An accurate power allocation control method for ISOP-DC-SST

Abstract

The application discloses an accurate power distribution control method of ISOP-DC-SST, and belongs to the technical field of power electronics. The method is as follows: single module control signal acquisition; balance coefficient design; accurate power distribution controller design to obtain a final control signal; according to different control requirements, corresponding modulation strategies are adopted to modulate the final control signal into inner and outer phase angles, so as to control the turn-on and turn-off of the switch tube of the DAB converter and realize the control of the output voltage and power. Based on the adaptive principle, the balance coefficient based on the Sigmoid function is introduced as an adjustment item to generate nonlinear negative feedback, dynamically adjust the output power of the single module, and stabilize the input voltage of the single module to the balance point. Compared with the prior art, the accurate power distribution controller can effectively balance the input voltage, has higher robustness and less calculation amount.

Description

TECHNICAL FIELD

[0001] The application relates to an accurate power distribution control method of ISOP-DC-SST, and belongs to the technical field of power electronics. BACKGROUND

[0002] As an important component in modern power electronic systems, ISOP-DC-SST (Input Series Output Parallel DC Solid State Transformer) usually consists of multiple DC-DC conversion modules in parallel output, such as dual active bridge DC-DC converters (DAB) and the like, to achieve efficient and flexible power conversion and distribution. In such systems, ensuring accurate power distribution of each module is the key to maintaining stable operation of the entire ISOP-DC-SST.

[0003] For ISOP-DC-SST, output current control mode is not usually a necessary condition for accurate power distribution, because when the input voltage of a module in the system is affected by external disturbances, although the output current (i.e. power) can still be accurately controlled by the controller, due to the positive feedback effect of the input voltage, the input voltage of the module is difficult to automatically restore to the original equilibrium point. This unbalanced state not only affects the stable operation of the system, but also reduces the efficiency of power conversion, and even causes damage to the equipment.

[0004] In order to overcome this problem, the industry often uses a balance control algorithm based on full model predictive control (MPC). This algorithm realizes effective regulation of output voltage and balance of power distribution by introducing input voltage into the cost function of the controller. This design fully utilizes the inherent advantages of MPC multi-objective optimization, providing a new solution for accurate power distribution of ISOP-DC-SST.

[0005] However, the accurate power distribution algorithm based on MPC still faces many challenges in practical application. First, solving a complex cost function will introduce heavy computational burden. Especially when the number of input voltage penalty terms in the cost function increases with the increase in the number of input series modules, the calculation amount increases significantly, thereby limiting the widespread application of this algorithm in real-time control systems. Second, since this method relies on the accuracy of the system model and parameters, it lacks sufficient robustness. Therefore, once the system parameters have errors or changes, the balanced state of the input voltage will be difficult to maintain, thereby affecting the stability and performance of the entire system.

[0006] In summary, for the problem of accurate power distribution of ISOP-DC-SST, it is urgent to invent a reliable and effective balance control strategy to overcome the limitations of existing technologies and improve the stability and robustness of the system. SUMMARY

[0007] To solve the problems in the background art, the application provides an accurate power distribution control method for ISOP-DC-SST.

[0008] To achieve the above object, the application adopts the following technical scheme: an accurate power distribution control method for ISOP-DC-SST, which comprises the following steps:

[0009] S1: single-module control signal acquisition: the control signal of the i th module at t=k is denoted as

[0010] S2: balance coefficient design;

[0011] S201: design of the balance coefficient based on the Sigmoid function to generate nonlinear negative feedback, so that the input voltage is stabilized at the balance point;

[0012] The expression of the balance coefficient α bali in S201 is as follows:

[0013]

[0014] In formula (1):

[0015] m represents the m th control period;

[0016] N represents the number of input-end series sub-modules;

[0017] U ini represents the input voltage of the i th sub-module;

[0018] η represents the slope of the balance coefficient;

[0019] e represents the exponential;

[0020] γ0 represents the midpoint of the Sigmoid function,

[0021] The change process of the balance coefficient α bali in S201 is as follows:

[0022] When the input voltage U ini of the i th sub-module is higher than the voltage balance point U inav , the value of the balance coefficient α bali decreases from the voltage balance point U ini with the increase of the input voltage U inav of the i th sub-module;

[0023] When the input voltage U ini of the i th sub-module is lower than the voltage balance point U inav , the value of the balance coefficient α baliThe value of the input voltage U of the i-th submodule ini The decrease from the voltage balance point U inav Start to grow.

[0024] S202: The balancing coefficient is calculated based on the input voltage U of the i-th module. ini Dynamically adjust control signals;

[0025] S203: The balancing coefficient adjusts the output current of the DAB converter to achieve even power distribution and balance the input voltages of the submodules.

[0026] S3: Design of precise power distribution controller to obtain the final control signal;

[0027] The controller expression of S3 is as follows:

[0028]

[0029] In formula (2):

[0030] Represents the final control signal of the i-th submodule after passing through the balancing controller.

[0031] S4: Adopting corresponding modulation strategies according to different control requirements, the final control signal is modulated into inner phase shift angle D1 and outer phase shift angle D2, thereby controlling the on and off of the DAB converter switch tube to achieve output voltage and power control.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] Based on the principle of self-adaptation, this invention introduces a sigmoid function-based balancing coefficient as a regulation term to generate nonlinear negative feedback, dynamically adjusting the output power of individual modules and stabilizing their input voltage to a balance point. Compared to existing technologies, this precise power distribution controller can effectively balance input voltages while offering greater robustness and requiring less computation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is an equivalent system block diagram of the ISOP-DC-SST of the present invention;

[0035] Figure 2 This is a waveform diagram showing the relationship between the balance coefficient and the input voltage at different slopes of the present invention;

[0036] Figure 3is an experimental waveform diagram of the present application in the case of different leakage inductance of each single module, the load resistance is reduced from 25Ω to 10Ω, the four waveforms from top to bottom represent the input voltage of each DAB module, the output voltage of the DC solid-state transformer, the output current of the DC solid-state transformer and the internal current of the module-high frequency transformer respectively, and the load resistance switching occurs at the step increase of the current waveform in the figure.

[0037] Figure 4 is an experimental waveform diagram of the present application in the case of different leakage inductance of each single module, the load resistance is reduced from 25Ω to 10Ω, the four waveforms from top to bottom represent the input voltage of each DAB module, the output voltage of the DC solid-state transformer, the output current of the DC solid-state transformer and the internal current of the module-high frequency transformer respectively, and the load resistance switching occurs at the step increase of the current waveform in the figure. DETAILED DESCRIPTION

[0038] The technical solutions in the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0039] A precise power distribution control method of ISOP-DC-SST, the method comprises the following steps:

[0040] S1: Single module control signal acquisition: the input series output parallel type solid-state transformer is usually modular structure, composed of a plurality of basic constant power dissipation basic units, such as double active bridge DC-DC converter (DAB) and the like. For a single module, the control signal is calculated by the controller of each basic module respectively, wherein the control signal of the i-th module at t=k moment is recorded as

[0041] S2: Design the balance coefficient based on the input voltage feedback, used for adaptive adjustment of the output power of single module, and then form a negative feedback after the input voltage of single module deviates from the balance point, so as to realize the balance of input voltage.

[0042] S201: In order to solve the problem that the input voltage cannot be restored to the original balance point due to the effect of positive feedback after the input voltage is disturbed under the traditional power distribution strategy, the present application designs the balance coefficient based on Sigmoid function as the balance coefficient, to produce nonlinear negative feedback, so as to stabilize the input voltage to the balance point.

[0043] The expression of the balance coefficient α bali in S201 is as follows:

[0044]

[0045] In formula (1):

[0046] m represents the mth control period;

[0047] N represents the number of input series sub-modules;

[0048] U ini represents the input voltage of the i-th sub-module;

[0049] η represents the slope of the equilibrium coefficient;

[0050] e represents the exponential;

[0051] γ0 represents the midpoint of the Sigmoid function,

[0052] S201 said equilibrium coefficient α bali changes as follows:

[0053] When the input voltage U ini of the i-th sub-module is higher than the voltage equilibrium point U inav , the value of the equilibrium coefficient α bali decreases with the increase of the input voltage U ini of the i-th sub-module from the voltage equilibrium point U inav ;

[0054] When the input voltage U ini of the i-th sub-module is lower than the voltage equilibrium point U inav , the value of the equilibrium coefficient α bali increases with the decrease of the input voltage U ini of the i-th sub-module from the voltage equilibrium point U inav .

[0055] The curve of the equilibrium coefficient with the change of the input voltage is shown in Figure 2 , it can be seen that at the voltage equilibrium point, the equilibrium coefficient is equal to the input voltage, and as the input voltage gradually shifts to the right of the equilibrium point, the equilibrium coefficient also decreases, and vice versa.

[0056] S202: the equilibrium coefficient dynamically adjusts the control signal according to the input voltage U ini of the i-th module;

[0057] S203: the equilibrium coefficient adjusts the output current of the DAB converter to achieve the average distribution of power and balance the input voltage of each sub-module.

[0058] S3: accurate power distribution controller design, obtain the final control signal;

[0059] The strategy proposed in the present application realizes the accurate power distribution control of the input end by adjusting the output power of the single DAB converter module, therefore, the controller expression of S3 is as follows:

[0060]

[0061] In formula (2):

[0062] Represents the final control signal of the i-th submodule after passing through the balancing controller.

[0063] Taking submodule 1 as an example, the input voltage U in1 Greater than the voltage balance point U inav When the balance coefficient α bal1 The value is less than the voltage balance point U inav , therefore, the gain The final control signal of the DAB converter Therefore, the current I 11 Will increase, the current I C1 The voltage across the capacitor is prevented from increasing, negative feedback control is achieved, and the system can converge to the original operating point.

[0064] S4: According to different control requirements, corresponding modulation strategies are adopted, such as dual phase shift modulation strategy (DPS) and triple phase shift modulation strategy (TPS), etc., to modulate the final control signal into inner phase shift angle D1 and outer phase shift angle D2, thereby controlling the on and off of the DAB converter switch tube to achieve output voltage and power control.

[0065] The present invention breaks away from the traditional design idea of ​​input voltage balancing based on the use of a model predictive control cost function, and is used to improve the input voltage balancing capability and robustness to disturbances of a DC solid-state transformer with series input and parallel output.

[0066] The present invention only requires a single module of the ISOP-DC-SST to obtain the input voltage value, and no additional hardware design is required, thereby reducing hardware costs.

[0067] The algorithm can be programmed and implemented in a digital control chip (DSP) and can be applied to a general ISOP-DC-SST controller, with extremely high application value and economic value.

[0068] The present invention is applied to an ISOP-DC-SST, in which the individual modules are a DC-DC converter and a dual active bridge DC-DC converter (DAB). The DAB converter is controlled by a dual phase shift strategy (DPS), i.e., changing the phase shift angles between different bridge arms in two H-bridges and between two different H-bridges.

[0069] The precise power distribution controller proposed in the present invention is based on the fact that the control signal of a single-module DC-DC converter is known and the output voltage can be controlled without static error.

[0070] like Figure 1 As shown in the figure, the input end of ISOP-DC-SST is composed of multiple DAB converters. Each converter can be equivalent to a constant power dissipation module. The output ends are connected in parallel to output the required voltage value to achieve DC-DC direct current voltage conversion.

[0071] In the present invention, a single module is a dual active bridge DC-DC converter (DAB), and the input of the solid-state transformer is composed of three converters connected in series. In the experimental verification, the total input voltage is 300V, and the leakage inductance values ​​of the three DAB conversions are different from each other.

[0072] like Figure 3 As shown, even if the parameters of each single module are different, the input voltage of each single module can be stabilized at the average value before and after the working conditions change.

[0073] like Figure 3 As shown, the transient process of output voltage switching is a ramp-down process. It can be seen that before and after the output voltage changes, the input voltage of each single module can be stabilized at the average value by the proposed precise power allocation strategy, which proves the effectiveness of the algorithm proposed in this invention.

[0074] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0075] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A precise power distribution control method for ISOP-DC-SST, characterized by: The method comprises the following steps: S1: Single module control signal acquisition: modules in The control signal at time ; S2: Balance coefficient design; The S2 comprises the following steps: S201: Designing a balancing coefficient based on the Sigmoid function Generate nonlinear negative feedback to stabilize the input voltage to the equilibrium point; S202: The balance coefficient According to the input voltage of the i-th module Dynamically adjust control signals; S203: The balance coefficient Adjust the output current of the DAB converter to achieve even power distribution and balance the input voltage of each submodule; S3: Design of precise power distribution controller to obtain the final control signal; The controller expression of S3 is as follows: （2） In formula (2): Represents the The final control signal of each sub-module after passing through the balancing controller; S4: Adopting corresponding modulation strategies according to different control requirements, the final control signal is modulated into inner phase shift angle D1 and outer phase shift angle D2, thereby controlling the on and off of the DAB converter switch tube to achieve output voltage and power control.

2. The precise power distribution control method of ISOP-DC-SST according to claim 1, characterized in that: S201 Balance coefficient The expression is as follows: （1） In formula (1): Representative control cycle, i.e. time; Represents the number of sub-modules connected in series at the input end; Representative Input voltage of each submodule; represents the slope of the balance coefficient; Representative index; represents the midpoint of the Sigmoid function, .

3. The precise power distribution control method of ISOP-DC-SST according to claim 2, characterized in that: S201 Balance coefficient The change process is as follows: When Input voltage of each submodule Above the voltage balance point When the balance coefficient The value of Input voltage of each submodule The increase from the voltage balance point Start to decrease; When Input voltage of each submodule Below the voltage balance point When the balance coefficient The value of Input voltage of each submodule The decrease from the voltage balance point Start to grow.

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