A dynamic electricity meter

Abstract

The present invention discloses a design scheme of a dynamic electric energy meter, including: a DA multiplier, an AD sampler, a data latch, an adder, an RC integrator, a V / F converter, an operational amplifier 1, an operational amplifier 2, a flip-flop, an OR gate, and a NOT gate; the binary result of the voltage collected by the AD sampler controls the amplification factor of the DA multiplier; the AC analog quantity of the current is connected to the V ref terminal of the DA multiplier, so that the output of the DA multiplier is proportional to the instantaneous power. The AD sampler is started by the flip-flop. After the sampling is completed, the flip-flop flips, and the collected binary result is sent to the DA multiplier, and the next AD sampling is started through the flip-flop to ensure that the AD sampler and the DA converter perform automatically. The output signal of the DA multiplier is processed by the operational amplifier 1 and the operational amplifier 2 to obtain the instantaneous power, and then the electric energy value is obtained through the RC integrator and the V / F converter. The present invention has the smallest measurement error of electric energy under a dynamically changing load current, and the flip-flop circuit can realize automatic trigger sampling, making the sampling points as dense as possible, and further improving the accuracy of electric energy measurement.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric energy metering, and more particularly, relates to a dynamic watt-hour meter for dynamic electric energy metering. Background Art

[0002] With the integration of variable and unstable distributed power sources such as wind power and photovoltaic power into the power grid, the conversion of DC power transmission to three-phase AC power supply through commutation and inversion, including electric arc furnace steelmaking, inverter medium-frequency electric furnace, variable-frequency speed regulation, etc., has caused many high-frequency fractional harmonics and high-frequency pulses in the load current of the power system. New problems have emerged in the metering of dynamic load electric energy. That is, using standard watt-hour meters composed of AD sampling or time-division separation principle may result in large errors.

[0003] Currently, watt-hour meters measure electric energy by AD sampling, digitize the analog voltage and current, and then calculate the instantaneous power and cumulative electric energy using the digitized values. However, restricted by the sampling rate and resolution of the AD collector, existing watt-hour meters have conversion errors when converting analog quantities to digital quantities. Especially when the load current changes rapidly, there is a possibility of missing the peak value of the current waveform during AD sampling of the current. Through the test of applying fractional harmonics and pulse interference to the sinusoidal current waveform, it is found that the metering error of the watt-hour meter will seriously exceed its allowable limit; indicating that the existing watt-hour meter design scheme does not meet the accuracy class requirements when measuring dynamic electric energy. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a dynamic watt-hour meter to ensure accurate metering of the watt-hour meter in both conventional and dynamic electric energy metering environments.

[0005] To solve the above technical problems, the present invention is realized through the following technical solutions:

[0006] A dynamic watt-hour meter mainly includes: a DA multiplier, an AD sampler, a trigger, a data latch, an adder, an RC integrator, a V / F converter, an operational amplifier 1, and an operational amplifier 2; the four-quadrant DA multiplier multiplies the voltage digital quantity and the current analog quantity to form the instantaneous power, and then obtains the electric energy value through the RC integrator and the V / F converter, and the entire circuit is automatically triggered and controlled by the trigger. First, the AC voltage quantity is converted into a positive analog quantity by the adder, and after AD sampling, its binary sampling result is input to the DA multiplier to control the amplification factor of the DA multiplier; secondly, the AC current analog quantity is directly connected to the V of the DA multiplier refterminal, making the output result of the DA multiplier proportional to the instantaneous power; finally, combined with operational amplifier 1, operational amplifier 2, RC integration circuit and V / F conversion control circuit, a design scheme for single-phase dynamic power metering is obtained, which is conducive to the accurate metering of dynamic unstable electric energy containing harmonics and high-frequency pulse loads.

[0007] Since the voltage waveform is relatively stable, it can be measured by digital sampling method, while the current directly uses the analog quantity itself, that is, a DA multiplier is adopted. Use the binary digital quantity of voltage digital sampling to control the amplification factor of the DA multiplier, and connect the analog quantity of the current to the reference voltage V of the DA multiplier ref terminal. In order to make the AC voltage become a positive number first, an adder is used to add M , M take 1.1 Um . The voltage after the adder is:

[0008]

[0009] In the above formula, Um is the effective value of the sine wave voltage times, is the power frequency angular frequency, is the time.

[0010] The number of bits of the AD sampler is N , and its maximum binary sampling value is . For the sake of simplicity of writing and illustration, taking a 6-bit AD sampler and a 6-stage DA resistor network as an example, the maximum binary sampling value is used to represent 2 M , that is . When the binary result of the AD sampler is: , the current flowing to out1 of the DA multiplier is:

[0011]

[0012] In the above formula, is the AC current formed by the electrical load.

[0013] At this time, the complementary voltage binary sampling value is: , then the current flowing to out2 of the DA multiplier is:

[0014]

[0015] Since and are complementary, there is , thus . The flows into the positive terminal of operational amplifier 1, since the resistors R on the positive and negative sides of the operational amplifier 1 are the same, so , and the current flowing into the negative terminal of the operational amplifier 2 is:

[0016]

[0017] Since the voltage output by the operational amplifier 2 is proportional to the instantaneous power, considering the current and voltage input transformation ratios, the electrical energy value can be obtained by integrating and summing the instantaneous power. When the resolution of the AD sampler is N bits, the general formula for calculating dynamic electrical energy can be obtained as:

[0018]

[0019] Among them, , are the transformation ratios of the voltage transformer and the current transformer respectively.

[0020] The present invention uses a trigger circuit to realize automatic trigger metering of electrical energy. Among them, the OR gate and the NOT gate are connected to the terminal of the AD sampler to start the AD sampler; when the AD sampler finishes collecting, the binary data collected by the AD sampler is sent to the data terminal of the DA multiplier through the data latch, and at the same time, the terminal of the signal indicating that the AD sampler has completed collection is connected to the A terminal of the trigger to flip the trigger; the Q terminal of the trigger is connected to the terminal of the DA multiplier to start the DA multiplier conversion; in addition, the Q terminal of the trigger is also connected to the OR gate and NOT gate circuit for automatic trigger control of the next AD sampling.

[0021] Compared with the prior art, the beneficial effects of the present invention are: the present invention proposes a design scheme for a dynamic watt-hour meter. When calculating electrical energy, the voltage uses digital quantity, and the current directly uses the analog quantity itself. The digitized voltage quantity and the analog current quantity are multiplied by the DA multiplier to obtain a value proportional to the instantaneous power; the dynamic watt-hour meter designed by adopting this scheme has the smallest measurement error of electrical energy under the dynamically changing load current; at the same time, a trigger circuit is specially designed to realize automatic trigger sampling, and the sampling points can be made as dense as possible, further improving the accuracy of electrical energy metering.

[0022] The above description is only an overview of the technical solution of this application. In order to be able to understand the technical means of this application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of this application more obvious and understandable, the following specifically exemplifies the specific implementation manners of this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0024] Figure 1 is the circuit schematic diagram of the dynamic electric energy meter of the present invention;

[0025] Figure 2 is the voltage waveform and current waveform diagram;

[0026] Figure 3 is the schematic diagram of the DA multiplier of the present invention for realizing instantaneous power conversion. Specific Embodiments

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0028] As Figure 1 shown, a dynamic electric energy meter of the present invention mainly includes: a DA multiplier, an AD sampler, a trigger, a data latch, an adder, an RC integrator, a V / F converter, an operational amplifier 1, and an operational amplifier 2; the four-quadrant DA multiplier multiplies the voltage digital quantity and the current analog quantity to form an instantaneous power, and then obtains the electric energy value through the RC integrator and the V / F converter, and the entire circuit is automatically triggered and controlled by the trigger. First, the AC voltage quantity is converted into a positive analog quantity by the adder, and after AD sampling, its binary sampling result is input to the DA multiplier to control the amplification factor of the DA multiplier; secondly, the AC current analog quantity is directly connected to the V ref terminal of the DA multiplier, so that the output result of the DA multiplier is proportional to the instantaneous power; finally, in cooperation with the operational amplifier 1, the operational amplifier 2, the RC integration circuit and the V / F conversion control circuit, a design scheme for single-phase dynamic electric energy metering is obtained, which is beneficial to the accurate metering of electric energy with dynamic instability and containing harmonic and high-frequency pulse loads.

[0029] First, through the current transformer and the adjustment circuit, the current is converted into a voltage and connected to the V ref terminal of the DA multiplier, and the secondary voltage of the voltage transformer , is converted into a positive voltage through the adder and connected to the analog input terminal of the AD sampler. The start of the AD sampler is controlled by the start button. After passing through the OR gate and the NOT gate, it is connected to the terminal of the AD sampler. The low level starts the AD conversion. After the AD conversion is completed, it is The AD sampling completion signal is sent out from the terminal. At the same time, the binary result of the sampled data is held by the data latch and sent to the data terminal of the DA multiplier. At this time, the pulse of the completed AD sampling is also sent to the A terminal of the flip-flop, causing the flip-flop to flip. The pulse signal is sent out in two paths from the Q terminal of the flip-flop. One path is sent to the terminal of the DA multiplier to start the DA multiplier conversion and realize the multiplication of the voltage digital quantity and the current analog quantity. The output of the four-quadrant DA multiplier is proportional to the instantaneous power , and after passing through the RC integration circuit and the V / F conversion, the electric energy value is obtained. The other path is from the Q terminal of the flip-flop, and after being transformed by the OR gate and the NOT gate, it is used to start the next AD sampling. Through this trigger control method, the entire sampling points can be made as dense as possible, which is beneficial to improving the accuracy of dynamic electric energy measurement.

[0030] As Figure 2 shown, in the actual power grid environment, the voltage waveform is relatively stable, and the dynamic change range of the current waveform is large.

[0031] Since the voltage waveform is relatively stable, it can be measured by the method of digital sampling, while the current directly uses the analog quantity itself, that is, the DA multiplier is used. The binary digital quantity of the voltage digital sampling is used to control the amplification factor of the DA multiplier, and the analog quantity of the current is connected to the reference voltage V ref terminal of the DA multiplier. In order to make the AC voltage become a positive number first, an adder is used to add M , M take 1.1 U m . The voltage after passing through the adder is:

[0032]

[0033] In the above formula, Um is the effective value of the sine wave voltage times, is the power frequency angular frequency, is the time.

[0034] As Figure 3 shown, taking a 6-bit AD sampler and a 6-stage DA resistor network as an example, the maximum binary sampling value is used to represent 2 M , that is, . When the binary result of the AD sampler is: , the current flowing to out1 of the DA multiplier is:

[0035]

[0036] In the above formula, is the AC current formed by the electrical load.

[0037] At this time, the complementary voltage binary sampling value is: , then the current flowing into out2 of the DA multiplier is:

[0038]

[0039] Since and are complementary, then , thus . Flowing into the positive terminal of operational amplifier 1 is . Since the resistances R on both the positive and negative sides of operational amplifier 1 are the same, so , and the current flowing into the negative terminal of operational amplifier 2 is:

[0040]

[0041] The voltage output by operational amplifier 2 is proportional to the instantaneous power. Considering the current and voltage input transformation ratios, the electrical energy value can be obtained by integrating and summing the instantaneous power.

[0042] When the resolution of the AD sampler is N bits, the general formula for calculating dynamic electrical energy can be obtained as

[0043]

[0044] Among them, , are the transformation ratios of the voltage transformer and the current transformer respectively.

[0045] As Figure 1 shown, when determining the transformation ratios of the voltage transformer and the current transformer, considering the fluctuations of the voltage and current in the power grid system, the voltage margin is taken as 1.1 times and the current margin is taken as 1.5 times. Then the transformation ratio of the voltage transformer is:

[0046]

[0047] Among them, is the effective value of the fundamental wave voltage input on the primary side, is the maximum peak voltage allowed to be output on the secondary side of the voltage transformer; the transformation ratio of the current transformer is:

[0048]

[0049] Among them, is the effective value of the fundamental wave current input on the primary side, is the equivalent resistance value on the primary side of the current transformer, is the maximum peak voltage allowed to be output on the secondary side of the current transformer.

[0050] As Figure 1As shown, the present invention uses a trigger circuit to achieve automatic trigger metering of electric energy. Among them, the OR gate and the NOT gate are connected to the terminal of the AD sampler to start the AD sampler; after the AD sampler finishes sampling, the binary data sampled by the AD sampler is sent to the data terminal of the DA multiplier through the data latch, and at the same time, the terminal of the signal indicating the completion of sampling by the AD sampler is connected to the A terminal of the trigger to flip the trigger; the Q terminal of the trigger is connected to the terminal of the DA multiplier to start the conversion of the DA multiplier; in addition, the Q terminal of the trigger is also connected to the OR gate and NOT gate circuits for automatic trigger control of the next AD sampling.

[0051] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dynamic electricity meter, characterized in that, Including: DA multiplier, AD sampler, flip-flop, data latch, adder, RC integrator, V / F converter, operational amplifier 1, operational amplifier 2; a four-quadrant DA multiplier is used to calculate the instantaneous power; during the power metering process, the voltage waveform is measured by the AD sampling method, and the current is directly the analog quantity itself; the voltage binary digital quantity collected by the AD sampler is used to control the amplification factor of the DA multiplier, and the AC quantity of the current is connected to the V ref terminal of the DA multiplier, and finally a result proportional to the instantaneous power is obtained; Cooperate with the trigger, the OR gate and the NOT gate are connected to the terminal of the AD sampler to start the AD sampler. After the AD sampler finishes sampling, the binary data sampled by the AD sampler is sent to the data terminal of the DA multiplier through the data latch. At the same time, the terminal of the signal indicating that the AD sampler has completed sampling is connected to the A terminal of the trigger to flip the trigger. At the same time, the Q terminal of the trigger is connected to the terminal of the DA multiplier to start the conversion of the DA multiplier. At the same time, the Q terminal of the trigger is also connected to the OR gate and the NOT gate to perform automatic trigger control for the next AD sampling.

2. The dynamic electricity meter according to claim 1, characterized in that, The voltage digital quantity and the current analog quantity are multiplied by a four-quadrant DA multiplier to form the instantaneous power; among them, the AC voltage quantity is converted into a positive analog quantity by an adder , where , is the angular frequency, t is the time, is the times of the effective value of the sinusoidal AC voltage quantity; The binary sampling result is input to the DA multiplier by AD sampling and is used to control the amplification factor of the DA multiplier; the AC current analog quantity is directly connected to the V ref terminal of the DA multiplier. The output of the DA multiplier is processed by operational amplifier 1 and operational amplifier 2 to obtain a result proportional to the instantaneous power. Finally, the single-phase dynamic electric energy is measured by an RC integrator and a V / F converter.

3. The dynamic electric energy meter according to claim 1, characterized in that, Two-element watt-hour meters that can form three phases, or three-element watt-hour meters for three phases.

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