DC-DC converter of switch linear series structure and control method of DC-DC converter

Abstract

The invention provides a DC-DC converter of a closed linear series structure and a control method of the DC-DC converter, and belongs to the technical field of DC-DC converters, and a main circuit comprises a primary side half-bridge switching network, a high-frequency transformer, a secondary side full-wave rectification circuit, an A-class linear amplification circuit, and respective control circuits of a switch and a linear converter. Compared with the prior art, the hybrid topology adopts a series connection structure of the switch and the linear converter, the switch converter serves as an input voltage source to provide input power for a post-stage linear current source, the linear converter is placed at the post stage, and a plurality of groups of A-class linear amplification circuits are connected in parallel and then connected in series in a main circuit to form a voltage-controlled current source. The wide current output range of the system is ensured, and the current output of the system is fast and accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of DC-DC converters, and in particular to a DC-DC converter with a switch linear series structure and a control method thereof. Background Art

[0002] The switch linear series structure not only has the characteristics of high output accuracy and fast response speed of the linear converter, but also retains the advantages of high efficiency and high power density of the switch converter. With the development of the new energy market, industries such as battery charging and discharging test, motor test, photovoltaic energy storage inverter test, etc. have put forward higher requirements on the efficiency, volume, output accuracy and dynamic response speed of power electronic converters. The power electronic devices in the switch converter work in the "switching" state. Although they have high efficiency and high power density, the high-speed switching action will bring serious switching noise, large system output ripple and slow dynamic response. The power electronic devices in the linear converter work in the "linear" state, which can achieve high accuracy and high response speed, but their heat loss is large, which reduces the efficiency of the converter. It can be seen that how to ensure the high efficiency and high power density of the converter while further improving the output performance of the converter poses a great challenge to the design of the switch linear series structure converter. Summary of the invention

[0003] The present invention aims to provide a DC-DC converter with a switch linear series structure to improve the converter accuracy and response speed, reduce the linear amplifier power loss, and improve the overall efficiency of the converter.

[0004] In order to achieve the above object, the present invention is implemented through the following technical solutions: A DC-DC converter with a switch linear series structure, comprising a switch converter, a linear converter and an LC filter circuit, wherein the output of the switch converter is connected to the input of the linear converter through the LC filter circuit, and the output of the linear converter is connected to a load; The switching converter includes a half-bridge inverter circuit, a high-frequency transformer and a full-wave rectifier circuit, wherein the half-bridge inverter circuit is connected to the primary side of the high-frequency transformer, and the full-wave rectifier circuit is connected to the secondary side of the high-frequency transformer; The linear converter comprises a plurality of groups of linear amplifier circuits, which are connected in parallel and then in series in the main circuit of the linear converter.

[0005] Further, the half-bridge inverter circuit is a voltage-type half-bridge inverter circuit, comprising two MOS tubes T1 and T2, for inverting the input DC power into a high-frequency AC output; the full-wave rectifier circuit comprises two diodes, and the secondary sideband of the high-frequency transformer is centrally tapped; One input end of each set of linear amplifier circuits is connected to the output of the outer loop, and the other input end is connected to the current sampling resistor and then connected to the load.

[0006] Furthermore, the switching converter is controlled by a switching converter control circuit, which adopts a digital control loop. The PWM output of the DSP in the digital control loop is connected to the drive circuit and the isolation transformer in sequence, and then input into the MOS tube gate of the half-bridge inverter.

[0007] Furthermore, the linear converter is controlled by a linear converter control circuit, which is a double closed-loop control loop constructed by an analog circuit, including an outer loop conditioning circuit, a compensation circuit and an inner loop conditioning circuit connected in sequence.

[0008] Furthermore, the linear converter output voltage The saturation voltage of the MOS tube in the linear amplifier circuit The sum is taken as the given voltage outer loop of the switching converter, and the output voltage of the switching converter is The sampling is used as the outer loop sampling input of the digital control loop, and the rectified current sampling value of the switching converter current sampling resistor is used as the inner loop input of the switching converter digital control loop.

[0009] Furthermore, the outer loop conditioning circuit includes an outer loop voltage conditioning circuit and an outer loop current conditioning circuit, and the outer loop voltage conditioning circuit and the outer loop current conditioning circuit each include an integrated operational amplifier, a voltage setting and a linear converter output voltage The sampling is used as the input of the outer loop voltage conditioning circuit, the current setting and the output current sampling are used as the input of the outer loop current conditioning circuit, the output of the outer loop voltage conditioning circuit and the outer loop current conditioning circuit are used as the input of the compensation circuit, the output of the compensation circuit and the drain current sampling of a single MOS tube in each group of linear amplifier circuits are used as the input of the inner loop conditioning circuit, and the output of the inner loop conditioning circuit is used as the drive of a single MOS tube in each group of linear amplifier circuits.

[0010] A control method for a DC-DC converter with a switch linear series structure is disclosed. Based on the DC-DC converter with the switch linear series structure, a half-bridge inverter circuit inverts the input DC power into a high-frequency AC power and outputs it to the primary winding of a high-frequency transformer. The secondary winding of the high-frequency transformer obtains an alternating voltage which is rectified by a full-wave rectifier circuit with a center tap on the secondary side of the transformer. The alternating voltage is then output through an LC filter to provide power to a linear converter. The output end of the linear converter is connected to a load.

[0011] Furthermore, the linear MOS tubes in the linear amplifier circuit all work at the boundary of the constant current region, and the voltage across the drain and source is at the critical point of the saturation voltage.

[0012] Furthermore, the control of the linear converter uses an analog circuit to build a double closed-loop control loop, and the linear converter output voltage The current sampling, voltage and current are given as the sampling input of the outer loop, and are used as the input of the inner loop conditioning circuit after passing through the outer loop conditioning circuit and the compensation circuit. The drain current of a single linear MOS tube flowing through the linear converter is converted into a voltage signal through a sampling resistor and given to the sampling input of the inner loop conditioning circuit. After passing through the inner loop conditioning circuit, it is directly given to the linear MOS gate using the strong driving capability of the operational amplifier. By adjusting the proportional coefficients of the inner and outer loop conditioning circuits and the compensation circuits, the voltage across the drain and source of the MOS tube in the linear converter is just at the critical point of the saturation voltage.

[0013] Furthermore, the linear converter output voltage Sampling and linear MOS tube drain-source saturation voltage The sum is used as the outer loop of the digital control loop and is compared with the output voltage of the switching converter. After the difference is made, the voltage loop is input, and the voltage loop output is subtracted from the rectified current sampling. The output PWM wave is enhanced by the drive circuit and given to the isolation transformer. The output end of the isolation transformer is connected to the gate source of the MOS tube in the half-bridge inverter circuit. The output of the switching converter is controlled by controlling the PWM duty cycle to ensure that the linear MOS tube is always located at the boundary of the constant current region: in, is the switching converter output voltage, is the input DC voltage, D is the duty cycle of the DSP output PWM, and N is the number of turns of the high-frequency transformer.

[0014] The advantages of the present invention are: The switching converter is used as the front stage, and its output provides power for the rear stage linear converter, while improving the efficiency and power density of the entire system. The linear converter is used as the rear stage. Through multiple groups of Class A linear amplifiers connected in parallel and then connected in series in the main circuit, the output current capacity of the system is improved, providing the system with high-precision and high dynamic response output characteristics. The switching converter is used as the front stage power supply module, and performs pre-voltage regulation in the front stage. By dividing the voltage, the voltage across the drain and source of the MOS tube in the linear amplifier circuit is at the critical point of the saturation voltage, ensuring the normal operation of the converter while reducing the loss of the MOS tube in the linear amplifier circuit. The switching topology of the front stage reduces the voltage across the linear current source, further improving the efficiency of the converter. The linear topology of the rear stage compensates for the ripple on the output voltage and current, and improves the dynamic response speed of the converter. The two work together to ensure the high efficiency and high precision output of the converter.

[0015] In addition, in order to solve the problem that the DC operating point of the linear MOS tube is offset due to the voltage conversion of the previous stage, a voltage control strategy based on the voltage drop across the drain and source of the subsequent MOS tube is proposed. The switching converter first outputs a voltage whose value is equal to the saturation voltage across the drain and source of the linear MOS. After a period of time, the output voltage of the switching converter and the output voltage of the overall converter rise synchronously, and remain stable after reaching a given value, and the voltage difference is always maintained at the voltage saturation critical point across the drain and source of the linear MOS.

[0016] The voltage loop of the digital loop of the switching converter is given by the overall output voltage of the converter plus the saturation voltage across the drain and source of the linear MOS. The output voltage of the previous switching converter is dynamically adjusted. This control strategy not only ensures that the MOS tube of the linear converter works at a suitable DC operating point, so that the converter can work normally, but also improves the converter efficiency by reducing the "excess" voltage across the linear MOS tube. The core of this strategy is to keep the DC operating point of the linear MOS tube at the boundary of the constant current region, ensuring that the voltage across the MOS tube is maintained at the lowest level. It should be noted that in the specific application process, the drain-source saturation voltage value should be modified according to the characteristics of the actual MOS tube device selected, so as to maximize the role of this strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The switch linear series structure converter and control circuit of the present invention; Figure 2 The main circuit topology diagram of the linear series switch structure converter of the present invention; Figure 3 The switch part control circuit of the switch linear series structure converter of the present invention; Figure 4 The linear part control circuit of the switch linear series structure converter of the present invention; Figure 5 It is a schematic diagram of the voltage drop control strategy of the linear MOS tube of the switch linear series structure converter of the present invention. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0019] Example 1 This embodiment discloses a DC-DC converter with a switch linear series structure. Figure 1 , Figure 2 , including a switching converter, a linear converter and an LC filter circuit. The output of the switching converter is connected to the input of the linear converter through the LC filter circuit to provide power for the linear converter. The output of the linear converter is connected to the load to supply power to the load.

[0020] The switching converter includes a half-bridge inverter circuit, a high-frequency transformer and a full-wave rectifier circuit. The half-bridge inverter circuit is a voltage-type half-bridge inverter circuit. This circuit has the characteristics of high inverter frequency, high-frequency noise suppression, and low output impedance. It includes two MOS tubes T1 and T2. The lower end of T1 is connected to the upper end of T2 and both are connected to one end of the primary capacitor Cr. The other end of Cr is connected to the upper end of the primary side of the high-frequency transformer. The lower end of T2 is connected to the input voltage. Negative connection, upper end of T1 and input voltage The positive pole is connected, T1 and T2 are respectively connected with a capacitor in parallel, the lower end of the primary side of the high-frequency transformer is connected to the midpoint of T1 and T2, and the secondary side of the high-frequency transformer is connected to the full-wave rectifier circuit. The full-wave rectifier circuit is composed of two diodes D1 and D2. The positive poles of D1 and D2 are respectively connected to the upper and lower ends of the secondary side of the high-frequency transformer. The secondary side of the high-frequency transformer has a center tap, and the AC voltage transformed by the high-frequency transformer is rectified and then outputted as a constant voltage through LC filtering to provide power to the linear converter.

[0021] The linear converter includes six groups of Class A linear amplifier circuits, which are connected in parallel and then in series in the main circuit of the linear converter. The MOS tubes in the amplifier circuits all work in the constant current region, and the voltage across their drain and source is at the critical point of the saturation voltage, ensuring the normal operation of the linear amplifier circuit while reducing the loss of the linear MOS.

[0022] The overall topology includes three types of current sampling. One end of R1 is connected to the cathode of diodes D1 and D2 through inductor L1. It is the current sampling resistor of the switching converter. It collects the rectified current as the inner loop input of the digital control loop of the switching converter. R2-R7 are the sampling resistors of the drain current of the six linear MOS tubes in the linear converter. The sampling value is used as the input of the inner loop conditioning circuit of the linear converter. R8 is the overall converter output current sampling resistor. The sampling value is connected to the outer loop conditioning circuit input of the linear converter.

[0023] The overall topology includes two voltage sampling, the switching converter output voltage The sampling is used as the outer loop sampling input of the digital control loop of the switching converter, and the overall converter output voltage The sampling is used as the sampling input of the outer loop conditioning circuit of the linear converter, and the output voltage is Add linear MOS tube drain-source saturation voltage It is used as the outer loop of the linear converter digital control loop to implement the linear MOS tube voltage drop control strategy.

[0024] Please refer to Figure 2The control block diagram of the switching converter is given. A digital controller is used to build the control loop. The compensation operation and the modulation output of the PWM drive are realized through the code inside the digital controller. The half-bridge inverter circuit uses fewer switching devices, the switch tube voltage is not high, the drive is simple, and the ability to resist circuit imbalance is strong. It can be used in small and medium power inverter circuits. The online half-bridge inverter circuit adopts a voltage and current dual closed-loop control method in control. The control methods of the current loop include current peak control, current hysteresis control and average current control. Considering the requirements of THD, control circuit and voltage regulation performance, the current loop in this design adopts the average current control method, and the voltage loop adopts a PI regulator without static error. The control of the dual loops is achieved by the complex change of the duty cycle D.

[0025] The output voltage and current of the switching converter are converted into appropriate values ​​through a conditioning circuit composed of resistors, capacitors and operational amplifiers and sent to the DSP AD sampling port as the sampling input of the voltage outer loop and the current inner loop respectively. The linear converter output voltage (i.e. the output voltage of the overall converter) plus the saturation voltage of the linear MOS As the given voltage outer loop of the switching converter, it ensures that the linear MOS tube is always located at the boundary of the constant current region. The output signal of the digital loop cuts the triangle wave to output the PWM wave. Since the output voltage amplitude of the DSP is low, a drive enhancement circuit is designed to enhance the drive. The PWM wave amplitude output by the DSP is converted to +12V and given to the drive isolation transformer. The other end of the transformer is connected to the MOS gate source in the half-bridge inverter. The output of the switching converter is controlled by controlling the PWM duty cycle.

[0026] Switching converter output voltage: in, is the switching converter output voltage, is the input DC voltage, D is the duty cycle of the DSP output PWM, and N is the number of turns of the high-frequency transformer.

[0027] Please refer to Figure 3The given linear converter control block diagram uses analog circuits to build a double closed-loop control loop to reduce control delay and increase system bandwidth. The input voltage and current sampling of the entire converter is used as the sampling input of the outer loop. The voltage and current of the outer loop are given to the loop by DSP through the DA chip, and then to the inner loop through the conditioning circuit and compensation circuit built by resistors and capacitors. The current flowing through the drain of a single linear MOS tube is converted into a voltage signal through the sampling resistor and then given to the sampling input of the inner loop. After passing through the conditioning circuit, it is directly given to the linear MOS gate using the strong driving capability of the op amp. In order to ensure that the MOS in the linear amplifier circuit is current-balanced, six groups of inner loop conditioning circuits are built. One end of the input of the six groups of conditioning circuits is connected to the output of the outer loop, and the other end is connected to the current sampling of six linear MOS. By adjusting the proportional coefficients of the inner and outer loop conditioning circuits and compensation circuits, the voltage across the drain and source of the linear MOS is just at the critical point of saturation voltage.

[0028] Please refer to Figure 4 Given the linear MOS tube voltage drop control strategy, the switching converter first outputs the voltage , which is equal to the saturation voltage across the drain and source of the linear MOS , after a period of time After that, the switching converter output voltage and the linear converter output voltage (overall converter output voltage) Synchronous rise, After a certain time, the output voltage reaches the set value, and its voltage difference is always maintained at the voltage saturation critical point across the drain and source of the linear MOS.

[0029] Example 2 The test data of this embodiment is: Input voltage U in =400V; Switching converter output voltage U z =85V; Linear converter output voltage U o =80V; Linear MOS tube drain-source voltage U z -U o =5V; Output current: 25A; Switching frequency during switching change period: 70kHZ; Control chip: DSP; The main circuit adopts Figure 1 plan; The main components used are as follows: Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A DC-DC converter with a switch linear series structure, characterized in that: It includes a switching converter, a linear converter and an LC filter circuit, wherein the output of the switching converter is connected to the input of the linear converter through the LC filter circuit, and the output of the linear converter is connected to a load; The switching converter includes a half-bridge inverter circuit, a high-frequency transformer and a full-wave rectifier circuit, wherein the half-bridge inverter circuit is connected to the primary side of the high-frequency transformer, and the full-wave rectifier circuit is connected to the secondary side of the high-frequency transformer; The linear converter comprises a plurality of groups of linear amplifying circuits, which are connected in parallel and then in series in the main circuit of the linear converter.

2. The DC-DC converter of the switch linear series structure according to claim 1, characterized in that: The half-bridge inverter circuit is a voltage-type half-bridge inverter circuit, comprising two MOS tubes T1 and T2, for inverting the input DC power into a high-frequency AC output; the full-wave rectifier circuit comprises two diodes, and the secondary sideband of the high-frequency transformer is centrally tapped; One input end of each set of linear amplifier circuits is connected to the output of the outer loop, and the other input end is connected to the current sampling resistor and then connected to the load.

3. The DC-DC converter of the switch linear series structure according to claim 2, characterized in that: The switching converter is controlled by a switching converter control circuit, which adopts a digital control loop. The PWM output of the DSP in the digital control loop is connected to the drive circuit and the isolation transformer in sequence, and then input into the MOS tube gate of the half-bridge inverter.

4. The DC-DC converter of the switch linear series structure according to claim 1, characterized in that: The linear converter is controlled by a linear converter control circuit, which is a double closed-loop control loop constructed by an analog circuit, including an outer loop conditioning circuit, a compensation circuit and an inner loop conditioning circuit connected in sequence.

5. The DC-DC converter of the switch linear series structure according to claim 3, characterized in that: Linear converter output voltage The sum of the saturation voltage of the MOS tube in the linear amplifier circuit is used as the given voltage outer loop of the switching converter. The output voltage of the switching converter The sampling is used as the outer loop sampling input of the digital control loop, and the rectified current sampling value of the switching converter current sampling resistor is used as the inner loop input of the switching converter digital control loop.

6. The DC-DC converter of the switch linear series structure according to claim 4, characterized in that: The outer loop conditioning circuit includes an outer loop voltage conditioning circuit and an outer loop current conditioning circuit, and the outer loop voltage conditioning circuit and the outer loop current conditioning circuit each include an integrated operational amplifier, a voltage setting circuit and a linear converter output voltage circuit. The sampling is used as the input of the outer loop voltage conditioning circuit, the current setting and the output current sampling are used as the input of the outer loop current conditioning circuit, the output of the outer loop voltage conditioning circuit and the outer loop current conditioning circuit are used as the input of the compensation circuit, the output of the compensation circuit and the drain current sampling of a single MOS tube in each group of linear amplifier circuits are used as the input of the inner loop conditioning circuit, and the output of the inner loop conditioning circuit is used as the drive of a single MOS tube in each group of linear amplifier circuits.

7. A control method for a DC-DC converter with a switch linear series structure, based on the DC-DC converter with a switch linear series structure according to any one of claims 1 to 6, characterized in that: The half-bridge inverter circuit inverts the input DC power into high-frequency AC and outputs it to the primary winding of the high-frequency transformer. The secondary winding of the high-frequency transformer obtains the alternating voltage, which is rectified by the full-wave rectifier circuit with the center tap of the secondary sideband of the transformer. It then outputs a constant voltage through LC filtering to provide power to the linear converter. The output end of the linear converter is connected to the load.

8. The control method of a DC-DC converter with a switch linear series structure according to claim 7, characterized in that: The linear MOS tubes in the linear amplifier circuit all work at the boundary of the constant current region, and the voltage across the drain and source is at the critical point of the saturation voltage.

9. The DC-DC converter control method of claim 8, characterized in that: The control of the linear converter uses an analog circuit to build a double closed-loop control loop, and the linear converter output voltage The current sampling, voltage and current are given as the sampling input of the outer loop, and are used as the input of the inner loop conditioning circuit after passing through the outer loop conditioning circuit and the compensation circuit. The drain current of a single linear MOS tube flowing through the linear converter is converted into a voltage signal through a sampling resistor and given to the sampling input of the inner loop conditioning circuit. After passing through the inner loop conditioning circuit, it is directly given to the linear MOS gate using the strong driving capability of the operational amplifier. By adjusting the proportional coefficients of the inner and outer loop conditioning circuits and the compensation circuits, the voltage across the drain and source of the MOS tube in the linear converter is just at the critical point of the saturation voltage.

10. The DC-DC converter control method of the switch linear series structure according to claim 8, characterized in that: Linear converter output voltage Sampling and linear MOS tube drain-source saturation voltage The sum is used as the outer loop of the digital control loop and is compared with the output voltage of the switching converter. After the difference is made, the voltage loop is input, and the voltage loop output is subtracted from the rectified current sampling. The output PWM wave is enhanced by the drive circuit and given to the isolation transformer. The output end of the isolation transformer is connected to the gate source of the MOS tube in the half-bridge inverter circuit. The output of the switching converter is controlled by controlling the PWM duty cycle to ensure that the linear MOS tube is always located at the boundary of the constant current region: in, is the switching converter output voltage, is the input DC voltage, D is the duty cycle of the DSP output PWM, and N is the number of turns of the high-frequency transformer.

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