CN105406700A - Photovoltaic inverter bus capacitance pressure equalization and bus overvoltage protection control circuit and system - Google Patents

Abstract

The invention discloses a photovoltaic inverter bus capacitor voltage equalization and bus overvoltage protection control circuit, which includes a boost module electrically connected to a photovoltaic array, an inverter module electrically connected to a municipal power grid, and a positive electrode connected to the module The bus bar and the negative bus bar also include: a bus capacitor group, including at least one series capacitor group, and each series capacitor group is connected in parallel between the positive bus bar and the negative bus bar; a capacitor voltage equalization module, which is connected in parallel between the positive bus bar and the negative bus bar Between them, it is used to equalize the voltage of each capacitor in the bus capacitor group; the overvoltage protection module is used to detect the voltage between the positive and negative bus bars, and when the voltage exceeds the set value, the output voltage is reduced through the feedback boost module. The protection circuit of the present invention has a simple circuit and can realize the balance of capacitor voltage without complex control circuit, and the balance of capacitor voltage is a self-balancing process; the hardware protection circuit has high and low voltage isolation, fast response to bus voltage, and reliable protection measure.

Description

A photovoltaic inverter bus capacitor voltage equalization and bus overvoltage protection control circuit and system

technical field

The invention relates to the technical field of photovoltaic inverters, in particular to a photovoltaic inverter bus capacitor voltage equalization and bus overvoltage protection control circuit.

Background technique

In the photovoltaic inverter, it needs to be connected to the inverter unit through the DC bus. The DC bus provides high-amplitude pulsating current to the inverter and generates pulsating voltage on the bus. Therefore, capacitors are required to support the DC bus. The bus capacitor mainly absorbs the high-amplitude pulsating current on the DC bus to keep the input voltage fluctuation within the allowable range. At the same time, the bus capacitor acts as a buffer between photovoltaic input power and grid-connected output power to achieve a balance between input energy and output energy. It is a necessary component for decoupling input DC power and output AC power. The reliability of the bus capacitor directly affects the reliability of the inverter and becomes an important part of the inverter performance.

In photovoltaic inverters, due to the high operating voltage of the DC bus and the difficulty in selecting capacitors of this withstand voltage level, two electrolytic capacitors with lower withstand voltage and the same withstand voltage and capacity are usually connected in series and multiple groups are connected. The way of parallel connection makes the total voltage adapt to the working voltage level of the busbar. Due to individual differences in capacitance, the voltages on the two voltage-dividing capacitors will be different during the operation of the inverter. One voltage is higher and the other is lower. The higher voltage may exceed the withstand voltage value of the capacitor, causing damage to the capacitor. In the prior art, the method of directly connecting the same resistors in parallel to the two series capacitors is usually adopted, and the excess energy on the capacitors is consumed through the resistors, thereby suppressing excessive high voltage, but this method cannot achieve equal voltage on the capacitors .

Small and medium power photovoltaic inverters generally adopt a two-stage power topology of boost and inverter. The bus voltage is obtained by boosting the photovoltaic input by the previous step-up circuit. Usually, the bus overvoltage protection is implemented by program software, and lacks corresponding hardware. Protection circuit, in fact, the response speed of software protection is relatively slow. For the above problems, the prior art still needs to be improved.

Contents of the invention

The purpose of the present invention is to overcome the above disadvantages, and provide a photovoltaic inverter protection circuit that realizes the voltage balance of each capacitor and the overvoltage protection of the bus voltage.

In order to achieve the purpose of the foregoing invention, the present invention is realized through the following technical solutions:

A photovoltaic inverter bus capacitor voltage equalization and bus overvoltage protection control circuit of the present invention includes a boost module electrically connected to the photovoltaic array, an inverter module electrically connected to the mains grid, and a positive electrode connected to the modules The busbar and the negative busbar also include:

The bus capacitor group includes at least one series capacitor group, and each series capacitor group is connected in parallel between the positive bus bar and the negative bus bar;

A capacitor voltage equalization module, which is connected in parallel between the positive bus and the negative bus, to balance the voltage of each capacitor in the bus capacitor group;

The overvoltage protection module is used to detect the voltage between the positive and negative bus bars, and when the voltage exceeds the set value, the output voltage is reduced by feeding back the boost module.

Further, the common points of each group of series capacitors of the bus capacitor group are connected, and also include a first dissipation resistor and a second dissipation resistor, one end of the first dissipation resistor is connected to the negative bus, and the other end is connected to the series capacitor One end of the second dissipation resistor is connected to the positive busbar, and the other end is connected to the common end of the series capacitor.

Further, the capacitor voltage equalization module includes a first triode and a second triode, the first triode is an NPN type triode, the second triode is a PNP type triode, and the emitter of the first triode It is connected to the common point of the emitter of the second-type triode, and connected to the common point of the series capacitor of the bus capacitor group (11). The collector of the first triode is electrically connected to the positive bus after at least one resistor is connected in series. The collectors of the two triodes are connected in series with at least one resistor and then electrically connected to the negative busbar. The bases of the first triode and the bases of the second triode are electrically connected at the common point A, and the common point is divided into There are two circuits, and at least one resistor is connected in series respectively to be electrically connected to the positive busbar and the negative busbar.

Further, the overvoltage protection module includes a third triode, a photocoupler and a comparator; the emitter of the third triode is connected to the negative bus wire, and the collector of the third triode passes through the photocoupler The light-emitting diode is connected in series with at least one resistor and then electrically connected to the positive busbar. The common point of the light-emitting diode and the resistor is also connected to the negative busbar after being connected in series with the first capacitor and resistor in parallel. The base of the third triode The pole series Zener diode is connected in series with at least one resistor and then electrically connected to the positive busbar, and the common point end of the Zener diode and the resistor is divided into a parallel circuit of the second capacitor and resistor connected in series and then connected to the negative busbar; The collector of the phototransistor of the coupler is externally connected to the first power supply terminal, and the emitter is electrically connected to the negative input pin of the comparator. The output pin of the comparator outputs an enabling signal to the boost module, and the output pin and the positive input pin A positive feedback circuit is also connected between them.

Further, the positive feedback circuit is: the output pin of the comparator is connected in series with the first feedback resistor, and then the diode is connected in reverse series with the positive input pin of the comparator, and the common point of the diode and the positive input pin is The second feedback resistor is connected in series to the second power supply terminal, and a protection capacitor is connected in series between the positive input pin and the ground terminal.

Further, a third capacitance-resistance parallel circuit is connected in series between the emitter of the phototransistor and the ground terminal.

A photovoltaic inverter bus capacitor voltage equalization and bus overvoltage protection control circuit of the present invention achieves the following technical effects:

1. The circuit is simple, and the balance of the capacitor voltage can be realized without complicated control circuits, and the balance of the capacitor voltage is a self-balancing process.

2. The hardware protection circuit has high and low voltage isolation, fast response to the bus voltage, and reliable protection measures.

Description of drawings

Fig. 1 is a schematic diagram of the principle of the photovoltaic inverter bus capacitor voltage equalization and bus overvoltage protection control circuit of the present invention.

Fig. 2 is the circuit diagram of photovoltaic inverter bus capacitor voltage equalization and bus overvoltage protection control circuit of the present invention;

detailed description

Example

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings and embodiments. Apparently, the described embodiments are only some of the embodiments of the present invention, not all of them.

Please refer to FIG. 1 , which are schematic diagrams of the photovoltaic inverter bus capacitor voltage equalization and bus overvoltage protection control circuits according to the present invention.

A photovoltaic inverter bus capacitor voltage equalization and bus overvoltage protection control circuit 10 of the present invention includes a boost module 14 electrically connected to the photovoltaic array 20, an inverter module 15 electrically connected to the mains grid 30 and The positive busbar and negative busbar connecting the above modules also include:

The bus capacitor group 11 includes at least one series capacitor group, and each series capacitor group is connected in parallel between the positive bus BUS+ and the negative bus BUS-;

Capacitor voltage equalization module 12, which is connected in parallel between the positive bus BUS+ and the negative bus BUS-, to balance the voltage of each capacitor of the bus capacitor group;

The overvoltage protection module 13 is used to detect the voltage between the positive and negative busbars BUS+ and BUS+, and when the voltage exceeds the set value, the output voltage is reduced through the feedback boost module 14.

Please refer to Fig. 2, the common point terminals of each group of series capacitors of the bus capacitor group 11 are connected in series, and in this embodiment, the common point terminals of the above series capacitors are marked as BUSN common point terminals, and also include a first dissipation resistor R40 and the second dissipative resistor R15, one end of the first dissipative resistor R40 is connected to the negative bus BUS-, the other end is connected to the common point of the series capacitor, one end of the second dissipative resistor R15 is connected to the positive bus BUS+, and the other end is connected to the series capacitor common point of the capacitor.

The capacitor voltage balancing module 12 includes a first transistor Q1 and a second transistor Q6, the first transistor Q1 is an NPN transistor, the second transistor Q6 is a PNP transistor, and the first transistor Q6 is a PNP transistor. The emitter of Q1 is connected to the common point of the emitter of the second type triode Q6, and is connected to the common point of the series capacitor of the bus capacitor group (11), and the collector of the first triode Q1 is connected to the positive pole after at least one resistor The bus BUS+ is electrically connected, the collector of the second transistor Q6 is electrically connected to the negative bus BUS- after being connected in series with at least one resistor, the base of the first transistor Q1 and the base of the second transistor Q6 are connected at A The common-point terminal is electrically connected, and the A-common-point terminal is divided into two circuits, and at least one resistor is connected in series respectively to be electrically connected to the positive bus BUS+ and the negative bus BUS-.

In this embodiment, after the common point terminal of A is divided into two circuits, one circuit is connected to the positive bus with the first equalizing resistor R2 and the second equalizing resistor R9 connected in series, and the other channel is connected in series with the third equalizing resistor R43 and the fourth equalizing resistor R50 Afterwards, it is connected to the negative busbar, and the voltage at the common point terminal of A is divided by the first to fourth equalizing resistors R2, R9, R43, and R50, so the voltage at the common point terminal of A is Vbus/2. The working principle of the circuit is that, according to the voltage difference between the A common point terminal and the BUSN common point terminal, the above voltage difference is added to the base-emitter of the first and second transistors Q1 and Q6, so that the corresponding transistors are turned on, forming Capacitor charging and discharging circuit. Specifically, let the capacitance between the common terminal of the positive bus BUS+ and BUSN be denoted as Ca, and its voltage be Va; the capacitance between BUSN and the negative bus BUS- be denoted as Cb, and its voltage be Vb. When the voltages of the series capacitors are not equal, if Va is greater than Vb, that is, Va>Vbus/2, that is, Vb<Vbus/2, at this time the first transistor Q1 is turned on, the second transistor Q6 is turned off, and the bus voltage passes through The series resistance of the collector of the first transistor Q1 and the first transistor Q1 charge the capacitor Cb, and the voltage Vb rises, and at the same time, the capacitor Ca is discharged through the series resistance of the collector of the first transistor Q1 and the transistor Q1, and the voltage Va decrease until Va and Vb are equal, that is, both are Vbus/2, and at this moment, the first transistor Q1 is turned off. Conversely, when Va is less than Vb, the second transistor Q6 is turned on, the first transistor Q1 is turned off, and the bus voltage charges the capacitor Ca through the series resistance of the collector of the second transistor Q6 and the second transistor Q6 , the voltage Va increases, and at the same time, the capacitor Cb is discharged through the series resistance of the collector of the second transistor Q6 and the second transistor Q6, the voltage Vb decreases, and finally the voltage reaches equilibrium.

The overvoltage protection module 13 includes a third transistor Q7, a photocoupler and a comparator U2A; the emitter of the third transistor Q7 is connected to the negative bus wire, and the collector of the third transistor Q7 passes through The light-emitting diode U1A of the photocoupler is connected in series with at least one resistor and then electrically connected to the positive bus bar. The common point of the light-emitting diode U1A and the resistor is also divided into a parallel circuit of the first capacitor resistor connected in series and then connected to the negative bus bar. The base of the transistor Q7 is connected in series with the Zener diode D2, and then at least one resistor is connected in series with the positive busbar. The common point of the Zener diode D2 and the resistor is also divided into a second capacitor and resistor connected in parallel. Connected to the negative bus bar; the collector of the phototransistor U1B of the photocoupler is externally connected to the first power supply terminal, the emitter is electrically connected to the negative input pin 2 of the comparator U2A, and the output pin 1 of the comparator U2A is connected to the boost module 14 outputs the enabling signal, and a positive feedback circuit is also connected between the output pin 1 and the positive input pin 3 .

The positive feedback circuit is as follows: the output pin 1 of the comparator U2A is connected in series with the first feedback resistor R55, and then the diode D3 is connected in reverse series with the positive input pin 3 of the comparator U2A, and the diode D3 is connected to the positive input pin 3. The common end of pin 3 is also connected in series with the second feedback resistor R54 to the second power supply end, and a protection capacitor C45 is connected in series between the positive input pin 3 and the ground end.

A third capacitance-resistance parallel circuit is connected in series between the emitter of the phototransistor U1B and the ground terminal.

In the overvoltage protection module, when the voltage between the positive and negative busbars BUS+ and BUS- is too high, so that the third transistor Q7 is turned on, the light-emitting diode U1A of the photocoupler is powered on and emits light, that is, the photocoupler is turned on, and The phototransistor U1B outputs a high level to the negative input pin of the comparator U2, so that the comparator output pin 1 outputs an enable signal OV with a low level of 0, and the enable signal OV is used as the enable signal of the boost module 14, The low level blocks the PWM pulse of the boost module 14 .

The foregoing embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; therefore, although the specification has described the present invention in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand , the present invention can still be modified or equivalently replaced; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered by the claims of the present invention.

Claims (6)

1. a photovoltaic DC-to-AC converter bus capacitor is all pressed and bus overvoltage protecting control circuit; the positive electrode bus and the negative electrode bus that include the boost module (14) be electrically connected with photovoltaic array, the inversion module (15) be electrically connected with utility grid and be connected above-mentioned module, is characterized in that: also include:

Bus capacitor group (11), comprises at least one group of series capacitor bank, and each group series capacitor bank is connected in parallel between positive electrode bus and negative electrode bus;

Capacitance voltage balance module (12), it is connected in parallel between positive electrode bus and negative electrode bus, in order to each condenser voltage of balanced bus capacitor group;

Overvoltage protective module (13), in order to detect the voltage between both positive and negative polarity bus, when voltage exceedes set point by feeding back boost module (14) to reduce its output voltage.

2. photovoltaic DC-to-AC converter bus capacitor according to claim 1 is all pressed and bus overvoltage protecting control circuit; it is characterized in that: the concurrent end of each group of series capacitance of described bus capacitor group (11) is connected; also include the first resistance for dissipation (R40) and the second resistance for dissipation (R15); one end of first resistance for dissipation (R40) connects negative electrode bus; the other end connects the concurrent end of series capacitance; one end of second resistance for dissipation (R15) connects positive electrode bus, and the other end connects the concurrent end of series capacitance.

3. photovoltaic DC-to-AC converter bus capacitor according to claim 1 and 2 is all pressed and bus overvoltage protecting control circuit, it is characterized in that: described capacitance voltage balance module (12) includes the first triode (Q1) and the second triode (Q6), first triode (Q1) is NPN type triode, second triode (Q6) is PNP type triode, the emitter of the first triode (Q1) is connected with the emitter concurrent of Second-Type triode (Q6), and be connected with the series capacitance concurrent end of bus capacitor group (11), the collector electrode of the first triode (Q1) is connected after at least one resistance and is electrically connected with positive electrode bus, the collector electrode of the second triode (Q6) is connected after at least one resistance and is electrically connected with negative electrode bus, the base stage of the first triode (Q1) and the base stage of the second triode (Q6) are electrically connected at A concurrent end, this concurrent end (A) separates two-way, be in series with respectively after at least one resistance with positive electrode bus, negative electrode bus is electrically connected.

4. the photovoltaic DC-to-AC converter bus capacitor according to claims 1 to 3 any one is all pressed and bus overvoltage protecting control circuit, it is characterized in that: described overvoltage protective module (13) includes the 3rd triode (Q7), photoelectrical coupler and comparator (U2A), described 3rd triode (Q7) emitter is connected with negative electrode bus electric wire, the collector electrode of the 3rd triode (Q7) is connected after at least one resistor and is electrically connected with positive electrode bus after the light-emitting diode (U1A) of photoelectrical coupler, light-emitting diode (U1A) and the concurrent end of resistor also separate a road and connect after the first capacitance resistance parallel circuits and be connected with negative electrode bus, connect again after the base series voltage stabilizing didoe (D2) of the 3rd triode (Q7) after at least one resistor and be electrically connected with positive electrode bus, voltage stabilizing didoe (D2) and the concurrent end of resistor also separate a road and connect after the second capacitance resistance parallel circuits and be connected with negative electrode bus, external first feeder ear of collector electrode of the phototriode (U1B) of described photoelectrical coupler, emitter is electrically connected the negative input pin (2) of comparator (U2A), the output pin (1) of comparator (U2A), to boost module (14) output enable signal, is also connected with regenerative circuit between output pin (1) and positive input pin (3).

5. photovoltaic DC-to-AC converter bus capacitor according to claim 4 is all pressed and bus overvoltage protecting control circuit, it is characterized in that: described regenerative circuit is: the output pin (1) of comparator (U2A) is connected the first feedback resistance (R55), differential concatenation diode (D3) is electrically connected with the positive input pin (3) of comparator (U2A) afterwards again, diode (D3) and the concurrent end of positive input pin (3) the second feedback resistance (R54) of also connecting is connected the second feeder ear afterwards, also be in series with between positive input pin (3) and earth terminal and protect electric capacity C45.

6. photovoltaic DC-to-AC converter bus capacitor according to claim 5 is all pressed and bus overvoltage protecting control circuit, it is characterized in that: be in series with the 3rd capacitance resistance parallel circuits between the emitter of described phototriode (U1B) and earth terminal.