A three-phase zero-voltage-switching resonant-pole inverter circuit and its control method

Abstract

The present invention relates to a three-phase zero-voltage-switching resonant pole inverter circuit and its control method. Among them, the three-phase zero-voltage-switching resonant pole inverter circuit changes the position of the capacitor on each phase auxiliary circuit of the original passive resonant pole inverter, and additionally adds an auxiliary switch tube. The purpose of this auxiliary switch tube is to control the resonant current by regulating the size of the resonant capacitor when the output current is large, thereby improving the efficiency of the circuit; this switch tube does not participate in resonance during all switching processes and only needs to be turned on when the load current is large. Therefore, it only needs to be switched several times within a load current conversion cycle, the control is simpler than that of the conventional active resonant pole inverter, the number of switches is less, the efficiency is higher, and the modular characteristic of the circuit is not lost.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter design, and in particular to a three-phase zero-voltage switching resonant pole inverter circuit and its control method. Background Art

[0002] With the rapid development of the new energy industry, inverters have been widely used in the fields of new energy technology and AC speed regulation. In order to miniaturize and lighten the inverter, the switching frequency is gradually developing towards high frequency. However, in a hard-switching inverter, the high-frequency switching loss accounts for a large proportion of the total loss, which is not conducive to improving the efficiency. At the same time, the large fluctuations in voltage and current during the hard-switching process will generate a large amount of harmonics, affecting the power quality and causing serious harmonic pollution to the surrounding environment. Soft-switching technology is beneficial to reducing the switching loss and increasing the switching frequency, so it has become an important research direction in the field of power electronics.

[0003] The resonant pole inverter is an important soft-switching inverter, and each phase leg of it has the same auxiliary circuit. In recent years, various resonant pole inverters have been proposed in the relevant literature, which are roughly divided into active resonant pole inverters and passive resonant pole inverters, but they still need to be further improved in terms of reliability. For example, factors such as the number of auxiliary switching devices and voltage stress of the resonant pole inverter will affect the reliability of the main switch.

[0004] In recent years, the active three-phase resonant pole inverter can achieve zero-voltage turn-on. Although this type of circuit has high efficiency, there are many auxiliary switches in the auxiliary circuit of each three-phase inverter, which not only increases the hardware cost but also makes the control more complex, and is not conducive to the application and promotion of the three-phase resonant pole inverter. Therefore, some three-phase passive resonant pole inverters have been proposed, in which the auxiliary circuit does not contain auxiliary switches, resulting in low hardware cost and simple control. However, in this type of circuit, there are two resonant inductors in series with the main switch on each phase leg, which participate in the resonant process and carry current for a long time, increasing the circuit loss and making it impossible to perform modular design and cannot be directly applied to the market.

[0005] In summary, the current mainstream active resonant pole inverters have a large number of switches and complex control, while the passive resonant pole inverters have low efficiency. Therefore, designing a more efficient and practical resonant pole inverter is of great significance for the development of soft-switching inverters. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the problem of unreasonable design of the resonant pole inverter in the prior art.

[0007] To solve the above technical problem, the present invention provides a three-phase zero-voltage switching resonant pole inverter circuit, including a power supply U d ,

[0008] The power supply U d has a first main switch module, a second main switch module, a third main switch module, a first auxiliary diode module, a second auxiliary diode module, and a third auxiliary diode module connected in parallel at both ends in sequence;

[0009] The first main switch module includes main switches S 1 and S 2 connected in series. The main switch S 1 is connected in parallel with a buffer capacitor C 1 . The main switch S 2 is connected in parallel with a buffer capacitor C 2 ;

[0010] The second main switch module includes main switches S 4 and S 5 connected in series. The main switch S 4 is connected in parallel with a buffer capacitor C 3 . The main switch S 5 is connected in parallel with a buffer capacitor C 4 ;

[0011] The third main switch module includes main switches S 7 and S 8 connected in series. The main switch S 7 is connected in parallel with a buffer capacitor C 5 . The main switch S 8 is connected in parallel with a buffer capacitor C 6 ;

[0012] The first auxiliary diode module includes auxiliary diodes D r1 and D r2 connected in series. The negative electrode of the auxiliary diode D r1 is connected to the positive electrode of the power supply U d . The positive electrode of the auxiliary diode D r1 is connected to the negative electrode of the auxiliary diode D r2 . The positive electrode of the auxiliary diode D r2 is connected to the negative electrode of the power supply U d ;

[0013] The second auxiliary diode module includes auxiliary diodes D r3 and D r4 connected in series. The negative electrode of the auxiliary diode D r3 is connected to the positive electrode of the power supply U d . The positive electrode of the auxiliary diode D r3 is connected to the negative electrode of the auxiliary diode D r4 . The positive electrode of the auxiliary diode D r4 is connected to the negative electrode of the power supply U d ;

[0014] The third auxiliary diode module includes auxiliary diodes D r5 and D r6 connected in series. The negative electrode of the auxiliary diode D r5 is connected to the positive electrode of the power supply U d . The positive electrode of the auxiliary diode D r5 is connected to the negative electrode of the auxiliary diode D r6 . The positive electrode of the auxiliary diode D r6 is connected to the negative electrode of the power supply U d ;

[0015] The main switches S 1 and S 2 are connected to form a first node. The positive electrode of the auxiliary diode D r1 is connected to the negative electrode of the auxiliary diode D r2 to form a second node. A resonant inductor L r1 is provided between the first node and the second node;

[0016] The main switches S 4 and S 5 are connected to form a third node. The positive electrode of the auxiliary diode D r3 is connected to the negative electrode of the auxiliary diode D r4 to form a fourth node. A resonant inductor L r2 is provided between the third node and the fourth node;

[0017] The main switches S 7 and S 8 are connected to form a fifth node. The positive electrode of the auxiliary diode D r5 is connected to the negative electrode of the auxiliary diode D r6 to form a sixth node. A resonant inductor L r3 is provided between the fifth node and the sixth node;

[0018] A first auxiliary switch module is provided between the positive electrode of the power supply U d and the second node. Among them, the main switch S 3 and the resonant capacitor C r2 are connected in series and then connected in parallel with the resonant capacitor C r1 to form the first auxiliary switch module;

[0019] A second auxiliary switch module is provided between the positive electrode of the power supply U d and the fourth node. Among them, the main switch S 6 and the resonant capacitor C r4 are connected in series and then connected in parallel with the resonant capacitor C r3 to form the second auxiliary switch module;

[0020] A third auxiliary switch module is provided between the positive pole of the power supply U d and the sixth node, wherein the main switch S 9 and the resonant capacitor C r6 are connected in series and then connected in parallel with the resonant capacitor C r5 to form the third auxiliary switch module.

[0021] In an embodiment of the present invention, the main switches S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8 , and S 9 are respectively anti-parallel connected with the diodes D 1 , D 2 , D 3 , D 4 , D 5 , D 6 , D 7 , D 8 , and D 9 .

[0022] In an embodiment of the present invention, the power supply U d , the first main switch module, the first auxiliary diode module, the first auxiliary switch module and the resonant inductor L r1 constitute the A-phase circuit of the three-phase zero-voltage switching resonant pole inverter;

[0023] The power supply U d , the second main switch module, the second auxiliary diode module, the second auxiliary switch module and the resonant inductor L r2 constitute the B-phase circuit of the three-phase zero-voltage switching resonant pole inverter;

[0024] The power supply U d , the third main switch module, the third auxiliary diode module, the third auxiliary switch module and the resonant inductor L r3 constitute the C-phase circuit of the three-phase zero-voltage switching resonant pole inverter.

[0025] In an embodiment of the present invention, the main switches S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8 , and S 9 are all IGBT tubes.

[0026] To solve the above technical problems, the present invention provides a control method for a three-phase zero-voltage switching resonant pole inverter circuit, adopting the three-phase zero-voltage switching resonant pole inverter circuit as described above. The operating modes of the A-phase circuit, B-phase circuit, and C-phase circuit are the same;

[0027] For the A-phase circuit, let 0 to t 10 be the time occupied by the operating mode when the main switch S 3 is turned on. The operating mode when the main switch S 3 is turned on includes:

[0028] Let 0 to t 1 be state 1: At this time, the main switch S 1 is conducting and in a stable operating state, and no resonance occurs in the auxiliary circuit; the load current I 0 flows through the resonant inductor L r1 , and at the same time, the current of the resonant inductor L r1 flows through the resonant inductor L r1 , the auxiliary diode D r1 and the main switch S 1 ; during state 1, the voltage across the resonant inductor L r1 is equal to U ES +U ED , where U ES and U ED respectively represent the conduction state voltages across the main switch S 1 and the auxiliary diode D r1 . Therefore, i Lr1 will gradually decrease. When the main switch S 1 is turned off, the current on the resonant inductor L r1 drops to I 1 , and state 1 ends. Here, i Lr1 is the current flowing through the resonant inductor L r1 ; the auxiliary circuit is composed of the buffer capacitors C 1 , C 2 , the auxiliary diodes D r1 , D r2 , the main switch S 3 , the resonant capacitors C r1 , C r2 , and the diode D 3 ; I 1 is expressed as:

[0029] (1);

[0030] The duration T 1 of state 1 is the total cycle time minus the time of the operating modes of the remaining states 2 - state 10, where I 6is the maximum resonant current;

[0031] Let t 1 ~t 2 be State 2: At t 1 the main switch S 1 turns off, and the buffer capacitor C 1 limits the rising speed of u S1 . u S1 is the voltage of the main switch S 1 , so the main switch S 1 realizes the zero-voltage turn-off function; then the buffer capacitors C 1 and C 2 , and the resonant inductor L r1 work in the resonant state; electrical energy begins to transfer from the resonant inductor L r1 and the buffer capacitor C 2 outward, resulting in the non-linear decrease of i Lr1 and u C2 . u C2 is the voltage of the buffer capacitor C 2 ; at the same time, electrical energy begins to transfer to the buffer capacitor C 1 , resulting in the non-linear increase of u C1 . u C1 is the voltage of the buffer capacitor C 1 ; when u C1 reaches the power supply U d and i Lr1 reaches I 2 , State 2 ends; where, I 2 is expressed as:

[0032] (2);

[0033] The duration T 2 of State 2 is expressed as:

[0034] (3);

[0035] where, Z r1 represents the resonant impedance of State 2, ;

[0036] Let t 2 ~t 3 be State 3: When u C1 reaches the power supply U d after that, the buffer capacitors C 1 and C 2 exit the resonance; at this time, i Lr1 flows through the auxiliary diode D r1 and the diode D 2 . Electrical energy still transfers from the resonant inductor L r1 resulting in iLr1 decrease linearly; when i Lr1 decreases to I 0 State 3 ends;

[0037] The duration T of State 3 3 is expressed as:

[0038] (4);

[0039] Let t 3 ~t 4 be State 4: when i Lr1 decreases to I 0 at this time, L r1 , C r1 and C r2 will work in the resonant state; electrical energy is transferred from the resonant inductor L r1 , resulting in a non-linear decrease in i Lr1 ; at the same time, electrical energy is still transferred to the resonant capacitors C r1 and C r2 , resulting in a non-linear increase in u Cr1 and u Cr2 , u Cr1 is the voltage of the resonant capacitor C r1 , u Cr2 is the voltage of the resonant capacitor C r2 ; when i Lr1 decreases to 0, u Cr1 increases to U 1 and State 4 ends; where U 1 is expressed as:

[0040] (5);

[0041] The duration T of State 4 4 is expressed as:

[0042] (6);

[0043] where, Z r2 represents the resonant impedance of State 4, ;

[0044] Let t 4 ~t 5 be State 5: the current starts to flow through the main switch S 4 at t 2 , since u S2 has decreased to zero at t 2 and continues to flow through the anti-parallel diode D 2 of the main switch S 2 , so the main switch S 2 at t 4Conduction at this time can achieve zero-voltage turn-on, where u S2 is the voltage of the main switch S 2 ; the resonant inductor L r1 , the resonant capacitors C r1 and C r2 are still in the resonant state; u Cr1 and u Cr2 increase non-linearly, while i Lr1 increases non-linearly in the negative direction; when u Cr1 reaches the power supply U d and i Lr1 reaches -I 3 , state 5 ends; where I 3 is expressed as:

[0045] (7);

[0046] where, C r = C r1 + C r2 ;

[0047] The duration T 5 of state 5 is expressed as:

[0048] (8);

[0049] Let t 5 ~t 6 be state 6: The resonance of the auxiliary circuit ends at t 5 , and the load current starts to flow through the auxiliary diode D r2 , and the circulating current on the resonant inductor L r1 starts to flow through the resonant inductor L r1 , the main switch S 2 and the auxiliary diode D r2 ; during this state, the voltage across L r1 is equal to U ES1 + U ED1 , where U ES1 and U ED1 respectively represent the on-state voltage across the main switch S 2 and the auxiliary diode D r2 , resulting in i Lr1 gradually decreasing in the negative direction; i Lr1 reaches -I 6 at t 4 , and state 6 ends; where I 4 is expressed as:

[0050] (9);

[0051] The duration T6 Expressed as:

[0052] (10);

[0053] Where T represents the switching period and m represents the modulation depth of the sinusoidal pulse width modulation of the main switches S 1 、S 2 and I represents the maximum load current; 0max Expressed as:

[0054] Let t 6 ~t 7 be state 7: The main switch S 2 turns off at t 6 . The buffer capacitor C 2 can limit the rising speed of u S2 . Therefore, the main switch S 2 achieves zero-voltage turn-off; then the resonant inductor L r1 , the buffer capacitor C 1 and C 2 operate in resonance; electrical energy begins to transfer out from the resonant inductor L r1 and the buffer capacitor C 1 , resulting in the non-linear decrease of i Lr1 and u C1 ; meanwhile, electrical energy begins to transfer to the buffer capacitor C 2 , resulting in the non-linear increase of u C2 ; when u C2 reaches the power supply U d and i Lr1 reaches -I 5 , state 7 ends; where I 5 is expressed as:

[0055] (11);

[0056] The duration T 7 of state 7 is expressed as follows:

[0057] (12);

[0058] Let t 7 ~t 8 be state 8: The current begins to flow through the diode D 7 at t 1 . The voltage across L r1 is equal to U d , causing the resonant inductor L r1 to continue discharging, resulting in the linear decrease of i Lr1 in the negative direction; when i Lr1 reaches zero, state 8 ends;

[0059] The duration T of state 8 8 It is expressed as:

[0060] (13);

[0061] Let t 8 ~t 9 be state 9: The current starts to flow through the main switch S 8 at t 1 because u S1 has decreased to zero at t 7 , so the main switch S 1 achieves zero-voltage turn-on at t 7 ; The voltage across the resonant inductor L r1 is still equal to the power supply U d , causing electrical energy to start transferring to the resonant inductor L r1 , resulting in a linear increase in i Lr1 in the positive direction; When i Lr1 reaches I 0 , state 9 ends;

[0062] Let t 9 ~t 10 be state 10: The resonant inductor L r1 , the resonant capacitors C r1 and C r2 start to work in the resonant state, and electrical energy starts to transfer out from the resonant capacitors C r1 and C r2 , resulting in a non-linear decrease in u Cr1 and u Cr2 ; Electrical energy starts to transfer to the resonant inductor L r1 , resulting in a non-linear increase in i Lr1 ; When u Cr1 reaches 0 and i Lr1 reaches I 6 , state 10 ends; where I 6 is expressed as:

[0063] (14);

[0064] The duration T of state 10 9 is expressed as:

[0065] (15).

[0066] In an embodiment of the present invention, when the change range of the load current I 0 is I 0min ~I 0max , to make the main switches S 1 , S 2To achieve the function of zero - voltage switching, the first condition and the second condition need to be met:

[0067] The first condition is that during the turn - off transient of the main switches S 1 and S 2 the maximum rising rate of u S1 and u S2 should not exceed the rated rising rate of u S1 and u S2 ;

[0068] The second condition is that for the zero - voltage turn - on of the main switch S 1 in state 7, u C2 must increase to the power supply U d so that u C1 can be reduced to zero; by setting the magnitude of I 4 to ensure that u C2 increases to the power supply U d ; where the magnitude of I 4 satisfies:

[0069] (16);

[0070] where I 0max is the maximum output current of the load, and I 0min is the minimum output current of the load.

[0071] In an embodiment of the present invention, Z r2 satisfies the following formula:

[0072] (17).

[0073] In an embodiment of the present invention, the criteria for the turn - on and turn - off of the main switch S 3 are as follows: if the load current is greater than the preset current value, then turn on the main switch S 3 ; if the load current is less than the preset current value, then turn off the main switch S 3 .

[0074] In an embodiment of the present invention, when the resonant capacitors C r1 and C r2 satisfy C r2 = 3C r1 the resonant current when the main switch S 3 turns off is reduced to half of the load current when the main switch S 3 turns on.

[0075] In an embodiment of the present invention, the preset current value is I 0 / 2.

[0076] The above technical solution of the present invention has the following advantages compared with the prior art:

[0077] The three-phase zero-voltage-switching resonant-pole inverter circuit of the present invention changes the position of the capacitor in each phase of the original passive resonant-pole inverter, and additionally adds an auxiliary switch tube (S 3 、S 6 、S 9 ). The purpose of this auxiliary switch tube is to control the resonant current by regulating the size of the resonant capacitors (C r1 、C r2 、C r3 、C r4 、C r5 、C r6 ) when the output current is large, so as to improve the efficiency of the circuit; this inverter still retains the advantages of the original passive resonant-pole inverter, such as simple control and modularization. The auxiliary switch tubes (S 3 、S 6 、S 9 ) do not participate in resonance during all switching processes, and only need to be turned on when the load current is large. Therefore, only a few switches are required within a load current conversion cycle, the control is simpler than that of a conventional active resonant-pole inverter, the number of switches is less, and the efficiency is higher;

[0078] The control method of the three-phase zero-voltage-switching resonant-pole inverter circuit of the present invention flexibly switches the capacitance value of the resonant circuit under different output conditions, so as to reduce the resonant current and circulating current loss of the circuit and achieve the purpose of improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention and in conjunction with the drawings.

[0080] Figure 1 FIG. is the circuit diagram of the three-phase zero-voltage-switching resonant-pole inverter in the embodiment of the present invention;

[0081] Figure 2 FIG. is the circuit diagram of phase A in the three-phase zero-voltage-switching resonant-pole inverter circuit in the embodiment of the present invention;

[0082] Figure 3 FIG. is the theoretical waveform diagram of the three-phase zero-voltage-switching resonant-pole inverter in the embodiment of the present invention;

[0083] Figure 4 FIG. is the schematic diagram of the working mode analysis of the three-phase zero-voltage-switching resonant-pole inverter when the load current is positive in the embodiment of the present invention;

[0084] Figure 5It is a schematic diagram for analyzing the working modes of a three-phase zero-voltage-switching resonant-pole inverter when the output load current of the embodiment of the present invention is reverse. Detailed implementation manners

[0085] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments cited are not intended to limit the present invention.

[0086] Embodiment 1

[0087] Referring to Figure 1 as shown, the present invention relates to a three-phase zero-voltage-switching resonant-pole inverter circuit, including a power supply U d , auxiliary diodes D r1 , D r2 , D r3 , D r4 , D r5 , D r6 ; buffer capacitors C 1 , C 2 , C 3 , C 4 , C 5 , C 6 ; resonant capacitors C r1 , C r2 , C r3 , C r4 , C r5 , C r6 ; resonant inductors L r1 , L r2 , L r3 ; main switches S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8 , S 9 ; the anti-parallel diodes belonging to S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8 , S 9 are D 1 , D 2 , D 3 , D 4 , D 5 , D 6 , D 7 , D8 , D 9 ;

[0088] The power supply U d has a first main switch module, a second main switch module, a third main switch module, a first auxiliary diode module, a second auxiliary diode module, and a third auxiliary diode module connected in parallel at both ends in sequence;

[0089] The first main switch module includes main switches S 1 and S 2 connected in series. The main switch S 1 is connected in parallel with the buffer capacitor C 1 , and the main switch S 2 is connected in parallel with the buffer capacitor C 2 ;

[0090] The second main switch module includes main switches S 4 and S 5 connected in series. The main switch S 4 is connected in parallel with the buffer capacitor C 3 , and the main switch S 5 is connected in parallel with the buffer capacitor C 4 ;

[0091] The third main switch module includes main switches S 7 and S 8 connected in series. The main switch S 7 is connected in parallel with the buffer capacitor C 5 , and the main switch S 8 is connected in parallel with the buffer capacitor C 6 ;

[0092] The first auxiliary diode module includes auxiliary diodes D r1 and D r2 connected in series. The negative electrode of the auxiliary diode D r1 is connected to the positive electrode of the power supply U d . The positive electrode of the auxiliary diode D r1 is connected to the negative electrode of the auxiliary diode D r2 . The positive electrode of the auxiliary diode D r2 is connected to the negative electrode of the power supply U d ;

[0093] The second auxiliary diode module includes auxiliary diodes D r3 and D r4 connected in series. The negative electrode of the auxiliary diode D r3 is connected to the positive electrode of the power supply U d . The positive electrode of the auxiliary diode D r3 is connected to the negative electrode of the auxiliary diode D r4 ​r4 The positive electrode of d is connected to the negative electrode of power supply U;

[0094] The third auxiliary diode module includes auxiliary diodes D r5 and D r6 connected in series. The negative electrode of auxiliary diode D r5 is connected to the positive electrode of power supply U d . The positive electrode of auxiliary diode D r5 is connected to the negative electrode of auxiliary diode D r6 . The positive electrode of auxiliary diode D r6 is connected to the negative electrode of power supply U d ;

[0095] The main switches S 1 and S 2 are connected to form a first node. The positive electrode of auxiliary diode D r1 is connected to the negative electrode of auxiliary diode D r2 to form a second node. A resonant inductor L r1 is provided between the first node and the second node;

[0096] The main switches S 4 and S 5 are connected to form a third node. The positive electrode of auxiliary diode D r3 is connected to the negative electrode of auxiliary diode D r4 to form a fourth node. A resonant inductor L r2 is provided between the third node and the fourth node;

[0097] The main switches S 7 and S 8 are connected to form a fifth node. The positive electrode of auxiliary diode D r5 is connected to the negative electrode of auxiliary diode D r6 to form a sixth node. A resonant inductor L r3 is provided between the fifth node and the sixth node;

[0098] A first auxiliary switch module is provided between the positive electrode of power supply U d and the second node. Among them, the main switch S 3 and the resonant capacitor C r2 are connected in series and then connected in parallel with the resonant capacitor C r1 to form the first auxiliary switch module;

[0099] A second auxiliary switch module is provided between the positive electrode of power supply U d and the fourth node. Among them, the main switch S 6 and the resonant capacitor C r4 are connected in series and then connected in parallel with the resonant capacitor Cr3 are connected in parallel to form a second auxiliary switch module;

[0100] Between the positive pole of the power supply U d and the sixth node, a third auxiliary switch module is provided, where the main switch S 9 and the resonant capacitor C r6 are connected in series and then connected in parallel with the resonant capacitor C r5 to form a third auxiliary switch module;

[0101] The first auxiliary switch module, the second auxiliary switch module, and the third auxiliary switch module are used to connect to a load;

[0102] Further, the main switches S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8 and S 9 are respectively anti-parallel connected with the diodes D 1 , D 2 , D 3 , D 4 , D 5 , D 6 , D 7 , D 8 and D 9 respectively.

[0103] Further, the power supply U d , the first main switch module, the first auxiliary diode module, the first auxiliary switch module, and the resonant inductor L r1 constitute the A-phase circuit of a three-phase zero-voltage-switching resonant pole inverter; the power supply U d , the second main switch module, the second auxiliary diode module, the second auxiliary switch module, and the resonant inductor L r2 constitute the B-phase circuit of a three-phase zero-voltage-switching resonant pole inverter; the power supply U d , the third main switch module, the third auxiliary diode module, the third auxiliary switch module, and the resonant inductor L r3 constitute the C-phase circuit of a three-phase zero-voltage-switching resonant pole inverter.

[0104] Further, the main switches S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8 and S 9Specifically, it is an IGBT tube.

[0105] The load in this embodiment includes an inductor L connected in series a and a resistor R a , an inductor L connected in series b and a resistor R b , an inductor L connected in series c and a resistor R c , and the resistors R a , resistor R b , resistor R c are connected to each other. It should be noted that the inductor L a and resistor R a of this embodiment serve as the load of the A-phase circuit, the inductor L b and resistor R b serve as the load of the B-phase circuit, and the inductor L c and resistor R c serve as the load of the C-phase circuit. Since the resistors R a , resistor R b , resistor R c are connected to each other, in practice, for example, the A-phase circuit is also affected by resistor R b , resistor R c , inductor L b , inductor L c .

[0106] Embodiment 2

[0107] This embodiment relates to a control method for a three-phase zero-voltage-switching resonant-pole inverter circuit. The three-phase zero-voltage-switching resonant-pole inverter circuit described in Embodiment 1 is adopted. The working modes of the A-phase circuit, B-phase circuit, and C-phase circuit are the same. The A-phase circuit, B-phase circuit, and C-phase circuit each include two working modes (i.e., the mode when the load current is positive and the mode when the load current is negative). For convenience, only the mode when the load current of the A-phase circuit is positive is introduced in this embodiment.

[0108] Figure 1 is the main circuit diagram of the three-phase zero-voltage-switching resonant-pole inverter circuit in this embodiment. The auxiliary circuits (each auxiliary circuit is composed of a buffer capacitor C 1 and S 2 connected in series to form a bridge arm) connected to each bridge arm are the same as each other. The auxiliary circuit is composed of a buffer capacitor C 1 , C 2 , an auxiliary diode D r1 , D r2 , a main switch S 3 , a resonant capacitor C r1 , C r2 , a diode D 3 . For Figure 2Taking the phase-A circuit shown as an example, its component schematic includes: the symbol of the auxiliary diode is D r1 , D r2 ; the symbol of the buffer capacitor is C 1 , C 2 ; the symbol of the resonant capacitor is C r1 , C r2 ; the symbol of the resonant inductor is L r1 ; the symbol of the main switch is S 1 , S 2 , S 3 ; belonging to S 1 , S 2 and S 3 , the symbols of the anti-parallel diodes of S 1 and D 2 and D 3 .

[0109] The design idea of the phase-A circuit is as follows: 1. To achieve zero-voltage turn-off of S 1 and S 2 , C 1 and C 2 are designed in parallel with S 1 and S 2 to limit the rate of change of u S1 and u S2 during the turn-off transient process; 2. To achieve zero-voltage turn-on of S 1 and S 2 , two paths composed of L r1 and D r1 (D r2 ), C r1 (C r2 ) are respectively designed in parallel with S 1 and S 2 . By using the resonance between C 1 , C 2 , L r1 , C r1 and C r2 , u S1 and u S2 are periodically reduced to zero before S 1 or S 2 is turned on; 3. To work more efficiently within the full load operating range, the turn-on and turn-off of S 3 can selectively make C r2 participate in the resonance process, thereby regulating the resonant current according to the load current magnitude.

[0110] The theoretical waveforms of the three-phase zero-voltage-switching resonant pole inverter circuit are as shown in Figure 3 , Figure 3 in which (Y) is the auxiliary switch tube S 3The timing diagram of the switch, which switches twice in each load current change cycle. When S 3 turns on, the theoretical waveform of this inverter is as shown by the solid line in Figure 3 (X). When S 3 turns off, the theoretical waveform of the inverter is as shown by the dashed line in Figure 3 (X). The working mode analysis during operation is shown in Figure 4 and Figure 5 . Figure 4 is the mode when the load current is positive, and Figure 5 is the mode when the load current is negative. When S 3 turns on, the working mode is the a mode of Figure 4 (some Stages in Stage 1 - Stage 10 have a mode and a b mode, and some Stages do not. If not, the a mode and b mode are shared). When S 3 turns off, the working mode is the b mode of Figure 4 .

[0111] For the A - phase circuit, let the time occupied by the working mode when the main switch S 10 turns on be 0 to t 3 . The following mode analysis is shown in Figure 4 and takes the case when S 3 turns on as an example:

[0112] State 1 (0 - t 1 ): At this time, S 1 is conducting and in a stable working state, and there will be no resonance in the auxiliary circuit. There is a stable load current I 0 flowing through L r1 . At the same time, the current of L r1 flows through L r1 , D r1 1 r1 ES ED ES ED 1 r1 Lr1 Lr1 r1 1 r1 1 1 and S 1 and D r1 . During this State 1, the voltage across L Lr1 (i Lr1 is the current flowing through the resonant inductor L r1 ) will slowly decrease. When S 1 turns off, the current on L r1 drops to I 1 , and State 1 ends. Where I 1 is expressed as follows:

[0113] (1)

[0114] The duration T of state 1 1 is the total cycle time minus the time of the remaining 9 working modes (state 2 - state 10, i.e., Figure 4 Stage 2 - Stage 10), where I 6 is the maximum resonant current, as shown in formula (14).

[0115] State 2 (t 1 ~t 2 ): At t 1 , S 1 turns off. C 1 limits the rising speed of u S1 (u S1 is the voltage of the main switch S 1 ), so S 1 achieves the zero - voltage turn - off function. Then C 1 , C 2 , L r1 work in the resonant state. Electric energy begins to transfer out from L r1 , C 2 , resulting in the non - linear decrease of i Lr1 and u C2 (u C2 is the voltage of the buffer capacitor C 2 ). At the same time, electric energy begins to transfer to C 1 , resulting in the non - linear increase of u C1 (u C1 is the voltage of the buffer capacitor C 1 ). When u C1 reaches the power supply U d , and i Lr1 reaches I 2 , state 2 ends. Where I 2 is expressed as follows:

[0116] (2)

[0117] The duration T of state 2 2 is expressed as follows:

[0118] (3)

[0119] Where:

[0120] Z r1 represents the resonant impedance of state 2, ;

[0121] State 3 (t 2 ~t 3 ): When UC1 Reach U d After that, C 1 and C 2 exit resonance. At this time, i Lr1 flows through D r1 and D 2 The electrical energy still transfers from L r1 resulting in a linear decrease in i Lr1 When i Lr1 decreases to I 0 State 3 ends.

[0122] The duration T of State 3 3 is expressed as follows:

[0123] (4)

[0124] State 4 (t 3 ~t 4 ) When i Lr1 decreases to I 0 At this time, L r1 , C r1 and C r2 will work in the resonant state. The electrical energy transfers from L r1 resulting in a non - linear decrease in i Lr1 At the same time, the electrical energy is still transferred to C r1 and C r2 resulting in a non - linear increase in u Cr1 and u Cr2 (u Cr1 is the voltage of the resonant capacitor C r1 , u Cr2 is the voltage of the resonant capacitor C r2 ). When i Lr1 decreases to 0, u Cr1 increases to U 1 State 4 ends. Where U 1 is expressed as follows:

[0125] (5)

[0126] The duration T of State 4 4 is expressed as follows:

[0127] (6)

[0128] Where:

[0129] Z r2 represents the resonant impedance of State 4, ;

[0130] State 5 (t 4 ~t5 ): Current at t 4 Start flowing through S 2 . Because u S2 (u S2 Main switch S 2 voltage) at t 2 has decreased to zero and passed S 2 Anti-parallel diode D 2 The continuous current, therefore S 2 In t 4 When it is turned on, zero voltage can be achieved. r1 , C r1 and C r2 Still in resonance. Cr1 and u Cr2 Nonlinear increase, while i Lr1 Negative nonlinearity increases. Cr1 Reach U d And i Lr1 Reach-I 3 When , state 5 ends. 3 It is expressed as follows:

[0131] (7)

[0132] Duration of state 5 T 5 It is expressed as follows:

[0133] (8)

[0134] State 6 (t 5 ~t 6 ): The resonance of the auxiliary circuit is at t 5 End. A stable load current begins to flow through D r2 , L r1 The circulating current on L begins to flow through r1 , S 2 and D r2 During this state, L r1 The voltage across the two ends is equal to U ES1 +U ED1 , where U ES1 and U ED1 Respectively represent S 2 and D r2 The on-state voltage across the terminals causes i Lr1 Slowly decreases in the negative direction. 2 In t 6 When turned off, i Lr1 Reach-I 4 , state 6 ends. 4 It is expressed as follows:

[0135] (9)

[0136] The duration T of state 6 6 is expressed as follows:

[0137] (10)

[0138] where T represents the switching period, and m represents the modulation depth of the sinusoidal pulse width modulation (SPWM) of the main switches S 1 、S 2 , and I 0max represents the maximum load current.

[0139] State 7 (t 6 ~t 7 ): S 2 turns off at t 6 . C 2 can limit the rising rate of u S2 , so S 2 achieves zero-voltage turn-off. Then L r1 , C 1 and C 2 operate in the resonant state. Electrical energy begins to transfer out from L r1 and C 1 , resulting in the non-linear decrease of i Lr1 and u C1 . At the same time, electrical energy begins to transfer to C 2 , resulting in the non-linear increase of u C2 . When u C2 reaches U d and i Lr1 reaches -I 5 , state 7 ends. Where I 5 is expressed as follows:

[0140] (11)

[0141] The duration T of state 7 7 is expressed as follows:

[0142] (12)

[0143] State 8 (t 7 ~t 8 ): The current begins to flow through D 7 at t 1 . The voltage across L r1 is equal to U d , causing L r1 to continue discharging, resulting in the linear decrease of i Lr1 in the negative direction. When i Lr1When it reaches zero, state 8 ends.

[0144] The duration T of state 8 8 is expressed as follows:

[0145] (13)

[0146] State 9 (t 8 ~t 9 ): The current starts to flow through S 8 at t 1 . Since u S1 has decreased to zero at t 7 , S 1 can achieve zero-voltage switching at t 7 . The voltage across L r1 remains equal to U d , causing electrical energy to start transferring to L r1 , resulting in a linear increase in i Lr1 in the positive direction. When i Lr1 reaches I 0 , state 9 ends.

[0147] State 10 (t 9 ~t 10 ): L r1 , C r1 and C r2 start to operate in resonance. Electrical energy starts to transfer out from C r1 and C r2 , resulting in a non-linear decrease in u Cr1 and u Cr2 . Electrical energy starts to transfer to L r1 , causing a non-linear increase in i Lr1 . When u Cr1 reaches 0 and i Lr1 reaches I 6 , state 10 ends. Where I 6 is expressed as follows:

[0148] (14)

[0149] The duration T of state 9 9 is expressed as follows:

[0150] (15)

[0151] I 0 represents the load current. When the variation range of I 0 is from I 0min ~I 0max , to make S 1 , S 2To achieve the function of zero - voltage switching, the first condition and the second condition need to be met:

[0152] The first condition is that: S 1 and S 2 In the turn - off transient, the maximum rising rates of u S1 and u S2 should not exceed the rated rising rates of u S1 and u S2 .

[0153] The second condition is that: Regarding the zero - voltage turn - on of S 1 , in state 7, u C2 must increase to U d so that u C1 can be reduced to zero. According to formulas (7), (9) and (11), formula (16) can be derived. I 4 must be large enough to ensure that u C2 can increase to U d .

[0154] (16)

[0155] where, I 0max is the maximum output current of the load, and I 0min is the minimum output current of the load.

[0156] In the process of designing parameters, according to formulas (7), (9) and (16), formula (17) can be obtained.

[0157] (17)

[0158] Since the load current I 0 is constantly changing, the resonant impedance Z r2 must be designed small enough to increase the resonant current to meet the limit conditions for realizing soft switching. However, the resonant impedance Z r2 should be as large as possible to reduce the peak current passing through S 1 and S 2 , thus minimizing the conduction loss. Therefore, the design goal of circuit parameters is to correctly select reactive components so that the circuit can operate under normal soft - switching conditions while minimizing the resonant current at the specified maximum load current. By Figure 4From states 1 and 6, it can be seen that due to the very small on-voltage drops of the switching transistor and the diode, there is a circulating current in the circuit. The magnitude of the circulating current affects the efficiency of the circuit. However, the circuit parameters are designed based on the maximum load current of the circuit. Regardless of how the load current changes, the resonant impedance remains unchanged, and thus the resonant current remains unchanged. This leads to a situation where when the load current is very low, the resonant current is still very large, which greatly reduces the efficiency of the inverter. To further reduce the circulating current loss caused by the resonant current, a control method based on variable adjustment of the resonant capacitor is designed here.

[0159] During operation, if the load current is large, then turn on S 3 , at this time C r = C r1 + C r2 , the resonant impedance Z r2 becomes smaller, and the resonant current becomes larger. This is the capacitance value designed to be able to operate at zero voltage even at the maximum load current. The theoretical waveform is as shown by the solid line in Figure 3 (X), and the operating state during resonance is as shown by the a-mode diagram in Figure 4 . If the load current is small, then turn off S 3 , at this time C r = C r1 , at this time the resonant impedance Z r2 becomes larger, and the theoretical waveform is as shown by the dashed line in Figure 3 (X), and the operating state during resonance is as shown by the b-mode diagram in Figure 4 . According to Figure 3 in (X), compared with turning on S 3 , it can be seen that after turning off S 3 , the resonant current and the current flowing through the switching transistor have a significant decrease.

[0160] Regarding the judgment criteria for the turn-on and turn-off of S 3 , if it is set to half of the load current, that is, when it is higher than the preset current value I 0 / 2, turn on S 3 , and when it is lower than the preset current value I 0 / 2, turn off S 3 . At the same time, by setting the values of C r1 and C r2 (in this embodiment, C r2 = 3C r1 ) to make the resonant current when S 3 is turned off reduced to half of the load current when S 3 is turned on, that is, the power can be increased as:

[0161] (18)

[0162] Since S3 does not participate in resonance in all switching cycles, so the number of switchings in a load current change cycle is very small, and because of the existence of C r1 , the switch of S 3 can also achieve zero-voltage switching, so the switching loss of S 3 is very small. At the same time, according to the design idea of the above resonance circuit parameters, the duty cycle range is designed to be as large as possible and the dead time is small, so the resonance time of the auxiliary circuit is very short. Only when C r3 participates in resonance, S 3 will conduct. The conduction time is much shorter than that of S 1 and S 2 , so the conduction loss of S 3 is also very small. Therefore, such a control method can reduce the resonance current without increasing the loss, and further improve the circuit efficiency.

[0163] Although the preferred embodiments of the present application have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concepts. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0164] Obviously, the above embodiments are only examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A three-phase zero voltage switching resonant pole inverter circuit, characterized in that: Including power supply U d , The power supply U d The two ends of are sequentially connected in parallel with a first main switch module, a second main switch module, a third main switch module, a first auxiliary diode module, a second auxiliary diode module, and a third auxiliary diode module; The first main switch module includes main switches S1 and S2 connected in series, the main switch S1 and the buffer capacitor C1 are connected in parallel, and the main switch S2 and the buffer capacitor C2 are connected in parallel; The second main switch module includes main switches S4 and S5 connected in series, the main switch S4 and the buffer capacitor C3 are connected in parallel, and the main switch S5 and the buffer capacitor C4 are connected in parallel; The third main switch module includes main switches S7 and S8 connected in series, the main switch S7 and the buffer capacitor C5 are connected in parallel, and the main switch S8 and the buffer capacitor C6 are connected in parallel; The first auxiliary diode module includes auxiliary diodes D connected in series r1 and D r2 , the auxiliary diode D r1 The negative pole of the power supply U d The positive electrode of the auxiliary diode D r1 The positive electrode of the auxiliary diode D r2 The cathode of the auxiliary diode D r2 The positive pole of the power supply U d The negative connection of The second auxiliary diode module includes auxiliary diodes D connected in series r3 and D r4 , the auxiliary diode D r3 The negative pole of the power supply U d The positive electrode of the auxiliary diode D r3 The positive electrode of the auxiliary diode D r4 The cathode of the auxiliary diode D r4 The positive pole of the power supply U d The negative connection of The third auxiliary diode module includes auxiliary diodes D connected in series r5 and D r6 , the auxiliary diode D r5 The negative pole of the power supply U d The positive electrode of the auxiliary diode D r5 The positive electrode of the auxiliary diode D r6 The cathode of the auxiliary diode D r6 The positive pole of the power supply U d The negative connection of The main switches S1 and S2 are connected to form a first node, and the auxiliary diode D r1 The positive electrode of the auxiliary diode D r2 The negative electrode of the first node is connected to form a second node, and a resonant inductor L is provided between the first node and the second node. r1 ; The main switches S4 and S5 are connected to form a third node, and the auxiliary diode D r3 The positive electrode of the auxiliary diode D r4 The negative electrode of the third node is connected to form a fourth node, and a resonant inductor L is provided between the third node and the fourth node. r2 ; The main switches S7 and S8 are connected to form a fifth node, and the auxiliary diode D r5 The positive electrode of the auxiliary diode D r6 The negative electrode of the fifth node is connected to form a sixth node, and a resonant inductor L is provided between the fifth node and the sixth node. r3 ; The power supply U d A first auxiliary switch module is provided between the positive electrode and the second node, wherein the main switch S3 and the resonant capacitor C r2 After being connected in series, it is then connected to the resonant capacitor C r1 connected in parallel to form a first auxiliary switch module; The power supply U d A second auxiliary switch module is provided between the positive electrode and the fourth node, wherein the main switch S6 and the resonant capacitor C r4 After being connected in series, it is then connected to the resonant capacitor C r3 connected in parallel to form a second auxiliary switch module; The power supply U d A third auxiliary switch module is provided between the positive electrode and the sixth node, wherein the main switch S9 and the resonant capacitor C r6 After being connected in series, it is then connected to the resonant capacitor C r5 The third auxiliary switch module is formed in parallel.

2. The three-phase zero voltage switching resonant pole inverter circuit according to claim 1, characterized in that: The main switches S1, S2, S3, S4, S5, S6, S7, S8 and S9 are anti-parallel connected to the diodes D1, D2, D3, D4, D5, D6, D7, D8 and D9 respectively.

3. The three-phase zero voltage switching resonant pole inverter circuit according to claim 2, characterized in that: The power supply U d , a first main switch module, a first auxiliary diode module, a first auxiliary switch module and a resonant inductor L r1 A phase circuit constituting a three-phase zero voltage switching resonant pole inverter; The power supply U d , a second main switch module, a second auxiliary diode module, a second auxiliary switch module and a resonant inductor L r2 A B-phase circuit constituting a three-phase zero voltage switching resonant pole inverter; The power supply U d , a third main switch module, a third auxiliary diode module, a third auxiliary switch module and a resonant inductor L r3 The C-phase circuit of the three-phase zero-voltage switching resonant pole inverter is constructed.

4. The three-phase zero voltage switching resonant pole inverter circuit according to claim 1, characterized in that: The main switches S1, S2, S3, S4, S5, S6, S7, S8 and S9 are all IGBT tubes.

5. A control method for a three-phase zero voltage switching resonant pole inverter circuit, using the three-phase zero voltage switching resonant pole inverter circuit as claimed in any one of claims 1 to 4, characterized in that: The working modes of the A-phase circuit, the B-phase circuit and the C-phase circuit are consistent; For the A phase circuit, let 0~t 10 The time taken by the working mode when the main switch S3 is turned on. The working mode when the main switch S3 is turned on includes: Let 0~t1 be state 1: At this time, the main switch S1 is turned on and is in a stable working state, and no resonance occurs in the auxiliary circuit; the load current I0 flows through the resonant inductor L r1 , while the resonant inductor L r1 The current flows through the resonant inductor L r1 、Auxiliary diode D r1 and main switch S1; during state 1, the resonant inductor L r1 The voltage across the two ends is equal to U ES +U ED , where U ES and U ED Represent the main switch S1 and the auxiliary diode D r1 The on-state voltage across the terminals, therefore i Lr1 Will gradually decrease. When the main switch S1 is turned off, the resonant inductor L r1 The current on the circuit drops to I1, and state 1 ends. Lr1 is the current flowing through the resonant inductor L r1 The auxiliary circuit is composed of buffer capacitors C1, C2, auxiliary diode D r1 , D r2 , main switch S3, resonant capacitor C r1 , C r2 , diode D3; I1 is expressed as: (1)； The duration T1 of state 1 is the total cycle time, minus the time of the remaining working modes of state 2-state 10, where I6 is the maximum resonant current; Let t1~t2 be state 2: at t1, the main switch S1 is turned off, and the buffer capacitor C1 limits u S1 The rising speed, u S1 is the voltage of the main switch S1, so the main switch S1 realizes the zero voltage turn-off function; then the buffer capacitors C1, C2, and the resonant inductor L r1 Working in the resonant state; the electric energy starts to flow from the resonant inductor L r1 , the buffer capacitor C2 is transferred outward, resulting in i Lr1 and u C2 The nonlinear decrease of u C2 is the voltage of buffer capacitor C2; at the same time, the electric energy begins to transfer to buffer capacitor C1, resulting in u C1 The nonlinear increase of u C1 is the voltage of buffer capacitor C1; when u C1 Reach power supply U d ,i Lr1 When I2 is reached, state 2 ends; where I2 is expressed as: (2)； The duration T2 of state 2 is expressed as: (3)； Among them, Z r1 represents the resonant impedance of state 2, ; Let t2~t3 be state 3: when u C1 Reach power supply U d After that, the buffer capacitors C1 and C2 exit the resonance; at this time, i Lr1 Flows through auxiliary diode D r1 and diode D2, the electrical energy still flows from the resonant inductor L r1 transfer, leading to Lr1 Linear decrease; when i Lr1 When it decreases to I0, state 3 ends; The duration T3 of state 3 is expressed as: (4)； Let t3~t4 be state 4: when i Lr1 When it decreases to I0, L r1 , C r1 and C r2 It will work in the resonant state; the electric energy is transferred from the resonant inductor L r1 transfer, leading to Lr1 The nonlinearity decreases; at the same time, the electrical energy is still transferred to the resonant capacitor C r1 and C r2 , resulting in u Cr1 and u Cr2 Nonlinear increase, u Cr1 is the resonant capacitor C r1 The voltage, u Cr2 is the resonant capacitor C r2 The voltage when i Lr1 When u decreases to 0, Cr1 When it increases to U1, state 4 ends; U1 is expressed as: (5)； The duration T4 of state 4 is expressed as: (6)； Among them, Z r2 represents the resonant impedance of state 4, ; Let t4~t5 be state 5: The current starts to flow through the main switch S2 at t4, due to u S2 At t2, it has decreased to zero and continues to flow through the anti-parallel diode D2 of the main switch S2. Therefore, the main switch S2 can be turned on at zero voltage when it is turned on at t4. S2 is the voltage of the main switch S2; the resonant inductor L r1 , resonant capacitor C r1 and C r2 Still in resonance state; u Cr1 and u Cr2 Nonlinear increase, while i Lr1 Negative nonlinearity increases; when u Cr1 Reach power supply U d And i Lr1 When -I3 is reached, state 5 ends; where I3 is represented by: (7)； Among them, C r =C r1 +C r2 ; The duration T5 of state 5 is expressed as: (8)； Let t5~t6 be state 6: the resonance of the auxiliary circuit ends at t5, and the load current begins to flow through the auxiliary diode D r2 , resonant inductor L r1 The circulating current starts to flow through the resonant inductor L r1 , main switch S2 and auxiliary diode D r2 During this state, L r1 The voltage across the two ends is equal to U ES1 +U ED1 , where U ES1 and U ED1 Represent the main switch S2 and the auxiliary diode D r2 The on-state voltage across the terminals causes i Lr1 Gradually decrease in the negative direction; i Lr1 When -I4 is reached at t6, state 6 ends; where I4 is expressed as: (9)； The duration T6 of state 6 is expressed as: (10)； Where T represents the switching period, m represents the modulation depth of the sinusoidal pulse width modulation of the main switches S1 and S2, and I 0max Indicates the maximum load current; Let t6~t7 be state 7: the main switch S2 is turned off at t6, and the buffer capacitor C2 can limit u S2 The rising speed of the main switch S2 is thus zero-voltage turned off; then the resonant inductor L r1 , buffer capacitors C1 and C2 work in a resonant state; the electrical energy begins to flow from the resonant inductor L r1 and buffer capacitor C1 to move outward, causing i Lr1 and u C1 The nonlinearity decreases; at the same time, the electric energy begins to transfer to the buffer capacitor C2, causing u C2 Nonlinear increase; when u C2 Reach power supply U d And i Lr1 When -I5 is reached, state 7 ends; where I5 ​​is represented by: (11)； The duration T7 of state 7 is expressed as follows: (12)； Let t7~t8 be state 8: the current starts to flow through diode D1 at t7, L r1 The voltage across the two ends is equal to U d , so that the resonant inductor L r1 Continue to discharge, resulting in i Lr1 It decreases linearly in the negative direction; when i Lr1 When it reaches zero, state 8 ends; The duration T8 of state 8 is expressed as: (13)； Let t8~t9 be state 9: The current starts to flow through the main switch S1 at t8, because u S1 At t7, it has decreased to zero, so the main switch S1 is turned on at zero voltage at t7; the resonant inductor L r1 The voltage across the two ends is still equal to the power supply U d , so that the electrical energy begins to transfer to the resonant inductor L r1 In, leading to Lr1 Increases linearly in the positive direction; when i Lr1 When I0 is reached, state 9 ends; Let t9~t 10 State 10: resonant inductor L r1 , resonant capacitor C r1 and C r2 It starts to work in the resonant state, and the electric energy starts to flow from the resonant capacitor C r1 and C r2 Outward transfer, resulting in u Cr1 and u Cr2 The nonlinearity decreases; the electrical energy begins to transfer to the resonant inductor L r1 , resulting in Lr1 Nonlinear increase; when u Cr1 Reach 0 and i Lr1 When I6 is reached, state 10 ends; where I6 is represented by: (14)； The duration T9 of state 10 is expressed as: (15)。 6. The control method of the three-phase zero voltage switching resonant pole inverter circuit according to claim 5, characterized in that: When the load current I0 changes within the range of I 0min ~I 0max In order for the main switches S1 and S2 to achieve the zero voltage switching function, the first and second conditions must be met: The first condition is: the main switches S1 and S2 are turned off in the transient state. S1 and u S2 The maximum rate of ascent should not exceed u S1 and u S2 Rated rate of ascent; The second condition is: about the zero voltage turn-on of the main switch S1, in state 7, u C2 Must be added to the power supply U d , so that u C1 can be reduced to zero; by setting the size of I4 to ensure that u C2 Add to power supply U d ; The size of I4 satisfies: (16)； Among them, I 0max is the maximum output current of the load, I 0min is the minimum output current of the load.

7. The control method of the three-phase zero voltage switching resonant pole inverter circuit according to claim 5, characterized in that: Z r2 Satisfies the following formula: (17)。 8. The control method of the three-phase zero voltage switching resonant pole inverter circuit according to claim 5, characterized in that: The criterion for turning on and off the main switch S3 is: if the load current is greater than a preset current value, the main switch S3 is turned on; if the load current is less than the preset current value, the main switch S3 is turned off.

9. The control method of the three-phase zero voltage switching resonant pole inverter circuit according to claim 8, characterized in that: Resonant capacitor C r1 and C r2 Satisfy C r2 =3C r1 In this case, the resonant current when the main switch S3 is turned off is reduced to half of the load current when the main switch S3 is turned on.

10. The control method of the three-phase zero voltage switching resonant pole inverter circuit according to claim 8, characterized in that: The preset current value is I0 / 2.

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