TW202404244A - Method of controlling resonant push-pull converter - Google Patents

Abstract

A method of controlling a resonant push-pull converter is disclosed. The resonant push-pull converter includes a transformer, a first switch, a second switch, a resonant tank, and a rectifying circuit. The method includes a step of a fixed on-time control. In the fixed on-time control, a first control signal with a fixed on-time is used to control the first switch, and a second control signal with the fixed on-time is used to control the second switch so that the first switch and the second switch are alternately switched.

Description

Control method of resonant push-pull converter

The present invention relates to a control method of a push-pull converter, in particular to a control method of a resonant push-pull converter with wide-range full resonance.

For online (on-line) uninterruptible power supply system (UPS), there are generally three working modes: online mode, backup mode and bypass mode. In the backup power supply mode, the battery supplies power to the load through the DC-DC converter and inverter. Usually, a DC-DC converter converts and boosts the battery voltage to the voltage required by the DC bus, and then the inverter converts the DC voltage of the DC bus into an AC voltage for output.

Limited by the voltage value of a single battery, battery packs in UPS systems generally use series power supply mode. In addition, in order to improve the reliability of the system, the number of batteries in the string is generally small, resulting in a low output voltage value of the battery pack. Compared with half-bridge and full-bridge architecture converters, push-pull converters have relatively low conduction losses.

In order to improve the power density of the UPS system, increasing the operating frequency of the power supply system is an inevitable choice. However, in order for the power system to operate at higher switching frequencies, switching losses must be reduced. In addition, since the electric energy provided by the battery itself is precious and limited, the efficiency requirements for the power supply system are relatively high. DC-DC converters used in current commercially available UPS systems, such as push-pull converters, mostly belong to the hard switching mode of power switching. Due to switching losses, the overall conversion efficiency is poor. Based on the above reasons, the research on various soft switching circuits has become very important.

Therefore, how to design a control method for a resonant push-pull converter to solve the problems and technical bottlenecks of the existing technology is an important issue in the industry.

The purpose of the present invention is to provide a control method for a resonant push-pull converter to solve the problems of the prior art.

In order to achieve the foregoing purpose, the present invention proposes a control method for a resonant push-pull converter, wherein the resonant push-pull converter includes a transformer, a first switch, a second switch, a resonant tank and a rectifier circuit. The transformer includes a primary side winding and a secondary side winding, wherein the primary side winding has a first center tap end, a first end and a second end, and the first center tap end is coupled to the DC input voltage. The first switch is coupled between the first terminal and a ground terminal that provides a ground level of the DC input voltage. The second switch is coupled between the second terminal and the ground terminal. The resonant tank is coupled to the secondary side winding or the primary side winding. The rectifier circuit is coupled to the secondary side winding and used to convert the AC power provided by the secondary side winding into a DC output voltage. The control method includes a fixed conduction time control step: controlling the first switch with a first control signal with a fixed conduction time, and controlling the second switch with a second control signal with a fixed conduction time, so that the first switch and the second switch are alternately conductive. switch.

In one embodiment, after the fixed on-time control step, a frequency switching control step is included: when the load decreases, the switching frequency of the first control signal and the switching frequency of the second control signal are reduced; when the load increases, the switching frequency is increased. The switching frequency of the first control signal and the switching frequency of the second control signal.

In one embodiment, after the frequency switching control step, the output voltage control step is included: adaptively adjusting the DC output voltage according to the DC input voltage and switching frequency.

In one embodiment, after the fixed on-time control step, the output voltage control step is included: adaptively adjusting the DC output voltage according to the DC input voltage and the switching frequency of the first control signal and the switching frequency of the second control signal.

In one embodiment, fixed on-time control is performed based on the input voltage signal and the output current signal corresponding to the DC input voltage.

In one embodiment, fixed on-time control is performed under different load draw levels.

In one embodiment, the resonant push-pull converter further includes an output capacitor. The output capacitor is coupled in parallel to the output side of the rectifier circuit to provide a DC output voltage.

In one embodiment, the resonant push-pull converter further includes a resonant tank. The resonant tank has a series connected resonant inductor and resonant capacitor.

In one embodiment, two output capacitors are connected in series. Two output capacitors connected in series are coupled in parallel to the output side of the rectifier circuit to provide a DC output voltage.

In one embodiment, the secondary side winding has two winding ends and a second center tap end. The resonant tank has two sets of series-connected resonant inductors and resonant capacitors. Each set of series-connected resonant inductors and resonant capacitors is coupled to each winding end, and the common contact point of the two series-connected output capacitors is coupled to the second center tap end.

In one embodiment, the fixed on-time control is performed by an analog controller or a digital controller.

Through the proposed control method of the resonant push-pull converter, the characteristics and advantages can be realized: 1. Through the fixed on-time control method, the control can be simplified and the resonance soft cut can be achieved. 2. The operating (switching) frequency is adjusted with the load and input voltage to achieve a wide range of full resonance operation with light load resonant operation. 3. Under a limited duty cycle, by adjusting the target value of the output voltage that can vary within a wide range, the range of allowable changes in the input voltage is enlarged, which is beneficial to the selection of batteries to provide flexibility and convenience in the input voltage. 4. Introduce series resonance technology through the resonant push-pull converter, change the converter power switch to soft switching, and achieve zero switching loss through inductor-capacitor resonance operation, improve conversion efficiency, and facilitate heat dissipation design; reduce power consumption. The crystal surge voltage allows the selected components to be rated lower and reduces the interference sources caused by electromagnetic compatibility.

In order to further understand the technology, means and effects adopted by the present invention to achieve the intended purpose, please refer to the following detailed description and drawings of the present invention. It is believed that the purpose, features and characteristics of the present invention can be understood in depth and For specific understanding, however, the attached drawings are only for reference and illustration, and are not intended to limit the present invention.

The technical content and detailed description of the present invention are as follows with reference to the drawings.

In order to improve the current push-pull series resonance technology, there is a problem that the converter cannot perform soft switching under light loads and high input voltages. Therefore, the present invention proposes an optimized control method to achieve resonance soft switching to improve efficiency and improve transistor surges. (Sharp wave, spike) problems, and reduce interference sources caused by electromagnetic compatibility.

Please refer to FIG. 1 and FIG. 2 , which are circuit diagrams of the resonant push-pull converter of the present invention applied to a single bus architecture and a dual bus architecture respectively. The resonant push-pull converter includes a transformer TR and a primary side circuit and a secondary side circuit isolated by the transformer TR. The transformer TR includes a primary side winding W1 and a secondary side winding W2, wherein the primary side winding W1 is coupled to the primary side circuit, and the secondary side winding W2 is coupled to the secondary side circuit. The primary side winding W1 has a first center tap terminal Nc, a first terminal N1 and a second terminal N2, and the first center tap terminal Nc is coupled to the DC input voltage Vin.

The primary side circuit includes a first switch SW1 and a second switch SW2. The first switch SW1 is coupled between the first terminal N1 and the ground terminal GND that provides the ground level of the DC input voltage Vin. The second switch SW2 is coupled between the second terminal N2 and the ground terminal GND.

The secondary side circuit includes a resonant tank 50 and a rectifier circuit 90 . In this embodiment, the resonant tank 50 is coupled to the secondary side winding W2. The rectifier circuit 90 is coupled to the resonant tank 50 and the secondary winding W2 to convert the AC power provided by the secondary winding W2 into a DC output voltage Vout. However, in different embodiments, the resonant tank 50 may be coupled to the primary side winding W1 and may also operate as a resonant conversion. In addition, the rectifier circuit 90 is represented by diodes D1 to D4 in the figure, but it is not limited to this.

As shown in Figure 1, the resonant push-pull converter is applied to a single bus architecture. The output DC bus of the resonant push-pull converter has an output capacitor Co, and the output capacitor Co is connected in parallel. The rectifier circuit 90 is coupled to provide the DC output voltage Vout to the back-end load (represented by R _L ). As shown in Figure 2, the resonant push-pull converter is applied in a dual bus architecture. The output DC bus of the resonant push-pull converter has two output capacitors Co, and the two outputs The capacitor Co is connected in series and coupled in parallel to the rectifier circuit 90 to provide the DC output voltage Vout. More specifically, in the dual bus architecture shown in Figure 2, the secondary side winding W2 is of center-tapped type, and the common contact point of the two series-connected output capacitors Co is connected to the center-tapped end of the secondary side winding W2. Furthermore, the resonant tank 50 is in a symmetrical form (there is a set of inductors and capacitors (Lr, Cr) on the upper and lower sides of the resonant tank 50). Therefore, the corresponding configurations in Figure 1 (single bus architecture) and Figure 2 (double bus architecture) are different. The bus structure (that is, the output capacitor Co) of the resonant push-pull converter is also different from the series resonance tank structure formed by the inductor-capacitor (Lr, Cr). Through the inductor-capacitor (Lr, Cr) resonance operation, It can achieve the following advantages: 1. The switching loss is zero, which improves the conversion efficiency and is conducive to heat dissipation design; 2. The transistor spike voltage is reduced, so that the rating of the selected components can be reduced, and the interference source generated by electromagnetic compatibility is reduced.

The resonant push-pull converter is used to boost the low-voltage (for example, 12 volts) battery voltage to 200~400 volts (on the output DC bus), and convert the resonant type through the downstream inverter. The output voltage Vout of the push-pull converter is switched to a high-frequency square wave, and the rectifier circuit performs output rectification to generate a low-frequency sinusoidal AC power supply that supplies the system load.

Please refer to FIG. 3 , which is a schematic diagram of the control method of the resonant push-pull converter of the present invention implemented by the control unit 100 . The control method of the resonant push-pull converter of the present invention is executed through the control unit. The control method mainly includes three dependent control methods for controlling the first switch SW1 and the second switch SW2 of the primary side circuit, including : 1. Fixed on-time control; 2. Frequency switching control; and 3. Output voltage control. Among them, the control method can adopt fixed on-time control alone, or on the basis of fixed on-time control, frequency switching control, or on the basis of fixed on-time control, combined with output voltage control, or on the basis of fixed on-time control. On the basis of time control, frequency switching control and output voltage control are used in conjunction. The content and description of different control methods are revealed above and will be detailed later.

As shown in FIG. 3 , the control unit 100 may be an analog control (integrated) circuit, which includes a microcontroller 102 and a pulse width modulation controller 104 . The microcontroller 102 receives the input voltage Vin signal (i.e., the battery voltage) and the output current signal of the resonant push-pull converter, and performs forward fixed on-time control, frequency switching control and output voltage control, so that through pulse width modulation The controller 104 generates switch driving signals, that is, the first control signal S1 and the second control signal S2, and then controls the switching of the first switch SW1 and the second switch SW2 via the driving circuit 200 accordingly. However, the control unit 100 is not limited to an analog control (integrated) circuit, which means that the control unit 100 can be a fully digital design. As shown in Figure 4, the control unit 100 can be implemented digitally to directly generate the first control The switch driving signals of the signal S1 and the second control signal S2 perform switching control on the first switch SW1 and the second switch SW2 through the driving circuit 200 .

Please refer to FIG. 5 , which is a flow chart of the control method of the resonant push-pull converter of the present invention. The control method includes a fixed on-time control step (S10): controlling the first switch SW1 with a first control signal S1 of fixed on-time, and controlling the first switch SW1 with a second control signal S1 of fixed on-time. The control signal S2 controls the second switch SW2 so that the first switch SW1 and the second switch SW2 are turned on and switched alternately. In this way, through the fixed on-time control method, the control can be simplified and resonance soft cutting can be achieved.

Take the circuit architecture of Figure 1 as an example. When the parameters of the series resonant tank inductor-capacitor (Lr, Cr) are designed, the resonant frequency can be determined. Since switching the switches (the first switch SW1 and the second switch SW2) at a time of zero current can make the switching loss zero, the time when the current flowing through the switch becomes zero can be known based on the resonant frequency. For example, assuming the resonant frequency is 100Hz, it can be seen that the switching current that can be achieved once every 10ms is zero. In other words, as long as the switch is switched every 10ms, the soft switching effect can be achieved, and there is no need to detect the voltage of the resonant capacitor or the resonant current to determine the switch switching time. Therefore, the present invention can simplify the design of the controller, so that the circuit can provide the first control signal S1 with a fixed conduction time to control the switching of the first switch SW1 and provide the second control signal under different load-carrying conditions. S2 controls the switching of the second switch SW2 to achieve resonant soft switching.

As shown in Figure 5, after the fixed on-time control, the control method further includes a frequency switching control step (S20): when the load decreases, reduce the switching frequency of the first control signal S1 and the switching frequency of the second control signal S2. ; When the load increases, the switching frequency of the first control signal S1 and the switching frequency of the second control signal S2 are increased, so that the resonant push-pull converter operates under an adjustable working cycle. In the frequency switching control step, since it involves frequency switching control based on load changes, optimization of resonance can be achieved at light loads.

Since the resonant frequency is fixed and the on-time is fixed (based on the fixed on-time control executed in step S10), when the load pumping amount becomes smaller and the switching frequency remains unchanged, excessive energy will occur. Since D=Ton/T, where D is the duty cycle and Ton is the on-time of one cycle T. Since Ton is fixed (based on the fixed on-time control performed in step S10), when the switching frequency decreases (the period T increases), the duty period D decreases; conversely, the duty period D increases. Therefore, in frequency switching control, if the load decreases, the switching frequency is controlled to decrease (lower), so that the energy provided during the duty cycle becomes smaller to achieve energy balance. On the contrary, if the load increases, the control switching frequency increases (rises), so that the energy provided during the duty cycle becomes larger, and energy balance can also be achieved.

As shown in Figure 5, after the frequency switching control, the control method further includes an output voltage control step (S30) auxiliary: an output voltage control step: adaptively adjusting the DC output voltage Vout target value according to the DC input voltage Vin.

Since the relationship between the output voltage and the input voltage of the resonant push-pull converter is as follows: Vout=2*N*D*Vin, where N is the transformer turns ratio (fixed value) and D is the duty cycle.

When the duty cycle D is not fixed, that is, operating under an adjustable duty cycle is achieved in the frequency switching control step (S20), so the variable output voltage Vout is not only related to the input voltage Vin, but also to the duty cycle D. However, based on the range of the limited duty cycle D, the target value of the DC output voltage Vout can be adjusted adaptively, so that the range of the input voltage Vin that can be allowed to change is increased.

For example, in circuit applications, the output voltage Vout of the resonant push-pull converter can be used to provide the input of a load with a wide voltage range, such as an inverter as a load, so the output voltage Vout is allowed to provide Wide range voltage output. The input voltage Vin of the resonant push-pull converter can be the battery voltage. Since the voltage of the battery is very different when the battery is fully charged and when the battery is low (the range of battery voltage changes is large), the limited duty cycle D By adjusting the target value of the output voltage Vout that can vary within a wide range, the allowable variation range of the input voltage Vin is enlarged, which is beneficial to the flexibility and convenience of using a battery to provide the input voltage Vin.

Incidentally, although Figure 5 represents the three control methods as steps (S10) ~ step (S30), in practical applications, the fixed on-time control of step (S10) is the necessary control method, and the remaining steps (S20) and step (S30) are optional ways to achieve resonance optimization to achieve energy balance. Therefore, the control method of the present invention can adopt fixed on-time control alone, that is, perform step (S10), or on the basis of fixed on-time control. on, cooperate with frequency switching control, that is, execute steps (S10) and step (S20), or on the basis of fixed on-time control, cooperate with output voltage control, that is, execute steps (S10) and step (S30), or in On the basis of fixed on-time control, frequency switching control and output voltage control are used in conjunction, that is, steps (S10), step (S20) and step (S30) should all be covered by the protection scope of this case.

To sum up, the present invention has the following features and advantages:

1. Under different load-carrying conditions, the fixed on-time control method can be used to simplify the control and achieve resonance soft cut.

2. The operating (switching) frequency is adjusted with the load and input voltage to achieve a wide range of full resonance operation with light load resonant operation.

3. Under the limited duty cycle variation range, by adjusting the target value of the output voltage that can vary within a wide range, the allowable variation range of the input voltage is enlarged, which is beneficial to the selection of batteries to provide flexibility and convenience in the input voltage.

4. Introduce series resonance technology through the resonant push-pull converter, change the converter power switch to soft switching, and achieve zero switching loss through inductor-capacitor resonance operation, improve conversion efficiency, and facilitate heat dissipation design; reduce power consumption. The crystal surge voltage allows the selected components to be rated lower and reduces the interference sources caused by electromagnetic compatibility.

The above are only detailed descriptions and drawings of the preferred embodiments of the present invention. However, the characteristics of the present invention are not limited thereto and are not used to limit the present invention. The entire scope of the present invention should be determined by the following patent application scope. Subject to the present invention, all embodiments that are within the spirit of the patentable scope of the present invention and similar changes thereof shall be included in the scope of the present invention. Anyone familiar with the art can easily think of such changes or modifications in the field of the present invention. Modifications may be covered by the following patent scope of this case.

TR: Transformer W1: Primary side winding W2: Secondary side winding Nc: First center tap terminal N1: First terminal N2: Second terminal Vin: Input voltage Vout: Output voltage SW1: First switch SW2: Second switch GND : Ground terminal 50: Resonance tank 90: Rectifier circuit 100: Control unit 102: Microcontroller 104: Pulse width modulation controller S1: First control signal S2: Second control signal D1~D4: Diode Co: Output capacitance R _L : Load S10, S20, S30: Step

FIG. 1 is a circuit diagram of the resonant push-pull converter of the present invention applied in a single bus architecture.

FIG. 2 is a circuit diagram of the resonant push-pull converter of the present invention applied in a dual-bus architecture.

FIG. 3 is a schematic diagram of the control method of the resonant push-pull converter of the present invention implemented by the control unit.

Figure 4 is a circuit block diagram of the resonant push-pull converter control of the present invention.

FIG. 5 is a flow chart of the control method of the resonant push-pull converter of the present invention.

S10, S20, S30: steps

Claims (11)

A control method for a resonant push-pull converter. The resonant push-pull converter includes: A transformer includes a primary side winding and a secondary side winding, wherein the primary side winding has a first center tapped end, a first end and a second end, and the first center tapped end is coupled to a DC input voltage ; a first switch coupled between the first terminal and a ground terminal providing a ground level of the DC input voltage; a second switch coupled between the second terminal and the ground terminal; a resonant tank coupled to the secondary side winding or the primary side winding; and a rectifier circuit coupled to the secondary side winding for converting the alternating current provided by the secondary side winding into a direct current output voltage; Wherein, the control method includes a fixed conduction time control step: controlling the first switch with a first control signal with a fixed conduction time, and controlling the second switch with a second control signal with a fixed conduction time, so that the first switch The switch and the second switch are alternately switched on and off. The control method of the resonant push-pull converter as described in claim 1, after the fixed on-time control step, includes: Frequency switching control step: when the load decreases, reduce the switching frequency of the first control signal and the switching frequency of the second control signal; when the load increases, increase the switching frequency of the first control signal and the second control signal The switching frequency of the signal. The control method of the resonant push-pull converter as described in claim 2, wherein after the frequency switching control step, it includes: Output voltage control step: adaptively adjust the DC output voltage according to the DC input voltage and the switching frequency. The control method of the resonant push-pull converter as described in claim 1, after the fixed on-time control step, includes: The output voltage control step: adaptively adjust the DC output voltage according to the DC input voltage, the switching frequency of the first control signal and the switching frequency of the second control signal. The control method of a resonant push-pull converter as described in claim 1, wherein fixed on-time control is performed based on an input voltage signal and an output current signal corresponding to the DC input voltage. The control method of the resonant push-pull converter as described in claim 1, wherein fixed on-time control is performed under different load pumping capacities. The control method of the resonant push-pull converter as described in claim 1, wherein the resonant push-pull converter further includes: An output capacitor is coupled in parallel to the output side of the rectifier circuit to provide the DC output voltage. The control method of a resonant push-pull converter as described in claim 7, wherein the resonant tank has a set of a resonant inductor and a resonant capacitor connected in series. The control method of the resonant push-pull converter as described in claim 1, wherein the resonant push-pull converter further includes: Two output capacitors are connected in series, and the output capacitors connected in series are coupled in parallel to the output side of the rectifier circuit to provide the DC output voltage. The control method of the resonant push-pull converter as described in claim 9, wherein the secondary side winding has two winding ends and a second center tap end; The resonant tank has two sets of a resonant inductor and a resonant capacitor connected in series. Each set of the resonant inductor and the resonant capacitor connected in series is coupled to each winding terminal, and the common point of the series-connected output capacitors is coupled to the winding terminal. Second center tap end. The control method of a resonant push-pull converter as described in claim 1, wherein the fixed on-time control is performed through an analog controller or a digital controller.

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