Three-port flyback dc-ac converter and modulation method thereof

Abstract

The application relates to the technical field of power electronic converter control, and provides a three-port flyback DC-AC converter, characterized in that the three-port flyback DC-AC converter comprises a flyback circuit, a power frequency reverse bridge, an AC-DC converter and a CL filter which are sequentially connected in cascade; the AC-DC converter is an AC-DC three-winding flyback converter which can realize power factor correction function, and is realized through active device multiplexing and magnetic component multiplexing, and comprises a flyback transformer T 2, excitation inductance L f , output switch Q 3, Q 4; the modulation method is to calculate instantaneous output power P o , judge the operation mode of the system, and respectively perform active modulation, reactive modulation or mixed modulation, so that the power factor is adjusted through the modulation method.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter control technology, specifically to a three-port flyback DC-AC converter and its modulation method. Background Technology

[0002] With the widespread integration of distributed energy resources, the reactive power demand of the power grid has become more complex and variable. Therefore, countries and regions worldwide have set higher standards and specifications for grid-connected technologies, among which power factor regulation has become one of the important requirements for grid-connected inverters. International distributed power grid-connected standards such as California's Rule 21 and IEEE-1547, as well as my country's national and industry standards for grid-connected inverters such as NB / T32004-2018, all clearly define the power factor regulation capabilities of grid-connected inverters.

[0003] Flyback topologies are widely used in various quasi-single-stage grid-connected inverters due to their advantages such as simple structure, fewer components, convenient control, and electrical isolation, forming the core DC / AC conversion unit. In these quasi-single-stage inverters, energy transfer is generally unidirectional, flowing from the DC side to the grid side.

[0004] However, traditional unidirectional grid-connected inverters struggle to achieve bidirectional energy flow and power factor regulation. Taking flyback DC / AC converters as an example, the inability to achieve power factor regulation stems primarily from two fundamental limitations: first, the output diodes of flyback converters possess unidirectional conductivity, meaning that the energy stored in the transformer can only be transferred unidirectionally to the grid; second, to reduce costs, the subsequent power frequency inversion bridge often uses thyristors. While the unidirectional conductivity of thyristors allows them to complete the power frequency commutation of the output current, it blocks the path for power to be fed back from the grid side.

[0005] Due to the unidirectional characteristics of diodes and thyristors, traditional flyback DC / AC converters exhibit strict unidirectionality in energy transmission and cannot achieve power factor regulation. Furthermore, their traditional control strategies primarily focus on the stable transmission of active power, failing to control reactive power. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to design a DC-AC converter and its modulation method to solve the problem that traditional unidirectional grid-connected inverters cannot achieve power factor regulation.

[0007] The present invention solves the above-mentioned technical problems through the following technical means: This invention provides a three-port flyback DC-AC converter, comprising a flyback circuit, a power frequency inverting bridge, an AC-DC converter, and a CL filter cascaded in sequence; the AC-DC converter is a circuit with bidirectional energy flow characteristics or a circuit capable of power factor correction.

[0008] Furthermore, the circuit with the bidirectional energy flow characteristic includes: a BUCK circuit, a BOOST circuit, a four-switch BUCK-BOOST circuit, and an H-bridge circuit; The circuit that enables power factor correction includes: a FLYBACK circuit, a DAB circuit, a high-frequency chain matrix converter, a Sepic single-stage bridgeless isolated PFC circuit, a single-stage half-bridge PFC circuit, and a half-bridge LLC circuit.

[0009] Furthermore, the AC-DC converter is an AC-DC three-winding flyback converter that has undergone active device multiplexing and magnetic component multiplexing.

[0010] Furthermore, the specific circuit topology includes: Input DC voltage U dc Decoupling capacitor C dc The switching transistors of the main flyback converter S w Main flyback transformer T 1, T 1 Magnetizing inductance L m , T Leakage inductance of 1 L k Output diodes of the main flyback converter D 1; Output capacitor of the main flyback converter C bus ; Thyristors constituting the power frequency inversion bridge S 1. S 2 and switching transistor Q 1. Q 2; Grid-side inductor L g Filter capacitor C f The flyback transformer of the AC-DC three-winding flyback converter T 2; Flyback transformer T 2 Magnetizing inductance L f Output switch of AC-DC three-winding flyback converter Q 3. Q 4; Grid voltage v g The main flyback transformer TThe number of turns of the primary and secondary windings of 1 are respectively N p and N s The flyback transformer T 2. Connected in series to the power grid side.

[0011] This invention also provides a modulation method for a three-port flyback DC-AC converter, based on a circuit topology that incorporates the aforementioned AC-DC three-winding flyback converter with active device multiplexing and magnetic component multiplexing, by inputting the grid-side sampled voltage into a phase-locked loop to obtain the grid voltage phase. θ The reference value of the output current is obtained by determining the output power factor PF. i g And by calculating the instantaneous output power P o Determining the system's operating mode includes: (1) If the instantaneous output power P o If the value is greater than 0, the system operates in DC / AC conversion mode, the modulation strategy is active modulation, and the high-frequency switching transistor for power transmission is... S w The on / off mode is intermittent. S w The duty cycle is ; (2) If the instantaneous output power P o If the value is less than 0, the system is in AC / DC conversion mode, the modulation strategy is reactive power modulation, and the high-frequency switch for power transmission is the switch of the lower arm of the power frequency inversion bridge. Q 1. Q 2. The current is in discontinuous mode near the zero-crossing point, and the voltage is in continuous mode near the zero-crossing point; and when v g When >0, Q 1. High-frequency action, Q 2. Turn off; when v g When <0, Q 1. Turn off, Q 2. High-frequency action; Q 1. Q The duty cycle of 2 is ; (3) If the instantaneous output power P o Near the zero-crossing point, the system operates in a hybrid mode of AC / DC conversion and DC / AC conversion, with a modulation strategy that includes both active and reactive power modulation. The high-frequency switching transistor for power transmission is... S w and the switching transistor of the lower arm of the power frequency reversing bridge.Q 1. Q 2, of which, Q 1. Q The switching mode and duty cycle of 2 are consistent with reactive power modulation. S w Energy is supplied through pulse conduction to maintain the output voltage of the main flyback converter, with a duty cycle of [value missing]. .

[0012] Furthermore, the instantaneous output power P o The calculation is as follows:

[0013] in, U grms This is the effective value of the grid-side voltage. I grms This is the effective value of the output current. θ The phase of the grid-side voltage. φ This represents the phase difference between the output voltage and current.

[0014] Furthermore, the active power modulation time S w duty cycle Specifically: S w The conduction time is:

[0015] in, L p For transformer T The magnetizing inductance of 1 n 1 is a transformer T A turns ratio of 1 t off2_S for S w and D 1. The time of all shutdowns U dc For input DC voltage, U grms This is the effective value of the grid-side voltage. I grms This is the effective value of the output current; D 1. The conduction time is:

[0016] S w The switching period and frequency are:

[0017] In the formula: t on_S for S w On-time, t off_S for D 1. On-time t off2_S for S w and D 1. The time of all shutdowns f s_S for S w The switching frequency; S w Duty cycle is:

[0018] in, for S w Duty cycle.

[0019] Furthermore, the reactive power modulation time Q 1. Q The duty cycle of 2 is Specifically: Q 1. Q 2. The conduction time is:

[0020] in, L f For transformer T 2 magnetizing inductance, n 2 is T 2 Transformers T A turns ratio of 2 t off2_Q for Q 1. Q 2. Q 3. Q 4. The time of shutdown. U dc For input DC voltage, U grms This is the effective value of the grid-side voltage. I grms This is the effective value of the output current; Q 3. Q 4. The conduction time is:

[0021] Q1. Q 2. The switching period and frequency are:

[0022] in, t on_Q for Q 1. Q 2. On-time t off_Q for Q 3. Q 4. On-time t off2_Q for Q 1. Q 2. Q 3. Q The shutdown time for all 4, of which, when running in continuous mode, t off2_Q =0, f s_Q for Q 1. Q 2. Switching frequency; Q 1. Q 2. Duty cycle is:

[0023] in, for Q 1. Q A duty cycle of 2.

[0024] Furthermore, during the hybrid modulation, S w duty cycle Specifically: The current is zero near the zero-crossing point; The duty cycle is 1% to 10% near the voltage zero crossing point.

[0025] The present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described method.

[0026] The advantages of this invention are: This invention, without altering the traditional unidirectional grid-connected inverter topology, integrates an AC / DC converter as a component into the conventional topology in series. It also proposes a family of AC / DC converter topologies and provides examples of several derived topologies, expanding the applicability and application scenarios of this type of topology. Furthermore, taking a flyback DC-AC converter as an example, it proposes a three-port flyback DC-AC converter topology and its modulation method, incorporating an AC-DC three-winding flyback converter with active device multiplexing and magnetic component multiplexing. This achieves precise power factor regulation. The proposed hybrid operating mode of the DC / AC conversion branch and the AC / DC conversion branch solves the problem that traditional unidirectional DC-AC converter topologies cannot achieve power factor regulation. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a conventional unidirectional grid-connected inverter according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a three-port DC-AC converter according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the topology of a three-port flyback DC-AC converter according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the AC-DC converter as a BUCK circuit in an embodiment of the present invention; Figure 5 This is a schematic diagram of the AC-DC converter as a BOOST circuit in an embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of the AC-DC converter of the present invention, which is a four-switch BUCK-BOOST circuit. Figure 7 This is a schematic diagram of the structure of the AC-DC converter as an H-bridge circuit in an embodiment of the present invention; Figure 8 This is a schematic diagram of the AC-DC converter as a FLYBACK circuit in an embodiment of the present invention; Figure 9 This is a schematic diagram of the AC-DC converter being a DAB circuit according to an embodiment of the present invention; Figure 10 This is a schematic diagram of the AC-DC converter circuit of the present invention, which is a high-frequency chain matrix converter circuit. Figure 11 This is a schematic diagram of the structure of the AC-DC converter of the present invention, which is a Sepic single-stage bridgeless isolated PFC circuit; Figure 12 This is a schematic diagram of the AC-DC converter of the present invention, which is a single-stage half-bridge PFC circuit. Figure 13The structural schematic diagram of the AC-DC converter in the embodiment of the present invention is a half-bridge LLC circuit; Figure 14 The structural schematic diagram of the AC-DC converter in the embodiment of the present invention is a three-winding flyback converter circuit; Figure 15 The schematic diagram of the time-sharing hybrid modulation strategy in the embodiment of the present invention; Figure 16 The schematic diagram of the equivalent circuit during active power modulation in the embodiment of the present invention; Figure 17 The schematic diagram of the equivalent circuit during reactive power modulation in the embodiment of the present invention; Figure 18 The schematic diagram of the equivalent circuit during hybrid modulation in the embodiment of the present invention; Figure 19 The flowchart of the hybrid modulation strategy in the embodiment of the present invention; Figure 20 The schematic diagram of the driving waveforms of all switching tubes under the condition of PF = 1 in the embodiment of the present invention; Figure 21 The schematic diagram of the driving waveforms of all switching tubes under the condition of PF ≠ 1 in the embodiment of the present invention; Figure 22 For the embodiment of the present invention under the condition of PF ≠ 1 Q 1 and Q The driving waveform schematic diagram of 2; Figure 23 The schematic diagram of the switching driving waveforms of all switching tubes during the hybrid modulation stage in the embodiment of the present invention; Figure 24 The schematic diagram of the bus voltage, grid-side voltage and output current waveforms when PF = 1 in the embodiment of the present invention; Figure 25 The schematic diagram of the bus voltage, grid-side voltage and output current waveforms when 0 < PF < 1 in the embodiment of the present invention; Figure 26 The schematic diagram of the bus voltage, grid-side voltage and output current waveforms when -1 < PF < 0 in the embodiment of the present invention. Detailed implementation manners

[0028] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] Embodiment 1 As Figure 1As shown, based on the traditional grid-connected inverter, this embodiment provides a three-port DC-AC converter, such as... Figure 2 As shown. Taking a three-port flyback DC-AC converter as an example, as... Figure 3 As shown, it includes a flyback circuit, a power frequency inverting bridge, an AC-DC converter, and a CL filter cascaded in sequence; the front stage is a single-input DC / DC circuit, whose main function is to convert the input DC voltage into a sine wave voltage; the rear stage is a power frequency inverting bridge circuit, whose main function is to convert the sine wave into an AC output. The two together constitute the DC-AC conversion function; the AC-DC converter is used as an additional branch to realize the AC-DC conversion function. The AC-DC converter only needs to meet any one of the following functions to be used as an additional branch: (1) bidirectional energy flow characteristics; (2) power factor correction function. Including but not limited to Figures 4-7 The circuit topology shown includes the following circuits with bidirectional energy flow characteristics: BUCK circuit, BOOST circuit, four-switch BUCK-BOOST circuit, and H-bridge circuit. Including but not limited to Figures 8-13 The circuit topology shown includes the following circuits for achieving power factor correction: FLYBACK circuit, DAB circuit, high-frequency chain matrix converter, Sepic single-stage bridgeless isolation PFC circuit, single-stage half-bridge PFC circuit, and half-bridge LLC circuit.

[0030] In this embodiment, the AC-DC converter used is a three-winding flyback AC-DC converter that has undergone active device multiplexing and magnetic component multiplexing. For example... Figure 14 As shown, the specific circuit topology includes: Input DC voltage U dc Decoupling capacitor C dc The switching transistors of the main flyback converter S w Main flyback transformer T 1, T 1 Magnetizing inductance L m , T Leakage inductance of 1 L k Output diodes of the main flyback converter D 1; Output capacitor of the main flyback converter C bus ; Thyristors constituting the power frequency inversion bridge S 1. S 2 and switching transistor Q 1. Q 2; Grid-side inductor L g Filter capacitorC f The flyback transformer of the AC-DC three-winding flyback converter T 2; Flyback transformer T 2 Magnetizing inductance L f Output switch of AC-DC three-winding flyback converter Q 3. Q 4; Grid voltage v g The main flyback transformer T The number of turns of the primary and secondary windings of 1 are respectively N p and N s The flyback transformer T 2. Connected in series to the power grid side.

[0031] Example 2 It should be further explained that, based on the same inventive concept, this embodiment provides a modulation method for a three-port flyback DC-AC converter. The core modulation strategy and the equivalent circuits corresponding to different strategies are as follows: Figures 15-18 As shown, based on the AC-DC three-winding flyback converter topology described in Example 1, the grid-side sampled voltage is input into the phase-locked loop to obtain the grid voltage phase. θ The reference value of the output current is obtained by determining the output power factor PF. i g And by calculating the instantaneous output power P o Determining the system's operating mode includes: (1) If the instantaneous output power P o If the value is greater than 0, the system operates in DC / AC conversion mode, the modulation strategy is active modulation, and the high-frequency switching transistor for power transmission is... S w The on / off mode is intermittent. S w The duty cycle is ; (2) If the instantaneous output power P o If the value is less than 0, the system is in AC / DC conversion mode, the modulation strategy is reactive power modulation, and the high-frequency switch for power transmission is the switch of the lower arm of the power frequency inversion bridge. Q 1. Q 2. The current is in discontinuous mode near the zero-crossing point, and the voltage is in continuous mode near the zero-crossing point; and when v g When >0, Q 1. High-frequency action, Q 2. Turn off; whenv g When <0, Q 1. Close Q 2. High-frequency action; Q 1. Q The duty cycle of 2 is ; (3) If the instantaneous output power P o Near the zero-crossing point, the system operates in a hybrid mode of AC / DC conversion and DC / AC conversion, with a modulation strategy that includes both active and reactive power modulation. The high-frequency switching transistor for power transmission is... S w and the switching transistor of the lower arm of the power frequency reversing bridge. Q 1. Q 2, of which, Q 1. Q The switching mode and duty cycle of 2 are consistent with reactive power modulation. S w Energy is supplied through pulse conduction to maintain the output voltage of the main flyback converter, with a duty cycle of [value missing]. During hybrid modulation, S w duty cycle Specifically, depending on the actual situation: the duty cycle is 0 near the current zero-crossing point; and the duty cycle is 1% to 10% near the voltage zero-crossing point.

[0032] The instantaneous output power P o The calculation is as follows:

[0033] in, U grms This is the effective value of the grid-side voltage. I grms This is the effective value of the output current. θ The phase of the grid-side voltage. φ This represents the phase difference between the output voltage and current.

[0034] The active power modulation S w duty cycle Specifically: S w The conduction time is:

[0035] in, L p For transformer T The magnetizing inductance of 1 n 1 is a transformerT A turns ratio of 1 t off2_S for S w and D 1. The time of all shutdowns U dc For input DC voltage, U grms This is the effective value of the grid-side voltage. I grms This is the effective value of the output current; D 1. The conduction time is:

[0036] S w The switching period and frequency are:

[0037] In the formula: t on_S for S w On-time, t off_S for D 1. On-time t off2_S for S w and D 1. The time of all shutdowns f s_S for S w The switching frequency; S w Duty cycle is:

[0038] in, for S w Duty cycle.

[0039] The reactive power modulation Q 1. Q The duty cycle of 2 is Specifically: Q 1. Q 2. The conduction time is:

[0040] in, L f For transformer T 2 magnetizing inductance, n2 is T 2 Transformers T A turns ratio of 2 t off2_Q for Q 1. Q 2. Q 3. Q 4. The time of shutdown. U dc For input DC voltage, U grms This is the effective value of the grid-side voltage. I grms This is the effective value of the output current; Q 3. Q 4. The conduction time is:

[0041] Q 1. Q 2. The switching period and frequency are:

[0042] in, t on_Q for Q 1. Q 2. On-time t off_Q for Q 3. Q 4. On-time t off2_Q for Q 1. Q 2. Q 3. Q The shutdown time for all 4, of which, when running in continuous mode, t off2_Q =0, f s_Q for Q 1. Q 2. Switching frequency; Q 1. Q 2. Duty cycle is:

[0043] in, for Q 1. Q A duty cycle of 2.

[0044] In this embodiment, the specific principle of the hybrid modulation method is as follows: According to such Figure 19 The control approach shown involves sampling the grid-side voltage to obtain the corresponding voltage phase. θ And by determining the power factor PF and the output rated apparent power. S ref Obtain the phase difference between the output voltage and current φ and the corresponding grid-side current reference value i g By determining the direction of instantaneous power transmission, the system can be divided into two modes: (1) unity power factor transmission mode and (2) non-unity power factor transmission mode.

[0045] If the transmission mode is unity power factor, the instantaneous output power during the entire power frequency cycle is... P o >0 indicates that the system is operating in the active phase, the modulation strategy is active modulation, and the mode is the DC / AC conversion branch operating mode.

[0046] If the transmission mode is not unity power factor, the system operates in three modes based on the instantaneous output power: DC / AC converter branch operating alone, AC / DC converter branch operating alone, and a mixed operating mode of DC / AC converter branch and AC / DC converter branch. Instantaneous output power P o When the output power is greater than 0, the system operates in the active power phase, using an active power modulation strategy, and the mode is the DC / AC converter branch operating alone mode; instantaneous output power P o When the power factor is less than 0, the system operates in two modes: a mode where the AC / DC conversion branch operates alone, and a mode where the DC / AC conversion branch and the AC / DC conversion branch operate in a hybrid mode. The system operates in the reactive power phase and the hybrid mode phase, respectively, corresponding to reactive power modulation and hybrid modulation strategies. This modulation strategy effectively ensures power factor accuracy and output power quality. Specifically: (1) When the system operates in unity power factor transmission mode, i.e., PF=1, the instantaneous output power during the entire power frequency cycle P o >0, the system operates in the active power phase, and the mode is the DC / AC conversion branch operating alone mode: the system's switching transistors and thyristors are driven within the power frequency cycle as follows: Figure 20 As shown in the left figure, t 0~ t 1 and t 2~ t All three stages are in the DC / AC conversion branch operation stage. t 1~ t Phase 2 is the dead time of the system commutation.

[0047] PF=1 working condition t 0~ t Phase 1: At this stage, the grid-side voltage...v g and output current i g All are greater than 0, i.e., instantaneous output power P o If the value is greater than 0, the system operates in the active power phase, and the system mode is the DC / AC converter branch operating alone mode. The modulation strategy is an active power modulation strategy. S w It can operate in both constant-frequency discontinuous mode and variable-frequency discontinuous mode; the thyristors of the power frequency inverting bridge S 1. Conduction, S 2. Turn off, switching transistor Q 1. Turn off Q 2. On, the specific switching cycle mode is as follows: Figure 20 Right image; PF=1 working condition t 1~ t Phase 2: During the dead time of the power frequency inversion bridge, all switches in the system are turned off and no energy is transferred. The dead time is set to prevent the bridge arm from being shot-through during the commutation process of the power frequency inversion bridge. PF=1 working condition t 2~ t Stage 3: At this point, the grid-side voltage... v g and output current i g All are less than 0, i.e., instantaneous output power P o If the value is greater than 0, the system operates in the active power phase, and the system mode is the DC / AC converter branch operating alone mode. The modulation strategy is an active power modulation strategy. S w It can operate in both constant-frequency intermittent mode and variable-frequency intermittent mode; the thyristors of the power frequency inverting bridge S 1. Turn off, S 2. On, switching transistor Q 1. Conductivity Q 2. Turn off.

[0048] PF=1 working condition t 0~ t 1 and t 2~ t 3-stage high-frequency flyback main switch S w Switching cycle drive waveform as follows Figure 20 As shown in the figure on the right, where: t 0~ t Stage 1: Main switching transistor of flyback circuit S w Turn on, the inductance of the primary side of the flyback transformer Lm Energy storage begins, and at this time the diodes on the secondary side of the transformer... D 1. The transformer is turned off due to reverse voltage. At this time, the transformer acts as an energy storage coupling inductor, and the primary current rises linearly until it reaches the sinusoidal reference envelope, entering the next stage. The expression for the primary current is:

[0049] in, i p The primary current, L m For primary magnetizing inductance, U dc Input voltage, t on (θ) represents the conduction time; t 1~ t Stage 2: Main switch of flyback circuit S w When switched off, due to the law of electromagnetic induction, the voltage polarity across the transformer reverses, and the freewheeling diode... D When diode 1 is turned on, the energy stored in the transformer is transferred to the secondary side. During this stage, the current in the secondary diode... i s It decreases linearly, and the expression for the secondary current is:

[0050] in, i s For secondary current, L s For secondary excitation inductance, U bus The flyback output voltage is the bus voltage. t off1 (θ) represents the conduction time of the freewheeling diode; t 2~ t Stage 3: Main Switch S w With freewheeling diode D When all 1s are turned off, the flyback primary inductor resonates with the system parasitic capacitance; during this stage, the instantaneous power transfer can be adjusted accordingly. S w Select a modulation strategy. S w It can perform both fixed-frequency modulation and variable-frequency modulation. Fixed-frequency modulation simply maintains a constant switching frequency, while variable-frequency modulation requires valley selection and calculation of the switching frequency and duty cycle to ensure the main switching transistor... S w exist tThe valley bottom conduction is achieved in 3 moments.

[0051] The specific valley selection logic is: to select the main switch transistor. S w The switching frequency is fixed at a certain value (taking an interrupt frequency of 150kHz as an example), and the total inductance of the primary side of the transformer in the system is... and the resonant capacitance value in the system C tot The flyback converter is obtained in t 2~ t 3-stage resonance period ,as well as t 2~ t Total duration of the 3 phases t off2 (θ); Calculate the total duration t off2 (θ) includes the resonant period t r The number of valleys is counted and rounded to the nearest integer. k ( k =1,2,3,…,N), different valley numbers are obtained based on the instantaneous power, and the corresponding duty cycle and switching frequency are obtained through the above calculation formula.

[0052] At this time, the main switch transistor S w The specific time required to open the valley floor is from t off2 (θ) is changed to the obtained valley bottom conduction resonant time. Switching cycle T s Depend on

[0053] Become The switching frequency is from Become Duty cycle from Become The valley-level turn-on strategy makes the main switch transistor... S w Turn on at the lowest point of resonance, reducing the switching power of the transistor. S w Switching losses can be reduced, improving system efficiency and reducing the THD of the system output current.

[0054] (2) When the system operates in a non-unity power factor transmission mode (PF≠1), the system operates in three modes based on the instantaneous output power: DC / AC conversion branch operating mode alone, AC / DC conversion branch operating mode alone, and a mixed operating mode of DC / AC conversion branch and AC / DC conversion branch. Specifically, this includes: The system operates under a power factor lag condition (PF>0, current lags voltage). During the power frequency cycle, the system's switching transistors and thyristors are driven as follows: Figure 21 As shown in the left figure. Instantaneous output power. P o When the value is greater than 0, the system operates in the active phase. t 0~ t 1, t 4~ t 5. The system mode is the DC / AC converter branch operating mode alone, and the system modulation is active power modulation; instantaneous output power P o When <0, the system operates in the reactive power phase, i.e. t 2~ t 3 and t 6~ t In stage 7, the system mode is the AC / DC converter branch operating alone, and the system modulation is reactive power modulation; the system operates in the mixed mode stage, i.e. t 1~ t 2. t 3~ t 4. t 5~ t 6. t 7~ t 8. The system mode is a hybrid operating mode of DC / AC conversion branch and AC / DC conversion branch, and the system modulation is hybrid modulation.

[0055] Lag power factor condition t 0~ t Phase 1: At this stage, the grid-side voltage... v g and output current i g All are greater than 0, i.e., instantaneous output power P o If the value is greater than 0, the system operates in the active power phase, the modulation strategy is active power modulation, and the mode is the DC / AC conversion branch operating alone mode. S w It can operate in both constant-frequency discontinuous mode and variable-frequency discontinuous mode; the thyristors of the power frequency inverting bridge S 1. Conductivity S 2. Turn off, switching transistor Q 1. Turn off Q 2. Conduction; Lag power factor condition t 1~ t Phase 2: At this time, the grid-side voltage v g At the zero point and v g Less than 0, output current ig Greater than 0 means instantaneous output power P o <0 indicates the system is operating in a mixed-mode phase, employing a hybrid modulation strategy. The mode is a hybrid operation of the DC / AC conversion branch and the AC / DC conversion branch, with both branches simultaneously active. The switching transistors of the power frequency inversion bridge... Q 2 and Q 4. Maintain high-frequency movements. Q 1. Q 3. Turn-off; Thyristors of the power frequency inverting bridge S 2. Shutdown S 1. Turn on; Switching transistor S w Power is transmitted in the form of pulse trains to sustain the bus. C bus Voltage, switching cycle waveform as follows Figure 23 As shown in the figure on the right.

[0056] Lag power factor condition t 2~ t Stage 3: At this point, the grid-side voltage... v g Less than 0, output current i g Greater than 0 means instantaneous output power P o When the value is less than 0, the system is operating in the reactive power phase, the modulation strategy is reactive power modulation, the system mode is AC / DC converter branch operating alone, the DC / AC converter branch is closed, and the AC / DC converter branch is open. S w Turn off; as the output current decreases, L f The excitation current transitions from continuous to discontinuous, and the high-frequency switching transistor of the power frequency inverting bridge... Q 2. There are two modes: transition from CCM mode to DCM mode. In DCM mode, it can operate in either fixed-frequency discontinuous mode or variable-frequency discontinuous mode obtained through a valley-conduction modulation strategy. The frequency and duty cycle in discontinuous mode are obtained using the formulas mentioned above. The thyristors of the power frequency inverting bridge... S 2. Switching transistor Q 1. Shutdown; Power frequency inversion bridge S 1. Activation S 2. Turn-off, the switching cycle waveform is as follows: Figure 22 As shown in the right figure: t 0~ t Phase 1: Q 2. At this time, the main switch of the reactive flyback circuit is turned on. Q 1. Q 3. Q4. Turn off, at this time the bus capacitor C bus pass S 1 and Q 2. Release energy to the grid side to prevent voltage surges at the switching points of different branches due to the clamping effect of the grid voltage, which could cause system oscillations. t 1~ t Phase 2: Q 1. Q 2. Q 3. Turn off, at this time Q 4. Conductivity; t 2~ t Phase 3: Q 2 and Q When all four are turned off, the flyback primary inductor resonates with the system parasitic capacitance, and the system does not transfer energy. During this stage, either fixed-frequency control or variable-frequency control is performed. Variable-frequency control requires valley selection based on instantaneous power transfer and calculation of switching frequency and duty cycle to ensure optimal power transfer. Q 2 in t The valley bottom conduction is achieved in 3 moments.

[0057] Lag power factor condition t 3~ t Stage 4: At this point, the grid-side voltage... v g Less than 0, output current i g At the zero point and i g Greater than 0 means instantaneous output power P o <0 indicates the system is operating in a mixed-mode phase, employing a hybrid modulation strategy. The mode is a hybrid operation of the DC / AC conversion branch and the AC / DC conversion branch, with both branches simultaneously active. The switching transistors of the power frequency inversion bridge... Q 2 and Q 4. Maintain high-frequency movements. Q 1. Q 3. Turn-off; Thyristors of the power frequency inverting bridge S 2. Shutdown S 1. Turn on; Switching transistor S w Power is transmitted in the form of pulse trains to sustain the bus. C bus Voltage, switching cycle waveform as follows Figure 23 As shown in the figure on the right.

[0058] Lag power factor condition t 4~ t Stage 5: At this point, the grid-side voltage... v g and output currenti g All are less than 0, i.e., instantaneous output power P o If the value is greater than 0, the system operates in the active power phase, the modulation strategy is active power modulation, and the mode is the DC / AC conversion branch operating alone mode. S w The thyristors of the power frequency inverting bridge can operate in both constant frequency discontinuous mode and variable frequency discontinuous mode. S 1. Turn off S 2. On, switching transistor Q 1. Conductivity Q 2. Turn off; Lag power factor condition t 5~ t Stage 6: At this point, the grid-side voltage... v g At the zero point and v g Greater than 0, output current i g Less than 0 means instantaneous output power P o <0 indicates the system is operating in a mixed-mode phase, employing a hybrid modulation strategy. The mode is a hybrid operation of the DC / AC conversion branch and the AC / DC conversion branch, with both branches simultaneously active. The switching transistors of the power frequency inversion bridge... Q 1 and Q 3. Maintain high-frequency movements. Q 2. Q 4. Turn-off; Thyristors of the power frequency inverting bridge S 1. Turn off S 2. Turn on; Switching transistor S w Power is transmitted in the form of pulse trains to sustain the bus. C bus Voltage, waveform of switching cycle as follows Figure 23 As shown in the left figure.

[0059] Lag power factor condition t 6~ t Stage 7: At this point, the grid-side voltage... v g Greater than 0, output current i g Less than 0 means instantaneous output power P o <0, the system operates in the reactive power stage, the modulation strategy is reactive power modulation, the mode is AC / DC converter branch operating alone, the DC / AC converter branch is closed, and the AC / DC converter branch is open. S w Keep off, as the output current decreases, Lf The excitation current transitions from continuous to discontinuous, and the high-frequency switching transistor of the power frequency inverting bridge... Q There are two modes: transitioning from CCM mode to DCM mode. In DCM mode, it can operate in either fixed-frequency discontinuous mode or variable-frequency discontinuous mode obtained through a valley-conduction modulation strategy. The frequency and duty cycle in discontinuous mode are obtained using the formulas mentioned above. The thyristors of the power frequency inversion bridge... S 1. Switching transistor Q 2. Shutdown; Power frequency inversion bridge S 2. On. The switching cycle waveform is as follows: Figure 22 As shown in the left figure: In this figure t 0~ t Phase 1: Q At this time, the main switch of the reactive flyback circuit is turned on. Q 2. Q 3. Q 4. Turn off, at this time the bus capacitor C bus pass S 2 and Q 1. This releases energy to the grid side, preventing voltage surges at the switching points of different branches due to grid voltage clamping, which could cause system oscillations. (See diagram.) t 1~ t Phase 2: Q 3 conduction, Q 1. Q 2. Q 4. Off. (This is shown in the diagram.) t 2~ t Phase 3: Q 1 and Q When all three are turned off, the flyback primary inductor resonates with the system parasitic capacitance, and the system does not transfer energy. During this stage, either fixed-frequency control or variable-frequency control is performed. Variable-frequency control uses valley selection and calculates the switching frequency and duty cycle based on the instantaneous power transfer, ensuring... Q 1 in t The valley bottom conduction is achieved in 3 moments.

[0060] Lag power factor condition t 7~ t Stage 8: At this point, the grid-side voltage... v g Greater than 0, output current i g At the zero point and i g Less than 0 means instantaneous output power P o<0 indicates the system is operating in a mixed-mode phase, employing a hybrid modulation strategy. The mode is a hybrid operation of the DC / AC conversion branch and the AC / DC conversion branch, with both branches simultaneously active. The switching transistors of the power frequency inversion bridge... Q 1 and Q 3. Maintain high-frequency movements. Q 2. Q 4. Turn-off; Thyristors of the power frequency inverting bridge S 1. Turn off S 2. Turn on; Switching transistor S w Power is transmitted in the form of pulse trains to sustain the bus. C bus Voltage, waveform of switching cycle as follows Figure 23 As shown in the left figure.

[0061] The system operates under a power factor (PF) < 0 leading power factor condition (current leads voltage). During the power frequency cycle, the system's switching transistors and thyristor drives are as follows: Figure 21 As shown in the right figure. Instantaneous output power P o When the value is greater than 0, the system operates in the active phase. t 0~ t 1, t 4~ t 5. The system mode is the DC / AC converter branch operating mode alone, and the system modulation is active power modulation; instantaneous output power P o When <0, the system operates in the reactive power phase, i.e. t 2~ t 3, t 6~ t 7. The system is modulated as reactive power modulation; the system operates in the mixed-mode phase, i.e. t 1~ t 2. t 3~ t 4. t 5~ t 6. t 7~ t 8. The system mode is a hybrid operating mode of DC / AC conversion branch and AC / DC conversion branch, and the system modulation is hybrid modulation.

[0062] Leading power factor operating conditions t 0~ t Phase 1: At this stage, the grid-side voltage... v g and output current i g All are greater than 0, i.e., instantaneous output power P oIf the value is greater than 0, the system operates in the active power phase, the modulation strategy is active power modulation, and the mode is the DC / AC conversion branch operating alone mode. S w It can operate in both constant-frequency discontinuous mode and variable-frequency discontinuous mode; the thyristors of the power frequency inverting bridge S 1. Conductivity S 2. Turn off, switching transistor Q 1. Turn off Q 2. Conduction; Leading power factor operating conditions t 1~ t Phase 2: At this time, the grid-side voltage v g Greater than 0, output current i g At the zero point and i g Less than 0 means instantaneous output power P o <0 indicates the system is operating in a mixed-mode phase, employing a hybrid modulation strategy. The mode is a hybrid operation of the DC / AC conversion branch and the AC / DC conversion branch, with both branches simultaneously active. The switching transistors of the power frequency inversion bridge... Q 1 and Q 3. Maintain high-frequency movements. Q 2 and Q 4. Turn-off; Thyristors of the power frequency inverting bridge S 1. Turn off S 2. Turn on; Switching transistor S w Power is transmitted in the form of pulse trains to sustain the bus. C bus Voltage, waveform of switching cycle as follows Figure 23 As shown in the left figure.

[0063] Leading power factor operating conditions t 2~ t Stage 3: At this point, the grid-side voltage... v g Greater than 0, output current i g Less than 0 means instantaneous output power P o <0, the system operates in the reactive power stage, the modulation strategy is reactive power modulation, the mode is AC / DC converter branch operating alone, the DC / AC converter branch is closed, and the AC / DC converter branch is open. S w Keep off, as the output current increases, L f The excitation current transitions from discontinuous to continuous, and the high-frequency switching transistor of the power frequency inverting bridge... QThere are two modes: transitioning from DCM mode to CCM mode. In DCM mode, it can operate in either fixed-frequency discontinuous mode or variable-frequency discontinuous mode obtained through a valley-conduction modulation strategy. The frequency and duty cycle in discontinuous mode are obtained using the formulas described above. Q 3 as Q The secondary freewheeling diode of the 1-phase circuit operates at high frequency; the thyristor of the power frequency inverting bridge... S 1. Switching transistor Q 2. Q 4. Shutdown; Power frequency inversion bridge S 2. Open.

[0064] Leading power factor operating conditions t 3~ t Stage 4: At this point, the grid-side voltage... v g At the zero point and v g Greater than 0, output current i g Less than 0 means instantaneous output power P o <0 indicates the system is operating in a mixed-mode phase, employing a hybrid modulation strategy. The mode is a hybrid operation of the DC / AC conversion branch and the AC / DC conversion branch, with both branches simultaneously active. The switching transistors of the power frequency inversion bridge... Q 1 and Q 3. Maintain high-frequency movements. Q 2 and Q 4. Turn-off; Thyristors of the power frequency inverting bridge S 1. Turn off S 2. Turn on; Switching transistor S w Power is transmitted in the form of pulse trains to sustain the bus. C bus Voltage, waveform of switching cycle as follows Figure 23 As shown in the left figure.

[0065] Leading power factor operating conditions t 4~ t Stage 5: At this point, the grid-side voltage... v g and output current i g All are less than 0, i.e., instantaneous output power P o If the value is greater than 0, the system operates in the active power phase, the modulation strategy is active power modulation, and the mode is the DC / AC conversion branch operating alone mode. S w It can operate in both constant-frequency discontinuous mode and variable-frequency discontinuous mode; the thyristors of the power frequency inverting bridge S1. Turn off S 2. On, switching transistor Q 1. Conductivity Q 2. Turn off; Leading power factor operating conditions t 5~ t Stage 6: At this point, the grid-side voltage... v g Less than 0, output current i g At the zero point and i g Greater than 0 means instantaneous output power P o <0 indicates the system is operating in a mixed-mode phase, employing a hybrid modulation strategy. The mode is a hybrid operation of the DC / AC conversion branch and the AC / DC conversion branch, with both branches simultaneously active. The switching transistors of the power frequency inversion bridge... Q 2 and Q 4. Maintain high-frequency movements. Q 1 and Q 3. Turn-off; Thyristors of the power frequency inverting bridge S 2. Shutdown S 1. Turn on; Switching transistor S w Power is transmitted in the form of pulse trains to sustain the bus. C bus Voltage, waveform of switching cycle as follows Figure 23 As shown in the figure on the right.

[0066] Leading power factor operating conditions t 6~ t Stage 7: At this point, the grid-side voltage... v g Less than 0, output current i g Greater than 0 means instantaneous output power P o When the value is less than 0, the system is operating in the reactive power phase, the modulation strategy is reactive power modulation, the mode is AC / DC converter branch operating alone, the DC / AC converter branch is closed, and the AC / DC converter branch is open. S w Keep off, as the output current increases, L f The excitation current transitions from discontinuous to continuous, and the high-frequency switching transistor of the power frequency inverting bridge... Q 2. There are two modes for transitioning from DCM mode to CCM mode. In DCM mode, it can operate in either fixed-frequency discontinuous mode or variable-frequency discontinuous mode obtained by the valley-conduction modulation strategy. The frequency and duty cycle in discontinuous mode are obtained from the above calculation formula. Q 4 asQ The secondary-side freewheeling diode of the 2-phase bridge operates at high frequency; the thyristor of the power frequency inverting bridge... S 2. Switching transistor Q 1. Q 3. Shutdown; Power frequency inversion bridge S 1. Activated.

[0067] Leading power factor operating conditions t 7~ t Stage 8: At this point, the grid-side voltage... v g At the zero point and v g Less than 0, output current i g Greater than 0 means instantaneous output power P o <0 indicates the system is operating in a mixed-mode phase, employing a hybrid modulation strategy. The mode is a hybrid operation of the DC / AC conversion branch and the AC / DC conversion branch, with both branches simultaneously active. The switching transistors of the power frequency inversion bridge... Q 2 and Q 4. Maintain high-frequency movements. Q 1 and Q 3. Turn-off; Thyristors of the power frequency inverting bridge S 2. Shutdown S 1. Turn on; Switching transistor S w Power is transmitted in the form of pulse trains to sustain the bus. C bus Voltage, waveform of switching cycle as follows Figure 23 As shown in the figure on the right.

[0068] The simulation results of this embodiment are as follows: Figures 24-26 As shown in the simulation, the output current waveform is... i g It can be seen that, under different PF values, the three-port flyback DC-AC converter topology and corresponding modulation strategy in this embodiment not only achieve adjustable system power factor, but also ensure power factor accuracy and output power quality, and the output current THD is guaranteed to be within 5%.

[0069] This embodiment addresses the traditional unidirectional DC-AC converter topology, taking a flyback DC-AC converter as an example. It proposes a three-port flyback DC-AC converter topology with adjustable power factor and a corresponding modulation strategy to achieve precise power factor adjustment. The proposed bus capacitor discharge circuit and the hybrid operation mode of the DC / AC conversion branch and the AC / DC conversion branch solve the problem that the traditional unidirectional DC-AC converter topology cannot achieve power factor adjustment. At the same time, it innovatively proposes a valley conduction strategy based on the center frequency, which also solves the problem of low system efficiency.

[0070] This embodiment also provides a computer-readable storage medium storing a computer program thereon, characterized in that, when the computer program is executed by a processor, it implements the above-described method based on the circuit topology described in Embodiment 1.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-port flyback DC-AC converter, characterized in that, It includes a flyback circuit, a power frequency inverting bridge, an AC-DC converter, and a CL filter cascaded in sequence; the AC-DC converter is a circuit with bidirectional energy flow characteristics or a circuit that can realize power factor correction function.

2. A three-port flyback DC-AC converter according to claim 1, characterized in that, The circuit with bidirectional energy flow characteristics includes: a BUCK circuit, a BOOST circuit, a four-switch BUCK-BOOST circuit, and an H-bridge circuit; The circuit that enables power factor correction includes: a FLYBACK circuit, a DAB circuit, a high-frequency chain matrix converter, a Sepic single-stage bridgeless isolated PFC circuit, a single-stage half-bridge PFC circuit, and a half-bridge LLC circuit.

3. A three-port flyback DC-AC converter according to claim 1, characterized in that, The AC-DC converter is a three-winding flyback AC-DC converter that has undergone active device multiplexing and magnetic component multiplexing.

4. A three-port flyback DC-AC converter according to claim 3, characterized in that, The specific circuit topology includes: Input DC voltage U dc Decoupling capacitor C dc The switching transistors of the main flyback converter S w Main flyback transformer T 1, T 1 Magnetizing inductance L m , T Leakage inductance of 1 L k Output diodes of the main flyback converter D 1; Output capacitor of the main flyback converter C bus ; Thyristors constituting the power frequency inversion bridge S 1. S 2 and switching transistor Q 1. Q 2; Grid-side inductor L g Filter capacitor C f The flyback transformer of the AC-DC three-winding flyback converter T 2; Flyback transformer T 2 Magnetizing inductance L f Output switch of AC-DC three-winding flyback converter Q 3. Q 4; Grid voltage v g The main flyback transformer T The number of turns of the primary and secondary windings of 1 are respectively N p and N s The flyback transformer T 2. Connected in series to the power grid side.

5. A modulation method for a three-port flyback DC-AC converter, characterized in that, Based on the circuit topology described in claim 4, the grid-side sampled voltage is input into the phase-locked loop to obtain the grid voltage phase. θ The reference value of the output current is obtained by determining the output power factor PF. i g And by calculating the instantaneous output power P o Determine the system's operating mode. include: (1) If the instantaneous output power P o If the value is greater than 0, the system operates in DC / AC conversion mode, the modulation strategy is active modulation, and the high-frequency switching transistor for power transmission is... S w The on / off mode is intermittent. S w The duty cycle is ; (2) If the instantaneous output power P o If the value is less than 0, the system is in AC / DC conversion mode, the modulation strategy is reactive power modulation, and the high-frequency switch for power transmission is the switch of the lower arm of the power frequency inversion bridge. Q 1. Q 2. The current is in discontinuous mode near the zero-crossing point, and the voltage is in continuous mode near the zero-crossing point; and when v g When >0, Q 1. High-frequency action, Q 2. Turn off; when v g When <0, Q 1. Close Q 2. High-frequency action; Q 1. Q The duty cycle of 2 is ; (3) If the instantaneous output power P o Near the zero-crossing point, the system operates in a hybrid mode of AC / DC conversion and DC / AC conversion, with a modulation strategy that includes both active and reactive power modulation. The high-frequency switching transistor for power transmission is... S w and the switching transistor of the lower arm of the power frequency reversing bridge. Q 1. Q 2, of which, Q 1. Q The switching mode and duty cycle of 2 are consistent with reactive power modulation. S w Energy is supplied through pulse conduction to maintain the output voltage of the main flyback converter, with a duty cycle of [value missing]. .

6. The modulation method for a three-port flyback DC-AC converter according to claim 5, characterized in that, The instantaneous output power P o The calculation is as follows: in, U grms This is the effective value of the grid-side voltage. I grms This is the effective value of the output current. θ The phase of the grid-side voltage. φ This represents the phase difference between the output voltage and current.

7. The modulation method for a three-port flyback DC-AC converter according to claim 5, characterized in that, The active power modulation S w duty cycle Specifically: S w The conduction time is: in, L p For transformer T The magnetizing inductance of 1 n 1 is a transformer T A turns ratio of 1 t off2_S for S w and D 1. The time of all shutdowns U dc For input DC voltage, U grms This is the effective value of the grid-side voltage. I grms This is the effective value of the output current; D 1. The conduction time is: S w The switching period and frequency are: In the formula: t on_S for S w On-time, t off_S for D 1. On-time t off2_S for S w and D 1. The time of all shutdowns f s_S for S w The switching frequency; S w Duty cycle is: in, for S w Duty cycle.

8. The modulation method for a three-port flyback DC-AC converter according to claim 5, characterized in that, The reactive power modulation Q 1. Q The duty cycle of 2 is Specifically: Q 1. Q 2. The conduction time is: in, L f For transformer T 2 magnetizing inductance, n 2 is T 2 Transformers T A turns ratio of 2 t off2_Q for Q 1. Q 2. Q 3. Q 4. The time of shutdown. U dc For input DC voltage, U grms This is the effective value of the grid-side voltage. I grms This is the effective value of the output current; Q 3. Q 4. The conduction time is: Q 1. Q 2. The switching period and frequency are: in, t on_Q for Q 1. Q 2. On-time t off_Q for Q 3. Q 4. On-time t off2_Q for Q 1. Q 2. Q 3. Q The shutdown time for all 4, of which, when running in continuous mode, t off2_Q =0, f s_Q for Q 1. Q 2. Switching frequency; Q 1. Q 2. Duty cycle is: in, for Q 1. Q A duty cycle of 2.

9. The modulation method for a three-port flyback DC-AC converter according to claim 5, characterized in that, During the hybrid modulation S w duty cycle Specifically: The current is zero near the zero-crossing point; The duty cycle is 1% to 10% near the voltage zero crossing point.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 5-9.

Images