Isolation module minimum power transmission method applied to isolation-non-isolation hybrid converter

Abstract

The invention discloses an isolation module minimum power transmission method applied to an isolation-non-isolation hybrid converter, and belongs to the technical field of power transmission control. Obtaining the power ratio of the isolation module to the non-isolation module according to the voltage-sharing boundary, and obtaining the minimum transmission power of the isolation module; and introducing the minimum transmission power of the isolation module into a DC-DC converter control strategy so as to change the power transmission size. According to the method, the minimum power capable of being transmitted by the isolation module is calculated by using the voltage-sharing boundary of the front-stage cascade converter, and the minimum transmission power of the isolation module is introduced into a DC-DC converter control strategy, so that the isolation module is adjusted to work at the minimum power transmission, the size of a high-frequency transformer in the DC-DC converter is effectively reduced, and the power consumption of the DC-DC converter is reduced. The size of the whole converter system is reduced, and the efficiency of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission control, and in particular to an isolation module minimum power transmission method applied to an isolation-non-isolation hybrid converter. Background Art

[0002] At present, cascade multilevel converters have been well developed in related fields such as high voltage, high power and motor drive. With the increase of cascade modules, if the voltage of each module is unbalanced, some modules will be subjected to excessive voltage stress, which will lead to reduced efficiency, overheating of equipment and even damage. Therefore, a voltage balancing strategy is generally used to control and adjust the voltage of each module so that the voltage of each module is maintained in a balanced state. In the hybrid cascade converter, how to use the voltage balancing boundary to minimize the power transmission of the isolation module to reduce the volume of the high-frequency transformer and improve efficiency is a technical problem that needs to be solved urgently. In the face of this problem, the main solution in the industry at this stage is: do not adjust the power of the isolation module, only use the power transmission difference to balance the DC voltage of each module, that is, by adjusting the power output of the non-isolated module, change the power flow of the entire converter system, thereby affecting the DC voltage of each module. For example, if the voltage of a module is higher than that of other modules, the power output of the module can be reduced to reduce its voltage. This method does not control the transmission power of the isolation module, resulting in the high-frequency transformer of the DC-DC converter being designed according to the maximum transmission power of the system when designing capacity, which greatly increases the size of the transformer. At the same time, when working at a higher power transmission, the loss of the DC-DC converter will also increase, reducing the efficiency of the system. Summary of the invention

[0003] The purpose of the present invention is to overcome the problems of the prior art and to provide an isolation module minimum power transmission method applied to an isolation-non-isolation hybrid converter.

[0004] The object of the present invention is to achieve the following technical solution: a minimum power transmission method of an isolation module applied to an isolation-non-isolation hybrid converter, applied to an isolation-non-isolation hybrid converter system, the method comprising the following steps:

[0005] Calculate the voltage-sharing boundary of the system: Calculate the difference between the converter transmission power under the maximum voltage vector level and the converter transmission power under normal load conditions based on the port level of the heavy-load module and the port level of the light-load module, and then obtain the relationship between the unbalanced load and the input current. Combined with the input-output power relationship, integrate and transform to obtain the relationship between the unbalanced load and the modulation degree, and introduce the proportional factor to calculate the voltage-sharing boundary.

[0006] The power ratio of the isolation module to the non-isolation module is obtained according to the voltage-sharing boundary, and the minimum transmission power of the isolation module is obtained;

[0007] The minimum transmission power of the isolation module is introduced into the DC-DC converter control strategy to change the power transmission size.

[0008] In one example, the port level of the heavy-load module is always 2E, and the port level of the light-load module is (6m*sinωt-4)E. The relationship between the unbalanced load and the input current is:

[0009]

[0010] Among them, I s Represents system input AC / DC; ω represents angular frequency; t represents time; m represents modulation index; E represents minimum voltage change unit; R1 is the equivalent resistance value of the DC side of the heavy-load module load, and R2 is the equivalent load of the light-load module.

[0011] In one example, the input-output power relationship is:

[0012] V s I s / 2=2E 2 (1 / R2+2 / R1);

[0013] Among them, V s Indicates input AC voltage; I s Indicates the system input AC and DC; E indicates the minimum voltage change unit; R1 is the equivalent resistance of the DC side of the heavy-load module load, and R2 is the equivalent load of the light-load module.

[0014] In one example, the relationship between unbalanced load and modulation is:

[0015]

[0016] Where m represents the modulation index; V s Indicates the input AC voltage; E indicates the minimum voltage change unit; R1 is the equivalent resistance of the DC side of the heavy-load module load, and R2 is the equivalent load of the light-load module.

[0017] In one example, the proportional factor k=R2 / R1, and the pressure equalization boundary k expression is:

[0018]

[0019] Here, m represents the modulation degree.

[0020] In one example, the minimum transmission power P* of the isolation module is:

[0021] P*=(R2 / (R2+2R1)*P in =(k / (k+2))*P in );

[0022] Among them, R1 is the equivalent resistance of the DC side of the heavy-load module load, R2 is the equivalent load of the light-load module; k = R2 / R1, is the proportional factor; P in is the current input power of the system.

[0023] In one example, the minimum transmission power of the isolation module is introduced into the DC-DC converter control strategy, including:

[0024] The given duty cycle is calculated according to the minimum transmission power of the isolation module and the DC voltage of the DC-DC converter, and then the actual duty cycle is obtained;

[0025] The actual duty cycle is input into the modulation module to obtain a switching signal, and the DC-DC converter is controlled based on the switching signal.

[0026] In one example, the calculation expression of the given duty cycle is:

[0027]

[0028] in, A PWM given duty cycle for a switching device in a first converter in the DC-DC converter; A PWM given duty cycle for a switching device in a second converter in the DC-DC converter; It represents the phase shift duty ratio between the primary and secondary sides of the transformer in the DC-DC converter; U1 is the DC voltage of the primary side of the DC-DC converter; r is the converter voltage gain nU2 / U1, n is the DC-DC converter ratio, U2 is the DC voltage output of the secondary side of the DC-DC converter; L is the equivalent inductance of the DC-DC converter; T s Represents the switching cycle.

[0029] In one example, calculating a given duty cycle further includes:

[0030] The synthetic given power is calculated based on the minimum transmission power and the compensation power generated by the PI controller;

[0031] The given duty cycle is calculated based on the synthesized given power and the DC-DC converter DC voltage.

[0032] In one example, the calculation expression of the given duty cycle is:

[0033]

[0034] in, A PWM given duty cycle for a switching device in a first converter in the DC-DC converter; A PWM given duty cycle for a switching device in a second converter in the DC-DC converter; It represents the phase shift duty ratio between the primary and secondary sides of the transformer in the DC-DC converter; U1 is the DC voltage of the primary side of the DC-DC converter; r is the converter voltage gain nU2 / U1, n is the DC-DC converter ratio, U2 is the DC voltage output of the secondary side of the DC-DC converter; L is the equivalent inductance of the DC-DC converter; T s Indicates the switching period; ΔP * To compensate power.

[0035] It should be further explained that the technical features corresponding to the above examples can be combined or replaced with each other to form a new technical solution.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The method of the present invention utilizes the voltage-sharing boundary of the preceding cascade converter to calculate the minimum power that can be transmitted by the isolation module, introduces the minimum transmission power of the isolation module into the DC-DC converter control strategy, and then adjusts the isolation module to operate at the minimum power transmission, thereby effectively reducing the volume of the high-frequency transformer in the DC-DC converter, thereby reducing the volume of the entire converter system, and improving the efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings. The accompanying drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The same reference numerals are used in these drawings to represent the same or similar parts. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0039] Figure 1 A schematic diagram of a non-isolated-isolated hybrid cascade converter provided as an example of the present invention;

[0040] Figure 2 A method flow chart provided for an example of the present invention;

[0041] Figure 3 A schematic diagram of the minimum power transmission control principle of the isolation module in a non-isolated-isolated hybrid cascade converter topology provided as an example of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only 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.

[0043] In the description of the present invention, it should be noted that the directions or positional relationships indicated by "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. are directions or positional relationships based on the drawings, which are only for the convenience of describing the present invention 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 the present invention. In addition, the use of ordinal numbers (e.g., "first and second", "first to fourth", etc.) is to distinguish objects, and is not limited to this order, and cannot be understood as indicating or implying relative importance.

[0044] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0046] The present invention discloses an isolation module minimum power transmission method for an isolation-non-isolation hybrid converter, which is applied to an isolation-non-isolation hybrid converter system. The system includes an isolation-non-isolation hybrid converter, a controller, etc. The isolation-non-isolation hybrid converter includes a cascaded isolation module (isolation converter module) and a non-isolation module (non-isolation converter module). The non-isolation module includes an AC / DC rectifier and a DC / AC inverter connected in sequence, and a capacitor is connected in parallel between the AC / DC rectifier and the DC / AC inverter. The isolation module includes an AC / DC rectifier, a DC-DC converter (direct-to-direct converter), and a DC / AC inverter connected in sequence. The DC-DC converter in this example is a dual active full-bridge (DAB) converter, including two full-bridge converters. Furthermore, the controller is connected to the switching devices in the rectifier, the inverter, and the DC-DC converter, and the control of the switching devices is realized by outputting a PWM signal by the controller. The topology of the isolation-non-isolation hybrid converter in this example is as follows: Figure 1As shown, it includes two non-isolated modules and one isolated module, the two non-isolated modules and the isolated module are cascaded, and the two non-isolated modules have the same structure. During the operation of the isolated-non-isolated hybrid converter system, when the power loads borne by different modules are uneven, it is in an unbalanced load state. At this time, the module that bears a larger power in the system is a heavy-load module. The present invention uses the non-isolated module as the heavy-load module; the module that bears a smaller power is a light-load module. The present invention uses the isolated module as the light-load module.

[0047] In one example, if Figure 2 As shown, a minimum power transmission method for an isolation module applied to an isolation-non-isolation hybrid converter includes the following steps:

[0048] S1: Calculate the voltage balancing boundary of the system: Calculate the difference between the converter transmission power under the maximum voltage vector level and the converter transmission power under normal load conditions according to the port level of the heavy-load module and the port level of the light-load module, and then obtain the relationship between the unbalanced load and the input current. Integrate and transform the input-output power relationship to obtain the relationship between the unbalanced load and the modulation degree, and introduce the proportional factor to calculate the voltage balancing boundary.

[0049] When the voltage balancing boundary is reached, the converter with large load power (heavy load module) tends to choose the vector that can transmit the maximum power to maximize the power transmission efficiency and avoid voltage imbalance. Therefore, the port level of the heavy load module is 2E or -2E most of the time, ignoring the 0 and smaller ±E vectors in the vector transfer path (smaller ±E vectors transmit less power at the same switching frequency). The essence of the voltage balancing boundary is the maximum power transmitted by the converter at ±2E. When calculating the load ratio, it can be considered as the difference between the power transmitted by the 2E level converter and the power transmitted by the normal load converter. This difference can reflect how much additional power the converter can provide to the load under the maximum power transmission condition.

[0050] S2: Obtain the power ratio of the isolation module to the non-isolation module according to the voltage-sharing boundary, and then obtain the minimum transmission power of the isolation module. The voltage-sharing boundary represents the power distribution ratio between the isolation module and the non-isolation module under the voltage-sharing boundary condition. The power ratio of the isolation module to the non-isolation module can be obtained from the voltage-sharing boundary, and then the minimum transmission power of the isolation module can be obtained.

[0051] S3: Introduce the minimum transmission power of the isolation module into the DC-DC converter control strategy to change the power transmission size. In order to implement the voltage balancing strategy, it is necessary to dynamically adjust the power distribution of each module. After calculating the minimum transmission power of the isolation module, the controller combines the minimum transmission power and the DC voltage of the DC-DC converter to calculate the corresponding PWM signal duty cycle. The controller generates a switching signal (PWM signal) through the duty cycle and the phase shift modulation strategy of the DC-DC converter to control the switching state of the switching device and realize the regulation of the output voltage and power transmission.

[0052] The present invention analyzes the maximum voltage-sharing boundary that the system can achieve under the current given conditions, and on this basis calculates the maximum power ratio that can be achieved between the heavy-load module (non-isolated module) and the light-load module (isolated module), and obtains the minimum power that can be transmitted by the light-load module, i.e., the isolation module. The obtained isolation module power is introduced into the DC-DC converter control strategy to change the power transmission size, thereby achieving minimum power transmission of the isolation module and improving system efficiency.

[0053] In one example, before calculating the pressure balancing boundary of the system, the method further includes:

[0054] S01: Calculate the current input power P of the system in , the system input power satisfies the following formula:

[0055] P in =V s ×I s ;

[0056] Where V s is the input AC voltage of the system, I s Input AC current.

[0057] S02: Solve the modulation index of the system. The output modulation index satisfies the following formula:

[0058]

[0059] Among them, θ * It is a reference instruction issued by the host computer, such as a DC voltage reference value.

[0060] In one example, taking a three-module cascade converter as an example, the port level of the heavy-load module is defined as 2E, and the light-load port level is defined as (6m*sinωt-4)E. The power transmitted by the converter in the stable state is equal within the half-cycle range, so only the power difference in the first half of the entire cycle can be calculated. The unbalanced load and the input current satisfy the following relationship

[0061]

[0062] Where ω represents the angular frequency; t represents the time; E represents the minimum voltage change unit; R1 is the equivalent resistance of the DC side of the heavy-load module load, and R2 is the equivalent load of the light-load module. Ignoring the energy stored in the inductor, the input and output power meet V s I s / 2=(2E) 2 (1 / R2+2 / R1), substituting into the relationship between unbalanced load and input current, we get:

[0063]

[0064] Integrating the above equation, we can get the relationship between unbalanced load and modulation index:

[0065]

[0066] Define the proportional factor k = R2 / R1, and the pressure-equalizing boundary k expression is:

[0067]

[0068] According to the voltage-sharing boundary, the minimum transmission power P* of the isolation module is:

[0069] P*=(R2 / (R2+2R1)*P in =(k / (k+2))*P in ).

[0070] In one example, the minimum transmission power of the isolation module is introduced into the DC-DC converter control strategy, including:

[0071] S31: Calculate a given duty cycle according to the minimum transmission power of the isolation module and the DC voltage of the DC-DC converter, and then obtain an actual duty cycle;

[0072] S32: Input the actual duty cycle into the modulation module to obtain a switching signal, and control the DC-DC converter based on the switching signal.

[0073] In step S31, the power to be transmitted by the isolation module and the DC voltage are used to calculate a given duty cycle, and direct power control is performed on the transmission power of the converter. pu for:

[0074]

[0075] Wherein, U1 is the primary DC voltage of the DC-DC converter; r is the converter voltage gain nU2 / U1, n is the DC-DC converter ratio, U2 is the secondary output DC voltage of the DC-DC converter; L is the equivalent inductance of the DC-DC converter; T s Indicates the switching cycle; Pbase In direct power control, if the expected output power can be achieved immediately, the converter will have excellent dynamic performance. pu P base =P*, the given duty cycle can be obtained:

[0076]

[0077] in, A PWM given duty cycle for a switching device in a first converter in the DC-DC converter; A PWM given duty cycle for a switching device in a second converter in the DC-DC converter; Represents the phase shift duty ratio between the primary and secondary sides of the DC-DC converter transformer. In order to ensure the real-time minimum power of the converter, r needs to be calculated using the real-time voltage.

[0078] Preferably, due to the influence of factors such as converter loss, model non-ideality, dead zone, etc., the accuracy of the model decreases, so there will be errors in the converter transmission power and load power. The actual output power cannot be simply expressed by a mathematical function of the output voltage U2. It is necessary to provide additional compensation power △P* to offset the voltage drop caused by the converter loss, so that the output duty cycle of the predictor accurately follows the actual duty cycle, and the synthesized given power is P0 * =P*+△P*, the accurate given duty cycle can be obtained:

[0079]

[0080] Among them, ΔP * To compensate the power, the compensation power △P* is calculated by the PI controller based on the error between the actual output DC voltage U2 of the secondary side of the DC-DC converter and the expected output voltage U2*. When the output of the non-isolated-isolated hybrid cascade converter reaches a steady state, the duty cycle is given. and the actual duty cycle Consistent, then the actual duty cycle The switching signal is input to the modulation module to realize the switching control of the switching device in the DC-DC converter, thereby realizing the regulation and control of the output voltage and power transmission.

[0081] Combining the above examples, we can obtain a preferred example of the present invention, such as Figure 3 As shown, the method now includes the following steps:

[0082] S10: Calculate the current input power of the system;

[0083] S20: solve the modulation degree of the system;

[0084] S30: Calculating the voltage balancing boundary of the system: Calculating the difference between the converter transmission power under the maximum voltage vector level and the converter transmission power under normal load conditions according to the port level of the heavy-load module and the port level of the light-load module, and then obtaining the relationship between the unbalanced load and the input current, integrating and transforming the input-output power relationship, and obtaining the relationship between the unbalanced load and the modulation degree, and introducing the proportional factor to calculate and obtain the voltage balancing boundary;

[0085] S40: Obtain a power ratio of the isolation module to the non-isolation module according to the voltage sharing boundary, and then obtain a minimum transmission power of the isolation module.

[0086] S50: Calculate the synthesized given power according to the minimum transmission power and the compensation power generated by the PI controller; calculate the given duty cycle according to the synthesized given power and the DC voltage of the DC-DC converter. When the system output reaches a steady state, the given duty cycle and the actual duty cycle The actual duty cycle is input into the modulation module to obtain a switching signal, and the DC-DC converter is controlled based on the switching signal.

[0087] The present invention, based on the voltage balancing strategy of the cascade converter, obtains the minimum power transmitted by the isolation module by calculating the voltage balancing boundary of the system, and can achieve the voltage balancing effect at the same time. By reducing the power transmission of the isolation module, the volume of the system is reduced and the efficiency is improved. In addition, the present invention does not require an additional voltage sensor and realizes accurate control of the transmission power of the isolation module. It is also possible to obtain the power transmitted by the isolation module conveniently and quickly according to the number of modules and power required by the user, providing a reference for system design.

[0088] The above specific implementation methods are detailed descriptions of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A minimum power transmission method for an isolation module applied to an isolation-non-isolation hybrid converter, applied to an isolation-non-isolation hybrid converter system, characterized in that: The following steps are involved: Calculate the voltage-sharing boundary of the system: Calculate the difference between the converter transmission power under the maximum voltage vector level and the converter transmission power under normal load conditions based on the port level of the heavy-load module and the port level of the light-load module, and then obtain the relationship between the unbalanced load and the input current. Combined with the input-output power relationship, integrate and transform to obtain the relationship between the unbalanced load and the modulation degree, and introduce the proportional factor to calculate the voltage-sharing boundary. The power ratio of the isolation module to the non-isolation module is obtained according to the voltage-sharing boundary, and the minimum transmission power of the isolation module is obtained; The minimum transmission power of the isolation module is introduced into the DC-DC converter control strategy to change the power transmission size.

2. The isolation module minimum power transmission method applied to the isolation-non-isolation hybrid converter according to claim 1, characterized in that: The port level of the heavy-load module is always 2E, and the port level of the light-load module is (6m*sinωt-4)E. The relationship between the unbalanced load and the input current is: Among them, I s Represents system input AC / DC; ω represents angular frequency; t represents time; m represents modulation index; E represents minimum voltage change unit; R1 is the equivalent resistance value of the DC side of the heavy-load module load, and R2 is the equivalent load of the light-load module.

3. The isolation module minimum power transmission method applied to the isolation-non-isolation hybrid converter according to claim 1, characterized in that: The input and output power relationship is: V s I s / 2=2E 2 (1 / R2+2 / R1); Among them, V s Indicates input AC voltage; I s Indicates the system input AC and DC; E indicates the minimum voltage change unit; R1 is the equivalent resistance of the DC side of the heavy-load module load, and R2 is the equivalent load of the light-load module.

4. The isolation module minimum power transmission method applied to the isolation-non-isolation hybrid converter according to claim 1, characterized in that: The relationship between unbalanced load and modulation degree is: Where m represents the modulation index; V s Indicates the input AC voltage; E indicates the minimum voltage change unit; R1 is the equivalent resistance of the DC side of the heavy-load module load, and R2 is the equivalent load of the light-load module.

5. The isolation module minimum power transmission method applied to the isolation-non-isolation hybrid converter according to claim 1, characterized in that: The proportional factor k=R2 / R1, and the pressure equalization boundary k expression is: Here, m represents the modulation degree.

6. The isolation module minimum power transmission method applied to the isolation-non-isolation hybrid converter according to claim 1, characterized in that: The minimum transmission power P* of the isolation module is: P*=(R2 / (R2+2R1)*P in =(k / (k+2))*P in ); Among them, R1 is the equivalent resistance of the DC side of the heavy-load module load, R2 is the equivalent load of the light-load module; k = R2 / R1, is the proportional factor; P in is the current input power of the system.

7. The isolation module minimum power transmission method applied to the isolation-non-isolation hybrid converter according to claim 6, characterized in that: Introducing the minimum transmission power of the isolation module into the DC-DC converter control strategy, including: The given duty cycle is calculated according to the minimum transmission power of the isolation module and the DC voltage of the DC-DC converter, and then the actual duty cycle is obtained; The actual duty cycle is input into the modulation module to obtain a switching signal, and the DC-DC converter is controlled based on the switching signal.

8. The isolation module minimum power transmission method applied to the isolation-non-isolation hybrid converter according to claim 7, characterized in that: The calculation expression of the given duty cycle is: in, A PWM given duty cycle for a switching device in a first converter in the DC-DC converter; A PWM given duty cycle for a switching device in a second converter in the DC-DC converter; It represents the phase shift duty ratio between the primary and secondary sides of the DC-DC converter; U1 is the DC voltage of the primary side of the DC-DC converter; r is the converter voltage gain nU2 / U1, n is the DC-DC converter ratio, U2 is the DC voltage output by the secondary side of the DC-DC converter; L is the equivalent inductance of the DC-DC converter; T s Represents the switching cycle.

9. The isolation module minimum power transmission method applied to the isolation-non-isolation hybrid converter according to claim 7, characterized in that: Calculating a given duty cycle also includes: The synthetic given power is calculated based on the minimum transmission power and the compensation power generated by the PI controller; The given duty cycle is calculated based on the synthesized given power and the DC-DC converter DC voltage.

10. The isolation module minimum power transmission method applied to the isolation-non-isolation hybrid converter according to claim 9, characterized in that: The calculation expression of the given duty cycle is: Among them, D1 * D2 is the PWM duty cycle of the switching device in the first converter of the DC-DC converter; * A PWM given duty cycle for a switching device in a second converter in the DC-DC converter; It represents the phase shift duty ratio between the primary and secondary sides of the DC-DC converter; U1 is the DC voltage of the primary side of the DC-DC converter; r is the converter voltage gain nU2 / U1, n is the DC-DC converter ratio, U2 is the DC voltage output by the secondary side of the DC-DC converter; L is the equivalent inductance of the DC-DC converter; T s Indicates the switching period; ΔP * To compensate power.

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