DC converter topology circuit and control method thereof, inverter system

Abstract

The present invention discloses a DC converter topology circuit and a control method thereof, and an inverter system. The DC converter topology circuit includes a working circuit connected to both ends of a photovoltaic array, and the working circuit has a Boost working mode and a Buck working mode. When the input voltage of the photovoltaic array is less than or equal to the DC bus voltage, the working circuit enters the Boost working mode to increase the input voltage. When the input voltage of the photovoltaic array is greater than the DC bus voltage, the working circuit enters the Buck mode to reduce the input voltage. Compared with the prior art, the present invention can keep the bus voltage stable when the photovoltaic array input voltage is higher than the DC bus, and has a simple structure and low cost.

Description

Technical Field

[0001] The invention relates to the field of photovoltaic power generation, and in particular to a direct current converter topology circuit and a control method thereof, and an inverter system. Background Art

[0002] With the development of new energy technology, inverters, as key power equipment, are increasingly used in photovoltaic power generation projects. Figure 1 It is a common inverter system topology, consisting of a photovoltaic array, DC / DC, bus capacitor C1, DC / AC and a power grid, which can feed back photovoltaic power generation to the power grid or AC load. However, since photovoltaic modules are easily affected by light, temperature and external obstructions, the open circuit voltage of photovoltaics will fluctuate within a certain range. In order to maximize the efficiency of photovoltaic power generation, combined with the PV curve of photovoltaic power generation, a DC / DC converter is generally used for maximum power point tracking (MPPT). Its general topology is as follows: Figure 2 As shown, this topology belongs to a Boost circuit, which works when the photovoltaic open-circuit voltage is lower than the DC bus voltage. However, when the photovoltaic open-circuit voltage is greater than the DC bus voltage, only the inductor and diode D1 work in this circuit, resulting in large losses.

[0003] The current improved topology is as follows Figure 3 As shown, the inductor L and the diode D1 can be bypassed to reduce the loss of the DC / DC converter and improve the DC / DC efficiency.

[0004] In the above two existing DC / DC converter solutions, when the photovoltaic input open-circuit voltage is greater than the DC bus voltage, the photovoltaic array and the DC bus are directly connected, and the photovoltaic array charges the DC bus capacitor, so the photovoltaic DC bus voltage will increase synchronously. In this state, the DC / DC cannot perform maximum power point tracking (MPPT) of the photovoltaic input. In addition, in the photovoltaic (volt) storage air conditioning system, there are usually multiple DC loads, energy storage or air conditioning equipment connected to the DC bus, requiring the DC bus voltage to remain relatively stable. Excessive bus voltage fluctuations can easily cause system instability or failure.

[0005] Therefore, how to design a DC converter topology circuit and its control method and inverter system that can still maintain bus voltage stability when the photovoltaic array input voltage is high is a technical problem that the industry urgently needs to solve. Summary of the invention

[0006] In view of the technical problem in the prior art that when the photovoltaic input voltage is greater than the bus voltage, the photovoltaic array will charge the DC bus capacitor to increase the bus voltage, which may cause system instability or failure, the present invention proposes a DC converter topology circuit and a control method thereof, and an inverter system.

[0007] The technical solution of the present invention is to propose a DC converter topology circuit, including a working circuit connected to both ends of a photovoltaic array, wherein the working circuit has a Boost working mode and a Buck working mode;

[0008] When the input voltage of the photovoltaic array is less than or equal to the DC bus voltage, the working circuit enters the Boost working mode to increase the input voltage;

[0009] When the input voltage of the photovoltaic array is greater than the DC bus voltage, the working circuit enters the Buck mode to reduce the input voltage.

[0010] Furthermore, the working circuit includes: a switch S1, a switch S2, a switch S3, an inductor L1, an inductor L2, a capacitor C1, a diode D0 and a switch tube S4, and a diode D4 disposed on the switch tube S4;

[0011] One end of the switch S1 is connected to the output end of the photovoltaic array, the other end of the switch S1 is connected to one end of the switch S3, the other end of the switch S3 is connected to the positive electrode of the diode D0, the negative electrode of the diode D0 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is connected to the input end of the photovoltaic array;

[0012] One end of the switch S2 is connected between the switch S1 and the output end of the photovoltaic array, the other end of the switch S2 is connected to one end of the inductor L1, the other end of the inductor L1 is connected between the switch S1 and the switch S2, one end of the inductor L2 is connected between the switch S1 and the switch S3, and the other end of the inductor L2 is connected between the cathode of the diode D0 and the capacitor C1;

[0013] A first end of the switch tube S4 is connected between the switch S1 and the switch S3 , and a second end of the switch tube S4 is connected between the capacitor C1 and the input end of the photovoltaic array.

[0014] Further, when the switch S1 is opened, the switches S2 and S3 are closed, and the switch tube S4 is in the high-frequency switching state, the working circuit enters the Boost working state.

[0015] Further, when the switch S1 is in the high-frequency switching state, the switches S2 and S3 are disconnected, and the switch tube S4 is turned off, the working circuit enters the Buck working mode.

[0016] Further, the working circuit includes: a switch tube S1, a switch tube S2, a switch tube S3, a switch tube S4, a diode D1 provided on the switch tube S1, a diode D2 provided on the switch tube S2, a diode D3 provided on the switch tube S3, a diode D4 provided on the switch tube S4, a diode D0, an inductor L1, an inductor L2, and a capacitor C1;

[0017] The first end of the switch tube S1 is connected to the output end of the photovoltaic array, the second end of the switch tube S1 is connected to the first end of the switch tube S3, the second end of the switch tube S3 is connected to the positive electrode of the diode D0, the negative electrode of the diode D0 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is connected to the input end of the photovoltaic array;

[0018] The first end of the switch tube S2 is connected between the first end of the switch tube S1 and the output end of the photovoltaic array, the second end of the switch tube S2 is connected to one end of the inductor L1, and the other end of the inductor L1 is connected between the second end of the switch tube S1 and the first end of the switch tube S3;

[0019] One end of the inductor L2 is connected between the second end of the switch tube S1 and the first end of the switch tube S3, and the other end is connected between the cathode of the diode D0 and the capacitor C1;

[0020] The first end of the switch tube S4 is connected between the second end of the switch tube S1 and the first end of the switch tube S3 , and the other end is connected between the input end of the photovoltaic array and the capacitor C1 .

[0021] Further, when the switch tube S1 is turned off, the switch tubes S2 and S3 are turned on, and the switch tube S4 is in a high-frequency switching state, the working circuit enters the Boost working mode.

[0022] Furthermore, when the switch tube S1 is in the high-frequency switching state and the switch tubes S2, S3 and S4 are turned off, the working circuit enters the Buck working mode.

[0023] Furthermore, it also includes a detection unit, which is used to detect the photovoltaic input voltage in real time.

[0024] The present invention also proposes a control method for a DC converter topology circuit, comprising detecting an input voltage of the photovoltaic array, comparing the input voltage with a DC bus voltage, and if the input voltage is greater than or equal to the DC bus voltage, the DC converter topology circuit enters a Boost working mode;

[0025] If the input voltage is less than the DC bus voltage, the DC converter topology circuit enters the Buck working mode.

[0026] The present invention also proposes an inverter system, including a photovoltaic array, a DC converter connected to the photovoltaic array, a bidirectional converter connected to the DC converter, and a power grid connected to the bidirectional converter. It also includes a DC load and a bus capacitor connected to a DC bus, a compressor drive, and a motor connected to the compressor drive. The DC converter adopts the above-mentioned DC converter topology circuit.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects:

[0028] 1. The DC converter of the present invention has a simple topological circuit structure and low cost;

[0029] 2. The DC converter can keep the bus voltage stable when the input voltage of the photovoltaic array is higher than the DC bus.

[0030] 3. When the photovoltaic input voltage is within the system's tolerable voltage range, the DC converter can operate in step-up / step-down mode within the full voltage range. By adjusting the photovoltaic input voltage for MPPT optimization, the photovoltaic input can be operated at the maximum power point to the maximum extent, thereby improving the efficiency of the DC converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 It is a topological diagram of an inverter system in the prior art;

[0033] Figure 2 It is a topological circuit diagram of a DC converter in the prior art;

[0034] Figure 3 It is a topological circuit diagram of a DC converter improved in the prior art;

[0035] Figure 4 This is a topological circuit diagram of a DC converter according to a first embodiment of the present invention;

[0036] Figure 5 This is a topological circuit diagram of a DC converter according to a second embodiment of the present invention;

[0037] Figure 6 This is a control logic diagram of the DC converter operating mode of the present invention;

[0038] Figure 7 This is a topological diagram of the improved inverter system of the present invention. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] Thus, a feature indicated in this specification will be used to illustrate one of the features of an embodiment of the present invention, rather than implying that each embodiment of the present invention must have the described feature. In addition, it should be noted that this specification describes many features. Although some features can be combined together to illustrate possible system designs, these features can also be used in other combinations that are not explicitly described. Thus, unless otherwise stated, the described combinations are not intended to be limiting.

[0041] The principle and structure of the present invention are described in detail below with reference to the accompanying drawings and embodiments.

[0042] The present invention proposes a DC converter topology circuit, which includes a working circuit connected at both ends of a photovoltaic array. The working circuit has two working modes: a Boost working mode and a Buck working mode. When the input voltage of the photovoltaic array is less than or equal to the DC bus voltage, the working circuit enters the Boost working mode to increase the input voltage of the photovoltaic array. When the input voltage of the photovoltaic array is greater than the DC bus voltage, the working circuit enters the Buck working mode to reduce the input voltage of the photovoltaic array.

[0043] For details, please refer to Figure 4 A topological circuit diagram of a DC converter according to a first embodiment of the present invention includes a switch S1, a switch S2, a switch S3, an inductor L1, an inductor L2, a capacitor C1, a diode D0, a switch tube S4, and a diode D4 disposed on the switch tube S4;

[0044] One end of the switch S1 is connected to the output end of the photovoltaic array, the other end of the switch S1 is connected to one end of the switch S3, the other end of the switch S3 is connected to the positive electrode of the diode D0, the negative electrode of the diode D0 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is connected to the input end of the photovoltaic array;

[0045] One end of the switch S2 is connected between the switch S1 and the output end of the photovoltaic array, the other end of the switch S2 is connected to one end of the inductor L1, the other end of the inductor L1 is connected between the switch S1 and the switch S2, one end of the inductor L2 is connected between the switch S1 and the switch S3, and the other end of the inductor L2 is connected between the cathode of the diode D0 and the capacitor C1;

[0046] A first end of the switch tube S4 is connected between the switch S1 and the switch S3 , and a second end of the switch tube S4 is connected between the capacitor C1 and the input end of the photovoltaic array.

[0047] Among them, when switch S1 is disconnected, switch S2 and switch S3 are closed, and switch tube S4 is in a high-frequency switching state, the working circuit enters the Boost working mode. Specifically, when switch tube S4 is turned on, the current flows out from the output end of the photovoltaic array and returns to the input end of the photovoltaic array through switch S2, inductor L1, and switch tube S4. At this time, the photovoltaic array charges the inductor L1. When switch tube S4 is disconnected, the current flows out from the output end of the photovoltaic array and returns to the input end of the photovoltaic array through switch S2, inductor L1, switch S3, diode D0, and capacitor C1. At this time, the inductor L1 is discharged, and the electric energy is transferred from the inductor L1 to the capacitor C1. When the circuit is stable, the charging and discharging of the inductor L1 are balanced. Assuming that the voltage across the photovoltaic array is E, the on and off time of switch tube S4 in one cycle are ton and toff respectively, then the output voltage Uo=E*(ton+toff) / ton. Since the output voltage is higher than the input voltage, the Boost circuit is a boost circuit. Furthermore, since the input voltage in the photovoltaic array will change with the output voltage, the input voltage is increased.

[0048] When switch S1 is in high-frequency switching state, switch S2 and switch S3 are disconnected, and switch tube S4 is cut off, the working circuit enters the Buck working mode. Specifically, when switch S1 is turned on, the current flows from the positive end of the photovoltaic array through switch S1, inductor L2, and capacitor C1 back to the negative end of the photovoltaic array. At this time, it is equivalent to the circuit magnetizing the inductor L2 and storing energy in the inductor L2; when switch S1 is turned off, the photovoltaic array and the inductor L2 are disconnected, the inductor L2 releases magnetic energy, and the current flows through the inductor L2, capacitor C1, and diode D4 back to the inductor L2, which is equivalent to the energy transfer from the inductor L2 to the capacitor C1. When the circuit is stable, the magnetization and demagnetization of the inductor L2 are balanced. Assuming that the voltage across the photovoltaic array is E, the on and off time of the switch tube S4 in one cycle are ton and toff respectively, then the output voltage Uo=E*ton / (ton+toff). Because the output voltage is lower than the input voltage, the Buck circuit is a step-down circuit. Since the input voltage in the photovoltaic array will change with the output voltage, the input voltage is reduced.

[0049] Please refer to Figure 5 The topological circuit diagram of the DC converter of the second embodiment of the present invention includes: a switch tube S1, a switch tube S2, a switch tube S3, a switch tube S4, a diode D1 disposed on the switch tube S1, a diode D2 disposed on the switch tube S2, a diode D3 disposed on the switch tube S3, a diode D4 disposed on the switch tube S4, a diode D0, an inductor L1, an inductor L2, and a capacitor C1;

[0050] The first end of the switch tube S1 is connected to the output end of the photovoltaic array, the second end of the switch tube S1 is connected to the first end of the switch tube S3, the second end of the switch tube S3 is connected to the positive electrode of the diode D0, the negative electrode of the diode D0 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is connected to the input end of the photovoltaic array;

[0051] The first end of the switch tube S2 is connected between the first end of the switch tube S1 and the output end of the photovoltaic array, the second end of the switch tube S2 is connected to one end of the inductor L1, and the other end of the inductor L1 is connected between the second end of the switch tube S1 and the first end of the switch tube S3;

[0052] One end of the inductor L2 is connected between the second end of the switch tube S1 and the first end of the switch tube S3, and the other end is connected between the cathode of the diode D0 and the capacitor C1;

[0053] The first end of the switch tube S4 is connected between the second end of the switch tube S1 and the first end of the switch tube S3 , and the other end is connected between the input end of the photovoltaic array and the capacitor C1 .

[0054] Among them, when the switch tube S1 is turned off, the switch tubes S2 and S3 are turned on, and the switch tube S4 is in a high-frequency switching state, the working circuit enters the Boost working mode, and its working principle is the same as the Boost working mode in the first embodiment of the present invention, which will not be repeated here.

[0055] When the switch tube S1 is in the high-frequency switching state and the switch tubes S2, S3 and S4 are turned off, the working circuit enters the Buck working mode, and its working principle is the same as the Buck working mode in the first embodiment of the present invention, which will not be described in detail here.

[0056] The DC converter topology circuit of the present invention further includes a detection unit, which is used to detect the working voltage of the photovoltaic array in real time.

[0057] The present invention also proposes a control method for a DC converter topology circuit, please refer to Figure 6 , which includes:

[0058] Detecting the input voltage of the photovoltaic array, comparing the input voltage with the DC bus voltage, and if the input voltage is greater than or equal to the DC bus voltage, the DC converter topology circuit enters a Boost working mode;

[0059] If the input voltage is less than the DC bus voltage, the DC converter topology circuit enters the Buck working mode.

[0060] Please refer to Figure 7The present invention also proposes an inverter system, which includes a photovoltaic array, a DC converter connected to the photovoltaic array, a bidirectional converter connected to the DC converter, and a power grid connected to the bidirectional converter, and also includes a DC load and a bus capacitor connected to the DC bus, a compressor drive, and a motor connected to the compressor drive, wherein the DC converter adopts the above-mentioned DC converter topology circuit.

[0061] Compared with the prior art, the present invention realizes control through switches and light-opening tubes, has a simple structure, low cost, and can make the DC converter still keep the bus voltage stable when the photovoltaic array input voltage is higher than the DC bus. And when the photovoltaic input voltage is within the system's tolerable voltage range, the DC converter can operate in the step-up / step-down mode within the full voltage range, and adjust the photovoltaic input voltage to perform MPPT optimization, which can maximize the photovoltaic input operation at the maximum power point and improve the efficiency of the DC converter.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A DC converter topology circuit, comprising a working circuit connected at both ends of a photovoltaic array, characterized in that: The working circuit has a Boost working mode and a Buck working mode; When the input voltage of the photovoltaic array is less than or equal to the DC bus voltage, the working circuit enters the Boost working mode to increase the input voltage; When the input voltage of the photovoltaic array is greater than the DC bus voltage, the working circuit enters the Buck mode to reduce the input voltage; The working circuit includes: a switch S1, a switch S2, a switch S3, an inductor L1, an inductor L2, a capacitor C1, a diode D0 and a switch tube S4, and a diode D4 arranged on the switch tube S4; One end of the switch S1 is connected to the output end of the photovoltaic array, the other end of the switch S1 is connected to one end of the switch S3, the other end of the switch S3 is connected to the positive electrode of the diode D0, the negative electrode of the diode D0 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is connected to the input end of the photovoltaic array; One end of the switch S2 is connected between the switch S1 and the output end of the photovoltaic array, the other end of the switch S2 is connected to one end of the inductor L1, the other end of the inductor L1 is connected between the switch S1 and the switch S2, one end of the inductor L2 is connected between the switch S1 and the switch S3, and the other end of the inductor L2 is connected between the cathode of the diode D0 and the capacitor C1; A first end of the switch tube S4 is connected between the switch S1 and the switch S3 , and a second end of the switch tube S4 is connected between the capacitor C1 and the input end of the photovoltaic array.

2. The DC converter topology circuit according to claim 1, characterized in that: When the switch S1 is opened, the switches S2 and S3 are closed, and the switch tube S4 is in a high-frequency switching state, the working circuit enters the Boost working mode.

3. The DC converter topology circuit according to claim 1, characterized in that: When the switch S1 is in the high-frequency switching state, the switches S2 and S3 are disconnected, and the switch tube S4 is turned off, the working circuit enters the Buck working mode.

4. The DC converter topology circuit according to claim 1, characterized in that: The working circuit includes: a switch tube S1, a switch tube S2, a switch tube S3, a switch tube S4, a diode D1 provided on the switch tube S1, a diode D2 provided on the switch tube S2, a diode D3 provided on the switch tube S3, a diode D4 provided on the switch tube S4, a diode D0, an inductor L1, an inductor L2, and a capacitor C1; The first end of the switch tube S1 is connected to the output end of the photovoltaic array, the second end of the switch tube S1 is connected to the first end of the switch tube S3, the second end of the switch tube S3 is connected to the positive electrode of the diode D0, the negative electrode of the diode D0 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is connected to the input end of the photovoltaic array; The first end of the switch tube S2 is connected between the first end of the switch tube S1 and the output end of the photovoltaic array, the second end of the switch tube S2 is connected to one end of the inductor L1, and the other end of the inductor L1 is connected between the second end of the switch tube S1 and the first end of the switch tube S3; One end of the inductor L2 is connected between the second end of the switch tube S1 and the first end of the switch tube S3, and the other end is connected between the cathode of the diode D0 and the capacitor C1; The first end of the switch tube S4 is connected between the second end of the switch tube S1 and the first end of the switch tube S3 , and the other end is connected between the input end of the photovoltaic array and the capacitor C1 .

5. The DC converter topology circuit according to claim 4, characterized in that: When the switch tube S1 is turned off, the switch tubes S2 and S3 are turned on, and the switch tube S4 is in a high-frequency switching state, the working circuit enters the Boost working mode.

6. The DC converter topology circuit according to claim 4, characterized in that: When the switch tube S1 is in the high-frequency switching state, and the switch tubes S2, S3, and S4 are turned off, the working circuit enters the Buck working mode.

7. The DC converter topology circuit according to claim 1, characterized in that: It also includes a detection unit, which is used to detect the photovoltaic input voltage in real time.

8. A control method for a DC converter topology circuit, wherein the DC converter topology circuit adopts the DC converter topology circuit according to any one of claims 1 to 7, characterized in that: The control method comprises: Detecting the input voltage of the photovoltaic array, comparing the input voltage with the DC bus voltage, and if the input voltage is less than or equal to the DC bus voltage, the DC converter topology circuit enters a Boost working mode; If the input voltage is greater than the DC bus voltage, the DC converter topology circuit enters the Buck operating mode.

9. An inverter system, comprising a photovoltaic array, a DC converter connected to the photovoltaic array, a bidirectional converter connected to the DC converter, and a power grid connected to the bidirectional converter, and also comprising a DC load and a bus capacitor connected to a DC bus, and a compressor drive, and a motor connected to the compressor drive, characterized in that: The DC converter adopts the DC converter topology circuit as claimed in any one of claims 1 to 7.

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