Research on Power Balance Control Method of Electronic Transformer

Aiming at the problem of poor output stability and power gain of the power electronic transformer of the microgrid energy storage system, a power balance control method for the power electronic transformer of the microgrid energy storage system based on parallel modular multi-level commutation control is proposed. The reactive power outer loop parameter fusion method is used to sample the power dynamic load parameters and information fusion processing for the transformers in the system. According to the static limit active power adjustment of the fuzzy parameter factors on the output voltage side of the DC port, the steady-state gain of the power electronic transformer of the microgrid energy storage system is calculated. The static current limiting adjustment method is used to construct the feedback compensation model of the power electronic transformer of the microgrid energy storage system. In the active power control loop, the optimal design of the power electronic transformer power balance control of the microgrid energy storage system is realized through transient stable power adjustment. The test results show that using this method to perform power balance control on the power electronic transformer of the microgrid energy storage system has high output stability and good active power balance, which improves the robustness and adaptability of the transformer balance control.


Introduction
With the rapid development of clean energy and the continuous maturity of smart grid technology, micro-grid energy storage system, as a flexible and efficient energy management solution, is gradually receiving widespread attention.In microgrid energy storage system, power electronic transformer plays a key role, and its power balance control directly affects the stability and reliability of the system.Therefore, research on how to improve the output stability and power balance control of power electronic transformers has become a hot topic in the field of micro-grid energy storage system [1,2].At present, the traditional power balance control methods of power electronic transformers in micro-grid energy storage systems mainly focus on output stability regulation and power parameter evaluation.Although some methods build the steady-state control model of power electronic transformer of micro-grid energy storage system by distributed adjustment of grid-connected parameters, or establish the parameter coordination scheduling model, the traditional methods still face challenges in adaptability and output gain in the face of complex and variable working conditions [3,4].
In order to improve the output stability of power electronic transformer of micro-grid energy storage system, advanced control algorithms and technologies, such as fuzzy logic control, neural network control or model predictive control, can be further introduced to optimize the power balance of power electronic transformer.In the power balance control of power electronic transformer, the technology based on parallel modular multilevel commutation control can be combined with power parameter adjustment and adaptive parameter scheduling.This method can not only improve the stability of power balance control of power electronic transformer, but also adapt to the needs of different working conditions.By studying the transformer in the microgrid energy storage system, more efficient energy storage and distribution can be achieved, thus improving the reliability and stability of the entire system.In addition, it is also possible to consider combining intelligent control technology, such as artificial intelligence algorithms, to achieve power balance control of power electronic transformers for micro-grid energy storage systems.With the learning and optimization ability of intelligent algorithms, the power balance control can be more accurate, thus further improving the response speed and stability of the system.
In short, through the introduction of advanced control algorithms and technologies, combined with modular multilevel commutation control, as well as intelligent adjustment and optimization methods, the power balance control and stability of the power electronic transformer of the micro-grid energy storage system can be comprehensively improved to meet the changing power demand and environmental conditions.Under this background, a power balance control method of electronic transformer is proposed and designed in this study.

Reactive outer loop parameter fusion
In order to realize the power balance control of the power electronic transformer in the microgrid energy storage system, the reactive power outer loop parameter fusion method is used to sample the power dynamic load parameters of the power electronic transformer in the microgrid energy storage system to obtain the fusion information [5].According to the steady-state characteristic distribution of power electronic transformers in the microgrid energy storage system, the anti-parallel voltage characteristic quantities of the power electronic transformers in the microgrid energy storage system are extracted , and the equivalent of the power electronic transformers in the microgrid energy storage system is established.Circuit structure model.The power electronic transformer in the microgrid energy storage system is obtained by using the distributed fusion method of transient and steady-state characteristics [6].
According to the equivalent circuit structure model shown in Figure 1, the power dynamic load parameter fusion model of power electronic transformer under current closed-loop control is obtained as follows: In the formula, comm E represents the output current command signal of the current loop controller; elec T P - represents the transformer to transformer ratio of a power electronic transformer, which is the voltage ratio between the input and output terminals; elec R P - represents the conversion ratio of a power electronic transformer, which is the voltage conversion ratio between the input and output terminals; Wherein.

 
1 The 2nd International Conference on Smart Energy Journal of Physics: Conference Series 2717 (2024) 012037 IOP Publishing doi:10.1088/1742-6596/2717/1/0120373 By using the static stability networking method of grid-connected converter, the optimal parameter analytical model of voltage collapse and power angle instability is obtained [7].By studying the equivalent characteristics of power electronic transformer in microgrid energy storage system under the condition of weak power grid, the DC voltage time scale is obtained as follows: In the formula, ( ) ( ) Wherein, k t , g t represent the output current closed-loop control parameters and low power consumption time sampling values respectively, k  ， g  represents parameters for closed-loop control of output current and low-power time control, and the AC/DC side interactive total power control is not constrained by unbalanced power, and the obtained time parameters are as follows [8]: In the formula, s The method of reactive power outer loop parameter fusion is used for power dynamic load parameter sampling and information fusion processing of power electronic transformer in microgrid energy storage system [9].According to the input of DC port output voltage side, the output equivalent gain of single port D-HBSM is obtained as follows: In the formula, TX E represents the electrical signal power of the transmitting end, RX E represents the electrical signal power of the receiving end, and N represents the noise factor.According to the above analysis, the power balance control model of power electronic transformer in microgrid energy storage system is constructed, and the characteristic parameters of equivalent current source are extracted by multi-parameter fusion configuration method.

Power electronic transformer parameter optimization estimation
According to the fuzzy parameter factors of DC port output voltage side, the static limit active power is adjusted, and the steady-state gain of power electronic transformer in microgrid energy storage system is calculated, and the fundamental frequency equivalent energy output is as follows: short short DD P I V  (10) In the formula, short P represents the equivalent energy output of the fundamental frequency, and short P represents the equivalent current at the fundamental frequency; DD V stands for positive pole power supply.According to the method of flux linkage topology control, the loss energy and dynamic power consumption of multi-source coordination of power electronic transformer in microgrid energy storage system are obtained: In the formula, Under the joint control of flux and torque, the rotor flux parameters in steady state are obtained, and the static output power loss of power electronic transformer in microgrid energy storage system is: The observation error of power electronic transformer current in microgrid energy storage system is: Where, leakage I is multi-source leakage current of power electronic transformer in microgrid energy storage system.According to the optimized parameter configuration of sliding mode control, the measured values of excitation inductance current of power electronic transformer in microgrid energy storage system are as follows: Where μ is the zero-sequence overcurrent parameter energy, tx I represents the excitation inductance current of the transformer, a and b represent the coefficients , and the cooperative state characteristic quantity of DC blocking/leveling device of power electronic transformer in microgrid energy storage system is: Where, S represents the DC-DC component of the regulated access of the power electronic transformer in the microgrid energy storage system, pre V represents model parameters, R  and D  represent the coefficients.Under the constraint of the maximum bias current parameters ε and K, the optimal estimation results of the power electronic transformer parameters are as follows: 0 sgn( ) ( ) sgn( ) According to the fuzzy parameter factors of DC port output voltage side, the static limit active power is adjusted to improve the multi-source coordinated stability of power electronic transformer in microgrid energy storage system.

Optimization design of control objective function
The steady-state gain of power electronic transformer in microgrid energy storage system is calculated, and the power gain of power electronic transformer in microgrid energy storage system is balanced by using the method of static limit current regulation, and the optimal solution of DC magnetic bias is obtained as follows [10]:  N is the maximum magnetic bias parameter of the power electronic transformer in microgrid energy storage system under DC operation conditions, and the maximum deviation parameter of each DC operation condition of the power electronic transformer in microgrid energy storage system is: Where represents the measured voltage and the ideal voltage, s represents the time.
The maximum magnetic bias ratio under DC operation condition is obtained, and the power adjustment factor of power electronic transformer in microgrid energy storage system is as follows: Where f R represents the feedback resistance.Get the maximum DC parameter that the neutral point can bear, and get the voltage level transformation value According to the stator current error term, the power coordination control current parameters of the power electronic transformer in the microgrid energy storage system are obtained as follows: Where S V represents the ideal voltage source or signal source of the voltage, CE V represents the collector-emitter voltage, and Z represents the complex impedance.Considering L P bias, the coordinated power of power electronic transformer is obtained as follows: Wherein, VCE is the static output voltage of the power electronic transformer, the steady voltage , and the transfer efficiency under the state limit current constraint is 0.56 cos . According to the above analysis, the power balance control function of power electronic transformer in microgrid energy storage system is constructed, and the transformer balance control is carried out under different operating frequencies.

Analytical optimization of control parameters
Based on the analysis method of excitation inductance current parameters, the slip frequency is analyzed, and the characteristic quantity of power output state of power electronic transformer in microgrid energy storage system is obtained as follows: 1 ( ) In the formula, r r represents the internal resistance of the power supply, and g l represents the conductivity of the inductance. k represents the conversion ratio of power electronic transformers.A represents the control parameters of the system.After the limiting link, the capacitance and voltage of the power electronic transformer of the microgrid energy storage system are obtained as follows: K respectively are the slip frequency parameters of the power electronic transformer of the microgrid energy storage system, under the control of magnetic inductor current, get that the optimized parameter characteristic quantities of the power electronic transformer of the microgrid energy storage system are K , R and L are unknown parameters, and according to the decoupling control results of the flux linkage and torque of the power electronic transformer of the microgrid energy storage system, get that the full-wave rectification characteristic parameters meet the load power compensation method, and get the iterative function of the balanced configuration of the power coordination of the power electronic transformer of the microgrid energy storage system as follows: In the formula, dq i represents the probability amplitude of qubits of power electronic transformer in microgrid energy storage system, cal dq i _ represents the stator current in the DC coordinate system (dq coordinate system)Under the constraint of equivalent impedance of each sequence, the comprehensive sensitivity parameters are as follows: Based on load degree estimation, the optimal power consumption for power coordination of power electronic transformer in microgrid energy storage system is obtained as follows:   eq G s represents the weight of the I-th line.Based on the above analysis, the feedback compensation model of power regulation of power electronic transformer in microgrid energy storage system is constructed by using the method of static limit current regulation.In the active power control loop, the optimal design of transformer balance control is realized by transient stable power regulation.

Simulation test analysis
In order to test the application performance of this method in power electronic transformer power control of microgrid energy storage system, a simulation experiment was carried out.In the experiment, the transmission power of the power electronic transformer is 250KW, the rated current is 1000A, the rated frequency is 15KHZ, the charge transfer capacity of the power electronic transformer is 30kV, and the peak AC line voltage is 14KV.Calculate the rated DC voltage of the MMC to obtain the input information of the power electronic transformer of the microgrid energy storage system.Taking the input information as the test set, using the microgrid energy storage power electronic transformer to adaptively adjust the output system is shown in Figure 1.

Figure 1.
Adaptive regulation of power multi-source of power electronic transformer in microgrid energy storage system By analyzing Figure 1, it is known that the power balance control of power electronic transformer in microgrid energy storage system realized by this method has higher stability and better parameter adaptive adjustment ability.The convergence of different methods for power balance control of power electronic transformer in microgrid energy storage system is tested, and the results are shown in Figure 2.

Figure 2.
Convergence test of power balance control of power electronic transformer in microgrid energy storage system It can be seen from the analysis in Figure 2 that this method is used to perform power balance control on power electronic transformers in the microgrid energy storage system.The control accuracy was tested, and the comparison results are shown in Table 1.
Table 1 Comparative test of control accuracy Iterations This method Reference [4]  Reference [5]    2, it can be clearly concluded that the control accuracy of this method is higher than 0.9315, and it maintains a stable level at different iteration times, which further verifies the good stability and reliability of this method.This indicates that the method can provide consistent and reliable power control effects in practical applications.

Conclusions
This paper proposes a power electronic transformer power balance control method based on parallel modular multilevel commutation control.According to the steady-state characteristic distribution of the power electronic transformer converter of the system, the characteristic quantity of the anti-parallel voltage of the transformer is extracted, the transformer power balance control model is established, and the static limit active power is adjusted according to the fuzzy parameter factors of the output voltage side of the DC port.The static current-limiting adjustment method is used to construct the power electronic transformer power adjustment feedback compensation model of the microgrid energy storage system.Analysis shows that using this method to control power electronic transformers in microgrid energy storage systems has high stability and good reliability.

tP 2 k
represents total power; R represents the total voltage; are both dynamic load parameters.
scale of DC voltage; l represents the length of the component, drop p represents the voltage drop.At higher voltage level, the active power loss and gain of power electronic transformer in microgrid energy storage system are as follows:

T
represents time parameter constraint, T represents time parameter, tnow represents current time, p T represents pulse width, and Tdelay represents delay time,  represents the attenuation factor.
energy of power electronic transformer multi-source coordination, dpc P represents the dynamic power consumption of power electronic transformer multi-source coordination, dd V represents the voltage amplitude, dd I represents the static current consumption of the entire circuit in working state, TC I represents the total current during operation, T C represents the current transformer, and Fp represents the power factor.

1 k
represents another parameter related to conversion ratio.g B represents the saturation permeability of power electronic transformers; r  represents the saturation frequency of power electronic transformers; s l represents the saturation inductance value of the power electronic The 2nd International Conference on Smart Energy Journal of Physics: Conference Series 2717 coefficient of the system; c k represents the control coefficient of the system; w A represents the weight parameter of the system; c