An ac-ac parallel operation converter based on virtual synchronous generator technology

Abstract

The application discloses an AC-AC parallel operation converter based on virtual synchronous generator technology and belongs to the field of power electronic conversion.The application comprises a power conversion module, a voltage and current sampling module, a VSG control module, a bootstrap drive module and a chopper full-bridge AC-AC conversion module.The application introduces the VSG control module, realizes parallel current sharing through double closed-loop control composed of PR and PID, and widens the application scenario of the AC-AC topology;the instantaneous energy of input AC power is taken as the kinetic energy source of a virtual rotor, inertia and damping simulation in the pure AC domain is realized, unstable poor-quality AC power is converted into stable high-quality sinusoidal AC power of the same frequency, the output voltage can be accurately controlled within a certain range, and the application has the advantages of high-frequency electrical isolation, simple circuit topology, high conversion efficiency, low harmonic distortion rate, strong load adaptability and low cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of power electronic conversion, and particularly relates to an AC-AC parallel operation converter based on virtual synchronous generator technology. BACKGROUND

[0002] In the new energy revolution and the wave of new power system construction, large-scale grid connection of renewable energy such as wind power and photovoltaic power, and deep access of energy storage systems have put forward higher requirements for power conversion equipment. The inertia characteristics and damping characteristics of the traditional power system rely on synchronous generators, but this characteristic is gradually being replaced by the power electronic grid connection of new energy. This structural change requires AC-AC converters to have new functions such as dynamic inertia support and adaptive adjustment to maintain grid frequency and voltage stability.

[0003] In the transformer technology field, the application value of AC-AC converter runs through all links of power system: supporting ultra-high voltage direct current transmission project stable operation at the power transmission side, realizing intelligent reactive power compensation and harmonic control at the power distribution side, and driving electric vehicle charging equipment upgrade at the user side. The high-frequency and high-efficiency technical breakthroughs significantly improve the power density and response speed of power equipment, helping power equipment to transform towards compactness and intelligence. In recent years, the application of AC-AC converter in the field of power electronics has gradually expanded, and it is used in reactive power compensation, active filtering and high-voltage power transmission, etc., improving the stability and reliability of the power system.

[0004] The current technical bottleneck lies in the insufficient adaptability of the traditional architecture: the traditional AC-DC-AC converter has the defects of efficiency decay and unidirectional power flow, and the conventional AC-AC scheme has the advantage of high power factor, but the fixed parameter control mode is difficult to cope with the complex working conditions caused by new energy grid connection. Especially in the scenes of grid frequency fluctuation and voltage regulation, the existing technology is difficult to dynamically adjust the virtual inertia and damping characteristics, which restricts the improvement of new energy consumption capacity. SUMMARY

[0005] In order to solve the above problems existing in the prior art, the present application provides an AC-AC parallel operation converter based on virtual synchronous generator technology. The technical problem to be solved by the present application is solved by the following technical scheme:

[0006] The present application provides an AC-AC parallel operation converter based on virtual synchronous generator technology, comprising:

[0007] The power conversion module, the voltage and current sampling module, the VSG control module, the bootstrap drive module and the chopper full-bridge AC-AC conversion module adopt a double-channel structure; wherein,

[0008] The power conversion module is used for converting an alternating current input voltage into a direct current voltage to supply power for the AC-AC parallel operation converter.

[0009] The voltage and current sampling module is used for sampling the alternating current input voltage to obtain two-way sampling voltage and sampling current, and transmitting the corresponding sampling voltage and sampling current to the VSG control module and the chopper full-bridge AC-AC conversion module of the corresponding way.

[0010] The VSG control module of each way is used for dynamically adjusting the virtual inertia and damping coefficient of the AC-AC parallel operation converter according to the sampling voltage, the sampling current, the feedback voltage and the feedback current received by itself, and outputting the corresponding control signal through the adaptive VSG virtual synchronization algorithm based on the double closed-loop control.

[0011] The bootstrap drive module is used for outputting the corresponding drive signal according to the control signal.

[0012] The chopper full-bridge AC-AC conversion module of each way is used for controlling the switching state of the MOSFET switch tube according to the drive signal, and dynamically adjusting the output frequency and the output voltage according to the sampling voltage and the sampling current received by itself, so as to realize the parallel current sharing control on the load side.

[0013] The present application has the following advantages:

[0014] In the scheme provided by the present application, the virtual synchronous generator (VSG) is directly applied to the AC-AC converter topology for the first time, the VSG control module is introduced, the double closed-loop control composed of PR and PID is realized, the parallel current sharing is realized, and the application scenarios of the AC-AC topology are widened; the instantaneous energy of the input alternating current is taken as the kinetic energy source of the "virtual rotor", the inertia and damping simulation in the pure alternating current domain is realized, the unstable poor quality alternating current is converted into stable high-quality sinusoidal alternating current of the same frequency, and the output voltage can be accurately controlled within a certain range, compared with the traditional AC-AC converter, the present application has the advantages of high-frequency electrical isolation, simple circuit topology, high conversion efficiency, low harmonic distortion rate, strong load adaptability and low cost, etc. The present application applies the VSG to the AC-AC topology, and fills the technical blank in the field. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A principle schematic view of the AC-AC parallel operation converter based on the virtual synchronous generator technology is provided for the embodiments of the present application.

[0016] Figure 2This invention provides a speed governor control block diagram for a synchronous generator in an AC-AC parallel operation converter based on virtual synchronous generator technology, as shown in an embodiment of the invention.

[0017] Figure 3 A schematic diagram of the active power-frequency droop curve in an AC-AC parallel converter based on virtual synchronous generator technology provided in an embodiment of the present invention;

[0018] Figure 4 A control block diagram of a virtual speed governor in a VSG active-frequency loop of an AC-AC parallel converter based on virtual synchronous generator technology, provided for an embodiment of the present invention;

[0019] Figure 5 This invention provides a control block diagram of the VSG active-frequency loop in an AC-AC parallel converter based on virtual synchronous generator technology, as shown in an embodiment of the invention.

[0020] Figure 6 The droop curve of reactive power-voltage in an AC-AC parallel converter based on virtual synchronous generator technology provided in an embodiment of the present invention;

[0021] Figure 7 This invention provides a control block diagram of the VSG reactive-voltage loop in an AC-AC parallel converter based on virtual synchronous generator technology, as shown in an embodiment of the invention.

[0022] Figure 8 This is a schematic diagram of the AC-AC conversion circuit in an AC-AC parallel converter based on virtual synchronous generator technology provided in an embodiment of the present invention;

[0023] Figure 9 This is a schematic diagram of the control loop of the VSG control module in an AC-AC parallel converter based on virtual synchronous generator technology, provided in an embodiment of the present invention.

[0024] Figure 10 This is a simulation diagram of an AC-AC parallel converter based on virtual synchronous generator technology, provided as an embodiment of the present invention. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0026] This invention provides an AC-AC parallel converter based on virtual synchronous generator technology, such as... Figure 1 As shown, it may include:

[0027] The power conversion module, the voltage and current sampling module, the VSG control module, the bootstrap drive module and the chopper full-bridge AC-AC conversion module adopt a double-path structure; wherein,

[0028] The power conversion module is used for converting an AC input voltage into a DC voltage to power the AC-AC parallel operation converter.

[0029] The voltage and current sampling module is used for sampling the AC input voltage to obtain two paths of sampling voltage and sampling current, and transmitting the corresponding sampling voltage and sampling current to the VSG control module and the chopper full-bridge AC-AC conversion module of the corresponding path; sampling the AC voltage and AC current output by each path of the chopper full-bridge AC-AC conversion module as feedback voltage and feedback current, and feeding back to the VSG control module of the corresponding path.

[0030] The VSG control module of each path is used for dynamically adjusting the virtual inertia and damping coefficient of the AC-AC parallel operation converter according to the sampling voltage, the sampling current, the feedback voltage and the feedback current received by itself through the adaptive VSG virtual synchronization algorithm based on double closed-loop control, and outputting the corresponding control signal.

[0031] The bootstrap drive module is used for outputting the corresponding drive signal according to the control signal.

[0032] The chopper full-bridge AC-AC conversion module of each path is used for controlling the switching state of the MOSFET switch tube according to the drive signal, and dynamically adjusting the output frequency and output voltage of itself according to the sampling voltage and sampling current received by itself, so as to realize the parallel current sharing control of the load side.

[0033] The embodiment of the application creatively applies a virtual synchronous generator (VSG) to a direct AC-AC converter topology for the first time, and realizes parallel current sharing through PR (Proportional Resonant) and PID (Proportional Integral Derivative) double-loop control, greatly widening the application scenarios of the AC-AC topology. Traditional VSG technology naturally relies on a DC-AC converter structure, because the DC bus provides a clear and easy-to-simulate power buffer link for the "rotor kinetic energy". The direct AC-AC converter lacks such an explicit energy storage link, and the input and output are both alternating current, and the power flow is instantaneous, bidirectional and strongly coupled. The embodiment of the application solves the problem of constructing a stable "virtual rotor" model in this complex AC environment. Through the unique control architecture, the instantaneous energy of the input AC power is used as the source of the "virtual rotor" kinetic energy, and the inertia and damping simulation in the pure AC domain is realized. Therefore, the application of VSG technology to the AC-AC topology is a non-obvious technical innovation, filling the technical gap in this field. Understandably, the AC-AC parallel operation converter proposed in the embodiment of the application deeply couples a specific hardware topology with a customized VSG. With the further promotion of the new energy strategy, photovoltaic microgrid power generation projects are increasing, and how to stabilize the microgrid and ensure the power transmission between microgrids is an important problem solved by the embodiment of the application. The embodiment of the application aims to solve the interconnection problem between a microgrid with high penetration of photovoltaic power generation and weak inertia, and a microgrid mainly supported by traditional power sources and strong inertia; replace the conventional tie line between multiple grids with a VSG-based AC-AC converter, thereby improving the overall stability of the interconnection system. Instead of simply and passively meeting the power demand of the microgrid with high penetration of photovoltaic power generation, the application provides power support with inertia and damping. This greatly smooths the power fluctuations on the tie line, directly solving the complex working conditions caused by new energy grid connection and the core problem of "the need for dynamic inertia support". The embodiment of the application uses an AC-AC converter to eliminate the traditional DC link, increase the inertia and damping support to improve the quality of the power grid, and solve the solution of multi-grid interconnection through parallel technology, realizing a great innovation in new energy grid connection.

[0034] For ease of understanding, the various modules of the AC-AC parallel operation converter based on the virtual synchronous generator technology proposed in the embodiment of the application are introduced below.

[0035] The power conversion module can include:

[0036] The AC-DC conversion submodule and the DC isolation submodule; wherein,

[0037] AC-DC conversion sub-module, for converting alternating current input voltage into direct current voltage;

[0038] DC isolation sub-module, for isolating direct current voltage to supply power for the parallel operation converter of AC-AC.

[0039] The power conversion module realizes the power supply for the parallel operation converter of AC-AC by converting the alternating current input voltage.

[0040] The voltage and current sampling module can include:

[0041] The first voltage and current sampling sub-module, the second voltage and current sampling sub-module, the third voltage and current sampling sub-module and the fourth voltage and current sampling sub-module; wherein,

[0042] The first voltage and current sampling sub-module is used for sampling the voltage and current of the alternating current input voltage, and outputs the first sampling voltage and the first sampling current to the first VSG control module.

[0043] The second voltage and current sampling sub-module is used for sampling the voltage and current of the alternating current input voltage, and outputs the second sampling voltage and the second sampling current to the second VSG control module.

[0044] The third voltage and current sampling sub-module is used for sampling the alternating current voltage and alternating current output by the first chopper full-bridge AC-AC conversion module, as the first feedback voltage and the first feedback current, and feeds back to the first VSG control module.

[0045] The fourth voltage and current sampling sub-module is used for sampling the alternating current voltage and alternating current output by the second chopper full-bridge AC-AC conversion module, as the second feedback voltage and the second feedback current, and feeds back to the second VSG control module.

[0046] It can be understood that for the two-way operation chopper full-bridge AC-AC conversion module, the voltage and current sampling module adopts a double-channel design, and the first voltage and current sampling sub-module and the third voltage and current sampling sub-module are used to respectively transmit the sampled sampling voltage and sampling current to the first VSG control module; the second voltage and current sampling sub-module and the fourth voltage and current sampling sub-module are used to respectively transmit the sampled voltage and current to the second VSG control module, so as to realize double-channel sampling of voltage and current.

[0047] The VSG control module adopts a double-channel structure, which can include:

[0048] The first VSG control module is used to dynamically adjust the virtual inertia and damping coefficient of the AC-AC parallel converter based on the first sampling voltage, the first sampling current, the first feedback voltage and the first feedback current, and the adaptive VSG virtual synchronization algorithm based on dual closed-loop control, and output the first control signal PWM1.

[0049] The second VSG control module is used to dynamically adjust the virtual inertia and damping coefficient of the AC-AC parallel converter based on the second sampling voltage, second sampling current, second feedback voltage and second feedback current, and through an adaptive VSG virtual synchronization algorithm based on dual closed-loop control, and output the second control signal PWM2.

[0050] The two-channel chopper-controlled full-bridge AC-AC converter module enables AC-AC parallel operation and can include active frequency components and reactive voltage components.

[0051] Specifically, to enable the AC-AC converter to accurately simulate the frequency characteristics of a synchronous generator, this embodiment of the invention first analyzes the frequency regulation principle of a synchronous generator. The frequency characteristics of a synchronous generator include dynamic and steady-state characteristics. First, the inertia and damping characteristics of the synchronous generator rotor enable it to effectively resist external disturbances; the rotor angular velocity changes slowly, exhibiting good frequency dynamic performance. Second, to ensure the power system frequency remains stable within a certain range, traditional synchronous generators use power frequency regulators to control the steady-state value of their output frequency.

[0052] When the load power of a synchronous generator changes abruptly, it can adjust its output frequency through a power frequency regulator to maintain it within a certain range. The control block diagram of the synchronous generator's speed governor is shown below. Figure 2 As shown, when the synchronous generator is operating at rated conditions, the electromagnetic power on the rotor shaft is... Equal to the load power, the rotor rotational angular velocity is equal to the VSG's rated output angular frequency. If the load power suddenly increases, the kinetic energy of the synchronous generator rotor will be converted into electromagnetic power to satisfy the power conservation principle. Therefore, the rotor angular velocity of the synchronous generator will decrease compared to the rated value, and the system speed governor will be activated to adjust the rotor angular velocity.

[0053] First, the deviation between the actual angular frequency of the synchronous generator and its rated value is detected and sent to the speed governor. The speed governor adjusts the mechanical power input to the prime mover, thereby compensating for the load power to some extent and increasing the kinetic energy on the rotor shaft, so that the rotor angular velocity of the synchronous generator returns to near its rated value. This frequency adjustment process is also known as the primary frequency regulation process of the synchronous generator. It should be noted that primary frequency regulation is a differential regulation, and the adjusted system output frequency will have a certain deviation from the rated frequency.

[0054] After the active-frequency regulation process, the steady-state value of the output frequency of the synchronous generator will change linearly with the load power. The active-frequency droop characteristic curve of the synchronous generator can be obtained as shown in FIG. 1, which shows that the output frequency of the synchronous generator will gradually decrease with the increase of the load power. When the load active power is equal to the active command value Figure 3 , the system frequency is equal to the rated output angular frequency of the VSG. When the load active power is less than the active command value , the system output frequency will be greater than the rated value. According to the frequency characteristic curve of the synchronous generator, the active-frequency expression satisfied by the synchronous generator can be obtained as follows:

[0055]

[0056] wherein, represents the actual output value of the active power, represents the active command value of the synchronous generator, represents the rated output angular frequency of the VSG, represents the actual output angular frequency of the VSG, represents the active-frequency droop coefficient of the synchronous generator.

[0057] Since the power electronic converter belongs to a static device, there is no actual prime mover and synchronous generator rotor mechanical structure, and thus a complex power-frequency regulator does not need to be designed to regulate the system frequency, and only a virtual governor needs to be added in the active loop of the VSG. The control block diagram of the virtual governor of the active-frequency loop of the virtual synchronous generator (VSG) is shown in FIG. 2. Figure 4 Figure 4 wherein, represents the active reference value of the VSG, represents the active-frequency coefficient of the VSG.

[0058] At the steady state of the system, if the actual output angular frequency of the VSG deviates from the rated output angular frequency of the VSG, an active droop regulation amount will be superimposed on the active reference value , thereby simulating the primary frequency modulation characteristic of the synchronous generator.

[0059] In order to enable the AC-AC converter to resist external interference and support the system frequency, the rotor mechanical motion equation of the synchronous generator is considered to be added to the active-frequency loop of the VSG, thereby simulating the rotor inertia and damping motion characteristics of the synchronous generator. The rotor motion equation contained in the active loop of the VSG is as follows:

[0060]

[0061] wherein, ​​​​reference phase representing VSG output voltage, active virtual inertia representing VSG, damping coefficient representing VSG, which is the same as active-frequency droop coefficient of synchronous generator, rated output angular frequency of VSG, which can be 50 HZ, actual output angular frequency of VSG, which can be 50 HZ, active reference value representing VSG, active actual output value, derivative of angular frequency with respect to time, derivative of reference phase with respect to time.

[0062] The control block diagram of VSG active-frequency loop can be seen from Figure 5 , which shows that the active-frequency loop can be composed of primary frequency modulation module and rotor motion module. When the output frequency of AC-AC converter deviates from the rated value, the primary frequency modulation module can automatically adjust the virtual mechanical power value, so as to increase the virtual mechanical power of VSG, so that the output active and frequency meet the active-frequency droop characteristic. The rotor motion module of VSG simulates the rotor inertia and damping motion characteristics of the synchronous generator, so as to slow down the speed of system frequency change and support frequency stability. Therefore, the above two links simulate the frequency characteristics of the synchronous generator from the aspects of steady state and transient state respectively.

[0063] Similar to the frequency regulator, the excitation regulator will detect the difference between the actual terminal voltage of the synchronous generator and the rated value of the terminal voltage of the synchronous generator , and send the voltage difference value to the voltage regulator to obtain the control instruction of the exciter, so as to adjust the rotor excitation current of the synchronous generator through the exciter, thereby adjusting the output voltage amplitude of the synchronous generator. The above process is also called primary voltage regulation process. The drooping curve diagram of the reactive power-voltage of the synchronous generator is shown in Figure 6 , which shows that when the output reactive power of the synchronous generator is equal to the reactive power reference value of the synchronous generator , the terminal voltage will remain at the rated value of the terminal voltage of the synchronous generator . When the load reactive power increases, the synchronous generator needs to increase the reactive power to realize power balance, and the terminal voltage of the synchronous generator will also decrease. Similarly, when the reactive load decreases, the terminal voltage of the synchronous generator will increase.

[0064] The reactive power-voltage expression of the synchronous generator can be obtained as follows:

[0065] ;

[0066] wherein, represents the reference value of the reactive power of the synchronous generator, represents the actual output value of the synchronous generator, represents the reactive voltage droop coefficient, and respectively represent the rated value and the actual value of the terminal voltage of the synchronous generator.

[0067] The result obtained by and further can derive the reference value of the output voltage of the VSG as follows:

[0068] .

[0069] According to the above expression, the control block diagram of the VSG reactive-voltage loop can be obtained as shown in Figure 7 , wherein represents the reference value of the VSG reactive power, represents the VSG reactive voltage coefficient, and respectively represent the rated value and the reference value of the output voltage of the VSG.

[0070] Finally, according to the output phase of the VSG active loop and the amplitude of the output voltage of the VSG reactive loop, the expression of the voltage reference value of the AC-AC converter is:

[0071] .

[0072] The output phase of the VSG active loop is the reference phase of the output voltage of the VSG , and the amplitude of the output voltage of the VSG reactive loop is the reference value of the output voltage of the VSG .

[0073] In the embodiment of the present application, two AC-AC converters are connected in parallel, which is equivalent to connecting two virtual synchronous generators in parallel.

[0074] In the embodiment of the present application, double closed-loop control is used, PR control is used as the inner loop, and the reference voltage is used as the reference signal of the inner loop, is the continuous domain form of the PR controller, represents a complex variable, represents an input voltage, represents the first parameter of the PR controller, and the first parameter is the gain at any frequency, represents the second parameter of the PR controller, and the second parameter is the gain within the frequency and its bandwidth range, represents the bandwidth of the PR controller, Power frequency (50HZ) is represented. Through the PR controller, the embodiment of the application realizes the zero-error accurate tracking of the sinusoidal voltage signal generated by the virtual synchronous generator.

[0075] The bootstrap drive module can include:

[0076] The first bootstrap drive circuit and the second bootstrap drive circuit; wherein,

[0077] The first bootstrap drive circuit is configured to output a first drive signal according to a first control signal PWM1.

[0078] The second bootstrap drive circuit is configured to output a second drive signal according to a second control signal PWM2.

[0079] The two chopper full-bridge AC-AC conversion modules adopt the same circuit structure; each chopper full-bridge AC-AC conversion module can include:

[0080] The input side filter sub-circuit, the chopper buck topology sub-circuit, the energy storage inductor, and the output side filter sub-circuit; wherein,

[0081] The input end of the input side filter sub-circuit is connected to the sampling voltage and the sampling current as the first input end of the corresponding chopper full-bridge AC-AC conversion circuit, the first output end is connected to the first input end of the chopper buck topology sub-circuit, and the second output end is connected to the second input end of the chopper buck topology sub-circuit.

[0082] The control end of the chopper buck topology sub-circuit is connected to the second input end of the corresponding chopper full-bridge AC-AC conversion circuit, and the output end is connected to the first end of the energy storage inductor.

[0083] The second end of the energy storage inductor is connected to the input end of the output side filter sub-circuit.

[0084] The output end of the output side filter sub-circuit is connected to the output end of the corresponding chopper full-bridge AC-AC conversion circuit.

[0085] As shown in Figure 8 , in the AC-AC conversion circuit, the input side filter sub-circuit includes capacitors C1 and C2 in parallel. The energy storage inductor is inductor L1. The output side filter sub-circuit includes capacitors C3, C4, and C5 in parallel.

[0086] Specifically, the chopper buck topology sub-circuit, as shown in Figure 8 , can include:

[0087] The first switch array, the second switch array, the third switch array, and the fourth switch array; wherein,

[0088] The first switch array and the third switch array have the same structure, and the second switch array and the fourth switch array have the same structure.

[0089] The control end of the first switch array is connected with the control end of the chopper-buck type topology sub-circuit, the input end is used as the first input end of the chopper-buck type topology sub-circuit, and the output end is connected with the input end of the second switch array.

[0090] The control end of the second switch array is connected with the control end of the chopper-buck type topology sub-circuit, and the output end is used as the output end of the chopper-buck type topology sub-circuit.

[0091] The control end of the third switch array is connected with the control end of the chopper-buck type topology sub-circuit, the input end is connected with the output end of the fourth switch array, and the output end is connected with the output end of the second switch array.

[0092] The control end of the fourth switch array is connected with the control end of the chopper-buck type topology sub-circuit, and the input end is used as the second input end of the chopper-buck type topology sub-circuit.

[0093] Any one of the first switch array or the third switch array, as shown in Figure 8 may include:

[0094] a first diode, a first resistor, a second resistor and a first MOSFET switch tube; wherein,

[0095] The input end of the first diode is connected with the second end of the first resistor, and the output end is connected with the first end of the first resistor.

[0096] The first end of the first resistor is used as the control end of the corresponding switch array, and the second end is connected with the gate of the first MOSFET switch tube.

[0097] The first end of the second resistor is connected with the second end of the first resistor, and the second end is used as the output end of the corresponding switch array.

[0098] The source of the first MOSFET switch tube is connected with the second end of the second resistor, and the drain is used as the input end of the corresponding switch array.

[0099] As can be understood, Figure 8 for the first switch array, the first diode is D1, the first resistor is R1, the second resistor is R2, and the first MOSFET switch tube is S1; for the third switch array, the first diode is D3, the first resistor is R5, the second resistor is R6, and the first MOSFET switch tube is S3.

[0100] Any one of the second switch array or the fourth switch array, as shown in Figure 8 may include:

[0101] a second diode, a third resistor, a fourth resistor and a second MOSFET switch tube; wherein,

[0102] the input end of the second diode is connected with the second end of the third resistor, and the output end is connected with the first end of the third resistor;

[0103] the first end of the third resistor is the control end of the corresponding switch array, and the second end is connected with the gate of the second MOSFET switch tube;

[0104] the first end of the fourth resistor is connected with the second end of the third resistor, and the second end is connected with the source of the second MOSFET switch tube;

[0105] the source of the second MOSFET switch tube is the input end of the corresponding switch array, and the drain is the output end of the corresponding switch array.

[0106] a body diode is connected in parallel between the source and the drain of each MOSFET switch tube.

[0107] It can be understood that, as Figure 8 shown, for the second switch array, the second diode is D2, the third resistor is R3, the fourth resistor is R4, and the second MOSFET switch tube is S2; for the fourth switch array, the second diode is D4, the third resistor is R7, the fourth resistor is R8, and the second MOSFET switch tube is S4.

[0108] In each buck-type full-bridge AC-AC conversion module: taking the first drive signal output by the first bootstrap drive circuit according to the first control signal PWM1 as an example, for the control signals P1, P2, P3 and P4 received by the buck-type topology sub-circuit, P1 and P3 are the same phase signals of the first drive signal corresponding to the first control signal PWM1, and P2 and P4 are the opposite phase signals of the first drive signal corresponding to the first control signal PWM1; taking the second drive signal output by the second bootstrap drive circuit according to the second control signal PWM2 as an example, for the control signals P1, P2, P3 and P4 received by the buck-type topology sub-circuit, P1 and P3 are the same phase signals of the second drive signal corresponding to the second control signal PWM2, and P2 and P4 are the opposite phase signals of the second drive signal corresponding to the second control signal PWM2.

[0109] The control link diagram of the VSG control module is shown in Figure 9 , the parallel current sharing module on the output side is a two-way AC-AC converter, which outputs through an interleaved parallel structure and realizes dynamic current sharing by using a PID strategy. The parallel current sharing control link on the load side calculates the current difference value by detecting the output currents of each module 、 . , represents an output current average value, represents an output current real-time value, suppresses circulating current and optimizes power distribution. The embodiment of the application uses a PID algorithm as outer loop control, combined with PR control as inner loop control, so as to realize double closed loop control, uses the inner loop control to perform phase control on the sinusoidal signal, the reference signal is a reference voltage of the virtual synchronous generator, the outer loop control is PID control, and is responsible for current sharing; the double closed loop control guarantees the accuracy of the phase and the amplitude, increases the stability of the current sharing, rapidly responds to load mutation, and ensures that the output voltage fluctuation is less than 0.5%.

[0110] In the actual performance verification link, the embodiment of the application realizes the effects of high efficiency, low loss, high dynamic response and high reliability. Buck topology is adopted, the input current is continuous, the total harmonic distortion (THD) is low (the test value is less than 5%), and the power factor of the power supply side is as high as 0.98 (distortion factor x phase shift factor). Combined with the soft switching technology, the switching loss is reduced by 30%, the overall efficiency reaches 97%; under the scenes of voltage / current step adjustment, load mutation and the like, the system response time is less than 2s, the overshoot is less than 3%, the demand of rapid frequency modulation is met, the overcurrent protection threshold is accurately adjustable, and the action error is less than 1%; the energy storage inductance current limiting function: when the load is short-circuited, the current rising rate is suppressed, sufficient action time (>10ms) is provided for the protection circuit (such as overcurrent protection), and the system reliability is significantly better than that of the traditional Buck topology, and N-way parallel expansion is supported, automatic switching is realized when a single module fails, and continuous operation of the system is ensured.

[0111] In order to verify the beneficial effects of the embodiment of the application, the simulation schematic diagram of the AC-AC parallel operation converter based on the virtual synchronous generator technology provided by the embodiment of the application is as shown in Figure 10 , Figure 10 is the corresponding simulation schematic diagram of the application on the simulink software, Figure 10 the horizontal coordinate is time, and the vertical coordinate is output voltage, and it can be seen from Figure 10 that the corresponding total harmonic distortion (THD) of the embodiment of the application is low, the power factor (PF) of the power supply side is high, the simulation can stably output 30V effective value sinusoidal alternating current under the condition of 220V power frequency alternating current input, the response time is less than 0.2s, and the system stability is very high.

[0112] The embodiment of the application first directly applies a virtual synchronous generator (VSG) to an AC-AC converter topology, realizes parallel current sharing through a double closed loop control composed of PR and PID, widens the application scenario of the AC-AC topology, takes the instantaneous energy of input alternating current as the kinetic energy source of a 'virtual rotor', realizes inertia and damping simulation in a pure alternating current domain, transforms unstable inferior alternating current into stable same-frequency superior sinusoidal alternating current, can accurately control the output voltage within a certain range, compared with a traditional AC-AC converter, has the advantages of high-frequency electrical isolation, simple circuit topology, high conversion efficiency, low harmonic distortion rate, strong load adaptability and low cost, etc. The application of the VSG to the AC-AC topology fills the technical blank in the field.

[0113] It should be noted that in the description of the application, it should be understood that the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0114] The above only describes the preferred embodiments of the application and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A grid-interactive AC-AC parallel operating converter based on virtual synchronous generator technology, characterized in that, The power conversion module, the voltage and current sampling module, the VSG control module, the bootstrap drive module and the chopper full-bridge AC-AC conversion module adopt a double-path structure; wherein, The power conversion module is used for converting an AC input voltage into a DC voltage to supply power for the AC-AC parallel operation converter; The voltage and current sampling module is used for sampling the AC input voltage to obtain two paths of sampling voltage and sampling current, and transmitting the corresponding sampling voltage and sampling current to the VSG control module and the chopper full-bridge AC-AC conversion module of the corresponding path; sampling the AC voltage and AC current output by each path of chopper full-bridge AC-AC conversion module as feedback voltage and feedback current, and feeding back to the VSG control module of the corresponding path; The VSG control module of each path is used for dynamically adjusting the virtual inertia and damping coefficient of the AC-AC parallel operation converter according to the sampling voltage, the sampling current, the feedback voltage and the feedback current received by itself through the adaptive VSG virtual synchronization algorithm based on double closed-loop control, and outputting the corresponding control signal; The bootstrap drive module is used for outputting the corresponding drive signal according to the control signal; The chopper full-bridge AC-AC conversion module of each path is used for controlling the switching state of the MOSFET switch tube according to the drive signal, and dynamically adjusting the output frequency and output voltage of itself according to the sampling voltage and sampling current received by itself to realize the parallel current sharing control on the load side. The power conversion module comprises:

2. The AC-AC parallel operation converter based on virtual synchronous generator technology according to claim 1, characterized in that, An AC-DC conversion submodule and a DC isolation submodule; wherein, The AC-DC conversion submodule is used for converting the AC input voltage into the DC voltage; The DC isolation submodule is used for isolating the DC voltage to supply power for the AC-AC parallel operation converter. The voltage and current sampling module comprises:

3. The AC-AC parallel operation converter based on virtual synchronous generator technology according to claim 1, characterized in that, A first voltage and current sampling submodule, a second voltage and current sampling submodule, a third voltage and current sampling submodule and a fourth voltage and current sampling submodule; wherein, The first voltage and current sampling submodule is used for sampling the voltage and current of the AC input voltage, and outputting the first sampling voltage and the first sampling current to the first path VSG control module; The second voltage and current sampling submodule is used for sampling the voltage and current of the AC input voltage, and outputting the second sampling voltage and the second sampling current to the second path VSG control module; The third voltage and current sampling submodule is used for sampling the AC voltage and AC current corresponding to the output of the first path chopper full-bridge AC-AC conversion module as the first feedback voltage and the first feedback current, and feeding back to the first path VSG control module; The fourth voltage and current sampling submodule is used for sampling the AC voltage and AC current corresponding to the output of the second path chopper full-bridge AC-AC conversion module as the second feedback voltage and the second feedback current, and feeding back to the second path VSG control module. The VSG control module adopts a double-path structure, comprising:

4. The AC-AC parallel operation converter based on virtual synchronous generator technology according to claim 3, characterized in that, ​ The first VSG control module is configured to dynamically adjust virtual inertia and damping coefficients of the AC-AC parallel operation converter according to the first sampling voltage, the first sampling current, the first feedback voltage and the first feedback current through an adaptive VSG virtual synchronization algorithm based on double closed-loop control, and output a first control signal PWM1. The second VSG control module is configured to dynamically adjust virtual inertia and damping coefficients of the AC-AC parallel operation converter according to the second sampling voltage, the second sampling current, the second feedback voltage and the second feedback current through an adaptive VSG virtual synchronization algorithm based on double closed-loop control, and output a second control signal PWM2.

5. The AC-AC parallel operating converter based on virtual synchronous generator technology according to claim 4, characterized in that, The bootstrap drive module comprises: a first bootstrap drive circuit and a second bootstrap drive circuit; wherein the first bootstrap drive circuit is configured to output a first drive signal according to the first control signal PWM1; the second bootstrap drive circuit is configured to output a second drive signal according to the second control signal PWM2.

6. The AC-AC parallel operating converter based on virtual synchronous generator technology according to claim 1, characterized in that, The two chopper full-bridge AC-AC conversion modules adopt the same circuit structure; each chopper full-bridge AC-AC conversion module comprises: an input side filter sub-circuit, a chopper buck topology sub-circuit, an energy storage inductor and an output side filter sub-circuit; wherein an input end of the input side filter sub-circuit is connected to a sampling voltage and a sampling current as a first input end of the corresponding chopper full-bridge AC-AC conversion circuit, a first output end is connected to a first input end of the chopper buck topology sub-circuit, and a second output end is connected to a second input end of the chopper buck topology sub-circuit; a control end of the chopper buck topology sub-circuit is connected to a second input end of the corresponding chopper full-bridge AC-AC conversion circuit, and an output end is connected to a first end of the energy storage inductor; a second end of the energy storage inductor is connected to an input end of the output side filter sub-circuit; an output end of the output side filter sub-circuit is connected to an output end of the corresponding chopper full-bridge AC-AC conversion circuit.

7. The AC-AC parallel operating converter based on virtual synchronous generator technology according to claim 6, characterized in that, The chopper buck topology sub-circuit comprises: a first switch array, a second switch array, a third switch array and a fourth switch array; wherein the first switch array and the third switch array have the same structure, and the second switch array and the fourth switch array have the same structure; a control end of the first switch array is connected to a control end of the chopper buck topology sub-circuit, an input end is connected to a first input end of the chopper buck topology sub-circuit, and an output end is connected to an input end of the second switch array; a control end of the second switch array is connected to the control end of the chopper buck topology sub-circuit, and an output end is connected to an output end of the chopper buck topology sub-circuit; a control end of the third switch array is connected to the control end of the chopper buck topology sub-circuit, an input end is connected to an output end of the fourth switch array, and an output end is connected to an output end of the second switch array; a control end of the fourth switch array is connected to the control end of the chopper buck topology sub-circuit, and an input end is connected to a second input end of the chopper buck topology sub-circuit.

8. The AC-AC parallel operating converter based on virtual synchronous generator technology according to claim 7, characterized in that, Any one of the first switch array or the third switch array comprises: A first diode, a first resistor, a second resistor and a first MOSFET switch tube; wherein, the input end of the first diode is connected with the second end of the first resistor, and the output end is connected with the first end of the first resistor; the first end of the first resistor is as a control end of the corresponding switch array, and the second end is connected with the gate of the first MOSFET switch tube; the first end of the second resistor is connected with the second end of the first resistor, and the second end is as an output end of the corresponding switch array; the source of the first MOSFET switch tube is connected with the second end of the second resistor, and the drain is as an input end of the corresponding switch array.

9. The AC-AC parallel operating converter based on virtual synchronous generator technology according to claim 7, characterized in that, Any one of the second switch array or the fourth switch array comprises: a second diode, a third resistor, a fourth resistor and a second MOSFET switch tube; wherein, the input end of the second diode is connected with the second end of the third resistor, and the output end is connected with the first end of the third resistor; the first end of the third resistor is as a control end of the corresponding switch array, and the second end is connected with the gate of the second MOSFET switch tube; the first end of the fourth resistor is connected with the second end of the third resistor, and the second end is connected with the source of the second MOSFET switch tube; the source of the second MOSFET switch tube is as an input end of the corresponding switch array, and the drain is as an output end of the corresponding switch array.

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