DC / DC Converter and Its Control Method

Abstract

The present invention discloses a DC / DC converter and a control method thereof. The DC / DC converter includes a first primary circuit and a second primary circuit with interconnected input ends, a first secondary circuit connected to the first primary circuit, a first transformer for connecting the first primary circuit and the first secondary circuit, a secondary second circuit connected to the second primary circuit, a second transformer for connecting the second primary circuit and the second secondary circuit, and a bus capacitor for supplying power to the first primary circuit and the second primary circuit. The input voltages of the first primary circuit and the second primary circuit are adjusted according to the voltage of the bus capacitor, and the output ends of the first secondary circuit and the second secondary circuit are connected to the same output end. Compared with the prior art, the present invention can meet a wide range of input voltages, and can not only achieve control under low-voltage input, but also be applicable to control under high-voltage input.

Description

Technical Field

[0001] The present invention relates to the technical field of electric locomotive charging, in particular to a DC / DC converter and a control method thereof. Background Art

[0002] With the gradual popularization of new energy electric vehicles in the market, users have higher requirements for the charging speed, and high-end electric vehicles are developing towards higher battery voltages. In particular, in order to improve the fast charging speed, in some vehicle battery pack architectures, the voltage of the battery pack components reaches 800 Vdc. However, conventional 650 V silicon MOS transistors cannot meet the voltage requirement of 800 V and are prone to damage the switching transistors. To solve the above problems, SiC devices that meet the 1200 V voltage are required in the prior art, and the design cost is high. However, for SiC devices with a voltage of 1200 V, when the input voltage is low, such as 200 V, due to the low voltage, they cannot achieve good control effects, and their applicable voltage range is small and they cannot achieve good control effects.

[0003] Therefore, how to design a DC / DC converter and a control method thereof that can be applicable to a wide voltage input range is a technical problem that the industry urgently needs to solve. Summary of the Invention

[0004] Aiming at the problem that the input voltage range of the DC / DC converter in the prior art is small and cannot well meet the high-voltage input of 800 V, the present invention proposes a DC / DC converter and a control method thereof.

[0005] The technical solution of the present invention is to propose a DC / DC converter, including a first primary circuit and a second primary circuit with interconnected input ends, a first secondary circuit connected to the first primary circuit, a first transformer for connecting the first primary circuit and the first secondary circuit, a secondary second circuit connected to the second primary circuit, a second transformer for connecting the second primary circuit and the second secondary circuit, and a bus capacitor for supplying power to the first primary circuit and the second primary circuit. The input voltages of the first primary circuit and the second primary circuit are adjusted according to the voltage of the bus capacitor, and the outputs of the first secondary circuit and the second secondary circuit are connected to the same output end.

[0006] Further, the first primary circuit includes a first full-bridge circuit and a first capacitor for providing voltage input to the first full-bridge circuit, and the first capacitor is connected in parallel across the first full-bridge circuit;

[0007] The second primary circuit includes a second full-bridge circuit and a second capacitor for providing voltage input to the second full-bridge circuit, and the second capacitor is connected in parallel across the second full-bridge circuit;

[0008] The first capacitor and the second capacitor are connected in series and then connected across the bus capacitor, and the voltages of the first capacitor and the second capacitor are adjusted according to the voltage of the bus capacitor.

[0009] Further, the first primary circuit includes a first half-bridge circuit, a third capacitor and a fourth capacitor that provide voltage input to the first half-bridge circuit, and the third capacitor and the fourth capacitor are connected in series and then connected in parallel across the first half-bridge circuit;

[0010] The second primary circuit includes a second half-bridge circuit, and a

[0011] fifth capacitor and a sixth capacitor that provide voltage input to the second half-bridge circuit, and the fifth capacitor and the sixth capacitor are connected in series and then connected in parallel across the second half-bridge circuit;

[0012] The third capacitor, the fourth capacitor, the fifth capacitor and the sixth capacitor are connected in series in sequence and then connected across the bus capacitor, and the voltages of the third capacitor, the fourth capacitor, the fifth capacitor and the sixth capacitor are adjusted according to the voltage of the bus capacitor.

[0013] Further, the DC / DC converter has two operating modes. When the voltage of the bus capacitor is lower than a preset voltage, the DC / DC converter is in the first operating mode, all the switching tubes in the second primary circuit are turned on, and all the switching tubes in the second secondary circuit are turned off, so that the voltage in the second primary circuit is zero, and the first primary circuit receives all the voltage of the bus capacitor;

[0014] When the voltage of the bus capacitor is higher than the preset voltage, the second primary circuit and the second primary circuit are normally turned on, so that the first primary circuit and the second primary circuit equally divide the voltage of the bus capacitor.

[0015] Further, it further includes a first current detection device for detecting the current in the first primary circuit, a second detection device for detecting the current in the second primary circuit, and a first voltage detection device for detecting the voltage between the first primary circuit and the second primary circuit. The DC / DC converter adjusts the bus capacitor voltage by adjusting the duty ratios of the switching tubes in the first primary circuit and the second primary circuit, so that the currents of the first primary circuit and the second primary circuit are set and adjusted, thereby achieving equal voltage sharing of the bus capacitor.

[0016] Further, it further includes a third current detection device for detecting the output current of the first secondary circuit, a fourth current detection device for detecting the output current of the second secondary circuit, and a second voltage detection device for detecting the voltage between the first primary circuit and the second primary circuit. The DC / DC converter adjusts the bus capacitor voltage by adjusting the duty cycles of the switching tubes in the first primary circuit and the second primary circuit, so as to adjust the current settings of the first primary circuit and the second primary circuit, thereby achieving equal voltage sharing of the bus capacitors.

[0017] Further, the switching tubes in the first primary circuit and the second primary circuit have the same conduction frequency and a phase difference of π or π / 2.

[0018] The present invention also proposes a control method for a DC / DC converter, including:

[0019] Detecting the voltage of the bus capacitor and comparing it with a preset voltage;

[0020] When the voltage of the bus capacitor is lower than the preset voltage, enter the first working mode, and control all the switching tubes in the second primary circuit to conduct and all the switching tubes in the second secondary circuit to cut off;

[0021] When the voltage of the bus capacitor is higher than the preset voltage, enter the second working mode, control the first primary circuit and the second primary circuit to work normally, and adjust the input voltages of the first primary circuit and the second primary circuit to be the same, both being half of the voltage of the bus capacitor.

[0022] Further, when in the second working mode, it further includes:

[0023] Detecting the currents on the first primary circuit and the second primary circuit;

[0024] Calculating the output currents of the first secondary circuit and the second secondary circuit based on the first primary circuit and the second primary circuit, and performing closed-loop control of the output voltage and output current;

[0025] Adjusting the voltage between the first primary circuit and the second primary circuit to be equal to half of the voltage of the bus capacitor;

[0026] Obtaining the peak current given values of the first primary circuit and the second primary circuit based on the voltage between the first primary circuit and the second primary circuit and the output currents of the first secondary circuit and the second secondary circuit, and performing current peak PWM processing on the working current to make it reach the peak current given value;

[0027] Adjusting the duty cycles of the switching tubes in the first primary circuit and the second primary circuit according to the PWM signal, balancing and distributing the power outputs of the first primary circuit and the second primary circuit, and achieving equal voltage sharing of the bus capacitors.

[0028] Further, when in the second working mode, it further includes:

[0029] Detect the output currents of the first secondary circuit and the second secondary circuit;

[0030] Adjust the voltage between the first primary circuit and the second primary circuit to be equal to half of the voltage of the bus capacitor;

[0031] Adopt closed-loop control for the output voltage and obtain the loop output at this time;

[0032] Use the loop output as the deviation compensation of the current loop reference, and adjust the duty cycles of the switching tubes in the first primary circuit and the second primary

[0033] circuit, so that the output current is equal to the loop output, and make the first primary circuit and the second primary circuit share the current equally and the bus capacitor share the voltage equally.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] 1. In the present invention, the first primary circuit and the second primary circuit are connected to each other to jointly share the voltage of the bus capacitor. When the voltage of the bus capacitor is too high, it can be jointly shared by the first primary circuit and the second primary circuit. When the voltage of the bus capacitor is too low, only the first primary circuit can be turned on. Through the switching between the first working mode and the second working mode, the present invention can be applicable to high-voltage and low-voltage inputs, so as to meet the wide voltage input range.

[0036] 2. In the present invention, the first primary circuit and the second primary circuit share the voltage of the bus capacitor equally, so that it can control the 800V high-voltage input by using ordinary 650V silicon switching tubes, replacing the use of 1200V SiC devices and reducing the cost.

[0037] 3. In the present invention, the switching tubes in the first primary circuit and the second primary circuit have the same control frequency and a phase difference of π or π / 2, greatly reducing the ripple noise of high-voltage input and low-voltage output, which is beneficial to the design of the EMC filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0039] Figure 1 It is the circuit topology diagram of the first embodiment of the present invention;

[0040] Figure 2 The circuit topology diagram of the second embodiment of the present invention;

[0041] Figure 3 The control logic diagram of the first embodiment of the present invention;

[0042] Figure 4 The control logic diagram of the second embodiment of the present invention. Detailed implementation manners

[0043] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clear, 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.

[0044] Therefore, a feature pointed out in this specification will be used to illustrate one of the features of one embodiment of the present invention, rather than implying that each embodiment of the present invention must have the described feature. In addition, it should be noted that this specification describes many features. Although some features may be combined together to show a possible system design, these features can also be used in other combinations that are not explicitly described. Therefore, unless otherwise stated, the described combination is not intended to be limiting.

[0045] The principle and structure of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0046] In the existing charging system, the DC / DC converter uses a common 650V silicon MOS tube, which cannot meet the high-voltage input of 800V, and SiC devices that meet 1200V need to be used, which increases the cost of the converter. However, for 1200V SiC devices, they cannot achieve good control effects in the case of low-voltage input, and the input voltage range they use is relatively narrow. The idea of the present invention is to propose a DC / DC converter, which is provided with a first primary circuit and a second primary circuit. Through the voltage distribution of the first primary circuit and the second primary circuit, it can adapt to high-voltage input and low-voltage input, achieve a wide voltage input range, without replacing the switching tube device, and reduce the design cost of the DC / DC converter.

[0047] Specifically, the DC / DC converter proposed by the present invention includes a first primary circuit, a second primary circuit, a first secondary circuit connected to the first primary circuit, a second secondary circuit connected to the second primary circuit, and a bus capacitor for providing an input voltage. Among them, a first transformer is provided between the first primary circuit and the first secondary circuit, and a second transformer is provided between the second primary circuit and the second secondary circuit. The DC / DC conversion is achieved through the first transformer and the second transformer, converting the input voltage into a low voltage and inputting it to the first secondary circuit and the second secondary circuit, and outputting the voltage through the first secondary circuit and the second secondary circuit.

[0048] Furthermore, the input sides of the first primary circuit and the second primary circuit are connected together to share the voltage of the bus capacitor. The outputs of the first secondary circuit and the second secondary circuit are connected to the same output terminal to output the voltage after DC / DC conversion. The whole of the present invention is equivalent to a single-channel DC / DC controller, which receives the input voltage of the bus capacitor and provides a corresponding output voltage. Among them, the input voltages of the first primary circuit and the second primary circuit are determined according to the voltage of the bus capacitor. When the voltage of the bus capacitor is too high and exceeds the withstand voltage of the switching tubes in the first primary circuit and / or the second primary circuit, at this time, the first primary circuit and the second primary circuit share the voltage of the bus capacitor, thereby reducing the input voltages of the first primary circuit and the second primary circuit, avoiding damage to the switching tubes. At the same time, since the outputs of the first secondary circuit and the second secondary circuit are connected to the same output terminal, it does not affect the final output result; when the voltage of the bus capacitor is low and meets the withstand voltage of the switching tubes in the first primary circuit and / or the second primary circuit, at this time, the control and regulation of this voltage can be achieved through the first primary circuit. At this time, only the first primary circuit needs to be turned on, all the switching tubes in the second primary circuit are turned on to make it short-circuited, and at the same time, all the switching tubes in the second secondary circuit are turned off to make it open-circuited. At this time, the second primary circuit and the second secondary circuit do not work, and only the first primary circuit works to adjust the low voltage input.

[0049] Furthermore, please refer to Figure 1 , the first primary circuit includes a first full-bridge circuit and a first capacitor for providing voltage input to the first full-bridge circuit. The first capacitor is connected in parallel across the two ends of the first full-bridge circuit; the second primary circuit includes a second full-bridge circuit and a second capacitor for providing voltage input to the second full-bridge circuit. The second capacitor is connected in parallel across the two ends of the second full-bridge circuit. Among them, the first capacitor and the second capacitor are connected in series across the two ends of the bus capacitor. The first capacitor is used to provide the input voltage for the first full-bridge circuit, and the second capacitor is used to provide the input voltage for the second full-bridge circuit. When adjusting the input voltages of the first primary circuit and the second primary circuit, only the voltage between the first capacitor and the second capacitor needs to be adjusted.

[0050] The first capacitor and the second capacitor can act as energy storage devices, can store and release energy, and their voltage is controllable. After the first capacitor and the second capacitor are connected in series at both ends of the bus capacitor, they can absorb the energy released by the bus capacitor and respectively supply power to the first primary circuit and the second primary circuit, thereby solving the problem of 800V bus capacitor power supply damaging the switch tube. In the present invention, the switch tubes all use ordinary 650V silicon switch tubes, which can withstand a withstand voltage of 650V. Although the voltages on the first primary circuit and the second primary circuit are 600V and 200V respectively, which are also within the tolerance range of the switch tube, the final output voltage cannot be well regulated in this case. Therefore, in the present invention, the voltages on the first primary circuit and the second primary circuit are controlled to be 400V. In the subsequent output voltage regulation, as long as the switching frequencies of the switch tubes are set to be the same, the same output waveform can be obtained, which is convenient for controlling the output voltage. During control, in order to make the voltage of the first primary circuit and the voltage of the second primary circuit both 400V, it is only necessary to adjust the voltage between the first capacitor and the second capacitor. When the voltage between the first capacitor and the second capacitor is 400V, it can be considered that the voltages on the first capacitor and the second capacitor are both 400V.

[0051] Wherein, the first full-bridge circuit includes an upper bridge arm and a lower bridge arm, which is composed of 4 switch tubes, and each of which is composed of a switch tube Q1 and a switch tube Q3 to form a bridge arm, wherein the switch tube Q1 forms the upper bridge arm, and the switch tube Q3 forms the lower bridge arm, and the switch tube Q2 and the switch tube Q4 form another bridge arm, wherein the switch tube Q2 forms the upper bridge arm, and the switch tube Q4 forms the lower bridge arm, and the middle of each bridge arm is connected to the primary winding of the transformer for providing input voltage. The output voltage of the first primary circuit can be adjusted by adjusting the duty cycle of the switch tubes Q1, Q2, Q3 and Q4. The first capacitor is connected to the two ends of the two bridge arms respectively to provide voltage to the first full-bridge circuit.

[0052] The second full-bridge circuit is the same as the first full-bridge circuit, which is composed of 4 switching tubes, wherein the switching tube Q5 and the switching tube Q7 form a bridge arm, the switching tube Q5 forms an upper bridge arm, the switching tube Q7 forms a lower bridge arm, the switching tube Q6 and the switching tube Q8 form another bridge arm, wherein the switching tube Q6 constitutes the upper bridge arm, and the switching tube Q8 constitutes the lower bridge arm. The output voltage of the second primary circuit can be adjusted by adjusting the switching tubes Q5, Q6, Q7 and Q8.

[0053] See also Figure 2, in another embodiment of the present invention, the first primary circuit includes a first half-bridge circuit, a third capacitor and a fourth capacitor for supplying power to the first half-bridge circuit. The third capacitor and the fourth capacitor are connected in series and then connected across the first half-bridge circuit; the second primary circuit includes a second half-bridge circuit, a fifth capacitor and a sixth capacitor for supplying power to the second half-bridge circuit. The fifth capacitor and the sixth capacitor are connected in series and then connected across the second half-bridge circuit. And the third capacitor, the fourth capacitor, the fifth capacitor and the sixth capacitor are connected in series in turn across the bus capacitor. At the same time, the sum of the voltages of the third capacitor and the fourth capacitor and the sum of the voltages of the fifth capacitor and the sixth capacitor are adjusted to be applicable to different bus voltages.

[0054] Wherein, the first half-bridge circuit is composed of a switching tube Q9 and a switching tube Q10 connected in series, and the second half-bridge circuit is composed of a switching tube Q11 and a switching tube Q12 connected in series. By adjusting the duty cycles of the 4 switching tubes, the outputs of the first half-bridge circuit and the second half-bridge circuit can be adjusted. Compared with the full-bridge circuit, the half-bridge circuit has fewer switching tubes, lower cost, and no problem of simultaneous on-off, and has strong anti-unbalance ability.

[0055] A first transformer for DC / DC conversion is provided between the first primary circuit and the first secondary circuit, and a second transformer for DC / DC conversion is provided between the second primary circuit and the second secondary circuit. They are respectively used for DC / DC conversion of the output voltages of the first primary circuit and the second primary circuit. Among them, the first transformer includes a first primary winding, a first secondary winding and a second secondary winding. Its first primary winding is connected to the first primary circuit and is used to receive the output voltage of the first primary circuit. The first secondary winding and the second secondary winding are connected to the first secondary circuit and are used to output the voltage after DC / DC conversion. A switching tube Q9 is provided at the connection of the first secondary circuit and the first secondary winding, and a switching tube Q10 is provided at the connection of the second secondary winding. By adjusting the duty cycles of the switching tube Q9 and the switching tube Q10, the magnitude of the output voltage can be adjusted.

[0056] The second transformer includes a second primary winding, a third secondary winding and a fourth secondary winding. The second primary winding is connected to the second primary circuit and is used to receive the output voltage of the second primary circuit. The third secondary winding and the fourth secondary winding are connected to the second secondary circuit and are used to output the voltage after DC / DC conversion. A switching tube Q11 is provided at the connection of the second secondary circuit and the third secondary winding, and a switching tube Q12 is provided at the connection of the fourth secondary winding. By adjusting the duty cycles of the switching tube Q11 and the switching tube Q12, the magnitude of the output voltage can be adjusted.

[0057] Furthermore, the output terminals of the first secondary circuit and the second secondary circuit are connected to the same output capacitor, serving as the total output of the entire circuit, which is equivalent to achieving the control and regulation of an input voltage. During control and regulation, since the voltages on the first primary circuit and the second primary circuit are the same, after setting the same coil windings, the same output voltage can be obtained, and the amplitudes of the resulting voltage ripples are the same. By setting the same switching frequency, the same voltage waveform can be obtained. Then, by phase-shifting the firing of the first primary circuit and the second primary circuit so that the phase difference between them is π or π / 2, the input and output ripple currents can be optimized while adjusting the output.

[0058] Specifically, the present invention also proposes a control method for a DC / DC converter, which includes detecting the voltage of the bus capacitor and comparing it with a preset voltage;

[0059] When the voltage of the bus capacitor is lower than the preset voltage, it enters the first working mode, and controls all the switching tubes in the second primary circuit to conduct and all the switching tubes in the second secondary circuit to cut off;

[0060] When the voltage of the bus capacitor is higher than the preset voltage, it enters the second working mode, controls the first primary circuit and the second primary circuit to work normally, and adjusts the input voltages of the first primary circuit and the second primary circuit to be the same, both being half of the voltage of the bus capacitor.

[0061] Among them, the preset voltage is 400V. When the voltage of the bus capacitor is lower than 400V, it is within the withstand voltage range of the switching tubes. At this time, there is no need for two-way control. Just enter the first working mode, conduct all the switching tubes in the second primary circuit, making it equivalent to a short circuit, and cut off all the switching tubes in the second secondary circuit, making it equivalent to an open circuit. At this time, the second primary circuit and the second secondary circuit do not work, and the voltage of the bus capacitor is all applied to the first primary circuit. The first primary circuit receives all the voltage of the bus capacitor and is within the withstand voltage range of the switching tubes. The control and regulation of this voltage can be achieved through the first primary circuit and the first secondary circuit.

[0062] When the voltage of the bus capacitor is higher than 400V, it can be controlled in two ways. However, for high-voltage inputs, especially voltages above 650V, it is very easy to damage the switching tubes. Therefore, at this time, it is necessary to enter the second working mode, conduct the first primary circuit and the second primary circuit normally, and divide the voltage of the bus capacitor by the first capacitor and the second capacitor, thereby reducing the voltage received by the switching tubes. For example, when the voltage of the bus capacitor is 800V, at this time, when dividing the voltage of the bus capacitor by the first primary circuit and the second primary circuit, the voltages of the first primary circuit and the second primary circuit are both 400V, which is within the 650V withstand voltage range of the switching tubes and can control them.

[0063] Further, in the second control mode, to implement the control of the DC / DC converter of the present invention, a first detection device for detecting the operating current of the first primary circuit is provided in the first primary circuit, a second detection device for detecting the operating current of the second primary circuit is provided in the second primary circuit, and a first voltage detection device for detecting the voltage between the first primary circuit and the second primary circuit is provided. Through the real-time monitoring of current and voltage, the DC / DC converter can achieve real-time control of high-voltage input.

[0064] Specifically, please refer to Figure 3 , which is the control schematic diagram under this embodiment. Among them, I_CT_up is the detected current on the first primary circuit, I_CT_down is the detected current on the second primary circuit, Vbus is the voltage of the bus capacitor, V_n is the voltage between the first capacitor and the second capacitor, I_pk_ref_up is the peak current set value of the first primary circuit, I_pk_ref_dowm is the peak current set value of the second primary circuit, and Vo_LV is the output voltage.

[0065] The specific control process is as follows: First, detect the currents I_CT_up and I_CT_down on the first primary circuit and the second primary circuit, then calculate the output current Iout based on I_CT_up and I_CT_down, and perform closed-loop control on the output voltage and output current to obtain I_pk_ref_up and I_pk_ref_down. Then, adjust the voltages on the first capacitor and the second capacitor to make V_n half of Vbus. Then, under the condition of this voltage input, compare I_CT_up with I_pk_ref_up and I_CT_down with I_pk_ref_down, and then perform current peak PWM processing based on the difference between the two to adjust the PWM signal of the control switch tube, and then adjust the duty cycle of the switch tubes in the first primary circuit and the second primary circuit according to the PWM signal, so as to achieve the effects of current sharing and equal voltage of the bus capacitor.

[0066] In another embodiment of the present invention, the DC / DC converter further includes a third current detection device for detecting the output current of the first secondary circuit, a fourth current detection device for detecting the output current of the second secondary circuit, and a second voltage detection device for detecting the voltage between the first primary circuit and the second primary circuit. Through the real-time monitoring of current and voltage, the DC / DC converter can achieve real-time control of high-voltage input.

[0067] Specifically, please refer to Figure 4, which is a control schematic diagram under this embodiment. Among them, I_out-up is the output current of the first secondary circuit, I_out-up is the output current of the second secondary circuit, Vbus is the voltage of the bus capacitor, V_n is the voltage between the first capacitor and the second capacitor, and I_out_ref is the output of the voltage loop.

[0068] The specific control process is as follows: First, detect the output currents I_out-up and I_out-down of the first secondary circuit and the second secondary circuit, and then perform closed-loop control on the output voltage, which is used as the given reference of the current inner loop. Then, perform HV input voltage balance control to make the voltage V_n between the first capacitor and the second capacitor equal to half of the bus capacitor voltage Vbus, and control the loop output as the deviation compensation of the current loop given. Then, adjust the duty cycle of the switching tubes in the first primary circuit and the second primary circuit according to this deviation compensation to achieve the purpose of current sharing and bus capacitor voltage equalization.

[0069] Two control methods are proposed in the present invention. By detecting the currents on the first primary circuit and the second primary circuit respectively, and then controlling according to the peak current given value, the power distribution of the first primary circuit and the second primary circuit is adjusted to make V-n equal to Vbus / 2. The other is to directly detect the output voltages and output currents of the first secondary circuit and the second secondary circuit and perform corresponding control. Both methods can achieve control under high-voltage input to achieve the purpose of current sharing and bus capacitor voltage equalization. According to the actual situation, those skilled in the art can adopt different control methods, which are applicable to the circuit topologies of Figure 1 and Figure 2 both embodiments. It should be noted that Figure 1 and Figure 2 in both embodiments, the current detection points I_CT_up, I_CT_down, I_out-up, and I_out-down are shown simultaneously for easy understanding. In the actual control process, only two current detection points need to be collected according to the control method. When the first control method is adopted, detect I_CT_up and I_CT_down; when the second control method is adopted, detect I_out-up and I_out-down.

[0070] Preferably, in the present invention, the switching frequencies of the switching tubes in the first primary circuit and the second primary circuit are the same, and the phase difference is π or π / 2. Through the above settings, the purpose of high-voltage input and low-voltage output ripple current can be achieved, and the design difficulty of the EMC filter is greatly reduced.

[0071] Compared with the prior art, through the settings of the first primary circuit and the second primary circuit, the present invention can meet the voltage of a wide input range by adjusting the input voltages of the first primary circuit and the second primary circuit, and can achieve a good control effect at voltages from 200V to 860V. At the same time, for high-voltage input, through the settings of the present invention, instead of using 1200V SiC devices, the control of high-voltage input can be achieved through ordinary 650V switching tubes, reducing the cost of the device. Since the present invention is provided with two adjustment circuits, it can adjust the ripple current of high-voltage input and low-voltage output by adjusting the phase difference between the first primary circuit and the second primary circuit, reducing the design difficulty of the EMC filter.

[0072] The above embodiments are only used to illustrate the specific embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and variations can be made, and these modifications and variations should all fall within the protection scope of the present invention.

Claims

1. A control method for a DC / DC converter, characterized in that the DC / DC converter includes: a first primary circuit and a second primary circuit with interconnected input ends, a first secondary circuit connected to the first primary circuit, a first transformer for connecting the first primary circuit and the first secondary circuit, a second secondary circuit connected to the second primary circuit, a second transformer for connecting the second primary circuit and the second secondary circuit, and a bus capacitor for supplying power to the first primary circuit and the second primary circuit. The input voltages of the first primary circuit and the second primary circuit are adjusted according to the voltage of the bus capacitor, and the outputs of the first secondary circuit and the second secondary circuit are connected to the same output terminal; the control method for the DC / DC converter includes: detecting the voltage of the bus capacitor and comparing it with a preset voltage; when the voltage of the bus capacitor is lower than the preset voltage, entering a first operating mode, controlling all the switching tubes in the second primary circuit to be fully conducting and all the switching tubes in the second secondary circuit to be fully cut off; when the voltage of the bus capacitor is higher than the preset voltage, entering a second operating mode, controlling the first primary circuit and the second primary circuit to operate normally, and adjusting the input voltages of the first primary circuit and the second primary circuit to be the same, both being half of the voltage of the bus capacitor; when in the second operating mode, it further includes: detecting the currents on the first primary circuit and the second primary circuit; calculating the output currents of the first secondary circuit and the second secondary circuit based on the currents on the first primary circuit and the second primary circuit, and performing closed-loop control of the output voltage and the output current; adjusting the voltage between the first primary circuit and the second primary circuit to be equal to half of the voltage of the bus capacitor; obtaining the peak current set values of the first primary circuit and the second primary circuit based on the voltage between the first primary circuit and the second primary circuit and the output currents of the first secondary circuit and the second secondary circuit, and performing current peak PWM processing on the working current to make it reach the peak current set value; adjusting the duty cycles of the switching tubes in the first primary circuit and the second primary circuit according to the PWM signal, evenly distributing the power outputs of the first primary circuit and the second primary circuit, and achieving equal voltage sharing of the bus capacitor.

2. The control method according to claim 1, wherein when in the second operating mode, it further includes: detecting the output currents of the first secondary circuit and the second secondary circuit; adjusting the voltage between the first primary circuit and the second primary circuit to be equal to half of the voltage of the bus capacitor; performing closed-loop control on the output voltage and obtaining the loop output at this time; using the loop output as the deviation compensation for the current loop set value, and adjusting the duty cycles of the switching tubes in the first primary circuit and the second primary circuit so that the output current is equal to the loop output, making the first primary circuit and the second primary circuit have equal current and achieving equal voltage sharing of the bus capacitor.

3. The control method according to claim 1, wherein the first primary circuit includes a first full-bridge circuit and a first capacitor for providing voltage input to the first full-bridge circuit, and the first capacitor is connected in parallel across the two ends of the first full-bridge circuit; The second primary circuit includes a second full-bridge circuit and a second capacitor that provides voltage input to the second full-bridge circuit. The second capacitor is connected in parallel across the two ends of the second full-bridge circuit. The first capacitor and the second capacitor are connected in series and then connected across the two ends of the bus capacitor. The voltages of the first capacitor and the second capacitor are adjusted according to the voltage of the bus capacitor.

4. The control method according to claim 1, wherein, The first primary circuit includes a first half-bridge circuit, a third capacitor and a fourth capacitor that provide voltage input to the first half-bridge circuit. The third capacitor and the fourth capacitor are connected in series and then connected in parallel across the two ends of the first half-bridge circuit. The second primary circuit includes a second half-bridge circuit and a fifth capacitor and a sixth capacitor that provide voltage input to the second half-bridge circuit. The fifth capacitor and the sixth capacitor are connected in series and then connected in parallel across the two ends of the second half-bridge circuit. The third capacitor, the fourth capacitor, the fifth capacitor and the sixth capacitor are connected in series in sequence and then connected across the two ends of the bus capacitor. The voltages of the third capacitor, the fourth capacitor, the fifth capacitor and the sixth capacitor are adjusted according to the voltage of the bus capacitor.

5. The control method according to claim 1, characterized in that The DC / DC converter has two operating modes. When the voltage of the bus capacitor is lower than a preset voltage, the DC / DC converter is in the first operating mode. All the switching tubes in the second primary circuit are turned on, and all the switching tubes in the second secondary circuit are turned off, making the voltage in the second primary circuit zero. The first primary circuit receives all the voltage of the bus capacitor. When the voltage of the bus capacitor is higher than the preset voltage, the second primary circuit and the second primary circuit are normally turned on, so that the first primary circuit and the second primary circuit share the voltage of the bus capacitor equally.

6. The control method according to claim 1, characterized in that It further includes a first current detection device for detecting the current in the first primary circuit, a second detection device for detecting the current in the second primary circuit, and a first voltage detection device for detecting the voltage between the first primary circuit and the second primary circuit. The DC / DC converter adjusts the voltage of the bus capacitor by adjusting the duty cycles of the switching tubes in the first primary circuit and the second primary circuit, so that the currents of the first primary circuit and the second primary circuit are set and adjusted, thereby achieving equal voltage sharing of the bus capacitor.

7. The control method according to claim 1, wherein It further includes a third current detection device for detecting the output current of the first secondary circuit, a fourth current detection device for detecting the output current of the second secondary circuit, and a second voltage detection device for detecting the voltage between the first primary circuit and the second primary circuit. The DC / DC converter adjusts the voltage of the bus capacitor by adjusting the duty cycles of the switching tubes in the first primary circuit and the second primary circuit, so that the currents of the first primary circuit and the second primary circuit are set and adjusted, thereby achieving equal voltage sharing of the bus capacitor.

8. The control method according to claim 1, characterized in that The switching tubes in the first primary circuit and the second primary circuit have the same conduction frequency and a phase difference of π or π / 2.

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