CN113394982B - Transient voltage and power balancing method for cascaded H-bridge type power electronic transformer - Google Patents
Transient voltage and power balancing method for cascaded H-bridge type power electronic transformer Download PDFInfo
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- CN113394982B CN113394982B CN202110697724.6A CN202110697724A CN113394982B CN 113394982 B CN113394982 B CN 113394982B CN 202110697724 A CN202110697724 A CN 202110697724A CN 113394982 B CN113394982 B CN 113394982B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
- H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
Abstract
The invention relates to the field of power transmission and distribution of a power system, and discloses a method for balancing transient voltage and power of a cascaded H-bridge type power electronic transformer, so as to realize the voltage balance of a middle direct current capacitor of the transient state of the power electronic transformer and the transmission power balance of all DAB converters. The method comprises the following steps: and performing closed-loop control on the difference value between the intermediate direct current voltage output by the cascade H bridge and the mean value of the intermediate direct current voltage to obtain a calculated leakage inductance value of the DAB converter, compensating the difference between the actual leakage inductance value and the designed leakage inductance value of the DAB converter by using the calculated leakage inductance value, and calculating the phase shift angle of each DAB converter, thereby thoroughly eliminating the problem of power imbalance caused by the leakage inductance parameter difference of the transformer. The invention realizes the steady-state and transient-state intermediate direct-current voltage balance and DAB converter transmission power balance, and avoids the overvoltage or overcurrent of the device caused by the balance problem of the power electronic transformer. The invention is easy to realize, and has the advantages of high reliability, wide application range and the like.
Description
Technical Field
The invention relates to the field of power transmission and distribution of a power system, in particular to a transient voltage and power balancing method for a cascaded H-bridge type power electronic transformer.
Background
As a novel power conversion device, the power electronic transformer not only can realize voltage grade conversion and electrical isolation of the traditional transformer, but also has the functions of electric energy quality isolation, active alternating current and direct current energy management, reactive power compensation and the like. In addition, the power electronic transformer also has the advantages of high power density, easy redundancy of modular design and the like. The two-stage cascaded H-bridge type power electronic transformer comprises a cascaded H-bridge rectifier on the front-stage alternating current side and a DAB converter on the rear stage. The alternating current measurement of the cascaded H bridge is directly connected with an alternating current distribution network, and a high-voltage direct current port is provided for a post-stage DAB converter; and the DAB converter at the rear stage is cascaded with the cascaded H bridge at the front stage through the high-voltage direct-current port, voltage conversion and electrical isolation are realized through the high-frequency transformer, and a low-voltage direct-current port is provided.
Aiming at a cascaded H-bridge type power electronic transformer, in order to solve the problems of voltage balance and power balance of the power electronic transformer, the traditional control method comprises the following steps: firstly, carrying out closed-loop control on low-voltage direct-current voltage output by the DAB converter to obtain a common phase shift angle of the DAB converter, then carrying out closed-loop control on a difference value of each intermediate direct-current capacitor voltage and an average value of the intermediate direct-current capacitor voltages to obtain a compensation phase shift angle of each DAB converter, and adding the compensation phase shift angle and the common phase shift angle to obtain a final phase shift angle of each DAB converter. According to the method, the phase shift angle of the DAB converter is modified through the PI controller, the phase shift angle needing to be compensated under different loads is not used, the transient balance performance is limited, overvoltage or overcurrent of the power electronic transformer is easily caused on occasions with frequent load fluctuation, and finally the power electronic transformer is stopped due to faults.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to disclose a transient voltage and power balancing method of a cascaded H-bridge type power electronic transformer, so that the voltage balancing and the power balancing of the power electronic transformer can be still realized under the condition of load fluctuation.
In order to achieve the purpose, the invention provides a transient voltage and power balancing method for a cascade H-bridge type power electronic transformer, which comprises the following steps:
1) carrying out basic voltage closed-loop control on the low-voltage direct-current voltage by adopting a PI (proportional integral) controller to obtain basic phase shift angles d of all DAB converters;
2) calculating the average value U of the intermediate DC capacitor voltage output by each rectifier dc Average value U of intermediate DC capacitor voltage output by rectifier dc Intermediate DC capacitor voltage U with each rectifier output dci (i is 1-N) and the PI controller is adopted to carry out closed-loop control on the difference result to obtain the calculated leakage inductance value L of each DAB converter cki ；
3) According to DAB power calculation formula to calculate leakage inductance value L cki Compensating the difference between the actual leakage inductance value and the designed leakage inductance value of each DAB converter, and directly calculating to obtain the final phase shift angle d of each DAB converter i And at the final phase shift angle d i Adjusting the transmission power of each DAB converter to realize the balance of the intermediate direct-current voltage and the balance of the transmission power of the DAB converters;
wherein L is kd Is the designed leakage inductance value.
The input signal of the basic voltage closed-loop controller is a power electronic transformerLow voltage dc voltage set value U L * With measured value U of low-voltage DC voltage L The difference of (a).
And the input signal of the voltage and power balancing closed-loop controller is the difference value of the average value of the voltage of each intermediate direct current capacitor and the voltage of each intermediate direct current capacitor.
The DAB converter transmission power balance can further realize the intermediate direct current capacitor voltage balance.
The phase shift angle obtained by the low-voltage direct-current voltage closed-loop control is the basic phase shift angle of the DAB converter, and the phase shift angle participates in the calculation of the final phase shift angle of each DAB converter.
The output of the PI controller of the voltage and power balancing closed-loop controller is the calculated leakage inductance value of each DAB converter, and the leakage inductance value compensation method directly compensates the leakage inductance parameter difference of the DAB converters.
In the voltage and power balancing closed-loop controller, the leakage inductance value is calculated, the leakage inductance parameter is directly compensated in the calculation of the final phase shift ratio of all DAB converters, and the influence of the difference of the leakage inductance parameter can be directly eliminated from software.
And the calculated leakage inductance value output by the PI controller for auxiliary balance control is not influenced by the load parameter.
The invention has the beneficial effects that: the invention carries out single-voltage closed-loop phase-shift control on the low-voltage direct-current voltage output by the DAB converter, and takes the phase-shift ratio output by the voltage loop as the basic phase-shift ratio. And then, carrying out closed-loop control on the difference value of the average value of each intermediate direct current capacitor voltage and the intermediate direct current capacitor voltage to obtain a calculated leakage inductance value of each DAB converter, compensating the error between a theoretically designed leakage inductance value and an actual leakage inductance value according to the calculated leakage inductance value, and directly calculating to obtain a final phase shift angle of each DAB converter so as to realize the balance of the intermediate direct current capacitor voltage and the balance of the transmission power of the DAB converters. The invention directly compensates the leakage inductance value of the DAB converter, and thoroughly solves the problem of unbalanced voltage and power. Compared with the traditional control method, the calculated leakage inductance value output by the PI controller of the balance controller provided by the invention is not influenced by load fluctuation, so that balanced intermediate direct current voltage and balanced transmission power can be provided when the load fluctuates. The control method has important significance for improving the reliability of the power electronic transformer on the occasion of frequent power fluctuation.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a schematic diagram of a topology of a cascaded H-bridge power electronic transformer according to an embodiment of the present invention;
fig. 2 is a control block diagram of a transient voltage and power balancing method for a cascaded H-bridge power electronic transformer according to an embodiment of the present invention.
Detailed Description
In order that the objects, aspects and advantages of the present invention will become more apparent, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be embodied in many different forms as defined and covered by the claims.
The topology of the cascaded H-bridge power electronic transformer adopts a series-in and parallel-out structure, as shown in figure 1. The single-phase rectifier of the front stage is connected in series to form a cascade H bridge, so that the effect of series connection and voltage division is achieved, and the intermediate direct-current capacitor voltage output by the cascade H bridge is used as an input power supply of the rear-stage DAB converter; the DAB converters at the later stage are connected in parallel to form an isolation stage of the power electronic transformer, so that the parallel shunt effect is achieved, a low-voltage direct-current voltage output port is provided, the port can be used as a power supply port to directly output power outwards, and the port can also be connected with an inverter to provide an alternating-current power supply port to supply power outwards.
The invention discloses a method for balancing transient voltage and power of a cascaded H-bridge type power electronic transformer by analyzing the root cause of unbalance of voltage and power of the power electronic transformer.
The DAB converter in the isolation stage can realize power transmission through phase-shifting control, and the transmission power can be calculated as
Wherein n is transformer transformation ratio, U dc For DAB converter input voltage, U L Is the output voltage of the DAB converter, d is the phase shift angle of the DAB converter, f s For the switching frequency, L, of the high-frequency transformer k Is the leakage inductance value of the high-frequency transformer.
When the transmission power of each DAB-converter is equalized, the intermediate dc-voltages of the power electronic transformers are also equalized. Assume each intermediate DC voltage U of the initial power electronic transformer dci Equalization, since the DAB converters output in parallel, the output voltage U L The same applies to the switching frequency, and the transmission power of the DAB converter is determined by the transformation ratio and the leakage inductance value of the high-frequency transformer. The leakage inductance of the transformer is difficult to design and has larger error, so that the transmission power of all DAB converters is inconsistent due to the leakage inductance difference among all DAB converters when the same phase shift angle is applied, and further the voltage of a direct current capacitor in the middle of the power electronic transformer is unbalanced.
In order to thoroughly solve the problem of unbalanced voltage and power caused by the difference of leakage inductance parameters of the high-frequency transformers of the DAB converters, the leakage inductance parameters of all the DAB converters are compensated, and the final phase shift angle of each DAB converter is obtained by calculating the compensated leakage inductance parameters.
Fig. 2 is a control block diagram of a transient voltage and power equalization method for a cascaded H-bridge power electronic transformer according to an embodiment of the present invention, and the implementation process of the present invention is described in detail with reference to fig. 2.
A method for balancing transient voltage and power of a cascaded H-bridge type power electronic transformer is divided into two parts, wherein the first part is basic voltage control, and the second part is auxiliary balance control.
The base voltage control adopts a PI controller to carry out power electronic controlLow-voltage direct-current voltage set value U of transformer L * With measured value U of low-voltage DC voltage L The difference value of the voltage difference value is subjected to closed-loop control, and the aim is to realize constant voltage control of low-voltage direct current voltage. The phase shift angle obtained by the PI controller is the basic phase shift angle d of the DAB converter, and the basic phase shift angle d participates in the calculation of the final phase shift angle of each DAB converter.
The auxiliary balance control adopts a PI controller to carry out closed-loop control on the difference value of the intermediate direct current capacitor voltage and the average value of the intermediate direct current capacitor voltage so as to obtain the calculated leakage inductance value L of each DAB converter cki . The calculated leakage inductance value L cki Designing the leakage inductance value L by the compensation theory kd The error compensation, which can be expressed as a scaling factor L, is compared with the actual leakage inductance value cki /L kd The proportionality coefficient will participate in the calculation of the final phase shift ratio of each DAB converter:
the control system compensates the leakage inductance error through the calculated leakage inductance parameter, and directly modifies the basic phase shift ratio by utilizing the compensated proportionality coefficient, and can directly calculate the final phase shift ratio d of each DAB converter i And adjusting the intermediate direct current capacitor voltage and the transmission power of each DAB converter according to the final phase shift ratio.
Claims (6)
1. A transient voltage and power equalization method for a cascaded H-bridge type power electronic transformer is characterized by comprising the following steps:
1) carrying out basic voltage closed-loop control on the low-voltage direct-current voltage by adopting a PI (proportional integral) controller to obtain basic phase shift angles d of all DAB converters;
2) calculating the average value U of the intermediate DC capacitor voltage output by each rectifier dc Average value U of intermediate DC capacitor voltage output by rectifier dc Intermediate DC capacitor voltage U with each rectifier output dci (i is 1-N) and adopting PI controller to make closed-loop control to the difference result to obtain every DAB converterIs calculated by calculating the leakage inductance value L cki ；
3) To calculate the leakage inductance value L cki Compensating the difference between the actual leakage inductance value and the designed leakage inductance value of each DAB converter, and directly calculating to obtain the final phase shift angle d of each DAB converter i And at the final phase shift angle d i Adjusting the transmission power of each DAB converter to realize the balance of the intermediate direct current voltage and the transmission power of the DAB converters, wherein the calculation formula of the final phase shift angle is as follows:
wherein L is kd Is the designed leakage inductance value.
2. The method according to claim 1, wherein the input signal of the fundamental voltage closed-loop control is a low-voltage DC voltage set value of the power electronic transformer
With measured value U of low-voltage DC voltage L The output signal is the basic phase shift angle d of the DAB converter.
3. The method according to claim 1, wherein said calculating leakage inductance value L is based on a voltage-to-current ratio of said power electronic transformer cki The input signal of the PI controller is the difference value of the voltage of each intermediate direct current capacitor and the average value of the voltage of the intermediate direct current capacitor.
4. The method according to claim 1, wherein said final phase shift angle calculation formula comprises the input variables of a base phase shift angle d and a calculated leakage inductance value L cki Calculating a leakage inductance value L cki To compensate DAB converters in the calculation formulaLeakage inductance parameter difference.
5. A method as claimed in claim 3, wherein said calculated leakage inductance value is not affected by load variations.
6. The method as claimed in claim 1, wherein the DAB converter transmission power equalization is capable of achieving intermediate DC capacitor voltage equalization.
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| JP2002350791A (en) * | 2001-05-30 | 2002-12-04 | Nippon Telegr & Teleph Corp <Ntt> | Light power equalizing device |
| CN102522906B (en) * | 2011-12-22 | 2014-01-08 | 东南大学 | Voltage balance and power balance control method of cascaded H bridge converter |
| CN103474984B (en) * | 2013-03-13 | 2015-04-01 | 湖南工业大学 | Cascade STATCOM direct-current capacitor voltage balance control method in wind power plant environment |
| CN103872920B (en) * | 2014-03-13 | 2016-10-05 | 北京理工大学 | The leakage inductance electric current direct slop control method of isolated two-way three-level converter |
| CN104538972B (en) * | 2014-12-12 | 2017-07-07 | 国网宁夏电力公司经济技术研究院 | A kind of reactive compensation configuration method and device based on transient voltage stability constraint |
| CN105471269A (en) * | 2015-12-30 | 2016-04-06 | 国网智能电网研究院 | Power electronic transformer power balance control method and system based on H-bridge chained mode |
| CN107134928A (en) * | 2017-06-01 | 2017-09-05 | 西南交通大学 | Multimode full-bridge isolates DC DC inverter powers balance control methods and device |
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Inventor after: Liu Zhi Inventor after: Li Shuaihu Inventor after: Hou Jie Inventor after: Wang Tingting Inventor before: Li Shuaihu Inventor before: Liu Zhi Inventor before: Hou Jie Inventor before: Wang Tingting |
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