CN103259442B - A kind of High-gain current type inverter - Google Patents

Abstract

The invention discloses a high-gain current-type inverter, which is characterized in that: a switching inductance network is composed of a diode D1, an inductor L1, an inductor L2, a diode D2, a diode D3 and a power switch tube T7; The tubes T1, T3, T5 and the power switch tubes T4, T6 and T2 of the lower bridge arm together form a three-phase current-type inverter bridge, and three filter capacitors Cf are set at the output end of the three-phase inverter bridge in a "Y" shape The capacitor filter is connected to form a three-phase filter output; the three-phase grid or three-phase AC load is connected to the three-phase filter output through the filter inductor Lf. The invention can effectively improve the DC input voltage range of the inverter, and at the same time, the DC side does not need an electrolytic capacitor, thereby improving reliability, having simple system structure, reducing cost and improving efficiency.

Description

A High Gain Current Mode Inverter

technical field

The invention relates to a high-gain current type inverter, which is suitable for fuel cell power supply systems, wind power generation systems and photovoltaic grid-connected power generation fields.

Background technique

The DC power generated by renewable energy such as solar energy, tidal energy, and geothermal energy is often low in voltage and unstable, and needs to be boosted and inverted by power electronic devices to supply AC loads or power grids. Inverter is an important part of power electronic devices, and the research on inverter technology is of great significance in today's rapid development of new energy grid-connected power generation.

Power inverter technologies in the prior art are mainly based on two traditional inverter topologies: voltage source inverters and current source inverters. However, both voltage source and current source inverters have certain limitations, which limit their application in some occasions. The recently proposed Z-source inverter has also been widely used in various occasions. It has advantages that traditional inverters do not have, but it also has its shortcomings.

1. The voltage-type inverter is a step-down inverter. The AC output voltage can only be lower than the DC bus voltage. For some occasions where the input DC voltage is low and unstable, such as fuel cells, photovoltaic power generation, and wind power generation, It is necessary to increase the DC-DC boost in the front stage, which increases the complexity and cost of the system, and reduces the efficiency and reliability of the system at the same time. It is also possible to boost the voltage and connect to the grid by connecting a power frequency transformer on the AC side, but the power frequency transformer is bulky, expensive, and heavy, and reduces efficiency. The upper and lower bridge arms of the same phase of the inverter cannot be connected directly, otherwise the inverter will be damaged. However, in practice, shoot-through occurs from time to time due to false triggering caused by electromagnetic interference. Usually, a dead zone needs to be added, but it will cause distortion of the output waveform. The electrolytic capacitor on the DC side of the voltage source inverter is greatly affected by temperature, and its low reliability reduces the life of the inverter.

2. The current-source inverter is a step-up inverter, but its step-up capability is limited, and the inductance on the DC side is generally large, which increases the cost. When used for new energy generation such as photovoltaics, it is difficult to achieve decoupling control of input and output power. The bridge arm of the inverter cannot be opened, otherwise the inverter will be damaged. Usually, it is necessary to add an overlapping conduction time between the upper and lower switching tubes of the same bridge arm, which will also cause distortion.

3. The Z-source inverter has a buck-boost function, and the bridge arm straight-through is a normal working state of it. However, due to the addition of an inductor-capacitor Z source network, under certain conditions, the inductor-capacitor may resonate, affecting the normal operation of the circuit. The inrush current is large during start-up, which may damage the inverter. The two capacitors are required to be exactly the same, otherwise the inverter will be damaged if the capacitors are inconsistent.

Contents of the invention

The present invention proposes a high-gain current-type inverter in order to avoid the disadvantages of the above-mentioned prior art. In order to increase the DC input voltage range of the inverter, at the same time, the DC side does not require electrolytic capacitors, which improves reliability, has a simple system structure, reduces costs, and improves efficiency.

The present invention solves technical problem and adopts following technical scheme:

The structural characteristics of the high-gain current-type inverter of the present invention are:

The switch inductor network is composed of diode D1, inductor L1, inductor L2, diode D2, diode D3 and power switch tube T7; the positive end of the DC power supply Vdc is connected to the cathode of the power switch tube T7, the anode of the diode D1, and one end of the inductor L2 Connection; the collector of the power switch tube T7 is connected to the cathode of the diode D2 and one end of the inductor L1; the cathode of the diode D1 is connected to the other end of the inductor L1 and the cathode of the diode D3; the other end of the inductor L2 is connected to the diode D2 The anode of the diode D3 and the anode of the diode D3 are commonly connected;

The power switch tubes T1, T3, T5 of the upper bridge arm and the power switch tubes T4, T6 and T2 of the lower bridge arm jointly form a three-phase current-type inverter bridge. The negative end of the DC power supply Vdc is connected to the power switch tubes T4, The cathodes of T6 and T2 are connected together as connection point n, and the collectors of the power switch tubes T1, T3 and T5 are connected together with the collector of the power switch tube T7 as connection point c; at the output of the three-phase inverter bridge A capacitor filter composed of three filter capacitors Cf connected in a "Y" shape is arranged at the end to form a three-phase filter output; a three-phase power grid or a three-phase AC load is connected to the three-phase filter output through a filter inductor Lf.

The structural characteristics of the high-gain current-type inverter of the present invention also lie in:

The power switch tubes T7, T1, T3, T5, T4, T6 and T2 are composed of insulated gate bipolar transistors IGBT series diodes, the emitters of the insulated gate bipolar transistors IGBTs are connected to the anodes of the diodes, and the insulated gate bipolar transistors The collector of the pole transistor IGBT is the collector of the power switch tube, and the cathode of the diode is the cathode of the power switch tube;

Or the power switching tubes T7, T1, T3, T5, T4, T6 and T2 are composed of power field effect transistor MOSFET series diodes, the source of the power field effect transistor MOSFET is connected to the anode of the diode, and the power field effect transistor MOSFET The drain of the MOSFET is the collector of the power switch tube, and the cathode of the diode is the cathode of the power switch tube;

Or the power switch tubes T7, T1, T3, T5, T4, T6 and T2 are a single reverse blocking transistor RB-IGBT, and the collector of the reverse blocking transistor RB-IGBT is the power switch tube The collector, the emitter of the reverse blocking transistor RB-IGBT is the cathode of the power switch tube.

The structural feature of the high-gain current-type inverter of the present invention is also that: the high-gain current-type inverter has three working states: respectively:

Straight-through state: the power switch tubes of the upper bridge arm and the lower bridge arm of the same phase in the three-phase current-type inverter bridge are turned on at the same time, and the three-phase current-type inverter bridge is in the through-state;

Freewheeling state: the three power switch tubes on the upper bridge arm or the lower bridge arm of the three-phase current-type inverter bridge are turned on at the same time, the power switch tube T7 is turned on, and the three-phase current-type inverter bridge is in freewheeling state;

Active state: in the three-phase current-source inverter bridge, the power switches of the upper bridge arm and the lower bridge arm of two different phases are turned on, and the three-phase current-source inverter bridge is in the active state.

When the three-phase current-type inverter bridge is in the straight-through state, both the diode D1 and the diode D2 are turned on, and the diode D3 is cut off; when the three-phase current-type inverter bridge is in the freewheeling state, the diode D1 Both the diode D1 and the diode D2 are turned on, and the diode D3 is turned off; when the three-phase current-type inverter bridge is in an active state, the diode D1 and the diode D2 are both turned off, and the diode D3 is turned on.

Compared with the prior art, the beneficial effects of the present invention are reflected in:

1. The present invention is a new type of high-gain inverter. When used in new energy power generation systems such as photovoltaics, it does not require a DC-DC stage, which reduces the number of components, reduces costs, and improves efficiency. Due to the high voltage gain, the number of photovoltaic modules required is small, which reduces the power loss caused by partial shading and mismatching of photovoltaic modules.

2. The present invention does not use electrolytic capacitors with poor reliability. Because electrolytic capacitors are greatly affected by temperature, it is an important factor affecting the life of the inverter, so the inverter of the present invention has a long life.

3. The present invention can work in the straight-through and open-circuit states, and does not need to add a dead zone to the switching signal of the bridge arm like the traditional voltage inverter, nor does it need to add a dead zone to the bridge arm switching signal like the traditional current source inverter. The stacking time is added to the switch signal, the control is simpler, and the output waveform quality is better. Due to the introduction of freewheeling state, the inverter can realize decoupling control of input and output power.

4. The present invention can be widely used in power generation of various new energy sources. Due to its low cost, high efficiency and high cost performance, it is helpful to promote the development of new energy sources. With the emergence of new devices such as reverse-blockable IGBTs, this kind of inverter no longer needs series diodes, which solves the loss problem of series diodes, and its advantages will be more obvious.

Description of drawings

Fig. 1 is the main circuit schematic diagram of the high-gain current type inverter of the present invention;

Fig. 2a, Fig. 2b and Fig. 2c are schematic diagrams of different forms of power switch tubes of the high-gain current-mode inverter in the present invention;

Fig. 3a is a schematic diagram of a high-gain current-mode inverter of the present invention in a straight-through state;

Fig. 3b is a schematic diagram of the freewheeling state of the high-gain current-mode inverter of the present invention;

Figure 3c is a schematic diagram of the active state of the high-gain current-mode inverter of the present invention;

Fig. 4a, Fig. 4b, Fig. 4c and Fig. 4d are respectively schematic diagrams of the implementation effect of the high-gain current-source inverter of the present invention.

detailed description:

As shown in Figure 1, the structural form of the high-gain current-mode inverter in this embodiment is that the switch inductor network is composed of diode D1, inductor L1, inductor L2, diode D2, diode D3 and power switch tube T7; The positive terminal is connected to the cathode of the power switch tube T7, the anode of the diode D1, and one end of the inductor L2; the collector of the power switch tube T7 is connected to the cathode of the diode D2, and one end of the inductor L1; the cathode of the diode D1 is connected to the inductor L1 The other end of L1 is connected to the cathode of diode D3; the other end of inductor L2 is connected to the anode of diode D2 and the anode of diode D3;

The power switch tubes T1, T3, T5 of the upper bridge arm and the power switch tubes T4, T6 and T2 of the lower bridge arm together form a three-phase current-type inverter bridge. The negative terminal of the DC power supply Vdc is connected to the power switch tubes T4, T6 and The cathodes of T2 are connected together as connection point n, and the collectors of power switch tubes T1, T3 and T5 are connected together with the collectors of power switch tube T7 as connection point c; at the output end of the three-phase inverter bridge, three filters are set The capacitor Cf is connected in a "Y" shape to form a capacitor filter to form a three-phase filter output; the three-phase grid or three-phase AC load is connected to the three-phase filter output through the filter inductor Lf.

As shown in Figure 2a, the power switch tubes T7, T1, T3, T5, T4, T6 and T2 in this embodiment can be composed of insulated gate bipolar transistors IGBT series diodes, the emitter of the insulated gate bipolar transistors IGBT and the diode The anode of the insulated gate bipolar transistor IGBT is connected to the collector of the power switch tube, and the cathode of the diode is the cathode of the power switch tube; or as shown in Figure 2b, the power switch tubes T7, T1, T3, T5, T4, T6 and T2 are composed of power field effect transistor MOSFET series diodes, the source of the power field effect transistor MOSFET is connected to the anode of the diode, the drain of the power field effect transistor MOSFET is the collector of the power switch tube, and the cathode of the diode is the power switch. The cathode of the switch tube; or as shown in Figure 2c, the power switch tubes T7, T1, T3, T5, T4, T6 and T2 are a single reverse blocking transistor RB-IGBT, and the reverse blocking transistor RB-IGBT The collector of the power switch is the collector of the power switch, and the emitter of the reverse blocking transistor RB-IGBT is the cathode of the power switch.

In this embodiment, the high-gain current-mode inverter has three working states: respectively:

The straight-through state shown in Figure 3a: the power switches of the upper bridge arm and the lower bridge arm of the same phase in the three-phase current-source inverter bridge are turned on at the same time, and the three-phase current-source inverter bridge is in the direct-through state.

The freewheeling state shown in Figure 3b: the three power switch tubes on the upper or lower bridge arm of the three-phase current-type inverter bridge are turned on at the same time, the power switch tube T7 is turned on, and the three-phase current-type inverter bridge is in freewheeling state.

Active state as shown in Figure 3c: in the three-phase current-mode inverter bridge, the power switches of the upper and lower bridge arms of two different phases are turned on, and the three-phase current-mode inverter bridge is in the active state.

When the bridge arm of one phase of the inverter is straight through, the diode D1 and the diode D2 are both in the conduction state, the direct short circuit of the inverter bridge is equivalent to a wire, and the inductors L1 and L2 are charged in parallel to store energy. Assuming that the switching period of the power switch tube of the inverter bridge is T, and the time in shoot-through is T _s , then D _s =T _s /T is the percentage of the shoot-through time in the entire switching period, which is called the shoot-through duty cycle. During the straight-through state, the voltage U _L at both ends of the inductors L1 and L2 =V _dc .

When the three power switch tubes of the upper bridge arm or the lower bridge arm are turned on at the same time, the drive power switch tube T7 is turned on, and the inductors L1 and L2 continue to flow through the power switch tube T7. At this time, the voltage U across the inductors L1 and L2 _L =0. When the upper and lower power switches from different phases are turned on, both diode D1 and diode D2 are turned off, and diode D3 is turned on. At this time, the two inductors L1, L2 and the DC voltage source Vdc together provide energy to the load or the grid. Assuming that within one switching cycle, the time for supplying power to the load or grid is T _a , then D _a =T _a /T is called the active duty cycle. During this period, the voltage across the inductors L1 and L2 Among them, V _dc is the DC power supply voltage, and Vo is the output line voltage of the inverter.

According to the volt-second balance principle of the inductor in a switching cycle, that is, the characteristic that the voltage across the inductor is integrated to zero in a switching cycle: $V_{\mathrm{dc}}*{\mathrm{D.}}_{\mathrm{the\; s}}+\frac{1}{2}(V_{\mathrm{dc}}-V_o)*{\mathrm{D.}}_a+0*(1-{\mathrm{D.}}_{\mathrm{the\; s}}-{\mathrm{D.}}_a)=0---\left(1\right)$

It can be deduced as formula (2):

$\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Using the same volt-second balance principle to analyze the traditional current-source inverter, the output voltage gain can be deduced as formula (3):

$\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the above formulas, V _dc is the DC power supply voltage, Vo is the output line voltage of the inverter, D _s is the direct duty cycle, and D _a is the active duty cycle. Comparing formula (2) and formula (3), it can be seen that the voltage gain of the high-gain current-source inverter in this embodiment is higher than that of the traditional current-source inverter. A higher voltage gain can be obtained by adjusting the active duty cycle and the direct duty cycle, thereby increasing the range of the inverter input DC voltage. Due to the introduction of the freewheeling state, the input and output can also achieve power decoupling.

Specific implementation effect:

The principle simulation verification of the high-gain current-source inverter shown in Figure 1 is carried out, and the simulation results are shown in Figure 4a, Figure 4b, Figure 4c and Figure 4d, the DC voltage source V _dc =60V, the inductance L1=L2=5mH ; Among them, Fig. 4a and Fig. 4b respectively show the inverter output line voltage and three-phase phase current waveforms when the modulation degree m=0.5 and the through-duty ratio D _s =0.4. It can be seen from the figure that the inverter output line voltage The peak value reaches _210V , and the waveform quality of the three-phase output phase current is good; Fig. 4c and Fig. 4d show the modulation degree m=0.5, and the inverter output line voltage and three-phase phase As for the current waveform, it can be seen from the figure that when D _s =0.3, the peak value of the output line voltage is 180V, and the dynamic characteristics of the inverter are good.

The high-gain current-type inverter of the present invention introduces a switch inductance network, and by inserting a part of the through-vector into the traditional zero-vector, the inverter can achieve a higher step-up and inversion capability, and is applied to grid-connected new energy sources such as photovoltaics During power generation, decoupling control of input power and grid-connected output power can also be realized. The inverter does not use electrolytic capacitors with poor reliability, so the life of the inverter is extended.

Claims (1)

1. a High-gain current type inverter, is characterized in that:

Switched inductors network is formed by diode D1, inductance L 1, inductance L 2, diode D2, diode D3 and power switch pipe T7; The anode of the positive terminal of DC power supply Vdc and the negative electrode of power switch pipe T7, diode D1, and one end of inductance L 2 connects jointly; The collector electrode of power switch pipe T7 and the negative electrode of diode D2, and one end of inductance L 1 connects jointly; The negative electrode of diode D1 and the other end of inductance L 1, and the negative electrode of diode D3 connects jointly; The other end of inductance L 2 and the anode of diode D2, and the anode of diode D3 connects jointly;

Three-phase current type inverter bridge is jointly formed by upper brachium pontis each power switch pipe T1, T3, T5 and lower brachium pontis each power switch pipe T4, T6 and T2, negative pole end and the negative electrode of described power switch pipe T4, T6 and T2 of DC power supply Vdc are connected for tie point n jointly, and described power switch pipe T1, T3 are connected for tie point c with the collector electrode of T5 and the collector electrode of power switch pipe T7 jointly; The capacitive filter connected and composed in " Y " shape by three filter capacitor Cf is set at the output of described three phase inverter bridge, forms three-phase filtering and export; Three phase network or three-phase alternating current load to be exported with described three-phase filtering by filter inductance Lf and are connected;

Described power switch pipe T7, T1, T3, T5, T4, T6 and T2 are made up of insulated gate bipolar transistor IGBT series diode, the emitter of described insulated gate bipolar transistor IGBT is connected with the anode of diode, the collector electrode of the very described power switch pipe of current collection of insulated gate bipolar transistor IGBT, the negative electrode of diode is the negative electrode of described power switch pipe;

Or described power switch pipe T7, T1, T3, T5, T4, T6 and T2 are made up of field of electric force effect transistor MOSFET series diode, the source electrode of described field of electric force effect transistor MOSFET is connected with the anode of diode, the drain electrode of field of electric force effect transistor MOSFET is the collector electrode of described power switch pipe, and the negative electrode of diode is the negative electrode of described power switch pipe;

Or described power switch pipe T7, T1, T3, T5, T4, T6 and T2 are single reverse blocking transistor npn npn RB-IGBT, the collector electrode of the very described power switch pipe of current collection of reverse blocking transistor npn npn RB-IGBT, the negative electrode of the very described power switch pipe of transmitting of reverse blocking transistor npn npn RB-IGBT;

Described High-gain current type inverter has three kinds of operating states: respectively:

Pass-through state: the upper brachium pontis of same phase and the conducting simultaneously of lower brachium pontis power switch pipe in described three-phase current type inverter bridge, described three-phase current type inverter bridge is in pass-through state; When described three-phase current type inverter bridge is pass-through state, described diode D1 and the equal conducting of diode D2, described diode D3 ends;

Freewheeling state: three power switch pipes conductings simultaneously on the upper brachium pontis of described three-phase current type inverter bridge or lower brachium pontis, described power switch pipe T7 conducting, described three-phase current type inverter bridge is in freewheeling state; When described three-phase current type inverter bridge is freewheeling state, described diode D1 and the equal conducting of diode D2, described diode D3 ends;

Active: two out of phase upper brachium pontis and the conducting of lower brachium pontis power switch pipe in described three-phase current type inverter bridge, described three-phase current type inverter bridge is active; When described three-phase current type inverter bridge is active, described diode D1 and diode D2 all ends, described diode D3 conducting;

When a phase bridge arm direct pass of inverter, diode D1 and diode D2 is all in conducting state, and inverter bridge direct short-circuit is equivalent to a wire, and the state that inductance L 1, L2 are in charged in parallel carries out energy storage, suppose that inverter bridge power switch pipe switch periods is T, the straight-through time is T _s, then D _s=T _s/ T is the percentage straight-through time accounting for whole switch periods, is called straight-through duty ratio, the voltage U at inductance L 1, L2 two ends during pass-through state _l=V _dc;

When three power switch pipes conducting simultaneously of upper brachium pontis or lower brachium pontis, driving power switch transistor T 7 conducting, inductance L 1, L2 by above-mentioned power switch pipe T7 afterflow, the now voltage U at inductance L 1, L2 two ends _l=0;

When from out of phase upper and lower two power switch pipe conductings, diode D1 and diode D2 all ends, diode D3 conducting, and now two inductance L 1, L2 provide energy to load or electrical network together with direct voltage source Vdc; If in a switch periods, the time to load or mains supply is T _a, then D _a=T _a/ T is called active duty ratio; During this, the voltage at inductance L 1, L2 two ends wherein V _dcfor direct current power source voltage, Vo is inverter output line voltage;

By the voltage-second balance principle of inductance in a switch periods, namely the integration of voltage in a switch periods at inductance two ends is the characteristic of zero: $V_{dc}*D_s+\frac{1}{2}(V_{dc}-V_o)*D_a+0*(1-D_s-D_a)=0---\left(1\right)$

Then derive formula (2): $\frac{V_o}{V_{dc}}=\frac{2D_s+D_a}{D_a}---\left(2\right)$

Wherein, V _dcfor direct current power source voltage, Vo is inverter output line voltage, D _sfor straight-through duty ratio, D _afor active duty ratio; By regulating active duty ratio D _awith straight-through duty ratio D _sobtain higher voltage gain, thus increase the scope of inverter input direct voltage, owing to introducing freewheeling state, input and output realize power decoupled.