Control method, control device and switching power supply

Abstract

The invention discloses a control method, a control device and a switching power supply, and the control method employs a variable frequency SVPWM modulation strategy, and comprises the following steps: calculating an SVPWM modulation wave for controlling the on and off of each phase bridge arm switching tube when an electrical parameter outputted by an N-phase converter reaches an expected value through double closed-loop control of a voltage outer loop and a current inner loop; calculating the frequency required for realizing ZVS of each phase of bridge arm switch tube by predicting the magnitude of the current pulsation of each phase of second filter inductor, comparing the frequencies of each phase, selecting the minimum frequency in N phases as the frequency of a triangular carrier wave, and generating a common triangular carrier wave by using the calculated frequency; and comparing the SVPWM modulation wave of each phase of bridge arm switch tube with the shared triangular carrier wave to obtain a PWM driving signal for controlling the on and off of each phase of bridge arm switch tube. According to the invention, each sector can realize soft switching through variable frequency, and each phase does not need to be clamped.

Description

Technical Field

[0001] The present invention relates to the field of three-phase converters, and in particular to a control method, a control device and a switching power supply. Background Art

[0002] With the rapid development of switching power supply technology, three-phase converters have been widely used, especially in energy storage systems, electric vehicle chargers and motor drives. However, most of the existing traditional solutions are modulated in a continuous conduction mode (CCM) hard switching manner, which increases the loss of switching devices. With the rapid development of switching devices such as silicon carbide (SIC) and gallium nitride (GaN), three-phase converters are also showing a trend of lightweight, miniaturization and high frequency. Traditional hard switching can no longer meet the above three-phase converter development trend, and then the three-phase converter soft switching modulation method is derived to achieve high efficiency and high power density of the three-phase converter, but the traditional soft switch has the following defects:

[0003] (1) Passive or active devices need to be added to assist in the realization of soft switching, such as adding a zero current detection (ZCD) circuit, which will increase the complexity of the corresponding control and the cost of the device;

[0004] (2) Since the current and voltage of the three-phase converter are coupled with each other, traditional soft switching requires decoupling and clamping of the current, which further increases the complexity of soft switching implementation. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a control method, a control device and a switching power supply, which do not require additional passive or active devices, and utilize variable frequency to achieve zero-voltage switching of the switch tubes of each phase bridge arm of an N-phase converter, thereby improving product efficiency and reducing product volume and inductance cost.

[0006] As a first aspect of the present invention, the technical solution of the control method provided is as follows:

[0007] A control method is applied to an N-phase converter, wherein the N-phase converter comprises an N-phase LCL filter and an N-phase bridge circuit, wherein each phase filter in the N-phase LCL filter comprises a first filter inductor, a second filter inductor and a filter capacitor, wherein each phase bridge arm in the N-phase bridge circuit comprises an upper switch tube and a lower switch tube, wherein one end of the first filter inductor of each phase is connected to the input end of the corresponding phase of the N-phase converter, and the other end is connected to one end of the second filter inductor of the corresponding phase, and the other end of the second filter inductor of each phase is connected to the midpoint of the bridge arm of the corresponding phase, and the filter capacitor of each phase is connected to the midpoint of the filter inductor of the corresponding phase and the midpoint of the filter inductor of the next phase, wherein each bridge arm is connected in parallel to form the output end of the N-phase bridge circuit, and the driving signals of the upper switch tube and the lower switch tube of each bridge arm are PWM complementary signals with dead time, and the N-phase converter operates in rectification and inversion states, wherein the control method adopts a variable frequency SVPWM modulation strategy, and comprises the following steps:

[0008] A modulation wave acquisition step, calculating the SVPWM modulation wave for controlling the on and off of the switch tubes of each phase bridge arm when the electrical parameters output by the N-phase converter reach the expected value through a voltage outer loop and a current inner loop double closed-loop control;

[0009] The triangular carrier acquisition step is to calculate the frequency required for each phase bridge arm switch tube to achieve ZVS by predicting the magnitude of the current pulsation of the second filter inductor of each phase, and compare the frequencies of each phase, select the smallest frequency among the N phases as the frequency of the triangular carrier, and use the calculated frequency to generate a common triangular carrier;

[0010] The PWM drive signal acquisition step compares the SVPWM modulation wave of each phase bridge arm switch tube with the common triangular carrier to obtain a PWM drive signal for controlling the on and off of each phase bridge arm switch tube.

[0011] Preferably, the SVPWM is a seven-segment SVPWM.

[0012] Furthermore, when N is equal to 3, the modulation wave acquisition step specifically includes the following steps:

[0013] Step 1: The first voltage signal representing the output voltage of the N-phase converter sampled by the voltage outer loop is compared with the reference signal of the voltage outer loop and then sent to the voltage outer loop PI controller to obtain the reference signal of the current inner loop;

[0014] Step 2: sampling the input voltage of each phase of the N-phase converter to obtain phase information, and sending the phase information to the DSP for rotating coordinate transformation of the N-phase current and voltage;

[0015] Step 3, the current inner loop samples the input current of each phase of the N-phase converter, obtains two-phase current information after N-phase rotation coordinate transformation, compares the two-phase current information with respective reference information, and then sends them to the current inner loop PI controller to obtain a first variation;

[0016] Step 4, performing N-phase rotation coordinate transformation on the input voltage of each phase of the N-phase converter to obtain two-phase voltage information;

[0017] Step 5: Add the values ​​of the d-axis and q-axis in the first variation to the values ​​of the d-axis and q-axis in the two-phase voltage information respectively and transform the two-phase rotating coordinates into the two-phase stationary coordinate system to obtain the voltage information uα in the two-phase stationary coordinate system. * and uβ * , which is used as the input end of the variable frequency SVPWM module, using uα * and uβ * The SVPWM modulation wave of the switch tube of each phase bridge arm is calculated.

[0018] Furthermore, the phase information is obtained by phase-locking the grid voltage using a digital controller.

[0019] Furthermore, when the two-phase current information is compared with respective reference information, the reference value of the q-axis is set to 0.

[0020] Furthermore, the condition for each phase bridge arm switch tube to achieve ZVS is that there is a negative current before each switch tube is turned on, ensuring that the parasitic capacitance of the switch tube that needs to be turned on is completely discharged.

[0021] As a second aspect of the present invention, the technical solution of the embodiment of the control device provided is as follows:

[0022] A control device is applied to an N-phase converter, wherein the N-phase converter comprises an N-phase LCL filter and an N-phase bridge circuit, wherein each phase filter in the N-phase LCL filter comprises a first filter inductor, a second filter inductor and a filter capacitor, wherein each phase bridge arm in the N-phase bridge circuit comprises an upper switch tube and a lower switch tube, wherein one end of the first filter inductor of each phase is connected to the input end of the corresponding phase of the N-phase converter, and the other end is connected to one end of the second filter inductor of the corresponding phase, and the other end of the second filter inductor of each phase is connected to the midpoint of the bridge arm of the corresponding phase, and the filter capacitor of each phase is connected to the midpoint of the filter inductor of the corresponding phase and the midpoint of the filter inductor of the next phase, wherein each bridge arm is connected in parallel to form the output end of the N-phase bridge circuit, and the driving signal of the upper switch tube and the lower switch tube of each bridge arm is a PWM complementary signal with a dead time, and the N-phase converter operates in a rectification and inversion state, wherein the control device adopts a variable frequency SVPWM modulation strategy, and the control device comprises the following units:

[0023] A modulation wave acquisition unit, which calculates the SVPWM modulation wave for controlling the on and off of the switch tubes of each phase bridge arm when the electrical parameter output by the N-phase converter reaches the expected value through a voltage outer loop and a current inner loop double closed-loop control;

[0024] The triangular carrier acquisition unit calculates the frequency required for each phase bridge arm switch to achieve ZVS by predicting the magnitude of the current pulsation of the second filter inductor of each phase, and compares the frequency of each phase, selects the smallest frequency among N phases as the frequency of the triangular carrier, and uses the calculated frequency to generate a common triangular carrier;

[0025] The PWM driving signal acquisition unit compares the SVPWM modulation wave of the bridge arm switch tube of each phase with the common triangle carrier to obtain a PWM driving signal for controlling the on and off of the bridge arm switch tube of each phase.

[0026] As a third aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows:

[0027] A switching power supply, comprising an N-phase converter, the N-phase converter comprising an N-phase LCL filter and an N-phase bridge circuit, each phase filter in the N-phase LCL filter comprising a first filter inductor, a second filter inductor and a filter capacitor, each phase bridge arm in the N-phase bridge circuit comprising an upper switch tube and a lower switch tube, one end of each phase first filter inductor is connected to the input end of the corresponding phase of the N-phase converter, and the other end is connected to one end of the corresponding phase second filter inductor, the other end of each phase second filter inductor is connected to the midpoint of the corresponding phase bridge arm, each phase filter capacitor is connected to the midpoint of the corresponding phase filter inductor and the midpoint of the next phase filter inductor, each bridge arm is connected in parallel to form the output end of the N-phase bridge circuit, the driving signal of the upper switch tube and the lower switch tube of each bridge arm is a PWM complementary signal with a dead time, and the N-phase converter operates in a rectification and inversion state, wherein: the switching power supply also includes the control device described in any one of the second aspects above.

[0028] Furthermore, the N-phase converter operates in a unity power factor state.

[0029] Furthermore, the N is 3.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The embodiments of the present invention predict the ripple current on the bridge arm side and then use a variable frequency SVPWM modulation strategy, so that no additional passive or active devices are required to achieve zero voltage turn-on of the switch tubes of each phase bridge arm of the N-phase converter, and ZVS can be achieved for the N-phase bridge arm at any time, keeping each phase working in the TCM mode, so that each bridge arm can naturally achieve soft switching, greatly reducing switching losses and improving product efficiency;

[0032] (2) The embodiments of the present invention use a variable frequency SVPWM modulation strategy by predicting the ripple current on the bridge arm side, thereby increasing the switching frequency. In addition, since the inductance value of the filter is very small, it is beneficial to reduce the volume and cost of the inductor, facilitate the planar design of the inductor, and reduce the overall volume of the three-phase converter, thereby increasing the power density.

[0033] (3) In the embodiment of the present invention, the smallest frequency among the N phases is selected as the frequency of the triangular carrier, and a common triangular carrier is generated using the calculated frequency. That is, the control device of the three-phase converter provided operates the first phase bridge arm, the second phase bridge arm and the third phase bridge arm at the same switching frequency, thereby greatly limiting the range of the converter switching frequency, so that the magnetic device and the EMI circuit can be conveniently designed, thereby reducing the cost of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a diagram for dividing three-phase voltage into six sectors;

[0035] Figure 2 The topology diagram of the three-phase converter used in the control method of the first embodiment of the present invention is as follows:

[0036] Figure 3 is a flow chart of a control method according to a first embodiment of the present invention;

[0037] Figure 4 is a flow chart of a control device according to a second embodiment of the present invention;

[0038] Figure 5 A specific control principle diagram of the switching power supply according to the third embodiment of the present invention;

[0039] Figure 6 This is a diagram showing the ripple current in the first sector of a switching power supply and a switch tube driving diagram according to the third embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the present invention and its beneficial effects are further described in detail below in combination with specific implementation methods and drawings of the specification, but the specific implementation methods of the present invention are not limited thereto. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0041] It should be noted that the terms "including" and "having" and any variations thereof described in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, the inclusion of a series of components, unit circuits, or control timings is not necessarily limited to those components, unit circuits, or control timings clearly listed, but may include components, unit circuits, or control timings that are not clearly listed or are inherent to these circuits. The embodiments in the present application and the features in the embodiments may be combined with each other without conflict.

[0042] In addition, the drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontroller devices.

[0043] First embodiment

[0044] The present embodiment improves a control method, which is applied to an N-phase converter. The N-phase converter includes an N-phase LCL filter and an N-phase bridge circuit. Each phase filter in the N-phase LCL filter includes a first filter inductor, a second filter inductor and a filter capacitor. Each phase bridge arm in the N-phase bridge circuit includes an upper switch tube and a lower switch tube. One end of the first filter inductor of each phase is connected to the input end of the corresponding phase of the N-phase converter, and the other end is connected to one end of the second filter inductor of the corresponding phase. The other end of the second filter inductor of each phase is connected to the midpoint of the corresponding phase bridge arm. The filter capacitor of each phase is connected to the midpoint of the filter inductor of the corresponding phase and the midpoint of the filter inductor of the next phase. Each bridge arm is connected in parallel to the output end of the N-phase bridge circuit. The driving signals of the upper switch tube and the lower switch tube of each bridge arm are PWM complementary signals with dead time. The N-phase converter operates in rectification and inversion states.

[0045] Figure 2The topology diagram of the three-phase converter applied by the control method of the first embodiment of the present invention is shown, that is, N is 3, and the three-phase converter includes a three-phase LCL filter and a three-phase bridge circuit; the a-phase LCL filter includes a first filter inductor La1, a second filter inductor La2 and a filter capacitor Ca1, the b-phase LCL filter includes a first filter inductor Lb1, a second filter inductor Lb2 and a filter capacitor Cb1, and the c-phase LCL filter includes a first filter inductor Lc1, a second filter inductor Lc2 and a filter capacitor Cc1; the a-phase bridge arm includes an upper switch tube Q1 and a lower switch tube Q2, the b-phase bridge arm includes an upper switch tube Q3 and a lower switch tube Q4, and the c-phase bridge arm includes an upper switch tube Q5 and a lower switch tube Q6; the bus capacitor C connected in parallel with each phase bridge arm is the output voltage filter capacitor of the three-phase converter.

[0046] Figure 3 This is a flow chart of the control method of the first embodiment of the present invention, see Figure 3 , wherein: the control method adopts variable frequency SVPWM modulation strategy, including the following steps:

[0047] Modulation wave acquisition step S100, calculating the SVPWM modulation wave for controlling the on and off of the switch tubes of each phase bridge arm when the electrical parameters output by the N-phase converter reach the expected value through the voltage outer loop and the current inner loop double closed-loop control;

[0048] The triangular carrier acquisition step S200 calculates the frequency required for each phase bridge arm switch to achieve ZVS by predicting the magnitude of the current pulsation of the second filter inductor of each phase, and compares the frequency of each phase, selects the smallest frequency among the N phases as the frequency of the triangular carrier, and uses the calculated frequency to generate a common triangular carrier;

[0049] In the PWM drive signal acquisition step S300, the SVPWM modulation wave of the switch tube of each phase bridge arm is compared with the common triangle carrier to obtain a PWM drive signal for controlling the on and off of the switch tube of each phase bridge arm.

[0050] The control method of this embodiment predicts the ripple current on the bridge arm side and then uses a variable frequency SVPWM modulation strategy, so that there is no need to add additional passive or active devices to achieve zero voltage turn-on of the switch tubes of each phase bridge arm of the N-phase converter, and ZVS can be achieved for the N-phase bridge arm at any time, keeping each phase working in the TCM mode, so that each bridge arm can naturally achieve soft switching, greatly reducing switching losses and improving product efficiency;

[0051] The control method of this embodiment can increase the switching frequency by predicting the ripple current on the bridge arm side and then using the variable frequency SVPWM modulation strategy. In addition, since the inductance value of the filter is very small, it is beneficial to reduce the volume and cost of the inductor, facilitate the planar design of the inductor, and reduce the overall volume of the three-phase converter, thereby improving the power density.

[0052] The control method of this embodiment selects the smallest frequency among the N phases as the frequency of the triangular carrier, and uses the calculated frequency to generate a common triangular carrier. That is, the control device of the three-phase converter provided operates the first phase bridge arm, the second phase bridge arm and the third phase bridge arm at the same switching frequency, which greatly limits the range of the converter switching frequency, so that the magnetic device and the EMI circuit can be conveniently designed, thereby reducing the cost of the product.

[0053] SVPWM is called space vector pulse width modulation in Chinese, including five-segment and seven-segment specific modulation schemes. The present invention prefers SVPWM as seven-segment SVPWM. Therefore, there is no need to decouple the N-phase converter in structure, nor to use control methods for phase decoupling. The traditional SVPWM modulation method can achieve ZVS of the bridge arm switch tubes of each phase of the N-phase converter.

[0054] When N is equal to 3, a specific implementation of the modulation wave acquisition step includes the following steps:

[0055] Step 1: a first voltage signal representing the output voltage of the N-phase converter sampled by the voltage outer loop is compared with a reference signal of the voltage outer loop and then sent to a voltage outer loop PI controller to obtain a reference signal of the current inner loop;

[0056] Step 2: The input voltage of each phase of the N-phase converter is sampled to obtain phase information, and the phase information is sent to the DSP for the rotation coordinate transformation of the N-phase current and voltage;

[0057] Step 3, the current inner loop samples the input current of each phase of the N-phase converter, obtains two-phase current information after N-phase rotation coordinate transformation, compares the two-phase current information with their respective reference information, and then sends them to the current inner loop PI controller to obtain a first variation;

[0058] Step 4, the input voltage of each phase of the N-phase converter is transformed by N-phase rotation coordinates to obtain two-phase voltage information;

[0059] Step 5: Add the values ​​of the d-axis and q-axis in the first variation to the values ​​of the d-axis and q-axis in the two-phase voltage information respectively and transform the two-phase rotating coordinates to the two-phase stationary coordinate system to obtain the voltage information uα in the two-phase stationary coordinate system. * and uβ * , which is used as the input end of the variable frequency SVPWM module, using uα* and uβ * Calculate the SVPWM modulation wave of each phase bridge arm switch tube.

[0060] In order to enable the specific implementation of the above-mentioned modulation wave acquisition step to be smooth and real-time, the specific control principle given in the third embodiment is introduced in more detail, and the modulation wave acquisition step therein is consistent with the specific implementation of the above-mentioned modulation wave acquisition step.

[0061] Furthermore, a digital controller is used to phase-lock the grid voltage to obtain phase information.

[0062] Further, when the two-phase current information is compared with the respective reference information, the reference value of the q-axis is set to 0.

[0063] Furthermore, the condition for each phase bridge arm switch tube to achieve ZVS is that there is a negative current before each switch tube is turned on, ensuring that the parasitic capacitance of the switch tube that needs to be turned on is completely discharged.

[0064] Second embodiment

[0065] The present embodiment provides a control device, which is applied to an N-phase converter. The N-phase converter includes an N-phase LCL filter and an N-phase bridge circuit. Each phase filter in the N-phase LCL filter includes a first filter inductor, a second filter inductor and a filter capacitor. Each phase bridge arm in the N-phase bridge circuit includes an upper switch tube and a lower switch tube. One end of the first filter inductor of each phase is connected to the input end of the corresponding phase of the N-phase converter, and the other end is connected to one end of the second filter inductor of the corresponding phase. The other end of the second filter inductor of each phase is connected to the midpoint of the bridge arm of the corresponding phase. The filter capacitor of each phase is connected to the midpoint of the filter inductor of the corresponding phase and the midpoint of the filter inductor of the next phase. Each bridge arm is connected in parallel to the output end of the N-phase bridge circuit. The driving signals of the upper switch tube and the lower switch tube of each bridge arm are PWM complementary signals with dead time. The N-phase converter works in rectification and inversion states. The control device adopts a variable frequency SVPWM modulation strategy. Figure 4 This is a flow chart of the control device of the second embodiment of the present invention, see Figure 4 , wherein the control device comprises the following units:

[0066] The modulation wave acquisition unit 100 calculates the SVPWM modulation wave for controlling the on and off of the switch tubes of each phase bridge arm when the electrical parameters output by the N-phase converter reach the expected value through the voltage outer loop and the current inner loop double closed-loop control;

[0067] The triangular carrier acquisition unit 200 calculates the frequency required for each phase bridge arm switch tube to achieve ZVS by predicting the magnitude of the current pulsation of the second filter inductor of each phase, and compares the frequency of each phase, selects the smallest frequency among N phases as the frequency of the triangular carrier, and uses the calculated frequency to generate a common triangular carrier;

[0068] The PWM driving signal acquisition unit 300 compares the SVPWM modulation wave of the bridge arm switch tube of each phase with the common triangle carrier to obtain a PWM driving signal for controlling the on and off of the bridge arm switch tube of each phase.

[0069] The technical means adopted by the control device of this embodiment are consistent with the control method of the first embodiment, and the beneficial effects are the same, so they are not repeated; 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 this embodiment, and this embodiment will not describe them one by one.

[0070] Third embodiment

[0071] The present embodiment provides a switching power supply, which includes an N-phase converter, the N-phase converter includes an N-phase LCL filter and an N-phase bridge circuit, each phase filter in the N-phase LCL filter includes a first filter inductor, a second filter inductor and a filter capacitor, each phase bridge arm in the N-phase bridge circuit includes an upper switch tube and a lower switch tube, one end of the first filter inductor of each phase is connected to the input end of the corresponding phase of the N-phase converter, and the other end is connected to one end of the second filter inductor of the corresponding phase, the other end of the second filter inductor of each phase is connected to the midpoint of the corresponding phase bridge arm, the filter capacitor of each phase is connected to the midpoint of the filter inductor of the corresponding phase and the midpoint of the filter inductor of the next phase, each bridge arm is connected in parallel to the output end of the N-phase bridge circuit, the driving signal of the upper switch tube and the lower switch tube of each bridge arm is a PWM complementary signal with a dead time, and the N-phase converter works in a rectification and inversion state, wherein: the switching power supply also includes any one of the control devices in the above-mentioned second embodiment.

[0072] Furthermore, the N-phase converter operates under a unity power factor state.

[0073] Furthermore, N is 3.

[0074] Figure 5 A specific control principle diagram of the switching power supply of the third embodiment of the present invention, wherein the N-phase converter is Figure 2 The sound line converter and the control device give a specific principle block diagram. The working principle of the control device is as follows:

[0075] Step 1: Sample the output voltage Vdc as the inverting input of the voltage comparator, and set the output port DC voltage reference value Vdc * As the in-phase input of the voltage comparator, it is sent to the voltage outer loop PI controller for comparison to obtain the reference value ID of the current inner loop * .

[0076] Step 2: In order to make the reactive power 0, set the reference value of the q axis to 0, that is, iq *Equal to 0, sample the three-phase grid voltage Va, Vb, Vc to obtain phase information, and then sample the current ia, ib, ic of the second filter inductor of each phase through the current sensor, and send the collected phase information and three-phase current information to DSP for rotating coordinate transformation to obtain two-phase current information id and iq.

[0077] Step 3: Use id and iq as the inverting input of the voltage comparator, id * , iq * As the in-phase input terminal of the voltage comparator, the comparison result is sent to the current inner loop PI controller. The output results of the PI controller are △ud and △uq. The collected three-phase voltages Va, Vb, and Vc are sent to the DSP controller to transform the voltage information of the two-phase stationary coordinate system through the two-phase rotating coordinate system to obtain the two-phase voltage information ud and uq, and add △ud and ud, and add △uq and uq. After the two-phase rotating coordinate system, the voltage information uα in the two-phase stationary coordinate system is obtained. * and uβ * ,uα * and uβ * As the input port of variable frequency SVPWM, the modulation wave of each phase is calculated;

[0078] Step 4: Calculate the minimum switching frequency of each phase in each sector. Take the first sector as an example to illustrate the conduction conditions for each switch tube to achieve ZVS. The specific drive waveform and current ripple are as follows: Figure 6 .

[0079] See also Figure 6 , where Q1 is the driving waveform of the upper switch tube of phase a, Q3 is the driving waveform of the upper switch tube of phase b, and Q5 is the driving waveform of the upper switch tube of phase c. When the driving signal is 1, the upper switch tube is turned on and the lower switch tube is turned off; when the driving signal is 0, the upper switch tube is turned off and the lower switch tube is turned on. ia, ib, and ic are the second filter inductor ripple currents of phases a, b, and c respectively. The current flowing through the upper switch tube of phase a at time t1 must be greater than 0, and the current flowing through the lower switch tube of phase a at time t7 must be less than 0. , the purpose is to achieve zero voltage turn-on of the upper and lower switches of phase a, the current flowing through the upper switch of phase b at time t2 needs to be greater than 0, and the current flowing through the lower switch of phase b at time t6 needs to be less than 0, the purpose is to achieve zero voltage turn-on of the upper and lower switches of phase b, the current flowing through the upper switch of phase c needs to be greater than 0 at time t3, and the current flowing through the lower switch of phase c at time t5 needs to be less than 0, the purpose is to achieve zero voltage turn-on of the upper and lower switches of phase c, the conditions for driving each phase to achieve ZVS at different times are:

[0080]

[0081] Combining the three equations, we can get:

[0082]

[0083] According to the above formula, the frequency required for each phase bridge arm switch to achieve ZVS is:

[0084]

[0085] In the above formula: f represents the frequency required for a certain phase bridge arm switch to achieve ZVS; i represents the input current of a certain phase; V represents the input voltage of a certain phase; V o represents the output voltage of the three-phase converter; L represents the inductance value of the second filter inductor of a certain phase; I bias In order to achieve the bias current of soft switching, its size is determined by the equivalent capacitance. Specifically, Ibias>2Ceq*Vds / Td, where Ceq is the equivalent capacitance, Vds is the voltage on the equivalent capacitance before the switch is turned on, Td is the set dead time, and I bias The value can also be determined based on actual experience. In order to meet the requirements of dynamic load switching, soft switching is still implemented. The value of Ibias is generally 1.5-2A; m represents the SVPWM modulation wave of a certain phase, which is calculated using a digital controller; the additional subscripts xyz added to each parameter correspond to the three phases abc in different sectors.

[0086] The calculation frequency of other sectors is consistent with that of the first sector and will not be described here.

[0087] Step 5: Specifically, compare the switching frequencies required for each phase bridge arm switch tube in each sector to achieve ZVS, select the switching frequency with a smaller value as the common switching frequency of the three phases, and use the same switching frequency to generate a common triangular carrier. The purpose is to unify the switching frequency, thereby increasing the frequency and reducing the volume of the inductor and output capacitor.

[0088] Here, the sector where the minimum frequency of the frequency required for each phase bridge arm switch tube in each sector to achieve ZVS is given, as shown in the following table:

[0089]

[0090] Step 6: Specifically, the minimum frequency calculated above is sent to the variable frequency carrier generator, and the reciprocal of the frequency is used as the period of the variable frequency carrier generator. The output of the variable frequency carrier generator is a triangular wave, and the calculated frequency is the frequency that changes in real time.

[0091] Step 7: Specifically, the triangular carrier is used as the inverting input of the voltage comparator, and the non-inverting input of the voltage comparator is the modulation wave mx calculated by DSP. The purpose is to compare the modulation wave with the carrier module to obtain the drive of the three-phase upper tubes a, b, and c. The upper tubes can be MOS tubes or IGBTs. The SVPWM modulation method does not require decoupling of the three phases, does not require changing the topology of the three-phase converter, and the harmonics generated by the SVPWM are smaller than those of other modulation strategies.

[0092] The N-phase converter in the switching power supply of this embodiment is controlled by any one of the control devices in the above-mentioned second embodiment, so that the N-phase converter can operate in the TCM mode without phase-to-phase decoupling. Each sector can achieve soft switching through variable frequency, and there is no need to clamp each phase. The N-phase switch tube can achieve zero voltage switching, thereby improving the efficiency of the N-phase converter. The frequency is calculated by the current ripple prediction method, which increases the switching frequency, reduces the volume of the N-phase converter, and thus improves the power density. The switching power supply of this embodiment can achieve the effect of reducing inductance cost and optimizing EMI while achieving zero voltage switching.

[0093] It should be understood that, although specific embodiments of the present invention are described to help better understand and appreciate the present invention, there are other embodiments equivalent to the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The above embodiments are given as examples in a graphical and non-limiting manner, so any modification or replacement of all or part of the technical features in the technical solution recorded in the embodiment without departing from the spirit or essence of the present invention should be deemed to be included in the scope of the claims.

Claims

1. A control method, applied to an N-phase converter, wherein the N-phase converter comprises an N-phase LCL filter and an N-phase bridge circuit, wherein each phase filter in the N-phase LCL filter comprises a first filter inductor, a second filter inductor and a filter capacitor, wherein each phase bridge arm in the N-phase bridge circuit comprises an upper switch tube and a lower switch tube, wherein one end of the first filter inductor of each phase is connected to the input end of the corresponding phase of the N-phase converter, and the other end is connected to one end of the second filter inductor of the corresponding phase, and the other end of the second filter inductor of each phase is connected to the midpoint of the corresponding phase bridge arm, and the filter capacitor of each phase is connected to the midpoint of the filter inductor of the corresponding phase and the midpoint of the filter inductor of the next phase, wherein each bridge arm is connected in parallel to form the output end of the N-phase bridge circuit, and the driving signals of the upper switch tube and the lower switch tube of each bridge arm are PWM complementary signals with dead time, wherein the N-phase converter operates in rectification and inversion states, characterized in that: The control method adopts a variable frequency SVPWM modulation strategy, including the following steps: A modulation wave acquisition step, calculating the SVPWM modulation wave for controlling the on and off of the switch tubes of each phase bridge arm when the electrical parameters output by the N-phase converter reach the expected value through a voltage outer loop and a current inner loop double closed-loop control; The triangular carrier acquisition step is to calculate the frequency required for each phase bridge arm switch tube to achieve ZVS by predicting the magnitude of the current pulsation of the second filter inductor of each phase, and compare the frequencies of each phase, select the smallest frequency among N phases as the frequency of the triangular carrier, and use the calculated frequency to generate a common triangular carrier; The PWM drive signal acquisition step compares the SVPWM modulation wave of each phase bridge arm switch tube with the common triangular carrier to obtain a PWM drive signal for controlling the on and off of each phase bridge arm switch tube.

2. The control method according to claim 1, characterized in that: The SVPWM is a seven-segment SVPWM.

3. The control method according to claim 1, characterized in that: When N is equal to 3, the modulation wave acquisition step specifically includes the following steps: Step 1: The first voltage signal representing the output voltage of the N-phase converter sampled by the voltage outer loop is compared with the reference signal of the voltage outer loop and then sent to the voltage outer loop PI controller to obtain the reference signal of the current inner loop; Step 2: sampling the input voltage of each phase of the N-phase converter to obtain phase information, and sending the phase information to the DSP for rotating coordinate transformation of the N-phase current and voltage; Step 3, the current inner loop samples the input current of each phase of the N-phase converter, obtains two-phase current information after N-phase rotation coordinate transformation, compares the two-phase current information with respective reference information, and then sends them to the current inner loop PI controller to obtain a first variation; Step 4, performing N-phase rotation coordinate transformation on the input voltage of each phase of the N-phase converter to obtain two-phase voltage information; Step 5: Add the values ​​of the d-axis and q-axis in the first variation to the values ​​of the d-axis and q-axis in the two-phase voltage information respectively and transform the two-phase rotating coordinates into the two-phase stationary coordinate system to obtain the voltage information uα in the two-phase stationary coordinate system. * and uβ * , which is used as the input end of the variable frequency SVPWM module, using uα * and uβ * The SVPWM modulation wave of the switch tube of each phase bridge arm is calculated.

4. The control method according to claim 3, characterized in that: The phase information is obtained by phase-locking the grid voltage using a digital controller.

5. The control method according to claim 3, characterized in that: When the two-phase current information is compared with the respective reference information, the reference value of the q-axis is set to 0.

6. The control method according to claim 1, characterized in that: The condition for each phase bridge arm switch tube to achieve ZVS is that there is a negative current before each switch tube is turned on, ensuring that the parasitic capacitance of the switch tube that needs to be turned on is completely discharged.

7. A control device, applied to an N-phase converter, the N-phase converter includes an N-phase LCL filter and an N-phase bridge circuit, each phase filter in the N-phase LCL filter includes a first filter inductor, a second filter inductor and a filter capacitor, each phase bridge arm in the N-phase bridge circuit includes an upper switch tube and a lower switch tube, one end of the first filter inductor of each phase is connected to the input end of the corresponding phase of the N-phase converter, and the other end is connected to one end of the second filter inductor of the corresponding phase, the other end of the second filter inductor of each phase is connected to the midpoint of the corresponding phase bridge arm, each phase filter capacitor is connected to the midpoint of the corresponding phase filter inductor and the midpoint of the next phase filter inductor, each bridge arm is connected in parallel to the output end of the N-phase bridge circuit, the driving signal of the upper switch tube and the lower switch tube of each bridge arm is a PWM complementary signal with a dead time, the N-phase converter works in rectification and inversion state, characterized in that The control device adopts variable frequency SVPWM modulation strategy, and the control device includes the following units: A modulation wave acquisition unit, which calculates the SVPWM modulation wave for controlling the on and off of the switch tubes of each phase bridge arm when the electrical parameters output by the N-phase converter reach the expected value through a voltage outer loop and a current inner loop double closed-loop control; The triangular carrier acquisition unit calculates the frequency required for each phase bridge arm switch to achieve ZVS by predicting the magnitude of the current pulsation of the second filter inductor of each phase, and compares the frequency of each phase, selects the smallest frequency among N phases as the frequency of the triangular carrier, and uses the calculated frequency to generate a common triangular carrier; The PWM driving signal acquisition unit compares the SVPWM modulation wave of each phase bridge arm switch tube with the common triangle carrier to obtain a PWM driving signal for controlling the on and off of each phase bridge arm switch tube.

8. A switching power supply, comprising an N-phase converter, the N-phase converter comprising an N-phase LCL filter and an N-phase bridge circuit, each phase filter in the N-phase LCL filter comprising a first filter inductor, a second filter inductor and a filter capacitor, each phase bridge arm in the N-phase bridge circuit comprising an upper switch tube and a lower switch tube, one end of the first filter inductor of each phase is connected to the input end of the corresponding phase of the N-phase converter, and the other end is connected to one end of the second filter inductor of the corresponding phase, the other end of the second filter inductor of each phase is connected to the midpoint of the corresponding phase bridge arm, the filter capacitor of each phase is connected to the midpoint of the filter inductor of the corresponding phase and the midpoint of the filter inductor of the next phase, each bridge arm is connected in parallel to the output end of the N-phase bridge circuit, the driving signal of the upper switch tube and the lower switch tube of each bridge arm is a PWM complementary signal with a dead time, the N-phase converter works in a rectification and inversion state, characterized in that: The switching power supply further comprises the control device as claimed in claim 7.

9. The switching power supply according to claim 8, characterized in that: The N-phase converter operates under a unity power factor state.

10. The switching power supply according to claim 8 or 9, characterized in that: The N is 3.

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