A high-frequency link single-stage soft-switching DC-AC converter and a control method thereof

Abstract

The application discloses a high-frequency chain single-stage soft-switching DC-AC converter and a control method thereof. The converter comprises a DC input power supply, a primary side inversion circuit, a resonance cavity, a high-frequency transformer, a cycle converter, a filter, a load and a controller. The DC input power supply is connected with the load in sequence through the primary side inversion circuit, the resonance cavity, the high-frequency transformer, the cycle converter and the filter, and the controller is connected with the load, the primary side inversion circuit and the cycle converter. The method can realize the soft switching of the high-frequency switch tube through the method without output zero-crossing detection without additional auxiliary circuit.

Description

Technical Field

[0001] This invention belongs to the field of power electronic converter technology, and relates to a high-frequency chain single-stage soft-switching DC-AC converter and its control method. Background Technology

[0002] In many specialized inverter applications related to national economy and people's livelihood, it is often necessary to output complex waveforms with extremely wide amplitude and frequency ranges. For example, the DC-AC converter in the sonar system of underwater vehicles needs to generate sine waves from several Hz to hundreds of kHz to drive broadband underwater acoustic transducers for comprehensive seabed detection. In lithography machines, electroplating, micro-arc oxidation, induction heating, and laser emitters, various complex high-frequency pulses or gradient waveforms are required for output. In nuclear magnetic resonance and ultrasonic imaging equipment, DC-AC converters are needed to generate waveforms with extremely large amplitude and frequency variations.

[0003] Unlike traditional grid-connected / off-grid inverters with fixed frequency, phase, and amplitude, the AC waveforms of arbitrary waveform output DC-AC converters in the aforementioned applications share a common characteristic: extremely wide variations in both frequency and amplitude. Therefore, it is difficult to accurately detect the zero-crossing point of the high-frequency output AC signal. Traditional isolated grid-connected / off-grid inverters mostly employ a front-stage isolated DC-DC converter followed by a rear-stage inverter structure, achieving soft switching by using different control timings during the positive and negative half-cycles through precise detection of the output zero-crossing point. However, in arbitrary waveform output DC-AC converters, it is impossible to accurately distinguish between the positive and negative half-waves, making it difficult to achieve full-range soft switching of all high-frequency switching transistors, thus limiting improvements in converter efficiency, switching frequency, and other characteristics. Although some high-frequency chain DC-AC converters achieve single-stage power conversion by adding complex auxiliary circuits, they still cannot achieve soft switching of all switching transistors. Therefore, in applications where it is difficult to detect the output zero-crossing point of arbitrary waveform output DC-AC converters, achieving soft switching of high-frequency switching transistors without additional auxiliary circuitry through a method without output zero-crossing detection has become a current research challenge and focus. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-frequency chain single-stage soft-switching DC-AC converter and its control method. This method can achieve soft switching of the high-frequency switching transistor without additional auxiliary circuitry by using a zero-crossing detection method without output.

[0005] To achieve the above objectives, the high-frequency chain single-stage soft-switching DC-AC converter of the present invention includes a DC input power supply, a primary-side inverter circuit, a resonant cavity, a high-frequency transformer, a frequency converter, a filter, a load, and a controller.

[0006] The DC input power supply is connected to the load in sequence through the primary-side inverter circuit, resonant cavity, high-frequency transformer, frequency converter and filter. The controller is connected to the load, primary-side inverter circuit and frequency converter.

[0007] The primary-side inverter circuit includes a primary-side first switch, a primary-side second switch, a primary-side third switch, and a primary-side fourth switch. The positive terminal of the DC input power supply is connected to one end of the primary-side first switch and one end of the primary-side third switch. The negative terminal of the DC input power supply is connected to one end of the primary-side second switch and one end of the primary-side fourth switch. The other end of the primary-side first switch is connected to the other end of the primary-side second switch and one end of the resonant cavity input terminal. The other end of the primary-side third switch is connected to the other end of the primary-side fourth switch and the other end of the resonant cavity input terminal.

[0008] The frequency converter includes a first inductor, a second inductor, a first bidirectional switch, a second bidirectional switch, a third bidirectional switch, and a fourth bidirectional switch;

[0009] One end of the secondary side of the high-frequency transformer is connected to one end of the first inductor, and the other end of the secondary side of the high-frequency transformer is connected to one end of the second inductor. The other end of the first inductor is connected to one end of the first bidirectional switch and one end of the second bidirectional switch. The other end of the second inductor is connected to one end of the third bidirectional switch and one end of the fourth bidirectional switch. The other ends of the first bidirectional switch, the second bidirectional switch, the third bidirectional switch, and the fourth bidirectional switch are connected to the input terminal of the filter.

[0010] The first bidirectional switch consists of a secondary-side first switch and a secondary-side first diode.

[0011] The second bidirectional switch consists of a secondary-side second switch and a secondary-side second diode.

[0012] The third bidirectional switch consists of a secondary-side third switch and a secondary-side third diode.

[0013] The fourth bidirectional switch consists of a secondary fourth switch and a secondary fourth diode.

[0014] The first, second, third, and fourth secondary-side switching transistors are wide-bandgap semiconductor devices, field-effect transistors, or bipolar junction transistors.

[0015] The control method of the high-frequency chain single-stage soft-switching DC-AC converter of the present invention uses the voltage signal at both ends of the load as the feedback signal and adopts pulse density control, pulse skipping period modulation and pulse frequency modulation control strategies to control the frequency and pulse width of the primary first switch, primary second switch, primary third switch and primary fourth switch in the primary inverter circuit and the secondary first switch, secondary second switch, secondary third switch and secondary fourth switch in the frequency converter, so that the switching frequency is always lower than the series resonant frequency and operates in the inductive region of the resonant cavity.

[0016] The present invention has the following beneficial effects:

[0017] In practical operation, the high-frequency chain single-stage soft-switching DC-AC converter and its control method described in this invention use the voltage signal across the load as a feedback signal. Pulse density control, pulse cycle skipping modulation, and pulse frequency modulation control strategies are employed to ensure that the switching frequency of each switch in the primary-side inverter circuit and the frequency converter is always lower than the series resonant frequency and operates in the inductive region of the resonant cavity. This achieves soft switching of the high-frequency switch without additional auxiliary circuitry, eliminating the freewheeling current requirements of leakage inductance and output filter inductor current. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the present invention;

[0019] Figure 2 This is a structural diagram of the present invention;

[0020] Figure 3 A diagram of a high-frequency chain single-stage DC-AC converter circuit and its control strategy.

[0021] Figure 4 A diagram of the pulse cross-cycle modulation strategy for a resonant high-frequency chain single-stage DC-AC converter;

[0022] Figure 5a The waveform of the resonant inductor current is shown below.

[0023] Figure 5b The waveforms of drain-source voltage and current of the first and second secondary-side switching transistors are shown.

[0024] Figure 6 The output voltage waveform and the drain-source voltage and current waveforms of the first and second secondary switching transistors are shown. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion regarding the concepts disclosed in the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0026] The accompanying drawings show structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not drawn to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0027] refer to Figure 1 and Figure 2 The high-frequency chain single-stage soft-switching DC-AC converter of the present invention includes a DC input power supply 1, a primary-side inverter circuit 2, a resonant cavity 3, a high-frequency transformer 4, a frequency converter 5, a filter 6, a load 7, and a controller 8.

[0028] The frequency converter 5 includes a first bidirectional switch, a second bidirectional switch, a third bidirectional switch, and a fourth bidirectional switch. The primary-side inverter circuit 2 includes a primary-side first switch, a primary-side second switch, a primary-side third switch, and a primary-side fourth switch. The positive terminal of the DC input power supply 1 is connected to one end of the primary-side first switch and one end of the primary-side third switch. The negative terminal of the DC input power supply 1 is connected to one end of the primary-side second switch and one end of the primary-side fourth switch. The other end of the primary-side first switch is connected to the other end of the primary-side second switch and one end of the input terminal of the resonant cavity 3. The other end of the primary-side third switch is connected to the other end of the primary-side fourth switch and the other end of the input terminal of the resonant cavity 3.

[0029] One end of the secondary side of the high-frequency transformer 4 is connected to one end of the first inductor, and the other end of the secondary side of the high-frequency transformer 4 is connected to one end of the second inductor. The other end of the first inductor is connected to one end of the first bidirectional switch and one end of the second bidirectional switch. The other end of the second inductor is connected to one end of the third bidirectional switch and one end of the fourth bidirectional switch. The other ends of the first bidirectional switch, the second bidirectional switch, the third bidirectional switch, and the fourth bidirectional switch are connected to the input terminal of the filter 6.

[0030] The first bidirectional switch consists of a secondary-side first switch and a secondary-side first diode; the second bidirectional switch consists of a secondary-side second switch and a secondary-side second diode; the third bidirectional switch consists of a secondary-side third switch and a secondary-side third diode; and the fourth bidirectional switch consists of a secondary-side fourth switch and a secondary-side fourth diode.

[0031] The output of filter 6 is connected to load 7. Controller 8 collects the voltage signal across load 7 via a detector. Controller 8 is connected to the first, second, third, and fourth secondary-side switches, and the first, second, third, and fourth primary-side switches.

[0032] The first, second, third, and fourth secondary-side switching transistors are wide-bandgap semiconductor devices, field-effect transistors, or bipolar junction transistors; the first, second, third, and fourth secondary-side diodes can be replaced by active switching transistors operating in synchronous mode.

[0033] refer to Figures 3 to 4 The DC-AC converter frequency converter switching transistor control method of the present invention includes the following steps:

[0034] The controller 8 collects the voltage signal across the load 7 as feedback and uses pulse density control, pulse skipping period modulation and pulse frequency modulation control strategies to control the frequency and pulse width of the primary first switch, primary second switch, primary third switch and primary fourth switch in the primary inverter circuit 2 and the secondary first switch, secondary second switch, secondary third switch and secondary fourth switch in the frequency converter 5, so that the switching frequency is always lower than the series resonant frequency and operates in the inductive region of the resonant cavity 3. The series resonant frequency is the resonant frequency of the series resonant inductor and the series resonant capacitor.

[0035] The control strategy of the DC-AC converter is characterized by the following: the primary-side inverter circuit 2 includes circuits such as full-bridge, half-bridge and push-pull that can generate inverter square waves, which invert the input DC chopper into a high-frequency square wave, and construct different square wave voltages by frequency conversion or phase shifting.

[0036] The resonant cavity 3 uses a series-parallel connection of resonant components and always operates in the inductive region. Taking the LLC resonant cavity 3 as an example, the inverter square wave is filtered into an approximate sinusoidal voltage, and electrical isolation and voltage ratio are achieved through the high-frequency transformer 4. The switching frequency is always lower than the series resonant frequency. The frequency converter 5 operates in the O-mode, OPO-mode, PO-mode, etc., which include the O-mode. The secondary current is zero in the O-mode. At this time, the frequency converter 5 performs commutation. Without auxiliary circuits, soft switching of all switching transistors is achieved, eliminating the leakage inductance current and the freewheeling current requirement of the output filter inductor.

[0037] Specifically, when the output voltage is positive, the second and fourth secondary switches are turned off, while the first and third secondary switches are turned on following the first and fourth primary switches. The first and third secondary switches are turned on earlier than the first and fourth primary switches to achieve soft switching. They are turned off at the end of the primary switching period, i.e., when the circuit enters the O mode, to achieve soft switching. When the output voltage feedback signal is lower than the reference signal, the secondary-side first, second, third, and fourth switches remain on, following the primary-side first, second, third, and fourth switches, to transfer energy to the load 7. When the output voltage feedback signal is higher than the reference signal, the secondary-side first, second, third, and fourth switches are off, while the primary-side first, second, third, and fourth switches maintain their switching action to provide freewheeling current for the inductor. If, after the secondary-side first, second, third, and fourth switches have reached the preset off time, the output voltage feedback signal is still higher than the reference signal, the secondary-side second and fourth switches turn on, following the primary-side first and fourth switches, causing the output voltage to become negative.

[0038] When the output voltage is negative, the first and third secondary-side switches are both turned off, while the second and fourth secondary-side switches turn on following the first and fourth primary-side switches. The second and fourth secondary-side switches turn on earlier than the first and fourth primary-side switches to achieve soft switching. They turn off at the end of the conduction period of the first and fourth primary-side switches, i.e., when the circuit enters the zero-mode, to achieve soft switching turn-off. When the output voltage feedback signal is higher than the reference signal, the secondary-side first, second, third, and fourth switches remain on, following the primary-side first, second, third, and fourth switches, to transfer energy to the load 7. When the output voltage feedback signal is lower than the reference signal, the secondary-side first, second, third, and fourth switches are off, while the primary-side first, second, third, and fourth switches maintain their switching action to provide freewheeling current for the inductor. If, after the secondary-side first, second, third, and fourth switches have reached the preset off time, the output voltage feedback signal is still lower than the reference signal, then the secondary-side first and third switches turn on, following the primary-side first and fourth switches, making the output voltage positive.

[0039] When the secondary-side switching transistors have a high continuous conduction frequency, the primary-side first, second, third, and fourth switching transistors, as well as the secondary-side first, second, third, and fourth switching transistors, undergo pulse frequency modulation. In the inductive region of resonant cavity 3, the switching frequencies of these transistors are reduced, increasing the converter gain and meeting the demand for high peak output voltage. In the inductive region of resonant cavity 3, the switching frequencies of these transistors are increased to near the series resonant frequency, reducing the effective value of the switching transistor current and meeting the efficiency improvement requirements under high load.

[0040] Figure 5a and Figure 5b These are simulated waveforms of the resonant inductor current, drain-source voltage and current of the switching transistor in the example circuit proposed in this invention. Figure 5a and Figure 5b It is understood that the present invention adopts a pulse cross-cycle modulation strategy to realize soft switching of the primary side first switch, primary side second switch, primary side third switch, primary side fourth switch, secondary side first switch, secondary side second switch, secondary side third switch and secondary side fourth switch. Figure 6 The diagram shows the output voltage waveform and the drain-source voltage and current waveforms of the first and second secondary switches in this embodiment. It can be seen that the output voltage has a high sinusoidal degree.

Claims

1. A high-frequency chain single-stage soft-switching DC-AC converter, characterized in that, Includes DC input power supply (1), primary-side inverter circuit (2), resonant cavity (3), high-frequency transformer (4), frequency converter (5), filter (6), load (7) and controller (8); The DC input power supply (1) is connected to the load (7) in sequence through the primary side inverter circuit (2), resonant cavity (3), high frequency transformer (4), frequency converter (5) and filter (6). The controller (8) is connected to the load (7), the primary side inverter circuit (2) and the frequency converter (5). The primary-side inverter circuit (2) includes a primary-side first switch, a primary-side second switch, a primary-side third switch, and a primary-side fourth switch. The positive terminal of the DC input power supply (1) is connected to one end of the primary-side first switch and one end of the primary-side third switch. The negative terminal of the DC input power supply (1) is connected to one end of the primary-side second switch and one end of the primary-side fourth switch. The other end of the primary-side first switch is connected to the other end of the primary-side second switch and one end of the input terminal of the resonant cavity (3). The other end of the primary-side third switch is connected to the other end of the primary-side fourth switch and the other end of the input terminal of the resonant cavity (3). The frequency converter (5) includes a first inductor, a second inductor, a first bidirectional switch, a second bidirectional switch, a third bidirectional switch, and a fourth bidirectional switch; One end of the secondary side of the high-frequency transformer (4) is connected to one end of the first inductor, and the other end of the secondary side of the high-frequency transformer (4) is connected to one end of the second inductor. The other end of the first inductor is connected to one end of the first bidirectional switch and one end of the second bidirectional switch. The other end of the second inductor is connected to one end of the third bidirectional switch and one end of the fourth bidirectional switch. The other ends of the first bidirectional switch, the second bidirectional switch, the third bidirectional switch, and the fourth bidirectional switch are connected to the input end of the filter (6).

2. The high-frequency chain single-stage soft-switching DC-AC converter according to claim 1, characterized in that, The first bidirectional switch consists of a secondary-side first switch and a secondary-side first diode.

3. The high-frequency chain single-stage soft-switching DC-AC converter according to claim 2, characterized in that, The second bidirectional switch consists of a secondary-side second switch and a secondary-side second diode.

4. The high-frequency chain single-stage soft-switching DC-AC converter according to claim 3, characterized in that, The third bidirectional switch consists of a secondary-side third switch and a secondary-side third diode.

5. The high-frequency chain single-stage soft-switching DC-AC converter according to claim 4, characterized in that, The fourth bidirectional switch consists of a secondary fourth switch and a secondary fourth diode.

6. The high-frequency chain single-stage soft-switching DC-AC converter according to claim 5, characterized in that, The first, second, third, and fourth secondary-side switches are wide-bandgap semiconductor devices.

7. A control method for the high-frequency chain single-stage soft-switching DC-AC converter as described in claim 1, characterized in that, The controller (8) collects the voltage signal at both ends of the load (7) as a feedback signal and uses pulse density control, pulse jump period modulation and pulse frequency modulation control strategies to control the frequency and pulse width of the primary first switch, primary second switch, primary third switch and primary fourth switch in the primary inverter circuit (2) and the secondary first switch, secondary second switch, secondary third switch and secondary fourth switch in the frequency converter (5), so that the switching frequency is always lower than the series resonant frequency and works in the inductive region of the resonant cavity (3).

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