. Specifically, within one power frequency cycle of the grid, the voltage of the grid is zero at a phase of 0 degrees and also zero at a phase of 180 degrees. Therefore, to facilitate the synchronous frequency dithering of each inverter, the zero voltage of the grid can be used as a reference and used as the starting point of each frequency dithering period of the first PWM signal and the second PWM signal within each power frequency cycle, that is, two frequency dithering periods are set within one power frequency cycle. In some other embodiments of this application, other phase angles of the grid can also be used as a reference. For example, within one power frequency cycle, every 60 degrees is set as the starting point of the frequency dithering period of the first PWM signal and the second PWM signal, that is, when the phase of the grid is 0 degrees, 60 degrees, 120 degrees, 180 degrees, 240 degrees, and 300 degrees, they are respectively used as the starting points of each frequency dithering period of the first PWM signal or the second PWM signal.

[0073] In some embodiments of the present application, within one dither frequency period, the multiple frequencies of the first PWM signal and the second PWM signal can be controlled to change in a stepped manner, so as to facilitate the frequency calculation and control of the first PWM signal and the second PWM signal. Exemplarily, within one dither frequency period, the first PWM signal and the second PWM signal can be controlled to start the dither frequency period from their respective corresponding reference frequencies (the reference frequency of the first PWM signal is the DC reference frequency, and the reference frequency of the second PWM signal is the AC reference frequency), that is, their respective corresponding reference frequencies serve as the starting point of a dither frequency period. Specifically, the multiple frequencies of the first PWM signal changing in a stepped manner can control the first PWM signal to be the DC reference frequency at the start of the dither frequency period and last for a set duration, then increase the set frequency on the basis of the DC reference frequency and adjust the first PWM signal to the first DC frequency and last for a set duration, then increase the set frequency on the basis of the first DC frequency and adjust the first PWM signal to the second DC frequency and last for a set duration, and so on, until the first PWM signal is adjusted to the DC maximum frequency and lasts for a set duration, then decrease the set frequency on the basis of the DC maximum frequency and adjust the first PWM signal to the third DC frequency and last for a set duration, and so on, until the first PWM signal is adjusted to the DC minimum frequency and lasts for a set duration, then increase the set frequency on the basis of the DC minimum frequency and adjust the first PWM signal to the fourth DC frequency and last for a set duration, and so on, until the first PWM signal is adjusted to the DC reference frequency. Specifically, the multiple frequencies of the second PWM signal changing in a stepped manner can control the second PWM signal to be the AC reference frequency at the start of the dither frequency period and last for a set duration, then increase the set frequency on the basis of the AC reference frequency and adjust the second PWM signal to the first AC frequency and last for a set duration, then increase the set frequency on the basis of the first AC frequency and adjust the second PWM signal to the second AC frequency and last for a set duration, and so on, until the second PWM signal is adjusted to the AC maximum frequency and lasts for a set duration, then decrease the set frequency on the basis of the AC maximum frequency and adjust the second PWM signal to the third AC frequency and last for a set duration, and so on, until the second PWM signal is adjusted to the AC minimum frequency and lasts for a set duration, then increase the set frequency on the basis of the AC minimum frequency and adjust the second PWM signal to the fourth AC frequency and last for a set duration, and so on, until the second PWM signal is adjusted to the AC reference frequency.In some other embodiments of the present application, within a dither frequency period, the first PWM signal or the second PWM signal may also start with their respective corresponding minimum frequencies (the minimum frequency of the first PWM signal is the DC minimum frequency, and the minimum frequency of the second PWM signal is the AC minimum frequency) or maximum frequencies (the maximum frequency of the first PWM signal is the DC maximum frequency, and the maximum frequency of the second PWM signal is the AC maximum frequency), etc. Moreover, the frequency variation within a dither frequency period is not limited to the above rules, and no exhaustive listing is made here.

[0074] In some embodiments of the present application, for the convenience of adjustment and control, within a dither frequency period, the frequency difference between two adjacent frequencies of the first PWM signal and the second PWM signal can be controlled to be the same. For example, the first PWM signal uses 130 kHz as the DC reference frequency, 140 kHz as the DC maximum frequency, 120 kHz as the DC minimum frequency, and 200 Hz as the frequency step for increase or decrease to set the frequencies within the dither frequency period; the second PWM signal uses 65 kHz as the AC reference frequency, 68 kHz as the AC maximum frequency, 62 kHz as the AC minimum frequency, and 100 Hz as the frequency step for increase or decrease to set the frequencies within the dither frequency period. And the frequency step can be set according to the difference between the reference frequency and the peak frequencies (including the maximum frequency and the minimum frequency). Generally, the larger the difference, the larger the frequency step.

[0075] In some embodiments of the present application, after fixing the frequencies of the first PWM signal (or the second PWM signal) within a dither frequency period, a fixed number of carrier signals can be maintained at each frequency. Different frequencies can maintain different numbers of carrier signals, or the same number of carrier signals, which is not limited here. This can ensure that within different dither frequency periods, at the same frequency, the number of pulses of the first PWM signal (or the second PWM signal) generated according to the carrier signals is the same. Ensure that within different power grid power frequency periods, the number of pulses of the first PWM signal (or the second PWM signal) at the same frequency is the same, so that each grid-connected inverter can set the phase of the first PWM signal (or the second PWM signal) at different frequencies according to a unified standard without communication, and realize that the phases of the frequency-time change curves of the first PWM signal and the second PWM signal differ by a fixed value.

[0076] In some embodiments of the present application, for the convenience of adjustment and control, within a dither frequency period, the duration of multiple frequencies of the first PWM signal and the second PWM signal can be controlled to be the same.

[0077] In some other embodiments of the present application, within a dithering frequency period, the durations of the DC maximum frequency and the DC minimum frequency among the multiple frequencies of the first PWM signal can also be controlled to be the same, and the durations of the DC maximum frequency and the DC minimum frequency are longer than those of other frequencies. Similarly, within a dithering frequency period, the durations of the AC maximum frequency and the AC minimum frequency among the multiple frequencies of the second PWM signal can also be controlled to be the same, and the durations of the AC maximum frequency and the AC minimum frequency are longer than those of other frequencies. Since the dithering frequency scheme presents a more ideal effect in the medium and high frequencies (generally referring to the frequency band greater than 1 MHz in EMI testing), the performance in the low frequencies (generally referring to the frequency band less than 1 MHz in EMI testing) becomes the main factor restricting the EMC design. Therefore, by increasing the durations of the maximum frequency and the minimum frequency within the dithering frequency period, the electromagnetic interference in the low frequencies can be improved, and the low-frequency EMC benefit can be enhanced. Moreover, by comparing the different durations of the maximum frequency and the minimum frequency within the dithering frequency period, it can be known that the greater the durations of the maximum frequency and the minimum frequency within the dithering frequency period, the higher the low-frequency EMC benefit. In specific implementation, the proportion of the durations of the maximum frequency and the minimum frequency within the dithering frequency period can be controlled between 0.1 and 0.4.

[0078] In some embodiments of the present application, by connecting the multiple frequencies in the dithering frequency period of the PWM signal according to the starting points of their durations, a frequency-versus-time curve can be established, obtaining the frequency-versus-time curves of the multiple frequencies in the dithering frequency period of the first PWM signal and the frequency-versus-time curves of the multiple frequencies in the dithering frequency period of the second PWM signal.

[0079] In some embodiments of the present application, when the frequency differences between adjacent two frequencies of the first PWM signal and the second PWM signal are the same, and the durations of the multiple frequencies of the first PWM signal and the second PWM signal are the same, the frequency-versus-time curves of the multiple frequencies in the dithering frequency periods of the first PWM signal and the second PWM signal change in a triangular wave pattern, that is, the dithering rule is the triangular wave mode in this case.

[0080] In some other embodiments of the present application, when the frequency differences between adjacent two frequencies of the first PWM signal and the second PWM signal are the same, and the durations of the maximum frequency and the minimum frequency of the first PWM signal and the second PWM signal are longer, the frequency-versus-time curves of the multiple frequencies in the dithering frequency periods of the first PWM signal and the second PWM signal change in a trapezoidal wave pattern, that is, the dithering rule is the trapezoidal wave mode in this case.

[0081] In some other embodiments of the present application, when the frequency difference between two adjacent frequencies of the first PWM signal and the second PWM signal is different, and the durations of the maximum frequency and the minimum frequency of the first PWM signal and the second PWM signal are relatively long, the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the second PWM signal can vary in a sine wave pattern, that is, in this case, the frequency hopping rule is a sine wave mode.

[0082] In some embodiments of the present application, the phase difference between the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal is controlled to be a fixed value. Specifically, it can be to control the phase of the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal to be consistent with the phase of the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal, or to control the phase difference between the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal to be 180 degrees, or to control the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal to be orthogonal to the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal. For example, the phase difference between the curves of multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies changing with time in the frequency hopping period of the second PWM signal is controlled to be 90 degrees or 270 degrees.

[0083] In some embodiments of the present application, since the circuit structure and control timing of DC / DC are simpler than those of DC / AC, the DC reference frequency of the first PWM signal can be set to be higher than the AC reference frequency of the second PWM signal. And, for the convenience of calculation and control, the DC reference frequency can also be set to be an integer multiple of the AC reference frequency. For example, the DC reference frequency is 130 kHz and the AC reference frequency is 65 kHz.

[0084] In some embodiments of the present application, for the convenience of calculation and control, the first PWM signal and the second PWM signal can change frequencies according to a fixed ratio within each frequency hopping period. For example, the maximum frequency and the minimum frequency are both set at ±5% of the reference frequency. Based on this, since the DC reference frequency of the first PWM signal is set to be higher than the AC reference frequency of the second PWM signal, generally, the difference between the DC minimum frequency and the DC maximum frequency of the first PWM signal is also greater than the difference between the AC minimum frequency and the AC maximum frequency of the second PWM signal.

[0085] As described above, it is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the said claims.

Claims

1. An inverter, characterized in that, Comprising: A DC conversion circuit, an inverter circuit, and a controller. The DC conversion circuit includes at least one first switching tube, and the inverter circuit includes at least one second switching tube; The DC conversion circuit is used to be connected between a DC source and the inverter circuit, and the DC conversion circuit is used to realize the conversion between direct current and direct current; the inverter circuit is used to be connected between a power grid and the DC conversion circuit, and the inverter circuit is used to realize the conversion of direct current into alternating current; The controller is used to: generate a first pulse width modulation (PWM) signal and a second PWM signal. The first PWM signal is used to control the first switching tube to switch between conduction and cutoff, and the second PWM signal is used to control the second switching tube to switch between conduction and cutoff; The first PWM signal has multiple frequencies within one power frequency period of the power grid, and the frequency hopping period of the first PWM signal is one over an integer multiple of the power frequency period; The second PWM signal has multiple frequencies within one power frequency period of the power grid, and the frequency hopping period of the second PWM signal is the same as that of the first PWM signal; The phase difference between the curves of the multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of the multiple frequencies changing with time in the frequency hopping period of the second PWM signal is a fixed value.

2. The inverter according to claim 1, wherein, The controller is used to: control the multiple frequencies of the first PWM signal and the second PWM signal to change in a stepped manner within one frequency hopping period.

3. The inverter according to claim 2, characterized in that, The controller is used to: control the frequency difference between two adjacent frequencies of the first PWM signal and the second PWM signal to be the same within one frequency hopping period.

4. The inverter according to claim 2 or 3, characterized in that, The controller is used to: control the duration of the maximum frequency and the duration of the minimum frequency among the multiple frequencies of the first PWM signal and the second PWM signal within one frequency hopping period to be the same, and both are longer than the duration of other frequencies.

5. The inverter according to claim 1 or 2, characterized in that, The controller is used to: control the curves of the multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the second PWM signal to change in a triangular wave, trapezoidal wave, or sine wave manner.

6. The inverter according to any one of claims 1-5, characterized in that, The controller is used to: control the phase difference between the curves of the multiple frequencies changing with time in the frequency hopping period of the first PWM signal and the curves of the multiple frequencies changing with time in the frequency hopping period of the second PWM signal to be 0 degrees, 90 degrees, 180 degrees, or 270 degrees.

7. The inverter according to any one of claims 1-6, characterized in that, The controller is used to: control the reference frequency of the first PWM signal to be higher than the reference frequency of the second PWM signal.

8. The inverter according to claim 7, characterized in that, The controller is used to: control the difference between the minimum frequency and the maximum frequency of the multiple frequencies in the frequency hopping period of the first PWM signal to be greater than the difference between the minimum frequency and the maximum frequency of the multiple frequencies in the frequency hopping period of the second PWM signal.

9. A control method for an inverter, characterized in that, Comprising: Generate a first pulse width modulation (PWM) signal and a second PWM signal. The first PWM signal is used to control the first switching tube of the DC conversion circuit in the inverter to switch between conduction and cutoff, and the second PWM signal is used to control the second switching tube of the inverter circuit in the inverter to switch between conduction and cutoff; The first PWM signal has multiple frequencies within one power frequency cycle of the power grid, and the frequency hopping period of the first PWM signal is one over an integer multiple of the power frequency cycle; The second PWM signal has multiple frequencies within one power frequency cycle of the power grid, and the frequency hopping period of the second PWM signal is the same as that of the first PWM signal; The phase difference between the curves of multiple frequencies varying with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies varying with time in the frequency hopping period of the second PWM signal is a fixed value.

10. The control method according to claim 9, characterized in that It further includes: Controlling the multiple frequencies of the first PWM signal and the second PWM signal to change in a stepped manner within one frequency hopping period.

11. The control method according to claim 10, characterized in that, It further includes: Controlling the frequency difference between adjacent two frequencies of the first PWM signal and the second PWM signal to be the same within one frequency hopping period.

12. The control method according to claim 10 or 11, characterized in that, It further includes: Controlling the duration of the maximum frequency and the duration of the minimum frequency among the multiple frequencies of the first PWM signal and the second PWM signal within one frequency hopping period to be the same, and both are longer than the durations of other frequencies.

13. The control method according to claim 9 or 10, characterized in that It further includes: Controlling the curves of multiple frequencies varying with time in the frequency hopping period of the first PWM signal and the second PWM signal to change in a triangular wave, trapezoidal wave or sine wave manner.

14. The control method according to any one of claims 9-13, characterized in that, It further includes: Controlling the phase difference between the curves of multiple frequencies varying with time in the frequency hopping period of the first PWM signal and the curves of multiple frequencies varying with time in the frequency hopping period of the second PWM signal to be 0 degree, 90 degrees, 180 degrees or 270 degrees.

15. The control method according to any one of claims 9-14, characterized in that, It further includes: Controlling the reference frequency of the first PWM signal to be higher than the reference frequency of the second PWM signal.

16. The control method according to claim 15, wherein It further includes: Controlling the difference between the minimum frequency and the maximum frequency of the multiple frequencies in the frequency hopping period of the first PWM signal to be greater than the difference between the minimum frequency and the maximum frequency of the multiple frequencies in the frequency hopping period of the second PWM signal.

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