Power conversion equipment, grid-connected system and control method of power conversion equipment

Abstract

The invention provides power conversion equipment, a grid-connected system and a control method of the power conversion equipment, the power conversion equipment comprises a power conversion circuit and a controller, the input end of the power conversion circuit is connected with a direct current power supply, and the output end is connected into a power grid; the controller is used for controlling the amplitude of a target current signal in the current signals adjusted and output by the power conversion circuit to be reduced when it is detected that a non-characteristic harmonic signal exists at the output end of the power conversion circuit, so that the equivalent impedance of the power conversion equipment relative to the non-characteristic harmonic signal is increased; wherein the frequency of the non-characteristic harmonic signal is a non-integer multiple of the fundamental frequency of the power grid, and the frequency of the target current signal is equal to the frequency of the non-characteristic harmonic signal. According to the power conversion equipment, the equivalent impedance relative to the non-characteristic harmonic signal can be increased, the attenuation of the non-characteristic harmonic signal passing through the power conversion equipment is reduced, and the applicability is high.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a power conversion device, a grid-connected system, and a control method for the power conversion device. Background Art

[0002] As the penetration rate of renewable energy power generation is increasing, more and more photovoltaic equipment, energy storage equipment, etc. are connected to the power grid through inverters. At the same time, in order to reduce the cost of setting up communication networks, power grid companies can use power line communication (PLC) technology to modulate data information or voice information into power line signals, and then use the existing power lines in the power grid as the transmission medium for transmission without the need for additional wiring.

[0003] However, after a large number of inverters are connected to the grid, the power carrier signal transmitted in the grid will be significantly attenuated. Therefore, how to reduce the impact of the inverter on the power carrier signal when using the inverter to connect to the grid is a technical problem that technicians in this field need to solve urgently. Summary of the invention

[0004] The present application provides a power conversion device, a grid-connected system, and a control method for the power conversion device. The power conversion device can increase the equivalent impedance relative to non-characteristic harmonic signals, reduce the attenuation of non-characteristic harmonic signals passing through the power conversion device, and has strong applicability.

[0005] In the first aspect, the present application provides a power conversion device, which includes a power conversion circuit and a controller, wherein the input end of the power conversion circuit is used to connect a DC power supply, and the output end of the power conversion circuit is connected to a power grid, and the controller is used to: when a non-characteristic harmonic signal is detected at the output end of the power conversion circuit, control the power conversion circuit to adjust the amplitude of the target current signal in the output current signal to decrease, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases; wherein the non-characteristic harmonic signal is a harmonic signal transmitted between loads in the power grid, the frequency of the non-characteristic harmonic signal is a non-integer multiple of the fundamental frequency of the power grid, the target current signal is a current signal with a frequency equal to the target frequency, and the target frequency is equal to the frequency of the non-characteristic harmonic signal. In the present application, when the power conversion device detects the presence of a non-characteristic harmonic signal in the power grid through the controller, the amplitude of the target current signal output by the power conversion circuit is reduced through the controller, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases, thereby avoiding a significant attenuation of the non-characteristic harmonic signal through the power conversion device and extending the transmission distance of the non-characteristic harmonic signal. Exemplarily, when a non-characteristic harmonic signal is transmitted as a power carrier signal in a power grid, the power conversion device provided in the embodiment of the present application can improve the communication quality by increasing the equivalent impedance relative to the power carrier signal, and has strong applicability. In addition, when the power conversion device detects the presence of a non-characteristic harmonic signal in the power grid through a controller, it starts the adjustment function of the equivalent impedance of the non-characteristic harmonic signal, which can reduce the adverse effects on other harmonic signals in the power grid.

[0006] In a possible implementation, the controller controls the power conversion circuit to reduce the amplitude of the target current signal in the current signal output by the DC power supply based on the DC power regulation, specifically for: controlling the reduction rate of the amplitude of the target current signal to be greater than or equal to the first rate threshold, and in the process of reducing the amplitude of the target current signal, controlling the reduction rate of the amplitude of the target current signal to gradually decrease. In the present application, in the present application, the power conversion device can control the amplitude reduction rate of the target current signal output by the power conversion circuit to be greater than or equal to the first rate threshold through the controller, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases rapidly, thereby improving the response speed of the power conversion device. Furthermore, in the process of reducing the amplitude of the target current signal, the power conversion device controls the reduction rate of the amplitude of the target current signal to gradually decrease through the controller, while reducing the adverse effects of other harmonic signals, and ensuring the stability of the power conversion device.

[0007] In a possible implementation, the controller controls the power conversion circuit to reduce the amplitude of a target current signal in a current signal outputted by a DC power supply based on the DC power regulation, specifically for: obtaining an error current signal based on a difference between a reference current signal and a feedback current signal at an output end of the power conversion circuit, and obtaining a modulation voltage signal based on a resonance coefficient, a resonance bandwidth, a resonance frequency and an error current signal of a resonance control module in the controller; and controlling the power conversion circuit to reduce the amplitude of the target current signal based on the modulation voltage signal; the modulation voltage signal satisfies:

[0008]

[0009] Where s is the error current signal, H(s) is the modulation voltage signal, and k r is the resonance coefficient, ω c is the resonant bandwidth, ω 0 In the present application, the controller can control the amplitude of the target current signal to decrease based on the resonance parameter, the reference current signal and the feedback current signal at the output end of the power conversion circuit, etc., and the implementation principle is simple and the reliability is strong.

[0010] In a possible implementation, the controller is also used to: obtain a feedback current signal after coordinate transformation of the sampled current signal at the output end of the power conversion circuit; obtain a reference current signal after coordinate transformation of the basic current signal, the basic current signal is obtained by the grid-connected power of the power conversion circuit; obtain a modulated voltage signal after coordinate inverse transformation of the voltage signal obtained based on the resonance coefficient, the resonance bandwidth, the resonance frequency and the error current signal. In the present application, when the power conversion circuit is connected to the power grid using a three-phase system, the controller can process current signals of different phases by using coordinate transformation and coordinate inverse transformation, which has rich application scenarios and strong applicability.

[0011] In one possible implementation, the size of the resonant bandwidth is proportional to the rate of decrease of the amplitude of the target current signal; the controller controls the power conversion circuit to reduce the amplitude of the target current signal in the current signal output based on the direct current provided by the direct current power supply, and is specifically used for: in the process of controlling the power conversion circuit to adjust the amplitude of the target current signal to decrease, the resonant bandwidth is adjusted to gradually decrease, so that the rate of decrease of the amplitude of the target current signal gradually decreases. In the present application, the power conversion device can adjust the reaction sensitivity of the controller by adjusting the resonant bandwidth. In the process of reducing the amplitude of the target current signal, the power conversion device can reduce the reaction sensitivity of the controller by adjusting the resonant bandwidth to gradually decrease, so that the rate of decrease of the amplitude of the target current signal gradually decreases, thereby achieving a rapid response of the power conversion device while reducing the adverse effects on other harmonic signals and ensuring the stability of the power conversion device.

[0012] In one possible implementation, the controller detects the presence of a non-characteristic harmonic signal at the output end of the power conversion circuit, and is specifically used to: detect the voltage signal at the output end of the power conversion circuit, and when it is detected that the frequency of the voltage signal is the target frequency and the signal amplitude is greater than or equal to the amplitude threshold, obtain the presence of a non-characteristic harmonic signal at the output end of the power conversion circuit. In the present application, the power conversion device detects whether the voltage signal at the output end of the power conversion circuit reaches the amplitude threshold through the controller to determine whether there is a non-characteristic harmonic signal at the output end of the power conversion circuit. The implementation principle is simple and the applicability is strong.

[0013] In a second aspect, the present application also provides a grid-connected system, which includes the power conversion device of the first aspect above, wherein the DC end of the power conversion device is used to connect to a DC power supply, and the AC end of the power conversion device is used to connect to a power grid.

[0014] In the third aspect, the present application also provides a control method for a power conversion device, the power conversion device includes a power conversion circuit, the input end of the power conversion circuit is used to connect a DC power supply, and the output end of the power conversion circuit is connected to a power grid; the control method includes: detecting an electrical signal at the output end of the power conversion circuit; when a non-characteristic harmonic signal is detected at the output end of the power conversion circuit, controlling the power conversion circuit to adjust the amplitude of a target current signal in the output current signal to decrease, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases; wherein the non-characteristic harmonic signal is a harmonic signal transmitted between loads in the power grid, the frequency of the non-characteristic harmonic signal is a non-integer multiple of the fundamental frequency of the power grid, the target current signal is a current signal having a frequency equal to the target frequency, and the target frequency is equal to the frequency of the non-characteristic harmonic signal.

[0015] In one possible implementation, the amplitude of a target current signal in a current signal output by a power conversion circuit is controlled to decrease based on direct current regulation provided by a direct current power supply, including: controlling the reduction rate of the amplitude of the target current signal to be greater than or equal to a first rate threshold, and in the process of reducing the amplitude of the target current signal, controlling the reduction rate of the amplitude of the target current signal to gradually decrease.

[0016] In a possible implementation, controlling the power conversion circuit to reduce the amplitude of a target current signal in a current signal outputted by a DC power supply based on the DC power regulation includes: obtaining an error current signal based on a difference between a reference current signal and a feedback current signal at an output end of the power conversion circuit, and obtaining a modulation voltage signal based on a resonance coefficient, a resonance bandwidth, a resonance frequency, and the error current signal of a resonance control module; controlling the power conversion circuit to reduce the amplitude of the target current signal based on the modulation voltage signal; and the modulation voltage signal satisfies:

[0017]

[0018] Where s is the error current signal, H(s) is the modulation voltage signal, and k r is the resonance coefficient, ω c is the resonant bandwidth, ω 0 is the resonant frequency.

[0019] In a possible implementation, the control method also includes: performing coordinate transformation on a sampled current signal at the output end of the power conversion circuit to obtain a feedback current signal, performing coordinate transformation on a basic current signal to obtain a reference current signal, and performing inverse coordinate transformation on a voltage signal obtained based on a resonance coefficient, a resonance bandwidth, a resonance frequency and an error current signal to obtain a modulated voltage signal; the basic current signal is obtained from the grid-connected power of the power conversion circuit.

[0020] In one possible implementation, the size of the resonant bandwidth is proportional to the rate of decrease of the amplitude of the target current signal; the amplitude of the target current signal in the current signal output by the control power conversion circuit based on the DC power provided by the DC power supply is reduced, including: in the process of controlling the power conversion circuit to adjust the amplitude of the target current signal to decrease, the resonant bandwidth is adjusted to gradually decrease so that the rate of decrease of the amplitude of the target current signal gradually decreases.

[0021] In one possible implementation, the presence of a non-characteristic harmonic signal at the output end of a power conversion circuit is detected, including: when it is detected that the frequency of the voltage signal at the output end of the power conversion circuit is a target frequency and the signal amplitude is greater than or equal to an amplitude threshold, obtaining the presence of a non-characteristic harmonic signal at the output end of the power conversion circuit.

[0022] It should be understood that the implementation and beneficial effects of the above-mentioned aspects of the present application can be referenced to each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of an application scenario of the grid-connected system provided in this application;

[0024] Figure 2 A schematic diagram of another application scenario of the grid-connected system provided in an embodiment of the present application;

[0025] Figure 3 A schematic diagram of a framework of a power conversion device provided in an embodiment of the present application;

[0026] Figure 4 A schematic diagram of a framework of a controller provided in an embodiment of the present application;

[0027] Figure 5 Another schematic diagram of the framework of the controller provided in the embodiment of the present application;

[0028] Figure 6A schematic diagram of a detection process of an enabling module provided in an embodiment of the present application;

[0029] Figure 7a A schematic diagram of a resonance bandwidth of a resonance control module provided in an embodiment of the present application;

[0030] Figure 7b A schematic diagram of another resonance bandwidth of the resonance control module provided in an embodiment of the present application;

[0031] Figure 7c A schematic diagram of another resonance bandwidth of the resonance control module provided in an embodiment of the present application;

[0032] Figure 8 A waveform diagram provided for an embodiment of the present application;

[0033] Fig. 9 Another waveform diagram provided for an embodiment of the present application;

[0034] Fig.10 Another schematic diagram of a power conversion device provided in an embodiment of the present application;

[0035] Fig.11 Another schematic diagram of a controller according to an embodiment of the present application;

[0036] Fig.12 A schematic flow chart of a control method for a power conversion device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0037] See also Figure 1 , Figure 1 A schematic diagram of an application scenario of the grid-connected system provided by the present application. The grid-connected system provided by the present application may include a DC power supply, at least one power conversion device and at least one load, wherein the DC power supply may specifically be an energy storage battery. Exemplarily, if the grid-connected system includes multiple power conversion devices, the DC end of each power conversion device may be connected to the energy storage battery, and the AC ends of multiple power conversion devices may be connected to the power grid after being connected in parallel. If the grid-connected system includes multiple loads, the AC ends of each load may be connected in parallel to the power grid. The power conversion device may invert the DC power provided by the energy storage battery, and output the AC power obtained after the inversion conversion to the power grid to supply power to the load connected to the power grid. Alternatively, the power conversion device may rectify and convert the AC power provided by the power grid, and provide the DC power obtained after the rectification conversion to the DC power supply for charging. Among them, the power grid refers to an AC network composed of substations and transmission and distribution lines of various voltages, which can provide industrial frequency AC power to the load. The power grid may be a single-phase AC power grid or a three-phase AC power grid, which is not specifically limited in the embodiments of the present application. The above-mentioned load may be a battery, a communication base station or a household appliance or other electrical equipment.

[0038] The DC power source in the grid-connected system can be a photovoltaic array. In this case, the structure diagram of the grid-connected system can be found in Figure 2 As shown, Figure 2 A schematic diagram of another application scenario of the grid-connected system provided in an embodiment of the present application. Figure 2 Among the multiple power conversion devices of the grid-connected system shown, the DC end of some of the power conversion devices can be connected to the corresponding photovoltaic array. The photovoltaic array is composed of one or more photovoltaic strings connected in parallel, and a photovoltaic string can be obtained by connecting one or more photovoltaic modules in series. The photovoltaic array can convert light energy into electrical energy, and transmit the generated electrical energy to the DC end of the power conversion device in the form of direct current, or transmit it to the energy storage battery for storage. It can be understood that the power conversion device connected to the photovoltaic array in the grid-connected system can be an inverter, and the power conversion device connected to the energy storage battery in the grid-connected system can be a converter.

[0039] exist Figure 1 or Figure 2 In the application scenario of the grid-connected system shown, the power conversion device can be connected to the grid through a live wire and a neutral wire, that is, the single-phase system is used to supply power to the grid. Alternatively, the power conversion device can be connected to the grid through three live wires and a neutral wire, that is, the three-phase four-wire system is used to supply power to the grid. Alternatively, the power conversion device can be connected to the grid through three live wires, a neutral wire and a ground wire, that is, the three-phase five-wire system is used to provide electrical energy to the grid. Among them, the neutral wire of the power conversion device serves as a wire that provides a current loop to the grid, which can ensure that the power conversion device and the grid form a power supply loop, and the ground wire of the power conversion device can lead the leakage current generated in the system into the ground to ensure the stability of the system and the grid.

[0040] It should be noted that PLC technology can achieve internal communication of the grid-connected system by transmitting high-frequency power carrier signals on the power lines of the power grid, including transmission of protection signals, remote monitoring and data collection, etc., to ensure the stable operation of the grid-connected system, without the need to lay additional communication lines, and has the advantages of low cost and fast deployment. For example, Figure 1 or Figure 2 A load in the grid-connected system shown can act as a communication transmitter, inject a power carrier signal into the power grid and transmit it using the power grid. One or more other loads in the grid-connected system can act as communication receivers, acquire and demodulate the power carrier signal transmitted in the power grid, thereby realizing data communication between different loads. Among them, the specific implementation principle of communication between different loads through PLC technology can refer to the relevant content of PLC technology, and the embodiments of this application will not be repeated here.

[0041] As the penetration rate of renewable energy power generation is increasing, more and more DC power sources such as photovoltaic arrays and energy storage batteries are connected to the power grid through power conversion equipment. After a large number of power conversion equipment are connected to the power grid, the power carrier signal transmitted in the power grid will be significantly attenuated.

[0042] To this end, an embodiment of the present application provides a power conversion device, which can increase the equivalent impedance relative to the power carrier signal when detecting the presence of a power carrier signal at the AC end, that is, when the power carrier signal is transmitted in the power grid, to avoid a significant attenuation of the power carrier signal through the power conversion device. The equivalent impedance of the power conversion device relative to the power carrier signal refers to the impedance presented by the power conversion device relative to the power carrier signal. The larger the equivalent impedance of the power conversion device relative to the power carrier signal, the smaller the attenuation of the power carrier signal through the power conversion device, thereby improving the stability and reliability of the power carrier signal transmission.

[0043] It should be noted that in order to ensure that the power carrier signal has better anti-interference ability and improve the reliability of data transmission, PLC technology usually uses non-characteristic harmonic signals as power carrier signals. Non-characteristic harmonic signals refer to harmonic signals whose frequencies are not integer multiples of the fundamental frequency of the power grid. For example, the fundamental frequency of the power grid is 50 Hz, and the frequency of non-characteristic harmonic signals can be 175 Hz, 210 Hz, 1025 Hz, etc. The communication sender can realize data encoding by adjusting the frequency and amplitude of the non-characteristic harmonic signal, and load the non-characteristic harmonic signal onto the power line for transmission through modulation technology. Non-characteristic harmonic signals can propagate farther in the power grid, thereby reducing signal attenuation and improving transmission efficiency. The communication receiver can restore the original data by demodulating the received non-characteristic harmonic signal. PLC technology is widely used in smart grids, automation control and other fields. The application of non-characteristic harmonic signals can make these systems run more stably and efficiently, meeting the requirements of modern power systems for communication quality.

[0044] To this end, the power conversion device provided in the embodiment of the present application can increase the equivalent impedance of the power conversion device relative to the power carrier signal by increasing the equivalent impedance relative to the non-characteristic harmonic signal, thereby avoiding a significant attenuation of the power carrier signal through the power conversion device, and ensuring the stability and reliability of the power carrier signal transmission. Similarly, in other application scenarios, when the non-characteristic harmonic signal is used as a harmonic signal for other purposes, the power conversion device provided in the embodiment of the present application can adjust the equivalent impedance relative to the non-characteristic harmonic signal.

[0045] The power conversion device provided in the embodiment of the present application can control the rapid increase of the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal when detecting the presence of a non-characteristic harmonic signal in the power grid, so as to avoid a significant attenuation of the non-characteristic harmonic signal through the power conversion device, thereby extending the transmission distance of the non-characteristic harmonic signal and improving the communication quality of the grid-connected system. The power conversion device has a fast response speed and strong applicability.

[0046] The power conversion device provided in the embodiment of the present application specifically includes a power conversion circuit and a controller. When the power conversion device is incorporated into the power grid, the input end (i.e., the DC end) of the power conversion circuit is connected to the DC power supply, and the output end (i.e., the AC end) of the power conversion circuit is connected to the power grid, and the DC power provided by the DC power supply can be inverted to supply power to the load incorporated into the power grid, or the power conversion circuit can rectify and convert the AC power provided by the power grid, and provide the rectification and conversion to the DC power supply for charging. It can be seen from the above that the power grid can also superimpose non-characteristic harmonic signals for transmission while transmitting electric energy, for example, transmitting power carrier signals between different loads. When non-characteristic harmonic signals are transmitted in the power grid, since the output end of the power conversion circuit is connected to the power grid, non-characteristic harmonic signals will also exist at the output end of the power conversion circuit. To this end, the power conversion device can detect the output end of the power conversion circuit through a controller, and when it is detected that there is a non-characteristic harmonic signal at the output end of the power conversion circuit, that is, when the non-characteristic harmonic signal is transmitted in the power grid, the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal is increased, thereby reducing the attenuation of the non-characteristic harmonic signal and extending the transmission distance of the non-characteristic harmonic signal.

[0047] It should be noted that when the controller does not detect the presence of a non-characteristic harmonic signal at the output end of the power conversion circuit, it indicates that there is no non-characteristic harmonic signal being transmitted in the power grid. At this time, the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal can remain unchanged, that is, the power conversion device does not adjust the equivalent impedance relative to the non-characteristic harmonic signal. In other words, the power conversion device can start adjusting the equivalent impedance of the non-characteristic harmonic signal only when the controller detects the presence of a non-characteristic harmonic signal at the output end of the power conversion circuit, thereby avoiding long-term activation of the adjustment of the equivalent impedance of the non-characteristic harmonic signal and reducing adverse effects on other harmonic signals in the power grid.

[0048] It is understandable that the power conversion device starts adjusting the equivalent impedance of the non-characteristic harmonic signal, specifically, it can be to control the switching action of each bridge arm in the above-mentioned power conversion circuit through the controller, so that the power conversion circuit performs inversion conversion based on the direct current provided by the direct current power supply, and then adjusts the amplitude of the target current signal in the current signal output by the power conversion circuit. Among them, the current signal output by the power conversion circuit includes a fundamental current signal and various harmonic current signals, and the target current signal refers to a current signal with a frequency equal to the target frequency, and the target frequency is equal to the frequency of the above-mentioned non-characteristic harmonic signal.

[0049] It should be noted that, since the frequency of the target current signal is equal to the frequency of the non-characteristic harmonic signal, when the amplitude of the target current signal output by the power conversion circuit decreases, it means that the current amplitude of the non-characteristic harmonic signal at the output end of the power conversion circuit decreases. Furthermore, it can be known from Ohm's law that under the same grid voltage, the smaller the current amplitude of the non-characteristic harmonic signal at the output end of the power conversion circuit, the greater the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal. To this end, the power conversion device can control the amplitude of the target current signal output by the power conversion circuit to decrease through a controller, thereby increasing the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal.

[0050] The power conversion device provided in the embodiment of the present application can start the adjustment function of the equivalent impedance of the non-characteristic harmonic signal when the controller detects the presence of the non-characteristic harmonic signal in the power grid, thereby reducing the adverse effects on other harmonic signals in the power grid. When starting the adjustment function of the equivalent impedance, the power conversion device can control the amplitude of the target current signal output by the power conversion circuit through the controller to reduce, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases, thereby avoiding the non-characteristic harmonic signal from being significantly attenuated through the power conversion device, extending the transmission distance of the non-characteristic harmonic signal and improving the communication quality of the grid-connected system, and has strong applicability.

[0051] In some feasible implementations, when the power conversion device is connected to the power grid using a single-phase system, the structure of the power conversion device can be as follows: Figure 3 As shown, Figure 3 A schematic diagram of a framework of a power conversion device provided in an embodiment of the present application. Figure 3The power conversion device shown includes a power conversion circuit and a controller. The input end of the power conversion circuit is connected to a DC power supply, and the output end of the power conversion circuit is connected to the power grid through a live wire A and a neutral wire N. The DC power supply can exchange electric energy with the power grid through the power conversion circuit. As can be seen from the above content, while the power grid transmits electric energy, it can also superimpose non-characteristic harmonic signals for transmission, for example, transmitting power carrier signals between different loads. In order to reduce the attenuation of the non-characteristic harmonic signal and extend the transmission distance of the non-characteristic harmonic signal, the power conversion device can detect whether there is a non-characteristic harmonic signal at the output end of the power conversion circuit through a controller.

[0052] In some feasible implementations, the power conversion device may further include a filter module, which is arranged between the power conversion circuit and the power grid. The power conversion circuit will generate noise and interference during operation, which will affect the stability of the power grid. The filter module can filter out the noise and interference output by the power conversion circuit before providing it to the power grid, ensuring that the output of the power conversion circuit is purer, thereby improving the overall performance of the power conversion device. Specifically, the filter module can be composed of two inductors connected in series on the live wire A, and a capacitor connected across the live wire A and the neutral wire N. In other application scenarios, the specific structure of the filter module can be flexibly deformed, and the embodiments of the present application are not limited to this.

[0053] It should be noted that the output end of the power conversion circuit may be a port where the power conversion circuit is connected to the filter module, or may be a port where the filter module is connected to the power grid. Figure 3 As shown, the controller can detect whether there is a non-characteristic harmonic signal at the output end of the power conversion circuit by detecting the port connected between the power conversion circuit and the filter module, or the controller can detect the port connected between the filter module and the power grid.

[0054] Specifically, Figure 3 The specific structure and implementation principle of the controller shown can be found in Figure 4 As shown, Figure 4 A schematic diagram of a framework of a controller provided in an embodiment of the present application. Figure 4The controller shown includes a resonance control module and a modulation module. The controller can obtain the feedback current signal Ig at the output end of the power conversion circuit, and obtain an error current signal after subtracting the feedback current signal Ig from the reference current signal Iref. The feedback current signal Ig can be understood as being obtained by the controller actually sampling the current signal at the output end of the power conversion circuit. The reference current signal Iref can be understood as being obtained by the controller according to the grid-connected power size of the power conversion device. Among them, the grid-connected power size of the power conversion device can be obtained by the dispatching power of the power grid, the charging and discharging power of the DC power supply, etc. The error current signal can reflect the error between the actual current at the output end of the current power conversion circuit and the target current. Further, the controller can transmit the error current signal to the resonance control module. The resonance control module can obtain a modulated voltage signal after resonant control of the error current signal based on the set resonance parameters. Among them, the resonance parameters of the resonance control module can include a resonance frequency, which is the frequency of the current signal for resonance control by the resonance control module, and can be equal to the frequency of the above-mentioned non-characteristic harmonic signal, that is, the target frequency. That is to say, the resonance control module can resonate the current signal whose frequency is equal to the target frequency in the input error current signal, and output a modulation voltage signal corresponding to the current signal of the target frequency to the modulation module. The modulation module can generate a pulse width modulation signal PWM according to the modulation voltage signal to drive the switch tubes in each bridge arm of the power conversion circuit to operate, so that the amplitude of the target current signal output from the adjustment output end of the power conversion circuit is reduced.

[0055] Exemplarily, it is assumed that the frequency of the non-characteristic harmonic signal transmitted in the power grid is 1025 Hz, that is, the above-mentioned target frequency is 1025 Hz. The controller can obtain an error current signal by subtracting the feedback current signal Ig sampled at the output end of the power conversion circuit from the reference current signal Iref, and transmit it to the resonance control module. The resonance control module can resonate the current signal with a frequency equal to 1025 Hz in the error current signal and output the corresponding modulation voltage signal to the modulation module. The modulation module outputs a pulse width modulation signal PWM according to the received modulation voltage signal to drive the switch tube of each bridge arm in the power conversion circuit to operate, and adjust the current signal output from the output end of the power conversion circuit to reduce the amplitude of the target current signal with a frequency equal to 1025 Hz.

[0056] It should be noted that the above control process of the controller is a closed-loop control process, that is, the controller can adjust the modulation voltage signal by continuously comparing the difference between the feedback current signal Ig at the output end of the power conversion circuit and the reference current signal Iref, so that the difference between the feedback current signal Ig at the output end of the power conversion circuit and the reference current signal Iref becomes smaller and smaller. For example, when the current signal amplitude of 1025hz in the reference current signal Iref is equal to 0, that is, the target amplitude of the target current signal output from the output end of the power conversion circuit is 0, the controller can perform the above closed-loop control process through the resonance control module and the modulation module, etc., until the amplitude of the target current signal output by the power conversion circuit is reduced to 0. The above is only an example and does not constitute a limitation on the embodiments of the present application.

[0057] It can be seen from this that in the embodiment of the present application, the controller can perform separate resonant control on the current signal in the error current signal whose frequency is equal to the target frequency through the resonance control module, so as to achieve subsequent independent control of the power conversion circuit to adjust the amplitude of the target current signal output at the output end to reduce, thereby increasing the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal.

[0058] From the above content, it can be known that the power conversion device can start adjusting the equivalent impedance of the non-characteristic harmonic signal only when the controller detects the presence of a non-characteristic harmonic signal at the output end of the power conversion circuit, thereby avoiding long-term activation of the equivalent impedance adjustment of the non-characteristic harmonic signal and reducing the adverse effects on other harmonic signals in the power grid. To this end, the controller in the embodiment of the present application can also be provided with an enabling module. At this time, the specific structure and implementation principle of the controller can be referred to Figure 5 As shown, Figure 5 Another schematic diagram of the framework of the controller provided in the embodiment of the present application. Figure 4 Compared to the controller shown, Figure 5 The controller shown also includes an enabling module. The enabling module can detect the voltage signal Ug at the output end of the power conversion circuit. The voltage signal Ug can be understood as being obtained by actually sampling the voltage signal at the output end of the power conversion circuit by the enabling module. When there is a non-characteristic harmonic signal at the output end of the power conversion circuit, the enabling module can detect that the amplitude of the voltage signal with a frequency equal to the target frequency in the above-mentioned voltage signal Ug is greater than or equal to the amplitude threshold.

[0059] It should be noted that the enabling module can be based on Figure 6 The detection process shown is to detect whether there is a non-characteristic harmonic signal at the output end of the power conversion circuit. Figure 6 A detection flow diagram of an enabling module provided in an embodiment of the present application. Figure 6As shown, first, the enabling module can sample the voltage signal at the output end of the power conversion circuit and receive the target frequency sent by the host computer. The host computer can be a computer or other intelligent terminal device. The enabling module can perform bandpass filtering on the sampled voltage signal through a bandpass filter, and only retain the voltage signal with a frequency equal to the above-mentioned target frequency. Further, the enabling module can calculate the amplitude of the voltage signal of the target frequency. Wherein, the voltage signal of the target frequency is an alternating current signal, and the controller can calculate the average value, absolute value or effective value of the voltage signal amplitude of the target frequency as the amplitude of the voltage signal of the target frequency. Further, the enabling module can compare the amplitude of the voltage signal of the calculated target frequency with the amplitude threshold. Wherein, the above-mentioned amplitude threshold represents the minimum value of the voltage amplitude of the non-characteristic harmonic signal at the output end of the power conversion circuit when there is a non-characteristic harmonic signal at the output end of the power conversion circuit. That is, when the enabling module detects that the amplitude of the voltage signal of the target frequency (i.e., the voltage amplitude of the non-characteristic harmonic signal) in the voltage signal at the output end of the power conversion circuit is less than the amplitude threshold, there is no non-characteristic harmonic signal at the output end of the power conversion circuit, otherwise there is a non-characteristic harmonic signal. Therefore, the enabling module can determine that there is a non-characteristic harmonic signal at the output end of the power conversion circuit when the amplitude of the voltage signal of the target frequency calculated is greater than the above-mentioned amplitude threshold, otherwise there is no non-characteristic harmonic signal.

[0060] Further, it can be known from the above content that when the enabling module detects that there is no non-characteristic harmonic signal at the output end of the power conversion circuit, the adjustment function of the equivalent impedance relative to the non-characteristic harmonic signal can be disabled, thereby avoiding the long-term activation of the adjustment of the equivalent impedance of the non-characteristic harmonic signal and reducing the adverse effects on other harmonic signals in the power grid. On the contrary, when the enabling module detects that there is a non-characteristic harmonic signal at the output end of the power conversion circuit, the controller can be enabled to activate the adjustment function of the equivalent impedance relative to the non-characteristic harmonic signal. Specifically, when the enabling module detects that there is a non-characteristic harmonic signal at the output end of the power conversion circuit, it can send an enable signal to the resonant control module of the controller to enable the resonant control module to operate, thereby reducing the amplitude of the target current signal adjusted to output by the power conversion circuit, and increasing the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal.

[0061] Please refer again Figure 5 , Figure 5The controller shown also includes a loop control module and a modulation module. The loop control module can obtain the feedback current signal Ig of the output end of the power conversion circuit, and obtain the error current signal after subtracting the feedback current signal Ig from the reference current signal Iref, and output it to the resonance control module. The resonance control module that receives the enable signal can resonate the error current signal based on the set resonance parameters, and output a modulation voltage signal corresponding to the current signal of the target frequency to the modulation module. The modulation module can generate a pulse width modulation signal PWM according to the modulation voltage signal to drive the switch tubes in each bridge arm of the power conversion circuit to act, so that the amplitude of the target current signal output from the power conversion circuit adjustment output end is reduced.

[0062] In addition, in order to adjust the current amplitude of other harmonic signals of frequency in the current signal output from the output end of the power conversion circuit accordingly, the loop control module may also include a current loop. Figure 5 As shown, the loop control module can input the error current signal into the current loop. The current loop is mainly used to control the current signal whose frequency is close to the fundamental frequency of the power grid in the input error current signal, and output the loop control voltage signal to the modulation module. The modulation module can generate a pulse width modulation signal PWM based on the voltage signal Ug at the output end of the current power conversion circuit, the modulation voltage signal output by the resonance control module, the loop control voltage signal output by the loop control module, and the DC bus voltage Udc of the power conversion circuit to drive the switch tubes of each bridge arm in the power conversion circuit to operate, thereby adjusting the amplitude of the current signal output from the output end of the power conversion circuit, such as controlling the amplitude of the target current signal to decrease and the amplitude of the current signal of the fundamental frequency to increase.

[0063] Exemplarily, it is assumed that the frequency of the non-characteristic harmonic signal transmitted in the power grid is 1025 Hz and the fundamental frequency is 50 Hz. When the enabling module of the controller detects that the amplitude of the voltage signal with a frequency of 1025 Hz in the voltage signal at the output end of the power conversion circuit is greater than or equal to the above-mentioned amplitude threshold, the enabling module determines that there is a non-characteristic harmonic signal at the output end of the power conversion circuit, and the enabling module sends an enabling signal to the resonance control module. At the same time, the loop control module can obtain an error current signal by subtracting the feedback current signal Ig sampled at the output end of the power conversion circuit from the reference current signal Iref, and output it to the resonance control module and the current loop in the loop control module. The resonance control module that receives the enabling signal can resonate the current signal with a frequency equal to 1025 Hz in the error current signal and output the corresponding modulation voltage signal to the modulation module. The current loop can control the current signal with a frequency close to 50 Hz in the error current signal and output the corresponding loop control voltage signal to the modulation module. The modulation module outputs a pulse width modulation signal PWM according to the received voltage signals to drive the switch tubes of each bridge arm in the power conversion circuit, and adjusts the current signal output from the output end of the power conversion circuit, reducing the amplitude of the target current signal with a frequency equal to 1025hz and increasing or decreasing the amplitude of the current signal in the 50hz frequency band.

[0064] In general, the controller in the embodiment of the present application can control the current signal whose frequency is close to the fundamental frequency of the power grid in the error current signal through the current loop, so as to realize the subsequent control of the current signal output from the power conversion circuit to adjust the amplitude of the current signal close to the fundamental frequency. At the same time, the controller in the embodiment of the present application also performs a separate resonance control on the current signal whose frequency is equal to the target frequency in the error current signal through the resonance control module, so as to realize the subsequent independent control of the target current signal output from the power conversion circuit to adjust the output end to reduce the amplitude, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal is increased.

[0065] In some feasible implementations, after the non-characteristic harmonic signal is injected into the power grid, in order to rapidly increase the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal and improve the response speed of the power conversion device, the power conversion device in the embodiment of the present application can detect the presence of a non-characteristic harmonic signal at the output end of the power conversion circuit through the controller, first, control the amplitude reduction rate of the target current signal output by the power conversion circuit to be greater than or equal to the first rate threshold. The first rate threshold can be understood as the maximum value of the reduction rate of the amplitude of the target current signal when the controller adjusts the amplitude of the target current signal to decrease without affecting the output characteristics of other harmonic signals output by the power conversion circuit. The specific value of the first rate threshold can be flexibly adjusted according to the actual application scenario, and the embodiments of the present application are not illustrated one by one here.

[0066] It can be understood that when the controller controls the decrease rate of the amplitude of the target current signal to be greater than or equal to the above-mentioned first rate threshold, the amplitude of the target current signal output by the power conversion circuit decreases rapidly, and the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases rapidly, thereby achieving a rapid response of the power conversion device.

[0067] In the power conversion device provided in the embodiment of the present application, the controller can control the amplitude of the target current signal output from the output end of the power conversion circuit to decrease rapidly by changing the resonance parameters of the resonance control module. The resonance control module can specifically be a proportional resonance controller, and the resonance parameters of the resonance control module can include resonance frequency, resonance bandwidth, resonance coefficient, etc.

[0068] In some feasible implementations, the transfer function of the resonance control module may be as shown in the following formula (1):

[0069]

[0070] Among them, k r is the resonance coefficient of the resonance control module, ω c is the resonant bandwidth, ω 0 The transfer function shown in formula (1) is only an example, and the transfer function of the resonance control module can be deformed according to different actual application scenarios, which is not limited in the embodiment of the present application.

[0071] It should be noted that the resonant bandwidth of the resonant control module refers to the range between the upper and lower limits of the resonant frequency, that is, the frequency range in which the resonant control module can perform resonant control. The smaller the resonant bandwidth, the better the frequency selectivity of the resonant control module, the purer the output signal frequency, but the stricter the requirements on the operating frequency. On the contrary, when the resonant bandwidth is larger, the oscillation response of the resonant control module will become wider, that is, the resonant control module can oscillate in a larger frequency range, so that the resonant control module maintains efficient signal transmission in a wider frequency range, thereby improving the response sensitivity of the resonant control module.

[0072] To this end, the controller adjusts the size of the resonant bandwidth of the resonant control module so that when the resonant control module performs resonant control with a larger resonant bandwidth, due to the high response sensitivity of the resonant control module, the controller controls the amplitude of the target current signal output by the power conversion circuit to be quickly reduced, thereby rapidly increasing the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal, thereby improving the response speed of the power conversion device.

[0073] In some feasible implementations, when the resonant bandwidth of the resonant control module takes a large value for a long time, it may have an adverse effect on other harmonic signals output by the power conversion circuit. To this end, in the embodiment of the present application, the controller can control the resonant bandwidth of the resonant control module to gradually decrease when the decrease rate of the amplitude of the target current signal is greater than or equal to the first rate threshold, so that the amplitude of the target current signal decreases rapidly, so as to reduce the response sensitivity of the resonant control module, so that the controller controls the amplitude decrease rate of the target current signal output by the power conversion circuit to gradually decrease, thereby achieving rapid response of the power conversion device while reducing the adverse effects on other harmonic signals and ensuring the stability of the power conversion device.

[0074] In some feasible implementations, the specific adjustment method of the controller to the resonance bandwidth of the resonance control module can be referred to in Figure 7a As shown, Figure 7a A schematic diagram of a resonance bandwidth of a resonance control module provided in an embodiment of the present application.

[0075] like Figure 7a As shown, assuming that at time t1, the controller detects that there is a non-characteristic harmonic signal at the output end of the power conversion circuit, the power conversion device starts the equivalent impedance adjustment function, and the controller adjusts the resonant bandwidth of the resonant control module to the first bandwidth threshold a, and the value of the first bandwidth threshold a is relatively large. At this time, please refer to Figure 5 As shown, the resonance control module can be based on the resonance bandwidth ω c, that is, the first bandwidth threshold a performs resonance control on the input error current signal. Since the value of the first bandwidth threshold a is relatively large, the controller can control the amplitude of the target current signal output by the power conversion circuit to decrease rapidly at a rate greater than or equal to the first rate threshold.

[0076] Furthermore, in order to reduce the adverse effects on other harmonic signals, Figure 7a When the time t2 shown in FIG. 1 arrives, the controller adjusts the resonance bandwidth of the resonance control module to the second bandwidth threshold b, and the value of the second bandwidth threshold b is less than the first bandwidth threshold a. Figure 5 As shown, the resonance control module can be based on the resonance bandwidth ω c , that is, the second bandwidth threshold b performs resonance control on the input error current signal. Since the value of the second bandwidth threshold b is small, the controller can control the amplitude reduction rate of the target current signal output by the power conversion circuit to decrease from the above-mentioned first rate threshold.

[0077] Further, in Figure 7a When the time t3 shown in FIG. 1 arrives, the controller adjusts the resonance bandwidth of the resonance control module to the third bandwidth threshold c, and the value of the third bandwidth threshold c is less than the second bandwidth threshold b. Figure 5 As shown, the resonance control module can be based on the resonance bandwidth ω c , that is, the third bandwidth threshold c performs resonance control on the input error current signal. Since the value of the third bandwidth threshold c is smaller, the controller can control the amplitude reduction rate of the target current signal output by the power conversion circuit to further decrease until the amplitude of the target current signal is reduced to 0.

[0078] In some feasible implementations, the specific manner in which the controller adjusts the resonance bandwidth of the resonance control module can also be found in Figure 7b As shown, Figure 7b A schematic diagram of another resonance bandwidth of the resonance control module provided in an embodiment of the present application.

[0079] like Figure 7b As shown, assuming that at time t1, the controller detects that there is a non-characteristic harmonic signal at the output end of the power conversion circuit, the power conversion device starts the equivalent impedance adjustment function, and the controller adjusts the resonant bandwidth of the resonance control module to the first bandwidth threshold a. At this time, Figure 5 As shown, the resonance control module can be based on the resonance bandwidth ω c , that is, the first bandwidth threshold a performs resonance control on the input error current signal, so that the controller controls the amplitude of the target current signal output by the power conversion circuit to decrease rapidly at a rate greater than or equal to the first rate threshold. Further, in order to reduce the adverse effects on other harmonic signals, such as Figure 7bAs shown, the controller adjusts the resonant bandwidth of the resonant control module to decrease from the first bandwidth threshold a, so that the controller controls the amplitude reduction rate of the target current signal output by the power conversion circuit to gradually decrease from the first rate threshold until the resonant bandwidth of the resonant control module is reduced to the third bandwidth threshold c. In this process, the controller controls the amplitude reduction rate of the target current signal output by the power conversion circuit to gradually decrease until the amplitude of the target current signal is reduced to 0.

[0080] In some feasible implementations, the specific manner in which the controller adjusts the resonance bandwidth of the resonance control module can also be found in Figure 7c As shown, Figure 7c A schematic diagram of another resonance bandwidth of the resonance control module provided in an embodiment of the present application.

[0081] like Figure 7c As shown, assuming that at time t1, the controller detects that there is a non-characteristic harmonic signal at the output end of the power conversion circuit, the power conversion device starts the equivalent impedance adjustment function, and the controller adjusts the resonant bandwidth of the resonance control module to the first bandwidth threshold a. The resonance control module can resonate the input error current signal based on the first bandwidth threshold a, so that the controller controls the amplitude of the target current signal output by the power conversion circuit to decrease rapidly at a rate greater than or equal to the first rate threshold. Furthermore, in order to reduce the adverse effects on other harmonic signals, such as Figure 7c As shown, the controller adjusts the resonant bandwidth of the resonant control module to gradually decrease from the first bandwidth threshold a at a certain decreasing rate, so that the amplitude decrease rate of the target current signal gradually decreases from the above-mentioned first rate threshold until the resonant bandwidth of the resonant control module is reduced to the above-mentioned third bandwidth threshold c. In this process, the controller controls the amplitude decrease rate of the target current signal output by the power conversion circuit to gradually decrease until the amplitude of the above-mentioned target current signal is reduced to 0.

[0082] It should be noted that the specific values ​​of the first bandwidth threshold a, the second bandwidth threshold b and the third bandwidth threshold c can be flexibly adjusted according to practical application scenarios. In addition, the controller can also adjust the resonance bandwidth of the resonance control module in more ways. Figure 7a , Figure 7b and Figure 7c Shown are examples only.

[0083] To facilitate understanding of the implementation process of the present application, the controller adjusts the resonant bandwidth of the resonant control module to rapidly reduce the amplitude of the target current signal output by the power conversion circuit. Figure 8 and Fig. 9 Give an example, Figure 8 A waveform diagram provided in an embodiment of the present application, Fig. 9Another waveform diagram provided for an embodiment of the present application.

[0084] In some feasible implementations, when the resonance bandwidth of the resonance control module is fixed, in order to produce adverse effects on other harmonic signals, the value of the resonance bandwidth is usually small. For example, Figure 8 As shown, the resonance bandwidth of the resonance control module is fixed to 0.1, and the voltage signal and current signal are electrical signals at the output end of the power conversion circuit. When the moment corresponding to 1s arrives, the voltage signal and current signal at the output end of the power conversion circuit begin to superimpose non-characteristic harmonic signals. The controller resonates the error current signal according to the resonance bandwidth of 0.1 through the resonance control module, so that the current signal amplitude of the non-characteristic harmonic signal is reduced. Figure 8 It can be seen that after the time corresponding to 1s arrives, the non-characteristic harmonic signal superimposed by the current signal output from the output end of the power conversion circuit begins to gradually decrease, while the non-characteristic harmonic signal superimposed by the voltage signal output from the output end of the power conversion circuit does not change. At the same time, due to the small value of the resonance bandwidth, the reduction rate of the non-characteristic harmonic signal superimposed by the current signal output by the power conversion circuit is slow, that is, the response speed of the power conversion device is slow.

[0085] In some feasible implementations, the controller provided in the embodiments of the present application can adjust the resonant bandwidth of the resonant control module so that the amplitude of the target current signal output by the power conversion circuit is rapidly reduced. For example, Fig. 9 As shown, the resonant bandwidth of the resonant control module can be reduced from 3 to 0, and the voltage signal and the current signal are electrical signals at the output end of the power conversion circuit. Specifically, when the moment corresponding to 1s arrives, the voltage signal and the current signal at the output end of the power conversion circuit begin to superimpose non-characteristic harmonic signals. At this time, the controller performs resonant control on the above-mentioned error current signal according to the resonant bandwidth equal to 1 through the resonant control module, so that the amplitude of the target current signal decreases rapidly. Furthermore, after the moment corresponding to 1s arrives, the controller can adjust the resonant bandwidth to gradually decrease, so that the reduction rate of the non-characteristic harmonic signal superimposed on the current signal output from the output end of the power conversion circuit gradually decreases. At the same time, the non-characteristic harmonic signal superimposed on the voltage signal output from the output end of the power conversion circuit does not change. It can be understood that because the controller adjusts the resonant bandwidth to a larger value, the current amplitude of the non-characteristic harmonic signal decreases rapidly. As shown Fig. 9As shown in the figure, after the arrival of the moment of 1.02s, the non-characteristic harmonic signal superimposed in the current signal has been greatly reduced. In other words, the power conversion device has a fast response speed, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal can be rapidly increased. At the same time, the controller can also gradually reduce the resonance bandwidth of the resonance control module by adjusting the resonance control module, reduce the response sensitivity of the resonance control module, and gradually reduce the amplitude reduction rate of the non-characteristic harmonic signal, thereby achieving a rapid response of the power conversion device while reducing the adverse effects on other harmonic signals and ensuring the stability of the power conversion device.

[0086] In some feasible implementations, when the power conversion device is connected to the power grid using a three-phase four-wire system or a three-phase five-wire system, the structure of the power conversion device can be as follows: Fig.10 As shown, Fig.10 Another schematic diagram of a power conversion device provided in an embodiment of the present application. Fig.10 The power conversion device shown includes a power conversion circuit and a controller. The input end of the power conversion circuit is connected to a DC power supply, and the output end of the power conversion circuit is connected to the power grid through live wire A, live wire B and live wire C. The DC power supply can exchange electric energy with the power grid through the power conversion circuit. From the above content, it can be seen that while transmitting electric energy, the power grid can also superimpose non-characteristic harmonic signals for transmission, for example, transmitting power carrier signals between different loads. In order to reduce the attenuation of the non-characteristic harmonic signal and extend the transmission distance of the non-characteristic harmonic signal, the power conversion device can control the power conversion circuit through the controller to adjust the amplitude of the output target current signal to decrease, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases.

[0087] In some feasible implementations, the power conversion device may further include a filter module, which is arranged between the power conversion circuit and the power grid. The filter module can filter out the noise and interference output by the power conversion circuit before providing it to the power grid, thereby improving the overall performance of the power conversion device. Specifically, the filter module may be composed of an inductor connected in series to live wire A, live wire B, and live wire C, and a capacitor connected across different live wires. In other application scenarios, the specific structure of the filter module can be flexibly adjusted, and the embodiments of the present application are not limited to this. In addition, the power conversion device may further include a grid-connected switch, which is used to switch to an on or off state, so that the power conversion device can be connected to the grid or off the grid.

[0088] It should be noted that the output end of the power conversion circuit may be a port where the power conversion circuit is connected to the filter module, or a port where the filter module is connected to the grid-connected switch, or a port where the filter module is connected to the grid. Fig.10As shown, the controller can detect whether there is a non-characteristic harmonic signal at the output end of the power conversion circuit by detecting the port connected between the power conversion circuit and the filter module, or by detecting the port connected between the filter module and the power grid, or by detecting the port connected between the filter module and the grid-connected switch.

[0089] Furthermore, from the above content, we can know that Fig.10 When the power conversion device shown detects the presence of a non-characteristic harmonic signal at the output end of the power conversion circuit through a controller, the equivalent impedance adjustment function relative to the non-characteristic harmonic signal can be started. Specifically, the controller can control the power conversion circuit to adjust the amplitude of the output target current signal to decrease, thereby increasing the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal.

[0090] Specifically, Fig.10 The specific structure and implementation principle of the controller shown can be found in Fig.11 As shown, Fig.11 Another schematic diagram of the framework of the controller provided in the embodiment of the present application. Fig.11 The controller shown includes an enabling module, a loop control module, a resonant control module and a modulation module. As can be seen from the above content, the loop control module can obtain the feedback current signal Ig at the output end of the power conversion circuit, and obtain the error current signal after subtracting the feedback current signal Ig from the reference current signal Iref, and output it to the resonant control module and the current loop. Among them, the above feedback current signal Ig can be understood as being obtained by the controller after coordinate transformation of the sampled current signal at the output end of the power conversion circuit. The above reference current signal Iref can be obtained by the controller after coordinate transformation of the basic current signal, and the basic current signal can be obtained by the controller according to the grid-connected power size of the power conversion equipment. Furthermore, the current loop is mainly used to control the current signal whose frequency is close to the fundamental frequency of the power grid in the input error current signal, and output the loop control voltage signal to the modulation module. At the same time, the resonant control module that receives the enabling signal can be based on the set resonant parameters, such as the resonant bandwidth ω c , after resonant control is performed on the error current signal, a modulated voltage signal corresponding to the current signal of the target frequency is output. The controller can perform inverse coordinate transformation on the modulated voltage signal and the loop control voltage signal and output them to the modulation module. The modulation module can generate a pulse width modulation signal PWM based on the voltage signal Ug, the modulated voltage signal and the loop control voltage signal after the inverse coordinate transformation, and the DC bus voltage Udc of the power conversion circuit to drive the switch tubes in each bridge arm of the power conversion circuit to operate, so that the amplitude of the target current signal output from the adjustment output end of the power conversion circuit is reduced.

[0091] In some feasible implementations, the above-mentioned coordinate transformation may specifically be to convert the signal of the three-phase AC system into a signal in a rotating coordinate system, and the inverse coordinate transformation is to convert the signal in the rotating coordinate system into a signal of the three-phase AC system. Alternatively, the above-mentioned coordinate transformation may also be a Clarke transformation, that is, to convert the signal of the three-phase AC system into a two-phase stationary coordinate system, and the inverse coordinate transformation may be to convert the two-phase stationary coordinate system back into a signal of the three-phase AC system. It is understandable that the controller can flexibly adjust the specific implementation method of the coordinate transformation according to the actual application scenario, and the embodiments of the present application are not limited to this.

[0092] Understandably, Fig.11 In the controller shown in FIG. 1 , the specific implementation principles of the enabling module, the resonance control module, the loop control module and the modulation module can be referred to in the above Figures 4 to 9 The specific implementation method of the present application will not be described in detail here.

[0093] In general, the power conversion device provided in the embodiment of the present application can start the adjustment function of the equivalent impedance of the non-characteristic harmonic signal when the controller detects the presence of a non-characteristic harmonic signal in the power grid. Specifically, the power conversion device can control the amplitude of the target current signal output by the power conversion circuit to decrease through the controller, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases, thereby avoiding the non-characteristic harmonic signal from being greatly attenuated through the power conversion device, extending the transmission distance of the non-characteristic harmonic signal and improving the communication quality of the grid-connected system, and having strong applicability. Furthermore, in order to enable the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal to increase rapidly and improve the response speed of the power conversion device, the power conversion device can also control the decrease rate of the amplitude of the target current signal output by the power conversion circuit to be greater than or equal to the first rate threshold after the controller detects the presence of a non-characteristic harmonic signal at the output end of the power conversion circuit through the controller. It can be understood that when the rate of decrease of the amplitude of the target current signal is greater than or equal to the above-mentioned first rate threshold, the amplitude of the target current signal output by the power conversion device decreases rapidly, and the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases rapidly, thereby achieving a rapid response of the power conversion device. At the same time, the power change device in the embodiment of the present application can also reduce the controller reaction sensitivity by gradually reducing the resonant bandwidth during the rapid decrease of the amplitude of the target current signal through the controller, so that the amplitude decrease rate of the target current signal gradually decreases, thereby achieving a rapid response of the power conversion device while reducing the adverse effects on other harmonic signals and ensuring the stability of the power conversion device. In addition, in the embodiment of the present application, when the power conversion device detects through the controller that there is no non-characteristic harmonic signal at the output end of the power conversion circuit, the adjustment function of the equivalent impedance relative to the non-characteristic harmonic signal can be disabled, thereby reducing the adverse effects on other harmonic signals in the power grid.

[0094] See also Fig.12 , Fig.12 A schematic diagram of a flow chart of a control method for a power conversion device provided in an embodiment of the present application. The control method for a power conversion device provided in an embodiment of the present application is applicable to Figures 3 to 11 Specifically, the control method of the power conversion device may include the steps of:

[0095] S101, detecting an electrical signal at an output end of a power conversion circuit.

[0096] It is understandable that when the power conversion device detects the presence of non-characteristic harmonic signals in the power grid, it can start the adjustment function of the equivalent impedance of the non-characteristic harmonic signals to reduce the adverse effects on other harmonic signals in the power grid.

[0097] The specific implementation of S102 can refer to the above Figures 3 to 11 The implementation method executed by the controller in the embodiment of the present application will not be repeated here.

[0098] S102. When a non-characteristic harmonic signal is detected at the output end of the power conversion circuit, the power conversion circuit is controlled to adjust the amplitude of the target current signal in the output current signal to decrease, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases.

[0099] It can be understood that the non-characteristic harmonic signal is a harmonic signal transmitted between loads in the power grid, the frequency of the non-characteristic harmonic signal is a non-integer multiple of the fundamental frequency of the power grid, the target current signal is a current signal with a frequency equal to the target frequency, and the target frequency is obtained by the frequency of the non-characteristic harmonic signal. When the power conversion device detects the presence of a non-characteristic harmonic signal in the power grid, it controls the amplitude of the target current signal output by the power conversion circuit to decrease so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases, thereby avoiding a significant attenuation of the non-characteristic harmonic signal through the power conversion device and extending the transmission distance of the non-characteristic harmonic signal. Exemplarily, when the non-characteristic harmonic signal is transmitted in the power grid as a power carrier signal, the power conversion device provided in the embodiment of the present application can improve the communication quality by increasing the equivalent impedance relative to the power carrier signal, and has strong applicability.

[0100] The specific implementation of S102 can refer to the above Figures 3 to 11 The implementation method executed by the controller in the embodiment of the present application will not be repeated here.

[0101] In an optional embodiment, the power conversion circuit is controlled to reduce the amplitude of a target current signal in a current signal output by a DC power regulation system provided by a DC power supply, including: controlling the reduction rate of the amplitude of the target current signal to be greater than or equal to a first rate threshold, and in the process of reducing the amplitude of the target current signal, controlling the reduction rate of the amplitude of the target current signal to gradually decrease.

[0102] It is understandable that the power conversion device can control the amplitude reduction rate of the target current signal output by the power conversion circuit to be greater than or equal to the first rate threshold, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases rapidly, thereby improving the response speed of the power conversion device. Furthermore, in the process of reducing the amplitude of the target current signal, the power conversion device controls the amplitude reduction rate of the target current signal through the controller to gradually decrease, while reducing the adverse effects of other harmonic signals, thereby ensuring the stability of the power conversion device.

[0103] In an optional embodiment, controlling the power conversion circuit to reduce the amplitude of a target current signal in a current signal outputted by a DC power supply based on the DC power regulation includes: obtaining an error current signal based on a difference between a reference current signal and a feedback current signal at an output end of the power conversion circuit, and obtaining a modulation voltage signal based on a resonance coefficient, a resonance bandwidth, a resonance frequency, and the error current signal of a resonance control module; controlling the power conversion circuit to reduce the amplitude of the target current signal based on the modulation voltage signal; and the modulation voltage signal satisfies:

[0104]

[0105] Where s is the error current signal, H(s) is the modulation voltage signal, and k r is the resonance coefficient, ω c is the resonant bandwidth, ω 0 is the resonant frequency.

[0106] It can be understood that the power conversion device can control the amplitude of the target current signal to decrease based on the resonance parameters, the reference current signal and the feedback current signal at the output end of the power conversion circuit, etc. The implementation principle is simple and the reliability is strong.

[0107] In an optional embodiment, the control method also includes: performing coordinate transformation on the sampled current signal at the output end of the power conversion circuit to obtain a feedback current signal, performing coordinate transformation on the basic current signal to obtain a reference current signal, and performing inverse coordinate transformation on the voltage signal obtained based on the resonance coefficient, resonance bandwidth, resonance frequency and error current signal to obtain a modulated voltage signal; the basic current signal is obtained from the grid-connected power of the power conversion circuit.

[0108] It can be understood that when the power conversion circuit is connected to the power grid using a three-phase system, the controller can process current signals of different phases by using coordinate transformation and inverse coordinate transformation, which has rich application scenarios and strong applicability.

[0109] In an optional embodiment, the size of the resonant bandwidth is proportional to the rate of decrease of the amplitude of the target current signal; the amplitude of the target current signal in the current signal output by the power conversion circuit based on the DC power provided by the DC power supply is reduced, including: in the process of controlling the power conversion circuit to adjust the amplitude of the target current signal to decrease, the resonant bandwidth is adjusted to gradually decrease so that the rate of decrease of the amplitude of the target current signal gradually decreases.

[0110] It is understandable that the power conversion device can adjust the reaction sensitivity by adjusting the resonance bandwidth. In the process of decreasing the amplitude of the target current signal, the power conversion device can reduce the reaction sensitivity by adjusting the resonance bandwidth to gradually decrease, so that the amplitude reduction rate of the target current signal gradually decreases, thereby achieving a rapid response of the power conversion device while reducing the adverse effects on other harmonic signals and ensuring the stability of the power conversion device.

[0111] In an optional embodiment, the presence of a non-characteristic harmonic signal at the output end of a power conversion circuit is detected, including: when it is detected that the frequency of the voltage signal at the output end of the power conversion circuit is a target frequency and the signal amplitude is greater than or equal to an amplitude threshold, obtaining the presence of a non-characteristic harmonic signal at the output end of the power conversion circuit.

[0112] It can be understood that the power conversion device determines whether there is a non-characteristic harmonic signal at the output end of the power conversion circuit by detecting whether the voltage signal at the output end of the power conversion circuit reaches the amplitude threshold. The implementation principle is simple and the applicability is strong.

Claims

1. A power conversion device, characterized in that: The power conversion device comprises a power conversion circuit and a controller, wherein the input end of the power conversion circuit is used to connect to a DC power supply, the output end of the power conversion circuit is connected to a power grid, and the controller is used to: When a non-characteristic harmonic signal is detected at the output end of the power conversion circuit, the amplitude of a target current signal in the current signal adjusted by the power conversion circuit is controlled to decrease, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases; Among them, the non-characteristic harmonic signal is a harmonic signal transmitted between loads in the power grid, the frequency of the non-characteristic harmonic signal is a non-integer multiple of the fundamental frequency of the power grid, the target current signal is a current signal with a frequency equal to the target frequency, and the target frequency is equal to the frequency of the non-characteristic harmonic signal.

2. The power conversion device according to claim 1, characterized in that: The controller controls the power conversion circuit to reduce the amplitude of a target current signal in a current signal outputted by the DC power supply based on the DC power regulation, specifically for: The decreasing rate of the amplitude of the target current signal is controlled to be greater than or equal to a first rate threshold, and in the process of decreasing the amplitude of the target current signal, the decreasing rate of the amplitude of the target current signal is controlled to gradually decrease.

3. The power conversion device according to claim 1 or 2, characterized in that: The controller controls the power conversion circuit to reduce the amplitude of a target current signal in a current signal outputted by the DC power supply based on the DC power regulation, specifically for: An error current signal is obtained based on the difference between a reference current signal and a feedback current signal at the output end of the power conversion circuit, and a modulation voltage signal is obtained based on a resonance coefficient, a resonance bandwidth, a resonance frequency of a resonance control module in the controller and the error current signal; the power conversion circuit is controlled based on the modulation voltage signal to adjust the amplitude of the target current signal to decrease; the modulation voltage signal satisfies: Wherein, s is the error current signal, H(s) is the modulation voltage signal, k r is the resonance coefficient, ω c is the resonance bandwidth, and ω0 is the resonance frequency.

4. The power conversion device according to claim 3, characterized in that: The controller is also used for: Performing coordinate transformation on the sampled current signal at the output end of the power conversion circuit to obtain the feedback current signal; The reference current signal is obtained by performing coordinate transformation on the basic current signal, wherein the basic current signal is obtained from the grid-connected power of the power conversion circuit; The modulated voltage signal is obtained by performing an inverse coordinate transformation on a voltage signal obtained based on the resonance coefficient, the resonance bandwidth, the resonance frequency and the error current signal.

5. The power conversion device according to claim 3 or 4, characterized in that: The size of the resonance bandwidth is proportional to the rate of decrease of the amplitude of the target current signal; the controller controls the power conversion circuit to reduce the amplitude of the target current signal in the current signal output based on the DC power provided by the DC power supply, specifically for: In the process of controlling the power conversion circuit to adjust the amplitude of the target current signal to decrease, the resonance bandwidth is adjusted to gradually decrease so that the decreasing rate of the amplitude of the target current signal gradually decreases.

6. The power conversion device according to any one of claims 1 to 5, characterized in that: The controller detects that a non-characteristic harmonic signal exists at the output end of the power conversion circuit, and is specifically used to: The voltage signal at the output end of the power conversion circuit is detected, and when it is detected that the frequency of the voltage signal is the target frequency and the signal amplitude is greater than or equal to the amplitude threshold, it is obtained that a non-characteristic harmonic signal exists at the output end of the power conversion circuit.

7. A grid-connected system, characterized in that: The grid-connected system comprises the power conversion device according to any one of claims 1 to 6, wherein the DC end of the power conversion device is used to connect to a DC power supply, and the AC end of the power conversion device is used to connect to a power grid.

8. A control method for a power conversion device, characterized in that: The power conversion device includes a power conversion circuit, the input end of the power conversion circuit is used to connect to a DC power supply, and the output end of the power conversion circuit is connected to a power grid; the control method includes: Detecting an electrical signal at an output end of the power conversion circuit; When a non-characteristic harmonic signal is detected at the output end of the power conversion circuit, the amplitude of a target current signal in the current signal adjusted by the power conversion circuit is controlled to decrease, so that the equivalent impedance of the power conversion device relative to the non-characteristic harmonic signal increases; Among them, the non-characteristic harmonic signal is a harmonic signal transmitted between loads in the power grid, the frequency of the non-characteristic harmonic signal is a non-integer multiple of the fundamental frequency of the power grid, the target current signal is a current signal with a frequency equal to the target frequency, and the target frequency is equal to the frequency of the non-characteristic harmonic signal.

9. The control method according to claim 8, characterized in that: The controlling the power conversion circuit to reduce the amplitude of a target current signal in a current signal outputted by the DC power supply based on the DC power regulation comprises: The decreasing rate of the amplitude of the target current signal is controlled to be greater than or equal to a first rate threshold, and in the process of decreasing the amplitude of the target current signal, the decreasing rate of the amplitude of the target current signal is controlled to gradually decrease.

10. The control method according to claim 8 or 9, characterized in that: The controlling the power conversion circuit to reduce the amplitude of a target current signal in a current signal outputted by the DC power supply based on the DC power regulation comprises: An error current signal is obtained based on the difference between a reference current signal and a feedback current signal at the output end of the power conversion circuit, and a modulation voltage signal is obtained based on a resonance coefficient, a resonance bandwidth, a resonance frequency of a resonance control module and the error current signal; the power conversion circuit is controlled based on the modulation voltage signal to adjust the amplitude of the target current signal to decrease; the modulation voltage signal satisfies: Wherein, s is the error current signal, H(s) is the modulation voltage signal, k r is the resonance coefficient, ω c is the resonance bandwidth, and ω0 is the resonance frequency.

11. The control method according to claim 10, characterized in that: The control method further comprises: The feedback current signal is obtained by performing coordinate transformation on the sampled current signal at the output end of the power conversion circuit, the reference current signal is obtained by performing coordinate transformation on the basic current signal, and the modulated voltage signal is obtained by performing inverse coordinate transformation on the voltage signal obtained based on the resonance coefficient, the resonance bandwidth, the resonance frequency and the error current signal; the basic current signal is obtained by the grid-connected power of the power conversion circuit.

12. The control method according to claim 10 or 11, characterized in that: The size of the resonance bandwidth is proportional to the rate of decrease of the amplitude of the target current signal; the control of the power conversion circuit to reduce the amplitude of the target current signal in the current signal output based on the DC power provided by the DC power supply comprises: In the process of controlling the power conversion circuit to adjust the amplitude of the target current signal to decrease, the resonance bandwidth is adjusted to gradually decrease so that the decreasing rate of the amplitude of the target current signal gradually decreases.

13. The control method according to any one of claims 8 to 12, characterized in that: The detecting that a non-characteristic harmonic signal exists at the output end of the power conversion circuit includes: When it is detected that the frequency of the voltage signal at the output end of the power conversion circuit is the target frequency and the signal amplitude is greater than or equal to the amplitude threshold, it is obtained that a non-characteristic harmonic signal exists at the output end of the power conversion circuit.

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