Test system and test method for testing harmonic transmission characteristics of power voltage transformer

Abstract

The invention discloses a test system and a test method for testing the harmonic transmission characteristics of a power voltage transformer, comprising a power frequency and harmonic voltage generating circuit and a harmonic measuring circuit. The power frequency and harmonic voltage generating circuit can realize the synthesis of power frequency high voltage and harmonic voltage. The latter measures the primary and secondary harmonic transmission characteristics of a voltage transformer TV and realizes value tracing, realizes the synthesis of high and low frequency harmonic voltages and power frequency high voltage, and solves the problem of attenuation of high frequency harmonics by leakage reactance of a power frequency transformer. At the same time, the invention proposes a method for measuring the primary and secondary harmonic transmission characteristics of a power voltage transformer and realizing value tracing under the condition of applying power frequency voltage.

Description

Technical Field

[0001] The invention belongs to the technical field of power system harmonic detection, and in particular relates to a test system and a test method for testing harmonic transmission characteristics of a power voltage transformer. Background Art

[0002] With the development of power systems, especially the development of new energy technologies, the use of a large number of nonlinear loads in power grids, especially power electronic equipment, has caused the harmonic problem of power systems to become more and more significant. In order to prevent harmonics from affecting the quality of power, affecting power metering and relay protection, and interfering with the normal operation of equipment, it is necessary to control the harmonics in the power system. Accurately measuring the harmonics of the power system is the basis for its control. Among the existing harmonic measurement methods, directly using the power voltage transformer of the power grid to measure harmonics is a more convenient method for measuring power system harmonics. The premise of applying this method is to accurately measure the voltage transmission characteristics of the power voltage transformer. Summary of the invention

[0003] The present invention provides a test system and a test method for testing the harmonic transmission characteristics of a power voltage transformer, the purpose of which is to add a mixed signal synthesized by power frequency high voltage and harmonic voltage to the power voltage transformer, and test the harmonic transmission characteristics of the power voltage transformer within the entire harmonic frequency range.

[0004] To achieve the above object, the test system for testing the harmonic transmission characteristics of the power voltage transformer of the present invention comprises a power frequency and harmonic voltage generating circuit and a harmonic measurement circuit; the power frequency and harmonic voltage generating circuit comprises a power frequency voltage source, a voltage regulator T 1 , Step-up transformer T 2 , high frequency harmonic damper, coupling capacitor C 1 , high frequency harmonic source, low frequency harmonic source and DDS standard signal source; the power frequency voltage source, voltage regulator T 1 , Step-up transformer T 2 The three primary sides are cascaded; the low-frequency harmonic source, the step-up transformer T 2 The secondary side is connected in series with the high-frequency harmonic damper, and the high-frequency harmonic damper is connected to the primary side of the voltage transformer under test; the high-frequency harmonic source is connected to the coupling capacitor C 1 Series, coupling capacitor C 1 and connected to the primary side of the voltage transformer under test; the first output end of the DDS standard signal source is connected to the low-frequency harmonic source, and the second output end is connected to the high-frequency harmonic source; the harmonic measurement circuit includes a capacitor C 2 , shunt resistor R s , preamplifier D, lock-in amplifier A and lock-in amplifier B; the capacitor C 2 Connected in parallel with the primary side of the voltage transformer TV under test, the shunt resistor R s With capacitor C2 Series, shunt resistor R s In parallel with the preamplifier D, the output end of the preamplifier D is connected to the input end of the phase-locked amplifier B, the secondary side of the voltage transformer TV under test is connected to the output end of the phase-locked amplifier A, and the third output end of the DDS standard signal source is connected to the reference ends of the phase-locked amplifier A and the phase-locked amplifier B.

[0005] Furthermore, the high frequency harmonic damper includes a parallel inductor L d and capacitor C d .

[0006] Furthermore, an attenuator is connected between the secondary side of the voltage transformer under test and the output end of the lock-in amplifier A.

[0007] Furthermore, the high frequency harmonic source includes an isolation transformer T n , rectifier bridge, transistor VT 1 , voltage stabilizing capacitor C 5 , linear voltage regulator module, H bridge and filter; the isolation transformer T n With the rectifier bridge, the voltage stabilizing capacitor C 5 , a linear voltage regulator module, an H bridge and a filter cascade; the linear voltage regulator module includes a base resistor R b , isolation operational amplifier D 1 , driving circuit, voltage divider resistor R 1 , voltage divider resistor R 2 and output capacitor C 6 ; The base resistor R b The first end of the transistor VT 1 The base of transistor VT is connected to the output terminal of the driving circuit. 1 The collector and the voltage stabilizing capacitor C 5 The first end of the transistor VT 1 The emitter of the drive circuit, the ground terminal, and the voltage divider resistor R 1 The first end of the output capacitor C 6 The first end of the isolation amplifier is connected to the same node, the output end of the isolation amplifier is connected to the input end of the driving circuit, and the reverse input end of the isolation amplifier is connected to the voltage divider resistor R 2 The first end and the voltage divider resistor R 1 The second end of the voltage divider resistor R 2 The second end of the voltage stabilizing capacitor C 5 The second terminal and output capacitor C 6 The second ends of are grounded.

[0008] Furthermore, the filter is an LCL filter.

[0009] Furthermore, the low frequency harmonic source includes an isolation transformer Tn , rectifier bridge, transistor VT 1 , voltage stabilizing capacitor C 5 , linear voltage regulator module, H bridge and LC filter; the isolation transformer T n With the rectifier bridge, the voltage stabilizing capacitor C 5 , a linear voltage regulator module, an H bridge and an LC filter cascade; the linear voltage regulator module includes a base resistor R b , isolation operational amplifier D 1 , driving circuit, voltage divider resistor R 1 , voltage divider resistor R 2 and output capacitor C 6 ; The base resistor R b One end of the transistor VT 1 The base of transistor VT is connected to the output terminal of the driving circuit. 1 The collector and the voltage stabilizing capacitor C 5 Connection, transistor VT 1 The emitter of the drive circuit, the ground, and the voltage divider resistor R 1 One end of the output capacitor C 6 The output of the isolation operational amplifier is connected to the input of the driving circuit, and the reverse input of the isolation operational amplifier is connected to the voltage divider resistor R 2 One end of the voltage divider resistor R 1 Connect one end of the voltage divider resistor R 2 , voltage stabilizing capacitor C 5 and output capacitor C 6 Both are grounded.

[0010] Furthermore, the H-bridge is composed of four silicon carbide MOS tubes.

[0011] A method for testing harmonic transmission characteristics of a power voltage transformer based on the test system of the claim comprises the following steps:

[0012] S1. Measure the primary and secondary voltages of the voltage transformer under test:

[0013] Regardless of the frequency of the harmonic signal expected to be applied, the power frequency test voltage is provided to the voltage sensor under test through the power frequency voltage source, and the secondary side voltage of the voltage transformer under test is measured through the lock-in amplifier A;

[0014] When the transmission efficiency of the low-frequency harmonic source is greater than or equal to 50% under the expected applied harmonic signal, the low-frequency harmonic source is used to provide the harmonic voltage for the voltage transformer under test, otherwise the high-frequency harmonic source is used to provide the harmonic voltage for the voltage transformer under test;

[0015] When the signal-to-noise ratio of the lock-in amplifier is greater than or equal to 0.01% under the expected harmonic signal, the primary voltage of the voltage transformer under test is measured with the lock-in amplifier B, otherwise the output voltage of the harmonic source is measured with a standard voltmeter as the primary voltage of the voltage transformer under test;

[0016] S2. Calculate the harmonic transmission characteristics of the voltage transformer under test based on the amplitude and phase of the primary side voltage and the secondary side voltage.

[0017] Furthermore, before the primary side voltage and the secondary side voltage of the voltage transformer under test, the test system is traced; the traceability includes: when only the harmonic voltage is contained, the capacitor C 2 The capacitance value of capacitor C is tested; when there are both harmonic voltage and power frequency voltage 2 The capacitance value is calibrated; the measurement accuracy of lock-in amplifier A, lock-in amplifier B and preamplifier is verified.

[0018] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0019] The present invention better realizes the synthesis of high and low frequency harmonic voltages and industrial frequency high voltage. Compared with the method of directly connecting the harmonic voltage source and the industrial frequency transformer in series, the connection method proposed by the present invention can effectively reduce the attenuation of high frequency harmonics by the leakage reactance of the industrial frequency transformer, thereby greatly reducing the capacity requirements for the harmonic voltage source.

[0020] The present invention connects the low-frequency harmonic source in series with the secondary side of the high-voltage step-up transformer, so that the transformer leakage reactance has a relatively small corresponding impedance value when the frequency is low. Therefore, the transformer leakage reactance has a relatively small attenuation on the low-frequency harmonics, the harmonic transmission efficiency is relatively high, and the capacity requirement for the low-frequency harmonic voltage source is not large; however, when the frequency is high, the transformer leakage reactance has a large attenuation on the harmonic voltage, which puts forward very high requirements on the capacity of the high-frequency harmonic source. Therefore, in the present invention, the high-frequency harmonic source is not connected in series with the secondary side of the transformer, but the high-frequency harmonic source and the coupling capacitor C are used. 1 In the series connection method, since the high-frequency harmonic damper resonates in parallel at the added harmonic frequency, the branch where the leakage reactance of the step-up transformer T2 is located is approximately open-circuited, so the voltage added to the primary side of the voltage transformer under test depends only on the coupling capacitor C. 1 And the standard capacitor C 2 The transformation ratio of the capacitive voltage divider is formed, which is independent of the leakage reactance, thereby greatly reducing the requirements on the capacity of the high-frequency harmonic source.

[0021] Furthermore, in the present invention, the high-frequency and low-frequency harmonic sources use a linear voltage regulator module to adjust the voltage, and the output voltage is adjusted by adjusting the voltage drop of the transistor, firstly, to resist the ripple generated by the rectifier bridge in front of the linear voltage regulator module, and secondly, to resist the voltage pulsation generated by the power frequency current on the output capacitor of the linear voltage regulator module, so that the voltage applied to the H bridge is a stable DC voltage. And the open-loop gain of the isolation operational amplifier D1 is as high as more than 10,000, so that the control bandwidth of the linear voltage regulator module can be very high, thereby effectively suppressing disturbances and improving waveform quality.

[0022] At the same time, the present invention proposes a method for measuring the primary and secondary harmonic transmission characteristics of a power voltage transformer under the condition of applying an industrial frequency voltage and realizing value traceability, so as to accurately measure the primary and secondary harmonic transmission characteristics of the voltage transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the implementation principle of the present invention;

[0024] Figure 2 It is an equivalent schematic diagram of the low-frequency harmonic source and the secondary side of the high-voltage step-up transformer in series;

[0025] Figure 3 It is an equivalent schematic diagram of high frequency harmonic source and coupling capacitor in series;

[0026] Figure 4 It is the implementation principle diagram of the high and low frequency harmonic sources in the present invention;

[0027] Figure 5 This is the calibration experimental circuit diagram of the lock-in amplifier B and the preamplifier;

[0028] Figure 6 This is the calibration experimental circuit diagram of the lock-in amplifier A;

[0029] Figure 7 The circuit diagram is for calibrating standard capacitors in the presence of both harmonics and power frequency voltage. DETAILED DESCRIPTION

[0030] In order to make the purpose and technical solution of the present invention clearer and easier to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more. In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] Example 1

[0033] The test system for testing the harmonic transmission characteristics of power voltage transformers includes two parts: a power frequency and harmonic voltage generating circuit and a harmonic measurement circuit. The power frequency and harmonic voltage generating circuit can realize the synthesis of power frequency high voltage and harmonic voltage. The latter measures the primary and secondary harmonic transmission characteristics of the voltage transformer TV and realizes value traceability.

[0034] The power frequency and harmonic voltage generation circuit consists of a power frequency voltage source, a voltage regulator T 1 , Step-up transformer T 2 , high frequency harmonic damper, coupling capacitor C 1 , high-frequency harmonic source, low-frequency harmonic source and DDS standard signal source. Among them, the high-frequency harmonic damper consists of an inductor L d and capacitor C d The power frequency voltage source regulator and the step-up transformer are connected in parallel to provide an adjustable power frequency high voltage source. 1 and step-up transformer T 2 Provide power frequency test high voltage for the primary side of the voltage transformer TV under test; low frequency harmonic source and step-up transformer T 2 The secondary side is connected in series to provide low-frequency harmonic voltage for the voltage transformer TV under test; the high-frequency harmonic source and the coupling capacitor C 1Connected in series, providing high-frequency harmonic voltage for voltage transformer TV; inductor L d and capacitor C d At the harmonic frequency, it generates an extremely high impedance, preventing the high-frequency harmonic current from passing through the step-up transformer T. 2 The high-frequency harmonic current flows almost entirely through the standard capacitor C 2 , so that the high-frequency harmonic voltage is relatively higher, improving the transmission efficiency. The second output end of the DDS standard signal source is connected to the high-frequency harmonic source, and the first output end is connected to the low-frequency harmonic source.

[0035] The function of the DDS standard signal source in this circuit is to generate a harmonic sinusoidal reference signal u ref1 and / or ref2 , U ref1 Relative to U ref2 The frequency is lower and the harmonic sinusoidal reference signal u ref1 Provided to the low-frequency harmonic source as its given signal, the harmonic sinusoidal reference signal u ref2 1 is provided to the high-frequency harmonic source as its given signal. Compared with the traditional method of directly connecting the harmonic voltage source and the power frequency transformer in series, the connection method proposed by the present invention can effectively reduce the attenuation of the high-frequency harmonics by the leakage reactance of the power frequency transformer, thereby greatly reducing the capacity requirements for the harmonic voltage source. Specifically, the low-frequency harmonic source is connected in series with the secondary side of the high-voltage step-up transformer, and its equivalent schematic diagram is shown in FIG. Figure 2 The advantage of this wiring method is that the transformer leakage reactance has a relatively small corresponding impedance value when the frequency is low, so the transformer leakage reactance has a relatively small attenuation on low-frequency harmonics, the harmonic transmission efficiency is relatively high, and the capacity requirement for the low-frequency harmonic voltage source is not large; however, when the frequency is high, the transformer leakage reactance has a large attenuation on the harmonic voltage, which puts forward high requirements on the capacity of the high-frequency harmonic source. Therefore, in the present invention, the high-frequency harmonic source is not connected in series with the secondary side of the transformer, but a high-frequency harmonic source and a coupling capacitor C are used. 1 For the concatenation method, see Figure 3 At this time, since the high-frequency harmonic damper has parallel resonance at the added harmonic frequency, the branch where the leakage reactance of the step-up transformer T2 is located is approximately open-circuited, so the voltage added to the primary side of the voltage transformer TV depends only on the coupling capacitor C 1 And the standard capacitor C 2 The transformation ratio of the capacitive voltage divider is independent of the leakage reactance. By properly selecting C 1 and C 2 The capacitance value of the harmonic transmission efficiency can reach Zc2 / / Zin / (Zc1+Zc2 / / Zin), where Zin refers to the input impedance of the voltage transformer TV, and Zc1 is C 1 The impedance of Zc2 is C 2 This greatly reduces the requirements for the capacity of high-frequency harmonic sources. 1and C 2 There is no fixed method for choosing the capacitance value. For the same system, C 1 and C 2 The value of is not unique, but it can be obtained through some calculations. 1 and C 2 When the capacitance value is constant, the test frequency range of high and low frequency harmonic sources.

[0036] The coupling capacitor C is selected according to the following three conditions 1 And the standard capacitor C 2 Capacitance value:

[0037] 1) ω1>ω2; ω1 is an intermediate variable. When ω=ω1, the relative error between the output voltage of the low-frequency harmonic source and the voltage applied to the voltage sensor under test is 0.1%; ω2 is an intermediate variable. When ω=ω2, the signal-to-noise ratio of the input channel of the lock-in amplifier is 1 / 10000;

[0038] 2) ω3>200; ω3 is an intermediate variable. When ω=ω3, the transmission efficiency of the low-frequency harmonic source is 50%;

[0039] 3) High-frequency power transmission efficiency E 高 >50%; C 1 >C 2 ;

[0040] The ω that satisfies formula (1) is denoted as ω1

[0041]

[0042] in,

[0043] It represents the total impedance of C1, C2 in parallel with the input impedance of the voltage transformer under test, is the total impedance of capacitors C1 and C2 in parallel, Z in is the input impedance of the voltage transformer under test; ω is the frequency; L 漏 is the leakage inductance of the voltage transformer under test;

[0044] The ω that satisfies formula (2) is denoted as ω2

[0045]

[0046] in,

[0047] Among them, I xHZ is the effective value of the harmonic current flowing through C2; I 50HZ is the effective value of the power frequency current flowing through capacitor C2; U 谐波源有效值is the effective value of the output voltage of the harmonic source; U 50HZ It is the effective value of the power frequency high voltage output by the step-up transformer T2; is the coupling capacitor C 1 Impedance; is the coupling capacitor C 2 Impedance; is the total impedance of C1 in parallel with the input impedance of the voltage transformer under test;

[0048] The ω that satisfies formula (3) is denoted as ω3

[0049]

[0050] The harmonic measurement circuit consists of capacitor C 2 , shunt resistor R s , preamplifier D, lock-in amplifier A, lock-in amplifier B and attenuator, capacitor C 2 is a high voltage standard capacitor, and the shunt resistor R s is a standard shunt resistor. Capacitor C 2 Connected in parallel with the primary side of the voltage transformer TV, the shunt resistor R s With capacitor C 2 Series, shunt resistor R s It is connected in parallel with the preamplifier D, the output end of the preamplifier D is connected to the input end of the phase-locked amplifier B, the secondary side of the voltage transformer TV is connected to the attenuator, and the attenuator is connected to the output end of the phase-locked amplifier A.

[0051] The third output terminal of the DDS standard signal source is connected to the reference terminal of the lock-in amplifier A and the reference terminal of the lock-in amplifier B; the capacitor C 2 The function is to convert the power frequency and harmonic test voltage applied to the primary side of the voltage transformer TV into current. The shunt resistor R s The current is converted into a small voltage signal and provided to the preamplifier D for amplification, and then the amplified signal is provided to the phase-locked amplifier B. The function of the phase-locked amplifier is to separate and measure the amplitude and phase of the signal component with the same frequency as the reference end signal from the mixed signal at the input end. This measurement circuit uses two phase-locked amplifiers (A and B), and the reference end signal is provided by the DDS standard signal source. The function of the phase-locked amplifier A is to measure the amplitude and phase of the harmonic voltage on the secondary side of the voltage transformer TV. The measured secondary side harmonic voltage amplitude U 2h Meet U 2h =K 2 U 2x , where K 2 is the attenuator ratio, U 2x is the effective value of the harmonic signal measured by the lock-in amplifier A, and the measured voltage secondary side harmonic voltage phase φ 2h Satisfy φ 2h =φ2x ,φ 2x It is the phase of the harmonic signal measured by the lock-in amplifier A; the function of the lock-in amplifier B is to measure the amplitude and phase of the harmonic voltage on the primary side of the voltage transformer TV. The measured voltage amplitude U 1h satisfy Where K 1 is the gain of the preamplifier D, U 1x is the effective value of the harmonic signal measured by the lock-in amplifier B, R s is the resistance value of the standard shunt resistor, ω is the signal frequency you want to measure, C 2 is the standard capacitor C 2 The capacitance value of the measured primary side harmonic voltage phase φ 1h Satisfy φ 1h =φ 1x -90°, φ 1x It is the phase of the harmonic signal measured by lock-in amplifier B.

[0052] The harmonic transmission characteristics of the voltage transformer VT include amplitude-frequency characteristics and phase-frequency characteristics:

[0053] The amplitude-frequency characteristic of the voltage transformer VT is obtained by the following formula:

[0054]

[0055] The phase-frequency characteristic of the voltage transformer VT is obtained by the following formula:

[0056]

[0057] The core of the measurement circuit is to take the capacitor current as the detection object of the phase-locked amplifier. The dynamic reserve of the phase-locked amplifier is very high. The phase-locked amplifier can have a dynamic reserve of up to 120dB, which means that it can achieve accurate measurement when the signal-to-noise ratio is as low as 1ppm. The principle of the phase-locked amplifier is that it works according to the orthogonality principle of the sine function. Specifically, the mixed signal at the input end of the phase-locked amplifier is multiplied by the signal of the reference channel, and then the product is integrated. Only the component with the same frequency as the reference end in the mixed signal can be retained after integration, and the integral result corresponding to any component with a different frequency from the reference end is zero, which realizes the separation of the mixed signal at the input end and the measurement of the signal component with the same frequency as the reference end signal.

[0058] Reference Figure 4 The function of high-frequency harmonic source is to generate high frequency. Its topology is composed of isolation transformer T n , rectifier bridge, transistor VT 1 , voltage stabilizing capacitor C 5, linear voltage regulator module, H-bridge, filter, SPWM modulator and isolation drive circuit. The filter is an LCL filter, and the H-bridge is composed of four MOS tubes. In order to generate high-frequency harmonics, a higher switching frequency is required, so the MOS tube uses silicon carbide MOSFET;

[0059] Isolation transformer T n With the rectifier bridge, the voltage stabilizing capacitor C 5 , linear voltage regulator module, H-bridge and LCL filter cascade. The output end of the SPWM modulator is connected to the input end of the isolation drive circuit, and the isolation drive circuit is connected to the H-bridge.

[0060] The linear voltage regulator module includes a base resistor R b , isolation operational amplifier D 1 , driving circuit, voltage divider resistor R 1 , voltage divider resistor R 2 and output capacitor C 6 . Voltage divider resistor R 1 , voltage divider resistor R 2 The base resistor R b The first end of the transistor VT 1 The base of transistor VT is connected to the output terminal of the driving circuit. 1 The collector and the voltage stabilizing capacitor C 5 The first end of the transistor VT 1 The emitter of the drive circuit, the ground, and the voltage divider resistor R 1 The first end of the output capacitor C 6 The first end of the isolation amplifier is connected to the same node, the output end of the isolation amplifier is connected to the input end of the driving circuit, and the reverse input end of the isolation amplifier is connected to the voltage divider resistor R 2 The first end and the voltage divider resistor R 1 The second end of the voltage divider resistor R 2 The second end of the voltage stabilizing capacitor C 5 The second terminal and output capacitor C 6 The second ends of are grounded.

[0061] Reference Figure 4 The function of the low-frequency harmonic source is to generate low-frequency harmonics. Its topology is different from that of the high-frequency harmonic source only in the filter. The low-frequency harmonic source uses an LC filter.

[0062] Because the harmonic content of the power grid is usually less than 5%, this means that the ratio of the harmonic voltage that needs to be applied to the upper TV to the power frequency high voltage is less than 5%, so the harmonic voltage of the TV is not large, the harmonic capacity that needs to be applied to the TV will not be large, and the power is naturally relatively small; on the other hand, the active loss of the TV is small, so the power is very small, so the current generated by the entire harmonic source in the entire system is not particularly large, and the power requirement is not very large, so this harmonic source uses a linear voltage regulator module to adjust the voltage, and adjusts the output voltage by adjusting the tube voltage drop of the triode. The function of this module is to resist the ripple generated by the rectifier bridge in front of the linear voltage regulator module, and secondly, to resist the power frequency current in the output capacitor C of the linear voltage regulator module. 6 The voltage pulsation generated on the H-bridge makes the voltage added to the H-bridge a stable DC voltage. The open-loop gain of the isolation operational amplifier D1 is as high as more than 10,000. The control bandwidth of the module can be very high, which can effectively suppress disturbances and improve the waveform quality. It should be noted that the maximum withstand voltage of the device limits the maximum output voltage of a single harmonic source. If a very high harmonic voltage needs to be output, just connect several identical high-frequency or low-frequency harmonic sources in series.

[0063] Example 2

[0064] The specific working process of the present invention is described by taking the transmission characteristic test of a capacitive voltage transformer CVT as an example:

[0065] Table 1 describes the specific working conditions and measured parameter values ​​of each device in this example, and Table 2 describes the harmonic sources and measurement methods applicable to different frequency ranges in this example.

[0066] Table 1

[0067]

[0068] The maximum dynamic reserve of the phase-locked amplifier is up to 130 dB, but in order to ensure that the measurement has sufficient accuracy, only 80 dB of the dynamic reserve is used, that is, the phase-locked amplifier is used for measurement under the condition of a signal-to-noise ratio of 0.01%.

[0069] Table 2

[0070]

[0071] When the frequency of the harmonic signal to be applied is less than 4 Hz, a low-frequency harmonic source is used to provide the harmonic voltage. At this time, the difference between the output voltage of the harmonic source and the harmonic voltage on the primary side of the CVT is less than 0.02%. Therefore, a direct measurement method is adopted, that is, a standard voltmeter is used to directly measure the output voltage of the low-frequency harmonic source as the primary side voltage of the CVT.

[0072] When the frequency of the harmonic signal to be applied is greater than 4 Hz and less than 468 Hz, a low-frequency harmonic source is used to provide the harmonic voltage. The signal-to-noise ratio of the input channel of the lock-in amplifier B is greater than 0.1%, and the power frequency noise has little effect. Therefore, the primary side harmonic voltage is measured by the lock-in amplifier B. It should be noted that when a low-frequency source is used to provide the harmonic voltage, the circuit will have series resonance near 300 Hz, but due to the 25 kΩ copper loss equivalent resistance on the secondary side of the transformer, no large current will be generated.

[0073] When the frequency of the harmonic signal to be applied is greater than 468 Hz, a high-frequency source is used to provide the harmonic voltage, and the primary-side harmonic voltage is obtained through the lock-in amplifier B.

[0074] Regardless of the frequency of the harmonic signal expected to be applied, the power frequency test high voltage is provided to the voltage sensor CVT under test through the power frequency voltage source, and the CVT secondary side voltage is measured through the phase-locked amplifier A.

[0075] The harmonic transmission characteristics of the voltage transformer under test are calculated based on the amplitude and phase of the primary and secondary voltages. When tracing the measurement system, since the capacitance of the high-voltage standard capacitor, the standard shunt resistor, and the DDS standard signal source are all standard instruments, as long as the measurement accuracy of the lock-in amplifier and the preamplifier D is verified, the accuracy of the entire measurement system can be determined, and then the value traceability can be achieved.

[0076] The specific method of realizing value traceability in this system includes two steps:

[0077] First, the high voltage standard capacitor C is tested when only harmonic voltage is present. 2 The capacitance value is tested; when there are both harmonic voltage and power frequency voltage, the high voltage standard capacitor C 2 The capacitance value is calibrated.

[0078] Second, the measurement accuracy of lock-in amplifier A, lock-in amplifier B and preamplifier is verified;

[0079] When there are both harmonic voltage and power frequency voltage, it is necessary to test the high voltage standard capacitor C of the standard instrument. 2 The reason for calibrating the capacitance is that the change in the amplitude of the power frequency high voltage may affect the high voltage standard capacitor C 2 The capacitance value of the capacitor deviates from the standard value, so it is necessary to obtain the high voltage standard capacitor C 2 The capacitance value under different power frequency high voltage amplitudes, that is, the high voltage standard capacitor C 2 Perform calibration.

[0080] (1) Under low voltage conditions, the high voltage standard capacitor C 2 The accuracy of

[0081] When only low-voltage harmonic source is added, the high-voltage standard capacitor C is measured by bridge method and other methods. 2 The capacitance value of the capacitor can be accurately verified to achieve value traceability. Since the low-voltage standard capacitor has a good frequency response characteristic, it can be used to verify the accuracy of the high-voltage standard capacitor C 2 The capacitance value can be verified and its value traceability can be achieved under low pressure conditions.

[0082] (2) Calibration of the lock-in amplifier

[0083] The calibration of the lock-in amplifier B and the preamplifier is as follows: Figure 5 As shown in the figure, the DDS standard signal source, attenuator A and attenuator B are all standard instruments. The function of attenuator A is to attenuate the harmonic signal to reduce the proportion of the harmonic signal in the power frequency signal, and the function of attenuator B is to attenuate the mixed signal to ensure that the mixed signal can be within the range of the input channel of the lock-in amplifier after the attenuator B and the preamplifier D.

[0084] The calibration of the lock-in amplifier A is as follows: Figure 6 As shown in the figure, the DDS standard signal source, attenuator A and attenuator B are all standard instruments. The function of attenuator A is to attenuate the harmonic signal to reduce the proportion of the harmonic signal in the power frequency signal, and the function of attenuator B is to attenuate the mixed signal to ensure that the mixed signal can be within the range of the input channel of the lock-in amplifier after the attenuator B and the preamplifier D.

[0085] (3) When both harmonics and power frequency voltage are present, the high voltage standard capacitor C 2 Calibration: It should be noted that the coupling capacitor C 1 It is necessary to select a high voltage standard capacitor C 2 High-voltage capacitors with the same material and manufacturing process are used to ensure that the subsequent adjustment of the power frequency voltage has no effect on the coupling capacitor C. 1 With high voltage standard capacitor C 2 The influence law is the same, so (C 1 +C 2 ) / C 1 This voltage division ratio remains unchanged to prevent changes in the power frequency high voltage from affecting the harmonic voltage applied to the high voltage standard capacitor.

[0086] like Figure 7 As shown, the power frequency high voltage is not applied first, only the low frequency voltage is applied, and the current flows through the high voltage standard capacitor C 2 The current I c2 Contains harmonic current components, but does not contain power frequency current components. The current flowing through the high voltage standard capacitor C is obtained through the phase-locked amplifier. 2 Harmonic current I ch2 , at this time the harmonic voltage U ch2, harmonic current I ch2 And the high voltage standard capacitor C when the frequency is not processed 2 Capacitance C 2 Satisfy the following formula

[0087]

[0088] Then change the power frequency voltage and keep the harmonic voltage source output unchanged; at this time, since the output of the harmonic voltage source is not adjusted, and the power frequency voltage has no effect on C 1 With C 2 The influence law is the same, that is, (C 1 +C 2 ) / C 1 This voltage division ratio remains unchanged during the adjustment of the power frequency voltage, so the change of the power frequency high voltage will not affect the harmonic voltage added to the high voltage standard capacitor. In other words, after changing the power frequency voltage, the harmonic voltage U ch2 There is no change compared to before the power frequency voltage is changed. However, the change of power frequency voltage may affect the high voltage standard capacitor C 2 With coupling capacitor C 1 The capacitance value causes the high voltage standard capacitor C 2 The harmonic current on the capacitor changes, and the current flowing through the high-voltage standard capacitor C after the power frequency voltage is changed is accurately measured. 2 Harmonic current I' ch2 , at this time the harmonic voltage U ch2 , harmonic current I' ch2 And the high voltage standard capacitor C after applying the power frequency high voltage 2 The capacitance value satisfies the following formula

[0089]

[0090] According to formula (1) and formula (2), we have formula (3)

[0091]

[0092] According to this formula, the capacitance C' of the high-voltage standard capacitor after applying the power frequency high voltage is obtained. 2 , thus achieving the high voltage standard capacitor C in the case of both harmonics and power frequency voltage 2 Perform calibration.

[0093] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A test system for testing harmonic transmission characteristics of power voltage transformer, characterized in that: Including power frequency and harmonic voltage generating circuit and harmonic measuring circuit; The power frequency and harmonic voltage generating circuit includes a power frequency voltage source, a voltage regulator T1, a step-up transformer T2, a high-frequency harmonic damper, a coupling capacitor C1, a high-frequency harmonic source, a low-frequency harmonic source and a DDS standard signal source; The power frequency voltage source, the voltage regulator T1, and the primary side of the step-up transformer T2 are cascaded; the low-frequency harmonic source, the secondary side of the step-up transformer T2 and the high-frequency harmonic damper are connected in series, and the high-frequency harmonic damper is connected to the primary side of the voltage transformer under test; the high-frequency harmonic source is connected in series with the coupling capacitor C1, and the coupling capacitor C1 is connected to the primary side of the voltage transformer under test; the first output end of the DDS standard signal source is connected to the low-frequency harmonic source, and the second output end is connected to the high-frequency harmonic source; The harmonic measurement circuit includes capacitor C2, shunt resistor R s , preamplifier D, lock-in amplifier A and lock-in amplifier B; the capacitor C2 is connected in parallel with the primary side of the voltage transformer TV under test, and the shunt resistor R s In series with capacitor C2, shunt resistor R s In parallel with the preamplifier D, the output end of the preamplifier D is connected to the input end of the phase-locked amplifier B, the secondary side of the voltage transformer TV under test is connected to the output end of the phase-locked amplifier A, and the third output end of the DDS standard signal source is connected to the reference ends of the phase-locked amplifier A and the phase-locked amplifier B.

2. A test system for testing harmonic transmission characteristics of a power voltage transformer according to claim 1, characterized in that: The high frequency harmonic damper includes a parallel inductor L d and capacitor C d .

3. A test system for testing harmonic transmission characteristics of a power voltage transformer according to claim 1, characterized in that: The secondary side of the voltage transformer under test and the output end of the phase-locked amplifier A are connected with an attenuator.

4. A test system for testing harmonic transmission characteristics of a power voltage transformer according to claim 1, characterized in that: The high frequency harmonic source includes an isolation transformer T n , rectifier bridge, transistor VT1, voltage stabilizing capacitor C5, linear voltage stabilizing module, H bridge and filter; The isolation transformer T n Cascaded with the rectifier bridge, voltage stabilizing capacitor C5, linear voltage stabilizing module, H bridge and filter; The linear voltage regulator module includes a base resistor R b , isolation operational amplifier D1, drive circuit, voltage divider resistor R1, voltage divider resistor R2 and output capacitor C6; the base resistor R b The first end is connected to the base of the transistor VT1, the second end is connected to the output end of the driving circuit, the collector of the transistor VT1 is connected to the first end of the voltage-stabilizing capacitor C5, the emitter of the transistor VT1, the ground end of the driving circuit, the first end of the voltage-dividing resistor R1, and the first end of the output capacitor C6 are connected at the same node, the output end of the isolation operational amplifier is connected to the input end of the driving circuit, the reverse input end of the isolation operational amplifier is connected to the first end of the voltage-dividing resistor R2 and the second end of the voltage-dividing resistor R1, and the second end of the voltage-dividing resistor R2, the second end of the voltage-stabilizing capacitor C5, and the second end of the output capacitor C6 are all grounded.

5. A test system for testing harmonic transmission characteristics of a power voltage transformer according to claim 4, characterized in that: The filter is an LCL filter.

6. A test system for testing harmonic transmission characteristics of a power voltage transformer according to claim 1, characterized in that: The low-frequency harmonic source includes an isolation transformer T n , rectifier bridge, transistor VT1, voltage stabilizing capacitor C5, linear voltage stabilizing module, H bridge and LC filter; The isolation transformer T n Cascaded with the rectifier bridge, voltage stabilizing capacitor C5, linear voltage stabilizing module, H bridge and LC filter; The linear voltage regulator module includes a base resistor R b , isolation operational amplifier D1, drive circuit, voltage divider resistor R1, voltage divider resistor R2 and output capacitor C6; the base resistor R b One end is connected to the base of the transistor VT1, and the other end is connected to the output end of the driving circuit. The collector of the transistor VT1 is connected to the voltage-stabilizing capacitor C5. The emitter of the transistor VT1, the ground of the driving circuit, one end of the voltage-dividing resistor R1, and one end of the output capacitor C6 are connected at the same node. The output end of the isolation operational amplifier is connected to the input end of the driving circuit. The reverse input end of the isolation operational amplifier is connected to one end of the voltage-dividing resistor R2 and one end of the voltage-dividing resistor R1. The voltage-dividing resistor R2, the voltage-stabilizing capacitor C5, and the output capacitor C6 are all grounded.

7. A test system for testing harmonic transmission characteristics of a power voltage transformer according to claim 4 or 6, characterized in that: The H bridge is composed of four silicon carbide MOS tubes.

8. A method for testing harmonic transmission characteristics of a power voltage transformer based on the test system of claim 1, characterized in that: The following steps are involved: S1. Measure the primary and secondary voltages of the voltage transformer under test: Regardless of the frequency of the harmonic signal expected to be applied, the power frequency test voltage is provided to the voltage sensor under test through the power frequency voltage source, and the secondary side voltage of the voltage transformer under test is measured through the lock-in amplifier A; When the transmission efficiency of the low-frequency harmonic source is greater than or equal to 50% under the expected applied harmonic signal, the low-frequency harmonic source is used to provide the harmonic voltage for the voltage transformer under test, otherwise the high-frequency harmonic source is used to provide the harmonic voltage for the voltage transformer under test; When the signal-to-noise ratio of the lock-in amplifier is greater than or equal to 0.01% under the expected harmonic signal, the primary voltage of the voltage transformer under test is measured with the lock-in amplifier B, otherwise the output voltage of the harmonic source is measured with a standard voltmeter as the primary voltage of the voltage transformer under test; S2. Calculate the harmonic transmission characteristics of the voltage transformer under test based on the amplitude and phase of the primary side voltage and the secondary side voltage.

9. A method for testing harmonic transmission characteristics of a power voltage transformer according to claim 8, characterized in that: Before the primary side voltage and the secondary side voltage of the voltage transformer under test, the test system is traced; the traceability includes: verifying the capacitance of capacitor C2 when only harmonic voltage is present; calibrating the capacitance of capacitor C2 when both harmonic voltage and power frequency voltage are present; and verifying the measurement accuracy of lock-in amplifier A, lock-in amplifier B and preamplifier.

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