CN116938025A - Direct inversion scheme based on direct voltage boosting - Google Patents

Abstract

The invention provides a direct inversion scheme based on direct boosting, which realizes the two functions of direct boosting and inversion into a whole, wherein two single-power-tube inductance energy-storage type direct-current boosting circuits in a main circuit work in a sine modulation state, the sine modulation direct-current boosting circuits adopt a self-inductance coupling boosting mode, the two boosting circuits respectively bear half-period sine boosting alternating output in positive and negative half cycles, and a load current loop is formed by matching with two potential pull-down switching tubes, so that positive and negative complete sine voltages are synthesized at a load port. The invention has the advantages of omitting the step of simply raising the low-voltage direct current into the high-voltage direct current in the prior inversion technology, simplifying the structure of an inverter circuit, reducing the number of power devices, lowering the product cost and improving the working efficiency and the working reliability of the inverter.

Description

Direct inversion scheme based on direct voltage boosting

Technical Field

The invention relates to a direct inversion scheme based on direct DC boosting, which belongs to a low-power electronic inversion device and can be used as a vehicle-mounted inversion power supply or a small-power mobile power supply.

Background

Most of the current electric equipment in China is designed by taking commercial power as a power supply source, such as an electric fan, a television, an electromagnetic oven, an electric cooker, an electric kettle, a charger, a laboratory common measuring instrument and the like, are powered by a 220V alternating current power grid, and cannot work once the electric equipment is separated from the alternating current power grid. In addition to the power from the ac power grid, another type of power source is typically a storage battery, and small solar energy and wind energy are all output through the storage battery. If the electric energy of the storage battery is used for supplying power to the electric appliances, the most basic method is to perform inversion treatment and convert the direct-current voltage of the storage battery into alternating-current power with proper frequency and voltage for output. Therefore, the inverter is a common component of mobile power supply and emergency power supply equipment.

In order to obtain 220V alternating voltage, the currently commonly adopted inversion technology is to convert the 220V alternating voltage into 220V sinusoidal alternating voltage output through a full-bridge high-frequency switch circuit on the basis of 400V direct voltage, and the basic circuit structure is shown in figure 2. The left and right sides of the single-phase full-bridge circuit structure are symmetrical, each side is divided into an upper power tube and a lower power tube which are connected in series, and single-phase inversion is formed by at least 4 power field effect tubes. The special control chip matched with the full-bridge inverter switching circuit has various types, such as EG8011, U3990F6 chips and the like. Even some low-cost inverter circuits with simple structures are only converted into 220V power frequency square wave output so as to reduce switching loss, and the inverter circuits can also meet the power supply requirements of most electric appliances.

For the occasion of adopting low-voltage storage battery to supply power, for example, when the battery of a common automobile is used for supplying power, the automobile only has a 12V storage battery, a large truck only has a 24V storage battery, and an inverter matched with the automobile in the market adopts a two-step method of boosting to 220-400V direct current and then inverting. The direct current boost is usually in a double-power tube structure, a push-pull structure or a voltage switch structure. The push-pull type boost circuit in a large number of vehicle-mounted inverters adopts a hard switching mode, and can be completely changed into a soft switching mode of a current switching mode, so that switching loss is reduced, working efficiency is improved, but the soft switching mode is not basically adopted in actual products. The direct current booster circuit and the inverter circuit are high-power circuits and are limited by the working efficiency of the two circuits, the whole working efficiency of the existing inverter is low, more power devices are needed to be adopted, the production cost is high, and the damage rate of the devices is high.

The boost function and the inversion function can be combined into one, the circuit structure can be greatly simplified, the number of power devices is reduced, and the working reliability is improved. The present invention has been achieved based on this idea.

Disclosure of Invention

The direct inversion scheme based on direct voltage boosting is a scheme combining direct voltage boosting and inversion functions, a structural block diagram is shown in a figure 1, a main circuit schematic diagram is shown in a figure 3, and the direct voltage boosting direct inversion scheme has the following characteristics from the technical aspect:

in the direct-current boosting direct inversion scheme, a main circuit consists of five parts, namely two single-power-tube inductance energy-storage type direct-current boosting circuits, two potential pull-down field effect transistors Q3 and Q4 which are connected with diodes in series, two independent SPWM circuits and driving circuits thereof, logic processing of the potential pull-down field effect transistors and driving circuits thereof and a sine reference signal generating circuit, wherein the two single-power-tube inductance energy-storage type direct-current boosting circuits are in a common-ground boosting mode, are respectively boosted independently relative to an input power negative electrode wire, alternately output power frequency half-cycle sine voltages, take a voltage difference value output by the two direct-current boosting circuits as inversion output voltages, and the two potential pull-down field effect transistors Q3 and Q4 which are connected with unidirectional diodes in series form a load current loop.

In the direct inversion scheme based on direct boosting, the single-power-tube inductance energy-storage type direct-current boosting circuit adopts an autotransformer mode, as shown in figure 4, the autotransformer ratio is 1:5.0-1:5.2, each single-power-tube inductance energy-storage type direct-current boosting circuit outputs power frequency half-period sinusoidal voltage relative to an input power supply positive line, and the duty ratio of the SPWM circuit is controlled after error comparison is carried out according to the feedback value of the output voltage and the amplitude of a sinusoidal reference signal, wherein a power tube is a power field-effect tube with withstand voltage of 100V.

In the direct inversion scheme based on direct boosting, sources of two potential pull-down field effect transistors Q3 and Q4 are connected to an input power supply positive line, drains are connected in series with a unidirectional diode and then are connected to a load end of the channel, as shown in figure 3, the two potential pull-down field effect transistors work in a power frequency half-period switching state, an opening condition is a half period corresponding to boosting of another channel, and the channel has no boosting driving pulse and is managed by a logic processing circuit.

In the direct-current boosting direct inversion scheme, two paths of inductors L3 and L4 formed by iron powder core magnetic rings are respectively connected in series between the output end of the single-power-tube inductance energy storage type direct-current boosting circuit and the corresponding two load ends.

The direct inversion scheme based on direct voltage boosting has the beneficial effects that:

the direct inversion scheme based on direct voltage boosting directly boosts direct current low voltage into alternating voltage to be output, compared with the existing two-step inversion scheme, the link of simply boosting low voltage direct current into high voltage direct current is omitted, the structure of an inversion circuit is simplified, the number of power devices is reduced, the product cost is reduced, the working efficiency of an inverter can be improved, and the working reliability is improved.

Fig. 3 is a single-phase inversion main circuit, wherein a boosting channel 1 is formed by a PWM chip IC1, an A channel of a pulse driving chip IC3, a power field effect transistor Q1, an autotransformer L1, a rectifier diode D1 and the like, and is used for carrying out inversion output in a positive half period; the PWM chip IC2, the B channel of the pulse driving chip IC3, the power field effect transistor Q2, the self-coupling boost inductor L2, the rectifier diode D2 and the like form a boost channel 2, and the negative half-cycle inversion output is born. The circuit structures of the two boost channels are identical, but the modulation polarities of the SPWMs are opposite to each other. When no sine reference signal is input, both the boosting channels are in a pause state, namely the PWM pulse duty ratio for controlling boosting is 0%. After the sinusoidal reference signal is input, the two half cycles respectively start 1-channel or 2-channel boosting.

The PWM chip selects TL494, and connects the 13 th end of TL494 with GND, as shown in fig. 3 and fig. 4, so that the maximum duty ratio of pulse width modulation is not less than 90%, and the continuous current operation mode can be entered during high power output. The PWM pulse frequency is set between 90 and 100 kHz.

The direct-current booster circuit belongs to a Boost working mode, only unidirectional current can be output to a load end, and reverse current of a load loop cannot be absorbed, so that potential pull-down field effect transistors Q3 and Q4 are arranged in the scheme to form loop current of the load. The two potential pull-down field effect transistors can simply work in a power frequency switch state, but in order to prevent the output filter capacitor from forming a short circuit effect, a filter inductor needs to be connected in series to inhibit pulse current, the inductance of the filter inductors L3 and L4 is not strictly required, the inductance is preferably set between 100 and 200 mu H, and the current carrying capacity of the filter inductors is basically suitable for the load current requirement.

The lowest output voltage of the single-power-tube inductance energy-storage type direct-current booster circuit working in the Boost mode is the input power supply voltage, if the input voltage is 24V, the boosted output voltage is not lower than 24V, and the boosting value which can be changed relative to GND is more than 24V. Therefore, the alternating voltage of the inversion output is based on the 24V power supply positive line, the source of the potential pull-down field effect transistor forming the load current loop should be connected to the input power supply positive line, the load current path of the positive half period is shown by the dotted line in fig. 3, the load current path of the negative half period forms a loop through the field effect transistor Q3, and the current direction on the load is reversed.

The logic processing circuit of the potential pull-down field effect transistor is shown in figure 5, and the square wave signal formed after the zero crossing voltage comparison of the sinusoidal reference signal is used for controlling the switching tube. The switching tube driving pulse default is designed to be of a low level scheme, VH1 and VH2 are two switching tube control levels, and when no power frequency square wave signal exists, VH1 and VH2 are both of low level.

The voltage comparator outputs a negative level during the positive half period, the input INA of the pulse driving chip IC5 is set low, the pulse output VH1 is low, and the potential pull-down field effect transistor Q3 connected with the boost channel 1 is closed. Normally, the input terminal INB of the pulse driving chip IC5 is set high, the pulse output VH2 is at a high level, and the potential pull-down fet Q4 connected to the boost channel 2 is turned on to form a positive half-cycle load current loop, as shown by the dotted line in fig. 3. However, if the boost channel 2 also generates a modulation pulse during the positive half period, the input terminal INB of the pulse driving chip is set low by the transistor Q5, so that the fet Q4 is turned off rapidly, and the off time of not less than 20 μs is maintained, and the duration of the off time is set by the capacity of the capacitor C35.

The voltage comparator outputs a positive level during the negative half period, the potential of the input end INB of the pulse driving chip IC5 is set low, the pulse output VH2 is low, and the potential pull-down field effect transistor Q4 connected with the boost channel 2 is closed. Under normal conditions, photocurrent is output through the photocoupler IC7, the potential of the input end INA of the pulse driving chip IC5 is set high, the pulse output VH1 is high, and the potential pull-down field effect transistor Q3 connected with the boost channel 1 is conducted to form a negative half-period load current loop. However, if the boost channel 1 also generates a modulation pulse during the negative half period, the input port of the photo coupler IC7 is closed by the transistor Q6, and the input terminal INA of the pulse driving chip is set low, so that the fet Q3 is turned off rapidly, and the off time of not less than 20 μs is maintained, and the duration of the off time is set by the capacity of the capacitor C34.

Abnormal operating conditions may occur during power up or power down of the circuit.

In the design scheme, the power frequency square wave signal is obtained through the voltage zero crossing comparison of the operational amplifier, and a long delay time exists when some operational amplifiers are used for voltage comparison, which is equivalent to the occurrence of a phase shift effect, so that the same phase shift amount is also obtained when the sinusoidal reference signal is sent to the SPWM circuit, and the sinusoidal boosting and the power frequency switch synchronously work. The RC integration network is arranged between the power frequency sinusoidal reference signal output end and the SPWM circuit, and the phase shift angle is determined by devices such as R22 and C6, and the like, as shown in a circuit on the left side of the figure 3.

For the two-step inversion scheme, the direct current voltage for supplying power to the full-bridge inversion circuit generally reaches 360-400V, and in the direct current boosting direct inversion scheme, when 220V alternating current voltage is output, the highest boosting value is 311V of a sine alternating current voltage peak value, the boosting ratio is smaller, and the boosting efficiency is higher. The single power tube inductance energy storage type direct current booster circuit adopts an auto-coupling booster mode, so that the voltage stress of the power field effect tube can be reduced, wherein the power tube adopts a power field effect tube with withstand voltage of 100V, is suitable for working in a high-frequency switch state, and can effectively reduce the volume of an energy storage inductor.

Drawings

Fig. 1 is a schematic block diagram of a direct inversion scheme based on direct dc boost.

Fig. 2 is a block diagram of a single-phase full-bridge inverter circuit commonly used at present.

Fig. 3 is a schematic diagram of a single-phase sinusoidal inversion body circuit.

In the figure, IC1 and IC2 are PWM chips, IC3 is a pulse driving chip of an excitation tube, Q1 and Q2 are power excitation field effect tubes, L1 and L2 are self-coupling boost inductors, IC5 is a pulse driving chip of a power frequency switch, Q3 and Q4 are load current loop switching tubes, and a dotted line is a positive half-period load current path.

Fig. 4 is a schematic diagram of a channel of the single-power-tube inductance energy-storage type direct-current boost circuit 1.

In the figure, IC1 is a PWM chip, IC3 is a pulse driving chip of an excitation tube, Q1 is a power excitation field effect tube, and L1 is an auto-coupled boost inductor.

Fig. 5 is a logic processing circuit of the potential pull-down fet.

In the figure, IC4A is a zero-crossing voltage comparator, IC7 is a photocoupler, Q5 is an inverter and potential transfer transistor, D13 is a clamp diode, Q3 and Q4 are load current loop switching transistors, and D7 and D11 are unidirectional diodes.

Fig. 6 is a sinusoidal reference signal generating circuit.

D6 in the figure is an electrodeless bidirectional red light emitting diode.

Fig. 7 is a graph of the inverted output voltage waveform measured on a template.

Detailed Description

The control chip matched with the full-bridge inversion output is more in types, but a circuit for realizing the inversion according to the scheme is not matched with a special control chip, and can only be realized by adopting a combination of a classical PWM chip and a driving chip. The practice of the invention will be further described with reference to the drawings.

The PWM pulse group of the same channel is ensured to correspond to the low-level time period of the power frequency switch pulse. And (3) observing a PWM pulse group signal and a power frequency pulse signal output by a certain channel by using a dual-trace oscilloscope, and changing the capacity of an integrating capacitor C6 according to the actual working condition of a circuit to correct the time corresponding relation. The PWM pulse group signal is required to be aligned with the low level of the power frequency pulse signal, and the capacitance of C6 is not less than 4.7nF.

The 1 channel is ensured to only bear positive half-cycle boosting, and the 2 channel only bears negative half-cycle boosting. The debugging method of the product sample piece of a certain batch is as follows: and removing the grid current limiting resistors R23 and R25 of the boost power tube, inputting the lowest allowable power supply voltage, observing the time width relation between the PWM pulse group signal output by the 1 channel and the power frequency pulse signal by using a dual trace oscilloscope, and adjusting the value of the voltage dividing resistor R4 to ensure that the time width of the PWM pulse group is slightly smaller than the low-level time width of the power frequency pulse. The same method measures the time relation between the 2-channel PWM pulse group and the power frequency pulse signal, and adjusts the resistance of the divider resistor R14.

The filter capacitors C13 and C14 are connected after the direct current boost rectification, but the capacitance of the filter capacitor is not excessively large as the direct inversion mode of the boost, and is generally 0.1-0.47 mu F. Because of the existence of the filter capacitor, the inverted sine voltage waveform can only completely appear after the resistive or inductive load is applied.

In fig. 5, the transistor Q5 is used to control the floating voltage, and the matching requirement of the collector resistor and the emitter resistor is to ensure that the INB end of the IC5 is set to a low level when Q5 is turned on, so as to prevent the chip IC5 from being damaged due to the excessively low level, and a schottky diode D5 is connected in the circuit to be used as a clamp. The method is suitable for an environment with stable +10V voltage and VCC voltage.

In the invention, the inverter circuit needs 3 groups of power supply voltages in total: +10V, -5V, 10V levitation. The levitation is 10V above 10V relative to the input power positive line, i.e., VCC in fig. 3. The 3 groups of voltage values do not need to be accurate, but must be stable, and can be output in a mutual inductance coupling mode by adopting a DC-DC voltage reduction circuit.

The self-coupling boost inductor is an important component of inversion and requires enough energy storage. The winding of the self-coupling boost inductor is divided into an exciting winding and a boost winding, and a pair of different-name ends of the two windings are connected together to form a three-terminal device. The ratio of the number of turns of the exciting winding to the number of turns of the boosting winding is defined as the ratio of the number of turns of the exciting winding to the number of turns of the boosting winding, for example, the number of turns of the exciting winding is 12 turns, the number of turns of the boosting winding is 60 turns, and the ratio of the autotransformer to the boosting winding is 1:5. The exciting winding is often operated in a high current state, and a multi-wire parallel winding mode is needed, for example, 3 wires of the phi 1.0mm enameled wire are adopted for parallel winding.

FIG. 7 shows the voltage curve of the output terminal measured when the load terminal of the first model was connected to a 30W/220V soldering iron. For the safety of the circuit operation, a certain dead time is left at the zero crossing of the voltage, which dead time can be reduced after the condition is complete. The output voltage curve is not a standard sinusoidal curve because a simple structure oscillating circuit as shown in fig. 6 is employed in this scheme. The output sine voltage harmonic component basically depends on the purity of a sine reference signal, if a singlechip, a special sine oscillation chip and the like are used for obtaining a sine signal with lower harmonic distortion, the output sine curve is more ideal, but the index is not necessarily improved for a common low-cost inverter. The output voltage amplitude is determined by the sine reference signal amplitude and the feedback network resistance ratio, and the magnitude of the output voltage feedback resistance can be changed to adjust the voltage amplitude of the inversion output. And the output voltage amplitude of the two boost channels is regulated to be basically equal, then the knob angle of the variable resistor R21 is changed, and the output voltage high-low relationship of the two channels is regulated.

As a practical inverter product, it is also necessary to add necessary functional circuits such as a control switch, overload protection, short-circuit protection, undervoltage protection, and soft start, considering reliability and safety of operation. In the inversion of the electric energy provided by the battery pack, the input power supply current is larger, and a mechanical contact switch is not suitable to be directly connected in series, but an electronic switch with large current carrying capacity can be adopted. In the inversion scheme, the 4 th end of the TL494 chip is utilized for switch control, the 4 th ends of the IC1 and IC2 chips are communicated, then the 4 th end is connected to GND through 10kΩ, a capacitor C29 is connected between the 4 th end and the 14 th end VREF of the TL494 chip, two ends of the C29 are connected with an inversion switch in parallel, and inversion output is closed when the inversion switch is turned on. Of course, other configurations of switching circuits may be employed.

The inversion method is suitable for a single-phase inversion system powered by a low-voltage storage battery pack, and a direct-current power supply is externally input.

Claims (4)

1. Direct inversion scheme based on direct voltage boost, its structural feature is: the main circuit consists of five parts, namely two single-power-tube inductance energy-storage type direct-current booster circuits, two potential pull-down field effect transistors Q3 and Q4 which are connected in series with diodes, two independent SPWM circuits and driving circuits thereof, logic processing of the potential pull-down field effect transistors and driving circuits thereof, and a sine reference signal generating circuit, wherein the two single-power-tube inductance energy-storage type direct-current booster circuits are in a common-ground booster mode and are respectively boosted relative to an input power negative electrode wire, power frequency half-cycle sine voltages are alternately output, the voltage difference value output by the two direct-current booster circuits is taken as inversion output voltage, and the two potential pull-down field effect transistors Q3 and Q4 which are connected in series with unidirectional diodes form a load current loop.

2. The direct-current boost direct-inversion-based scheme according to claim 1, characterized in that: the single power tube inductance energy storage type direct current booster circuit adopts an auto-coupling booster mode, the auto-coupling booster ratio is 1:5.0-1:5.2, each single power tube inductance energy storage type direct current booster circuit outputs power frequency half-period sine voltage relative to an input power supply positive line, and the duty ratio of the SPWM circuit is controlled after error comparison is carried out according to the feedback value of the output voltage and the amplitude of a sine reference signal, wherein the power tube is a power field effect tube with withstand voltage of 100V.

3. The direct-current boost direct-inversion-based scheme according to claim 1, characterized in that: the sources of the two potential pull-down field effect transistors Q3 and Q4 are connected with an input power supply positive line, the drains are connected with a unidirectional diode in series and then connected with the load end of the channel, the two potential pull-down field effect transistors work in a power frequency half-period switch state, the opening condition is a half period corresponding to the boosting of the other channel, and the channel has no boosting driving pulse and is managed by a logic processing circuit.

4. The direct-current boost direct-inversion-based scheme according to claim 1, characterized in that: the two paths of single-power-tube inductance energy storage type direct current booster circuit output ends and two corresponding load ends are respectively connected in series with an inductor L3 and an inductor L4 which are formed by iron powder core magnetic rings.