A high-frequency auxiliary converter and its control method

Abstract

This invention discloses a high-frequency auxiliary converter and its control method. The high-frequency auxiliary converter includes a current sharing module, multiple DC / DC isolation modules, and an inverter module. The multiple DC / DC isolation modules are connected in parallel and then connected to the inverter module. Each DC / DC isolation module uses a silicon carbide switching transistor. The current sharing module is connected to each of the DC / DC isolation modules to achieve current sharing control of each DC / DC isolation module. This invention has advantages such as light weight, small size, easy assembly and disassembly, high efficiency, good current sharing effect, high reliability, and long service life.

Description

Technical Field

[0001] This invention mainly relates to the field of auxiliary converter technology, specifically to a high-frequency auxiliary converter and its control method. Background Technology

[0002] Most existing high-speed train sets and urban rail auxiliary converters use traditional IGBTs as switching transistors. The main disadvantages of this are: 1. Low switching frequency, resulting in a large size and heavy weight of the entire power module with magnetic components; 2. High losses, resulting in low efficiency of the entire product (efficiency less than 90%); 3. The entire power module is particularly inconvenient to disassemble and assemble, which is time-consuming and labor-intensive, resulting in high maintenance costs. Summary of the Invention

[0003] The technical problem to be solved by this invention is: in view of the problems existing in the prior art, this invention provides a high-frequency auxiliary converter that is lightweight, small in size, highly efficient and highly reliable, and its control method.

[0004] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0005] A high-frequency auxiliary converter includes a current sharing module, multiple DC / DC isolation modules, and an inverter module; the multiple DC / DC isolation modules are connected in parallel and then connected to the inverter module; each of the DC / DC isolation modules uses a silicon carbide switching transistor; the current sharing module is connected to each of the DC / DC isolation modules respectively to realize the current sharing control of each of the DC / DC isolation modules.

[0006] As a further improvement to the above technical solution:

[0007] It also includes a charger module, the input of which is connected to the output of a parallel DC / DC isolation module; wherein the charger module uses a silicon carbide switching transistor.

[0008] The number of DC / DC isolation modules is 3-5; the number of inverter modules is 1-4. When there are multiple inverter modules, they are connected in parallel.

[0009] This invention also discloses a control method based on the high-frequency auxiliary converter described above, including a current sharing control method, specifically comprising the following steps:

[0010] One of the DC / DC isolation modules is pre-configured as the master, and the other DC / DC isolation modules are slaves;

[0011] Then set the host's first output voltage and output current limit value;

[0012] During normal load operation, the master unit operates according to its corresponding first output voltage and corresponding output current limit value, while the slave unit operates according to the second output voltage. The corresponding output current limit value starts from zero and gradually increases to the final output current limit value, ultimately achieving current sharing among the DC / DC isolation modules. The final output current limit value = the sum of the output currents of multiple DC / DC isolation modules / n, where n is the number of DC / DC isolation modules. The second output voltage is greater than the first output voltage.

[0013] As a further improvement to the above technical solution:

[0014] When the output current limit value of the slave device increases to the final output current limit value, the slave device enters the current limiting loop and pulls its output voltage down from the second output voltage to the first output voltage.

[0015] The output current limit value of the slave device gradually increases in the range of 3-8A / ms.

[0016] The difference between the second output voltage and the first output voltage is 1-10V.

[0017] The number of DC / DC isolation modules is four. The four DC / DC isolation modules are used to isolate and step down DC1500V to DC650V output. The power of a single DC / DC isolation module is 37.5kW, and the total power of the four DC / DC isolation modules is 150kW. The first output voltage of the master is DC650V, with a corresponding output current limit of 57A. The second output voltage of the slave is DC652V.

[0018] Each of the aforementioned DC / DC isolation modules is assigned a consecutive ID number, with the normal DC / DC isolation module having the smallest ID number serving as the master and the other DC / DC isolation modules serving as slaves.

[0019] After current sharing control, the master unit performs constant voltage loop control, and the slave unit performs constant current loop control.

[0020] Compared with the prior art, the advantages of the present invention are as follows:

[0021] 1. The high-frequency auxiliary converter of the present invention uses SiC as the switching transistor. Compared with the traditional power frequency auxiliary converter (which uses IGBT as the switching transistor), the switching frequency is higher, making it smaller and lighter. For example, the commonly used 120kVA+15kW power frequency auxiliary converter weighs about 1200kg, while the high-frequency auxiliary converter of the same power weighs only 720kg, which is 40% lighter.

[0022] 2. The high-frequency auxiliary converter of this invention uses SiC as the switching transistor, which improves the efficiency of the entire product and saves more energy compared to the traditional power frequency auxiliary converter (which uses IGBT as the switching transistor). The commonly used 120kVA+15kW power frequency auxiliary converter has an efficiency of less than 90% under rated conditions, while the high-frequency auxiliary converter of the same power reaches 94% under rated conditions, which is more efficient and more energy-saving.

[0023] 3. The high-frequency auxiliary converter of this invention uses SiC as the switching transistor. Compared with the traditional power frequency auxiliary converter (which uses IGBT as the switching transistor), it adopts a modular design and multiple modules can work in parallel. If a single module fails, the remaining modules can continue to provide output and achieve current sharing, resulting in high redundancy. Each module is lightweight, making it easy to maintain and replace on-site, saving time, effort and cost.

[0024] 4. The DC / DC isolation modules of this invention are connected in parallel and then current sharing control is adopted to ensure the reliability of each DC / DC isolation module and improve its service life. Moreover, the second output voltage of the slave is set higher than the first output voltage of the master (e.g., 2V higher), and the current limit value of the slave is gradually released (e.g., at a speed of 10A / 2ms), which can ensure that fast current sharing can be achieved even under small loads. Attached Figure Description

[0025] Figure 1 This is a block diagram of the high-frequency auxiliary converter of the present invention in an embodiment.

[0026] Figure 2 This is a schematic diagram of the current sharing of each DC / DC isolation module of the present invention.

[0027] Figure 3 This is a flowchart of the control method of the present invention in an embodiment. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 As shown, this embodiment of the invention provides a high-frequency auxiliary converter, including a current sharing module, multiple DC / DC isolation modules, and an inverter module; the multiple DC / DC isolation modules are connected in parallel and then connected to the inverter module; each DC / DC isolation module uses a silicon carbide switching transistor; the current sharing module is connected to each DC / DC isolation module to realize current sharing control of each DC / DC isolation module. The aforementioned current sharing module can be an independent control module or integrated into the control module (such as a controller) of the high-frequency auxiliary converter.

[0030] In one specific embodiment, a charger module is also included. The input terminal of the charger module is connected to the output terminal of the parallel DC / DC isolation module. The charger module also uses silicon carbide switching transistors to form a high-frequency charger module. The high-frequency charger module isolates and converts the input DC650V to DC110V output (adjustable according to battery temperature). A single charger module has a power of 15kW, a weight of 25kg, and a maximum switching frequency of 100kHz. The charger module is lightweight and easy to maintain and replace in the field.

[0031] In one specific embodiment, the number of DC / DC isolation modules is 3-5, preferably 4; the number of inverter modules is 1-4, preferably 2; when there are multiple inverter modules, they are connected in parallel. Of course, in other embodiments, the appropriate number of DC / DC isolation modules and inverter modules can be selected according to the actual situation.

[0032] Specifically, four parallel high-frequency DC / DC isolation modules are used to isolate and transform the input DC1500V to a stable DC650V output. Each high-frequency DC / DC isolation module has a power of 37.5kW, weighs 25kg, and has a maximum switching frequency of 100kHz. The lightweight design of each module facilitates on-site maintenance and replacement. Each of the four high-frequency DC / DC isolation modules is assigned an ID, with the minimum ID being the master and the others defaulting to slave. The master module performs constant voltage loop control, while the slave modules perform constant current loop control. The sum of the total current of all operating DC / DC isolation modules divided by the number of operating modules is used as the output current of each module for current sharing control. Two parallel inverter modules are used to convert the input DC650V to AC380V / 50Hz output. Each inverter module has a capacity of up to 90kVA and weighs only 17kg, facilitating on-site maintenance and replacement. No communication is required between the two inverter modules; only one inverter module needs to be started, and the other inverter module follows the AC output bus to achieve in-phase current sharing output.

[0033] The high-frequency auxiliary converter of this invention uses SiC as the switching transistor, which has a higher switching frequency than the traditional power frequency auxiliary converter (which uses IGBT as the switching transistor), making it smaller and lighter. For example, the commonly used 120kVA+15kW power frequency auxiliary converter weighs about 1200kg, while the high-frequency auxiliary converter of the same power weighs only 720kg, a weight reduction of 40%.

[0034] The high-frequency auxiliary converter of this invention uses SiC as the switching transistor, which improves the overall efficiency and saves energy compared to the traditional power frequency auxiliary converter (which uses IGBT as the switching transistor). The commonly used 120kVA+15kW power frequency auxiliary converter has an efficiency of less than 90% under rated conditions, while the high-frequency auxiliary converter of the same power reaches an efficiency of 94% under rated conditions, which is more efficient and energy-saving.

[0035] The high-frequency auxiliary converter of this invention uses SiC as its switching transistor. Compared with the traditional power frequency auxiliary converter (which uses IGBT as its switching transistor), it adopts a modular design and multiple modules can work in parallel. If a single module fails, the remaining modules can continue to provide output and achieve current sharing, resulting in high redundancy. Each module is lightweight, making it easy to maintain and replace in the field, saving time, effort and cost.

[0036] like Figure 2 and Figure 3 As shown, this embodiment of the invention also provides a control method based on the high-frequency auxiliary converter described above, including a current sharing control method, specifically including the following steps:

[0037] One of the DC / DC isolation modules is pre-configured as the master, and the other DC / DC isolation modules are slaves;

[0038] Then set the host's first output voltage and output current limit value;

[0039] During normal load operation, the master unit operates according to its corresponding first output voltage and corresponding output current limit value, while the slave unit operates according to the second output voltage. The corresponding output current limit value starts from zero and gradually increases to the final output current limit value, thereby achieving current sharing among the DC / DC isolation modules. The final output current limit value = the sum of the output currents of multiple DC / DC isolation modules / n, where n is the number of DC / DC isolation modules. The second output voltage is greater than the first output voltage.

[0040] In one specific embodiment, when the slave device's output current limit value increases to the final output current limit value, the slave device enters a current limiting loop to pull its output voltage down from the second output voltage to the first output voltage. The difference between the second output voltage and the first output voltage is 1-10V; the slave device's output current limit value gradually increases in increments of 3-8A / ms.

[0041] The DC / DC isolation modules of this invention are connected in parallel and then current sharing control is adopted to ensure the reliability of each DC / DC isolation module and improve its service life. Moreover, the second output voltage of the slave is set higher than the first output voltage of the master (e.g., 2V higher), and the current limiting value of the slave is gradually released at a speed of 10A / 2ms, which can ensure that fast current sharing can be achieved even under small loads.

[0042] The present invention will be further described in detail below with reference to a complete specific embodiment:

[0043] like Figure 2 Taking the parallel connection of four high-frequency DC / DC isolation modules as an example, the current sharing logic is explained. The four high-frequency modules in parallel isolate and step down the input DC1500V to DC650V output. The power of a single DC / DC isolation module is 37.5kW, and the total power of the four high-frequency DC / DC isolation modules is 150kW.

[0044] The four high-frequency DC / DC isolation modules UP1_1 / UP1_2 / UP1_3 / UP1_4 are each assigned a different ID, namely 1, 2, 3 and 4. Regardless of which module fails, the module with the smallest ID value will be designated as the master, and the other modules will be designated as slaves.

[0045] During normal no-load operation, the master unit is set to output voltage DC650V and output current limit is set to 57A; the slave unit is set to output voltage DC652V and output current limit is 0A. After loading, the current limit is gradually released at a rate of 10A / 2ms. The master unit operates in the voltage loop, and the slave unit operates in the current limiting loop. The master unit's output voltage is lower than the slave unit's output voltage to avoid the master unit bearing the entire current under small loads, thus preventing current sharing. (If the slave unit and master unit output the same voltage of 650V, the master unit's output current limit will always be 57A, while the slave unit's initial current limit will be 0. When a small load is applied (output current ≤ 57A), the entire current will be borne by the master unit, making it impossible for the master and slave units to share the current.)

[0046] When the load is applied, the master unit's output current limit is kept at 57A. The slave units will release the output current limit at 10A / 2ms until the final current limit is equal to the sum of the output current values ​​of the four high-frequency DC / DC isolation modules / 4. After the output current limit of each slave unit is released to the final current limit, the slave unit will enter the current limiting loop to pull the output voltage down to DC650V. The current exceeding the current limit is automatically distributed to the master unit, thus achieving current sharing among the four DC / DC isolation modules.

[0047] Since the slave output voltage of 652V is higher than the master output voltage of 650V, the load will be initially borne by the slave with the higher output voltage during loading. At this time, the slave output current limit is not released, which will pull down the slave output voltage. When the voltage drops below 650V, the master and slave will share the load. At this time, the master and the three slaves will sum up the output current and divide it into four equal parts. The equal current value is used as the output current limit value of the three slaves, thereby continuously adjusting to complete the current sharing of the four modules.

[0048] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A control method based on a high-frequency auxiliary converter, characterized in that, The high-frequency auxiliary converter includes a current sharing module, multiple DC / DC isolation modules, and an inverter module; the multiple DC / DC isolation modules are connected in parallel and then connected to the inverter module; each of the DC / DC isolation modules uses a silicon carbide switching transistor; the current sharing module is connected to each of the DC / DC isolation modules respectively to realize the current sharing control of each of the DC / DC isolation modules; Control methods include flow sharing control methods, which specifically include the following steps: One of the DC / DC isolation modules is pre-configured as the master, and the other DC / DC isolation modules are slaves; Then set the host's first output voltage and output current limit value; During normal load operation, the master unit operates according to its corresponding first output voltage and corresponding output current limit value, while the slave unit operates according to the second output voltage, and its corresponding output current limit value starts from zero and gradually increases to the final output current limit value, thereby achieving current sharing among the DC / DC isolation modules. The final output current limit value = the sum of the output currents of multiple DC / DC isolation modules / n, where n is the number of DC / DC isolation modules; The second output voltage is greater than the first output voltage; When the output current limit value of the slave device increases to the final output current limit value, the slave device enters the current limiting loop and pulls its output voltage down from the second output voltage to the first output voltage; The output current limit value of the slave device gradually increases in the range of 3-8A / ms; The difference between the second output voltage and the first output voltage is 1-10V.

2. The control method for the high-frequency auxiliary converter according to claim 1, characterized in that, The number of DC / DC isolation modules is four. The four DC / DC isolation modules are used to isolate and step down DC1500V to DC650V output. The power of a single DC / DC isolation module is 37.5kW, and the total power of the four DC / DC isolation modules is 150kW. The first output voltage of the master is DC650V, with a corresponding output current limit of 57A. The second output voltage of the slave is DC652V.

3. The control method for the high-frequency auxiliary converter according to claim 1 or 2, characterized in that, Each of the aforementioned DC / DC isolation modules is assigned a consecutive ID number, with the normal DC / DC isolation module having the smallest ID number serving as the master and the other DC / DC isolation modules serving as slaves.

4. The control method for the high-frequency auxiliary converter according to claim 1 or 2, characterized in that, After current sharing control, the master unit performs constant voltage loop control, and the slave unit performs constant current loop control.

5. The control method for the high-frequency auxiliary converter according to claim 1 or 2, characterized in that, It also includes a charger module, the input of which is connected to the output of a parallel DC / DC isolation module; wherein the charger module uses a silicon carbide switching transistor.

6. The control method for the high-frequency auxiliary converter according to claim 1 or 2, characterized in that, The number of DC / DC isolation modules is 3-5; the number of inverter modules is 1-4. When there are multiple inverter modules, they are connected in parallel.

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