Low-electric-stress high-gain direct-current boost converter for hydrogen fuel cell grid-connected system and converter control method and device

Abstract

The invention discloses a low-electric-stress high-gain direct-current boost converter for a hydrogen fuel cell grid-connected system. The low-electric-stress high-gain direct-current boost converter comprises inductors L1, L2 and L3, capacitors C1, C2, C3, C4 and C5, diodes D1, D2 and D3 and a full-control device S1. Compared with an existing converter, the direct-current boost converter has the advantages of being low in electric stress and high in voltage gain under the condition that devices are almost the same or even fewer. According to the direct-current boost converter, high-voltage gain is achieved through the single switching tube, low voltage of the hydrogen fuel cell can be fully converted into high voltage, and then grid connection is achieved through the inverter. The voltage stress of the full-control device and the diode device of the direct-current boost converter is low, the loss of a power device is reduced, the efficiency of the converter is improved, the service life of the converter is prolonged, and safe, stable and efficient operation of a hydrogen fuel cell grid-connected converter is facilitated. The invention further discloses a direct-current boost converter control method and device.

Description

Technical Field

[0001] The present invention relates to the field of hydrogen fuel cell power generation, and in particular to a low electrical stress and high gain DC boost converter for a hydrogen fuel cell grid-connected system, and a converter control method and device. Background Art

[0002] Hydrogen fuel cell grid-connected power generation is one of the important scenarios for the current use of hydrogen energy. However, high-power hydrogen fuel cells have nonlinear volt-ampere characteristics, low voltage, high current and large fluctuations, and cannot be directly connected to the load. A DC converter that matches its output characteristics is required to regulate the power and then connect to the grid through an inverter. At present, the DC converter has problems such as insufficient boost capability and high device stress, which leads to a reduction in the working life and increased power loss of the DC converter for hydrogen fuel cells, making it difficult to match the power generation capacity of high-power hydrogen fuel cells.

[0003] In recent years, breakthroughs have been made in the topology design of high voltage gain DC converters for clean energy grid-connected power generation systems. Although the prior art has proposed many topological structures suitable for clean energy grid-connected power generation in terms of hydrogen fuel cell input voltage ripple, input current ripple, switch stress and voltage gain, the existing topological designs often have too many switches, resulting in poor economic efficiency, and the prior art rarely considers both achieving high voltage gain and taking into account switch device stress.

[0004] Therefore, a new technical solution is urgently needed to solve the technical problem of how to design a DC boost converter and its control method that can adapt to the operating characteristics of hydrogen fuel cells and have the characteristics of high voltage gain, low electrical stress and high economy. Summary of the invention

[0005] The present invention provides a low electrical stress and high gain DC boost converter, a converter control method and a device for a hydrogen fuel cell grid-connected system, so as to solve the technical problem of how to design a DC boost converter and a control method thereof which can adapt to the operating characteristics of hydrogen fuel cells and have the characteristics of high voltage gain, low electrical stress and high economy.

[0006] To achieve the above object, the present invention provides a low electrical stress and high gain DC boost converter for a hydrogen fuel cell grid-connected system, comprising an inductor L 1 , L 2 and L 3 , capacitor C 1 , C 2 , C 3 , C 4 and C 5 , diode D 1 , D 2 and D 3 , fully controlled device S 1 ;

[0007] Inductance L 1 The first terminal and capacitor C 1 The first end is connected to serve as the positive input electrode of the converter;

[0008] Inductance L 1 The second end of the diode D 1 The positive electrode and capacitor C 4 The first end of the diode D 1 The negative electrode and the inductor L 2 The first end and capacitor C 3 The first end of the inductor L 2 The second end of the capacitor C 4 The second end of the fully controlled device S 1 The collector of diode D 2 The positive electrode and capacitor C 2 connected to the first end of

[0009] Capacitor C 1 The second end of the diode D 2 The negative electrode and the inductor L 3 The first end of the inductor L 3 The second end of the capacitor C 2 The second end of the diode D 3 The positive pole of diode D 3 The negative electrode and capacitor C 5 The first end of the capacitor C is connected to the positive output of the converter; 5 The second end of the fully controlled device S 1 The emitter and capacitor C 3 The second end is connected as the input negative pole and output negative pole of the converter.

[0010] The present invention also provides a DC boost converter control method. Based on the DC boost converter of the present invention, the method comprises:

[0011] Set the output voltage reference value of the converter; monitor the actual output voltage of the converter in real time;

[0012] According to the output voltage reference value and the actual output voltage, the fully controlled device S 1 Duty cycle reference value;

[0013] According to the fully controlled device S 1 A first switching signal is obtained by using a duty cycle reference value and a preset triangular carrier;

[0014] The first switch signal is input to the fully controlled device S 1 , low voltage to high voltage output is achieved through the converter.

[0015] Preferably, the fully controlled device S is obtained according to the output voltage reference value and the actual output voltage. 1 The duty cycle reference values ​​include:

[0016]

[0017] Among them, d ref Indicates fully controlled device S 1 Duty cycle reference value, U ref Indicates the output voltage reference value of the converter, U out represents the actual output voltage of the converter, k p With k i They represent the proportional coefficient and the integral coefficient respectively, and s represents the complex frequency domain variable.

[0018] Preferably, it also includes:

[0019] The first switch signal is input to the fully controlled device S 1 After that, the converter operates in the first mode and the second mode in sequence at preset time intervals within a working cycle.

[0020] Preferably, the first mode includes: a fully controlled device S 1 Conductivity, diode D 1 , D 2 and D 3 All are turned off;

[0021] The second mode includes: fully controlled device S 1 Turn off, diode D 1 , D 2 and D 3 All are conducting.

[0022] The present invention also provides a DC boost converter control device, comprising a memory and a processor; the memory is used to store a computer program for implementing the DC boost converter control method of the present invention; the processor is used to execute the computer program and implement the DC boost converter control method of the present invention.

[0023] The present invention has the following beneficial effects:

[0024] Compared with the existing converters, the DC boost converter of the present invention has the characteristics of low electrical stress and high voltage gain while having almost the same or even fewer devices. The DC boost converter of the present invention achieves high voltage gain through a single switch tube, and can fully realize the conversion of the low voltage of the hydrogen fuel cell into a high voltage and then connect to the grid through the inverter. The fully controlled devices and diode devices of the DC boost converter of the present invention have low voltage stress, which is conducive to reducing the loss of power devices, improving the efficiency and service life of the converter, and is conducive to the safe, stable and efficient operation of the hydrogen fuel cell grid-connected converter.

[0025] The DC boost converter control method of the present invention is based on the DC boost converter of the present invention and has the same beneficial effects as the DC boost converter of the present invention.

[0026] The DC boost converter control device of the present invention is used in the DC boost converter control method of the present invention, and has the same beneficial effects as the DC boost converter control method of the present invention.

[0027] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0029] Figure 1 1 is a schematic diagram of a topology of a DC boost converter according to a preferred embodiment of the present invention.

[0030] Figure 2 It is a schematic diagram of a DC boost converter connected to a power grid via an inverter according to a preferred embodiment of the present invention.

[0031] Figure 3 It is a flow chart of a preferred embodiment of the present invention.

[0032] Figure 4 Schematic diagram of the first mode of the preferred embodiment of the present invention.

[0033] Figure 5 Schematic diagram of the second mode of the preferred embodiment of the present invention.

[0034] Figure 6 Schematic diagram of the converter equivalent circuit in steady state according to the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0035] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0036] See also Figure 1 to Figure 2 In a preferred embodiment of the present invention, a low electrical stress high gain DC boost converter for a hydrogen fuel cell grid-connected system is provided, comprising an inductor L 1 , L 2 and L 3 , capacitor C 1 , C 2 , C 3 , C4 and C 5 , diode D 1 , D 2 and D 3 , fully controlled device S 1 .

[0037] Inductance L 1 The first terminal and capacitor C 1 The first end is connected as the positive input of the converter.

[0038] Inductance L 1 The second end of the diode D 1 The positive electrode and capacitor C 4 The first end of the diode D 1 The negative electrode and the inductor L 2 The first end and capacitor C 3 The first end of the inductor L 2 The second end of the capacitor C 4 The second end of the fully controlled device S 1 The collector of diode D 2 The positive electrode and capacitor C 2 connected to the first end of .

[0039] Capacitor C 1 The second end of the diode D 2 The negative electrode and the inductor L 3 The first end of the inductor L 3 The second end of the capacitor C 2 The second end of the diode D 3 The positive pole of diode D 3 The negative electrode and capacitor C 5 The first end of the capacitor C is connected to the positive output of the converter; 5 The second end of the fully controlled device S 1 The emitter and capacitor C 3 The second end is connected as the input negative pole and output negative pole of the converter.

[0040] In a preferred embodiment of the present invention, the fully controlled device S 1 The current shunting of the diode D 2 and D 3 of current stress.

[0041] exist Figure 1 Middle,U in Indicates the input power supply voltage between the positive input and negative input of the converter; U C1 , U C2 , U C3 , U C4 and U C5 Respectively represent the capacitance C1 , C 2 , C 3 , C 4 and C 5 The voltage across the two ends of L1 Indicates that the inductor L 1 The current i L2 Indicates that through the inductor L 2 The current i L3 Indicates that through the inductor L 3 The current; U out It represents the voltage on the equivalent resistor R between the positive and negative output electrodes of the converter, i.e., the output voltage of the converter; I out Represents the current passing through the equivalent resistance R.

[0042] Figure 2 The schematic diagram is a diagram of the DC boost converter of the present invention being connected to a power grid via an inverter.

[0043] See also Figure 3 In a preferred embodiment of the present invention, a DC boost converter control method is also provided. Based on the DC boost converter of the present invention, the method includes:

[0044] A1. Set the output voltage reference value of the converter; monitor the actual output voltage of the converter in real time.

[0045] A2. Obtain the fully controlled device S based on the output voltage reference value and the actual output voltage 1 Duty cycle reference value. Specifically include:

[0046]

[0047] Among them, d ref Indicates fully controlled device S 1 Duty cycle reference value, U ref Indicates the output voltage reference value of the converter, U out Indicates the actual output voltage of the converter, k p With k i They represent the proportional coefficient and the integral coefficient respectively, and s represents the complex frequency domain variable.

[0048] A3, according to the fully controlled device S 1 The first switching signal is obtained by combining the duty cycle reference value and the preset triangular carrier.

[0049] A4. Input the first switch signal to the fully controlled device S 1 , low voltage to high voltage output is achieved through the converter.

[0050] In a preferred embodiment of the present invention, the first switch signal is input to the fully controlled device S 1After that, the converter operates in the first mode and the second mode in sequence at preset time intervals within a working cycle.

[0051] See also Figure 4 , the first mode includes: fully controlled device S 1 Conductivity, diode D 1 , D 2 and D 3 All turned off.

[0052] See also Figure 5 , the second mode includes: fully controlled device S 1 Turn off, diode D 1 , D 2 and D 3 All are conducting.

[0053] In the first mode:

[0054] Inductance L 1 The voltage across the terminals is U L1 It can be expressed as:

[0055] U L1 =U in +U C4 (1)

[0056] Inductance L 2 The voltage across the terminals is U L2 It can be expressed as:

[0057] U L2 =U C3 (2)

[0058] Inductance L 3 The voltage across the terminals is U L3 It can be expressed as:

[0059] U L3 =U in +U C1 -U C2 (3)

[0060] In the second mode:

[0061] Inductance L 1 The voltage across the terminals is U L1 It can be expressed as:

[0062] U L1 =U in -U C3 (4)

[0063] Inductance L 2 The voltage across the terminals is U L2 It can be expressed as:

[0064] UL2 =-U C4 (5)

[0065] Inductance L 3 The voltage across the terminals is U L3 It can be expressed as:

[0066] U L3 =-U C2 (6)

[0067] Based on the inductor volt-second balance characteristics within a switching cycle, the U under the first mode and the second mode are combined. L1 , U L2 and U L3 , that is, (1), (2), (3), (4), (5) and (6), we can get:

[0068]

[0069] Among them, U L1 , U L2 , U L3 Respectively represent the inductance L 1 , L 2 and L 3 The voltage across the two ends of the 1 The duty cycle, T S Represents the switching cycle.

[0070] Steady state capacitance C 5 The voltage at both ends remains unchanged, and the fully controlled device S 1 When turned off, the capacitor C 5 Voltage across the terminals U C5 That is, the converter output voltage U out It can be expressed as:

[0071] U out =U C5 =U C1 +U C2 +U in (8)

[0072] Combining equations (1), (2), (3), (4), (5), (6), (7) and (8), we can obtain:

[0073]

[0074] From formula (9), we can know that the voltage gain of the converter of the present invention is This reflects the strong boosting characteristics of this converter.

[0075] Fully controlled device S 1 When shut down, Figure 5 It can be seen that the fully controlled device S 1Voltage stress U S It can be expressed as:

[0076]

[0077] Fully controlled device S 1 When opened, Figure 4 It can be seen that the diode D 1 , D 2 and D 3 The voltage stress U D1 , U D2 and U D3 It can be expressed as:

[0078]

[0079] From equations (10) and (11), we can see that the diode D 1 , D 2 and D 3 And fully controlled devices S 1 The voltage stress is equal.

[0080] From the law of conservation of power:

[0081]

[0082] Among them, I in Indicates the converter input current.

[0083] When the converter works in steady state, the average current of each capacitor in the converter is 0. Therefore, the equivalent circuit of the converter in steady state is as follows: Figure 6 As shown, the inductance L 1 , L 2 and L 3 The average current I L1 ,I L2 and I L3 for:

[0084]

[0085] Through the fully controlled device S 1 、Diode D 1 , D 2 and D 3 The average current stress I S ,I D1 ,I D2 and I D3 for:

[0086]

[0087] From formula (14), we can see that except for the diode D 1In addition to the large current stress, the switch tube S 1 、Diode D 2 and D 3 The current stress is low.

[0088] The converter of the present invention is compared with the converters proposed in the four existing documents and the traditional Z-source boost, and the comparison results are shown in Table 1, wherein the four inductors in Document 2 include a coupled inductor. As can be seen from Table 1, compared with the existing converters, the DC boost converter of the present invention has a stronger boost capability when the number of devices is almost the same or even less, and can convert the low voltage of a high-power hydrogen fuel cell into a high voltage under a smaller duty cycle, thereby achieving grid connection through an inverter. As can be seen from Table 1, the DC boost converter of the present invention has smaller switch stress and diode stress, which is beneficial to reducing the loss of power devices, improving the efficiency and service life of the converter, and is beneficial to the safe, stable and efficient operation of the hydrogen fuel cell grid-connected converter.

[0089] Table 1 Comparison between the converter of the present invention and the existing converter

[0090]

[0091] There are four existing literature sources:

[0092] Document 1: WANG Zhishuang, WANG Ping, LI Bo, et al. Abidirectional DC-DCconverter with high voltage conversion ratio and zero ripple current for battery energy storage system [J]. IEEE Transactions on Power Electronics, 2021, 36(7): 8012-8027.

[0093] Document 2: MISHRAAK, SINGH B. High gain single ended primary inductorconverter with ripple free input current for solar powered water pumping system utilizing cost-effective maximum power point tracking technique [J]. IEEE Transactions on Industry Applications, 2019, 55(6): 6332-6343.

[0094] Document 3: ZHANG GD, ZHANG B, LI Z, et al.A 3-Z-networkBoost converter[J]. IEEE transactions on industrialelectronics, 2015, 62(1): 278-288.

[0095] Document 4: ATHIKKAL S, CHOKKALINGAM B, GANESAN SI, et al. Performance evaluation of a dual-input hybrid step-up DC-DC converter[J]. IEEE Transactions on Industry Applications, 2022, 58(3): 3769-3782.

[0096] In document 1, coupled inductors are used to eliminate input current ripples. However, the switching devices of this type of topology are subjected to large voltage stress when they are turned off, and high-voltage withstand devices are required, which increases system costs.

[0097] In Document 2, a ripple elimination unit is used to construct the input current into two equal and opposite currents and superimpose them to eliminate the input current ripple. However, there are many components in the auxiliary unit, which makes the converter efficiency and power density low.

[0098] In reference 3, a high boost ratio is achieved by using three Z-source networks, but the switching device stress is the output voltage.

[0099] In document 4, a dual-input DC / DC converter is proposed based on the switching inductor technology. This converter can not only be expanded to multiple inputs, but also has the advantages of high power density and high efficiency. However, it still has limitations in achieving high gain.

[0100] In summary, the DC boost converter of the present invention has the characteristics of low electrical stress and high voltage gain when the devices are almost the same or even less than the existing converters. The DC boost converter of the present invention achieves high voltage gain through a single switch tube, which can fully realize the conversion of the low voltage of the hydrogen fuel cell into a high voltage and then connect to the grid through the inverter. The fully controlled devices and diode devices of the DC boost converter of the present invention have low voltage stress, which is conducive to reducing the loss of power devices, improving the efficiency and service life of the converter, and is conducive to the safe, stable and efficient operation of the hydrogen fuel cell grid-connected converter.

[0101] In a preferred embodiment of the present invention, a DC boost converter control device is also provided, comprising a memory and a processor; the memory is used to store a computer program for implementing the method of the present invention; and the processor is used to execute the computer program and implement the method of the present invention.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low electrical stress and high gain DC boost converter for a hydrogen fuel cell grid-connected system, characterized in that: It includes inductors L1, L2 and L3, capacitors C1, C2, C3, C4 and C5, diodes D1, D2 and D3, and a fully controlled device S1; The first end of the inductor L1 and the first end of the capacitor C1 are connected to serve as the positive input electrode of the converter; The second end of the inductor L1 is connected to the anode of the diode D1 and the first end of the capacitor C4; the cathode of the diode D1 is connected to the first end of the inductor L2 and the first end of the capacitor C3; the second end of the inductor L2 is connected to the second end of the capacitor C4, the collector of the fully controlled device S1, the anode of the diode D2 and the first end of the capacitor C2; The second end of capacitor C1 is connected to the cathode of diode D2 and the first end of inductor L3; the second end of inductor L3 is connected to the second end of capacitor C2 and the anode of diode D3; the cathode of diode D3 is connected to the first end of capacitor C5 as the output anode of the converter; the second end of capacitor C5 is connected to the emitter of fully-controlled device S1 and the second end of capacitor C3 as the input cathode and output cathode of the converter.

2. A DC boost converter control method, based on the DC boost converter according to claim 1, characterized in that: The method comprises: Setting an output voltage reference value of the converter; monitoring the actual output voltage of the converter in real time; Obtaining a duty cycle reference value of the fully-controlled device S1 according to the output voltage reference value and the actual output voltage; Obtaining a first switching signal according to a duty cycle reference value of the fully-controlled device S1 and a preset triangular carrier; The first switch signal is input to the fully-controlled device S1, and the converter is used to convert low voltage into high voltage output.

3. The DC boost converter control method according to claim 2, characterized in that: Obtaining a duty cycle reference value of the fully-controlled device S1 according to the output voltage reference value and the actual output voltage includes: Among them, d ref Indicates the duty cycle reference value of the fully controlled device S1, U ref Indicates the output voltage reference value of the converter, U out Indicates the actual output voltage of the converter, k p With k i They represent the proportional coefficient and the integral coefficient respectively, and s represents the complex frequency domain variable.

4. The DC boost converter control method according to claim 3, characterized in that: Also includes: After the first switch signal is input to the fully-controlled device S1, the converter sequentially operates in the first mode and the second mode at preset time intervals within a working cycle.

5. The DC boost converter control method according to claim 4, characterized in that: The first mode includes: the fully controlled device S1 is turned on, and the diodes D1, D2 and D3 are all turned off; The second mode includes: the fully controlled device S1 is turned off, and the diodes D1, D2 and D3 are all turned on.

6. A DC boost converter control device, characterized in that: It comprises a memory and a processor; the memory is used to store a computer program for implementing the method described in any one of claims 2 to 5; the processor is used to execute the computer program and implement the method described in any one of claims 2 to 5.

Images