Dc / ac conversion device and power supply system

Abstract

A DC / AC conversion device and a power supply system. The DC / AC conversion device comprises a transformer, a DC / AC conversion circuit located at the primary side of the transformer, a rectification circuit and a phase switching circuit located at the secondary side of the transformer, and a controller; wherein: the transformer is coupled with the DC / AC conversion circuit, and is adapted to step up a first alternating current signal output by the DC / AC conversion circuit to obtain a second alternating current signal; the rectification circuit is coupled with the transformer, and is adapted to rectify the second alternating current signal to obtain a second direct current signal; the phase switching circuit is coupled with the rectification circuit, and is composed of a plurality of switching tubes, and is adapted to phase switch the second direct current signal to obtain a third alternating current signal, the third alternating current signal being adapted to be input to an alternating current grid; and the controller. By using the above scheme, the loss of the switching tube in the DC / AC conversion device can be reduced.

Description

Technical Field

[0001] This invention relates to the field of power supply technology, and more specifically to a DC / AC converter and power supply system. Background Technology

[0002] A DC / AC converter is a power conversion device that inverts direct current into alternating current.

[0003] DC / AC converters have a wide range of applications, from traditional motor drives and uninterruptible power supplies (UPS) to new energy fields such as photovoltaic power generation, wind power generation, and fuel cell power generation. A DC / AC converter can convert the direct current (DC) output from a DC power source into alternating current (AC) that the electrical equipment can use.

[0004] Most existing DC / AC converters use controllers to control switching transistors to convert direct current to alternating current.

[0005] However, existing DC / AC converters suffer from significant losses in their switching transistors, which affects the reliability of the power supply system. Summary of the Invention

[0006] The problem this invention aims to solve is: how to reduce the losses of switching transistors in DC / AC converters.

[0007] To address the above problems, this invention provides a DC / AC converter, comprising: a transformer, a DC / AC conversion circuit located on the primary side of the transformer, a rectifier circuit and a phase switching circuit located on the secondary side of the transformer, and a controller; wherein:

[0008] The DC / AC conversion circuit is coupled to a DC power supply and consists of multiple switching transistors, and is adapted to convert the first DC signal output by the DC power supply into a first AC signal.

[0009] The transformer is coupled to the DC / AC conversion circuit and is adapted to boost the first AC signal output by the DC / AC conversion circuit to obtain a second AC signal.

[0010] The rectifier circuit is coupled to the transformer and is adapted to rectify the second AC signal to obtain a second DC signal;

[0011] The phase switching circuit, coupled to the rectifier circuit, is composed of multiple switching transistors and is adapted to perform phase switching on the second DC signal to obtain a third AC signal, which is adapted to be input to the AC power grid.

[0012] The controller is coupled to the DC / AC conversion circuit and the phase switching circuit, and is adapted to control the switching of the switching transistor in the DC / AC conversion circuit by frequency conversion and to control the switching of the switching transistor in the phase switching circuit by fixed frequency, so as to realize the conversion of the first DC signal to the third AC signal.

[0013] Optionally, the phase switching circuit includes: a first switch, a second switch, a third switch, and a fourth switch; wherein:

[0014] The first terminal of the first switching transistor is coupled to the rectifier circuit and the second terminal of the second switching transistor, and the second terminal of the first switching transistor is coupled to the transformer;

[0015] The second terminal of the second switch is coupled to the rectifier circuit and the first terminal of the fourth switch;

[0016] The second terminal of the third switch is coupled to the rectifier circuit and the second terminal of the fourth switch, and the first terminal of the third switch is coupled to the transformer;

[0017] The control terminals of the first, second, third, and fourth switching transistors are coupled to the controller; the first terminal of the fourth switching transistor and the first terminal of the third switching transistor are the output terminals of the phase switching circuit.

[0018] Optionally, the rectifier circuit includes: a first diode and a second diode; wherein:

[0019] The anode of the first diode is coupled to the first terminal of the first switching transistor, and the cathode of the first diode is coupled to the transformer.

[0020] The anode of the second diode is coupled to the transformer, and the cathode of the second diode is coupled to the second terminal of the third switching transistor.

[0021] Optionally, the rectifier circuit includes: a fifth switching transistor and a sixth switching transistor; wherein:

[0022] The first end of the fifth switch is coupled to the first end of the first switch and the first end of the second switch; the second end of the fifth switch is coupled to the transformer and the first end of the sixth switch.

[0023] The second end of the sixth switch is coupled to the second end of the third switch and the second end of the fourth switch;

[0024] The control terminals of the fifth and sixth switching transistors are coupled to the controller, which is adapted to control one of the fifth and sixth switching transistors to be turned on and the other switching transistor to be turned off.

[0025] Optionally, the transformer includes: an ideal transformer, a primary leakage inductance, a magnetizing inductance, and a secondary leakage inductance; the DC / AC conversion device further includes: a first capacitor and a second capacitor located on the secondary side of the transformer; the first capacitor and the second capacitor, together with the primary leakage inductance and the magnetizing inductance of the transformer, form an LLC resonant circuit.

[0026] Optionally, one end of the first capacitor and one end of the second capacitor are coupled to the first end of the secondary side of the ideal transformer; the other end of the first capacitor and the other end of the second capacitor are coupled to the phase switching circuit.

[0027] Optionally, the DC / AC conversion circuit is a full-bridge circuit.

[0028] Optionally, the DC / AC converter further includes a third capacitor located on the primary side of the transformer, the third capacitor being connected in parallel across the DC power supply.

[0029] Optionally, the DC / AC converter further includes a common-mode signal suppression circuit located on the secondary side of the transformer, coupled to the phase switching circuit, and adapted to suppress common-mode signals.

[0030] Optionally, the number of the transformer, the DC power supply, the DC / AC conversion circuit, and the rectifier circuit are the same, and there are two or more of each; each of the rectifier circuits is coupled to the same phase switching circuit.

[0031] This invention also provides a power supply system, which includes a DC power supply and any of the DC / AC conversion devices described in the above embodiments.

[0032] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages:

[0033] The present invention provides a rectifier circuit and a phase switching circuit on the secondary side of the converter. The rectifier circuit rectifies the second AC signal into a second DC signal, which is then phase-switched by the phase switching circuit. Since the phase switching circuit only performs the phase switching operation and does not need to rectify the second AC signal, the controller can use a fixed-frequency method to control the switching transistors in the phase switching circuit. Compared to a variable-frequency method, this effectively reduces the number of switching operations of the switching transistors in the phase switching circuit, thereby reducing switching losses and improving the reliability of the power supply system.

[0034] Furthermore, since the rectifier circuit includes a first diode and a second diode, the anode of the first diode is coupled to the first terminal of the first switching transistor, the cathode of the first diode is coupled to the transformer, the anode of the second diode is coupled to the transformer, and the cathode of the second diode is coupled to the second terminal of the third switching transistor. Thus, when the controller controls the phase switching circuit to switch the phase of the second DC signal, at the same time, only one of the two switching transistors conducting in the phase switching circuit has current flowing through it, while no current flows through the other switching transistor. Compared to the case where current flows through both switching transistors, the conduction loss of the switching transistors in the phase switching circuit can be significantly reduced.

[0035] Furthermore, since the rectifier circuit includes a fifth switch and a sixth switch, when the controller controls the phase switching circuit to switch the phase of the second DC signal, it can control one of the fifth and sixth switches to be turned on and the other to be turned off. This also ensures that at the same time, only one of the two switches that are turned on in the phase switching circuit has current flowing through it, while the other switch has no current flowing through it. Compared to the case where current flows through both switches, this can significantly reduce the conduction loss of the switches in the phase switching circuit.

[0036] Furthermore, by setting a first capacitor and a second capacitor, which together with the primary leakage inductance and magnetizing inductance of the transformer form an LLC resonant circuit, the losses of the primary switching transistors and rectifier circuit components of the transformer can be reduced. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of a DC / AC converter according to an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the circuit structure of a DC / AC converter according to an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of the circuit structure of another DC / AC converter in an embodiment of the present invention;

[0040] Figures 4 to 11 This is a schematic diagram of the current flow direction of the DC / AC converter at different times in an embodiment of the present invention;

[0041] Figure 12 This is a schematic diagram of the structure of another DC / AC converter in an embodiment of the present invention;

[0042] Figure 13 This is a schematic diagram of the circuit structure of a DC / AC converter according to an embodiment of the present invention. Detailed Implementation

[0043] Existing DC / AC converters suffer from high losses in their switching transistors, which affects the reliability of the DC / AC conversion.

[0044] To address this issue, this invention provides a DC / AC converter. In this DC / AC converter, the phase switching circuit is only used for phase switching and does not require rectification of the second AC signal. Therefore, the controller can use a fixed-frequency method to control the switching transistor in the phase switching circuit. Compared with the variable-frequency method, this effectively reduces the number of switching operations of the switching transistor in the phase switching circuit, thereby reducing the switching losses and improving the reliability of the DC / AC conversion.

[0045] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0046] Reference Figure 1 This invention provides a DC / AC converter, which may include: a transformer 10, a DC / AC conversion circuit 12 located on the primary side of the transformer, a rectifier circuit 13 and a phase switching circuit 14 located on the secondary side of the transformer, and a controller 15. Wherein:

[0047] The DC / AC conversion circuit 12 is coupled to the DC power supply 11 and consists of multiple switching transistors. It is adapted to convert the first DC signal dc1 output by the DC power supply 11 into the first AC signal ac1.

[0048] The transformer 10 is coupled to the DC / AC conversion circuit 12 and is adapted to boost the first AC signal ac1 output by the DC / AC conversion circuit 12 to obtain the second AC signal ac2.

[0049] The rectifier circuit 13 is coupled to the transformer 10 and is adapted to rectify the second AC signal ac2 to obtain the second DC signal dc2.

[0050] The phase switching circuit 14, coupled to the rectifier circuit 13, is composed of multiple switching transistors and is adapted to perform phase switching on the second DC signal dc2 to obtain a third AC signal ac3. The third AC signal ac3 is adapted to be input to the AC power grid.

[0051] The controller 15 is coupled to the DC / AC conversion circuit 12 and the phase switching circuit 14, and is adapted to control the switching transistors in the DC / AC conversion circuit 12 by frequency conversion and to control the switching transistors in the phase switching circuit 14 by fixed frequency, so as to realize the conversion of the first DC signal ac1 to the third AC signal ac3.

[0052] Since the phase switching circuit 14 is only used for phase switching and does not require rectification, the controller can control the switching of the switching transistor in the phase switching circuit 14 at a fixed frequency, thereby reducing the number of switching cycles of the switching transistor in the phase switching circuit 14, thus reducing the switching losses of the phase switching circuit 14 and improving the reliability of the power supply system.

[0053] It should be noted that the "coupling" described in the embodiments of the present invention refers to a direct or indirect connection. For example, A and B are coupled, which can be either a direct connection between A and B or an indirect connection between A and B through one or more other electrical components. For example, A can be directly connected to C, and C can be directly connected to B, thereby achieving coupling between A and B through C.

[0054] In specific implementations, the DC power supply 11 can be an energy storage battery (such as a nickel-cadmium battery, a nickel-metal hydride battery, a lithium-ion battery, a lithium polymer battery, etc.), a solar panel, or some converters (such as an AC / DC converter or a DC / DC converter). There are no restrictions here, as long as it can provide DC power.

[0055] In specific implementations, the controller 15 may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0056] For example, DC power supply 201 is a solar panel that converts solar energy signals into DC voltage, and controller 15 can control DC / AC conversion circuit 12 to convert the first DC signal dc1 output by the solar panel into a first AC signal ac1 of a preset frequency.

[0057] In specific implementation, the phase switching circuit can be composed of four switching transistors, and there can be various circuit structures. No restrictions are imposed here, as long as it can perform phase switching on the second DC signal dc2 to obtain the third AC signal ac3.

[0058] In one embodiment of the present invention, the phase switching circuit includes: a first switch, a second switch, a third switch, and a fourth switch. Wherein:

[0059] The first terminal of the first switching transistor is coupled to the rectifier circuit and the second terminal of the second switching transistor, and the second terminal of the first switching transistor is coupled to the transformer. The second terminal of the second switching transistor is coupled to the rectifier circuit and the first terminal of the fourth switching transistor. The second terminal of the third switching transistor is coupled to the rectifier circuit and the second terminal of the fourth switching transistor, and the first terminal of the third switching transistor is coupled to the transformer.

[0060] The control terminals of the first, second, third, and fourth switching transistors are coupled to the controller; the first terminal of the fourth switching transistor and the first terminal of the third switching transistor are the output terminals of the phase switching circuit.

[0061] In specific implementations, at least one of the first, second, third, and fourth switching transistors can be a metal-oxide-semiconductor field-effect transistor (MOSFET) or other semiconductor devices such as an insulated-gate bipolar transistor (IGBT).

[0062] In one embodiment, the first, second, third, and fourth switching transistors are all high-voltage MOSFETs with an operating voltage of at least 325V. A diode is formed between the source and drain of each MOSFET, which serves as the body diode of that MOSFET.

[0063] For example, refer to Figure 2 and Figure 3 The first switch Q1, the second switch Q2, the third switch Q3 and the fourth switch Q4 are all NMOS transistors.

[0064] In other embodiments, the first switch, the second switch, the third switch, and the fourth switch may all be PMOS transistors.

[0065] In specific implementation, the rectifier circuit can be implemented in various structures, and there are no restrictions here, as long as it can ensure that one of the two switching transistors that are simultaneously turned on in the phase switching circuit has current flowing through it, while the other switching transistor does not have current flowing through it.

[0066] In one embodiment, the rectifier circuit can be implemented using diodes. Specifically, refer to... Figure 2The rectifier circuit may include a first diode D1 and a second diode D2. The anode of the first diode D1 is coupled to the first terminal of the first switching transistor Q1, and the cathode of the first diode D1 is coupled to the transformer 10. The anode of the second diode D2 is coupled to the transformer 10, and the cathode of the second diode D2 is coupled to the second terminal of the third switching transistor Q3.

[0067] In a specific implementation, the first diode D1 and the second diode D2 can be silicon carbide diodes. Compared to silicon diodes, silicon carbide diodes have lower voltage drops and are resistant to high temperatures, high voltages, and high frequencies.

[0068] Taking an NMOS transistor as an example, the first terminal of the switch is the source of the NMOS transistor, and the second terminal is the drain of the NMOS transistor. Specifically, refer to... Figure 2 The anode of the first diode D1 is coupled to the source of the first switch Q1. The cathode of the second diode D2 is coupled to the drain of the third switch Q3. The source of the first switch Q1 is also coupled to the source of the second switch Q2, and the drain of the second switch Q2 is coupled to the source of the fourth switch Q4. The drain of the third switch Q3 is coupled to the drain of the fourth switch Q4.

[0069] In specific implementation, refer to Figure 2 The controller can simultaneously turn on the second switch Q2 and the third switch Q3, while simultaneously turning off the first switch Q1 and the fourth switch Q4. Alternatively, the controller can simultaneously turn on the first switch Q1 and the fourth switch Q4, while simultaneously turning off the second switch Q2 and the third switch Q3.

[0070] Specifically, when the controller turns on the second switch Q2 and the third switch Q3 and turns off the first switch Q1 and the fourth switch Q4, current flows through either the second switch Q2 or the third switch Q3, rather than both switches. Therefore, compared to the case where both switches have current flowing through them, the conduction loss is significantly reduced.

[0071] Similarly, when the controller turns on the first switch Q1 and the fourth switch Q4, and turns off the second switch Q2 and the third switch Q3, current flows through either the first switch Q1 or the first switch Q4, rather than both the first switch Q1 and the fourth switch Q4. Therefore, compared to the case where current flows through both switches, the conduction loss is significantly reduced.

[0072] In practical implementation, the controller can control the switching transistors in the phase switching circuit using a fixed frequency method (e.g., power frequency, with a frequency of 50Hz). For example, the controller can output a 50Hz pulse signal to control the switching transistors. Specifically, in the first half-cycle, the controller keeps two fixed transistors (e.g., the second transistor Q2 and the third transistor Q3) on and the remaining two transistors (e.g., the first transistor Q1 and the fourth transistor Q4) off. In the second half-cycle, the controller keeps the remaining two transistors (i.e., the first transistor Q1 and the fourth transistor Q4) on and the two fixed transistors (i.e., the second transistor Q2 and the third transistor Q3) off, thus achieving current phase switching. For the primary-side transistors of the transformer, the controller can output a frequency-varying pulse signal to control the switching transistors on the primary side of the transformer.

[0073] In another embodiment, the rectifier circuit can be implemented using a switching transistor. Specifically, refer to... Figure 3 The rectifier circuit includes a fifth switch Q5 and a sixth switch Q6. The first terminal of the fifth switch Q5 is coupled to the first terminals of the first switch Q1 and the second switch Q2. The second terminal of the fifth switch Q5 is coupled to the transformer and the first terminal of the sixth switch Q6. The second terminal of the sixth switch Q6 is coupled to the second terminals of the third switch Q3 and the fourth switch Q4. The control terminals of the fifth switch Q5 and the sixth switch Q6 are coupled to a controller, which is adapted to control one of the fifth switch Q5 and the sixth switch Q6 to be turned on and the other switch to be turned off.

[0074] In specific implementations, the fifth switch Q5 and the sixth switch Q6 can be MOSFETs or other semiconductor devices such as IGBTs. When the fifth switch Q5 and the sixth switch Q6 are MOSFETs, they can be either PMOS or NMOS transistors. The fifth switch Q5 and the sixth switch Q6 can be the same device or different devices.

[0075] For example, refer to Figure 3 The fifth switch Q5 and the sixth switch Q6 are both NMOS transistors. At this point, the first terminal of the fifth switch Q5 and the sixth switch Q6 is the source of the NMOS transistor. The second terminal of the fifth switch Q5 and the sixth switch Q6 is the drain of the NMOS transistor.

[0076] Specifically, the source of the fifth switch Q5 is connected to the source of the first switch Q1 and the source of the second switch Q2, and the drain of the sixth switch Q6 is connected to the drain of the third switch Q3 and the drain of the fourth switch Q4. The drain of the fifth switch Q5 and the source of the sixth switch Q6 are connected to the transformer.

[0077] When the controller turns on the second switch Q2 and the third switch Q3, and turns off the first switch Q1 and the fourth switch Q4, it can simultaneously turn on the sixth switch Q6 and turn off the fifth switch Q5. At this time, only one of the second switch Q2 and the third switch Q3 has current flowing through it, thereby reducing conduction losses.

[0078] When the controller turns on the first switch Q1 and the fourth switch Q4, and turns off the second switch Q2 and the third switch Q3, it can simultaneously turn on the sixth switch Q6 and turn off the fifth switch Q5. At this time, only one of the first switch Q1 and the fourth switch Q4 has current flowing through it, thereby reducing conduction losses.

[0079] In specific implementation, refer to Figure 2 Transformer 10 may include: an ideal transformer T, a primary leakage inductance Lr1, a magnetizing inductance Lm, and a secondary leakage inductance Lr2. The ideal transformer T is a transformer whose primary and secondary port voltages are proportional and has no power loss. The ideal transformer T, along with the primary leakage inductance Lr1, magnetizing inductance Lm, and secondary leakage inductance Lr2, can be concretely implemented as a single, actual transformer.

[0080] One end of the transformer secondary leakage inductance Lr2 is connected to the secondary terminal of the ideal transformer T, and the other end is connected to the rectifier circuit. It should be noted that one end of the transformer secondary leakage inductance Lr2 can be connected to either the same-name terminal or the opposite-name terminal of the ideal transformer T's secondary side; there is no restriction here.

[0081] Reference Figure 2 When the rectifier circuit is implemented using diodes, the other end of the transformer secondary leakage inductance Lr2 is connected to the cathode of the first diode D1 and the anode of the second diode D2. (Refer to...) Figure 3 When the rectifier circuit is implemented by switching transistors, the other end of the leakage inductance Lr2 on the secondary side of the transformer is connected to the drain of the fifth switching transistor Q5 and the source of the sixth switching transistor Q6.

[0082] In one embodiment of the present invention, reference is made to... Figure 2 and Figure 3The DC / AC conversion device further includes: a first capacitor C1 and a second capacitor C2 located on the secondary side of the transformer 10; the first capacitor C1 and the second capacitor C2, together with the leakage inductance Lr1 and the magnetizing inductance Lm of the primary side of the transformer, form an LLC resonant circuit.

[0083] In a specific implementation, one end of the first capacitor C1 and one end of the second capacitor C2 can be coupled to the first end of the secondary side of the ideal transformer T. The other end of the first capacitor C1 and the other end of the second capacitor C2 can be coupled to the phase switching circuit.

[0084] It should be noted that the first terminal of the secondary side of the ideal transformer T may be either the same-name terminal or a different-name terminal of the secondary side of the ideal transformer T. When the leakage inductance Lr2 of the transformer secondary side is connected to the same-name terminal of the secondary side of the ideal transformer T, the first capacitor C1 and the second capacitor C2 are connected to the different-name terminal of the secondary side of the ideal transformer T.

[0085] In practical implementation, the controller can control the switching frequency of the primary-side switching transistor of the transformer, thereby changing the phase of the current signal flowing through the secondary-side leakage inductance Lr2 and magnetizing inductance Lm of the transformer. The controller controls the switching frequency of the secondary-side switching transistor, changing the phase of the voltage signal across either the first capacitor C1 or the second capacitor C2, ultimately making the phase of the current signal across the secondary-side leakage inductance Lr2 and magnetizing inductance Lm the same as the phase of the voltage signal across either the first capacitor C1 or the second capacitor C2, thus causing the circuit to resonate.

[0086] By setting the first capacitor C1 and the second capacitor C2, the circuit can achieve resonance. In the resonant state, zero-voltage turn-on (ZVS) of the transformer primary-side switch and zero-current turn-off of the devices in the transformer secondary-side rectifier circuit can be achieved without reverse recovery problems. This reduces the switching and conduction losses of the transformer primary-side switch and the devices in the rectifier circuit, thereby reducing the power system losses and improving the efficiency of the DC / AC converter.

[0087] In a specific implementation, the DC / AC conversion circuit can be a full-bridge circuit composed of MOSFETs. Specifically, refer to... Figure 2 and Figure 3The DC / AC conversion circuit may include a seventh switch Q7, an eighth switch Q8, a ninth switch Q9, and a tenth switch Q10. The seventh switch Q7 and the eighth switch Q8 are connected in series to form one arm of the full-bridge circuit. The ninth switch Q9 and the tenth switch Q10 are connected in series to form the other arm of the full-bridge circuit. One output terminal of the DC power supply 11 is connected to the drain of the seventh switch Q7 and the drain of the ninth switch Q9, and the other output terminal of the DC power supply 11 is connected to the source of the eighth switch Q8 and the source of the tenth switch Q10. Thus, the first DC signal output by the DC power supply 11 can be converted into a first AC signal by the full-bridge circuit and then input to the transformer 10.

[0088] In practical implementation, the controller can control the switching frequencies of the seventh switch Q7, the eighth switch Q8, the ninth switch Q9, and the tenth switch Q10, thereby changing the frequency of the first AC signal input to the transformer 10. Specifically, the controller can monitor the power output to the AC grid. When the power output to the AC grid does not reach the maximum power, it adjusts the switching frequencies of the seventh switch Q7, the eighth switch Q8, the ninth switch Q9, and the tenth switch Q10 to change the frequency of the first AC signal, thereby changing the power output to the AC grid.

[0089] In practice, the seventh switch Q7, the eighth switch Q8, the ninth switch Q9, and the tenth switch Q10 are all low-voltage MOSFETs, and their operating voltage is usually less than 60V.

[0090] In one embodiment of the present invention, reference is made to... Figure 2 and Figure 3 The DC / AC converter may further include a third capacitor C3 located on the primary side of the transformer, wherein the third capacitor C3 is connected in parallel across the DC power supply 11.

[0091] Specifically, the third capacitor C3 filters the first DC signal input from the DC power supply 11 and stores energy. The third capacitor C3 can form a resonant circuit with the transformer's primary leakage inductance Lr1 and magnetizing inductance Lm, thereby enabling zero-voltage turn-on of the switching transistors in the full-bridge circuit. The third capacitor C3 can be an electrolytic capacitor, which has a very large capacitance, tens to hundreds of times that of ordinary capacitors, thus facilitating energy storage.

[0092] In one embodiment of the present invention, the DC / AC converter may further include: a common-mode signal suppression circuit located on the secondary side of the transformer, coupled to the phase switching circuit, adapted to suppress common-mode signals. Specifically, refer to... Figure 2 and Figure 3The common-mode signal suppression circuit may include a fourth capacitor C4 and a common-mode inductor L0. The fourth capacitor C4 and the common-mode inductor L0 are connected in parallel at the output of the DC / AC converter to suppress common-mode signals and prevent common-mode signals from interfering with the AC power grid.

[0093] Taking the rectifier circuit implemented using diodes as an example, combined with Figures 4 to 11 The specific control process of the DC / AC converter is described as follows:

[0094] Reference Figure 4 At time t0, on the primary side of the transformer, the controller turns on the seventh switch Q7 and the tenth switch Q10, and turns off the ninth switch Q9 and the eighth switch Q8. On the secondary side of the transformer, the controller turns on the second switch Q2 and the third switch Q3, and turns off the first switch Q1 and the fourth switch Q4.

[0095] At this time, the current path on the primary side of the transformer is: DC power supply 11 → seventh switch Q7 → transformer primary leakage inductance Lr1 → magnetizing inductance Lm → tenth switch Q10 → DC power supply 11.

[0096] The current in the transformer secondary side follows one path: Transformer → Transformer secondary leakage inductance Lr2 → Second diode D2 → Third switch Q3 → AC power grid → Second capacitor C2 → Transformer. Another path is: Transformer → Transformer secondary leakage inductance Lr2 → Second diode D2 → Third switch Q3 → First capacitor C1 → Transformer. In other words, after flowing through the third switch Q3, the current in the transformer secondary side returns to the third capacitor C3 via different paths. During this process, the switch through which current flows is the third switch Q3.

[0097] Reference Figure 5 At time t1 (t1 > t0), on the primary side of the transformer, the controller disconnects the seventh switch Q7, the eighth switch Q8, the ninth switch Q9, and the tenth switch Q10. On the secondary side of the transformer, the controller keeps the second switch Q2 and the third switch Q3 on, and the first switch Q1 and the fourth switch Q4 off.

[0098] At this point, on the primary side of the transformer, due to the presence of the magnetizing inductance Lm, only the magnetizing current exists. Its path is: magnetizing inductance Lm → tenth switch Q10 → third capacitor C3 → seventh switch Q7 → transformer primary leakage inductance Lr1 → magnetizing inductance Lm. The magnetizing current flows to the third capacitor C3 through the parasitic capacitance within the tenth switch Q10. The magnetizing current flows to the transformer primary leakage inductance Lr1 through the parasitic capacitance within the seventh switch Q7.

[0099] On the secondary side of the transformer, one current path is: transformer → first capacitor C1 → source of third switch Q3 → AC power grid → source of fourth switch Q4 → second switch Q2 → first diode D1 → transformer secondary leakage inductance Lr2 → transformer. Another current path is: transformer → second capacitor C2 → second switch Q2 → first diode D1 → transformer secondary leakage inductance Lr2 → transformer. In this path, the transformer secondary current flows through the parasitic capacitance within the second switch Q2 to the first diode D1. During this process, the switch through which current flows is the second switch Q2.

[0100] Reference Figure 6 At time t2 (t2 > t1), on the primary side of the transformer, the controller turns on the ninth switch Q9 and the eighth switch Q8, and turns off the seventh switch Q7 and the tenth switch Q10. On the secondary side of the transformer, the controller keeps the second switch Q2 and the third switch Q3 on, and the first switch Q1 and the fourth switch Q4 off.

[0101] At this time, the current path on the primary side of the transformer is: magnetizing inductance Lm → transformer primary leakage inductance Lr1 → eighth switch Q8 → third capacitor C3 → ninth switch Q9 → drain of tenth switch Q10 → magnetizing inductance Lm.

[0102] On the secondary side of the transformer, the current path is... Figure 5 The current path is the same on the secondary side of the transformer. During this process, the only switching transistor with current flowing through it is the second switching transistor Q2.

[0103] Reference Figure 7 At time t3 (t3 > t2), on the primary side of the transformer, the controller disconnects the seventh switch Q7, the eighth switch Q8, the ninth switch Q9, and the tenth switch Q10. On the secondary side of the transformer, the controller keeps the second switch Q2 and the third switch Q3 on, and the first switch Q1 and the fourth switch Q4 off.

[0104] At this point, on the primary side of the transformer, due to the presence of the magnetizing inductance Lm, only the magnetizing current exists. Its path is: magnetizing inductance Lm → transformer primary leakage inductance Lr1 → seventh switch Q7 → third capacitor C3 → tenth switch Q10 → magnetizing inductance Lm. The magnetizing current flows to the magnetizing inductance Lm through the parasitic capacitance within the tenth switch Q10. The magnetizing current also flows to the third capacitor C3 through the parasitic capacitance within the seventh switch Q7.

[0105] On the secondary side of the transformer, the current path is... Figure 4 The current path on the secondary side of the transformer is the same. During this process, the only switching transistor with current flowing through it is the third switching transistor Q3.

[0106] The time interval from t0 to t3 is the positive half-cycle control timing of the third AC signal.

[0107] Reference Figure 8 At time t4 (t4 > t3), on the primary side of the transformer, the controller disconnects the seventh switch Q7, the eighth switch Q8, the ninth switch Q9, and the tenth switch Q10. On the secondary side of the transformer, the controller turns on the first switch Q1 and the fourth switch Q4, and turns off the second switch Q2 and the third switch Q3.

[0108] At this moment, on the primary side of the transformer, the current path is... Figure 4 The current path on the primary side of the transformer is the same.

[0109] On the secondary side of the transformer, one current path is: transformer → transformer secondary leakage inductance Lr2 → second diode D2 → fourth switch Q4 → AC power grid → source of third switch Q3 → first capacitor C1 → transformer. In this process, only the fourth switch Q4 carries current. Another current path is: transformer → transformer secondary leakage inductance Lr2 → second diode D2 → fourth switch Q4 → second capacitor C2 → transformer.

[0110] Reference Figure 9 At time t5 (t5 > t4), on the primary side of the transformer, the controller disconnects the seventh switch Q7, the eighth switch Q8, the ninth switch Q9, and the tenth switch Q10. On the secondary side of the transformer, the controller keeps the first switch Q1 and the fourth switch Q4 on, and the second switch Q2 and the third switch Q3 off.

[0111] At this moment, on the primary side of the transformer, the current path is... Figure 5 The current path is the same on the primary side of the transformer.

[0112] On the secondary side of the transformer, one current path is: transformer → first capacitor C1 → first switch Q1 → first diode D1 → transformer secondary leakage inductance Lr2 → transformer. Another current path is: transformer → second capacitor C2 → source of fourth switch Q4 → AC power grid → source of third switch Q3 → first switch Q1 → first diode D1 → transformer secondary leakage inductance Lr2 → transformer. In this process, only the first switch Q1 carries current.

[0113] Reference Figure 10 At time t6 (t6 > t5), on the primary side of the transformer, the controller turns on the ninth switch Q9 and the eighth switch Q8, and turns off the seventh switch Q7 and the tenth switch Q10. On the secondary side of the transformer, the controller keeps the first switch Q1 and the fourth switch Q4 on, and the second switch Q2 and the third switch Q3 off.

[0114] At this moment, on the primary side of the transformer, the current path is... Figure 6 The current path on the primary side of the transformer is the same.

[0115] On the secondary side of the transformer, the current path is... Figure 9 The current path is the same on the secondary side of the transformer. During this process, only the first switching transistor Q1 carries current.

[0116] Reference Figure 11 At time t7 (t7 > t6), on the primary side of the transformer, the controller disconnects the seventh switch Q7, the eighth switch Q8, the ninth switch Q9, and the tenth switch Q10. On the secondary side of the transformer, the controller keeps the first switch Q1 and the fourth switch Q4 on, and the second switch Q2 and the third switch Q3 off.

[0117] At this moment, on the primary side of the transformer, the current path is... Figure 7 The current path on the primary side of the transformer is the same.

[0118] On the secondary side of the transformer, the current path is... Figure 9 The current path on the secondary side of the transformer is the same. During this process, the only switching transistor with current flowing through it is the fourth switching transistor Q4.

[0119] The time interval from t4 to t7 is the negative half-cycle control timing of the third AC signal.

[0120] Therefore, by employing the phase switching circuit in this embodiment of the invention, since only current phase switching operation needs to be performed, the controller can control the switching of the transistors at a fixed frequency, thereby reducing the number of switching operations of the transistors in the phase switching circuit, and thus reducing the switching losses of the transistors in the phase switching circuit. Furthermore, in actual control, of the two transistors that are conducting in the phase switching circuit, only one transistor carries current, while the other transistor carries no current, thereby reducing the conduction losses of the transistors in the phase switching circuit.

[0121] Furthermore, in the phase switching circuit of this embodiment, the primary side of the transformer is frequency-controlled, but the secondary side of the transformer is frequency-controlled, thereby reducing the control difficulty.

[0122] In practical applications, a power system can include multiple DC power sources, which together provide power to the AC grid. For example, in a photovoltaic power generation system, there may be multiple solar panels that can work together to provide power to the AC grid.

[0123] In the existing technology, due to the limitations of the DC / AC converter circuit structure, the controller needs to control each DC / AC converter by frequency conversion. Therefore, in order to enable multiple solar panels to jointly provide power to the AC grid, a transformer and a DC / AC converter need to be set up for each solar panel. This results in more components, more complex control, and a larger circuit area for the DC / AC conversion device when two or more solar panels jointly provide power to the AC grid.

[0124] In one embodiment of the present invention, since the controller controls the switching of the switching transistor in the phase switching circuit at a fixed frequency, when two or more DC power sources provide power to the same AC power grid, the secondary side of the transformer can share the same phase switching circuit. The shared phase switching circuit can combine the second DC signals output by each DC power source through the corresponding rectifier circuit before performing phase switching.

[0125] For example, taking two DC power sources providing power to the same AC power grid as an example, refer to... Figure 12 DC power supplies 111 and 112 provide power to the same AC power grid. Specifically, the first DC signal dc1 output by DC power supply 111 is converted by the corresponding DC / AC converter circuit 121 to obtain the first AC signal ac1. The first AC signal ac1 is boosted by transformer 101 to obtain the second AC signal ac2. The second AC signal ac2 is rectified by rectifier circuit 131 to obtain the second DC signal dc2. The first DC signal dc1' output by DC power supply 112 is converted by the corresponding DC / AC converter circuit 122 to obtain the first AC signal ac1'. The first AC signal ac1' is boosted by transformer 102 to obtain the second AC signal ac2'. The second AC signal ac2' is rectified by rectifier circuit 132 to obtain the second DC signal dc2'. The second DC signal dc2 and the second DC signal dc2' are combined and input to the same phase switching circuit 14 for current phase switching to obtain the third AC signal ac3, which is then output to the AC power grid.

[0126] It should be noted that when two or more DC power sources supply power to the same AC grid, if a resonant circuit is required, a first capacitor and a second capacitor can be added to one end of each transformer to form a resonant circuit with the primary leakage inductance and magnetizing inductance of the connected transformers. The specific circuit diagram is as follows: Figure 13 As shown.

[0127] It is understood that the above-mentioned two DC power sources providing power to the same AC power grid is only one embodiment of the present invention. In practice, there may be three or more DC power sources providing power to the same AC power grid, and the specific number of DC power sources is not limited. Those skilled in the art can refer to the above description of two DC power sources providing power to the same AC power grid to carry out the implementation, which will not be repeated here.

[0128] Compared to existing circuit structures where two or more DC power sources provide power to the same AC power grid, the solution of this invention allows two or more DC power sources to share the same phase switching circuit, thereby reducing the number of components in the DC / AC converter, simplifying control, and reducing the circuit area.

[0129] Furthermore, in the embodiments of the present invention, the DC / AC conversion device isolates the DC / AC conversion circuit and the phase switching circuit through a transformer, and has fewer components and higher power density.

[0130] Furthermore, by setting a capacitor to form a resonant circuit with the primary leakage inductance and magnetizing inductance of the transformer, full resonant control of the DC / AC converter can be achieved, resulting in low switching losses of power devices and high power efficiency.

[0131] Embodiments of the present invention also provide a power supply system, which includes the DC / AC converter described above and a DC power supply. The DC / AC converter can convert a first DC signal output from the DC power supply into a third AC signal and output it to the AC power grid.

[0132] It should be noted that the DC power source includes, but is not limited to, solar panels, and may also be a DC power source such as a fuel cell.

[0133] Because the secondary-side switching transistors of the transformer in the aforementioned DC / AC converter have lower losses, the power supply system has higher reliability. Furthermore, the power supply system has higher power efficiency, simpler control, and lower cost.

[0134] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A DC / AC converter, characterized in that, Includes: a transformer, a DC / AC conversion circuit located on the primary side of the transformer, a rectifier circuit and a phase switching circuit located on the secondary side of the transformer, and a controller; wherein: The DC / AC conversion circuit is coupled to a DC power supply and consists of multiple switching transistors, and is adapted to convert the first DC signal output by the DC power supply into a first AC signal. The transformer is coupled to the DC / AC conversion circuit and is adapted to boost the first AC signal output by the DC / AC conversion circuit to obtain a second AC signal. The rectifier circuit is coupled to the transformer and is adapted to rectify the second AC signal to obtain a second DC signal; The phase switching circuit, coupled to the rectifier circuit, is composed of multiple switching transistors and is adapted to perform phase switching on the second DC signal to obtain a third AC signal, which is adapted to be input to the AC power grid. The controller is coupled to the DC / AC conversion circuit and the phase switching circuit, and is adapted to control the switching of the switching transistor in the DC / AC conversion circuit by frequency conversion and to control the switching of the switching transistor in the phase switching circuit by fixed frequency, so as to realize the conversion of the first DC signal to the third AC signal. The phase switching circuit includes: a first switch, a second switch, a third switch, and a fourth switch; wherein: a first terminal of the first switch is coupled to the rectifier circuit and a second terminal of the second switch; a second terminal of the second switch is coupled to the rectifier circuit and a first terminal of the fourth switch; and a second terminal of the third switch is coupled to the rectifier circuit and a second terminal of the fourth switch. The transformer includes: an ideal transformer, a primary leakage inductance of the transformer, a magnetizing inductance, and a secondary leakage inductance of the transformer; the DC / AC conversion device further includes: a first capacitor and a second capacitor located on the secondary side of the transformer; the first capacitor and the second capacitor, together with the primary leakage inductance and the magnetizing inductance of the transformer, form an LLC resonant circuit. One end of the first capacitor and one end of the second capacitor are coupled to the first end of the secondary side of the ideal transformer; the other end of the first capacitor is coupled to the second end of the first switching transistor and the first end of the third switching transistor; the other end of the second capacitor is coupled to the first end of the fourth switching transistor; and the rectifier circuit is coupled to the second end of the secondary side of the ideal transformer.

2. The DC / AC converter as described in claim 1, characterized in that, The rectifier circuit includes: a first diode and a second diode; wherein: The anode of the first diode is coupled to the first terminal of the first switching transistor, and the cathode of the first diode is coupled to the transformer. The anode of the second diode is coupled to the transformer, and the cathode of the second diode is coupled to the second terminal of the third switching transistor.

3. The DC / AC converter as described in claim 1, characterized in that, The rectifier circuit includes: a fifth switching transistor and a sixth switching transistor; wherein: The first end of the fifth switch is coupled to the first end of the first switch and the first end of the second switch; the second end of the fifth switch is coupled to the transformer and the first end of the sixth switch. The second end of the sixth switch is coupled to the second end of the third switch and the second end of the fourth switch; The control terminals of the fifth and sixth switching transistors are coupled to the controller, which is adapted to control one of the fifth and sixth switching transistors to be turned on and the other switching transistor to be turned off.

4. The DC / AC converter as described in claim 1, characterized in that, The DC / AC conversion circuit is a full-bridge circuit.

5. The DC / AC converter as described in claim 1, characterized in that, Also includes: The third capacitor is located on the primary side of the transformer and is connected in parallel across the DC power supply.

6. The DC / AC converter as described in claim 1, characterized in that, Also includes: The common-mode signal suppression circuit located on the secondary side of the transformer is coupled to the phase switching circuit and is suitable for suppressing common-mode signals.

7. The DC / AC converter as described in claim 1, characterized in that, The number of transformers, DC power supplies, DC / AC conversion circuits and rectifier circuits are the same, and there are two or more of each; each rectifier circuit is coupled to the same phase switching circuit.

8. A power supply system, characterized in that, It includes a DC power supply and a DC / AC conversion device as described in any one of claims 1 to 7.

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