Parallel current sharing control method for wide power range full-bridge LLC resonant converter

Abstract

The application relates to a parallel current sharing control method for a wide power range full-bridge LLC resonant converter, which comprises the following steps: a given working switch frequency f w is obtained to obtain a duty ratio D1; a current error of each LLC resonant converter is obtained, the current error is sent into a PI regulator to obtain a duty ratio D2; the duty ratio D2 is superposed with the duty ratio D1 to obtain a duty ratio D; a PWM signal with the duty ratio D is generated to drive switch tubes Sn1 and Sn3, and the PWM signals of switch tubes Sn2 and Sn4 always remain unchanged with D=0.5. The application further discloses a parallel current sharing control system for a wide power range full-bridge LLC resonant converter. Through the voltage and current double-loop control mode, the application solves the problem of uneven output current of the parallel full-bridge LLC resonant converter caused by the circuit parameter difference; through the fixed frequency+PWM control mode, the application solves the problem of limited frequency range existing in the frequency control and the problem of difficult current sharing in parallel at light load, and realizes the parallel current sharing function of the full-bridge LLC resonant converter in a wide power range.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics and power conversion, and particularly relates to a parallel current sharing control method for a wide power range full-bridge LLC resonant converter. BACKGROUND

[0002] LLC resonant converters are widely used due to their high power density and easy realization of soft switching. In high power applications, a single LLC resonant converter cannot meet the power requirement, and multiple converter modules are usually used in parallel. However, the voltage gain of the LLC resonant converter is sensitive to the parameters of the resonant devices. In practical applications, due to the influence of manufacturing process and natural environment, the parameters of the resonant devices of each module are difficult to remain consistent, which leads to differences in the output load current of each parallel module, which seriously affects the reliability and service life of the LLC resonant converter.

[0003] Currently, there are control methods for realizing parallel current sharing through phase shift, but this method requires a host computer. If the host computer fails, the other slave computers cannot work normally. There are also control methods for realizing parallel current sharing of LLC resonant converters through virtual impedance. This method adjusts the frequency to change the size of the converter gain, which can achieve good current sharing effect under heavy load conditions. However, the operating frequency range of the converter is limited, and it is difficult to realize the current sharing function of the converter through frequency adjustment under light load conditions. SUMMARY

[0004] To solve the problem of uneven output current and limited power range caused by differences in circuit parameters when full-bridge LLC resonant converters are used in parallel, the purpose of the present application is to provide a parallel current sharing control method for a wide power range full-bridge LLC resonant converter, which can ensure equal output current of each parallel module in the full load range.

[0005] To achieve the above purpose, the present application adopts the following technical solution: a parallel current sharing control method for a wide power range full-bridge LLC resonant converter, which comprises the following steps in sequence:

[0006] (1) Given the operating switching frequency Make the LLC resonant converter work in a fixed frequency condition, and detect the output voltage online Subtract the output voltage From the given reference voltage To get the voltage error Send the voltage error Into a PI regulator to get the duty cycle D1 for compensating the voltage error, to ensure that the converter outputs a given voltage value;

[0007] (2) Detect the current at the output end of the diode rectifier bridge online The current of each LLC resonant converter is summed to obtain an average current The current of the diode rectifier bridge output end of each LLC resonant converter is summed to obtain an average current The average current The difference is obtained to obtain the current error of each LLC resonant converter, and the current error is sent to a PI regulator to obtain a duty cycle D2 for compensating the current error;

[0008] (3) The duty cycle D2 is taken as a feedback signal and is superimposed with the duty cycle D1 to obtain a duty cycle D for regulating the gain of the LLC resonant converter to realize current sharing, and the duty cycle D is D1+D2;

[0009] (4) A PWM signal with the duty cycle D is generated to drive the switch tubes Sn1 and Sn3, and the PWM signals of the switch tubes Sn2 and Sn4 always remain unchanged at D=0.5; the drain of Sn1 is connected with the drain of Sn3, the source of Sn1 is connected with the drain of Sn2, the source of Sn3 is connected with the drain of Sn4, and the source of Sn2 is connected with the source of Sn4.

[0010] In step (1), the working switching frequency The voltage gain at the frequency is greater than the actual required voltage gain Gr, and the relationship between the voltage gain and the working switching frequency is:

[0011]

[0012] In the formula: , , , , , ; is the ratio of the resonant inductance to the magnetizing inductance , is the ratio of the working switching frequency to the resonant frequency , is the equivalent impedance, is the equivalent resistance of the secondary side load of the transformer to the primary side resistance, is the resonant capacitance, is the ratio of the primary side to the secondary side of the transformer, is the actual resistance value of the secondary side load of the transformer, is the quality factor;

[0013] The actual required voltage gain is:

[0014]

[0015] In the formula: For output voltage, This is the input voltage value.

[0016] In step (1), the duty cycle D1 ranges from 0 to 0.5.

[0017] In step (2), the average current for:

[0018]

[0019] In the formula: For the first The output current of the diode rectifier bridge in the LLC resonant converter. This represents the number of LLC resonant converters.

[0020] The current error of each LLC resonant converter is:

[0021]

[0022] In the formula, No. Output current error of the LLC resonant converter The average current, For the first The output current of the diode rectifier bridge of the LLC resonant converter.

[0023] In step (2), the duty cycle D2 is between -0.5 and 0.5.

[0024] In step (3), the duty cycle D ranges from 0 to 0.5.

[0025] In step (4), the driving signals of the switching transistors Sn2 and Sn4 are complementary, and the driving signals of the switching transistors Sn1 and Sn3 are 180 degrees out of phase.

[0026] Another objective of this invention is to provide a system for parallel current sharing control of a wide power range full-bridge LLC resonant converter, comprising multiple PI regulators, multiple PWM control units, and a parallel full-bridge LLC resonant converter composed of multiple converter modules connected in parallel. Each converter module's primary side includes switching transistors Sn1, Sn2, Sn3, and Sn4, a resonant capacitor Crn, a resonant inductor Lrn, and a magnetizing inductor Lmn. The resonant capacitor Crn, resonant inductor Lrn, and magnetizing inductor Lmn together form a resonant cavity. The switching transistors Sn1, Sn2, Sn3, and Sn4 form a full bridge. Each switching transistor is connected in parallel with a diode and a capacitor. One end of the resonant inductor Lrn is connected in series with one end of the resonant capacitor Crn. After series connection, the resonant current sharing is... The other end of the inductor Lrn is connected to the midpoint An of the left arm of the primary bridge. The other end of the series resonant capacitor Crn is connected to one end of the primary winding of the transformer Tn. The other end of the primary winding of the transformer Tn is connected to the midpoint Bn of the right arm of the full bridge. The magnetizing inductor Lmn is connected in parallel across the two ends of the primary winding of the transformer Tn. The secondary side of the converter module includes diodes Dn1, Dn2, Dn3, and Dn4. Diodes Dn1, Dn2, Dn3, and Dn4 form a diode rectifier bridge. One end of the secondary winding of the transformer Tn is connected to the midpoint Cn of the left arm of the diode rectifier bridge, and the other end is connected to the midpoint Dn of the right arm of the diode rectifier bridge. A filter capacitor Con is connected in parallel at the output of the diode rectifier bridge. The load resistor RLoad is connected in parallel with the filter capacitor Con.

[0027] The PI controller consists of a proportional element and an integral element, mathematically expressed as P + I / S, where P is the proportional coefficient, I is the integral coefficient, and S is the integrator. The error signal is linearly combined with the proportional and integral elements to form the control quantity, which controls the controlled object. The control quantity is the duty cycle D of the drive signals of switching transistors Sn1 and Sn3. By changing the duty cycle D of the drive signals of switching transistors Sn1 and Sn3, the controlled object is controlled. The duty cycle D and the given operating switching frequency are used to control the controlled object. The signal is sent to the PWM control unit, which then adjusts the switching frequency accordingly. The generation cycle of the four-way switch is 1 / drive signal g sn1 g sn2、 g sn3、 g sn4 Set the drive signal g in the PWM control unit sn2 The duty cycle is 0.5, and then the complementary module of the PWM control unit generates the drive signal g. sn2 Complementary driving signal g sn4 Set the drive signal g sn1 The duty cycle is D, and the drive signal g is controlled by the phase-shifting module of the PWM control unit. sn1 Phase shift 1 / (2*) ) switch cycle can be obtained with the drive signal g sn1 drive signal g sn3， with the drive signal g sn1 , g sn2、 g sn3、 g sn4 Corresponding switch tube Sn1, Sn2, Sn3, Sn4 are driven respectively, and the output voltage stabilization and the current sharing function of each parallel module in a wide power range are realized.

[0028] From the above technical solution, the beneficial effects of the present application are: first, through the voltage and current double-loop control mode, the output current uneven problem caused by the circuit parameter difference of the parallel full-bridge LLC resonant converter is solved; second, through the fixed frequency + PWM control mode, the frequency range limitation existing in the frequency control, the parallel current sharing problem at light load, and the parallel current sharing function of the full-bridge LLC resonant converter in a wide power range are realized. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the topology diagram of the parallel full-bridge LLC resonant converter;

[0030] Figure 2 is the closed-loop control block diagram of the parallel full-bridge LLC resonant converter;

[0031] Figure 3 is the drive signal waveform of the switch tube of the full-bridge LLC resonant converter;

[0032] Figure 4 is the diode rectifier bridge output current simulation waveform diagram of two LLC resonant converters in parallel under 5% rated load;

[0033] Figure 5 is the diode rectifier bridge output current simulation waveform diagram of two LLC resonant converters in parallel under 100% rated load;

[0034] Figure 6 is the resonant cavity current simulation waveform diagram of two LLC resonant converters in parallel under 5% rated load;

[0035] Figure 7 is the resonant cavity current simulation waveform diagram of two LLC resonant converters in parallel under 100% rated load. DETAILED DESCRIPTION

[0036] A wide power range full-bridge LLC resonant converter parallel current sharing control method, the method comprises the following sequential steps:

[0037] (1) Given working switch frequency ​Make LLC resonant converter work in the fixed frequency condition, online detection output voltage , , , , , ,

[0038] (2) online detection diode rectifier bridge output current , , , , ,

[0039] (3) duty cycle D2 as feedback signal, duty cycle D1 superposition, get for regulating LLC resonant converter gain to achieve current sharing duty cycle D, duty cycle D = D1 + D2;

[0040] (4) generate duty cycle D PWM signal for driving switch tube Sn1, Sn3, switch tube Sn2, Sn4 PWM signal always keep D = 0.5 unchanged; Sn1 drain and Sn3 drain connection, Sn1 source and Sn2 drain connection, Sn3 source and Sn4 drain connection, Sn2 source and Sn4 source connection.

[0041] In step (1), the working switch frequency Need to meet the frequency at the voltage gain Greater than the actual required voltage gain Gr, voltage gain And working switch frequency The relationship is:

[0042]

[0043] In the formula: , , , , , ; Resonant inductance And excitation inductance The ratio of, Working switch frequency And resonant frequency The ratio of, is an equivalent impedance, is an equivalent impedance of a transformer secondary side load to a primary side resistance, is a resonance capacitor, is a transformer primary-secondary side turns ratio, is an actual resistance value of a transformer secondary side load, is a quality factor;

[0044] actual required voltage gain is:

[0045]

[0046] wherein: is an output voltage, is an input voltage value.

[0047] In step (1), the duty ratio D1 is in the range of 0 to 0.5.

[0048] In step (2), the average current is:

[0049]

[0050] wherein: is an output current of the first LLC resonant converter diode rectifier bridge, is the number of LLC resonant converters;

[0051] The current error of each LLC resonant converter is:

[0052]

[0053] wherein, is an output current error of the first LLC resonant converter, is an average current, is an output current of the first LLC resonant converter diode rectifier bridge.

[0054] In step (2), the duty ratio D2 is in the range of -0.5 to 0.5.

[0055] In step (3), the duty ratio D is in the range of 0 to 0.5.

[0056] In step (4), the driving signals of the switching tubes Sn2 and Sn4 are complementary, and the driving signals of the switching tubes Sn1 and Sn3 are 180 degrees out of phase, as shown in Figure 3 .

[0057] as shown in Figure 1 ,2 As shown, this system includes multiple PI regulators, multiple PWM control units, and a parallel full-bridge LLC resonant converter composed of multiple converter modules connected in parallel. Each converter module's primary side includes switching transistors Sn1, Sn2, Sn3, and Sn4, a resonant capacitor Crn, a resonant inductor Lrn, and a magnetizing inductor Lmn. These components together form a resonant cavity. Switches Sn1, Sn2, Sn3, and Sn4 form a full bridge. Each switching transistor is connected in parallel with a diode and a capacitor. One end of the resonant inductor Lrn is connected in series with one end of the resonant capacitor Crn. The other end of the resonant inductor Lrn is connected to the left arm of the primary side full bridge. The midpoint An is connected, and the other end of the series resonant capacitor Crn is connected to one end of the primary winding of transformer Tn. The other end of the primary winding of transformer Tn is connected to the midpoint Bn of the right bridge arm of the full bridge. The magnetizing inductor Lmn is connected in parallel across the two ends of the primary winding of transformer Tn. The secondary side of the converter module includes diodes Dn1, Dn2, Dn3, and Dn4. Diodes Dn1, Dn2, Dn3, and Dn4 form a diode rectifier bridge. One end of the secondary winding of transformer Tn is connected to the midpoint Cn of the left bridge arm of the diode rectifier bridge, and the other end is connected to the midpoint Dn of the right bridge arm of the diode rectifier bridge. A filter capacitor Con is connected in parallel at the output of the diode rectifier bridge. The load resistor RLoad is connected in parallel with the filter capacitor Con.

[0058] like Figure 2 As shown, the PI controller consists of a proportional element and an integral element, with the mathematical expression P + I / S, where P is the proportional coefficient, I is the integral coefficient, and S is the integrator. The error signal is linearly combined with the proportional and integral elements to form the control quantity, which controls the controlled object. The control quantity is the duty cycle D of the drive signals of switching transistors Sn1 and Sn3. By changing the duty cycle D of the drive signals of switching transistors Sn1 and Sn3, the controlled object is controlled. The duty cycle D and the given operating switching frequency are used to control the controlled object. The signal is sent to the PWM control unit, which then adjusts the switching frequency accordingly. The generation cycle of the four-way switch is 1 / drive signal g sn1 g sn2、 g sn3、 g sn4 Set the drive signal g in the PWM control unit sn2 The duty cycle is 0.5, and then the complementary module of the PWM control unit generates the drive signal g. sn2 Complementary driving signal g sn4 Set the drive signal g sn1 The duty cycle is D, and the drive signal g is controlled by the phase-shifting module of the PWM control unit. sn1 Phase shift 1 / (2*) The switching cycle can then be used to obtain the drive signal g. sn1 Drive signals g that are 180 degrees out of phase sn3， Use drive signal g sn1 g sn2、 g sn3、 g sn4 The corresponding switching transistors Sn1, Sn2, Sn3, and Sn4 are driven respectively to achieve output voltage regulation and current sharing of each parallel module over a wide power range.

[0059] Figure 4 , 5 This indicates that the peak output current of the two converters is the same, and the parallel current sharing effect is achieved under both light and heavy load conditions.

[0060] Figure 6 , 7 This indicates that the peak current in the resonant cavity of the two converters is the same under light load, and the voltage gain of the two converters is equal under both light and heavy load conditions.

[0061] In summary, this invention solves the problem of uneven output current caused by differences in circuit parameters in parallel full-bridge LLC resonant converters by using a dual-loop control method of voltage and current; and solves the problem of limited frequency range and difficulty in current sharing in parallel connection under light load by using a fixed-frequency + PWM control method, thus realizing the parallel current sharing function of full-bridge LLC resonant converters over a wide power range.

Claims

1. A parallel current sharing control method for a wide power range full-bridge LLC resonant converter, characterized in that: The method includes the following steps in sequence: (1) Given the operating switching frequency This allows the LLC resonant converter to operate under constant frequency conditions, enabling online detection of the output voltage. , output voltage With a given reference voltage By subtracting, we obtain the voltage error. Voltage error The voltage is fed into a PI regulator to obtain the duty cycle D1 used to compensate for voltage errors, so as to ensure that the converter outputs the given voltage value. (2) Online detection of the current at the output terminal of the diode rectifier bridge The average current is obtained by summing the currents of each LLC resonant converter. The current at the output of the diode rectifier bridge of each LLC resonant converter is... With average current The difference is calculated to obtain the current error of each LLC resonant converter. The current error is then fed into the PI regulator to obtain the duty cycle D2 used to compensate for the current error. (3) The duty cycle D2 is used as a feedback signal and superimposed with the duty cycle D1 to obtain the duty cycle D used to adjust the gain of the LLC resonant converter to achieve current sharing. The duty cycle D = D1 + D2. (4) Generate a PWM signal with a duty cycle of D to drive the switching transistors Sn1 and Sn3. The PWM signals of the switching transistors Sn2 and Sn4 are always kept at D=0.

5. The drain of Sn1 is connected to the drain of Sn3, the source of Sn1 is connected to the drain of Sn2, the source of Sn3 is connected to the drain of Sn4, and the source of Sn2 is connected to the source of Sn4. In step (1), the operating switching frequency The voltage gain at this frequency must be satisfied. The voltage gain is greater than the actual required voltage gain Gr. With operating switching frequency The relationship is: ； In the formula: , , , , , ; For resonant inductors With magnetizing inductor The ratio, Operating switching frequency With resonant frequency The ratio, For equivalent impedance, The secondary load of the transformer is equivalent to the primary resistance. It is a resonant capacitor. This represents the primary-to-secondary turns ratio of the transformer. This represents the actual resistance value of the load on the secondary side of the transformer. For quality factor; Actual required voltage gain for: ； In the formula: For output voltage, This refers to the input voltage value. In step (4), the driving signals of the switching transistors Sn2 and Sn4 are complementary, and the driving signals of the switching transistors Sn1 and Sn3 are 180 degrees out of phase.

2. The parallel current sharing control method for a wide power range full-bridge LLC resonant converter according to claim 1, characterized in that: In step (1), the duty cycle D1 ranges from 0 to 0.

5.

3. The parallel current sharing control method for a wide power range full-bridge LLC resonant converter according to claim 1, characterized in that: In step (2), the average current for: ； In the formula: For the first The output current of the diode rectifier bridge in the LLC resonant converter. This represents the number of LLC resonant converters. The current error of each LLC resonant converter is: ； In the formula, No. Output current error of the LLC resonant converter The average current, For the first The output current of the diode rectifier bridge of the LLC resonant converter.

4. The parallel current sharing control method for a wide power range full-bridge LLC resonant converter according to claim 1, characterized in that: In step (2), the duty cycle D2 is between -0.5 and 0.

5.

5. The parallel current sharing control method for a wide power range full-bridge LLC resonant converter according to claim 1, characterized in that: In step (3), the duty cycle D ranges from 0 to 0.

5.

6. A system for implementing the parallel current sharing control method for a wide power range full-bridge LLC resonant converter according to any one of claims 1 to 5, characterized in that: It includes multiple PI regulators, multiple PWM control units, and a parallel full-bridge LLC resonant converter composed of multiple converter modules connected in parallel. Each converter module's primary side includes switching transistors Sn1, Sn2, Sn3, and Sn4, a resonant capacitor Crn, a resonant inductor Lrn, and a magnetizing inductor Lmn. These components together form a resonant cavity. Switches Sn1, Sn2, Sn3, and Sn4 form a full bridge. Each switching transistor is connected in parallel with a diode and a capacitor. One end of the resonant inductor Lrn is connected in series with one end of the resonant capacitor Crn. The other end of the resonant inductor Lrn is connected to the midpoint A of the left arm of the primary side full bridge. The resonant capacitor Crn is connected in series with n. The other end of the resonant capacitor Crn is connected to one end of the primary winding of the transformer Tn. The other end of the primary winding of the transformer Tn is connected to the midpoint Bn of the right arm of the full bridge. The magnetizing inductor Lmn is connected in parallel across the two ends of the primary winding of the transformer Tn. The secondary side of the converter module includes diodes Dn1, Dn2, Dn3, and Dn4. Diodes Dn1, Dn2, Dn3, and Dn4 form a diode rectifier bridge. One end of the secondary winding of the transformer Tn is connected to the midpoint Cn of the left arm of the diode rectifier bridge, and the other end is connected to the midpoint Dn of the right arm of the diode rectifier bridge. A filter capacitor Con is connected in parallel at the output of the diode rectifier bridge. The load resistor RLoad is connected in parallel with the filter capacitor Con. The PI controller consists of a proportional element and an integral element, and its mathematical expression is P+I / S, where P is the proportional coefficient, I is the integral coefficient, and S is the integrator. The error signal is used to form the control quantity through a linear combination of proportional and integral elements to control the controlled object. The control quantity is the duty cycle D of the drive signals of switching transistors Sn1 and Sn3. The controlled object is controlled by changing the duty cycle D of the drive signals of switching transistors Sn1 and Sn3; the duty cycle D and the given operating switching frequency are used to control the controlled object. The signal is sent to the PWM control unit, which then adjusts the switching frequency accordingly. The generation cycle of the four-way switch is 1 / drive signal g sn1 g sn2、 g sn3、 g sn4 Set the drive signal g in the PWM control unit sn2 The duty cycle is 0.5, and then the complementary module of the PWM control unit generates the drive signal g. sn2 Complementary driving signal g sn4 Set the drive signal g sn1 The duty cycle is D, and the drive signal g is controlled by the phase-shifting module of the PWM control unit. sn1 Phase shift 1 / (2*) The switching cycle can then be used to obtain the drive signal g. sn1 Drive signals g that are 180 degrees out of phase sn3， Use drive signal g sn1 g sn2、 g sn3、 g sn4 The corresponding switching transistors Sn1, Sn2, Sn3, and Sn4 are driven respectively to achieve output voltage regulation and current sharing of each parallel module over a wide power range.

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