A voltage transformer for DC-resistant photovoltaic power generation

Abstract

The present invention discloses a voltage transformer for anti-DC photovoltaic power generation, which belongs to the field of electrical measurement technology. It includes a closed-loop iron core T, a primary coil N1, a DC current detection module SC1, a conversion control module, a relay switch module SC2 and a current limiting resistor R b The DC current detection module SC1 detects the DC component flowing through the sampling resistor R0 and inputs it to the conversion control module. The conversion control module controls the on and off of the normally closed relay J according to the DC component of the sampling resistor R0 to control the primary coil N1 and the current limiting resistor R b Whether connected in series. The present invention controls the switching of the series current limiting resistor on the primary coil according to the magnitude of the DC current component of the primary coil, ensuring that the voltage transformer operates in the non-saturated region within the maximum allowable DC voltage bias rate range, avoiding the saturation or even burning problem of the traditional electromagnetic voltage transformer under DC bias conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical measurement, and in particular relates to a voltage transformer for direct current photovoltaic power generation. Background Art

[0002] The voltage transformer for photovoltaic power generation is used to monitor the output voltage of the photovoltaic inverter. Traditional voltage transformers have the characteristics of high accuracy, strong load adaptability, safe and reliable use, and are widely used in AC power supply systems. In theory, photovoltaic inverters only output AC power, but due to the asymmetric on and off time of the power switch tube of the inverter circuit, unbalanced pulse width during PWM modulation, mismatched drive signals, and grid-connected detection errors, the output voltage of the photovoltaic inverter will have a DC component, that is, the output voltage has a DC bias phenomenon.

[0003] Traditional electromagnetic voltage transformers cannot convert DC voltage signals, so the DC bias voltage directly generates a DC bias current in the primary coil of the voltage transformer, which leads to saturation or even burning of the voltage transformer core. Some voltage transformers improve their anti-saturation capability by adding air gaps to the core, or reduce the magnetic saturation caused by the DC component by reducing the working magnetic flux density, but these methods have limited ability to resist DC saturation. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a voltage transformer for DC resistant photovoltaic power generation, which controls the switching of the series current limiting resistor on the primary coil according to the size of the DC current component of the primary coil, thereby avoiding the saturation or even burning problem that is prone to occur in traditional electromagnetic voltage transformers under DC bias conditions.

[0005] The present invention provides the following technical solutions:

[0006] A voltage transformer for anti-DC photovoltaic power generation, comprising a closed-loop iron core T, a primary coil , DC current detection module , conversion control module, relay switch module and current limiting resistor The primary coil Wound on the closed-loop core T, the primary coil The same-name end of the current limiting resistor is electrically connected to , the non-identical terminals are electrically connected to the DC current detection module ; The DC current detection module , conversion control module and relay switch module The DC current detection module is electrically connected in sequence; Including sampling resistor , sampling resistor Connecting the primary coil , the relay switch module It includes a normally closed relay J, an output terminal of the normally closed relay J and a current limiting resistor In parallel; the DC current detection module Detect the current flowing through the sampling resistor The DC component is input to the conversion control module, which uses the sampling resistor The DC component controls the on and off of the normally closed relay J to control the primary coil With current limiting resistor Whether to connect in series.

[0007] As an optional technical solution of the present invention, the DC current detection module Also includes a first diode , the second diode , Voltage Follower , a first low-pass filter and a second low-pass filter; the first diode and the second diode connected in reverse parallel and together with the sampling resistor Parallel; sampling resistor One end is connected to the ground, and the other end is connected to the primary coil The non-same-name terminal and voltage follower The input terminal is connected to the primary coil The current flows through the sampling resistor Generate a sampling voltage; the voltage follower , a first low-pass filter and a second low-pass filter are connected in sequence; the first low-pass filter includes a first operational amplifier , the second low pass filter includes a second operational amplifier ; The first operational amplifier and the second operational amplifier Both are used to amplify the DC component in the sampled voltage to obtain the sampling resistance The DC component signal.

[0008] As an optional technical solution of the present invention, the conversion control module includes an analog-to-digital converter connected and microprocessor ; The analog-to-digital converter The input end is connected to the output end of the second low-pass filter to convert the sampling resistor The DC component is converted into a digital signal and input into the microprocessor The microprocessor The output end of the relay switch module is connected , used to calculate the primary coil according to the digital signal The DC current component value of the primary coil The DC current component value controls the on and off of the normally closed relay J.

[0009] As an optional technical solution of the present invention, the primary coil is obtained by calculating the digital signal The DC current component value of the primary coil The DC current component value controls the on and off of the normally closed relay J, including:

[0010] Calculate a coil The DC current component value is expressed as:

[0011] ;

[0012] in, Indicates the primary coil The DC current component value, Indicates sampling resistance The DC component value of Indicates gain;

[0013] The primary coil The DC current component value With preset limit For comparison, if , then the normally closed relay J is conducted, the current limiting resistor is short-circuited; if , the normally closed relay J is cut off and maintained for the preset time , current limiting resistor With primary coil Series, elapsed time Then proceed to the next round of coil The DC current component value Calculation of measurements.

[0014] As an optional technical solution of the present invention, the current limiting resistor When short-circuited, the voltage transformer has an accuracy of 0.2; when the current limiting resistor With primary coil When connected in series, the accuracy of the voltage transformer is Class 1 or Class 2.

[0015] As an optional technical solution of the present invention, the preset limit Use 2 / 3 of the maximum DC deviation current of the voltage transformer;

[0016] The current limiting resistor in the voltage transformer The resistance values ​​used are expressed as:

[0017] ;

[0018] in, Indicates the maximum DC voltage bias rate of the voltage transformer, Indicates the rated primary voltage of the voltage transformer. Indicates the maximum DC deviation current of the voltage transformer, Indicates the resistance of the primary coil.

[0019] As an optional technical solution of the present invention, the relay switch module It also includes a photoelectric isolation drive circuit and a relay control circuit; the photoelectric isolation drive circuit is used to connect the current limiting resistor and normally closed relay J and DC current detection module , the conversion control module is isolated; the relay control circuit is used to control the on and off of the normally closed relay J; the microprocessor The output end is connected to the photoelectric isolation drive circuit.

[0020] As an optional technical solution of the present invention, it also includes a power module And the secondary coil wound on the closed-loop iron core T , positive and negative dual power supply coil and single supply coil ; The power module Including positive and negative dual power supply and single power supply, positive and negative dual power supply coil Connect positive and negative dual power supplies, single power supply coil Connect a single power supply to power the positive and negative dual power supplies and single power supply respectively.

[0021] As an optional technical solution of the present invention, the output ends of the positive and negative dual power supplies are respectively connected to the DC current detection module , conversion control module and relay switch module , used for DC current detection module , conversion control module and relay switch module Power supply; the output end of the single power supply is connected to the relay switch module , used for relay switch modules powered by.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The voltage transformer for DC-resistant photovoltaic power generation provided by the present invention controls the switching of the series current-limiting resistor on the primary coil by measuring the DC current component of the primary coil, thereby ensuring that the voltage transformer operates in a non-saturated region within the range of the maximum allowable DC bias rate, avoiding the saturation or even burning problem that is prone to occur in traditional electromagnetic voltage transformers under DC bias conditions, and has DC-resistant capability within a preset DC bias rate range, and is suitable for measuring the output voltage of a photovoltaic inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of a voltage transformer for DC-resistant photovoltaic power generation in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0026] Example 1

[0027] This embodiment provides a voltage transformer for DC-resistant photovoltaic power generation, such as Figure 1 As shown, it includes a closed-loop iron core T, a DC current detection module , conversion control module, relay switch module , Current limiting resistor , Power Module And a primary coil wound on the closed-loop iron core T , Secondary coil , positive and negative dual power supply coil and single supply coil .

[0028] The primary coil Wound on the closed-loop core T, the primary coil The same-name end of the current limiting resistor is electrically connected to The non-same-name end is electrically connected to the DC current detection module In this embodiment, the current limiting resistor The other end and the ground constitute the primary voltage input port of the voltage transformer for DC photovoltaic power generation.

[0029] The DC current detection module , conversion control module and relay switch module The DC current detection module is electrically connected in sequence; Including sampling resistor , sampling resistor Connecting the primary coil , the relay switch module It includes a normally closed relay J, an output terminal of the normally closed relay J and a current limiting resistor in parallel.

[0030] The DC current detection module Detect the current flowing through the sampling resistor The DC component is input to the conversion control module, which uses the sampling resistor The DC component controls the on and off of the normally closed relay J to control the primary coil With current limiting resistor Whether to connect in series.

[0031] The DC current detection module Also includes a first diode , the second diode , Voltage Follower , a first low pass filter and a second low pass filter. The first diode and the second diode connected in reverse parallel and together with the sampling resistor Parallel; sampling resistor One end is connected to the ground, and the other end is connected to the primary coil The non-same-name terminal and voltage follower The input terminal is connected to the primary coil The current flows through the sampling resistor Generates a sampling voltage. The voltage follower , a first low-pass filter and a second low-pass filter are connected in sequence; the first low-pass filter includes a first operational amplifier , the first resistor , the second resistor , the third resistor , the first capacitor and the second capacitor , the second low pass filter includes a second operational amplifier , the fourth resistor , the fifth resistor , the sixth resistor , the third capacitor and the fourth capacitor ; The first operational amplifier and the second operational amplifier Both are used to amplify the DC component in the sampled voltage to obtain the sampling resistance The DC component signal.

[0032] The conversion control module includes an analog-to-digital converter connected and microprocessor The analog-to-digital converter The input end is connected to the output end of the second low-pass filter to convert the sampling resistor The DC component is converted into a digital signal and input into the microprocessor The microprocessor The output end of the relay switch module is connected , used to calculate the primary coil according to the digital signal The DC current component value of the primary coil The DC current component value controls the on and off of the normally closed relay J.

[0033] The relay switch module It also includes a photoelectric isolation drive circuit and a relay control circuit. The photoelectric isolation drive circuit includes a photoelectric isolator , the seventh resistor and the eighth resistor , used to change the current limiting resistor and normally closed relay J and DC current detection module , the conversion control module is isolated; the relay control circuit includes a transistor 、Diode No. 3 、Ninth resistor 、10th resistor and the eleventh resistor , used to control the on and off of the normally closed relay J; the microprocessor The output end of the microprocessor is connected to a photoelectric isolation resistor. of The pin is connected to the opto-isolating resistor.

[0034] The power module Including positive and negative dual power supply and single power supply, positive and negative dual power supply coil Connect positive and negative dual power supplies, single power supply coil Connect a single power supply to supply power to the positive and negative dual power supplies and the single power supply. The positive and negative dual power supplies include a first rectifier , the fifth capacitor 、The sixth capacitor , Seventh capacitor , the first three-terminal regulator and the second three-terminal regulator , a single power supply includes a second rectifier 、Eighth capacitor and the third three-terminal regulator .

[0035] The output ends of the positive and negative dual power supplies are respectively connected to the DC current detection modules , conversion control module and relay switch module , used for DC current detection module , conversion control module and relay switch module The output end of the single power supply is connected to the relay switch module , used for relay switch modules The voltage transformer adopts the self-powered solution of electronic circuit, which avoids the problem of voltage sensors such as Hall sensors requiring auxiliary power supply, and facilitates the on-site installation and use of the voltage transformer. Specifically, the positive and negative dual power supply has , peacefully Three outputs, single supply with and suspended ground Two output terminals, the positive and negative dual power supply , peacefully The three output terminals are respectively connected to the DC current detection module Voltage Follower in , the first operational amplifier , the second operational amplifier Power supply and relay switch module Photoelectric isolation drive circuit in the conversion control module, analog-to-digital converter and microprocessor power supply, the single power supply and suspended ground Two output terminals for relay switch module The coil of the normally closed relay J in the circuit is powered.

[0036] Working principle:

[0037] Voltage transformer primary coil The current flows through the sampling resistor , generating a sampling voltage. When the sampling voltage increases, the first diode is connected in parallel , the second diode Plays a clamping role, limiting the voltage follower Below this clamping voltage, the first low-pass filter and the second low-pass filter are clamped at a certain gain. Amplify the DC component in the sampled voltage , and the DC component in the sampled voltage Input ADC , after the input analog-to-digital converter After being converted into digital signals, they are input into the microprocessor , can quickly determine the status of the DC current component of the primary coil, avoiding long-term overcurrent and heating of the voltage transformer. Microprocessor Calculate a coil The DC current component value is expressed as:

[0038] ;

[0039] in, Indicates the primary coil The DC current component value, Represents sampling resistance The DC component value of Indicates gain.

[0040] The primary coil The DC current component value With preset limit For comparison, if , then the normally closed relay J is conducted, the current limiting resistor is short-circuited; if , the normally closed relay J is cut off and maintained for the preset time , current limiting resistor With primary coil Series, elapsed time Then proceed to the next round of coil The DC current component value Calculation of measurements.

[0041] In this embodiment, the current limiting resistor When short-circuited, the voltage transformer has an accuracy of 0.2; when the current limiting resistor With primary coil When connected in series, the accuracy of the voltage transformer is Class 1 or Class 2.

[0042] In this embodiment, the preset limit value of the primary coil DC current component, the current limiting resistor value, and the holding time of the current limiting resistor switching can be adjusted in advance to improve the versatility of the voltage transformer. (DC bias voltage and voltage transformer rated primary voltage ratio) is not greater than 0.15% and the primary coil No series current limiting resistor Under the condition of , the voltage transformer is designed to operate in the non-saturated region. =0.15%, primary coil The DC bias current flowing is the maximum DC bias current , preset limit Use 2 / 3 of the maximum DC deviation current of the voltage transformer.

[0043] The current limiting resistor in the voltage transformer The resistance values ​​used are expressed as:

[0044] ;

[0045] in, Indicates the maximum DC voltage bias rate of the voltage transformer, Indicates the rated primary voltage of the voltage transformer. Indicates the maximum DC deviation current of the voltage transformer, Indicates the resistance of the primary coil.

[0046] Example 2

[0047] This embodiment provides an implementation of a voltage transformer based on Embodiment 1.

[0048] In this embodiment, the rated primary voltage of the voltage transformer is , rated secondary voltage is , rated frequency is 50Hz, rated load is 10VA. When the DC current component of the primary coil is less than or equal to the preset limit When the DC current component of the primary coil is greater than the preset limit, the accuracy level is 0.2. When the accuracy level is 2, the maximum DC voltage bias rate of the voltage transformer is 1%, the closed-loop core T section is 20 , primary coil The number of turns is 1400, and the secondary coil The number of turns is 175 turns, the positive and negative dual power supply coil The number of turns is 50 turns, single power supply coil The number of turns is 25. The voltage transformer has a DC voltage bias rate 0.15% and the primary coil is not connected with a current limiting resistor The maximum DC bias current allowed 0.02A, preset limit for . Positive and negative dual power supply output +5V and -5V voltage, single power supply output +5V voltage. Current limiting resistor The resistance is 200 ohms, the temperature drift is no more than 100ppm / °C, and the effective value of the current that can flow is 0.1A. The resistance is 1 ohm, the temperature drift is no more than 10ppm / °C, and the effective value of the current that can flow is 0.5A. and the second diode Use Schottky diode with forward voltage drop of about 0.3V, voltage follower , the first operational amplifier and the second operational amplifier The OP07 operational amplifier is used. The first low-pass filter uses a low-pass filter with a gain of 10 and a cutoff frequency of 10Hz, and the second low-pass filter uses a low-pass filter with a gain of 1 and a cutoff frequency of nearly 10Hz. Microprocessor Adopt 8051 single chip microcomputer, normally closed relay Select a PCB direct-plug normally closed solid-state relay with a load current greater than 0.5A.

[0049] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0050] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0051] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A voltage transformer for DC-resistant photovoltaic power generation, characterized in that: Including closed-loop iron core T, primary coil , DC current detection module , conversion control module, relay switch module and current limiting resistor ; The primary coil Wound on the closed-loop core T, the primary coil The same-name end of the current limiting resistor is electrically connected to , the non-identical terminals are electrically connected to the DC current detection module ; The DC current detection module , conversion control module and relay switch module The DC current detection module is electrically connected in sequence; Including sampling resistor , sampling resistor Connecting the primary coil , the relay switch module It includes a normally closed relay J, an output terminal of the normally closed relay J and a current limiting resistor in parallel; The DC current detection module Detect the current flowing through the sampling resistor The DC component is input to the conversion control module, which uses the sampling resistor The DC component controls the on and off of the normally closed relay J to control the primary coil With current limiting resistor Whether to connect in series; The DC current detection module Also includes a first diode , the second diode , Voltage Follower , a first low-pass filter and a second low-pass filter; the first diode and the second diode connected in reverse parallel and together with the sampling resistor Parallel; sampling resistor One end is connected to the ground, and the other end is connected to the primary coil The non-same-name terminal and voltage follower The input terminal is connected to the primary coil The current flows through the sampling resistor Generate a sampling voltage; the voltage follower , a first low-pass filter and a second low-pass filter are connected in sequence; The conversion control module includes an analog-to-digital converter connected and microprocessor ; The analog-to-digital converter The input end is connected to the output end of the second low-pass filter to convert the sampling resistor The DC component is converted into a digital signal and input into the microprocessor The microprocessor The output end of the relay switch module is connected , used to calculate the primary coil according to the digital signal The DC current component value of the primary coil The DC current component value controls the on and off of the normally closed relay J.

2. The voltage transformer for anti-DC photovoltaic power generation according to claim 1, characterized in that: The first low-pass filter includes a first operational amplifier , the second low pass filter includes a second operational amplifier ; The first operational amplifier and the second operational amplifier Both are used to amplify the DC component in the sampled voltage to obtain the sampling resistance The DC component signal.

3. The voltage transformer for anti-DC photovoltaic power generation according to claim 1, characterized in that: The primary coil is obtained by calculating the digital signal The DC current component value of the primary coil The DC current component value controls the on and off of the normally closed relay J, including: Calculate a coil The DC current component value is expressed as: ； in, Indicates the primary coil The DC current component value, Indicates sampling resistance The DC component value of Indicates gain; The primary coil The DC current component value With preset limit For comparison, if , then the normally closed relay J is conducted, the current limiting resistor is short-circuited; if , the normally closed relay J is cut off and maintained for the preset time , current limiting resistor With primary coil Series, elapsed time Then proceed to the next round of coil The DC current component value Calculation of measurements.

4. The voltage transformer for DC-resistant photovoltaic power generation according to claim 3, characterized in that: The current limiting resistor When short-circuited, the voltage transformer has an accuracy of 0.2; when the current limiting resistor With primary coil When connected in series, the accuracy of the voltage transformer is Class 1 or Class 2.

5. The voltage transformer for DC-resistant photovoltaic power generation according to claim 3, characterized in that: The preset limit Use 2 / 3 of the maximum DC deviation current of the voltage transformer; The current limiting resistor in the voltage transformer The resistance values ​​used are expressed as: ； in, Indicates the maximum DC voltage bias rate of the voltage transformer, Indicates the rated primary voltage of the voltage transformer. Indicates the maximum DC deviation current of the voltage transformer, Indicates the resistance of the primary coil.

6. The voltage transformer for DC-resistant photovoltaic power generation according to claim 1, characterized in that: The relay switch module It also includes a photoelectric isolation drive circuit and a relay control circuit; The photoelectric isolation driving circuit is used to connect the current limiting resistor and normally closed relay J and DC current detection module , the conversion control module is isolated; the relay control circuit is used to control the on and off of the normally closed relay J; The microprocessor The output end is connected to the photoelectric isolation drive circuit.

7. The voltage transformer for photovoltaic power generation with DC resistance according to claim 1, characterized in that: Also includes power module And the secondary coil wound on the closed-loop iron core T , positive and negative dual power supply coil and single supply coil ; The power module Including positive and negative dual power supply and single power supply, positive and negative dual power supply coil Connect positive and negative dual power supplies, single power supply coil Connect a single power supply to power the positive and negative dual power supplies and single power supply respectively.

8. The voltage transformer for DC-resistant photovoltaic power generation according to claim 7, characterized in that: The output ends of the positive and negative dual power supplies are respectively connected to the DC current detection modules , conversion control module and relay switch module , used for DC current detection module , conversion control module and relay switch module powered by; The output end of the single power supply is connected to the relay switch module , used for relay switch modules powered by.

Images