Single-stage bidirectional power conversion topological structure capable of realizing wide-range soft switching and control method thereof

Abstract

The invention discloses a single-stage bidirectional power conversion topological structure capable of realizing wide-range soft switching and a control method of the single-stage bidirectional power conversion topological structure. In-bridge and inter-bridge phase shift control of a double-half-bridge circuit and a high-frequency switch matrix provides a basis for realizing soft switching of all power tubes; the switching frequency is adjusted in real time according to the magnitude of the port voltage, soft switching within a wide voltage change range is achieved, the current of a bridge arm connected with the primary side of the second transformer is the sum of the primary side current of the second transformer and the current of an inductor connected in parallel with the second transformer, and the inductance value of the inductor connected in parallel with the primary side of the second transformer is designed. The current of the bridge arm connected with the primary side of the second transformer can be effectively changed, so that the soft switching implementation range of the switching tube of the bridge arm connected with the primary side of the second transformer in a wide power transmission range can be expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of high-frequency isolated single-stage converters in power electronic converters, and in particular to a single-stage bidirectional power conversion topology structure capable of realizing wide-range soft switching and a control method thereof. Background Art

[0002] The dual-active bridge converter has the advantages of electrical isolation, simple circuit structure, easy modularization, bidirectional power transmission, and soft switching. It has been widely studied and applied in many bidirectional direct current / direct current (DC / DC) conversion and bidirectional alternating current / direct current (AC / DC) conversion fields such as battery energy storage, new energy electric vehicles, solid-state transformers, and household energy storage systems.

[0003] The original application scenario of the dual active bridge converter is bidirectional DC / DC conversion. The single-stage high-frequency isolated bidirectional DC converter based on the dual active bridge (DAB) can realize soft switching of all the switch tubes of the converter when it is fully loaded or the transmission power is large. However, when the transmission power of the converter becomes smaller or the voltage of the two DC ports deviates from the optimized ratio determined by the transformer ratio (that is, the voltage of the two ports does not match), it is difficult for the converter to realize soft switching of all the switch tubes. The loss of soft switching of the switch tube will increase the switching loss of the converter, reduce the efficiency, and increase the electromagnetic interference (EMI), which will seriously reduce the performance and reliability of the converter, and even make it unable to work normally. Therefore, a large number of researchers have analyzed and studied the circuit structure and control technology of DAB converters, including proposing modulation technologies such as dual phase shift control (DPS), extended phase shift (EPS) and triple phase shift (TPS) based on the basic single phase shift control (SPS) and the combined application method of these modulation technologies, as well as the use of variable structure power circuits to reduce the degree of voltage deviation to expand the soft switching range. However, whether changing the modulation strategy or changing the circuit structure, there are problems such as complex design calculations, complex modulation algorithms, and complex power circuit structures, which are difficult to apply in practice or difficult to improve the overall performance.

[0004] With the development of electrochemical energy storage technology, bidirectional AC / DC converter technology has been widely valued and applied in recent years. Existing bidirectional AC / DC converters are mostly composed of a two-stage structure of a non-isolated bidirectional AC / DC converter (PWM (pulse width modulation) converter) and an isolated bidirectional DC / DC converter (such as the aforementioned DAB converter). Since the battery port voltage varies in a wide range, the two-stage converter also has the problem of wide voltage range application of the DAB DC converter. Although the output voltage of the AC / DC converter can be adjusted to match the voltage at the two ends of the DAB converter, this makes the control of the converter complicated. In order to overcome the shortcomings of the two-stage bidirectional AC / DC converter solution, such as the large number of power conversion stages and the AC / DC conversion being a hard switch, many researchers have carried out research on high-frequency isolated single-stage bidirectional AC / DC conversion technology based on the DAB converter in recent years. The bidirectional AC / DC converter based on DAB reduces the number of power conversion stages, and through the optimization design of circuit parameters and control strategies, it can realize soft switching of power switches under certain load sizes and partial periods of AC voltage, reflecting certain technical advantages over the two-stage conversion scheme. However, due to the inherent wider instantaneous value variation range of the AC side voltage (from 0 to peak value), the disadvantage of the DAB converter's poor performance in a wide voltage range is more prominent.

[0005] The existing optimization methods for the soft switching of single-stage bidirectional AC / DC converters based on DAB are all optimized from the modulation strategy, but these methods only optimize the soft switching range of the converter when it is fully loaded. For example, some scholars have proposed a modulation strategy based on variable switching frequency to achieve critical current continuous mode operation, which can achieve soft switching of all switches under full load, but when the transmission power decreases, this modulation strategy will cause the switching frequency of the converter to be very high, and soft switching cannot be achieved in most voltage periods, thus greatly increasing the switching loss and not being practical.

[0006] Therefore, it is of great theoretical and practical significance to propose a bidirectional power converter structure and modulation technology that can achieve wide-range soft switching of the power tube under a wide voltage and load range. Summary of the invention

[0007] Purpose of the invention: The present invention provides a single-stage bidirectional power conversion topology structure and a control method thereof that can realize wide-range soft switching, which can effectively solve the problem of limited soft switching range of converter switch tubes when the voltage is mismatched or lightly loaded in converters based on DAB structure.

[0008] Technical solution: The single-stage bidirectional power conversion topology structure capable of realizing wide-range soft switching described in the present invention includes: a dual half-bridge circuit, a first transformer, a second transformer, an inductor, a power transmission inductor, a high-frequency switch matrix circuit and a filter; the dual half-bridge circuit is connected to the first port of the converter, and the first port is a DC input or output port; the dual half-bridge circuit includes two capacitors C d1 With C d2 and four power switches S1~S4, the primary sides of the first transformer and the second transformer are connected in series, and the connection point of the primary sides of the two transformers and C d1 With C d2 The connection point of the second transformer is connected in parallel with an inductor, the secondary sides of the first transformer and the second transformer are connected in series, and the power transmission inductor is connected in series with the secondary side of the series transformer; the two switches of each bridge arm of the double half-bridge circuit adopt 50% duty cycle complementary operation, the switching frequency is the same as the switching frequency of the power tube of the high-frequency switch matrix circuit, the DC power is converted into a frequency-variable positive and negative amplitude symmetrical alternating square wave, and added to the primary side of the corresponding transformer, the switches of the two bridge arms adopt the phase shift control within the bridge, the secondary side output of the series transformer is a quasi-square wave, and the quasi-square wave width is determined by the phase shift control angle θ within the bridge; the power switch of the high-frequency switch matrix circuit also adopts 50% duty cycle modulation, the industrial frequency AC or DC voltage of the other port is converted into a high-frequency modulated AC voltage with a duty cycle of 50%, and the switching frequency of the high-frequency switch tube is determined by the instantaneous value of the voltage at the port; the voltages at both ends of the power transmission inductor are the quasi-square wave voltage output by the series transformer and the alternating voltage modulated by the high-frequency switch matrix, respectively, and the phases of the two waveforms are determined by the bridge-to-bridge phase shift control angle θ between the double half-bridge circuit and the high-frequency switch matrix circuit. Determine; the filter is connected between the high frequency switch matrix and the second port of the converter, and the second port is a DC or AC output or input port.

[0009] Furthermore, the high-frequency switch matrix circuit selects a full-bridge matrix circuit, a half-bridge matrix circuit or other circuits that can convert a DC or low-frequency AC voltage into a high-frequency alternating voltage output.

[0010] Furthermore, the power transmission inductor is an independent inductor or the sum of the secondary equivalent leakage inductances of the first transformer and the second transformer, or is composed of one or more independent inductors and the leakage inductances of the first transformer and the second transformer.

[0011] Furthermore, the first transformer and the second transformer are transformers with independent magnetic cores, or are magnetic integrated transformers composed of a single magnetic circuit combined magnetic core.

[0012] Furthermore, the inductor connected in parallel with the primary side of the second transformer may be an independent magnetic core, or may be integrated with the magnetic core of the second transformer into a single magnetic core.

[0013] Furthermore, the filter is an LC filter, a C filter or other types of low-pass filters in which low-frequency current components pass through the AC (or DC) port and high-frequency current components are filtered out.

[0014] Furthermore, the AC side of the converter is connected to the power grid to realize applications such as rectifier, grid-connected inverter or energy storage converter; or it can be used as an off-grid inverter to supply power to AC loads.

[0015] Accordingly, a control method for a single-stage bidirectional power conversion topology structure capable of realizing wide-range soft switching includes the following steps:

[0016] Step 1: When used for AC / DC conversion, derive the AC side current i according to modal analysis ac The magnitude of the phase shift angle θ and relationship;

[0017] Step 2: Control the phase shift angle between bridges It is proportional to the phase shift angle θ in the bridge, that is, The proportionality coefficient k is a constant determined according to the circuit performance optimization design;

[0018] Step 3: Make the AC current and the phase shift control angle θ in the bridge into a linear relationship to simplify the implementation of the control strategy.

[0019] Furthermore, in step 1, the AC side current i is derived based on modal analysis. ac The magnitude of the phase shift angle θ and Relationship:

[0020]

[0021] Where: C = 2 or 4 or other constants. When the amplitude of the high-frequency modulated AC voltage output by the high-frequency switch matrix circuit is equal to the amplitude of the AC side voltage, C = 2. When the amplitude of the high-frequency modulated AC voltage output by the high-frequency switch matrix circuit is half of the amplitude of the AC side voltage, C = 4. V dc is the voltage of the DC port, n is the turns ratio of the secondary side to the primary side of the first transformer and the second transformer, T s is the switching cycle, L lk is the power transfer inductance including the equivalent leakage inductance of the two transformers to the secondary side.

[0022] Furthermore, in step 2, the AC side current i ac The relationship between the size of and the control phase shift angle θ becomes:

[0023]

[0024] Furthermore, in step 3, determine:

[0025]

[0026] Among them, T smin The switching cycle T is the minimum switching cycle of the converter switch tube determined after the type of power device is selected according to the specific power level of the converter, input and output voltage, and the comprehensive electrical performance of the system is optimized. s Determined by θ according to the following functional relationship:

[0027]

[0028] The switching frequency of the high-frequency switch tube changes with the instantaneous value of the AC side voltage. The switching frequency is higher when the voltage is lower.

[0029] When the AC side voltage changes sinusoidally, that is:

[0030] |v ac |=V acpeak |sinωt|

[0031] Among them, V acpeak is the AC side voltage v ac When the peak value of the bridge is reached and the unity power factor control is achieved, the phase shift control angle θ in the bridge is:

[0032] θ=θ peak |sinωt|

[0033] where θ peak The maximum value of the phase shift control angle θ in the double half-bridge selected for design;

[0034] The switching period T s The relationship with the AC side voltage is:

[0035]

[0036] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the intra-bridge and inter-bridge phase shift control of the dual half-bridge circuit and the high-frequency switch matrix in the present invention provides a basis for realizing soft switching of all power tubes; the switching frequency is adjusted in real time according to the port voltage to realize soft switching in a wide voltage variation range; the bridge arm current connected to the primary side of the second transformer is the sum of the primary current of the second transformer and the inductor current connected in parallel with the second transformer. By designing the inductance value of the inductor connected in parallel with the primary side of the second transformer, the bridge arm current connected to the primary side of the second transformer can be effectively changed, thereby expanding the soft switching realization range of the switch tube of the bridge arm connected to the primary side of the second transformer under a wide power transmission range. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the converter circuit structure of the present invention.

[0038] Figure 2 A bidirectional AC / DC converter circuit topology diagram applied in the present invention.

[0039] Figure 3 The present invention is applied Figure 2 The working waveform of a switching cycle in the positive half cycle of the converter AC.

[0040] Figure 4 for Figure 3 The corresponding working cycle flows into the lagging power tube current i son Analysis diagram of .

[0041] Figure 5(a) shows Figure 2 Circuit modal diagram of the topology at the [t0-t1] stage.

[0042] Figure 5(b) shows Figure 2 Circuit modal diagram of the topology at the [t1-t2] stage.

[0043] Figure 5(c) shows Figure 2 Circuit modal diagram of the topology in the [t2-t3] phase.

[0044] Figure 5(d) shows Figure 2 Circuit modal diagram of the topology at the [t3-t4] stage.

[0045] Figure 5(e) shows Figure 2 Circuit modal diagram of the topology at the [t4-t5] stage.

[0046] Figure 5(f) shows Figure 2 Circuit modal diagram of the topology at the [t5-t6] stage.

[0047] Figure 5(g) shows Figure 2 Circuit modal diagram of the topology at the [t6-t7] stage.

[0048] Figure 5(h) shows Figure 2 Circuit modal diagram of the topology at the [t7-t8] stage.

[0049] Figure 5(i) shows Figure 2 Circuit modal diagram of the topology at stage [t8-t9].

[0050] Figure 5(j) shows Figure 2 Circuit modal diagram of the topology at the [t9-t10] stage.

[0051] Figure 6(a) shows Figure 2 Experimental waveform of the AC voltage peak of switch tube S2 when the topology is lightly loaded.

[0052] Figure 6(b) shows Figure 2 Experimental waveform of switch tube S2 at a certain middle moment in the power frequency cycle when the topology is lightly loaded.

[0053] Figure 6(c) shows Figure 2 Experimental waveform when the AC voltage of switch tube S2 passes through zero when the topology is lightly loaded.

[0054] Figure 6(d) shows Figure 2 Experimental waveform of the AC voltage peak of switch tube S5 when the topology is lightly loaded.

[0055] Figure 6(e) shows Figure 2 Experimental waveform of switch tube S5 at a certain middle moment in the power frequency cycle when the topology is lightly loaded.

[0056] Figure 6(f) shows Figure 2 Experimental waveform diagram of the AC voltage of switch tube S5 when the topology is lightly loaded and passes through zero.

[0057] Figure 6(g) shows Figure 2 Experimental waveform of the AC voltage peak of switch tube S4 when the topology is lightly loaded.

[0058] Figure 6(h) shows Figure 2 Experimental waveform of switch tube S4 at a certain middle moment in the power frequency cycle when the topology is lightly loaded.

[0059] Figure 6(i) shows Figure 2 Experimental waveform diagram when the AC voltage of switch tube S4 passes through zero when the topology is lightly loaded.

[0060] Figure 7 The topological diagram of a bidirectional DC / DC converter circuit applied in the present invention. DETAILED DESCRIPTION

[0061] like Figure 1 As shown, a single-stage bidirectional power conversion topology structure capable of realizing wide-range soft switching includes: a power conversion circuit consisting of a dual half-bridge circuit, a first transformer, a second transformer, an inductor connected in parallel with the second transformer, a power transmission inductor, a high-frequency switch matrix circuit, a filter, etc.; two capacitors C d1 With C d2 The dual half-bridge circuit is formed by the four power switches S1 to S4 (including active switches and anti-parallel freewheeling diodes); the dual half-bridge circuit is connected to the first port of the converter, the first port is a DC input or output port; the primary sides of the first transformer and the second transformer are connected in series, and the connection point of the primary sides of the two transformers and C d1 With C d2The connection point of the second transformer is connected in parallel with an inductor, the secondary sides of the first transformer and the second transformer are connected in series, and the power transmission inductor is connected in series with the secondary side of the series transformer; the two switches of each bridge arm of the double half-bridge circuit adopt 50% duty cycle complementary operation, the switching frequency is the same as the switching frequency of the power tube of the high-frequency switch matrix, the DC power is converted into a frequency-variable positive and negative amplitude symmetrical alternating square wave, which is added to the primary side of the corresponding transformer, the switches of the two bridge arms adopt phase shift control, the secondary side output of the series transformer is a quasi-square wave, and the quasi-square wave width is determined by the phase shift control angle θ in the bridge; the power switch of the high-frequency switch matrix circuit also adopts 50% duty cycle modulation, and the industrial frequency AC or DC voltage of the other port is converted into a high-frequency modulated AC voltage with a duty cycle of 50%, and the switching frequency of the high-frequency switch tube is determined by the instantaneous value of the voltage at the port; the voltages at the two ends of the power transmission inductor are the quasi-square wave voltage output by the series transformer and the high-frequency alternating voltage modulated by the high-frequency switch matrix, and the phases of the two waveforms are controlled by the phase shift control phase angle between the double half-bridge circuit and the high-frequency switch matrix circuit The phase angle determines the effective value of the current of the power transmission inductor, that is, determines the transmission power between the two ports; the filter is connected between the high-frequency switch matrix and the second port of the converter, and the second port is a DC or AC output or input port.

[0062] like Figure 2 As shown, a specific implementation circuit of the present invention during AC / DC conversion, wherein the high-frequency switch matrix circuit is composed of capacitor C b , switch tubes S5 to S8, capacitors C1 and C2. Take the converter working in the inverter mode as an example. Figure 3 As a typical working waveform, the driving signal of the switch tube S4 lags behind the driving signal of the switch tube S1 by (0.5-θ)T. s , the time that the driving signal of the switch tube S4 leads the driving signal of the switch tube S5 is where θ is Twice the switching period T s The size of the AC side voltage is a function of the AC side output current i ac The magnitude of is linearly related to the phase shift angle θ. Under this modulation strategy, all switches on the AC side and switches S1 and S2 on the DC side can achieve zero voltage switching in the full power frequency cycle within the full output power range. However, when the output power decreases, switches S4 and S3 on the DC side lagging bridge arm are difficult to achieve zero voltage switching. For switches S3 and S4 on the DC side, the inductor L in parallel with transformer T2 is m2 The existence of helps its zero voltage conduction, such as Figure 4 When the load is light, the converter is connected to the grid and the AC side voltage v ac The modal analysis is as follows, where the switch tubes S7 and S8 are at the AC side voltage v acIt is in a constant flow state when it is positive.

[0063] Mode 1 [t0, t1]: As shown in Figure 5(a), at this time, the switches S1, S3, S6, S7, and S8 are turned on. During this period, the voltage v ab is 0, the voltage at the right end of the inductor v cd -v ac / 2. In this stage, the inductor current increases linearly.

[0064] Mode 2 [t1, t2]: As shown in Figure 5(b), at this time, the switch tube S3 is turned off, S4 has not yet turned on, the switch tubes S1, S6, S7, and S8 are turned on, and the leakage inductance current i lk Greater than zero, transformer T2 primary current i p is greater than zero, but at this time due to the inductance L m2 The existence of makes the current i flowing into the bridge arms of the switch tubes S3 and S4 son Less than zero, current i son The junction capacitance of the switch tube S4 is discharged to 0, and the junction capacitance of the switch tube S3 is charged to V dc , creating conditions for soft switching of switch tube S4.

[0065] Mode 3 [t2, t3]: As shown in Figure 5(c), this mode is still in the dead time of switches S3 and S4, and switches S1, S6, S7, and S8 are turned on. son The current flows through the body diode of the switch tube S4, so that the switch tube S4 is turned on at zero voltage in the next mode.

[0066] Mode 4 [t3.t4]: As shown in Figure 5(d), at time t3, switch tube S4 is turned on at zero voltage, and switches S1, S6, S7, and S8 are turned on. At this stage, the voltage at the left end of the inductor is nV. dc , the voltage at the right end of the inductor is v cd v ac / 2. The inductor current increases linearly.

[0067] Mode 5 [t4, t5]: As shown in Figure 5 (e), at time t4, switch tube S6 is turned off. In this stage, switch tube S5 is not turned on. In this stage, switch tubes S1, S4, S7, and S8 are turned on. In this stage, the leakage inductance current i lk The junction capacitance of the switch tube S5 is discharged to zero, and the junction capacitance of the switch tube S6 is charged to v ac , creating conditions for soft switching of switch tube S5.

[0068] Mode 6 [t5, t6]: As shown in Figure 5(f), this mode is still in the dead time of switches S5 and S6. At t5, the junction capacitance voltage of switch S5 drops to zero. During this stage, switches S1, S4, S7, and S8 are turned on, and the leakage inductance current continues to flow through the body diode of switch S5, creating conditions for the zero voltage turn-on of switch S5.

[0069] Mode 7 [t6, t7]: As shown in Figure 5(g), since the body diode of switch tube S5 has been turned on in the previous stage, at time t6, switch tube S5 is turned on with zero voltage. In this mode, switch tubes S1, S4, S5, S7, and S8 are turned on, and the voltage at the left end of the inductor is nV. dc , the voltage at the right end of the inductor is v ac / 2, the inductor current increases linearly.

[0070] Mode 8 [t7, t8]: As shown in Figure 5(h), at time t7, switch tube S1 is turned off and switch tube S2 is not turned on. In this stage, switch tubes S4, S5, S7, and S8 are turned on. In this mode, the current i p The junction capacitance of the switch tube S1 is charged to V dc , discharge the junction capacitance of the switch tube S2 to 0.

[0071] Mode 9 [t8, t9]: As shown in Figure 5 (i), this mode is still in the dead time of the switch tubes S1 and S2. At t8, the junction capacitance voltage of the switch tube S2 is 0. In this stage, the switch tubes S4, S5, S7, and S8 are turned on. In this stage, the primary current i p The body diode of the switch tube S2 is turned on by freewheeling, creating a zero-voltage turn-on condition for the switch tube S2.

[0072] Mode 10 [t9, t10]: As shown in Figure 5(j). Since the body diode of switch S2 has been turned on in the previous stage, at time t9, switch S2 is turned on with zero voltage. At this time, the voltage v ab is 0, the voltage at the right end of the inductor v cd -v ac / 2, the inductor current decreases linearly.

[0073] The modal principle of the second half switching cycle is symmetrical with that of the first half cycle and will not be elaborated here.

[0074] In the implementation circuit, the switching period T s The size of the AC side voltage is a function of the AC side output current i ac A specific scheme for the linear relationship between the size of and the control phase shift angle θ is:

[0075] Step 1: Derivation of AC side current i based on modal analysis ac The magnitude of the phase shift angle θ and Relationship:

[0076]

[0077] Step 2: Control the phase shift angle between bridges It is proportional to the phase shift angle θ in the bridge, that is, The proportionality coefficient k is a constant determined by optimizing the circuit performance. ac The relationship between the size of and the control phase shift angle θ becomes:

[0078]

[0079] Step 3: Make the AC current and the phase shift control angle θ in the bridge linear to simplify the implementation of the control strategy and determine:

[0080]

[0081] Among them, T smin The minimum switching cycle (maximum switching frequency) of the converter switch tube is determined based on the type of power device selected according to the specific power level of the converter, input and output voltage, and the optimization of the system's comprehensive electrical performance. s Determined by θ according to the following functional relationship:

[0082]

[0083] In this way, the switching frequency of the high-frequency switching tube changes with the instantaneous value of the AC side voltage. When the voltage is lower, the switching frequency is higher.

[0084] When the AC side voltage changes sinusoidally, that is:

[0085] |v ac |=V acpeak |sinωt|

[0086] Among them, V acpeak is the AC side voltage v ac When achieving unity power factor control, the phase shift control angle θ in the bridge is:

[0087] θ=θ peak |sinωt|

[0088] where θ peak The maximum value of the phase shift control angle θ within the double half-bridge selected in the design.

[0089] The switching period T s The relationship with the AC side voltage is:

[0090]

[0091] When the converter is actually working, the switching frequency of the high-frequency switch tube can be determined based on the above formula according to the pre-designed parameters and the instantaneous value of the AC side voltage detected in real time, and the turn-on and turn-off times of each switch tube can be determined based on this and the phase shift angle.

[0092] The aforementioned switching period T s The size of the AC side voltage is a function of the AC side output current i ac The linear relationship between the size of and the phase shift angle θ is an implementation scheme that can simplify the control algorithm, but it is not the only solution. Based on the power conversion circuit topology of the present invention and the principle of phase shift and frequency conversion hybrid control to achieve wide range soft switching, only changing θ and The relationship or / and change of switching period T s The functional relationship between θ and θ all falls within the protection scope of the present invention.

[0093] The key to the single-stage bidirectional power conversion topology and control method proposed in the present invention that can achieve wide-range soft switching is that the intra-bridge and inter-bridge phase shift control of the dual half-bridge circuit and the high-frequency switch matrix provides a basis for realizing soft switching of all power tubes; the switching frequency is adjusted in real time according to the port voltage to realize soft switching in a wide voltage variation range; the bridge arm current connected to the primary side of the second transformer is the sum of the primary current of the second transformer and the inductor current connected in parallel with the second transformer. By designing the inductance value of the inductor connected in parallel with the primary side of the second transformer, the bridge arm current connected to the primary side of the second transformer can be effectively changed, thereby expanding the soft switching realization range of the switch tube of the bridge arm connected to the primary side of the second transformer under a wide power transmission range.

[0094] For structures such as Figure 2 The converter is experimentally verified. Figure 6 is an experimental waveform diagram of the drive voltage and drain-source voltage of the converter MOSFET switch tube under different power frequency voltage periods when the load is light (30% of the rated load). It can be seen from Figure 6 that all the switch tubes of the converter achieve zero voltage turn-on within the entire power frequency cycle range when the load is light. Among them, the DC side switch tube S4 (S3), which is the most difficult to meet the soft switching conditions, also achieves zero voltage turn-on within the entire power frequency cycle when the load is light. The experimental results show that the power conversion topology and control method proposed in the present invention can realize the soft switching of all the switch tubes of the converter under a wide voltage range and a wide transmission power range.

Claims

1. A single-stage bidirectional power conversion topology capable of realizing wide range soft switching, characterized in that: include: A dual half-bridge circuit, a first transformer, a second transformer, an inductor, a power transmission inductor, a high-frequency switch matrix circuit and a filter; The double half-bridge circuit is connected to the first port of the converter, the first port is a DC input or output port; the double half-bridge circuit includes two capacitors C d1 With C d2 and four power switches S1~S4, the primary sides of the first transformer and the second transformer are connected in series, and the connection point of the primary sides of the two transformers and C d1 With C d2 The connection point of the second transformer is connected in parallel with an inductor, the secondary sides of the first transformer and the second transformer are connected in series, and the power transmission inductor is connected in series with the secondary side of the series transformer; the two switches of each bridge arm of the double half-bridge circuit adopt 50% duty cycle complementary operation, the switching frequency is the same as the switching frequency of the power tube of the high-frequency switch matrix circuit, the DC power is converted into a frequency-variable positive and negative amplitude symmetrical alternating square wave, and added to the primary side of the corresponding transformer, the switches of the two bridge arms adopt the phase shift control within the bridge, the secondary side output of the series transformer is a quasi-square wave, and the quasi-square wave width is determined by the phase shift control angle θ within the bridge; the power switch of the high-frequency switch matrix circuit also adopts 50% duty cycle modulation, the industrial frequency AC or DC voltage of the other port is converted into a high-frequency modulated AC voltage with a duty cycle of 50%, and the switching frequency of the high-frequency switch tube is determined by the instantaneous value of the voltage at the port; the voltages at both ends of the power transmission inductor are the quasi-square wave voltage output by the series transformer and the alternating voltage modulated by the high-frequency switch matrix, respectively, and the phases of the two waveforms are determined by the bridge-to-bridge phase shift control angle θ between the double half-bridge circuit and the high-frequency switch matrix circuit. Determine; the filter is connected between the high frequency switch matrix and the second port of the converter, and the second port is a DC or AC output or input port.

2. The single-stage bidirectional power conversion topology structure capable of realizing wide range soft switching according to claim 1, characterized in that: The high-frequency switch matrix circuit selects a full-bridge matrix circuit, a half-bridge matrix circuit or other circuits that can convert a DC or low-frequency AC voltage into a high-frequency alternating voltage output.

3. The single-stage bidirectional power conversion topology structure capable of realizing wide range soft switching according to claim 1, characterized in that: The power transmission inductor is an independent inductor or the sum of the secondary equivalent leakage inductances of the first transformer and the second transformer, or is composed of one or more independent inductors and the leakage inductances of the first transformer and the second transformer.

4. The single-stage bidirectional power conversion topology structure capable of realizing wide range soft switching according to claim 1, characterized in that: The first transformer and the second transformer are transformers with independent magnetic cores, or are magnetic integrated transformers composed of a single magnetic circuit combined magnetic core.

5. The single-stage bidirectional power conversion topology structure capable of realizing wide range soft switching according to claim 1, characterized in that: The inductor connected in parallel with the primary side of the second transformer may be an independent magnetic core, or may be integrated with the magnetic core of the second transformer into a single magnetic core.

6. The single-stage bidirectional power conversion topology structure capable of realizing wide range soft switching according to claim 1, characterized in that: The filter is an LC filter, a C filter or other types of low-pass filters that allow low-frequency current components to pass through the AC (or DC) port while filtering out high-frequency current components.

7. A control method for a single-stage bidirectional power conversion topology structure capable of realizing wide range soft switching as claimed in claim 1, characterized in that: The steps include: Step 1: When used for AC / DC conversion, derive the AC side current i according to modal analysis ac The magnitude of the phase shift angle θ and relationship; Step 2: Control the phase shift angle between bridges It is proportional to the phase shift angle θ in the bridge, that is, The proportionality coefficient k is a constant determined according to the circuit performance optimization design; Step 3: Make the AC current and the phase shift control angle θ in the bridge into a linear relationship to simplify the implementation of the control strategy.

8. The control method of a single-stage bidirectional power conversion topology structure capable of realizing wide range soft switching as claimed in claim 7, characterized in that: In step 1, the AC side current i is derived based on modal analysis ac The magnitude of the phase shift angle θ and Relationship: Where: C = 2 or 4 or other constants. When the amplitude of the high-frequency modulated AC voltage output by the high-frequency switch matrix circuit is equal to the amplitude of the AC side voltage, C = 2. When the amplitude of the high-frequency modulated AC voltage output by the high-frequency switch matrix circuit is half of the amplitude of the AC side voltage, C = 4. V dc is the voltage of the DC port, n is the turns ratio of the secondary side to the primary side of the first transformer and the second transformer, T s is the switching cycle, L lk is the power transfer inductance including the equivalent leakage inductance of the two transformers to the secondary side.

9. The control method of a single-stage bidirectional power conversion topology structure capable of realizing wide range soft switching according to claim 7, characterized in that: In step 2, the AC side current i ac The relationship between the size of and the control phase shift angle θ becomes:

10. The control method of a single-stage bidirectional power conversion topology structure capable of realizing wide range soft switching according to claim 7, characterized in that: In step 3, determine: Among them, T smin The switching cycle T is the minimum switching cycle of the converter switch tube determined after the type of power device is selected according to the specific power level of the converter, input and output voltage, and the comprehensive electrical performance of the system is optimized. s Determined by θ according to the following functional relationship: The switching frequency of the high-frequency switch tube changes with the instantaneous value of the AC side voltage. When the voltage is low, the switching frequency is higher. When the AC side voltage changes sinusoidally, that is: |in ac |=V acpeak |sinωt| Among them, V acpeak is the AC side voltage v ac When the peak value of the bridge is reached and the unity power factor control is achieved, the phase shift control angle θ in the bridge is: θ=θ peak |sinωt| where θ peak The maximum value of the phase shift control angle θ in the double half-bridge selected for design; The switching period T s The relationship with the AC side voltage is:

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