Simulated sine wave inverter circuit

Abstract

The utility model discloses a simulated sine wave inverter circuit, which comprises a direct current booster circuit, a rectifying circuit, an inverter output circuit and an SPWM (sinusoidal pulse width modulation) driving circuit, and is characterized in that the direct current booster circuit is used for boosting input direct current and outputting the boosted direct current; the rectifying circuit is used for rectifying the output of the direct current booster circuit into stable secondary direct current; the inverter output circuit comprises a full-bridge inverter circuit and a sine wave filter circuit, and the SPWM drive circuit is used for outputting a sine pulse width modulation signal SPWM so as to invert the secondary direct current into alternating current through the full-bridge inverter circuit. And the sine wave filter circuit filters the square wave alternating current output by the full-bridge inverter circuit into simulated sine wave alternating current. Therefore, the original square wave inversion is improved to output the simulated sine wave alternating current of which the top and the bottom are leveled in amplitude, and a component with a relatively low withstand voltage value can be selected for rectification filtering and inversion output, so that the cost is reduced. And meanwhile, a load containing a PFC circuit and an adapter can be better compatible.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply, in particular to a simulated sine wave inverter circuit. Background Art

[0002] A car inverter is a device that can convert battery voltage such as DC12V, DC24V or DC36V into AC220V or AC110V. Most electrical appliances require high-voltage AC power supply. A car inverter can facilitate users to use various electrical appliances in the car.

[0003] At present, the inverters on the market are mainly square wave inverters and pure sine wave inverters. The output waveform of low-power (less than 300W) car inverters is generally square wave pulses. The inherent disadvantage of square wave waveforms is that they have a large impact on the current of the adapter. With the development of electronic technology and the popularization of PD fast charging, portable electronic products such as laptops are now generally equipped with PD fast charging. The trend of increasing the power of adapters is becoming more and more obvious. At the same time, adapters with power exceeding 75W need to have PFC (Power Factor Correction) circuits. Such adapters are not suitable for use on square wave inverters. It will trigger the protection function of the inverter. At the same time, the PFC circuit of the adapter will also emit a sharp and piercing current whistling sound, which will affect the life of the electrical appliances. Using a pure sine wave inverter can be well compatible with adapters with PFC, but the pure sine wave inverter is expensive, and the overall cost-effectiveness of using it on a small power inverter is poor. The cost pressure of using it on a small power of 250W is very high. Utility Model Content

[0004] The utility model aims to solve one of the technical problems in the related art at least to a certain extent. To this end, one purpose of the utility model is to provide a simulated sine wave inverter circuit.

[0005] To achieve the above object, the simulated sine wave inverter circuit according to the embodiment of the utility model includes:

[0006] A DC boost circuit, the DC boost circuit is used to boost the input DC power and then output it;

[0007] A rectifier circuit, the rectifier circuit is connected to the output end of the DC boost circuit and is used to rectify the output of the DC boost circuit into a stable secondary DC power;

[0008] An inverter output circuit, wherein the inverter output circuit comprises a full-bridge inverter circuit and a sine wave filter circuit, wherein an input end of the full-bridge inverter circuit is connected to an output end of the rectifier circuit, and an output end of the full-bridge inverter circuit is connected to the sine wave filter circuit;

[0009] An SPWM drive circuit is connected to the inverter output circuit, the SPWM drive circuit is used to output a sinusoidal pulse width modulation signal SPWM to invert the secondary DC power into AC power through the full-bridge inverter circuit, and the sinusoidal wave filter circuit filters the square wave AC power output by the full-bridge inverter circuit into simulated sinusoidal wave AC power.

[0010] Further, according to an embodiment of the present invention, the simulated sinusoidal alternating current is a sinusoidal alternating current with flattened top and bottom amplitudes.

[0011] Further, according to an embodiment of the utility model, the sine wave filter circuit includes:

[0012] An inductor L3, one end of which is connected to an output end of the full-bridge inverter circuit;

[0013] Capacitor C50, one end of the capacitor C50 is connected to the other end of the inductor L3, and the other end of the capacitor C50 is connected to the other output end of the full-bridge inverter circuit.

[0014] Furthermore, according to an embodiment of the present utility model, the DC boost circuit comprises:

[0015] A push-pull boost circuit, wherein the input end of the push-pull boost circuit is connected to the input DC output end, and the output end of the push-pull boost circuit is connected to the output end of the rectifier circuit;

[0016] A complementary PWM drive circuit, wherein the complementary PWM drive circuit is connected to the push-pull boost circuit;

[0017] The front-stage control circuit includes a front-end controller U1, and the front-end controller U1 is connected to the complementary PWM drive circuit to control the complementary PWM drive circuit to output two complementary PWM pulse drive signals to drive the push-pull boost circuit to boost the input DC power and output it.

[0018] Furthermore, according to an embodiment of the present utility model, the simulated sine wave inverter circuit further includes:

[0019] A secondary voltage closed-loop feedback circuit is connected to the secondary DC output terminal of the rectifier circuit and the front-end controller U1 respectively. The secondary voltage closed-loop feedback circuit is used to feed back the voltage error signal of the secondary DC to the front-end controller U1. The front-end controller U1 is used to adjust the dead time of the complementary two-way PWM pulse drive signal according to the voltage error signal fed back by the secondary DC, so as to maintain the output of the secondary DC at a stable voltage value.

[0020] Further, according to an embodiment of the utility model, the secondary voltage closed-loop feedback circuit includes:

[0021] A secondary voltage detection circuit, the secondary voltage detection circuit is connected to the secondary DC output terminal of the rectifier circuit to detect and output the secondary DC;

[0022] A three-terminal comparator U3, wherein an input terminal of the three-terminal comparator U3 is connected to an output terminal of the secondary voltage detection circuit to generate a secondary voltage error signal;

[0023] The optocoupler U2 is connected to the three-terminal comparator U3 to feed back the secondary voltage error signal to the dead time setting terminal of the front-end controller U1.

[0024] Furthermore, according to an embodiment of the utility model, the simulated sinusoidal wave inverter circuit also includes an input voltage detection circuit, which is respectively connected to the voltage output end of the input direct current and the positive input end of the error amplifier of the front-end controller U1, and the inverting input end of the error amplifier of the front-end controller U1 is connected to a first reference voltage. The front-end controller U1 is also used to adjust the complementary two-way PWM pulse drive signal according to the feedback voltage value of the input direct current and the first reference voltage.

[0025] Furthermore, according to an embodiment of the present utility model, the simulated sine wave inverter circuit further includes:

[0026] A current detection circuit, the current detection circuit is connected to the inverter output circuit to detect the inverter output current;

[0027] A post-stage control circuit is connected to the current detection circuit and the SPWM drive circuit respectively to control the SPWM drive circuit to output the sinusoidal pulse width modulation signal SPWM and perform load overcurrent protection.

[0028] Further, according to an embodiment of the utility model, the push-pull boost circuit includes:

[0029] Transformer T1, wherein the middle joint of the primary coil of the transformer T1 is connected to the input DC output terminal, and the two ends of the secondary coil of the transformer T1 are respectively connected to the rectifier circuit;

[0030] a first MOS transistor Q3, wherein a drain of the first MOS transistor Q3 is connected to one end of the primary coil of the transformer T1, and a source of the first MOS transistor Q3 is connected to a reference ground;

[0031] a second MOS transistor Q6, wherein the drain of the second MOS transistor Q6 is connected to the other end of the primary coil of the transformer T1, and the source of the second MOS transistor Q6 is connected to the reference ground;

[0032] The gate of the first MOS transistor Q3 and the gate of the second MOS transistor Q6 are respectively connected to the two PWM pulse drive signal output ends of the complementary PWM drive circuit.

[0033] Further, according to an embodiment of the utility model, the complementary PWM drive circuit includes: a first drive circuit and a second drive circuit, and the first drive circuit and the second drive circuit are respectively connected to the two PWM control signal output ends of the front-end controller U1 to convert the two PWM control signals into two complementary PWM pulse drive signals.

[0034] The simulated sine wave inverter circuit provided by the embodiment of the utility model is used to output the input direct current after boosting through the direct current boost circuit; the rectifier circuit is connected to the output end of the direct current boost circuit, and is used to rectify the output of the direct current boost circuit into a stable secondary direct current; the inverter output circuit includes a full-bridge inverter circuit and a sine wave filter circuit, the input end of the full-bridge inverter circuit is connected to the output end of the rectifier circuit, and the output end of the full-bridge inverter circuit is connected to the sine wave filter circuit; the SPWM drive circuit is connected to the inverter output circuit, and the SPWM drive circuit is used to output a sinusoidal pulse width modulation signal SPWM, so as to invert the secondary direct current into alternating current through the full-bridge inverter circuit, and the sine wave filter circuit filters the square wave alternating current output by the full-bridge inverter circuit into simulated sinusoidal alternating current. In this way, the original square wave inverter is improved to output simulated sine wave AC with flattened top and bottom amplitudes, which can reduce the withstand voltage of the components of the rectifier circuit and inverter output circuit. Components with lower withstand voltage can be selected for use as rectifier filter and inverter output. At the same time, it can be better compatible with loads and adapters containing PFC circuits. In addition, compared with pure sine wave inverters, it can effectively save costs while ensuring load compatibility, and has great advantages in small power inverters within 300W. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The circuit structure diagram of the simulated sine wave inverter provided by the utility model;

[0036] Figure 2 A schematic diagram of the circuit structure of a simulated sine wave inverter provided by the utility model;

[0037] Figure 3 A schematic diagram of the secondary voltage closed-loop feedback circuit structure provided by the utility model;

[0038] Figure 4 This is a schematic diagram of the structure of the front-stage control circuit, complementary PWM drive circuit and input voltage detection circuit provided by the utility model;

[0039] Figure 5 A schematic diagram of the SPWM drive circuit structure provided by the utility model;

[0040] Figure 6 This is a schematic diagram of the structure of the post-stage control circuit provided by the utility model.

[0041] Reference numerals:

[0042] DC input interface 1;

[0043] Overload protection circuit 2;

[0044] Push-pull boost circuit 3;

[0045] Complementary PWM drive circuit 4;

[0046] Rectification circuit 5;

[0047] Secondary voltage closed loop feedback circuit 6;

[0048] Inverter output circuit 7;

[0049] SPWM driving circuit 8;

[0050] Current detection circuit 9;

[0051] Input voltage detection circuit 10;

[0052] Pre-stage control circuit 11;

[0053] Post-stage control circuit 12;

[0054] AC output interface 13;

[0055] A first reference voltage circuit 14;

[0056] Dead time bias circuit 15.

[0057] The realization of the purpose, functional features and advantages of the utility model will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0058] In order to make the technical personnel in the technical field better understand the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described in combination with the drawings in the embodiment of the present invention. Unless otherwise defined, all technical and scientific terms used in this article have the same meaning as those commonly understood by the technical personnel in the technical field of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0059] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0060] See also Figure 1 , Figure 2 and Figure 5 The embodiment of the utility model provides a simulated sinusoidal wave inverter circuit, comprising: a DC boost circuit, a rectifier circuit 5, an inverter output circuit 7 and an SPWM drive circuit 8, wherein the DC boost circuit is used to boost the input DC power and output it; Figure 1 and Figure 2 As shown in , the input DC power can be introduced through a DC input interface 1, and the DC input interface 1 can be connected to the DC12V, DC24V or DC36V DC power output terminal of the car battery to introduce the input DC power. An overload protection circuit 2 may also be provided between the DC input interface 1 and the DC boost circuit, and the overload protection circuit 2 may include a fuse F1 and a fuse F2 to protect the power supply circuit from overload. The input DC power is boosted and then output by the DC boost circuit. Since the power output of the transformer is not a stable DC power, the power output of the transformer needs to be rectified into a stable DC power. The rectifier circuit 5 is connected to the output terminal of the DC boost circuit, and is used to rectify the output of the DC boost circuit into a stable secondary DC power; as shown in FIG. Figure 2 As shown in the figure, the rectifier circuit 5 may include a diode D1, a diode D2, a diode D5, a diode D8 and a capacitor C35. The diode D1, the diode D2, the diode D5 and the diode D8 form a full-bridge rectifier circuit 5, and the output of the DC boost circuit is rectified and output to the capacitor C35. After further voltage stabilization by the capacitor C35, a stable secondary DC power can be output.

[0061] The inverter output circuit 7 includes a full-bridge inverter circuit and a sine wave filter circuit, the input end of the full-bridge inverter circuit is connected to the output end of the rectifier circuit 5, and the output end of the full-bridge inverter circuit is connected to the sine wave filter circuit; the SPWM drive circuit 8 is connected to the inverter output circuit 7, and the SPWM drive circuit 8 is used to output a sinusoidal pulse width modulation signal SPWM, so as to invert the secondary direct current into alternating current through the full-bridge inverter circuit, and the sine wave filter circuit filters the square wave alternating current output by the full-bridge inverter circuit into a simulated sinusoidal alternating current.

[0062] like Figure 2 As shown in , by adding a sine wave filter circuit to the inverter H bridge, the sine wave filter circuit may include an LC filter element. When the AC passes through zero, the LC filter circuit modulates the rise and fall speed of the SPWM modulated AC voltage output by the bridge arm, so that it rises and falls slowly in a manner close to a sine wave. In this way, the original square wave inverter is improved, and the voltage is allowed to rise smoothly at the zero point of the AC output alternating current, similar to the waveform of a sine wave, and the peak is flattened after rising to a certain amplitude and then slowly falls. As a result, the withstand voltage of the components of the rectifier circuit 5 and the inverter output circuit 7 can be reduced, and components with lower withstand voltage values ​​can be selected for use as rectifier filtering and inverter output. Output simulated sine wave AC with flattened top and bottom amplitudes. It can be better compatible with loads and adapters containing PFC circuits. In addition, compared with a pure sine wave inverter, it can effectively save costs while ensuring load compatibility, and has great advantages in small power inverters within 300W. In this way, the current and voltage of the PFC circuit follow each other in phase. Because the voltage at the zero-crossing position changes slowly, it is also very compatible with inductive devices such as motors and oxygen generators. In terms of comprehensive cost performance, it is much better than square wave and pure sine wave inverters.

[0063] Among them, Figure 2 As shown in , the sine wave filter circuit includes: an inductor L3 and a capacitor C50, one end of the inductor L3 is connected to an output end of the full-bridge inverter circuit; one end of the capacitor C50 is connected to the other end of the inductor L3, and the other end of the capacitor C50 is connected to the other output end of the full-bridge inverter circuit. The inductor L3 and the capacitor C50 can form an LC filter circuit to filter the SPWM modulated power output by the full-bridge inverter circuit and then output it. In this way, when the AC passes through zero, the LC filter circuit modulates the rise and fall speed of the SPWM modulated AC voltage output by the bridge arm, so that it rises and falls slowly in a manner close to a sine wave.

[0064] Among them, Figure 2As shown in, the full-bridge inverter circuit includes a MOS tube Q10, a MOS tube Q21, a MOS tube Q11 and a MOS tube Q22, the drain of the MOS tube Q10 is connected to the secondary DC positive terminal, the source of the MOS tube Q10 is connected to the drain of the MOS tube Q21, the source of the MOS tube Q21 is connected to the reference ground or the source of the MOS tube Q21 is connected to the reference ground through a current detection resistor, the drain of the MOS tube Q11 is connected to the secondary DC positive terminal, and the MOS tube The source of Q11 is connected to the drain of the MOS tube Q22, the source of the MOS tube Q21 is connected to the source of the MOS tube Q21, one end of the inductor L3 is connected to the source of the MOS tube Q10, the other end of the inductor L3 is connected to one end of the capacitor C50, and the other end of the capacitor C50 is connected to the source of the MOS tube Q11; the SPWM drive circuit 8 is connected to the gates of the MOS tube Q10, the MOS tube Q21, the MOS tube Q11, and the MOS tube Q22 respectively. The MOS tube Q10, the MOS tube Q21, the MOS tube Q11, and the MOS tube Q22 form an H-bridge circuit, and the gates of the MOS tube Q10, the MOS tube Q21, the MOS tube Q11, and the MOS tube Q22 are respectively connected to the sinusoidal pulse width modulation signal SPWM. In this way, the secondary direct current can be inverted and SPWM modulated and then output. By forming an LC filter circuit, the waveform can be shaped and filtered into a waveform similar to a sine wave.

[0065] like Figure 5 As shown in , the SPWM drive circuit 8 may include drivers IC4 and IC5, which, under the action of control signals (FD_UP, FD_DW, MD_DW, MD_UP), output sinusoidal pulse width modulation signals SPWM to the inverter circuit through FD_Ho, FD_Lo, MD_Ho, and MD_Lo, and modulate the full-bridge inverter circuit with the sinusoidal pulse width modulation signal SPWM. In this way, the inverter output circuit can be driven to invert and SPWM-modulate the secondary DC power for output.

[0066] See also Figure 1 and Figure 2The DC boost circuit includes: a push-pull boost circuit 3, a complementary PWM drive circuit 4 and a front-stage control circuit 11, wherein the input end of the push-pull boost circuit 3 is connected to the input DC output end, and the output end of the push-pull boost circuit 3 is connected to the output end of the rectifier circuit 5; the complementary PWM drive circuit 4 is connected to the push-pull boost circuit 3; the front-stage control circuit 11 includes a front-end controller U1, which is connected to the complementary PWM drive circuit 4 to control the complementary PWM drive circuit 4 to output two complementary PWM pulse drive signals to drive the push-pull boost circuit 3 to boost the input DC and output it. In order to provide a larger power range for the back-end circuit, the push-pull boost circuit 3 structure is used in the embodiment of the utility model to transform the input DC and output it.

[0067] Among them, Figure 2 As shown in , the push-pull boost circuit 3 includes: a transformer T1, a first MOS transistor Q3 and a second MOS transistor Q6, the middle joint of the primary coil of the transformer T1 is connected to the input DC output terminal, and the two ends of the secondary coil of the transformer T1 are respectively connected to the rectifier circuit 5; the drain of the first MOS transistor Q3 is connected to one end of the primary coil of the transformer T1, and the source of the first MOS transistor Q3 is connected to the reference ground; the drain of the second MOS transistor Q6 is connected to the other end of the primary coil of the transformer T1, and the source of the second MOS transistor Q6 is connected to the reference ground; the gate of the first MOS transistor Q3 and the gate of the second MOS transistor Q6 are respectively connected to the two PWM pulse drive signal output ends of the complementary PWM drive circuit 4. The working process of the push-pull boost circuit 3 is that the complementary PWM pulse width modulation signals can be respectively connected through the PWM1 signal terminal and the PWM2 signal terminal, so that the first MOS transistor Q3 and the second MOS transistor Q6 can be alternately turned on. When the first MOS transistor Q3 is turned on and the second MOS transistor Q6 is turned off, the input DC power is output from the middle joint of the transformer to the first MOS transistor Q3 and then flows to the circuit ground. When the second MOS transistor Q6 is turned on and the first MOS transistor Q3 is turned off, the input DC power is output from the middle joint of the transformer to the second MOS transistor Q6 and then flows to the circuit ground. In this way, after push-pull modulation of the input DC power, it is output to the rectifier circuit 5 through the secondary coil of the transformer T1 for rectification and filtering as a stabilized DC power output.

[0068] Among them, see Figure 4The complementary PWM drive circuit 4 includes: a first drive circuit and a second drive circuit, the first drive circuit and the second drive circuit are respectively connected to the two PWM control signal output ends of the front-end controller U1 to convert the two PWM control signals into two complementary PWM pulse drive signals. The two output signals of the front-end controller U1 can be converted into corresponding drive signals through the first drive circuit and the second drive circuit, so as to drive the first MOS tube Q3 and the second MOS tube Q6 of the push-pull boost circuit 3 to be quickly turned on and off.

[0069] Among them, Figure 4 As shown in , the first driving circuit includes: a transistor Q1, the base of the transistor Q1 is connected to the first PWM signal output terminal of the front-end controller U1, the collector of the transistor Q1 is connected to the reference ground, the emitter of the transistor Q1 is connected to the cathode of the diode D1, the anode of the diode D1 is connected to the base of the transistor Q1, the base of the transistor Q1 is also connected to the reference ground through a resistor R13, and the emitter of the transistor Q1 is also connected to the reference ground through a resistor R15. See as Figure 2 and Figure 4 The working process of the first driving circuit is that when the PWM signal outputted by the front-end controller U1 through the E2 pin is a high-level signal, the high-level signal can act on the gate of the transistor Q3 through the diode D1, so that the transistor Q3 is turned on. On the contrary, when the E2 pin of the front-end controller U1 is a low-level signal, the gate of the transistor Q3 can be quickly discharged through the transistor Q1 and the resistor R15, so that the transistor Q3 is turned off, thereby realizing the on or off driving control of the transistor Q1.

[0070] Among them, Figure 4 As shown in, the second driving circuit includes: a transistor Q2, the base of the transistor Q2 is connected to the second PWM signal output terminal of the front-end controller U1, the collector of the transistor Q2 is connected to the reference ground, the emitter of the transistor Q2 is connected to the cathode of the diode D2, the anode of the diode D2 is connected to the base of the transistor Q2, the base of the transistor Q2 is also connected to the reference ground through a resistor R14, and the emitter of the transistor Q2 is also connected to the reference ground through a resistor R16; the emitter of the transistor Q1 and the emitter of the transistor Q1 are used to output two complementary PWM pulse driving signals. The circuit structure and working principle of the second driving circuit are basically the same as those of the first driving circuit, and will not be repeated here.

[0071] See also Figures 1 to 3, the simulated sine wave inverter circuit also includes: a secondary voltage closed-loop feedback circuit 6, the secondary voltage closed-loop feedback circuit 6 is connected to the secondary DC output end of the rectifier circuit 5 and the front-end controller U1 respectively, the secondary voltage closed-loop feedback circuit 6 is used to feed back the voltage error signal of the secondary DC to the front-end controller U1, and the front-end controller U1 is used to adjust the dead time of the complementary two-way PWM pulse drive signal according to the voltage error signal fed back by the secondary DC, so as to maintain the output of the secondary DC at a stable voltage value. In the embodiment of the utility model, by adding a voltage closed-loop control to the secondary boost output, sampling the secondary output voltage to adjust the primary boost PWM to achieve a voltage closed loop, so that the secondary boost is stabilized at a set value without changing with the input voltage, thereby reducing the voltage stress of the secondary filter capacitor and the H-bridge inverter circuit. In this way, the boosted energy storage capacitor and the MOS tube voltage used in the full-bridge inverter circuit (H-bridge circuit of the inverter output circuit 7) can use devices with lower withstand voltage. In addition, since the LC device of the LC filter circuit of the inverter output circuit 7 works only within a period of time when it crosses zero, the actual working ripple current is much smaller than that of the pure sine wave inverter, so the specification of the LC filter component can be reduced by one level for use.

[0072] Among them, see Figure 3 The secondary voltage closed-loop feedback circuit 6 includes: a secondary voltage detection circuit, a three-terminal comparator U3 and an optical coupler U2. The secondary voltage detection circuit is connected to the secondary DC output terminal of the rectifier circuit 5 to detect and output the secondary DC power; Figure 3 As shown in , the secondary voltage detection circuit may include a voltage dividing resistor R22, a resistor R27 and a resistor R32, so that the secondary direct current can be output to the three-terminal comparator U3 after voltage division detection.

[0073] The input end of the three-terminal comparator U3 is connected to the output end of the secondary voltage detection circuit to generate a secondary voltage error signal; the voltage comparison end of the three-terminal comparator U3 is connected to the voltage detection output end of the secondary voltage detection circuit, the anode end of the three-terminal comparator U3 is connected to the reference ground, the cathode end of the three-terminal comparator U3 is connected to one end of the resistor R25, the other end of the resistor R25 is connected to one end of the resistor R19, and the other end of the resistor R19 is connected to the power supply; a reference voltage is provided in the three-terminal comparator U3, and the voltage value output by the voltage division of the secondary voltage detection circuit can be compared with the reference voltage and then output to generate a corresponding secondary voltage error feedback signal.

[0074] The optocoupler U2 is connected to the three-terminal comparator U3 to feed back the secondary voltage error signal to the dead time setting terminal of the front-end controller U1. The anode of the light-emitting diode terminal of the optocoupler U2 is connected to the other end of the resistor R25, the cathode of the light-emitting diode terminal of the optocoupler U2 is connected to the one end of the resistor R25, the collector of the phototransistor terminal of the optocoupler U2 is connected to the reference voltage, and the emitter of the phototransistor terminal of the optocoupler U2 is connected to the PWM pulse signal lock control terminal of the front-end controller U1. When the secondary direct current is higher than the set value, the cathode terminal and the anode terminal of the three-terminal comparator U3 generate a large current, so that the optocoupler U2 emits light, and then the secondary voltage error feedback signal is fed back to the dead time setting terminal of the front-end controller U1 through the 7500_DTC signal terminal. The front-end controller U1 adjusts the dead time of the complementary two-way PWM control signal, thereby adjusting the boost output of the adjustable push-pull boost circuit 3, and then stabilizing the secondary direct current at the set voltage value.

[0075] See also Figure 3 and Figure 4 The secondary voltage closed-loop feedback circuit 6 includes a dead time bias circuit 15, which is connected to the PWM pulse signal lock control terminal of the front-end controller U1 to set the minimum dead time of the two complementary PWM control signals output by the front-end controller U1. Figure 4 As shown in , the dead time bias circuit 15 includes: a resistor R12 and a resistor R8, one end of the resistor R12 is connected to the reference voltage, and the other end of the resistor R12 is connected to the PWM pulse signal lock control end of the front-end controller U1; one end of the resistor R8 is connected to the other end of the resistor R12, and the other end of the resistor R8 is connected to the reference ground. A voltage divider circuit is formed between the resistor R12 and the resistor R8, and a bias voltage is provided to the PWM pulse signal lock control end of the front-end controller U1 after dividing the 5V reference voltage, thereby achieving the minimum dead time of the two complementary PWM control signals output by the front-end controller U1. The minimum dead time can ensure the alternating conduction of the first MOS tube Q3 and the MOS tube Q4 of the push-pull boost circuit 3, and avoid the occurrence of simultaneous conduction.

[0076] See also Figure 1 and Figure 4, the simulated sine wave inverter circuit also includes an input voltage detection circuit 10, the input voltage detection circuit 10 is respectively connected to the voltage output end of the input direct current and the positive phase input end of the error amplifier of the front-end controller U1, the inverting input end of the error amplifier of the front-end controller U1 is connected to the first reference voltage, and the front-end controller U1 is also used to adjust the complementary two-way PWM pulse drive signal according to the feedback voltage value of the input direct current and the first reference voltage. Since the input direct current can be DC12V, DC24V or DC36V direct current. The input voltage value can be detected by the input voltage detection circuit 10 and fed back to the positive phase input end of the error amplifier of the front-end controller U1. In this way, after the error amplifier performs calculations, it is used as a PWM adjustment signal to adjust the two-way PWM pulse drive signals, so that the output of the boost circuit is a stable voltage value.

[0077] Among them, Figure 4 As shown in , the input voltage detection circuit 10 includes: a resistor R1 and a resistor R2, one end of the resistor R1 is connected to the input DC power, and the other end of the resistor R1 is connected to the positive phase input end of the error amplifier of the front-end controller U1; one end of the resistor R2 is connected to the other end of the resistor R1, and the other end of the resistor R2 is connected to the reference ground. Figure 4 As shown in , after the input DC power VINA+ passes through the resistor R8, it is divided by the voltage divider circuit formed by the resistor R1 and the resistor R2, and then output to the non-phase input terminal of the error amplifier of the front-end controller U1.

[0078] See also Figure 1 , Figure 2 and Figure 6 The simulated sine wave inverter circuit further includes: a current detection circuit 9 and a post-stage control circuit 12, wherein the current detection circuit 9 is connected to the inverter output circuit 7 to detect the inverter output current; Figure 2As shown in , the current detection circuit 9 may include one or more resistors R8, R82 and R83. The current detection circuit 9 is connected in series to the return current of the output AC power. In this way, the output current can be detected, and the post-stage control circuit 12 is respectively connected to the current detection circuit 9 and the SPWM drive circuit 8 to control the SPWM drive circuit 8 to output the sinusoidal pulse width modulation signal SPWM and perform load overcurrent protection. In normal operation, the post-stage control circuit 12 outputs the SPWM control signal to the SPWM drive circuit 8, so that the SPWM drive circuit 8 generates a sinusoidal pulse width modulation signal SPWM, which acts on the H-bridge inverter circuit, thereby performing a sinusoidal pulse width modulation signal SPWM inversion output on the secondary DC power, and filtering it into a similar sinusoidal wave AC power through the LC filter circuit to supply power to the load. When the current detection circuit 9 detects that the load is short-circuited and overcurrent, the post-stage control circuit 12 controls the inverter output circuit 7 to stop the AC power output to perform short-circuit overcurrent protection.

[0079] like Figure 6 As shown in , the post-stage control circuit 12 may include a controller IC2, which may output an SPWM control signal to the SPWM drive circuit 8 through the FD_UP, FD_DW, MD_DW, and MD_UP signal terminals, and output a drive signal to the inverter output circuit 7 through the SPWM drive circuit 8 to drive the inverter output circuit to invert and SPWM modulate the secondary DC power for output. The controller IC2 may also collect the output current signal value of the current detection circuit 9 through the IFB / SC signal terminal, and perform safety protection control such as short circuit and overload.

[0080] The above are only embodiments of the utility model, but they do not limit the patent scope of the utility model. Although the utility model is described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions recorded in the above specific implementations, or replace some of the technical features therein with equivalents. Any equivalent structure made by using the contents of the utility model specification and drawings, directly or indirectly used in other related technical fields, is also within the scope of protection of the utility model patent.

[0081] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0082] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are illustrative and cannot be understood as limitations on the present invention. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A simulated sine wave inverter circuit, characterized in that: include: A DC boost circuit, the DC boost circuit is used to boost the input DC power and then output it; A rectifier circuit, the rectifier circuit is connected to the output end of the DC boost circuit and is used to rectify the output of the DC boost circuit into a stable secondary DC power; An inverter output circuit, wherein the inverter output circuit comprises a full-bridge inverter circuit and a sine wave filter circuit, wherein an input end of the full-bridge inverter circuit is connected to an output end of the rectifier circuit, and an output end of the full-bridge inverter circuit is connected to the sine wave filter circuit; An SPWM drive circuit is connected to the inverter output circuit, the SPWM drive circuit is used to output a sinusoidal pulse width modulation signal SPWM to invert the secondary DC power into AC power through the full-bridge inverter circuit, and the sinusoidal wave filter circuit filters the square wave AC power output by the full-bridge inverter circuit into simulated sinusoidal wave AC power.

2. The simulated sine wave inverter circuit according to claim 1, characterized in that: The simulated sinusoidal alternating current is a sinusoidal alternating current with flattened top and bottom amplitudes.

3. The simulated sine wave inverter circuit according to claim 1 or 2, characterized in that: The sine wave filter circuit comprises: an inductor (L3), one end of the inductor (L3) being connected to an output end of the full-bridge inverter circuit; A capacitor (C50), one end of the capacitor (C50) is connected to the other end of the inductor (L3), and the other end of the capacitor (C50) is connected to the other output end of the full-bridge inverter circuit.

4. The simulated sine wave inverter circuit according to claim 1, characterized in that: The DC boost circuit comprises: A push-pull boost circuit, wherein the input end of the push-pull boost circuit is connected to the input DC output end, and the output end of the push-pull boost circuit is connected to the output end of the rectifier circuit; A complementary PWM drive circuit, wherein the complementary PWM drive circuit is connected to the push-pull boost circuit; A front-stage control circuit, the front-stage control circuit comprising a front-end controller (U1), the front-end controller (U1) being connected to the complementary PWM drive circuit to control the complementary PWM drive circuit to output two complementary PWM pulse drive signals to drive the push-pull boost circuit to boost the input direct current and then output it.

5. The simulated sine wave inverter circuit according to claim 4, characterized in that: Also includes: A secondary voltage closed-loop feedback circuit, the secondary voltage closed-loop feedback circuit is respectively connected to the secondary direct current output end of the rectifier circuit and the front-end controller (U1), the secondary voltage closed-loop feedback circuit is used to feed back the voltage error signal of the secondary direct current to the front-end controller (U1), and the front-end controller (U1) is used to adjust the dead time of the two complementary PWM pulse drive signals according to the voltage error signal fed back by the secondary direct current, so as to maintain the output of the secondary direct current at a stable voltage value.

6. The simulated sine wave inverter circuit according to claim 5, characterized in that: The secondary voltage closed-loop feedback circuit comprises: A secondary voltage detection circuit, the secondary voltage detection circuit is connected to the secondary DC output terminal of the rectifier circuit to detect and output the secondary DC; A three-terminal comparator (U3), wherein an input end of the three-terminal comparator (U3) is connected to an output end of the secondary voltage detection circuit to generate a secondary voltage error signal; An optical coupler (U2), the optical coupler (U2) is connected to the three-terminal comparator (U3) to feed back the secondary voltage error signal to the dead time setting terminal of the front-end controller (U1).

7. The simulated sine wave inverter circuit according to claim 4, characterized in that: The invention also comprises an input voltage detection circuit, wherein the input voltage detection circuit is respectively connected to the voltage output end of the input direct current and the positive phase input end of the error amplifier of the front-end controller (U1); the negative phase input end of the error amplifier of the front-end controller (U1) is connected to a first reference voltage; the front-end controller (U1) is also used for adjusting the complementary two-channel PWM pulse drive signals according to the feedback voltage value of the input direct current and the first reference voltage.

8. The simulated sine wave inverter circuit according to claim 1, characterized in that: Also includes: A current detection circuit, the current detection circuit is connected to the inverter output circuit to detect the inverter output current; A post-stage control circuit is connected to the current detection circuit and the SPWM drive circuit respectively to control the SPWM drive circuit to output the sinusoidal pulse width modulation signal SPWM and perform load overcurrent protection.

9. The simulated sine wave inverter circuit according to claim 4, characterized in that: The push-pull boost circuit comprises: A transformer (T1), wherein the middle joint of the primary coil of the transformer (T1) is connected to the input DC output terminal, and the two ends of the secondary coil of the transformer (T1) are respectively connected to the rectifier circuit; a first MOS transistor (Q3), wherein a drain of the first MOS transistor (Q3) is connected to one end of the primary coil of the transformer (T1), and a source of the first MOS transistor (Q3) is connected to a reference ground; a second MOS transistor (Q6), wherein a drain of the second MOS transistor (Q6) is connected to the other end of the primary coil of the transformer (T1), and a source of the second MOS transistor (Q6) is connected to a reference ground; The gate of the first MOS transistor (Q3) and the gate of the second MOS transistor (Q6) are respectively connected to the two PWM pulse drive signal output ends of the complementary PWM drive circuit.

10. The simulated sine wave inverter circuit according to claim 9, characterized in that: The complementary PWM drive circuit comprises: a first drive circuit and a second drive circuit, wherein the first drive circuit and the second drive circuit are respectively connected to two PWM control signal output ends of the front-end controller (U1) to convert the two PWM control signals into two complementary PWM pulse drive signals.

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