Droop current sharing control method and control device for high-power direct-current power supply system

Abstract

The invention provides a droop current-sharing control method and control device for a high-power direct-current power supply system, and the control method comprises the steps: carrying out the independent control of each converter, taking the high-frequency component of the output current of the converter obtained through sampling as a control variable to participate in current-sharing droop, and in the transient process, when unbalanced current occurs, the current-sharing droop does not occur. Wherein the high-frequency component amplitude of the converter with fast current sudden increase and large amplitude is larger, the reference quantity input into a voltage loop controller in the transient process of the converter is lower due to a transient droop control method, so that the duty ratio increase rate of the converter is reduced, and the high-frequency component amplitude of the converter with slow current sudden increase and small amplitude is smaller, so that the duty ratio increase rate of the converter is reduced. The converter is small in transient voltage droop amount, the reference amount of a transient process input voltage loop controller is large, the duty ratio is gradually increased, and the purpose of balancing current in the transient process is achieved.

Description

Technical Field

[0001] The present invention relates to the field of power supply current balancing, and more specifically, to a droop current balancing control method and a control device for a high-power direct current power supply system. Background Art

[0002] With the development of new energy vehicles, aerospace, medical equipment and other technologies, high-power DC power supplies have been widely used. At the same time, with the advancement of digital control technology, DC power supplies are rapidly developing in the direction of miniaturization, modularization and intelligent control. However, the application of high-power DC equipment has led to an increasing capacity required for DC power supplies, and the input power of a single module often cannot meet the requirements. Therefore, it is generally considered to use multiple modules in parallel to achieve the output requirements of a larger power capacity. The parallel connection of multiple modules inevitably involves the problem of current sharing between modules. Ideally, the total output load current of the parallel DC power supply system is evenly divided by each individual module participating in the parallel connection. However, in actual engineering, it is impossible to ensure that the output external characteristics between modules are exactly the same. There will always be certain differences. Therefore, the current between modules is often unbalanced when a certain control method is not applied. This will cause the module with a large load to bear higher current stress and thermal stress for a long time, thereby weakening the reliability and service life of the entire parallel power supply system.

[0003] Common parallel current sharing methods include: average current method, master-slave setting method, maximum current sharing method, external controller method, virtual impedance droop method, etc. Among them, the average current method and the maximum current sharing method require an external current sharing bus to control the current sharing of each parallel module connection, but the failure of a single module will affect the average current bus and cause the system to shut down due to failure; the master-slave setting method selects one module as a fixed master module and the rest as slave modules, but if the designated master module fails, the entire system will not work properly; the external controller method transmits the voltage and current signals detected by each module and the voltage and current signals on the load to an external processor, and then adopts various control strategies to control the current sharing of the parallel system, but it requires the use of many signal connection circuits, and information transmission is easily interfered with.

[0004] The most widely used parallel current sharing technology is virtual impedance droop control technology, which does not require additional communication between modules or additional sensors. At the same time, due to the use of virtual impedance, it will not cause energy loss and has a clear principle and simple implementation, and is widely used in industry. However, during the use of droop control, there may be certain differences between modules, resulting in different responses of the two converters to the output during the transient process of sudden increase or decrease in load, resulting in output overcurrent faults, and then the protections are withdrawn one by one during the transient process of load change, resulting in failure of sudden increase or decrease in load, and the requirements cannot be met.

[0005] The specific reason is that the current droop control can achieve a good current sharing effect for steady-state operation, ensuring the normal output of the parallel current sharing between modules in steady-state operation, but the dynamic process is not considered enough. When the module adopts a single voltage loop control method, since the accuracy of voltage sampling of each module cannot be guaranteed to be completely consistent, the impact on the single voltage loop feedback control is also inconsistent, which will cause its dynamic performance to be affected to a certain extent. Specifically, the output of each module is at the same voltage level, but the sampling values ​​of the voltage received by each module are different due to the different voltage sampling coefficients. In the transient process of a sudden increase in load, the modules share the process of current increase unbalancedly, which may cause the module to trigger an output current overcurrent fault and exit work, and fail to meet the requirements of a sudden increase in load. In severe cases, it may even cause the module to burn out and be damaged. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a droop current sharing control method and a control device for a high-power DC power supply system, aiming to solve the problem of a multi-module parallel DC power supply system when the load increases suddenly. According to a first aspect of the present invention, a droop current sharing control method for a high-power DC power supply system is provided, wherein the high-power DC power supply system includes a plurality of converters connected in parallel, and droop current sharing control is performed on each converter, comprising: Obtain the original reference voltage and output current given by the converter; According to the output current of the converter, a first voltage droop amount is calculated based on a steady-state droop control algorithm, and a second voltage droop amount is calculated based on a transient droop control algorithm; taking the difference between the original reference voltage and the sum of the first voltage droop amount and the second voltage droop amount as a new reference voltage; Inputting the new reference voltage into a voltage loop controller to obtain a duty cycle control signal generated by the voltage loop controller, and controlling the converter to output a power supply voltage based on the duty cycle control signal; The step of calculating the second voltage droop amount based on the transient droop control algorithm includes: The output current of the converter is subjected to high-pass filtering to obtain a high-frequency component of the output current of the converter, and a second voltage droop amount is calculated based on the high-frequency component.

[0007] According to a second aspect of the present invention, there is provided a droop current sharing control device for a high-power DC power supply system, wherein the high-power DC power supply system comprises a plurality of converters connected in parallel, and the droop current sharing control device comprises a plurality of droop current sharing control modules, each of the droop current sharing control modules being used to perform droop current sharing control on a corresponding converter, and each of the droop current sharing control modules comprising a digital controller, and the digital controller comprising a voltage loop controller; The digital controller is used to obtain an original reference voltage and an output current given by the converter; calculate a first voltage droop amount based on a steady-state droop control algorithm and a second voltage droop amount based on a transient droop control algorithm according to the output current of the converter; use a difference between the original reference voltage and the sum of the first voltage droop amount and the second voltage droop amount as a new reference voltage; and input the new reference voltage into a voltage loop controller; The voltage loop controller is used to generate a duty cycle control signal according to the new reference voltage, and control the converter to output a power supply voltage based on the duty cycle control signal; The digital controller calculates the second voltage droop amount based on the transient droop control algorithm, including: The output current of the converter is subjected to high-pass filtering to obtain a high-frequency component of the output current of the converter, and the second voltage droop amount is calculated according to the high-frequency component.

[0008] The present invention provides a droop current sharing control method and control device for a high-power DC power supply system, which individually controls each converter connected in parallel in the high-power DC power supply system, and uses the high-frequency component of the sampled output current of the converter as a control quantity to participate in the current sharing droop. In a transient process, an unbalanced current appears, wherein the converter with a fast current surge and a large amplitude has a larger amplitude of its high-frequency component. Due to the transient droop control method, the reference quantity of the converter input to the transient process voltage loop controller is lower, thereby reducing the rate of increase of its duty cycle. On the contrary, the converter with a slow current surge and a small amplitude has a smaller amplitude of its high-frequency component, and the transient voltage droop of the converter is small, and the reference quantity of the transient process input voltage loop controller is large, and the duty cycle is gradually increased to achieve the purpose of balancing the current in the transient process. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A flow chart of a droop current sharing control method for a high-power DC power supply system provided by the present invention; Figure 2 It is the transient droop control block diagram; Figure 3 A schematic diagram of the structure of a droop current sharing control device for a high-power DC power supply system provided by the present invention; Figure 4 This is a schematic diagram of the sudden load waveform without transient control; Figure 5 This is a schematic diagram of the sudden load waveform with transient control added. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In addition, the technical features in the various embodiments or single embodiments provided by the present invention can be arbitrarily combined with each other to form a feasible technical solution. This combination is not subject to the constraints of the sequence of steps and / or the structural composition mode, but must be based on the ability of ordinary technicians in this field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0011] In order to solve the problem that the dynamic performance of a high-power DC power supply system with multiple converters in parallel cannot meet the requirements when the load changes suddenly, and the responses between the converters are inconsistent, the present invention proposes an improved control method for a high-power DC power supply system, the purpose of which is to optimize the transient performance and improve the system reliability, while ensuring that there is no adverse effect on the steady-state performance of the system.

[0012] The present invention provides a droop current sharing control method for a high-power DC power supply system, wherein the high-power DC power supply system includes multiple converters connected in parallel, and when performing droop current sharing control, each converter is controlled separately. Figure 1 The droop control method for each converter specifically includes the following steps: Step 1: Obtain the original reference voltage and output current given by the converter.

[0013] It is understandable that, for each converter, the original reference voltage given by the converter and the output current of the converter are obtained.

[0014] Step 2: Calculate a first voltage droop amount based on a steady-state droop control algorithm according to the output current of the converter, and calculate a second voltage droop amount based on a transient droop control algorithm.

[0015] It is understandable that when the present invention performs droop current balancing control on the converter, taking into account the steady-state working state and transient working state of the converter, a two-part droop balancing control will be designed. The so-called steady-state working state refers to the slow change of the output current of the converter, and the so-called transient working state refers to the fact that due to sudden load changes, such as a sudden increase in load, the output current of the converter changes at a relatively fast rate.

[0016] Specifically, the present invention introduces a transient control scheme to enhance the transient response capability of the parallel converter system during load mutations and adjust the ability to coordinate current changes between converters. By adding transient output current droop control on the basis of traditional steady-state droop control, the transient performance of the entire power supply system is improved.

[0017] The steady-state droop control in the present invention is a traditional droop control, that is, drooping the steady-state DC output current to balance the current between converters when the converter is working in a steady state. According to the output current of the converter, the first voltage droop in the steady state is calculated, and the calculation formula is: ; in, is the output current of the converter, is the proportionality coefficient, is the first voltage droop.

[0018] The present invention adds transient droop control on the basis of traditional steady-state droop control. Transient droop control is transient output current droop control. The high-frequency component of the output current between each converter is drooped after the low-frequency component is filtered out by high-pass filtering, so as to balance the current between each converter in the transient process of load mutation. According to the output current of the converter, the second voltage droop amount of transient control is calculated by a differential operator. The specific calculation formula is:

[0019] in, is the output current of the converter, is the differential operator, is the gain of the high-pass filter, is the cutoff frequency of the high-pass filter, is the second voltage droop.

[0020] Step 3: taking the difference between the original reference voltage and the sum of the first voltage droop amount and the second voltage droop amount as a new reference voltage.

[0021] See also Figure 2 , is the droop control principle diagram of each converter. The first voltage droop and the second voltage droop are calculated for the steady-state state and transient state of the converter, respectively. The new reference voltage entering the voltage loop controller is the difference between the original reference voltage and the sum of the first voltage droop and the second voltage droop, that is: ;

[0022]

[0023] In the formula, is the new reference voltage, is the original reference voltage, is the first voltage droop, is the second voltage droop.

[0024] According to the calculation formula of the first voltage droop and the second voltage droop, Usually smaller, When the converter is in steady state, due to the differential calculation of the second voltage droop, the change rate of the converter's output current is very small, so the calculated second voltage droop is very small and approaches 0, so the first voltage droop Plays a major role. Among them, is a relatively small value, the first voltage droop It will not be too large, which can ensure that the final voltage output of the converter meets the voltage output requirements.

[0025] When the converter is in transient state, due to is relatively small, therefore, the first voltage droop Relatively small, is relatively large, and the rate of change of the output current of the converter is relatively large, so the second voltage droop Relatively large, in droop control, the second voltage droop Plays a major role in the transient state, the new reference voltage Reduce it to a relatively small level to avoid the converter exiting due to overcurrent.

[0026] Step 4: input the new reference voltage into the voltage loop controller to obtain a duty cycle control signal generated by the voltage loop controller, and control the converter output power supply voltage based on the duty cycle control signal.

[0027] It is understandable that the droop control principle of the converter in the transient state is: the high-frequency component in the sampled output current of the converter is used as the control quantity to participate in the droop. In the transient process, unbalanced current appears, in which the converter with a fast current surge and a large amplitude has a larger high-frequency component amplitude. Due to the transient droop control method, the reference quantity of the converter input voltage loop controller in the transient process is lower, thereby reducing its duty cycle increase rate. On the contrary, the high-frequency component amplitude of the converter with a slow current surge and a small amplitude is smaller, the converter transient voltage droop is small, the reference quantity of the transient process input voltage loop controller is large, and the duty cycle is gradually increased to achieve the purpose of balancing the current in the transient process.

[0028] See also Figure 3, a droop current sharing control device for a high-power DC power supply system provided by the present invention, the high-power DC power supply system includes a plurality of converters connected in parallel, the droop current sharing control device includes a plurality of droop current sharing control modules, each of the droop current sharing control modules is used to perform droop current sharing control on a corresponding converter, each of the droop current sharing control modules includes a digital controller, and the digital controller includes a voltage loop controller.

[0029] The droop control process of the droop current sharing control module for each converter is as follows: The digital controller is used to obtain the original reference voltage and output current given by the converter; calculate the first voltage droop amount based on the steady-state droop control algorithm according to the output current of the converter, and calculate the second voltage droop amount based on the transient droop control algorithm; use the difference between the original reference voltage and the sum of the first voltage droop amount and the second voltage droop amount as the new reference voltage; and input the new reference voltage into the voltage loop controller; wherein, the digital controller calculates the second voltage droop amount based on the transient droop control algorithm, including: high-pass filtering the output current of the converter using a high-pass filter to filter out the low-frequency components in the output current, retaining the high-frequency components in the output current, and calculating the second voltage droop amount based on the high-frequency components.

[0030] The voltage loop controller is used to generate a duty cycle control signal according to the new reference voltage, and control the converter to output the power supply voltage based on the duty cycle control signal.

[0031] It can be understood that the droop current balancing control device for a high-power DC power supply system provided by the present invention corresponds to the droop current balancing control method for a high-power DC power supply system provided by the aforementioned embodiments. The relevant technical features of the droop current balancing control device for a high-power DC power supply system can refer to the relevant technical features of the droop current balancing control method for a high-power DC power supply system, and will not be repeated here.

[0032] The droop current sharing control method for a high-power DC power supply system provided by the present invention is described below using simulation.

[0033] In the simulation, two converter parallel models are built. Two converters with rated output of 2000V are operated in parallel, and the rated output power of a single converter is 100kW. When two converters are started under light load of 5kW, during the sudden increase of 200kW load, the current of the first converter decreases, while the current of the second converter suddenly increases. This corresponds to the overcurrent protection failure that may occur in actual engineering, causing the converter to quit working. In order to solve the problem of sudden load increase failure, the virtual impedance droop control technology proposed in this invention is introduced.

[0034] Specific implementation method: In the simulation, two parallel converters without transient process are first tested. Start the machine under 5kW light load condition, and then increase the load by 200kW after reaching steady-state output. Figure 4 As shown, it can be seen that the output current of the first converter decreases after the step ( Figure 4 io1 represents the output current of the first converter), which outputs a very small current and then recovers after a period of time. The output current of the second converter increases sharply ( Figure 4 io2 represents the output current of the first converter), and the output is close to 95A, and then decreases after a period of time. In this case, the converter with a sharp increase in output current will exit due to overcurrent protection, and all loads will be borne by the converter that has not experienced protection exit. At this time, the total load exceeds the rated output load of a single converter, so the converter will also exit protection because it cannot bear the load exceeding the rated load, and eventually both converters will exit work, and the sudden load increase process will fail.

[0035] After adding the transient virtual impedance droop control method, the same simulation model is tested. Two parallel converters are started with 5kW, and a 200kW load is suddenly added after reaching the steady-state output. Figure 5 As shown, Figure 4 Similarly, io1 represents the output current of the first converter, and io2 represents the output current of the second converter. The peak current of the converter with a sharp increase in output current is about 70A, which is nearly 25A lower than before the transient control is added. The converter with a small output current also begins to bear the load after a short drop. Compared with the sudden load process without transient control, the addition of transient virtual impedance significantly reduces the peak output current of the converter, which can avoid the failure of the sudden load process of the entire parallel system due to the exit of the output current overcurrent protection of a single converter. In addition, the test results show that the transient virtual impedance droop control will not affect the steady-state current sharing. By setting a reasonable transient droop coefficient and the cutoff frequency of the high-pass filter, the unbalanced current in the transient process can be optimized to prevent the failure of the converter sudden load process due to inconsistent parameters.

[0036] The embodiment of the present invention provides a droop current sharing control method and control device for a high-power DC power supply system, which has the following beneficial effects: (1) No need to add additional inter-module communication, reducing the impact of interference: This technical solution adopts a distributed control strategy to avoid the need for direct communication between converters, and realizes transient current sharing control through independent sampling and feedback of each converter. Traditional current sharing methods (such as the average current method) require sharing current sharing bus information through communication between modules, which increases signal transmission lines and interface circuits. The signal transmission process is susceptible to electromagnetic interference, resulting in reduced control accuracy or system instability. The solution of the present invention realizes the transient current sharing function between converters by introducing a virtual impedance transient adjustment process, completely getting rid of the need for communication between converters, fundamentally eliminating performance problems caused by signal interference, and improving the robustness and reliability of the system.

[0037] (2) No need to add additional current-sharing busbars and controllers, reducing costs: The solution of the present invention adopts droop control based on a digital controller. By directly adding a control algorithm strategy into the digital controller and utilizing existing module sampling signals and feedback control, the control process is optimized without relying on additional hardware equipment. This method effectively reduces system costs.

[0038] (3) The control method is based on a digital controller and has high portability: The solution of the present invention adopts digital control algorithm, which is convenient for transplantation and modular application. The digital controller can switch the control strategy through simple software upgrade and parameter configuration, and quickly adapt to the power requirements of different systems. Digital design makes the control algorithm clearer, facilitates expansion and optimization, and improves the flexibility and applicability of the system.

[0039] (4) The control method has clear principles and is simple to implement: Based on transient virtual impedance droop control, the control method is simple to implement. It only needs to adjust the control algorithm of the digital controller. The control principle is clear and intuitive, and it is easy to debug and implement.

[0040] (5) Adding a transient control process on the basis of the original droop control will not affect the original steady-state droop process: The solution of the present invention is directly proposed based on the original traditional droop control method, and optimizes the control for the transient unbalanced process without causing other impacts on the steady-state working process.

[0041] It should be noted that in the above embodiments, the description of each embodiment has its own emphasis, and for parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0042] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0043] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A droop current sharing control method for a high-power DC power supply system, wherein the high-power DC power supply system comprises multiple converters connected in parallel, characterized in that: Perform droop and current sharing control on each converter, including: Obtain the original reference voltage and output current given by the converter; According to the output current of the converter, a first voltage droop amount is calculated based on a steady-state droop control algorithm, and a second voltage droop amount is calculated based on a transient droop control algorithm; taking the difference between the original reference voltage and the sum of the first voltage droop amount and the second voltage droop amount as a new reference voltage; Inputting the new reference voltage into a voltage loop controller to obtain a duty cycle control signal generated by the voltage loop controller, and controlling the converter to output a power supply voltage based on the duty cycle control signal; The step of calculating the second voltage droop amount based on the transient droop control algorithm includes: The output current of the converter is subjected to high-pass filtering to obtain a high-frequency component of the output current of the converter, and a second voltage droop amount is calculated based on the high-frequency component.

2. The droop current sharing control method according to claim 1, characterized in that: The calculating the first voltage droop amount based on the output current of the converter and a steady-state droop control algorithm comprises: ； in, is the output current of the converter, is the proportionality coefficient, is the first voltage droop.

3. The droop current sharing control method according to claim 1, characterized in that: The calculating the second voltage droop amount based on the transient droop control algorithm comprises: ； in, is the output current of the converter, is the differential operator, is the gain of the high-pass filter, is the cut-off frequency of the high-pass filter, and the output current of the converter is subjected to high-pass filtering by the high-pass filter. is the second voltage droop.

4. The droop current sharing control method according to claim 1, characterized in that: The method further comprises: taking the difference between the original reference voltage and the sum of the first voltage droop amount and the second voltage droop amount as a new reference voltage. ； in, is the new reference voltage, is the original reference voltage, is the first voltage droop, is the second voltage droop.

5. A droop current sharing control device for a high-power DC power supply system, the high-power DC power supply system comprising multiple converters connected in parallel, characterized in that: The droop current sharing control device comprises a plurality of droop current sharing control modules, each of which is used to perform droop current sharing control on a corresponding converter, and each of which comprises a digital controller, and the digital controller comprises a voltage loop controller; The digital controller is used to obtain the original reference voltage and output current given by the converter; calculate the first voltage droop amount based on the steady-state droop control algorithm according to the output current of the converter, and calculate the second voltage droop amount based on the transient droop control algorithm; taking the difference between the original reference voltage and the sum of the first voltage droop amount and the second voltage droop amount as a new reference voltage; and inputting the new reference voltage into a voltage loop controller; The voltage loop controller is used to generate a duty cycle control signal according to the new reference voltage, and control the converter to output a power supply voltage based on the duty cycle control signal; The digital controller calculates the second voltage droop amount based on the transient droop control algorithm, including: The output current of the converter is subjected to high-pass filtering to obtain a high-frequency component of the output current of the converter, and the second voltage droop amount is calculated according to the high-frequency component.

6. The droop current balancing control device according to claim 5, characterized in that: The digital controller includes a high-pass filter, and the high-pass filtering is performed on the output current of the converter to obtain the high-frequency component of the output current of the converter, including: Based on the high-pass filter, low-frequency components in the output current of the converter are filtered out, and high-frequency components are retained, so as to obtain the high-frequency components of the output current of the converter.

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