High and low frequency combined two-stage four-tube DC-AC conversion system

Abstract

The invention discloses a high and low frequency combined two-stage four-tube DC-AC conversion system. The system mainly comprises a non-isolated DC / pulsating DC conversion circuit unit, an isolated pulsating DC / AC conversion circuit unit, a first driving circuit unit, a second driving circuit unit and a digital control circuit unit. The digital control circuit unit calculates an SPWM control pulse width and a power frequency cycle time switching point according to a voltage detection signal fed back by a system, and sends a control instruction to the first drive circuit unit and the second drive circuit unit. The non-isolated DC / pulsating DC conversion circuit unit completes conversion from a DC input voltage to a sine pulsating DC voltage in a buck / boost combination mode, and the isolated pulsating DC / AC conversion circuit unit completes conversion from the sine pulsating DC voltage to a power frequency AC voltage in a two-tube push-pull mode isolated by a transformer according to a power frequency period. The system has the advantages of low switching loss, wide input direct-current voltage range, high output alternating-current voltage precision, high waveform quality and the like.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics technology, relates to power conversion technology, and in particular to a two-stage four-tube DC-AC conversion system combining high and low frequencies. Background Art

[0002] Existing DC / AC converters convert DC to AC by controlling the inverter bridge with high-frequency SPWM (Sine Wave Pulse Width Modulation) to convert DC into a pulse wave with a width modulated by sinusoidal AC. After proper filtering, the output is a sinusoidal AC signal. The existing technology has the following shortcomings:

[0003] 1. The input voltage range of the existing DC / AC converter is not wide enough due to the fixed isolation transformer ratio and the limited PWM pulse duty cycle of the inverter bridge;

[0004] 2. The SPWM operating frequency of existing DC / AC converters is relatively low, requiring large capacitive and inductive components, which results in a large device size.

[0005] 3. The SPWM operating frequency of existing DC / AC converters is relatively low, and the voltage output accuracy and waveform smoothness are limited;

[0006] 4. When the inverter bridge of the existing DC / AC converter further increases the operating frequency of the switching tube, the switching tube in the same bridge arm is prone to shoot-through, causing damage to components;

[0007] 5. The control of existing DC / AC converters is relatively complex and the cost of digital implementation is high. Summary of the Invention

[0008] The present invention aims to solve the technical problems existing in the above-mentioned existing DC / AC converters and provide a two-stage four-tube DC-AC conversion system combining high and low frequencies.

[0009] The specific technical solution adopted by the present invention is: a two-stage four-tube DC-AC conversion system with a combination of high and low frequencies, including a non-isolated DC / pulsating DC conversion circuit unit, an isolated pulsating DC / AC conversion circuit unit, a first drive circuit unit, a second drive circuit unit, a digital control circuit unit, and a power supply circuit unit;

[0010] The non-isolated DC / pulsating DC conversion circuit unit is configured to convert a DC input voltage into a sinusoidal pulsating DC voltage in a buck / boost combination manner under high-frequency SPWM control, input the converted sinusoidal pulsating DC voltage to the isolated pulsating DC / AC conversion circuit unit, and feed back a voltage detection signal;

[0011] The isolated pulsating DC / AC conversion circuit unit is configured to convert a sinusoidal pulsating DC voltage into an industrial frequency AC voltage in a two-transistor push-pull manner with transformer isolation according to the industrial frequency cycle, output the converted industrial frequency AC voltage, and feed back a voltage detection signal;

[0012] The first driving circuit unit is configured to receive an SPWM control pulse signal to drive the opening and closing of two step-up / step-down switching tubes of the non-isolated DC / pulsating DC conversion circuit unit;

[0013] The second driving circuit unit is configured to receive a power frequency control pulse signal to drive the two push-pull switching tubes of the isolated pulsating DC / AC conversion circuit unit to turn on and off;

[0014] The digital control circuit unit is configured to calculate the SPWM control pulse width and the power frequency cycle time switching point according to the voltage detection signal fed back by the system, and generate a corresponding control pulse signal to drive the corresponding switch tube to turn on and off after passing through the first drive circuit unit and the second drive circuit unit;

[0015] The power supply circuit unit is configured to convert a DC input voltage into a DC voltage required by the system to supply power to the first driving circuit unit, the second driving circuit unit and the digital control circuit unit.

[0016] The two switching tubes of the non-isolated DC / pulsating DC conversion circuit unit are turned on and off under high-frequency SPWM control, while the two switching tubes of the isolated pulsating DC / AC conversion circuit unit operate at the industrial frequency, which greatly reduces switching losses, avoids the risk of switch tube shoot-through when using an inverter bridge, simplifies the control algorithm of the digital control circuit unit, and reduces control costs.

[0017] A more optimal solution is to further include a first conversion protection circuit unit, which is configured to isolate and process the voltage detection signal fed back from the non-isolated DC / pulsating DC conversion circuit unit, generate an intermediate-level DC input voltage detection signal, a DC input current detection signal, and an intermediate-level sinusoidal pulsating DC voltage detection signal, compare each signal with the corresponding reference voltage, and when the signal voltage is greater than the reference voltage, generate a high-level protection signal to control the first drive circuit unit to shut down the two step-up / step-down switching tubes in the non-isolated DC / pulsating DC conversion circuit unit; and feed the intermediate-level DC input voltage detection signal, DC input current detection signal, and intermediate-level sinusoidal pulsating DC voltage detection signal back to the digital control circuit unit for calculation of the SPWM control pulse width and generation of the control pulse signal. This solution can achieve real-time and reliable overvoltage and overcurrent protection for the non-isolated DC / pulsating DC conversion circuit unit.

[0018] A more optimal solution is to further include a second conversion protection circuit unit, which is configured to isolate and process the voltage detection signal fed back from the isolated pulsating DC / AC conversion circuit unit, generate an intermediate-level pulsating DC input voltage detection signal, a pulsating DC input current detection signal, and an intermediate-level AC output voltage detection signal, compare each signal with the corresponding reference voltage, and when the signal voltage is greater than the reference voltage, generate a high-level protection signal to control the second drive circuit unit to shut down the two push-pull switches of the isolated pulsating DC / AC conversion circuit unit; and feed back the intermediate-level pulsating DC input voltage detection signal, the pulsating DC input current detection signal, and the intermediate-level AC output voltage detection signal to the digital control circuit unit for calculation of the power frequency cycle time switching point and generation of the control pulse signal. This solution can achieve real-time and reliable overvoltage and overcurrent protection for the isolated pulsating DC / AC conversion circuit unit.

[0019] A more optimal solution further includes a first sensor and a second sensor. The first sensor is used to sense the temperature detection signal of the non-isolated DC / pulsating DC conversion circuit unit. The first conversion and protection circuit unit compares the temperature detection signal with a corresponding reference voltage. When the signal voltage is greater than the reference voltage, a high-level protection signal is generated, and the first driver circuit unit is controlled to shut down the two step-up / step-down switches in the non-isolated DC / pulsating DC conversion circuit unit. The first sensor feeds back the temperature detection signal to the digital control circuit unit. The second sensor is used to sense the temperature detection signal of the isolated pulsating DC / AC conversion circuit unit. The second conversion and protection circuit unit compares the temperature detection signal with a corresponding reference voltage. When the signal voltage is greater than the reference voltage, a high-level protection signal is generated, and the second driver circuit unit is controlled to shut down the two push-pull switches in the isolated pulsating DC / AC conversion circuit unit. The second sensor feeds back the temperature detection signal to the digital control circuit unit. This solution can achieve real-time and reliable overtemperature protection.

[0020] A better solution is that the non-isolated DC / pulsating DC conversion circuit unit includes a buck switch tube Q1, a boost switch tube Q2, a high-frequency inductor L1, a freewheeling diode D1, a unidirectional isolation diode D2, a filter capacitor C1, an input voltage sampling resistor and an output voltage sampling resistor; one end of the buck switch tube Q1 is used to connect to the DC input voltage, the other end of the buck switch tube Q1 is connected to one end of the high-frequency inductor L1 and the negative electrode of the freewheeling diode D1, and the control end of the buck switch tube Q1 is connected to the first drive circuit unit; one end of the boost switch tube Q2 is connected to the high-frequency The other end of the inductor L1 is connected to the positive electrode of the unidirectional isolation diode D2, the negative electrode of the isolation diode D2 is connected to one end of the filter capacitor C1, the other end of the boost switch tube Q2 is connected to the positive electrode of the freewheeling diode D1 and the other end of the filter capacitor C1 and is used to be connected to the ground end, the control end of the boost switch tube Q2 is connected to the first drive circuit unit, the input voltage sampling resistor is used to connect the input power supply and the ground end to collect and feedback the DC input voltage detection signal, and the output voltage sampling resistor is connected to one end of the capacitor C1 and the ground end to collect and feedback the sinusoidal pulsating DC voltage detection signal.

[0021] A better solution is that the isolated pulsating DC / AC conversion circuit unit includes a sinusoidal pulsating DC voltage sampling resistor, a push-pull switch tube Q3, a push-pull switch tube Q4, an industrial frequency transformer T1, a first buffer absorption circuit, a second buffer absorption circuit, a filter capacitor C4 and an AC output voltage sampling resistor; the source of the push-pull switch tube Q3 and the source of the push-pull switch tube Q4 are connected to each other and used to connect to the ground end, the drain of the push-pull switch tube Q3 and the opposite-name end of the first group of primary coils of the industrial frequency transformer T1, and the same-name end of the first group of primary coils of the industrial frequency transformer T1 is used to connect to the sinusoidal pulsating DC voltage, the control end of the push-pull switch tube Q3 is connected to the second drive circuit unit, and the first buffer absorption circuit is connected to the second drive circuit unit. In parallel with the first group of primary coils of the power frequency transformer T1; the drain of the push-pull switch tube Q4 is connected to the same-name end of the second group of primary coils of the power frequency transformer T1, and the opposite-name end of the second group of primary coils of the power frequency transformer T1 is used to connect to the sinusoidal pulsating DC voltage. The control end of the push-pull switch tube Q4 is connected to the second drive circuit unit, and the second buffer absorption circuit is connected in parallel with the second group of primary coils of the power frequency transformer T1; the secondary coil of the power frequency transformer T1 is connected in parallel with the filter capacitor C4, and the sinusoidal pulsating DC voltage sampling resistor is used to collect and feed back the sinusoidal pulse DC voltage detection signal; the AC output voltage sampling resistor is connected at both ends of the filter capacitor C4 to collect and feed back the AC output voltage detection signal.

[0022] Compared with the existing technology, this high- and low-frequency combined two-stage four-tube DC-AC conversion system has the following advantages:

[0023] (1) The DC / pulsating DC conversion main circuit adopts the buck / boost automatic switching mode, which makes the DC input voltage range wide.

[0024] (2) Detecting current through potential detection and calculation avoids the defect of large error caused by small signal when directly detecting current.

[0025] (3) The DC / pulsating DC conversion adopts a high-frequency SPWM control method with a high operating frequency, which makes the output voltage high in accuracy and good in waveform quality.

[0026] (4) The pulsating DC / AC conversion adopts a two-tube push-pull switching method to avoid the hidden danger of direct-through during inversion.

[0027] (5) The two switching tubes in the pulsating DC / AC conversion operate at the industrial frequency, which reduces switching losses and avoids the risk of shoot-through when using an inverter bridge.

[0028] (6) The protection circuit adopts analog circuit, which has good real-time performance and high reliability.

[0029] (7) Optocouplers are used to electrically isolate the control circuit from the main circuit, ensuring high circuit safety.

[0030] (8) The driving signal enhances the driving capability through the driving circuit, so that the switch tube is turned on with a deeper conduction degree and the loss is reduced.

[0031] (9) The main circuit is controlled by digital control, and the control algorithm has low implementation cost, strong flexibility and good intelligence.

[0032] (10) The input of the power supply circuit unit can be switched between multiple power supply levels and has a wide adaptable voltage range.

[0033] (11) The power supply circuit unit adopts a combination of switching power supply and linear power supply. The switching power supply makes the overall efficiency of the circuit high, and the linear power supply improves the working reliability and signal quality of the digital control circuit unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 , schematic diagram of the first module structure of the DC-AC conversion system of the present invention.

[0035] Figure 2 , circuit diagram of the non-isolated DC / pulsating DC conversion circuit unit in the present invention.

[0036] Figure 3 , circuit diagram of the isolated pulsating DC / AC conversion circuit unit in the present invention.

[0037] Figure 4 , circuit diagram of the first driving circuit unit in the present invention.

[0038] Figure 5 , circuit diagram of the second driving circuit unit in the present invention.

[0039] Figure 6 , schematic diagram of the second module structure of the DC-AC conversion system of the present invention.

[0040] Figure 7 , circuit diagram of the first conversion protection circuit unit in the present invention.

[0041] Figure 8 , circuit diagram of the second transformation protection circuit unit in the present invention.

[0042] Figure 9 , circuit diagram of the digital control circuit unit in the present invention.

[0043] Figure 10 , circuit diagram of the power supply circuit unit in the present invention.

[0044] Figure 11 , a control flow chart of the digital control circuit unit of the present invention.

[0045] Figure 12 , schematic diagram of control pulses output by the two driving circuit units in the present invention.

[0046] Figure 13 , DC / pulsating DC conversion output effect diagram of the non-isolated DC / pulsating DC conversion drive circuit unit in the present invention.

[0047] Figure 14 , a pulsating DC / AC conversion output effect diagram of the isolated pulsating DC / AC conversion circuit unit in the present invention. DETAILED DESCRIPTION

[0048] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0049] The following descriptions of the embodiments are made with reference to the accompanying diagrams to illustrate specific embodiments that can be implemented in this application. The "circuit unit" herein is a circuit module that performs a basic function. The serial numbers of the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The terms "connect", "connect", and "couple" mentioned in this application, unless otherwise specified, include direct or indirect electrical connections, and are intended to describe the signal transmission relationship between circuit units. The contents of the specification should be used for accurate understanding.

[0050] Example 1, please refer to Figure 1 , Figure 1 Schematic diagram of the module structure of the two-stage four-tube DC-AC conversion system with high and low frequency combination in this embodiment. Figure 1 As shown, this high- and low-frequency combined two-stage four-transistor DC-AC conversion system includes a non-isolated DC / pulsating DC conversion circuit unit, an isolated pulsating DC / AC conversion circuit unit, a first drive circuit unit, a second drive circuit unit, a digital control circuit unit, and a power supply circuit unit. The non-isolated DC / pulsating DC conversion circuit unit and the isolated pulsating DC / AC conversion circuit unit form a two-stage cascade structure of conversion circuit units. This differs from the existing DC-AC circuit structure that uses half-bridge and full-bridge inverter circuits. As a result, the present invention offers performance advantages that cannot be achieved by existing bridge-type DC-AC inverter circuit structures.

[0051] In this embodiment, the non-isolated DC / pulsating DC conversion circuit unit is configured to convert the DC input voltage into a sinusoidal pulsating DC voltage in a buck / boost combination according to the high-frequency SPWM control pulse signal, input the sinusoidal pulsating DC voltage to the isolated pulsating DC / AC conversion circuit unit, and simultaneously feed back a voltage detection signal to the digital control circuit unit. Figure 1 As shown, the input end of the non-isolated DC / pulsating DC conversion circuit unit is externally connected to the UIN-GIN port for receiving the external DC input voltage, and the output end is connected to the UDA-GIN intermediate port. The non-isolated DC / pulsating DC conversion circuit unit adopts the buck / boost automatic switching buck / boost mode to perform voltage and power conversion on the DC input voltage, so that the circuit unit can convert a wide range of DC input voltages. The two switching tubes adopt a high-frequency SPWM control method with a high operating frequency, which can improve the accuracy and waveform quality of the output sinusoidal pulsating DC voltage.

[0052] like Figure 2 As shown, preferably, the non-isolated DC / pulsating DC conversion circuit unit includes a buck switch tube Q1, a boost switch tube Q2, a high-frequency inductor L1, a freewheeling diode D1, a unidirectional isolation diode D2, a filter capacitor C1, an input voltage sampling resistor and an output voltage sampling resistor; one end of the buck switch tube Q1 is used to connect to the DC input voltage through the UIN-GIN port, the other end of the buck switch tube Q1 is connected to one end of the high-frequency inductor L1 and the negative electrode of the freewheeling diode D1, and the control end of the buck switch tube Q1 is connected to the first drive circuit unit; one end of the boost switch tube Q2 is connected to the other end of the high-frequency inductor L1 and the positive electrode of the unidirectional isolation diode D2, the negative electrode of the isolation diode D2 and one end of the filter capacitor C1, and the other end of the boost switch tube Q2 is connected to the positive electrode of the freewheeling diode D1. The control end of the boost switch tube Q2 is connected to the first drive circuit unit, and the input voltage sampling resistor is used to connect the input power supply and the ground end to collect and feedback the DC input voltage detection signal U1 in a voltage division manner. Preferably, the input voltage sampling resistor uses resistors R1 and R2, and the output voltage sampling resistor is connected to one end of the capacitor C1 and the ground end to collect and feedback the sinusoidal pulsating DC voltage detection signal UDAo in a voltage division manner. Preferably, the output voltage sampling resistor uses resistors R8 and R9; then the DC input voltage detection signal and the sinusoidal pulsating DC voltage detection signal can be processed by a digital control circuit unit or other existing circuits, so that the digital control circuit unit can easily analyze the detection signal.

[0053] When the DC input voltage is lower than the sinusoidal pulsating DC voltage, the buck switch Q1 is turned on under the control of the pulse signal PQ1, and the boost switch Q2 is turned on and off according to the high-frequency SPWM law under the control of the pulse signal PQ2. The boost switch Q2 is turned on, and the DC input voltage is boosted by the high-frequency inductor L1 according to the sinusoidal law. The boost switch Q2 is turned off, and the boosted DC input voltage is isolated by the unidirectional isolation diode D2 and properly filtered by the filter capacitor C1 to generate a sinusoidal pulsating DC voltage. The voltage value of the sinusoidal pulsating DC voltage can be increased by controlling the duty cycle of the pulse signal of the boost switch Q2. When the DC input voltage is higher than the sinusoidal pulsating DC voltage, the boost switch Q2 is turned off under the control of the pulse signal PQ2, and the buck switch Q1 is turned on and off according to the high-frequency SPWM rule under the control of the pulse signal PQ1. The buck switch Q1 is turned on, and the DC input voltage is filtered by L1-C1 and isolated by the unidirectional isolation diode D2 to generate a sinusoidal pulsating DC voltage UDA. The buck switch Q1 is turned off, and the freewheeling diode D1 provides a freewheeling path for the inductor current when the switch Q1 is turned off. By controlling the duty cycle of the pulse signal of the buck switch Q1, the voltage value of the sinusoidal pulsating DC voltage can be reduced. Therefore, the non-isolated DC / pulsating DC conversion circuit unit can handle a wide range of DC input voltages while ensuring the accurate output of the sinusoidal pulsating DC voltage, and has the advantages of improving the output voltage accuracy and waveform quality. Figure 13 The figure shows the effect of a non-isolated DC / pulsating DC conversion circuit unit on converting a DC input voltage into a sinusoidal pulsating DC voltage. The input and output of the non-isolated DC / pulsating DC conversion circuit unit are not electrically isolated, completing the DC to pulsating DC conversion.

[0054] like Figure 1 As shown, the isolated pulsating DC / AC conversion circuit unit is configured to convert a sinusoidal pulsating DC voltage into a power-frequency AC voltage using a transformer-isolated two-transistor push-pull method according to the power-frequency control pulse signal and the power-frequency cycle. The converted power-frequency AC voltage is then output and a voltage detection signal is fed back to the digital control circuit unit. The output of the non-isolated DC / pulsating DC conversion circuit unit is connected to the input of the isolated pulsating DC / AC conversion circuit unit via the UDA-GIN intermediate port. The isolated pulsating DC / AC conversion circuit unit performs DC / AC conversion on the input sinusoidal pulsating DC voltage. The output of the isolated pulsating DC / AC conversion circuit unit is connected to the UA1-UA2 AC output ports to output the power-frequency AC voltage. The two switching transistors of the isolated pulsating DC / AC conversion circuit unit are turned on and off under the control of the power-frequency pulse signal, reducing switching losses.

[0055] like Figure 3As shown, the isolated pulsating DC / AC conversion circuit unit includes a sinusoidal pulsating DC voltage sampling resistor, a push-pull switch tube Q3, a push-pull switch tube Q4, an industrial frequency transformer T1, a first buffer absorption circuit, a second buffer absorption circuit, a filter capacitor C4, and an AC output voltage sampling resistor; the source of the push-pull switch tube Q3 and the source of the push-pull switch tube Q4 are connected to each other and are used to connect to the ground terminal, the drain of the push-pull switch tube Q3 is connected to the opposite-name terminal of the first group of primary coils of the industrial frequency transformer T1, and the same-name terminal of the first group of primary coils of the industrial frequency transformer T1 is used to connect to the sinusoidal pulsating DC voltage, the control terminal of the push-pull switch tube Q3 is connected to the second drive circuit unit, the first buffer absorption circuit is connected in parallel with the first group of primary coils of the industrial frequency transformer T1; the drain of the push-pull switch tube Q4 is connected to the industrial frequency transformer T 1, and the opposite-name terminals of the second primary coil of the power frequency transformer T1 are connected to a sinusoidal pulsating DC voltage. The control terminal of the push-pull switch Q4 is connected to the second drive circuit unit. The second buffer absorption circuit is connected in parallel with the second primary coil of the power frequency transformer T1. The secondary coil of the power frequency transformer T1 is connected in parallel with the filter capacitor C4. The sinusoidal pulsating DC voltage sampling resistor is used to collect and feedback the sinusoidal pulsed DC voltage detection signal UD1 by voltage division. Preferably, the sinusoidal pulsating DC voltage sampling resistor is a resistor R11 and a resistor R12. The AC output voltage sampling resistor is connected across the filter capacitor C4 to collect and feedback the AC output voltage detection signal UAo by voltage division. Preferably, the AC output voltage sampling resistor is a resistor R20 and a resistor R21. The sinusoidal pulsed DC voltage detection signal and the AC output voltage detection signal are processed to facilitate analysis of the detection signals by the digital control circuit unit. The first buffer absorption circuit consists of a resistor R17, a capacitor C2, and a diode D3; the second buffer absorption circuit consists of a resistor R18, a capacitor C3, and a diode D4.

[0056] During the positive half-cycle of the sinusoidal AC cycle, switch Q3 is turned on by control signal PQ3, and switch Q4 is turned off by control signal PQ4. The sinusoidal pulsating DC voltage is transmitted to the secondary winding of the power-frequency transformer T1 via its first primary winding, and then filtered by capacitor C4 to form the positive half-cycle waveform of the AC output. During the negative half-cycle of the sinusoidal AC cycle, switch Q3 is turned off by control signal PQ3, and switch Q4 is turned on by control signal PQ4. The sinusoidal pulsating DC voltage is transmitted to the secondary winding of the power-frequency transformer T1 via its second primary winding, and then filtered by capacitor C4 to form the negative half-cycle waveform of the AC output. During the switching period between switches Q3 and Q4, the first snubber absorber circuit absorbs energy stored in the first primary winding of the power-frequency transformer T1, protecting switch Q3. The second snubber absorber circuit absorbs energy stored in the second primary winding of the power-frequency transformer T1, protecting switch Q4. The input and output of the isolated pulsating DC / AC conversion circuit unit are electrically isolated by the power frequency transformer T1, completing the conversion from pulsating DC to power frequency AC. Figure 14 As shown, the effect diagram of the isolated pulsating DC / AC conversion circuit unit on converting the sinusoidal pulsating DC voltage into AC output voltage.

[0057] The first driver circuit unit is configured to drive the opening and closing of the two step-up / step-down switching transistors in the non-isolated DC / pulsating DC conversion circuit unit according to control instructions from the digital control circuit unit. The second driver circuit unit is configured to drive the opening and closing of the two push-pull switching transistors in the isolated pulsating DC / AC conversion circuit unit according to control instructions from the digital control circuit unit. The first and second driver circuit units are capable of performing signal amplification based on the control instructions from the digital control circuit unit, increasing signal driving capability, thereby strengthening the driving capability of the switching transistors and improving the conduction level of the switching transistors, thereby further reducing switching losses.

[0058] like Figure 4As shown, preferably, the first driving circuit unit includes a first optocoupler O4, a second optocoupler O5, a first driving chip circuit U4 and a second driving chip circuit U5, the first input end of the first optocoupler O4 is connected to the digital control circuit unit, the second input end of the first optocoupler O4 is used to connect to the ground end after connecting to a resistor, the first output end of the first optocoupler O4 is connected to the power supply circuit unit, the second output end of the first optocoupler O4 is connected to the input end of the first driving chip circuit U4, and the output end of the first driving chip circuit U4 is connected to the step-down switch tube Q1; the first input end of the second optocoupler O5 is connected to the digital control circuit unit, the second input end of the second optocoupler O5 is used to connect to the ground end after connecting to a resistor, the first output end of the second optocoupler O5 is connected to the power supply circuit unit, the second output end of the second optocoupler O5 is connected to the input end of the second driving chip circuit U5, and the output end of the second driving chip circuit U5 is connected to the boost switch tube Q2, the two driving chip circuits play a role in signal amplification of the control instructions of the digital control circuit unit, the first optocoupler O4 and the second optocoupler O5 play an isolation role to protect the digital control circuit unit.

[0059] like Figure 5 As shown, preferably, the second driving circuit unit includes a third optocoupler O9, a fourth optocoupler O10, a first driving chip circuit U9 and a second driving chip circuit U10, the first input end of the third optocoupler O9 is connected to the digital control circuit unit, the second input end of the third optocoupler O9 is connected to the ground end through a resistor, the first output end of the third optocoupler O9 is connected to the power supply circuit unit, the second output end of the third optocoupler O9 is connected to the input end of the third driving chip circuit U9, and the output end of the third driving chip circuit U9 is connected to the push-pull switch tube Q3; the first input end of the fourth optocoupler O10 is connected to the digital control circuit unit, the second input end of the fourth optocoupler O10 is connected to the ground end through a resistor, the first output end of the fourth optocoupler O10 is connected to the power supply circuit unit, the second output end of the fourth optocoupler O10 is connected to the input end of the fourth driving chip circuit U10, and the output end of the fourth driving chip circuit U10 is connected to the push-pull switch tube Q4, the two driving chip circuits play a role in signal amplification of the control instructions of the digital control circuit unit, the third optocoupler O9 and the fourth optocoupler O10 play an isolation role to protect the digital control circuit unit.

[0060] The digital control circuit unit (abbreviated as digital controller or controller) is configured to calculate the SPWM control pulse width and the power frequency cycle time switching point based on the voltage detection signal fed back by the system, and generate corresponding control pulse signals to input into the first drive circuit unit and the second drive circuit unit for signal amplification, thereby controlling the switching of the switching tubes in the non-isolated DC / pulsating DC conversion circuit unit and the isolated pulsating DC / AC conversion circuit unit.

[0061] like Figure 9 As shown, preferably, the digital control circuit unit includes a DSP control module DSPB1, a first level conversion circuit consisting of a resistor R50, a transistor T1, and a resistor R54, a second level conversion circuit consisting of a resistor R51, a transistor T2, and a resistor R55, a third level conversion circuit consisting of a resistor R52, a transistor T3, and a resistor R56, and a fourth level conversion circuit consisting of a resistor R53, a transistor T4, and a resistor R57. The DSP control module DSPB1 analyzes the DC input voltage detection signal, the sinusoidal pulsating DC voltage detection signal, and the AC output voltage detection signal, then calculates the SPWM control pulse width and the power frequency cycle time switching point based on the detection signals, and generates a 3.3V low-level active control pulse based on the AC synchronization signal. The 3.3V low-level active control pulse is converted into a 12V high-level active control pulse through four level conversion circuits.

[0062] The power supply circuit unit is configured to convert a DC input voltage into a DC voltage required by the system to supply power to the first driving circuit unit, the second driving circuit unit and the digital control circuit unit.

[0063] like Figure 10 As shown, the power circuit unit mainly includes a capacitor filter circuit composed of capacitor E5, capacitor E6, resistor R48 and resistor R49, a double-pole double-throw switch K1, a switching power module PM1, a three-terminal linear regulator PM3, and a switching power module PM2. The capacitor filter circuit performs energy storage filtering and voltage division on the DC input voltage, generating two high and low DC outputs (UINo-GIN and UINo-UB, UB-GIN) for the double-pole double-throw switch K1. The double-pole double-throw switch K1 selects the input voltage for the switching power modules PM1 and PM2, thereby increasing the switching power modules' wide adaptability to input voltages. When the voltage at the input terminal UINo-GIN is low, switch K1 throws the switch upward, and both switching power modules PM1 and PM2 use UINo-GIN as their input. When the voltage at the input terminal UINo-GIN is high, switch K1 throws the switch downward, and switching power module PM1 uses UINo-UB as its input, while switching power module PM2 uses UB-GIN as its input. Switching power module PM1 performs isolated conversion from the input DC to 12V. The three-terminal linear regulator PM3 converts the 12V power supply into a 3.3V power supply, which provides operating power to the digital control circuit unit in the control circuit. Switching power module PM2 converts the DC input to 15V, shares a common ground with the main circuit, and provides operating power to the drive circuit. The power supply circuit unit's input can switch between multiple power levels, adapting to a wide voltage range. The power supply circuit unit utilizes a combination of switching and linear power supplies. The switching power supply improves overall circuit efficiency, while the linear power supply enhances the reliability and signal quality of the digital control circuit unit.

[0064] The conversion system in this embodiment utilizes a two-stage cascade structure consisting of a non-isolated DC / pulsating DC conversion circuit unit and an isolated pulsating DC / AC conversion circuit unit. The non-isolated DC / pulsating DC conversion circuit unit crucially converts the DC input voltage into a sinusoidal pulsating DC voltage, providing the isolated pulsating DC / AC conversion circuit unit with a suitable sinusoidal pulsating DC voltage to complete the DC / AC conversion. Therefore, the DC / AC conversion cannot be completed without any of the circuit units. Compared to existing full-bridge inverters, this system offers the following technical advantages: the two switching transistors in the non-isolated DC / pulsating DC conversion circuit unit are switched on and off under high-frequency SPWM control, while the two switching transistors in the isolated pulsating DC / AC conversion circuit unit operate at the power frequency. This significantly reduces switching losses, avoids the risk of switch shoot-through associated with an inverter bridge, simplifies the control algorithm of the digital control circuit unit, and reduces control costs.

[0065] Figure 12 The figure shows a schematic diagram of the control pulses output by the two drive circuit units. The digital control circuit unit can directly or indirectly process and analyze various voltage detection signals fed back by the two-stage DC / AC main conversion circuit. Based on the detection signals, it determines whether the non-isolated DC / pulsating DC conversion circuit unit is operating in buck mode or boost mode. It also calculates the pulse width using the PID algorithm and SPWM modulation algorithm based on the error signal between the sinusoidal pulsating DC voltage and the expected voltage value. The expected voltage value can be calculated based on the preset AC output voltage Ug. Control pulses P1 and P2 are output based on the pulse width and then pass through the first drive circuit unit to control the operation of the non-isolated DC / pulsating DC conversion circuit unit, thereby outputting a sinusoidal pulsating DC voltage with precision and high quality. The digital control circuit unit synchronously generates control signals P3 and P4 based on the AC signal cycle and passes through the second drive circuit unit to control the isolated pulsating DC / AC conversion circuit unit to operate according to the industrial frequency AC output requirements, thereby outputting an industrial frequency AC voltage.

[0066] Example 2: Based on Example 1, Figure 6As shown, the high-low frequency combined two-stage four-tube DC-AC conversion system of the present invention also includes a first conversion protection circuit unit, which is configured to isolate and convert the voltage detection signal fed back by the non-isolated DC / pulsating DC conversion circuit unit to generate an intermediate-stage DC input voltage detection signal, a DC input current detection signal, and an intermediate-stage sinusoidal pulsating DC voltage detection signal. Each signal is compared with a corresponding reference voltage. When the signal voltage is greater than the reference voltage, a high-level protection signal is generated to control the first drive circuit unit to shut down the two step-up / step-down switching tubes in the non-isolated DC / pulsating DC conversion circuit unit; and the intermediate-stage DC input voltage detection signal, the DC input current detection signal, and the intermediate-stage sinusoidal pulsating DC voltage detection signal are fed back to the digital control circuit unit for calculating the SPWM control pulse width and generating the control pulse signal.

[0067] The high- and low-frequency combined two-stage four-tube DC-AC conversion system of this embodiment further includes a second conversion protection circuit unit, which is configured to isolate and convert the voltage detection signal fed back from the isolated pulsating DC / AC conversion circuit unit to generate an intermediate-stage pulsating DC input voltage detection signal, a pulsating DC input current detection signal, and an intermediate-stage AC output voltage detection signal; compare each signal with a corresponding reference voltage; and when the signal voltage is greater than the reference voltage, generate a high-level protection signal to control the second drive circuit unit to shut down the two push-pull switching tubes of the isolated pulsating DC / AC conversion circuit unit; and feed back the intermediate-stage pulsating DC input voltage detection signal, the pulsating DC input current detection signal, and the intermediate-stage AC output voltage detection signal to the digital control circuit unit for calculation of the power frequency cycle time switching point and generation of the control pulse signal.

[0068] The high- and low-frequency combined two-stage four-transistor DC-AC conversion system in this embodiment further includes a first sensor and a second sensor. The first sensor is used to sense a temperature detection signal TDA of the non-isolated DC / pulsating DC conversion circuit unit. The first conversion protection circuit unit compares the temperature detection signal with a corresponding reference voltage. When the signal voltage is greater than the reference voltage, a high-level protection signal is generated, and the first drive circuit unit is controlled to shut down the step-up / step-down switching tube in the non-isolated DC / pulsating DC conversion circuit unit. The first sensor feeds back the temperature detection signal to the digital control circuit unit. The second sensor is used to sense a temperature detection signal TA of the isolated pulsating DC / AC conversion circuit unit. The second conversion protection circuit unit compares the temperature detection signal with a corresponding reference voltage. When the signal voltage is greater than the reference voltage, a high-level protection signal is generated, and the second drive circuit unit is controlled to shut down the two push-pull switching tubes in the isolated pulsating DC / AC conversion circuit unit. The second sensor feeds back the temperature detection signal to the digital control circuit unit.

[0069] See Figure 2 and Figure 3 The non-isolated DC / pulsating DC conversion circuit unit includes a buck switch Q1, a boost switch Q2, a high-frequency inductor L1, a freewheeling diode D1, a unidirectional isolation diode D2, a filter capacitor C1, an input voltage sampling resistor, and an output voltage sampling resistor. One end of the buck switch Q1 is connected to a DC input voltage through a terminal, the other end of the buck switch Q1 is connected to one end of the high-frequency inductor L1 and the cathode of the freewheeling diode D1, and the control end of the buck switch Q1 is connected to the first drive circuit unit. One end of the boost switch Q2 is connected to the other end of the high-frequency inductor L1 and the anode of the unidirectional isolation diode D2, the cathode of the isolation diode D2, and one end of the filter capacitor C1. The other end of the boost switch Q2 is connected to the anode of the freewheeling diode D1 and the other end of the filter capacitor C1 and is connected to ground. The control end of the boost switch Q2 is connected to the first drive circuit unit. The input voltage sampling resistor includes resistors R1-R2, resistors R4-R5, and resistor R3. The output voltage sampling resistor is resistors R8-R9. Resistors R1-R2 obtain a detection signal UI of the DC input voltage UIN through voltage division, resistors R3-R4 obtain a detection signal UIo of the rear end voltage UINo of resistor R3 through voltage division, and resistors R8-R9 obtain a detection signal UDAo of the sinusoidal pulsating DC voltage UDA through voltage division.

[0070] The isolated pulsating DC / AC conversion circuit unit includes a sinusoidal pulsating DC voltage sampling resistor, a push-pull switch tube Q3, a push-pull switch tube Q4, an industrial frequency transformer T1, a first buffer absorption circuit, a second buffer absorption circuit, a filter capacitor C4 and an AC output voltage sampling resistor; the source of the push-pull switch tube Q3 and the source of the push-pull switch tube Q4 are connected to each other and used to be connected to the ground end, the drain of the push-pull switch tube Q3 and the opposite-name end of the first group of primary coils of the industrial frequency transformer T1, and the same-name end of the first group of primary coils of the industrial frequency transformer T1 are used to be connected to the sinusoidal pulsating DC voltage, the control end of the push-pull switch tube Q3 is connected to the second drive circuit unit, the first buffer absorption circuit is connected to the industrial frequency The first set of primary windings of transformer T1 is connected in parallel; the drain of the push-pull switch Q4 is connected to the same-name terminal of the second set of primary windings of the power-frequency transformer T1, and the opposite-name terminal of the second set of primary windings of the power-frequency transformer T1 is connected to a sinusoidal pulsating DC voltage. The control terminal of the push-pull switch Q4 is connected to a second drive circuit unit, and the second buffer absorption circuit is connected in parallel with the second set of primary windings of the power-frequency transformer T1. The secondary winding of the power-frequency transformer T1 is connected in parallel with the filter capacitor C4. The sinusoidal pulsating DC voltage sampling resistor is used to collect and feedback the sinusoidal pulsed DC voltage detection signal. The AC output voltage sampling resistor is connected across the filter capacitor C4 to collect and feedback the AC output voltage detection signal. The sinusoidal pulsed DC voltage detection signal and the AC output voltage detection signal are processed to facilitate analysis of the detection signals by the digital control circuit unit. The first buffer absorption circuit consists of a resistor R17, a capacitor C2, and a diode D3; the second buffer absorption circuit consists of a resistor R18, a capacitor C3, and a diode D4. The sinusoidal pulsating DC voltage sampling resistors include resistors R11-R12, resistors R13-R14, and resistor R10; the DC output voltage sampling resistors are resistors R20-R21. Resistors R11-R12 obtain the detection signal UD1 of the pulsating DC input UDA through voltage division, resistors R13-R14 obtain the detection signal UD2 of the voltage behind the resistor R10 through voltage division, and resistors R20-R21 obtain the detection signal UAo of the AC output terminal UA1-UA2 voltage through voltage division.

[0071] See Figure 7The first conversion protection circuit unit includes a first electrical isolation circuit composed of a resistor R22, an optocoupler O1 and a potentiometer RW1; a second photoelectric isolation circuit composed of a resistor R23, an optocoupler O2 and a potentiometer RW2; a third photoelectric isolation circuit composed of a resistor R24, an optocoupler O3 and a potentiometer RW3; a follower amplifier circuit composed of comparators U1A, U1B and resistors R25\R26; a constant voltage circuit composed of a resistor R27, a Zener diode Z1 and a capacitor C5; a first reference circuit composed of a potentiometer RW4 and a capacitor C6 voltage circuit, a second reference voltage circuit composed of potentiometer RW5 and capacitor C7, a third reference voltage circuit composed of potentiometer RW6 and capacitor C8, a fourth reference voltage circuit composed of potentiometer RW7 and capacitor C9, a first comparison circuit composed of comparator U2A, diode D5, thermistor RT1 and resistor R28, a second comparison circuit composed of comparator U2B and diode D6, a third comparison circuit composed of comparator U3A and diode D7, and a fourth comparison circuit composed of comparator U3B and diode D8.The first optoelectronic isolation circuit isolates the DC input voltage detection signal UI through an optocoupler to form an intermediate-level DC input voltage detection signal UIS that is shared with the control circuit. The second optoelectronic isolation circuit isolates the voltage detection signal UIo at the back end of the DC input current sampling resistor through an optocoupler to form an intermediate-level voltage detection signal UIoS that is shared with the control circuit. The third optoelectronic isolation circuit isolates the pulsating DC output voltage sampling signal UDAo through an optocoupler to form an intermediate-level sinusoidal pulsating DC voltage detection signal UDAoS. The follower amplifier circuit differentially amplifies UIS and UIoS to form an input intermediate-level DC input current detection signal IIS. The constant voltage circuit provides a highly stable DC voltage for the reference voltage generation circuit. The first reference voltage circuit generates a DC input voltage overvoltage reference. The second reference voltage circuit generates a pulsating DC output voltage overvoltage reference. The third reference voltage circuit generates a DC input current overcurrent reference. The fourth reference voltage circuit generates a DC / pulsating DC conversion main voltage. The first comparison circuit compares the temperature detection signal TDA with the overtemperature reference to generate an overtemperature protection signal. The second comparison circuit compares the DC input current detection signal IIS with the overcurrent reference to generate an overcurrent protection signal. The third comparison circuit compares the DC input voltage detection signal UIS with the overvoltage reference to generate a DC input overvoltage protection signal. The fourth comparison circuit compares the pulsating DC output voltage detection signal UDAoS with the output overvoltage reference to generate an output overvoltage protection signal. These four protection signals are simultaneously input to the second ends of the two optocouplers of the first driver circuit unit. When the level of any one of the protection signals is sufficiently high, the difference between the protection signal level and the control pulse signal level of the digital control circuit unit is sufficiently small to disconnect the two optocouplers, causing the first driver circuit unit to output a low level to the switch tubes Q1 and Q2. Switch tubes Q1 and Q2 are disconnected, thus providing overvoltage, overcurrent, and overtemperature protection for the non-isolated DC / pulsating DC conversion circuit unit.

[0072] See Figure 8The second conversion protection circuit unit includes a fourth photoelectric isolation circuit composed of a resistor R35, an optical coupler O6 and a potentiometer RW8, a fifth photoelectric isolation circuit composed of a resistor R36, an optical coupler O7 and a potentiometer RW9, a sixth photoelectric isolation circuit composed of a resistor R37, an optical coupler O8 and a potentiometer RW10, a follower amplifier circuit composed of comparators U6A, U6B, a resistor R38 and a resistor R39, a second constant voltage circuit composed of a resistor R40, a Zener diode Z2 and a capacitor C10, a fifth reference voltage circuit composed of a potentiometer RW11 and a capacitor C11, and a potentiometer RW12 and A sixth reference voltage circuit composed of capacitor C12, a seventh reference voltage circuit composed of potentiometer RW13 and capacitor C13, an eighth reference voltage circuit composed of potentiometer RW14 and capacitor C14, a fifth comparison circuit composed of comparator U7A, diode D13, thermistor RT2, and resistor R41, a sixth comparison circuit composed of comparator U7B and diode D14, a seventh comparison circuit composed of comparator U8A and diode D15, an eighth comparison circuit composed of comparator U8B and diode D16, and an industrial frequency rectifier bridge composed of diodes D9, D10, D11, and D12.The fourth optoelectronic isolation circuit forms a pulsating DC input voltage detection signal UDA1S that is shared with the control circuit after isolating the pulsating DC input voltage detection signal UD1 through an optocoupler. The fifth optoelectronic isolation circuit forms a voltage detection signal UDA2S that is shared with the control circuit after isolating the voltage detection signal UD2 at the back end of the pulsating DC input current sampling resistor through an optocoupler. The power frequency rectifier bridge D9~D12 rectifies the output AC voltage detection signal (UA2-UAo) into a DC voltage signal. The sixth optoelectronic isolation circuit forms an AC output voltage sampling signal UAS after isolating the rectified AC output voltage sampling signal (UA2-UAo) through an optocoupler. The follower amplifier circuit differentially amplifies UDA2S and UDA1S to form an input pulsating DC current detection signal IDS. The constant voltage circuit provides a highly stable DC voltage for the reference voltage generating circuit. The fifth reference voltage circuit generates a pulsating DC input voltage overvoltage reference. The sixth reference voltage circuit generates an AC output voltage overvoltage reference. The seventh reference voltage circuit generates a pulsating DC An input current overcurrent reference is provided, an eighth reference voltage circuit generates an overtemperature reference for the pulsating DC / AC conversion circuit, a fifth comparison circuit compares the temperature detection signal with the overtemperature reference to generate an overtemperature protection signal, a sixth comparison circuit compares the pulsating DC input current detection signal with the overcurrent reference to generate an overcurrent protection signal, a seventh comparison circuit compares the pulsating DC input voltage detection signal with the overvoltage reference to generate a pulsating DC input overvoltage protection signal, and an eighth comparison circuit compares the AC output voltage detection signal with the output overvoltage reference to generate an output overvoltage protection signal. These four protection signals are simultaneously input to the second terminals of the two optocouplers of the second drive circuit unit. When the level of any one of the protection signals is sufficiently high, the difference between the protection signal level and the control pulse signal level of the digital control circuit unit is sufficiently small to disconnect the two optocouplers, causing the second drive circuit unit to output a low level to the switch transistors Q3 and Q4, disconnecting the switch transistors Q3 and Q4, thereby providing overvoltage, overcurrent, and overtemperature protection for the isolated pulsating DC / AC conversion circuit unit.

[0073] As can be seen from the above, in this embodiment, the first conversion protection circuit unit and the second conversion protection circuit unit process the voltage detection signal and the temperature detection signal through optoelectronic isolation and analog circuits, directly generate protection signals, and act on the optocouplers of the first driving circuit unit and the second driving circuit unit to directly control the coupling relationship of the optocouplers, thereby greatly improving the real-time and reliability of the over-temperature, overvoltage and over-current protection of the two-stage DC\AC main conversion circuit.

[0074] The detection signals from the two-stage main conversion circuit unit are optically isolated by the first and second conversion protection circuit units before being input into the digital control circuit unit. The control pulses from the digital control circuit unit are optically coupled by the first and second drive circuit units for signal amplification, ultimately driving the switches in the main conversion circuit. The digital control circuit unit utilizes optocouplers for both signal reception and transmission, achieving optical isolation from the two-stage DC / AC main conversion circuit, significantly improving the control circuit's safety.

[0075] In this embodiment, Figure 11 Figure 2 shows the control flow of the digital control circuit unit. The digital controller performs functions such as signal detection, operating state determination, parameter calculation, and control pulse formation. When the digital controller detects parameters such as UIS, IIS, UDAoS, UAS, IDS, TDA, and TA, if the two-stage DC / AC main conversion circuit exceeds a limit, the control pulse is disabled. When the two-stage DC / AC main conversion circuit is operating normally, the digital control circuit unit determines whether the non-isolated DC / pulsating DC conversion circuit unit is operating in buck or boost mode based on the detection signal. It calculates the pulse width based on the error signal between the sinusoidal pulsating DC voltage and the set voltage using the PID algorithm and SPWM modulation algorithm. Based on the pulse width, it outputs control pulses P1 and P2 to control the operation of the non-isolated DC / pulsating DC conversion circuit unit, achieving a precise and high-quality output of the sinusoidal pulsating DC voltage. The digital control circuit unit also generates control signals P3 and P4 synchronously with the AC signal cycle to control the isolated pulsating DC / AC conversion circuit unit to operate according to the power frequency AC output requirements, outputting a power frequency AC voltage.

[0076] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications based on the present invention to solve substantially the same technical problems and achieve substantially the same technical effects are all within the scope of protection of the present invention.

Claims

1. A two-stage four-tube DC-AC conversion system combining high and low frequencies, characterized in that: It includes a non-isolated DC / pulsating DC conversion circuit unit, an isolated pulsating DC / AC conversion circuit unit, a first driving circuit unit, a second driving circuit unit, a digital control circuit unit and a power supply circuit unit; The non-isolated DC / pulsating DC conversion circuit unit is configured to convert a DC input voltage into a sinusoidal pulsating DC voltage in a buck / boost combination according to a high-frequency SPWM control pulse signal, input the converted sinusoidal pulsating DC voltage to the isolated pulsating DC / AC conversion circuit unit, and feed back a voltage detection signal; The isolated pulsating DC / AC conversion circuit unit is configured to convert a sinusoidal pulsating DC voltage into an industrial frequency AC voltage in a two-transistor push-pull manner isolated by a transformer according to an industrial frequency control pulse signal and according to an industrial frequency cycle, output the converted industrial frequency AC voltage, and feed back a voltage detection signal; The first driving circuit unit is configured to drive the opening and closing of two step-up / step-down switching tubes of the non-isolated DC / pulsating DC conversion circuit unit according to the control instruction of the digital control circuit unit; The second driving circuit unit is configured to drive the two push-pull switching tubes of the isolated pulsating DC / AC conversion circuit unit to turn on and off according to the control instruction of the digital control circuit unit; The digital control circuit unit is configured to calculate the SPWM control pulse width and the power frequency cycle time switching point according to the feedback voltage detection signal, and generate a control pulse signal to send a control instruction to the first drive circuit unit and the second drive circuit unit; The power supply circuit unit is configured to convert a DC input voltage into a DC voltage required by the system to supply power to the first driving circuit unit, the second driving circuit unit and the digital control circuit unit.

2. A two-stage four-tube DC-AC conversion system combining high and low frequencies as claimed in claim 1, characterized in that: It also includes a first conversion protection circuit unit, which is configured to isolate and process the voltage detection signal fed back by the non-isolated DC / pulsating DC conversion circuit unit, generate an intermediate-level DC input voltage detection signal, a DC input current detection signal and an intermediate-level sinusoidal pulsating DC voltage detection signal, compare each signal with the corresponding reference voltage, and when the signal voltage is greater than the reference voltage, generate a high-level protection signal to control the first drive circuit unit to turn off the step-up / step-down switch tube in the non-isolated DC / pulsating DC conversion circuit unit; and feed back the intermediate-level DC input voltage detection signal, the DC input current detection signal and the intermediate-level sinusoidal pulsating DC voltage detection signal to the digital control circuit unit for calculating the SPWM control pulse width and generating the control pulse signal.

3. A two-stage four-tube DC-AC conversion system combining high and low frequencies as claimed in claim 2, characterized in that: It also includes a second conversion protection circuit unit, which is configured to isolate and process the voltage detection signal fed back by the isolated pulsating DC / AC conversion circuit unit, generate an intermediate-level pulsating DC input voltage detection signal, a pulsating DC input current detection signal and an intermediate-level AC output voltage detection signal, compare each signal with the corresponding reference voltage, and when the signal voltage is greater than the reference voltage, generate a high-level protection signal to control the second drive circuit unit to turn off the two push-pull switching tubes of the isolated pulsating DC / AC conversion circuit unit; and feed back the intermediate-level pulsating DC input voltage detection signal, the pulsating DC input current detection signal and the intermediate-level AC output voltage detection signal to the digital control circuit unit for it to calculate the power frequency cycle time switching point and generate a control pulse signal.

4. A two-stage four-tube DC-AC conversion system combining high and low frequencies as claimed in claim 3, characterized in that: It also includes a first sensor and a second sensor. The first sensor is used to sense the temperature detection signal of the non-isolated DC / pulsating DC conversion circuit unit. The first conversion protection circuit unit compares the temperature detection signal with the corresponding reference voltage. When the signal voltage is greater than the reference voltage, a high-level protection signal is generated, and the first drive circuit unit is controlled to turn off the step-up / step-down switch tube in the non-isolated DC / pulsating DC conversion circuit unit. The first sensor feeds back the temperature detection signal to the digital control circuit unit; the second sensor is used to sense the temperature detection signal of the isolated pulsating DC / AC conversion circuit unit. The second conversion protection circuit unit compares the temperature detection signal with the corresponding reference voltage. When the signal voltage is greater than the reference voltage, a high-level protection signal is generated, and the second drive circuit unit is controlled to turn off the two push-pull switch tubes of the isolated pulsating DC / AC conversion circuit unit. The second sensor feeds back the temperature detection signal to the digital control circuit unit.

5. A high-low frequency combined two-stage four-transistor DC-AC conversion system according to any one of claims 1 to 4, characterized in that: The non-isolated DC / pulsating DC conversion circuit unit includes a buck switch tube Q1, a boost switch tube Q2, a high-frequency inductor L1, a freewheeling diode D1, a unidirectional isolation diode D2, a filter capacitor C1, an input voltage sampling resistor, and an output voltage sampling resistor; one end of the buck switch tube Q1 is used to connect to the DC input voltage, the other end of the buck switch tube Q1 is connected to one end of the high-frequency inductor L1 and the negative electrode of the freewheeling diode D1, and the control end of the buck switch tube Q1 is connected to the first drive circuit unit; one end of the boost switch tube Q2 is connected to the high-frequency inductor L1 The other end of the boost switch tube Q2 is connected to the positive electrode of the unidirectional isolation diode D2, the negative electrode of the isolation diode D2 is connected to one end of the filter capacitor C1, the other end of the boost switch tube Q2 is connected to the positive electrode of the freewheeling diode D1 and the other end of the filter capacitor C1 and is used to be connected to the ground end, the control end of the boost switch tube Q2 is connected to the first drive circuit unit, the input voltage sampling resistor is used to connect the input power supply and the ground end to collect and feedback the DC input voltage detection signal, and the output voltage sampling resistor is connected to one end of the capacitor C1 and the ground end to collect and feedback the sinusoidal pulsating DC voltage detection signal.

6. A high- and low-frequency combined two-stage four-transistor DC-AC conversion system as claimed in claim 5, characterized in that: The isolated pulsating DC / AC conversion circuit unit includes a sinusoidal pulsating DC voltage sampling resistor, a push-pull switch tube Q3, a push-pull switch tube Q4, an industrial frequency transformer T1, a first buffer absorption circuit, a second buffer absorption circuit, a filter capacitor C4 and an AC output voltage sampling resistor; the source of the push-pull switch tube Q3 and the source of the push-pull switch tube Q4 are connected to each other and used to be connected to the ground end, the drain of the push-pull switch tube Q3 and the opposite-name end of the first group of primary coils of the industrial frequency transformer T1, and the same-name end of the first group of primary coils of the industrial frequency transformer T1 are used to be connected to the sinusoidal pulsating DC voltage, the control end of the push-pull switch tube Q3 is connected to the second drive circuit unit, the first buffer absorption circuit is connected to the industrial frequency The first set of primary coils of the transformer T1 is connected in parallel; the drain of the push-pull switch tube Q4 is connected to the same-name terminal of the second set of primary coils of the power-frequency transformer T1, and the opposite-name terminal of the second set of primary coils of the power-frequency transformer T1 is used to connect to the sinusoidal pulsating DC voltage. The control end of the push-pull switch tube Q4 is connected to the second drive circuit unit, and the second buffer absorption circuit is connected in parallel with the second set of primary coils of the power-frequency transformer T1; the secondary coil of the power-frequency transformer T1 is connected in parallel with the filter capacitor C4, and the sinusoidal pulsating DC voltage sampling resistor is used to collect and feed back the sinusoidal pulse DC voltage detection signal; the AC output voltage sampling resistor is connected across the filter capacitor C4 to collect and feed back the AC output voltage detection signal.

7. A high-low frequency combined two-stage four-transistor DC-AC conversion system as claimed in claim 6, characterized in that: The first driving circuit unit includes a first optocoupler O4, a second optocoupler O5, a first driving chip circuit U4 and a second driving chip circuit U5. The first input end of the first optocoupler O4 is connected to the digital control circuit unit, the second input end of the first optocoupler O4 is used to connect to the ground end through a resistor, the first output end of the first optocoupler O4 is connected to the power supply circuit unit, the second output end of the first optocoupler O4 is connected to the input end of the first driving chip circuit U4, and the output end of the first driving chip circuit U4 is connected to the step-down switch tube Q1; the first input end of the second optocoupler O5 is connected to the digital control circuit unit, the second input end of the second optocoupler O5 is used to connect to the ground end through a resistor, the first output end of the second optocoupler O5 is connected to the power supply circuit unit, the second output end of the second optocoupler O5 is connected to the input end of the second driving chip circuit U5, and the output end of the second driving chip circuit U5 is connected to the boost switch tube Q2.

8. The high-low frequency combined two-stage four-transistor DC-AC conversion system according to claim 7, characterized in that: The second driving circuit unit includes a third optocoupler O9, a fourth optocoupler O10, a first driving chip circuit U9 and a second driving chip circuit U10. The first input end of the third optocoupler O9 is connected to the digital control circuit unit, the second input end of the third optocoupler O9 is used to connect to the ground end through a resistor, the first output end of the third optocoupler O9 is connected to the power supply circuit unit, the second output end of the third optocoupler O9 is connected to the input end of the third driving chip circuit U9, and the output end of the third driving chip circuit U9 is connected to the push-pull switch tube Q3; the first input end of the fourth optocoupler O10 is connected to the digital control circuit unit, the second input end of the fourth optocoupler O10 is used to connect to the ground end through a resistor, the first output end of the fourth optocoupler O10 is connected to the power supply circuit unit, the second output end of the fourth optocoupler O10 is connected to the input end of the fourth driving chip circuit U10, and the output end of the fourth driving chip circuit U10 is connected to the push-pull switch tube Q4.

9. A high-low frequency combined two-stage four-transistor DC-AC conversion system according to any one of claims 1 to 4, characterized in that: The power supply circuit unit includes a capacitor filter circuit consisting of a capacitor E5, a capacitor E6, a resistor R48 and a resistor R49, a double-pole double-throw switch K1, a switching power supply module PM1, a three-terminal linear regulator PM3 and a switching power supply module PM2. The capacitor filter circuit completes energy storage filtering and voltage division of the DC input voltage, generating high and low DC outputs to the double-pole double-throw switch K1; the double-pole double-throw switch K1 completes input voltage selection for the switching power supply modules PM1 and PM2, the switching power supply module PM1 completes isolation conversion from input DC to 12V, the three-terminal linear regulator PM3 converts the 12V power supply into a 3.3V power supply, and the switching power supply module PM2 completes conversion from DC input to 15V.

Images