Power conversion system

Abstract

The invention provides a power conversion system comprising a bidirectional cascade DC-DC module which is connected to a DC power supply with a wide voltage range through an input side protection module; the voltage detection module is used for detecting an output voltage value of the bidirectional cascade DC-DC module; the DC-DC controller is used for acquiring a voltage difference value between the output voltage value and a target voltage value, adaptively adjusting an input side gain value according to the voltage difference value, and adjusting the output voltage value of the bidirectional cascade DC-DC module to the target voltage value; the input end of the DC-AC module is connected to the output end of the bidirectional cascade DC-DC module, and the output end of the DC-AC module is connected to a power grid through an output side protection module; the digital phase-locked loop is used for detecting a phase difference value between an output voltage phase of the DC-AC module and a voltage phase of the power grid; the DC-AC controller is used for adaptively adjusting an output side gain value according to the phase difference value, so that the output voltage phase of the DC-AC module is synchronized with the voltage phase of the power grid; and the DSP controller is respectively connected to the DC-DC controller and the DC-AC controller, and the DSP controller is used as a master controller for realizing operation logic and protection functions of the whole system.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply systems, and in particular to a power conversion system of a backup power supply converter-level grid-connected strategy capable of realizing power supply in a wide voltage range. Background Art

[0002] Power electronics technology is an important part of modern power systems. It mainly studies how to effectively convert, control and transmit electrical energy. Among them, power supply technology and inverter technology are important branches of power electronics technology, which respectively study how to generate and control electrical energy.

[0003] The existing power conversion system (PCS) mainly adopts unidirectional DC-DC technology and two-level inverter technology. Unidirectional DC-DC technology can realize the unidirectional flow of electric energy, while two-level inverter technology can generate sinusoidal wave output. These two technologies have been widely used in the fields of power electronics technology and power supply technology.

[0004] There are some problems with the existing PCS technology. First, the unidirectional DC-DC technology can only realize the unidirectional flow of electric energy, which cannot meet the application requirements of some applications that require bidirectional flow of electric energy. Secondly, the output voltage generated by the two-level inverter technology contains a large number of harmonics, which not only affects the quality of electric energy, but also may cause pollution to the power grid. In addition, the reliability and efficiency of the existing PCS technology need to be improved, which to a certain extent limits its application in the power system. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a power conversion system which can realize a backup power converter-level grid-connected strategy for power supply in a wide voltage range, so as to improve the efficiency and reliability of the equipment.

[0006] In order to solve the above problems, the present invention provides a power conversion system, comprising: a bidirectional cascade DC-DC module, connected to a DC power supply with a wide voltage range through an input side protection module, the voltage range of the DC power supply being 550V to 1100V; a voltage detection module, used to detect the output voltage value of the bidirectional cascade DC-DC module; a DC-DC controller, used to obtain the voltage difference between the output voltage value of the bidirectional cascade DC-DC module and the target voltage value, and adaptively adjust the input side gain value according to the voltage difference, and control the operation of the bidirectional cascade DC-DC module to adjust the output voltage value of the bidirectional cascade DC-DC module to the target voltage value; a DC-AC A module, whose input end is connected to the output end of the bidirectional cascade DC-DC module, and whose output end is connected to the power grid through the output side protection module; a digital phase-locked loop, used to detect the phase difference between the output voltage phase of the DC-AC module and the voltage phase of the power grid; a DC-AC controller, used to adaptively adjust the output side gain value according to the phase difference, and control the operation of the DC-AC module so that the output voltage phase of the DC-AC module is synchronized with the voltage phase of the power grid; a DSP controller, respectively connected to the DC-DC controller and the DC-AC controller, and the DSP controller is used as a master controller to realize the overall operation logic and protection functions of the system.

[0007] The beneficial effects of the technical solution of the above embodiment of the present invention are as follows:

[0008] 1. Improve reliability: By adopting bidirectional cascade DC-DC technology and neutral point clamped three-level inverter technology, bidirectional flow of electric energy can be achieved, improving the reliability of PCS. Compared with the existing unidirectional DC-DC technology, the present invention can meet more application requirements that require bidirectional flow of electric energy.

[0009] 2. Improve efficiency: By adopting bidirectional cascade DC-DC technology and neutral point clamped three-level inverter technology, high-quality sinusoidal wave output can be generated, harmonic content is reduced, and the quality of electric energy is improved. Compared with the existing two-level inverter technology, the present invention can reduce the pollution to the power grid.

[0010] 3. The two-layer control system mainly composed of DC-DC controller, DC-AC controller and DSP controller improves the reliability and stability of the system.

[0011] 4. Use adaptive gain adjustment to flexibly control the output voltage value after boosting to the target voltage value.

[0012] 5. The introduction of digital phase-locked loop, digital filter and adaptive gain enables the inverter voltage to track the grid voltage in real time, thus improving the reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0014] Figure 1 A schematic diagram of the architecture of a power conversion system provided by an embodiment of the present invention;

[0015] Figure 2 A circuit connection diagram of a power conversion system provided by an embodiment of the present invention;

[0016] Figure 3 for Figure 2 An enlarged schematic diagram of the bidirectional cascade DC-DC module and the input side protection module;

[0017] Figure 4 for Figure 2 A magnified schematic diagram of the DC-AC module;

[0018] Figure 5 for Figure 2 Enlarged schematic diagram of the output side protection module. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] An embodiment of the present invention provides a power conversion system.

[0021] Please also read Figure 1 to Figure 5 ,in, Figure 1 A schematic diagram of the architecture of a power conversion system provided by an embodiment of the present invention. Figure 2 A circuit connection diagram of a power conversion system provided by an embodiment of the present invention, Figure 3 for Figure 2 The enlarged schematic diagram of the bidirectional cascade DC-DC module and the input side protection module. Figure 4 for Figure 2 An enlarged schematic diagram of the DC-AC module in the figure. Figure 5 for Figure 2 Enlarged schematic diagram of the output side protection module.

[0022] like Figure 1 As shown, the power conversion system described in this embodiment includes: a bidirectional cascade DC-DC module 11, a voltage detection module 12, a DC-DC controller 13, a DC-AC module 14, a digital phase-locked loop 15, a DC-AC controller 16 and a DSP controller 17.

[0023] Specifically, the bidirectional cascade DC-DC module 11 is connected to a DC power supply 10 with a wide voltage range through an input side protection module 181, and the voltage range of the DC power supply is 550V to 1100V. The voltage detection module 12 is used to detect the output voltage value of the bidirectional cascade DC-DC module 11. The DC-DC controller 13 is used to obtain the voltage difference between the output voltage value of the bidirectional cascade DC-DC module 11 and the target voltage value, and adaptively adjust the input side gain value according to the voltage difference to control the operation of the bidirectional cascade DC-DC module 11 to adjust the output voltage value of the bidirectional cascade DC-DC module 11 to the target voltage value. The input end of the DC-AC module 14 is connected to the output end of the bidirectional cascade DC-DC module 11, and its output end is connected to the power grid 19 through the output side protection module 182. The digital phase-locked loop (DPLL) 15 is used to detect the phase difference between the output voltage phase of the DC-AC module 14 and the voltage phase of the power grid 19. The DC-AC controller 16 is used to adaptively adjust the output side gain value according to the phase difference value, and control the operation of the DC-AC module 14, so that the output voltage phase of the DC-AC module 14 is synchronized with the voltage phase of the power grid 19. The DSP controller 17 is connected to the DC-DC controller 13 and the DC-AC controller 16 respectively, and the DSP controller 17 is used as a master controller to realize the operation logic and protection functions of the whole system.

[0024] In some embodiments, the DC power supply 10 is composed of a plurality of battery packs connected in series. The battery pack is composed of a plurality of battery cells and is used to provide a large capacity of power supply.

[0025] In some embodiments, the bidirectional cascade DC-DC module 11 includes a bidirectional cascade circuit (such as a bidirectional cascade circuit) composed of cascaded multi-channel IGBT devices and diodes. Figure 2 and Figure 3 As shown in FIG. 1 , each path of the bidirectional cascade circuit includes two IGBT devices IGBT_i connected in series, and each IGBT device IGBT_i is connected in parallel with a diode D_i. The voltage detection module 12 uses an output side voltage sensor VOLT2 (as shown in FIG. 1 ) disposed on the output side of the bidirectional cascade DC-DC module 11. Figure 2As shown), a first IGBT driving module 131 is provided between the DC-DC controller 13 and the bidirectional cascade DC-DC module 11. The output side voltage sensor VOLT2 is used to measure the output voltage of the bidirectional cascade DC-DC module 11 and convert it into an electrical signal that can be recognized by the DC-DC controller 13 and then transmit it to the DC-DC controller 13 as the output voltage value of the bidirectional cascade DC-DC module 11. The DC-DC controller 13 calculates the voltage difference between the received output voltage value of the bidirectional cascade DC-DC module 11 and the target voltage value, adaptively adjusts the input side gain value according to the voltage difference and generates a first control signal. The first IGBT driving module 131 receives and outputs a PWM signal with a corresponding duty cycle according to the first control signal to drive and control the on and off of the IGBT device of the bidirectional cascade DC-DC module 11, thereby adjusting the output voltage value of the bidirectional cascade DC-DC module 11 to the target voltage value. In the field of power supply technology, the bidirectional cascade DC-DC technology is an important power conversion technology, which can realize the bidirectional flow of electric energy and has the advantages of high efficiency and high power density. The output voltage value of the bidirectional cascade DC-DC module 11 can be adjusted by controlling the on and off of the IGBT (Insulated Gate Bipolar Transistor) device, so that the corresponding output voltage is maintained at the target voltage (for example, about 1750V). For example, the duty cycle of the PWM signal can be increased to prolong the closing time of the IGBT device (that is, the on time of the IGBT device becomes longer), thereby increasing the output voltage and maintaining it near the target voltage.

[0026] In some embodiments, the DC-DC controller 13 adaptively adjusts the input side gain value according to the voltage difference between the output voltage value of the bidirectional cascade DC-DC module 11 and the target voltage value using the following formula:

[0027] K p11 =K p10 +α1·|Δu|

[0028] K i11 =K i10 +β1·|Δu|

[0029] Among them, K p10 is the basic proportional gain value, K i10 is the basic integral gain value, α1 and β1 are the corresponding gain adjustment coefficients, and Δu is the voltage difference. K p11 , K i11 The parameter is affected by the voltage difference between the actual output voltage of the bidirectional cascade DC-DC module 11 and a given target voltage.

[0030] The specific adjustment process of adaptive adjustment includes: voltage detection link, difference calculation link, controller link and IGBT control link. 1) Voltage detection link: By setting an output side voltage sensor 121 on the output side of the bidirectional cascade DC-DC module 11, it can directly measure the output voltage and convert it into an electrical signal (such as a voltage signal or a digital signal) that can be recognized by the DC-DC controller 13, and then transmit it to the DC-DC controller 13. In other embodiments, a voltage divider resistor network can also be used for output voltage detection. The voltage divider resistor network divides the output high voltage so that the high voltage is reduced to the input range of the DC-DC controller 13, so that it can be collected by the DC-DC controller 13. 2) Difference calculation link: The DC-DC controller 13 receives the actual detected output voltage value and the given target voltage value, and then calculates the voltage difference between the two. This voltage difference is a key control signal. Its size and positive and negative directions determine how to control the on and off of the IGBT device of the bidirectional cascade DC-DC module 11 in the future. 3) Controller link: The DC-DC controller 13 generates a control signal according to the voltage difference to adjust the on and off of the IGBT device. The DC-DC controller 13 can use some control algorithms to generate control signals according to the voltage difference, such as proportional-integral-differential (PID) control algorithm. 4) IGBT control link: The control signal generated by the DC-DC controller 13 is sent to the first IGBT drive module 131, and the first IGBT drive module 131 converts the control signal into a suitable voltage and current signal to drive the on and off of the IGBT device. For example, when the voltage difference is positive and large enough, the IGBT device is driven to turn on to increase the output voltage; when the voltage difference is negative or a small positive value, the IGBT device is driven to turn off or reduce the on time, so that the output voltage drops. By continuously adjusting the on and off state of the IGBT device according to the voltage difference, the output voltage value will gradually approach the given target voltage value. This process is a dynamic cycle process, through continuous detection, calculation and adjustment, until the output voltage value stabilizes near the target voltage value.

[0031] like Figure 2 and Figure 3 As shown, in some embodiments, the input side protection module 181 includes: an input side isolating switch QF1, input side fuses FU1, FU2, an input side DC contactor KM1, a plurality of Hall sensors HALL0, HALL1~HALLn, and an input side voltage sensor VOLT1.

[0032] Specifically, one end of the input side isolation switch QF1 is connected to the DC power supply 10, and the other end is coupled to the bidirectional cascade DC-DC module 11 through the input side fuses FU1, FU2 and the input side DC contactor KM1. The input side isolation switch QF1 is used to switch and connect the connection between the bidirectional cascade DC-DC module 11 and the DC power supply 10. Among the multiple Hall sensors HALL0, HALL1~HALLn, one Hall sensor HALL0 is used to collect the current of the DC power supply 10 and transmit it to the DC-DC controller 13, and the Hall sensors HALL1~HALLn respectively collect the current of each input end of the bidirectional cascade circuit and transmit it to the DC-DC controller 13 to realize the protection function according to whether the currents of each path are balanced. The input side voltage sensor VOLT1 is used to detect whether the DC power supply 10 has voltage input, and transmit it to the DC-DC controller 13 to start the bidirectional cascade DC-DC module 11 when there is voltage input. The protection mechanisms of the input side protection module 181 may refer to the prior art and will not be described in detail here.

[0033] In some embodiments, the DC-AC module 14 includes a three-level neutral point clamped inverter circuit (such as Figure 2 and Figure 4As shown), each path of the three-level neutral point clamped inverter circuit includes a plurality of (for example, 4) IGBT devices IGBT_o connected in series, each IGBT device IGBT_o is connected in parallel with a diode D_o, and the two IGBT devices IGBT_o in the middle of each path of IGBT devices are further connected in parallel with a resistor R_o, and a diode string (the diode string is composed of two diodes D_o connected in series), and each path of IGBT devices is further connected in parallel with a capacitor string (the capacitor string is composed of two capacitors C_o connected in series). A second IGBT driving module 161 is provided between the DC-AC controller 16 and the DC-AC module 14. The DC-AC controller 16 adaptively adjusts the output side gain value and generates a second control signal according to the phase difference value transmitted by the digital phase-locked loop 15; the second IGBT driving module 161 receives and outputs a PWM signal with a corresponding duty cycle according to the second control signal to drive and control the IGBT device of the DC-AC module 14 to be turned on in advance or delayed, thereby adjusting the output voltage phase of the DC-AC module 14 to be synchronized with the voltage phase of the power grid 19. In the field of inverter technology, the neutral point clamped three-level inverter technology is an advanced inverter technology that can generate high-quality sinusoidal wave output with the advantages of low harmonic content and high power factor. For a three-level inverter, the magnitude and phase of its output voltage are determined by the switching state of the IGBT device, and the purpose of phase locking can be achieved by controlling the early conduction or delayed conduction of the IGBT device. The DC-AC controller 16 can change the phase of the output voltage by adjusting the on and off moments of the IGBT device. For example, the duty cycle or phase shift angle of the pulse width modulation (PWM) signal of the IGBT device can be changed according to the control signal. If the phase difference value indicates that the output voltage phase lags behind the grid voltage phase, the PWM signal is adjusted to advance the switching action of the IGBT device, thereby advancing the output voltage phase and gradually reducing the phase difference with the grid voltage.

[0034] By detecting the grid information (which can be detected by setting up an additional voltage detection board), the grid voltage is detected in real time to obtain information such as the voltage amplitude, phase and frequency. By introducing digital phase-locked loop technology and taking advantage of digital signal processing, the accuracy and response speed of phase tracking are improved to achieve three-phase grid connection.

[0035] The following is a specific example to demonstrate how to achieve efficient phase tracking in the three-phase grid-connected process through DPLL.

[0036] 1) Basic model of digital phase-locked loop

[0037] Assume that the three-phase voltage signal is:

[0038] V a (t) = V mcos(ωt+θ a )

[0039]

[0040] Where ω is the angular frequency of the signal, θ a ,θ b ,θ c It's the phase.

[0041] 2) Clarke and Park transform

[0042] To simplify phase detection, the three-phase signal can be converted to the α-β coordinate system by Clarke transformation:

[0043]

[0044] Next, the signal is converted to the dq coordinate system through Park transformation to convert the rotating three-phase system into a DC quantity:

[0045]

[0046] in, is the rotation angle of the voltage vector.

[0047] 3) Improvement of phase-locking algorithm

[0048] A phase-locked loop can be constructed using the above dq transformation. A conventional DPLL uses a phase detector to detect the phase difference between the input signal and the locally generated signal, and corrects it through a control loop. The digital phase-locked loop 15 described in this embodiment uses an improved DPLL algorithm based on enhanced proportional integral (EPI) control to improve response speed and tracking accuracy.

[0049] The control equation is specifically:

[0050] Δθ(t)=K p V q +K i ∫0 t V q (τ)dτ

[0051] Where Δθ(t) is the phase error, V q is the q-axis component after dq transformation, K p is the proportional gain, K i is the integral gain. V q It reflects the phase difference of the signal.

[0052] In order to further improve the phase-locking performance, this embodiment introduces an adaptive gain adjustment mechanism, and the DC-AC controller 16 adaptively adjusts the output side gain value according to the phase difference between the output voltage of the DC-AC module 14 and the grid voltage phase to optimize the tracking effect. Specifically, the following formula is used:

[0053] K p21 =K p20 +α2·|Δθ(t)|

[0054] K i21 =K i20 +β2·|Δθ(t)|

[0055] Among them, K p20 is the basic proportional gain value, K i20 is the basic integral gain value, α2 and β2 are the corresponding gain adjustment coefficients, and Δθ(t) is the phase error. K p21 , K i21 The parameter is affected by the phase difference between the actual output voltage phase of the DC-AC module 14 and the voltage phase of the power grid.

[0056] The DC-AC controller 16 adaptively adjusts the output side gain value according to the phase difference value, adjusts and controls the duty cycle of the second IGBT driving module 161, so that the IGBT device of the DC-AC module 14 is turned on in advance or delayed, so as to achieve the purpose of phase locking, so that the output voltage phase of the DC-AC module is synchronized with the voltage phase of the power grid.

[0057] 4) Digital filter design

[0058] In order to eliminate high-frequency noise and harmonic interference, a digital filter DF1 (such as Figure 2 As shown), the digital filter is used to eliminate high-frequency noise and harmonic interference in the signal. The filter coefficient of the digital filter is adjusted in real time by the minimum mean square error algorithm (LMS):

[0059] h(n+1)=h(n)+μ·e(n)·x(n)

[0060] Where h(n) is the filter coefficient, e(n) is the current error signal, x(n) is the input signal, and μ is the step size factor used to control the learning rate.

[0061] The digital filter DF1 can use an adaptive FIR filter to pre-process the input signal. The design goal of the FIR filter is to retain the phase information of the signal to the maximum extent while suppressing high-frequency interference. Its filter coefficients can be adjusted in real time through the aforementioned minimum mean square error algorithm.

[0062] like Figure 2 and Figure 5 As shown, in some embodiments, the output side protection module 182 includes: an output side isolating switch QF2, output side fuses FU3, FU4, FU5, output side DC contactors KM2, KM3, an LC filter LC1 and three current transformers CT1, CT2, CT3.

[0063] Specifically, one end of the output side isolating switch QF2 is connected to the power grid 19, and the other end is coupled to the DC-AC module 14 through the output side fuses FU3, FU4, FU5, the output side DC contactors KM2, KM3, and the LC filter LC1. The output side isolating switch QF2 is used to switch and connect the connection between the DC-AC module 14 and the power grid 19. The LC filter LC1 is used to filter out high-frequency harmonics in the output voltage of the DC-AC module 14. The three current transformers CT1, CT2, and CT3 respectively collect the three output currents of the three-level neutral point clamped inverter circuit and transmit them to the DC-AC controller 16 to implement the protection function according to whether the three output currents are balanced. Specifically, each current transformer is connected to the common end of the two IGBT devices in the middle of the corresponding IGBT device. The various protection mechanisms of the output side protection module 182 can refer to the prior art and will not be repeated here.

[0064] In addition to solving the phase synchronization problem, the grid-connected strategy may also need to solve the frequency matching problem, the voltage amplitude matching problem, the power control problem and the power quality problem. In some embodiments, the power conversion system also includes at least one of a frequency control module, a voltage amplitude control module, a power control module and a power quality control module.

[0065] The frequency control module is used to monitor the frequency difference between the output frequency of the DC-AC module and the grid frequency in real time, and adjust the corresponding control parameters of the DC-AC module according to the frequency difference, so that the output frequency of the DC-AC module matches the grid frequency. The grid frequency is generally fixed (for example, the grid frequency in my country is 50Hz). If the output frequency is different from the grid frequency, it will also lead to difficulties in grid connection. When the frequency is inconsistent, it will cause inconsistent periodic changes in the voltage and current waveforms, making the transmission of active power and reactive power unstable. The grid connection strategy can adopt a frequency regulation mechanism, such as adding a frequency feedback control link, monitoring the difference between the output frequency and the grid frequency in real time, and adjusting the corresponding control parameters of the DC-AC module to gradually approach and stabilize the grid frequency to ensure the stable transmission of electric energy.

[0066] The voltage amplitude control module is used to monitor the amplitude difference between the output voltage amplitude of the DC-AC module and the grid voltage amplitude in real time, and adjust the corresponding control parameters of the DC-AC module according to the amplitude difference, so that the output voltage amplitude of the DC-AC module matches the grid voltage amplitude. The output voltage amplitude and the grid voltage amplitude need to be reasonably matched. If the amplitude difference between the two is too large, a large impact current will also be generated at the moment of grid connection. The grid connection strategy can use voltage regulation measures, such as voltage closed-loop control, to monitor and adjust the output voltage in real time, so that the output voltage amplitude is close to the grid voltage amplitude, thereby achieving smooth grid connection.

[0067] The power control module is used to control the active power output by the DC-AC module according to the needs of the power grid and the actual situation of the power generation equipment, and improve the power factor through reactive power compensation technology. The grid-connected strategy must also consider the effective control of the output power. After the grid connection, it is necessary to reasonably allocate active power and reactive power according to the needs of the power grid and the actual situation of the power generation equipment. For example, for a photovoltaic grid-connected system, it is necessary to control the active power output by the inverter according to factors such as light intensity, and improve the power factor through reactive power compensation technology.

[0068] The power quality control module is used to reduce the harmonic components so that the output power of the DC-AC module meets the power quality standards of the power grid. The grid connection strategy also involves the improvement of power quality, including reducing harmonic content. By adopting appropriate filters and control strategies, such as active power filters (APFs) or specific pulse width modulation (PWM) technology, the harmonic components can be reduced so that the output power meets the power quality standards of the power grid and ensures the safe and stable operation of the power grid.

[0069] In this embodiment, a DC power supply with a wide voltage range (550V to 1100V) is converted to a target voltage (e.g., 1750V) through a bidirectional cascade DC-DC module 11, and after being inverted by a DC-AC module 14 of a three-level neutral point clamped inverter circuit, the output is a three-phase 1140V / 660V (optional).

[0070] Compared with the existing technology, the technical solution of the above embodiment of the present invention has the following beneficial effects: 1. Improve reliability: By adopting the bidirectional cascade DC-DC technology and the mid-point clamped three-level inverter technology, the bidirectional flow of electric energy can be realized, and the reliability of the PCS is improved. Compared with the existing unidirectional DC-DC technology, the present invention can meet more application requirements that require bidirectional flow of electric energy. 2. Improve efficiency: By adopting the bidirectional cascade DC-DC technology and the mid-point clamped three-level inverter technology, high-quality sinusoidal wave output can be generated, the harmonic content is reduced, and the quality of electric energy is improved. Compared with the existing two-level inverter technology, the present invention can reduce the pollution to the power grid. 3. The two-layer control system based on the DC-DC controller, the DC-AC controller, and the DSP controller improves the reliability and stability of the system. 4. The output voltage value after boosting is flexibly controlled to the target voltage value by using the adaptive adjustment gain. 5. The introduction of the digital phase-locked loop, the digital filter and the adaptive gain enables the inverter voltage to track the grid voltage in real time, thereby improving the reliability of the system.

[0071] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "also includes a..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. It should be noted that a person skilled in the art may make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications shall also be regarded as the protection scope of the present invention.

Claims

1. A power conversion system, characterized in that: include: A bidirectional cascade DC-DC module is connected to a DC power supply with a wide voltage range through an input side protection module, wherein the voltage range of the DC power supply is 550V to 1100V; A voltage detection module, used to detect the output voltage value of the bidirectional cascade DC-DC module; A DC-DC controller, used for obtaining a voltage difference between an output voltage value of the bidirectional cascade DC-DC module and a target voltage value, and adaptively adjusting an input side gain value according to the voltage difference, to control the operation of the bidirectional cascade DC-DC module, so as to adjust the output voltage value of the bidirectional cascade DC-DC module to the target voltage value; A DC-AC module, whose input end is connected to the output end of the bidirectional cascade DC-DC module, and whose output end is connected to the power grid through an output side protection module; A digital phase-locked loop, used to detect a phase difference between an output voltage phase of the DC-AC module and a voltage phase of the power grid; A DC-AC controller, configured to adaptively adjust an output side gain value according to the phase difference value, and control the operation of the DC-AC module so that an output voltage phase of the DC-AC module is synchronized with a voltage phase of the power grid; The DSP controller is connected to the DC-DC controller and the DC-AC controller respectively. The DSP controller is used as a master controller to realize the operation logic and protection functions of the entire system.

2. The power conversion system according to claim 1, characterized in that: The bidirectional cascade DC-DC module comprises a bidirectional cascade circuit composed of cascaded multi-path IGBT devices and diodes, the voltage detection module adopts an output side voltage sensor arranged on the output side of the bidirectional cascade DC-DC module, and a first IGBT driving module is arranged between the DC-DC controller and the bidirectional cascade DC-DC module; The output side voltage sensor is used to measure the output voltage of the bidirectional cascade DC-DC module and convert it into an electrical signal that can be recognized by the DC-DC controller and then transmit it to the DC-DC controller as the output voltage value of the bidirectional cascade DC-DC module; The DC-DC controller calculates a voltage difference between an output voltage value of the received bidirectional cascade DC-DC module and a target voltage value, adaptively adjusts an input side gain value according to the voltage difference and generates a first control signal; The first IGBT driving module receives and outputs a PWM signal with a corresponding duty cycle according to the first control signal to drive and control the on and off of the IGBT device of the bidirectional cascade DC-DC module, thereby adjusting the output voltage value of the bidirectional cascade DC-DC module to the target voltage value.

3. The power conversion system according to claim 1, characterized in that: The DC-DC controller adaptively adjusts the input side gain value according to the voltage difference between the output voltage value of the bidirectional cascade DC-DC module and the target voltage value, specifically using the following formula: K p11 =K p10 +α1 |Δu|, K i11 =K i10 +β1·|Δu|, Among them, K p10 is the basic proportional gain value, K i10 is the basic integral gain value, α1 and β1 are the corresponding gain adjustment coefficients, and Δu is the voltage difference.

4. The power conversion system according to claim 2, characterized in that: The input side protection module comprises: An input-side isolating switch, one end of which is connected to the DC power supply, and the other end of which is coupled to the bidirectional cascade DC-DC module through an input-side fuse and an input-side DC contactor, wherein the input-side isolating switch is used to switch and connect the connection between the bidirectional cascade DC-DC module and the DC power supply; A plurality of Hall sensors respectively collect the current of the DC power supply and the current of each input end of the bidirectional cascade circuit, and transmit the currents to the DC-DC controller to realize a protection function according to whether the currents of each path are balanced; The input side voltage sensor is used to detect whether the DC power supply has voltage input and transmit it to the DC-DC controller to start the bidirectional cascade DC-DC module when there is voltage input.

5. The power conversion system according to claim 1, characterized in that: The DC-AC module comprises a three-level neutral point clamped inverter circuit composed of three IGBT devices and corresponding diodes, resistors and capacitors, and a second IGBT driving module is arranged between the DC-AC controller and the DC-AC module; The DC-AC controller adaptively adjusts the output side gain value according to the phase difference value transmitted by the digital phase-locked loop and generates a second control signal; The second IGBT driving module receives and outputs a PWM signal with a corresponding duty cycle according to the second control signal to drive and control the IGBT device of the DC-AC module to be turned on in advance or delayed, thereby adjusting the output voltage phase of the DC-AC module to be synchronized with the voltage phase of the power grid.

6. The power conversion system according to claim 1, characterized in that: The digital phase-locked loop adopts an improved DPLL algorithm based on enhanced proportional integral control to improve the response speed and tracking accuracy. The control equation is specifically: Where Δθ(t) is the phase error, V q is the q-axis component after dq transformation, K p is the proportional gain, K i is the integral gain.

7. The power conversion system according to claim 1, characterized in that: The DC-AC controller adaptively adjusts the output side gain value according to the phase difference between the output voltage of the DC-AC module and the grid voltage phase using the following formula: K p21 =K p20 +α2·|Δθ(t)|, K i21 =K i20 +β2·|Δθ(t)|, Among them, K p20 is the basic proportional gain value, K i20 is the basic integral gain value, α2 and β2 are the corresponding gain adjustment coefficients, and Δθ(t) is the phase error.

8. The power conversion system according to claim 1, characterized in that: A digital filter is provided between the digital phase-locked loop and the power grid, and the digital filter is used to eliminate high-frequency noise and harmonic interference in the signal. The filter coefficient of the digital filter is adjusted in real time by a minimum mean square error algorithm: h(n+1)=h(n)+μ·e(n)·x(n), Where h(n) is the filter coefficient, e(n) is the current error signal, x(n) is the input signal, and μ is the step size factor used to control the learning rate.

9. The power conversion system according to claim 5, characterized in that: The output side protection module comprises: an output-side isolating switch, one end of which is connected to the power grid, and the other end of which is coupled to the DC-AC module through an output-side fuse, an output-side DC contactor, and an LC filter, wherein the output-side isolating switch is used to switch and connect the DC-AC module to the power grid, and the LC filter is used to filter out high-frequency harmonics in the output voltage of the DC-AC module; Three current transformers respectively collect three output currents of the three-level neutral point clamped inverter circuit and transmit them to the DC-AC controller to implement a protection function according to whether the three output currents are balanced.

10. The power conversion system according to claim 1, characterized in that: It also includes at least one of a frequency control module, a voltage amplitude control module, a power control module, and a power quality control module; the frequency control module is used to monitor the frequency difference between the output frequency of the DC-AC module and the grid frequency in real time, and adjust the corresponding control parameters of the DC-AC module according to the frequency difference, so that the output frequency of the DC-AC module matches the grid frequency; The voltage amplitude control module is used to monitor the amplitude difference between the output voltage amplitude of the DC-AC module and the grid voltage amplitude in real time, and adjust the corresponding control parameters of the DC-AC module according to the amplitude difference, so that the output voltage amplitude of the DC-AC module matches the grid voltage amplitude; the power control module is used to control the active power output by the DC-AC module according to the needs of the grid and the actual situation of the power generation equipment, and improve the power factor through reactive power compensation technology; the power quality control module is used to reduce harmonic components so that the output power of the DC-AC module meets the power quality standard of the grid.

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