A method for detecting insulation of an AC port of an AC inverter

Abstract

The invention discloses an insulation detection method for an AC port of an AC inverter, which relates to the technical field of detection circuits and comprises an input circuit installed between an input line L and a neutral line N for input filtering, wherein the input circuit is connected with a control circuit for current detection control, the right side of the control circuit is connected with a main power conversion circuit, an IGBA circuit component input end is connected with the control circuit, and an IGBA circuit component output end is connected with a load module. The invention uses only a small amount of electronic components and some simple resistors to send signals to a CPU when performing insulation detection, and only needs to control the conduction of different IGBAs in different working states to complete the insulation detection function at any time. Compared with traditional insulation detection, the detection response time is greatly shortened, and the device cost is saved to a great extent, making the later maintenance easier.

Description

Technical Field

[0001] The invention relates to the technical field of detection circuits, and in particular to an insulation detection method for an AC port of an AC inverter. Background Art

[0002] With the rapid development of electric vehicle technology, energy storage technology, and photovoltaic technology, the inverter function of electric energy has become popular. On-board chargers are particularly important in the field of new energy electric vehicles, and electricity safety is an area that cannot be ignored. Insulation testing is to prevent electric shock to the human body when using inverter power supply. When the insulation resistance value is low, the high-voltage output is quickly cut off, which has a good protective effect on the safety of human electricity use.

[0003] Insulation resistance refers to the resistance value of the phase line or neutral line to the ground, such as Figure 7 RN and RP are shown in the figure. The reason for the reduction of insulation resistance is usually human contact or foreign matter. Foreign matter causes low insulation resistance. When the resistance is low, it may cause heating or even fire in a working environment where voltage is applied. At the same time, the insulation detection circuit on the current market usually uses an unbalanced bridge for insulation detection. Figure 8 This method requires two expensive high-voltage relays K2 and K3, and the detection reference ground needs to be at the PE (earth) end. The detection of the earth port also requires the signal to be transmitted to the CPU through isolation for control. The switching time of the high-voltage relay is relatively long, which will affect the speed of the entire detection process, especially when frequent detection is required. At the same time, the cost of the electronic devices of the entire detection circuit is high and the response time is long. Summary of the invention

[0004] The object of the present invention is to provide an insulation detection method for an AC port of an AC inverter, which can complete the insulation resistance detection function by using very few resistors and a common single-chip microcomputer sampling, so as to solve the problems raised in the above background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: an AC port insulation detection method for an AC inverter, comprising an input circuit installed between an input line L and a neutral line N for input filtering, the input circuit is connected to a control circuit for current detection control, the right side of the control circuit is connected to a main power conversion circuit, the main power conversion circuit comprises at least one group of IGBT circuit components, the input end of the IGBT circuit component is connected to the control circuit, the output end of the IGBT circuit component is connected to a load module, a capacitor C1 is arranged in the IGBT circuit component, the two ends of the capacitor C1 are respectively connected to the two ends of a filter capacitor CX2 in the input circuit, and the insulation resistance value is obtained by dividing the voltage across the capacitor C1 and the voltage across the filter capacitor CX2 through a voltage divider resistor RS installed in the control circuit.

[0006] Preferably, the IGBT circuit components are divided into two groups, the first group of IGBT circuit components includes IGBT Q1-Q6, and the second group of IGBT circuit components includes IGBT Q7-Q12, wherein the collectors of Q1, Q2, Q5 and Q6 are respectively connected to the positive end of the DC bus, the collectors of Q3, Q4, Q9 and Q10 are respectively connected to the emitters of Q1, Q2, Q5 and Q6, the emitters of Q3, Q4, Q9 and Q10 are all connected to the ground line, and a transformer T1 is arranged between Q6 and Q7, one end of the primary side of the transformer T1 is connected between Q6 and Q10, and the other end is connected between Q5 and Q9, and one end of the secondary side of the transformer TQ is connected between Q7 and Q11, and the other end is connected between Q8 and Q12.

[0007] Preferably, the capacitor C1 is installed between Q2 and Q5, one end of the capacitor C1 is connected to the DC bus, and the other end is connected to the ground line.

[0008] Preferably, the input circuit includes a common-mode choke LM1 and two filter capacitors CX1 and CX2, one end of the primary winding of the common-mode choke LM1 is connected to the input line L, and the other end is connected to the neutral line N, the secondary winding of the common-mode choke LM1 is respectively connected to both ends of the filter capacitor CX2, one end of the filter capacitor CX2 is connected between Q1 and Q3, and the other end is connected between Q2 and Q4.

[0009] Preferably, the control circuit includes an MCU and a UIB, a ground pin of the MCU is connected to the filter capacitor CX2, a current transformer L1A is connected between the ground pin of the MCU and Q1 and Q3, a current pin of the MCU is connected to an input line L, and the voltage-dividing resistor RS is connected in series, the voltage-dividing resistor RS is set to two, namely, a voltage-dividing resistor RS3 and a voltage-dividing resistor RS4, an analog input pin of the MCU is connected to the output end of the UIB, the input end of the UIB is connected to one end of the voltage-dividing resistor RS3, and is also connected to the common end of Q1 and the DC bus, and current-limiting resistors RS2 and RS1 are connected in series.

[0010] As a preferred embodiment, the specific steps of detecting the insulation resistance before starting are as follows: turn on Q3 and Q4, detect the voltage Vrs on the voltage divider resistor RS and the voltage Vc1 on the capacitor C1, and the resistance of the insulation resistor Rins is:

[0011] .

[0012] As a preferred embodiment, the specific steps of detecting the insulation resistance after starting are as follows:

[0013] MCU is used to control Q2 and Q4 to conduct alternately at the set frequency. The filter capacitor CX2 is an AC voltage with an average voltage of zero. Multiple sampling is performed to obtain the average voltage Vrs on the voltage divider resistor RS. During sampling, half of the time is full voltage and half of the time is zero voltage. After averaging, the voltage on the capacitor C1 is 0.5Vc1, so the resistance of the insulation resistor Rins is:

[0014] .

[0015] Preferably, the frequency of alternating conduction is set to 50 Hz-200 Hz, and is a multiple of 50 Hz.

[0016] Preferably, a relay K1 is connected between the current limiting resistor RS2 and RS1.

[0017] In summary, the beneficial effects of the present invention are:

[0018] The present invention uses only a small number of electronic components and some simple resistors to send signals to the CPU when performing insulation detection. At the same time, it only needs to control the conduction of different IGBTs under different working conditions to complete the insulation detection function at any time. Compared with traditional insulation detection, the detection response time is greatly shortened, and the device cost is saved to a great extent, making the later maintenance easier and the maintenance cost low. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, 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 invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 A schematic diagram of the structure of an input circuit and a control circuit of an AC port insulation detection method for an AC inverter according to the present invention;

[0021] Figure 2 A schematic diagram of the connection structure of a main power conversion circuit and a load module of an AC port insulation detection method for an AC inverter according to the present invention;

[0022] Figure 3 Schematic diagram of equivalent circuit structure of input circuit and control circuit in an AC port insulation detection method for an AC inverter of the present invention

[0023] Figure 4 It is a schematic diagram of an equivalent circuit structure when Q4 is turned on in an AC port insulation detection method for an AC inverter according to the present invention;

[0024] Figure 5 It is a schematic diagram of an equivalent circuit structure when Q3 is turned on in an AC port insulation detection method for an AC inverter according to the present invention;

[0025] Figure 6 It is a schematic diagram of an equivalent circuit structure of a post-operation detection of an AC port insulation detection method for an AC inverter according to the present invention;

[0026] Figure 7 A schematic diagram for explaining insulation resistance detection in an AC port insulation detection method for an AC inverter according to the present invention;

[0027] Figure 8 The present invention is a schematic diagram for explaining the prior art in an AC port insulation detection method for an AC inverter.

[0028] The symbols in the attached drawings are described as follows: 1. Input circuit; 2. Control circuit; 3. Main power conversion circuit; 4. Load module. DETAILED DESCRIPTION

[0029] The present invention will now be further described in detail in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. These drawings are all simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic way, and therefore they only show the structures related to the present invention.

[0030] To facilitate understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0031] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0032] Any feature disclosed in this specification (including any additional claims, abstract and drawings), unless otherwise stated, may be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0033] In the present invention, unless otherwise clearly defined and specified, the terms "installed", "connected", "connected", "fixed" and the like 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, a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of at least two elements or the interaction relationship between at least two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] Combine the following Figure 1-8 The present invention is described in detail with reference to Figure 1 and Figure 2 ,in Figure 1 and Figure 2 The two are combined into a general circuit diagram of an AC port insulation detection method for an AC inverter. An embodiment provided by the present invention includes an input circuit 1, a control circuit 2, a main power conversion circuit 3 and a load module 4;

[0035] The input circuit 1 includes two filter capacitors CX1 and CX2, a common mode choke LM1 is connected between the two filter capacitors, one end of the primary winding of the common mode choke LM1 is connected to the input line L, and the other end is connected to the neutral line N, and the secondary winding of the common mode choke LM1 is connected to both ends of the filter capacitor CX2, these components constitute an EMI (electromagnetic interference) filter for reducing noise and interference on the power line;

[0036] The control circuit 2 includes an MCU and a UIB, and a current transformer L1A, which is used to detect current and feed it back to the MCU for adjustment, wherein the MCU is a microcontroller unit responsible for the control and management of the entire system; U1B is an operational amplifier used for signal processing and amplification, and the ground pin of the MCU is connected to the filter capacitor CX2, and the current transformer L1A is connected between the ground pin of the MCU and Q1 and Q3, the current pin of the MCU is connected to the input line L, and two voltage-dividing resistors RS3 and RS4 are connected in series, the analog input pin of the MCU is connected to the output end of the UIB, the input end of the UIB is connected to one end of the voltage-dividing resistor RS3, and is also connected to a 400V DC bus, and current-limiting resistors RS2 and RS1 are connected in series, a relay K1 is connected between the current-limiting resistors RS2 and RS1, and the end is connected to the ground terminal to ensure the safety of the equipment.

[0037] The main power conversion circuit 3 includes two groups of IGBT circuit components, each group contains six IGBTs, the first group of IGBT circuit components includes IGBT Q1-Q6, the second group of IGBT circuit components includes IGBT Q7-Q12, and a transformer T1 is arranged between Q6 and Q7, these IGBTs are connected in a three-phase full-bridge manner, used to convert direct current into alternating current and output it to the primary side of the transformer T1, the secondary side of the transformer T1 has a rectifier bridge composed of four IGBTs, which converts the alternating current into direct current again, and the rectified direct current passes through another three-phase full-bridge inverter composed of IGBT Q7-Q12 to control the current to flow to the load module 4, this configuration allows the circuit to achieve bidirectional power flow, which can charge the battery from the power grid and supply power to the load from the battery;

[0038] The collectors of Q1, Q2, Q5 and Q6 are respectively connected to the positive end of the DC bus, the collectors of Q3, Q4, Q9 and Q10 are respectively connected to the emitters of Q1, Q2, Q5 and Q6, the emitters of Q3, Q4, Q9 and Q10 are all connected to the ground wire, one end of the primary side of the transformer T1 is connected between Q6 and Q10, and the other end is connected between Q5 and Q9, one end of the secondary side of the transformer TQ is connected between Q7 and Q11, and the other end is connected between Q8 and Q12, the capacitor C1 is installed between Q2 and Q5, one end of the capacitor C1 is connected to the DC bus, and the other end is connected to the ground wire, one end of the filter capacitor CX2 is connected between Q1 and Q3, and the other end is connected between Q2 and Q4;

[0039] When performing insulation testing, we only need to use the voltage on capacitor C1 and the voltage difference on capacitor CX2 to divide the resistance value through current limiting resistors RS1, RS2, and voltage divider resistors RS3, RS4, and combine the two voltage divider resistors into one voltage divider resistor RS, so the equivalent circuit is as follows: Figure 3 As shown;

[0040] If the insulation resistance is tested before starting:

[0041] Before starting, turn on Q3 and Q4, which is equivalent to short-circuiting CX2. The insulation resistance Rins = RN / / RP. As long as the voltage Vrs on the voltage divider resistor RS and the voltage Vc1 on the capacitor C1 are measured, the resistance value of Rins can be calculated. Since Vc1 is a known quantity in the circuit operation, the resistance of Rins is:

[0042] ;

[0043] If the insulation resistance is tested after startup:

[0044] After the work is detected, due to the voltage output after startup, Q2 and Q4 are controlled to conduct alternately at a certain frequency. Here, the frequency of 50hz is selected. The voltage on CX2 is an AC voltage, and the average voltage of the AC voltage is 0. The method of using multiple sampling to obtain the average value can be used to calculate the resistance value of the insulation resistance Rins in the same way;

[0045] On CX2 is a sine wave AC. The actual AD sampling frequency is 30khz, and a 50hz sine wave has a cycle of 20ms, so the upper half cycle when the voltage is positive is 10ms, and the lower half cycle when the voltage is negative is 10ms. The number of samples per half cycle is 30k*0.1s=3000 times;

[0046] When working at positive voltage (the voltage on the L line is greater than the N line), Q4 is turned on, and its equivalent circuit is as follows: Figure 4, since the inductor is a current source device, it is equivalent to an open circuit in circuit analysis, so the voltage value on the voltage divider resistor RS can be easily derived;

[0047] If it works at a negative voltage (the voltage on the L line is less than the N line), Q3 is turned on, and its equivalent circuit is as follows Figure 5 , the inductor is equivalent to the open circuit analysis, and the voltage value on the voltage divider resistor RS can be easily derived. Since the data is sampled up to 6,000 times in one AC cycle, if the 6,000 times are averaged, the average voltage on CX2 is 0, and the average voltage on the N line is 0.5Vc1. The total equivalent circuit diagram is as follows Figure 6 , since the average voltage of CX2 is 0, it is equivalent to a short-circuit state, so the resistance of the insulation resistor Rins is:

[0048] .

[0049] In summary, the present invention uses only a small number of electronic components and some simple resistors to send signals to the CPU during insulation detection. At the same time, it only needs to control the conduction of different IGBTs under different working conditions to complete the insulation detection function at any time. Compared with traditional insulation detection, the detection response time is greatly shortened, and the device cost is saved to a great extent, making the later maintenance easier and the maintenance cost low.

[0050] The above is only a specific implementation of the invention, but the protection scope of the invention is not limited to it. Any changes or substitutions that are not conceived through creative work should be included in the protection scope of the invention. Therefore, the protection scope of the invention should be based on the protection scope defined in the claims.

Claims

1. A method for detecting insulation of an AC port of an AC inverter, comprising an input circuit installed between an input line L and a neutral line N for input filtering, characterized in that: The input circuit is connected to a control circuit for current detection control, the right side of the control circuit is connected to a main power conversion circuit, the main power conversion circuit includes an IGBT circuit component, the input end of the IGBT circuit component is connected to the control circuit, the output end of the IGBT circuit component is connected to a load module, the IGBT circuit component includes a capacitor C1 and an IGBT Q1-Q6, wherein the collectors of Q1, Q2, Q5 and Q6 are respectively connected to the positive terminal of the DC bus, Q1 and Q3 are connected in series, Q2 and Q4 are connected in series, the capacitor C1 is installed between Q2 and Q5, one end of the capacitor C1 is connected to the positive terminal of the DC bus, and the other end is connected to the ground wire, the two ends of the capacitor C1 are respectively connected to the two ends of the filter capacitor CX2 in the input circuit, one end of the filter capacitor CX2 is connected between Q1 and Q3, and the other end is connected between Q2 and Q4, the input circuit includes a common mode choke LM1 and two filter capacitors CX1 and CX2, one end of the primary winding of the common mode choke LM1 is connected to the input line L, and the other end is connected to the neutral line N, the secondary winding of the common mode choke LM1 is respectively connected to the two ends of the filter capacitor CX2, the control circuit includes an MCU and an operational amplifier U1B, and the ground wire of the MCU leads The pin is connected to one end of the filter capacitor CX2, the current pin of the MCU is connected to the input line L, and a voltage-dividing resistor RS is connected in series. The voltage-dividing resistor RS is set to two, namely, voltage-dividing resistor RS3 and voltage-dividing resistor RS4. The analog input pin of the MCU is connected to the output end of the operational amplifier U1B, the inverting input end of the operational amplifier U1B is connected to the analog input pin of the MCU, and the non-inverting input end of the operational amplifier U1B is connected to one end of the voltage-dividing resistor RS3. At the same time, the series current-limiting resistors RS2 and RS1 are connected to the positive terminal of the DC bus, and the other end of the voltage-dividing resistor RS3 is connected to the current pin of the MCU. The insulation resistance value is calculated using the voltage Vc1 across the capacitor C1, the voltage-dividing resistor RS and its sampling voltage Vrs, and the current-limiting resistors RS2 and RS1 to perform insulation detection on the AC port.

2. The AC port insulation detection method for an AC inverter according to claim 1, characterized in that: The IGBT circuit assembly also includes IGBTs Q7-Q12, the collectors of Q3, Q4, Q9 and Q10 are connected to the emitters of Q1, Q2, Q5 and Q6 respectively, the emitters of Q3, Q4, Q9 and Q10 are all connected to the ground line, a transformer T1 is arranged between Q6 and Q7, one end of the primary side of the transformer T1 is connected between Q6 and Q10, and the other end is connected between Q5 and Q9, one end of the secondary side of the transformer TQ is connected between Q7 and Q11, and the other end is connected between Q8 and Q12.

3. The AC port insulation detection method for an AC inverter according to claim 2, characterized in that: A current transformer L1A is connected between the ground pin of the MCU and Q1 and Q3.

4. The AC port insulation detection method for an AC inverter according to claim 3, characterized in that: The specific steps for detecting the insulation resistance before starting are as follows: turn on Q3 and Q4, the filter capacitor CX2 is short-circuited, the voltage across the filter capacitor CX2 approaches zero, detect the voltage Vrs on the voltage divider resistor RS and the voltage Vc1 on the capacitor C1, and the resistance of the insulation resistor Rins is: 。 5. The AC port insulation detection method for an AC inverter according to claim 4, characterized in that: The specific steps for detecting insulation resistance after startup are as follows: MCU is used to control Q2 and Q4 to conduct alternately at the set frequency. The filter capacitor CX2 is an AC voltage with an average voltage of zero. Multiple sampling is performed to obtain the average voltage Vrs on the voltage divider resistor RS. During sampling, half of the time is full voltage and half of the time is zero voltage. After averaging, the voltage on the capacitor C1 is 0.5Vc1, so the resistance of the insulation resistor Rins is: 。 6. The AC port insulation detection method for an AC inverter according to claim 5, characterized in that: The frequency of alternating conduction is set to 50 Hz - 200 Hz and is a multiple of 50 Hz.

7. The AC port insulation detection method for an AC inverter according to claim 6, characterized in that: A relay K1 is connected between the current limiting resistor RS2 and RS1.

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