Direct current and even harmonic load balancing and modeling method based on piezoelectric impedance

Abstract

The invention relates to a direct current and even harmonic load balancing and modeling method based on piezoelectric impedance. The method comprises the following steps: step 1, sampling a voltage value V1 flowing through a sampling resistor RA1 of a positive half-cycle waveform of a measured electric energy meter unit and a load resistor RZ1, and a voltage value V2 flowing through a sampling resistor RA2 adopting a balance meter as a balance impedance EUT2 and a load resistor RZ2; 2, judging whether the effective values of the voltage value V1 and the current value V2 are equal or not; if not, adjusting the resistance value of the balance impedance through the microprocessor corresponding to the load resistor, and returning to the step 1; the device is reasonable in design, compact in structure and convenient to use.

Description

Technical Field

[0001] The invention belongs to the technical field of communication detection of electric metering equipment, and relates to a direct current and even-order harmonic load balancing and modeling method based on piezoelectric impedance. Background Art

[0002] For direct access meters, when ordinary current transformers are used as current sensors, half-wave DC current causes the core of the current transformer to be magnetized in one direction. Under large currents, the core is easily saturated and loses the current signal transmission function. In domestic power grids, single-phase smart meters have the function of monitoring the neutral current. Most solutions use ordinary current transformers as current sampling components. When half-wave DC loads appear, it is easy to cause inaccurate monitoring of the neutral current, resulting in unequal neutral and live currents and misjudgment of bypass. The specifications of three-phase smart meters with direct access generally use ordinary current transformers as current sampling components. In actual load use, if half-wave loads are included, it is easy to cause inaccurate energy metering, affecting the energy metering and charging situation.

[0003] The DC resistance of the meter is tested by DC and even harmonic-half-wave rectifier waveform tests. When performing such tests, the loads of the two DC circuits are required to be accurately balanced, but in actual operation, it is extremely difficult to achieve complete load balance of the two circuits due to factors such as power source output stability, wiring differences, and connection impedance uncertainty. At the same time, during long-term power-on, the connection parts may heat up, which will cause impedance changes, further increasing the complexity of load balancing. Therefore, large measurement errors often occur in actual tests.

[0004] At present, the equipment used for DC and even harmonic performance testing of smart meters mostly connects the meter under test and a reference meter of the same model or an equivalent resistance load in parallel to the same test system. However, in actual testing, the test results will deviate too much due to the slight impedance difference inside the loop. This situation is very unfavorable for enterprise product inspection and bidding.

[0005] In order to accurately match the load and control the test deviation within an acceptable range, the present invention innovatively proposes an auxiliary DC and even-order harmonic load balancing method and device that can be directly connected to a test device.

[0006] In addition, the impedance matching technology before the improvement was to use high-power electronic loads to achieve load balancing. This method has high requirements for the power capacity, accuracy and temperature performance indicators of the electronic load components, and the purchase of complete sets of equipment is too expensive. The overall implementation cost is high and the implementation is complex. In addition, the technical means of using relays for load balancing also has obvious problems: because the relays may be inaccurate when matching the actual impedance difference, the relays are frequently switched to find the appropriate impedance matching point, which is not only difficult to achieve the ideal impedance adaptation state, but also easy to cause arcing, thus affecting the reliability and safety of the system. Summary of the invention

[0007] The technical problem to be solved by the present invention is generally to provide a DC and even-order harmonic load balancing and modeling method based on piezoelectric impedance.

[0008] In view of the actual situation, in order to solve the above problems, the present invention innovatively proposes an auxiliary DC load balancing and even harmonic processing method and its supporting device. The core technology is to apply the piezoelectric impedance principle to match the load impedance of the two test loops by adjusting the internal characteristic changes caused by different preload forces of PZT. The test loop current is collected through the sampling resistor and the signal is transmitted to the microprocessor. The microprocessor controls the rotation of the motor to adjust the bolt preload according to the sampling signal, and the impedance of the two loops is infinitely adjusted by changing the piezoelectric admittance of PZT, so as to realize real-time accurate monitoring and balanced control of the load.

[0009] To solve the above problems, the technical solution adopted by the present invention is:

[0010] A DC and even-order harmonic load balance modeling method based on piezoelectric impedance, wherein an electric energy meter is built during power grid operation to perform DC component and even-order harmonic tests, and the modeling method comprises the following steps;

[0011] S1, build a test circuit model and adjust it; the test circuit model has a load resistor; the load resistor uses a PZT piezoelectric ceramic resistor;

[0012] S2, identifying the piezoelectric equation of the PZT used by the load resistor based on the admittance of the piezoelectric material of the load resistor;

[0013] Among them, the piezoelectric admittance and impedance of the piezoelectric material of PZT are reciprocal to each other:

[0014] Y = I / V;

[0015] Where Y is the piezoelectric admittance, I is the output current generated by the load resistor, and V is the excitation voltage of the load resistor;

[0016] V=E 3 h a ;

[0017] Among them, E 3 is the electric field strength, h a is the longitudinal thickness of PZT;

[0018] S3, introduce the mechanical impedance of PZT, apply a continuous excitation force signal to PZT, and obtain the piezoelectric admittance equation of PZT;

[0019] S4, determine the fuzzy control system based on building the test circuit model.

[0020] Further, in step S1, the test circuit includes a load balancing device, a test instrument EUT1, a balancing impedance EUT2, and diodes DA1 and DA2;

[0021] The first branch where the test instrument EUT1 is located and the second branch where the balanced impedance EUT2 is located are connected in parallel between IAin and IAout;

[0022] The load balancing device includes sampling resistors RA1, RA2 and load resistors RZ1, RZ2;

[0023] In the first branch, the diode DA1, the sampling resistor RA1, the test instrument EUT1 and the load resistor RZ1 are arranged in series;

[0024] In the second branch, the reverse diode DA2, the sampling resistor RA2, the test instrument EUT1 and the load resistor RZ2 are arranged in series;

[0025] The sampling resistors RA1 and RA2 are electrically connected to a standard electric energy meter;

[0026] The standard electric energy meter is electrically connected to a microprocessor; the microprocessor is electrically connected to a controller; the controller is electrically connected to an actuator, and the actuator drives the load resistor RZ1 and / or the load resistor RZ2 to perform linear adjustment.

[0027] Furthermore, in the test instrument EUT1, the loop current is I 1 , the loop impedance of the balanced impedance RA1 is R 1 ;

[0028] In balanced impedance, the loop current is I 2 , the loop impedance of the balanced impedance RA2 is R 2 ;

[0029] The total input current source is I.

[0030] Further, wherein the test instrument EUT1 and the test instrument EUT2 use the same type of instrument and have the same impedance;

[0031] The actuator adopts a motor, and the controller is a permanent magnet synchronous electric controller;

[0032] Load resistors RZ1 and RZ2 are made of PZT material;

[0033] The resistance value of the sampling resistor RA1 is equal to the resistance value of the sampling resistor RA2;

[0034] The resistance values ​​of the sampling resistors RA1 and RA2 are several times the resistance value of the test instrument EUT1.

[0035] In step S2, first, the current I is calculated according to the PZT electric displacement equation (1);

[0036] I=jω∫∫D 3 dxdy (1);

[0037] Where D 3 is the electrical displacement of PZT; x, y are the longitudinal and lateral displacement variables of PZT respectively;

[0038] Then, considering only the longitudinal deformation of PZT, the piezoelectric equation of PZT is obtained;

[0039]

[0040] Where: ε 1 is the strain of the load resistor; σ 1 is the stress of the load resistor;

[0041] is the complex elastic compliance coefficient when the electric field strength is 0 or constant;

[0042] is the complex dielectric constant when the stress is 0 or constant;

[0043] d 31 is the piezoelectric strain constant;

[0044] E 3 is the electric field strength of the load resistor;

[0045] Secondly, the equation of motion of the PZT in the x direction is expressed as:

[0046]

[0047] Where: u is the longitudinal displacement of PZT;

[0048] is the mechanical loss factor of PZT;

[0049] p is the density of PZT, and the solution of equation (4) is:

[0050]

[0051] Where: A and B are unknown coefficients; k is the wave number, i.e. k = 2π / λ; the boundary conditions are So B = 0; at the same time, at the connection point between PZT and the load matching device, x = la, the resistance generated by the load matching device structure That is, the stress state of the PZT section at the connection is:

[0052]

[0053] Where: Z s is the mechanical impedance of the structure; b a is the width of PZT; h a is the thickness of PZT; l a is the length of PZT, and the horizontal line above the variable represents the spatial component of the variable;

[0054] Again, substituting equation (6) into equation (2) yields the strain:

[0055]

[0056] Depend on The coefficient A of equation (7) and equation (5) is solved as follows:

[0057]

[0058] Further, in step S3, first, the driving response of the PZT is determined according to the derivation of equations (5) to (8); the mechanical impedance of the PZT is expressed as the ratio of the excitation force signal to the electrical signal speed response:

[0059]

[0060] Where: is the static stiffness of PZT;

[0061] After introducing the PZT mechanical impedance, equation (8) is simplified to:

[0062]

[0063] Then, by substituting equation (10) and B = 0 into equation (5), the output displacement of the PZT self-sensing actuator is obtained as:

[0064]

[0065] Afterwards, the strain of the PZT self-sensing actuator is and Combining formula (2), we can get the PZT stress:

[0066]

[0067] Substituting equation (12) into equation (3), we can get the electric displacement D of PZT: 3 :

[0068]

[0069] Substituting equation (13) into equation (1) yields the output current I of the PZT:

[0070]

[0071] Substituting equation (14) into Y = I / V, we get the piezoelectric admittance equation of PZT:

[0072]

[0073] Then, the load resistor has an adjustment bolt for adjusting the resistance. According to the admittance equation (15) of the piezoelectric material, the piezoelectric sheet is pasted on the load resistor adjustment bolt, and the internal characteristics of the piezoelectric material are changed by adjusting the pre-tightening force of the bolt to adjust the load resistor impedance.

[0074] Further, in step S4, first, the parameters of the fuzzy control system are determined;

[0075] The EUT loop current is I1, and the loop impedance is R1. The balanced loop current is I2, and the loop impedance is R2. The total test input current is I. Among them, And I=I 1 +I 2 ; When R1 is unchanged, R 2 Increase I 1 Reduce I 2 Increase, when R 2 When R is unchanged 1 Increase I 2 Reduce I 1 Increase;

[0076] Then, select the effective value of the test loop current I 1 , the effective value of the balanced loop current I 2 ; The controlled variables are the piezoelectric conductance of the PZT and the bolt rotation angle θ when the PZT is fixed between the bolt and the nut; the output variable is the balance relationship between the two test loops;

[0077] Secondly, the input variables and output variables are fuzzified and quantified into three language values, each of which corresponds to a membership function;

[0078] The three language values ​​include I 1 >I 2 ,I 2 >I 1 and I 1 =I 2 ;

[0079] Thirdly, the voltage of the sampling resistor is compared to obtain the current of the two circuits.

[0080] When V 1 Less than V 2 When the effective value of the current in the tested circuit is I 1 Less than the effective value of the balanced loop current I 2 When, according to Kirchhoff's law, the balanced loop impedance R 2 Less than the impedance of the tested circuit R 1 , then increase the resistance of the test circuit to achieve a load balance state.

[0081] A DC and even-order harmonic load balancing method based on piezoelectric impedance comprises the following steps;

[0082] Step 1: Sample the voltage value V of the sampling resistor RA1 of the positive half-cycle waveform flowing through the measured energy meter unit and the load resistor RZ1 1 , and the voltage value V flowing through the sampling resistor RA2 using the balance meter as the balancing impedance EUT2 and the load resistor RZ2 2 ;

[0083] Step 2: Determine the voltage value V 1 and current value V 2 If they are not equal, the microprocessor adjusts the resistance value of the balancing impedance through the load resistor, and then returns to step 1.

[0084] Furthermore, the preload force of the load resistor is controlled by a motor, and the resistance of the balanced impedance is regulated by the motor;

[0085] In step 1, the modeling as claimed in claim 1 is performed, a load balancing device is installed in the current loop of the test equipment, and a test meter and a balancing meter are installed; after the modeling, the voltage value is sampled as follows;

[0086] Step 1-1: Install the load balancing device test circuit and put in the test instrument EUT1;

[0087] Step 1-2: Connect the sampling resistor RA1 to the output end of the electric energy meter unit under test, and connect the sampling resistor RA2 to the output end of the balance meter;

[0088] Step 1-3: Collect the voltage signal flowing through the sampling resistor RA1 and the sampling resistor RA2 to determine the voltage value V 1 and voltage value V 2 The voltage waveform;

[0089] In step 2;

[0090] Step 2-1: Obtain the effective value of the voltage of the load resistor and send the calculation result to the microprocessor;

[0091] Step 2-2: The microprocessor compares the voltage RMS value V 1 And the current effective value V 2 :

[0092] If the effective value of the current V 1 >V 2 , the microprocessor controls the motor to increase the balance loop impedance and increase the voltage RMS value V 2 ;

[0093] If the effective value of the current V 1 <V 2 , the microprocessor controls the motor to increase the impedance of the tested circuit and increase the effective value of the current V 1 ;

[0094] If the effective value of the current V 1 =V 2 , the load is balanced.

[0095] In step 2-1, first, the device is restored to its original position, that is, the PZT material is restored to its original state, and the bolt position of the load resistor at this time is recorded as the initial position 0°; then, the loop voltage is sampled through the sampling resistor, and the voltage of the sampling resistor I is recorded as V 1 , the voltage of sampling resistor II is V 2 ;

[0096] The load resistor is crimped by bolts made of PZT material, and the impedance of the two circuits is balanced by adjusting the bolt preload using a motor.

[0097] The present invention aims to solve the problem of unbalanced DC and even-order harmonic loads. The present method can add a load balancing function to the test equipment without changing the original DC and even-order harmonic test equipment. In addition, the present invention is insensitive to temperature rise, can reach an impedance balance state before thermal stabilization, and maintain dynamic impedance balance during the subsequent thermal stabilization process. Compared with other resistance adjustment methods, the present method has the best effect, low cost, simple operation, and high test efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] Figure 1 It is the DC and even harmonic test circuit diagram of the present invention.

[0099] Figure 2 It is the fuzzy control system diagram of the present invention.

[0100] Figure 3 It is a system structure block diagram of the present invention.

[0101] Figure 4 It is an application logic block diagram of the present invention.

[0102] Figure 5 This is a schematic diagram of the structure of the PZT impedance adjustment part of the present invention. DETAILED DESCRIPTION

[0103] like Figure 1-5 In order to solve the problem that harmonics generated by nonlinear electrical equipment in the operation of the power grid affect the accuracy of electric energy meter measurement, a test method and related requirements including DC component and even harmonic test were developed based on existing technologies. Such tests are carried out in accordance with the strict procedures specified in the standard, aiming to verify the accuracy of static active energy meter measurement in the face of DC even harmonic environment.

[0104] like Figure 1 , DC and even harmonic test circuit includes the test circuit including load balancing device, test instrument EUT1, balanced impedance EUT2 and diodes DA1, DA2;

[0105] The first branch where the test instrument EUT1 is located and the second branch where the balanced impedance EUT2 is located are connected in parallel between IAin and IAout;

[0106] The load balancing device includes sampling resistors RA1, RA2 and load resistors RZ1, RZ2;

[0107] In the first branch, the diode DA1, the sampling resistor RA1, the test instrument EUT1 and the load resistor RZ1 are arranged in series;

[0108] In the second branch, the reverse diode DA2, the sampling resistor RA2, the test instrument EUT1 and the load resistor RZ2 are arranged in series;

[0109] The sampling resistors RA1 and RA2 are electrically connected to a standard electric energy meter;

[0110] The standard electric energy meter is electrically connected to a microprocessor; the microprocessor is electrically connected to a controller; the controller is electrically connected to an actuator, and the actuator drives the load resistor RZ1 and / or the load resistor RZ2 to perform linear adjustment.

[0111] Among them, the resistance values ​​of resistors RA1 and RA2 should be approximately 10 times the resistance value of the test instrument (EUT), the balanced impedance of the balanced impedance is equal to the impedance of the test instrument (EUT), and the test balanced impedance recommended by the standard is an instrument of the same model as the test instrument (EUT).

[0112] First, the basic principle of the piezoelectric impedance technology of this embodiment is to identify damage based on the admittance of the piezoelectric material. The piezoelectric admittance and impedance of the piezoelectric material are reciprocal to each other, namely:

[0113] Y = I / V;

[0114] Where Y is the piezoelectric admittance, I is the output current generated by the piezoelectric ceramic resistor PZT, and V is the excitation voltage of PZT; and, V = E 3 h a ;

[0115] Among them, E 3 is the electric field strength, h a is the longitudinal thickness of PZT, and the current I is calculated according to the electric displacement equation (1) of the piezoelectric ceramic sheet resistance PZT.

[0116] I=jω∫∫D 3 dxdy (1);

[0117] Where D 3 —Electric displacement of PZT;

[0118] x, y—longitudinal and lateral displacement variables of the PZT.

[0119] Then, considering only the longitudinal deformation of PZT, the piezoelectric equation of PZT can be obtained;

[0120]

[0121] Where: ε 1 -strain;

[0122] σ 1 -stress;

[0123] E—complex elastic compliance coefficient when the electric field strength is 0 or constant;

[0124] c 11

[0125] σ—complex dielectric constant when stress is 0 or constant;

[0126] ε 33

[0127] d 31 —piezoelectric strain constant;

[0128] E 3 —Electric field strength;

[0129] Secondly, the longitudinal (x-direction) motion equation of the PZT can be expressed as:

[0130]

[0131] Where: u—longitudinal displacement of PZT;

[0132] Mechanical loss factor;

[0133] p—density of PZT, assuming that the solution of equation (4) is:

[0134]

[0135] Where: A, B—undetermined coefficients; k—wave number, i.e. k=2π / λ; Boundary conditions So B = 0; at the same time, at the structural connection point between PZT and the load balancing device (x = la), the resistance generated by the structure is That is, the stress state of the PZT section at the connection is:

[0136]

[0137] Where: Z s — mechanical impedance of the structure;

[0138] b a —Width of PZT;

[0139] h a —Thickness of PZT;

[0140] l a —The length of the PZT. The horizontal bar above the variable indicates its spatial component;

[0141] Again, substituting equation (6) into equation (2) yields the strain:

[0142]

[0143] Depend on The coefficient A of equation (7) and equation (5) can be solved as follows:

[0144]

[0145] After that, the mechanical impedance of PZT is introduced and a continuous excitation force signal is applied to PZT. Then, the driving response of PZT can be determined according to the derivation of equations (5) to (8); the mechanical impedance of PZT can be expressed as the ratio of the excitation force signal to the speed response of the electrical signal:

[0146]

[0147] Where: The static stiffness of

[0148] After that, after introducing the PZT mechanical impedance, equation (8) can be simplified to:

[0149]

[0150] Substituting equation (10) and B = 0 into equation (5), the output displacement of the PZT self-sensing actuator is obtained as:

[0151]

[0152] The strain of the PZT self-sensing actuator is and Combining formula (2), we can get the PZT stress:

[0153]

[0154] Substituting equation (12) into equation (3) yields the electric displacement D of PZT: 3 :

[0155]

[0156] Substituting equation (13) into equation (1) yields the output current I of the PZT:

[0157]

[0158] Substituting equation (14) into Y = I / V, the piezoelectric admittance equation of PZT can be obtained:

[0159]

[0160] According to the admittance equation (15) of piezoelectric materials, the impedance of piezoelectric materials is affected by the mechanical impedance of the structure in which they are located, and the mechanical impedance of the structure is a reflection of the internal characteristics of the structure. Therefore, it is theoretically feasible to change the internal characteristics of the piezoelectric material by attaching the piezoelectric sheet to the bolt and adjusting the preload of the bolt to control its impedance (e.g. Figure 5 ).

[0161] For this model, the traditional control method needs to use an accurate mathematical model to describe the controlled system. However, the interference signal cannot be estimated when modeling the mechanism of the model, and it involves too many parameters and nonlinear coupling, which is too complicated overall. Therefore, fuzzy control is more suitable.

[0162] Next, design the fuzzy control system:

[0163] The EUT loop current is I 1 , the loop impedance is R 1 The balancing loop current is I 2 , the loop impedance is R 2 , the total test input current is I. From the test circuit diagram, we can see And I=I 1 +I 2 When R1 is unchanged, R 2 Increase I 1 Reduce I 2 Increase, when R 2 When R is unchanged1 Increase I 2 Reduce I 1 Increase.

[0164] Select two key input variables, namely the test loop current I 1 and the balanced loop current I 2 The controlled variables are the piezoelectric nanoconductance of the PZT and the bolt rotation angle θ when the PZT is fixed between the bolt and the nut.

[0165] The input and output variables are fuzzified and quantified into three linguistic values ​​(“I 1 >I 2 ","I 2 >I 1 ","I 1 =I 2 ”), each linguistic value corresponds to a membership function.

[0166] The fuzzy rule set and fuzzy reasoning are concentrated in the microprocessor, driven by a motor and controlled by a chip. The two circuits use the same sampling resistor. Since the current ratio is equivalent to the voltage ratio when the resistance is the same, the sampling resistor voltage is compared to save the calculation steps.

[0167] Because the sampling resistor is directly connected in series in the loop, the current magnitudes of the two loops can be obtained by comparing the voltage magnitudes. 1 Less than V 2 When the effective value of the current in the tested circuit is I 1 Less than the effective value of the balanced loop current I 2 When, according to Kirchhoff's law, it is easy to know that the balanced loop impedance R 2 Less than the impedance of the tested circuit R 1 Therefore, it is necessary to increase the resistance of the tested circuit to achieve load balance. Figure 2 .

[0168] The method specifically includes the following steps:

[0169] Step 1: Sample the sampling resistor voltage value V of the positive half-cycle waveform flowing through the measured energy meter unit and the load resistor 1 , and the sampling resistor voltage value V flowing through the balance meter and the load resistor 2 ;

[0170] Step 2: Determine the voltage value V 1 and current value V 2 are equal; if not equal, the microprocessor adjusts the resistance value of the balancing impedance in the load resistor and returns to step 1;

[0171] Preferably, the balancing impedance is made of PZT material, and its preload force is controlled by a motor, and its resistance is regulated by the motor;

[0172] Preferably, sampling the voltage value in step 1 includes:

[0173] Step 1-1: Install the balancing device in the current loop of the equipment to be tested, and also hang the device on the load end. Install the meter to be tested on the balancing device, and hang a meter of the same model as a balancing load on the load end;

[0174] Step 1-2: Connect the sampling resistor RA1 in the load resistor to the output end of the electric energy meter unit to be measured, and connect the sampling resistor RA2 to the output end of the balance meter;

[0175] Step 1-3: Collect the voltage signal flowing through the sampling resistor RA1 and the sampling resistor RA2 to determine the voltage value V 1 and voltage value V 2 The voltage waveform;

[0176] Preferably, the step 2 comprises:

[0177] Step 2-1: The metering unit of the load resistor calculates the effective value of the voltage value and sends the calculation result to the microprocessor;

[0178] Step 2-2: The microprocessor compares the voltage effective value V 1 And the current effective value V 2 :

[0179] If the effective value of the current V 1 >V 2 , the microprocessor controls the motor to increase the balance loop impedance, increasing the voltage effective value V 2 ;

[0180] If the effective value of the current V 1 <V 2 , the microprocessor controls the motor to increase the impedance of the tested circuit and increase the effective value of the current V 1 ;

[0181] The following embodiments are combined with the attached Figure 3 , the technical solution of the present invention is further specifically described.

[0182] First, build the test environment, install the load balancing device in the current loop of the test equipment, and install the test meter and the balancing meter on the balancing device.

[0183] Then the test started. The specific steps of the automatic load matching method are:

[0184] Step 1: The equipment is restored to its original position, i.e. the PZT material is restored to its original state, and the bolt position at this time is recorded as the initial position 0°;

[0185] Step 2: Sample the loop voltage through the sampling resistor, and record the voltage of the sampling resistor I as V 1 , the voltage of sampling resistor II is V 2 ;

[0186] Step 3: Compare the voltage values ​​of the two circuits and determine V 1 Is it equal to V 2 If they are not equal, go to step 4; if they are equal, go to step 7;

[0187] Step 4: Determine whether the resistance has been adjusted. If it has been adjusted, proceed to step 5; if it has not been adjusted, proceed to step 6.

[0188] Step 5: Reversely adjust the previous resistor and go to step 3;

[0189] Step 6: Determine whether V 1 Less than V 2 If it is less than, increase the load of the circuit of the test meter. If it is not less than, increase the load of the balancing circuit and go to step 3;

[0190] Step 7: The load is balanced.

[0191] Specific judgment methods such as Figure 4 Shown

[0192] If the adjustable resistance range still cannot meet the test requirements, other materials can be used, or multiple PZT materials can be connected in series.

[0193] The present invention uses PZT material in a bolt crimping manner, and uses a motor to adjust the preload to balance the impedance of the two circuits, thereby realizing the function of stepless regulation. The present invention uses fuzzy control to achieve dynamic regulation of its parameters, and the equipment does not need to reach thermal equilibrium, which can effectively reduce the time required to reach impedance balance.

[0194] The present invention is fully described for a clearer disclosure, and the prior art is not listed one by one.

[0195] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some of the technical features therein with equivalents; it is obvious for those skilled in the art to combine multiple technical solutions of the present invention. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention. The technical contents not described in detail in the present invention are all known technologies.

Claims

1. A DC and even-order harmonic load balancing modeling method based on piezoelectric impedance, characterized by: An electric energy meter is built during grid operation to test DC components and even harmonics. The modeling method includes the following steps: S1, build a test circuit model and adjust it; the test circuit model has a load resistor; The load resistor uses a PZT piezoelectric ceramic resistor; S2, the piezoelectric equation of PZT used to identify the load resistor based on the admittance of the piezoelectric material of the load resistor; Among them, the piezoelectric admittance and impedance of the piezoelectric material of PZT are reciprocal to each other: Y=I / V; Where Y is the piezoelectric admittance, I is the output current generated by the load resistor, and V is the excitation voltage of the load resistor; V=E3h a ; Where E3 is the electric field strength, h a is the longitudinal thickness of PZT; S3, introduce the mechanical impedance of PZT, apply a continuous excitation force signal to PZT, and obtain the piezoelectric admittance equation of PZT; S4, determine the fuzzy control system based on building the test circuit model.

2. The DC and even-order harmonic load balancing modeling method based on piezoelectric impedance according to claim 1 is characterized in that: In step S1, the test circuit includes a load balancing device, a test instrument EUT1, a balancing impedance EUT2, and diodes DA1 and DA2; The first branch where the test instrument EUT1 is located and the second branch where the balanced impedance EUT2 is located are connected in parallel between IAin and IAout; The load balancing device includes sampling resistors RA1, RA2 and load resistors RZ1, RZ2; In the first branch, the diode DA1, the sampling resistor RA1, the test instrument EUT1 and the load resistor RZ1 are arranged in series; In the second branch, the reverse diode DA2, the sampling resistor RA2, the test instrument EUT1 and the load resistor RZ2 are arranged in series; The sampling resistors RA1 and RA2 are electrically connected to a standard electric energy meter; The standard electric energy meter is electrically connected to a microprocessor; the microprocessor is electrically connected to a controller; the controller is electrically connected to an actuator, and the actuator drives the load resistor RZ1 and / or the load resistor RZ2 to perform linear adjustment.

3. The DC and even-order harmonic load balancing modeling method based on piezoelectric impedance according to claim 1 is characterized in that: In the test instrument EUT1, the loop current is I1, and the loop impedance of the balancing impedance RA1 is R1; In the balanced impedance, the loop current is I2, and the loop impedance of the balanced impedance RA2 is R2; The total input current source is I.

4. The DC and even-order harmonic load balancing modeling method based on piezoelectric impedance according to claim 1 is characterized in that: in, The instrument under test EUT1 and the instrument under test EUT2 use the same instrument model and have the same impedance; The actuator adopts a motor, and the controller is a permanent magnet synchronous electric controller; Load resistors RZ1 and RZ2 are made of PZT material; The resistance value of the sampling resistor RA1 is equal to the resistance value of the sampling resistor RA2; The resistance values ​​of the sampling resistors RA1 and RA2 are several times the resistance value of the test instrument EUT1.

5. The DC and even-order harmonic load balancing modeling method based on piezoelectric impedance according to claim 1 is characterized in that: In step S2, first, the current I is calculated according to the PZT electric displacement equation (1); I = jω∫∫D3dxdy (1); Where D3 is the electrical displacement of PZT; x and y are the longitudinal and lateral displacement variables of PZT respectively; Then, considering only the longitudinal deformation of PZT, the piezoelectric equation of PZT is obtained; Where: ε1 is the strain of the load resistor; σ1 is the stress of the load resistor; is the complex elastic compliance coefficient when the electric field strength is 0 or constant; is the complex dielectric constant when the stress is 0 or constant; d 31 is the piezoelectric strain constant; E3 is the electric field strength of the load resistor; Secondly, the equation of motion of the PZT in the x direction is expressed as: Where: u is the longitudinal displacement of PZT; is the mechanical loss factor of PZT; p is the density of PZT, and the solution of equation (4) is: Where: A and B are unknown coefficients; k is the wave number, i.e. k = 2π / λ; the boundary conditions are So B = 0; at the same time, at the connection point between PZT and the load matching device, x = la, the resistance generated by the load matching device structure That is, the stress state of the PZT section at the connection is: Where: Z s is the mechanical impedance of the structure; b a is the width of PZT; h a is the thickness of PZT; l a is the length of PZT, and the horizontal line above the variable represents the spatial component of the variable; Again, substituting equation (6) into equation (2) yields the strain: Depend on The coefficient A of equation (7) and equation (5) is solved as follows:

6. The DC and even-order harmonic load balancing modeling method based on piezoelectric impedance according to claim 1 is characterized in that: In step S3, first, the driving response of the PZT is determined according to the derivation of equations (5) to (8); the mechanical impedance of the PZT is expressed as the ratio of the excitation force signal to the electrical signal speed response: Where: is the static stiffness of PZT; After introducing the PZT mechanical impedance, equation (8) is simplified to: Then, by substituting equation (10) and B = 0 into equation (5), the output displacement of the PZT self-sensing actuator is obtained as: Afterwards, the strain of the PZT self-sensing actuator is and Combining formula (2), we can get the PZT stress: Substituting equation (12) into equation (3), we can get the electric displacement D3 of PZT: Substituting equation (13) into equation (1) yields the output current I of the PZT: (14)； Substituting equation (14) into Y = I / V, we get the piezoelectric admittance equation of PZT: Then, the load resistor has an adjustment bolt for adjusting the resistance. According to the admittance equation (15) of the piezoelectric material, the piezoelectric sheet is pasted on the adjustment bolt of the load resistor, and the internal characteristics of the piezoelectric material are changed by adjusting the pre-tightening force of the bolt to adjust the impedance of the load resistor.

7. The DC and even-order harmonic load balancing modeling method based on piezoelectric impedance according to claim 1 is characterized in that: In step S4, first, the parameters of the fuzzy control system are determined; The EUT loop current is I1, and the loop impedance is R1. The balanced loop current is I2, and the loop impedance is R2. The total test input current is I; in, And I=I1+I2; when R1 is unchanged, R2 increases, I1 decreases, and I2 increases; when R2 is unchanged, R1 increases, I2 decreases, and I1 increases; Then, the effective value I1 of the test loop current and the effective value I2 of the balance loop current are selected; the control variables are the piezoelectric conductance of the PZT and the bolt rotation angle θ when the PZT is fixed between the bolt and the nut; the output variable is the balance relationship between the two test loops; Secondly, the input variables and output variables are fuzzified and quantified into three language values, each of which corresponds to a membership function; The three language values ​​include I1>I2, I2>I1 and I1=I2; Thirdly, the voltage of the sampling resistor is compared to obtain the current of the two circuits. When V1 is less than V2, that is, the effective value of the tested loop current I1 is less than the effective value of the balanced loop current I2, Kirchhoff's law shows that the balanced loop impedance R2 is less than the tested loop impedance R1, then the tested loop resistance is increased to achieve a load balance state.

8. A DC and even-order harmonic load balancing method based on piezoelectric impedance, characterized in that: The steps include: Step 1: Sample the voltage value V1 of the sampling resistor RA1 of the positive half-cycle waveform flowing through the electric energy meter unit under test and the load resistor RZ1, and the voltage value V2 flowing through the sampling resistor RA2 using the balancing meter as the balancing impedance EUT2 and the load resistor RZ2; Step 2: Determine whether the effective values ​​of the voltage value V1 and the current value V2 are equal; if not, adjust the resistance value of the balancing impedance through the microprocessor corresponding to the load resistor, and then return to step 1.

9. The DC and even-order harmonic load balancing method based on piezoelectric impedance according to claim 8, characterized in that: The preload force of the load resistor is controlled by a motor, which regulates the resistance of the balanced impedance; In step 1, the modeling as claimed in claim 1 is performed, a load balancing device is installed in the current loop of the test equipment, and a test meter and a balancing meter are installed; after the modeling, the voltage value is sampled as follows; Step 1-1: Install the load balancing device test circuit and put in the test instrument EUT1; Step 1-2: Connect the sampling resistor RA1 to the output end of the electric energy meter unit under test, and connect the sampling resistor RA2 to the output end of the balance meter; Step 1-3: collecting voltage signals flowing through the sampling resistors RA1 and RA2, thereby determining voltage waveforms of the voltage values ​​V1 and V2; In step 2; Step 2-1: Obtain the effective value of the voltage of the load resistor and send the calculation result to the microprocessor; Step 2-2: The microprocessor compares the voltage RMS value V1 and the current RMS value V2: If the effective value of the current V1>V2, the microprocessor controls the motor to increase the impedance of the balancing loop and increase the effective value of the voltage V2; If the effective value of the current V1 is less than V2, the microprocessor controls the motor to increase the impedance of the tested circuit and increase the effective value of the current V1; If the effective current value V1 = V2, the load is balanced.

10. The DC and even-order harmonic load balancing method based on piezoelectric impedance according to claim 9, characterized in that: In step 2-1, first, the device is restored to its original position, that is, the PZT material is restored to its original state, and the bolt position of the load resistor at this time is recorded as the initial position 0°; then, the loop voltage is sampled through the sampling resistor, and the voltage of the sampling resistor I is recorded as V1, and the voltage of the sampling resistor II is recorded as V2; The load resistor is crimped by bolts made of PZT material, and the impedance of the two circuits is balanced by adjusting the bolt preload using a motor.

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