CN110797922A - Energy balance control method of power electronic transformer in AC-DC hybrid system - Google Patents

Abstract

The invention discloses an energy balance control method for a power electronic transformer in an AC/DC hybrid system. According to the power flow relationship of the rectifier, the energy balance relationship in a certain period of time is listed, that is, grid input energy=inductance energy change+capacitance energy Change + rectifier output energy; and according to the characteristic that inductance energy does not change in half grid cycle, simplify the energy balance relationship in half grid cycle as grid input energy = capacitance energy change + rectifier output energy; according to the final energy balance obtained The relationship and the relevant parameters of the power electronic transformer can obtain the command value of the grid side current, so as to complete the control of the rectifier. The control method can improve the dynamic response including startup and load sudden change, so that the overshoot of the bus voltage is greatly reduced, and the response time is also significantly reduced, which effectively improves the dynamic performance of the system.

Description

Energy balance control method of power electronic transformer in AC-DC hybrid system

technical field

The invention belongs to the technical field of power electronics, and in particular relates to an energy balance control method of a power electronic transformer in an AC/DC hybrid system.

Background technique

Under the background that a large number of new energy sources are connected to the power grid, large-capacity power electronic technology is widely used in AC and DC hybrid systems, and the complex power electronic transformer has a core position and plays the role of an energy hub. At present, the control of power electronic transformers requires a lot of experience and debugging in the selection of parameters, and the efficiency is low. And traditional PI control has limitations, and it is difficult to take into account multiple indicators in dynamic performance.

Energy balance control is a control strategy that makes the converter reach the energy steady state corresponding to the control target value at the fastest speed according to the transient electromagnetic energy distribution and flow law in the converter. There is no need to adjust the characteristics of the PI parameters.

DC bus plays an important role in power electronic transformers, and its dynamic performance is one of the determinants of whether the system can run stably. Therefore, it is hoped that there is an energy balance control strategy for power electronic transformers in AC-DC hybrid systems, which can effectively control the DC bus voltage and achieve better performance than traditional PI control.

SUMMARY OF THE INVENTION

The present invention provides an energy balance control method for a power electronic transformer in an AC/DC hybrid system, comprising the following steps:

Step 1: According to the topology, capacity and parameter design of the power electronic transformer, extract the input and output power of the rectifier, the energy storage elements, load elements and their corresponding values included in the rectifier;

Step 2: According to the power flow relationship of the rectifier, list the energy balance relationship within the time multiples of half a grid cycle, that is, grid input energy = inductance energy change + capacitance energy change + rectifier output energy;

Step 3: According to the characteristic that the inductance energy does not change in a half grid cycle, the energy balance relationship in a half grid cycle is simplified as grid input energy = capacitance energy change + rectifier output energy;

Step 4: The command value of the grid side current can be obtained from the energy balance relationship in the step 3 and the relevant parameters of the power electronic transformer, and the command value is used as the control input of the rectifier to complete the control of the rectifier.

Further, the grid input energy is obtained from the product of grid input power and time, and the rectifier output energy is obtained from the product of load power and time.

The present invention has the following advantages:

First, the energy balance control method proposed in the present invention can effectively control the rectifier part in the power electronic transformer, which can not only reduce the overshoot of the DC bus voltage, but also reduce the time of the dynamic process.

Second, the energy balance control method proposed by the present invention does not need to adjust parameters, and the control method is directly obtained by solving the energy balance equation.

Description of drawings

Figure 1 is a schematic diagram of a rectifier topology and energy flow;

Fig. 2 is the control block diagram of the energy balance control method of the present invention;

Fig. 3 is the busbar voltage waveform obtained after applying the energy balance control method of the present invention;

Figure 4 is the bus voltage waveform obtained after applying the traditional PI control method.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be described in more detail below with reference to the accompanying drawings in the embodiments of the present invention. Throughout the drawings, the same or similar reference numbers refer to the same or similar elements or elements having the same or similar functions. The described embodiments are some, but not all, of the embodiments of the present invention. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The present invention provides an energy balance control method for a power electronic transformer in an AC/DC hybrid system, which is achieved through the following steps:

Step 1: According to the topology, capacity and parameter design of the power electronic transformer, extract the input and output power of the rectifier. The energy storage element, load element and corresponding numerical value included in the rectifier;

As shown in Figure 1, the rectifier contains a capacitive element and an inductive element. In addition to the input and output energy of these two elements, it is necessary to consider the energy changes of these two elements over a period of time.

Step 2: According to the power flow relationship of the rectifier, list the energy balance relationship within a certain period of time, that is, grid input energy = inductance energy change + capacitance energy change + rectifier output energy. In general, a certain time is a multiple of half a grid period.

The grid input energy is obtained by the product of the input power and time, and the rectifier output energy is obtained by the product of the load power and time.

Step 3: Since the inductive energy does not change in half a grid cycle, the energy balance relationship in a half grid cycle can be simplified as: grid input energy = capacitance energy change + rectifier output energy.

Step 4: The command value of the grid side current can be obtained from the energy balance relationship in Step 3 and the relevant parameters of the power electronic transformer, and the command value is used as the control input of the rectifier to complete the control of the rectifier.

代表电网电流的实时相位；T_s代表采样频率。The overall control block diagram is shown in Figure 2. Among them, U ^* is the reference value of the bus voltage, U and p _out are the measured value of the bus voltage and the real-time value of the output power respectively, u _ac is the instantaneous value of the grid-side voltage; _IL ^* is the command value of the RMS current of the grid-side;

represents the real-time phase of the grid current; T _s represents the sampling frequency.

Use the bus voltage reference value U ^* and the measured value U to calculate the capacitance energy change, and use the grid side voltage and current RMS to calculate the grid input energy. Therefore, the command value _IL ^* of the grid-side current can be calculated by using the energy balance equation relationship in step 3, and the control of the rectifier can be implemented.

Using traditional PI control in power electronic transformers, the overshoot of the DC bus voltage and the response time restrict each other, and it is difficult to optimize at the same time. By applying the energy balance control method of the present invention to a power electronic transformer, the dynamic performance of the DC bus voltage can be optimized, and the overshoot and response time can be reduced at the same time.

Below we illustrate the advantages of the control method of the present invention through a specific embodiment. The method of the present invention is applied to the simulation of a conventional rectifier circuit, the input is grid-side alternating current, and the output has a load resistance, and the energy balance control method of the present invention and the traditional PI control method are compared under the same other parameters. The busbar voltage is set to 1500V, and the simulation results in Figures 3 and 4 are obtained. Comparing the results of the two figures, it can be concluded that the control method proposed in the present invention can shorten the response time from 0.5s to about 0.05s, and there is almost no bus voltage overshoot, which is reduced by about 220V compared to PI control.

Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements to some of the technical features; and these Modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (2)

1. A power electronic transformer energy balance control method in an AC/DC hybrid system, comprising the following steps: Step 1: According to the topology, capacity and parameter design of the power electronic transformer, extract the input and output power of the rectifier, the energy storage elements, load elements and their corresponding values included in the rectifier; Step 2: According to the power flow relationship of the rectifier, list the energy balance relationship within the time multiples of half a grid cycle, that is, grid input energy = inductance energy change + capacitance energy change + rectifier output energy; Step 3: According to the characteristic that the inductance energy does not change in a half grid cycle, the energy balance relationship in a half grid cycle is simplified as grid input energy = capacitance energy change + rectifier output energy; Step 4: The command value of the grid side current can be obtained from the energy balance relationship in the step 3 and the relevant parameters of the power electronic transformer, and the command value is used as the control input of the rectifier to complete the control of the rectifier. 2. The power electronic transformer energy balance control method in an AC-DC hybrid system according to claim 1, wherein the grid input energy is obtained by the product of grid input power and time, and the rectifier output energy is obtained by The product of load power and time is obtained.

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