Bidirectional monopole resonant AC-DC converter and modulation method

Abstract

The invention relates to the technical field of power electronics and AC-DC converters, in particular to a bidirectional unipolar resonant AC-DC converter and a modulation method. The modulation method comprises the following steps: S1, constructing a corresponding working mode according to a power transmission direction between an alternating current side circuit and a direct current side circuit of the bidirectional monopole resonant AC-DC converter; s2, based on an equivalent circuit of the bidirectional monopole resonant AC-DC converter, generating a corresponding optimization modulation scheme for the working mode; and S3, modulating the bidirectional single-pole resonant AC-DC converter based on the optimized modulation scheme to enable the bidirectional single-pole resonant AC-DC converter to enter a corresponding working mode, and meanwhile, realizing soft switching of a device by utilizing excitation current flowing through an excitation inductor. The design of the converter fully considers the power frequency voltage change of the alternating current side, and bidirectional energy flow can be realized; and meanwhile, soft switching of the device is realized by utilizing exciting current of the transformer, the soft switching range is expanded by optimizing a modulation scheme, the operation loss of the converter is reduced, and the overall operation efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics and AC-DC converters, and in particular to a bidirectional unipolar resonant AC-DC converter and a modulation method. Background Art

[0002] In recent years, bidirectional isolated AC-DC converters have developed rapidly and are widely used in electric vehicles, DC power supplies, new energy grid-connected and energy storage systems. At present, the mainstream bidirectional isolated AC-DC converters include bidirectional two-stage AC-DC converters and bidirectional unipolar AC-DC converters. Since the bidirectional two-stage AC-DC converter uses two-stage power conversion, the efficiency, reliability and power density of the converter are limited. In addition, the converter uses a large number of components, and the complex control loop increases the cost of the system.

[0003] A bidirectional unipolar AC-DC converter is a power conversion device that can achieve bidirectional energy transmission between an AC power source and a DC power source. A bidirectional unipolar AC-DC converter is usually composed of high-frequency transformers, passive devices, and switch tubes. Due to its unipolar structure and device reuse, it has the advantages of compact structure, high efficiency, and flexible control. However, a bidirectional unipolar AC-DC converter must be connected to an AC power grid, and there are some problems in terms of grid-connected current quality, power control, and power factor correction (PFC), which affects its application scope.

[0004] Bidirectional unipolar AC-DC converters can be divided into two categories, one is DAB type and the other is resonant type. Unipolar DAB type AC-DC converters have problems such as input current cannot be decoupled, cannot achieve complete soft switching, and reflux power. The operating efficiency and current control accuracy need to be improved. The operating efficiency of resonant converters is generally higher than that of similar DAB converters. Applying resonant converters to unipolar AC-DC converters is a solution, but resonant converters also have problems such as the resonant current is not zero at the initial moment of the switching cycle and the analytical solution of the resonant current is difficult to obtain.

[0005] Therefore, how to design a bidirectional unipolar resonant AC-DC converter and modulation method that can achieve bidirectional energy flow and has high operating efficiency is a technical problem that needs to be solved urgently. Summary of the invention

[0006] In view of the deficiencies of the above-mentioned prior art, the technical problem to be solved by the present invention is: how to provide a bidirectional unipolar resonant AC-DC converter and a modulation method, wherein the design of the converter fully considers the industrial frequency voltage changes on the AC side and can realize bidirectional energy flow; at the same time, the excitation current of the transformer is used to realize soft switching of the device, and the soft switching range is expanded by optimizing the modulation scheme, thereby reducing the operating loss of the converter and improving the overall operating efficiency of the converter.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A bidirectional unipolar resonant AC-DC converter, comprising:

[0009] AC side circuit, set at the AC side power supply U g The AC side includes a half bridge and an H full bridge connected in parallel with the half bridge; the half bridge is composed of a totem pole upper switch tube Q5 and a totem pole lower switch tube Q6 connected in series; the H full bridge is composed of a first AC side upper switch tube Q1 and a first AC side lower switch tube Q2 connected in series, and a second AC side upper switch tube Q3 and a second AC side lower switch tube Q4 connected in parallel;

[0010] DC side circuit, set at the DC side power supply U s The DC side includes a half bridge consisting of a DC side upper switch tube S1 and a DC side lower switch tube S2 connected in series;

[0011] Transformer, connected between the AC side circuit and the DC side circuit; the transformer's excitation inductance is L m ;

[0012] The resonant circuit is connected between the DC side circuit and the transformer, and includes a resonant inductor L connected in series with the transformer. r , and the resonant capacitor C in parallel with the half bridge of the DC side circuit r ; Resonant capacitor C r Including the series resonant capacitor C r1 and C r2 .

[0013] Preferably, the AC side circuit also includes a grid side inductor L g1 , L g2 And the grid side capacitor C p ;

[0014] Grid side inductance L g1 and L g2 One end of each is connected to the AC power supply U g The other end is connected to the two terminals on the low voltage side of the transformer; the grid side capacitor C p It is arranged between the half bridge and the H full bridge of the AC side circuit and is connected in parallel with the half bridge and the H full bridge respectively.

[0015] A modulation method for a bidirectional unipolar resonant AC-DC converter is implemented based on the bidirectional unipolar resonant AC-DC converter of the present invention, comprising:

[0016] S1: constructing a corresponding working mode according to the power transmission direction between the AC side circuit and the DC side circuit of the bidirectional unipolar resonant AC-DC converter;

[0017] S2: Generate the corresponding optimized modulation scheme for the working mode based on the equivalent circuit of the bidirectional unipolar resonant AC-DC converter;

[0018] S3: Based on the optimized modulation scheme, the bidirectional unipolar resonant AC-DC converter is modulated to enter the corresponding working mode, and the excitation current flowing through the excitation inductor is used to realize the soft switching of the device.

[0019] Preferably, in step S1, the working mode includes working mode 1 in which power is transmitted in a forward direction from the AC side circuit to the DC side circuit.

[0020] Preferably, in step S2, the optimized modulation scheme corresponding to the working mode 1 is:

[0021] The upper switch tube Q5 and the lower switch tube Q6 of the totem pole follow the AC side power supply U g Switching at 50Hz power frequency;

[0022] The first AC side upper switch tube Q1 and the first AC side lower switch tube Q2 are connected in series, and the second AC side upper switch tube Q3 and the second AC side lower switch tube Q4 are connected in series, and are complementary turned on in pairs at a 50% duty cycle;

[0023] By means of phase shifting, the rising edge of the PWM drive signal of the second AC side upper switch tube Q3 is aligned with the rising edge of the PWM drive signal of the DC side upper switch tube S1, and the rising edge of the PWM drive signal of the second AC side lower switch tube Q4 is aligned with the rising edge of the PWM drive signal of the DC side lower switch tube S2;

[0024] The duty ratios of the PWM drive signals of the upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side are equal and less than 0.5;

[0025] The upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side adopt variable pulse width modulation, and the pulse width changes with the input AC power and the industrial frequency AC voltage.

[0026] Preferably, in the optimized modulation scheme of working mode 1, the transmission power calculation formula of the resonant circuit is:

[0027]

[0028] U p =2U g ;

[0029] Where: T s is the switching cycle; is the resonant angular frequency; D b is the duty cycle of the DC side switch;

[0030]

[0031] P S =P PFC ,

[0032] U gm is the amplitude of the industrial frequency AC voltage;

[0033] The falling edge of the PWM driving signal of the first AC side lower switch tube Q2 lags behind the rising edge of the PWM driving signal of the DC side upper switch tube S1, and the lag time is the action time of the resonant current;

[0034] The falling edge of the PWM driving signal of the first AC side upper switch tube Q1 lags behind the rising edge of the PWM driving signal of the DC side lower switch tube S2, and the lag time is the action time of the resonant current;

[0035] After a switch tube in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the excitation inductor, and the anti-parallel diode of the other switch tube is turned on in advance to achieve zero voltage turn-on.

[0036] Preferably, in step S1, the working mode includes working mode 2 in which power is transmitted reversely from the DC side circuit to the AC side circuit.

[0037] Preferably, in step S2, the optimized modulation scheme corresponding to the working mode 2 is:

[0038] The upper switch tube Q5 and the lower switch tube Q6 of the totem pole follow the AC side power supply U g Switching at 50Hz power frequency;

[0039] The first AC side upper switch tube Q1 and the first AC side lower switch tube Q2 are connected in series, and the second AC side upper switch tube Q3 and the second AC side lower switch tube Q4 are connected in series, and are complementary turned on in pairs at a 50% duty cycle;

[0040] By means of phase shifting, the rising edge of the PWM drive signal of the second AC side lower switch tube Q4 is aligned with the rising edge of the PWM drive signal of the DC side upper switch tube S1, so that the rising edge of the PWM drive signal of the second AC side upper switch tube Q3 is aligned with the rising edge of the PWM drive signal of the DC side lower switch tube S2;

[0041] The duty ratios of the PWM drive signals of the upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side are equal and less than 0.5;

[0042] The upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side adopt variable pulse width modulation, and the pulse width changes with the output AC power and the industrial frequency AC voltage.

[0043] Preferably, in the optimized modulation scheme of working mode 2, the transmission power calculation formula of the resonant circuit is:

[0044]

[0045] U p =2U g ;

[0046] Where: T s is the switching cycle; is the resonant angular frequency; D f is the duty cycle of the DC side switch;

[0047]

[0048] P S =-P PFC ,

[0049] U gm is the amplitude of the industrial frequency AC voltage;

[0050] The falling edge of the PWM driving signal of the switch tube Q1 on the first AC side lags behind the rising edge of the PWM driving signal of the switch tube S1 on the DC side, and the lag time is the action time of the resonant current;

[0051] The falling edge of the PWM driving signal of the first AC side lower switch tube Q2 lags behind the rising edge of the PWM driving signal of the DC side lower switch tube S2, and the lag time is the action time of the resonant current;

[0052] After a switch tube in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the excitation inductor, and the anti-parallel diode of the other switch tube is turned on in advance to achieve zero voltage turn-on.

[0053] Compared with the prior art, the bidirectional unipolar resonant AC-DC converter and modulation method of the present invention have the following beneficial effects:

[0054] First, the bidirectional unipolar resonant AC-DC converter and its modulation method of the present invention fully consider the power frequency voltage change on the AC side, can realize the bidirectional flow of energy, and at the same time use the excitation current of the transformer to realize the soft switching of the device, expand the soft switching range by optimizing the modulation scheme, reduce the operating loss of the converter, and improve the overall operating efficiency of the converter. Secondly, all the switch tubes in the bidirectional unipolar resonant AC-DC converter can realize zero voltage opening, and only two tubes have losses when turning off, and the others realize zero current shutdown, and the overall loss of the converter is small. Then, the resonant current is zero at the initial moment of each switching cycle in the converter, and the analytical solution of the resonant current can be calculated, which improves the accuracy of power control. Finally, by shifting the phase of the AC side switch tube and changing the pulse width of the DC side switch tube, the power factor correction of the bidirectional unipolar resonant AC-DC converter, flexible bidirectional flow of energy, and no reflux power are realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to make the purpose, technical solution and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0056] Figure 1 The circuit diagram of a bidirectional unipolar resonant AC-DC converter.

[0057] Figure 2 This is the driving state waveform timing diagram under forward power transmission.

[0058] Figure 3 This is the driving state waveform timing diagram under reverse power transmission. DETAILED DESCRIPTION

[0059] In order to make the purpose, 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 drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but only represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0060] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invention product is usually placed when used, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0061] The following is a further detailed description through specific implementation methods:

[0062] Embodiment 1:

[0063] This embodiment discloses a bidirectional unipolar resonant AC-DC converter.

[0064] like Figure 1 As shown, a bidirectional unipolar resonant AC-DC converter comprises:

[0065] AC side circuit, set at the AC side power supply U g The AC side includes a half bridge and an H full bridge in parallel with the half bridge, as well as a grid-side inductor L g1 , L g2 And the grid side capacitor C p The half bridge is composed of a series-connected totem pole upper switch tube Q5 and a series-connected totem pole lower switch tube Q6; the H full bridge is composed of a series-connected first AC side upper switch tube Q1 and a series-connected first AC side lower switch tube Q2, and a series-connected second AC side upper switch tube Q3 and a series-connected second AC side lower switch tube Q4 in parallel; the grid-side inductor L g1 and Lg2 One end of each is connected to the AC power supply U g The other end is connected to the two terminals on the low voltage side of the transformer; the grid side capacitor C p It is arranged between the half bridge and the H full bridge of the AC side circuit and is connected in parallel with the half bridge and the H full bridge respectively.

[0066] DC side circuit, set at the DC side power supply U s The DC side includes a half bridge consisting of a DC side upper switch tube S1 and a DC side lower switch tube S2 connected in series;

[0067] Transformer, connected between the AC side circuit and the DC side circuit; the transformer's excitation inductance is L m ;

[0068] The resonant circuit is connected between the DC side circuit and the transformer, and includes a resonant inductor L connected in series with the transformer. r , and the resonant capacitor C in parallel with the half bridge of the DC side circuit r ; Resonant capacitor C r Including the series resonant capacitor C r1 and C r2 .

[0069] The transformer has two terminals on the low-voltage side and the high-voltage side respectively; the two terminals on the low-voltage side are connected to the AC power supply U g One terminal of the high voltage side is connected between the upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side, and the other terminal is connected to the resonant capacitor C r1 and C r2 between.

[0070] AC power supply U g The AC side is equipped with an output capacitor C p , used to filter out the high-frequency components in the rectified voltage; power supply U s The DC side is equipped with a voltage stabilizing capacitor C S .

[0071] The totem pole upper switch tube Q5, the totem pole lower switch tube Q6, the first AC side upper switch tube Q1, the first AC side lower switch tube Q2, the second AC side upper switch tube Q3, the second AC side lower switch tube Q4, the DC side upper switch tube S1 and the DC side lower switch tube S2 are respectively provided with corresponding anti-parallel diodes and parasitic capacitors: D Q5 and C Q5 , D Q6 and C Q6 , D Q1 and C Q1 , D Q2 and C Q2 , D Q3 and C Q3, D Q4 and C Q4 , D S1 and C S2 , D S2 and C S2 .

[0072] In this embodiment, the AC side power supply U g To the DC side power supply U s The transmission is forward transmission, the DC side power supply U s To the AC side power supply U g The transmission is in the reverse direction.

[0073] Embodiment 2:

[0074] This embodiment discloses a modulation method for a bidirectional unipolar resonant AC-DC converter, which is implemented based on the bidirectional unipolar resonant AC-DC converter in the first embodiment.

[0075] A modulation method for a bidirectional unipolar resonant AC-DC converter, comprising:

[0076] S1: constructing a corresponding working mode according to the power transmission direction between the AC side circuit and the DC side circuit of the bidirectional unipolar resonant AC-DC converter;

[0077] S2: Generate the corresponding optimized modulation scheme for the working mode based on the equivalent circuit of the bidirectional unipolar resonant AC-DC converter;

[0078] S3: Based on the optimized modulation scheme, the bidirectional unipolar resonant AC-DC converter is modulated to enter the corresponding working mode, and the excitation current flowing through the excitation inductor is used to realize the soft switching of the device.

[0079] First, the bidirectional unipolar resonant AC-DC converter and its modulation method of the present invention fully consider the power frequency voltage change on the AC side, can realize the bidirectional flow of energy, and at the same time use the excitation current of the transformer to realize the soft switching of the device, expand the soft switching range by optimizing the modulation scheme, reduce the operating loss of the converter, and improve the overall operating efficiency of the converter. Secondly, all the switch tubes in the bidirectional unipolar resonant AC-DC converter can realize zero voltage opening, and only two tubes have losses when turning off, and the others realize zero current shutdown, and the overall loss of the converter is small. Then, the resonant current is zero at the initial moment of each switching cycle in the converter, and the analytical solution of the resonant current can be calculated, which improves the accuracy of power control. Finally, by shifting the phase of the AC side switch tube and changing the pulse width of the DC side switch tube, the power factor correction of the bidirectional unipolar resonant AC-DC converter, flexible bidirectional flow of energy, and no reflux power are realized.

[0080] In order to better introduce the technical solution of the present invention, this embodiment is described through the following parts.

[0081] 1. Working Mode 1

[0082] In this embodiment, the working mode includes working mode 1 in which power is transmitted in a forward direction from the AC side circuit to the DC side circuit.

[0083] In working mode 1, U s ≥2*nU p =4*nU g .

[0084] The optimized modulation scheme corresponding to working mode 1 is:

[0085] The upper switch tube Q5 and the lower switch tube Q6 of the totem pole follow the AC side power supply U g Switching at 50Hz power frequency;

[0086] The first AC side upper switch tube Q1 and the first AC side lower switch tube Q2 are connected in series, and the second AC side upper switch tube Q3 and the second AC side lower switch tube Q4 are connected in series, and are complementary turned on in pairs at a 50% duty cycle;

[0087] By means of phase shifting, the rising edge of the PWM drive signal of the second AC side upper switch tube Q3 is aligned with the rising edge of the PWM drive signal of the DC side upper switch tube S1, and the rising edge of the PWM drive signal of the second AC side lower switch tube Q4 is aligned with the rising edge of the PWM drive signal of the DC side lower switch tube S2;

[0088] The duty ratios of the PWM drive signals of the upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side are equal and less than 0.5;

[0089] The upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side adopt variable pulse width modulation, and the pulse width changes with the input AC power and the industrial frequency AC voltage.

[0090] Specifically, in the optimized modulation scheme of working mode 1:

[0091] The formula for calculating the transmission power of the resonant circuit is:

[0092]

[0093] U p =2U g ;

[0094] Where: T s is the switching cycle; is the resonant angular frequency; D b is the duty cycle of the DC side switch;

[0095] To ensure the realization of open-loop PFC, the industrial frequency AC voltage and input current are in phase, and the calculation formula for the input AC power is:

[0096]

[0097] The variable pulse width modulation strategy precisely controls the resonant circuit transmission power of each switching cycle to be equal to the input AC power:

[0098] P S =P PFC ;

[0099] The expression of pulse width changing with input AC power and industrial frequency AC voltage is:

[0100]

[0101] In order to ensure the stability of the bidirectional unipolar resonant AC-DC converter during operation, the range of the resonant capacitor voltage is set to:

[0102] Determines the range of input AC power U gm is the amplitude of the industrial frequency AC voltage;

[0103] The falling edge of the PWM driving signal of the first AC side lower switch tube Q2 lags behind the rising edge of the PWM driving signal of the DC side upper switch tube S1, and the lag time is the action time of the resonant current;

[0104] The falling edge of the PWM driving signal of the first AC side upper switch tube Q1 lags behind the rising edge of the PWM driving signal of the DC side lower switch tube S2, and the lag time is the action time of the resonant current;

[0105] After a switch tube in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the excitation inductor, and the anti-parallel diode of the other switch tube is turned on in advance to achieve zero voltage turn-on.

[0106] Figure 2 is the PWM driving waveform in the forward power transmission mode from the AC side circuit to the DC side circuit, and the current i flowing through the input inductor g And the resonant inductor L r The resonant current i Lr .

[0107] In working mode 1, the mode of the bidirectional unipolar resonant AC-DC converter in half a PWM control cycle (t0~t5) is as follows: Figure 2 shown.

[0108] like Figure 2Description, Mode 1 [t0, t1]: At t0, switches S2, Q1, and Q4 are turned on, and inductor L r The resonant current i Lr There are the following expressions:

[0109]

[0110]

[0111] Resonance Impedance

[0112] In half a switching cycle, the DC side switch conduction time t1-t0=T s D b .

[0113] like Figure 2 Description, Mode 2 [t1, t2]: At t1, switch S1 is turned off, switches Q1 and Q4 are turned on, and inductor L r The resonant current i Lr There are the following expressions:

[0114]

[0115] The action time of the resonant current:

[0116] like Figure 2 Description, mode 3 [t2, t3]: At time t2, the switch tube Q1 is turned off, where Q1 is turned off with close to zero current.

[0117] like Figure 2 Description, Mode 4 [t3, t4]: At t3, the switches Q2 and Q4 are turned on, with Q2 being turned on at zero voltage, and the current flowing through Q2 and Q4 is the excitation current i Lm .

[0118] like Figure 2 Description, mode 5 [t4, t5]: At time t4, the switch tube Q4 is turned off, where Q4 is turned off with close to zero current.

[0119] 2. Working Mode 2

[0120] In this embodiment, the working mode includes working mode 2 in which power is transmitted reversely from the DC side circuit to the AC side circuit.

[0121] In working mode 2, U s ≥2*nU p =4*nU g .

[0122] The optimized modulation scheme corresponding to working mode 2 is:

[0123] The upper switch tube Q5 and the lower switch tube Q6 of the totem pole follow the AC side power supply U g Switching at 50Hz power frequency;

[0124] The first AC side upper switch tube Q1 and the first AC side lower switch tube Q2 are connected in series, and the second AC side upper switch tube Q3 and the second AC side lower switch tube Q4 are connected in series, and are complementary turned on in pairs at a 50% duty cycle;

[0125] By means of phase shifting, the rising edge of the PWM drive signal of the second AC side lower switch tube Q4 is aligned with the rising edge of the PWM drive signal of the DC side upper switch tube S1, so that the rising edge of the PWM drive signal of the second AC side upper switch tube Q3 is aligned with the rising edge of the PWM drive signal of the DC side lower switch tube S2;

[0126] The duty ratios of the PWM drive signals of the upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side are equal and less than 0.5;

[0127] The upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side adopt variable pulse width modulation, and the pulse width changes with the output AC power and the industrial frequency AC voltage.

[0128] Specifically, in working mode 2:

[0129] The formula for calculating the transmission power of the resonant circuit is:

[0130]

[0131] U p =2U g ;

[0132] Where: T s is the switching cycle, is the resonant angular frequency, D f is the duty cycle of the DC side switch;

[0133] To ensure the realization of open-loop PFC, the industrial frequency AC voltage and input current are in anti-phase, and the output AC power expression is:

[0134]

[0135] The variable pulse width modulation strategy precisely controls the resonant circuit transmission power of each switching cycle to be equal to the output AC power:

[0136] P S =-P PFC ;

[0137] The expression of pulse width changing with output AC power and industrial frequency AC voltage:

[0138]

[0139] In order to ensure the stability of the bidirectional unipolar resonant AC-DC converter during operation, the range of the resonant capacitor voltage is set to:

[0140] Determines the output AC power range U gm is the amplitude of the industrial frequency AC voltage;

[0141] The falling edge of the PWM driving signal of the switch tube Q1 on the first AC side lags behind the rising edge of the PWM driving signal of the switch tube S1 on the DC side, and the lag time is the action time of the resonant current;

[0142] The falling edge of the PWM driving signal of the first AC side lower switch tube Q2 lags behind the rising edge of the PWM driving signal of the DC side lower switch tube S2, and the lag time is the action time of the resonant current;

[0143] After a switch tube in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the excitation inductor, and the anti-parallel diode of the other switch tube is turned on in advance to achieve zero voltage turn-on.

[0144] Figure 3 is the PWM driving waveform in the reverse power transmission mode from the DC side circuit to the AC side circuit, and the current i flowing through the input inductor g And the resonant inductor L r The resonant current i Lr .

[0145] In the second working mode, the mode of the bidirectional unipolar resonant AC-DC converter in half a PWM control period (t0~t5) is as follows: Figure 3 shown.

[0146] like Figure 3 Description, Mode 1 [t0, t1]: At t0, switches S1, Q1, and Q4 are turned on, and inductor L r The resonant current i Lr There are the following expressions:

[0147]

[0148] Resonance Impedance

[0149] In half a switching cycle, the DC side switch conduction time t1-t0=T s D f .

[0150] like Figure 3Description, Mode 2 [t1, t2]: At t1, switches Q1 and Q4 continue to be turned on, switch S1 is turned off, and inductor L r The resonant current i Lr There are the following expressions:

[0151]

[0152] The action time of the resonant current:

[0153] like Figure 3 Description, mode 3 [t2, t3]: At time t2, the switch tube Q1 is turned off, where Q1 is turned off with close to zero current.

[0154] like Figure 3 Description, Mode 4 [t3, t4]: At t3, the switches Q2 and Q4 are turned on, with Q2 being turned on at zero voltage, and the current flowing through Q2 and Q4 is the excitation current i Lm .

[0155] like Figure 3 Description, mode 5 [t4, t5]: At time t4, the switch tube Q4 is turned off, where Q4 is turned off with close to zero current.

[0156] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A bidirectional unipolar resonant AC-DC converter, characterized in that: include: AC side circuit, set at the AC side power supply U g The AC side includes a half bridge and an H full bridge connected in parallel with the half bridge; the half bridge is composed of a totem pole upper switch tube Q5 and a totem pole lower switch tube Q6 connected in series; the H full bridge is composed of a first AC side upper switch tube Q1 and a first AC side lower switch tube Q2 connected in series, and a second AC side upper switch tube Q3 and a second AC side lower switch tube Q4 connected in parallel; DC side circuit, set at the DC side power supply U s The DC side includes a half bridge consisting of a DC side upper switch tube S1 and a DC side lower switch tube S2 connected in series; Transformer, connected between the AC side circuit and the DC side circuit; the transformer's excitation inductance is L m ; The resonant circuit is connected between the DC side circuit and the transformer, and includes a resonant inductor L connected in series with the transformer. r , and the resonant capacitor C in parallel with the half bridge of the DC side circuit r ; Resonant capacitor C r Including the series resonant capacitor C r1 and C r2 .

2. The bidirectional unipolar resonant AC-DC converter and modulation method according to claim 1, characterized in that: The AC side circuit also includes the grid side inductor L g1 , L g2 and grid side capacitor C p ; Grid side inductance L g1 and L g2 One end of each is connected to the AC power supply U g The other end is connected to the two terminals on the low voltage side of the transformer; the grid side capacitor C p It is arranged between the half bridge and the H full bridge of the AC side circuit and is connected in parallel with the half bridge and the H full bridge respectively.

3. A modulation method for a bidirectional unipolar resonant AC-DC converter, characterized in that: The bidirectional unipolar resonant AC-DC converter according to claim 1 is implemented as follows: S1: constructing a corresponding working mode according to the power transmission direction between the AC side circuit and the DC side circuit of the bidirectional unipolar resonant AC-DC converter; S2: Generate the corresponding optimized modulation scheme for the working mode based on the equivalent circuit of the bidirectional unipolar resonant AC-DC converter; S3: Based on the optimized modulation scheme, the bidirectional unipolar resonant AC-DC converter is modulated to enter the corresponding working mode, and the excitation current flowing through the excitation inductor is used to realize the soft switching of the device.

4. The modulation method of the bidirectional unipolar resonant AC-DC converter according to claim 3, characterized in that: In step S1 , the working mode includes working mode 1 in which power is transmitted in a forward direction from the AC side circuit to the DC side circuit.

5. The modulation method of the bidirectional unipolar resonant AC-DC converter according to claim 4, characterized in that: In step S2, the optimized modulation scheme corresponding to working mode 1 is: The upper switch tube Q5 and the lower switch tube Q6 of the totem pole follow the AC side power supply U g Switching at 50Hz power frequency; The first AC side upper switch tube Q1 and the first AC side lower switch tube Q2 are connected in series, and the second AC side upper switch tube Q3 and the second AC side lower switch tube Q4 are connected in series, and are complementary turned on in pairs at a 50% duty cycle; By means of phase shifting, the rising edge of the PWM drive signal of the second AC side upper switch tube Q3 is aligned with the rising edge of the PWM drive signal of the DC side upper switch tube S1, and the rising edge of the PWM drive signal of the second AC side lower switch tube Q4 is aligned with the rising edge of the PWM drive signal of the DC side lower switch tube S2; The duty ratios of the PWM drive signals of the upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side are equal and less than 0.5; The upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side adopt variable pulse width modulation, and the pulse width changes with the input AC power and the industrial frequency AC voltage.

6. The modulation method of the bidirectional unipolar resonant AC-DC converter according to claim 5, characterized in that: In the optimized modulation scheme of working mode 1, the transmission power calculation formula of the resonant circuit is: And p =2U g ; Where: T s is the switching cycle; is the resonant angular frequency; D b is the duty cycle of the DC side switch; P S =P PFC , U gm is the amplitude of the industrial frequency AC voltage; The falling edge of the PWM driving signal of the first AC side lower switch tube Q2 lags behind the rising edge of the PWM driving signal of the DC side upper switch tube S1, and the lag time is the action time of the resonant current; The falling edge of the PWM driving signal of the first AC side upper switch tube Q1 lags behind the rising edge of the PWM driving signal of the DC side lower switch tube S2, and the lag time is the action time of the resonant current; After a switch tube in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the excitation inductor, and the anti-parallel diode of the other switch tube is turned on in advance to achieve zero voltage turn-on.

7. The modulation method of the bidirectional unipolar resonant AC-DC converter according to claim 3, characterized in that: In step S1 , the working mode includes working mode 2 in which power is transmitted reversely from the DC side circuit to the AC side circuit.

8. The modulation method of the bidirectional unipolar resonant AC-DC converter according to claim 7, characterized in that: In step S2, the optimized modulation scheme corresponding to the working mode 2 is: The upper switch tube Q5 and the lower switch tube Q6 of the totem pole follow the AC side power supply U g Switching at 50Hz power frequency; The first AC side upper switch tube Q1 and the first AC side lower switch tube Q2 are connected in series, and the second AC side upper switch tube Q3 and the second AC side lower switch tube Q4 are connected in series, and are complementary turned on in pairs at a 50% duty cycle; By means of phase shifting, the rising edge of the PWM drive signal of the second AC side lower switch tube Q4 is aligned with the rising edge of the PWM drive signal of the DC side upper switch tube S1, so that the rising edge of the PWM drive signal of the second AC side upper switch tube Q3 is aligned with the rising edge of the PWM drive signal of the DC side lower switch tube S2; The duty ratios of the PWM drive signals of the upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side are equal and less than 0.5; The upper switch tube S1 on the DC side and the lower switch tube S2 on the DC side adopt variable pulse width modulation, and the pulse width changes with the output AC power and the industrial frequency AC voltage.

9. The modulation method of the bidirectional unipolar resonant AC-DC converter according to claim 8, characterized in that: In the optimized modulation scheme of working mode 2, the transmission power calculation formula of the resonant circuit is: And p =2U g ; Where: T s is the switching cycle; is the resonant angular frequency; D f is the duty cycle of the DC side switch; P S =-P PFC , U gm is the amplitude of the industrial frequency AC voltage; The falling edge of the PWM driving signal of the switch tube Q1 on the first AC side lags behind the rising edge of the PWM driving signal of the switch tube S1 on the DC side, and the lag time is the action time of the resonant current; The falling edge of the PWM driving signal of the first AC side lower switch tube Q2 lags behind the rising edge of the PWM driving signal of the DC side lower switch tube S2, and the lag time is the action time of the resonant current; After a switch tube in the same bridge arm of the AC side circuit is turned off, the resonant current flows through the excitation inductor, and the anti-parallel diode of the other switch tube is turned on in advance to achieve zero voltage turn-on.

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