High-capacity frequency doubling type three-level bidirectional DC-DC converter and control method thereof

Abstract

The invention discloses a high-capacity frequency doubling type three-level bidirectional DC-DC converter and a modulation method thereof. According to the frequency doubling type bidirectional DC-DC converter, the number of switching devices is doubled on the basis of a hybrid three-level full-bridge converter, and under the condition that the switching frequency of the devices is not changed, the signal duty ratio is controlled by compressing the switching devices, so that the frequency doubling effect of neutral-point voltage of primary and secondary side bridge arms and the frequency of current flowing through an inductor and a transformer is achieved. The modulation method is phase shift modulation, real-time power control is realized by adjusting external phase shift angles of sixteen switching devices Sa1-Sa8 and Sb1-Sb8 on the high-voltage direct-current side and eight switching devices Qa1-Qa4 and Qb1-Qb4 on the low-voltage direct-current side, and finally, flexible adjustment of electric energy of the direct-current power supply system can be realized. The invention has the beneficial effects that the working frequency of the magnetic element is multiplied through hardware frequency multiplication, the volume of the magnetic element can be reduced, the power density of the converter is improved, the loss of a single switching device is reduced, and the heat distribution problem of the device is improved.

Description

Technical Field

[0001] The present invention relates to the field of high-power power conversion system design, and can be used as an effective means to regulate DC power distribution in a large-capacity new energy energy storage system, especially more applicable when it comes to the control of high-frequency and large-capacity bidirectional DC-DC converters. Background Art

[0002] As a key device used between the high-voltage DC side of new energy power generation and the low-voltage side of energy storage, the bidirectional DC-DC converter can effectively regulate the unstable output and power quality of new energy power generation. Compared with traditional non-isolated converters, the full-bridge bidirectional isolated DC-DC converter has greater advantages in terms of safety, anti-interference performance, and power transmission ability across voltage levels, and can achieve electrical isolation between the faulty side and the non-faulty side during a fault. With the increase in switching frequency, the volume of magnetic components has been significantly reduced, but the device switching loss increases and the heating situation becomes more serious.

[0003] In a bidirectional DC-DC converter applied to high-voltage and high-current occasions, IGBTs are often used as switching devices because they can withstand large currents and voltages and are suitable for high-power and high-voltage applications. However, in terms of switching frequency, the upper limit of the switching frequency that IGBTs can withstand is not high, and when IGBTs are at a relatively high switching frequency, their switching losses are also very high.

[0004] The proposed topology of the frequency-doubling three-level bidirectional DC-DC converter doubles the voltage and current frequencies of the inductor and transformer without changing the switching frequency of the IGBT, effectively reducing the volume of the inductor and transformer, and at the same time making the IGBT heating more dispersed, greatly alleviating the heat dissipation pressure. Summary of the Invention

[0005] The object of the present invention is to provide a large-capacity frequency-doubling three-level bidirectional DC-DC converter and its control method.

[0006] The technical solution to achieve the object of the present invention is as follows:

[0007] The first step: Installation of the frequency-doubling DC-DC converter

[0008] 1. The 1.1-times frequency three-level bidirectional DC-DC converter mainly consists of a power bidirectional transmission unit, a signal acquisition unit, a control unit, and an external environment unit. Among them, the power bidirectional transmission unit includes input filter capacitors C1 and C2(1), DC high-voltage module a(2), DC high-voltage module b(3), inductor L(4), high-frequency isolation transformer T(5), DC low-voltage module a(6), DC low-voltage module b(7), and output filter capacitor C3(8); the signal acquisition unit includes a low-voltage side current detector(9), a low-voltage side voltage detector(10), an inductor current detector(11), a high-voltage side voltage detector(12), and a high-voltage side current detector(13); the control unit includes an embedded microprocessor(14); the external environment unit includes a DC bus(15) and an energy storage load(16).

[0009] 1.2 According to the structural relationship in step 1.1, install and arrange the large-capacity bidirectional DC-DC converter:

[0010] Both the DC high-voltage module a(2) and the DC high-voltage module b(3) are diode-clamped three-level full-bridge structures. Among them, the fully controlled devices S a1 ~S a4 and the diodes D a1 and D a2 constitute a diode-clamped three-level bridge arm of the DC high-voltage module a(2); the fully controlled devices S a5 ~S a8 and the diodes D a3 and D a4 constitute another diode-clamped three-level bridge arm of the DC high-voltage module a(2); the fully controlled devices S b1 ~S b4 and the diodes D b1 and D b2 constitute a diode-clamped three-level bridge arm of the DC high-voltage module b(3); the fully controlled devices S b5 ~S b8 and the diodes D b3 and D b4 constitute another diode-clamped three-level bridge arm of the DC high-voltage module b(3); the positive poles of both the DC high-voltage module a(2) and the DC high-voltage module b(3) are connected to the positive pole of the input filter capacitor C1 and the positive pole of the DC bus, and the negative poles are connected to the negative pole of C2 and the negative pole of the DC bus(14); the diode neutral points of the two bridge arms of the DC high-voltage module a(2) and the diode neutral points of the two bridge arms of the DC high-voltage module b(3) are connected to the series midpoint of C1 and C2(1); the AC sides of the two DC high-voltage modules are connected to the primary side of the transformer T(5) through the inductor L(4).

[0011] The positive poles of the DC low-voltage module a (6) and the DC low-voltage module b (7) are connected to the positive pole of the output filter capacitor C3 (8) and the positive pole of the energy storage load (16), and the negative poles are connected to the negative pole of the output filter capacitor C3 (8) and the negative pole of the energy storage load (16). The AC sides of the two DC low-voltage modules are connected to the secondary side of the transformer T (5);

[0012] Step 2: Control of the drive signal of the DC-DC converter

[0013] Control signals are applied to the switching devices in the DC high-voltage module and the DC low-voltage module respectively through the embedded microprocessor (14), and the duty cycle of the PWM drive signal of all switching devices is 0.25; S a1 、S a2 、S b3 and S b4 have the same drive signal PWM1; S a3 、S a4 、S b1 and S b2 have the same drive signal PWM2; S a5 、S a6 、S b7 and S b8 have the same drive signal PWM3; S a7 、S a8 、S b5 and S b6 have the same drive signal PWM4; Q a1 and Q b2 have the same drive signal PWM5; Q a2 and Q b1 have the same drive signal PWM6; Q a3 and Q b4 have the same drive signal PWM7; Q a4 and Q b3 have the same drive signal PWM8;

[0014] The phase of PWM2 lags behind the phase of PWM1 by 1 / 4 of the switching period T s ; The phase of PWM3 lags behind the phase of PWM2 by 1 / 4 of the switching period T s ; The phase of PWM4 lags behind the phase of PWM3 by 1 / 4 of the switching period T s ; The phase of PWM6 lags behind the phase of PWM5 by 1 / 4 of the switching period T s ; The phase of PWM7 lags behind the phase of PWM6 by 1 / 4 of the switching period T s ; The phase of PWM8 lags behind the phase of PWM7 by 1 / 4 of the switching period T s ; The phase difference between PWM1 and PWM5 is named the primary-secondary phase shift angle where Ts = 1 / f s , where f s is the switching frequency of the converter; after being controlled by the above driving signal, the high-frequency square-wave voltages V ab and V cd at the midpoints of the primary and secondary bridge arms of the transformer T(5) have a frequency of 2f s ;

[0015] Step 3: Collect the high-voltage side voltage V1, the low-voltage side voltage V2, and the output load current I through the signal sampling unit. Set the turns ratio of the primary and secondary sides of the high-frequency isolation transformer T(5) to N, and define the reference voltage V ref and the voltage deviation Δv;

[0016] Step 4: Subtract the voltage feedback V2 from the voltage reference value Vref to obtain the voltage deviation Δv. The voltage deviation Δv is input into the embedded microprocessor (14), and the phase shift angle is calculated through Equation (1) :

[0017]

[0018] where K p is the proportional constant and K i is the integral constant;

[0019] Based on phase-shift modulation, the phase shift angle feedforward calculation amount can be calculated from the output load current I:

[0020]

[0021] where f s is the switching frequency of the converter and L is the inductance value of the inductor L(4);

[0022] Step 5: Add the phase shift angle compensation amount obtained in the second step to the phase shift angle feedforward calculation amount obtained in the third step to obtain the phase shift angle control amount To ensure the normal bidirectional operation of the converter, the phase shift angle needs to be limited in the program. The range of the phase shift angle control amount is between -π / 4 and π / 4; if is greater than π / 4, then takes the value of π / 4; if is less than -π / 4, then takes the value of -π / 4; when is less than π / 4, the converter operates in the forward direction and transfers energy from the high-voltage side to the low-voltage side; conversely, when is less than 0, the converter operates in the reverse direction and transfers energy from the low-voltage side to the high-voltage side;

[0023] Step 6: Input the phase-shift angle control quantity obtained in Step 4 into the microcontroller (14). According to the driving signal relationship between the switching devices given in Step 2, use the internal timer of the microcontroller (14) to generate PWM driving signals with corresponding duty cycles and phases for the high-side and low-side switching devices. According to the actual adjustment effect, repeat Steps 3, 4, and 5 until the output voltage V2 is stabilized at the voltage reference value V ref . Description of the Drawings

[0024] Figure 1 is the topological structure diagram of the large-capacity frequency-doubling three-level bidirectional DC-DC converter of the present invention.

[0025] Figure 2 is the timing diagram of the driving signals of the switching devices for the modulation method of the large-capacity frequency-doubling three-level bidirectional DC-DC converter of the present invention.

[0026] Figure 3 is the implementation flowchart of the large-capacity frequency-doubling three-level bidirectional DC-DC converter of the present invention. Detailed Embodiment

[0027] The present invention will be further described below with reference to the drawings.

[0028] Figure 1 is the topological structure diagram of the large-capacity frequency-doubling three-level bidirectional DC-DC converter of the present invention. It can be used in combination with Figure 2 the implementation flowchart of the large-capacity frequency-doubling three-level bidirectional DC-DC converter shown in the figure to achieve the purpose of increasing the voltage and current frequencies of the inductor and transformer through hardware frequency doubling, reducing the volume of magnetic components, increasing the power density of the converter, and reducing the loss of a single switching device. Its usage method includes the following content:

[0029] Step 1: Installation of the frequency-doubling DC-DC converter

[0030] 1.1 Figure 1As shown in the topological structure diagram of the high-capacity frequency-doubling three-level bidirectional DC-DC converter of the present invention, the frequency-doubling three-level bidirectional DC-DC converter mainly consists of a power bidirectional transmission unit, a signal acquisition unit, a control unit, and an external environment unit. Among them, the power bidirectional transmission unit includes input filter capacitors C1 and C2(1), DC high-voltage module a(2), DC high-voltage module b(3), inductor L(4), high-frequency isolation transformer T(5), DC low-voltage module a(6), DC low-voltage module b(7), and output filter capacitor C3(8); the signal acquisition unit includes a low-voltage side current detector(9), a low-voltage side voltage detector(10), an inductor current detector(11), a high-voltage side voltage detector(12), and a high-voltage side current detector(13); the control unit includes an embedded microprocessor(14); the external environment unit includes a DC bus(15) and an energy storage load(16);

[0031] 1.2 According to the structural relationship in step 1.1, install and arrange the high-capacity bidirectional DC-DC converter:

[0032] Both the DC high-voltage module a(2) and the DC high-voltage module b(3) are diode neutral-point clamped three-level full-bridge structures. Among them, the fully controlled devices S a1 ~S a4 and the diodes D a1 and D a2 constitute a diode clamped three-level bridge arm of the DC high-voltage module a(2); the fully controlled devices S a5 ~S a8 and the diodes D a3 and D a4 constitute another diode clamped three-level bridge arm of the DC high-voltage module a(2); the fully controlled devices S b1 ~S b4 and the diodes D b1 and D b2 constitute a diode clamped three-level bridge arm of the DC high-voltage module b(3); the fully controlled devices S b5 ~S b8 and the diodes D b3 and D b4 constitute another diode clamped three-level bridge arm of the DC high-voltage module b(3); the positive poles of both the DC high-voltage module a(2) and the DC high-voltage module b(3) are connected to the positive pole of the input filter capacitor C1 and the positive pole of the DC bus, and the negative poles are connected to the negative pole of C2 and the negative pole of the DC bus(14); the diode neutral points of the two bridge arms of the DC high-voltage module a(2) and the diode neutral points of the two bridge arms of the DC high-voltage module b(3) are connected to the series midpoint of C1 and C2(1); the AC sides of the two DC high-voltage modules are connected to the primary side of the transformer T(5) through the inductor L(4);

[0033] The positive poles of the DC low-voltage module a (6) and the DC low-voltage module b (7) are connected to the positive pole of the output filter capacitor C3 (8) and the positive pole of the energy storage load (16), and the negative poles are connected to the negative pole of the output filter capacitor C3 (8) and the negative pole of the energy storage load (16). The AC sides of the two DC low-voltage modules are connected to the secondary side of the transformer T (5);

[0034] Step 2: Control of the driving signals of the DC-DC converter

[0035] As Figure 2 shown in the driving signal timing diagram of the switching devices of the large-capacity frequency-doubling three-level bidirectional DC-DC converter modulation method, drive control signals are applied to the switching devices in the DC high-voltage module and the DC low-voltage module respectively through the embedded microprocessor (14). The duty cycle of the PWM drive signals of all switching devices is 0.25; S a1 、S a2 、S b3 and S b4 have the same driving signal PWM1; S a3 、S a4 、S b1 and S b2 have the same driving signal PWM2; S a5 、S a6 、S b7 and S b8 have the same driving signal PWM3; S a7 、S a8 、S b5 and S b6 have the same driving signal PWM4; Q a1 and Q b2 have the same driving signal PWM5; Q a2 and Q b1 have the same driving signal PWM6; Q a3 and Q b4 have the same driving signal PWM7; Q a4 and Q b3 have the same driving signal PWM8;

[0036] The phase of PWM2 lags behind the phase of PWM1 by 1 / 4 of the switching period Ts; the phase of PWM3 lags behind the phase of PWM2 by 1 / 4 of the switching period T s ; the phase of PWM4 lags behind the phase of PWM3 by 1 / 4 of the switching period Ts; the phase of PWM6 lags behind the phase of PWM5 by 1 / 4 of the switching period T s ; the phase of PWM7 lags behind the phase of PWM6 by 1 / 4 of the switching period T s ; the phase of PWM8 lags behind the phase of PWM7 by 1 / 4 of the switching period T s; The phase difference between PWM1 and PWM5 is named the primary-secondary phase-shift angle. ; where T s = 1 / f s , f s is the switching frequency of the converter; after being controlled by the above driving signals, the high-frequency square-wave voltages V ab , V cd at the midpoints of the primary and secondary bridge arms of the transformer T(5) have a frequency of 2f s ;

[0037] Step 3: The implementation flowchart of the large-capacity frequency-doubling three-level bidirectional DC-DC converter as shown in Figure 3 . The high-voltage side voltage V1, low-voltage side voltage V2, and output load current I are collected by the signal sampling unit, the turns ratio of the primary and secondary sides of the high-frequency isolation transformer T(5) is set to N, and the reference voltage V ref , voltage deviation Δv are defined;

[0038] Step 4: The voltage reference value V ref is compared and subtracted from the voltage feedback V2 to obtain the voltage deviation Δv. The voltage deviation Δv is input into the embedded microprocessor (14), and the phase-shift angle is calculated through Equation (1):

[0039]

[0040] In the formula, K p is the proportional constant, and K i is the integral constant;

[0041] Based on phase-shift modulation, the phase-shift angle feedforward calculation amount can be calculated from the output load current I:

[0042]

[0043] In the formula, f s is the switching frequency of the converter, and L is the inductance value of the inductor L(4);

[0044] Step 5: Add the phase-shift angle compensation amount obtained in the second step to the phase-shift angle feedforward calculation amount obtained in the third step to obtain the phase-shift angle control amount To ensure the normal bidirectional operation of the converter, it is necessary to limit the range of the phase-shift angle control amount between -π / 4 and π / 4; if is greater than π / 4, then takes the value of π / 4; if is less than -π / 4, then takes the value of -π / 4; when When it is less than π / 4, the converter operates in the forward direction, transmitting energy from the high-voltage side to the low-voltage side; conversely, when is less than 0, the converter operates in the reverse direction, transmitting energy from the low-voltage side to the high-voltage side;

[0045] Step 6: Input the phase-shift angle control quantity obtained in the fourth step into the microcontroller (14). According to the driving signal relationship between the switching devices given in the second step, the PWM driving signals of the duty cycle and phase corresponding to the switching devices on the high-voltage side and the low-voltage side are generated by the internal timer of the microcontroller (14). According to the actual adjustment effect, repeat steps three, four, and five until the output voltage V2 is stabilized at the voltage reference value V ref .

Claims

1. A high-capacity frequency-doubling three-level bidirectional DC-DC converter and its control method for flexible power regulation and optimal control of a DC power supply system, characterized by the following steps: Step 1: Installation of the frequency-doubling DC-DC converter 1. The 1.1 - frequency - doubling three - level bidirectional DC - DC converter mainly consists of a power bidirectional transmission unit, a signal acquisition unit, a control unit, and an external environment unit. Among them, The bidirectional power transmission unit includes input filter capacitors C1 and C2 (1), high-voltage DC module a (2), high-voltage DC module b (3), inductor L (4), high-frequency isolation transformer T (5), low-voltage DC module a (6), low-voltage DC module b (7), and output filter capacitor C3 (8); the signal acquisition unit includes a low-voltage side current detector (9), a low-voltage side voltage detector (10), an inductor current detector (11), a high-voltage side voltage detector (12), and a high-voltage side current detector (13); the control unit includes an embedded microprocessor (14); the external environment unit includes a DC bus (15) and an energy storage load (16); 1.2 According to the structural relationship in step 1.1, install and arrange the large-capacity bidirectional DC-DC converter: The DC high-voltage module a (2) and the DC high-voltage module b (3) both adopt a diode neutral-point clamped three-level full-bridge structure, where, Fully controlled device S a1 ~S a4 and diode D a1 and D a2 constitute a diode-clamped three-level bridge arm of the DC high-voltage module a(2); the fully controlled device S a5 ~S a8 and diode D a3 and D a4 constitute another diode-clamped three-level bridge arm of the DC high-voltage module a(2); the fully controlled device S b1 ~S b4 and diode D b1 and D b2 constitute a diode-clamped three-level bridge arm of the DC high-voltage module b(3); the fully controlled device S b5 ~S b8 and diode D b3 and D b4 constitute another diode-clamped three-level bridge arm of the DC high-voltage module b(3); the positive poles of the DC high-voltage module a(2) and the DC high-voltage module b(3) are both connected to the positive pole of the input filter capacitor C1 and the positive pole of the DC bus, and the negative poles are connected to the negative pole of C2 and the negative pole of the DC bus (14); the diode neutral points of the two bridge arms of the DC high-voltage module a(2) and the diode neutral points of the two bridge arms of the DC high-voltage module b(3) are connected to the series midpoint of C1 and C2(1); the AC sides of the two DC high-voltage modules are connected to the primary side of the transformer T(5) through the inductor L(4); The positive poles of the low-voltage DC module a (6) and the low-voltage DC module b (7) are connected to the positive pole of the output filter capacitor C3 (8) and the positive pole of the energy storage load (16), and the negative poles are connected to the negative pole of the output filter capacitor C3 (8) and the negative pole of the energy storage load (16). The AC sides of the two low-voltage DC modules are connected to the secondary side of the transformer T (5); Step 2: Control the drive signal of the DC-DC converter Control signals are applied to the switching devices in the DC high-voltage module and the DC low-voltage module respectively through the embedded microprocessor (14), and the duty cycle of the PWM drive signals of all the switching devices is 0.25; S a1 、S a2 、S b3 and S b4 have the same drive signal PWM1; S a3 、S a4 、S b1 and S b2 have the same drive signal PWM2; S a5 、S a6 、S b7 and S b8 have the same drive signal PWM3; S a7 、S a8 、S b5 and S b6 have the same drive signal PWM4; Q a1 and Q b2 have the same drive signal PWM5; Q a2 and Q b1 have the same drive signal PWM6; Q a3 and Q b4 have the same drive signal PWM7; Q a4 and Q b3 have the same drive signal PWM8; The phase of PWM2 lags behind the phase of PWM1 by 1 / 4 of the switching period T s ; The phase of PWM3 lags behind the phase of PWM2 by 1 / 4 of the switching period T s ; The phase of PWM4 lags behind the phase of PWM3 by 1 / 4 of the switching period T s ; The phase of PWM6 lags behind the phase of PWM5 by 1 / 4 of the switching period T s ; The phase of PWM7 lags behind the phase of PWM6 by 1 / 4 of the switching period T s ; The phase of PWM8 lags behind the phase of PWM7 by 1 / 4 of the switching period T s ; The phase difference between PWM1 and PWM5 is named the primary-secondary phase shift angle where T s = 1 / f s , f s is the switching frequency of the converter; After being controlled by the above drive signals, the high-frequency square-wave voltages V ab , V cd at the midpoints of the primary and secondary bridge arms of the transformer T(5) have a frequency of 2f s ; Step 3: Collect the high-voltage side voltage V1, the low-voltage side voltage V2, and the output load current I through the signal sampling unit, set the turns ratio of the primary and secondary sides of the high-frequency isolation transformer T(5) as N, and define the reference voltage V ref , and the voltage deviation Δv; Step 4: Voltage reference value V ref is compared with and subtracted from the voltage feedback V2 to obtain a voltage deviation Δv. The voltage deviation Δv is input into the embedded microprocessor (14), and the phase shift angle compensation amount is calculated through formula (1). where K p is a proportionality constant, and K i is an integral constant; Based on phase-shift modulation, the calculation amount of the phase-shift angle feedforward can be calculated from the output load current I: where f s is the switching frequency of the converter, and L is the inductance value of inductor L(4); Step 5: The phase shift angle compensation amount obtained in Step 2 is added to the phase shift angle feedforward calculation amount obtained in Step 3 to obtain the phase shift angle control amount To ensure the normal bidirectional operation of the converter, the phase shift angle needs to be limited during program writing. The range of the phase shift angle control amount is between -π / 4 and π / 4; if is greater than π / 4, then is set to π / 4; if is less than -π / 4, then is set to -π / 4; when is less than π / 4, the converter operates in the forward direction, transferring energy from the high-voltage side to the low-voltage side; conversely, when is less than 0, the converter operates in the reverse direction, transferring energy from the low-voltage side to the high-voltage side; Step 6: Input the phase-shift angle control quantity obtained in Step 4 into the microcontroller (14). According to the driving signal relationship between the switching devices given in Step 2, generate PWM driving signals with corresponding duty cycles and phases for the high-side and low-side switching devices through the internal timer of the microcontroller (14). According to the actual adjustment effect, repeat Step 3, Step 4, and Step 5 until the output voltage V2 is stabilized to the voltage reference value V ref .

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