A control method, control device and switching power supply

Abstract

The application discloses a control method, a control device and a switching power supply, wherein the control method is applied to a three-phase converter, and the control method comprises the following steps in a time interval: a sampling signal acquisition step, acquiring a first sampling signal representing a state of each phase, the state being capable of representing a size relationship of maximum average switching current absolute values of each phase bridge arm; and a working mode selection step, selecting a working mode of a corresponding phase bridge arm according to the first sampling signal of each phase, wherein: when the maximum average switching current absolute value represented by the first sampling signal is the largest, the corresponding phase bridge arm works in a clamping mode; when the maximum average switching current absolute value represented by the first sampling signal is in the middle, the corresponding phase bridge arm works in a CRM mode; and when the maximum average switching current absolute value represented by the first sampling signal is the smallest, the corresponding phase bridge arm works in a TCM mode. The application can provide a soft switching condition for three bridge arms of the three-phase converter.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of three-phase converter, in particular to a control method, a control device and a switching power supply. BACKGROUND

[0002] With the rapid development of switching power supply technology, three-phase converters are widely used in various industrial equipment and civil devices. The traditional three-phase converter usually adopts a hard switching (CCM) modulation scheme, and the switching loss of the switching device is large. With the development trend of lightweight and high frequency of three-phase converters, it is difficult for the hard switching modulation scheme to ensure high operating frequency, high power density and high efficiency of the converter at the same time. Therefore, a series of soft switching modulation schemes are proposed by researchers, which eliminates the overlap of voltage and current during the switching process of the device, thereby greatly reducing the switching loss.

[0003] However, the traditional soft switching modulation scheme is difficult to analyze and design due to the three-phase coupling, and usually needs to increase passive or active devices to provide soft switching conditions, such as Figure 1 As shown in FIG. 1, it is a three-phase converter circuit diagram of the prior art which increases passive devices (i.e. DC voltage side inductance Lo) to provide soft switching conditions. The voltage across the switch tube can be periodically resonated to zero, thereby completing all switching actions during the bus voltage Vbus = 0 (i.e. the voltage across the capacitor Co). However, the converter switch tube voltage stress of this traditional soft switching modulation scheme is high, and the additional auxiliary resonance circuit is large in size, so it is difficult to be used as an effective high power density soft switching solution. SUMMARY

[0004] In view of this, the technical problem to be solved by the present application is to provide a control method, a control device and a switching power supply to realize decoupling control of a three-phase converter, which is conducive to providing soft switching conditions for the converter, and does not need to increase passive or active devices, thereby improving product efficiency and reducing product size.

[0005] As a first aspect of the present application, the technical scheme of the control method embodiment is as follows:

[0006] A control method applied to a three-phase converter, the three-phase converter comprising a three-phase filter, a three-phase bridge circuit and a bus capacitor, each phase filter in the three-phase filter comprising a filter inductance and a filter capacitor, each bridge arm in the three-phase bridge circuit comprising an upper switch tube and a lower switch tube, one end of each phase filter capacitor and one end of each phase filter inductance being connected to the input end of the corresponding phase of the three-phase converter, the other end of each phase filter capacitor being connected together, the other end of each phase filter inductance being connected to the midpoint of the corresponding bridge arm, and each bus capacitor being connected in parallel with each bridge arm, wherein: the control method comprises the following steps in a time interval:

[0007] a sampling signal obtaining step, obtaining a first sampling signal representing a state of each phase, the state representing a size relationship of maximum average switching current absolute values of each phase leg;

[0008] a working mode selecting step, selecting a working mode of a corresponding phase leg according to the first sampling signal of each phase, wherein: when the maximum average switching current absolute value represented by the first sampling signal is the largest, the corresponding phase leg works in a clamping mode; when the maximum average switching current absolute value represented by the first sampling signal is in the middle, the corresponding phase leg works in a CRM mode; when the maximum average switching current absolute value represented by the first sampling signal is the smallest, the corresponding phase leg works in a TCM mode.

[0009] Preferably, the first sampling signal of each phase is obtained by detecting a current of a filter inductor of each phase, wherein: the phase with the largest average current absolute value of the filter inductor represents the largest average switching current absolute value of the corresponding phase; the phase with the middle average current absolute value of the filter inductor represents the middle average switching current absolute value of the corresponding phase; the phase with the smallest average current absolute value of the filter inductor represents the smallest average switching current absolute value of the corresponding phase; or the first sampling signal of each phase is obtained by detecting an input voltage of each phase of the three-phase converter, wherein: the phase with the largest average value of the input voltage represents the largest average switching current absolute value of the corresponding phase; the phase with the middle average value of the input voltage represents the middle average switching current absolute value of the corresponding phase; the phase with the smallest average value of the input voltage represents the smallest average switching current absolute value of the corresponding phase.

[0010] Further, the clamping mode comprises: when the maximum average switching current of the phase leg selected to work in the clamping mode is positive, the voltage across the phase leg is clamped to a positive DC bus voltage; when the maximum average switching current of the phase leg selected to work in the clamping mode is negative, the voltage across the phase leg is clamped to a negative DC bus voltage.

[0011] Further, the switching frequency of the phase leg working in the CRM mode is the same as that of the phase leg working in the TCM mode.

[0012] Further, for the phase leg selected to work in the CRM mode, wherein a main auxiliary pulse width modulation signal is generated by an RS flip-flop, and an auxiliary pulse width modulation signal is complementary to the main auxiliary pulse width modulation signal; the S signal of the RS flip-flop is a zero-crossing detection signal of the phase leg selected to work in the CRM mode, used to realize that the phase leg selected to work in the CRM mode works in the CRM mode; the R signal of the RS flip-flop is a control loop signal of the corresponding phase, used to make the electrical parameter output by the three-phase converter reach a desired value.

[0013] wherein, when the three-phase converter works in the rectification state: the lower switch is the main switch and the upper switch is the auxiliary switch when the phase input voltage corresponding to the bridge arm selected to work in the TCM mode is greater than zero; the upper switch is the main switch and the lower switch is the auxiliary switch when the phase input voltage corresponding to the bridge arm selected to work in the TCM mode is less than zero;

[0014] wherein, when the three-phase converter works in the inverting state: the upper switch is the main switch and the lower switch is the auxiliary switch when the phase input voltage corresponding to the bridge arm selected to work in the TCM mode is greater than zero; the lower switch is the main switch and the upper switch is the auxiliary switch when the phase input voltage corresponding to the bridge arm selected to work in the TCM mode is less than zero.

[0015] Further, the control loop adopts a peak current loop or an average current loop.

[0016] Further, for the bridge arm selected to work in the TCM mode, the main switch pulse width modulation signal is generated by an RS flip-flop, the auxiliary switch pulse width modulation signal is complementary to the main switch pulse width modulation signal plus a delay time, the delay time is set to realize the bridge arm selected to work in the TCM mode; the S signal of the RS flip-flop is the zero-crossing detection signal of the bridge arm selected to work in the CRM mode at this time, used to realize the switching frequency synchronization of the bridge arm selected to work in the TCM mode and the bridge arm selected to work in the CRM mode at this time, aiming to limit the peak switching frequency of the bridge arm selected to work in the TCM mode; the R signal of the RS flip-flop is the control loop signal of the corresponding phase, used to make the electrical parameters output by the three-phase converter reach the expected value.

[0017] wherein, when the three-phase converter works in the rectification state: the lower switch is the main switch and the upper switch is the auxiliary switch when the phase input voltage corresponding to the bridge arm selected to work in the TCM mode is greater than zero; the upper switch is the main switch and the lower switch is the auxiliary switch when the phase input voltage corresponding to the bridge arm selected to work in the TCM mode is less than zero.

[0018] wherein, when the three-phase converter works in the inverting state: the upper switch is the main switch and the lower switch is the auxiliary switch when the phase input voltage corresponding to the bridge arm selected to work in the TCM mode is greater than zero; the lower switch is the main switch and the upper switch is the auxiliary switch when the phase input voltage corresponding to the bridge arm selected to work in the TCM mode is less than zero.

[0019] Further, when the a-phase bridge arm of the three-phase converter works in the clamping mode and the voltage across the a-phase bridge arm is clamped to the positive DC bus voltage, the b-phase bridge arm works in the TCM mode, and the c-phase bridge arm works in the CRM mode, the delay time is T delayis solved by using the following equation:

[0020]

[0021] wherein: v b is the b-phase input voltage of the three-phase converter; v c is the c-phase input voltage of the three-phase converter; V o is the output-side DC bus voltage; i bavg is the average current of the b-phase filter inductor; L b is the inductance of the b-phase filter inductor; k is the current coefficient, which is determined by the power or feedback loop;

[0022] wherein one switching period is divided into five time periods, which include, in sequence:

[0023] The t1 time period is the time for c-phase filter inductor excitation, and the b-phase filter inductor is also excited at this stage;

[0024] The t2 time period is the time for b-phase filter inductor continuous excitation;

[0025] The t3 time period is the time for b-phase filter inductor demagnetization to zero;

[0026] The t4 time period is the delay time T delay , and the b-phase filter inductor is reversely excited at this stage;

[0027] The t5 time period is the time for b-phase filter inductor demagnetization, and the end time of t5 is the start time of the next switching period.

[0028] Further, the phase filter inductor current corresponding to the bridge arm working in the TCM mode is just demagnetized to 0 at the start time of the next switching period.

[0029] As a second aspect of the present application, the control device embodiment technical solution is as follows:

[0030] A control device applied to a three-phase converter, the three-phase converter comprising a three-phase filter, a three-phase bridge circuit and a bus capacitor, each phase filter in the three-phase filter comprising a filter inductor and a filter capacitor, each phase bridge arm in the three-phase bridge circuit comprising an upper switch tube and a lower switch tube, one end of each phase filter capacitor and one end of each phase filter inductor being connected to the input end of the corresponding phase, the other end of each phase filter capacitor being connected together, the other end of each phase filter inductor being connected to the midpoint of the corresponding phase bridge arm, and the bus capacitor being connected in parallel with each bridge arm, wherein: the control device comprises a unit for performing the following working content in a time interval:

[0031] A sampling signal acquisition unit for acquiring a first sampling signal representing the state of each phase, which can represent the size relationship of the maximum average switching current absolute value of each phase bridge arm;

[0032] The working mode selection unit is configured to select a working mode of a corresponding phase bridge arm according to the first sampling signal of each phase, wherein: when the maximum average switch current absolute value represented by the first sampling signal is the largest, the corresponding phase bridge arm works in the clamping mode; when the maximum average switch current absolute value represented by the first sampling signal is in the middle, the corresponding phase bridge arm works in the CRM mode; and when the maximum average switch current absolute value represented by the first sampling signal is the smallest, the corresponding phase bridge arm works in the TCM mode.

[0033] As a third aspect of the present application, the provided switching power supply embodiment technical solutions are as follows:

[0034] The switching power supply comprises a three-phase converter, wherein the three-phase converter comprises three-phase filters, a three-phase bridge circuit and a bus capacitor, each phase filter in the three-phase filters comprises a filter inductor and a filter capacitor, each phase bridge arm in the three-phase bridge circuit comprises an upper switch tube and a lower switch tube, one end of each phase filter capacitor and one end of each phase filter inductor are connected to a corresponding input end, the other end of each phase filter capacitor is connected together, the other end of each phase filter inductor is connected to a midpoint of the corresponding phase bridge arm, and the bus capacitor is connected in parallel with each bridge arm, and the switching power supply further comprises the control device in any one of the second aspect.

[0035] Compared with the prior art, the present application has the following technical effects:

[0036] (1) The three-phase converter applied in the embodiment of the present application does not need to additionally increase passive or active devices to provide an auxiliary ZVS network, and according to the first sampling signal of each phase, the corresponding phase bridge arm is selected to work in the clamping mode, the CRM mode or the TCM mode, so that soft switching can be naturally realized for each bridge arm, the switching loss is greatly reduced, the high frequency and planarization of the product are beneficial, the efficiency of the product is improved, and the volume of the product is reduced.

[0037] (2) When the bridge arms working in the CRM mode and the bridge arms working in the TCM mode operate at the same switching frequency, the three-phase converter switching frequency variation range can be greatly limited, so that the magnetic device and the EMI circuit can be conveniently designed, and the cost of the product is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a three-phase converter circuit principle diagram for applying a traditional soft switching modulation scheme;

[0039] Figure 2 It is a three-phase converter circuit principle diagram for applying a three-phase decoupling type CRM modulation scheme;

[0040] Figure 3 It is a three-phase converter topology structure suitable for the present application;

[0041] Figure 4 Flow chart of the control method of the first embodiment of the present application;

[0042] Figure 5 Key waveform diagram in the range of 90°-120° for applying the control method of the first embodiment of the present application;

[0043] Figure 6 Principle block diagram of the control device of the second embodiment of the present application. DETAILED DESCRIPTION

[0044] In order to make the above objectives, features and advantages of the present application more apparent, further specific embodiments and the drawings of the specification will be described below, but the specific embodiments of the present application are not limited thereto. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

[0045] It should be noted that the terms "comprising" and "having" and any variations thereof described in the specification and claims of the present application are intended to cover non-exclusive inclusion, for example, a series of components, unit circuits or control sequences do not have to be limited to those clearly listed, but can include components, unit circuits or control sequences that are not clearly listed or inherent to these circuits. The embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0046] In addition, the drawings of the present disclosure are only schematic and not necessarily to scale. The same reference numerals in the drawings represent the same or similar parts, and thus repeated description thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities, which do not necessarily have to correspond to physically or logically independent entities. These functional entities can be implemented by software, or in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0047] With the development trend of light weight and high frequency of three-phase converters, the soft switching control method suitable for three-phase converters has become a research hotspot. CRM, as an effective way to achieve soft switching, has been widely used in single-phase converters by relevant researchers, and has good power factor. However, for three-phase converter systems, only two of the three phases are independent, because the sum of the currents in the three phases is always zero. The coupling characteristics of three-phase converters make it impossible to simultaneously achieve independent CRM control for all three phases.

[0048] Different from the traditional soft-switching control which provides soft-switching conditions by adding passive or active devices, the patent CN112821790B, the document "Adaptive Hysteresis Current Based ZVS Modulation and Voltage Gain Compensation for High-Frequency Three-Phase Converters", etc. disclose a scheme of electrically coupling the midpoint of the filter capacitor in the three filter circuits of the three-phase converter with the DC capacitor midpoint of the capacitor module, as shown in Figure 2 Through this circuit connection, decoupling of the three phases can be achieved, so that the current in each phase is determined only by the switching state of that phase, and the three phases can be independently controlled as CRM operation. However, this scheme shows a very wide switching frequency variation range under typical operating conditions, thereby increasing the related switching loss. Therefore, this CRM method of decoupling three phases is not suitable for high-frequency design.

[0049] The patent CN113541522B discloses a design scheme using five-stage discontinuous pulse width modulation (DPWM). By using DPWM, at any moment of a single line voltage period of the alternating current power supply, a certain phase in the three phases is clamped to the positive DC bus or the negative DC bus, while the other two phases remain PWM operation. This scheme clamps the current maximum phase, reduces switching loss and improves overall efficiency, but the THD is worse than continuous pulse width modulation due to the clamping of one phase.

[0050] In order to facilitate control, the inventors of the present application have proposed a control scheme based on DPWM modulation to realize three-phase decoupling, so that the three phases work in clamping mode, CRM mode and TCM mode. The three-phase converter topology suitable for the present application is shown in Figure 3 The control scheme of the present application divides the single line voltage period of the alternating current power supply into six time intervals for control switching, so as to determine the peak value and polarity of the alternating current power supply voltage in each time interval, and further determine the DPWM clamping mode. The current in the phase working in clamping mode depends on the sum of the currents in the other two independently controlled phases, therefore, DPWM can be used as a decoupling method, so that independent CRM control can be realized for the three phases simultaneously in the entire line voltage period of the alternating current power supply.

[0051] Continuing to take the 60°-120° interval as an example, the interval is further evenly divided into two time periods, so as to determine the peak value of the alternating power voltage in each time period, and further determine the phase under the CRM mode or the TCM mode. For example, in the 60°-90° interval, the absolute value of the average voltage of the B phase is greater than that of the C phase, and under the condition of the unit power factor, the B phase has greater average switching current than the C phase, so the second phase bridge arm, i.e., the B phase, is selected to work in the CRM mode, and the third phase bridge arm, i.e., the C phase, is selected to work in the TCM mode; in the 90°-120° interval, the absolute value of the average voltage of the B phase is less than that of the C phase, so the second phase bridge arm, i.e., the C phase, is selected to work in the CRM mode, and the third phase bridge arm, i.e., the B phase, is selected to work in the TCM mode.

[0052] First embodiment

[0053] The embodiment provides a control method, which is applied to Figure 3 The three-phase converter shown in the figure comprises three-phase filters, a three-phase bridge circuit and bus capacitors. Each phase filter in the three-phase filters comprises a filter inductor and a filter capacitor. Each phase bridge arm in the three-phase bridge circuit comprises an upper switch tube and a lower switch tube. One end of each phase filter capacitor and one end of each phase filter inductor are connected to the input end of the corresponding phase of the three-phase converter. The other end of each phase filter capacitor is connected together. The other end of each phase filter inductor is connected to the midpoint of the corresponding phase bridge arm. Each bus capacitor is connected in parallel with each bridge arm.

[0054] Please refer to Figure 3 In the figure, the a-phase filter in the three-phase filter comprises a filter inductor La and a filter capacitor Ca, the b-phase filter comprises a filter inductor Lb and a filter capacitor Cb, and the c-phase filter comprises a filter inductor Lc and a filter capacitor Cc. The a-phase bridge arm in the three-phase bridge circuit comprises an upper switch tube S1 and a lower switch tube S2, the b-phase bridge arm comprises an upper switch tube S3 and a lower switch tube S4, and the c-phase bridge arm comprises an upper switch tube S5 and a lower switch tube S6. The bus capacitor Co is connected in parallel with each bridge arm, and the voltage across the bus capacitor Co is the bus voltage (the voltage is the same as Vbus and Vo in the background art).

[0055] Figure 4 The control method of the first embodiment of the application is shown in the figure, wherein the control method comprises the following steps in a time interval:

[0056] In the sampling signal acquisition step S100, a first sampling signal representing the state of each phase is acquired, and the state can represent the size relationship of the absolute values of the maximum average switching currents of the bridge arms of each phase.

[0057] The working mode selection step S200 selects the working mode of the corresponding phase bridge arm according to the first sampling signal of each phase, wherein: when the maximum average switch current absolute value represented by the first sampling signal is the maximum, the corresponding phase bridge arm works in the clamping mode; when the maximum average switch current absolute value represented by the first sampling signal is in the middle, the corresponding phase bridge arm works in the CRM mode; and when the maximum average switch current absolute value represented by the first sampling signal is the minimum, the corresponding phase bridge arm works in the TCM mode.

[0058] The control method of the embodiment is switched according to the phase in specific application, and a single line voltage period (i.e. one power frequency period) of the AC switching power supply is evenly divided into six time intervals, so that the bridge arm working in the clamping mode will be converted once every 60° in a single line voltage period, and the bridge arm working in the CRM mode or the TCM mode will be converted once every 30° in a single line voltage period, thereby determining the running mode distribution of all three phase bridge arms in the whole line voltage period. For example, in the 60°-90° interval, the A-phase bridge arm is selected to work in the clamping mode, the B-phase bridge arm is selected to work in the CRM mode, and the C-phase bridge arm is selected to work in the TCM mode; in the 90°-120° interval, the A-phase bridge arm is selected to work in the clamping mode, the C-phase bridge arm is selected to work in the CRM mode, and the B-phase bridge arm is selected to work in the TCM mode; and in the 120°-150° interval, the C-phase bridge arm is selected to work in the clamping mode, the A-phase bridge arm is selected to work in the CRM mode, and the B-phase bridge arm is selected to work in the TCM mode.

[0059] The control method provided by the embodiment does not need to additionally increase passive or active devices to provide an auxiliary ZVS network when applied to a three-phase converter, and selects the corresponding phase bridge arm to work in the clamping mode, the CRM mode or the TCM mode according to the first sampling signal of each phase, so that each bridge arm can naturally realize soft switching, greatly reduces the switching loss, is conducive to the high frequency and planarization of the product, improves the efficiency of the product, and reduces the volume of the product.

[0060] The three-phase converter of the embodiment can obtain the first sampling signal of each phase by detecting the current of the filter inductor of each phase, wherein: the phase with the maximum average filter inductor current absolute value represents that the corresponding phase average switch current absolute value is the maximum; the phase with the average filter inductor current absolute value in the middle represents that the corresponding phase average switch current absolute value is in the middle; and the phase with the minimum average filter inductor current absolute value represents that the corresponding phase average switch current absolute value is the minimum. Alternatively, the three-phase converter can obtain the first sampling signal of each phase by detecting the input voltage of each phase, wherein: the phase with the maximum input voltage average value represents that the corresponding phase average switch current absolute value is the maximum; the phase with the average input voltage average value in the middle represents that the corresponding phase average switch current absolute value is in the middle; and the phase with the minimum input voltage average value represents that the corresponding phase average switch current absolute value is the minimum.

[0061] Specifically, when the maximum average switching current of the phase leg selected to operate in the clamping mode is positive, the voltage across the phase leg is clamped to the positive DC bus voltage; when the maximum average switching current of the phase leg selected to operate in the clamping mode is negative, the voltage across the phase leg is clamped to the negative DC bus voltage. For example, in the 60°-120° interval, the A phase has the maximum average input voltage and is positive, and under the condition of unity power factor, the A phase has the maximum average switching current at the same time, and thus the A phase leg is selected to be clamped to the positive DC bus voltage in this time interval, corresponding to the A phase leg being selected to operate in the clamping mode. In the 120°-180° interval, the A phase has the maximum average input voltage and is negative, and under the condition of unity power factor, the A phase has the maximum average switching current at the same time, and thus the A phase leg is selected to be clamped to the negative DC bus voltage in this time interval, corresponding to the A phase leg being selected to operate in the clamping mode. Figure 3 The switch S1 is always kept in the on state, and the switch S2 is always kept in the off state.

[0062] Further, the switching frequency of the bridge leg operating in the CRM mode and the bridge leg operating in the TCM mode is the same, and the control method provided in the embodiment can greatly limit the variation range of the switching frequency of the three-phase converter when the bridge leg operating in the CRM mode and the bridge leg operating in the TCM mode are operated at the same switching frequency, so that the magnetic device and the EMI circuit can be conveniently designed, and the cost of the product is reduced.

[0063] For the bridge leg selected to operate in the CRM mode, the main-branch pulse width modulation signal is generated by an RS flip-flop, and the auxiliary-branch pulse width modulation signal is complementary to the main-branch pulse width modulation signal and ignores the dead time; the S signal of the RS flip-flop is the zero-crossing detection signal of the bridge leg selected to operate in the CRM mode, and is used to realize that the bridge leg selected to operate in the CRM mode operates in the CRM mode; and the R signal of the RS flip-flop is the control loop signal of the corresponding phase, and is used to make the electrical parameters output by the three-phase converter reach the expected value. The zero-crossing detection signal represents the zero-crossing moment of the current of the bridge leg selected to operate in the CRM mode; the control loop of the corresponding phase adopts a peak current loop or an average current loop, and both the peak current loop and the average current loop are common technologies known to those skilled in the art. The CRM mode using the peak current loop or the average current loop for control can independently control the bridge leg selected to operate in the CRM mode, and good power factor and THD value can be obtained; when the three-phase converter operates in the rectification state: when the input voltage of the phase corresponding to the bridge leg selected to operate in the TCM mode is greater than zero, the lower switch is the main switch and the upper switch is the auxiliary switch; when the input voltage of the phase corresponding to the bridge leg selected to operate in the TCM mode is less than zero, the upper switch is the main switch and the lower switch is the auxiliary switch; when the three-phase converter operates in the inversion state: when the input voltage of the phase corresponding to the bridge leg selected to operate in the TCM mode is greater than zero, the upper switch is the main switch and the lower switch is the auxiliary switch; when the input voltage of the phase corresponding to the bridge leg selected to operate in the TCM mode is less than zero, the lower switch is the main switch and the upper switch is the auxiliary switch.

[0064] For the selected bridge arm working in TCM mode, the auxiliary PWM signal is ignored, and the main PWM signal is complemented with a delay time, which is set to make the selected bridge arm work in TCM mode; the S signal of the RS flip-flop is the zero-crossing detection signal of the bridge arm working in CRM mode, which is used to synchronize the switching frequency of the selected bridge arm working in TCM mode and the bridge arm working in CRM mode, so as to limit the peak switching frequency of the selected bridge arm working in TCM mode; the R signal of the RS flip-flop is the control loop signal of the corresponding phase, which is used to make the electrical parameters of the three-phase converter output reach the expected value; when the three-phase converter works in the rectification state: when the input voltage of the selected bridge arm working in TCM mode is greater than zero, the lower switch is the main switch, and the upper switch is the auxiliary switch; when the input voltage of the selected bridge arm working in TCM mode is less than zero, the upper switch is the main switch, and the lower switch is the auxiliary switch.

[0065] When the three-phase converter works in the inverter state: when the input voltage of the selected bridge arm working in TCM mode is greater than zero, the upper switch is the main switch, and the lower switch is the auxiliary switch; when the input voltage of the selected bridge arm working in TCM mode is less than zero, the lower switch is the main switch, and the upper switch is the auxiliary switch; the control loop can adopt a conventional single-phase PFC control loop.

[0066] When the a-phase bridge arm of the three-phase converter works in the clamping mode and the voltage across the a-phase bridge arm is clamped to the positive DC bus voltage, the b-phase bridge arm works in the TCM mode, and the c-phase bridge arm works in the CRM mode, the above delay time is represented by T dealy , and the calculation includes the following steps:

[0067] Step one: sample the three-phase alternating current source phase voltages va, vb, vc and the output side DC bus voltage Vo;

[0068] Step two: calculate the duration of each working mode in a single line voltage period according to the time interval in which the three-phase converter is located;

[0069] Figure 5 For the key waveform diagram of the control method of the first embodiment of the application in the 90°-120° interval, please refer to Figure 5, Ia, Ib, Ic are the inductor ripple currents of the a-phase bridge arm, the b-phase bridge arm, and the c-phase bridge arm, respectively, and the inductor ripple currents flowing into the bridge arms in the time period t1-t5 have different current slopes, wherein t1 can be obtained by timing the on duration of the switch S5 by a timer inside the controller, (t1+t2) can be obtained by timing the on time of the switch S5 to the on time of the switch S4 by a timer inside the controller, and t3 can be obtained by timing the on duration of the switch S4 by a timer inside the controller. Considering that the ideal converter ignores the dead time, according to the volt-second balance principle, t4 and t5 can be derived from the following equation:

[0070]

[0071] wherein v b is the b-phase input voltage of the three-phase converter; v c is the c-phase input voltage of the three-phase converter; V o is the output side DC bus voltage; i bavg is the b-phase filter inductor average current; L b is the inductance of the b-phase filter inductor; and k is the current coefficient, which is determined by the power or feedback loop.

[0072] wherein one switching period is divided into five time periods, including:

[0073] t1 time period, which is the time for c-phase filter inductor excitation, and the b-phase filter inductor is also excited at this stage;

[0074] t2 time period, which is the time for b-phase filter inductor to continue excitation;

[0075] t3 time period, which is the time for b-phase filter inductor to demagnetize to zero;

[0076] t4 time period, which is the time delay T delay , and the b-phase filter inductor is reversely excited at this stage;

[0077] t5 time period, in which the b-phase filter inductor demagnetizes, and the end time of t5 is the start time of the next switching period.

[0078] Step three: assigning the value of t4 obtained by solving to the b-bridge auxiliary tube off time delay T delay , and the control device updates the b-bridge auxiliary tube off time delay T delay in real time according to the derivation result, so as to realize that the b-phase bridge arm works in TCM mode.

[0079] Further, the phase filter inductor current corresponding to the bridge arm working in TCM mode is demagnetized to 0 at the start time of the next switching period, so as to realize zero voltage turn-on of the b-phase bridge arm main tube.

[0080] Second embodiment

[0081] The embodiment provides a control device, which is applied to a three-phase converter, the three-phase converter comprising a three-phase filter, a three-phase bridge circuit and a bus capacitor, each phase filter in the three-phase filter comprising a filter inductor and a filter capacitor, each bridge arm in the three-phase bridge circuit comprising an upper switch tube and a lower switch tube, one end of each phase filter capacitor and one end of each phase filter inductor being connected to a corresponding input end, the other end of each phase filter capacitor being connected together, the other end of each phase filter inductor being connected to a midpoint of the corresponding bridge arm, and the bus capacitor being connected in parallel with each bridge arm. Figure 6 The control device of the second embodiment of the application is a principle block diagram, wherein: the control device comprises units for performing the following work contents in a time interval:

[0082] A sampling signal acquisition unit 100 is configured to acquire a first sampling signal representing a state of each phase, the state being capable of representing a size relationship of maximum average switching current absolute values of each phase bridge arm.

[0083] A working mode selection unit 200 is configured to select a working mode of the corresponding phase bridge arm according to the first sampling signal of each phase, wherein: when the maximum average switching current absolute value represented by the first sampling signal is the largest, the corresponding phase bridge arm works in a clamping mode; when the maximum average switching current absolute value represented by the first sampling signal is in the middle, the corresponding phase bridge arm works in a CRM mode; and when the maximum average switching current absolute value represented by the first sampling signal is the smallest, the corresponding phase bridge arm works in a TCM mode.

[0084] The technical means adopted by the control device of the embodiment is consistent with the control method of the first embodiment, and has the same beneficial effects, and thus is not described herein. In addition, the preferred technical means or further improved means of each step in the control method of the first embodiment can be extended to the corresponding units of the embodiment, and thus is not described herein.

[0085] Third embodiment

[0086] The embodiment provides a switching power supply, which comprises a three-phase converter, the three-phase converter comprising a three-phase filter, a three-phase bridge circuit and a bus capacitor, each phase filter in the three-phase filter comprising a filter inductor and a filter capacitor, each bridge arm in the three-phase bridge circuit comprising an upper switch tube and a lower switch tube, one end of each phase filter capacitor and one end of each phase filter inductor being connected to a corresponding input end, the other end of each phase filter capacitor being connected together, the other end of each phase filter inductor being connected to a midpoint of the corresponding bridge arm, and the bus capacitor being connected in parallel with each bridge arm, and the switching power supply further comprises any one of the control devices in the second embodiment.

[0087] The switching power supply of the embodiment can naturally realize soft switching of each bridge arm, greatly reduce switching loss, be beneficial to high frequency and planarization of the product, improve efficiency of the product, and reduce volume of the product.

[0088] It should be understood that, although the specific embodiments of the present application are described to help better understand and understand the present application, there are other embodiments equivalent to the embodiments. The embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The above embodiments are given as examples in an illustrative rather than limiting manner, so any modification or replacement of all or part of the technical features of the technical solutions described in the embodiments without departing from the spirit or essence of the present application should be considered as covered within the scope of the claims.

Claims

1. A control method applied to a three-phase converter, the three-phase converter comprising a three-phase filter, a three-phase bridge circuit, and bus capacitors, wherein each phase filter of the three-phase filter includes a filter inductor and a filter capacitor, each phase arm of the three-phase bridge circuit includes an upper switch and a lower switch, one end of each phase filter capacitor and one end of each filter inductor are connected to the input terminal of the corresponding phase of the three-phase converter, the other ends of each phase filter capacitor are connected together, the other end of each phase filter inductor is connected to the midpoint of the corresponding phase arm, and each bus capacitor is connected in parallel with each arm, characterized in that: The control method includes the following steps within a time interval: The sampling signal acquisition step involves acquiring the first sampling signal that represents the state of each phase. This state can characterize the magnitude relationship of the absolute value of the maximum average switching current of each phase arm. The working mode selection step is to select the working mode of the corresponding phase bridge arm based on the first sampling signal of each phase, wherein: when the absolute value of the maximum average switching current represented by the first sampling signal is the largest, the corresponding phase bridge arm works in clamping mode; when the absolute value of the maximum average switching current represented by the first sampling signal is in the middle, the corresponding phase bridge arm works in CRM mode; when the absolute value of the maximum average switching current represented by the first sampling signal is the smallest, the corresponding phase bridge arm works in TCM mode. For the bridge arm selected to operate in TCM mode, the main pulse width modulation signal is generated by an RS flip-flop. Ignoring dead time, the auxiliary pulse width modulation signal and the main pulse width modulation signal are complemented by a delay time. The purpose of setting the delay time is to ensure that the bridge arm selected to operate in TCM mode operates in TCM mode. The S signal of the RS flip-flop is the zero-crossing detection signal of the bridge arm selected to operate in CRM mode, used to synchronize the switching frequencies of the bridge arm selected to operate in TCM mode and the bridge arm selected to operate in CRM mode, with the purpose of limiting the peak switching frequency of the bridge arm selected to operate in TCM mode. The R signal of the RS flip-flop is the control loop signal of the corresponding phase, used to ensure that the electrical parameters output by the three-phase converter reach the desired values. When the a-phase bridge arm of the three-phase converter operates in clamping mode and the voltage across the a-phase bridge arm is clamped to the positive DC bus voltage, the b-phase bridge arm operates in TCM mode, and the c-phase bridge arm operates in CRM mode, the delay time is denoted by T. delay The following equations are used to solve the problem: Where: v b This refers to the input voltage of phase b of the three-phase converter; v c V is the c-phase input voltage of the three-phase converter. o i is the output-side DC bus voltage; bavg The average current of the b-phase filter inductor; L b is the inductance value of the b-phase filter inductor; k is the current coefficient, determined by the power or feedback loop. One switching cycle is divided into 5 time periods, which include: The time period t1 is the time when the c-phase filter inductor is energized, and the b-phase filter inductor is also energized during this period. The time interval t2 is the time during which the b-phase filter inductor continues to be energized; The time interval t3 is the time it takes for the b-phase filter inductor to demagnetize to zero. The time period t4 is the delay time T. delay During this stage, the b-phase filter inductor is reverse-excited; During the t5 time period, the b-phase filter inductor is demagnetized, and the end time of t5 is the start time of the next switching cycle.

2. The control method according to claim 1, characterized in that: The first sampling signal of each phase is obtained by detecting the current of the filter inductor of each phase. Among them, the phase with the largest absolute value of the average current of the filter inductor represents the phase with the largest absolute value of the average switching current; the phase with the middle absolute value of the average current of the filter inductor represents the phase with the middle absolute value of the average switching current; and the phase with the smallest absolute value of the average current of the filter inductor represents the phase with the smallest absolute value of the average switching current. Alternatively, the first sampling signal of each phase can be obtained by detecting the input voltage of each phase of the three-phase converter, wherein: the phase with the largest average input voltage represents the phase with the largest absolute value of the average switching current; the phase with the middle average input voltage represents the phase with the middle absolute value of the average switching current; and the phase with the smallest average input voltage represents the phase with the smallest absolute value of the average switching current.

3. The control method according to claim 1, characterized in that, The clamping modes include: When the maximum average switching current of the phase bridge arm selected to operate in clamping mode is positive, the voltage across the bridge arm is clamped to the positive DC bus voltage. When the maximum average switching current of the phase bridge arm selected to operate in clamping mode is negative, the voltage across the bridge arm is clamped to the negative DC bus voltage.

4. The control method according to claim 1, characterized in that: The switching frequency of the bridge arm operating in CRM mode and the bridge arm operating in TCM mode is the same.

5. The control method according to claim 1, characterized in that: For the bridge arm selected to operate in CRM mode, the main pulse width modulation signal is generated by an RS flip-flop, and the auxiliary pulse width modulation signal is complementary to the main pulse width modulation signal, ignoring dead time. The S signal of the RS flip-flop is the zero-crossing detection signal of the bridge arm selected to operate in CRM mode, used to realize the operation of the bridge arm selected to operate in CRM mode. The R signal of the RS flip-flop is the control loop signal of the corresponding phase, used to make the electrical parameters output by the three-phase converter reach the desired value. When the three-phase converter is operating in rectification mode: when the phase input voltage of the bridge arm selected to operate in TCM mode is greater than zero, the lower switch is the main switch and the upper switch is the auxiliary switch; when the phase input voltage of the bridge arm selected to operate in TCM mode is less than zero, the upper switch is the main switch and the lower switch is the auxiliary switch. When the three-phase converter is operating in inverter mode: when the phase input voltage of the bridge arm selected to operate in TCM mode is greater than zero, the upper switch is the main switch and the lower switch is the auxiliary switch; when the phase input voltage of the bridge arm selected to operate in TCM mode is less than zero, the lower switch is the main switch and the upper switch is the auxiliary switch.

6. The control method according to claim 5, characterized in that: The control loop adopts either a peak current loop or an average current loop.

7. The control method according to claim 1, characterized in that: The current of the phase filter inductor corresponding to the bridge arm operating in TCM mode is demagnetized to 0 at the beginning of the next switching cycle.

8. A control device applied to a three-phase converter, the three-phase converter comprising a three-phase filter, a three-phase bridge circuit, and a bus capacitor, wherein each phase filter of the three-phase filter includes a filter inductor and a filter capacitor, each phase arm of the three-phase bridge circuit includes an upper switch and a lower switch, one end of each phase filter capacitor and one end of each phase filter inductor are connected to the input terminal of the corresponding phase, the other ends of each phase filter capacitor are connected together, the other end of each phase filter inductor is connected to the midpoint of the corresponding phase arm, and the bus capacitor is connected in parallel with each arm, characterized in that: The control device includes a unit that performs the following tasks within a time interval: The sampling signal acquisition unit is used to acquire the first sampling signal that represents the state of each phase, which can characterize the magnitude relationship of the absolute value of the maximum average switching current of each phase arm. The operating mode selection unit is used to select the operating mode of the corresponding phase bridge arm based on the first sampling signal of each phase, wherein: when the absolute value of the maximum average switching current represented by the first sampling signal is the largest, the corresponding phase bridge arm operates in clamping mode; when the absolute value of the maximum average switching current represented by the first sampling signal is in the middle, the corresponding phase bridge arm operates in CRM mode; when the absolute value of the maximum average switching current represented by the first sampling signal is the smallest, the corresponding phase bridge arm operates in TCM mode. For the bridge arm selected to operate in TCM mode, the main pulse width modulation signal is generated by an RS flip-flop. Ignoring dead time, the auxiliary pulse width modulation signal and the main pulse width modulation signal are complemented by a delay time. The purpose of setting the delay time is to ensure that the bridge arm selected to operate in TCM mode operates in TCM mode. The S signal of the RS flip-flop is the zero-crossing detection signal of the bridge arm selected to operate in CRM mode, used to synchronize the switching frequencies of the bridge arm selected to operate in TCM mode and the bridge arm selected to operate in CRM mode, with the purpose of limiting the peak switching frequency of the bridge arm selected to operate in TCM mode. The R signal of the RS flip-flop is the control loop signal of the corresponding phase, used to ensure that the electrical parameters output by the three-phase converter reach the desired values. When the a-phase bridge arm of the three-phase converter operates in clamping mode and the voltage across the a-phase bridge arm is clamped to the positive DC bus voltage, the b-phase bridge arm operates in TCM mode, and the c-phase bridge arm operates in CRM mode, the delay time is denoted by T. delay The following equations are used to solve the problem: Where: v b This refers to the input voltage of phase b of the three-phase converter; v c V is the c-phase input voltage of the three-phase converter. o i is the output-side DC bus voltage; bavg The average current of the b-phase filter inductor; L b is the inductance value of the b-phase filter inductor; k is the current coefficient, determined by the power or feedback loop. One switching cycle is divided into 5 time periods, which include: The time period t1 is the time when the c-phase filter inductor is energized, and the b-phase filter inductor is also energized during this period. The time interval t2 is the time during which the b-phase filter inductor continues to be energized; The time interval t3 is the time it takes for the b-phase filter inductor to demagnetize to zero. The time period t4 is the delay time T. delay During this stage, the b-phase filter inductor is reverse-excited; During the t5 time period, the b-phase filter inductor is demagnetized, and the end time of t5 is the start time of the next switching cycle.

9. A switching power supply, comprising a three-phase converter, the three-phase converter comprising a three-phase filter, a three-phase bridge circuit, and a bus capacitor, wherein each phase filter of the three-phase filter comprises a filter inductor and a filter capacitor, each phase arm of the three-phase bridge circuit comprises an upper switch transistor and a lower switch transistor, one end of each phase filter capacitor and one end of each phase filter inductor are connected to the input terminal of the corresponding phase, the other ends of each phase filter capacitor are connected together, the other end of each phase filter inductor is connected to the midpoint of the corresponding phase arm, and the bus capacitor is connected in parallel with each arm, characterized in that: The switching power supply also includes the control device as described in claim 8.

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