A DC-AC converter with power decoupling function

Abstract

The application discloses a DC-AC converter with power decoupling function, belonging to the field of power electronics, which can be used as an AC lighting circuit. The DC-AC converter mainly comprises a conversion circuit, a control circuit and a detection circuit. The conversion circuit comprises first to fourth power switches, first to second diodes, a DC inductor, a decoupling capacitor, a filter inductor, a filter capacitor and an AC lighting load. The control circuit controls the opening and closing of the first to fourth power switches according to a working mode signal, a DC output voltage signal, a decoupling capacitor terminal voltage, an AC voltage signal between the lighting load and the AC voltage signal and an AC current signal in the lighting load. The DC side terminal and the AC side terminal are directly connected, belonging to an AC / DC common ground structure, and the common mode leakage current can be effectively inhibited.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to a DC-AC converter with power decoupling function, which is particularly suitable for an AC lighting system powered by photovoltaic. BACKGROUND

[0002] In recent years, impedance source inverters (ISI) have shown unique application value in the field of photovoltaic power supply lighting in building. As typical representatives, Z-source inverters (ZSI) and quasi-Z-source inverters (Q-ZSI) integrate step-down / step-up conversion and inverter functions in a single circuit, significantly improving system efficiency, and their unique anti-through characteristics further enhance operational reliability. However, the four-element impedance network contained in this type of topology results in a device that is too large. For this reason, the academic community has proposed improved schemes such as switch boost inverters (SBI) and current-fed inverters (CFSI). This type of topology reduces impedance elements to two and introduces additional switching tubes, maintaining equivalent voltage gain while achieving compact structure. It is worth noting that new ISI topologies based on active switching enhanced voltage gain can reduce device voltage withstand requirements, but the increase in the number of passive elements still restricts system integration.

[0003] In terms of technical challenges, the leakage current problem faced by non-isolated ISI topologies is particularly prominent. When the system lacks electrical isolation, the common-mode voltage caused by switching action forms a high-frequency leakage path through the parasitic capacitance of the photovoltaic module, affecting lighting safety and system efficiency. In existing solutions, the space vector modulation strategy effectively suppresses high-frequency leakage components by maintaining constant CMV, while the virtual ground technique can reconstruct the leakage path but cannot eliminate the residual current caused by the switching capacitor. The present application uses an AC-DC common ground structure to make the parasitic capacitance common-mode voltage fluctuate constantly at 0V, thereby cutting off the leakage current path from the root.

[0004] The technical bottleneck at the system level is reflected in the power decoupling requirement. The inherent two-frequency power pulsation of single-phase DC-AC converters forces the DC side to be equipped with large-capacity electrolytic capacitors, which not only increases the volume and cost, but also causes the capacitor to degrade due to the periodic thermal stress of the inductor. Traditional solutions achieve power buffering through expanding energy storage elements or adding auxiliary decoupling circuits, but the former reduces power density, and the latter increases system complexity and cost. The latest research trend shows that active decoupling technology based on control algorithms can effectively reduce two-frequency ripple, but in practical applications, it still faces the problem of ripple deterioration caused by uneven capacitor voltage. It is particularly important to note that some five-switch decoupling schemes have theoretical advantages, but their complex driving logic and increased conduction loss limit their engineering application value.

[0005] In view of the above technical problems, the application provides a DC-AC converter with power decoupling function and AC / DC common ground boost type, so as to realize photovoltaic power supply lighting of building. SUMMARY

[0006] 1. Technical problems to be solved:

[0007] In view of the problems in the prior art, the application aims to provide a safe, reliable, efficient, low-cost and long-life DC-AC converter, which can make the parasitic capacitance common-mode voltage fluctuate at 0V through the AC / DC common ground structure, thereby cutting off the leakage current path from the root.

[0008] 2. Technical solutions:

[0009] To solve the above problems, the application adopts the following technical solutions.

[0010] A DC-AC converter with power decoupling function and AC / DC common ground boost type, comprising a conversion circuit, a control circuit and a detection circuit.

[0011] The conversion circuit comprises first to fourth power switches, first to second diodes, a DC inductor, a decoupling capacitor, a filter inductor, a filter capacitor and an AC lighting load.

[0012] The first end of the first power switch is connected with the cathode of the first diode, the first end of the decoupling capacitor and the first end of the third power switch respectively, the anode of the first diode is connected with the first end of the DC inductor and the first end of the fourth power switch respectively, the second end of the fourth power switch is connected with the second end of the second power switch, the second end of the decoupling capacitor and the anode of the second diode respectively, the first end of the second power switch is connected with the second end of the third power switch and the first end of the filter inductor respectively, the second end of the filter inductor is connected with the first end of the filter capacitor and the first end of the AC lighting load respectively, the second end of the DC inductor is connected with the first end of the DC power supply, and the second end of the DC power supply is connected with the second end of the first power switch, the cathode of the second diode, the second end of the filter capacitor and the second end of the AC lighting load respectively.

[0013] The filter capacitor is used for filtering the AC power output by the conversion circuit.

[0014] The decoupling capacitor is used for power decoupling of AC / DC power of the conversion circuit, which can eliminate the need for a voltage stabilizing capacitor on the DC side, thereby reducing the system cost and volume.

[0015] The detection circuit is used for detecting the direct current voltage signal inputted by the current conversion circuit, the decoupling capacitor terminal voltage, the alternating current voltage signal between the lighting load and the alternating current signal in the lighting load, and sending the detected direct current voltage signal, the decoupling capacitor terminal voltage, the alternating current voltage signal between the lighting load and the alternating current signal in the lighting load to the control circuit.

[0016] The control circuit is used for sending the signal controlling the opening and closing of the first to fourth power switches to the controlled ends of the first to fourth power switches according to the working mode signal from the outside and the sampling signal of the detection circuit, wherein the working mode signal comprises the first to eighth working mode signals according to the polarity of the alternating current voltage signal between the lighting load and the alternating current signal in the lighting load.

[0017] Preferably, when the received working mode signal is the first to eighth working mode signals, the control circuit sends the signal controlling the opening and closing of the first to fourth power switches to the controlled ends of the first to fourth power switches according to the direct current voltage signal inputted by the current conversion circuit, the decoupling capacitor terminal voltage, the alternating current voltage signal between the lighting load and the alternating current signal in the lighting load measured by the detection circuit.

[0018] The first working mode signal: at this time, the alternating current voltage and the alternating current are both greater than zero, the third and fourth power switches are closed, and the first and second power switches are opened.

[0019] The second working mode signal: at this time, the alternating current voltage is zero, the alternating current is greater than zero, the decoupling capacitor is charged, the second power switch is closed, and the first, third and fourth power switches are opened.

[0020] The third working mode signal: at this time, the alternating current voltage is zero, the alternating current is greater than zero, the decoupling capacitor is discharged, the second power switch is opened, and the first, third and fourth power switches are closed.

[0021] The fourth working mode signal: at this time, the alternating current voltage is less than zero, the alternating current is greater than zero, the first and second power switches are closed, and the third and fourth power switches are opened.

[0022] The fifth working mode signal: at this time, the alternating current voltage is greater than zero, the alternating current is less than zero, the third and fourth power switches are closed, and the first and second power switches are opened.

[0023] The sixth working mode signal: at this time, the alternating current voltage is zero, the alternating current is less than zero, the decoupling capacitor is charged, the second power switch is closed, and the first, third and fourth power switches are opened.

[0024] The seventh working mode signal: at this time, the alternating current voltage is zero, the alternating current is less than zero, the decoupling capacitor is discharged, the first, third and fourth power switches are closed, and the second power switch is opened.

[0025] Eighth working mode signal: at this time, the alternating voltage and the alternating current are both less than zero, the first and second power switches are closed, and the third and fourth power switches are opened.

[0026] Preferably, the decoupling capacitor can also be replaced by a thin film capacitor, and the capacitance is configured to absorb the double-frequency power pulsation, and the parasitic capacitor common-mode voltage fluctuation is always 0V in cooperation with the AC-DC common ground structure.

[0027] 3. Beneficial effects:

[0028] Compared with the prior art, the technical scheme provided by the application has the following beneficial effects:

[0029] The boost type DC-AC converter of the application has fewer power circuit devices in any working state of the converter, and the state of the first to fourth power switches is controlled by the control circuit according to the DC voltage, the decoupling capacitor terminal voltage, the AC voltage and the AC current, so that the AC current output by the converter circuit maintains good sinusoidal degree, the AC-DC common ground structure makes the parasitic capacitor common-mode voltage fluctuation always 0V, and the leakage current path is completely eliminated; through the dynamic setting Vref =1.5 ·V dc Without DC capacitor: under the conditions of output power 100W and decoupling capacitor 10uF, the double-frequency power pulsation suppression rate is greater than or equal to 90%, and the voltage fluctuation at the lighting load end is less than 2%, the DC-AC converter of the application has power decoupling function, does not need DC capacitor, and is beneficial to reduce the size and cost of the lighting system.

[0030] It should be noted that the structures not introduced in the application are the same as or can be realized by the prior art, and are not described here. BRIEF DESCRIPTION OF DRAWINGS

[0031] The features and advantages of the application will become more apparent through the following specific embodiment part provided with reference to the accompanying drawings, in which:

[0032] Figure 1 Z-source DC-AC converter of the prior art common ground structure;

[0033] Figure 2 Quasi-Z-source DC-AC converter of the prior art common ground structure;

[0034] Figure 3Part circuit schematic diagram of AC-DC common ground boost type DC-AC converter with power decoupling function, wherein the common ground point (G) is directly connected to three points to form 0V common mode voltage reference;

[0035] Figure 4 Part circuit schematic diagram of AC-DC common ground boost type DC-AC converter with power decoupling function, wherein the common ground point (G) is directly connected to three points to form 0V common mode voltage reference;

[0036] Figure label description:

[0037] 100, converter circuit; 200, detection circuit; 300, control circuit;

[0038] S1, first power switch; S2, second power switch; S3, third power switch; S4, fourth power switch;

[0039] D1, first diode; D2, second diode;

[0040] C d , decoupling capacitor; C f , filter capacitor;

[0041] E, equivalent DC power supply;

[0042] L dc , DC inductor; L f , filter inductor; L, AC lighting load;

[0043] V ac , AC voltage; i ac , AC current. DETAILED DESCRIPTION

[0044] The exemplary embodiments of the present application will be described in detail with reference to the accompanying drawings. The description of the exemplary embodiments is merely given for the purpose of illustration and is by no means intended to limit the present application and its application or use.

[0045] For Figure 1 and Figure 2To address the shortcomings of the common-ground (quasi-) Z-source DC-AC converter shown above, the present invention provides a common-ground AC / DC boost DC-AC converter with power decoupling. The main concept of the present invention is to achieve AC / DC power decoupling through decoupling capacitors, eliminating the need for DC smoothing capacitors. Furthermore, in any state, fewer components are required in the circuit, effectively reducing losses. The control circuit then controls the states of the first through fourth power switches based on the DC voltage, decoupling capacitor terminal voltage, AC voltage, and AC current detected by the detection circuit. This ensures that the output AC current has a good sinusoidal quality, which helps to increase the service life of the AC lighting load.

[0046] The following is combined with Figures 3-4 The embodiments of the present invention are described in detail. Figure 3 and Figure 4 Schematic diagrams of partial structures of a boost DC-AC converter according to an embodiment of the present invention are shown respectively. The DC-AC converter according to an embodiment of the present invention comprises: a converter circuit 100, a detection circuit 200, and a control circuit 300;

[0047] The current conversion circuit includes the first to fourth power switches S1-S4, the first diode D1 to the second diode D2, the DC inductor L dc , decoupling capacitor C d , filter inductor L f , filter capacitor C f , AC lighting load L.

[0048] The first end of the first power switch S1 is connected to the cathode of the first diode D1 and the decoupling capacitor C d The first end of the first diode D1 is connected to the first end of the third power switch S3, and the anode of the first diode D1 is connected to the DC inductor L dc The first end of the fourth power switch S4 is connected to the first end of the fourth power switch S4, and the second end of the fourth power switch S4 is connected to the second end of the second power switch S2 and the decoupling capacitor C d The first end of the second power switch S2 is connected to the second end of the third power switch S3 and the anode of the filter inductor L. f The first end of the filter inductor L f The second end of the filter capacitor C f The first end of the AC lighting load L is connected to the first end of the DC inductor L dc The second end of the DC power supply E is connected to the first end of the DC power supply E, and the second end of the DC power supply E is connected to the second end of the first power switch S1, the cathode of the second diode D2, and the filter capacitor C f and the second end of the AC lighting load L.

[0049] In the embodiment of the present application, the first to fourth power switches S1-S4 can be insulated gate bipolar transistors (IGBT), integrated gate-commutated thyristors (IGCT), or the like. Preferably, the first to fourth power switches S1-S4 can be replaced by N-channel field effect transistors to further reduce the on-state loss.

[0050] Filtering capacitor C f for filtering the alternating current output by the current conversion circuit.

[0051] The detection circuit 200 is configured to detect the direct current voltage of the current conversion circuit 100, the voltage at the end of the decoupling capacitor, the alternating current voltage signal across the lighting load, and the alternating current signal in the lighting load, and send the detected direct current voltage, the voltage at the end of the decoupling capacitor, the alternating current voltage, and the alternating current signal in the lighting load to the control circuit 300.

[0052] The control circuit 300 is configured to send signals for controlling the opening and closing of the first to fourth power switches to the controlled ends of the first to fourth power switches according to the working mode signals from the outside and the sampling signals from the detection circuit; wherein the working mode signals include the first to eighth working mode signals.

[0053] When the control circuit 300 receives the first to eighth working mode signals, the control circuit 300 sends signals for controlling the opening and closing of the first to fourth power switches to the controlled ends of the first to fourth power switches according to the direct current voltage signal of the current conversion circuit, the voltage at the end of the decoupling capacitor, the alternating current voltage signal across the lighting load, and the alternating current signal measured by the detection circuit, including:

[0054] The received working mode signal is the first working mode signal: at this time, the alternating current voltage and the alternating current are both greater than zero, the third and fourth power switches S3, S4 are closed, and the first and second power switches S1, S2 are opened.

[0055] The received working mode signal is the second working mode signal: at this time, the alternating current voltage is zero, the alternating current is greater than zero, and the decoupling capacitor is charged, the second power switch S2 is closed, and the first, third, and fourth power switches S1, S3, S4 are opened.

[0056] The received working mode signal is the third working mode signal: at this time, the alternating current voltage is zero, the alternating current is greater than zero, the decoupling capacitor is discharged, the second power switch S2 is opened, and the first, third, and fourth power switches S1, S3, S4 are closed.

[0057] The received working mode signal is the fourth working mode signal: at this time, the alternating current voltage is less than zero, the alternating current is greater than zero, the first and second power switches S1, S2 are closed, and the third and fourth power switches S3, S4 are opened.

[0058] The received working mode signal is the fifth working mode signal: at this time, the AC voltage is greater than zero, the AC current is less than zero, the third and fourth power switches S3, S4 are closed, and the first and second power switches S1, S2 are open.

[0059] The received working mode signal is the sixth working mode signal: at this time, the AC voltage is zero, the AC current is less than zero, and the decoupling capacitor is charged: the second power switch S2 is closed, and the first, third and fourth power switches S1, S3, S4 are open.

[0060] The received working mode signal is the seventh working mode signal: at this time, the AC voltage is zero, the AC current is less than zero, the decoupling capacitor is discharged, the first, third and fourth power switches S1, S3, S4 are closed, and the second power switch S2 is open.

[0061] The received working mode signal is the eighth working mode signal: at this time, the AC voltage and the AC current are both less than zero, the first and second power switches S1, S2 are closed, and the third and fourth power switches S3, S4 are open.

[0062] Through the above control, the AC current output by the DC-AC converter has good sinusoidal degree, so as to prolong the service life of the AC lighting load.

[0063] The specific charging and discharging state judgment logic of the scheme is as follows:

[0064] When V ac <0.05V~ V ac-max , the control circuit compares the decoupling capacitor voltage V cd with the reference value Vref (taking 1.5 times of the DC input voltage):

[0065] If V cd < Vref , the charging mode (second / sixth mode) is activated

[0066] If V cd > Vref , the discharging mode (third / seventh mode) is activated

[0067] The reference value Vref is dynamically set according to the DC input voltage:

[0068] Vref = k · V dc ( k =1.2~1.8);

[0069] According to the characteristics of the lighting load, preferably k =1.5:

[0070] When V dc =200V (photovoltaic input), Vref = 300 V ;

[0071] At this time, the decoupling capacitor voltage fluctuation is ≤10V, which can ensure that the current harmonic distortion rate (THD) of the LED lighting load is less than 5%, and the visible frequency flicker is eliminated.

[0072] Current path analysis (mode 3 discharging process):

[0073] Discharge loop: C d positive electrode→S1→L dc →E positive electrode→E negative electrode→load negative electrode→load positive electrode→S3→C d negative electrode;

[0074] Free-wheeling path: S4→D2→load (guarantee i ac continuity).

[0075] General load supplement:

[0076] When the DC input voltage V cd =220V (corresponding to 220V LED lighting system), set Vref =1.5×220V=330V, at this time, the decoupling capacitor voltage fluctuation is ≤10V, which can ensure that the lighting output current THD<5% (complying with GB 17625.1 harmonic standard).

[0077] Working mode control table:

[0078]

[0079] The basic implementation scheme of the scheme in use includes the following:

[0080] DC power supply E: 200V photovoltaic module;

[0081] Power switches S1-S4: Infineon IGW40N120H3 IGBT (switching frequency 20kHz);

[0082] Decoupling capacitor C d : 10μF / 450V film capacitor;

[0083] Control process:

[0084] The detection circuit 200 samples V ac , iac ;

[0085] When V ac <0.05 V ac-max , the comparison V cd with the dynamic reference value Vref ( Vref =1.5× V dc ):

[0086] V cd Activate charging mode (mode 2 / 6) when

[0087] V cd Activate discharging mode (mode 3 / 7) when

[0088] C d : Decoupling capacitor, thin film capacitor for power decoupling;

[0089] V cd : Real-time voltage value across decoupling capacitor C d ;

[0090] Vref : Decoupling capacitor voltage reference value, taking 1.5 times of the DC input voltage.

[0091] The optimized implementation scheme of the present scheme when in use includes the following:

[0092] Power switch is replaced by: Anson NTMFS5C628NL MOSFET;

[0093] AC load L: Replaced by motor driver;

[0094] Control circuit 300 adds PI regulator, maintains V cd =300±10V by adjusting the duty cycle of mode 2 / 6.

[0095] In the embodiment of the present application, in any working state of the converter, the number of devices in the power circuit is small, which is conducive to reducing the conduction loss. The DC voltage of the conversion circuit, the decoupling capacitor end voltage, the AC voltage and the AC current of the lighting load are detected by the detection circuit, and then the state of the first to fourth power switches is controlled by the control circuit, so that the normal operation of the DC-AC converter can be ensured under various working conditions. Under the conditions of parasitic capacitance 10nF and switching frequency 20kHz, the actual measurement of the common mode voltage fluctuation peak-peak value is less than or equal to 10mV, and the third party detection agency verifies that under the standard test conditions of IEC 62109-1, the common mode leakage current is not detected (<0.1mA). Compared with the prior art, the new DC-AC converter of the present application has a power decoupling function, a small number of passive devices, and is conducive to reducing the cost and size of the lighting system.

[0096] Although the present application has been described with reference to the example embodiments, it is to be understood that the application is not limited to the precise embodiments described and shown, and that various modifications can be made by those skilled in the art without departing from the scope of the claims.

Claims

1. A DC-AC converter with power decoupling function, characterized in that: include: The current conversion circuit (100) comprises first to fourth power switches S1-S4, a first diode D1, a second diode D2, a DC inductor L dc , decoupling capacitor C made of thin film material d , filter inductor L f , filter capacitor C f and AC lighting load L; The AC lighting load L is an LED lamp or a fluorescent lighting system; The detection circuit (200) is used to collect the input voltage of the equivalent DC power supply E and the decoupling capacitor C d Terminal voltage, AC voltage across AC lighting load L V ac and the AC current flowing through the load i ac ; A control circuit (300) generates drive signals for the first to fourth power switches S1 to S4 according to the working mode signal and the sampling signal of the detection circuit; The topological connection of the converter circuit satisfies: Negative pole of equivalent DC power supply E, filter capacitor C f The negative electrode and the negative electrode of the AC lighting load L are connected to the common ground, so that the common mode voltage across the parasitic capacitor fluctuates to 0V; The topological connection of the converter circuit is specifically as follows: The first end of the first power switch S1 is connected to the cathode of the first diode D1 and the decoupling capacitor C d a first terminal and a first terminal of a third power switch S3; The anode of the first diode D1 is connected to the DC inductor L dc a first terminal and a first terminal of a fourth power switch S4; The second terminal of the fourth power switch S4 is connected to the second terminal of the second power switch S2 and the decoupling capacitor C d a second terminal and an anode of a second diode D2; The first terminal of the second power switch S2 is connected to the second terminal of the third power switch S3 and the filter inductor L f First end; Filter inductor L f The second end is connected to the filter capacitor C f a first end and a first end of an AC lighting load L; DC inductor L dc The second end is connected to the positive pole of the equivalent DC power supply E; The negative electrode of the equivalent DC power supply E, the second end of the first power switch S1, the cathode of the second diode D2, the filter capacitor C f The second end and the second end of the AC lighting load L are connected to a common ground.

2. The AC-DC common ground boost type DC-AC converter with power decoupling function according to claim 1, characterized in that: The working mode signal of the control circuit (300) is based on the AC voltage V ac and the alternating current i ac The polarity combination of the detection circuit generates eight operating modes, and generates driving signals for the first to fourth power switches S1 to S4 according to the operating mode signal and the sampling signal of the detection circuit.

3. The AC-DC common ground boost type DC-AC converter with power decoupling function according to claim 2, characterized in that: The working modes include: when V ac >0 and i ac When >0, it is the first mode: S3 and S4 are turned on, and S1 and S2 are turned off; when V ac =0 and i ac >0, according to the decoupling capacitor C d The charge and discharge state switches between the second mode and the third mode: When charging, it is the second mode: S2 is turned on, and S1, S3, and S4 are turned off; During discharge, it is the third mode: S1, S3, and S4 are turned on, and S2 is turned off; when V ac <0 and i ac When >0, it is the fourth mode: S1 and S2 are turned on, and S3 and S4 are turned off; when V ac >0 and i ac When <0, it is the fifth mode: S3 and S4 are turned on, and S1 and S2 are turned off; when V ac =0 and i ac <0, according to the decoupling capacitor C d The charge and discharge state switches between the sixth mode and the seventh mode: When charging, it is the sixth mode: S2 is turned on, and S1, S3, and S4 are turned off; During discharge, it is the seventh mode: S1, S3, and S4 are turned on, and S2 is turned off; when V ac <0 and i ac When <0, it is the eighth mode: S1 and S2 are turned on, and S3 and S4 are turned off.

4. The AC-DC common ground boost type DC-AC converter with power decoupling function according to claim 1, characterized in that: The control circuit (300) switches the working mode in the AC voltage zero-crossing region by comparing the decoupling capacitor C in real time. d Terminal voltage and reference value Vref To realize the charge and discharge status judgment, the reference value Vref satisfy Vref=k·V dc ,in, V dc is the DC input voltage, k=1.5±0.3 The adjustment coefficient.

5. The AC-DC common ground boost type DC-AC converter with power decoupling function according to claim 1, characterized in that: The number of the first to fourth power switches S1 - S4 that are turned on in any working mode is 1, 2 or 3.

6. The AC-DC common ground boost type DC-AC converter with power decoupling function according to claim 1, characterized in that: The first to fourth power switches S1 - S4 are N-channel field effect transistors with a switching frequency greater than 20 kHz.

7. The AC-DC common ground boost type DC-AC converter with power decoupling function according to claim 1, characterized in that: The AC / DC common ground structure directly connects the negative electrode of the DC power supply, the negative electrode of the filter capacitor and the negative electrode of the load through the common ground point G, so that the common mode voltage fluctuation across the parasitic capacitor is 0V.

8. The AC-DC common ground boost type DC-AC converter with power decoupling function according to claim 4, characterized in that: The decoupling capacitor C d Capacitance meets: ； Among them, P o is the output power, is the angular frequency, To allow voltage fluctuations.

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