LLC multi-machine parallel current sharing control method and system

Abstract

The invention discloses an LLC multi-machine parallel current sharing control method and system, and the system comprises multiple LLC resonant converters and a CAN bus, and the LLC resonant converters are in communication connection through the CAN bus. One path of the multi-path LLC resonant converter is a host, and the other paths of LLC resonant converters are slaves; the host sends a secondary side current of the host to the slave through the CAN bus, and the secondary side current is used as a slave current sharing ring input instruction; the secondary side current of the slave is compared with a slave current-sharing ring input instruction, first PID adjustment is carried out, and the secondary side current is used as current-sharing ring output of the slave; the current sharing ring output of the slave is added to a set slave voltage instruction to serve as a new slave voltage instruction, the difference between the new slave voltage instruction and the slave secondary side voltage is obtained, then second PID adjustment is conducted, slave secondary side current is obtained, adjustment is conducted continuously, and current sharing is achieved; the invention has the advantages of low cost, stable control loop and high reliability.

Description

Technical Field

[0001] The present invention relates to the field of electronic equipment for measuring and testing, and in particular to a LLC multi-machine parallel current sharing control method and system. Background Art

[0002] In the field of electronic technology, LLC resonant converter is a widely used topology in DC / DC converters. The unique advantage of LLC resonant converter is that it can realize zero voltage turn-on (ZVS) of the primary switch tube of the converter and zero current turn-off (ZCS) of the secondary rectifier diode. It has the advantages of low loss and high power density under high-frequency working conditions. Therefore, it is widely used in distributed power supply, electric vehicles, LED drive, aerospace power supply and other fields. In high-power applications, multi-channel parallel technology is often used. Because this can not only reduce the current stress of each switch device of the resonant converter, but also reduce the size of the transformer, reduce losses, and facilitate heat dissipation. However, due to the difference in actual manufacturing process, there is a certain degree of dispersion between components, so the parameters of the parallel modules of multi-channel LLC resonant converters cannot be completely consistent, and there is a problem of current sharing between parallel modules. This will inevitably cause some modules to bear greater voltage or current stress, and even cause damage to the switch device and circuit paralysis in severe cases. Therefore, it is very important to achieve current sharing in multi-channel parallel LLC resonant converters.

[0003] The existing method uses hardware current sharing bus or total current sampling to adjust the resonant capacitor, resonant inductor, switching frequency or phase angle and other parameters of each path according to the size of each resonant current detected, so that each path can obtain the same and achieve better current sharing characteristics. For example, the half-bridge LLC resonant converter staggered parallel circuit and its current sharing control method disclosed in Chinese Patent Publication No. CN110572040A adjusts the gain of the converter by detecting the resonant current. In the above method, each LLC resonant converter requires a set of detection circuits and control circuits, which makes the entire system complex in structure, reduces reliability, and increases circuit cost. In addition, as the switching frequency is adjusted, the output voltage ripple will increase, which makes the output filter capacitor value larger, the output voltage adjustment becomes slower, and it is easy to cause the control loop to be unstable and the reliability is low. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the existing LLC multi-machine parallel current sharing control method and system have the problems of high cost, unstable control loop and low reliability.

[0005] The present invention solves the above technical problems through the following technical means: a LLC multi-machine parallel current sharing control method, the method comprising:

[0006] Step 1: One of the multiple LLC resonant converters is the master and the others are slaves;

[0007] Step 2: The host sends its secondary current to the slave via the CAN bus;

[0008] Step 3: All slaves synchronously receive the secondary current of the master and use the value as the input instruction of the slave current sharing loop;

[0009] Step 4: The secondary current of the slave is used as feedback of the current sharing loop, and compared with the input command of the slave current sharing loop to obtain the error, and then the error is adjusted by the first PID as the output of the slave current sharing loop;

[0010] Step 5. The output of the current sharing loop of the slave is added to the set slave voltage command as the new slave voltage command. The new slave voltage command is subtracted from the slave secondary voltage and a second PID adjustment is performed. The voltage value after the second PID adjustment is divided by the resistance of the slave to obtain the slave secondary current. Return to step 4 and continue to adjust to achieve current sharing of multiple LLC resonant converters.

[0011] The present invention does not require hardware sampling of total current or software communication to summarize total current and then equalize the current. It only needs to transmit resonant current through single-channel CAN communication. CAN communication is stable, fast, and simple to connect. It can not only simplify the system structure and reduce costs, but also realize multiple LLCs in parallel and the slaves can receive instructions at the same time with good synchronization and high reliability. At the same time, the host transmits the secondary current to each slave, and the slave receives the secondary current of the host as the current equalizing loop setting. Through the first PID adjustment, the first PID adjustment output result is added to the voltage setting of the voltage loop. The slave voltage instruction is adjusted by continuous feedback of the slave secondary current to achieve current equalization. The adjustment speed is fast, and the feedback adjustment mechanism makes the control loop stable.

[0012] Furthermore, a plurality of communication nodes are mounted on the CAN bus, and signals between the communication nodes are transmitted via the CAN bus.

[0013] Furthermore, the LLC resonant converters are all arranged on communication nodes, and each communication node includes a CAN controller and a CAN transceiver, the CAN controller is connected to the CAN transceiver, and the CAN transceiver is connected to the CAN bus.

[0014] Furthermore, the communication protocol between each LLC resonant converter is a CAN communication protocol.

[0015] Furthermore, the CAN controller and the CAN transceiver are connected via CAN_Tx and CAN_Rx signal lines.

[0016] Furthermore, the CAN transceiver is connected to the CAN bus using CAN_High and CAN_Low signal lines, which are a pair of differential signal lines.

[0017] Furthermore, the step 2 includes:

[0018] The host voltage given value is subtracted from the host secondary voltage, and the third PID adjustment is performed after the subtraction. The voltage value after the third PID adjustment is divided by the host resistance to obtain the host secondary current.

[0019] Furthermore, in the step three, all slaves synchronously receive the secondary current of the host by collecting current through a sampling module.

[0020] Furthermore, the sampling module is a current transformer.

[0021] Furthermore, the regulation principle of step five is as follows: when the secondary current of the slave is greater than the slave current equalizing loop input instruction, the difference between the slave current equalizing loop input instruction and the slave secondary current is a negative number, and then a first PID adjustment is performed on it as the slave current equalizing loop output, and the slave current equalizing loop output is negative. At this time, the slave current equalizing loop output is added to the set slave voltage instruction, and the set slave voltage instruction is reduced to obtain a new slave voltage instruction; and when the current of the slave is less than the slave current equalizing loop input instruction, the difference between the slave current equalizing loop input instruction and the slave secondary current is a positive number, and then a first PID adjustment is performed on it as the slave current equalizing loop output, and the slave current equalizing loop output is positive. At this time, the slave current equalizing loop output is added to the set slave voltage instruction, and then the set slave voltage instruction is increased to obtain a new slave voltage instruction, and the slave voltage instruction is adjusted by continuous feedback of the slave secondary current, thereby achieving current equalization.

[0022] The present invention also provides an LLC multi-machine parallel current sharing control system, the system includes multiple LLC resonant converters and a CAN bus, each LLC resonant converter is connected via the CAN bus communication, and the system executes the above-mentioned LLC multi-machine parallel current sharing control method.

[0023] The advantages of the present invention are:

[0024] (1) The present invention does not require hardware sampling of total current or software communication to summarize total current and then equalize the current. It only needs to transmit resonant current through single-channel CAN communication. CAN communication is stable, fast, and simple to connect. It can not only simplify the system structure and reduce costs, but also realize multiple LLCs in parallel and the slaves can receive instructions at the same time with good synchronization and high reliability. At the same time, the host transmits the secondary current to each slave, and the slave receives the secondary current of the host as the current equalizing loop setting. Through the first PID adjustment, the first PID adjustment output result is added to the voltage setting of the voltage loop. The slave voltage command is adjusted by the slave secondary current to achieve current equalization. The adjustment speed is fast, and the feedback adjustment mechanism makes the control loop stable.

[0025] (2) The CAN transceiver of the present invention is connected to the CAN bus using CAN_High and CAN_Low signal lines. The CAN_High and CAN_Low signal lines are a pair of differential signal lines. The differential signal transmission has strong anti-interference ability, can effectively suppress its external electromagnetic interference, and has accurate timing positioning, thereby improving the anti-interference ability and stability of the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A CAN closed-loop bus network in the LLC multi-machine parallel current sharing control system disclosed in an embodiment of the present invention;

[0027] Figure 2 This is the current sharing information flow diagram when the CAN communication current sharing mode is serial;

[0028] Figure 3 The CAN communication current sharing method is that each slave first transmits the secondary current to the host, and the host accumulates the secondary current of all slaves and the host itself.

[0029] Figure 4 It is an information flow diagram of the CAN communication current sharing method used in the present invention;

[0030] Figure 5 It is a flow chart of the control method after the slave receives the secondary side current of the host in a LLC multi-machine parallel current sharing control method disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] like Figure 1As shown, the present invention provides an LLC multi-machine parallel current sharing control method, which is applied to the LLC multi-machine parallel current sharing control system, and the system includes a multi-channel LLC resonant converter and a CAN bus. A plurality of communication nodes are mounted on the CAN bus, and the signals between the communication nodes are transmitted through the CAN bus to realize inter-node communication. The CAN communication protocol does not encode the address of the node, but encodes the data content. The LLC resonant converters are all arranged on the communication nodes, so that each LLC resonant converter is connected through the CAN bus communication. Each communication node includes a CAN controller and a CAN transceiver, and the CAN controller and the CAN transceiver are connected through CAN_Tx and CAN_Rx signal lines. In practical applications, when data needs to be transmitted, each LLC resonant converter feeds back its own current, voltage and other data to the CAN controller of the corresponding communication node, and transmits it to the CAN controller of the corresponding communication node of other LLC resonant converters through the corresponding CAN transceiver. The CAN transceiver is connected to the CAN bus using CAN_High and CAN_Low signal lines, where CAN_Tx and CAN_Rx use ordinary TTL-like logic signals, while CAN_High and CAN_Low are a pair of differential signal lines. Differential signal transmission has the following advantages: strong anti-interference ability, can effectively suppress its external electromagnetic interference, and accurate timing positioning.

[0033] The following describes the specific implementation and advantages of the present invention based on different communication modes of the CAN link. Figure 1 As shown, there are N communication nodes in total, and the CAN controller and CAN transceiver of each communication node are numbered from 1 to N. Taking CAN controller 1 as the host as an example, the arrow represents the direction of information flow between CAN nodes.

[0034] like Figure 2 The CAN communication current sharing method shown is serial. The host transmits the secondary current to the first slave. The first slave receives the secondary current of the host plus its own secondary current, obtains the secondary current and transmits it to the second slave. The second slave and subsequent slaves accumulate the secondary currents in the same way. The last slave transmits the sum of the secondary currents of the host and all slaves back to the host. The host averages the secondary current and then transmits the current sharing value to each slave. The master and slave then use the current sharing value as the current sharing loop given to achieve current sharing. This method requires multiple LLCs to transmit information, the current sharing communication line is long, the communication information flow is complicated, the current sharing process is slow, and the software algorithm is complex.

[0035] like Figure 3The CAN communication current sharing method shown is that each slave first transmits the secondary current to the host, the host accumulates the secondary currents of all slaves and the host itself, the host averages the secondary currents, and then transmits the current sharing value to each slave. The master and slave use the current sharing value as the current sharing loop given to achieve current sharing. This method requires multiple LLCs to transmit information, the communication lines are numerous and complex, the communication information flow is complicated, the current sharing process is slow, and the software algorithm is complex.

[0036] like Figure 4 The CAN communication current sharing method used in the present invention is shown. The host only needs to transmit the secondary current to each slave. The slave receives the secondary current of the host as the current sharing loop setting. Through PID control, the PID output result is added to the voltage setting of the voltage loop, and the voltage command is fine-tuned to achieve current sharing. This method only requires unidirectional transmission of the secondary current of a single LLC to achieve current sharing. The communication line is very simple, fast, and has good synchronization. The software algorithm is simple. The control method after the slave receives the secondary current of the host is as follows. Figure 5 The specific process of the LLC multi-machine parallel current sharing control method is as follows:

[0037] Step 1: One of the multi-channel LLC resonant converters is the master and the others are slaves; the master has no current balancing ring and the slaves use a current balancing ring.

[0038] Step 2: The host sends its secondary current to the slave through the CAN bus, and the slave does not need to send any instructions to the host. Specifically, the host voltage set value is subtracted from the host secondary voltage, and the third PID adjustment is performed after the difference. The voltage value after the third PID adjustment is divided by the resistance of the host to obtain the secondary current of the host.

[0039] Step 3: All slaves synchronously receive the secondary current of the host, and use the value as the slave current sharing loop input instruction; wherein all slaves synchronously receive the secondary current of the host by current collection through a sampling module. The sampling module is a current transformer.

[0040] Step 4: The secondary current of the slave is used as feedback of the current sharing loop, and compared with the input command of the slave current sharing loop to obtain the error, and then the error is adjusted by the first PID as the output of the slave current sharing loop;

[0041] Step 5: The output of the current sharing loop of the slave is added to the set slave voltage command as the new slave voltage command. The new slave voltage command is subtracted from the slave secondary voltage and the second PID adjustment is performed. The voltage value after the second PID adjustment is divided by the resistance of the slave to obtain the slave secondary current. Return to step 4 and continue to adjust to achieve current sharing of multiple LLC resonant converters. Among them, the first PID adjustment, the second PID adjustment and the third PID adjustment are all existing conventional PID adjustment methods, but they are distinguished by "first", "second" and "third" in order to distinguish different links for PID adjustment.

[0042] The regulation principle of the whole process is: the output of the current sharing loop of the slave is added to the set voltage command as a new voltage command. When the current of the slave is greater than the current given value, the voltage command is reduced, and when the current of the slave is less than the current given value, the voltage command is increased. In this way, current sharing is achieved by fine-tuning the voltage command. For detailed principles, please refer to Figure 5 When the secondary current of the slave is greater than the slave current sharing loop input instruction, the difference between the slave current sharing loop input instruction and the slave secondary current is a negative number, and then the first PID adjustment is performed on it as the slave current sharing loop output. The slave current sharing loop output is negative. At this time, the slave current sharing loop output is added to the set slave voltage instruction, and the set slave voltage instruction is reduced to obtain a new slave voltage instruction; and when the current of the slave is less than the slave current sharing loop input instruction, the difference between the slave current sharing loop input instruction and the slave secondary current is a positive number, and then the first PID adjustment is performed on it as the slave current sharing loop output. The slave current sharing loop output is positive. At this time, the slave current sharing loop output is added to the set slave voltage instruction, and then the set slave voltage instruction is increased to obtain a new slave voltage instruction. The slave voltage instruction is adjusted by continuous feedback of the slave secondary current, thereby achieving current sharing.

[0043] Through the above technical scheme, the present invention does not need hardware sampling of total current or software communication to summarize total current and then equalize the current. It only needs to transmit resonant current through single-channel CAN communication, which can ensure that the efficiency of the power supply is not affected. CAN communication is stable, fast, and simple to connect. It does not require changes in hardware circuits. It can not only simplify the system structure and reduce costs, but also realize multiple LLCs in parallel and the slaves can receive instructions at the same time, with good synchronization, good product performance, and high reliability. At the same time, the host transmits the secondary current to each slave, and the slave receives the secondary current of the host as the current equalizing loop given. Through the first PID adjustment, the first PID adjustment output result is added to the voltage given of the voltage loop. The slave voltage command is adjusted by continuous feedback of the slave secondary current to achieve current equalization. The adjustment speed is fast, and the feedback adjustment mechanism makes the control loop stable, the logic clear, and the algorithm simple.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A LLC multi-machine parallel current sharing control method, characterized in that: The method comprises: Step 1: One of the multiple LLC resonant converters is the master and the others are slaves; Step 2: The host sends its secondary current to the slave via the CAN bus; Step 3: All slaves synchronously receive the secondary current of the master and use the value as the input instruction of the slave current sharing loop; Step 4: The secondary current of the slave is used as feedback of the current sharing loop, and compared with the input command of the slave current sharing loop to obtain the error, and then the error is adjusted by the first PID as the output of the slave current sharing loop; Step 5. The output of the current sharing loop of the slave is added to the set slave voltage command as the new slave voltage command. The new slave voltage command is subtracted from the slave secondary voltage and a second PID adjustment is performed. The voltage value after the second PID adjustment is divided by the resistance of the slave to obtain the slave secondary current. Return to step 4 and continue to adjust to achieve current sharing of multiple LLC resonant converters.

2. The LLC multi-machine parallel current sharing control method according to claim 1 is characterized in that: A plurality of communication nodes are mounted on the CAN bus, and signals between the communication nodes are transmitted via the CAN bus.

3. The LLC multi-machine parallel current sharing control method according to claim 2 is characterized in that: The LLC resonant converters are all arranged on communication nodes, and each communication node includes a CAN controller and a CAN transceiver. The CAN controller is connected to the CAN transceiver, and the CAN transceiver is connected to the CAN bus.

4. The LLC multi-machine parallel current sharing control method according to claim 3 is characterized in that: The CAN controller and the CAN transceiver are connected via CAN_Tx and CAN_Rx signal lines.

5. The LLC multi-machine parallel current sharing control method according to claim 3 is characterized in that: The CAN transceiver is connected to the CAN bus using CAN_High and CAN_Low signal lines, which are a pair of differential signal lines.

6. The LLC multi-machine parallel current sharing control method according to claim 1 is characterized in that: The second step comprises: The host voltage given value is subtracted from the host secondary voltage, and the third PID adjustment is performed after the subtraction. The voltage value after the third PID adjustment is divided by the host resistance to obtain the host secondary current.

7. The LLC multi-machine parallel current sharing control method according to claim 1, characterized in that: In the step 3, all slaves synchronously receive the secondary current of the host by collecting the current through the sampling module.

8. The LLC multi-machine parallel current sharing control method according to claim 7, characterized in that: The sampling module is a current transformer.

9. The LLC multi-machine parallel current sharing control method according to claim 1, characterized in that: The regulation principle of step five is as follows: when the secondary current of the slave is greater than the slave current equalizing loop input instruction, the difference between the slave current equalizing loop input instruction and the slave secondary current is a negative number, and then a first PID adjustment is performed on it as the slave current equalizing loop output, and the slave current equalizing loop output is negative. At this time, the slave current equalizing loop output is added to the set slave voltage instruction, and the set slave voltage instruction is reduced to obtain a new slave voltage instruction; and when the current of the slave is less than the slave current equalizing loop input instruction, the difference between the slave current equalizing loop input instruction and the slave secondary current is a positive number, and then a first PID adjustment is performed on it as the slave current equalizing loop output, and the slave current equalizing loop output is positive. At this time, the slave current equalizing loop output is added to the set slave voltage instruction, and then the set slave voltage instruction is increased to obtain a new slave voltage instruction, and the slave voltage instruction is adjusted by continuous feedback of the slave secondary current, thereby achieving current equalization.

10. An LLC multi-machine parallel current sharing control system, characterized in that: The system includes multiple LLC resonant converters and a CAN bus, each LLC resonant converter is connected to each other through the CAN bus communication, and the system executes the LLC multi-machine parallel current sharing control method described in any one of claims 1-9.

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