A control method and system for a droop controller in a flexible DC traction power supply system

Abstract

This invention provides a control method and system for a droop controller in a flexible DC traction power supply system. The method includes: acquiring the current and voltage values ​​of the droop controller and calculating the actual active power value; calculating the active power deviation value based on a preset active power reference value and the actual active power value; determining a first DC voltage compensation amount; calculating the real-time DC voltage deviation value based on the actual DC voltage value and the preset DC voltage reference value; and determining a second DC voltage compensation amount; calculating the current reference value of the d-axis of the current inner loop based on the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value, and the second DC voltage compensation amount; and inputting the data to the droop controller for dynamic power response and DC voltage stabilization. This invention reduces DC system voltage deviation, improves system transient and steady-state performance, and effectively promotes the integration of DC systems based on modular multilevel converters with traction power supply systems.

Description

Technical Field

[0001] This invention relates to the field of flexible DC traction power supply technology, and in particular to a control method and system for a droop controller of a flexible DC traction power supply system. Background Technology

[0002] Traction power supply systems typically employ a single-phase AC power supply structure, forming a unique electrified traction network link with phase separation. This structure leads to voltage imbalance, reactive power demand, and various types of power quality issues. With the increasing demand for electrified railways, these problems have become increasingly severe, resulting in reduced system stability and reliability. With the development of fully controlled power electronics technology, traditional power industries, such as traction power supply systems, have begun to research the use of converters to overcome existing shortcomings. DC technology based on multi-level modular converters (MMC-MTDC TPSS) is increasingly being applied in the renovation and construction of new electrified railways due to its advantages such as independent and rapid control of reactive and active power, ability to supply power to passive networks, provision of reactive power support, and multi-point power supply. The new electrified railway traction power supply system based on multi-level modular flexible DC transmission (MMC-MTDC TPSS) is gradually becoming an important research area. Among them, the droop control strategy is very suitable for application in MMC-MTDC TPSS projects because it can achieve multi-terminal coordination, has low dependence on real-time communication, and has strong scalability.

[0003] However, unlike high-voltage direct current (HVDC) transmission and distribution systems based on modular multilevel converters, traditional droop control can cause significant DC voltage deviations, and even lead to stability point shifts, considering the rapid and nonlinear changes in power demand in traction power supply systems, especially during steady-state and transient states (train entry, start-up, acceleration, and deceleration). With the increasing research and application of flexible DC systems based on modular multilevel converters in electrified railways, improving traditional droop control to ensure stable and rapid DC voltage and power regulation has become essential. Summary of the Invention

[0004] The purpose of this invention is to propose a control method and system for a droop controller of a flexible DC traction power supply system, which solves the technical problem that existing methods suffer from steady-state deviations in DC voltage due to large and frequent load changes, and large DC voltage fluctuations during transient processes when the system experiences transients.

[0005] On the one hand, a control method for a droop controller in a flexible DC traction power supply system is provided, comprising:

[0006] Obtain the current and voltage values ​​of the droop controller, and calculate the actual active power value based on the current and voltage values;

[0007] The active power deviation value is calculated based on the preset active power reference value and the actual active power value; and the corresponding first DC voltage compensation amount is determined based on the active power deviation value.

[0008] The actual DC voltage value measured by the droop controller is obtained, and the real-time DC voltage deviation value is calculated based on the actual DC voltage value and the preset DC voltage reference value; and the corresponding second DC voltage compensation amount is determined based on the actual DC voltage value and the preset compensation coefficient.

[0009] The reference value of the current along the d-axis of the inner current loop is calculated based on the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value, and the second DC voltage compensation amount.

[0010] The current reference value of the d-axis of the inner current loop is input into the droop controller for dynamic power response and DC voltage stabilization.

[0011] Preferably, the step of calculating the active power deviation value based on the preset active power reference value and the actual active power value specifically includes:

[0012] The difference between the active power reference value and the actual active power value is calculated and used as the active power deviation value.

[0013] Preferably, determining the corresponding first DC voltage compensation amount based on the active power deviation value specifically includes:

[0014] The result of multiplying the active power deviation value by a preset DC voltage compensation coefficient is output as the corresponding first DC voltage compensation amount.

[0015] Preferably, the step of calculating the real-time DC voltage deviation value based on the actual DC voltage value and the preset DC voltage reference value specifically includes:

[0016] The difference between the actual DC voltage value and the DC voltage reference value is calculated and used as the real-time DC voltage deviation value.

[0017] Preferably, determining the corresponding second DC voltage compensation amount based on the actual DC voltage value and a preset compensation coefficient specifically includes:

[0018] The result of multiplying the actual value of the DC voltage by a preset compensation coefficient is output as the corresponding second DC voltage compensation amount.

[0019] Preferably, the step of calculating the current reference value of the inner current loop d-axis based on the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value, and the second DC voltage compensation amount specifically includes:

[0020] The corresponding droop adjustment parameters are calculated based on the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value, and the second DC voltage compensation amount.

[0021] The droop adjustment parameters are input into a preset PI controller to obtain the current reference value of the d-axis of the current inner loop.

[0022] Preferably, the corresponding droop adjustment parameter is calculated according to the following formula:

[0023]

[0024] in, k droop This indicates the droop adjustment parameters of the droop controller. P ref This indicates the active power reference value preset by the droop controller. P This represents the actual active power value of the droop controller. U dcref This indicates the preset DC voltage reference value of the droop controller. U dc This indicates the actual value of the DC voltage of the droop controller. G vdc This represents the preset compensation coefficient. G P This represents the DC voltage compensation coefficient.

[0025] On the other hand, a control system for a droop controller of a flexible DC traction power supply system is also provided to implement the method, comprising:

[0026] The first DC voltage compensation module is used to obtain the current value and voltage value of the droop controller, and calculate the actual value of active power based on the current value and voltage value; calculate the active power deviation value based on the preset active power reference value and the actual value of active power; and determine the corresponding first DC voltage compensation amount based on the active power deviation value.

[0027] The second DC voltage compensation module is used to obtain the actual DC voltage value measured by the droop controller, calculate the real-time DC voltage deviation value based on the actual DC voltage value and the preset DC voltage reference value, and determine the corresponding second DC voltage compensation amount based on the actual DC voltage value and the preset compensation coefficient.

[0028] The PI controller is used to calculate the current reference value of the d-axis of the current inner loop based on the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value, and the second DC voltage compensation amount; and input the current reference value of the d-axis of the current inner loop into the droop controller for dynamic power response and DC voltage stabilization.

[0029] Preferably, it further includes:

[0030] The first DC voltage compensation module is used to calculate the difference between the active power reference value and the actual active power value as an active power deviation value; and to output the result of multiplying the active power deviation value by a preset DC voltage compensation coefficient as the corresponding first DC voltage compensation amount.

[0031] The second DC voltage compensation module is specifically used to calculate the difference between the actual DC voltage value and the DC voltage reference value as the real-time DC voltage deviation value; and to output the result of multiplying the actual DC voltage value by a preset compensation coefficient as the corresponding second DC voltage compensation amount.

[0032] Preferably, the PI controller is specifically used to calculate the corresponding droop adjustment parameter based on the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value, and the second DC voltage compensation amount;

[0033] The droop adjustment parameters are input into a preset PI controller to obtain the current reference value of the d-axis of the current inner loop;

[0034] The corresponding droop adjustment parameter is calculated according to the following formula:

[0035]

[0036] in, k droop This indicates the droop adjustment parameters of the droop controller. P ref This indicates the active power reference value preset by the droop controller. P This represents the actual active power value of the droop controller. U dcref This indicates the preset DC voltage reference value of the droop controller. U dc This indicates the actual value of the DC voltage of the droop controller. G vdc This represents the preset compensation coefficient. G P This represents the DC voltage compensation coefficient.

[0037] In summary, implementing the embodiments of the present invention has the following beneficial effects:

[0038] The present invention provides a control method and system for a droop controller in a flexible DC traction power supply system. The improved controller adds active power-DC voltage compensation and DC voltage secondary compensation links, which optimizes the DC voltage deviation problem caused by the traditional droop controller under the conditions of frequent and large power changes in railway traction load. It reduces the DC system voltage deviation, improves the transient and steady-state performance of the system, and effectively promotes the application scenarios of combining DC systems based on modular multilevel converters with traction power supply systems. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0040] Figure 1 This is a schematic diagram of a flexible DC traction power supply system in the background art.

[0041] Figure 2 This is a schematic diagram of the dynamic response curve of a traditional droop controller used in a flexible DC traction power supply system in the background technology.

[0042] Figure 3 This is a schematic diagram of the main flow of a control method for a droop controller of a flexible DC traction power supply system according to an embodiment of the present invention.

[0043] Figure 4 This is a logic diagram of a control method for a droop controller of a flexible DC traction power supply system according to an embodiment of the present invention.

[0044] Figure 5 This is a schematic diagram of the control system of a droop controller for a flexible DC traction power supply system according to an embodiment of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0046] like Figure 1 As shown, the MMC-MTDCTPSS flexible DC traction power supply system based on symmetrical bipolar configuration provided in this application, such as... Figure 2 As shown, the three-phase AC grid-side converter station in the MMC-MTDC TPSS flexible DC traction power supply system uses a traditional droop controller outer loop control. The left side shows the controllers used by the MMC U1 and MMC L1 converters.P ref The active power reference value is preset for the droop controller; P The actual value of active power calculated by the droop controller by collecting current and voltage signals; U dcref The DC voltage reference value is preset for the droop controller. U dc This represents the actual DC voltage value collected by the droop controller via the sensor. i dref The result obtained after calculation by the outer loop controller d The shaft inner loop current reference signal is sent to the controller inner loop. k droop The droop adjustment coefficient is preset for the controller. The right side shows the dynamic response curve of the MMC-MTDC TPSS three-phase grid-side converter station using a traditional droop controller when the traction load power changes. As shown in the figure, when the locomotive power on the traction load side changes (the actual active power operating point in the figure changes from point A to point B), both MMC U1 and MMC L1 exhibit DC deviation in order to participate in the active power balance regulation of the MMC-MTDC TPSS. When the load-side power change is large, the DC deviation value will also increase accordingly.

[0047] like Figure 3 and Figure 4 The diagram shown is a schematic representation of an embodiment of a control method for a droop controller in a flexible DC traction power supply system provided by the present invention. In this embodiment, the method includes the following steps:

[0048] The current and voltage values ​​of the droop controller are obtained, and the actual active power value is calculated based on the current and voltage values; that is, the droop controller calculates the actual active power value by collecting current and voltage signals.

[0049] Furthermore, the active power deviation value is calculated based on the preset active power reference value and the actual active power value; and the corresponding first DC voltage compensation amount is determined based on the active power deviation value; that is, the active power reference value and the actual active power value of the droop controller during system operation are compared to determine the active power deviation value. This deviation value is then multiplied by a preset active power-DC voltage coefficient. G P This value is used as a feedback value and is added to the DC voltage control circuit as an input quantity.

[0050] In this embodiment, the difference between the active power reference value and the actual active power value is calculated as the active power deviation value. The active power deviation value is then multiplied by a preset DC voltage compensation coefficient, and the result is output as the corresponding first DC voltage compensation amount. That is, to alleviate the problem of large errors in DC voltage when the active power on the load side changes (especially during the transient processes of traction load trains during startup, acceleration, and deceleration), voltage compensation is used to calculate the real-time measured value of active power. P ) and predetermined value ( P ref The power error value (Δ) between ) P ), multiplied by the preset active power-DC voltage coefficient ( G P The DC voltage is used as a feedback value to compensate the DC voltage control loop.

[0051] Furthermore, the actual DC voltage value measured by the droop controller is obtained, and the real-time DC voltage deviation value is calculated based on the actual DC voltage value and a preset DC voltage reference value; and the corresponding second DC voltage compensation amount is determined based on the actual DC voltage value and a preset compensation coefficient; that is, the real-time DC voltage deviation value (Δ) is obtained by subtracting the actual DC voltage value measured by the droop controller from the DC voltage reference value twice during system operation. U dc A voltage compensation circuit is used to multiply the DC voltage by a preset compensation coefficient. G vdc Then add it to the voltage error calculation stage of the controller.

[0052] In this embodiment, the difference between the actual DC voltage value and the reference DC voltage value is calculated as the real-time DC voltage deviation value. The result of multiplying the actual DC voltage value by a preset compensation coefficient is output as the corresponding second DC voltage compensation amount. That is, to compensate for the DC voltage drop problem present in the steady state of a traditional droop controller, a secondary voltage compensation stage is used to multiply the DC voltage by a preset compensation coefficient (…). G vdc And add it to the voltage error calculation stage of the droop controller.

[0053] Furthermore, the reference current value of the inner current loop d-axis is calculated based on the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value, and the second DC voltage compensation amount; that is, the active power minus the DC voltage compensation amount and the secondary DC voltage compensation amount, and the calculated active power value and DC voltage value are then processed through a droop control coefficient. k droop The inner current loop can be obtained after calculation with the PI controller. d Shaft current reference value.

[0054] In this embodiment, the corresponding droop adjustment parameter is calculated based on the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value, and the second DC voltage compensation amount; specifically, the corresponding droop adjustment parameter is calculated according to the following formula:

[0055]

[0056] in, k droop This indicates the droop adjustment parameters of the droop controller. P ref This indicates the active power reference value preset by the droop controller. P This represents the actual active power value of the droop controller. U dcref This indicates the preset DC voltage reference value of the droop controller. U dc This indicates the actual value of the DC voltage of the droop controller. G vdc This represents the preset compensation coefficient. G P This represents the DC voltage compensation coefficient.

[0057] The droop adjustment parameters are input into a preset PI controller to obtain the current reference value of the d-axis of the current inner loop. In other words, by inputting the determined adjustment parameters into the PI controller, the corresponding current reference value of the d-axis of the current inner loop can be calculated. It should be noted that calculating the corresponding current reference value of the d-axis of the current inner loop by inputting the adjustment parameters into the PI controller is a common method in the art. This invention mainly addresses the problem of large deviations in the original adjustment of the adjustment parameters, which will not be elaborated further here.

[0058] Furthermore, the current reference value of the d-axis of the inner current loop is input to the droop controller for dynamic power response and DC voltage stabilization. That is, the control parameter values ​​obtained above are transmitted to the droop controller in the MMC-MTDC TPSS, namely the MMC U1 and MMC L1 converter station controllers in this patent, which can ultimately realize the dynamic power response capability and DC voltage stabilization capability in the MMC-MTDC TPSS.

[0059] like Figure 5 As shown, in this embodiment, a control system for a droop controller of a flexible DC traction power supply system is also provided to implement the control method for the droop controller of the flexible DC traction power supply system, including:

[0060] A DC voltage compensation module is used to obtain the current and voltage values ​​of the droop controller, and calculate the actual active power value based on the current and voltage values; calculate the active power deviation value based on a preset active power reference value and the actual active power value; and determine the corresponding first DC voltage compensation amount based on the active power deviation value.

[0061] In this embodiment, the DC voltage compensation module is used to calculate the difference between the active power reference value and the actual active power value as the active power deviation value; and to output the result of multiplying the active power deviation value by a preset DC voltage compensation coefficient as the corresponding first DC voltage compensation amount.

[0062] A DC voltage compensation module is used to obtain the actual value of the DC voltage measured by the droop controller, calculate the real-time DC voltage deviation value based on the actual value of the DC voltage and a preset DC voltage reference value, and determine the corresponding second DC voltage compensation amount based on the actual value of the DC voltage and a preset compensation coefficient.

[0063] In this embodiment, the second DC voltage compensation module is specifically used to calculate the difference between the actual DC voltage value and the DC voltage reference value as the real-time DC voltage deviation value; and to output the result of multiplying the actual DC voltage value by a preset compensation coefficient as the corresponding second DC voltage compensation amount.

[0064] The PI controller is used to calculate the current reference value of the d-axis of the current inner loop based on the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value, and the second DC voltage compensation amount; and input the current reference value of the d-axis of the current inner loop into the droop controller for dynamic power response and DC voltage stabilization.

[0065] In this embodiment, the PI controller is specifically used to calculate the corresponding droop adjustment parameter based on the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value, and the second DC voltage compensation amount;

[0066] The droop adjustment parameters are input into a preset PI controller to obtain the current reference value of the d-axis of the current inner loop;

[0067] The corresponding droop adjustment parameter is calculated according to the following formula:

[0068]

[0069] in, k droop This indicates the droop adjustment parameters of the droop controller. P ref This indicates the active power reference value preset by the droop controller.P This represents the actual active power value of the droop controller. U dcref This indicates the preset DC voltage reference value of the droop controller. U dc This indicates the actual value of the DC voltage of the droop controller. G vdc This represents the preset compensation coefficient. G P This represents the DC voltage compensation coefficient.

[0070] It should be noted that the system described in the above embodiments corresponds to the method described in the above embodiments. Therefore, the parts of the system described in the above embodiments that are not described in detail can be obtained by referring to the content of the method described in the above embodiments, and will not be repeated here.

[0071] In summary, implementing the embodiments of the present invention has the following beneficial effects:

[0072] The present invention provides a control method and system for a droop controller in a flexible DC traction power supply system. The improved controller adds active power-DC voltage compensation and DC voltage secondary compensation links, which optimizes the DC voltage deviation problem caused by the traditional droop controller under the conditions of frequent and large power changes in railway traction load. It reduces the DC system voltage deviation, improves the transient and steady-state performance of the system, and effectively promotes the application scenarios of combining DC systems based on modular multilevel converters with traction power supply systems.

[0073] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A control method of a droop controller of a flexible DC traction power supply system, characterized by, The method comprises the following steps: obtaining the current value and voltage value of the droop controller, and calculating the active power actual value according to the current value and the voltage value; calculating the active power deviation value according to the preset active power reference value and the active power actual value; and determining the corresponding first DC voltage compensation amount according to the active power deviation value; obtaining the DC voltage actual value measured by the droop controller, calculating the real-time DC voltage deviation value according to the DC voltage actual value and the preset DC voltage reference value; and determining the corresponding second DC voltage compensation amount according to the DC voltage actual value and the preset compensation coefficient; calculating the current reference value of the current inner loop d-axis according to the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value and the second DC voltage compensation amount; inputting the current reference value of the current inner loop d-axis into the droop controller for dynamic power response and DC voltage stabilization.

2. The method of claim 1, wherein, The method comprises the following steps: calculating the difference between the active power reference value and the active power actual value as the active power deviation value.

3. The method of claim 2, wherein, The method comprises the following steps: multiplying the active power deviation value by the preset DC voltage compensation coefficient to obtain the corresponding first DC voltage compensation amount.

4. The method of claim 1, wherein, The method comprises the following steps: calculating the difference between the DC voltage actual value and the DC voltage reference value as the real-time DC voltage deviation value.

5. The method of claim 4, wherein, The method comprises the following steps: multiplying the DC voltage actual value by the preset compensation coefficient to obtain the corresponding second DC voltage compensation amount.

6. The method of claim 1, wherein, The method comprises the following steps: calculating the corresponding droop adjustment parameter according to the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value and the second DC voltage compensation amount; inputting the droop adjustment parameter into the preset PI controller to obtain the current reference value of the current inner loop d-axis.

7. The method of claim 6, wherein, The corresponding droop adjustment parameter is calculated according to the following formula: wherein, k droop denotes a droop regulation parameter of the droop controller, P ref denotes a preset active power reference value of the droop controller, P denotes an active power actual value of the droop controller, U dcref denotes a preset DC voltage reference value of the droop controller, U dc denotes a DC voltage actual value of the droop controller, G vdc denotes a preset compensation coefficient, G P denotes a DC voltage compensation coefficient.

8. A control system of a droop controller of a flexible HVDC traction power supply system for implementing the method according to any one of claims 1-7, characterized in that The method comprises the following steps: The first DC voltage compensation module is used to obtain the current value and voltage value of the droop controller, and calculate the active power actual value according to the current value and the voltage value; calculating the active power deviation value according to the preset active power reference value and the active power actual value; and determining the corresponding first DC voltage compensation amount according to the active power deviation value; The second DC voltage compensation module is configured to obtain an actual DC voltage value measured by the droop controller, calculate a real-time DC voltage deviation value according to the actual DC voltage value and a preset DC voltage reference value, and determine a corresponding second DC voltage compensation amount according to the actual DC voltage value and a preset compensation coefficient. The PI controller is configured to calculate a current reference value of a d-axis of a current inner loop according to the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value and the second DC voltage compensation amount, and input the current reference value of the d-axis of the current inner loop into the droop controller to realize dynamic power response and DC voltage stabilization.

9. The system of claim 8, wherein, Further comprising: The first DC voltage compensation module is configured to calculate a difference between the active power reference value and the active power actual value as an active power deviation value. The active power deviation value is multiplied by a preset DC voltage compensation coefficient, and a result is output as a corresponding first DC voltage compensation amount. The second DC voltage compensation module is configured to calculate a difference between the actual DC voltage value and the DC voltage reference value as a real-time DC voltage deviation value, and multiply the actual DC voltage value by a preset compensation coefficient, and a result is output as a corresponding second DC voltage compensation amount.

10. The system of claim 8, wherein, The PI controller is configured to calculate a corresponding droop adjustment parameter according to the first DC voltage compensation amount, the active power deviation value, the real-time DC voltage deviation value and the second DC voltage compensation amount. The droop adjustment parameter is input into a preset PI controller to obtain a current reference value of a d-axis of a current inner loop. The corresponding droop adjustment parameter is calculated according to the following formula: wherein, k droop represents a droop regulation parameter of the droop controller, P ref represents an active power reference value preset by the droop controller, P represents an active power actual value of the droop controller, U dcref represents a DC voltage reference value preset by the droop controller, U dc represents a DC voltage actual value of the droop controller, G vdc represents a preset compensation coefficient, G P represents a DC voltage compensation coefficient.

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