CN217883245U - Three-phase three-level converter circuit - Google Patents
Three-phase three-level converter circuit Download PDFInfo
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- CN217883245U CN217883245U CN202222200683.8U CN202222200683U CN217883245U CN 217883245 U CN217883245 U CN 217883245U CN 202222200683 U CN202222200683 U CN 202222200683U CN 217883245 U CN217883245 U CN 217883245U
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Abstract
The utility model discloses a three-phase three-level converter circuit, which comprises a direct current bus, a three-phase three-level converter, a filter, a power grid and a switch; a three-phase three-level converter is connected between the anode and the cathode of the direct current bus and used for direct current support and ripple absorption of the three-phase three-level converter; the output end of the three-phase three-level converter is connected with the input end of the filter and used for converting the direct current into alternating current three-phase electricity; the output end of the filter is connected with the input ends of the power grid and the switch and the midpoint of the direct current bus, and is used for limiting the switching sub-ripple current of the three-phase three-level switch circuit and smoothing the output voltage of the three-phase three-level converter; and the power grid and the switch are used for connecting or disconnecting the three-phase three-level converter and the power grid. The utility model discloses reduced three level converter direct current bus midpoint voltage low frequency fluctuation, reduced the demand to converter direct current bus capacitance capacity effectively to reduce the cost of converter, improve the control stability of converter, reduce the control degree of difficulty.
Description
Technical Field
The utility model relates to a converter technical field, especially a three-phase three-level converter circuit.
Background
Currently, the main current PWM modulation method of the three-phase converter includes: SPWM sinusoidal pulse width modulation, SHEPWM specific harmonic elimination pulse width modulation, and SVPWM space vector pulse width modulation. The SPWM carrier modulation technology has the advantages of relatively simple principle, wide application range and high regulation performance, and mainly has the defects of low voltage utilization rate and higher switching loss. The space vector pulse width modulation method is widely applied to a voltage source type converter of digital control. Compared with the two modulation methods, the SVPWM has lower harmonic content, and the three-phase voltage is output by simulating the sinusoidal flux linkage circle of the three-phase voltage, so that the output voltage is closer to a sine wave. And the voltage utilization rate is 15% higher than that of the traditional modulation method, so that the efficiency of the converter is improved. The SHEPWM method for eliminating the pulse width modulation of specific harmonic waves has the advantages that higher fundamental wave voltage can be obtained under lower switching frequency, and the voltage utilization rate is improved.
In a DC/AC power supply system, a direct current bus electrolytic capacitor is taken as a key component, the service life of the direct current bus electrolytic capacitor directly affects the whole power supply system, and the direct current bus non-electrolytic capacitor control technology aims to reduce the capacitance value of the direct current bus, so that a metal film capacitor with small capacitance value and long service life is used for replacing an electrolytic capacitor with large capacitance value and short service life. The main idea of the method for realizing the electrolytic-capacitor-free control is to improve the control strategy and reduce the requirement of the direct current bus on the capacitance value, thereby realizing the electrolytic-capacitor-free technology. In the literature, a control method of maximum amplitude current is adopted, voltage fluctuation on a direct current side is transferred to a decoupling capacitor through a parallel decoupling structure, power fluctuation of a capacitor on the direct current bus side of an inverter is actually reduced through energy flowing, and therefore a capacitance value on the direct current bus side can be greatly reduced. However, seven switching tubes are added to the alternating-current side parallel structure of the method, the duty ratio of each switching tube needs to be calculated to achieve the electrolytic capacitor-free technology, and the hardware cost and the calculated amount of a modulation algorithm are increased. Also, a Buck-boost power decoupling technology-based inverter structure is proposed in the literature, and a decoupling circuit is designed to enable bidirectional flow of fluctuation energy on a direct-current bus side to be achieved when the decoupling circuit is connected in parallel with an inverter, so that an electrolytic capacitor-free technology is achieved.
The method reduces the cost of the decoupling capacitor and reduces the cost of the parallel topology structure. There is proposed a voltage single-loop control method using only inductor current feedback, which can effectively suppress the second harmonic current flowing into the preceding stage circuit and effectively improve the dynamic characteristics of the intermediate dc bus voltage when the load suddenly changes, thereby reducing the capacitance value of the dc bus side capacitor. Some researches have studied a control method for reducing bus capacitance of a frequency conversion system, and the power fluctuation of a direct current bus is reduced by controlling a specific parallel decoupling circuit, but the method is only limited to a specific circuit topology structure.
SUMMERY OF THE UTILITY MODEL
In view of this, the utility model provides a three-phase three-level converter circuit to solve above-mentioned technical problem.
The utility model discloses a three-phase three-level converter circuit, which comprises a direct current bus, a three-phase three-level converter, a filter, a power grid and a switch;
the three-phase three-level converter is connected between the positive electrode and the negative electrode of the direct current bus and is used for direct current support and ripple absorption of the three-phase three-level converter;
the output end of the three-phase three-level converter is connected with the input end of the filter and used for converting the direct current into alternating current three-phase electricity;
the output end of the filter is connected with the input ends of the power grid and the switch and the midpoint of the direct current bus, and is used for limiting the switching sub-ripple current of the three-phase three-level switch circuit and smoothing the output voltage of the three-phase three-level converter;
and the power grid and the switch are used for connecting or disconnecting the three-phase three-level converter and the power grid.
Furthermore, the direct current bus is formed by connecting two symmetrical capacitors in series; the capacitor midpoint BUSN of the direct current bus is the midpoint of the direct current bus and is connected with the capacitor midpoint in the filter so as to realize that harmonic current generated by third harmonic voltage in the modulation signal of the three-phase three-level converter flows back to the capacitor midpoint BUSN of the direct current bus;
the filter comprises a first inductance group and a first capacitance group; the first inductance group comprises three first inductances connected in parallel, and the first capacitance group comprises three capacitances connected in parallel;
the three parallel-connected inductors and the three parallel-connected capacitors are in one-to-one correspondence and are connected in series;
the power grid and the switches comprise a second inductance group and a plurality of switch groups connected with the first inductance group in series; the second inductor group comprises three second inductors which are connected in parallel;
each second inductor is connected in series with one switch in each switch group.
Further, a common end of the three capacitors connected in parallel is a capacitor midpoint in the filter;
the topology of the three-phase three-level converter consists of switching tubes, and the three-phase three-level converter can be a three-phase three-level circuit topology and is provided with a T-shaped three-level circuit or a diode clamping three-level circuit.
Further, the three-phase three-level converter comprises a first switching tube branch, a second switching tube branch and a third switching tube branch which are connected in parallel, a first reverse switching branch connected between the capacitance midpoint BUSN and the midpoint of the first switching tube branch, a second reverse switching branch connected between the capacitance midpoint BUSN and the midpoint of the second switching tube branch, and a third reverse switching branch connected between the capacitance midpoint BUSN and the midpoint of the third switching tube branch.
Furthermore, the first switching tube branch, the second switching tube branch and the third switching tube branch are respectively formed by connecting two switches including a reverse diode in series.
Further, the first reverse switching branch, the second reverse switching branch and the third reverse switching branch are respectively formed by connecting a switch containing a reverse diode and a switch containing a forward diode in series.
Furthermore, the current input ends of the three first inductors in the first inductor group are connected with the midpoint of the first switching tube branch, the midpoint of the second switching tube branch and the midpoint of the third switching tube branch in a one-to-one correspondence manner.
Since the technical scheme is used, the utility model discloses following advantage has: the utility model discloses a connect direct current bus electric capacity mid point and converter filter electric capacity mid point, additional amplitude and the suitable third harmonic voltage of phase place simultaneously in three-phase modulation signal, with the offsetting each other of realizing direct current bus mid point electric current, thereby reach the low frequency fluctuation of restraining direct current bus mid point voltage, make the capacity that no electrolytic capacitor three-phase inverter supported the electric capacity to direct current bus reduce greatly, the volume and the cost of converter have also been reduced simultaneously, the stability and the reliability of control have been improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required to be used in the description of the embodiments are briefly introduced below, it is obvious that the drawings in the description below are only some embodiments described in the embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings.
Fig. 1 is a schematic diagram of a modulation circuit and a modulation method of a three-phase three-level converter according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a T-type three-level three-phase inverter circuit according to an embodiment of the present invention.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and examples, it being understood that the described embodiments are only some of the embodiments of the invention and are not intended to limit the invention to the embodiments shown. All other embodiments available to those of ordinary skill in the art are intended to be within the scope of the embodiments of the present invention.
Referring to fig. 1, the present invention provides an embodiment of a three-phase three-level converter circuit, which includes a dc bus, a three-phase three-level converter, a filter, a grid, and a switch;
a three-phase three-level converter is connected between the anode and the cathode of the direct current bus and used for direct current support and ripple absorption of the three-phase three-level converter;
the output end of the three-phase three-level converter is connected with the input end of the filter and used for converting the direct current into alternating current three-phase electricity;
the output end of the filter is connected with the power grid, the input end of the switch and the midpoint of the direct current bus, and is used for limiting the switching sub-ripple current of the three-phase three-level switch circuit and smoothing the output voltage of the three-phase three-level converter;
the power grid and the switch are used for connecting or disconnecting the three-phase three-level converter and the power grid.
In this embodiment, the dc bus is formed by connecting two symmetrical capacitors in series; the capacitor midpoint BUSN of the direct current bus is the midpoint of the direct current bus and is connected with the capacitor midpoint in the filter so as to realize that harmonic current generated by third harmonic voltage in a modulation signal of the three-phase three-level converter flows back to the capacitor midpoint BUSN of the direct current bus;
the filter comprises a first inductance group and a first capacitance group; the first inductance group comprises three first inductances connected in parallel, and the first capacitance group comprises three capacitances connected in parallel;
the three parallel-connected inductors are in one-to-one correspondence with the three parallel-connected capacitors and are connected in series;
the power grid and the switches comprise a second inductance group and a plurality of switch groups connected with the first inductance group in series; the second inductance group comprises three second inductances connected in parallel;
each second inductor is connected in series with a respective one of the switches in each switch set.
In the embodiment, the common end of the three capacitors connected in parallel is the capacitor midpoint in the filter;
the topology of the three-phase three-level converter consists of switching tubes, and the three-phase three-level converter can be a three-phase three-level circuit topology and is provided with a T-shaped three-level circuit or a diode clamping three-level circuit.
In this embodiment, the three-phase three-level converter includes a first switching tube branch, a second switching tube branch, a third switching tube branch, a first reverse switching branch connected between a capacitance midpoint BUSN and a midpoint of the first switching tube branch, a second reverse switching branch connected between the capacitance midpoint BUSN and a midpoint of the second switching tube branch, and a third reverse switching branch connected between the capacitance midpoint BUSN and a midpoint of the third switching tube branch.
In this embodiment, the first switching tube branch, the second switching tube branch and the third switching tube branch are respectively formed by connecting two switches including a diode in parallel in series.
In this embodiment, the first reverse switching branch, the second reverse switching branch and the third reverse switching branch are respectively formed by serially connecting a switch including a reverse diode and a switch including a forward diode.
In this embodiment, the current input ends of the three first inductors in the first inductor group are connected to the midpoint of the first switching tube branch, the midpoint of the second switching tube branch, and the midpoint of the third switching tube branch in a one-to-one correspondence.
Referring to fig. 2, the present invention further provides an embodiment of a modulation method of a three-phase three-level converter circuit, which includes:
the sampling and adjusting module outputs modulation voltages ua, ub and uc;
the PWM module adds third harmonic modulation voltage signals to ua, ub and uc to obtain additional modulation signals;
and the PWM modulation module compares the additional modulation signal with a carrier signal of the three-phase three-level converter to generate a PWM signal.
In the embodiment, the sampling and adjusting module acquires the voltage and current information of a filter and a power grid of the three-phase three-level converter, calculates the modulation voltages ua, ub and uc which need to reach the adjustment target in real time through the adjuster, and transmits the modulation voltages ua, ub and uc to the PWM module;
the PWM module adds the modulation voltages ua, ub and uc with the additional signals, compares the additional signals with three-phase three-level carrier signals to generate switching tube driving signals of the three-phase three-level converter, and outputs the switching tube driving signals to the three-phase three-level converter to complete closed-loop control.
In this embodiment, the phase of the third harmonic modulation signal added by the PWM modulation module is the same as the phase of ua, ub, uc, and the amplitude thereof is 0.17 to 0.267 times of ua, ub, uc.
Referring to fig. 2, a T-type three-level inverter circuit topology is adopted, in which the output current at the midpoint of the dc bus capacitor is io, the direction is shown by an arrow in the figure, and the input current is iio, the direction is shown in the figure.
The two current relationships are described as follows:
i0＝ia*(1-|ua/udc|)+ib*(1-|ub/udc|)+ic*(1-|uc/udc|) (1)
ii0＝ua0*(2*pi*f0*C0)+ub0*(2*pi*f0*C0)+uc0*(2*pi*f0*C0) (2)
ia, ib, and ic are inverter output currents, ua, ub, and uc are modulation voltages of the inverter, and the inverter output voltages are also obtained without considering device loss. udc is the bus capacitance voltage, pi is the circumference ratio, C0 is the filter capacitance value, f0 is the frequency of the additional third harmonic, ua0, ub0, uc0 are the additional third harmonic.
i0 and ii0 both represent current components of third harmonic frequency, and the circuit principle shows that the neutral point voltage fluctuation of the direct current bus is greatly influenced by the third harmonic current, and other influence factors such as voltage fluctuation caused by the switching current harmonic are very small and can be ignored. Formula (1) and formula (2) describe the principle of the generation of the neutral point ripple current of the dc bus and the related factors, wherein the parameters also satisfy the following two relations:
1/(2*pi*f1*C0)>20*ua/ia (3)
f0＝3*f1 (4)
where f1 represents the fundamental frequency. The relation described by the equation (3) indicates that the filter capacitor fundamental wave impedance is more than 20 times of the rated impedance of the inverter when the inverter is generally designed so as to meet the capacitive reactive power requirement of the grid on the inverter.
By combining the above expressions, the fluctuation of the dc bus under various application conditions can be numerically enumerated.
The present invention is directed to the circuit connections described in the claims and to the common design and common operating ranges, defining the amplitude of the additional third harmonic in the modulated wave as 0.17 to 0.267 times ua, ub, uc, the phase being the same as ua, ub, uc. Through a large amount of simulation and experimental verification, the voltage fluctuation of the midpoint of the direct current bus capacitor can be effectively inhibited.
Finally, it should be noted that: the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents of the embodiments of the invention may be made without departing from the spirit and scope of the invention, which should be construed as falling within the scope of the claims of the invention.
Claims (7)
1. A three-phase three-level converter circuit is characterized by comprising a direct current bus, a three-phase three-level converter, a filter, a power grid and a switch;
the three-phase three-level converter is connected between the positive electrode and the negative electrode of the direct current bus and is used for direct current support and ripple absorption of the three-phase three-level converter;
the output end of the three-phase three-level converter is connected with the input end of the filter and used for converting the direct current into alternating current three-phase electricity;
the output end of the filter is connected with the input ends of the power grid and the switch and the midpoint of the direct current bus, and is used for limiting the switching sub-ripple current of the three-phase three-level switch circuit and smoothing the output voltage of the three-phase three-level converter;
and the power grid and the switch are used for connecting or disconnecting the three-phase three-level converter and the power grid.
2. A three-phase three-level converter circuit according to claim 1, wherein said dc bus is formed by two symmetrical capacitors connected in series; the capacitor midpoint BUSN of the direct current bus is the midpoint of the direct current bus and is connected with the capacitor midpoint in the filter so as to realize that harmonic current generated by third harmonic voltage in a modulation signal of the three-phase three-level converter flows back to the capacitor midpoint BUSN of the direct current bus;
the filter comprises a first inductance group and a first capacitance group; the first inductance group comprises three first inductances connected in parallel, and the first capacitance group comprises three capacitances connected in parallel;
the three parallel-connected inductors and the three parallel-connected capacitors are in one-to-one correspondence and are connected in series;
the power grid and the switches comprise a second inductance group and a plurality of switch groups connected with the first inductance group in series; the second inductor group comprises three second inductors which are connected in parallel;
each of the second inductors is connected in series with one of the switches in each of the switch groups.
3. A three-phase three-level converter circuit according to claim 2, wherein the common terminal of said three parallel connected capacitors is the capacitor midpoint in said filter;
the topology of the three-phase three-level converter consists of switching tubes, and the three-phase three-level converter can be a three-phase three-level circuit topology and is provided with a T-shaped three-level circuit or a diode clamping three-level circuit.
4. The three-phase three-level converter circuit according to claim 2, wherein the three-phase three-level converter comprises a first switching tube branch, a second switching tube branch and a third switching tube branch which are connected in parallel, a first inverting switch branch connected between the capacitance midpoint BUSN and a midpoint of the first switching tube branch, a second inverting switch branch connected between the capacitance midpoint BUSN and a midpoint of the second switching tube branch, and a third inverting switch branch connected between the capacitance midpoint BUSN and a midpoint of the third switching tube branch.
5. The three-phase three-level converter circuit according to claim 4, wherein the first, second and third switching tube branches are each formed by two switches comprising a zener diode connected in series.
6. A three-phase three-level converter circuit according to claim 4, wherein said first reverse switching leg, said second reverse switching leg and said third reverse switching leg are each formed by a series connection of a switch comprising a reverse diode and a switch comprising a forward diode.
7. The three-phase three-level converter circuit according to claim 4, wherein the current input terminals of the three first inductors of the first inductor group are connected to the middle point of the first switching tube branch, the middle point of the second switching tube branch and the middle point of the third switching tube branch in a one-to-one correspondence.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117572135A (en) * | 2024-01-16 | 2024-02-20 | 新风光电子科技股份有限公司 | Three-level direct current bus capacitor life online monitoring method and device |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117572135A (en) * | 2024-01-16 | 2024-02-20 | 新风光电子科技股份有限公司 | Three-level direct current bus capacitor life online monitoring method and device |
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