CN103312210A - Three-phase four-wire type three-level photovoltaic grid-connected inverter - Google Patents

Abstract

A three-phase four-wire system three-level photovoltaic grid-connected inverter relates to an inverter. At present, the number of components in the inverter is large, the loss is relatively large, and the cost is relatively high. The present invention is characterized in that: the three-level inverter circuit includes a capacitor circuit and a three-phase bridge arm, and the midpoint of each phase bridge arm leads to three phase wires, and the midpoint of the capacitor circuit leads to a neutral wire; the three phase wires and the neutral wire pass through The filter circuit is connected to the three-phase power grid; the first and fourth switching tubes are connected in series across the two ends of the DC bus, and the connecting point between the first switching tube and the fourth switching tube and the connecting point between the first capacitor and the second capacitor A third switching tube and a second switching tube are arranged between them; a diode with an anode connected to a drain is connected in parallel between the source and the drain of each switching tube. The technical scheme has few components and components, and two freewheeling diode devices are arranged on each bridge arm, which has low cost, good stability, high efficiency, and low conduction loss of each bridge arm in one cycle.

Description

A three-phase four-wire system three-level photovoltaic grid-connected inverter

technical field

The invention relates to a circuit topology of an inverter. the

Background technique

With the improvement of people's living standards and the technological progress of society, electric energy has become the energy that people must rely on in their daily lives. However, the primary energy sources such as coal and oil are decreasing day by day, and when people use them, they also cause huge pollution to the environment. The fundamental way to solve the energy problem is to develop environmentally friendly renewable energy, among which solar power generation is an important development direction. the

In the field of solar power generation, the photovoltaic grid-connected inverter is the core equipment. It realizes the inversion of the DC power generated by the solar panel into the AC power consistent with the grid in the system and incorporates it into the grid. On the one hand, it is a power generating equipment, and it is also a very important power-consuming electrical equipment in the electrical system. For the sake of safety, most of the current power supply systems are TN-S electrical systems. It is required that the zero line and the ground line on the user side are two separate lines. ACCIDENT. From the perspective of electrical safety, the inverter also needs to adopt a three-phase four-wire wiring method. the

There are generally two types of three-phase inverters commonly used at present: two-level and multi-level (commonly known as three-level). There are two ways for the two-level inverter to realize the three-phase four-wire system connection: one is three bridge arms, and the neutral line is led out by the voltage splitting of the bus capacitor; the other is a three-phase four bridge arm structure, and more than two switches are used The tube builds the fourth bridge arm, leads out the neutral line from it, and simulates the neutral point voltage output. The first method reduces the utilization rate of the DC bus voltage, and the second three-level method uses two switching tubes to increase the cost, but it can improve the utilization rate of the DC bus voltage and is more and more widely used. the

The topology of the diode-clamped voltage-type three-level inverter is shown in Figure 1, which has the following disadvantages:

1. The number of components is large. Each phase bridge arm has 4 switching tubes of high-power devices and 2 high-voltage anti-parallel diodes. There are many components, and the stability needs to be improved.

2. The loss is relatively large. There are 4 switching tubes in each phase, and 2 switching tubes have losses every time they are turned on and off. The loss superposition will be larger in each cycle. the

3. The cost is relatively high. The number of components is large and the cost is high. the

Contents of the invention

The technical problem to be solved and the technical task proposed by the present invention are to improve and improve the existing technical solutions, and to provide a three-phase four-wire three-level photovoltaic grid-connected inverter to achieve work stability and loss and cost purposes. For this reason, the present invention takes the following technical solutions. the

A three-phase four-wire three-level photovoltaic grid-connected inverter, including a boost circuit, a three-level inverter circuit, a filter circuit and a controller, characterized in that: the three-level inverter circuit includes a parallel At the capacitor circuit and the three-phase bridge arm at both ends of the DC bus bar, the midpoint of each phase bridge arm leads to the three phase wires A, B, and C, and the midpoint of the capacitor circuit leads to the neutral wire; the three phase wires A, B, and C and the neutral wire The neutral line is connected to the three-phase power grid after passing through the filter circuit; the capacitor circuit includes a first capacitor and a second capacitor, and the first capacitor and the second capacitor are connected in series across the two ends of the DC bus; the three-phase bridge arm Including the first switching tube, the second switching tube, the third switching tube, and the fourth switching tube, the first and fourth switching tubes are connected in series across the two ends of the DC bus, and the connection point between the first switching tube and the fourth switching tube A third switch tube and a second switch tube are arranged between the connection point of the first capacitor and the second capacitor; a diode with an anode connected to a drain is connected in parallel between the source and the drain of each switch tube. the

As a further improvement and supplement to the above technical solutions, the present invention also includes the following additional technical features. the

Described capacitive circuit is made up of first electric capacity, second electric capacity; The fourth switching tube is composed of first, second, third and fourth diodes connected in parallel; the source of the first switching tube and the positive pole of the first capacitor are connected to the positive pole of the DC bus; the drain of the first switching tube and the fourth The source of the switching tube is connected to the source of the third switching tube, the drain of the fourth switching tube and the negative pole of the second capacitor are connected to the negative pole of the DC bus, and the drain of the third switching tube is connected to the drain of the second switching tube , the source of the second switching tube, the negative pole of the first capacitor, and the positive pole of the second capacitor are connected. the

The filter circuit includes four sets of filter branches respectively connected to three phase lines A, B, and C and the neutral line, and each set of filter branches includes a resistor and an inductance connected in series with the resistor. the

The boost circuit includes a filter capacitor, a filter inductor, a fifth switch tube, a sixth diode and a fifth diode, and the two ends of the filter capacitor are respectively connected to the positive and negative poles of the input source, and one end of the filter inductor It is connected to the anode, the other end is connected to the anode of the sixth diode and the source of the switch tube, the drain of the switch tube is connected to the negative pole of the input source, and the source and drain of the switch tube are connected in parallel between the anode and the drain. The cathodes of the fifth diode and the sixth diode are connected to the input terminal of the three-level inverter circuit. the

Beneficial effects: the technical scheme has few components and parts, and two freewheeling diode devices are arranged on each bridge arm, which has low cost, good stability, high efficiency, and low conduction loss of each bridge arm in one cycle. the

Description of drawings

Fig. 1 is a schematic structure diagram of an existing inverter. the

Fig. 2 is a principle structural diagram of the present invention;

Fig. 3 is a comparison diagram of the efficiency of the present invention and the NPC topology inverter.

In the figure: C ₁ - the first capacitor, C ₂ - the second capacitor, S ₁ - the first switch tube, S ₂ - the second switch tube, S ₃ - the third switch tube, S ₄ - the fourth switch tube, S _b - the fifth switching tube, D ₁ - the first diode, D ₂ - the second diode, D ₃ - the third diode, D ₄ - the fourth diode, D _b0 - the fifth diode Tube, D _b - the sixth diode, L _b - filter inductor, C _b - filter capacitor, R - resistor, L - filter inductor.

Detailed ways

The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings. the

The present invention includes a boost circuit, a three-level inverter circuit, a filter circuit and a controller. The three-level inverter circuit includes a capacitor circuit and three-phase bridge arms connected in parallel at both ends of the DC bus, and the center of each phase bridge arm The three phase wires A, B, and C are drawn from the point, and the neutral wire is drawn out from the midpoint of the capacitor circuit; the three phase wires and the neutral wire of A, B, and C are connected to the three-phase power grid after passing through the filter circuit; the capacitor circuit includes the first A capacitor C ₁ , a second capacitor C ₂ , the first capacitor C ₁ and the second capacitor C ₂ are connected in series across the two ends of the DC bus; the three-phase bridge arm includes a first switch tube S ₁ , a second switch tube The tube S ₂ , the third switching tube S ₃ , the fourth switching tube S ₄ , the first and fourth switching tubes S ₁ and S ₄ are connected in series across the two ends of the DC bus, the first switching tube S ₁ and the fourth switching tube Between the connection point of the tube _S4 and the connection point of the first capacitor _C1 and the second capacitor _C2 , a third switching tube _S3 and a second switching tube _S2 are arranged; between the source and the drain of each switching tube Connect a diode with its anode connected to its drain in parallel.

The capacitor circuit is composed of the first capacitor C ₁ and the second capacitor C ₂ ; each phase bridge arm of the three-phase bridge arm is composed of the first, second, third, and fourth switching tubes S ₁ , S ₂ , and S ₃ , S ₄ and the first, second, third and fourth diodes D ₁ and D connected in parallel with the first, second, third and fourth switching tubes S ₁ , S ₂ , S ₃ and S ₄ respectively _2. Composed of D ₃ and D ₄ ; the source of the first switching tube S ₁ and the positive pole of the first capacitor C ₁ are connected to the positive pole of the DC bus, the drain of the first switching tube S ₁ and the source of the fourth switching tube S ₄ , the source of the third switching tube _S3 is connected, the drain of the fourth switching tube _S4 and the negative pole of the second capacitor _C2 are connected to the negative pole of the DC bus, the drain of the third switching tube _S3 is connected to the second switching tube S ₂ , the source of the second switching transistor _S2 , the negative pole of the first capacitor _C1 , and the positive pole of the second capacitor _C2 are connected. The filter circuit includes four sets of filter branches, which are respectively connected to the three phase lines A, B, and C and the neutral line. Each set of filter branches includes a resistor R and an inductance L _b connected in series with the resistor R.

The boost circuit includes a filter capacitor C _b , a filter inductor L _b , a fifth switch tube S _b , a sixth diode D _b and a fifth diode D _b0 , and the two ends of the filter capacitor C _b are respectively connected to the input The positive and negative poles of the source are connected, one end of the filter inductance L _b is connected to the positive pole, the other end is connected to the positive pole of the sixth diode D _b , the source of the fifth switching tube Sb, and the drain of the fifth switching tube _Sb Connect to the negative pole of the input source, connect the fifth diode D _b0 with the anode connected to the drain in parallel between the source and the drain of the fifth switching tube S _b , and connect the negative pole of the sixth diode D _b to the three-level inverter input to the circuit.

The controller is composed of TI's TMS320F2812 DSP chip, which is responsible for detecting the voltage at both ends of the solar panel and the output current, the three-phase voltage of the grid and the three-phase current output by the inverter, the calculation of the control algorithm and the realization of the circuit protection function, and the generation of BOOST and The drive pulses of the inverter circuit are sent to the IGBT switch tubes respectively to control the normal operation of the circuit. the

The existing NPC topological structure (as shown in Figure 1) and the T-shaped topological structure of the present invention (as shown in Figure 2), using a phase bridge arm as a comparison unit, make the following comparison:

1. Quantity of components

On each bridge arm, the T-type topology has two freewheeling diode devices D ₅ and D ₆ less than the NPC topology, and the cost of each diode is about 100 RMB, so the T-type topology can save 200 RMB in cost compared with the NPC.

2. Loss

a. In positive Vbus power supply state,

The NPC circuit current is powered by +Bus via S ₁ and S ₂ , and its losses include Loss_S ₁ _turnon&off, Loss_S _{1_On} and Loss_S ₂ _On;

The current of the T-type topology circuit is powered by +Bus through _S1 , and its losses include Loss_S ₁ _turnon&off and Loss_S ₁ _On.

In this state, the T-type has one S ₂ less conduction loss than the NPC topology.

b. In negative Vbus power supply state,

The NPC circuit current flows from the filter inductance L _b to -Bus through S ₃ and S ₄ , and its losses include Loss_S ₄ _turnon&off, Loss_S ₃ _On and Loss_S ₄ _On;

The T-type topology circuit current flows from the filter inductance L _b to -Bus through S ₄ , and its losses include Loss_S ₄ _turnon&off and Loss_S ₄ _On.

In this state, the T-type has one S ₃ less conduction loss than the NPC topology.

c. In positive Vbus freewheeling state,

The NPC circuit current flows from the filter inductor through D ₁ and D ₂ to +Bus, and its losses include Loss_D ₁ _ turnon&turnoff&On, Loss_D ₂ _turnon&turnoff&On;

The T-type topology circuit current flows from the filter inductor to +Bus through D ₁ , and its loss includes Loss_D ₁ _ turnon&turnoff&On.

In this state, the T-type has one S ₂ less conduction loss than the NPC topology.

d. In negative Vbus freewheeling state,

NPC circuit current is from -Bus to filter inductance through _D1 and _D2 , and its loss includes _{Loss_S3_turnon} &turnoff&On, _{Loss_S4_turnon} &turnoff&On;

The current of the T-type topology circuit is from -Bus to the filter inductor through D ₁ , and its loss includes Loss_S ₄ _ turnon&turnoff&On.

In this state, the T-type has one S ₃ less conduction loss than the NPC topology.

It can be seen from the comparison of losses during the above operation that the T-type topology of each bridge arm has two less conduction losses of S ₂ and S ₃ than the NPC topology in one cycle.

3. Experimental data

The two topological structure schemes are applied to the 17KT three-phase photovoltaic inverter, the input is 600V DC, the switching tube frequency of the inverter part is 20KHz, and the output is from 20% load to 100% load. The experimental data of the comparative efficiency is shown in the figure As shown in 3, when the inverter is running at full load, the T-type topology efficiency is 98%, while the NPC topology efficiency is 97.5%, then it can be calculated that the T-type topology loss is nearly 90W smaller than that of NPC when the inverter is running at full load.

A three-phase four-wire system three-level photovoltaic grid-connected inverter shown in Figure 2 above is a specific embodiment of the present invention, which has already demonstrated the outstanding substantive features and significant progress of the present invention, and can be used according to actual use Need, under the enlightenment of the present invention, equivalent modification of its shape, structure and other aspects are all within the scope of protection of this scheme. the

Claims (4)

1. three-phase four-wire system three-level photovoltaic grid-connected inverter, comprise booster circuit, tri-level inversion circuit, filter circuit and controller, it is characterized in that: described tri-level inversion circuit comprises condenser network and the three-phase brachium pontis that is connected in parallel on the dc bus two ends, the mid point of every phase brachium pontis is drawn A, B, three phase lines of C, and the mid point of condenser network is drawn the neutral line; A, B, three phase lines of C and the neutral line access three phase network behind the wave circuit after filtration; Described condenser network comprises the first electric capacity (C ₁), the second electric capacity (C ₂), the first electric capacity (C ₁), the second electric capacity (C ₂) be connected across the dc bus two ends after the series connection; Described three-phase brachium pontis comprises the first switching tube (S ₁), second switch pipe (S ₂), the 3rd switching tube (S ₃), the 4th switching tube (S ₄), the first, the 4th switching tube (S ₁, S ₄) be connected across the dc bus two ends, the first switching tube (S after the series connection ₁) and the 4th switching tube (S ₄) tie point and the first electric capacity (C ₁) and the second electric capacity (C ₂) tie point between establish the 3rd switching tube (S ₃), second switch pipe (S ₂); The diode that a positive pole in parallel links to each other with drain electrode between the source electrode of each switching tube and the drain electrode.

2. a kind of three-phase four-wire system three-level photovoltaic grid-connected inverter according to claim 1, it is characterized in that: described condenser network is by the first electric capacity (C ₁), the second electric capacity (C ₂) form; Every phase brachium pontis of three-phase brachium pontis is by first, second, third, fourth switching tube (S ₁, S ₂, S ₃, S ₄) and respectively with first, second, third, fourth switching tube (S ₁, S ₂, S ₃, S ₄) first, second, third, fourth diode (D in parallel ₁, D ₂, D ₃, D ₄) form; The first switching tube (S ₁) source electrode and the first electric capacity (C ₁) anodal link to each other the first switching tube (S with dc bus is anodal ₁) drain electrode, the 4th switching tube (S ₄) source electrode, the 3rd switching tube (S ₃) source electrode link to each other the 4th switching tube (S ₄) drain electrode and the second electric capacity (C ₂) negative pole link to each other the 3rd switching tube (S with the dc bus negative pole ₃) drain electrode and second switch pipe (S ₂) drain electrode link to each other second switch pipe (S ₂) source electrode, the negative pole of the first electric capacity (C1), the second electric capacity (C ₂) positive pole link to each other.

3. a kind of three-phase four-wire system three-level photovoltaic grid-connected inverter according to claim 2, it is characterized in that: filter circuit comprises four groups of filter branch, four groups of filter branch link to each other with A, B, three phase lines of C and the neutral line respectively, and every group of filter branch comprises resistance (R), the inductance (L) of connecting with resistance (R).

4. a kind of three-phase four-wire system three-level photovoltaic grid-connected inverter according to claim 3, it is characterized in that: described booster circuit comprises filter capacitor (C _b), filter inductance (L _b), the 5th switching tube (S _b), the 6th diode (D _b) and the 5th diode (D _B0), filter capacitor (C _b) two ends be connected with the input source positive and negative electrode respectively; Described filter inductance (L _b) end is connected the other end and the 6th diode (D with anodal _b) positive pole, the 5th switching tube (S _b) source electrode connect the 5th switching tube (S _b) drain electrode be connected the 5th switching tube (S with the input source negative pole _b) source electrode and drain electrode between in parallel anodal and the 5th diode (D that drain electrode links to each other _B0), the 6th diode (D _b) negative pole connect the input of tri-level inversion circuit.

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