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

Abstract

The application provides a droop current-sharing control method and a control device for a high-power direct-current power supply system. The control method is to separately control each converter, and to take the high-frequency component of the output current of the converter obtained through sampling as a control quantity to participate in current-sharing droop. In a transient process, unbalanced current occurs. The high-frequency component amplitude of the converter with fast current surge and large amplitude is larger. Due to the transient droop control method, the reference quantity of the input voltage loop controller of the converter in the transient process is lower, so as to reduce the increase rate of the duty cycle. On the contrary, the high-frequency component amplitude of the converter with slow current surge and small amplitude is smaller. The transient voltage droop quantity of the converter is small, the reference quantity of the input voltage loop controller of the converter in the transient process is large, and the duty cycle is gradually increased, so as to achieve the purpose of balancing the current in the transient process.

Description

Technical Field

[0001] This invention relates to the field of power supply current balancing, and more specifically, to a droop current sharing control method and control device for high-power DC power supply systems. Background Technology

[0002] With the development of technologies such as new energy vehicles, aerospace, and medical equipment, high-power DC power supplies are widely used. Simultaneously, with advancements in digital control technology, DC power supplies are rapidly evolving towards miniaturization, modularization, and intelligent control. However, the application of high-power DC equipment leads to increasingly larger required DC power supply capacities, often exceeding the input power of a single module. Therefore, parallel connection of multiple modules is commonly considered to achieve higher power output. However, parallel connection inevitably involves current sharing among the modules. Ideally, the total output load current of a parallel DC power supply system is evenly distributed among the individual modules. But in actual engineering, it's impossible to guarantee that the output characteristics of the modules are exactly the same; there will always be some differences. Therefore, without appropriate control methods, the current between modules is often unbalanced. This can cause modules bearing larger loads to experience higher current and thermal stresses over extended periods, thus weakening the reliability and lifespan 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, and virtual impedance droop method. 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. However, the failure of a single module will affect the average current bus and cause the system to fail and shut down. The master-slave setting method selects one module as a fixed master module and the rest as slave modules. However, 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 uses various control strategies to control the current sharing of the parallel system. However, it requires the use of many signal connection circuits, and the information transmission is easily interfered with.

[0004] Currently, the most widely used parallel current sharing technology is virtual impedance droop control. It requires no additional communication between modules or additional sensors, and because it uses virtual impedance, it does not cause energy loss. Its principle is clear and its implementation is simple, making it commonly used in industry. However, during droop control operation, differences may exist between modules. This can lead to instantaneous energy changes during sudden increases or decreases in load, causing different output responses from the two converters. This can result in output overcurrent faults, and consequently, during load changes, the protection mechanisms may shut down one by one, leading to failure of the sudden load increase or decrease and ultimately failing to meet requirements.

[0005] The specific reasons are as follows: Currently, droop control achieves good current sharing in steady-state operation, ensuring normal output during steady-state parallel current sharing among modules. However, it does not adequately consider dynamic processes. When the modules adopt a single voltage loop control method, the accuracy of voltage sampling by each module cannot be guaranteed to be completely consistent, resulting in inconsistent impacts on the single voltage loop feedback control, which can affect dynamic performance to some extent. Specifically, although the outputs of each module are at the same voltage level, the voltage sampled values ​​received by each module differ due to different voltage sampling coefficients. During transient processes of sudden load increases, the uneven distribution of current increase among modules may trigger an overcurrent fault in the output current of the module, causing it to shut down and fail to meet the requirements of sudden load increases. In severe cases, it may even lead to module burnout and damage. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a droop current sharing control method and control device for high-power DC power supply systems, aiming to solve the problem of multi-module parallel DC power supply systems under sudden load increases.

[0007] 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, the high-power DC power supply system comprising multiple parallel converters, wherein droop current sharing control is performed on each converter, comprising:

[0008] Obtain the original reference voltage and output current given by the converter;

[0009] Based on the output current of the converter, a first voltage droop is calculated using a steady-state droop control algorithm, and a second voltage droop is calculated using a transient droop control algorithm.

[0010] The difference between the original reference voltage and the sum of the first voltage droop and the second voltage droop is taken as the new reference voltage.

[0011] The new reference voltage is input to the voltage loop controller to obtain the duty cycle control signal generated by the voltage loop controller. Based on the duty cycle control signal, the converter output power supply voltage is controlled.

[0012] The calculation of the second voltage droop based on the transient droop control algorithm includes:

[0013] The output current of the converter is high-pass filtered to obtain the high-frequency component of the output current of the converter. Based on the high-frequency component, the second voltage droop is calculated.

[0014] According to a second aspect of the present invention, a droop current sharing control device for a high-power DC power supply system is provided, the high-power DC power supply system including multiple parallel converters, the droop current sharing control device including multiple 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, each of the droop current sharing control modules including a digital controller, the digital controller including a voltage loop controller;

[0015] The digital controller is configured to acquire the original reference voltage and output current given by the converter; calculate a first voltage droop based on a steady-state droop control algorithm and a second voltage droop based on a transient droop control algorithm according to the output current of the converter; take the difference between the original reference voltage and the sum of the first voltage droop and the second voltage droop as the new reference voltage; and input the new reference voltage into the voltage loop controller.

[0016] The voltage loop controller is used to generate a duty cycle control signal based on the new reference voltage, and control the converter output power supply voltage based on the duty cycle control signal;

[0017] The digital controller calculates the second voltage droop based on a transient droop control algorithm, including:

[0018] The output current of the converter is high-pass filtered to obtain the high-frequency component of the output current of the converter, and the second voltage droop is calculated based on the high-frequency component.

[0019] This invention provides a droop current sharing control method and control device for high-power DC power supply systems. It individually controls each parallel converter in the high-power DC power supply system, using the sampled high-frequency component of the converter's output current as a control quantity to participate in current sharing and droop control. During transient processes, unbalanced currents occur. Converters with rapid current surges and large amplitudes have larger high-frequency component amplitudes. Due to the transient droop control method, the reference quantity of the input voltage loop controller for these converters during transient processes is lower, thereby reducing the rate of increase in their duty cycle. Conversely, converters with slow current surges and small amplitudes have smaller high-frequency component amplitudes, resulting in smaller transient voltage droop. The reference quantity of the input voltage loop controller for these converters during transient processes is larger, gradually increasing the duty cycle and achieving the goal of balancing the current during transient processes. Attached Figure Description

[0020] Figure 1 A flowchart of a droop current sharing control method for a high-power DC power supply system provided by the present invention;

[0021] Figure 2 This is a block diagram of the transient droop control.

[0022] Figure 3A schematic diagram of a droop current sharing control device for a high-power DC power supply system provided by the present invention;

[0023] Figure 4 A schematic diagram of a sudden load surge without the application of transient control;

[0024] Figure 5 A schematic diagram of a sudden load increase waveform with transient control added. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In addition, the technical features of the various embodiments or individual embodiments provided by the present invention can be arbitrarily combined with each other to form feasible technical solutions. Such combinations are not constrained by the order of steps and / or structural composition patterns, but must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0026] To address the issue of inconsistent dynamic performance and responses among converters in high-power DC power supply systems with multiple converters connected in parallel during sudden load changes, this invention proposes an improved control method for high-power DC power supply systems. The aim is to optimize transient performance and improve system reliability while ensuring no adverse effects on the system's steady-state performance.

[0027] This invention provides a droop current sharing control method for high-power DC power supply systems, wherein the high-power DC power supply system includes multiple converters connected in parallel, and each converter is controlled individually during droop current sharing control. See also... Figure 1 The droop control method for each converter specifically includes the following steps:

[0028] Step 1: Obtain the original reference voltage and output current given by the converter.

[0029] Understandably, for each converter, the original reference voltage and the converter's output current are obtained.

[0030] Step 2: Based on the output current of the converter, calculate the first voltage droop amount using a steady-state droop control algorithm, and calculate the second voltage droop amount using a transient droop control algorithm.

[0031] Understandably, when performing droop current equalization control on the converter, this invention considers both the steady-state and transient operating states of the converter and designs two parts of droop equalization control. The so-called steady-state operating state refers to the converter's output current changing slowly, while the so-called transient operating state refers to the converter's output current changing at a relatively fast rate due to sudden load changes, such as a sudden increase in load.

[0032] Specifically, this invention enhances the transient response capability of parallel converter systems during load surges by introducing a transient control scheme, and adjusts the ability to coordinate current changes between converters. By adding transient output current droop control to the traditional steady-state droop control, the transient performance of the entire power supply system is improved.

[0033] The steady-state droop control in this invention is a traditional droop control, i.e., drooping the steady-state DC output current to balance the currents between converters during steady-state operation. Based on the converter's output current, the first voltage droop in the steady-state state is calculated using the following formula:

[0034] ;

[0035] in, The output current of the converter, This is the proportionality coefficient. This is the first voltage droop.

[0036] This invention adds transient droop control to the traditional steady-state droop control. Transient droop control, specifically transient output current droop control, reduces the high-frequency component of the output current between each converter after filtering out low-frequency components using a high-pass filter. This balances the current between the converters during transient processes caused by load changes. Specifically, based on the converter's output current, a second voltage droop amount for transient control is calculated using a differential operator. The specific calculation formula is as follows:

[0037]

[0038] in, The output current of the converter, For differential operators, This represents the gain of the high-pass filter. This is the cutoff frequency of the high-pass filter. This is the second voltage droop.

[0039] Step 3: Take the difference between the original reference voltage and the sum of the first voltage droop and the second voltage droop as the new reference voltage.

[0040] See Figure 2The diagram below illustrates the droop control principle for each converter. The first and second voltage droop values ​​were calculated for both the steady-state and transient states of the converter. The new reference voltage entering the voltage loop controller is the difference between the original reference voltage and the sum of the first and second voltage droop values, i.e.:

[0041] ;

[0042]

[0043]

[0044] In the formula, For the new reference voltage, The original reference voltage, This is the first voltage droop. This is the second voltage droop.

[0045] According to the calculation formulas for the first voltage droop and the second voltage droop, where, Usually relatively small, Typically, the value is relatively large. When the converter is in steady state, due to the differential calculation of the second voltage droop, the rate of change of the converter's output current is very small, therefore the calculated second voltage droop... Very small, approaching 0, therefore the first voltage droop is It plays a major role. Among them, For a relatively small value, the first voltage droop. It won't be too large, enough to ensure that the converter's final voltage output meets the voltage output requirements.

[0046] When the converter is in a transient state, because The first voltage droop is relatively small, therefore. Relatively small, and The second voltage droop is relatively large, and the rate of change of the converter's output current is also relatively large. The droop is relatively large; in droop control, the second voltage droop is... It plays a major role in the transient state, by setting the new reference voltage. Reduce the current to a relatively small value to prevent the converter from shutting down due to overcurrent.

[0047] Step 4: Input the new reference voltage into the voltage loop controller to obtain the duty cycle control signal generated by the voltage loop controller. Based on the duty cycle control signal, control the converter to output power supply voltage.

[0048] Understandably, the droop control principle during the transient state of the converter is as follows: the high-frequency component of the sampled converter output current is used as the control quantity to participate in the droop control. During the transient process, an unbalanced current occurs. For converters with a rapid current surge and large amplitude, the high-frequency component amplitude is even larger. Due to the transient droop control method, the reference quantity of the input voltage loop controller for this converter during the transient process is lower, thereby reducing its duty cycle increase rate. Conversely, for converters with a slow current surge and small amplitude, the high-frequency component amplitude is smaller, the transient voltage droop of this converter is smaller, the reference quantity of the input voltage loop controller during the transient process is larger, and the duty cycle is gradually increased to achieve the purpose of balancing the current during the transient process.

[0049] See Figure 3 The present invention provides a droop current sharing control device for a high-power DC power supply system. The high-power DC power supply system includes multiple parallel converters. The droop current sharing control device includes multiple droop current sharing control modules. Each droop current sharing control module is used to perform droop current sharing control on a corresponding converter. Each droop current sharing control module includes a digital controller, and the digital controller includes a voltage loop controller.

[0050] The droop control module performs the following droop control process for each converter:

[0051] The digital controller is configured to acquire the original reference voltage and output current given by the converter; calculate a first voltage droop based on a steady-state droop control algorithm and a second voltage droop based on a transient droop control algorithm based on the output current of the converter; take the difference between the original reference voltage and the sum of the first voltage droop and the second voltage droop as a new reference voltage; and input the new reference voltage into a voltage loop controller; wherein, the digital controller calculates the second voltage droop based on the transient droop control algorithm by: performing high-pass filtering on the output current of the converter using a high-pass filter to filter out low-frequency components in the output current and retain high-frequency components in the output current, and calculating the second voltage droop based on the high-frequency components.

[0052] The voltage loop controller is used to generate a duty cycle control signal based on the new reference voltage, and control the converter output power supply voltage based on the duty cycle control signal.

[0053] It is understood that the droop current sharing control device for high-power DC power supply systems provided by the present invention corresponds to the droop current sharing control method for high-power DC power supply systems provided in the foregoing embodiments. The relevant technical features of the droop current sharing control device for high-power DC power supply systems can be referred to the relevant technical features of the droop current sharing control method for high-power DC power supply systems, and will not be repeated here.

[0054] The droop current sharing control method for high-power DC power supply systems provided by this invention will be illustrated below using simulation.

[0055] In the simulation, a parallel model of two converters was built, with two 2000V rated output converters operating in parallel. The rated output power of each converter is 100kW. When starting the two converters under a light load of 5kW, and then suddenly increasing the load to 200kW, a phenomenon occurred where the current of the first converter decreased while the current of the second converter suddenly increased. This corresponds to an overcurrent protection fault that might occur in actual engineering, causing the converter to shut down. To solve the problem of sudden load increase faults, the virtual impedance droop control technology proposed in this invention is introduced.

[0056] Specific implementation method: The simulation first tests two parallel converters without transient processes. The converters are started under a 5kW light load condition, and after reaching steady-state output, a sudden increase of 200kW load is applied, such as... Figure 4 As shown, the output current of the first converter drops after a step jump. Figure 4 In this context, io1 represents the output current of the first converter, which is very small and recovers after a period of time. The output current of the second converter suddenly increases dramatically. Figure 4 In this case, io2 represents the output current of the first converter, which is close to 95A and then decreases after a period of time. In this situation, the converter with the surge in output current will shut down due to overcurrent protection, and all the load will be borne by the converter that has not shut down due to protection. At this time, the total load exceeds the rated output load of a single converter, so the converter also shuts down due to its inability to handle the load exceeding the rated load. Ultimately, both converters shut down, and the sudden load increase process fails.

[0057] After incorporating a transient virtual impedance droop control method, the same simulation model was tested. Two parallel converters with a power output of 5kW were started up, and after reaching steady-state output, a sudden increase of 200kW load occurred. Figure 5 As shown, with 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 sudden increase in output current is approximately 70A, a decrease of nearly 25A compared to before the transient control was implemented. The converter with the smaller output current also begins to bear the load after a brief decrease. Compared to the sudden load increase process without transient control, the addition of transient virtual impedance significantly reduces the peak output current of the converter, preventing the entire parallel system from failing due to the overcurrent protection of a single converter malfunctioning during a sudden load increase. Furthermore, test results show that transient virtual impedance droop control does not affect steady-state current sharing. By setting a reasonable transient droop coefficient and the cutoff frequency of the high-pass filter, the unbalanced current during the transient process can be optimized, preventing converter failure due to parameter inconsistencies during sudden load increases.

[0058] The present invention provides a droop current sharing control method and control device for high-power DC power supply systems, which has the following beneficial effects:

[0059] (1) No additional inter-module communication is required, reducing the impact of interference:

[0060] This technical solution employs a distributed control strategy, avoiding the need for direct communication between converters. Transient current sharing control is achieved through independent sampling and feedback by each converter. Traditional current sharing methods (such as the average current method) require inter-module communication to share current sharing bus information, increasing signal transmission lines and interface circuits. Furthermore, the signal transmission process is susceptible to electromagnetic interference, leading to decreased control accuracy or system instability. This invention, by introducing a virtual impedance transient adjustment process, achieves transient current sharing between converters, completely eliminating the need for inter-converter communication. This fundamentally eliminates performance problems caused by signal interference, improving the system's robustness and reliability.

[0061] (2) No additional current sharing bus and controller are required, reducing costs:

[0062] The present invention adopts droop control based on digital controller. By directly adding control algorithm strategy into digital controller, and using existing module sampling signal and feedback control, the control process is optimized without relying on additional hardware equipment. This method effectively reduces system cost.

[0063] (3) The control method is based on a digital controller, which has high portability:

[0064] This invention employs a digital control algorithm, facilitating portability and modular application. The digital controller can switch control strategies through simple software upgrades and parameter configurations, quickly adapting to the power requirements of different systems. Digital design makes the control algorithm clearer, facilitating expansion and optimization, and improving system flexibility and applicability.

[0065] (4) The control method has a clear principle and is simple to implement:

[0066] Based on transient virtual impedance droop control, the control method is simple to implement, requiring only adjustments to the digital controller control algorithm. The control principle is clear and intuitive, and it is easy to debug and implement.

[0067] (5) Adding a transient control process to the existing droop control will not affect the original steady-state droop process:

[0068] The present invention is based directly on the original traditional droop control method, and optimizes the control of transient imbalance process without causing other effects on steady-state operation.

[0069] It should be noted that the descriptions of each embodiment in the above embodiments have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0070] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0071] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A droop current-sharing control method for a high-power DC power supply system comprising multiple parallel-connected converters, characterized in that, The droop current-sharing control is performed on each converter, including: obtaining a given original reference voltage and an output current of the converter; calculating a first voltage droop based on a steady-state droop control algorithm and a second voltage droop based on a transient-state droop control algorithm according to the output current of the converter; the calculation of the first voltage droop based on the steady-state droop control algorithm according to the output current of the converter includes: ； wherein, is the output current of the converter, is a proportional factor, is a first voltage droop amount; subtracting the first voltage droop from the original reference voltage and then subtracting the second voltage droop to obtain 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; wherein the calculation of the second voltage droop based on the transient-state droop control algorithm includes: high-pass filtering the output current of the converter to obtain a high-frequency component of the output current of the converter, and calculating the second voltage droop according to the high-frequency component; the calculation of the second voltage droop based on the transient-state droop control algorithm includes: ； wherein is an output current of the converter, is a differential operator, is a gain of a high-pass filter, is a cut-off frequency of the high-pass filter, the output current of the converter being high-pass filtered by the high-pass filter, is a second voltage droop.

2. The droop current-sharing control method of claim 1, wherein subtracting the first voltage droop from the original reference voltage and then subtracting the second voltage droop to obtain a new reference voltage, including: ； wherein, is a new reference voltage, is an original reference voltage, is a first voltage droop amount, is a second voltage droop amount.

3. A droop current-sharing control device for a high-power DC power supply system comprising multiple parallel-connected converters, based on the droop current-sharing control method according to any one of claims 1 and 2, characterized in that, The droop current-sharing control device includes a plurality of droop current-sharing control modules, each of which is used to control a corresponding converter, and each of the droop current-sharing control modules includes a digital controller, and the digital controller includes a voltage loop controller; the digital controller is configured to obtain a given original reference voltage and an output current of the converter, calculate a first voltage droop based on a steady-state droop control algorithm and a second voltage droop based on a transient-state droop control algorithm according to the output current of the converter, and calculate the second voltage droop based on the transient-state droop control algorithm; subtracting the first voltage droop from the original reference voltage and then subtracting the second voltage droop to obtain a new reference voltage; and inputting the new reference voltage into a voltage loop controller; the voltage loop controller is configured 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; wherein the digital controller calculates the second voltage droop based on the transient-state droop control algorithm, including: high-pass filtering the output current of the converter to obtain a high-frequency component of the output current of the converter, and calculating the second voltage droop according to the high-frequency component.

4. The droop current-sharing control apparatus according to claim 3, wherein The digital controller includes a high-pass filter, and the high-pass filtering of the output current of the converter to obtain a high-frequency component of the output current of the converter includes: filtering out low-frequency components of the output current of the converter based on the high-pass filter and retaining high-frequency components to obtain a high-frequency component of the output current of the converter.

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