Multi-port isolated input series output photovoltaic dc collection converter and control method

Abstract

The application discloses a multi-port isolated input series output photovoltaic direct current collection converter and a control method thereof, and the converter comprises N photovoltaic arrays, N primary side boost half-bridges, N secondary side half-bridges, a multi-winding transformer T and a grid-connected reactor L out The application is aimed at the application occasion of adopting distributed multi-port photovoltaic direct current voltage-boosting and being incorporated into a medium and high voltage direct current power grid, the primary side of the converter adopts a boost half-bridge unit, the input current is continuous and small in ripple, is suitable for a photovoltaic power generation occasion, and a multi-winding transformer is used to realize electrical isolation between the input side and the output side; through the control method, independent MPPT control is conducted on each primary side boost half-bridge, average power control is conducted on each secondary side half-bridge, the output voltages of all the secondary side half-bridges can be balanced, overvoltage damage of the devices is avoided, and safe and stable operation of the converter is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic multi-port DC converter, and particularly relates to a multi-port isolated input series output photovoltaic DC collection converter and a control method. BACKGROUND

[0002] The "input independent, output series" type converter combination system has simple and clear architecture, can realize independent control of multiple input ports and series high-gain output under the condition of maintaining the overall single-stage power conversion structure of the converter, and is suitable for large power capacity, large space range, distributed integrated photovoltaic power generation DC collection occasions.

[0003] However, in the field of photovoltaic power generation, the existing "input independent, output series" type converter is subject to its inherent physical characteristics, and has the problem of unbalanced output power. This unbalanced output power may cause the output voltage to deviate, i.e. the offset problem, thereby affecting the stability and power quality of the system, and limiting the further promotion and application of this type of converter in the field of photovoltaic power generation.

[0004] At present, there are some solutions, such as adding an additional switching network for power transmission, constructing a topology including a buck-boost type circuit and a series lc branch, etc., but these solutions often have problems such as complex control strategy, too many devices, long regulation time, etc. Therefore, how to effectively solve the problem of unbalanced output power while maintaining the simplicity and efficiency of the system is the direction of future research and development in this field. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a multi-port isolated input series output photovoltaic DC collection converter and a control method, which solves the problem of unbalanced output power of the converter and improves the stability of the converter.

[0006] The present application adopts the following technical scheme: a multi-port isolated input series output photovoltaic DC collection converter, comprising: N photovoltaic arrays, N primary side boost half bridges, N secondary side half bridges, one multi-winding transformer T and one grid-connected reactor L out ;

[0007] Wherein, N is a natural number greater than or equal to 2, the multi-winding transformer T has N windings, including inductors L p,1 -L p,N , inductors L s,2 -L s,N , windings n p,1 -n p,N , windings n s,1 -n s,N , for electrical isolation between the input side and the output side.

[0008] On the input side, each photovoltaic array k is connected to the k-th inductor L of the multi-winding transformer T through the k-th primary-side boost half-bridge. p,k and winding n p,k On the output side, the k-th inductor L of the multi-winding transformer T... s,k and winding n s,k Connect the k-th secondary half-bridge and pass through the grid-connected reactor L. out Output balanced voltage, k = 1, 2, ..., N;

[0009] Each primary-side boost half-bridge includes the filter capacitor C. pv,k Input inductance L in,k Switching transistor Q 1,k Q 2,k Capacitor C 1,k C 2,k The filter capacitor C pv,k The positive terminal of the photovoltaic array k and the input inductor L in,k The positive terminal is connected to the filter capacitor C. pv,k The negative terminal and the switching transistor Q 2,k emitter, capacitor C 2,k The negative terminal of the input inductor L is connected to the negative terminal of the photovoltaic array k; in,k The negative terminal and the switching transistor Q 1,k emitter, switch Q 2,k The capacitor C is connected to the collector. 1,k The positive terminal and the switching transistor Q 1,k The collector of the capacitor C is connected to the capacitor C. 1,k The negative terminal and capacitor C 2,k The positive terminals are connected.

[0010] Each secondary half-bridge contains a switching transistor Q. 3,k Q 4,k Capacitor C 3,k C 4,k The switching transistor Q 3,k collector and capacitor C 3,k The positive terminal is connected; the switch Q is connected to the positive terminal. 3,k The emitter and the switch Q 4,k The capacitor C is connected to the collector. 4,k The negative terminal and the switching transistor Q 4,k The emitters are connected.

[0011] In a multi-winding transformer T, the inductor L p,k The positive terminal and the switching transistor Q 1,k emitter, Q 2,k collector and input inductance L in,k The negative terminal of the inductor L is connected.p,k negative pole of the inductor L p,k the same name end of the winding n

[0012] the same name end of the winding n p,k negative pole of the inductor L p,k non-same name end of the winding n p,k negative pole of the capacitor C 1,k positive pole of the capacitor C 2,k

[0013] negative pole of the inductor L s,k emitter of the switch tube Q 3,k collector of the switch tube Q 4,k

[0014] the same name end of the winding n s,k positive pole of the inductor L s,k non-same name end of the winding n s,k negative pole of the capacitor C 3,k positive pole of the capacitor C 4,k

[0015] Further, the positive pole of the capacitor C 3,1 positive pole of the inductor L out collector of the switch tube Q 3,1 3,k negative pole of the capacitor C 4,k-1 positive pole of the capacitor C 4，k 3,k+1

[0016] The technical scheme of the present application also provides a control method of the multi-port isolated input series output photovoltaic direct current collection converter, MPPT controllers are used to independently control each primary boost half-bridge, and average power controllers are used to control each secondary half-bridge, and the specific steps are as follows:

[0017] S1, a first high-frequency pulse signal with a duty cycle of 50% is used as a gate trigger signal of the switch tube Q 3,1

[0018] S2, the first high-frequency pulse signal is input to an inverter to obtain a second high-frequency pulse signal;

[0019] S3, the second high-frequency pulse signal is used as a gate trigger signal of the switch tube Q 4,1

[0020] ​​​​​​​​S4, collect the input side current i of the primary side boost half bridge pv , input side voltage v pv and input it to the MPPT controller, and the MPPT controller outputs the phase shift angle d Lp of the conversion module

[0021] S5, input the first high-frequency pulse signal and the phase shift angle d Lp to the phase shifter to obtain a third high-frequency pulse signal

[0022] S6, the third high-frequency pulse signal is used as the gate trigger signal of the switch tube Q 1，1 ;

[0023] S7, input the third high-frequency pulse signal to the inverter to obtain a fourth high-frequency pulse signal

[0024] S8, the fourth high-frequency pulse signal is used as the gate trigger signal of the switch tube Q 2，1 .

[0025] S9, collect the second secondary side half bridge voltage v o，2 and input it to the average power controller, and the average power controller outputs the phase shift angle d Ls of the conversion module

[0026] S10, input the first high-frequency pulse signal and the phase shift angle d Ls to the phase shifter to obtain a fifth high-frequency pulse signal

[0027] S11, the fifth high-frequency pulse signal is used as the gate trigger signal of the switch tube Q 3，2 to the switch tube Q 3，N ;

[0028] S12, input the fifth high-frequency pulse signal to the inverter to obtain a sixth high-frequency pulse signal

[0029] S13, the sixth high-frequency pulse signal is used as the gate trigger signal of the switch tube Q 4，2 to the switch tube Q 4，N .

[0030] Compared with the prior art, the above technical scheme has the following technical effects:

[0031] This invention relates to a multi-port isolated input-series-output photovoltaic DC-DC converter, designed for applications involving distributed multi-port photovoltaic DC boost converters connected to medium- and high-voltage DC power grids. The primary side of this converter employs a Boost half-bridge unit, resulting in continuous input current and low ripple, making it suitable for photovoltaic power generation applications. A multi-winding transformer is used to achieve electrical isolation between the input and output sides. Through the control strategy of the proposed control method, the output voltages of all secondary half-bridges are balanced, preventing overvoltage damage to components and ensuring the safe and stable operation of the converter. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the photovoltaic DC-DC converter circuit topology of the present invention;

[0033] Figure 2 This is a schematic diagram of the control signals and trigger pulses of the photovoltaic DC-DC converter of the present invention;

[0034] Figure 3 This is a schematic diagram of the circuit waveforms of the photovoltaic DC-DC converter of the present invention.

[0035] Figures 4(a) to 4(f) The equivalent circuit diagrams are shown for the six working modes of the second-side first half-bridge, the primary-side half-bridge k, and the second-side half-bridge j during the switching cycle of this invention.

[0036] Figure 5(a) is a schematic diagram comparing the output voltage waveforms of the six conversion modules when the input power of the photovoltaic array changes at t=0.43s and t=0.67s.

[0037] Figure 5(b) is a schematic diagram comparing the input current at each port of the six conversion modules when the input power of the photovoltaic array changes at t=0.43s and t=0.67s. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the application are further described in detail below with reference to the accompanying drawings. This invention can be implemented in many different forms and should not be considered limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure is thorough and complete, and will fully express the scope of the invention to those skilled in the art. All non-inventive embodiments of this invention by other researchers in the art are within the scope of protection of this invention. In the accompanying drawings, components are enlarged for clarity.

[0039] This invention discloses a multi-port isolated input series output photovoltaic DC-DC converter, such as... Figure 1 As shown, it includes N photovoltaic arrays, N primary-side boost half-bridges, N secondary-side half-bridges, a multi-winding transformer T, and a grid-connected reactor L. out N is a natural number greater than or equal to 2;

[0040] The primary side boost half-bridge of the converter comprises a filter capacitor C pv,k , an input inductor L in,k , a switch tube Q 1,k , Q 2,k , a capacitor C 1,k , C 2,k ;

[0041] The positive pole of the filter capacitor C pv,k is connected with the positive pole of the photovoltaic array k and the positive pole of the input inductor L in,k , and the negative pole of the filter capacitor C pv,k is connected with the emitter of the switch tube Q 2,k , the negative pole of the capacitor C 2,k , and the negative pole of the photovoltaic array k;

[0042] The negative pole of the input inductor L in,k is connected with the emitter of the switch tube Q 1,k and the collector of the switch tube Q 2,k ;

[0043] The positive pole of the capacitor C 1,k is connected with the collector of the switch tube Q 1,k , and the negative pole of the capacitor C 1,k is connected with the positive pole of the capacitor C 2,k .

[0044] The secondary side half-bridge of the converter comprises a switch tube Q 3,k , Q 4,k , a capacitor C 3,k , C 4,k ;

[0045] The collector of the switch tube Q 3,k is connected with the positive pole of the capacitor C 3,k , and the emitter of the switch tube Q 3,k is connected with the collector of the switch tube Q 4,k ;

[0046] The negative pole of the capacitor C 4,k is connected with the emitter of the switch tube Q 4,k ;

[0047] The multi-winding transformer T comprises an inductor L p,1 -L p,N , an inductor L s,2 -L s,N , a winding n p,1 -n p,N , and a winding n s,1 -n s,N ;

[0048] The inductor Lp,k The positive terminal and the switching transistor Q 1,k emitter, Q 2,k collector and input inductance L in,k The negative terminal of the inductor L is connected. p,k The negative terminal and winding n p,k Connected to the same-named ends;

[0049] The winding n p,k The same terminal as the inductor L p,k The negative terminal is connected, and the winding n p,k The non-identical terminals of the capacitor C 1,k negative terminal, capacitor C 2,k The positive terminals are connected;

[0050] The inductor L s,k The negative terminal and the switching transistor Q 3,k emitter, Q 4,k The collector is connected;

[0051] The winding n s,k The same terminal as the inductor L s,k The positive terminal is connected, and the winding n s,k The non-identical terminals of the capacitor C 3,k negative terminal, capacitor C 4,k The positive terminals are connected;

[0052] The capacitor C 3,1 The positive electrode of the grid-connected reactor L out The positive terminal and the switching transistor Q 3,1 The collector is connected;

[0053] The capacitor C 3,k The positive terminal and capacitor C 4,k-1 The negative terminal is connected;

[0054] The capacitor C 4，k The negative terminal and capacitor C 3,k+1 The positive terminals are connected.

[0055] Based on the aforementioned multi-port isolated input series output photovoltaic DC-DC converter, the drive signal is controlled, such as... Figure 2 As shown, independent MPPT control is implemented for each primary-side boost half-bridge, and average power control is implemented for each secondary-side half-bridge. The specific steps are as follows:

[0056] Step S1: Use a high-frequency pulse signal 1 with a duty cycle of 50% as the switching transistor Q. 3,1 The gate trigger signal;

[0057] Step S2: Input high-frequency pulse signal 1 into the inverter to obtain high-frequency pulse signal 2;

[0058] Step S3, the high-frequency pulse signal 2 is taken as the gate trigger signal of the switching tube Q 4,1 of the conversion module;

[0059] Step S4, the input side current i pv and the input side voltage v pv of the primary side boost half-bridge are collected and input to the MPPT controller, and the MPPT controller outputs the phase shift angle d Lp of the conversion module;

[0060] Step S5, the high-frequency pulse signal 1 and the phase shift angle d Lp are input to the phase shifter to obtain the high-frequency pulse signal 3;

[0061] Step S6, the high-frequency pulse signal 3 is taken as the gate trigger signal of the switching tube Q 1，1 of the conversion module;

[0062] Step S7, the high-frequency pulse signal 3 is input to the inverter to obtain the high-frequency pulse signal 4;

[0063] Step S8, the high-frequency pulse signal 4 is taken as the gate trigger signal of the switching tube Q 2，1 of the conversion module.

[0064] Step S9, the second secondary side half-bridge voltage v o，2 is collected and input to the average power controller, and the average power controller outputs the phase shift angle d Ls of the conversion module;

[0065] Step S10, the high-frequency pulse signal 1 and the phase shift angle d Ls are input to the phase shifter to obtain the high-frequency pulse signal 5;

[0066] Step S11, the high-frequency pulse signal 5 is taken as the gate trigger signal of the switching tube Q 3，2 ~ the switching tube Q 3，N of the secondary side half-bridge;

[0067] Step S12, the high-frequency pulse signal 5 is input to the inverter to obtain the high-frequency pulse signal 6;

[0068] Step S13, the high-frequency pulse signal 6 is taken as the gate trigger signal of the switching tube Q 4，2 ~ the switching tube Q 4，N of the conversion module.

[0069] The circuit waveforms in the normal working state are shown in FIG. Figure 3 In the first secondary side half-bridge, the driving signals of the switching tubes Q 3,1 and Q 4,1 are g Q3,1 and gQ4,1 ; the driving signal of the switch Q 1,k and Q 2,k is g Q1,k and g Q2,k ; the driving signal of the switch Q 3,j and Q 4,j is g Q3,j and g Q4,j ; the current of the input inductor L in,k is i in,k ; the voltage of the inductor L p,k is v Lp,k , and the current is i Lp,k ; the voltage of the inductor L s,j is v Ls,j , and the current is i Ls,j .

[0070] In a switching cycle, the circuit can be divided into six modes. In a certain switching cycle, the equivalent circuit diagrams of the six working modes of the first half-bridge on the secondary side, the half-bridge k on the primary side, and the half-bridge j on the secondary side are shown in FIG. 4, and are as follows: Figures 4(a) to 4(f)

[0071] FIG. 4(a) is the equivalent circuit diagram of mode 1, at this time, Q 4，j , Q 1，k and Q 3，1 are in the on state. Since the voltage of L p，k (v Lp,k ) is 0, the current of L p，j (i Lp,j ) remains I Lp，k .

[0072] In addition, the voltage of L s，j (v Ls,j ) is 2V in，k , and the current of L s，j (i Ls,j ) changes from negative to positive, so that the ZVS of Q 4，j can be realized.

[0073] FIG. 4(b) is the equivalent circuit diagram of mode 2, at this time, Q 4，j is off, and D 3，j is forced to conduct and continue to flow. Since the voltage of L s，j (v Ls,j ) is 0, the current of L s，j (i Ls,j ) is still I Ls，j .

[0074] FIG. 4(c) is the equivalent circuit diagram of mode 3, at this time, Q 1，k is off, and D 2，k is forced to conduct and continue to flow, and since​p，k (v Lp,k The voltage is -2V in，k L p，k (i Lp,k When the current changes from positive to negative, Q can be achieved. 2，k ZVS.

[0075] After that, Q 2，k Activation, L in，k The voltage is -V in，k L in，k (i in,k The current begins to increase.

[0076] Figure 4(d) shows the equivalent circuit diagram for mode 4, where Q... 3，1 Off, D 4，1 Forced to conduct current, L p，k (v Lp,k The voltage of L is 0. p，j (i Lp,j The current remains at -I Lp，k Because of L s，j (v Ls,j The voltage is -2V in，k L s，j (i Ls,j The current will change from negative to positive, which can realize Q. 3，j ZVS.

[0077] Figure 4(e) shows the equivalent circuit diagram for mode 5, where Q... 3，j Off, D 4，j Forced to conduct current continuation, due to L s，j (v Ls,j The voltage of L is 0. s，j (i Ls,j The current remains at -I Ls，j .

[0078] Figure 4(f) shows the equivalent circuit diagram for mode 6, where Q... 1，k Off, D 2，k Conducting freewheeling, due to L p，k (v Lp,k The voltage is 2V. in，k L p，k (i Lp,k When the current changes from negative to positive, Q can be achieved. 1，k ZVS.

[0079] After that, Q 1，k Open. In addition, L in，k The voltage is -V in，k L in，k (i in,k The current began to decrease.

[0080] In order to verify the performance of the photovoltaic DC bus converter, in a specific embodiment, a 31.5kW photovoltaic grid-connected system simulation model with 3kV bus voltage is built.

[0081] As shown in Fig. 5(a), at the beginning, the irradiance of the 6 PVs is the same (900W / m2), and the input current is the same (average current is about 21A). Then at t=0.04s, the irradiance of a single photovoltaic changes suddenly, so the input current of the PV changes suddenly, and the input current of the other 5 PVs remains unchanged. in，1 -i in，6 The inconsistency starts. Finally at t=0.83s, the irradiance becomes the same again, and the simulation well simulates the actual working condition.

[0082] As shown in Fig. 5(b), due to the decrease of the total input power of the converter at t=0.04s, the power of the second to sixth auxiliary half-bridge cannot support the DC side capacitor voltage. Therefore, the relaxation port voltage decreases, and a transient voltage drop (DV1=32V, Dt1=5ms) occurs. At this time, the closed loop will adjust d Ls decreases, and the relaxation port passes through the transient under-voltage. Similarly, at t=0.83s, due to the increase of the total input power of the converter, the relaxation port voltage rises, and there is an overvoltage (DV2=10V, Dt1=4ms).

[0083] Those skilled in the art can understand that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with those in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless otherwise defined.

[0084] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A multi-port isolated input series output photovoltaic DC-DC converter, characterized in that, include: N photovoltaic arrays, N primary-side boost half-bridges, N secondary-side half-bridges, one multi-winding transformer T, and one grid-connected reactor L. out ; N is a natural number greater than or equal to 2, and the multi-winding transformer T has N windings, including an inductor L. p,1 -L p,N Inductor L s,2 -L s,N Winding n p,1 -n p,N and winding n s,1 -n s,N Used for electrical isolation between the input and output sides; On the input side, each photovoltaic array k is connected to the k-th inductor L of the multi-winding transformer T through the k-th primary-side boost half-bridge. p,k and winding n p,k On the output side, the k-th inductor L of the multi-winding transformer T... s,k and winding n s,k Connect the k-th secondary half-bridge and pass through the grid-connected reactor L. out Output balanced voltage, k = 1, 2, ..., N; Each primary-side boost half-bridge includes the filter capacitor C. pv,k Input inductance L in,k Switching transistor Q 1,k Q 2,k and capacitor C 1,k C 2,k Each secondary half-bridge contains a switching transistor Q. 3,k Q 4,k and capacitor C 3,k C 4,k ; In each primary-side boost half-bridge, the filter capacitor C pv,k The positive terminal of the photovoltaic array k and the input inductor L in,k The positive terminal is connected to the filter capacitor C. pv,k The negative terminal and the switching transistor Q 2,k emitter, capacitor C 2,k The negative terminal of the input inductor L is connected to the negative terminal of the photovoltaic array k; in,k The negative terminal and the switching transistor Q 1,k emitter and switch Q 2,k The capacitor C is connected to the collector. 1,k The positive terminal and the switching transistor Q 1,k The collector of the capacitor C is connected to the capacitor C. 1,k The negative terminal and capacitor C 2,k The positive terminals are connected; In each secondary half-bridge, the switching transistor Q 3,k collector and capacitor C 3,k The positive terminal is connected; the switch Q 3,k The emitter and the switch Q 4,k The capacitor C is connected to the collector. 4,k The negative terminal and the switching transistor Q 4,k The emitters are connected; In a multi-winding transformer T, the inductor L p,k The positive terminal and the switching transistor Q 1,k emitter, Q 2,k collector and input inductance L in,k The negative terminal of the inductor L is connected. p,k The negative terminal and winding n p,k Connect the same-named ends; The winding n p,k The non-identical terminals of the capacitor C 1,k The negative electrode and capacitor C 2,k The positive terminals are connected; The inductor L s,k The negative terminal and the switching transistor Q 3,k emitter and switch Q 4,k The collector is connected; The winding n s,k The same terminal as the inductor L s,k The positive terminal is connected, and the winding n s,k The non-identical terminals of the capacitor C 3,k The negative electrode and capacitor C 4,k The positive terminals are connected; The capacitor C in the first secondary half-bridge 3,1 The positive electrode of the grid-connected reactor L out The positive terminal and the switching transistor Q 3,1 The collectors are connected; the capacitance C in the k-th secondary half-bridge is... 3,k The positive terminal and the capacitor C in the (k-1)th secondary half-bridge 4,k-1 The negative terminals are connected; the capacitor C in the kth secondary half-bridge 4，k The negative terminal and the capacitor C in the (k+1)th secondary half-bridge 3,k+1 The positive terminals are connected.

2. A control method for a multi-port isolated input series output photovoltaic DC-DC converter, applied to the photovoltaic DC-DC converter of claim 1, characterized in that, Each primary-side boost half-bridge is independently controlled by an MPPT controller for maximum power point tracking, while each secondary-side half-bridge is controlled by an average power controller for average power. The specific steps are as follows: S1. A first high-frequency pulse signal with a duty cycle of 50% is used as the switching transistor Q. 3,1 The gate trigger signal; S2. Input the first high-frequency pulse signal into the inverter to obtain the second high-frequency pulse signal; S3. Use the second high-frequency pulse signal as the switching transistor Q. 4,1 The gate trigger signal; S4. Collect the input current i of the primary-side boost half-bridge. pv Input voltage v pv This is then input to the MPPT controller, which outputs the phase shift angle d from the conversion module. Lp ; S5. Combine the first high-frequency pulse signal with the phase shift angle d Lp The signal is input to the phase shifter to obtain the third high-frequency pulse signal; S6. Use the third high-frequency pulse signal as the switching transistor Q. 1，1 The gate trigger signal; S7. Input the third high-frequency pulse signal into the inverter to obtain the fourth high-frequency pulse signal; S8. Use the fourth high-frequency pulse signal as the switching transistor Q. 2，1 The gate trigger signal; S9, Collect the second secondary half-bridge voltage v o，2 The input is then fed into the average power controller, which outputs the phase shift angle d of the conversion module. Ls ; S10, Combine the first high-frequency pulse signal with the phase shift angle d Ls The signal is input to the phase shifter to obtain the fifth high-frequency pulse signal; S11. Use the fifth high-frequency pulse signal as the secondary half-bridge switch Q. 3，2 To the switching transistor Q 3，N The gate trigger signal; S12. Input the fifth high-frequency pulse signal into the inverter to obtain the sixth high-frequency pulse signal; S13. Use the sixth high-frequency pulse signal as the switching transistor Q. 4，2 To the switching transistor Q 4，N The gate trigger signal.

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