CN107612335B - An Interleaved Parallel Control Method for Three-level LLC Resonant Converters - Google Patents

Abstract

The invention discloses an interleaved parallel control method for three-level LLC resonant converters, which at least includes: outputting drive signals to the LLC resonant converters of each phase; comparing the currents of the LLC resonant converters of each phase; and based on the comparison results The time increment is superimposed on the second dead time of the driving signal of the LLC resonant converter of each phase with larger current. The present invention firstly compares the currents of the LLC resonant converters of each phase, and then superimposes the time increment on the second dead time of the driving signals of the LLC resonant converters of each phase with larger currents based on the comparison results, so that the LLCs of these phases The second dead time T _d2 of the driving signal of the resonant converter becomes larger, thereby reducing the time for the input voltage to act on the resonant cavity, and reducing the resonant current of the LLC resonant converter of this phase, so that each LLC The power balance of the resonant converter improves the efficiency and reliability of the power supply.

Description

An Interleaved Parallel Control Method for Three-level LLC Resonant Converters

technical field

The invention relates to the technical field of power supplies, in particular to an interleaved parallel control method of a three-level LLC resonant converter.

Background technique

The LLC resonant converter is widely used in today's power supply design because of its simple structure, high efficiency and the ability to realize zero voltage switching (ZeroVoltage Switch, ZVS for short) in the full load range. Applying the three-level (Three-Level) structure to the LLC resonant converter can increase the input voltage of the converter and make the converter suitable for high voltage applications. At the same time, connecting the LLC converters in parallel in an interleaving manner can not only increase the output current of the power supply, but also reduce the input and output filter capacitance.

However, when LLC resonant converters are interleaved and connected in parallel, a deviation of less than 5% in the parameters of the resonant components will cause a large power imbalance, which will damage the efficiency and reliability of the entire power supply.

Contents of the invention

The invention solves the technical problem of power imbalance in the prior art by providing an interleaved parallel control method of the three-level LLC resonant converter, and realizes the technical effect of improving the efficiency and reliability of the power supply.

The present invention provides an interleaved parallel control method for a three-level LLC resonant converter, which at least includes:

Output drive signals to LLC resonant converters of each phase;

comparing the currents of the LLC resonant converters of each phase;

The time increment is superimposed on the second dead time of the drive signal of each phase of the LLC resonant converter with a larger current based on the comparison result.

Further, the outputting the driving signal to the LLC resonant converter of each phase at least includes:

Outputting drive signals with a phase difference φ of 360°/N to the LLC resonant converters of each phase; wherein, N is the number of the LLC resonant converters.

Further, the comparing the currents of the LLC resonant converters of each phase at least includes:

The input current or output current of the LLC resonant converter of each phase is compared.

Further, the superimposing the time increment on the second dead time of the driving signal of the LLC resonant converter of each phase with larger current based on the comparison result at least includes:

determining a minimum current in each phase of the LLC resonant converter based on the comparison result;

taking the difference between the current of the LLC resonant converter of each phase and the minimum current;

Obtaining the time increment of the LLC resonant converter of each phase based on the current difference;

Each of said time increments is superimposed on a second dead time of a drive signal of said respective LLC resonant converter.

Further, the obtaining the time increment of the LLC resonant converter of each phase based on the current difference at least includes:

Each current difference is passed through a proportional-integral controller to obtain the time increment of each phase of the LLC resonant converter.

Further, after passing each current difference value through the proportional-integral controller, it also includes at least:

Each current difference value is passed through the limiter to obtain the time increment of the LLC resonant converter of each phase.

One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

The currents of the LLC resonant converters of each phase are compared first, and then based on the comparison results, the time increment is superimposed on the second dead time of the driving signal of the LLC resonant converter of each phase with a larger current, so that the LLC resonant conversion of these phases The second dead time T _d2 of the driving signal of the inverter becomes larger, thereby reducing the time for the input voltage to act on the resonant cavity, reducing the resonant current of the LLC resonant converter of this phase, so that each LLC resonant conversion The power balance of the inverter improves the efficiency and reliability of the power supply.

Description of drawings

Figure 1 is a circuit diagram of a three-level LLC resonant converter;

FIG. 2 is a waveform diagram of a driving signal of a single three-level LLC resonant converter;

Figure 3 is a circuit diagram of a three-level LLC resonant converter interleaved in parallel;

4 is a flow chart of an interleaved parallel control method for a three-level LLC resonant converter provided by an embodiment of the present invention;

Fig. 5 is a schematic diagram of the phase of each drive signal when the three-level LLC resonant converter is interleaved and connected in parallel;

FIG. 6 is a flowchart of the first part of step S130 in the interleaved parallel control method of the three-level LLC resonant converter provided by the embodiment of the present invention;

FIG. 7 is a flowchart of the second part of step S130 in the interleaved parallel control method of the three-level LLC resonant converter provided by the embodiment of the present invention;

Figure 8 is a waveform diagram of the output power when the three-level LLC resonant converters are interleaved and connected in parallel without applying balance control;

Fig. 9 is a waveform diagram of the output power after the balance control is applied when the three-level LLC resonant converters are interleaved and connected in parallel.

Detailed ways

The embodiment of the present invention solves the technical problem of power imbalance in the prior art by providing an interleaved parallel control method of the three-level LLC resonant converter, and achieves the technical effect of improving the efficiency and reliability of the power supply.

The technical solution in the embodiment of the present invention is to solve the above-mentioned problems, and the general idea is as follows:

The currents of the LLC resonant converters of each phase are compared first, and then based on the comparison results, the time increment is superimposed on the second dead time of the driving signal of the LLC resonant converter of each phase with a larger current, so that the LLC resonant conversion of these phases The second dead time T _d2 of the driving signal of the inverter becomes larger, thereby reducing the time for the input voltage to act on the resonant cavity, reducing the resonant current of the LLC resonant converter of this phase, so that each LLC resonant conversion The power balance of the inverter improves the efficiency and reliability of the power supply.

In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

Before explaining the interleaved parallel control method of the three-level LLC resonant converter provided by the embodiment of the present invention, it is necessary to first understand the circuit structure of the three-level LLC resonant converter, the control method of the three-level LLC resonant converter and the three-level The circuit structure of the flat LLC resonant converter interleaved in parallel will be described. First, the circuit structure of the three-level LLC resonant converter is explained:

Referring to Figure 1, the circuit structure of the three-level LLC resonant converter consists of a transformer XFR1, a primary side resonant circuit and a secondary side rectifier circuit. Wherein, the primary side of the transformer XFR1 adopts one winding. The primary side resonant circuit includes four switching tubes S1, S2, S3, S4, two diodes D1, D2, and a resonant cavity composed of a resonant inductor Lr and a resonant capacitor Cr; the secondary side rectifier circuit includes two diodes D3 , D4. The four switch tubes S1-S4 on the primary side are connected in series in sequence. After the two diodes are connected in series, they are connected in parallel with the switch tubes S2 and S3. After the resonant inductor Lr, the resonant capacitor Cr and the primary winding of the transformer XFR1 are connected in series, one end is connected to the junction of S2 and S3 (the s end of S2), and the other end is connected to the junction of diodes D1 and D2. The positive pole Vin+ of the input is connected to the d terminal of the switch tube S1, the negative pole Vin- of the input is connected to the s terminal of the switch tube S4, and the midpoint N of the input is connected to the junction of the diodes D1 and D2. Transformer XFR1 secondary side winding and diodes form a rectifier circuit. One terminal p2 of the first winding is connected to the anode of the diode D3, the other terminal m2 is connected to the opposite terminal p3 of the second winding, and connected to the output negative pole Vout-. The other terminal m3 of the second winding is connected to the anode of the diode D4. The cathodes of diodes D3 and D4 are connected and connected to the positive output Vout+. The driving signals g1, g2, g3, g4 generated by the controller respectively control the switching on and off of the switching tubes S1, S2, S3, S4. When the driving signal is at a high level, the corresponding switching tube is turned on; when the driving signal is at a low level, the corresponding switching tube is turned off.

Referring to Fig. 2, if the dead time is not considered, the driving signals g1, g2, g3, g4 are square waves of the same frequency with a duty ratio of 0.5, and their frequency is f _sw . Among them, g1 and g2 have the same phase, and g3 and g4 have the same phase; g1, g2 and g3, g4 have opposite phases, that is, the phase difference is 180°. The controller controls the output voltage of the LLC converter by changing the frequency f _sw of the driving signal.

In order to avoid straight-through of the switching tubes and realize ZVS, a first dead time T _d1 and a second dead time T _d2 are added between the driving signals g1 , g2 , g3 , and g4 . Specifically, after the driving signal g1 goes low, delay for a period of T _d2 , and then make the driving signal g2 go low; after g2 goes low, delay for a period of T _d1 , and then make the driving signals g3 and g4 high. Similarly, after the drive signal g4 goes low, delay for a period of time T _d2 , and then drive the drive signal g3 to go low; after g3 goes low, delay for a period of time T _d1 , and then make the drive signals g3 and g4 high.

Referring to FIG. 3 , the circuit structure of three-level LLC resonant converters connected in parallel is composed of n three-level LLC resonant converters, where n≥2. The positive pole of the input is connected to one end of two capacitors C1 and C2 of equal capacitance in series, and the negative pole of the input is connected to the other end of the two capacitors C1 and C2 in series. The positive input pole Vin+ of all LLC resonant converters is connected to the positive pole of the input; the negative pole Vin- of the input of all LLC resonant converters is connected to the negative pole of the input; the midpoint N of all LLC resonant converters is connected to the connection point of capacitors C1 and C2. The output positive pole Vout+ of all LLC resonant converters is connected to the positive pole of the output, and the output negative pole Vout- of all LLC resonant converters is connected to the negative pole of the output. The capacitor C3 is connected between the positive and negative poles of the output.

Referring to Fig. 4, the interleaved parallel control method of the three-level LLC resonant converter provided by the embodiment of the present invention at least includes:

Step S110: outputting driving signals to the LLC resonant converters of each phase;

To illustrate this step:

The LLC resonant converters of each phase output drive signals with a phase difference φ of 360°/N; wherein, N is the number of LLC resonant converters. Since the fundamental wave of the input current is the switching frequency, and the fundamental wave of the output current is twice the switching frequency, this not only reduces the output ripple current, but also eliminates the ripple of the switching frequency of the input current. Taking the three-way parallel connection as an example, as shown in Figure 5, the phase difference of each driving signal is 120°, so as to reduce the input and output ripples at the same time.

Step S120: comparing the currents of the LLC resonant converters of each phase;

To illustrate this step:

The input current or output current of each phase LLC resonant converter is compared.

What needs to be explained here is that since comparing the input current and comparing the output current are equivalent and there is no difference, therefore, in any case, both the input current and the output current can be compared.

Step S130: Based on the comparison result, superimpose the time increment on the second dead time of the driving signal of the LLC resonant converter of each phase with larger current, so that the second dead time T _d2 of the LLC resonant converter of these phases becomes larger .

To illustrate this step:

Determining the minimum current in the LLC resonant converter of each phase based on the comparison result;

Calculate the difference between the current of each phase LLC resonant converter and the minimum current;

What needs to be explained here is that if the comparison result is the comparison result of the input current, the minimum current is the minimum input current; the difference between the input current of each phase LLC resonant converter and the minimum input current is calculated; if the comparison result is the comparison result of the output current , then the minimum current is the minimum output current; the difference between the output current of each phase LLC resonant converter and the minimum output current is calculated.

The time increment of the LLC resonant converter of each phase is obtained based on the current difference;

Each time increment is superimposed on the second dead time of the drive signal of each LLC resonant converter.

Wherein, the time increment of the LLC resonant converter of each phase is obtained based on the current difference, at least including:

Each current difference is passed through a proportional-integral controller to obtain the time increment of each phase LLC resonant converter.

Specifically, after each current difference is passed through the proportional-integral controller, it also includes at least:

Each current difference is passed through the limiter to obtain the time increment of each phase LLC resonant converter.

More specifically, step S130 is completed in two parts, as shown in FIG. 6 and FIG. 7 . In the first part, a phase LLC converter is selected as the reference phase. Specifically, it includes: taking the converter without changing the second dead time (that is, the converter with ΔT _d = 0) as the candidate object, comparing their output currents, and selecting the phase with the smallest current (assumed to be the mth phase phase) as the reference phase. And take the current of the reference phase as the current reference. In the second part, each phase generates its own second dead time increment ΔT _d . Specifically, it includes: if the phase is the reference phase (ie m=i), then the dead zone increment is set to zero (ie ΔT _d =0). If the phase is not the reference phase (that is, m≠i), then the difference between the output current of the phase and the output current of the reference phase is calculated, and through the proportional-integral controller and the limiter, a dead time increment ΔT _d is generated. Wherein, the function of the limiter is to make the time increment greater than or equal to zero. If the dead time increment ΔT _d generated by the proportional-integral controller is less than zero, the limiter will make ΔT _d =0. The dead time increment ΔT _d generated by each phase is superimposed on the original second dead time T _d2 , so that the second dead time increases as T _d2 +ΔT _d .

What needs to be explained here is that the increment of dead time generated by each phase is sent back to the first part as the basis for generating the reference phase.

The figure shows the effect of paralleling three LLC resonant converters when interleaved paralleling is used but no balancing control is applied. The staggered parallel connection makes each drive signal different from each other by 120°. The peak values of the current are staggered from each other due to the phase difference, and the ripple becomes smaller. However, due to the inconsistency of the resonance parameters (there is a 5% deviation), when the balance control is not applied, the output power of each channel is unbalanced.

The figure shows the effect of interleaved paralleling after applying the balance control. The balance control makes the second dead time of the driving signal of each LLC converter different, so that the output power of each converter tends to be consistent.

1. First compare the currents of the LLC resonant converters of each phase, and then superimpose the time increment on the second dead time of the driving signal of the LLC resonant converter of each phase with a larger current based on the comparison results, so that the LLCs of these phases The second dead time T _d2 of the driving signal of the resonant converter becomes larger, thereby reducing the time for the input voltage to act on the resonant cavity, and reducing the resonant current of the LLC resonant converter of this phase, so that each LLC The power balance of the resonant converter improves the efficiency and reliability of the power supply.

2. For the LLC resonant converter of each phase, the drive signal with a phase difference φ of 360°/N is output. Since the fundamental wave of the input current is the switching frequency, and the fundamental wave of the output current is twice the switching frequency, this can not only make The output ripple current is reduced, and the ripple of the switching frequency of the input current can also be eliminated.

The embodiment of the present invention can not only reduce the input and output ripple current, especially the input current ripple of the switching frequency, but also overcome the power imbalance phenomenon that occurs when multiple LLC resonant converters are interleaved and connected in parallel. Thereby, the power density of the converter is improved, and its operation is safer, more reliable and more efficient.

While preferred embodiments of the invention have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (5)

1. a kind of crisscross parallel control method of three-level LLC resonance inverter, which is characterized in that include at least:

To each phase LLC resonant converter output drive signal；

The electric current of each phase LLC resonant converter is compared；

Based on comparative result by incremental time be added to the biggish each phase LLC resonant converter of electric current driving signal it is second dead On area's time；

It is described based on comparative result by incremental time be added to the biggish each phase LLC resonant converter of electric current driving signal In two dead times, include at least:

The minimum current in each phase LLC resonant converter is determined based on comparative result；

The electric current of each phase LLC resonant converter and the minimum current are asked poor；

The incremental time of each phase LLC resonant converter is obtained based on current differential；

Each incremental time is added in the second dead time of the driving signal of each LLC resonant converter；

Wherein, the second dead time be driving signal g1 be lower with driving signal g2 be lower between delay time, and the drive Dynamic signal g1 is identical as the phase of the driving signal g2.

2. the method as described in claim 1, which is characterized in that it is described to each phase LLC resonant converter output drive signal, until Include: less

The driving signal for being 360 °/N to each phase LLC resonant converter phase difference output φ；Wherein, N is the LLC resonance The number of converter.

3. the method as described in claim 1, which is characterized in that the electric current by each phase LLC resonant converter carries out Compare, include at least:

The input current of each phase LLC resonant converter or output electric current are compared.

4. the method as described in claim 1, which is characterized in that described to obtain each phase LLC resonance change based on current differential The incremental time of parallel operation, includes at least:

By each current differential by proportional-plus-integral controller, the incremental time of each phase LLC resonant converter is obtained.

5. method as claimed in claim 4, which is characterized in that each current differential is passed through proportional-plus-integral controller described Later, it also includes at least:

By each current differential by limiter, the incremental time of each phase LLC resonant converter is obtained.