Hybrid quasi-resonant soft-switching three-level ANPC converter and its commutation strategy

Abstract

A hybrid quasi-resonant soft-switching three-level ANPC converter and its commutation strategy belong to the technical field of new energy grid-connected power electronics, aiming to solve the problem of reducing switching losses. In the converter topology of the present invention, two switching devices connected to the output end of the bridge arm are made of SiC devices, and the remaining switching devices are made of Si devices. A quasi-resonant soft-switching circuit is designed between the two SiC switching devices. During the positive half-cycle of the output voltage: when it is positive, the switching sequence is (110001), and when it is zero, the switching sequence is (101001). During the negative half-cycle of the output voltage: when it is negative, the switching sequence is (001110), and when it is zero, the switching sequence is (010110). The combination of the converter topology and the commutation strategy of the present invention realizes the improvement of the output switching frequency of the converter, reduces the switching losses of the converter, and the voltage stress borne by the switching devices is the same in any level state, improving the stability of the converter and having high cost performance at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy grid-connected power electronics, and relates to a hybrid quasi-resonant soft-switching three-level ANPC converter and its commutation strategy. Background Art

[0002] With the rapid increase in the proportion of new energy power generation, the new power system gradually shows the characteristics of "double highs" (high proportion of renewable energy and high proportion of power electronic devices). Compared with the traditional three-level topology, as Figure 10 shown, the active neutral point clamped (ANPC) three-level converter (all using silicon devices) is suitable for medium and high power fields due to its low switching stress and high output performance, and its cost is lower than that of multi-level converters, and the control is simple, making it suitable for application in large-scale new energy access systems.

[0003] Compared with traditional silicon (Si) devices, wide bandgap power devices such as silicon carbide (SiC) have the advantages of fast switching speed, high temperature resistance, and lower switching loss per switch of the device than traditional silicon devices. However, there is also a problem that when the switching frequency increases, the switching loss will increase significantly after accumulation, resulting in increased electromagnetic interference and reduced circuit efficiency.

[0004] Due to the high cost of SiC devices, it is an urgent task to study how to balance the cost of SiC devices with the advantages of switching frequency and heat dissipation. Summary of the Invention

[0005] The technical solution of the present invention is used to solve the problem of how to reduce switching losses.

[0006] The present invention solves the above technical problems through the following technical solutions:

[0007] The present invention provides a hybrid quasi-resonant soft-switching three-level ANPC single-phase converter for inversion or rectification. In the three-level ANPC single-phase converter, two switching tubes connected to the output end of the bridge arm and adopt SiC type switching devices, and the switching tubes , , and adopt Si type switching devices; and a quasi-resonant soft-switching circuit is designed between the two SiC type switching tubes and . During the dead time of the turn-on and turn-off of the switching tube and the switching tube , the resonant capacitor and the resonant inductor in the quasi-resonant soft-switching circuit are connected in series to form a resonant loop, so that zero-voltage turn-on and zero-current turn-off are achieved, and the switching tube Natural zero-voltage turn-on is achieved through the commutation process. When the resonant inductor of the quasi-resonant soft-switching circuit is pre-charged, zero-current turn-off is achieved by controlling the turn-off of the switching transistor.

[0008] Preferably, the quasi-resonant soft-switching circuit includes: a resonant capacitor , a resonant inductor , and a resonant switching transistor ; the resonant capacitor is connected in parallel between the drain and source of the switching transistor , and the resonant inductor is connected in series with the resonant switching transistor and then connected in parallel across the output filter inductor ; the drain of the resonant switching transistor is connected to the positive pole of the load, and the source of the resonant switching transistor is connected to one end of the resonant inductor .

[0009] Preferably, the SiC type switching device adopts a SiC type MOSFET device.

[0010] Preferably, the Si type switching device adopts a Si type IGBT device.

[0011] The present invention also provides a commutation strategy applied to the above-mentioned hybrid quasi-resonant soft-switching three-level ANPC single-phase converter: the commutation strategy for the positive half-cycle of the output voltage of the single-phase converter is as follows: the switching sequence of the switching transistors ~ corresponding to the positive level is (1 1 0 0 0 1), and the switching sequence of the switching transistors ~ corresponding to the zero level is (1 0 1 0 0 1); the commutation strategy for the negative half-cycle of the output voltage of the single-phase converter is as follows: the switching sequence of the switching transistors ~ corresponding to the negative level is (0 0 1 1 1 0), and the switching sequence of the switching transistors ~ corresponding to the zero level is (0 1 0 1 1 0).

[0012] Furthermore, when the output of the three-level ANPC single-phase converter switches from the positive level to the zero level, at this time, the switching transistors , remain conducting, the switching transistor turns off, and after a dead time, the anti-parallel diode of the switching transistor turns on, and no current flows through the switching transistor .

[0013] ​Further, when the output of the three-level ANPC single-phase converter switches from the zero level to the positive level, at this time, the switching transistors and remain conducting, the switching transistor turns off. After a dead time, the switching transistor turns on, and no current flows through the switching transistor .

[0014] Further, when the output of the three-level ANPC single-phase converter switches from the negative level to the zero level, at this time, the switching transistors and remain conducting, the switching transistor turns off. After a dead time, the anti-parallel diode of the switching transistor turns on, and no current flows through the switching transistor .

[0015] Further, when the output of the three-level ANPC single-phase converter switches from the zero level to the negative level, at this time, the switching transistors and remain conducting, the switching transistor turns off. After a dead time, the switching transistor turns on, and no current flows through the switching transistor .

[0016] The present invention also provides a hybrid quasi-resonant soft-switching three-level ANPC three-phase converter, and the three-level ANPC three-phase converter is constituted by the above-mentioned hybrid quasi-resonant soft-switching three-level ANPC single-phase converter.

[0017] The beneficial effects of the present invention are as follows:

[0018] In the topology of the hybrid quasi-resonant soft-switching three-level ANPC converter proposed by the present invention, the two switching transistors and connected to the output end of the bridge arm adopt SiC type switching devices, and the switching transistors , , and adopt Si type switching devices; the commutation strategy in the positive half cycle of the converter output voltage is: the switching sequence of the switching transistors ~ corresponding to the positive level is (1 1 0 0 0 1), and the switching sequence of the switching transistors ~ corresponding to the zero level is (1 0 1 0 0 1); the commutation strategy in the negative half cycle of the converter output voltage is: the switching sequence of the switching transistors ~ The switching sequence is (0 0 1 11 0), and the switching tube corresponding to the zero level ~ The switching sequence is (0 1 0 1 1 0); The topology of the hybrid three-level ANPC converter of the present invention is combined with the commutation strategy to improve the output switching frequency of the converter, greatly reduce the switching loss of the converter, make the voltage stress borne by each switching tube the same under any level state, and improve the stability of the topology. At the same time, by comparing with other types of topologies, while ensuring the circuit advantages of the SiC and Si hybrid three-level ANPC converter, the cost is controlled to achieve better cost performance; The quasi-resonant soft-switching circuit realizes zero-voltage switching or zero-current switching during the switching process, significantly reduces the switching loss, and improves the overall conversion efficiency; The current and voltage changes during the switching process are smoother than those of the hard-switching three-level circuit, which can effectively reduce electromagnetic interference; At the same time, the cost only increases with a resonant capacitor and a resonant inductor with very small capacitance and inductance values and ordinary MOSFETs, and the circuit is simple. Description of the Drawings

[0019] Figure 1 It is the topology diagram of the hybrid quasi-resonant soft-switching three-level ANPC single-phase converter according to the first embodiment of the present invention;

[0020] Figure 2 It is the switching sequence table of the three-level ANPC converter;

[0021] Figure 3(a) is a schematic diagram of the switching tube states when the converter is in the switching states P and OL1;

[0022] Figure 3(b) is a schematic diagram of the switching tube states when the converter is in the switching states N and OU1;

[0023] Figure 4 It is the switching signal waveform diagram within one switching period of the hybrid quasi-resonant soft-switching three-level ANPC single-phase converter according to the first embodiment of the present invention;

[0024] Figure 5(a) is the current loop diagram when the OL1 state is in one switching period of the positive half cycle;

[0025] Figure 5(b) is the current loop diagram when the resonant state is in one switching period of the positive half cycle;

[0026] Figure 5(c) is the current loop diagram when the P state is in one switching period of the positive half cycle;

[0027] Figure 5(d) is the current loop diagram when natural zero-voltage turn-on occurs in one switching period of the positive half cycle;

[0028] Figure 6Topological diagram of a hybrid quasi-resonant soft-switching three-level ANPC three-phase converter according to Embodiment 2 of the present invention;

[0029] Figure 7(a) is a curve graph of switching losses and conduction losses of the three-level ANPC converter of the present invention and its commutation strategy;

[0030] Figure 7(b) is a curve graph of switching losses and conduction losses of a three-level ANPC converter composed of 4 SiC type switching devices and 2 Si type (abbreviated as 4-SiC hybrid type) switching devices;

[0031] Figure 7(c) is a curve graph of switching losses and conduction losses of a three-level ANPC converter composed of all 6 switching devices of SiC type (abbreviated as all-SiC type);

[0032] Figure 7(d) is a curve graph of switching losses and conduction losses of a three-level ANPC converter composed of all 6 switching devices of Si type (abbreviated as all-Si type);

[0033] Figure 8(a) is a comparison diagram of the total loss distribution of 4 single-phase three-level ANPC topologies under their respective optimal modulation strategies when the apparent frequency of the phase voltage output is high (2000 Hz) and the power factor is 1;

[0034] Figure 8(b) is a comparison diagram of the total loss distribution of 4 single-phase three-level ANPC topologies under their respective optimal modulation strategies when the apparent frequency of the phase voltage output is high (2000 Hz) and the power factor is -1;

[0035] Figure 9(a) is a comparison diagram of the total loss distribution of 4 single-phase three-level ANPC topologies under their respective optimal modulation strategies when the apparent frequency of the phase voltage output is low (500 Hz) and the power factor is 1;

[0036] Figure 9(b) is a comparison diagram of the total loss distribution of 4 single-phase three-level ANPC topologies under their respective optimal modulation strategies when the apparent frequency of the phase voltage output is low (500 Hz) and the power factor is -1;

[0037] Figure 10 Circuit diagram of an existing ANPC three-level converter that uses all silicon devices. Detailed implementation manners

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will, in conjunction with the embodiments of the present invention, clearly and completely describe the technical solutions in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0039] The following further describes the technical solutions of the present invention in conjunction with the accompanying drawings of the specification and specific embodiments:

[0040] Embodiment 1

[0041] As Figure 1 shown, an embodiment of the present invention provides a hybrid quasi-resonant soft-switching three-level ANPC single-phase converter for an inverter or a rectifier. In this single-phase converter, two switching tubes connected to the output end of the bridge arm and adopt SiC-type switching devices, and the switching tubes , , and adopt Si-type switching devices. Taking the switching tubes and adopting SiC-type MOSFET devices and the switching tubes , , and adopting Si-type IGBT devices as an example for detailed description.

[0042] The single-phase converter includes: a quasi-resonant soft-switching circuit, switching tubes ~ , diodes ~ , input voltage-dividing capacitors and with the same model; the quasi-resonant soft-switching circuit includes: a resonant capacitor , a resonant inductor , and a resonant switching tube ; the voltage-dividing capacitors and are connected in series. The non-series end of the voltage-dividing capacitor is connected to the positive pole of the DC bus, the non-series end of the voltage-dividing capacitor is connected to the negative pole of the DC bus, and the series common point of the voltage-dividing capacitors and is connected to the midpoint of the DC bus; the switching tubes ~ are respectively anti-parallel connected with diodes ~ , the switching tube 's collector is connected to the positive pole of the DC bus, and the emitter of the switching tube is connected to the negative pole of the DC bus. The emitter of the switching tube is respectively connected to the drain of the switching tube and the collector of the switching tube . The collector of the switching tube is respectively connected to the source of the switching tube and the emitter of the switching tube . The emitter of the switching tube is connected to the collector of the switching tube and then connected to the midpoint O of the DC bus. The source of the switching tube is connected to the drain of the switching tube , and the connection point is used as the bridge arm output terminal; the resonant capacitor is connected in parallel between the drain and source of the switching tube . The resonant inductor is connected in series with the resonant switching tube and then connected in parallel across the output filter inductor . The drain of the resonant switching tube is connected to the positive pole of the load, and the source of the resonant switching tube is connected to one end of the resonant inductor .

[0043] As Figure 2 shown, it is the switching sequence table of the three-level ANPC converter. In the table, the three levels are: positive level, zero level, and negative level;

[0044] The positive level corresponds to the switching state P. At this time, the switching sequence of the switching tubes ~ is (1 1 0 0 0 1);

[0045] The negative level corresponds to the switching state N. At this time, the switching sequence of the switching tubes ~ is (0 0 1 1 1 0);

[0046] The zero level corresponds to four switching states, namely switching state OU1, switching state OU2, switching state OL1, and switching state OL2; the switching sequence of switching state OU1 is (0 1 0 1 1 0), the switching sequence of switching state OU2 is (0 1 0 01 0), the switching sequence of switching state OL1 is (1 0 1 0 0 1), and the switching sequence of switching state OL2 is (0 0 1 0 01).

[0047] The commutation strategy of the hybrid quasi-resonant soft-switching three-level ANPC converter provided by the embodiment of the present invention is as follows:

[0048] (1)Positive half-cycle of the output voltage of the single-phase converter

[0049] During the positive half-cycle of the converter output voltage, the output of the converter has only positive level and zero level.

[0050] At this time, the commutation strategy of the present invention is: the positive level selects the switch state P, and the corresponding switching tubes ~ The switching sequence is (1 1 0 0 0 1), and the zero level selects the switch state OL1, and the corresponding switching tubes ~ The switching sequence is (1 0 1 0 0 1).

[0051] As shown in Fig. 3(a), when the output of the converter is at the positive level, that is, when the converter is in the switch state P (the red path in Fig. 3(a)), at this time, the switching tubes , , conduct, and the rest of the switching tubes are turned off, and there is no current flowing through the switching tube ;

[0052] When the output of the converter switches from the positive level to the zero level, that is, when the converter switches from the switch state P to the switch state OL1, at this time, the switching tubes , remain conducting, the switching tube is turned off, and after a dead time, the anti-parallel diode of the switching tube turns on, and there is no current flowing through the switching tube ;

[0053] When the output of the converter is at the zero level, that is, when the converter is in the switch state OL1 (the blue path in Fig. 3(a)), at this time, the switching tubes , , conduct, and the rest of the switching tubes are turned off, and there is no current flowing through the switching tube ;

[0054] When the output of the converter switches from the zero level to the positive level, that is, when the converter switches from the switch state OL1 to the switch state P, at this time, the switching tubes , remain conducting, the switching tube is turned off, and after a dead time, the switching tube turns on, and there is no current flowing through the switching tube .

[0055] The advantage of the above commutation strategy is that during the positive half-cycle of the converter output voltage, each state switching process maintains , remains conducting, and only the switching transistor performs high-frequency switching operations. , , and the switching transistor , uses SiC-based switching devices, which can take full advantage of the high switching frequency and low losses of SiC-based switching devices, thereby reducing switching losses in the high frequency range.

[0056] (2) Negative half-cycle of the output voltage of the single-phase converter

[0057] During the negative half-cycle of the output voltage of the converter, the output of the converter has only negative and zero levels.

[0058] At this time, the commutation strategy of the present invention is: for the negative level, select the switch state N, and the switching sequence of the corresponding switching transistors ~ is (0 0 1 1 1 0); for the zero level, select the switch state OU1, and the switching sequence of the corresponding switching transistors ~ is (0 1 0 1 1 0).

[0059] As shown in Fig. 3(b), when the output of the converter is at the negative level, that is, when the converter is in the switch state N (the purple path in Fig. 3(b)), at this time, the switching transistors , , conduct, and the remaining switching transistors are turned off, and no current flows through the switching transistor ;

[0060] When the output of the converter switches from the negative level to the zero level, that is, when the converter switches from the switch state N to the switch state OU1, at this time, the switching transistors , remain conducting, the switching transistor is turned off, and after a dead time, the anti-parallel diode of the switching transistor turns on, and no current flows through the switching transistor ;

[0061] When the output of the converter is at the zero level, that is, when the converter is in the switch state OU1 (the green path in Fig. 3(b)), at this time, the switching transistors , , conduct, and the remaining switching transistors are turned off, and no current flows through the switching transistor ;

[0062] When the output of the converter switches from the zero level to the negative level, that is, when the converter switches from the switch state OU1 to the switch state N, at this time, the switching transistor , Keep conducting, the switching device Turn off. After a dead time, the switching device Turn on, the switching device Has no current flowing through it.

[0063] The advantage of the above commutation strategy is that in the negative half cycle of the converter output voltage, each state switching process maintains , Keep conducting, and the only switching devices that perform high-frequency switching operations are the switching devices , , while the switching devices , Use SiC-type switching devices, so that the advantages of high switching frequency and low loss of SiC-type switching devices can be fully utilized, thereby reducing the switching loss in high frequency.

[0064] The stress analysis of the switching device is as follows:

[0065] (1) Positive half cycle of the converter output voltage

[0066] When the converter is in the switching state P, at this time the switching devices , , Conduct, and the switching devices , , Turn off; the collector of the switching device Is connected to the positive pole of the DC bus, and the emitter is connected to the midpoint of the voltage dividing capacitors And , and the voltage borne by the switching device Is ; the drain of the switching device Is connected to the positive pole of the DC bus, and the source is connected to the midpoint of the voltage dividing capacitors And , and the voltage borne by the switching device Is ; the collector of the switching device Is connected to the midpoint of the voltage dividing capacitors And , and the emitter is connected to the negative pole of the DC bus, and the voltage borne by the switching device Is .

[0067] When the converter is in the switching state OL1, at this time the switching devices , , Conduct, and the switching devices , , Turn off; the switching device The collector of [device] is connected to the positive pole of the DC bus, and the emitter is connected to the voltage-dividing capacitor and the midpoint of [components]. The switching device is subjected to a voltage of ; The switching device has its drain connected to the positive pole of the DC bus and its source connected to the midpoint of the voltage-dividing capacitor and The switching device is subjected to a voltage of ; The switching device has its collector connected to the midpoint of the voltage-dividing capacitor and and its emitter connected to the negative pole of the DC bus. The switching device is subjected to a voltage of ; where is the DC bus voltage.

[0068] (2) Negative half-cycle of the converter output voltage

[0069] When the converter is in switching state N, at this time, the switching devices , , are turned on and the switching devices , , are turned off; The collector of the switching device is connected to the midpoint of the voltage-dividing capacitor and and its emitter is connected to the negative pole of the DC bus. The switching device is subjected to a voltage of ; The collector of the switching device is connected to the positive pole of the DC bus and its emitter is connected to the midpoint of the voltage-dividing capacitor and The switching device is subjected to a voltage of ; The drain of the switching device is connected to the midpoint of the voltage-dividing capacitor and and its source is connected to the negative pole of the DC bus. The switching device is subjected to a voltage of ;

[0070] When the converter is in switching state OU1, at this time, the switching devices , , are turned on and the switching devices , , are turned off; The emitter of the switching device is connected to the positive pole of the DC bus and its emitter is connected to the midpoint of the voltage-dividing capacitor and The switching device The voltage borne is ; the drain of the switching transistor is connected to the midpoint of the voltage-dividing capacitors and , the source is connected to the negative pole of the DC bus. The voltage borne by the switching transistor is ; the switching transistor has its collector connected to the midpoint of the voltage-dividing capacitors and , the emitter is connected to the negative pole of the DC bus. The voltage borne by the switching transistor is ; where is the DC bus voltage.

[0071] From the above analysis, it can be seen that all the turned-off switching transistors bear the same voltage under the commutation strategy provided in the embodiment of the present invention, which is , so as to improve the quality of the output waveform and extend the service life of the device.

[0072] The working principle of the quasi-resonant soft-switching circuit is as follows:

[0073] During the dead time of the turn-on and turn-off of the switching transistor and the switching transistor , the resonant capacitor and the resonant inductor are connected in series to form a loop, and resonance occurs to make achieve zero-voltage turn-on and zero-current turn-off. The switching transistor realizes natural zero-voltage turn-on through the commutation process. When the resonant inductor is pre-charged, zero-current turn-off is achieved by controlling the turn-off of the switching transistor .

[0074] As shown in Fig. 5(a), it is the current loop in the OL1 state during a switching period in the positive half-cycle, corresponding to Figure 4 of . In this state, At the moment, the resonant switching transistor is turned on, and the resonant inductor starts to charge. Among them, the value of the resonant inductor is relatively small and can be fully charged quickly. The value of the output filter inductor is relatively large, and the current in this path can be considered almost unchanged. Then When it increases, according to Kirchhoff's current law, it can be known that decreases. When decreases to 0, at this time ; where makes the current rise slowly when the resonant switching transistor is turned on, which can reduce the area where the voltage and current intersect during turn-on and reduce the switching transistor Turn-on loss. By selecting the inductance value, at the critical point of overcharge and undercharge, when , by regulating the turn-off time of the switching transistor , making it turn off within the time period of can make achieve zero-current turn-off.

[0075] As shown in Fig. 5(b), it is the current loop in the resonant state ( and dead time) during a switching cycle in the positive half-cycle, corresponding to Figure 4 of . In this state, the resonant switching transistor remains on. When turns off, the resonant capacitor and the resonant inductor form a resonant loop. The resonant inductor charges . When decreases to 0, the resonant capacitor reaches the resonant peak. Subsequently, the resonant capacitor charges in the reverse direction. The current direction is as shown by the blue arrow in Fig. 5(b). The current of the resonant inductor changes direction and increases in the reverse direction. When , at this time, the voltage across the resonant inductor is 0, reaches the resonant peak and charges in the reverse direction until , is clamped to 0. At this time, the voltage across is . The reverse current of starts to decrease. By regulating the turn-on time of the switching transistor to turn on within this time period can achieve zero-voltage turn-on.

[0076] As shown in Fig. 5(c), it is the current loop in the P state during a switching cycle in the positive half-cycle, corresponding to Figure 4 of . In this state, after turns on, at after , turn off the resonant switching transistor to achieve zero-current turn-off. At a certain moment before turns off, turn on , the resonant inductor When starting to charge, then When linearly increasing, according to KCL's law, it can be known that decreases. When decreases to 0, at this time ; when , by regulating the turn-off time of the switching tube to make it turn off within the time period of can make also achieve zero-current turn-off.

[0077] As shown in Fig. 5(d), it shows the current loop during natural zero-voltage turn-on in a switching period of the positive half-cycle, corresponding to the Figure 4 state. During the dead time between and and , when resonance starts and the resonant capacitor reaches near the resonant peak , turn off the resonant switching tube , which can almost achieve zero-current turn-off. Since the output filter inductor is relatively large, it can be considered that its current will not change suddenly. Then, the voltage difference across the freewheeling diode of the switching tube is approximately 0, and the freewheeling diode is in the off state. Subsequently, the output filter inductor theoretically first charges . When the capacitor voltage rises to the forward conduction voltage of the freewheeling diode , the freewheeling diode starts to conduct, and the current starts to pass through the diode. Since has reached near the resonant peak, the capacitor is quickly filled, and it can almost be regarded as the diode conducting immediately. This state corresponds to the Figure 4 state of . After the diode conducts, the voltage across the switching tube is clamped at 0 by the diode . By regulating the turn-on time of the switching tube and turning it on within this stage, zero-voltage turn-on can be achieved.

[0078] Embodiment 2

[0079] As Figure 6 shown, the embodiment of the present invention provides a hybrid quasi-resonant soft-switching three-level ANPC three-phase converter. In this three-phase converter, the two switching tubes and connected to the output end of the A-phase bridge arm adopt SiC-type switching devices. The switching tubes , , and The two switching devices connected to the output terminal of the B-phase bridge arm adopt Si-type switching devices, and the switching device , , and adopt SiC-type switching devices. The two switching devices connected to the output terminal of the C-phase bridge arm and adopt Si-type switching devices, and the switching device , , and adopt Si-type switching devices.

[0080] Taking the switching devices and , and , and adopting SiC-type MOSFET devices, and the switching devices , , and , the switching devices , , and , , , and adopting Si-type IGBT devices as an example for detailed description.

[0081] The three-phase converter includes: an A-phase bridge arm, a B-phase bridge arm, a C-phase bridge arm, input voltage-dividing capacitors and with the same model; the voltage-dividing capacitors and are connected in series. The non-series connection end of the voltage-dividing capacitor is connected to the positive pole of the DC bus, the non-series connection end of the voltage-dividing capacitor is connected to the negative pole of the DC bus, and the series common point of the voltage-dividing capacitors and is connected to the midpoint of the DC bus.

[0082] The A-phase bridge arm is composed of switching devices ~ . The switching devices ~ respectively correspond to anti-parallel diodes ~ . The switching device The collector is connected to the positive pole of the DC bus, and the switch tube The emitter is connected to the negative pole of the DC bus, and the switch tube The emitters are respectively connected to the drain of the switch tube And the collector of the switch tube The collector of the switch tube The collectors are respectively connected to the source of the switch tube And the emitter of the switch tube The emitter of the switch tube Is connected to the collector of the switch tube And then connected to the midpoint of the DC bus. The source of the switch tube Is connected to the drain of the switch tube Together, and the connection point is used as the output terminal of the A-phase bridge arm; The A-phase bridge arm also includes a quasi-resonant soft-switching circuit, and the quasi-resonant soft-switching circuit includes: a resonant capacitor , a resonant inductor , a resonant switch tube ; Among them, the resonant capacitor Is connected in parallel between the drain and source of the switch tube , the resonant inductor Is connected in series with the resonant switch tube And then connected in parallel across the output filter inductor , the drain of the resonant switch tube Is connected to the positive pole of the load, and the source of the resonant switch tube Is connected to one end of the resonant inductor .

[0083] The B-phase bridge arm is composed of switch tubes ~ , and the switch tubes ~ Are respectively anti-parallel diodes ~ , the collector of the switch tube Is connected to the positive pole of the DC bus, the emitter of the switch tube Is connected to the negative pole of the DC bus, and the emitter of the switch tube Is respectively connected to the drain of the switch tube And the collector of the switch tube , the collector of the switch tube Is respectively connected to the source of the switch tube And the emitter of the switch tube , the emitter of the switch tube Is connected to the collector of the switch tube And then connected to the midpoint of the DC bus. The source of the switch tube Is connected to the drain of the switch tube The drains are connected together, and the connection point serves as the output terminal of the B-phase bridge arm; the B-phase bridge arm further includes a quasi-resonant soft-switching circuit, and the quasi-resonant soft-switching circuit includes: a resonant capacitor , a resonant inductor , and a resonant switching transistor ; wherein, the resonant capacitor is connected in parallel between the drain and the source of the switching transistor , the resonant inductor is connected in series with the resonant switching transistor and then connected in parallel across the output filter inductor , the drain of the resonant switching transistor is connected to the positive pole of the load, and the source of the resonant switching transistor is connected to one end of the resonant inductor .

[0084] The C-phase bridge arm is composed of switching transistors ~ ; the switching transistors ~ are respectively anti-parallel connected with diodes ~ , the collector of the switching transistor is connected to the positive pole of the DC bus, the emitter of the switching transistor is connected to the negative pole of the DC bus, the emitter of the switching transistor is respectively connected to the drain of the switching transistor and the collector of the switching transistor , the collector of the switching transistor is respectively connected to the source of the switching transistor and the emitter of the switching transistor , the emitter of the switching transistor is connected to the collector of the switching transistor and then connected to the midpoint of the DC bus, the source of the switching transistor is connected to the drain of the switching transistor together, and the connection point serves as the output terminal of the C-phase bridge arm; the C-phase bridge arm further includes a quasi-resonant soft-switching circuit, and the quasi-resonant soft-switching circuit includes: a resonant capacitor , a resonant inductor , and a resonant switching transistor ; wherein, the resonant capacitor is connected in parallel between the drain and the source of the switching transistor , the resonant inductor is connected in series with the resonant switching transistor and then connected in parallel across the output filter inductor , the drain of the resonant switching transistor is connected to the positive pole of the load, and the source of the resonant switching transistor is connected to the resonant inductor One end of

[0085] The commutation strategy of phase A of the hybrid quasi-resonant soft-switching three-level ANPC three-phase converter in the embodiment of the present invention is the same as that of the single-phase converter in Embodiment 1, which is specifically as follows:

[0086] (1) Positive half-cycle of the output voltage of phase A bridge arm of the three-phase converter

[0087] In the positive half-cycle of the output voltage of phase A bridge arm of the converter, the output of the converter only has positive level and zero level.

[0088] At this time, the commutation strategy of the present invention is: select the switch state P for the positive level, and the switching sequence of the corresponding switching tubes ~ is (1 1 0 0 0 1), select the switch state OL1 for the zero level, and the switching sequence of the corresponding switching tubes ~ is (1 01 0 0 1).

[0089] (2) Negative half-cycle of the output voltage of phase A bridge arm of the three-phase converter

[0090] In the negative half-cycle of the output voltage of phase A bridge arm of the converter, the output of the converter only has negative level and zero level.

[0091] At this time, the commutation strategy of the present invention is: select the switch state N for the negative level, and the switching sequence of the corresponding switching tubes ~ is (0 0 1 1 1 0), select the switch state OU1 for the zero level, and the switching sequence of the corresponding switching tubes ~ is (0 10 1 1 0).

[0092] The stress analysis of the switching tubes is also the same as that of the single-phase converter in Embodiment 1, which will not be elaborated here.

[0093] The quasi-resonant soft-switching circuit in phase A is achieved by connecting a resonant capacitor in parallel at both ends of . During the dead time of the turn-on and turn-off of the switching tube and the switching tube , the resonant capacitor and the resonant inductor are connected in series to form a loop, and resonance occurs to make achieve zero-voltage turn-on and zero-current turn-off. The switching tube realizes natural zero-voltage turn-on through the commutation process. When the resonant inductor is pre-charged, zero-current turn-off can be achieved by controlling the turn-off of the switching tube . In this quasi-resonant soft-switching topology, there is no need to add a capacitor in parallel at the switching tube Resonant capacitors are connected in parallel at both ends, saving costs and enabling zero-voltage turn-on and zero-current turn-off for two SiC MOSFETs in one phase.

[0094] The working principle of the quasi-resonant soft-switching circuit of phase B and phase C of the hybrid quasi-resonant soft-switching three-level ANPC three-phase converter in the embodiment of the present invention is the same as that of phase A, and will not be elaborated here.

[0095] The commutation strategy of phase B and phase C of the hybrid quasi-resonant soft-switching three-level ANPC three-phase converter in the embodiment of the present invention is the same as that of phase A, and will not be elaborated here.

[0096] Comparison and verification

[0097] Figure 7(a) is the curve of switching loss and conduction loss of the three-level ANPC converter and its commutation strategy of the present invention; Figure 7(b) is the curve of switching loss and conduction loss of the three-level ANPC converter composed of 4 SiC-type switching devices and 2 Si-type (abbreviated as 4-SiC hybrid) switching devices; Figure 7(c) is the curve of switching loss and conduction loss of the three-level ANPC converter composed of 6 switching devices all using SiC-type (abbreviated as all-SiC type) switching devices; Figure 7(d) is the curve of switching loss and conduction loss of the three-level ANPC converter composed of 6 switching devices all using Si-type (abbreviated as all-Si type) switching devices; it can be seen from the figure that the switching losses of the converter of the present invention and the 4-SiC hybrid converter are basically all concentrated on the SiC devices; the switching losses of other types of converters are distributed among 6 switching tubes.

[0098] Figures 8(a) and 8(b) are the comparison diagrams of the total loss distributions of 4 single-phase three-level ANPC topologies under their respective optimal modulation strategies when the apparent frequency of the phase voltage output is high and the power factors are 1 and -1 respectively; Figures 9(a) and 9(b) are the comparison diagrams of the total loss distributions of 4 single-phase three-level ANPC topologies under their respective optimal modulation strategies when the apparent frequency of the phase voltage output is low and the power factors are 1 and -1 respectively; Considering that the cost of SiC devices is about twice that of Si devices, considering the SiC cost of the three-phase phase converter, the 6-SiC type converter saves about 30% in cost compared with the 12-SiC type converter, and the 6-SiC type converter saves about 50% in cost compared with the all-SiC type converter. It can be seen from Figures 8(a) and 8(b) that at high switching frequencies, compared with the 4-SiC hybrid three-level ANPC converter, the total power loss of the three-level ANPC converter of the present invention is basically equal, but the loss distribution is more balanced. The high power loss of the three-level ANPC converter of the present invention is on two SiC MOSFET devices. Considering the high temperature resistance characteristics of SiC devices, there is no need to keep the junction temperatures of SiC MOSFET and Si IGBT balanced, and the uneven power loss is no longer a problem. It can be seen from Figures 9(a) and 9(b) that at low switching frequencies, the 4-SiC hybrid three-level ANPC converter has no obvious advantage compared with the converter in the present invention. Although the total power loss of the all-SiC three-level ANPC topology is better than that of the 2-SiC type, considering the cost when the number of converters required for large projects is large, it is more cost-effective to choose the converter of the present invention. Therefore, to optimize the balance between performance and cost, the present invention can give full play to the advantages of SiC devices in switching frequency and heat dissipation while minimizing the manufacturing cost, and improve the system power density.

[0099] The topology of the hybrid three-level ANPC converter of the present invention is combined with the commutation strategy to achieve an increase in the output switching frequency of the converter, greatly reducing the switching losses of the converter, making the voltage stress borne by each switching device the same in any level state, and improving the stability of the topology. At the same time, by comparing with other types of topologies at present, while ensuring the circuit advantages of the SiC and Si hybrid three-level ANPC converter, cost control is achieved to realize better cost performance; while efficiently exerting the performance of SiC devices, considering that although the switching losses of SiC switching devices are significantly lower than those of Si devices, the switching losses of SiC devices operating at high frequencies of several hundred or several thousand KHz cannot be ignored. A resonant soft-switching circuit is designed for SiC devices on the classic ANPC three-level inverter topology. By precisely regulating the switching time, zero-current turn-off and zero-voltage turn-on of SiC devices can be achieved simultaneously. Through the combination of the circuit topology of the SiC MOSFET and Si IGBT hybrid three-level ANPC inverter based on quasi-resonant soft switching and the commutation strategy, the output switching frequency of the overall circuit is increased, the switching losses of the circuit are greatly reduced, the voltage stress borne by each switching device is the same in any level state, and the stability of the topology is improved. At the same time, by comparing with other types of topologies at present, while ensuring the circuit advantages of the SiC and Si hybrid three-level ANPC inverter, cost control of the main switching device and the resonant circuit is achieved.

[0100] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hybrid quasi-resonant soft-switching three-level ANPC single-phase converter, characterized in that, In the single-phase converter, the switching transistor has its collector connected to the positive pole of the DC bus, and the switching transistor has its emitter connected to the negative pole of the DC bus. The emitter is respectively connected to the drain of the switching transistor and the collector of the switching transistor for connection. The collector is respectively connected to the source of the switching transistor and the emitter of the switching transistor for connection. After the emitter is connected to the collector and then connected to the midpoint of the DC bus. The source is connected to the drain and their connection point serves as the output terminal of the bridge arm; Switching transistor and adopt SiC type devices, and the switching transistor , , and adopt Si type devices; and a quasi-resonant soft-switching circuit is designed between and . During the switching dead time between and , the resonant capacitor and inductor in the quasi-resonant soft-switching circuit are connected in series to form a series resonant circuit, enabling to achieve zero-voltage turn-on and zero-current turn-off, to achieve natural zero-voltage turn-on through the commutation process. When the resonant inductor is pre-charged, controlling to turn off achieves zero-current turn-off; The quasi-resonant soft-switching circuit includes: a resonant capacitor , a resonant inductor , and a resonant switching transistor ; The resonant capacitor is connected in parallel between the drain and the source. The resonant inductor is connected in series with the resonant switching transistor and then connected in parallel across both ends of the output filter inductor . The drain of the resonant switching transistor is connected to the positive pole of the load, and the source of the resonant switching transistor is connected to one end of the resonant inductor .

2. The hybrid quasi-resonant soft-switching three-level ANPC single-phase converter according to claim 1, wherein The SiC type switching device uses a SiC type MOSFET device.

3. The hybrid quasi-resonant soft-switching three-level ANPC single-phase converter according to claim 1, wherein The Si type switching device uses a Si type IGBT device.

4. The hybrid quasi-resonant soft-switching three-level ANPC single-phase converter according to claim 1, wherein For inversion.

5. The hybrid quasi-resonant soft-switching three-level ANPC single-phase converter according to claim 1, wherein For rectification.

6. A commutation strategy applied to the hybrid quasi-resonant soft-switching three-level ANPC single-phase converter according to any one of claims 1-5, characterized in that, The commutation strategy for the positive half-cycle of the output voltage of the single-phase converter is as follows: for the switching tubes corresponding to the positive level, ~ the switching sequence is (1 1 0 0 0 1), and for the switching tubes corresponding to the zero level, ~ the switching sequence is (1 0 1 0 0 1); the commutation strategy for the negative half-cycle is as follows: for the switching tubes corresponding to the negative level, ~ the switching sequence is (0 0 1 1 1 0), and for the switching tubes corresponding to the zero level, ~ the switching sequence is (0 1 0 1 1 0).

7. The commutation strategy according to claim 6, characterized in that, When the output of the three-level ANPC single-phase converter switches from positive level to zero level, the switch tube , Keep conducting, switch After a period of dead time, the switch tube The anti-parallel diode Open, switch tube No current flows.

8. The commutation strategy according to claim 6, wherein When the output of the three-level ANPC single-phase converter switches from the zero level to the positive level, at this time, the switching transistors and remain conducting, the switching transistor turns off. After a dead time, the switching transistor turns on, and no current flows through the switching transistor .

9. The commutation strategy according to claim 6, characterized in that When the output of the three-level ANPC single-phase converter switches from a negative level to a zero level, at this time, the switching transistors and remain conducting, the switching transistor turns off. After a dead time, the anti-parallel diode of the switching transistor turns on, and no current flows through the switching transistor .

10. The commutation strategy according to claim 6, characterized in that When the output of the three-level ANPC single-phase converter switches from zero level to negative level, at this time, the switching transistors and remain conducting, the switching transistor turns off. After a dead time, the switching transistor turns on, and there is no current flowing through the switching transistor .

11. A hybrid quasi-resonant soft-switching three-level ANPC three-phase converter, characterized in that, The three-level ANPC three-phase converter is constituted by using the hybrid quasi-resonant soft-switching three-level ANPC single-phase converter described in any one of claims 1 to 5.

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