Coordinated control strategy of integrated new energy hydrogen production converter

Abstract

The integrated new energy hydrogen production converter cooperative control strategy shapes the DC link voltage without using the DC link capacitor voltage sensor and the corresponding control loop, the circuit structure of the converter includes a three-phase filter circuit, a rectifier and booster circuit connected with the three-phase filter circuit and composed of six switching devices, a DC link capacitor connected with the rectifier and booster circuit, a DC conversion and voltage reduction circuit connected with the DC link capacitor and composed of six switching devices, and an interleaved parallel Buck DC conversion inductor circuit connected with the DC conversion and voltage reduction circuit, through the cooperative control strategy, the coupling relationship between the rectifier freedom and the interleaved parallel Buck DC converter freedom is utilized to avoid using the DC link capacitor voltage sensor and the control loop, and the control loop complexity is simplified.

Description

Technical Field

[0001] This invention relates to the field of hydrogen production converter control, and more specifically to a collaborative control strategy for integrated new energy hydrogen production converters. Background Technology

[0002] Hydrogen energy, as a clean and efficient secondary energy source, is of great significance for building a clean, low-carbon, safe, and efficient energy system. Hydrogen energy can effectively complement electricity in areas such as deep industrial decarbonization, transportation, and cross-seasonal energy storage. Currently, large-scale renewable energy hydrogen production, hydrogen storage, transportation, distribution, and applications in industry and transportation are all in the early stages of technology demonstration and key equipment development, requiring significant investment in research and development. Currently, new energy hydrogen production converters typically use thyristor technology, but this approach suffers from high harmonic content and slow dynamic response, affecting system efficiency. To address this issue, a two-stage circuit scheme is used in industry. However, the inefficiency caused by the two-stage circuit is particularly pronounced. Therefore, academia and industry have successively proposed solutions to improve overall efficiency by eliminating the two zero vectors on the rectifier side. This solution is called amplitude modulation technology, but its core lies in using a later-stage interleaved parallel Buck circuit to shape the waveform of the DC link capacitor voltage—pulsating it at six times the grid voltage frequency. However, traditional shaping schemes require sampling the DC link capacitor voltage and constructing a corresponding control loop. Therefore, while improving converter efficiency, this increases the complexity of the control loop. In fact, traditional control strategies focus solely on shaping the DC-link capacitor voltage through interleaved parallel Buck circuits, neglecting the crucial coupling between the rectifier and DC-DC converter sides. The technical challenge of shaping the DC-link voltage without using a DC-link capacitor voltage sensor and its corresponding control loop, thereby simplifying the control loop and reducing costs, urgently needs to be addressed. Summary of the Invention

[0003] To address the problems of the prior art, this invention designs a collaborative control strategy for an integrated new energy hydrogen production converter. By utilizing the coupling relationship between the degrees of freedom of the front-stage boost rectifier and the back-stage interleaved parallel Buck converter, the duty cycle of the interleaved parallel Buck circuit is reasonably adjusted. The DC link voltage is shaped without using a DC link capacitor voltage sensor and its corresponding control loop. Two zero vectors are eliminated on the rectifier side, simplifying the traditional control loop, saving hardware costs, and improving power density.

[0004] The technical solution adopted in this invention is a collaborative control strategy for an integrated new energy hydrogen production converter, including a converter connected to the grid side. The converter's circuit structure includes a three-phase filter circuit, a rectifier-boost circuit composed of six switching devices connected to the three-phase filter circuit, a DC-DC link capacitor connected to the rectifier-boost circuit, a DC-DC converter-buck circuit composed of six switching devices connected to the DC-DC link capacitor, and an interleaved parallel Buck DC-DC converter inductor circuit connected to the DC-DC converter-buck circuit. Based on this, the specific steps of the collaborative control strategy are as follows:

[0005] a. The duty cycle of the first switching control device group of the front-end rectifier boost circuit is calculated by comparing the three-phase modulated wave on the grid side with the carrier wave with the DC link capacitor voltage amplitude pulsating at six times the grid frequency through the PI controller.

[0006] b. The high-frequency adjustment variable is obtained by processing the error between the current reference value and the current feedback value of the six times grid frequency pulsation through the PI controller.

[0007] c. The voltage of the DC link capacitor is divided by the unit pulse of six times the grid frequency, and then combined with the high-frequency adjustment variable obtained in step a to obtain the duty cycle of the second switching control device group of the DC-DC converter buck circuit. Each duty cycle is 120° different from the others, and after being compared with the unit carrier, a pulse is directly emitted.

[0008] d. When the converter output voltage command is lower than When the grid voltage amplitude is twice that of the DC-DC converter step-down circuit, the second switching control device group operates at high frequency. If the converter output voltage command is higher than or equal to the grid voltage amplitude, the converter will continue to operate at high frequency. When the grid voltage amplitude is twice that of the DC-DC converter step-down circuit, the second switch control device group remains in the on state.

[0009] In step a, the current reference value for six times the grid frequency pulsation is obtained by multiplying the maximum absolute value of the three-phase modulation wave on the grid side by the reference admittance.

[0010] In step b, the current feedback value of six times the grid frequency pulsation is obtained by multiplying the maximum absolute value of the three-phase current feedback value on the grid side by the reference admittance.

[0011] The aforementioned three-phase modulated wave on the power grid side is obtained through the following steps:

[0012] S1. The output voltage error is obtained by calculating the error between the output voltage reference value and the output voltage feedback value after filtering by the low-pass filter. The grid-connected active power error is obtained by calculating the error between the grid-connected power reference value and the grid-connected active power feedback value. The d-axis component and q-axis component of the grid-connected current are calculated based on the instantaneous power method.

[0013] S2. Subtract the d-axis component of the grid-connected current feedback value from the d-axis reference value of the grid-connected current to obtain the d-axis error of the grid-connected current. Subtract the q-axis component of the grid-connected current feedback value from the q-axis reference value of the grid-connected current to obtain the q-axis error of the grid-connected current. The d-axis error and q-axis error of the grid-connected current are processed by the PI controller and then the d-axis decoupling component and q-axis decoupling component are added to obtain the modulated wave in the d-axis and q-axis.

[0014] S3. The three-phase modulation wave on the grid side is obtained by transforming the modulation wave under the d-axis and q-axis.

[0015] The beneficial effects of this invention are that, through the cooperative control strategy of this invention, the coupling relationship between the rectifier degree of freedom and the interleaved parallel Buck DC-DC converter degree of freedom is utilized to avoid the use of DC link capacitor voltage sensors and their control loops, eliminate the use of two types of zero vectors, simplify the complexity of the control loop, reduce the number of switching actions, and improve efficiency and reliability.

[0016] In addition, this invention can coordinate the control of the degrees of freedom of the front and rear stages. Based on the control of the grid current amplitude, a high-frequency adjustment variable is generated to calculate the duty cycle of the interleaved parallel Buck in the rear stage. By reasonably adjusting the duty cycle of the interleaved parallel Buck, the DC link capacitor voltage can be pulsated at six times the grid frequency. It can maintain a highly sinusoidal grid current under the premise of eliminating two zero vectors in the front stage rectifier, thereby improving the reliability of the converter. Attached Figure Description

[0017] Figure 1 This is a system topology diagram of an embodiment of the present invention.

[0018] Figure 2 This is a control block diagram for the output voltage control circuit and the grid-side active current generation circuit.

[0019] Figure 3 This is a block diagram for the control of active and reactive current on the grid side.

[0020] Figure 4 A block diagram for generating the duty cycle of an interleaved parallel Buck DC-DC converter inductor circuit.

[0021] Figure 5 This is a block diagram of circuit signal sampling and its overall control.

[0022] In the attached diagram, V a V b V c Representing three-phase electricity, S1-S6 are six common switching devices in the rectifier boost circuit, L fThis represents a three-phase filter circuit. S7-S9 are three switching control devices, S10-S12 are three general-purpose switching devices, L1-L3 are the inductors of an interleaved parallel Buck converter, and C... link It is a DC link capacitor. Detailed Implementation

[0023] See Figure 1 The proposed converter consists of a rectifier boost circuit S1-S6, a DC-DC converter buck circuit S7-S12, an interleaved parallel Buck converter inductor circuit L1-L3, and a DC link capacitor C. link , grid-side filter circuit L f And the power grid section. The rectifier-side converter section adopts a three-phase, six-switch topology, and the DC-DC buck converter is a classic interleaved parallel Buck DC-DC converter.

[0024] The core of this invention is to reduce control complexity and eliminate the need for a DC-link capacitor voltage sensor and its control loop by accurately controlling the switching of the rectifier-side converter and the DC-DC buck converter based on actual changes. Since a DC-link capacitor voltage sensor is not used, and voltage drops exist extensively in the converter, the DC-link capacitor voltage value cannot be accurately controlled and estimated; therefore, a high-frequency adjustment variable needs to be introduced.

[0025] By leveraging the coupling relationship between the degrees of freedom of the boost side and the interleaved parallel buck side of the rectifier under coordinated control, the DC-link capacitor voltage sensor and its corresponding control circuit can be omitted. Specifically, the output voltage error V... dc_ref -V dc The output voltage reference value V dc_ref With the low-pass filter LPF Filtered output voltage feedback value V dc The error; the grid-connected active power error is P. G_ref -P G Grid-connected power reference value P G_ref With grid-connected active power feedback value P G The error; and the d-axis component I of the grid-connected current feedback value is calculated based on the instantaneous power method. d And the q-axis component of the grid-connected current feedback value I q For details, please see Figure 2 .

[0026] The d-axis error of the grid-connected current is I. d_ref -I d The grid-connected current q-axis error is I. q_ref -I q Among them, I d_ref I is the reference value for the d-axis of the grid-connected current. q_ref I is the reference value for the grid-connected current q-axis.d For the d-axis component of the grid-connected current feedback value, I q This refers to the q-axis component of the grid-connected current feedback value; see details below. Figure 3 ; Grid-connected current d-axis error I d_ref -I d With grid-connected current q-axis I q_ref -I q After being processed by a PI controller, the decoupled components ωL of the d-axis and q-axis are added. f I q ,ωL f I d The modulation wave M in the d-axis and q-axis is obtained. d With M q The specific formula is as follows:

[0027] The reference value for the grid-side current at six times the frequency is the three-phase voltage modulation wave M. a M b M c The maximum absolute value, multiplied by the reference admittance I. d_ref / M m : The current feedback value of the grid side at six times the frequency is the three-phase current feedback value I. a ,I b ,I c The maximum absolute value, multiplied by the reference admittance I. d_ref / M m : The error between the two is processed by a PI controller to calculate the high-frequency adjustment variable ε. The DC link capacitor voltage V is then calculated using the high-frequency adjustment variable ε. dc Duty cycle of the shaped interleaved parallel bucks: For detailed algorithm information, please refer to [link / reference]. Figure 4 .

[0028] In addition, the coordinate transformations used in the specific implementation are as follows:

[0029] Coordinate transformation 1: Grid-side three-phase current I a I b I c Converted to I through coordinate transformation d I q :

[0030]

[0031] Three-phase voltage V on the grid side a V b V c Transformed into V through coordinate transformation d V q :

[0032]

[0033] Coordinate Transformation 2: Rectifier-Side Modulated Wave M d With M q The amplitude M of the modulated wave can be calculated through the following coordinate transformation. m The specific formula is as follows:

[0034]

[0035] Coordinate Transformation 3: Network-Side Modulated Wave M d With M q The coordinates are transformed into M through the following coordinate transformation. a M b and M c The specific formula is as follows:

[0036]

Claims

1. A coordinated control strategy for integrated new energy hydrogen production converters, comprising a converter connected to a power grid, characterized in that: The converter's circuit structure includes a three-phase filter circuit, a rectifier-boost circuit composed of six switching devices connected to the three-phase filter circuit, a DC-link capacitor connected to the rectifier-boost circuit, a DC-to-buck converter circuit composed of six switching devices connected to the DC-link capacitor, and an interleaved parallel Buck DC-to-buck converter inductor circuit connected to the DC-to-buck converter circuit. Based on this, the specific steps of the cooperative control strategy are as follows: a. The duty cycle of the first switching control device group (S1, S2, S3) of the front-stage rectifier boost circuit is calculated by comparing the three-phase modulated wave on the grid side with the carrier wave with the DC link capacitor voltage amplitude pulsating at six times the grid frequency using a PI controller. b. The high-frequency adjustment variable is obtained by processing the error between the current reference value and the current feedback value of the six times grid frequency pulsation through the PI controller. c. Divide the voltage of the DC link capacitor by six times the unit pulse of the grid frequency, and then combine it with the high-frequency adjustment variable obtained in step a to obtain the duty cycle of the second switching control device group (S7, S8, S9) of the DC-DC converter step-down circuit. Each duty cycle is 120° apart, and after comparing it with the unit carrier, a pulse is directly emitted. d. When the converter output voltage command is lower than twice the grid voltage amplitude, the second switching control device group (S7, S8, S9) of the DC-DC buck converter circuit operates at high frequency. If the converter output voltage command is higher than or equal to twice the grid voltage amplitude, the second switching control device group (S7, S8, S9) of the DC-DC buck converter circuit remains in a continuous on state. In step b, the current reference value for six times the grid frequency pulsation is obtained by multiplying the maximum absolute value of the three-phase modulation wave on the grid side by the reference admittance, and the current feedback value for six times the grid frequency pulsation is obtained by multiplying the maximum absolute value of the three-phase current feedback value on the grid side by the reference admittance.

2. The collaborative control strategy for the integrated new energy hydrogen production converter according to claim 1, characterized in that: The aforementioned three-phase modulated wave on the power grid side is obtained through the following steps: S1. The output voltage error is obtained by calculating the error between the output voltage reference value and the output voltage feedback value after filtering by the low-pass filter. The grid-connected active power error is obtained by calculating the error between the grid-connected power reference value and the grid-connected active power feedback value. The d-axis component and q-axis component of the grid-connected current are calculated based on the instantaneous power method. S2. Subtract the d-axis component of the grid-connected current feedback value from the d-axis reference value of the grid-connected current to obtain the d-axis error of the grid-connected current. Subtract the q-axis component of the grid-connected current feedback value from the q-axis reference value of the grid-connected current to obtain the q-axis error of the grid-connected current. The d-axis error and q-axis error of the grid-connected current are processed by the PI controller and then the d-axis decoupling component and q-axis decoupling component are added to obtain the modulated wave in the d-axis and q-axis. S3. The three-phase modulation wave on the grid side is obtained by transforming the modulation wave under the d-axis and q-axis.

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