DC / DC conversion system and control method thereof

Abstract

The invention relates to a direct current / direct current conversion system and a control method thereof, the direct current / direct current conversion system is used for supplying power to a load and comprises two two-stage circuits, the two two-stage circuits are connected in parallel, each two-stage circuit comprises a direct current / direct current converter, a bus capacitor and an isolation type resonance circuit, and the control method comprises the steps that the two two-stage circuits are connected in parallel; when the DC / DC conversion system works in a light load mode, controlling the first two-stage circuit to operate so as to supply power to a load, controlling the DC / DC converter of the second two-stage circuit to operate so as to charge a corresponding bus capacitor, and controlling the isolated resonant circuit of the second two-stage circuit not to operate; when the DC / DC conversion system works in a heavy load mode, the two isolated resonant circuits of the first two-stage circuit and the second two-stage circuit are controlled to operate so as to jointly supply power to a load.

Description

Technical Field

[0001] This disclosure relates to conversion systems, and more particularly to a DC / DC conversion system and its control method. Background Technology

[0002] DC / DC converters are an essential component of electric vehicles, used to convert the electrical energy from the high-voltage power battery in new energy vehicles into low-voltage DC power to power, for example, 12-48V low-voltage vehicle electrical appliances or equipment, such as car air conditioning, lights, or steering wheels.

[0003] To enhance safety, DC / DC converter systems typically employ a redundant design with multiple parallel circuits. Furthermore, to meet the requirements of a wide range of input and output voltages, DC / DC converter systems usually include a two-stage circuit topology. In addition, DC / DC converter systems are often used under light load conditions and have high requirements for instantaneous dynamic load handling.

[0004] In traditional DC / DC converter systems using a multi-parallel design, one or more circuits are often shut down to improve efficiency under light loads. However, when an external load is instantaneously applied, the shut-down circuits require time to fully start up and handle the load power. Therefore, all power is borne by the remaining circuits, resulting in disadvantages such as instantaneous overpower and low regulation capability. Furthermore, traditional DC / DC converters have poor dynamic performance and cannot meet power demands.

[0005] Therefore, it is necessary to develop a DC / DC conversion system and its control method to solve the problems faced by existing technologies. Summary of the Invention

[0006] The purpose of this disclosure is to provide a DC / DC conversion system and its control method. When the DC / DC conversion system operates in light-load mode, it controls the operation of a first two-stage circuit to supply power to the load, and controls the operation of the DC / DC converter in a second two-stage circuit to charge the corresponding bus capacitor. Furthermore, it controls the isolation resonant circuit of the second two-stage circuit to remain inactive. In other words, when the DC / DC conversion system operates in light-load mode, the first two-stage circuit is sufficient to handle the power supplied to the load, while simultaneously pre-charging the bus capacitor of the second two-stage circuit. However, the inactivity of the isolation resonant circuit in the second two-stage circuit reduces power loss, thereby improving the efficiency of the DC / DC conversion system. Moreover, when the DC / DC conversion system operates in heavy-load mode, both the isolation resonant circuits of the first and second two-stage circuits are controlled to operate to jointly supply power to the load. In other words, since the bus capacitor of the second two-stage circuit is pre-charged in light-load mode, the isolated resonant circuit of the second two-stage circuit can be instantly turned on when the DC / DC converter system switches from light-load mode to heavy-load mode. The second two-stage circuit can quickly take over the power supplied to the load, avoiding damage to the devices and having better dynamic performance. Therefore, the DC / DC converter system of this disclosure, by utilizing the first two-stage circuit for power supply and the second two-stage circuit for pre-charging, significantly improves the efficiency when switching from light-load mode to heavy-load mode, while also improving the overall dynamic performance.

[0007] To achieve the above objectives, one embodiment of this disclosure provides a control method applied to a DC / DC converter system. The DC / DC converter system supplies power to a load and includes at least two two-stage circuits connected in parallel. Each two-stage circuit includes a DC / DC converter, a bus capacitor, and an isolated resonant circuit. The control method includes the following steps: When the DC / DC converter system operates in light-load mode, the first two-stage circuit is controlled to operate to supply power to the load, and the DC / DC converter of the second two-stage circuit is controlled to operate to charge the corresponding bus capacitor. The isolated resonant circuit of the second two-stage circuit is controlled to not operate. When the DC / DC converter system operates in heavy-load mode, both the first and second isolated resonant circuits are controlled to operate to jointly supply power to the load.

[0008] To achieve the above objectives, another embodiment of this disclosure provides a DC / DC converter system for converting input electrical energy to supply power to a load, and includes a control unit and at least two two-stage circuits. The at least two two-stage circuits are connected in parallel. Each two-stage circuit includes a DC / DC converter, a bus capacitor, and an isolated resonant circuit. The DC / DC converter converts the input electrical energy. The bus capacitor is connected to the DC / DC converter to store the converted input electrical energy as a bus voltage. The isolated resonant circuit is connected to the bus capacitor to convert the bus voltage to supply power to the load. When the DC / DC converter system operates in light-load mode, the control unit controls the first two-stage circuit of the at least two two-stage circuits to operate to supply power to the load, and controls the DC / DC converter of the second two-stage circuit of the at least two two-stage circuits to operate to charge the corresponding bus capacitor, and controls the isolated resonant circuit of the second two-stage circuit to not operate; when the DC / DC converter system operates in heavy-load mode, the control unit controls both the first two-stage circuit and the two isolated resonant circuits of the second two-stage circuit to operate together to supply power to the load. Attached Figure Description

[0009] Figure 1 This is a circuit architecture diagram of the DC / DC conversion system disclosed herein; Figure 2 A flowchart of the control method for a first embodiment of the DC / DC converter system disclosed herein; and Figure 3 This is a flowchart of the control method for a second embodiment of the DC / DC conversion system disclosed herein.

[0010] Explanation of reference numerals in the attached figures: 1: DC / DC conversion system 31: Input end 311: Input positive terminal 312: Input negative terminal 32: Output terminal 321: Output positive terminal 322: Output negative terminal Co: Input capacitance 4a: The first two-stage circuit 4b: The second two-stage circuit 41: DC / DC converter M1: First switching transistor D1: First diode L1: First Inductor M2: Second switching transistor D2: Second diode M3: Third switching transistor M4: Fourth switching transistor C1: First capacitor C2: Second capacitor 431: Transformer 431a: Primary winding 431b: First secondary winding 431c: Secondary winding Lr: Resonant inductance M5: Fifth switching transistor M6: Sixth switching transistor A: First connection point B: Second connection point 42: Bus capacitor 43: Isolated resonant circuit 5: Control Unit 51: First Controller 52: Second controller 9: Load S1-S3, M1-M7: Steps Detailed Implementation

[0011] Some typical embodiments embodying the features and advantages of this disclosure will be described in detail in the following description. It should be understood that this disclosure can have various variations in different forms, all of which do not depart from the scope of this disclosure, and the descriptions and drawings therein are for illustrative purposes only and not for limiting this disclosure.

[0012] Please see Figure 1 This is a circuit architecture diagram of the DC / DC converter system disclosed herein. As shown, the DC / DC converter system 1 of this disclosure is used to convert input electrical energy to supply power to a load 9, and includes an input terminal 31, an output terminal 32, two two-stage circuits, an output capacitor Co, and a control unit 5. The input terminal 31 includes a positive input terminal 311 and a negative input terminal 312, and the output terminal 32 includes a positive output terminal 321 and a negative output terminal 322. The DC / DC converter system 1 receives input electrical energy through the positive input terminal 311 and the negative input terminal 312 of the input terminal 31, and outputs the converted output electrical energy through the positive output terminal 321 and the negative output terminal 322 of the output terminal 32. The two two-stage circuits include a first two-stage circuit 4a and a second two-stage circuit 4b, which are connected in parallel. The first two-stage circuit 4a and the second two-stage circuit 4b respectively include a DC / DC converter 41, a bus capacitor 42, and an isolated resonant circuit 43. It is understood that the number of two-stage circuits in the DC / DC conversion system 1 can be flexibly adjusted according to the actual power requirements, for example, three, four or more, and this disclosure does not impose any restrictions.

[0013] The DC / DC converter 41 can be, but is not limited to, a boost circuit, a buck circuit, or a buck-boost circuit, used to receive and convert input electrical energy. In this embodiment, the DC / DC converter 41 is illustrated as a buck-boost circuit, including a first switch M1, a first diode D1, a first inductor L1, a second switch M2, and a second diode D2. The first terminal of the first switch M1 is connected to the positive input terminal 311 of the input terminal 31. The cathode of the first diode D1 is connected to the second terminal of the first switch M1, and the anode of the first diode D1 is connected to the negative input terminal 312 of the input terminal 31. The first terminal of the first inductor L1 is connected to the second terminal of the first switch M1. The second switch M2 is connected between the second terminal of the first inductor L1 and the negative input terminal 312 of the input terminal 31. The anode of the second diode D2 is connected to the second terminal of the first inductor L1.

[0014] The bus capacitor 42 is connected between the cathode of the second diode D2 of the DC / DC converter 41 and the negative input terminal 312 of the input terminal 31 to store the input electrical energy converted by the DC / DC converter 41. The DC / DC converter 41 can be used to adjust the bus voltage on the bus capacitor 42.

[0015] The isolated resonant circuit 43 can be, but is not limited to, an isolated LLC circuit or an isolated CLLC circuit. It is connected to the bus capacitor 42 to convert and isolate the bus voltage on the bus capacitor 42 to supply power to the load 9. In this embodiment, the isolated resonant circuit 43 is illustrated as an isolated LLC circuit, including a third switch M3, a fourth switch M4, a first capacitor C1, a second capacitor C2, a transformer 431, a resonant inductor Lr, a fifth switch M5, and a sixth switch M6. The third switch M3 and the fourth switch M4 are connected in series to form a first connection point A and are connected in parallel with the bus capacitor 42. The first capacitor C1 and the second capacitor C2 are connected in series to form a second connection point B and are connected in parallel with the bus capacitor 42. The transformer 431 includes a primary winding 431a, a first secondary winding 431b, and a second secondary winding 431c, wherein the first secondary winding 431b and the second secondary winding 431c are connected in series. The resonant inductor Lr is connected between one end of the primary winding 431a and the first connection point A, and the other end of the primary winding 431a is connected to the second connection point B. The fifth switch M5 is connected between the first end of the first secondary winding 431b and the positive output terminal 321 of the output terminal 32. The second end of the first secondary winding 431b is connected to the first end of the second secondary winding 431c and to the negative output terminal 322 of the output terminal 32. The sixth switch M6 is connected between the second end of the second secondary winding 431c and the positive output terminal 321 of the output terminal 32. The output capacitor Co is connected between the positive output terminal 321 and the negative output terminal 322 of the output terminal 32.

[0016] Control unit 5 confirms the operating status of DC / DC converter system 1. For example, when control unit 5 confirms that the output power of DC / DC converter system 1 is greater than 800W, it is in heavy load mode; when control unit 5 confirms that the output power of DC / DC converter system 1 is less than 800W, it is in light load mode. When control unit 5 confirms that DC / DC converter system 1 is operating in light load mode, it controls the first two-stage circuit 4a to operate to supply power to load 9, and controls the DC / DC converter 41 of the second two-stage circuit 4b to operate to charge the corresponding bus capacitor 42, and controls the isolated resonant circuit 43 of the second two-stage circuit 4b to not operate. In other words, when DC / DC converter system 1 is operating in light load mode, the bus capacitor 42 of the second two-stage circuit 4b is pre-charged, and the isolated resonant circuit 43 of the second two-stage circuit 4b is not operating, which reduces the power loss of the second two-stage circuit 4b, thereby improving the efficiency of the second two-stage circuit 4b.

[0017] When the control unit 5 confirms that the DC / DC converter system 1 is operating in heavy-load mode (e.g., the load 9 is momentarily loaded), it controls both the isolated resonant circuit 43 of the first two-stage circuit 4a and the isolated resonant circuit 43 of the second two-stage circuit 4b to operate together to supply power to the load 9. For example, when the control unit 5 confirms that the DC / DC converter system 1 is switching from light-load mode to heavy-load mode, the control unit 5 controls the power supplied to the load 9 by the first two-stage circuit 4a to decrease, and controls the isolated resonant circuit 43 of the second two-stage circuit 4b to operate and gradually increase the power supplied to the load 9, and finally controls the isolated resonant circuits 43 of the first two-stage circuit 4a and the second two-stage circuit 4b to balance and jointly supply power to the load 9. In other words, since the bus capacitor 42 of the second two-stage circuit 4b has been pre-charged in the light-load mode, the isolated resonant circuit 43 of the second two-stage circuit 4b can be turned on instantly when the DC / DC converter system 1 switches from the light-load mode to the heavy-load mode. The second two-stage circuit 4b can quickly take over the power supplied to the load 9, avoid damage to the devices and have better dynamic performance.

[0018] In this embodiment, the control unit 5 further includes a first controller 51 and a second controller 52. The first controller 51 is a front-end controller that controls the operation of the DC / DC converter 41 in the first two-stage circuit 4a and the DC / DC converter 41 in the second two-stage circuit 4b to perform closed-loop control, thereby controlling the output voltage and output current of the DC / DC conversion system 1. The second controller 52 is a back-end controller that controls the isolated resonant circuit 43 in the first two-stage circuit 4a and the isolated resonant circuit 43 in the second two-stage circuit 4b to perform open-loop control.

[0019] Please see Figure 2 and cooperate Figure 1,in Figure 2 This is a flowchart of the control method for a first embodiment of the DC / DC converter system disclosed herein. First, step S1 is executed to confirm whether the DC / DC converter system 1 is operating in light-load mode. If the confirmation result of step S1 is yes, i.e., the DC / DC converter system 1 is operating in light-load mode, step S2 is executed to control the first two-stage circuit 4a to operate to supply power to the load 9, and to control the DC / DC converter 41 of the second two-stage circuit 4b to operate to charge the corresponding bus capacitor 42, and to control the isolated resonant circuit 43 of the second two-stage circuit 4b to not operate. If the confirmation result of step S1 is no, i.e., the DC / DC converter system 1 is operating in heavy-load mode, step S3 is executed to control both the isolated resonant circuit 43 of the first two-stage circuit 4a and the isolated resonant circuit 43 of the second two-stage circuit 4b to operate together to supply power to the load 9.

[0020] As can be seen from the above, when the DC / DC converter system 1 of this disclosure operates in light-load mode, it controls the operation of the first two-stage circuit 4a to supply power to the load 9, and controls the operation of the DC / DC converter 41 of the second two-stage circuit 4b to charge the corresponding bus capacitor 42, while controlling the isolation resonant circuit 43 of the second two-stage circuit 4b to not operate. In other words, when the DC / DC converter system 1 operates in light-load mode, the first two-stage circuit 4a is sufficient to provide power to the load 9, while pre-charging the bus capacitor 42 of the second two-stage circuit 4b. However, the non-operation of the isolation resonant circuit 43 of the second two-stage circuit 4b reduces the power loss of the second two-stage circuit 4b, thereby improving the efficiency of the DC / DC converter system 1. Furthermore, when the DC / DC converter system 1 operates in heavy-load mode, it controls the operation of both the isolation resonant circuit 43 of the first two-stage circuit 4a and the isolation resonant circuit 43 of the second two-stage circuit 4b to jointly supply power to the load 9. In other words, since the bus capacitor 42 of the second two-stage circuit 4b has been pre-charged in light-load mode, the isolated resonant circuit 43 of the second two-stage circuit 4b can be instantly turned on when the DC / DC converter system 1 switches from light-load mode to heavy-load mode. The second two-stage circuit 4b can quickly take over the power supplied to the load 9, avoiding damage to the devices and having better dynamic performance. Therefore, the DC / DC converter system 1 of this disclosure, by using the first two-stage circuit 4a for power supply and the second two-stage circuit 4b for pre-charging, significantly improves the efficiency when switching from light-load mode to heavy-load mode, and simultaneously improves the overall dynamic performance.

[0021] Because the bus capacitor 42 of the second two-stage circuit 4b has a pre-charged bus voltage, the DC / DC converter system 1 can reduce the current surge to the isolated resonant circuit 43 of the second two-stage circuit 4b when switching from light-load mode to heavy-load mode by changing the switching duty cycle of the isolated resonant circuit 43. In this embodiment, when the DC / DC converter system 1 switches from light-load mode to heavy-load mode, the second controller 52 of the control unit 5 controls the isolated resonant circuit 43 of the second two-stage circuit 4b to operate with a first switching duty cycle and then switch to a second switching duty cycle. The first switching duty cycle corresponds, for example, to at least two switching cycles of the isolated resonant circuit 43 of the second two-stage circuit 4b; when the DC / DC converter system 1 operates in heavy-load mode, the second controller 52 of the control unit 5 controls the isolated resonant circuit 43 of the second two-stage circuit 4b to operate with a second switching duty cycle, wherein the first switching duty cycle is less than the second switching duty cycle. In other words, when the DC / DC converter system 1 switches from light load mode to heavy load mode, the switching duty cycle of the isolated resonant circuit 43 of the second two-stage circuit 4b first operates with a smaller first switching duty cycle and then increases to a larger second switching duty cycle. This can mitigate the impact on the isolated resonant circuit 43 of the second two-stage circuit 4b during switching. In some embodiments, the isolated resonant circuit 43 of the second two-stage circuit 4b can reduce its switching duty cycle by increasing the drive dead time, and restore the normal dead time and switching duty cycle after at least two switching cycles, thereby simultaneously taking into account the advantages of mitigating impact and normal operation.

[0022] Since the bus capacitor 42 of the second two-stage circuit 4b has a pre-charged bus voltage, the DC / DC converter system 1 can also reduce the current surge to the isolated resonant circuit 43 of the second two-stage circuit 4b when switching from light-load mode to heavy-load mode by reducing the bus voltage on the bus capacitor 42 of the second two-stage circuit 4b. In this embodiment, when the DC / DC converter system 1 operates in light-load mode, the second controller 52 of the control unit 5 controls the voltage of the bus capacitor 42 of the second two-stage circuit 4b to the first bus voltage; when the DC / DC converter system 1 switches from light-load mode to heavy-load mode, the second controller 52 of the control unit 5 controls the voltage of the bus capacitor 42 of the second two-stage circuit 4b to increase from the first bus voltage to the second bus voltage; when the DC / DC converter system 1 operates in heavy-load mode, the second controller 52 of the control unit 5 controls the voltage of the bus capacitor 42 of the second two-stage circuit 4b to be maintained at the second bus voltage, wherein the first bus voltage is less than the second bus voltage. Therefore, when the DC / DC converter system 1 is operating in light load mode, controlling the voltage of the bus capacitor 42 of the second two-stage circuit 4b to be a lower first bus voltage can reduce the instantaneous impact on the isolated resonant circuit 43 of the second two-stage circuit 4b when the DC / DC converter system 1 switches from light load mode to heavy load mode. Then, the voltage of the bus capacitor 42 is quickly increased to the second bus voltage, thereby rapidly improving the dynamic performance.

[0023] In one embodiment, the DC / DC converter system 1 further adjusts the operation of the two two-stage circuits according to the operating time. When the DC / DC converter system 1 switches from heavy load mode to light load mode, the control unit 5 further confirms whether the operating time of the DC / DC converter system 1 is less than a preset time threshold (e.g., 500ms). If the control unit 5 confirms that the operating time of the DC / DC converter system 1 is less than the time threshold, it controls the power supplied to the load 9 by the second two-stage circuit 4b to decrease and controls the power supplied to the load 9 by the first two-stage circuit 4a to increase. If the control unit 5 confirms that the operating time of the DC / DC converter system 1 is greater than the time threshold, it controls the DC / DC converter 41 of the second two-stage circuit 4b to operate to charge the bus capacitor 42 of the second two-stage circuit 4b, and controls the isolated resonant circuit 43 of the second two-stage circuit 4b to not operate.

[0024] Please see Figure 3 and cooperate Figure 1 ,in Figure 3This is a flowchart of the control method for a second embodiment of the DC / DC converter system disclosed herein. First, step M1 is executed to confirm whether the output power of the DC / DC converter system 1 is greater than a first power threshold, for example, whether it is greater than 1000W. When the confirmation result of step M1 is yes, that is, the output power of the DC / DC converter system 1 is greater than the first power threshold (i.e., heavy load mode), step M2 is executed to control the isolation resonant circuit 43 of the second two-stage circuit 4b to turn on, so that the isolation resonant circuit 43 of the first two-stage circuit 4a and the isolation resonant circuit 43 of the second two-stage circuit 4b both operate to jointly supply power to the load 9. When the confirmation result of step M1 is no, that is, the output power of the DC / DC converter system 1 is less than or equal to the first power threshold, step M3 is executed to confirm whether the output power of the DC / DC converter system 1 is greater than a second power threshold, for example, whether it is greater than 800W. If the confirmation result of step M3 is yes, i.e., the output power of DC / DC converter system 1 is greater than the second power threshold, step M4 is executed to maintain the operation of the isolated resonant circuit 43 of the first two-stage circuit 4a and the isolated resonant circuit 43 of the second two-stage circuit 4b to jointly supply power to the load 9. If the confirmation result of step M3 is no, i.e., the output power of DC / DC converter system 1 is less than or equal to the second power threshold (i.e., light load mode), step M5 is executed to confirm whether the operating time of DC / DC converter system 1 is less than a preset time threshold, for example, whether it is less than 500ms. If the confirmation result of step M5 is yes, i.e., the operating time of DC / DC converter system 1 is less than the preset time threshold, step M6 is executed to control the power supplied to the load 9 by the second two-stage circuit 4b to decrease and the power supplied to the load 9 by the first two-stage circuit 4a to increase. When the confirmation result of step M5 is negative, that is, when the working time of DC / DC converter system 1 is greater than or equal to the preset time threshold, step M7 is executed to control the DC / DC converter 41 of the second two-stage circuit 4b to operate to charge the bus capacitor 42 of the second two-stage circuit 4b, and to control the isolated resonant circuit 43 of the second two-stage circuit 4b to not operate.

[0025] In summary, when the DC / DC converter system of this disclosure operates in light-load mode, it controls the operation of the first two-stage circuit to supply power to the load, and controls the operation of the DC / DC converter in the second two-stage circuit to charge the corresponding bus capacitor, while keeping the isolated resonant circuit of the second two-stage circuit inactive. In other words, when the DC / DC converter system operates in light-load mode, the first two-stage circuit is sufficient to handle the power supplied to the load, while simultaneously pre-charging the bus capacitor of the second two-stage circuit. However, the inactivity of the isolated resonant circuit in the second two-stage circuit reduces power loss, thereby improving the efficiency of the DC / DC converter system. Furthermore, when the DC / DC converter system operates in heavy-load mode, both the isolated resonant circuits of the first and second two-stage circuits operate to jointly supply power to the load. In other words, since the bus capacitor of the second two-stage circuit is pre-charged in light-load mode, the isolated resonant circuit of the second two-stage circuit can be instantly turned on when the DC / DC converter system switches from light-load mode to heavy-load mode. The second two-stage circuit can quickly take over the power supplied to the load, avoiding damage to the devices and having better dynamic performance. Therefore, the DC / DC converter system of this disclosure, by utilizing the first two-stage circuit for power supply and the second two-stage circuit for pre-charging, significantly improves the efficiency when switching from light-load mode to heavy-load mode, while also improving the overall dynamic performance.

Claims

1. A control method applied to a DC / DC converter system for supplying power to a load, the DC / DC converter system comprising at least two two-stage circuits connected in parallel, each of the two-stage circuits comprising a DC / DC converter, a bus capacitor, and an isolated resonant circuit, wherein the control method comprises: When the DC / DC converter system operates in a light-load mode, the first two-stage circuit of the at least two two-stage circuits is controlled to operate to supply power to the load, and the DC / DC converter of the second two-stage circuit of the at least two two-stage circuits is controlled to operate to charge the corresponding bus capacitor, while the isolated resonant circuit of the second two-stage circuit is controlled not to operate; and When the DC / DC converter system is operating in a heavy load mode, both isolated resonant circuits controlling the first two-stage circuit and the second two-stage circuit operate together to supply power to the load.

2. The control method as described in claim 1, wherein when the DC / DC converter system switches from the light load mode to the heavy load mode, the isolated resonant circuit of the second two-stage circuit is controlled to operate with a first switching duty cycle and then switch to a second switching duty cycle; when the DC / DC converter system is operating in the heavy load mode, the isolated resonant circuit of the second two-stage circuit is controlled to maintain the second switching duty cycle, wherein the first switching duty cycle is less than the second switching duty cycle.

3. The control method as described in claim 2, wherein the first switch duty cycle corresponds to at least two switching cycles of the isolated resonant circuit.

4. The control method as described in claim 1, wherein when the DC / DC converter system operates in the light load mode, the voltage of the bus capacitor of the second two-stage circuit is controlled to be a first bus voltage; when the DC / DC converter system switches from the light load mode to the heavy load mode, the voltage of the bus capacitor of the second two-stage circuit is controlled to increase from the first bus voltage to a second bus voltage; when the DC / DC converter system operates in the heavy load mode, the voltage of the bus capacitor of the second two-stage circuit is controlled to be maintained at the second bus voltage, wherein the first bus voltage is less than the second bus voltage.

5. The control method as described in claim 1, wherein when the DC / DC converter system switches from the heavy load mode to the light load mode, it is further confirmed whether an operating time of the DC / DC converter system is less than a time threshold, wherein when the operating time is less than the time threshold, the power supplied to the load by the second two-stage circuit is reduced, and the power supplied to the load by the first two-stage circuit is increased, wherein when the operating time is greater than the time threshold, the DC / DC converter of the second two-stage circuit is controlled to operate to charge the corresponding bus capacitor, and the isolated resonant circuit of the second two-stage circuit is controlled not to operate.

6. The control method as described in claim 1, wherein when the DC / DC converter system switches from the light load mode to the heavy load mode, the power supplied to the load by the first two-stage circuit is reduced, and the isolated resonant circuit of the second two-stage circuit is operated to gradually increase the power supplied to the load, and finally the power supplied to the load by the first two-stage circuit and the second two-stage circuit is balanced.

7. A DC / DC converter system for converting an input electrical energy to supply power to a load, comprising: At least two two-stage circuits, wherein the at least two two-stage circuits are connected in parallel, wherein each of the two-stage circuits comprises: A DC / DC converter to convert the input electrical energy; A bus capacitor is connected to the DC / DC converter to store the converted input energy as a bus voltage; and An isolated resonant circuit is connected to the bus capacitor to convert the bus voltage to supply power to the load; and A control unit, when the DC / DC converter system is operating in a light load mode, controls the first two-stage circuit of the at least two two-stage circuits to operate to supply power to the load, controls the DC / DC converter of the second two-stage circuit of the at least two two-stage circuits to operate to charge the corresponding bus capacitor, and controls the isolated resonant circuit of the second two-stage circuit to not operate; when the DC / DC converter system is operating in a heavy load mode, controls both the first two-stage circuit and the two isolated resonant circuits of the second two-stage circuit to operate to jointly supply power to the load.

8. The DC / DC converter system of claim 7, wherein the DC / DC converter is a boost circuit, a buck circuit, or a buck-boost circuit.

9. The DC / DC converter system as described in claim 7, wherein the isolated resonant circuit is an isolated LLC circuit or an isolated CLLC circuit.

10. The DC / DC converter system of claim 7, wherein the control unit includes a first controller and a second controller, wherein the first controller performs closed-loop control of the DC / DC converter in the at least two two-stage circuits, and the second controller performs open-loop control of the isolated resonant circuit in the at least two two-stage circuits.

11. The DC / DC converter system of claim 7, wherein when the DC / DC converter system switches from the light load mode to the heavy load mode, the control unit controls the isolated resonant circuit of the second two-stage circuit to operate at a first switching duty cycle and then switch to a second switching duty cycle; when the DC / DC converter system operates in the heavy load mode, the control unit controls the isolated resonant circuit of the second two-stage circuit to maintain the second switching duty cycle, wherein the first switching duty cycle is less than the second switching duty cycle.

12. The DC / DC converter system of claim 11, wherein the first switch duty cycle corresponds to at least two switching cycles of the isolated resonant circuit.

13. The DC / DC converter system of claim 7, wherein when the DC / DC converter system operates in the light load mode, the control unit controls the voltage of the bus capacitor of the second two-stage circuit to a first bus voltage; when the DC / DC converter system switches from the light load mode to the heavy load mode, the control unit controls the voltage of the bus capacitor of the second two-stage circuit to increase from the first bus voltage to a second bus voltage; and when the DC / DC converter system operates in the heavy load mode, the control unit controls the voltage of the bus capacitor of the second two-stage circuit to be maintained at the second bus voltage.

14. The DC / DC converter system of claim 7, wherein when the DC / DC converter system switches from the heavy load mode to the light load mode, the control unit further confirms whether an operating time of the DC / DC converter system is less than a time threshold, wherein when the operating time is less than the time threshold, the control unit controls the power supplied to the load by the second two-stage circuit to decrease, and controls the power supplied to the load by the first two-stage circuit to increase, wherein when the operating time is greater than the time threshold, the control unit controls the DC / DC converter of the second two-stage circuit to operate to charge the corresponding bus capacitor, and controls the isolated resonant circuit of the second two-stage circuit not to operate.

15. The DC / DC converter system as claimed in claim 7, wherein when the DC / DC converter system switches from the light load mode to the heavy load mode, the control unit controls the first two-stage circuit to reduce the power supplied to the load, and controls the isolated resonant circuit of the second two-stage circuit to operate and gradually increase the power supplied to the load, and the control unit ultimately controls the first two-stage circuit and the second two-stage circuit to supply power to the load in a balanced manner.

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