CN101599713B - Three-level inverter of single-phase mixed bridge - Google Patents

Abstract

The invention discloses a three-level inverter of a single-phase mixed bridge, comprising six switching tubes T1 to T6, four diodes D1 to D4, two electrolytic capacitors C1 to C2 and one output filter; wherein the four switching tubes T1 to T4, the two electrolytic capacitors C1 to C2 and the diodes D1 and D2 form a three-level single-phase converter unit of a diode middle point clamping position, the switching tubes T5 and T6, and the two electrolytic capacitors C1 to C2 form a single-phase half-bridge converter unit, a serial-connection branch circuit of D3 and D4 is connected with a serial-connection branch circuit of D1 and D2 in parallel, and the middle point of the D3 and D4 is connected with the middle point of the bridge arm of T5 and T6. The three-level inverter can effectively inhibit ground leakage current of the inverter, and has the advantages of high efficiency and simple modulating method, and the three-level inverter is suitable for a power supply inverter system which has strict ground leakage current, such as no-transformer type photovoltaic grid-connection inverter and the like.

Description

A kind of three-level inverter of single-phase mixed bridge

Technical field

The present invention relates to DC-AC inversion transformation technique field, be specifically related to a kind of single-phase three-level inverter.

Background technology

Along with the attention of countries in the world, extensive studies and application have been obtained based on the generation technology of new forms of energy such as photovoltaic to new energy development and application.In grid-connected photovoltaic power generation system, generally the direct current energy inversion of photovoltaic array being sent by combining inverter is the AC energy supply load or is connected to the grid.The outlet side of a large amount of combining inverters all has Industrial Frequency Transformer on the market, realize functions such as electrical isolation and voltage matches, yet the existence of Industrial Frequency Transformer has increased the volume and weight of combining inverter greatly, is not suitable for the middle low power applications; And in the inversion topological that adopts conventional no industrial frequency transformer, because existing, the zero line of electrical network and photovoltaic array directly be electrically connected, and there is bigger distributed capacitance over the ground in photovoltaic array, distributed capacitance, inverter bridge and filter element constitute the common mode resonance loop by electrical network and the earth over the ground for these, the common-mode voltage that changes will motivate bigger common mode current in the common mode resonance loop be Ground leakage current, increase system loss, reduced the fail safe of equipment.

In order to suppress the Ground leakage current in the grid-connected inverting system, method commonly used is to add common-mode filter in the common mode resonance loop, can effectively suppress Ground leakage current, but common-mode filter can increase the volume and weight of equipment.Patent CN1375902 discloses a kind of drain current suppressing method of inverter, needs to increase one-level DC-DC converter and relevant Detection ﹠ Controling circuit, has increased the complexity and the cost of system, has reduced system effectiveness and reliability.

Summary of the invention:

The object of the present invention is to provide a kind of three-level inverter of single-phase mixed bridge, be applicable to that transless type photovoltaic combining inverter etc. is to the strict inverter system of leakage current restriction.

A kind of three-level inverter of single-phase mixed bridge is characterized in that, the first, two electrochemical capacitor C ₁, C ₂Serial connection, first～the 4th switch transistor T ₁～T ₄Mode according to emitter connection collector electrode is connected in series the five, six switch transistor T successively ₅, T ₆The mode that connects collector electrode according to emitter is connected in series; The first electrochemical capacitor bridge C ₁Positive pole connect first switch transistor T ₁With the 5th switch transistor T ₅Collector electrode, the second electrochemical capacitor C ₂Negative pole connect the 4th switch transistor T ₄With the 6th switch transistor T ₆Emitter;

Two electrochemical capacitor C ₁, C ₂The phase contact connect the first diode D ₁Anode, the first diode D ₁Negative electrode connect the first, two switch transistor T ₁, T ₂The phase contact, two electrochemical capacitor C ₁, C ₂The phase contact also connect the second diode D ₂Negative electrode, the second diode D ₂Anode connect the three, four switch transistor T ₃, T ₄The phase contact; The five, six switch transistor T ₅, T ₆The phase contact connect the 3rd diode D ₃Anode, the 3rd diode D ₃Negative electrode connect the first, two switch transistor T ₁, T ₂The phase contact, the five, six switch transistor T ₅, T ₆The phase contact connect the 4th diode D ₄Negative electrode, the 4th diode D ₄Anode connect the three, four switch transistor T ₃, T ₄The phase contact; The second, three switch transistor T ₂, T ₃Phase contact and the five, six switch transistor T ₅, T ₆The phase contact connect two inputs of output filter respectively.

The invention provides a kind of three-level inverter of single-phase mixed bridge that can effectively suppress Ground leakage current, compare with the inverter that routine has a drain current suppressing function and have the following advantages:

(1) theoretical leakage current is zero, is suitable for transless type photovoltaic combining inverter etc. to the strict inverter system of leakage current restriction;

(2) the brachium pontis output voltage of three-level inverter of single-phase mixed bridge contains three kinds of level states, under the same switch frequency condition, has better output waveform quality;

(3) need not to increase extra detection and control circuit, system is succinct, cost is low.

Description of drawings

Fig. 1 is the main circuit topology figure of three-level inverter of single-phase mixed bridge;

Fig. 2 is the modulator approach schematic diagram of three-level inverter of single-phase mixed bridge;

Fig. 3 is a three-level inverter of single-phase mixed bridge key waveforms schematic diagram.

Embodiment

Fig. 1 is a three-level inverter of single-phase mixed bridge provided by the invention, comprises six switch transistor T ₁～T ₆, four diode D ₁～D ₄, two electrochemical capacitor C ₁And C ₂, an inductance L _fWith an ac filter capacitor C _f, T wherein ₁～T ₄, C ₁, C ₂, D ₁, D ₂Constitute the tri-level single phase inversion unit of a diode neutral point clamp, T ₅, T ₆, C ₁And C ₂Constitute a single-phase semi-bridge converter unit, D ₃With D ₄Series arm and D ₁And D ₂The series arm parallel connection, D ₃With D ₄Mid point and T ₅And T ₆The mid point of brachium pontis is connected.The output of inverter bridge leg is through L _fAnd C _fThe LC filter that constitutes inserts electrical network.The voltage that is input as of three-level inverter of single-phase mixed bridge is V _bBatteries, be in series by the more piece lead acid accumulator, the rated voltage of batteries must be higher than the peak value of line voltage.

The switching frequency of three-level inverter of single-phase mixed bridge can be taken all factors into consideration factors such as power system capacity, switching tube and heat radiation and rationally choose the schematic diagram of its modulator approach such as Fig. 2.As seen from the figure, T ₁The positive half wave of drive signal relatively form T by the positive half wave and the triangular carrier of sinusoidal modulation wave ₁The negative half-wave perseverance of drive signal is low; T ₆With T ₁Drive signal identical; T ₃With T ₁The drive signal complementation; T ₄The positive half wave perseverance of drive signal be low, negative half-wave is relatively formed by the absolute value and the triangular carrier of the negative half-wave of sinusoidal modulation wave; T ₅With T ₄Drive signal identical; T ₂With T ₄The drive signal complementation.V among Fig. 2 _PWMBe sinusoidal modulation wave V _rWith triangular carrier V _cThe SPWM ripple of Xing Chenging relatively, V _DirBe the power frequency square wave synchronous, V when modulating wave is in positive half wave with modulating wave _DirBe high level, modulating wave is in when bearing half-wave, modulating wave V _DirBe low level.T ₁With T ₆Drive waveforms can be by V _PWMWith V _DirObtain T by logic and operation ₄With T ₅Drive waveforms can be by V _PWMWith V _DirNon-signal obtain T by logic and operation ₂Drive signal can be by T ₄Drive signal obtain T by the logic NOT computing ₃Drive signal can be by T ₁Drive signal obtain by the logic NOT computing.

According to above-mentioned type of drive, three-level inverter of single-phase mixed bridge comprises three kinds of switch mode in the course of the work:

Mode 1:T ₁, T ₂And T ₆Conducting, T ₃, T ₄And T ₅Turn-off inverter bridge output V _AB=V _b, this moment, the common-mode voltage of topology was

$V_{\mathrm{cm}}=\frac{V_{\mathrm{AO}}+V_{\mathrm{BO}}}{2}=\frac{V_b+0}{2}=\frac{V_b}{2}---\left(1\right)$

Mode 2:T ₂And T ₃Conducting, T ₁, T ₄, T ₅And T ₆Turn-off inverter bridge output V _AB=0, this moment V _AOAnd V _BOVoltage all by C ₁, C ₂, D ₁And D ₂Be clamped to V _b/ 2, therefore the common-mode voltage of topology is

$V_{\mathrm{cm}}=\frac{V_{\mathrm{AO}}+V_{\mathrm{BO}}}{2}=\frac{V_b/2+V_b/2}{2}=\frac{V_b}{2}---\left(2\right)$

Mode 3:T ₃, T ₄And T ₅Conducting, T ₁, T ₂And T ₆Turn-off inverter bridge output V _AB=-V _b, this moment, the common-mode voltage of topology was

$V_{\mathrm{cm}}=\frac{V_{\mathrm{AO}}+V_{\mathrm{BO}}}{2}=\frac{0+V_b}{2}=\frac{V_b}{2}---\left(3\right)$

The output of single-phase mixed bridge formula tri-level inversion topology contains V _b, 0 and-V _bThree kinds of level states, when output was in positive half wave, topology was in mode 1 and mode 2 alternate run states, and when output was in negative half-wave, topology was in by mode 2 and mode 3 alternate run states.By formula (1) to formula (3) as can be seen, the instantaneous common-mode voltage of system is constant to be V _b/ 2, leakage current in theory.Fig. 3 is the key waveforms of three-level inverter of single-phase mixed bridge, is respectively the brachium pontis output voltage V among the figure from top to bottom _AB, output current i _gWith common-mode voltage V _Cm, the brachium pontis output voltage of three-level inverter of single-phase mixed bridge has V as seen from Figure 3 _b, 0 and-V _bThree kinds of level states, and instantaneous common-mode voltage is steady state value, can not motivate common mode current in the common mode resonance loop is Ground leakage current.

Claims (1)

1. a three-level inverter of single-phase mixed bridge is characterized in that, the first, two electrochemical capacitor (C ₁, C ₂) serial connection, first ~ the 4th switching tube (T ₁～T ₄) mode that connects collector electrode according to emitter successively is connected in series the five, six switching tube (T ₅, T ₆) be connected in series according to the mode of emitter connection collector electrode; First electrochemical capacitor (the C ₁) positive pole connect the first switching tube (T ₁) and the 5th switching tube (T ₅) collector electrode, the second electrochemical capacitor (C ₂) negative pole connect the 4th switching tube (T ₄) and the 6th switching tube (T ₆) emitter;

Two electrochemical capacitor (C ₁, C ₂) the phase contact connect the first diode (D ₁) anode, the first diode (D ₁) negative electrode connect the first, two switching tube (T ₁, T ₂) the phase contact, two electrochemical capacitor (C ₁, C ₂) the phase contact also connect the second diode (D ₂) negative electrode, the second diode (D ₂) anode connect the three, four switching tube (T ₃, T ₄) the phase contact; The five, six switching tube (T ₅, T ₆) the phase contact connect the 3rd diode (D ₃) anode, the 3rd diode (D ₃) negative electrode connect the first, two switching tube (T ₁, T ₂) the phase contact, the five, six switching tube (T ₅, T ₆) the phase contact connect the 4th diode (D ₄) negative electrode, the 4th diode (D ₄) anode connect the three, four switching tube (T ₃, T ₄) the phase contact; The second, three switching tube (T ₂, T ₃) phase contact and the five, six switching tube (T ₅, T ₆) the phase contact connect two inputs of output filter respectively;

Wherein, the first switching tube (T ₁) the positive half wave of drive signal relatively form the first switching tube (T by the positive half wave and the triangular carrier of sinusoidal modulation wave ₁) the negative half-wave perseverance of drive signal is low; The 6th switching tube (T ₆) and the first switching tube (T ₁) drive signal identical; The 3rd switching tube (T ₃) and the first switching tube (T ₁) the drive signal complementation; The 4th switching tube (T ₄) the positive half wave perseverance of drive signal be low, negative half-wave is relatively formed by the absolute value and the triangular carrier of the negative half-wave of sinusoidal modulation wave; The 5th switching tube (T ₅) and the 4th switching tube (T ₄) drive signal identical; Second switch pipe (T ₂) and the 4th switching tube (T ₄) the drive signal complementation.

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