Modulation method and system of four-switch Buck-Boost converter

Abstract

The invention discloses a modulation method of a four-switch Buck-Boost converter. The modulation method comprises the following steps: acquiring an output voltage; calculating error voltage; when the output power is larger than or equal to the preset power, the converter works in a first working mode, switches in the converter are turned on according to a first switch time sequence, and when the input voltage is larger than or equal to the output voltage, target inductive current is generated to enable a third switch to be turned on according to zero voltage; when the input voltage is smaller than or equal to the output voltage, target inductive current is generated to turn on the second switch at zero voltage; and when the output power is smaller than the preset power, the converter works in a second working mode, the switches in the converter are turned on according to a second switch time sequence, and target inductive current is generated, so that the second switch and the third switch are turned on at zero voltage. By means of the modulation method, the effective value and the peak value of the target inductive current are smaller than those of traditional modulation, and the efficiency of the converter under the light load is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and particularly relates to a modulation method and system for a four-switch Buck-Boost converter. Background Art

[0002] In application scenarios such as renewable energy power generation systems, residential energy storage systems, and electric vehicles, bidirectional DC-DC is used to connect a DC bus to an energy storage unit (such as a battery or a supercapacitor) to achieve optimal energy allocation. The four-switch Buck-Boost converter has the advantages of step-up and step-down, the same polarity of input and output, few passive devices, and bidirectional power transmission, and is suitable for application scenarios with a wide voltage range and bidirectional power transfer.

[0003] Since new energy power generation systems are vulnerable to external factors such as light and temperature and have the characteristics of large randomness and intermittency, the four-switch Buck-Boost converter, as a connection link between the new energy power generation end and the energy storage unit, often operates under light load conditions.

[0004] However, under traditional quadrilateral modulation, the four-switch Buck-Boost converter has a long inductor negative current freewheeling section under light load, which causes high conduction losses and affects efficiency. This shortcoming limits the application of the four-switch Buck-Boost converter in scenarios with a wide load range. Summary of the Invention

[0005] Therefore, the present invention proposes a modulation method and system for a four-switch Buck-Boost converter. By generating a target inductor current, the switches in the converter are turned on with zero voltage. Compared with the traditional modulation method, when the switches are turned on with the target inductor current, both the effective value and the peak value of the inductor current will decrease, improving the efficiency under light load.

[0006] To achieve the above object, the present invention provides a modulation method for a four-switch Buck-Boost converter. The four-switch Buck-Boost converter includes a power input terminal, a voltage output terminal, and four switches: a first switch, a second switch, a third switch, and a fourth switch. The input terminal of the first switch is connected to the positive pole of the input power supply, the output terminal of the second switch is connected to the negative pole of the power input terminal, the output terminal of the fourth switch is connected to the negative pole of the voltage output terminal, the input terminal of the third switch is connected to the positive pole of the voltage output terminal, and an inductor is connected between the connection point of the first switch and the second switch and the connection point of the third switch and the fourth switch. The modulation method includes:

[0007] Obtain the output voltage of the Buck-Boost converter, and calculate an error voltage according to the output voltage and a reference voltage;

[0008] Calculate the output power according to the error voltage, and compare the output power with a preset power, where:

[0009] When the output power is greater than or equal to the preset power, the Buck - Boost converter operates in a first operating mode, and the switches in the Buck - Boost converter are turned on in a first switching sequence. When the input voltage is greater than or equal to the output voltage, a target inductor current is generated such that the third switch is turned on with zero voltage. When the input voltage is less than or equal to the output voltage, a target inductor current is generated such that the second switch is turned on with zero voltage; and

[0010] When the output power is less than the preset power, the Buck - Boost converter operates in a second operating mode, and the switches in the Buck - Boost converter are turned on in a second switching sequence, and a target inductor current is generated such that the second switch and the third switch are turned on with zero voltage.

[0011] Preferably, the method for determining the operating mode of the Buck - Boost converter according to the output power is as follows:

[0012]

[0013] where, T s is the switching period, I zvs represents the target inductor current for zero - voltage turn - on of the switch, and its calculation method is:

[0014]

[0015] where, t d is the dead - time of the four - switch Buck - Boost converter, represents the preset power, C oss is the parasitic capacitance of the switch.

[0016] Preferably, the first switching sequence in the first operating mode includes: the first switch and the fourth switch are turned on, the first switch and the third switch are turned on, the second switch and the third switch are turned on, and the first switch, the second switch, the third switch, and the fourth switch are all turned off; the second switching sequence in the second operating mode includes: the first switch and the fourth switch are turned on; the second switch and the third switch are turned on, and the first switch, the second switch, the third switch, and the fourth switch are all turned off.

[0017] Preferably, when the Buck - Boost converter operates in the first operating mode, the switch includes six operating stages in one switching period:

[0018] At the starting moment of the first stage, the first switch and the fourth switch are turned on with zero current, and in the first stage, the first switch and the fourth switch are turned on;

[0019] Turn off the fourth switch at the starting moment of the second stage. In the second stage, the third switch and the fourth switch are in the dead time, and the junction capacitance of the third switch discharges.

[0020] At the starting moment of the third stage, the third switch turns on with zero voltage. In the third stage, the first switch and the third switch are on.

[0021] Turn off the first switch at the starting moment of the fourth stage. In the fourth stage, the first switch and the second switch are in the dead time, and the junction capacitance of the second switch discharges.

[0022] At the starting moment of the fifth stage, the second switch turns on with zero voltage. In the fifth stage, the second switch and the third switch are on.

[0023] At the starting moment of the sixth stage, the second switch and the third switch turn off with zero current. In the sixth stage, all switches are off, the inductor current is zero, and the voltage across the inductor is zero.

[0024] Preferably, the switch-on time in the first switch timing is as follows:

[0025] When the input voltage is less than the output voltage,

[0026]

[0027] When the input voltage is greater than the output voltage,

[0028]

[0029] where T 1A is the duration of the first stage and the second stage in the first switch timing, T 2A is the duration of the third stage and the fourth stage, T 3A is the duration of the fifth stage, T 4A is the duration of the sixth stage, V in is the input voltage of the four-switch Buck-Boost converter; V o is the output voltage of the four-switch Buck-Boost converter, L is the inductance value, P is the output power, T s is the switching period.

[0030] Preferably, there are five working stages in the second switch timing in the second working mode, which are respectively:

[0031] At the starting moment of the first stage, the first switch and the fourth switch turn on with zero current. In the first stage, the first switch and the fourth switch are on.

[0032] Turn off the first switch and the fourth switch at the starting moment of the second stage. The junction capacitances of the second switch and the third switch discharge.

[0033] At the starting moment of the third stage, the second switch and the third switch are turned on with zero voltage, and the second switch and the third switch are turned on during the third stage;

[0034] At the starting moment of the fourth stage, the second switch and the third switch are turned off, and during the fourth stage, the inductor current flows reversely and freewheels through the body diodes of the first switch and the fourth switch;

[0035] At the starting moment of the fifth stage, the inductor current is cut off when it passes through zero, and the body diodes of the first switch and the fourth switch achieve zero-current turn-off. During the fifth stage, the inductor current is zero and the voltage across the inductor is zero.

[0036] Preferably, the switch-on time in the second switch timing is as follows:

[0037]

[0038] where T 1B is the duration of the first stage and the second stage in the second switch timing, T 2B is the duration of the third stage, T 3B is the duration of the fourth stage, T 4B is the duration of the fifth stage, V in is the input voltage of the four-switch Buck-Boost converter, V o is the output voltage of the four-switch Buck-Boost converter, L is the inductance value, I zvs represents the target inductor current for the switch to turn on with zero voltage, and P is the output power.

[0039] The present invention discloses a modulation system for a four-switch Buck-Boost converter, including the above-mentioned Buck-Boost converter, a calculation module, a controller, a mode selection module, a look-up table module, and a PWM module. The calculation module is used to calculate the difference between the output voltage and the reference voltage of the Buck-Boost converter;

[0040] The controller is used to calculate the output power of the Buck-Boost converter;

[0041] The mode selection module is used to determine the working mode of the Buck-Boost converter according to the output power. When the output power is greater than or equal to the preset power, the Buck-Boost converter operates in the first working mode. When the output power is less than the preset power, the Buck-Boost converter operates in the second working mode;

[0042] A look-up table module for storing information on the turn-on and turn-off of switches in the Buck-Boost converter during the first switching sequence in the first operating mode, and information on the turn-on and turn-off of switches in the Buck-Boost converter during the second switching sequence in the second operating mode; and

[0043] A PWM module that outputs a drive signal for the switch according to the operating mode of the Buck-Boost converter to drive the Buck-Boost converter.

[0044] Preferably, in the first switching sequence, the operating stages of the first switch - fourth switch include:

[0045] At the start of the first stage, the first switch and the fourth switch are turned on with zero current, and the first switch and the fourth switch are on during the first stage;

[0046] At the start of the second stage, the fourth switch is turned off, and during the second stage, the third switch and the fourth switch are in a dead time, and the junction capacitance of the third switch discharges;

[0047] At the start of the third stage, the third switch is turned on with zero voltage, and during the third stage, the first switch and the third switch are on;

[0048] At the start of the fourth stage, the first switch is turned off, and during the fourth stage, the first switch and the second switch are in a dead time, and the junction capacitance of the second switch discharges;

[0049] At the start of the fifth stage, the second switch is turned on with zero voltage, and during the fifth stage, the second switch and the third switch are on;

[0050] At the start of the sixth stage, the second switch and the third switch are turned off with zero current, and during the sixth stage, all switches are off, the inductor current remains zero, and the voltage across the inductor is zero;

[0051] Among them, the turn-on time of the first switch - fourth switch can be calculated by the following formula:

[0052] When the input voltage is less than the output voltage,

[0053]

[0054] When the input voltage is greater than the output voltage,

[0055]

[0056] Where T 1A is the duration of the first stage and the second stage in the first switching sequence, T 2Ais the duration of the third and fourth phases, T 3A is the duration of the fifth phase, T 4A is the duration of the sixth phase, V in is the input voltage of the four-switch Buck-Boost converter; V o is the output voltage of the four-switch Buck-Boost converter, L is the inductance value, P is the output power, T s is the switching period.

[0057] Preferably, in the second switching timing, the operating phases of the first switch - fourth switch include:

[0058] At the starting moment of the first phase, the first switch and the fourth switch are turned on with zero current, and the first switch and the fourth switch are on during the first phase;

[0059] At the starting moment of the second phase, the first switch and the fourth switch are turned off, and the junction capacitors of the second switch and the third switch discharge;

[0060] At the starting moment of the third phase, the second switch and the third switch are turned on with zero voltage, and the second switch and the third switch remain on during the third phase;

[0061] At the starting moment of the fourth phase, the second switch and the third switch are turned off, and during the fourth phase, the inductor current flows reversely and continues to flow through the body diodes of the first switch and the fourth switch;

[0062] At the starting moment of the fifth phase, the inductor current becomes zero and cuts off, and the body diodes of the first switch and the fourth switch achieve zero-current turn-off. During the fifth phase, the inductor current remains zero and the voltage across the inductor is zero;

[0063] Among them, the turn-on time of the first switch - fourth switch can be calculated by the following formula:

[0064]

[0065] where T 1B is the duration of the first and second phases in the second switching timing, T 2B is the duration of the third phase, T 3B is the duration of the fourth phase, T 4B is the duration of the fifth phase, V in is the input voltage of the four-switch Buck-Boost converter; V o is the output voltage of the four-switch Buck-Boost converter, L is the inductance value, I zvs represents the target inductor current for zero-voltage turn-on of the switch, and P is the output power.

[0066] Generally speaking, through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0067] In the traditional quadrilateral modulation method, there is a long inductive negative current freewheeling section under light load conditions, resulting in a relatively high effective value of the inductive current, causing a large conduction loss and affecting the efficiency. While using the modulation method of the present invention, by generating the target inductive current for zero-voltage turn-on of the switch, the effective value of the inductive current is greatly reduced on the premise of realizing soft switching of all switches, thus optimizing the efficiency.

[0068] Therefore, the present invention conforms to the development trend of high efficiency and high power density in power electronics and is applicable to application scenarios with wide input voltage and wide load range. Description of the Drawings

[0069] Figure 1 FIG. is a topology diagram of a four-switch Buck-Boost converter provided according to an embodiment of the present invention;

[0070] Figure 2 FIG. is a waveform diagram of two operating modes under an optimized modulation method of a four-switch Buck-Boost converter provided according to an embodiment of the present invention;

[0071] Figures 3a - 3b FIG. is a waveform diagram of the inductive current of a four-switch Buck-Boost converter under different loads provided according to an embodiment of the present invention;

[0072] Figures 4a - 4b FIG. is a comparison diagram of the effective values of the inductive currents of the modulation of a four-switch Buck-Boost converter and the traditional modulation provided according to an embodiment of the present invention;

[0073] Figures 5a - 5c FIG. is a waveform diagram of the simulation results under the modulation method of a four-switch Buck-Boost converter provided according to an embodiment of the present invention.

[0074] Figure 6 FIG. is a control strategy diagram of a modulation system of a four-switch Buck-Boost converter provided according to an embodiment of the present invention. Detailed Embodiments

[0075] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0076] In the present invention, terms such as "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence.

[0077] Generally, the control schemes of traditional four-switch Buck-Boost converters can be divided into three operating modes: Buck, Buck-Boost, and Boost. Among them, as Figure 1 shown, in the Buck mode: S3 is kept on, S4 is kept off, and S1 and S2 are alternately turned on; in the Buck-Boost mode: S1 and S2 are alternately turned on, and S3 and S4 are alternately turned on; in the Boost mode: S1 is kept on, S2 is kept off, and S3 and S4 are alternately turned on. In each cycle, the circuit operates in only one operating mode. When the input voltage is greater than the desired output voltage, the circuit operates in the Buck mode; when the input voltage is close to the desired output voltage, the circuit operates in the Buck-Boost mode; when the input voltage is less than the desired output voltage, the circuit operates in the Boost mode.

[0078] In addition, the four-switch Buck-Boost converter has the characteristic of flexible control strategies, and various pulse width modulation (PWM) strategies can be combined by the four MOS transistors S1, S2, S3, and S4.

[0079] The present invention discloses a modulation method for a four-switch Buck-Boost converter, which enables zero-voltage or zero-current turn-on of all switches and zero-current turn-off of half of the switches under light load conditions, aiming to reduce the switch turn-on loss and the current stress of the switching devices, thereby improving the efficiency.

[0080] Embodiment 1:

[0081] The present invention discloses a modulation method for a four-switch Buck-Boost converter. The modulation method includes: obtaining the output voltage of the Buck-Boost converter and calculating an error voltage based on the output voltage and a reference voltage; calculating the output power of the Buck-Boost converter according to the error voltage and comparing the output power with a preset power. When the output power is greater than or equal to the preset power, the Buck-Boost converter operates in a first operating mode, and the switches in the Buck-Boost converter are turned on in a first switching sequence. When the input voltage is greater than or equal to the output voltage, a target inductor current is generated so that the third switch S3 is turned on with zero voltage. When the input voltage is less than or equal to the output voltage, a target inductor current is generated so that the second switch S2 is turned on with zero voltage; and when the output power is less than the preset power, the Buck-Boost converter operates in a second operating mode, and the switches in the Buck-Boost converter are turned on in a second switching sequence, generating a target inductor current so that the second switch S2 and the third switch S3 are turned on with zero voltage.

[0082] Wherein, Figure 1 Fig. is the topology diagram of the four-switch Buck-Boost converter in the optimized modulation method in Embodiment 1. As Figure 1 shown, it includes: an input voltage V in connected to both ends of a filter capacitor C in and an output voltage V o drawn from both ends of the filter capacitor C o The first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are connected in a bridge configuration, hereinafter simply referred to as S1, S2, S3, and S4. Among them, S1 and S2 form a half-bridge, and S3 and S4 form another half-bridge. An inductor L is connected between the connection point a of S1 and S2 and the connection point b of S3 and S4. In the embodiment of the present invention, when the current flowing through the inductor flows from point a to point b, it means that the inductor current flows in the positive direction, and vice versa means that the inductor current flows in the reverse direction. This set direction is only for describing the implementation manner of the present invention and is not a limitation, and it can also be set conversely. Among them, S1-S4 are switching tubes, including but not limited to NMOS tubes, etc.

[0083] In an alternative embodiment, the value of the preset power is set to where I zvs represents the target inductor current for the switch to turn on with zero voltage, and its calculation formula is as follows:

[0084]

[0085] where t d is the dead time of the four-switch Buck-Boost converter, which is a known value, and C oss is the parasitic capacitance of the switch.

[0086] Specifically, when the output power P of the four-switch Buck-Boost converter is greater than or equal to the preset power, the Buck-Boost converter operates in the first operating mode, and S1 - S4 are turned on in the manner of the first switching sequence, which altogether includes six operating stages, as Figure 2 shown below:

[0087] At the starting moment t 0a of the first stage, S1 and S4 are turned on with zero current. In the first stage, S1 and S4 are turned on, and the inductor current increases linearly. The voltage across the inductor is the input voltage V in , and the first stage ends at t 1a and enters the second stage;

[0088] At the starting moment t 1a of the second stage, S4 is turned off. In the second stage, S3 and S4 are in the dead time, the inductor current flows in the positive direction, and the junction capacitance of S3 discharges. The second stage ends at t 2a and enters the third stage;

[0089] At the starting moment t 2a of the third stage, S3 is turned on with zero voltage. In the third stage, S1 and S3 are turned on, and the voltage across the inductor is the difference between the input voltage and the output voltage V in - V o , and the third stage ends at t 3a and enters the fourth stage;

[0090] At the starting moment t 3a of the fourth stage, S1 is turned off. In the fourth stage, S1 and S2 are in the dead time, the inductor current flows in the positive direction, and the junction capacitance of S2 discharges. The fourth stage ends at t 4a and enters the fifth stage;

[0091] At the starting moment t 4a of the fifth stage, S2 is turned on with zero voltage. In the fifth stage, S2 and S3 are turned on, and the inductor current decreases linearly. The voltage across the inductor is -V o , and the fifth stage ends at t 5a and enters the sixth stage;

[0092] At the starting moment t 5a of the sixth stage, S2 and S3 are turned off with zero current. In the sixth stage, all of S1 - S4 are turned off, the inductor current remains zero, and the voltage across the inductor is zero.

[0093] Among them, under the first switching sequence, the durations of the first stage and the second stage are denoted as T 1A , which includes the on-duration of the fourth switch in the first stage and the dead time t of S3 and S4 in the second staged , in other words, the duration of the second stage is t d , and the duration of the first stage is (T 1A -t d ), that is to say, under the first switching timing, the on-duration of S4 is (T 1A -t d ). Similarly, under the first switching timing, the on-duration and the starting moment of the on-time of S1, S2, S3 and S4 can all be calculated through T 1A , T 2A , T 3A , T 4A and t d . The specific calculation method refers to the calculation idea of the on-duration of S4 and the Figure 2 timing diagram therein. For the sake of brevity, it will not be elaborated here.

[0094] Further, in the first operating mode, the values of T 1A , T 2A , T 3A , T 4A are calculated through the following formula. When the input voltage V in is less than the output voltage V o ,

[0095]

[0096] And when the input voltage V in is greater than the output voltage V o ,

[0097]

[0098] where T 1A is the duration of the first and second stages in the first switching timing, T 2A is the duration of the third and fourth stages, T 3A is the duration of the fifth stage, T 4A is the duration of the sixth stage, V in is the input voltage of the four-switch Buck-Boost converter; V o is the output voltage of the four-switch Buck-Boost converter, L is the inductance value, P is the output power, and T S is the switching period.

[0099] In addition, when the output power P of the four-switch Buck-Boost converter is less than the preset power, the Buck-Boost converter operates in the second operating mode, and S1 - S4 are turned on in the manner of the second switching timing, which altogether includes five operating stages, as Figure 2 shown, specifically as follows:

[0100] At the starting moment \(t\) of the first stage 0b , \(S1\) and \(S4\) are turned on with zero current. In the first stage, \(S1\) and \(S4\) are turned on, and the inductor current increases linearly. The voltage across the inductor is \(V\). in , The first stage ends at \(t\) 1b and enters the second stage;

[0101] At the starting moment \(t\) of the second stage 1b , \(S1\) and \(S4\) are turned off. The inductor current flows forward to discharge the junction capacitors of \(S2\) and \(S3\). The second stage ends at \(t\) 2b and enters the third stage. The duration of the second stage is also called the dead time of the Buck - Boost converter;

[0102] At the starting moment \(t\) of the third stage 2b , \(S2\) and \(S3\) are turned on with zero voltage. In the third stage, \(S2\) and \(S3\) are turned on, and the inductor current decreases linearly. The voltage across the inductor is \(-V\). o , The third stage ends at \(t\) 3a and enters the fourth stage;

[0103] At the starting moment \(t\) of the fourth stage 3b , \(S2\) and \(S3\) are turned off. In the fourth stage, the inductor current flows reversely and continues to flow through the body diodes of \(S1\) and \(S4\). The inductor current increases linearly. The voltage across the inductor is \(V\). in , The fourth stage ends at \(t\) 4b and enters the fifth stage;

[0104] At the starting moment \(t\) of the fifth stage 4b , the inductor current is cut off when it crosses zero, and the body diodes of \(S1\) and \(S4\) achieve zero - current turn - off. In the fifth stage, the inductor current remains zero, and the voltage across the inductor is zero.

[0105] Among them, in the second switching sequence, the turn - on moments and turn - on durations of \(S1 - S4\) are calculated through \(T\) 1B , \(T\) 2B , \(T\) 3B , \(T\) 4B . For the specific calculation method, refer to the calculation idea of the switch - on time in the first switching sequence, which will not be elaborated here.

[0106] Furthermore, in the second operating mode, \(T\) 1B , \(T\) 2B , \(T\) 3B and \(T\) 4B are calculated by the following formula:

[0107]

[0108] Among them, \(T\) 1Bis the duration of the first and second phases in the second switching sequence, T 2B is the duration of the third stage, T 3B is the duration of the fourth stage, T 4B is the duration of the fifth stage, V in is the input voltage of the four-switch Buck-Boost converter; V o is the output voltage of the four-switch Buck-Boost converter, L is the inductance value, I zvs It represents the target inductor current when the switch is turned on at zero voltage, and P is the output power.

[0109] In an embodiment of the present invention, T 1A , T 2A , T 3A , T 4A , T 1B , T 2B , T 3B and T 4B The specific derivation process selects the algorithm based on the optimization principle of minimum effective value of inductor current and full switch soft switching. The process is as follows:

[0110] In the first working mode, firstly, according to the voltage volt-second product balance of the inductor, the equation can be listed:

[0111] V in (T 1A +T 2A )=V o (T 2A +T 3A )

[0112] According to the output power P, the equation can be listed:

[0113]

[0114] The embodiment of the present invention adopts constant frequency control, so the switching period is T s satisfy:

[0115] T 1A +T 2A +T 3A +T 4A =T s

[0116] When the full switch tube soft switching and the effective value of the inductor current are optimized, the optimal here means the minimum effective value, we can get:

[0117]

[0118] Combining the above four equations, we can solve the above T 1A , T 2A, T 3A , T 4A The specific derivation process of solving the equation is well known to those skilled in the art and will not be described in detail to avoid redundancy.

[0119] Furthermore, in the second working mode, firstly according to the voltage volt-second product balance of the inductor, the equation can be listed:

[0120] V in (T 1B +T 3B )=V o T 2B

[0121] The equation can be listed based on the output power:

[0122]

[0123] The embodiment of the present invention adopts constant frequency control, and the switching period is T s , so it satisfies:

[0124] T 1B +T 2B +T 3B +T 4B =T s

[0125] When the full switch tube soft switching and the effective value of the inductor current are optimized, the optimal here means the minimum effective value, we can get:

[0126]

[0127] Combining the above four equations, we can solve the above T 1B , T 2B , T 3B and T 4B The computational expression of .

[0128] It should be noted that the first working mode has four degrees of freedom, namely T 1A , T 2A , T 3A , T 4A The first degree of freedom is T 1A and the third degree of freedom T 3A Used to achieve zero voltage turn-on and zero current turn-off of S2 and S3, optimize the effective value of inductor current, and the second degree of freedom T 2A Used to adjust the output power of the Buck-Boost converter, the fourth degree of freedom T 4A Used to ensure a constant switching frequency.

[0129] Similarly, the second working mode also has four degrees of freedom, namely T 1B , T2B , T 3B , T 4B . The first degree of freedom T 1B is used to achieve zero-voltage turn-on of S2 and S3, and the second degree of freedom T 2B is used to adjust the output power, and the third degree of freedom T 3B is used to ensure the balance of the inductor volt-second product per unit cycle, and the fourth degree of freedom T 4B is used to ensure a fixed switching frequency.

[0130] In the embodiment of the present invention, the algorithm is determined by selecting based on the principle of minimizing the effective value of the inductor current and full-switch soft switching to determine T 1A , T 2A , T 3A , T 4A and T 1B , T 2B , T 3B , T 4B The calculation formula of, and then determine the duration of different switching timings. The process of deriving and determining the algorithm based on the principle of minimizing the effective value of the inductor current and the full-switch soft-switching target belongs to mathematical formula derivation, which will not be elaborated here.

[0131] Through the switching modulation method of the four-switch Buck-Boost converter disclosed in the present invention, in the light-load condition of the four-switch Buck-Boost converter, there is no free circulating current in the converter, and zero-voltage or zero-current turn-on of all switches and zero-current turn-off of half of the switches are achieved, reducing the conduction loss of the converter and the current stress of the switching devices and improving the efficiency.

[0132] Further, Figures 3a - 3b is a waveform diagram of the inductor current of a four-switch Buck-Boost converter under different loads according to an embodiment of the present invention. As Figure 3a shown, in the first operating mode of the Buck-Boost converter, when the input voltage is greater than the output voltage, the waveform of the inductor current reaches I at the end of the second stage zvs , ensuring zero-voltage turn-on of S3. As the load is reduced, T 2A decreases, and the output power decreases. When T 2A drops to zero, the positive triangular area surrounded by the T 3A segment and the horizontal axis is still transferring energy to the load. Therefore, there is a limit to the minimum output power in the first operating mode. To solve the problem that the first operating mode has a minimum power limit and cannot achieve no-load output, when the power in the first operating mode decreases to the minimum output power, that is, the preset power, as the power continues to decrease, it operates in the second operating mode. The second operating mode introduces a triangular negative current by extending the T 3B segment. As T 3BAs it increases, the output power gradually decreases. When T 3B increases to satisfy that the current magnitude at the end of the third stage is equal to -I zvs the areas of the positive and negative triangles are the same, and no-load output is achieved at this time.

[0133] Figures 4a - 4b Fig. is a comparison diagram of the effective values of the inductor current between the efficiency-optimized modulation and the traditional modulation provided according to an embodiment of the present invention. Among them Figure 4a is a diagram of the change in the effective value of the inductor current when the input voltage is less than the output voltage. Among them Figure 4b is a diagram of the change in the effective value of the inductor current when the input voltage is greater than the output voltage. It can be seen from the figure that the effective values of the current inductors of the proposed modulation under different working conditions are all lower than those of the traditional modulation, indicating that the proposed modulation has smaller conduction losses, and the lighter the load, the more obvious the advantage of the effective value of the current.

[0134] Figures 5a - 5c Fig. is a waveform diagram of the simulation results under a modulation method of a four-switch Buck-Boost converter provided according to an embodiment of the present invention. In this embodiment, the simulation input voltage V in is 60V, the reference voltage is 84V, the rated power is 420W, and the switching frequency is 500kHz. At this time, the output power is half load, 210W. Under the traditional quadrilateral modulation, at this time, it is in a light-load working condition, and there is a long inductor negative current freewheeling section, resulting in a high effective value of the inductor current, causing large conduction losses and affecting the efficiency. However, by using the modulation method proposed in the present invention, the effective value of the inductor current can be greatly reduced on the premise of realizing soft switching of all switches, and efficiency optimization can be achieved.

[0135] As Figure 5a shown, the Buck-Boost converter works in the first working mode. The switch drive waveform and the inductor current waveform are consistent with the theoretical derivation, and soft switching can be achieved for all switches. The waveform of the inductor current within the T 4A time period shows a decaying sine wave fluctuation near the zero scale line. This is caused by the resonance phenomenon between the inductor and the parasitic capacitance of the switch when the inductor current passes through zero. The amplitude of the resonance current is very small and can be ignored. As Figure 5b shown, the output voltage, output current, and output power are all consistent with the preset values. Figure 5c Fig. is the waveform of the drive voltage of S2 and its drain-source voltage V ds at a certain moment. It can be seen that before the arrival of the drive rising edge, that is, before the switch is turned on, its V ds voltage has dropped to zero, that is, zero-voltage switching is achieved.

[0136] The simulation experiment results show that the efficiency optimization modulation method disclosed by the present invention can achieve a smaller effective value of the inductor current under the same operating conditions while ensuring full-switch soft-switching, thereby improving the efficiency under light load, and can be applied to scenarios with wide input voltage and wide load range.

[0137] Embodiment 2:

[0138] The present invention discloses a modulation system for a four-switch Buck-Boost converter, including the above-mentioned Buck-Boost converter, a calculation module, a controller, a mode selection module, a look-up table module, and a PWM module. Under light load conditions, the efficiency optimization modulation method disclosed in Embodiment 1 is used to modulate the Buck-Boost converter. The calculation module is used to calculate the difference between the output voltage and the reference voltage of the Buck-Boost converter; the controller is used to calculate the output power of the Buck-Boost converter; the mode selection module is used to determine the working mode of the Buck-Boost converter according to the output power. When the output power is greater than or equal to the preset power, the Buck-Boost converter operates in the first working mode. When the output power is less than the preset power, the Buck-Boost converter operates in the second working mode; the look-up table module is used to store the information of the turn-on and turn-off of the switches in the Buck-Boost converter in the first switching timing in the first working mode, and the information of the turn-on and turn-off of the switches in the Buck-Boost converter in the second switching timing in the second working mode; and the PWM module outputs the drive signal of the switch according to the working mode of the Buck-Boost converter to drive the Buck-Boost converter. Specifically, the control strategy of the modulation system of the four-switch Buck-Boost converter refers to Figure 6 as shown.

[0139] It should be noted that the switching timing or the working stage of the switches in the Buck-Boost converter in Embodiment 2 in the first working mode and the second working mode is the same as that in Embodiment 1. To avoid repetition, it will not be elaborated here.

[0140] Specifically, as Figure 6 shown, V ref is the reference voltage, V o is the output voltage sampling value, V ref and V oFirst, perform a subtraction operation; the obtained result is sent to a PI controller to perform PI operation to obtain an intermediate variable P, which is the output power of the converter; then, perform mode selection judgment based on P, that is, compare the output power P with a preset power, and determine the working mode of the Buck-Boost converter, namely the first working mode or the second working mode, according to the comparison result. The determination of the specific working mode is the same as the description in Embodiment 1 and will not be elaborated here. Further, the variable representing the current working mode, the input voltage sampling value V in and P are sent to a look-up table module to look up and obtain modulation variables T1 - T4. The modulation variables T1 - T4 in the look-up table module are the modulation variable values T 1A , T 2A , T 3A , T 4A in the first working mode in Embodiment 1, and the modulation variable values T 1B , T 2B , T 3B , T 4B in the second working mode. After obtaining the modulation variables by looking up, they are sent to a PWM module to determine the drive signals of S1 - S4, that is, to determine the PWM signals for turning on and off S1 - S4.

[0141] In summary, through the modulation method and system of the four-switch Buck-Boost converter disclosed in the present invention, the inductor current can automatically achieve zero-crossing cutoff without the need for hardware current detection. Due to the small errors caused by non-ideal factors such as the delay of the drive circuit and the parasitic resistance in the circuit, when the T3 (T 3A or T 3B ) section ends, the inductor current may not exactly be zero. Assuming that the inductor current is greater than 0 at this time, the inductor current will flow through the body diodes of S2 and S3 for freewheeling. At this time, the voltage across the inductor is -V o , and the inductor current linearly decreases until it decreases to zero, and the body diodes of S2 and S3 achieve zero-current turn-off. After that, the inductor current remains zero. Assuming that the inductor current is less than 0 at the end of the T3 section, the inductor current will flow through the body diodes of S1 and S4 for freewheeling. At this time, the voltage across the inductor is V in , and the inductor current linearly increases until it increases to zero, and the body diodes of S1 and S4 achieve zero-current turn-off. After that, the inductor current remains zero.

[0142] It is easy for those skilled in the art to understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A modulation method for a four-switch Buck-Boost converter, the four-switch Buck-Boost converter comprising a power input terminal, a voltage output terminal and four switches: a first switch, a second switch, a third switch and a fourth switch. The input terminal of the first switch is connected to the positive pole of the input power supply, the output terminal of the second switch is connected to the negative pole of the power input terminal, the output terminal of the fourth switch is connected to the negative pole of the voltage output terminal, the input terminal of the third switch is connected to the positive pole of the voltage output terminal, and an inductor is connected between the connection point of the first switch and the second switch and the connection point of the third switch and the fourth switch. It is characterized in that, The modulation method includes: Obtaining the output voltage of the Buck - Boost converter and calculating the error voltage based on the output voltage and the reference voltage; Calculating the output power according to the error voltage and comparing the output power with a preset power, where: When the output power is greater than or equal to the preset power, the Buck - Boost converter operates in the first operating mode, and the switches in the Buck - Boost converter are turned on in the first switching sequence. When the input voltage is greater than or equal to the output voltage, a target inductor current is generated so that the third switch is turned on with zero voltage. When the input voltage is less than or equal to the output voltage, a target inductor current is generated so that the second switch is turned on with zero voltage; and When the output power is less than the preset power, the Buck - Boost converter operates in the second operating mode, and the switches in the Buck - Boost converter are turned on in the second switching sequence, generating a target inductor current so that the second switch and the third switch are turned on with zero voltage.

2. The modulation method of the four-switch Buck-Boost converter according to claim 1, wherein The method for determining the operating mode of the Buck - Boost converter according to the output power is as follows: Among them, T s is the switching period, and I zvs represents the target inductor current for zero-voltage turn-on of the switch, and its calculation method is as follows: where t d is the dead time of the four-switch Buck-Boost converter, represents the preset power, and C oss is the switch parasitic capacitance.

3. The modulation method of the four-switch Buck-Boost converter according to claim 1, characterized in that The first switching sequence in the first operating mode includes: the first switch and the fourth switch are turned on, the first switch and the third switch are turned on, the second switch and the third switch are turned on, and the first switch, the second switch, the third switch, and the fourth switch are all turned off; the second switching sequence in the second operating mode includes: the first switch and the fourth switch are turned on, the second switch and the third switch are turned on, and the first switch, the second switch, the third switch, and the fourth switch are all turned off.

4. The modulation method of the four-switch Buck-Boost converter according to claim 3, characterized in that, Includes: When the Buck - Boost converter operates in the first operating mode, the switch has six operating stages in one switching cycle: At the start of the first stage, the first switch and the fourth switch are turned on with zero current, and the first switch and the fourth switch are turned on in the first stage; At the start of the second stage, the fourth switch is turned off. In the second stage, the third switch and the fourth switch are in the dead - time, and the junction capacitance of the third switch discharges; At the start of the third stage, the third switch is turned on with zero voltage, and the first switch and the third switch are turned on in the third stage; At the start of the fourth stage, the first switch is turned off. In the fourth stage, the first switch and the second switch are in the dead - time, and the junction capacitance of the second switch discharges; At the start of the fifth stage, the second switch is turned on with zero voltage, and the second switch and the third switch are turned on in the fifth stage; At the start of the sixth stage, the second switch and the third switch are turned off with zero current, and in the sixth stage, all switches are turned off, the inductor current is zero, and the voltage across the inductor is zero.

5. The modulation method of the four-switch Buck-Boost converter according to claim 4, characterized in that, The on - time of the switch in the first switching sequence satisfies the following expression: When the input voltage is less than the output voltage, When the input voltage is greater than the output voltage, Among them, T 1A is the duration of the first and second stages in the first switching timing, T 2A is the duration of the third and fourth stages, T 3A is the duration of the fifth stage, T 4A is the duration of the sixth stage, V in is the input voltage of the four-switch Buck-Boost converter; V o is the output voltage of the four-switch Buck-Boost converter, L is the inductance value, P is the output power, T s is the switching period.

6. The modulation method of the four-switch Buck-Boost converter according to claim 3, characterized in that There are five operating stages in the second switching sequence in the second operating mode, which are respectively: At the start of the first stage, the first switch and the fourth switch are turned on with zero current, and the first switch and the fourth switch are turned on in the first stage; At the start of the second stage, the first switch and the fourth switch are turned off, and the junction capacitances of the second switch and the third switch discharge; At the starting moment of the third stage, the second switch and the third switch are turned on with zero voltage, and the second switch and the third switch are turned on during the third stage; At the starting moment of the fourth stage, the second switch and the third switch are turned off. During the fourth stage, the inductor current flows reversely and freewheels through the body diodes of the first switch and the fourth switch; At the starting moment of the fifth stage, the inductor current becomes zero and is cut off, and the body diodes of the first switch and the fourth switch are turned off with zero current. During the fifth stage, the inductor current is zero and the voltage across the inductor is zero.

7. The modulation method of the four-switch Buck-Boost converter according to claim 6, characterized in that, In the second switch timing, the on-time of the switch satisfies the following expression: Among which T 1B is the duration of the first stage and the second stage in the second switching timing, T 2B is the duration of the third stage, T 3B is the duration of the fourth stage, T 4B is the duration of the fifth stage, V in is the input voltage of the four-switch Buck-Boost converter, V o is the output voltage of the four-switch Buck-Boost converter, L is the inductance value, I zvs represents the target inductor current for zero-voltage turn-on of the switch, and P is the output power.

8. A modulation system for a four-switch Buck-Boost converter, characterized in that, Including the Buck-Boost converter, calculation module, controller, mode selection module, look-up table module, and PWM module described in any one of claims 1-7, wherein the calculation module is used to calculate the difference between the output voltage and the reference voltage of the Buck-Boost converter; The controller is used to calculate the output power of the Buck-Boost converter; The mode selection module is used to determine the working mode of the Buck-Boost converter according to the output power. When the output power is greater than or equal to the preset power, the Buck-Boost converter operates in the first working mode. When the output power is less than the preset power, the Buck-Boost converter operates in the second working mode; A look-up table module, which is used to store the information about the turn-on and turn-off of the switches in the Buck-Boost converter in the first switch timing when the Buck-Boost converter is in the first working mode, and the information about the turn-on and turn-off of the switches in the Buck-Boost converter in the second switch timing when the Buck-Boost converter is in the second working mode; And A PWM module, which outputs the drive signal of the switch according to the working mode of the Buck-Boost converter to drive the Buck-Boost converter.

9. The modulation system of the four-switch Buck-Boost converter according to claim 8, characterized in that, Under the first switch timing, the working stages of the first switch - the fourth switch include: At the starting moment of the first stage, the first switch and the fourth switch are turned on with zero current, and the first switch and the fourth switch are turned on during the first stage; At the starting moment of the second stage, the fourth switch is turned off. During the second stage, the third switch and the fourth switch are in the dead time, and the junction capacitance of the third switch discharges; At the starting moment of the third stage, the third switch is turned on with zero voltage, and the first switch and the third switch are turned on during the third stage; At the starting moment of the fourth stage, the first switch is turned off. During the fourth stage, the first switch and the second switch are in the dead time, and the junction capacitance of the second switch discharges; At the starting moment of the fifth stage, the second switch is turned on with zero voltage, and the second switch and the third switch are turned on during the fifth stage; At the starting moment of the sixth stage, the second switch and the third switch are turned off with zero current. During the sixth stage, all the switches are turned off, the inductor current remains zero, and the voltage across the inductor is zero; Among them, the on-time of the first switch - the fourth switch can be calculated by the following formula: When the input voltage is less than the output voltage, When the input voltage is greater than the output voltage, Among which T 1A is the duration of the first and second stages in the first switching timing, T 2A is the duration of the third and fourth stages, T 3A is the duration of the fifth stage, T 4A is the duration of the sixth stage, V in is the input voltage of the four-switch Buck-Boost converter; V o is the output voltage of the four-switch Buck-Boost converter, L is the inductance value, P is the output power, T s is the switching period.

10. The modulation system of the four-switch Buck-Boost converter according to claim 8, characterized in that, Under the second switching timing, the operating phases of the first switch - the fourth switch include: At the start of the first phase, the first switch and the fourth switch turn on with zero current, and the first switch and the fourth switch are on during the first phase; At the start of the second phase, the first switch and the fourth switch are turned off, and the junction capacitances of the second switch and the third switch discharge; At the start of the third phase, the second switch and the third switch turn on with zero voltage, and the second switch and the third switch remain on during the third phase; At the start of the fourth phase, the second switch and the third switch are turned off, and during the fourth phase, the inductor current flows in the reverse direction and freewheels through the body diodes of the first switch and the fourth switch; At the start of the fifth phase, the inductor current becomes zero and stops, and the body diodes of the first switch and the fourth switch turn off with zero current. During the fifth phase, the inductor current remains zero and the voltage across the inductor is zero; Among them, the turn - on time of the first switch - the fourth switch can be calculated by the following formula: Where T 1B is the duration of the first and second stages in the second switching timing, T 2B is the duration of the third stage, T 3B is the duration of the fourth stage, T 4B is the duration of the fifth stage, V in is the input voltage of the four-switch Buck-Boost converter; V o is the output voltage of the four-switch Buck-Boost converter, L is the inductance value, I zvs represents the target inductor current for zero-voltage turn-on of the switch, and P is the output power.

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