Cascade circuit of isolated converter and control method

Abstract

The application provides a cascade circuit of an isolated converter and a control method, wherein the cascade circuit of the isolated converter comprises a control module, a non-isolated converter and an open-loop isolation module. According to the application, the non-isolated converter respectively feeds back a bus voltage determined according to a first duty cycle of the non-isolated converter to the open-loop isolation module and the control module, the open-loop isolation module feeds back an output voltage determined according to the bus voltage to the control module, the control module determines a second duty cycle according to the bus voltage and the output voltage, and feeds back the second duty cycle to the non-isolated converter, and the bus voltage is determined again through the second duty cycle, so that the adjusting speed of the non-isolated converter and the open-loop isolation module of the two stages of the isolated converter is accelerated, the dynamic characteristic is relatively strong, and the application is suitable for fast charging. Meanwhile, the open-loop isolation module is adopted to avoid resource waste, and is especially suitable for the non-isolated converter with a wide voltage regulating range of the front stage.

Description

Technical Field

[0001] The present application belongs to the field of power electronics technology, and in particular relates to a cascade circuit and a control method of an isolation converter. Background Art

[0002] With technological advancements, charging equipment, particularly isolated DC-DC converters (DC / DC converters) and AC-DC converters (AC / DC converters), has become widely used in the charging field. Traditional charging equipment typically utilizes a two-stage cascade connection, with the front stage consisting of a non-isolated AC / DC converter or DC / DC converter, and the back stage consisting of a closed-loop isolation module. These two stages operate independently, slowly adjusting the front stage bus voltage based on the back stage output voltage via communication, ensuring optimal operation of the back stage closed-loop isolation module. Outside the voltage regulation range of the front stage, the closed-loop system gain of the back stage closed-loop isolation module is used to further adjust the output voltage.

[0003] However, because the regulation speed of the front-end and back-end stages is limited by communication speed, the dynamic characteristics of the back-end output are often poor, making it only suitable for slow charging rather than fast charging. Furthermore, the wide voltage regulation range of the front-end non-isolated converter is sufficient to regulate the output voltage, resulting in a waste of closed-loop system resources in the back-end closed-loop isolation module. Summary of the Invention

[0004] The purpose of this application is to provide a cascade circuit and control method for an isolation converter, aiming to solve the problems of poor dynamic characteristics and waste of resources in traditional isolation converters.

[0005] To achieve the above objectives, in a first aspect, an embodiment of the present application provides a cascade circuit of an isolation converter, comprising: a control module, a non-isolated converter, and an open-loop isolation module;

[0006] The control module is used to control the state of the non-isolated converter and the open-loop isolation module; the state includes starting or shutting down;

[0007] The non-isolated converter is used to feed back a bus voltage determined according to a first duty cycle of the non-isolated converter to the open-loop isolation module and the control module respectively;

[0008] The open-loop isolation module is used to feed back an output voltage determined according to the bus voltage to the control module;

[0009] The control module is further configured to determine a second duty cycle according to the bus voltage and the output voltage, and feed the second duty cycle back to the non-isolated converter, wherein the second duty cycle is used to redetermine the bus voltage.

[0010] In a possible implementation manner of the first aspect, the control module includes a non-isolated controller and an isolated controller that are communicatively connected;

[0011] The isolation controller is used to control the soft start of the open-loop isolation module and send a message of the soft start of the open-loop isolation module to the non-isolated controller through the communication connection; the non-isolated controller is used to start the non-isolated converter according to the message of the soft start of the open-loop isolation module;

[0012] The non-isolated controller is further configured to control the non-isolated converter to shut down, and to send a message indicating the non-isolated converter is shut down to the isolation controller via the communication connection; the isolation controller is configured to control the open-loop isolation module to shut down according to the message indicating the non-isolated converter is shut down.

[0013] In another possible implementation manner of the first aspect, the non-isolated controller includes an output voltage loop, a bus voltage loop, a comparator, and a current loop;

[0014] The output voltage loop is used to determine a first current set value based on the output voltage and the output voltage given; the bus voltage loop is used to determine a second current set value based on the bus voltage and the bus voltage given; the comparator is used to compare the first current set value and the second current set value to determine a final current set value; the current loop is used to determine a second duty cycle of the non-isolated converter based on the final current set value and the inductor current in the non-isolated converter.

[0015] In another possible implementation of the first aspect, the bus voltage setting is determined by the output voltage setting and an increment.

[0016] In another possible implementation of the first aspect, the non-isolated converter includes a non-isolated AC / DC converter or a non-isolated DC / DC converter; and the open-loop isolation module includes an open-loop resonant circuit.

[0017] In a second aspect, an embodiment of the present application provides a control method applied to a cascade circuit of an isolated converter, wherein the cascade circuit of the isolated converter includes a control module, a non-isolated converter, and an open-loop isolation module; the control module is connected to the non-isolated converter and the open-loop isolation module, respectively, and the non-isolated converter is connected to the open-loop isolation module;

[0018] The control module is configured to perform at least one of the following steps:

[0019] During startup, the open-loop isolation module is controlled to soft-start, and then the non-isolated converter is controlled to start;

[0020] When shutting down, the non-isolated converter is controlled to shut down, and then the open-loop isolation module is controlled to shut down.

[0021] In a possible implementation manner of the second aspect, controlling the open-loop isolation module to soft-start includes:

[0022] The first duty cycle is widened at a preset speed until the first duty cycle reaches a preset duty cycle, and the open-loop isolation module is controlled to soft start.

[0023] In another possible implementation manner of the second aspect, after controlling the non-isolated converter to shut down, controlling the open-loop isolation module to shut down includes:

[0024] After the non-isolated converter is controlled to be turned off, the open-loop isolation module is controlled to be turned off after a preset time.

[0025] In another possible implementation of the second aspect, before controlling the soft start of the open-loop isolation module, the control method further includes: when a first parameter does not exceed a preset parameter range, controlling the soft start of the open-loop isolation module, the first parameter includes one or more of the output voltage and the bus voltage, and the preset parameter range includes one or more of a preset output voltage range and a preset bus voltage range.

[0026] In another possible implementation manner of the second aspect, when the first parameter is the bus voltage and the preset parameter range is the bus voltage range, the control method further includes:

[0027] When the bus voltage exceeds the bus voltage range, the open-loop isolation module is continuously discharged at a minimum duty cycle until the bus voltage reaches the preset bus voltage range, and the open-loop isolation module is controlled to soft-start.

[0028] Compared with the prior art, the embodiments of the present application have the following beneficial effects: the cascade circuit of the above-mentioned isolated converter feeds back the bus voltage determined according to the first duty cycle of the non-isolated converter to the open-loop isolation module and the control module respectively through the non-isolated converter, feeds back the output voltage determined according to the bus voltage to the control module through the open-loop isolation module, determines the second duty cycle according to the bus voltage and the output voltage through the control module, and feeds back the second duty cycle to the non-isolated converter, and redetermines the bus voltage through the second duty cycle, thereby accelerating the adjustment speed of the non-isolated converter and the open-loop isolation module before and after the isolation converter, having stronger dynamic characteristics, and being suitable for fast charging. At the same time, the use of the open-loop isolation module avoids waste of resources, and is particularly suitable for non-isolated converters with a wider voltage regulation range at the front stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0030] Figure 1 A schematic structural diagram of a cascade circuit of an isolation converter provided in an embodiment of the present application;

[0031] Figure 2 A circuit diagram of a cascade circuit of an isolation converter provided in an embodiment of the present application;

[0032] Figure 3 A control block diagram of a non-isolated controller of a cascade circuit of an isolated converter provided in an embodiment of the present application;

[0033] Figure 4 This is a flow chart of a method for controlling a cascade circuit of an isolation converter provided in an embodiment of the present application.

[0034] Description of reference numerals:

[0035] 1-control module, 11-non-isolated controller, 12-isolated controller, 2-non-isolated converter, 3-open-loop isolation module. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is 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 this application and are not intended to limit this application.

[0037] It should be noted that when an element is referred to as being “fixed on” or “disposed on” another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or indirectly connected to the other element.

[0038] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0040] Currently, traditional isolated converters typically utilize a two-stage cascade connection: a front-stage non-isolated converter and a rear-stage closed-loop isolation module. These two stages operate independently and communicate with each other. However, the regulation speed of these two stages is limited by the communication speed, resulting in poor dynamic characteristics and unsuitable for fast charging. Furthermore, traditional isolated converters typically use the gain of the rear-stage closed-loop isolation module to further adjust the output range outside the front-stage voltage regulation range. However, for non-isolated converters with a wider front-stage voltage regulation range, the front-stage voltage regulation range is sufficient, eliminating the need for the closed-loop system gain of the rear-stage closed-loop isolation module, resulting in a waste of resources.

[0041] To this end, the present application provides a cascade circuit of an isolated converter, which directly controls the front-stage isolated converter and the open-loop isolation module through a control module, thereby accelerating the feedback and adjustment speed. At the same time, because the open-loop isolation module eliminates the closed-loop system, it avoids resource waste and is particularly suitable for non-isolated converters with a wide front-stage voltage regulation range.

[0042] The following is an exemplary description of the cascade circuit of the isolation converter provided by the present application with reference to the accompanying drawings:

[0043] Figure 1 A schematic diagram of the structure of the cascade circuit of the isolation converter provided in the embodiment of the present application is shown in FIG. Figure 1 As shown, for the sake of convenience of explanation, only the parts related to this embodiment are shown, which are detailed as follows: For example, the cascade circuit of the isolated converter may include: a control module 1, a non-isolated converter 2 and an open-loop isolation module 3; wherein the control module 1 is respectively connected to the non-isolated converter 2 and the open-loop isolation module 3, and the non-isolated converter 2 is connected to the open-loop isolation module 3.

[0044] The control module 1 is used to control the status of the non-isolated converter 2 and the open-loop isolation module 3; the status includes start or shut down; the non-isolated converter 2 is used to feed back the bus voltage determined according to the first duty cycle of the non-isolated converter 2 to the open-loop isolation module 3 and the control module 1 respectively; the open-loop isolation module 3 is used to feed back the output voltage determined according to the bus voltage to the control module 1; the control module 1 is also used to determine a second duty cycle based on the bus voltage and the output voltage, and feed the second duty cycle back to the non-isolated converter 2, and the second duty cycle is used to redetermine the bus voltage.

[0045] In the embodiment, the control module 1 is used to control the sequence of starting state and closing state of the non-isolated converter 2 and the open-loop isolation module 3, so as to ensure the normal operation of the whole isolation converter. When starting initially, the non-isolated converter 2 determines the bus voltage according to the input voltage at the input end and the first duty ratio, and the open-loop isolation module 3 determines the output voltage according to the bus voltage and sends it to the output end. The first duty ratio can be an initial value preset when starting, can be a feedforward initial value of the input voltage, or can be a duty ratio of the non-isolated converter 2 after the last round of adjustment, for example, a second duty ratio. The control module 1 determines a new duty ratio according to the bus voltage fed back by the non-isolated converter 2 and the output voltage fed back by the open-loop isolation module 3, and feeds back to the non-isolated converter 2 to determine the bus voltage again, so as to form a loop and adjust the output voltage in real time and dynamically.

[0046] In the embodiment, the non-isolated converter 2 can include a non-isolated AC / DC converter or a non-isolated DC / DC converter. The commonly used circuit of the non-isolated DC / DC converter is a step-down circuit, a step-up circuit or a combination thereof, for example, a bidirectional step-down circuit, a step-up circuit, a step-down-step-up circuit and a step-down-step-up circuit of a four-switch H-bridge, etc. The commonly used circuit of the non-isolated AC / DC converter is a step-up circuit. The open-loop isolation module 3 can include a resonant circuit (i.e., a resonant network circuit composed of a resonant inductor L, a resonant capacitor C and an excitation inductor L, which achieves voltage stabilization by frequency conversion, referred to as an LLC circuit).

[0047] Figure 2 The circuit diagram of the cascade circuit of the isolation converter provided in the embodiment is shown in Figure 2 As an example, the control module 1 includes a non-isolated controller 11 and an isolation controller 12 connected in communication. The isolation controller 12 is used to control the soft start of the open-loop isolation module 3, and send the message of the soft start of the open-loop isolation module 3 to the non-isolated controller 11 through the communication connection. The non-isolated controller 11 is used to start the non-isolated converter 2 according to the message of the soft start of the open-loop isolation module 3. The non-isolated controller 11 is also used to control the closing of the non-isolated converter 2, and send the message of the closing of the non-isolated converter 2 to the isolation controller 12 through the communication connection. The isolation controller 12 is used to control the closing of the open-loop isolation module 3 according to the message of the closing of the non-isolated converter 2.

[0048] In this embodiment, the non-isolated controller 11 controls the startup and shutdown of the non-isolated converter 2, and the isolated controller 12 controls the soft start and shutdown of the open-loop isolation module 3. During the startup process, the open-loop isolation module 3 is started first, and then the non-isolated converter 2 is started, to ensure the stability of the output side of the open-loop isolation module 3. During the shutdown process, the non-isolated converter 2 is shut down first, and then the open-loop isolation module 3 is shut down, so that the open-loop isolation module 3 continues to consume the residual voltage of the bus voltage that was not fully released during the regulation process. The open-loop isolation module 3 can include two open-loop LLC circuits (i.e., a first open-loop LLC circuit and a second open-loop LLC circuit) connected through a transformer with a transformation ratio of k, or an open-loop LLC circuit and a diode connected through a transformer with a transformation ratio of k. The isolated controller 12 causes the open-loop LLC circuit to operate at a resonant point (i.e., the switching frequency is equal to the resonant frequency) with a duty cycle of 0.5. When in a normal steady state, the ratio of the output voltage of the open-loop isolation module 3 to the bus voltage is approximately equal to the transformation ratio k of the transformer, and the gain of the open-loop LLC circuit at the resonant point is approximately 1.

[0049] Figure 3 A control block diagram of a non-isolated controller of a cascade circuit of an isolated converter provided in an embodiment of the present application, such as Figure 3 As shown, exemplarily, the non-isolated controller 11 may include an output voltage loop, a bus voltage loop, a comparator and a current loop; the output voltage loop is used to determine a first current set value based on the output voltage and the output voltage given; the bus voltage loop is used to determine a second current set value based on the bus voltage and the bus voltage given; the comparator is used to compare the first current set value and the second current set value to determine a final current set value; the current loop is used to determine a second duty cycle of the non-isolated converter 2 based on the final current set value and the inductor current in the non-isolated converter 2.

[0050] In this embodiment, the output voltage Vo is sampled and sent to the voltage loop, and the bus voltage Vdc is sampled and sent to the bus voltage loop. The output voltage loop determines a first set current value based on the output voltage Vo and the output voltage reference Vo*; the bus voltage loop determines a second set current value based on the bus voltage Vdc and the bus voltage reference Vdc*. The bus voltage loop is provided to further ensure the controllability and safety of the bus voltage Vdc. In abnormal operating conditions, without the bus voltage loop, the bus voltage Vdc would rapidly increase in a short period of time, causing faults and even damaging components. For example, if the output end of an open-loop LLC circuit is fault-locked or damaged, causing the entire circuit to open, without the bus voltage loop, the bus voltage Vdc would overshoot, triggering overvoltage protection and causing a fault. Therefore, after the bus voltage loop is implemented, if the output voltage loop experiences an abnormal operating condition, resulting in a high first set current value, the comparator Min selects the second set current value output by the bus voltage loop to protect the safety of the entire circuit.

[0051] The comparator Min compares the first current set value and the second current set value based on the smaller comparison principle to determine the final current set value I*; the current loop determines the second duty cycle D of the non-isolated converter 2 based on the final current set value I* and the inductor current I in the non-isolated converter 2, thereby acting on the input end of the non-isolated converter 2 of the previous stage to adjust the output voltage of the output end of the subsequent open-loop isolation module 3.

[0052] In this embodiment, the bus voltage setting is determined by the output voltage setting and the increment, and can be specifically: Vdc*=k*Vo*+ΔV, wherein Vdc* is the bus voltage setting, Vo* is the output voltage setting, and k is a coefficient, which can be, for example, the transformer ratio within the open-loop LLC circuit. k*Vo* is the bus voltage near normal operation. At the same time, because the load affects the regulation rate, the limit value of the bus voltage needs to be greater than the normal operating value range, so the increment ΔV is added to ensure the necessary margin, and the value is generally taken as above 20V.

[0053] In this embodiment, the open-loop isolation module 3 (e.g., an open-loop LLC circuit) is fully incorporated into the control feedback loop, with the final output of the open-loop isolation module 3 (i.e., output voltage Vo) serving as the direct control target and the bus voltage Vdc serving as the indirect control target, thereby ensuring optimal overall performance. For example, the open-loop isolation module 3 may include an open-loop LLC circuit. Because the gain variation of the open-loop LLC circuit is relatively small with respect to the load, it can be approximately considered an excellent "DC transformer." Therefore, it has a minimal impact on the stability of the control loop of the preceding non-isolated converter 2 and can form an integrated control feedback loop with the preceding non-isolated converter 2.

[0054] In this embodiment, the cascade circuit of the isolated converter may include: a non-isolated DC / DC converter 2, a bus capacitor, a first open-loop LLC circuit, a transformer, a second open-loop LLC circuit, a non-isolated controller 11 and an isolated controller 12, the input end of the non-isolated DC / DC converter is connected to the input voltage, the output end of the non-isolated DC / DC converter is connected to the two ends of the bus capacitor (i.e., the DC+ end and the DC- end), the input end of the first open-loop LLC circuit and the non-isolated controller 11, the output end of the first open-loop LLC circuit is connected to the second open-loop LLC circuit via a transformer with a transformation ratio of K, the output end of the second open-loop LLC circuit is connected to the output voltage (i.e., the Vo+ end and the Vo- end) and the non-isolated controller 11; the non-isolated controller 11 drives the connection to the non-isolated DC / DC converter, the isolated controller 12 drives the connection to the first open-loop LLC circuit, and the non-isolated controller 11 and the isolated controller 12 are internally communicated.

[0055] In this embodiment, the bus voltage is determined by the non-isolated converter 2 according to the input voltage at the input end and the first duty cycle, the output voltage is determined by the open-loop isolation module 3 according to the bus voltage, and the second duty cycle is determined by the control module 1 according to the bus voltage and the output voltage, and is fed back to the non-isolated converter 2 to redetermine the bus voltage, so that the open-loop isolation module 3 always operates at the highest efficiency point, and the output voltage is completely adjusted by the non-isolated converter 2. The open-loop isolation module 3 has the characteristics of simple control, low cost, and excellent output performance.

[0056] Figure 4 This is a flow chart of a control method for a cascade circuit of an isolation converter provided in an embodiment of the present application, such as Figure 4 As shown, this embodiment discloses a control method for a cascade circuit of an isolated converter, which is applied to the cascade circuit of the isolated converter. The cascade circuit of the isolated converter includes a control module 1, a non-isolated converter 2 and an open-loop isolation module 3; the control module 1 is connected to the non-isolated converter 2 and the open-loop isolation module 3 respectively, and the non-isolated converter 2 is connected to the open-loop isolation module 3.

[0057] The control module 1 is used to perform at least one of the following steps: when starting, it controls the open-loop isolation module 3 to soft-start, and then controls the non-isolated converter 2 to start; when shutting down, it controls the non-isolated converter 2 to shut down, and then controls the open-loop isolation module 3 to shut down. As an example, the structure of the cascade circuit of the isolation converter can be as follows: Figure 1 shown.

[0058] In this embodiment, in order to ensure the normal startup and shutdown of the entire isolation converter, a corresponding control method needs to be set, which can be: at startup, first soft-start the open-loop isolation module 3 to ensure that the output side of the open-loop isolation module 3 is stable, and then start the non-isolated converter 2 to start power transfer, that is, boost or buck; at shutdown, first shut down the non-isolated converter 2, shut down the power transfer, and then shut down the open-loop isolation module 3 to exhaust the residual voltage in the bus voltage.

[0059] Exemplarily, controlling the open-loop isolation module 3 to soft-start includes: widening the first duty cycle at a preset speed until the first duty cycle reaches a preset duty cycle, and then controlling the open-loop isolation module 3 to soft-start.

[0060] In this embodiment, the non-isolated converter may include a buck converter or a boost converter. The buck converter is inoperative before startup, and the bus voltage Vdc is generally initially 0V or at a capacitor residual voltage. The bus voltage Vdc of the boost converter before startup is the same as its input voltage. Therefore, the subsequent open-loop isolation module 3 can be divided into two operating conditions: bus voltage 0V and startup with capacitor residual voltage. To account for startup with capacitor residual voltage, the bus voltage Vdc of the subsequent open-loop isolation module 3 (e.g., an open-loop LLC circuit) is adjusted to a first duty cycle at a preset speed according to a soft-start strategy. The first duty cycle is gradually increased at a preset speed to a steady-state preset duty cycle (e.g., 0.5), after which the open-loop isolation module 3 is soft-started. This ensures controllable startup of the open-loop LLC circuit and avoids faults such as overcurrent. Specifically, when the bus voltage is 0V, the soft-start of the open-loop LLC circuit can be ignored. When the bus voltage has capacitor residual voltage, the output voltage is first gradually increased before implementing other control changes.

[0061] Exemplarily, controlling the non-isolated converter 2 to shut down and then controlling the open-loop isolation module 3 to shut down includes: controlling the non-isolated converter 2 to shut down and then controlling the open-loop isolation module 3 to shut down after a preset time has passed.

[0062] In this embodiment, during the shutdown process, a preset delay is included before shutting down the open-loop isolation module. If the open-loop isolation module (e.g., the open-loop LLC circuit) is shut down prematurely, the preceding non-isolated converter may open circuit, causing the bus voltage to overshoot, thereby triggering bus voltage loop activation. This hinders the maximum output of bus energy to the load through the open-loop LLC circuit, resulting in excessively high residual bus voltage and difficulties with the next startup. The preset delay can be categorized into two scenarios: if the shutdown is an emergency shutdown due to a sudden fault, the shutdown is performed with a minimum delay; if the output is normal, the shutdown may be appropriately delayed to maximize bus energy transfer and utilization.

[0063] Exemplarily, before controlling the open-loop isolation module 3 to soft start, the control method also includes: when the first parameter does not exceed the preset parameter range, controlling the open-loop isolation module 3 to soft start, the first parameter includes one or more of the output voltage and the bus voltage, and the preset parameter range includes one or more of the preset output voltage range and the preset bus voltage range.

[0064] In this embodiment, before controlling the soft start of the open-loop isolation module 3, it is possible to only detect whether the output voltage exceeds the preset output voltage range according to the application example, or only detect whether the bus voltage exceeds the preset bus voltage range according to the application example, or simultaneously detect whether the output voltage exceeds the preset output voltage range and whether the bus voltage exceeds the preset bus voltage range, so as to achieve the best starting effect of the open-loop isolation module 3 and the non-isolated converter 2.

[0065] Exemplarily, when the first parameter is the bus voltage and the preset parameter range is the bus voltage range, the control method may further include: when the bus voltage exceeds the bus voltage range, continuously discharging at a minimum duty cycle through the open-loop isolation module 3 until the bus voltage reaches the preset bus voltage range, and controlling the open-loop isolation module 3 to soft start.

[0066] In this embodiment, before soft-starting the open-loop isolation module 3 (e.g., the open-loop LLC circuit), it is also possible to determine whether the bus voltage exceeds a preset bus voltage range to prevent the output voltage from exceeding the range due to the soft start of the open-loop LLC circuit. If the bus voltage Vdc exceeds the preset bus voltage range, for example, greater than k*Vo*, the open-loop LLC circuit can continuously generate a wave discharge at a minimum duty cycle. After the bus voltage is reduced to an appropriate range due to losses such as switching transistor operation, the open-loop isolation module 3 can be soft-started.

[0067] In this embodiment, the open-loop isolation module 3 includes a unidirectional open-loop isolation circuit or a bidirectional open-loop isolation circuit. When the first parameter is the output voltage and the preset parameter range is the output voltage range, the control method may further include: detecting whether the output voltage exceeds the preset output voltage range, and when the output voltage does not exceed the preset output voltage range, soft-starting the open-loop isolation module 3; when the output voltage exceeds the preset output voltage range, an alarm is issued and feedback is given to the non-isolated controller 11.

[0068] In this embodiment, the open-loop isolation module 3 includes a unidirectional open-loop isolation circuit or a bidirectional open-loop isolation circuit with the same control method, such as a unidirectional open-loop LLC circuit or a bidirectional open-loop LLC circuit, wherein Figure 2 As shown in the figure, the bidirectional open-loop LLC circuit adopts the primary and secondary side switches at the resonance point and the simultaneous opening and closing wave control strategy, making the open-loop LLC circuit a high-frequency power electronic "DC transformer" operating at the highest resonance efficiency point. Regardless of the load conditions, the output voltage and input voltage approximately follow the transformer ratio relationship, and the performance is better than the output performance of the unidirectional open-loop LLC circuit.

[0069] When the bidirectional open-loop LLC circuit is used as the input or output side, the output voltage Vo is detected before startup to see if it exceeds the preset output voltage range. If it does not, a soft start is performed, gradually increasing the bus voltage Vdc to Vo*k, completing the soft start. If it exceeds, the soft start is aborted and an alarm is issued. After that, the normal control mode of the preceding non-isolated converter is activated.

[0070] In one possible implementation, after the control module 1 controls the non-isolated converter 2 and the open-loop isolation module 3 to start, or when the open-loop isolation module 3 soft-starts and the non-isolated converter 2 starts, the method provided in the embodiment of the present application further includes:

[0071] The non-isolated converter 2 feeds back a bus voltage determined according to a first duty cycle of the non-isolated converter 2 to the open-loop isolation module 3 and the control module 1 respectively; the open-loop isolation module 3 feeds back an output voltage determined according to the bus voltage to the control module 1; the control module 1 determines a second duty cycle according to the bus voltage and the output voltage, and feeds the second duty cycle back to the non-isolated converter 2, and the second duty cycle is used to redetermine the bus voltage.

[0072] The control module 1 includes a non-isolated controller 11 and an isolated controller 12 that are communicatively connected; the isolated controller 12 controls the soft start of the open-loop isolation module 3 and sends the soft start message of the open-loop isolation module 3 to the non-isolated controller 11 through the communication connection; the non-isolated controller 11 starts the non-isolated converter 2 according to the soft start message of the open-loop isolation module 3.

[0073] The non-isolated controller 11 also controls the non-isolated converter 2 to shut down, and sends a shutdown message of the non-isolated converter 2 to the isolation controller 12 via a communication connection; the isolation controller 12 controls the open-loop isolation module 3 to shut down according to the shutdown message of the non-isolated converter 2.

[0074] The non-isolated controller 11 includes an output voltage loop, a bus voltage loop, a comparator, and a current loop. The output voltage loop is used to determine a first current setting value based on the output voltage and the output voltage setting. The bus voltage loop is used to determine a second current setting value based on the bus voltage and the bus voltage setting. The comparator is used to compare the first current setting value and the second current setting value to determine a final current setting value. The current loop is used to determine a second duty cycle of the non-isolated converter 2 based on the final current setting value and the inductor current within the non-isolated converter 2. The bus voltage setting is determined by the output voltage setting and the increment.

[0075] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0076] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0077] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0078] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0079] In the embodiments provided in this application, it should be understood that the disclosed control method can be implemented in other ways. For example, the control method embodiments described above are merely schematic. For example, the division of modules or units is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0080] Units described as separate components may or may not be physically separate, and components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0081] In addition, each functional unit in each embodiment of the present application can be integrated in one processing unit, or each unit can exist physically, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional unit.

[0082] The above embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A cascade circuit of an isolation converter, characterized in that: include: A control module (1), a non-isolated converter (2) and an open-loop isolation module (3); The control module (1) is used to control the states of the non-isolated converter (2) and the open-loop isolation module (3); the states include start-up or shutdown; The non-isolated converter (2) is used to feed back a bus voltage determined according to a first duty cycle of the non-isolated converter (2) to the open-loop isolation module (3) and the control module (1) respectively; The open-loop isolation module (3) is used to feed back an output voltage determined according to the bus voltage to the control module (1); The control module (1) is further configured to determine a second duty cycle based on the bus voltage and the output voltage, and feed the second duty cycle back to the non-isolated converter (2), wherein the second duty cycle is used to redetermine the bus voltage; The control module (1) comprises an output voltage loop, a bus voltage loop, a comparator and a current loop; The output voltage loop is used to determine a first current given value according to the output voltage and the output voltage given value; the bus voltage loop is used to determine a second current given value according to the bus voltage and the bus voltage given value; The comparator is used to compare the first current set value and the second current set value, and determine the smaller value between the two as the final current set value; The current loop is used to determine a second duty cycle of the non-isolated converter (2) according to the final current set value and the inductor current in the non-isolated converter (2).

2. The cascade circuit of the isolation converter according to claim 1, characterized in that: The control module (1) includes a non-isolated controller (11) and an isolated controller (12) that are communicatively connected; The isolation controller (12) is used to control the soft start of the open-loop isolation module (3), and send a message of the soft start of the open-loop isolation module (3) to the non-isolated controller (11) through the communication connection; the non-isolated controller (11) is used to start the non-isolated converter (2) according to the message of the soft start of the open-loop isolation module (3); The non-isolated controller (11) is further configured to control the non-isolated converter (2) to be turned off, and to send a message of the non-isolated converter (2) being turned off to the isolation controller (12) via the communication connection; the isolation controller (12) is configured to control the open-loop isolation module (3) to be turned off according to the message of the non-isolated converter (2) being turned off.

3. The cascade circuit of the isolation converter according to claim 1, wherein: The bus voltage setting is determined by the output voltage setting and the increment.

4. The cascade circuit of the isolation converter according to any one of claims 1 to 3, characterized in that: The non-isolated converter (2) includes a non-isolated AC / DC converter or a non-isolated DC / DC converter; the open-loop isolation module (3) includes an open-loop resonant circuit.

5. A control method, characterized in that: A cascade circuit of an isolated converter according to any one of claims 1 to 4, the cascade circuit of the isolated converter comprising a control module (1), a non-isolated converter (2) and an open-loop isolation module (3); the control module (1) is connected to the non-isolated converter (2) and the open-loop isolation module (3) respectively, and the non-isolated converter (2) is connected to the open-loop isolation module (3); The control module (1) is used to perform at least one of the following steps: During startup, the open-loop isolation module (3) is controlled to soft-start, and then the non-isolated converter (2) is controlled to start; When shutting down, the non-isolated converter (2) is controlled to shut down, and then the open-loop isolation module (3) is controlled to shut down.

6. The control method according to claim 5, wherein: After controlling the non-isolated converter (2) to be turned off, the open-loop isolation module (3) is then controlled to be turned off, comprising: After the non-isolated converter (2) is controlled to be turned off, the open-loop isolation module (3) is controlled to be turned off after a preset time has passed.

7. The control method according to claim 5 or 6, characterized in that: Before controlling the open-loop isolation module (3) to soft-start, the control method further comprises: controlling the open-loop isolation module (3) to soft-start when a first parameter does not exceed a preset parameter range, the first parameter comprising one or more of an output voltage and a bus voltage, and the preset parameter range comprising one or more of a preset output voltage range and a preset bus voltage range.

8. The control method according to claim 7, wherein: When the first parameter is the bus voltage and the preset parameter range is the bus voltage range, the control method further includes: When the bus voltage exceeds the bus voltage range, the open-loop isolation module (3) is continuously discharged at a minimum duty cycle until the bus voltage reaches the preset bus voltage range, and the open-loop isolation module (3) is controlled to soft-start.

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