Ring current suppression method, device, medium and system for hydrogen production power supply grid-connected converter

Abstract

The invention discloses a circulating current suppression method, device, medium and system for a hydrogen production power supply grid-connected converter, and the method comprises the steps: building a three-level parallel system circulating current model based on carrier wave lamination modulation, and analyzing the zero-sequence component of the circulating current model according to the piecewise function of the superposed zero-sequence component and a Fourier analysis means, obtaining a harmonic component in the zero-sequence component; harmonic components in circulating current in each converter are suppressed from the power angle by adopting a proportional complex integral mode, and the harmonic components in the circulating current are eliminated through reverse superposition of direct current quantity. According to the method, stable input / output of the power can be guaranteed, the size of the circulating current is dynamically reduced on the power instruction level, and stable work of the IPOP type connection converter is effectively guaranteed.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of hydrogen production, and in particular to a method, device, medium and system for suppressing circulating current of a grid-connected converter of a hydrogen production power supply. Background Art

[0002] The hydrogen production power source requires a large input power, and a distributed three-level converter with parallel input and parallel output is often used to ensure the input of AC power. This structure can not only give full play to the advantages of high equivalent switching frequency, low harmonic content, and sufficient DC voltage utilization of the three-level converter, but also adopt the IPOP structure to greatly increase the capacity of the converter, and there is no higher requirement for the stress of each converter switch device. At the same time, it can realize the redundant design of the converter, improve the reliability of operation, achieve cost reduction and efficiency improvement, and facilitate maintenance. Figure 1 It is an IPOP type connected three-level converter topology (hydrogen production power grid-connected converter).

[0003] When two or more converters are connected to the grid using the IPOP structure, there will inevitably be a circulating current path. Usually, there will inevitably be slight differences in the hardware parameters of each converter in parallel. In addition, the differences in control parameters and start-stop times make it difficult for the switching actions of each converter to remain consistent. Therefore, the generation of circulating current is aggravated under these asynchronous conditions. Circulating current belongs to the internal cycle between parallel systems, but its impact on converters is huge. The voltage and current distortion caused by circulating current increases the loss of switching devices, aggravates the midpoint imbalance of three-level converters, reduces the operating efficiency of parallel systems, and increases the possibility of converter damage or shutdown due to overvoltage and overcurrent risks. Therefore, suppressing circulating current in the IPOP system plays a vital role in the stable and efficient operation of the system. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in response to the technical problems existing in the prior art, the present invention provides a method, device, medium and system for suppressing circulating current of a hydrogen production power supply grid-connected converter on the basis of ensuring stable power input / output.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0006] A method for suppressing circulating current of a grid-connected converter of a hydrogen production power supply comprises the following steps:

[0007] A circulating current model of a three-level parallel system based on carrier stacking modulation is established. The zero-sequence component of the circulating current model is analyzed according to the piecewise function of the superimposed zero-sequence component and Fourier analysis to obtain the harmonic components in the zero-sequence component.

[0008] The proportional complex integration method is used to suppress the harmonic components in the circulating current of each converter from the power point of view, and the harmonic components in the circulating current are eliminated by reverse superposition of DC quantities.

[0009] Preferably, a piecewise function of the superimposed zero-sequence component is obtained according to the relationship between the instantaneous maximum value, the minimum value and the waveform of the three-phase modulation wave.

[0010] Preferably, the expression of the piecewise function is as follows:

[0011]

[0012]

[0013] Where V offset Represents the calculated value of the zero-sequence component; k represents the kth power frequency cycle in which the superimposed zero-sequence component is located; ω0=2×π×f, m represents the number of Fourier expansions, E represents the amplitude of the modulation wave, and t represents time;.

[0014] Preferably, Fourier decomposition is performed on formula (2) within one period to obtain the expression of formula (3):

[0015]

[0016] Where m represents the number of Fourier expansions; since the integral of the sine function in the symmetric interval is 0, the parameter b m is always equal to 0; since the zero-sequence component fluctuates at three times the fundamental frequency, ω=3ω0, and the harmonic expansion form of the superimposed zero-sequence component is obtained:

[0017]

[0018] Preferably, the transfer function of the proportional complex integral is in the form of:

[0019]

[0020] In the above formula, k p is the scale parameter, k ci is the complex integral parameter and j is the complex quantity.

[0021] Preferably, based on the transfer function of the proportional complex integral, the second-order generalized integral form is selected to perform phase shifting, and the final proportional complex integral control transfer function is constructed in combination with the second-order generalized integral transfer function.

[0022] Preferably, the expression of the control transfer function is:

[0023] G`G PCI (s):

[0024]

[0025] where ω c is the cutoff frequency of the proportional complex integral controller, ω th It represents the harmonic frequency of a specific frequency controlled by the proportional complex integral controller, and k is the filtering parameter of SOGI.

[0026] The present invention also discloses a circulating current suppression device for a grid-connected converter of a hydrogen production power supply, which performs the steps of the above method, including:

[0027] The first program module is used to establish a circulating current model of a three-level parallel system based on carrier stacking modulation, analyze the zero-sequence component of the circulating current model according to the piecewise function of the superimposed zero-sequence component and Fourier analysis, and obtain the harmonic component in the zero-sequence component;

[0028] The second program module is used to suppress the harmonic components in the circulating current of each converter from the power perspective by adopting the proportional complex integration method, and eliminate the harmonic components in the circulating current by reverse superposition of the DC quantity.

[0029] The present invention further discloses a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method described above are executed.

[0030] The present invention also discloses a circulating current suppression system for a hydrogen production power grid-connected converter, comprising a memory and a processor connected to each other, wherein a computer program is stored on the memory, and when the computer program is run by the processor, the steps of the method described above are executed.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] The circulating current model of the three-level parallel system based on carrier stacking modulation is established. The Fourier expansion form of the zero-sequence circulating current is obtained by deriving the piecewise function of the superimposed zero-sequence component and combining it with Fourier analysis. The Fourier expansion form of the zero-sequence component generated by the modulation wave generated by zero-sequence superposition and carrier stacking on the IPOP type connected converter is derived more clearly, and the harmonics of different components in the zero-sequence component caused by modulation are obtained, providing theoretical support for the design of subsequent controllers; the proportional complex integration method is used to suppress the harmonic components in the circulating current of each converter from the power perspective, and the harmonic components in the circulating current are eliminated by reverse superposition of DC quantities, which not only ensures the stable input / output of power, but also dynamically reduces the size of the circulating current at the power command level, effectively ensuring the stable operation of the IPOP type connected converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a topological diagram of an IPOP type three-level converter in the prior art.

[0034] Figure 2 This is a waveform diagram of the modulation signal and zero-sequence component in the present invention.

[0035] Figure 3 This is a block diagram of the circulating current harmonic suppression of the PCI modified modulation signal in the present invention.

[0036] Figure 4 The flowchart of the circulation suppression method in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0038] like Figure 4 As shown, the present invention aims at the circulating current problem in a three-level hydrogen production power grid-connected converter system using a distributed three-level converter through input parallel output parallel (IPOP), and the specific circulating current suppression method adopted is:

[0039] The circulating current model of the three-level parallel system based on carrier stacking modulation is established. The Fourier expansion form of the zero-sequence circulating current is obtained by deriving the piecewise function of the superimposed zero-sequence component and combining it with Fourier analysis. The Fourier expansion form of the zero-sequence component generated by the modulation wave generated by zero-sequence superposition and carrier stacking on the IPOP type connected converter is derived more clearly, and the harmonics of different components in the zero-sequence component caused by modulation are obtained, providing theoretical support for the design of subsequent controllers.

[0040] The proportional complex integration method is used to suppress the harmonic components in the circulating current of each converter from the power perspective, and the harmonic components in the circulating current are eliminated by reverse superposition of DC quantity, which not only ensures the stable input / output of power, but also dynamically reduces the size of the circulating current at the power command level, effectively ensuring the stable operation of the IPOP-connected converter.

[0041] Since the method of superimposing zero-sequence components is often used in engineering applications to equivalently achieve the effect of SVPWM modulation, the components of the zero-sequence components induced by modulation are unknown when multiple converters are connected in IPOP type. Therefore, it is of great significance to analyze the components of zero-sequence components between converters in combination with modulation. Specifically, a power equivalent model is established for the zero-sequence circulating current, and the harmonic components in the circulating current are analyzed based on the carrier stacking modulation of the injected zero-sequence voltage. The SPWM modulation strategy of superimposing zero-sequence voltage components has the same effect as SVPWM modulation. It not only does not require sector division and vector decomposition, but also helps to conduct in-depth analysis of zero-sequence circulating current. The SPWM modulation strategy of superimposing zero-sequence voltage components finally modulates the wave as follows: Figure 2 As shown:

[0042] The three-phase modulation wave after superimposing the zero-sequence component is as follows:

[0043]

[0044]

[0045] In the above formula, V sn (n = a, b, c) represents the modulation signal (original modulation signal) generated by the control link, V*sn represents the modulation signal after superimposing the zero-sequence voltage component, V offset Represents the calculated value of the zero-sequence component.

[0046] Therefore, according to the relationship between the instantaneous maximum and minimum values ​​of the three-phase modulation wave and the waveform, the piecewise function expression of the superimposed zero-sequence component can be obtained as follows:

[0047]

[0048]

[0049] In the above formula, k represents the kth power frequency period in which the superimposed zero-sequence component is located, ω0=2×π×f, m represents the number of Fourier expansions, E represents the amplitude of the modulation wave, and t represents time.

[0050] Performing Fourier decomposition on equation (2) within one period, we can obtain equation (3):

[0051]

[0052] Wherein, m represents the number of Fourier expansions, k represents the kth power frequency period in which the superimposed zero-sequence component is located, ω0=2×π×f, and m represents the number of Fourier expansions;

[0053] Since the integral of the sine function in the symmetric interval is 0, the parameter b in the above formula is m Always equal to 0, according to Figure 3 From the relationship between the modulation signal and the zero-sequence superimposed component, it can be seen that the zero-sequence component fluctuates at three times the fundamental frequency, and ω=3ω0, the harmonic expansion form of the superimposed zero-sequence component can be obtained:

[0054]

[0055] From the analysis in the previous article, it can be seen that under the modulation method of zero-sequence voltage injection, there are odd harmonic components in multiples of 3. If proportional integral control is used, it is difficult to control the components outside the fundamental frequency, and there are shortcomings such as steady-state error and insufficient anti-disturbance ability. Although proportional resonant control (PIR) can control harmonics of different frequencies, it is still difficult to meet the requirement of steady-state error of 0.

[0056] The DC component and harmonic component in the zero-sequence component need to be controlled separately to prevent the circulating current in the IPOP-connected converter from exceeding the limit. Specifically, the proportional complex integral (PCI) method is used for each independent controller to compensate for the zero-sequence modulation amount and suppress the low-frequency circulating current between the converters.

[0057] The proportional complex integral (PCI) controller can generate infinite gain at a specific frequency, achieve zero steady-state error, and exhibit strong anti-disturbance capability. Therefore, this control method is used to suppress the harmonic components in the circulating current.

[0058] The proportional complex integral can be described as the following transfer function:

[0059]

[0060] In the above formula, k p is the scale parameter, k ci is the complex integral parameter, from which we can know that there is a complex quantity j in the PCI control link. In the complex frequency domain, there is a 90° phase difference between the imaginary axis and the real axis. The second-order generalized integrator (SOGI) is selected to realize this phase shift process. Specifically, the zero-sequence current is subtracted from the reference value 0, and the modulation wave superposition V of the zero-sequence component is generated through the 150Hz (3rd), 450Hz (9th), and 750Hz (15th) proportional complex integral links. PCI , V generated by the control link sabc Then add the zero-sequence component, and then add the modulation wave superposition amount V of PCI zero-sequence suppression PCI Generate the final modulation wave V*sa; combined with the SOGI transfer function, the following PCI control transfer function G can be constructed ` PCI (s):

[0061]

[0062] In the above formula, ω c is the cut-off frequency of the controller, and its value range is generally 1 to 5 rad / s; ω th represents the harmonic frequency of a specific frequency controlled by the PCI controller; k is the filter parameter of SOGI, which is selected as 1.414; according to the above analysis, the 3rd, 9th and 15th harmonics are dominant in the zero-sequence circulating current, so ω th Take 3×π×f respectively w ,9×π×f w , 15×π×fw , f w is the fundamental frequency of the power grid, which is 50 Hz, and s represents the integral operator.

[0063] For the requirements of different characteristic sub-frequencies of 150Hz, 450Hz, and 750Hz, the PCI controller can generate a higher gain at this frequency, but has no control effect on other frequency bands. This can better control the 3rd, 9th, and 15th harmonics, control the influence of high-order harmonics caused by superimposed zero-sequence voltage, and achieve harmonic suppression in the circulating current.

[0064] Therefore, in the modulation strategy of zero-sequence voltage injection, the zero-sequence current component is suppressed by the PCI controller, and its 3rd, 9th, and 15th harmonics are suppressed to 0, thus constructing Figure 3 The harmonic component suppression controller in the invention can realize the circulating current control effect without synchronization for parallel converters controlled by different controllers, realize the plug-and-play effect and reduce the cost.

[0065] Specifically, in Figure 3 In the process, the zero-sequence current (circulating current) is PCI-controlled in the independent controller of each distributed converter to generate the harmonic suppression correction value V of the modulation signal injected into the zero-sequence voltage. PCI , thereby generating a modulation wave V of the modulation V` after the harmonic suppression optimization sn .

[0066] The present invention also discloses a circulating current suppression device for a hydrogen production power grid-connected converter, comprising:

[0067] The first program module is used to establish a circulating current model of a three-level parallel system based on carrier stacking modulation, analyze the zero-sequence component of the circulating current model according to the piecewise function of the superimposed zero-sequence component and Fourier analysis, and obtain the harmonic component in the zero-sequence component;

[0068] The second program module is used to suppress the harmonic components in the circulating current of each converter from the power perspective by adopting the proportional complex integration method, and eliminate the harmonic components in the circulating current by reverse superposition of the DC quantity.

[0069] The present invention further discloses a computer-readable storage medium, on which a computer program is stored, and the computer program executes the steps of the above method when it is run by a processor. The present invention also discloses a circulating current suppression system for a hydrogen production power grid-connected converter, comprising a memory and a processor connected to each other, the memory storing a computer program, and the computer program executes the steps of the above method when it is run by the processor.

[0070] The suppression device, medium and system of the present invention correspond to the above-mentioned suppression method and also have the advantages described in the above-mentioned suppression method.

[0071] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for suppressing circulating current of a grid-connected converter of a hydrogen production power supply, characterized in that: Includes steps: A circulating current model of a three-level parallel system based on carrier stacking modulation is established. The zero-sequence component of the circulating current model is analyzed according to the piecewise function of the superimposed zero-sequence component and Fourier analysis to obtain the harmonic components in the zero-sequence component. The proportional complex integration method is used to suppress the harmonic components in the circulating current of each converter from the power point of view, and the harmonic components in the circulating current are eliminated by reverse superposition of DC quantities.

2. The method for suppressing circulating current of a grid-connected converter for a hydrogen production power supply according to claim 1, characterized in that: According to the relationship between the instantaneous maximum and minimum values ​​of the three-phase modulation wave and the waveform, a piecewise function of the superimposed zero-sequence component is obtained.

3. The method for suppressing circulating current of a grid-connected converter for a hydrogen production power supply according to claim 2, characterized in that: The expression of the piecewise function is as follows: Where V offset represents the calculated value of the zero-sequence component; k represents the kth power frequency cycle in which the superimposed zero-sequence component is located; ω0=2×π×f, m represents the number of Fourier expansions, E represents the amplitude of the modulation wave, and t represents time.

4. The method for suppressing circulating current of a grid-connected converter for a hydrogen production power supply according to claim 3, characterized in that: Performing Fourier decomposition on equation (2) within one period, we obtain equation (3): Where m represents the order of Fourier expansion. Since the integral of the sine function in the symmetric interval is 0, the parameter b in equation (3) is m is always equal to 0; since the zero-sequence component fluctuates at three times the fundamental frequency, ω=3ω0, and the harmonic expansion form of the superimposed zero-sequence component is obtained:

5. The method for suppressing circulating current of a grid-connected converter for a hydrogen production power source according to any one of claims 1 to 4, characterized in that: The transfer function form of the proportional complex integral is: In the above formula, k p is the scale parameter, k ci is the complex integral parameter and j is the complex quantity.

6. The method for suppressing circulating current of a grid-connected converter for a hydrogen production power supply according to claim 5, characterized in that: Based on the transfer function of the proportional complex integral, the second-order generalized integral form is selected for phase shifting, and the final proportional complex integral control transfer function is constructed in combination with the second-order generalized integral transfer function.

7. The method for suppressing circulating current of a grid-connected converter for a hydrogen production power supply according to claim 6, characterized in that: The expression of the control transfer function is: G` PCI (s): where ω c is the cutoff frequency of the proportional complex integral controller, ω th It represents the harmonic frequency of a specific frequency controlled by the proportional complex integral controller, and k is the filtering parameter of SOGI.

8. A circulating current suppression device for a grid-connected converter of a hydrogen production power source, used to perform the steps of the method as described in any one of claims 1 to 7, characterized in that: include: The first program module is used to establish a circulating current model of a three-level parallel system based on carrier stacking modulation, analyze the zero-sequence component of the circulating current model according to the piecewise function of the superimposed zero-sequence component and Fourier analysis, and obtain the harmonic component in the zero-sequence component; The second program module is used to suppress the harmonic components in the circulating current of each converter from the power perspective by adopting the proportional complex integration method, and eliminate the harmonic components in the circulating current by reverse superposition of the DC quantity.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 7.

10. A circulating current suppression system for a grid-connected converter of a hydrogen production power source, comprising a memory and a processor connected to each other, wherein a computer program is stored in the memory, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 7.

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