A cascaded power unit based on press-pack type devices

Abstract

The application relates to a cascaded power unit based on a press-pack type device and belongs to the technical field of power electronics. The power unit topology is divided into three-phase uncontrolled rectification, a DC bus capacitor and an inverter H bridge three parts, each part can be independently disassembled, the rectification part is further divided into three independent rectification bridge arms. The DC bus capacitor is connected with a DC bus through a separable connecting sheet, and the single capacitor is convenient to replace. The loss calculation comprehensively considers the on-state, turn-off and off-state losses of diodes, and the design reliability is improved. In terms of water channels, the rectification bridge arm adopts a double-face water channel radiator and two single-face water channel radiators in series, the inverter H bridge adopts a series water channel with water inlet in the middle and water outlet at two ends, and the series water channels are connected through a three-way joint, so that the global water channel resistance and flow balance are realized. The application effectively improves the modularization level and maintenance convenience of the power unit, optimizes the heat dissipation configuration, and improves the loss calculation precision of the device.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and in particular to a cascaded power unit based on press-fit devices. Background Technology

[0002] In industrial applications, large-scale mechanical transmission equipment in fields such as blast furnace blowers, wind tunnels, high-power experimental equipment, LNG compressors, and natural gas transportation requires high-power, high-voltage variable frequency speed control devices. These devices mostly employ cascaded topologies, forming large-scale equipment with maximum power exceeding tens of megawatts and maximum voltage exceeding tens of kilovolts. Such large equipment occupies significant space and is heavy; most commercially available products suffer from cumbersome maintenance and disassembly, requiring bulky tools. Therefore, a rational electrical and structural layout must be designed to meet the needs of modular assembly production and equipment maintenance.

[0003] In terms of component selection, power devices include modular packages and press-fit packages. Press-fit packages offer double-sided heat dissipation, and their thermal resistance between the casing and the heat sink is half that of modular packages, resulting in better heat dissipation performance and further enhancing the output of power devices. Simultaneously, clarifying the specific losses of power devices is crucial for better design of cooling water circuits. In conventional engineering applications, diode losses are only calculated based on conduction losses, requiring a very large allowance for heat dissipation thresholds. Patent CN 116108641 A proposes a loss calculation method for a three-phase full-bridge uncontrolled rectifier circuit. While simple, this method is not comprehensive. With increasingly refined design requirements, a more comprehensive consideration of device losses is needed to avoid excessive redundancy and cost waste. Regarding water circuit design, the water resistance of multiple parallel water circuits should be matched. CN 216357991 U describes multiple parallel water circuits with varying numbers of heat sinks and single / double-sided heat sinks connected in parallel. When the minimum water flow requirement of a water-cooled branch is met, the water flow of other branches significantly exceeds the design value, wasting water resources. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and propose a cascaded power unit based on press-fit devices, which can maintain the stable operation of the power grid, quickly and accurately provide the optimal load transfer scheme, greatly improve the work efficiency of dispatchers, and ensure the safe and stable operation of the power grid.

[0005] The technical problem solved by this invention is achieved through the following technical solution: A cascaded power unit based on press-fit devices includes a rectifier module, a DC bus capacitor module, and an inverter module. The rectifier module is connected to the inverter module via the DC bus capacitor module. The rectifier module includes rectifier bridge arms A, B, and C. The AC sides of rectifier bridge arms A, B, and C are respectively connected to the three-phase AC input lines. The positive terminals of rectifier bridge arms A, B, and C are short-circuited and connected to the positive terminal of the DC bus. The negative terminals of rectifier bridge arms A, B, and C are short-circuited and connected to the negative terminal of the DC bus.

[0006] Furthermore, the DC bus capacitor is composed of multiple capacitors connected in parallel. Each DC bus capacitor connection point is connected to the DC busbar through a detachable connecting piece. The IGCT power devices in the inverter module maintain a power string, and the diodes maintain a power string, and are electrically connected according to the circuit principle.

[0007] Moreover, the rectifier bridge arm A, rectifier bridge arm B and rectifier bridge arm C have the same structure.

[0008] Furthermore, the rectifier bridge arm A includes three water-cooled radiators. The radiator in the middle position is a double-sided water channel radiator, in which the double-sided water channels are independent of each other. The radiators at both ends are single-channel radiators. The water channels of the single-channel radiators are all designed on one side of the surface that contacts the diode. The cooling water first flows through the middle radiator, and then connects to the upper and lower single-sided radiators through a T-connector. The cooling water output ports of the upper and lower single-sided radiators are then connected to the main pipe through a T-connector. This reduces the number of water-cooled branches and avoids the situation of different water resistance and different flow rates when multiple branches are connected in parallel.

[0009] Furthermore, the IGCT devices in the inverter module are assembled into a power string, which is separated by an insulating block in the middle to form two bridge arms. Each bridge arm has three heat sinks, and cooling water enters from the middle heat sink and exits from the heat sinks at both ends. The diode devices in the inverter module are assembled into a power string, which is separated by an insulating block in the middle to form two bridge arms. Each bridge arm has three heat sinks, and cooling water enters from the middle heat sink and exits from the heat sinks at both ends. An absorption diode is then pressed onto the upper end of the front bridge arm, and a single-sided heat sink is pressed onto the upper end of the diode for heat dissipation. The single-sided heat sink, the absorption resistor, and the buffer inductor form a water-cooled branch, and the water resistance of the absorption resistor and the buffer inductor is the same as that of the single-sided heat sink.

[0010] Furthermore, the diode losses in the aforementioned three-phase uncontrolled rectifier circuit should include the diode's conduction loss, turn-off loss, cut-off loss, and turn-on loss. In engineering applications, except for the turn-on loss which can be ignored, conduction loss is the main loss component. Calculating the turn-off and cut-off losses can make the total device loss more accurate and reduce the overheating margin. To accurately calculate the device's maximum power, the data in the following device datasheets are all measured values ​​under maximum junction temperature conditions.

[0011] The formula for calculating on-state loss is: in, For on-state loss, This is the forward voltage drop of the diode. This is the on-state resistance of the diode. This is the average value flowing through the diode, which is equal to one-third of the direct current. This is the effective value of the current flowing through the diode, which is equal to the average value. times.

[0012] Turn-off losses show a strong positive correlation with the rate of change of current and the load current. in, This refers to the diode turn-off loss. The rate of change of diode turn-off current; This is the diode turn-off current; and These are the reference values ​​for the diode's turn-off current rate of change and turn-off current from the manual data. The switching cycle is denoted as . E Doff If the formula cannot be obtained from the manual, it can be obtained through simulation or testing. The calculation formula is as follows: Where n is the number of times data is recorded, and n_max is the total number of times data is recorded. U n , I n These are the n different voltage and current values ​​recorded during the turn-off process. T off This refers to the shutdown time.

[0013] Cutoff loss is related to DC voltage and leakage current: in, and This is the reference value for the diode leakage current from the datasheet. For the current state time.

[0014] The total loss is equal to the sum of the above parts. .

[0015] The advantages and positive effects of this invention are: 1. Based on the modular design of the power unit, this invention further refines the sub-modules of the rectifier section, DC bus capacitor section and inverter H-bridge section, thereby improving the modularity. In this example, the entire power unit can be divided into 7 sub-parts, which greatly improves the portability of product manufacturing, assembly and maintenance.

[0016] 2. In the electrical structure of this invention, the DC bus capacitor adopts a detachable connection design, which can avoid capacitor replacement and shorten equipment downtime.

[0017] 3. This invention provides a more practical and accurate method for calculating diode losses. It converts the on-state loss, turn-off loss, and cut-off loss to conform to actual operating conditions, thereby improving the accuracy of device losses under extreme conditions.

[0018] 4. By employing a single double-sided radiator and two single-sided radiators connected in series, the present invention achieves balanced pressure and flow in all parallel branches of the overall power unit, avoiding the uneven number of radiators connected in series and parallel and the uneven number of water channels in some designs. Attached Figure Description

[0019] Figure 1 This invention presents an overall electrical structure design diagram for a power unit.

[0020] Figure 2 The present invention provides a circuit schematic diagram of a power unit.

[0021] Figure 3 This invention presents a schematic diagram of the press-fit sequence and water circuit connection sequence of a single rectifier diode bridge arm in a power unit.

[0022] Figure 4 This invention proposes a design diagram for a separable DC bus capacitor in a power unit.

[0023] Figure 5 This invention presents a schematic diagram of the press-fit sequence and water circuit connection sequence of the inverter H-bridge in a power unit.

[0024] Label Explanation 1-Rectifier module, 2-DC bus capacitor module, 3-Inverter module, 4-Rectifier bridge arm A, 5-Rectifier bridge arm B, 6-Rectifier bridge arm C, 7-DC bus capacitor connection point, 8-Connecting piece, 9-DC busbar. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings.

[0026] A cascaded power unit based on press-fit devices, such as Figure 1 As shown, it includes a rectifier module 1, a DC bus capacitor module 2, and an inverter module 3, wherein the rectifier module is connected to the inverter module through the DC bus capacitor module, as shown. Figure 2 As shown, the rectifier module includes rectifier bridge arms A4, B5, and C6. The AC sides of rectifier bridge arms A, B, and C are connected to the three-phase AC input lines, respectively. The positive terminals of rectifier bridge arms A, B, and C are short-circuited and connected to the positive terminal of the DC bus. The negative terminals of rectifier bridge arms A, B, and C are short-circuited and connected to the negative terminal of the DC bus.

[0027] like Figure 4 As shown, the DC bus capacitor is composed of multiple capacitors connected in parallel. Each DC bus capacitor connection point 7 and DC bus 9 are connected through a detachable connecting piece 8. The IGCT power devices in the inverter module maintain a power string, and the diodes maintain a power string, and are electrically connected according to the circuit principle.

[0028] Rectifier bridge arm A, rectifier bridge arm B, and rectifier bridge arm C have the same structure. For example... Figure 3 As shown, rectifier bridge arm A includes three water-cooled heat sinks. The middle heat sink is a double-sided water channel heat sink, with the double-sided water channels being independent of each other. The heat sinks at both ends are single-channel heat sinks. The water channels of the single-channel heat sinks are all designed on one side of the surface that contacts the diode. The cooling water first flows through the middle heat sink, and then connects to the upper and lower single-sided heat sinks through a T-connector. The cooling water output ports of the upper and lower single-sided heat sinks are then connected to the main pipe through a T-connector. This reduces the number of water-cooled branches and avoids the situation of different water resistance and different flow rates when multiple branches are connected in parallel.

[0029] like Figure 5 As shown, the IGCT devices in the inverter module are assembled into a power string, which is separated by an insulating block in the middle to form two bridge arms. Each bridge arm has three heat sinks, and cooling water enters from the middle heat sink and exits from the heat sinks at both ends. The diode devices in the inverter module are also assembled into a power string, which is separated by an insulating block in the middle to form two bridge arms. Each bridge arm has three heat sinks, and cooling water enters from the middle heat sink and exits from the heat sinks at both ends. An absorption diode is then press-fitted onto the upper end of the front bridge arm, and a single-sided heat sink is press-fitted onto the upper end of the diode for heat dissipation. This single-sided heat sink, the absorption resistor, and the buffer inductor form a water-cooled branch, and the water resistance of the absorption resistor and the buffer inductor is the same as the water resistance of the single-sided heat sink.

[0030] In a three-phase uncontrolled rectifier circuit, diode losses should include conduction losses, turn-off losses, cut-off losses, and turn-on losses. In engineering applications, except for turn-on losses which can be ignored, conduction losses are the main component of losses. Calculating turn-off and cut-off losses can make the total device losses more accurate and reduce the overheating margin. To accurately calculate the device's maximum power, the data in the following device datasheets are all measured under maximum junction temperature conditions.

[0031] The formula for calculating on-state loss is: in, For on-state loss, This is the forward voltage drop of the diode. This is the on-state resistance of the diode. This is the average value flowing through the diode, which is equal to one-third of the direct current. This is the effective value of the current flowing through the diode, which is equal to the average value. times.

[0032] Turn-off losses show a strong positive correlation with the rate of change of current and the load current. in, This refers to the diode turn-off loss. The rate of change of diode turn-off current; This is the diode turn-off current; and These are the reference values ​​for the diode's turn-off current rate of change and turn-off current from the manual data. The switching cycle is denoted as . E Doff If the formula cannot be obtained from the manual, it can be obtained through simulation or testing. The calculation formula is as follows: Where n is the number of times data is recorded, and n_max is the total number of times data is recorded. U n , I n These are the n different voltage and current values ​​recorded during the turn-off process. T off This refers to the shutdown time.

[0033] Cutoff loss is related to DC voltage and leakage current: in, and This is the reference value for the diode leakage current from the datasheet. For the current state time.

[0034] The total loss is equal to the sum of the above parts. .

[0035] The power unit in this embodiment of the invention has a power rating of 3MW and a DC rated voltage of 1800V. It is known that the average current flowing through the diode is 556A, the effective value is 963A, and the current change rate is 2A / µs. Based on the selected diode parameters, to accurately calculate the device's maximum power, all data from the device datasheet are measured under maximum junction temperature conditions. According to various loss calculation formulas... The conduction loss, turn-off loss, and cut-off loss of the diode are 737.8W, 72W, and 22.68W, respectively, totaling 832.48W. Especially for high-power diodes, even in a power frequency rectification environment, considering all losses results in a 12.8% increase compared to considering only conduction losses, making the design more reliable and avoiding uncertainties in design margins.

[0036] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementations derived by those skilled in the art based on the technical solutions of this invention are also within the scope of protection of this invention.

Claims

1. A cascaded power unit based on press-fit devices, characterized in that: It includes a rectifier module, a DC bus capacitor module, and an inverter module. The rectifier module is connected to the inverter module through the DC bus capacitor module. The rectifier module includes rectifier bridge arm A, rectifier bridge arm B, and rectifier bridge arm C. The AC side of rectifier bridge arm A, rectifier bridge arm B, and rectifier bridge arm C are respectively connected to the three-phase AC input line. The positive terminals of rectifier bridge arm A, rectifier bridge arm B, and rectifier bridge arm C are short-circuited and connected to the positive terminal of the DC bus. The negative terminals of rectifier bridge arm A, rectifier bridge arm B, and rectifier bridge arm C are short-circuited and connected to the negative terminal of the DC bus.

2. The cascaded power unit based on press-fitted devices according to claim 1, characterized in that: The DC bus capacitor is composed of multiple capacitors connected in parallel. Each DC bus capacitor connection point is connected to the DC busbar through a detachable connecting piece. The IGCT power devices in the inverter module maintain a power string, and the diodes maintain a power string, and are electrically connected according to the circuit principle.

3. The cascaded power unit based on press-fitted devices according to claim 1, characterized in that: The rectifier bridge arm A, rectifier bridge arm B, and rectifier bridge arm C have the same structure.

4. A cascaded power unit based on a press-fit device according to claim 1, characterized in that: The rectifier bridge arm A includes three water-cooled radiators. The radiator in the middle position is a double-sided water channel radiator, in which the double-sided water channels are independent of each other. The radiators at both ends are single-channel radiators. The water channels of the single-channel radiators are all designed on one side of the surface that contacts the diode. The cooling water first flows through the middle radiator, and then connects to the upper and lower single-sided radiators through a T-connector. The cooling water output ports of the upper and lower single-sided radiators are then connected to the main pipe through a T-connector. This reduces the number of water-cooled branches and avoids the situation of different water resistance and different flow rates when multiple branches are connected in parallel.

5. A cascaded power unit based on a press-fit device according to claim 1, characterized in that: The IGCT devices in the inverter module are assembled into a power string, which is separated by an insulating block in the middle to form two bridge arms. Each bridge arm has three heat sinks, and cooling water enters from the middle heat sink and exits from the heat sinks at both ends. The diode devices in the inverter module are also assembled into a power string, which is separated by an insulating block in the middle to form two bridge arms. Each bridge arm has three heat sinks, and cooling water enters from the middle heat sink and exits from the heat sinks at both ends. An absorption diode is then press-fitted onto the upper end of the front bridge arm, and a single-sided heat sink is press-fitted onto the upper end of the diode for heat dissipation. This single-sided heat sink, the absorption resistor, and the buffer inductor form a water-cooled branch, and the water resistance of the absorption resistor and the buffer inductor is the same as the water resistance of the single-sided heat sink.

6. A cascaded power unit based on a press-fit device according to claim 1, characterized in that: The diode losses in the three-phase uncontrolled rectifier circuit shown should include the diode's conduction loss, turn-off loss, cut-off loss, and turn-on loss. The calculation method for conduction loss is as follows: ； in, For on-state losses, This is the forward voltage drop of the diode. This is the on-state resistance of the diode. This is the average value of the current flowing through the diode. This is the effective value of the current flowing through the diode; Turn-off losses are positively correlated with the rate of change of current and the load current. ； in, This refers to the diode turn-off loss. The rate of change of diode turn-off current; This is the diode turn-off current; and These are the reference values ​​for the diode's turn-off current rate of change and turn-off current from the manual data. For the switching cycle, Cutoff loss is related to DC voltage and leakage current: ； and This is the reference value for the diode leakage current from the datasheet. For the current state time. Ignoring activation losses, the total loss is: 。

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