Bilateral blocking isolation converter and control method

Abstract

The invention discloses a bilateral blocking isolation converter and a control method thereof. The bilateral blocking isolation converter comprises a primary side current-limiting bridge arm, a primary side full-bridge circuit, a CLLLC resonant cavity, a secondary side full-bridge circuit and a secondary side current-limiting bridge arm. The control method adopts a frequency modulation-phase shift composite soft switching voltage regulation technology, specifically, frequency modulation control changes the resonant state of a resonant cavity by regulating the switching frequency of full-bridge arms on two sides, so that accurate regulation of output voltage is realized, meanwhile, the phase relation of voltage and current of the CLLLC resonant cavity is changed, and the soft switching range is further widened; the phase shift control realizes the adjustment of the output voltage of the primary side full-bridge circuit by adjusting the size of the conduction angle of the primary side current limiting bridge arm, so that the output voltage adjustment capability is realized. Besides, the converter also has a double-side short-circuit protection function, and by setting a short-circuit current reference value, the current-limiting bridge arms at the primary side and the secondary side can quickly respond when detecting that the short-circuit current exceeds the reference value, so that the double-side short-circuit protection effect is achieved.

Description

Technical Field

[0001] The invention relates to a power electronic converter, and in particular to a double-side blocked isolation converter and a control method. Background Art

[0002] The core power module of the DC transformer in the low-voltage distribution network has a narrow voltage regulation range, which makes it difficult to adapt to the application requirements of DC distribution points in many areas, large ranges and multiple scenarios, increasing the investment and operation and maintenance costs of the distribution network. At the same time, the existing DC transformers do not have the short-circuit fault current limiting capability, and are prone to generate large short-circuit currents, making it difficult to meet the requirements of high-reliability power supply.

[0003] The CLLLC resonant converter adds a set of LC devices to the secondary side of the original LLC transformer, so that the circuit topology is completely symmetrical when the converter works in the forward or reverse direction, and the forward and reverse working characteristics of the converter are completely consistent. It also has the advantages of a wide soft switching range, a large power density, and a wide voltage regulation range. It has broad research prospects in high-voltage, high-frequency, and high-power applications. The CLLLC converter usually has a simple control principle and a wide soft switching range under variable frequency control (pulse frequency modulation, PFM), but in situations where a wide voltage gain range is required, the switching frequency changes greatly, which reduces the overall efficiency of the converter; while in single phase shift control (single phase shift, SPS), the switching frequency is not changed and only the original secondary side phase shift angle is controlled, but the voltage gain adjustment range is narrow and it is easy to generate a large reflux power. By establishing a frequency modulation-phase shift composite soft switching voltage regulation control technology, it has two control degrees of freedom of frequency modulation and phase shift, realizes a wide range of voltage regulation, and broadens the soft switching range. Secondly, the current limiting bridge arms on both sides achieve the double-sided short-circuit protection by setting the short-circuit current reference value. Summary of the invention

[0004] Purpose of the invention: The first purpose of the present invention is to provide an isolated converter with double-sided blocking that can adjust voltage over a wide range, expand the soft switching range, and realize double-sided short-circuit protection; the second purpose of the present invention is to provide a control method for an isolated converter with double-sided blocking that can adjust voltage over a wide range, expand the soft switching range, and realize double-sided short-circuit protection.

[0005] Technical solution: A double-side blocking isolation converter according to the present invention comprises a primary-side current limiting bridge arm 100, a primary-side full-bridge circuit 200, a CLLLC resonant cavity, a secondary-side full-bridge circuit 300 and a secondary-side current limiting bridge arm 400;

[0006] Among them, the primary side current limiting bridge arm 100 is composed of a primary side switch tube S1 and a primary side switch tube S2, the primary side current limiting bridge arm 100 is connected in parallel with the primary side filter capacitor C1, and the midpoint of the primary side current limiting bridge arm 100 is connected in series with the primary side filter inductor L1; the secondary side current limiting bridge arm 400 is composed of a secondary side switch tube S11 and a secondary side switch tube S12, the secondary side current limiting bridge arm 300 is connected in parallel with the secondary side filter capacitor C2, and the midpoint of the secondary side current limiting bridge arm 300 is connected in series with the secondary side filter inductor L2; the CLLLC resonant cavity includes a transformer T, a primary side resonant tank and a secondary side resonant tank arranged on both sides of the transformer T; the primary side resonant tank is composed of a resonant inductor Lp, an excitation inductor Lm and a resonant capacitor Cp; the secondary side resonant tank is composed of a resonant inductor Ls and a resonant capacitor Cs; the primary side full bridge 200 is composed of a primary side switch tube S3, a primary side switch tube S4, a primary side switch tube S5 and a primary side switch tube S6. The primary side switch tube S3 and the primary side switch tube S5 are connected in series and then connected in parallel to the series circuit of the switch tube S4 and the switch tube S6. One side of the primary side full bridge 200 inputs a parallel filter capacitor C1, and the other side outputs a parallel CLLLC resonant cavity; the secondary side full bridge 300 is composed of a secondary side switch tube S7, a secondary side switch tube S8, a secondary side switch tube S9 and a secondary side switch tube S10. The switch tube S7 and the switch tube S9 are connected in series and then connected in parallel to the series circuit of the switch tube S8 and the switch tube S10. One side of the secondary side full bridge circuit 300 inputs a parallel secondary side resonant tank, and the other side outputs a parallel secondary side filter capacitor C2.

[0007] A control method for a double-side blocking isolation converter according to the present invention comprises the following steps:

[0008] S1, the isolation converter is functionally divided into two modules: frequency conversion control and phase shift control;

[0009] S2. Analyze the working state of the isolation converter under variable frequency control based on the fundamental wave approximation method;

[0010] S3. Analyze the working state of the isolation converter under phase shift control based on the fundamental wave approximation method;

[0011] S4. Analyze the bidirectional impedance variation characteristics of the isolation converter based on the fundamental wave approximation method, select the lower frequency limit under frequency conversion control and the minimum phase shift angle α of phase shift control according to the soft switching margin of different voltage regulation methods, and establish a frequency modulation-phase shift composite soft switching voltage regulation control technology;

[0012] S5. Based on the wide-area measurement system, the DC power grid short-circuit response trajectory is obtained, and the transient response characteristic components of the voltage and current at the DC power module port and the resonant cavity voltage and current caused by the power grid short circuit are extracted to establish a DC power module safety protection technology with the ability to ride through double-sided bus short-circuit faults.

[0013] Preferably, in step S1, under the variable frequency control, the duty cycle of the current limiting bridge arms on both sides is fixed, and the CLLLC resonant converters on both sides control the switching pulse frequency according to the output voltage feedback; under the phase shift control, the switching pulse frequency of the CLLLC resonant converters on both sides is fixed, and the switch tubes of the current limiting bridge arms on both sides control the pulse phase shift angle α according to the output voltage feedback.

[0014] Preferably, under the variable frequency control of step S2, the primary-side current limiting bridge arm switch tube S1 and the primary-side current limiting bridge arm switch tube S2 are controlled by a pair of complementary pulses to form a bridge arm H1, the secondary-side current limiting bridge arm switch tube S11 and the secondary-side current limiting bridge arm switch tube S12 are controlled by a pair of complementary pulses to form a bridge arm H2, the bridge arm H1 and the bridge arm H2 are turned on at the same time, and the duty cycle is the same; the primary-side switch tube S3 and the primary-side switch tube S4 are controlled by a pair of complementary pulses with a duty cycle of 50% to form the bridge arm H3, the primary-side switch tube S5 and the primary-side switch tube S6 are controlled by a pair of complementary pulses with a duty cycle of 50% to form the bridge arm H4, the bridge arm H3 and the bridge arm H4 are turned on at the same time, and the switching frequency is equal to the series resonant frequency of the resonant capacitor Cp and the resonant inductor Lp; the switching pulse frequency of the bridge arm H3 and the bridge arm H4 is controlled by the output voltage feedback, so that the bridge arm H3 and the bridge arm H4 operate near the resonant frequency but less than the resonant frequency.

[0015] Preferably, under the phase shift control of step S3, the primary side switch tube S3 and the primary side switch tube S4 are controlled by a pair of complementary pulses with a duty cycle of 50% to form a bridge arm H1, the primary side switch tube S5 and the primary side switch tube S6 are controlled by a pair of complementary pulses with a duty cycle of 50% to form a bridge arm H2, the bridge arm H1 and the bridge arm H2 are turned on at the same time, and the switching frequency is equal to the series resonance frequency of the resonant capacitor Cp and the resonant inductor Lp; the primary side current limiting bridge arm switch tube S1 and the primary side current limiting bridge arm switch tube S2 are controlled by a pair of complementary pulses to form a bridge arm H3, the secondary side current limiting bridge arm switch tube S11 and the secondary side current limiting bridge arm switch tube S12 are controlled by a pair of complementary pulses to form a bridge arm H4, and the switching pulse phases of the bridge arm H3 and the bridge arm H4 are the same; the switch tube phase shift angle α of the bridge arm H3 and the bridge arm H4 is controlled by the output voltage feedback, and the switching pulse frequency of the bridge arm H3 and the bridge arm H4 operates at the resonant frequency.

[0016] Preferably, the frequency modulation-phase shift composite soft switching voltage regulation control technology in step S4 analyzes the bidirectional impedance change characteristics of the CLLLC resonant converter; combines the change of the phase margin under frequency modulation control with the switching frequency to select the lower limit value fmin of the switching frequency; analyzes the influence of the phase shift control on the soft switching range, and selects the maximum phase shift angle αmax.

[0017] Preferably, the frequency modulation-phase shift composite soft switching voltage regulation control technology sets the output reference voltage Uref according to the demand on the demand side of the low-voltage distribution network; enters the frequency modulation control loop to sample the output voltage value Uo; obtains the compensation frequency according to the output voltage sampling value and the reference voltage target value, combined with the mapping relationship of the frequency modulation control loop, and obtains the modulation frequency according to the sum of the compensation frequency and the resonant frequency of the converter, so that the output voltage sampling value is consistent with the reference voltage target value.

[0018] Preferably, when the modulation frequency is greater than the lower limit value of the switching frequency, the output voltage sampling value is consistent with the reference voltage target value, and the frequency control loop realizes a closed loop; when the modulation frequency is equal to the lower limit value of the switching frequency, the output voltage sampling value is greater than the reference voltage target value, the modulation frequency is fixed equal to the lower limit value of the switching frequency, and the phase shift control loop is entered; in the phase shift control loop, according to the output voltage sampling value and the reference voltage target value, combined with the mapping relationship of the phase shift control loop, a compensation phase shift angle is obtained to make the output voltage sampling value consistent with the reference voltage target value.

[0019] Preferably, the DC power module safety protection technology in step S5 analyzes the DC power grid short-circuit response trajectory, as well as the transient response characteristic components of the voltage and current of the DC power module port and the resonant cavity voltage and current caused by the DC power grid short-circuit; analyzes the transient response characteristics of the port short-circuit current taking into account the control loop response characteristics under the double-sided current limiting bridge arm soft switching modulation mode; and analyzes the influence of the port filter capacitor, filter inductor, switching frequency, resonant inductor and resonant capacitor on the fault transient response waveform.

[0020] Preferably, the S5 DC power module safety protection technology is based on the fault transient response characteristics of the DC power module. When the DC power grid is short-circuited, the short-circuit current upper limit of the current limiting bridge arms on both sides is set to imax; the current of the current limiting bridge arms on both sides is extracted, and when the current of the current limiting bridge arms on both sides reaches the upper limit value, that is, ir≥imax; the switch tubes S1, S2, S11 and S12 of the current limiting bridge arms on both sides are disconnected at the same time.

[0021] Beneficial effect: Compared with the prior art, the present invention has the following significant effects: the present invention can control the two control degrees of freedom of frequency modulation and phase shift, realize wide range of voltage regulation, broaden the soft switching range, and set the short-circuit current reference value through the current-limiting bridge arm to achieve double-sided short-circuit protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a structural diagram of a double-side blocking isolation converter in the present invention;

[0023] Figure 2It is a bridge arm definition diagram of a double-side blocking isolation converter under variable frequency control in the present invention;

[0024] Figure 3 It is a bridge arm definition diagram of a double-side blocking isolation converter under phase-shift control in the present invention;

[0025] Figure 4 is a switching state diagram of the CLLLC resonant converter under frequency control in the present invention;

[0026] Figure 5 is a switching state diagram of the current limiting bridge arm under phase shift control in the present invention;

[0027] Figure 6 is the gain curve of different Q values ​​in the present invention;

[0028] Figure 7 is a gain curve for different conduction angle values ​​in the present invention;

[0029] Figure 8 It is a simplified equivalent circuit of the CLLLC resonant converter in the present invention;

[0030] Fig. 9 It is an output gain effect diagram of the present invention;

[0031] Fig.10 This is a diagram showing the boundary effect of soft switch operation in the present invention;

[0032] Fig.11 It is a control flow chart of the frequency modulation-phase shift composite soft switch voltage regulation control technology in the present invention;

[0033] Fig.12 It is a schematic diagram of the derivation and calculation of losses in different directions in the present invention;

[0034] Fig.13 It is a schematic diagram of the derivation and calculation of the main line loss including energy storage in the present invention;

[0035] Fig.14 is the efficiency curve of the present invention;

[0036] Fig.15 It is a schematic diagram of a bipolar short circuit fault of a DC / DC converter in the present invention;

[0037] Fig.16 It is a schematic diagram of the double-side busbar short-circuit fault ride-through process in the present invention;

[0038] Fig.17 This is a diagram showing the effect of the fault current limiting control in the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below in conjunction with the embodiments and drawings.

[0040] The topological structure of the present invention is as follows Figure 1 As shown, it consists of a primary-side current limiting bridge arm 100, a primary-side full-bridge circuit 200, a CLLLC resonant cavity, a secondary-side full-bridge circuit 300 and a secondary-side current limiting bridge arm 400; wherein, the primary-side current limiting bridge arm 100 is composed of a primary-side switch tube S1 and a primary-side switch tube S2, the primary-side current limiting bridge arm 100 is connected in parallel with the primary-side filter capacitor C1, and the midpoint of the primary-side current limiting bridge arm 100 is connected in series with the primary-side filter inductor L1; the secondary-side current limiting bridge arm 400 is composed of a secondary-side switch tube S11 and a secondary-side switch tube S12, the secondary-side current limiting bridge arm 300 is connected in parallel with the secondary-side filter capacitor C2, and the midpoint of the secondary-side current limiting bridge arm 300 is connected in series with the secondary-side filter inductor L2; the CLLLC resonant cavity includes a transformer T, a primary-side resonant tank and a secondary-side resonant tank arranged on both sides of the transformer T; the primary-side resonant tank is composed of a resonant inductor Lp, an excitation inductor L m and resonant capacitor Cp; the secondary side resonant tank is composed of a resonant inductor Ls and a resonant capacitor Cs; the primary side full bridge 200 is composed of a primary side switch tube S3, a primary side switch tube S4, a primary side switch tube S5 and a primary side switch tube S6, the primary side switch tube S3 and the primary side switch tube S5 are connected in series and then connected in parallel to the series circuit of the switch tube S4 and the switch tube S6, and one side of the primary side full bridge 200 inputs a parallel filter capacitor C1, and the other side outputs a parallel CLLLC resonant cavity; the secondary side full bridge 300 is composed of a secondary side switch tube S7, a secondary side switch tube S8, a secondary side switch tube S9 and a secondary side switch tube S10, the switch tube S7 and the switch tube S9 are connected in series and then connected in parallel to the series circuit of the switch tube S8 and the switch tube S10, one side of the secondary side full bridge circuit 300 inputs a parallel secondary side resonant tank, and the other side outputs a parallel secondary side filter capacitor C2.

[0041] The control method of the double-side blocking isolation converter comprises the following specific steps: Figure 4 As shown:

[0042] Step 1: Divide the main circuit into two modules according to its function: frequency conversion control and phase shift control.

[0043] like Figure 4 and Figure 5 As shown, the control methods of the double-sided blocked isolation converter include frequency conversion control and phase shift control. Under frequency conversion control: the duty cycle of the current limiting bridge arms on both sides is fixed, and the CLLLC resonant converters on both sides control the switching pulse frequency according to the output voltage feedback; the phase shift control fixes the switching pulse frequency of the CLLLC resonant converters on both sides, and the switching tubes of the current limiting bridge arms on both sides control the pulse phase shift angle α according to the output voltage feedback.

[0044] Step 2, such as Figure 6As shown in the figure, the relationship between the voltage gain G and the angular frequency ω of the CLLLC converter. When the switching frequency is equal to 1, the voltage gain does not change with the change of the Q value. From the gain curve, it can be seen that when the Q value remains unchanged, G will first increase and then decrease with the increase of fs. The larger the Q value, the peak point of the gain curve shifts to the left, and the smaller the peak gain, the narrower the switching frequency variation range. When the Q value continues to increase, the converter will enter the capacitive region, two peak points will appear, and the primary switch tube cannot achieve ZVS. At the same time, as the switching frequency increases, the voltage gain of the resonant network is also rising, and the original negative feedback becomes positive feedback, which leads to the converter being unable to work stably. In order to meet the wide range of voltage input, the Q value should be selected to be smaller, but the voltage gain curve becomes steeper, which is not conducive to the stable operation of the converter, and when the voltage gain is less than 1, the switching frequency needs to change within a larger range to achieve voltage reduction, and its voltage reduction range is limited.

[0045] The voltage gain G is:

[0046]

[0047] Where A(fn) and B(fn) are:

[0048]

[0049] fn is the normalized switching frequency:

[0050]

[0051] fr is the normalized switching frequency:

[0052]

[0053] Q is the quality factor:

[0054]

[0055] Req is the equivalent resistance:

[0056]

[0057] k is the inductance ratio:

[0058]

[0059] Step 3, such as Figure 7 As shown in FIG. 1 , the relationship between the voltage gain G and the conduction angle θ under phase shift control. When the conduction angle is zero, the upper bridge arm switch tube of the current limiting bridge arm is always turned on, and the output voltage gain is maximum at this time. As the conduction angle increases, the voltage gain decreases. The conduction angle θ cannot increase all the time. In order to achieve soft switching, a maximum conduction angle θmax needs to be set.

[0060] The relationship between the conduction angle θ and the phase shift angle α:

[0061] θ+α=π

[0062] Step 4, such as Figure 8-Figure 11 As shown, based on the fundamental wave approximation method, the bidirectional impedance change characteristics of the CLLLC resonant converter are analyzed, and the CLLLC converter circuit is simplified into a linear circuit in which a sinusoidal power supply supplies energy to a purely resistive load through a resonant network. At the same time, according to the soft switching margin under different voltage regulation methods, the frequency lower limit under frequency conversion control and the minimum phase shift angle α of phase shift control are selected to establish a frequency modulation-phase shift composite soft switching voltage regulation control technology.

[0063] Ls' is the equivalent secondary side series resonant inductance:

[0064] L s '=n 2 L s

[0065] Cs' is the equivalent secondary series resonant capacitor:

[0066] C s '=n 2 C s

[0067] The steps of the frequency modulation-phase shift composite soft switch voltage regulation control are as follows:

[0068] 1) Select the output reference voltage Uref;

[0069] 2) First, enter the frequency control and set the lower limit reference value fref of the switching frequency during frequency control. At this time, the phase shift angle of the current limiting bridge arm is fixed, and the output voltage is controlled by modulating the switching pulse frequency of the switch tube drive signal of the bridge arm on both sides of the CLLLC resonant converter;

[0070] 3) According to the output voltage feedback, the switching pulse frequency fs is controlled. In the frequency control loop, changing the switching pulse frequency of the switch tubes on both sides of the bridge arm of the CLLLC resonant converter can make the output voltage reach the output reference voltage Uref, that is, fs>fref, and will continue to enter the frequency control loop;

[0071] 3) In the frequency control loop, a compensation frequency is obtained according to the output voltage sampling value and the reference voltage target value in combination with a frequency modulation control loop mapping relationship, so as to obtain a modulation frequency according to the sum of the compensation frequency and the resonant frequency of the converter, so that the output voltage sampling value is consistent with the reference voltage target value,

[0072] 4) When the modulation frequency is greater than the lower limit of the switching frequency, the output voltage sampling value is consistent with the reference voltage target value, and the frequency control loop realizes a closed loop; optionally, when the modulation frequency is equal to the lower limit of the switching frequency, the output voltage sampling value is greater than the reference voltage target value, the modulation frequency is fixed to be equal to the lower limit of the switching frequency, and the phase shift control loop is entered;

[0073] 5) In the phase shift control loop, according to the output voltage sampling value and the reference voltage target value, combined with the phase shift control loop mapping relationship, a compensation phase shift angle is obtained to make the output voltage sampling value consistent with the reference voltage target value.

[0074] 6) When in the phase shift control loop, if an output voltage reference value fref is given again, the phase shift angle α of the current limiting bridge arm is controlled according to the output voltage feedback. Under its action, when the phase shift angle α is zero, there is still a difference between the output voltage and the reference value, and it will return to the frequency control loop, and frequency control will be performed at this time.

[0075] Step 5, from Figure 12-14 As shown in the figure, considering the evaluation indicators such as system investment cost, operation loss, maintenance cost, etc., the economic feasibility of source-load storage AC and DC collection schemes is quantitatively analyzed. Based on the loss quantification analysis model of a single conduction direction, a loss model of the isolated converter with double-side blocking is established. The specific steps are as follows:

[0076] 1) The double-side blocked isolation converter has the ability to transfer energy in both directions. The losses in forward conduction and reverse conduction are calculated. Fig.11 As shown,

[0077] Ppv_grid(t) is the real-time power on the photovoltaic side:

[0078] P pv_grid (t) = P pv (t)-ΔCon pv (t)-ΔLine pv (t)

[0079] Pload_grid(t) is the real-time power on the load side:

[0080] P load_grid (t) = P load (t)-ΔCon load (t)-ΔLine load (t)

[0081] 2) The energy storage device cannot be charged and discharged at the same time, so the total loss calculation result varies with the operating state of the energy storage device. When the energy storage device is in the charging state, it can be regarded as a DC load, and the device loss is:

[0082]

[0083] 3) The grid-connected power of the energy storage line is Pes_ch_grid(t), and the grid-connected power of the main line is PS_grid(t). The expressions are as follows:

[0084] P es_grid (t) = P es_ch (t)-ΔCon es_ch (t)-ΔLine es_ch (t)

[0085] P S_grid (t) = P load_grid (t)-P es_grid (t)-P pv_grid (t)

[0086] 4) When the energy storage is in the discharge state, the device loss is:

[0087]

[0088] 5) The grid-connected power of the energy storage line Pes_dis_grid(t) and the grid-connected power of the main line PS_grid(t) are respectively shown as follows:

[0089] P es_grid (t) = P es_dis (t)-ΔCon es_dis (t)-ΔLine es_dis (t)

[0090] P S_grid (t) = P load_grid (t)-P es_grid (t)-P pv_grid (t)

[0091] 6) For the main line device loss, the power transmission direction is opposite to the loss calculation direction, so the power loss generated by the main line AC-DC is:

[0092]

[0093] 7) Combined with the main line loss, the formula is derived:

[0094]

[0095] 8) According to the above steps, the total power of the power grid PS(t) can be obtained as:

[0096] P S (t) = P S_grid (t)+ΔCon S (t)+ΔLine S(t)

[0097] 9) Based on the above loss model of single conduction direction and the main line loss model, the total loss model of the distribution network in the energy storage charging and discharging mode of the double-side blocked isolation converter is established:

[0098] P loss (t)=∑ΔLine item (t)+∑ΔCon item (t)

[0099] Step 6, from Figure 14-17 As shown, the present invention provides a DC power module safety protection technology with double-side busbar short-circuit fault ride-through capability, and the specific steps are as follows:

[0100] 1) A short circuit occurs at the outlet of the DC / DC converter. The resistance in the discharge loop is extremely small, and the underdamping of the loop is extremely high. The fault is most serious at this time, and the fault rises very quickly, and the bridge arm current quickly exceeds the limit. Therefore, the DC / DC converter needs to detect whether the bridge arm current exceeds the limit. Once the bridge arm current exceeds the set value, the submodule is directly locked;

[0101] 2) When a fault occurs at the far end of the line, the resistance on the line increases the equivalent resistance of the system. At this time, the underdamping degree of the discharge circuit is weakened, and it no longer exhibits a strong underdamping characteristic. The fault current rise speed decreases, and when the bridge arm current has not exceeded the limit, the control strategy is switched to the current control mode in time;

[0102] 3) Set the given value of the DC current to a voltage lower than 0.7 times the rated value as a trigger switching signal to suppress the fault current in a non-locking manner;

[0103] 4) When the current of the current-limiting bridge arms on both sides reaches the upper limit value, the switch tubes S1, S2, S11 and S12 of the current-limiting bridge arms on both sides are disconnected at the same time, and when a double-sided bus short-circuit fault occurs, the DC power module safety protection function is realized.

Claims

1. A double-side blocking isolation converter, characterized in that: It comprises a primary-side current limiting bridge arm (100), a primary-side full-bridge circuit (200), a CLLLC resonant cavity, a secondary-side full-bridge circuit (300) and a secondary-side current limiting bridge arm (400); The primary-side current limiting bridge arm (100) is composed of a primary-side switch tube S1 and a primary-side switch tube S2, the primary-side current limiting bridge arm (100) is connected in parallel with the primary-side filter capacitor C1, and the midpoint of the primary-side current limiting bridge arm (100) is connected in series with the primary-side filter inductor L1; the secondary-side current limiting bridge arm (400) is composed of a secondary-side switch tube S11 and a secondary-side switch tube S12, the secondary-side current limiting bridge arm (300) is connected in parallel with the secondary-side filter capacitor C2, and the midpoint of the secondary-side current limiting bridge arm (300) is connected in series with the secondary-side filter inductor L2; the CLLLC resonant cavity comprises a transformer T, a primary-side resonant tank and a secondary-side resonant tank arranged on both sides of the transformer T; the primary-side resonant tank is composed of a resonant inductor Lp, an excitation inductor Lm and a resonant capacitor Cp; the secondary-side resonant tank is composed of a resonant inductor Ls and a resonant The primary side full bridge (200) is composed of a primary side switch tube S3, a primary side switch tube S4, a primary side switch tube S5 and a primary side switch tube S6, the primary side switch tube S3 and the primary side switch tube S5 are connected in series and then connected in parallel to the series circuit of the switch tube S4 and the switch tube S6, and one side of the primary side full bridge (200) inputs a parallel filter capacitor C1, and the other side outputs a parallel CLLLC resonant cavity; the secondary side full bridge (300) is composed of a secondary side switch tube S7, a secondary side switch tube S8, a secondary side switch tube S9 and a secondary side switch tube S10, the switch tube S7 and the switch tube S9 are connected in series and then connected in parallel to the series circuit of the switch tube S8 and the switch tube S10, and one side of the secondary side full bridge circuit (300) inputs a parallel secondary resonant tank, and the other side outputs a parallel secondary filter capacitor C2.

2. A control method for a double-side blocking isolation converter according to claim 1, characterized in that: The following steps are involved: S1, the isolation converter is functionally divided into two modules: frequency conversion control and phase shift control; S2. Analyze the working state of the isolation converter under variable frequency control based on the fundamental wave approximation method; S3. Analyze the working state of the isolation converter under phase shift control based on the fundamental wave approximation method; S4. Analyze the bidirectional impedance variation characteristics of the isolation converter based on the fundamental wave approximation method, select the lower frequency limit under frequency conversion control and the minimum phase shift angle α of phase shift control according to the soft switching margin of different voltage regulation methods, and establish a frequency modulation-phase shift composite soft switching voltage regulation control technology; S5. Based on the wide-area measurement system, the short-circuit response trajectory of the DC power grid is obtained, and the transient response characteristic components of the voltage and current at the DC power module port and the resonant cavity voltage and current caused by the grid short circuit are extracted to establish a DC power module safety protection technology with the ability to ride through double-sided bus short-circuit faults.

3. The control method of the double-side blocking isolation converter according to claim 2, characterized in that: In the step S1, under the variable frequency control, the duty cycle of the current limiting bridge arms on both sides is fixed, and the CLLLC resonant converters on both sides control the switching pulse frequency according to the output voltage feedback; under the phase shift control, the switching pulse frequency of the CLLLC resonant converters on both sides is fixed, and the switching tubes of the current limiting bridge arms on both sides control the pulse phase shift angle α according to the output voltage feedback.

4. The control method of the double-side blocking isolation converter according to claim 2, characterized in that: In the step S2, under the variable frequency control, the primary-side current limiting bridge arm switch tube S1 and the primary-side current limiting bridge arm switch tube S2 are controlled by a pair of complementary pulses to form a bridge arm H1, the secondary-side current limiting bridge arm switch tube S11 and the secondary-side current limiting bridge arm switch tube S12 are controlled by a pair of complementary pulses to form a bridge arm H2, the bridge arm H1 and the bridge arm H2 are turned on at the same time, and the duty cycle is the same; the primary-side switch tube S3 and the primary-side switch tube S4 are controlled by a pair of complementary pulses with a duty cycle of 50% to form the bridge arm H3, the primary-side switch tube S5 and the primary-side switch tube S6 are controlled by a pair of complementary pulses with a duty cycle of 50% to form the bridge arm H4, the bridge arm H3 and the bridge arm H4 are turned on at the same time, and the switching frequency is equal to the series resonant frequency of the resonant capacitor Cp and the resonant inductor Lp; the switching pulse frequency of the bridge arm H3 and the bridge arm H4 is controlled by the output voltage feedback, so that the bridge arm H3 and the bridge arm H4 operate near the resonant frequency but less than the resonant frequency.

5. The control method of the double-side blocking isolation converter according to claim 2, characterized in that: In the phase shift control of step S3, the primary side switch tube S3 and the primary side switch tube S4 are controlled by a pair of complementary pulses with a duty cycle of 50% to form a bridge arm H1, the primary side switch tube S5 and the primary side switch tube S6 are controlled by a pair of complementary pulses with a duty cycle of 50% to form a bridge arm H2, the bridge arm H1 and the bridge arm H2 are turned on at the same time, and the switching frequency is equal to the series resonance frequency of the resonant capacitor Cp and the resonant inductor Lp; the primary side current limiting bridge arm switch tube S1 and the primary side current limiting bridge arm switch tube S2 are controlled by a pair of complementary pulses to form a bridge arm H3, the secondary side current limiting bridge arm switch tube S11 and the secondary side current limiting bridge arm switch tube S12 are controlled by a pair of complementary pulses to form a bridge arm H4, and the switch pulse phases of the bridge arm H3 and the bridge arm H4 are the same; the switch tube phase shift angle α of the bridge arm H3 and the bridge arm H4 is controlled by the output voltage feedback, and the switch pulse frequency of the bridge arm H3 and the bridge arm H4 operates at the resonant frequency.

6. The control method of the double-side blocking isolation converter according to claim 2, characterized in that: The frequency modulation-phase shift composite soft switching voltage regulation control technology in step S4 analyzes the bidirectional impedance change characteristics of the CLLLC resonant converter; combines the change of the phase margin under frequency modulation control with the switching frequency to select the lower limit value fmin of the switching frequency; analyzes the influence of the phase shift control on the soft switching range, and selects the maximum phase shift angle αmax.

7. The control method of the double-side blocking isolation converter according to claim 2, characterized in that: The frequency modulation-phase shift composite soft switch voltage regulation control technology sets the output reference voltage Uref according to the demand of the low-voltage distribution network demand side; enters the frequency modulation control loop and samples the output voltage value Uo; According to the output voltage sampling value and the reference voltage target value, combined with the frequency modulation control loop mapping relationship, the compensation frequency is obtained, and the modulation frequency is obtained according to the sum of the compensation frequency and the resonant frequency of the converter, so that the output voltage sampling value is consistent with the reference voltage target value.

8. The control method of the double-side blocking isolation converter according to claim 2, characterized in that: When the modulation frequency is greater than the lower limit value of the switching frequency, the output voltage sampling value is consistent with the reference voltage target value, and the frequency control loop is closed; When the modulation frequency is equal to the lower limit value of the switching frequency, the output voltage sampling value is greater than the reference voltage target value, the modulation frequency is fixed to be equal to the lower limit value of the switching frequency, and the phase shift control loop is entered; In the phase shift control loop, a compensation phase shift angle is obtained according to the output voltage sampling value and the reference voltage target value in combination with a phase shift control loop mapping relationship, so that the output voltage sampling value is consistent with the reference voltage target value.

9. The control method of the double-side blocking isolation converter according to claim 2, characterized in that: The DC power module safety protection technology in step S5 analyzes the DC power grid short-circuit response trajectory, as well as the transient response characteristic components of the voltage and current at the DC power module port and the resonant cavity voltage and current caused by the DC power grid short-circuit; under the double-side current limiting bridge arm soft switch modulation mode, the transient response characteristic analysis of the port short-circuit current taking into account the control loop response characteristics; Analyze the influence of port filter capacitance, filter inductance, switching frequency, resonant inductance and resonant capacitance on the fault transient response waveform.

10. The control method of the double-side blocking isolation converter according to claim 2, characterized in that: The S5 DC power module safety protection technology is based on the fault transient response characteristics of the DC power module. When the DC power grid is short-circuited, the short-circuit current upper limit value of the current limiting bridge arms on both sides is set to imax; the current of the current limiting bridge arms on both sides is extracted, and when the current of the current limiting bridge arms on both sides reaches the upper limit value, that is, ir≥imax; the switch tubes S1, S2, S11 and S12 of the current limiting bridge arms on both sides are disconnected at the same time.

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