Universal insulation detection circuit

Abstract

The invention discloses a universal insulation detection circuit, and belongs to the field of integrated circuit development. Insulation detection modes in various industries are different, and different schemes have advantages and disadvantages. A universal circuit is designed, various traditional insulation detection modes can be covered, the circuit is based on the low-voltage injection type insulation detection principle, a very exquisite injection measurement point is designed, the requirements for matched circuits such as an injection voltage generation circuit and an injection point measurement circuit are lowered, and the detection accuracy is improved. The whole scheme is simple in structure, low in cost and simple in software calculation, and meanwhile various advantages of a traditional insulation detection mode are also achieved in the method. Through different external wiring modes and software configuration, the circuit can be suitable for insulation resistance measurement of a direct current system, an alternating current system and a passive system, so that the circuit has the characteristic of universality.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit development and is applicable to application scenarios such as BMS battery management systems, insulation testing instruments or modules. The technical solution is compatible with DC applications, AC applications, and passive applications (insulation resistance measurement between two unenergized points). Background Technology

[0002] With the long-term development and application of power-related systems in various industries, insulation monitoring, as an essential function of a product, has led to the development of various solutions with different principles and characteristics within the industry.

[0003] In traditional applications, the bridge and low-voltage injection methods have been the mainstream solutions used in various industries, resulting in various circuit versions. The bridge method is simple and easy to use but has poor measurement performance, while the low-voltage injection method offers good measurement results but has complex circuitry. Therefore, it is necessary to unify the advantages and disadvantages of each solution and design a universal insulation detection solution. This invention integrates the practical advantages and disadvantages of each solution, proposing a universal solution that covers past traditional methods, achieving both affordability and ease of use. Summary of the Invention

[0004] This invention is based on the low-voltage injection insulation detection principle of DC systems. It designs an ingenious injection measurement point to make the entire circuit extremely simple, resulting in a final circuit with the characteristics of low cost, simple structure, high measurement accuracy, and high applicability.

[0005] The technical features of this invention are the injection measurement circuit and the injection voltage drive circuit. Other circuits are industry-standard circuits, such as boost circuits and differential amplifier circuits.

[0006] Low-frequency and high-frequency injection can be achieved by real-time driving of the injection voltage to meet the requirements of different software algorithms. Basic measurements can be performed using low-frequency injection, i.e., controlling the injection voltage to 0V and the injection voltage value. Two sample values ​​are measured at the injection measurement point corresponding to two different injection values. Since the unknowns are the positive and negative values ​​of the insulation resistance, the corresponding values ​​of the two sample values ​​and the two unknowns can be obtained by using a linear equation in two variables.

[0007] The specific steps are as follows:

[0008] S1: Injection voltage output 0V, AD sampling reads the first injection point measurement value.

[0009] S2: The injection voltage output is the designed voltage value (generally around 12-24V is suitable). The AD sample reads the second injection point measurement value and the current injection voltage measurement value (this invention requires accurate measurement of the injection voltage value).

[0010] S3: Calculate the insulation resistance using the formula. , , .

[0011] Furthermore, this invention also possesses good adaptability to both AC and passive application scenarios, such as... Figure 2 In the formula, and Total voltage is irrelevant, so it can be used in AC and passive applications. , By shorting them together, the insulation resistance measurement of a single end to ground can be achieved. Attached Figure Description

[0012] Figure 1 The basic circuit principle of this invention includes a driving circuit and a measurement circuit.

[0013] Figure 2 This is an equivalent model of the basic circuit principle of this invention, which facilitates subsequent formula establishment and data analysis.

[0014] Figure 3 This is a model for the insulation resistance measurement circuit adapted to three-phase AC systems and passive systems in this invention. Detailed Implementation

[0015] The basic circuit is as shown above. Figure 1 As shown, the injection measurement point is designed as the non-inverting input terminal of the operational amplifier in the positive bridge arm of the differential amplifier circuit. The advantage of choosing this point is that the total voltage measurement value and the injection measurement value of the differential amplifier circuit are proportional to R1 and R2, and have the same maximum measurement range. This allows for compatibility with the same measurement range design in the back-end AD sampling circuit. The specific definitions of each point are as follows.

[0016] VB: DC system voltage

[0017] Vb: The measured value of the voltage corresponding to VB after passing through the differential amplifier circuit.

[0018] V+: Voltage between the positive terminal of the DC system and the GND of the measuring circuit.

[0019] V-: Voltage between the negative terminal of the DC system and the GND of the measuring circuit.

[0020] R1, R2: Ratio adjustment resistors for differential amplifier circuit

[0021] R+, R-: Theoretical positive and negative values ​​of the insulation resistance to be measured

[0022] Parallel values ​​of R+ and R-

[0023] VI: Injected Voltage Source

[0024] VI_EN: Injection control, low-frequency / high-frequency drive can be customized by software.

[0025] Vc: The op-amp comparator output reference voltage, which can be obtained by simply dividing the voltage with resistors at VI to a suitable value.

[0026] Vi: Injection point measurement

[0027] VCC5: Measures the basic power supply voltage of the circuit, which is 5V. This voltage can be adjusted according to actual needs.

[0028] according to Figure 1 As can be seen from the circuit structure, the entire measurement and driving circuit structure is very simple. In practical applications, it only requires a differential amplifier circuit, an injection voltage boost circuit, an injection voltage driving circuit, an injection point measurement circuit, and a regular MCU. The overall cost can be controlled below 20 yuan. If higher precision measurement is required, a dedicated ADC chip can be added.

[0029] For detailed principles and formula derivations, please refer to... Figure 2 The equivalent circuit model.

[0030] Given conditions:

[0031]

[0032]

[0033]

[0034] Formula derivation:

[0035] according to Figure 2 Model analysis, in order to measure and The value must first establish a relationship with... Formulas relating values, because The value is a known value measured by the circuit using two different injection voltages. and Two different results were obtained from the corresponding measurements. and The two results are calculated accordingly. and The value of .

[0036] The basic formula can be established using calculation. The current flowing through the branch is used as a reference. According to the superposition theorem, The current flowing through it is from , , The components of the three voltage sources can be calculated using Thevenin's theorem, and the following formula can be derived for each component.

[0037] (R1+R2 is temporarily replaced by Rx for easier calculation)

[0038] Branch current: + +

[0039] Introducing two different injection voltages and The formula is as follows.

[0040] Formula 1: + +

[0041] Formula 2: + +

[0042] Subtracting Formula 2 from Formula 1 yields:

[0043] Simplify to get value.

[0044] Formula 3:

[0045] Calculated The value is replaced with the original formula, where Equivalent simplification to It can be simplified to obtain The value can also be obtained by reverse substitution. The value of . Because of The value itself contains and The two-dimensional data calculation results, therefore the specific formula can be used arbitrarily. or The value is used as a reference (the actual data is the same for insulation resistance values ​​calculated using any injection voltage value).

[0046] Formula 4:

[0047] Formula 5:

[0048] Do not use Value, will and The following formula can be obtained by calculating it separately (actual software calculations are complex and not recommended).

[0049] Formula 6:

[0050] Formula 7:

[0051] Based on the characteristics of formulas 3, 4, and 5, the following conclusions can be drawn.

[0052] 1. Value and total voltage of DC system It is irrelevant; its accuracy depends on the measurement accuracy of the injection voltage and the measurement accuracy of the injection point.

[0053] 2. Setting one of the two injected values ​​to 0V can greatly simplify the actual circuit and the software algorithm.

[0054] 3. Value at and When the value is on the order of magnitude, it has a certain impact; when the actual insulation is low... It can be ignored.

[0055] Insulation resistance measurement of single-phase AC systems

[0056] According to Formula 1, Voltage changes will affect in real time The sampled values ​​therefore require special processing in the software. Firstly, the software algorithm needs to... The changing pattern is used to identify the power frequency, and then... The value is sampled based on the power frequency, and at the same time... The injection voltage switching frequency is at a multiple of the power frequency, and a stable voltage is obtained. After the value is obtained, the stable value can be calculated. , , value.

[0057] Insulation resistance measurement of three-phase AC system

[0058] Reference Figure 3 In this way, the original The two measuring wires are shorted together to form a single-ended insulation resistance measuring circuit. By connecting three insulation acquisition modules to a three-phase AC system, the insulation resistance of each phase can be measured separately. The calculation is performed using a non-zero injection voltage state.

[0059] Formula 8:

[0060] Insulation resistance measurement of passive systems

[0061] Similar to the single-ended insulation resistance measurement circuit mentioned above, it can perform real-time measurements on passive systems such as cables and pipes.

[0062] In summary, this invention possesses advantages such as simple circuitry, high PCB space utilization, low cost, high software adaptability, and wide applicability, resulting in significant economic benefits. It can unify the design of various traditional insulation detection circuits. The scope of protection of this invention is defined by the appended claims and their equivalents.

[0063] This invention only covers basic circuit principles. The actual operating conditions of bus-to-ground parasitic capacitance and common-mode interference are not analyzed here. Further software algorithm development needs to be gradually improved in combination with actual application conditions.

Claims

1. A general-purpose insulation detection circuit, characterized in that... Based on the simplified circuit structure of the low-voltage injection detection principle, an ingenious injection measurement point was designed. Through the inherent total voltage measurement differential amplifier circuit, the middle section of its positive bridge arm was taken as the injection measurement point, and the result was output to the AD sampling circuit after passing through a voltage follower buffer circuit.

2. A general-purpose insulation detection circuit is designed for high-frequency / low-frequency injection. A simple, safe and reliable custom frequency drive circuit with injection voltage down to 0V is realized through a rail-to-rail operational amplifier with a high power supply voltage.

3. A general-purpose insulation detection circuit, due to the characteristic that the parallel value of insulation resistance is independent of the total voltage value in its formula, can be applied to measurement requirements in any scenario, including DC applications, AC applications, and passive applications (insulation resistance measurement between two unenergized points). Specifically, the application requirements can be met through external wiring and software parameter configuration.

4. A general-purpose insulation detection circuit presents a basic circuit structure, and any extensions or developments based on this circuit are also included within the scope of this invention.

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