CN110346644B - Dual-level ground insulation impedance detection circuit, self-checking method and measuring method thereof - Google Patents
Dual-level ground insulation impedance detection circuit, self-checking method and measuring method thereof Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/025—Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/16—Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
- G01R27/18—Measuring resistance to earth, i.e. line to ground
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/14—Circuits therefor, e.g. for generating test voltages, sensing circuits
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
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Abstract
The invention discloses a double-level ground insulation impedance detection circuit, a self-checking method and a measuring method thereof, which have the advantages of simple circuit, lower cost, higher precision, perfect self-checking, high reliability, wide impedance measurement range and capability of avoiding detection blind areas caused by a common-mode voltage of PV (photovoltaic) to ground. The double-level ground insulation resistance detection circuit comprises a first resistor and a second resistor which are connected in series to form a first branch, wherein the first branch is connected with a BUS+ BUS; the third resistor and the fourth resistor are connected in series to form a second branch, and the second branch is connected with the BUS-BUS; the first branch and the second branch are connected and then connected to the shell or the ground through a third controllable switch; the first voltage division measuring resistor and the second voltage division measuring resistor are connected in series to form a measuring voltage division loop; the BUS supporting capacitor is connected in parallel between the BUS+ BUS and the BUS-BUS; the first controllable switch is connected in parallel with the first resistor, and the second controllable switch is connected in parallel with the third resistor; the fifth resistor is connected to the housing of the electrical energy device or the ground and the negative terminal of the photovoltaic module.
Description
Technical Field
The invention belongs to the field of power electronic energy equipment, relates to a double-level ground insulation impedance detection circuit, a self-checking method and a measuring method thereof, and in particular relates to a double-level ground insulation impedance detection circuit of a photovoltaic inverter or an energy storage inverter, a self-checking method and a measuring method thereof.
Background
The ground insulation impedance detection module is a circuit module for safety regulations, which is widely applied to power electronic energy equipment such as photovoltaic inverters, energy storage inverters and the like. Taking a photovoltaic inverter as an example, when the photovoltaic inverter detects that the input voltage of the battery plate and the output voltage of the power grid meet the operation requirement, grid connection is prepared. In order to meet the safety requirements, the insulation resistance between the primary electrified loop of the photovoltaic inverter and the inverter shell (the shell is grounded) must be detected before grid connection of the photovoltaic inverter, and when the requirements are met, the inverter can start inversion and output power for grid connection. Such operation may ensure electrical safety in areas of the inverter that are accessible to humans.
In the industry, the positive pole (PV+), the negative pole (PV-) and the loop of the casing of the photovoltaic module are basically formed by a resistor network, a relay or other switching devices. The state of a switching element such as a relay on a switching path is changed, the parameters of an introduced resistor network are changed, different readings of a measured value at a certain place are obtained, and then the insulation impedance measured value is obtained by a method of solving a circuit loop equation. Such methods generally suffer from the following problems:
1. when multiple paths of photovoltaic component inputs exist, a switching element and a resistor network with the same input number are needed; otherwise, the specific impedance of each path cannot be obtained, so that the circuit is complex, the cost is high, the self-checking is difficult, and the reliability is low;
2. the PV+ is used as a power supply source of the resistor network, the input voltage is unstable, the measurement accuracy is obviously affected, the measured value at the protection threshold is fuzzy, the safety cannot be reliably ensured, or false alarm insulation detection errors are caused by measurement errors;
3. the PV+ is used as a power supply source of the resistor network, the input voltage variable of the resistor network is single, so that a measurement blind area is generated when an initial common-mode voltage of a certain path in the input of the multi-path photovoltaic module is close to the PV+ input voltage, the real impedance value to the ground cannot be measured, and different measurement errors are generated due to the difference of the common-mode voltage, so that the measurement accuracy is obviously affected.
Disclosure of Invention
In order to solve the above problems, one of the purposes of the present invention is to provide a dual-level ground insulation impedance detection circuit, which has the advantages of simple circuit, low cost, high precision, perfect self-detection, high reliability, wide impedance measurement range, and capability of avoiding detection dead zones caused by common mode voltage of PV to ground.
The second purpose of the invention is to provide a self-checking method of the double-level ground insulation resistance detection circuit, which has perfect self-checking and high reliability.
The invention further provides a measuring method of the double-level ground insulation impedance detection circuit, which has high measuring precision and can realize a disordered impedance measuring range.
In order to achieve the above purpose, the invention adopts a technical scheme that:
a dual-level insulation resistance detection circuit for grounding comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a first voltage division measuring resistor, a second voltage division measuring resistor, a bus supporting capacitor, a first controllable switch, a second controllable switch and a third controllable switch;
the first resistor and the second resistor are connected in series to form a first branch, and the first end of the first branch is connected with a BUS+ BUS; the third resistor and the fourth resistor are connected in series to form a second branch, and the first end of the second branch is connected with a BUS-BUS; the second end of the first branch is connected with the second end of the second branch and then is connected with a shell of the electric power energy equipment or the ground through the third controllable switch;
the first voltage division measuring resistor and the second voltage division measuring resistor are connected in series to form a measuring voltage division loop, and the measuring voltage division loop is connected between the connection point of the first branch and the second branch and the negative electrode end of the photovoltaic module;
the BUS supporting capacitor is connected in parallel between the BUS+ BUS and the BUS-BUS;
the first controllable switch is connected in parallel with two ends of the first resistor, and the second controllable switch is connected in parallel with the third resistor;
the fifth resistor is connected to the casing of the electric power source equipment or the negative end of the ground and the photovoltaic module.
Preferably, the bus+ BUS and the BUS-BUS are connected with a DC/DC boost circuit to power the photovoltaic module through the DC/DC boost circuit.
Preferably, the dual-level insulation resistance detection circuit further comprises an operational amplifier loop for leading in the voltage across the second voltage division measuring resistor, and the resistance of the first voltage division measuring resistor is larger than the resistance of the second voltage division measuring resistor.
More preferably, the dual-level insulation resistance detection circuit further includes a DSP control device connected to the op-amp loop through its own AD conversion module, or connected to the op-amp loop through the AD conversion device.
Preferably, the dual-level ground insulation resistance detection circuit further comprises a fifth resistor connected between the casing of the electric power source device or the ground and the negative terminal of the photovoltaic module.
Preferably, the dual-level ground insulation resistance detection circuit further comprises a control device for controlling on-off of the first controllable switch, the second controllable switch and the third controllable switch respectively.
More preferably, the first controllable switch, the second controllable switch and the third controllable switch are relays, respectively.
Preferably, the BUS-bar is grounded.
The invention adopts another technical scheme that:
a self-checking method of the double-level ground insulation resistance detection circuit comprises the following steps:
A. keeping the third controllable switch open;
B. respectively obtaining actual measurement voltage values of two ends of a second voltage division measuring resistor in the state that the first controllable switch is closed and the second controllable switch is opened when the first controllable switch and the second controllable switch are opened,
or respectively obtaining measured voltage values at two ends of the second voltage division measuring resistor in three or four of the following four states: the first controllable switch and the second controllable switch are opened, the first controllable switch is closed, the second controllable switch is opened, the first controllable open end is opened, the second controllable switch is closed, and the first controllable switch and the second controllable switch are closed;
C. judging whether the actually measured voltage value in each state meets the theoretical voltage calculation value of the two ends of the second voltage division measuring resistor in the corresponding state, and if so, passing the self-checking; if the result is negative, the dual-level insulation resistance to ground detection circuit fails.
Preferably, the self-checking method further includes a third controllable switch detecting step, the third controllable switch detecting step includes: keeping the third controllable switch closed, respectively measuring the voltage values of two ends of the second voltage division measuring resistor under two states of closing the first controllable switch, opening the second controllable switch, opening the first controllable switch and closing the second controllable switch, establishing the following equation,
wherein:
R′ x refers to the parallel connection value of the ground insulation resistance and the fifth resistance;
U iso1 the voltage on the second voltage dividing measuring resistor in the state that the first controllable switch is closed and the second controllable switch is opened;
U iso2 the voltage on the second voltage dividing measuring resistor is measured under the two states that the first controllable switch is opened and the second controllable switch is closed;
U 0 is the BUS voltage (i.e. the voltage between BUS+ BUS and BUS-BUS), R iso Measuring the impedance of the resistor for the second voltage division, R 0 Measuring the impedance of the resistor for the first partial pressure;
R a1 ＝R 2 ，R a2 ＝R 2 +R 1 ；R b1 ＝R 4 +R 3 ，R b2 ＝R 4 ；R 1 、R 2 、R 3 、R 4 the resistance values of the first resistor, the second resistor, the third resistor and the fourth resistor are respectively;
judging R' x If the voltage is larger than the fifth resistance, if so, the third controllable switch is not closed and fails; if the result is negative, the third controllable switch is normally closed.
The invention adopts another technical scheme that:
the measuring method of the double-level ground insulation resistance detecting circuit is characterized by comprising the following steps of: keeping the third controllable switch closed, respectively measuring the voltage values of two ends of the second voltage division measuring resistor in two states of closing the first controllable switch, opening the second controllable switch, opening the first controllable switch and closing the second controllable switch, establishing the following equation, solving the ground insulation resistance Rx,
wherein:
R′ x refers to the parallel connection value of the ground insulation resistance and the fifth resistance;
U iso1 the voltage on the second voltage dividing measuring resistor in the state that the first controllable switch is closed and the second controllable switch is opened;
U iso2 the voltage on the second voltage dividing measuring resistor is measured under the two states that the first controllable switch is opened and the second controllable switch is closed;
U 0 is the BUS voltage (i.e. the voltage between BUS+ BUS and BUS-BUS), R iso Measuring the impedance of the resistor for the second voltage division, R 0 Measuring the impedance of the resistor for the first partial pressure;
R a1 ＝R 2 ，R a2 ＝R 2 +R 1 ；R b1 ＝R 4 +R 3 ，R b2 ＝R 4 ；R 1 、R 2 、R 3 、R 4 the resistance values of the first resistor, the second resistor, the third resistor and the fourth resistor are respectively.
Compared with the prior art, the invention has the following advantages:
the double-level ground insulation impedance detection circuit provided by the invention uses the same circuit no matter how many photovoltaic components are actually connected, and can avoid a measurement blind area generated by common-mode voltage to ground due to the use of BUS+ and BUS-two levels, and has higher precision; the method has strict self-checking flow, perfect self-checking and high reliability; by indirectly measuring the parallel resistance to ground, a wider impedance measurement range can be achieved. The double-level ground insulation impedance detection circuit can be applied to power energy equipment such as a photovoltaic inverter, an energy storage inverter and the like, provides a novel topology and a self-detection and measurement method thereof, realizes accurate measurement of insulation impedance of a primary electrified loop in a shell and equipment, reduces circuit cost and complexity, improves measurement accuracy, measurement range and reliability, has no measurement blind area, and can be completely self-detected.
Drawings
In order to more clearly illustrate the technical solutions of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a circuit diagram of a dual-level ground isolation impedance detection circuit according to an embodiment;
FIG. 2 is a measurement flow chart of an embodiment;
fig. 3 is a self-checking flowchart of an embodiment.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art. The description of these embodiments is provided to assist understanding of the present invention, but is not intended to limit the present invention. In addition, technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The embodiment provides a double-level ground insulation impedance detection circuit of a photovoltaic inverter or an energy storage inverter. Referring to fig. 1, the dual-level ground insulation impedance detection circuit is generally composed of a DC/DC boost circuit, a bus supporting capacitor, an impedance detection resistor network, a state change-over switch, a measurement voltage division loop, an operational amplifier loop and a DSP. R in FIG. 1 x And U x Is the lumped parameter of the abstracted ground insulation impedance and the initial ground common mode voltage, and the abstracted ground insulation impedance and the initial ground common mode voltage form an equivalent ground impedance model.
As shown in FIG. 1, the dual-level insulation resistance detection circuit comprises a first resistor R 1 A second resistor R 2 Third resistor R 3 Fourth resistor R 4 First voltage dividing measuring resistor R 0 Second voltage division measuring resistor R iso The bus support capacitor, the first controllable switch, the second controllable switch and the third controllable switch. In this embodiment, the first controllable switch, the second controllable switch, and the third controllable switch are respectively relays, and are respectively labeled as a relay K 1 Relay K 2 Relay K 3 . The first resistor R 1 And the second resistor R 2 The first ends of the first branches are connected with BUS+ buses; the third resistor R 3 And the fourth resistor R 4 Forming a second branch in series, wherein the first end of the second branch is connected with a BUS-BUS; the second end of the first branch is connected with the second end of the second branch and then passes through a relay K 3 The shell is connected to the photovoltaic inverter or the energy storage inverter, and the shell of the photovoltaic inverter or the energy storage inverter is connected to the ground. The first voltage division measuring resistor R 0 And the second voltage division measuring resistor R iso A measuring voltage division loop is formed by series connection, and the measuring voltage division loop is connected with the connection point of the first branch and the second branch and the negative electrode end PV-Between, a first voltage dividing measuring resistor R 0 Is greater than the second voltage dividing measuring resistor R iso And a first voltage dividing measuring resistor R 0 For a single resistor or a resistor string formed by a plurality of resistor strings connected in parallel, the first voltage division measuring resistor R 0 Is connected with the junction of the first branch and the second branch and the relay K 3 And one end of the second voltage division measuring resistor is connected with the negative electrode end PV-of the photovoltaic module. The BUS supporting capacitor is connected in parallel between the BUS+ BUS and the BUS-BUS. Relay K 1 In parallel with the first resistor R 1 Relay K 2 In parallel with the third resistor R 3 . The BUS-BUS is grounded.
The dual-level ground insulation resistance detection circuit also comprises a fifth resistor R connected between the shell of the photovoltaic inverter or the energy storage inverter and the negative electrode end PV-of the photovoltaic module 1 . It should also be noted that the first resistor R of the present invention 1 A second resistor R 2 Third resistor R 3 Fourth resistor R 4 Fifth resistor R 5 Is an equivalent circuit, which is a single resistor or a resistor string formed by a plurality of resistor strings connected in parallel. Fifth resistor R 5 Is connected with the relay K 3 And the other end of the shell is connected with the negative electrode end PV-of the photovoltaic module.
The dual-level ground insulation resistance detection circuit also comprises a second voltage division measuring resistor R for leading in iso An operational amplifier circuit of the voltage at two ends, the first voltage dividing measuring resistor R 0 Is greater than the second voltage division measuring resistor R iso Is a high-frequency power source. The double-level ground insulation impedance detection circuit further comprises a DSP control device, wherein the DSP control device is connected to the operational amplifier circuit through an AD conversion module of the DSP control device, or the DSP control device is connected to the operational amplifier circuit through an AD conversion device. In this embodiment, the DSP control device has an AD conversion module, and the op-amp loop is connected to the AD conversion module, and the measured voltage signal is sent to the DSP control device for AD conversion.
The DSP control device is also used for respectively controlling the relays K 1 Relay K 2 Relay K 3 Is provided. The DSP control device is respectively connected with the relay K 1 Relay K 2 Relay K 3 Is electrically connected with the control end of the control circuit.
The BUS+ BUS is connected with the BUS-BUS and the DC/DC booster circuit to power the photovoltaic module through the DC/DC booster circuit. The whole double-level ground insulation resistance detection circuit takes power from the PV end (PV+, PV-) of the photovoltaic module and supplies power to the DC/DC booster circuit. The voltage is boosted by a DC/DC booster circuit to form BUS (BUS) voltage BUS+ and BUS-, and the BUS+ BUS is connected with R in series 1 、R 2 Two groups of resistors, the BUS-BUS is connected with R in series in turn 3 、R 4 Two sets of resistors. The DC/DC booster circuit is also electrically connected with the DSP control device.
The embodiment also provides a measuring method of the double-level ground insulation impedance detection circuit of the photovoltaic inverter or the energy storage inverter. When measurements are made, the BUS voltage is still maintained stable by the DC/DC boost circuit. Then resume relay K 1 Relay K 2 Is customizable, closes relay K 3 . By measuring and taking the relay K 1 Closing relay K 2 Disconnecting and relay K 1 Disconnecting relay K 2 Second voltage division measuring resistor R in two closed states iso The voltage values at two ends are used for establishing an equation to counteract the common-mode voltage U to the ground x The effect of (3) is solved for the actual insulation resistance to ground. The equation is specifically as follows:
wherein:
R′ x insulation resistance R to ground x And a fifth resistor R 5 Parallel values of (2);
U iso1 refers to the first controllable switch being closed and the firstSecond voltage division measuring resistor R in two controllable switch off state iso A voltage on;
U iso2 refers to a second voltage division measuring resistor R in a state that a first controllable switch is opened and a second controllable switch is closed iso A voltage on;
U 0 for bus voltage, R iso For measuring resistance R for second voltage division iso R, R 0 Measuring resistance R for a first partial pressure 0 Impedance of (c);
R a1 ＝R 2 ，R a2 ＝R 2 +R 1 ；R b1 ＝R 4 +R 3 ，R b2 ＝R 4 ；R 1 、R 2 、R 3 、R 4 respectively are a first resistor R 1 A second resistor R 2 Third resistor R 3 Fourth resistor R 4 Is a resistance value of (a).
The measuring method can also detect the relay K 3 Whether it is faulty. Due to U iso The upper limit of accuracy exists in the measured value, and R 'is returned' x There is a fixed upper limit that is only related to system parameters. Thus designing a fifth resistor R 5 Less than this upper limit. Due to a fifth resistance R 5 Ground impedance R with insulation x In parallel relationship, normal R' x The return value must be less than R 5 . When the returned measured value R' x Greater than R 5 When the relay K is judged 3 Without closing, a fault occurs. R in parallel at the same time 5 Also by combining R' x Is limited within a certain value by back-calculating R x Amplifying the measurable R x And breaks through the upper limit of measurement due to system reasons.
Fig. 2 shows a measurement flow specifically adopted in the present embodiment. Referring to fig. 2, the measurement method of the present embodiment specifically includes the following steps:
starting detection;
disconnecting relay K 1 Relay K 2 Closing relay K 3 ；
Calculating a second voltage division measuring resistor R iso Sampling voltage at two endsAn average value;
closing relay K 1 Disconnecting relay K 2 Closing relay K 3 ；
Calculating a second voltage division measuring resistor R iso Average value of sampling voltage at two ends;
disconnecting relay K 1 Closing relay K 2 Closing relay K 3 ；
Calculating a second voltage division measuring resistor R iso Average value of sampling voltage at two ends and bus voltage;
constructing the equation and calculating R' x ；
Judging R' x Whether or not it is greater than the fifth resistance R 5 If the result is yes, the relay K 3 Without closing, failure occurs; if the result is negative, the relay K 3 Normal closure, R is calculated x ；
Judging R x If the voltage is less than the threshold value, if so, the photovoltaic inverter or the energy storage inverter system is qualified in insulation; if the result is negative, the insulation of the photovoltaic inverter or the energy storage inverter system is not qualified.
The embodiment further provides a self-checking method of the double-level ground insulation resistance detection circuit of the photovoltaic inverter or the energy storage inverter. When the photovoltaic module works, the BUS voltage is raised to a stable value higher than the output voltage of the photovoltaic module through the DC/DC booster circuit, so that a stable working voltage source is provided. When no fluctuation of the voltage is detected within a certain time, self-checking is started. Self-test has two alternative ways:
1. during self-checking, the relay K is controlled first 3 Keeping it in the off state. Then respectively switch to three or four states (relay K 1 Disconnecting relay K 2 Off state, relay K 1 Closing relay K 2 Off state, relay K 1 Disconnecting relay K 2 Closed state, relay K 1 Closing relay K 2 Closed state, the four states are not in sequence, and only three of the four states can be selected), and the second partial pressure measurement is respectively measured under each stateResistor R iso Voltage U at both ends iso . Three or four circuit topologies are formed by the states of the switching devices under three or four states, and each circuit topology corresponds to one U iso Theoretical calculations, i.e. forming three or four U' s iso And (5) an index. Three or four times U as measured in the self-test process iso When all the corresponding indexes are met (according to the device characteristics), the self-test passes.
2. During self-checking, the relay K is controlled first 3 Keeping it in the off state. Then respectively switch to the relay K 1 Disconnecting relay K 2 Off state, relay K 1 Closing relay K 2 In the off state, the second voltage division measuring resistor R in two states is respectively measured iso Voltage U at both ends iso . Two circuit topologies are formed by the states of the switching devices under two states, and each circuit topology corresponds to one U iso Theoretical calculation, i.e. forming two U' s iso And (5) an index. When two times of U are measured in the self-checking process iso When all the corresponding indexes are met (according to the device characteristics), the self-test passes.
Fig. 3 shows a self-checking flow specifically adopted in the present embodiment. As can be seen from fig. 3, the first mode is preferable in this embodiment, in which each single point fault deviates less under a single index and cannot be detected within an error range, and the divide relay K can be detected by three or four index amounts 3 And single-point open-circuit and short-circuit faults of all devices outside the device ensure the reliability of the measured value of the insulation resistance detection module. Relay K 3 Self-tests for failure to close faults can be detected by subsequent operations.
The self-checking method of the embodiment further comprises a relay K 3 A detection step of detecting three or four times of U iso When all corresponding indexes are satisfied, namely, when the indexes are respectively within the range, the relay K is carried out 3 And (3) a detection step. Relay K 3 The specific flow of the detection step is shown in fig. 2, and comprises the following steps:
disconnecting relay K 1 Relay K 2 Closing relay K 3 ；
Calculating a second voltage division measuring resistorR iso Average value of sampling voltage at two ends;
closing relay K 1 Disconnecting relay K 2 Closing relay K 3 ；
Calculating a second voltage division measuring resistor R iso Average value of sampling voltage at two ends;
disconnecting relay K 1 Closing relay K 2 Closing relay K 3 ；
Calculating a second voltage division measuring resistor R iso Average value of sampling voltage at two ends and bus voltage;
constructing the equation and calculating R' x ；
Judging R' x Whether or not it is greater than the fifth resistance R 5 If the result is yes, the relay K 3 Without closing, failure occurs; if the result is negative, the relay K 3 The closure is normal.
The embodiment provides a ground insulation impedance detection circuit, which uses the same circuit no matter the number of the photovoltaic components which are actually connected, and a DC/DC module for stably measuring and supplying power can use a DC/DC booster circuit inherent to an inverter and the like, so that the circuit is simple and has lower cost; because two levels of BUS+ and BUS-are used, a measurement blind area generated by common mode voltage to ground can be avoided, and the precision is higher; the method has strict self-checking flow, perfect self-checking and high reliability; by indirectly measuring the parallel resistance to ground, a wider impedance measurement range can be achieved. The method can be applied to electric power energy equipment such as a photovoltaic inverter and an energy storage inverter, and provides a novel topology and a self-detection and measurement method thereof. The insulation impedance of the primary electrified loop inside the shell and the equipment is accurately measured, the circuit cost and the complexity are reduced, the measurement precision, the measurement range and the reliability are improved, no measurement blind area exists, and the complete self-detection can be realized.
The above-described embodiments are provided for illustrating the technical concept and features of the present invention, and are intended to be preferred embodiments for those skilled in the art to understand the present invention and implement the same according to the present invention, not to limit the scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of the present invention.
Claims (8)
1. The double-level ground insulation resistance detection circuit is characterized by comprising a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a first voltage division measuring resistor, a second voltage division measuring resistor, a bus support capacitor, a first controllable switch, a second controllable switch and a third controllable switch;
the first resistor and the second resistor are connected in series to form a first branch, and the first end of the first branch is connected with a BUS+ BUS; the third resistor and the fourth resistor are connected in series to form a second branch, and the first end of the second branch is connected with a BUS-BUS; the second end of the first branch is connected with the second end of the second branch and then is connected with a shell of the electric power energy equipment or the ground through the third controllable switch;
the first voltage division measuring resistor and the second voltage division measuring resistor are connected in series to form a measuring voltage division loop, and the measuring voltage division loop is connected between the connection point of the first branch and the second branch and the negative electrode end of the photovoltaic module;
the BUS supporting capacitor is connected in parallel between the BUS+ BUS and the BUS-BUS;
the first controllable switch is connected in parallel with two ends of the first resistor, and the second controllable switch is connected in parallel with two ends of the third resistor;
the fifth resistor is connected to the shell of the electric power energy equipment or the negative end of the ground and the photovoltaic module;
the dual-level ground insulation impedance detection circuit further comprises an operational amplifier loop for introducing voltages at two ends of the second voltage division measuring resistor, and the impedance of the first voltage division measuring resistor is larger than that of the second voltage division measuring resistor;
the double-level ground insulation resistance detection circuit further comprises a control device for respectively controlling the on-off of the first controllable switch, the second controllable switch and the third controllable switch.
2. The dual level ground isolation impedance detection circuit of claim 1, wherein: and the BUS+ BUS and the BUS-BUS are connected with the DC/DC booster circuit so as to power the photovoltaic module through the DC/DC booster circuit.
3. The dual level ground isolation impedance detection circuit of claim 1, wherein: the double-level ground insulation impedance detection circuit further comprises a DSP control device, wherein the DSP control device is connected to the operational amplifier circuit through an AD conversion module of the DSP control device, or the DSP control device is connected to the operational amplifier circuit through the AD conversion device.
4. The dual level ground isolation impedance detection circuit of claim 1, wherein: the first controllable switch, the second controllable switch and the third controllable switch are relays respectively.
5. The dual level ground isolation impedance detection circuit of claim 1, wherein: the BUS-BUS is grounded.
6. A self-test method of a dual-level ground-isolation impedance detection circuit according to any one of claims 1-5, comprising the steps of:
A. keeping the third controllable switch open;
B. respectively obtaining actual measurement voltage values of two ends of a second voltage division measuring resistor in the state that the first controllable switch is closed and the second controllable switch is opened when the first controllable switch and the second controllable switch are opened,
or respectively obtaining measured voltage values at two ends of the second voltage division measuring resistor in three or four of the following four states: the first controllable switch and the second controllable switch are opened, the first controllable switch is closed, the second controllable switch is opened, the first controllable open end is opened, the second controllable switch is closed, and the first controllable switch and the second controllable switch are closed;
C. judging whether the actually measured voltage value in each state meets the theoretical voltage calculation value of the two ends of the second voltage division measuring resistor in the corresponding state, and if so, passing the self-checking; if the result is negative, the dual-level insulation resistance to ground detection circuit fails.
7. The self-test method of claim 6, further comprising a third controllable switch detection step, the third controllable switch detection step comprising: keeping the third controllable switch closed, respectively measuring the voltage values of two ends of the second voltage division measuring resistor under two states of closing the first controllable switch, opening the second controllable switch, opening the first controllable switch and closing the second controllable switch, establishing the following equation,
wherein:
R′ x refers to the parallel connection value of the ground insulation resistance and the fifth resistance;
U iso1 the voltage on the second voltage dividing measuring resistor in the state that the first controllable switch is closed and the second controllable switch is opened;
U iso2 the voltage on the second voltage dividing measuring resistor is measured under the two states that the first controllable switch is opened and the second controllable switch is closed;
U 0 for bus voltage, R iso Measuring the impedance of the resistor for the second voltage division, R 0 Measuring the impedance of the resistor for the first partial pressure;
R a1 ＝R 2 ，R a2 ＝R 2 +R 1 ；R b1 ＝R 4 +R 3 ，R b2 ＝R 4 ；R 1 、R 2 、R 3 、R 4 the resistance values of the first resistor, the second resistor, the third resistor and the fourth resistor are respectively;
judging R' x If the voltage is larger than the fifth resistance, if so, the third controllable switch is not closed and fails; if the result is thatIf not, the third controllable switch is normally closed.
8. A method of measuring a dual level ground isolation impedance detection circuit according to any one of claims 1 to 5, comprising the steps of: keeping the third controllable switch closed, respectively measuring the voltage values of two ends of the second voltage-dividing measuring resistor in two states of closing the first controllable switch and opening the second controllable switch, opening the first controllable switch and closing the second controllable switch, establishing the following equation, and solving the ground insulation resistance R x ，
Wherein:
R′ x refers to the parallel connection value of the ground insulation resistance and the fifth resistance;
U iso1 the voltage on the second voltage dividing measuring resistor in the state that the first controllable switch is closed and the second controllable switch is opened;
U iso2 the voltage on the second voltage dividing measuring resistor is measured under the two states that the first controllable switch is opened and the second controllable switch is closed;
U 0 for bus voltage, R iso Measuring the impedance of the resistor for the second voltage division, R 0 Measuring the impedance of the resistor for the first partial pressure;
R a1 ＝R 2 ，R a2 ＝R 2 +R 1 ；R b1 ＝R 4 +R 3 ，R b2 ＝R 4 ；R 1 、R 2 、R 3 、R 4 the resistance values of the first resistor, the second resistor, the third resistor and the fourth resistor are respectively.
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