CN110797922B - Energy balance control method for power electronic transformer in alternating current-direct current hybrid system - Google Patents
Energy balance control method for power electronic transformer in alternating current-direct current hybrid system Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
The invention discloses an energy balance control method for a power electronic transformer in an alternating current-direct current hybrid system, which lists an energy balance relation in a certain time according to a power flow relation of a rectifier, namely that input energy of a power grid is inductance energy change, capacitance energy change and rectifier output energy; according to the characteristic that the inductance energy does not change in a half power grid period, simplifying the energy balance relationship in the half power grid period into power grid input energy which is capacitance energy change plus rectifier output energy; and obtaining the instruction value of the current at the side of the power grid according to the finally obtained energy balance relation and the related parameters of the power electronic transformer, thereby completing the control of the rectifier. The control method can improve the dynamic response including starting and load sudden change, greatly reduces the overshoot of the bus voltage, obviously reduces the response time, and effectively improves the dynamic performance of the system.
Description
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a power electronic transformer energy balance control method in an alternating current-direct current hybrid system.
Background
Under the background that a large amount of new energy is connected into a power grid nowadays, a large-capacity power electronic technology is widely applied to an alternating-current and direct-current hybrid system, and a complex power electronic transformer has a core position and plays a role of an energy hub. At present, for the control of the power electronic transformer, a great amount of experience and debugging are needed in parameter selection, and the efficiency is low. And the traditional PI control has limitation, and is difficult to give consideration to multiple indexes in the aspect of dynamic performance.
The energy balance control is a control strategy for enabling the converter to reach an energy steady state corresponding to a control target value at the fastest speed according to the transient electromagnetic energy distribution and flow rule in the converter, and has the characteristics of single control quantity, high response speed and no need of adjusting PI parameters.
The direct current bus plays an important role in the power electronic transformer, and the quality of the dynamic performance of the direct current bus is one of the determining factors for determining whether the system can stably operate. Therefore, an energy balance control strategy oriented to a power electronic transformer in an alternating current-direct current hybrid system is expected to effectively control the voltage of a direct current bus and realize the performance superior to that of the traditional PI control.
Disclosure of Invention
The invention provides an energy balance control method for a power electronic transformer in an alternating current-direct current hybrid system, which comprises the following steps:
step 1: according to the topology, capacity and parameter design of the power electronic transformer, extracting input power and output power of a rectifier, wherein the rectifier comprises an energy storage element, a load element and corresponding numerical values of the energy storage element and the load element;
step 2: according to the power flow relation of the rectifier, listing the energy balance relation in the time of multiple of half power grid period, namely the power grid input energy is inductance energy change + capacitance energy change + rectifier output energy;
and step 3: according to the characteristic that inductance energy does not change in a half power grid period, simplifying the energy balance relationship in the half power grid period into power grid input energy which is capacitance energy change plus rectifier output energy;
and 4, step 4: and 3, obtaining a command value of the current at the side of the power grid according to the energy balance relation in the step 3 and the related parameters of the power electronic transformer, and using the command value as the control input of the rectifier to complete the control of the rectifier.
Further, the input energy of the power grid is obtained by the product of the input power of the power grid and the time, and the output energy of the rectifier is obtained by the product of the load power and the time.
The invention has the following advantages:
the energy balance control method provided by the invention can effectively control the rectifier part in the power electronic transformer, and not only can reduce the overshoot of the direct current bus voltage, but also can reduce the time of a dynamic process.
Secondly, the energy balance control method provided by the invention does not need to adjust parameters, and the control method is directly obtained by resolving an energy balance equation.
Drawings
FIG. 1 is a schematic diagram of a rectifier topology and energy flow;
FIG. 2 is a control block diagram of the energy balance control method of the present invention;
FIG. 3 is a bus voltage waveform resulting from application of the energy balance control method of the present invention;
fig. 4 is a bus voltage waveform obtained by applying a conventional PI control method.
Detailed Description
In order to make the implementation objects, 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. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some, but not all embodiments of the invention. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides an energy balance control method for a power electronic transformer in an alternating current-direct current hybrid system, which is realized by the following steps:
step 1: and (3) extracting input and output power of the rectifier according to the topology, capacity and parameter design of the power electronic transformer. The rectifier comprises an energy storage element, a load element and corresponding numerical values;
as shown in fig. 1, the rectifier includes a capacitive element and an inductive element, and the energy change of the two elements in a period of time needs to be considered in addition to the energy input and output by the two elements.
Step 2: according to the power flow relation of the rectifier, the energy balance relation in a certain time is listed, namely the input energy of the power grid is inductance energy change + capacitance energy change + output energy of the rectifier. Typically the certain time is a multiple of half a grid cycle.
The input energy of the power grid is obtained by the product of the input power and the time, and the output energy of the rectifier is obtained by the product of the load power and the time.
And step 3: since the inductive energy does not change during a half grid cycle, the energy balance relationship during the half grid cycle can be simplified to the grid input energy, i.e., the capacitive energy change + the rectifier output energy.
And 4, step 4: and 3, obtaining a command value of the current at the side of the power grid according to the energy balance relation in the step 3 and the related parameters of the power electronic transformer, and using the command value as the control input of the rectifier to complete the control of the rectifier.
The overall control block diagram is shown in fig. 2. Wherein U is*For bus voltage reference, U, poutRespectively a bus voltage measurement value and an output power real-time value uacIs a net side voltage instantaneous value; i isL *The instruction value is the effective value of the network side current;
representing the real-time phase of the grid current; t issRepresenting the sampling frequency.
Using a reference value U of the bus voltage*And calculating the capacitance energy change by using the measured value U, and calculating the input energy of the power grid by using the voltage and current effective values of the power grid side. Therefore, the command value I of the grid-side current can be calculated by using the energy balance equation relation in step 3L *And control of the rectifier is performed.
The traditional PI control is applied to the power electronic transformer, the overshoot of the DC bus voltage and the response time are mutually restricted, and the simultaneous optimization is difficult. The energy balance control method is applied to the power electronic transformer, so that the dynamic performance of the voltage of the direct current bus can be optimized, and the overshoot and response time can be reduced.
The advantages of the control method according to the invention are illustrated below by means of a specific example. The method is applied to the simulation of a conventional rectifier circuit, the input is the alternating current of the side of a power grid, the output is provided with a load resistor, and the energy balance control method is compared with the traditional PI control method under the condition that other parameters are the same. The bus voltage value was set to 1500V, and the simulation results in fig. 3 and 4 were obtained. Comparing the two graphs, the conclusion can be drawn that the control method provided by the invention can shorten the response time from 0.5s to about 0.05s, and has almost no bus voltage overshoot, which is reduced by about 220V compared with PI control.
Finally, it should be pointed out that: the above examples are only for illustrating the technical solutions of the present invention, and are not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (1)
1. A power electronic transformer energy balance control method in an alternating current-direct current hybrid system comprises the following steps:
step 1: according to the topology, capacity and parameter design of the power electronic transformer, extracting input power and output power of a rectifier, wherein the rectifier comprises an energy storage element, a load element and corresponding numerical values of the energy storage element and the load element;
step 2: according to the power flow relation of the rectifier, listing the energy balance relation in the time of multiple of half power grid period, namely the power grid input energy is inductance energy change + capacitance energy change + rectifier output energy;
and step 3: according to the characteristic that inductance energy does not change in a half power grid period, simplifying the energy balance relationship in the half power grid period into power grid input energy which is capacitance energy change plus rectifier output energy, and utilizing a bus voltage reference value U*Calculating the capacitance energy change by using the measured value U, and calculating the input energy of the power grid by using the voltage and current effective values of the power grid side;
and 4, step 4: obtaining a command value of the current at the side of the power grid according to the energy balance relation in the step 3 and the related parameters of the power electronic transformer, and using the command value as the control input of the rectifier to complete the control of the rectifier; the input energy of the power grid is obtained by the product of the input power of the power grid and time, and the output energy of the rectifier is obtained by the product of the load power and time; calculating the capacitance energy change by using the bus voltage reference value and the measured value; the response time of the energy balance control method is 0.05 s.
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| US5191520A (en) * | 1989-02-06 | 1993-03-02 | Boral Johns Perry Industries Pty. Ltd. | Power supply system |
| US8254072B2 (en) * | 2009-11-05 | 2012-08-28 | Schneider Electric USA, Inc. | Electrical load center |
| US9917520B2 (en) * | 2015-06-09 | 2018-03-13 | Google Llc | Power supply including a flyback controller and buck converter |
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