CN100492845C - Tri-switch single-stage voltage boosting/reducing inverter - Google Patents

Abstract

A three-switch single-stage buck-boost inverter, which specifically relates to a single-stage buck-boost (Buck-Boost) inverter that can be used in distributed power generation systems, which solves the problem of existing single-stage buck-boost inverters. The inverter either has a complex circuit structure and inflexible voltage amplitude adjustment, or the inverter is difficult to control and the output voltage is small, or the switching loss and switching stress of the switching tube used are large. The inverter of the present invention adopts a high-frequency flyback transformer (3), and through the main self-off switch (S1), the first auxiliary self-off switch tube (S2), the second auxiliary self-off switch tube (S3 ) PWM control to achieve single-stage inverter; it is based on the basic Buck-BoostDC-DC circuit, and combines two Buck-Boost DC-DC circuits organically to realize boosting and inverter, thus obtaining a new type of single-stage Buck-Boost inverter. The invention has simple circuit structure, small switch tube loss and stress, and is easy to control.

Description

A three-switch single-stage buck-boost inverter

technical field

The invention belongs to the technical field of electric engineering, and in particular relates to a single-stage buck-boost inverter which can be used in a distributed power generation system.

Background technique

With the increasing demand for energy in modern society, the available primary energy such as coal and oil is getting less and less, and the combustion of coal in the process of power generation, the waste gas and waste generated by oil have seriously polluted the natural environment, which is harmful to human health and production. Life has done a lot of harm. In order to avoid energy crisis and protect the environment, people began to use renewable energy. This has led to the rapid development of distributed power generation systems using renewable energy, which can be used as small and medium power generation systems for emergency backup of electric energy, supplementary power grid systems, and power generation in local or remote areas. The new energy power generation used in the distributed power generation system, such as the voltage generated by variable-speed wind power generation, the voltage generated by solar cells or fuel cells, cannot be directly connected to the grid or supply power to AC loads, and a DC-AC inverter circuit is required to convert The direct current becomes the required alternating current. The most common DC-AC inverter circuit structure is Buck inverter, which is the most widely used and most important topology in PWM power conversion circuits. However, because the instantaneous average output voltage of the Buck inverter is always lower than the input DC voltage, its application is greatly limited. In order to generate an output voltage higher than the input voltage, it is necessary to add a Boost DC-DC converter in the front stage of the Buck inverter. This is a two-stage inverter. It needs to boost the input voltage DC-DC to A certain level, and then generate an output voltage higher than the input DC voltage through inversion. This leads to some problems, such as high noise, high loss, large volume, high cost and low efficiency. However, the single-stage inverter does not have the above-mentioned problems. It does not need DC-DC boost conversion, and can realize boost and inversion in one power stage, and can directly obtain an output voltage higher than the input voltage. The structure is compact and the conversion efficiency is greatly improved, thus becoming the preferred choice for distributed generation inverters. In recent years, some single-stage inverter topologies have been reported, but they either have complex circuit structures, inflexible voltage amplitude adjustment, or difficult inverter control, low output voltage, or large switching losses and switching stress of the switching tubes used. , so it is necessary to find a single-stage inverter topology that can overcome the above shortcomings.

Contents of the invention

In order to solve the problems of the existing single-stage inverters that either the circuit structure is complex and the voltage amplitude adjustment is inflexible, or the inverter is difficult to control and the output voltage is small, or the switching loss and switching stress of the switching tubes used are large, the present invention A three-switch single-stage buck-boost inverter is provided, which is a single-stage Buck-Boost inverter used in a distributed power generation system. The inverter of the present invention includes a high-pass filter 2 and a control circuit 5, the output end of the high-pass filter 2 is connected to a load or a power grid 4, and the inverter also includes a main self-off switching tube S1, a first auxiliary self-off The switch tube S2, the second auxiliary self-turn-off switch tube S3, the high-frequency flyback transformer 3, the resonant capacitor Cr and the power diode D1, the positive output terminal of the DC power supply 1 is connected to the collector of the main self-turn-off switch tube S1, and the main self-turn-off switch tube S1 Turn off the emitter of the switch tube S1 and connect the same-named terminal of the primary coil L1 of the high-frequency flyback transformer 3 and the negative terminal of the power diode D1, and connect the positive terminal of the power diode D1 to the secondary coil L2 of the high-frequency flyback transformer 3 The non-identical terminal and one end of the resonant capacitor Cr, the terminal with the same name of the secondary coil L2 of the high-frequency flyback transformer 3 is connected to the emitter of the second auxiliary self-turn-off switch tube S3, and the primary coil L1 of the high-frequency flyback transformer 3 The terminal with the same name is connected to the collector of the first auxiliary self-turn-off switch S2, the collector of the second auxiliary self-turn-off switch S3, the emitter of the first auxiliary self-turn-off switch S2, and the other end of the resonant capacitor Cr. Connected to the negative output terminal of the DC power supply 1, the gates of the main self-off switch tube S1, the first auxiliary self-off switch tube S2 and the second auxiliary self-off switch tube S3 are respectively connected to the three outputs of the control circuit 5 The two ends of the resonant capacitor Cr are connected in parallel between the two input ends of the high-pass filter 2.

As shown in FIG. 1 , the input DC power source 1 is provided by one of the DC power sources generated by solar photovoltaic power source, fuel cell or variable speed wind power. The primary coil L1 and the secondary coil L2 of the high-frequency flyback transformer 3 act as the resonant inductance of the Buck-Boost DC-DC converter respectively, and play the role of storing energy and transferring energy. High-pass filter 2 can make the output not contain high-order harmonics. When the inverter is connected to a resistive load, it constitutes an independently operating inverter; and when it is connected to the grid, it constitutes a grid-connected inverter. As shown in Figure 2, a schematic diagram of the SPWM modulation method of the inverter is given; in Figure 2, from top to bottom are: AC output voltage Vo or current Io, modulation wave Vref and carrier Vtri comparison, master and self-off switch The trigger signal G1 of the tube S1, the trigger signal G2 of the first auxiliary self-turn-off switch S2, and the trigger signal G3 of the second auxiliary self-turn-off switch S3. In PWM modulation, the modulation wave is a sinusoidal rectified pulse wave, which contains two half-sine waves in one cycle of the AC output; the carrier wave is a sawtooth wave, and its frequency determines the switching frequency of the switching tube. Comparing the modulated wave with the carrier, the intersection point determines the conduction angle and pulse width of the high-frequency switching action. Figure 2 shows the trigger signals of three self-shutoff switches, 1 means high level (turn on), 0 means low level (turn off), as can be seen from the figure, in the positive half wave of AC output, S1 and S2 The trigger pulse is the same, the trigger signal of S3 is complementary to that of S1 and S2, and all three switches operate at high frequency; in the negative half-wave of AC output, S3 is always kept off, and the gate of S2 is always given a conduction signal, only S1 Operates at high frequency.

The inverter of the present invention has the following four operating modes: (a). Charging mode: in this state, S1 and S2 are turned on, and S3 is turned off, and the DC power supply 1 charges the primary side coil L1, and the secondary side coil L2 Disconnected, there is no electrical connection between the input and output of the inverter system. This pattern exists for both positive and negative half-waves of the AC output. (b). Positive half-wave resonance mode: In this state, S3 is turned on, while S1 and S2 are turned off, and the energy stored in the transformer is transferred to the resonant capacitor Cr and the load or grid 4 through the secondary coil L2 to form a resonant circuit. This mode exists only on the positive half-wave of the AC output. (c). Negative half-wave resonance mode: In this state, S2 is turned on, while S1 and S3 are turned off. The energy stored in the transformer is transmitted to the resonant capacitor Cr and the load or the grid 4 through the primary coil L1 to form a resonant circuit. This mode exists only in the negative half-wave of the AC output. (d). Discharge mode: In this state, the inductance current on the primary side and the secondary side of the transformer has dropped to 0, S1, S2 and S3 are all kept off, and the energy stored in the resonant capacitor Cr is released to the load or Grid 4.

The present invention is based on the basic Buck-Boost DC-DC circuit, and organically combines two Buck-Boost DC-DC circuits together to realize boosting and inverting in one power stage, thereby obtaining a new type of single-stage Buck -Boost inverter, which uses a high-frequency flyback transformer to achieve single-stage inverter through PWM control of three power switches. The inverter of the present invention has the following advantages: (1) its circuit structure is simple, and only three self-shutoff devices are used, which reduces the volume and cost of the device; (2) it can adopt traditional control methods such as SPWM The operation of the device is simple and reliable, and it is easy to control and implement; (3) When the inverter operates in the discontinuous conduction mode (DCM), the main self-off switch tube and one of the auxiliary self-off switch tubes can be zero The current is turned on to realize soft switching, which reduces the loss of the device and improves the efficiency of the system; (4) it can complete boosting and inversion in one power level, and has a compact structure, which can further improve the efficiency of the device; ( 5) Because it works at a higher switching frequency, it only needs a small filter to obtain high-quality output current or voltage; (6) the voltage stress of the switching device in the inverter of the present invention is low, which means Therefore, it can use switching devices with smaller capacity, thereby reducing the cost of the entire inverter.

Description of drawings

Fig. 1 is a schematic diagram of the circuit structure of the present invention, and Fig. 2 is a schematic diagram of the SPWM modulation waveform of the present invention, and the abscissa in the figure represents time.

Detailed ways

Specific implementation mode 1: Referring to Fig. 1, the inverter in this specific implementation mode is composed of a high-pass filter 2, a control circuit 5, a main self-off switching tube S1, a first auxiliary self-closing switching tube S2, a second auxiliary self-closing Composed of disconnection switch S3, high-frequency flyback transformer 3, resonant capacitor Cr and power diode D1, the positive output terminal of DC power supply 1 is connected to the collector of the main self-shutdown switch S1, and the emitter of the main self-shutdown switch S1 Connect the same-named end of the primary coil L1 of the high-frequency flyback transformer 3 to the negative end of the power diode D1, and the positive end of the power diode D1 is connected to the non-identical ends of the secondary coil L2 of the high-frequency flyback transformer 3 and the resonant capacitor Cr One end of the high-frequency flyback transformer 3 secondary coil L2 with the same name is connected to the emitter of the second auxiliary self-turn-off switch S3, and the non-identical end of the primary coil L1 of the high-frequency flyback transformer 3 is connected to the first auxiliary The collector of the self-turn-off switch S2, the collector of the second auxiliary self-turn-off switch S3, the emitter of the first auxiliary self-turn-off switch S2, and the other end of the resonant capacitor Cr are all connected to the negative output of the DC power supply 1 The gates of the main self-off switch tube S1, the first auxiliary self-off switch tube S2 and the second auxiliary self-off switch tube S3 are respectively connected to the three output terminals of the control circuit 5, and the resonant capacitor Cr The two ends are connected in parallel between the two input ends of the high-pass filter 2 , and the output end of the high-pass filter 2 is connected to the load or the grid 4 . The DC power supply 1 is provided by a fuel cell; the main self-off switch tube S1, the first auxiliary self-off switch tube S2, and the second auxiliary self-off switch tube S3 are all unidirectional switches, and they are all IGBT, GTO or MOSFET One of the self-turn-off devices, when S1, S2, and S3 use existing switch modules with anti-parallel diodes on the market, a power diode must be connected in series to ensure the unidirectionality of the switch.

Specific embodiment two: referring to Fig. 1, the difference between this specific embodiment and specific embodiment one is: the high-pass filter 2 contains a filter inductor Lf, one end of the resonant capacitor Cr is connected to one end of the filter inductor Lf, and the filter inductor Lf The other end of the resonant capacitor Cr is connected to the load or one input end of the grid 4, and the other end of the resonant capacitor Cr is connected to the load or the other input end of the grid 4. Other components and connections are the same as those in the first embodiment.

Specific embodiment three: referring to Fig. 1, the difference between this specific embodiment and specific embodiment two is: the high-pass filter 2 also includes a filter capacitor Cf, and the filter capacitor Cf is connected in parallel to the two input ends of the load or the grid 4 between. Other compositions and connections are the same as those in the second embodiment. Embodiment 3 Compared with Embodiment 2, the filter capacitor Cf is omitted, which will reduce the burden of the filter inductor Lf.

Claims (5)

1, a kind of tri-switch single-stage voltage boosting/reducing inverter, described inverter comprises high pass filter (2) and control circuit (5), the output of high pass filter (2) connects load or electrical network (4), it is characterized in that described inverter also comprises main self-on-off switching tube (S1), the first auxiliary self-on-off switching tube (S2), the second auxiliary self-on-off switching tube (S3), high frequency flyback transformer (3), resonant capacitance (Cr) and Power Diode Pumped (D1), the cathode output end of DC power supply (1) connects the collector electrode of main self-on-off switching tube (S1), the end of the same name of the primary coil (L1) of the emitter connection high frequency flyback transformer (3) of main self-on-off switching tube (S1) and the negative pole end of Power Diode Pumped (D1), the non-same polarity of the secondary coil (L2) of the positive terminal connection high frequency flyback transformer (3) of Power Diode Pumped (D1) and an end of resonant capacitance (Cr), the end of the same name of the secondary coil (L2) of high frequency flyback transformer (3) connects the emitter of the second auxiliary self-on-off switching tube (S3), the non-same polarity of the primary coil (L1) of high frequency flyback transformer (3) connects the collector electrode of the first auxiliary self-on-off switching tube (S2), the collector electrode of the second auxiliary self-on-off switching tube (S3), the emitter of the first auxiliary self-on-off switching tube (S2), the other end of resonant capacitance (Cr) all is connected with the cathode output end of DC power supply (1), main self-on-off switching tube (S1), the gate pole of the first auxiliary self-on-off switching tube (S2) and the second auxiliary self-on-off switching tube (S3) links to each other with three outputs of control circuit (5) respectively, and the two ends of resonant capacitance (Cr) are connected in parallel between two inputs of high pass filter (2).

2, a kind of tri-switch single-stage voltage boosting/reducing inverter according to claim 1 is characterized in that described DC power supply (1) is by a kind of the providing in the DC power supply of solar photovoltaic power, fuel cell or variable speed wind generating generation.

3, a kind of tri-switch single-stage voltage boosting/reducing inverter according to claim 1 is characterized in that described main self-on-off switching tube (S1), the first auxiliary self-on-off switching tube (S2), the second auxiliary self-on-off switching tube (S3) are single-way switch.

4, a kind of tri-switch single-stage voltage boosting/reducing inverter according to claim 1, it is characterized in that described high pass filter (2) contains a filter inductance (Lf), one end of resonant capacitance (Cr) connects an end of filter inductance (Lf), the other end of filter inductance (Lf) connects an input of load or electrical network (4), and the other end of resonant capacitance (Cr) links to each other with another input of load or electrical network (4).

5, a kind of tri-switch single-stage voltage boosting/reducing inverter according to claim 4 is characterized in that described high pass filter (2) also contains a filter capacitor (Cf), and filter capacitor (Cf) is connected in parallel between two inputs of load or electrical network (4).

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