Zero voltage switching ac-dc power conversion system

Abstract

The present case relates to an AC-DC power conversion system with zero voltage switching. The circuit technique of the present case utilizes an active soft switching unit to substantially reduce switching losses in the AC-DC power conversion system caused by the turn-on characteristics of the main switch and the reverse recovery characteristics of the rectifier. The active soft switching unit includes a series inductor, a series capacitor, a main switch, a rectifier switch, and an auxiliary switch. The series inductor connected between the main switch and the rectifier switch reduces the associated losses of the reverse recovery and further controls the current slew rate of the body diode of the rectifier switch during its turn-off period. The main switch, the rectifier switch, and the auxiliary switch all operate with ZVS.

Description

Technical Field

[0001] This case relates to a power conversion system, and more particularly to a bidirectional AC-DC power conversion circuit with soft-switching capability. Background Technology

[0002] To interface with a public AC system (i.e., the public power grid), a power supply must comply with input current harmonic standards. Due to stringent limitations on low-frequency harmonic distortion, these limitations are typically met by applying a sinusoidal input current to the power converter. Furthermore, high efficiency, high power density, and low electromagnetic interference (EMI) noise are also important considerations. A power converter that interfaces with a public AC system and achieves low harmonic distortion is similar to a resistive load of an AC power supply; that is, the input current of the power converter follows the waveform of the input voltage. For example... Figure 1 As shown, this type of power converter can be, for example, a conventional AC-DC boost converter. As a resistive load, the power converter has a sinusoidal input current.

[0003] like Figure 1 As shown, a conventional AC-DC boost converter 100 includes an input diode bridge arm, a boost inductor L, a switching device S, a boost diode D, a filter capacitor C, and a load R, wherein the input diode bridge arm consists of rectifiers D1, D2, D3, and D4. Figure 1 In this context, the load R is represented by a resistor. However, the load R can also be another downstream converter, such as an isolated DC-DC converter used to regulate the DC voltage supplied to the actual end-user load. Under proper control, the AC-DC boost converter 100 can receive an approximately sinusoidal AC input current, thereby making the power factor approximately one.

[0004] Besides pursuing a high power factor, designers also seek to achieve an optimal balance between efficiency and power density. Increasing the switching frequency of the power converter can achieve high power density in terms of volume, thereby reducing the required size of magnetic components (such as boost inductors and EMI filters). However, operating at high switching frequencies increases switching losses and reduces efficiency. In the prior art, the switching device S and boost diode D in the AC-DC boost converter 100 are typically silicon MOSFETs (metal-oxide-semiconductor field-effect transistors) and silicon PN diodes. When operating in hard-switching mode, silicon MOSFETs generate excessive turn-on and turn-off losses due to the severe reverse recovery losses of silicon diodes. Therefore, higher switching frequencies significantly reduce the power conversion efficiency of the AC-DC boost converter 100. To overcome the severe losses at high switching frequencies, soft-switching technology has been developed to achieve a smooth transition when the switching device S is turned on and off. The reduced rate of change of rectifier diode current thus helps to reduce reverse recovery current losses and associated boost diode losses.

[0005] Figure 2 An AC-DC power converter 200 based on soft-switching technology is shown. For example... Figure 2 As shown, input diodes D1, D2, D3, and D4, boost inductor L1, switching device S1, and boost diode D5 form a conventional boost converter. Furthermore, the AC-DC power converter 200 includes an auxiliary circuit 205 formed by auxiliary inductor L2, auxiliary capacitor C2, auxiliary switching device S2, and auxiliary diodes D6 and D7. When boost diode D5 is turned off, the auxiliary circuit 205 can reduce the rate of change of current in boost diode D5. This effectively eliminates reverse recovery losses, enabling the switching device S1 to achieve soft conduction, i.e., zero-voltage switching (ZVS). Therefore, even when achieving high power density by increasing the switching frequency, efficiency can still be significantly improved through ZVS. Until recently, most boost converters employed soft-switching circuits to reduce reverse recovery losses in the boost diode. However, recently it has become possible to fabricate Schottky barrier diodes with virtually no reverse recovery losses using wide-bandgap materials (such as silicon carbide (SiC)). Therefore, the AC-DC boost converter 100 using SiC diodes has become a preferred topology due to its superior power factor correction characteristics. The combination of silicon MOSFETs and silicon carbide diodes offers both cost-effectiveness and a suitable balance between efficiency and power density. Furthermore, compared to silicon MOSFETs, silicon carbide MOSFETs have better switching speeds and lower switching losses, thus promising better performance.

[0006] Figure 3 A conventional totem-pole AC-DC boost converter 300 is illustrated, employing silicon carbide MOSFET switching devices S1 and S2. The totem-pole AC-DC boost converter 300 contains only two input rectifiers (i.e., input rectifiers D1 and D2) and operates substantially differently from the AC-DC boost converter 100, using the body diodes of switching devices S1 and S2 to function as the boost diode D. Besides the topological difference, the totem-pole AC-DC boost converter 300 allows bidirectional power flow, thus further expanding its application range compared to the AC-DC boost converter 100. Therefore, the silicon carbide MOSFETs can operate at higher switching frequencies while simultaneously achieving high efficiency.

[0007] Currently, silicon carbide MOSFETs are still limited in use due to significant conduction losses and small reverse recovery losses in the body diode when operating at high frequencies. Summary of the Invention

[0008] According to one embodiment of this invention, soft-switching technology is applied to make the turn-on and turn-off transitions in the silicon carbide MOSFET switching device of an AC-DC power converter (e.g., a totem-pole boost converter) smoother. This avoids excessive turn-on and reverse recovery losses when operating at high switching frequencies. Therefore, the AC-DC power converter can achieve high-efficiency operation, high power density, and bidirectional power flow, while reducing EMI noise.

[0009] According to one embodiment of this invention, a power converter is provided, suitable for coupling to an AC circuit and a DC circuit, and includes a first inductor, a first rectifier, a second rectifier, and an active soft-switching unit. The AC circuit has a first terminal and a second terminal. The first inductor has a first terminal and a second terminal. The first terminal of the first inductor is coupled to the first terminal of the AC circuit. The first rectifier and the second rectifier are connected to a common node, and the series circuit formed by the first rectifier and the second rectifier is coupled in parallel to the DC circuit, with the common node coupled to the second terminal of the AC circuit. The active soft-switching unit includes a second inductor, a first switch, a second switch, a third switch, and a first capacitor. The series circuit formed by the first switch, the second inductor, and the second switch is coupled in parallel to the series circuit formed by the first rectifier and the second rectifier. The series circuit formed by the third switch and the first capacitor is coupled in parallel to the second inductor. The second terminal of the first inductor is coupled to the second inductor. In some embodiments, the active soft-switching unit can reduce losses related to reverse recovery in the AC-DC power converter, and the active soft-switching unit facilitates ZVS for the first switch, the second switch, and the third switch, wherein at least one switch is a silicon carbide MOSFET.

[0010] In some embodiments, the power converter architecture is designed for bidirectional operation. For example, the DC circuit may include a DC power source (e.g., a battery), or the AC-DC power converter may include a power inverter. The first and second rectifiers may be passive diodes or synchronous rectifiers. The first inductor is coupled to a common electrical node between the first switch and the second inductor, or coupled to a common electrical node between the second switch and the second inductor.

[0011] According to one embodiment of this invention, the AC-DC power converter is a multiphase power converter suitable for coupling to an AC circuit and a DC circuit. The AC circuit includes multiple phase terminals, each phase terminal being coupled to one phase of a multiphase AC power supply. The multiphase power converter includes multiple phase arms. In some embodiments, each phase arm of the multiphase power converter includes a first inductor and an active soft-switching unit. The first inductor is coupled to one of the phase terminals of the AC circuit. The active soft-switching unit includes a second inductor, a first switch, a second switch, a third switch, and a first capacitor. A series circuit formed by the first switch, the second switch, and the second inductor is coupled in parallel to the DC circuit. A series circuit formed by the first capacitor and the third switch is coupled in parallel to the second inductor. The first inductor is coupled to the second inductor of the active soft-switching unit.

[0012] Since the active soft-switching unit of this invention does not increase the voltage and current stress in traditional AC-DC power converters, the active soft-switching unit of this invention can also be applied to traditional AC-DC power converters to achieve the technical effects of this invention. Attached Figure Description

[0013] Figure 1 A conventional AC-DC boost converter 100 is shown.

[0014] Figure 2 A conventional AC-DC power converter 200 based on soft-switching technology is shown.

[0015] Figure 3 A conventional AC-DC totem-pole boost converter 300 is shown, which is practical due to the use of silicon carbide MOSFET switching devices S1 and S2.

[0016] Figure 4 This invention illustrates a totem-pole PWM (pulse-width-modulated) PFC (power-factor-correction) power converter 400 according to an embodiment of this invention.

[0017] Figure 5 A circuit model 450 is shown, which represents a totem-pole PWM PFC power converter 400 at an input voltage V. AC During the positive half-cycle (i.e., V) AC The equivalent circuit of >0).

[0018] Figure 6A , Figure 6B , Figure 6C , Figure 6D , Figure 6E , Figure 6F , Figure 6G , Figure 6H and Figure 6I This illustrates a totem-pole PWM PFC power converter 400 at an input voltage V. AC The switching period T during the positive half-cycle S The topological state.

[0019] Figure 7 It shows the input voltage V AC During the positive half-cycle (i.e., V) AC Switching period T >0) S The key power stage waveform.

[0020] Figure 8 A circuit model 480 is shown, which represents a totem-pole PWM PFC power converter 400 at an input voltage V. AC During the negative half-cycle (i.e., V) AC The equivalent circuit of <0).

[0021] Figure 9A , Figure 9B , Figure 9C , Figure 9D , Figure 9E , Figure 9F , Figure 9G , Figure 9H and Figure 9I This illustrates a totem-pole PWM PFC power converter 400 at an input voltage V. AC The switching period T during the negative half-cycle S The topological state.

[0022] Figure 10 It shows the input voltage V AC During the negative half-cycle (i.e., V) AC The switching period T of <0) S The key power stage waveform.

[0023] Figure 11 This invention illustrates a unidirectional AC-DC totem-pole power converter 1100 including an active soft-switching unit 401, which, unlike the totem-pole PWM PFC power converter 400, has an AC-DC totem-pole power converter 1100 coupled to a series inductor L. S and auxiliary switch S A The boost inductor L at the common electrical node between them.

[0024] Figure 12 This invention illustrates a bidirectional AC-DC totem-pole power converter 1200 including an active soft-switching unit 401, which differs from the totem-pole PWM PFC power converter 400 in that it replaces diodes D1 and D2 with synchronous rectifiers S3 and S4.

[0025] Figure 13 This invention illustrates an AC-DC totem-pole power converter 1300 including an active soft-switching unit 401, which differs from the totem-pole PWM PFC power converter 400 in that its diode D... PRE1 and D PRE2 The DC output side is charged when the active soft-switching unit 401 is in the start-up or non-actuated state, thereby bypassing the active soft-switching unit 401.

[0026] Figure 14 This invention illustrates a bidirectional AC-DC totem-pole power converter 1400 including an active soft-switching unit 401, which differs from the totem-pole PWM PFC power converter 400 in that it replaces diodes D1 and D2 with synchronous rectifiers S3 and S4.

[0027] Figure 15This invention illustrates a bidirectional AC-DC totem-pole power converter 1500 including an active soft-switching unit 401, which differs from the bidirectional AC-DC totem-pole power converter 1400 in that the boost inductor L of the AC-DC totem-pole power converter 1500 is coupled to a series inductor L. S With auxiliary switch S A The common electrical nodes between them.

[0028] Figure 16 A multiphase power converter 1600 including an active soft-switching unit 401 is shown in one embodiment of this invention.

[0029] Figure 17 A multiphase power converter 1700 according to an embodiment of the present invention is shown. Unlike the bidirectional three-phase AC-DC power converter 1600, each boost inductor in the multiphase power converter 1700 is coupled to a common electrical node between the series inductor and the auxiliary switch in the corresponding active soft-switching unit.

[0030] The reference numerals in the attached figures are explained as follows:

[0031] AC-DC boost converter: 100

[0032] V AC Input voltage

[0033] V O Output voltage

[0034] L, L1, L2: Inductors

[0035] S, S1, S2: Switches

[0036] D, D1, D2, D3, D4, D5, D6, D7: Diodes

[0037] C, C1, C2: Capacitors

[0038] R: Load

[0039] 200: AC-DC power converter

[0040] 205: Auxiliary Circuit

[0041] 300: Totem Pole AC-DC Boost Converter

[0042] 400: Power Converter

[0043] 401: Active Soft Switching Unit

[0044] 402: Series circuit

[0045] L S :inductance

[0046] S A :switch

[0047] C S :capacitance

[0048] i L i LS Current

[0049] V IN :Voltage

[0050] C OSS1 C OSS2 C OSSA :capacitance

[0051] 450, 480: Circuit Model

[0052] T S Switching cycle

[0053] i S1 i S2 i SC i SA Current

[0054] V S1 V CS V SA V S2 :Voltage

[0055] T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T 10 :time

[0056] T ON T OFF :cycle

[0057] D': Duty cycle

[0058] 1100: Unidirectional AC-DC Totem Pole Power Converter

[0059] 1200: Bidirectional AC-DC Totem Pole Power Converter

[0060] S3, S4: Switches

[0061] 1300: AC-DC Totem Pole Power Converter

[0062] D PRE1 D PRE2 :diode

[0063] 1400: Bidirectional AC-DC Totem Pole Power Converter

[0064] 1500: Bidirectional AC-DC Totem Pole Power Converter

[0065] 1600: Multiphase Power Converter

[0066] S5, S6, S A1 S A2 S A3 :switch

[0067] L3, L S1 L S2 L S3 :inductance

[0068] C S1 C S2 C S3 :capacitance

[0069] V CS1 V CS2 V CS3 :Voltage

[0070] 1700: Multiphase Power Converter Detailed Implementation

[0071] Some typical embodiments that embody the features and advantages of this invention will be described in detail in the following description. It should be understood that this invention can have various variations in different forms, all of which do not depart from the scope of this invention, and the descriptions and illustrations therein are for illustrative purposes only and are not intended to limit this invention.

[0072] Figure 4 A power converter 400 according to one embodiment of this invention is shown. For example... Figure 4 As shown, the power converter 400 is a totem-pole PWM PFC power converter capable of rectification. According to subsequent descriptions, the totem-pole PWM PFC power converter 400 can achieve low switching losses. Figure 4 As shown, the totem-pole PWM PFC power converter 400 is coupled between an AC circuit and a DC circuit, and includes an inductor L, rectifiers D1 and D2 connected in series, and an active soft-switching unit 401. The inductor L is coupled to one end of the AC circuit, and the other end of the AC circuit is coupled to a common node in the series circuit formed by rectifiers D1 and D2. The active soft-switching unit 401 includes the inductor L. S Switch S1, Switch S2, Switch S A and capacitor C S In the active soft-switching unit 401, the inductor L S A series circuit is formed with switch S1, which is coupled in parallel to the series circuit formed by rectifiers D1 and D2. Furthermore, switch S... A and capacitor C S Forming a parallel coupling connected to inductor L S The series circuit 402, and the inductor L is coupled to the inductor L SEither end. At Figure 4 In the middle, inductor L is coupled to switch S1 and inductor L S The common electrical node between them. In some embodiments, switches S1, S2 and S... A At least one of them includes a silicon carbide MOSFET. In some embodiments, the totem-pole PWM PFC power converter 400 also includes a filter capacitor C connected in parallel with rectifiers D1 and D2. During operation, switch S1 or S2 can function as a boost switch or a rectifier switch depending on the polarity of the AC circuit. A It then serves as an auxiliary switch.

[0073] like Figure 4 As shown, different Figure 3 The AC-DC totem-pole boost converter 300 and the totem-pole PWM PFC power converter 400 have a series inductor L connected between the boost or rectifier switches S1 and S2. S This allows control of the rate of change of current in the body diode of the rectifier switch when the rectifier switch is turned off. During the positive half-cycle of each cycle of the input AC voltage, switch S2 acts as a main switch or boost switch, while switch S1 acts as a rectifier switch; conversely, during the negative half-cycle of the input AC voltage, switch S1 acts as a main switch or boost switch, while switch S2 acts as a rectifier switch. The capacitors C connected in series... S and auxiliary switch S A Parallel connection to series inductor L S .like Figure 4 The dashed lines indicate switches S1 and S2, and the series inductor L. S Auxiliary switch S A and capacitor C S A soft switching unit 401 is formed.

[0074] According to one embodiment of this case, switches S1, S2 and S... A Both operate in ZVS mode. Furthermore, the control signals for switches S1 and S2 do not overlap, therefore switches S1 and S2 cannot be in the conducting state simultaneously. In the specific description, when the control signal of the switch rises from a low level to a high level, the switch is closed, or "conducting"; conversely, when the control signal of the switch falls from a high level to a low level, the switch is open, or "off". In some embodiments, at any given time, switch S1 or S2 functions as a rectifier switch in conjunction with switch S... A Simultaneously on or off. When the rectifier switch is off, the inductor L... S This can reduce the rate of change of current. Auxiliary switch S A The control signal of the main switch is synchronized with the control signal of the rectifier switch (i.e., switch S1 during the positive half-cycle of the linear cycle and switch S2 during the negative half-cycle of the linear cycle). The turn-off time of the main switch is synchronized with the control signals of the rectifier switch and the auxiliary switch S1.A There is a small delay (i.e., dead time) between the turn-on and turn-off times. In this embodiment, when the main switch is turned off, the input current flows through the series inductor L. S Part (i.e. i) LS The autonomous switch shifts and is redirected to flow through the rectifier switch and auxiliary switch S. A The body diode. This allows the rectifier switch and auxiliary switch S to... A The parasitic output capacitor discharges, thereby enabling the rectifier switch and auxiliary switch S to conduct under ZVS conditions. A Then, when the rectifier switch and auxiliary switch S... A When turned off, the series inductor L S The current i in LS The body diode of the rectifier switch can still flow, discharging the parasitic output capacitance of the main switch and thus creating a ZVS condition for the main switch to turn on. In the existing topology, since the parasitic output capacitance of the main switch is not discharged, turning on the main switch results in significant conduction losses. Furthermore, in this case, when the main switch is turned on, the series inductor L... S The rate of change of the rectifier switch current is reduced, thereby significantly reducing the reverse recovery loss of the rectifier switch.

[0075] The following analysis uses an AC totem-pole PWM PFC power converter 400 as an example. The analysis also applies to bidirectional operation, where a DC voltage source (e.g., a battery) is used instead. Figure 4 The resistive load R is used, and in this bidirectional configuration, the filter capacitor C is optional. For more information on the bidirectional configuration, please refer to [reference needed]. Figure 14 The bidirectional AC-DC power converter 1400 is shown.

[0076] In the totem-pole PWM PFC power converter 400, switches S1, S2, and S... A The switching frequency is much higher than the input voltage V. AC The line frequency. Therefore, for the following analysis, the input voltage V is within a time range of several switching cycles. AC It can be regarded as a practically constant voltage V IN Furthermore, compared to the inductance and capacitance values ​​of other circuit components in the totem-pole PWM PFC power converter 400, the inductance value of the boost inductor L and the capacitance value of the filter capacitor C are both relatively large, therefore the inductor current i L The ripple and voltage ripple on the filter capacitor C are negligible. Therefore, the voltage on the output filter capacitor C can be supplied by a constant voltage source V. O This indicates that switches S1, S2, and S... AEach switch has a negligible resistance (i.e., on-resistance) in its respective on-state. Furthermore, each switch can be considered a short circuit during its on-time. However, these switches have parasitic output capacitance (i.e., capacitance C). OSS1 C OSS2 and C OSSA The reverse recovery charge in the body diode of each switch cannot be ignored. Based on the above considerations, Figure 5 and Figure 8 Circuit models 450 and 480 are shown respectively to represent the totem-pole PWM PFC power converter 400 at input voltage V. AC The positive half-cycle (i.e., V) AC >0) and the negative half-cycle (i.e., V) AC The equivalent circuit when <0).

[0077] based on Figure 4 The circuit model shown is 450. Figures 6A to 6I This illustrates a totem-pole PWM PFC power converter 400 at an input voltage V. AC During the positive half-cycle (i.e., V) AC Switching period T >0) S The topological state. Figure 7 It shows the input voltage V AC During the positive half-cycle (i.e., V) AC Switching period T >0) S The key power stage waveform.

[0078] Similarly, based on Figure 8 The circuit model shown is 480. Figures 9A to 9I This illustrates a totem-pole PWM PFC power converter 400 at an input voltage V. AC During the negative half-cycle (i.e., V) AC The switching period T of <0) S The topological state. Figure 10 It shows the input voltage V AC During the negative half-cycle (i.e., V) AC The switching period T of <0) S The key power stage waveform.

[0079] like Figure 6A As shown, during the period from T0 to T1, the main switch S2 is in the on state (until it is turned off at time T1), and the boost inductor current i L and series inductor current i LS All current flows through the main switch S2, while the rectifier switch S1 and auxiliary switch S2... A Both are in the off state. This is because the inductance of the boost inductor L is much larger than that of the series inductor L. S The inductance value, therefore, in essence, all the input voltage V INBoth are applied to the boost inductor L. Therefore, the voltage V across the filter capacitor C is... O The capacitor C is applied to the main switch S2 and connected in series. S Voltage V on CS Applied to auxiliary switch S A Above, and the input voltage V IN The boost inductor L and the series inductor L are connected in series. S Above. Based on this, the boost inductor current i L and series inductor current i LS All increase linearly according to the following equation:

[0080]

[0081] Among them L and L S In equation (1) and other equations, the inductance value of the boost inductor L and the series inductor L are respectively represented. S The inductance value.

[0082] Figure 6B The topology of the totem-pole PWM PFC power converter 400 during T1 to T2 is shown. Figure 6B As shown, after the main switch S2 is turned off at time T1, the series inductor current i LS Start by checking the parasitic output capacitance C of the main switch S2. OSS2 Charging, wherein the series inductor current i LS At time T1, it is essentially equal to the boost inductor current i. L Therefore, the voltage V on the main switch S2 S2 Start increasing. Based on rectifier switch S1 and auxiliary switch S... A Main switch S2, series capacitor C S and output voltage V O The Kirchhoff's Voltage Loop (KVL) between them can be obtained as follows:

[0083] V S1 -V CS +V SA +V S2 =V O (2)

[0084] Where V S1 V CS V SA and V S2 These are the rectifier switch S1 and the series capacitor C. S Auxiliary switch S A and the voltage on the main switch S2.

[0085] Due to the series capacitor CS The capacitance value is much larger than the parasitic output capacitance of the switch (i.e., C). S >>C OSS1 C OSS2 and C OSSA Therefore, a series capacitor C is connected. S Voltage V on CS It can be considered constant. According to equation (2), we can obtain:

[0086]

[0087] In other words, during the period from T1 to T2, the parasitic output capacitance C of the rectifier switch S1 OSS11 and auxiliary switch S A parasitic output capacitance C OSSA The discharge occurs, and the parasitic output capacitance C of the main switch S2... OSS2 It is being charged. Furthermore, when switch S... A Voltage V on SA When 0V is reached, auxiliary switch S A When the body diode is turned on, the voltage relationship between rectifier switch S1 and main switch S2 is as follows:

[0088]

[0089] like Figure 7 As shown, due to the parasitic output capacitance C of rectifier switch S1 and main switch S2 OSS1 and C OSS2 Typically less than 1nF, therefore the duration from T1 to T2 is relative to the switching period T. S Very short.

[0090] Figure 6C The topology of the totem-pole PWM PFC power converter 400 during T2 to T3 is shown. At time T2, when the parasitic output capacitance C of the rectifier switch S1... OSS1 The circuit is fully discharged, and the body diode of rectifier switch S1 begins to conduct and carry the boost inductor current i. L This transfers power from the input voltage source to the output load. During the period from T2 to T3, the voltage across the boost inductor L is equal to the output voltage V. O With input voltage V IN The difference between them, therefore the boost inductor current i L According to the equation Linear decrease. Simultaneously, auxiliary switch S... A The conduction current i of the body diode LS This makes the series capacitor C S Voltage V on CS Applied to series inductor L S Above. Therefore, the series inductor current i LS According to the equation Linear decrease.

[0091] Figure 6D The topology of the totem-pole PWM PFC power converter 400 during time T3 to T4 is shown. At time T3, auxiliary switch S... A The rectifier switch S1 is turned on at ZVS. At this time, the commutation cycle is completed, and the totem-pole PWM PFC power converter 400 enters the topology state from T3 to T5, in which virtually all of the boost inductor current i L All of them are transmitted to the output terminal.

[0092] Figure 6E The topology of the totem-pole PWM PFC power converter 400 is shown during T4 to T5. At auxiliary switch S... A After the circuit is turned on at time T3, at time T4, the series inductor current i LS It crosses zero and turns negative, while the auxiliary switch S A The current i in SA The polarity is reversed to positive.

[0093] Figure 6F The topology of the totem-pole PWM PFC power converter 400 during time T5 to T6 is shown. At time T5, rectifier switch S1 and auxiliary switch S... A Both are turned off. Since the input current still flows through the body diode of switch S1, the voltage V across rectifier switch S1 is reduced. S1 It remains at a relatively small value. Furthermore, due to the series inductor current i... LS Since the value is negative, the auxiliary switch S A parasitic output capacitance C OSSA Charging begins, which in turn activates the auxiliary switch S. A The voltage on it increases. According to the aforementioned equation (2), when the auxiliary switch S A When the voltage on the main switch S2 increases, it will correspondingly increase the parasitic output capacitance C of the main switch S2. OSS2 The voltage drops, where the voltage drop is caused by the parasitic output capacitance C. OSS2 This is caused by the discharge.

[0094] Figure 6G The topology of the totem-pole PWM PFC power converter 400 during T6 to T7 is shown. At time T6, the parasitic output capacitance C of the main switch S2 is... OSS2 It has been fully discharged, therefore the entire series inductor current i LS The current flowing through the body diode of the main switch S2 is i. L and series inductor current i LSThey have substantially equal magnitudes but opposite polarities. Therefore, the body diode of rectifier switch S1 briefly carries twice the input current (i.e., the boost inductor current i). L The peak current is of the size of ). The body diodes of rectifier switch S1 and main switch S2 both carry current during T6 to T7. According to equation (2), auxiliary switch S A Voltage V on SA Equal to output voltage V O and series capacitor voltage V CS The sum (i.e., V) O +V CS This causes the output voltage V to... O Fully applied to series inductor L S Up. Therefore, auxiliary switch S A It does not carry any current, the inductor current i LS The current i in the rectifier switch S1 increases linearly. S1 It falls at the same rate as it:

[0095]

[0096] As shown in equation (5), the rate of current decrease in rectifier switch S1 is determined by the series inductor L S Control. Therefore, this can be achieved by connecting a series inductor L. S Choosing an appropriate inductance value can reduce the rectifier's recovery charge and related losses. Generally, a larger inductance value will reduce the rate of current decrease and significantly reduce losses related to reverse recovery.

[0097] Figure 6H The topology of the totem-pole PWM PFC power converter 400 is shown during T7 to T8. At time T7, the main switch S2 carries essentially the entire series inductor current i. LS To achieve ZVS in the main switch S2, the series inductor current i LS The polarity turns positive before conduction. Therefore, as... Figure 7 As shown, at time T7, the main switch S2 is in series with the inductor current i LS Before the polarity reverses to positive, the circuit is turned on. If the control signal of the main switch S2 is relative to the series inductor current i... LS If there is a delay in the polarity reversal time, then the parasitic output capacitance C of the main switch S2 will be... OSS2 It may be fully or partially charged, making ZVS impossible.

[0098] During the period from T6 to T8, the boost inductor current i L by The rate increases linearly, while the series inductor current i LS by The rate increases linearly. Series inductor L S Ideally, the inductance value should be much smaller than that of the boost inductor L, so that the series inductor current i LS The rate of change is substantially higher than that of the boost inductor current i. L The rate of change.

[0099] Figure 6I The topology of the totem-pole PWM PFC power converter 400 is shown during T8 to T9. At time T8, the boost inductor current i L and series inductor current i LS Since they are equal, the current in rectifier switch S1 becomes zero. When the series inductor current i LS Rise to above the boost inductor current i L At that time, the parasitic output capacitance C of rectifier switch S1 OSS1 Start charging. According to equation (2), when the voltage V on rectifier switch S1... S1 When added, it will also be accompanied by auxiliary switch S A Voltage V on SA Increase. That is, increase the auxiliary switch S. A parasitic output capacitance C OSSA Discharge and reduce the amount applied to the series inductor L S The voltage across. As shown in Figure 6I, the series inductor current i LS Eventually, it drops to the level of the boost inductor current i L Equal. In addition, auxiliary switch S A Voltage V on SA It becomes the voltage V of the series capacitor. CS Equal, making the series inductance L S The voltage on it actually becomes zero, and the output voltage V O In fact, the force is entirely applied to the rectifier switch S1.

[0100] like Figure 7 As shown, the main switch S2, the rectifier switch S1, and the auxiliary switch S A The voltage stress on the output voltage V O With series capacitor C S Voltage V on CS The sum (i.e., V) O +V CS Therefore, the stress on the main switch S2 and rectifier switch S1 is higher than that on a traditional hard-switching boost converter (e.g., Figure 3 The stress on the corresponding switch in the AC-DC totem-pole boost converter 300. Therefore, for the series capacitor C S Choosing an appropriate capacitor value can thus ensure voltage V CS This is a reasonable value, thereby maintaining the voltage stress on the switch within a reasonable range.

[0101] By understanding that the durations of T1 to T3 and T5 to T8 (i.e., the commutation cycle) are shorter than the conduction times of the main switch S2 and rectifier switch S1, the circuit parameters and voltage V in the totem-pole PWM PFC power converter 400 are analyzed. CS The derivation of the relationships between them can be simplified. For example... Figure 7 As shown, during the period from T1 to T4, a series capacitor C is connected. S By connecting the inductor current i LS Discharge. Series inductor current i LS The polarity reverses at time T4, and the series capacitor C is connected between T4 and T6. S Charging. Except during the commutation cycles (i.e., T1 to T3 and T5 to T8) and T8 to T9, the series capacitor C... S The current in it has a substantially constant slope. (During T8 to T9, the series capacitor C) S The current in it is essentially zero. L For the boost inductor current i L The average value of the main switch S2 and the auxiliary switch S. A Achieving ZVS (i.e., at time T3, the series inductor current i) LS equal to -I L (at time T5) and to enable the rectifier switch S1 to achieve ZVS (i.e., at time T5, the series inductor current i LS equals I L (Time), by the slope of the current change during T3 to T5 We can obtain:

[0102]

[0103] Where D' is the duty cycle of rectifier switch S1, T S The duration of the switching cycle is T3 to T5, which is essentially the period T. ON The period T ON This refers to the period during which rectifier switch S1 is turned on. For a lossless totem-pole power stage, the voltage conversion ratio V... O / V IN This can be represented by equation (7), where in a lossless totem pole power stage, the commutation time of the current (i.e., the time from T1 to T3 and the time from T5 to T8) is much shorter than T. ON .

[0104]

[0105] Where I O Let be the average value of the output load current. Based on this, equation (6) can be rewritten as:

[0106]

[0107] Where f S This refers to the switching frequency.

[0108] According to equation (8), the voltage V CS At full load (i.e., I) L (at its maximum value) and the line voltage is minimum (i.e., V) IN It is maximum when it is the minimum value. Under given input and output specifications (i.e., given maximum I), L and output voltage V O This can be achieved by reducing L. S *f S To reduce the series capacitor voltage V by multiplying the product of the two. CS .

[0109] Totem-pole rectifiers are primarily used in input current shaping applications to reduce harmonic content and improve the power factor of line current. In any current shaping application, even if the input voltage V... IN If the output voltage V changes during the online cycle, it also needs to be adjusted. O Maintaining a substantially constant, while the duty cycle of the totem-pole rectifier changes from 0 to... In a PFC rectifier, the shape of the input current should ideally follow the shape of the input voltage. Therefore, according to equation (8), the voltage V CS It is essentially constant throughout the entire line period.

[0110] Figure 8 Circuit model 480 is shown, which represents the totem-pole PWM PFC power converter 400 at input voltage V. AC During the negative half-cycle (i.e., V) AC The equivalent circuit of <0). Figures 9A to 9I This illustrates a totem-pole PWM PFC power converter 400 at an input voltage V. AC The switching period T during the negative half-cycle S The topological state. Figure 10 It shows the input voltage V AC During the negative half-cycle (i.e., V) AC The switching period T of <0) S The key power stage waveform. At the input voltage V... AC During the negative half-cycle, the active soft-switching unit 401 of the totem-pole PWM PFC power converter 400 essentially operates as... Figures 6A to 6I and Figure 7 It operates as described above, except that the function of the switches is reversed (i.e., switch S1 is changed to act as the main switch and switch S2 as the rectifier switch). Therefore, details regarding... Figures 9A to 9I and Figure 10 A detailed explanation is provided. However, it should be noted that the comparison... Figures 6A to 6I and Figures 9A to 9I During the periods T0 to T1 and T8 to T9, at the input voltage V... AC During the negative half-cycle, when the main switch S1 is turned on, the input voltage V AC The current is entirely applied to the boost inductor L, therefore no current flows through the series inductor L. S Therefore, the current flows through the series inductor L S The peak current during the negative half-cycle is approximately twice that during the positive half-cycle.

[0111] The control circuit of the totem-pole PWM PFC power converter 400 can be constructed in the same way as the corresponding part in a traditional hard-switching totem-pole rectifier, requiring only an auxiliary switch S. A An additional gate drive circuit can be added. Specifically, for input current shaping applications, any suitable control technique (such as average current control, peak current control, or hysteresis control) can be used to control the totem-pole PWM PFC power converter 400.

[0112] Figure 11 This illustration shows a unidirectional AC-DC totem-pole power converter 1100 including an active soft-switching unit 401 in one embodiment of this invention. Unlike the totem-pole PWM PFC power converter 400, the AC-DC totem-pole power converter 1100 has a series inductor L coupled to the totem-pole PWM PFC power converter 400. S and auxiliary switch S A The boost inductor L is connected to the common electrical node between the series inductor Ls and the switch S2. For any power converter in this case that includes an active soft-switching unit, the boost inductor L can be connected to the common electrical node between the series inductor Ls and the switch S2, or to the common electrical node between the series inductor Ls and the switch S1. This is due to the input voltage V... AC This phenomenon can also be observed in the equivalent circuits of various configurations during the positive and negative half-cycles. During the positive half-cycle (i.e., V... AC >0), the equivalent circuit of the AC-DC totem pole power converter 1100 is Figure 8 The model shown is 480, where switch S2 is used as the rectifier switch. During the negative half-cycle (i.e., V... AC <0), the equivalent circuit of the AC-DC totem pole power converter 1100 is Figure 5 The model 450 shown uses switch S1 as the rectifier switch. Therefore, the operation of the totem-pole PWM PFC power converter 400 in the positive and negative half-cycles is consistent with the operation of the AC-DC totem-pole power converter 1100 in the negative and positive half-cycles, respectively.

[0113] Figure 12A bidirectional AC-DC totem-pole power converter 1200 including an active soft-switching unit 401 is shown in one embodiment of this invention. Unlike the totem-pole PWM PFC power converter 400, it replaces diodes D1 and D2 with synchronous rectifiers S3 and S4. The voltage drop of the synchronous rectifiers S3 and S4 (e.g., switches S3 and S4) is much lower than that of the passive diodes D1 and D2, thus improving conversion efficiency. It should be noted that diodes D1 and D2 in any totem-pole configuration of this invention can be replaced with synchronous rectifiers to achieve the conversion efficiency advantage.

[0114] Figure 13 An AC-DC totem-pole power converter 1300 including an active soft-switching unit 401 is shown in one embodiment of this invention. Unlike the totem-pole PWM PFC power converter 400, the AC-DC totem-pole power converter 1300 uses diode D... PRE1 and D PRE2 When the active soft-switching unit 401 is in the start-up or non-actuated state, the output DC side (e.g., both ends of the filter capacitor C) is charged, thereby bypassing the active soft-switching unit 401. Diode D PRE1 and D PRE2 This is a typical silicon element. Once the DC side is charged, the current from the AC source will flow through the active soft-switching unit 401, therefore diode D... PRE1 and D PRE2 It is no longer conducting.

[0115] Figure 14 A bidirectional AC-DC totem-pole power converter 1400 including an active soft-switching unit 401 is shown in one embodiment of the present invention, which replaces diodes D1 and D2 with synchronous rectifiers S3 and S4, as previously described, to obtain higher conversion efficiency.

[0116] Figure 15 This illustration shows a bidirectional AC-DC totem-pole power converter 1500 including an active soft-switching unit 401 in one embodiment of this invention. Unlike the bidirectional AC-DC totem-pole power converter 1400, the boost inductor L of the AC-DC totem-pole power converter 1500 is coupled to a series inductor L... S With auxiliary switch S A The common electrical nodes between them. As mentioned earlier, these configurations can all operate in a substantially equivalent manner.

[0117] Figure 16 A multiphase power converter 1600 including an active soft-switching unit 401 is shown in one embodiment of this invention. For example... Figure 16 As shown, the multiphase power converter 1600 is a bidirectional three-phase AC-DC power converter, which includes... Figure 4The active soft-switching unit 401 is located in the multiphase power converter 1600, which is coupled between an AC circuit and a DC circuit. The AC circuit may be a multiphase AC source and include multiple phase terminals. The DC circuit may be a resistive load or a DC power supply. The multiphase power converter 1600 includes multiple component circuits (i.e., multiple phase arms), each component circuit being coupled to a phase terminal of the AC circuit. Each phase arm of the multiphase power converter 1600 includes an inductor (i.e., inductor L1, L2, or L3) and an active soft-switching unit, wherein the inductor couples the phase arm to the corresponding phase terminal. The active soft-switching unit of each phase arm includes a series inductor (i.e., inductor L...). S1 L S2 or L S3 ), first and second switches (i.e., switches S1 and S2, switches S3 and S4 or switches S5 and S6), auxiliary switches (i.e., switches S1 and S2, S3 and S4 or S5 and S6), and auxiliary switches (i.e., switches S1 and S2). A1 S A2 or S A3 ) and auxiliary capacitor (i.e. C) S1 C S2 Or C S3 All switches are turned off under ZVS conditions, and at least one switch is a carbide MOSFET. In any phase bridge arm, the series inductor and the first and second switches form a series circuit in the DC circuit. Furthermore, in any phase bridge arm, the first switch (i.e., the first switch S1, S3, or S5) or the second switch (i.e., S2, S4, or S6) acts as a rectifier switch, which, together with the auxiliary switch (i.e., switch S... A1 S A2 or S A3 Simultaneously turn on and off. In any phase bridge arm, when the rectifier switch is off, the series inductor (i.e., series inductor L) is simultaneously turned on and off. S1 L S2 or L S3 This can reduce the rate of current change. By reducing the rate of current change, the reverse recovery loss in the rectifier switch can be further reduced.

[0118] At Figure 16 In the middle, the three-phase AC source provides the voltage V of the three wires. A V B and V C These three voltage lines can be connected using Y-type, WYE-type, or Δ-type configurations. For example... Figure 16 As shown, each phase arm in the three-phase converter includes an active soft-switching unit 401 coupled to the corresponding boost inductor (i.e., boost inductors L1, L2, and L3). Depending on the application, the number of phase arms can be any suitable value sufficient to transmit the required power. It should be noted that in multiphase power converters, the return path for each phase arm is provided by the other phase arms, thus eliminating the need for a totem-pole rectifier stage (e.g., diodes or synchronous rectifiers).

[0119] Figure 17 A multiphase power converter 1700 according to one embodiment of this invention is shown. Similar to multiphase power converter 1600, multiphase power converter 1700 is coupled to an AC circuit and a DC circuit. The AC circuit may be a multiphase AC source and includes multiple phase terminals. The DC circuit may be a resistive load or a DC power supply. Unlike multiphase power converter 1600, each boost inductor (i.e., inductor L1, L2, or L3) in multiphase power converter 1700 is coupled to a series inductor (i.e., series inductor L...). S1 L S2 or L S3 ) and the auxiliary switch (i.e., switch S) in the corresponding active soft switching unit A1 S A2 or S A3 The common electrical node between the phase bridge arm and the first and second switches. In any phase bridge arm, the series inductor and the first and second switches form a series circuit in the DC circuit. Furthermore, in any phase bridge arm, the first switch (i.e., the first switch S1, S3, or S5) or the second switch (i.e., S2, S4, or S6) acts as a rectifier switch, which, together with the auxiliary switch (i.e., switch S... A1 S A2 or S A3 Simultaneous turn-on and turn-off. All switches are turned off under ZVS conditions, and at least one switch is a carbide MOSFET. In any phase bridge arm, when the rectifier switch is turned off, the series inductor (i.e., series inductor L) S1 L S2 or L S3 This reduces the rate of current change. The decrease in the rate of current change further reduces reverse recovery losses in the rectifier switch. Similar to the multiphase power converter 1600, the number of phase terminals and phase arms can be any suitable value sufficient to transmit the required power, depending on the application.

[0120] As illustrated in the foregoing embodiments, this invention substantially reduces switching losses in AC-DC power conversion systems caused by the conduction characteristics of the main switch and the reverse recovery characteristics of the rectifier. Specifically, the series inductor in the active soft-switching unit reduces losses associated with reverse recovery, wherein the series inductor lowers the rate of current change of the body diode of the rectifier switch during its turn-off period. The switches in the active soft-switching unit can operate in a zero-voltage switching (ZVS) manner.

[0121] It should be noted that the above are merely preferred embodiments for illustrative purposes, and the scope of this application is not limited to the described embodiments. The scope of this application is determined by the claims attached. Furthermore, this application may be modified in various ways by those skilled in the art, but all such modifications shall not depart from the protection sought by the appended claims.

Claims

1. A power converter adapted to be coupled to an AC circuit and a DC circuit, wherein the AC circuit has a first terminal and a second terminal, the power converter comprising: A first inductor having a first terminal and a second terminal, wherein the first terminal of the first inductor is coupled to the first terminal of the AC circuit; A first rectifier and a second rectifier connected to a common node, wherein the series circuit formed by the first rectifier and the second rectifier is coupled in parallel to the DC circuit, and the common node is coupled to the second terminal of the AC circuit; and An active soft-switching unit, comprising: A second inductor having a first terminal and a second terminal; A first switch and a second switch, wherein the first switch, the second inductor and the second switch form a series circuit and are coupled to the series circuit formed by the first rectifier and the second rectifier; A third switch; and A first capacitor, wherein the third switch and the first capacitor form a series circuit and are coupled to the second inductor; The second terminal of the first inductor is coupled to either the first terminal or the second terminal of the second inductor. The first switch or the second switch acts as a rectifier switch that is turned on and off simultaneously with the third switch, and the second inductor has an inductance value suitable for reducing the rate of current change when the rectifier switch is turned off.

2. The power converter of claim 1, wherein at least one of the switches comprises a silicon carbide MOSFET.

3. The power converter of claim 1, wherein the power converter is configured to operate bidirectionally.

4. The power converter of claim 1, wherein the AC circuit includes an AC power source, and the DC circuit includes at least one of a resistive load and a DC power source.

5. The power converter of claim 1 further includes a filter capacitor connected in parallel to the first rectifier and the second rectifier.

6. The power converter of claim 1, wherein at least one of the first rectifier and the second rectifier comprises a synchronous rectifier.

7. The power converter of claim 1, wherein the reduction in the rate of change of current reduces the reverse recovery loss in the rectifier switch.

8. The power converter of claim 1, wherein at least one of the first switch, the second switch and the third switch is turned off under zero-voltage switching (ZVS) conditions.

9. The power converter of claim 1, wherein the first inductor is coupled to a common electrical node between the first switch and the second inductor.

10. The power converter of claim 1, wherein the first inductor is coupled to a common electrical node between the second switch and the second inductor.

11. A multiphase power converter suitable for coupling to an AC circuit and a DC circuit, wherein the AC circuit includes a plurality of phase terminals, each phase terminal being coupled to one phase of a multiphase AC power supply, the multiphase power converter having a plurality of phase arms, each phase arm comprising: A first inductor having a first terminal and a second terminal, wherein the first terminal of the first inductor is coupled to one of the phase terminals of the AC circuit; and An active soft-switching unit, comprising: A second inductor having a first terminal and a second terminal; The first switch and the second switch, wherein the first switch, the second inductor and the second switch form a series circuit and are coupled to the DC circuit; A third switch; and A first capacitor, wherein the third switch and the first capacitor form a series circuit and are coupled to the second inductor; The second terminal of the first inductor is coupled to either the first terminal or the second terminal of the second inductor. In any of the phase bridge arms, the first switch or the second switch acts as a rectifier switch that is turned on and off simultaneously with the third switch, and the second inductor has an inductance value suitable for reducing the rate of current change when the rectifier switch is turned off.

12. The multiphase power converter of claim 11, wherein at least one of the switches comprises a silicon carbide MOSFET.

13. The multiphase power converter of claim 11, wherein the multiphase power converter is configured to operate bidirectionally.

14. The multiphase power converter of claim 11 further includes a filter capacitor connected in parallel to the DC circuit.

15. The multiphase power converter of claim 11, wherein the reduction in the rate of change of current reduces the reverse recovery loss in the rectifier switch.

16. The multiphase power converter of claim 11, wherein in any one of the phase arms, at least one of the first switch, the second switch, and the third switch is turned off under zero-voltage switching (ZVS) conditions.

17. The multiphase power converter of claim 11, wherein the first inductor in any phase arm is coupled to a common electrical node between the first switch and the second inductor of the corresponding active soft-switching unit.

18. The multiphase power converter of claim 11, wherein the first inductor in any phase arm is coupled to a common electrical node between the second switch and the second inductor of the corresponding active soft-switching unit.

Images