Junction temperature balancing method and system of multi-level converter for electrolytic hydrogen production

Abstract

The invention provides a junction temperature balancing method and system for a multi-level converter for electrolytic hydrogen production. The dynamic response capability and reliability of the multi-level converter for electrolytic hydrogen production can be improved. The junction temperature of the converter power device can be balanced, overheating of some devices can be effectively prevented, the failure risk of the devices is reduced, and the service life of the converter is prolonged; in addition, the reliability of the electrolytic hydrogen production system can be enhanced, and the reliability and stability of the system are improved by optimizing temperature distribution and reducing local hot spots.

Description

Technical Field

[0001] The present invention relates to the technical field of junction temperature balancing for hydrogen production by electrolysis, and in particular to a junction temperature balancing method and system for a multi-level converter for hydrogen production by electrolysis. Background Art

[0002] Hydrogen energy has the advantages of being clean, environmentally friendly, high in energy density, and widely applicable. However, the existing electrolysis hydrogen production system involves multiple power electronic control links, resulting in low system efficiency and reliability and complex control; the existing traditional PI control strategy has a slow response speed and poor control effect, which affects the system's dynamic response and steady-state performance; the existing control strategy often ignores the uneven distribution of junction temperature of the components in the converter, which can easily lead to fluctuations and instability in system performance under high load or different working conditions, which can cause system failure in severe cases and pose safety risks. Summary of the invention

[0003] In view of this, the present invention provides a junction temperature balancing method and system for a multi-level converter for hydrogen production by electrolysis, which can improve the dynamic response capability and reliability of the multi-level converter for hydrogen production by electrolysis.

[0004] To achieve the above object, the present invention provides a junction temperature balancing method for a multi-level converter for hydrogen production by electrolysis, comprising:

[0005] Based on the equivalent switching function, an evaluation function of the level function used for level vector selection is designed to solve the optimal level vector;

[0006] Using the redundant voltage vector simplification principle, a simplified voltage vector set is obtained;

[0007] By using the DC side support capacitor voltage sorting, the optimal simplified voltage vector is selected from the simplified voltage vector set;

[0008] By using the zero vector switch state adjustment strategy and based on the junction temperature data, the zero vector switch state in the optimal simplified voltage vector is dynamically adjusted to achieve junction temperature balance of the converter.

[0009] This also includes building an equivalent model of a DAB-type DC / DC converter, dynamically adjusting the duty cycle based on the power demand for hydrogen production by electrolysis, and aggregating the power of the H-bridge sub-modules of the multi-level converter to the DC bus to achieve hydrogen production.

[0010] The specific method of solving the optimal level vector is: according to the level function evaluation function, the optimal level vector corresponding to the optimal level function is determined.

[0011] Among them, the method of obtaining the optimal simplified voltage vector is: combining the obtained optimal level vector, the grid-side current direction and the DC-side support capacitor voltage sorting of the H-bridge sub-modules of each multi-level converter, comprehensively considering the voltage vector simplification principle, and selecting the optimal simplified voltage vector.

[0012] The specific method of achieving junction temperature balance of the converter is as follows: determine whether the switching function of the H-bridge submodule of each multi-level converter is 0, if so, determine whether the junction temperature of IGBT No. 1 and IGBT No. 3 in the H-bridge submodule of each multi-level converter is higher than the junction temperature of IGBT No. 2 and IGBT No. 4, if so, dynamically adjust the zero vector working state of the switching device to S according to the principle of the junction temperature balance method. ia S ib =00; if not, maintain the original zero vector switch state S ia S ib =11; if not, then according to the judgment result, the H-bridge submodule switch state of the multi-level converter corresponding to each switch device is generated, and finally the control effect of the converter junction temperature balancing method is achieved, and the original switch state is maintained.

[0013] The present invention also provides a junction temperature balancing system for a multi-level converter for hydrogen production by electrolysis, which is used to implement the junction temperature balancing method described in the present invention, including an equivalent switching function module, a redundant voltage vector simplification module, an evaluation function module, a DC side support capacitor voltage sorting algorithm module and a junction temperature balancing method module; wherein the equivalent switching function module is used to regard the cascaded H-bridge converter as a whole and establish a level function; the redundant voltage vector simplification module is used to simplify the voltage vector; the evaluation function module is used to predict the level vector and solve the optimal level function; the DC side support capacitor voltage sorting algorithm module is used to solve the optimal simplified voltage vector; the junction temperature balancing method module is used to dynamically adjust the zero vector switching state of the converter.

[0014] It also includes a DAB type DC / DC converter module, which is used to increase the DC bus voltage and improve the hydrogen production efficiency; and an electrolysis hydrogen production module, which is used to produce hydrogen by electrolysis.

[0015] Beneficial effects:

[0016] 1. The method of the present invention can balance the junction temperature of the converter power devices, effectively prevent overheating of certain devices, reduce their failure risk, and extend the service life of the converter; in addition, it can enhance the reliability of the electrolytic hydrogen production system, improve the reliability and stability of the system by optimizing the temperature distribution and reducing local hot spots.

[0017] 2. The method of the present invention can ensure the stability and high efficiency of electric energy conversion during hydrogen production by electrolysis, thereby improving the overall hydrogen production efficiency.

[0018] 3. In the method of the present invention, in a multi-level converter, by reasonably distributing the voltage vector space, the number of required voltage vectors is reduced, and redundant voltage vectors are reduced without affecting system performance, so as to simplify redundant voltage vectors. By selecting the optimal or most representative voltage vector, the complexity of the control algorithm is reduced while maintaining or improving system performance; it is used to optimize control strategies, improve efficiency and reduce system complexity.

[0019] 4. In the method of the present invention, in a multi-level converter, the voltage of the DC side support capacitor may be unbalanced. In order to ensure the normal operation of the system, a voltage sorting algorithm is used to effectively control and balance these capacitor voltages. The basic idea is to sort them according to the voltage values ​​of the support capacitors and select appropriate voltage vectors based on the sorting results to achieve balance and stability of the DC side support capacitor voltages. This needs to be achieved by monitoring capacitor voltages, voltage sorting, determining voltage vectors, optimizing targets and control strategies.

[0020] 5. In the system of the present invention, stable control of the DC side support capacitor voltage is achieved; junction temperature balance and efficient hydrogen production of the converter are achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a topology diagram of a multi-level converter used for hydrogen production by electrolysis.

[0022] Figure 2 S in the multilevel converter ia S ib =10, S ia S ib =01, S ia S ib =11 and S ia S ib =00 is a schematic diagram of the working state of the H-bridge submodule of the H-bridge multi-level converter.

[0023] Figure 3 The figure is a schematic diagram of the model predictive control process in the method of the present invention.

[0024] Figure 4 It is a schematic diagram of the process flow of the junction temperature balancing method of the present invention.

[0025] Figure 5 Schematic diagram of the method system of the present invention.

[0026] Figure 6 It is a comparison chart of the junction temperature of each IGBT in the prior art and the present invention under steady-state conditions.

[0027] in, Figure 6 (a) is the junction temperature of each IGBT in the prior art under steady-state conditions; Figure 6(b) is the junction temperature of each IGBT of the proposed technology under steady-state conditions.

[0028] Figure 7 It is a comparison diagram of the junction temperature of each IGBT in the prior art and the present invention under power mutation conditions.

[0029] in, Figure 7 (a) is the junction temperature of each IGBT in the prior art under power mutation conditions; Figure 7 (b) is the junction temperature of each IGBT in the present invention under power mutation conditions. DETAILED DESCRIPTION

[0030] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0031] The present invention provides a junction temperature balancing method for a multi-level converter for hydrogen production by electrolysis, which improves the dynamic response capability and reliability of the multi-level converter for hydrogen production by electrolysis. Taking a cascaded H-bridge converter as an example, the topology of a multi-level converter for hydrogen production by electrolysis is as follows: Figure 1 As shown, Figure 1 In, C dci is the DC side support capacitor of the i-th H-bridge submodule of the multilevel converter; U dci is the DC side support capacitor voltage of the i-th H-bridge submodule of the multilevel converter; S i1 , S i2 , S i3 and S i4 are four switching power devices of the H bridge of the i-th H bridge submodule of the multi-level converter; abi The AC side voltage is connected to the i-th H-bridge submodule of the multi-level converter; u ab For the AC side voltage; R s , L s are the grid-side equivalent resistance and inductance respectively; u s 、i s are the AC side voltage and current respectively. The method of the present invention comprises the following steps:

[0032] Step 101: Based on the equivalent switching function, an evaluation function of a level function for level vector selection is designed to solve the optimal level vector;

[0033] Specifically, the equivalent switching function is defined as S i , and gives the AC side voltage u of the H-bridge submodule of the i-th multilevel converter abi The DC side support capacitor voltage U dci relation:

[0034] S i =S ia -S ib (1)

[0035] u abi =S i ·U dci (2)

[0036] In the formula, S i is the equivalent switching function; u abi is the output voltage of the H-bridge submodule of the i-th multilevel converter; U dci is the DC side support capacitor voltage of the H-bridge submodule of the i-th multilevel converter.

[0037] Combination Figure 2 The working status of the submodules of the H-bridge multilevel converter can be seen: each H-bridge submodule contains 2 2 Working states, corresponding to Figure 2 Upper left middle S i =1; Figure 2 Upper right middle S i = -1; Figure 2 Lower left middle S i =0; Figure 2 Lower right middle S i =0.

[0038] according to Figure 3 The model predictive control flow chart shown in the figure performs the following steps:

[0039] According to Kirchhoff's voltage law, the single-phase cascade H-bridge circuit equation is established. Since the network resistance R s Very small, modeling can be ignored:

[0040]

[0041] The above formula is decomposed in the dq rotating coordinate system:

[0042]

[0043] In the formula, u abd 、u abq u ab In the d-axis and q-axis components; i sd 、i sq i s In the d-axis and q-axis components; ω is the grid-side voltage u s Angular velocity; u sm for u s Fundamental component amplitude;

[0044] According to the instantaneous power theory, the above formula can be rewritten as:

[0045]

[0046] In the formula, ps ,q s They are respectively the active and reactive power output from the grid side;

[0047] Adjusting the above formula to the change of active and reactive power on the grid side over time, we can get:

[0048]

[0049] Based on the Euler forward method, equation (6) can be transformed into equation (7):

[0050]

[0051] After sorting, we can get the state quantity of active and reactive power on the grid side at time k+1:

[0052]

[0053] In the formula, p s (k), p s (k+1) are p s Take values ​​at time k and k+1; q s (k), q s (k+1) are q s Take values ​​at time k and k+1; T s is the sampling period; u sm (k) is u sm Take the value at time k; u abd (k) and u abq (k) are u abd 、u abq Take the value at time k;

[0054] Grid side input voltage u ab Available level function lev and DC side support capacitor voltage average value U av It is expressed as:

[0055] u ab =lev·U av (9)

[0056] Based on this, the evaluation function of the level function is set as:

[0057]

[0058] In the formula, J1(k) is the expression of the evaluation function at time k; For p s (k+1) reference quantity; for q s (k+1) reference quantity; λ1 is the control weight coefficient of the level function; U av (k+1) is U avTake the value at time k+1;

[0059] The control objective is to balance the system power and select the optimal level function lev to achieve voltage balance of the DC side support capacitor.

[0060] Step 102: using the redundant voltage vector simplification principle to obtain a simplified voltage vector set;

[0061] Specifically, the principle of redundant voltage vector simplification is to reduce the number of required voltage vectors in a multi-level converter by reasonably distributing the voltage vector space. The key to redundant voltage vector simplification is to reduce redundant voltage vectors without affecting system performance. It is used to optimize control strategies, improve efficiency and reduce system complexity. The main purpose of simplifying redundant voltage vectors is to reduce the complexity of the control algorithm while maintaining or improving system performance, which can be achieved by selecting the optimal or most representative voltage vector.

[0062] In order to avoid unnecessary calculations and increased complexity, the redundant voltage vector is simplified. When the output voltages of two H-bridge submodules of a multilevel converter cancel each other, it means that their contributions cancel each other and do not generate gain to the output voltage of the final cascaded H-bridge converter. In this case, the sum of the output voltages is not a simple addition, but a partial cancellation of the voltages. Based on this, let: lev>0, the switching function S i Only 0 and 1 are taken; when lev = 0, the switching function S i Only 0; when lev=±N, the switching function S i Only ±1 is taken; when lev<0, the switching function S i Just take 0 and -1.

[0063] Step 103: using a DC side support capacitor voltage sorting algorithm to select an optimal simplified voltage vector from a simplified voltage vector set;

[0064] Among them, in the multi-level converter, the voltage of the DC side support capacitor may be unbalanced. In order to ensure the normal operation of the system, these capacitor voltages need to be effectively controlled and balanced. The basic idea of ​​the voltage sorting algorithm is to sort according to the voltage value of the support capacitor and select the appropriate voltage vector according to the sorting result to achieve the balance and stability of the DC side support capacitor voltage. A series of steps need to be implemented through monitoring capacitor voltage, voltage sorting, determining voltage vector, optimizing target and control strategy:

[0065] First, it is necessary to determine the voltage with the largest difference from the mean voltage and give a switching function that meets the requirements; secondly, determine the voltage with the second largest difference from the mean voltage, and then combine the constraints of the number of levels to give a switching function that meets the requirements; the switching function determination method of the H-bridge sub-modules of the remaining multi-level converters is the same, and finally the switching functions of the H-bridge sub-modules of each multi-level converter are obtained.

[0066] Step 104: Adopting a zero vector switch state adjustment strategy, based on the junction temperature data, dynamically adjusting the zero vector switch state in the optimal simplified voltage vector to achieve junction temperature balance of the converter;

[0067] The zero vector switch state is fixed to S ia S ib =11 or S ia S ib = 00, the switching function S i Always 0, the output voltage u of the cascaded H-bridge converter dci , grid-side current i s The control effect has no impact, and the choice of its switching state only affects the number of times the switch device is turned on and the junction temperature. Therefore, without affecting the power quality, the purpose of balancing the junction temperature of the converter can be achieved by dynamically adjusting the zero vector switching state;

[0068] When the zero vector switch state is fixed to S ia S ib =11, then T ji1 、T ji3 >T ji2 、T ji4 , the switch state needs to be dynamically adjusted to S ia S ib =00, while limiting the continuous increase of the junction temperature of IGBT 1 and IGBT 3, the junction temperature of IGBT 2 and IGBT 4 is increased; similarly, when the zero vector switch state is fixed to S ia S ib = 00, at this time T ji1 、T ji3 <T ji2 、T ji4 , the switch state needs to be dynamically adjusted to S ia S ib =11, while limiting the continuous increase in the junction temperature of IGBT No. 2 and IGBT No. 4, the junction temperature of IGBT No. 1 and IGBT No. 3 is increased, ultimately achieving junction temperature balance of the converter.

[0069] Table 1 Principle of dynamic adjustment of zero vector switch state before and after junction temperature balancing

[0070]

[0071] Before implementing the junction temperature balancing method, the junction temperature relationship of the H-bridge submodules of each multilevel converter needs to be summarized to provide a basis for the subsequent dynamic selection of the zero vector switch state. Table 2 shows the junction temperature relationship of the H-bridge submodules of each multilevel converter.

[0072] Table 2 H-bridge submodule junction temperature relationship table of each multi-level converter

[0073]

[0074]

[0075] Table 2 summarizes the H-bridge submodules of the three multi-level converters. 3 (Corresponding to numbers ① to ⑧ in the table) Junction temperature of the switching device IGBT in the following combinations.

[0076] Table 2 summarizes the H-bridge submodules of the three multi-level converters. 3 (Corresponding to the serial numbers ① to ⑧ in the table) The junction temperature of the IGBT switching devices in the permutation and combination forms. Based on Table 1 and Table 2, Table 3 gives the simplified voltage vector V with cascade number N = 3 svol Dynamic selection table of zero vector switching states of H-bridge submodules of all multi-level converters under .

[0077] Table 3 Dynamic selection table of zero vector switch state considering junction temperature balance method

[0078]

[0079]

[0080] Combining the H-bridge submodule junction temperature balancing theory of the above multi-level converters, Figure 4 A flow chart of the junction temperature balancing method is given. The specific steps to achieve the junction temperature balancing method are summarized as follows:

[0081] Step 1: According to the level function evaluation function, determine the optimal level vector corresponding to the optimal level function.

[0082] Step 2: Combine the optimal level vector obtained in step 1, the grid-side current direction, and the voltage sorting of the DC-side support capacitors of the H-bridge sub-modules of each multi-level converter, comprehensively consider the voltage vector simplification principle, and select the optimal simplified voltage vector to provide a basis for the switching state of the subsequent junction temperature balancing method.

[0083] Step 3: Determine whether the switching function of the H-bridge submodule of each multi-level converter is 0. If so, jump to step 4 for further determination; if not, jump to step 5 to maintain the original switching state.

[0084] Step 4: Determine whether the junction temperature of IGBT No. 1 and IGBT No. 3 in the H-bridge submodule of each multi-level converter is higher than the junction temperature of IGBT No. 2 and IGBT No. 4. If so, it is necessary to dynamically adjust the zero vector working state of the switching device to S according to the principle of the junction temperature balancing method. ia S ib =00; if not, maintain the original zero vector switch state S ia S ib =11.

[0085] Step 5: According to the judgment result of step 3 or step 4, the switching state of the H-bridge submodule of the multi-level converter corresponding to each switching device is generated, and finally the control effect of the converter junction temperature balancing method is achieved.

[0086] Furthermore, the method of the present invention further comprises the following steps:

[0087] An equivalent model of a DAB-type DC / DC converter is built. Based on the power demand of hydrogen production by electrolysis, the duty cycle is dynamically adjusted to aggregate the power of the H-bridge sub-modules of the multi-level converter to the DC bus to achieve efficient hydrogen production.

[0088] The volt-second balance formula is: on T on =U off T off (11)

[0089] Where U on , U off They are the inductance L when the switch device is turned on and off respectively. i Voltage on both sides; T on , T off are the on-time and off-time of the switch device respectively; the DC side support capacitor voltage U can be established by the volt-second balance formula in the Boost working mode of the DAB type DC / DC converter. dci The mathematical logic relationship between the DC bus voltage U defines the duty cycle D of the H-bridge submodule of the i-th multilevel converter. i is the conduction time of the switch device T on With the switching period T sw Ratio of:

[0090] Where D i is the duty cycle of the H-bridge submodule of the i-th multilevel converter; T sw is the switching cycle.

[0091] When the DAB type DC / DC converter works in Boost mode: U dci ·T on =(UU dci )·Toff (13)

[0092] Combined with the above formula, the DC side support capacitor voltage U of the DAB type DC / DC converter in Boost mode can be obtained: dci , whose expression is:

[0093] Furthermore, the effectiveness of the method of the present invention can be verified by simulation, and the verification results are as follows: Figure 6-Figure 7 shown.

[0094] Depend on Figure 6-Figure 7 It can be seen that the junction temperature balancing method proposed in the present invention can effectively balance the junction temperature and keep the junction temperature difference of each IGBT at a relatively low level. Under steady-state conditions, after considering the junction temperature balancing, the junction temperature of each IGBT is stabilized at about 131.617°C, which can effectively reduce the junction temperature by 38.070°C; similarly, under power mutation conditions, after considering the junction temperature balancing, the junction temperature of each IGBT is stabilized at about 135.998°C, which can effectively reduce the junction temperature by 39.258°C.

[0095] The junction temperature balancing system of the multi-level converter for hydrogen production by electrolysis of the present invention can be implemented by software and / or hardware, and can generally be integrated in electronic equipment. The system includes an equivalent switching function module, a redundant voltage vector simplification module, an evaluation function module, a DC side support capacitor voltage sorting algorithm module and a junction temperature balancing method module. Among them, the equivalent switching function module is used to regard the cascaded H-bridge converter as a whole and establish a level function; the redundant voltage vector simplification module is used to simplify the voltage vector; the evaluation function module is used to predict the level vector and solve the optimal level function; the DC side support capacitor voltage sorting algorithm module is used to solve the optimal simplified voltage vector; the junction temperature balancing method module is used to dynamically adjust the zero vector switch state of the converter.

[0096] Furthermore, it also includes a DAB type DC / DC converter module for increasing the DC bus voltage and improving the hydrogen production efficiency; and an electrolysis hydrogen production module for electrolysis hydrogen production.

[0097] The junction temperature balancing system of a multi-level converter for producing hydrogen by electrolysis provided in an embodiment of the present invention can execute the junction temperature balancing method of a multi-level converter for producing hydrogen by electrolysis provided in any embodiment of the present invention, and has functional modules and beneficial effects corresponding to the execution method.

[0098] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A junction temperature balancing method for a multi-level converter for hydrogen production by electrolysis, characterized in that: include: Based on the equivalent switching function, an evaluation function of the level function used for level vector selection is designed to solve the optimal level vector; Using the redundant voltage vector simplification principle, a simplified voltage vector set is obtained; By using the DC side support capacitor voltage sorting, the optimal simplified voltage vector is selected from the simplified voltage vector set; By using the zero vector switch state adjustment strategy and based on the junction temperature data, the zero vector switch state in the optimal simplified voltage vector is dynamically adjusted to achieve junction temperature balance of the converter.

2. The method according to claim 1, characterized in that It also includes building an equivalent model of a DAB-type DC / DC converter, dynamically adjusting the duty cycle based on the power demand for hydrogen production by electrolysis, and aggregating the power of the H-bridge sub-modules of the multi-level converter to the DC bus to achieve hydrogen production.

3. The method according to claim 1 or 2, characterized in that ,The specific method of solving the optimal level vector is as follows: ,determine the optimal level vector corresponding to the optimal level ,function according to the level function evaluation function.

4. The method according to claim 3, characterized in that ,The way to obtain the optimal simplified voltage vector is as follows: ,Combining the obtained optimal level vector, the grid side current direction, and the ,sequencing of the DC side support capacitor voltages of the H-bridge sub-modules of each ,multilevel converter, comprehensively considering the voltage vector simplification principle, ,select the optimal simplified voltage vector.

5. The method according to claim 4, characterized in that ,The specific method of achieving junction temperature balance of the converter is: determine whether the switching function of the H-bridge submodule of each multi-level converter is 0, if so, determine whether the junction temperature of IGBT No. 1 and IGBT No. 3 in the H-bridge submodule of each multi-level converter is higher than the junction temperature of IGBT No. 2 and IGBT No. 4, if so, dynamically adjust the zero vector working state of the switching device to S according to the principle of the junction temperature balance method ia S ib =00; if not, maintain the original zero vector switch state S ia S ib =11; if not, then according to the judgment result, the H-bridge submodule switch state of the multi-level converter corresponding to each switch device is generated, and finally the control effect of the converter junction temperature balancing method is achieved, and the original switch state is maintained.

6. A junction temperature balancing system for a multi-level converter for hydrogen production by electrolysis, characterized in that: A junction temperature balancing method for implementing any one of claims 1 to 5, comprising an equivalent switching function module, a redundant voltage vector simplification module, an evaluation function module, a DC side support capacitor voltage sorting algorithm module and a junction temperature balancing method module; wherein the equivalent switching function module is used to regard the cascaded H-bridge converter as a whole and establish a level function; the redundant voltage vector simplification module is used to simplify the voltage vector; the evaluation function module is used to predict the level vector and solve the optimal level function; the DC side support capacitor voltage sorting algorithm module is used to solve the optimal simplified voltage vector; the junction temperature balancing method module is used to dynamically adjust the zero vector switching state of the converter.

7. The system according to claim 6, characterized in that It also includes a DAB type DC / DC converter module, which is used to increase the DC bus voltage and improve the hydrogen production efficiency; and an electrolysis hydrogen production module, which is used to produce hydrogen by electrolysis.

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