CN212367153U

CN212367153U - An Improved Switch-Coupled Inductor Quasi-Z Source Inverter

Info

Publication number: CN212367153U
Application number: CN202022169646.6U
Authority: CN
Inventors: 李海滨; 张民; 周明珠; 韦正怡; 陈�光; 李恺; 郝杨阳; 曹益畅; 王凤莲
Original assignee: Qingdao University of Technology
Current assignee: Qingdao University of Technology
Priority date: 2020-09-28
Filing date: 2020-09-28
Publication date: 2021-01-15
Anticipated expiration: 2030-09-28

Abstract

The utility model belongs to the technical field of DC-AC conversion equipment, and relates to an improved switch coupled inductor quasi-Z source inverter. The main structure comprises a DC power supply, a first inductor, a first capacitor, a first diode, a second two tube, the third diode, the second capacitor, the third capacitor, the first winding, the second winding, the third winding, the fourth winding and six power switch tubes, of which the second diode, the third diode The tube, the third capacitor, the first winding, the second winding, the third winding and the fourth winding form a boost unit; the first winding, the second winding, the third winding and the fourth winding are coupled in pairs and are all coupled in the same direction , The unique connection method between the four coupled inductors with the same name can effectively reduce the current stress of the winding, reduce the loss, and reduce the resonance problem of the converter circuit, and the output efficiency is high.

Description

Improved switch coupling inductor quasi Z source inverter

The technical field is as follows:

the utility model belongs to the technical field of DC-AC conversion equipment, a accurate Z source DC-to-AC converter of improved generation switch coupling inductance (MSCL qZSI) is related to.

Background art:

since the 21 st century, with the increasing severity of energy crisis and environmental pollution problems, the rapid development of renewable clean energy has become the focus of energy development in all countries of the world. Renewable clean energy sources such as solar energy, wind energy, water energy, nuclear energy and the like are widely applied, and a photovoltaic system based on the solar energy is generally concerned by countries in the world due to the advantages of no pollution, no noise, rich development resources and the like, is determined as a new energy technology with the most development prospect in the future, and is widely applied to various fields of industrial production and national economy nowadays. The voltage source inverter is used as a converter which is most mature in application and is widely applied to the fields of uninterruptible power supplies, alternating current motor speed regulation, new energy power generation and the like. As a Power Conditioning System (PCS), inverters play a vital role in solar power generation systems. Conventional single-stage photovoltaic power generation systems use DC/AC inverters to directly transfer the energy output by the photovoltaic cells to the grid. Firstly, a plurality of photovoltaic modules are required to be connected in series due to the requirement of higher input voltage, which greatly increases the system cost and the failure rate and causes serious power loss under non-ideal conditions; secondly, in actual work, in order to track the maximum power point voltage of the photovoltaic cell, the direct-current bus voltage of the inverter needs to fluctuate in a large range, which leads to additional increase of the power capacity of the inverter during design. The above problems can be solved by a two-stage control structure of a cascaded DC-DC circuit on the basis of a single-stage power generation system. A DC/DC circuit with a maximum power point tracking function is added between the photovoltaic module and the inverter, the DC circuit can be used for boosting so as to reduce the series connection number of the photovoltaic modules and obtain constant direct current link voltage, and the independent control and the maximum power point tracking of the photovoltaic cell during the grid-connected work of the inverter are realized, but some defects also exist: firstly, the efficiency of the whole system is reduced due to the addition of a DC-DC converter; secondly, the number of hardware circuits in the system is increased, the working reliability of the system is reduced, and the maintenance cost is increased. In order to solve the problems of low gain and low efficiency, professor f.z.peng in 2002 proposes a novel single-stage buck-boost Inverter, namely a Z-Source Inverter (ZSI), which can boost and reduce the voltage of the single-stage Inverter and has certain advantages when used in a photovoltaic power generation grid-connected system. The development of the capacity of a single-chip photovoltaic module promotes the rapid development of a micro-inverter grid-connected system, and the high-voltage gain ZSI is very suitable for the application scenes, however, experimental researches find that the traditional ZSI also has some defects: firstly, the voltage gain is low due to the self topological structure; secondly, the current at the input side is in an interrupted state; thirdly, the voltage born by the two ends of the energy storage capacitor is larger; fourth, there are problems of starting rush current, common mode noise, etc. In order to solve the problems, a series of improvements are made on the traditional ZSI by broad scholars, wherein the most classical improved circuit is a quasi-Z-source inverter (qZSI) circuit, and the quasi-Z-source inverter (qZSI) is used for a photovoltaic power generation grid-connected system, so that Maximum Power Point Tracking (MPPT) of a photovoltaic module can be realized, and grid connection of the inverter is facilitated. The continuous input current of qZSI helps MPPT of photovoltaic modules, while the "low" voltage overshoot of the DC bus helps the type selection of switches and improves the electromagnetic Environment (EMI) of the inverter, but the lower DC link boost capability of qZSI requires a large number of photovoltaic modules to be connected in series to reach the grid-connected voltage level, which results in high cost and failure rate of the photovoltaic module system, embedding a specific boost unit in the qZSI framework results in a new high voltage gain qZSI, such an inverter can achieve the required grid-connected voltage level by adjusting the turn ratio n of the coupling inductors and the direct duty ratio D, it can maintain continuous input current and lower DC bus voltage overshoot, and increase the boost capability of the inverter, but the current stress of the components in the boost unit is higher, increasing the difficulty and cost of component selection. Therefore, emphasis is placed on embedding improved boost units in qZSI. Hafiz Furqan Ahmed, Honnyong Cha et al propose SCL qZSI, where a bootstrap capacitor and a symmetrical parallel structure are used to improve boost capability at a small through duty cycle D, the symmetrical parallel structure can reduce current stress of the assembly, and furthermore, the addition of a third winding N23 in the coupled inductor improves boost capability of the inverter, however, copper losses in the windings in the non-through state reduce efficiency. The mSSCL qZSI proposed by Saeed sharfi and Mohammad Monfared achieves high voltage gain at small D by using a bootstrap capacitor and a switched coupling inductor unit, however, during the pass-through and non-pass-through states, the third winding N23 of the switched coupling inductor has high current stress, which results in high copper loss of the coupling inductor, thereby reducing inverter efficiency. Therefore, it has become a challenging task in a photovoltaic power generation system to find an inverter circuit with a simple structure, high conversion efficiency, and low current stress winding suitable for high-boost applications.

The invention content is as follows:

the present invention is directed to overcoming the disadvantages of the prior art and providing an improved switch coupled inductor quasi-Z source inverter (MSCL qZSI) that provides continuous input current and low dc bus voltage spikes.

In order to achieve the above object, the main structure of the improved switch coupling inductor quasi-Z source inverter includes a dc power supply, a first inductor, a first capacitor, a first diode, a second diode, a third diode, a second capacitor, a third capacitor, a first winding, a second winding, a third winding, a fourth winding and six power switch tubes, wherein the second diode, the third diodeThe third capacitor, the first winding, the second winding, the third winding and the fourth winding form a boosting unit; two ends of the first inductor are respectively connected with the anode of the direct current power supply, the anode of the first diode and the cathode of the second capacitor, the cathode of the first diode is respectively connected with the anode of the first capacitor, the dotted terminal of the first winding is connected with the anode of a third diode, the cathode of the third diode is connected with the dotted terminal of a fourth winding, the dotted terminal of the first winding is respectively connected with the dotted terminal of the third winding and the cathode of a third capacitor, the dotted terminal of the third winding is connected with the anode of a second diode, the anode of the third capacitor is respectively connected with the dotted terminal of the second winding and the dotted terminal of the fourth winding, the cathode of the second diode is respectively connected with the anode of the second capacitor and the dotted terminal of the second winding, the drain electrode of the upper bridge wall power switch tube is respectively connected with the anode of the second capacitor, the cathode of the second diode and the dotted terminal of the second winding, and the source electrode of the lower bridge arm power switch tube is respectively connected with the cathode of the direct-current power supply and the cathode of the first capacitor; the first winding, the second winding, the third winding and the fourth winding are coupled in pairs, and the corresponding turn ratio is N₂₃/N₂₁＝N₂₄/N₂₂＝n，0<n<1, and are all coupled in the same direction.

The utility model discloses a switch on or end carrying out circuit operating condition's switching of control power switch tube to whether control DC power supply provides the energy that circuit work needs to the coupling inductance, through the winding turn ratio who changes the size of duty cycle and coupling inductance, realize the change of input/output voltage gain, thereby realize that output voltage is right DC power supply's buck-boost control.

Compared with the prior art, the utility model realizes the continuous charging and discharging process of the coupling inductance unit due to the on and off of the switch tube in the actual work, thereby achieving the purpose of high boost gain; and the unique connection mode between the homonymous ends of the four coupling inductors can effectively reduce the current stress of the winding, reduce the loss, reduce the resonance problem of the converter circuit and have high output efficiency.

Description of the drawings:

fig. 1 is a schematic diagram of the main structure circuit principle of the present invention.

FIG. 2 shows a power switch tube S₁-S₆(denoted by S in the figure)_eq) And the working state of the circuit when the circuit is conducted.

FIG. 3 shows a power switch tube S₁-S₆The working state of the circuit when the circuit is turned off is shown.

Fig. 4 is a graph showing the relationship between the boost factor B and the direct duty ratio D of the three inverters according to the embodiment of the present invention.

Fig. 5 is a diagram of winding current versus voltage gain G for three inverters according to an embodiment of the present invention.

Fig. 6 is a graph of efficiency as a function of output power for three inverters according to an embodiment of the present invention.

The specific implementation mode is as follows:

the present invention will be further described with reference to the accompanying drawings and the following detailed description.

Example (b):

the main structure of the MSCL qZSI described in this embodiment is shown in fig. 1, where a boost unit with a coupling winding is used to replace a single independent energy storage inductor in a conventional boost topology, and by using the feature that the coupling inductor charges and discharges simultaneously, on the basis that an original inverter only has an adjustment factor of duty ratio D, a free factor that can be adjusted, i.e., turn ratio, is increased, and by changing the turn ratio of the coupling winding, the capability of high voltage conversion is realized, specifically including a dc power supply V_gA first inductor L₁A first capacitor C₁A first diode D₁A second diode D₂₁A third diode D₂₂A second capacitor C₂A third capacitor C₂₁A first winding N₂₁A second winding N₂₂A third winding N₂₃A fourth winding N₂₄And six power switch tubes S₁-S₆Wherein the second diode D₂₁A third diode D₂₂A third capacitor C₂₁A first winding N₂₁A second winding N₂₂A third winding N₂₃And a fourth windingGroup N₂₄Forming a boosting unit; first inductance L₁Are respectively connected with a DC power supply V_gPositive electrode of (2), first diode D₁And a second capacitor C₂Is connected to the cathode of a first diode D₁Respectively with the first capacitor C₁Anode of (2), first winding N₂₁End of same name and third diode D₂₂Is connected to the anode of a third diode D₂₂Cathode and fourth winding N₂₄Are connected with each other, a first winding N₂₁Are respectively connected with the third winding N₂₃And a third capacitor C₂₁Is connected to the cathode of the third winding N₂₃End of same name and second diode D₂₁Is connected to the anode of a third capacitor C₂₁Respectively with the second winding N₂₂End of same name and fourth winding N₂₄Is connected to the same name terminal of the first diode D₂₁Respectively with a second capacitor C₂Anode and second winding N₂₂The different name ends of the upper bridge wall are connected with each other, and a power switch tube S is arranged on the upper bridge wall₁-S₃Respectively with the second capacitor C₂Anode of (2), second diode D₂₁Cathode and second winding N₂₂The different name ends are connected, the lower bridge arm power switch tube S₄-S₆Respectively with a DC power supply V_gNegative pole of (2) and first capacitor C₁The cathodes of the two electrodes are connected; first winding N₂₁A second winding N₂₂A third winding N₂₃And a fourth winding N₂₄Coupled in pairs with a corresponding turn ratio of N₂₃/N₂₁＝N₂₄/N₂₂N, and are all co-directionally coupled.

This embodiment adopts switching on or shutting off of unipolar SPWM mode control power switch pipe, accomplishes different working method's switching to reduce switching loss in the whole circuit structure, very high circuit's whole work efficiency, the different operating condition of circuit is shown as fig. 2 and fig. 3 respectively when the switch tube switches off and switches on:

in the through state, the first diode D₁Is reverse biased and the second diode D₂₁And a third diode D₂₂Conducting the first inductor L₁From a second capacitor C₂And an input power supply V_gCharging, four windings N₂₁、N₂₂、N₂₃And N₂₄All formed by the first capacitor C₁Charging a third capacitor C₂₁Storing data from a first capacitor C₁The specific current loop is shown in fig. 2. In this case, the circuit has the following voltage-current relationship:

in the non-through state, the second diode D₂₁And a third diode D₂₂Is reverse biased, the first diode D₁Is conducted and stored in the first winding N₂₁A second winding N₂₂And a first inductance L₁Medium energy and dc power supply V_gCombined to supply power to the load, a first capacitor C₁And a second capacitor C₂When the battery is charged in this state, and a specific current loop is shown in fig. 3, the circuit configuration has the following voltage-current relationship:

wherein, V_L1-ON，V_N-ON，V_L1-OFF，V_N-OFFVoltage across the magnetic elements (inductor and winding) in the through-state and in the non-through state, respectively, V_CIs the capacitor voltage, V_PNIs the peak dc link voltage and is,

applying volt-second equilibrium theory to L₁And N₂₁Obtaining:

applying the ampere-second equilibrium theory to C₂Obtaining:

from the current relationship in the non-through state:

wherein V_N23＝V_N24＝-nV_N21＝-nV_N22

V_L1-ON＝(1-D)V_PN

Thereby obtaining the peak value direct current link boost factor B of the MSCL qZSI:

where B is the peak DC link boost factor of the inverter and D is the through duty cycle (0)<D<1)，n＝N₂₃/N₂₁＝N₂₄/N₂₂Is the turns ratio, 0<n<1，N₂₁＝N₂₂(ii) a In the prior art, the peak direct current link boost factors of SCL qZSI and mSCL qZSI are as follows:

the three inverters described above have the same type of boost factor, i.e., B ═ k_N/1-kD，k＞1，k_N> 1 is a coefficient associated with the structure of the inverter, although the proposed inverter has four windings, in order to make the comparison more valuable, in the present embodiment the comparison is based on the same total turns ratio of the coupled inductances in the different inverters, so the total turns ratio N in the MSCL qZSI₂₃/N₂₁+N₂₄/N₂₂0.15+ 0.15-0.3 and a ratio of the number of turns in SCL qZSI and mSCL qZSI of N-N₂₃/N₂₁Equal to 0.3, in the relation graph of the boosting factor B and the through duty ratio D (as shown in fig. 4), the boosting factor of MSCL qZSI is between the boosting factors of mSSCL qZSI and SCL qZSI;

using a simple boost control method, the relationship between D and M is: D-1-M

Winding N of MSCL qZSI in a plot of winding current versus voltage gain G (as shown in FIG. 5)₂₃And N₂₄The electric lumen of (A) is significantly lower than that of mSCL qZSI and SCL qZSI, winding N₂₁And N₂₂The currents mSCL qZSI and SCL qZSI are comparable; efficiency as a function of output power for three inverters as shown in fig. 6, MSCL qZSI has higher efficiency than the other two inverters due to lower current stress on windings N23 and N24, although MSCL qZSI has a very high boost capability, its efficiency is lowest among the three inverters due to high current stress in windings N23 and N24, and the power consumption of the coupled inductor in MSCL qZSI is much smaller than the other two candidates.

In the embodiment, the MSCL qZSI is tested under the test conditions of 100V of input voltage, 120V of effective value of output phase voltage and 1kW of output power, the maximum efficiency reaches 92.8 percent, and the design requirement is basically met. The above analysis and experimental results show that the MSCL qZSI of the present embodiment has the advantages of high voltage gain and high efficiency, provides continuous input current and low dc bus voltage spike, and can implement Maximum Power Point Tracking (MPPT) of the photovoltaic module; due to the unique design of the coupling inductance, the winding current stress in the proposed MSCL qZSI is lower than SCL qZSI and mSSCL qZSI, reducing the power loss of the winding and improving the efficiency of the proposed inverter.

Although the present invention has been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without inventive work are still within the scope of the present invention.

Claims

1. An improved switch coupling inductor quasi-Z source inverter is characterized in that a main structure comprises a direct-current power supply, a first inductor, a first capacitor, a first diode, a second diode, a third diode, a second capacitor, a third capacitor, a first winding, a second winding, a third winding, a fourth winding and six power switch tubes, wherein the second diode, the third capacitor, the first winding, the second winding, the third winding and the fourth winding form a boosting unit; two ends of the first inductor are respectively connected with the anode of the direct current power supply, the anode of the first diode and the cathode of the second capacitor, the cathode of the first diode is respectively connected with the anode of the first capacitor, the dotted terminal of the first winding is connected with the anode of a third diode, the cathode of the third diode is connected with the dotted terminal of a fourth winding, the dotted terminal of the first winding is respectively connected with the dotted terminal of the third winding and the cathode of a third capacitor, the dotted terminal of the third winding is connected with the anode of a second diode, the anode of the third capacitor is respectively connected with the dotted terminal of the second winding and the dotted terminal of the fourth winding, the cathode of the second diode is respectively connected with the anode of the second capacitor and the dotted terminal of the second winding, the drain electrode of the upper bridge wall power switch tube is respectively connected with the anode of the second capacitor, the cathode of the second diode and the dotted terminal of the second winding, and the source electrode of the lower bridge arm power switch tube is respectively connected with the cathode of the direct current power supply.Is connected with the cathode of the first capacitor; the first winding, the second winding, the third winding and the fourth winding are coupled in pairs, and the corresponding turn ratio is N₂₃/N₂₁＝N₂₄/N₂₂＝n，0<n<1, and are all coupled in the same direction.