AVR transformer control method and device comprising same

Abstract

The invention provides a control method of an AVR transformer connected in a loop, a primary side of the AVR transformer is provided with a first winding and a second winding for receiving input voltage, a secondary side of the AVR transformer is provided with a third winding for providing output voltage, and the AVR transformer is provided with a temperature control switch capable of disconnecting the first winding from the primary side in an abnormal state; the method comprises the following steps: judging whether the AVR transformer is in a step-down mode or not, and if not, judging whether the temperature control switch is switched off or not by adopting an effective value of output voltage; if yes, whether the temperature control switch is disconnected or not is judged according to the difference of the harmonic components of the input voltage and the output voltage, and when the temperature control switch is judged to be disconnected, the AVR transformer is disconnected from the loop or bypassed. Multiple and multi-level judgment standards are introduced into the control method, so that the judgment efficiency is higher, and the calculation speed is higher. The durability of an existing AVR transformer can be improved under the condition that the cost is reduced, and the cost is saved.

Description

Technical Field

[0001] The present invention relates to the field of power management and control, and particularly to an AVR transformer control method and a device including the same. Background Art

[0002] An AVR transformer (also known as an active regulating transformer) is mainly applied to voltage regulation in the mains mode of an interactive UPS. Cooperating with an AVR transformer relay, the AVR transformer can realize functions such as voltage boosting, voltage bucking, or outputting an unregulated voltage during normal mains power. Among them, by sampling the input voltage and performing software processing, the on / off of the AVR transformer relay is controlled. When the AVR transformer overheats due to abnormalities such as overload or internal short circuit, the AVR transformer can provide overheat protection.

[0003] There are three operating modes of the AVR transformer in the prior art: boost boost mode, no regulation in the normal range, and buck buck mode.

[0004] Figure 1 The schematic diagram of the corresponding topological circuit of the primary side and the secondary side of the AVR transformer is shown. Figure 1 The left side is the primary side, which receives the input voltage, and the right side is the secondary side, which outputs the regulated or unregulated voltage to the load.

[0005] The overheat protection usually disconnects some or all of the winding coils in the transformer through a temperature control switch. The current design of the temperature control switch 1 is connected in series on the first winding N1 of the primary side, as Figure 1 shown. When the transformer overheats due to heavy load, short circuit, or other reasons, the temperature control switch 1 disconnects. After disconnection, the effective value of the output voltage of the AVR transformer is detected through software. When the output voltage value Vo > K1 or Vo < K2, or K3 < Vin / Vo < K4, because the output voltage value is abnormal, the UPS will judge that the AVR transformer is abnormal and output a "fault" signal, report a fault, and disconnect all AVR transformer relays, thereby cutting off the transformer input and avoiding overheating and ignition or burning out of the AVR transformer. Summary of the Invention

[0006] The inventors found in the test analysis that there is an obvious defect in the above method of the prior art. When the AVR transformer operates in the buck buck mode and an abnormal over-temperature occurs as described above and the temperature control switch disconnects, on the primary side, the N1 coil is disconnected from the circuit, and the voltage will only flow through the N2 coil. However, the turn ratio of the transformer winding N2 is limited, and it is very easy to saturate under the condition of power frequency input.

[0007] Figure 2The corresponding curves of the secondary side output voltage, the primary side input voltage, the voltage difference between the secondary side output voltage and the primary side input voltage, and the secondary side output current are shown when the load side is at rated R load.

[0008] Figure 3 The corresponding curves of the secondary side output voltage, the primary side input voltage, the voltage difference between the secondary side output voltage and the primary side input voltage, and the secondary side output current are shown when the load side is a rated RCD load.

[0009] The inventor found that after the N1 coil is disconnected from the circuit, Figure 2 and Figure 3 The nonlinear characteristics shown in the figure will cause the voltage waveform to be distorted when working under load, and the effective value will also be reduced, so that the system cannot normally detect the abnormality of the AVR transformer.

[0010] In view of the above problems existing in the prior art, the first aspect of the present application provides an AVR transformer control method connected in a loop, wherein the primary side of the AVR transformer has a first winding and a second winding for receiving an input voltage, and the secondary side thereof has a third winding for providing an output voltage, wherein the AVR transformer is arranged with a temperature control switch capable of disconnecting the first winding from the primary side in an abnormal state;

[0011] The method comprises:

[0012] It is determined whether the AVR transformer is in a step-down mode. If not, the effective value of the output voltage is used to determine whether the temperature-controlled switch is disconnected. If yes, it is determined whether the temperature-controlled switch is disconnected according to the difference between the harmonic components of the input and output voltages. When the temperature-controlled switch is determined to be disconnected, the AVR transformer is disconnected from the loop or bypassed.

[0013] Preferably, the control method further includes:

[0014] After determining that the AVR transformer is in the step-down mode, first determine whether the output current of the AVR transformer is greater than a first threshold value. If so, determine whether the temperature control switch is disconnected based on the difference between the harmonic components of its input and output voltages; if not, determine whether the temperature control switch is disconnected using the effective value of the output voltage.

[0015] Preferably, in the control method, the harmonic component includes at least one of the following odd harmonic components: a third harmonic component, a fifth harmonic component, and a seventh harmonic component; and

[0016] Determining whether the temperature-controlled switch is disconnected based on the difference between the harmonic components of the input and output voltages includes: using a Fourier transform method to calculate the harmonic components of the input and output voltages and obtain the difference, and determining whether the temperature-controlled switch is disconnected based on a comparison result of the difference with a second threshold.

[0017] Preferably, in the control method, the second threshold is determined according to at least one of the following factors:

[0018] The level of current or voltage of the loop, or the turns ratio of at least two of the first, second and third windings.

[0019] Preferably, in the control method, determining whether the temperature control switch is disconnected according to the comparison result between the difference and the second threshold value comprises:

[0020] It is determined whether the difference is greater than the second threshold for T1 consecutive cycles. If so, it is determined that the temperature control switch is disconnected; if not, it is determined that the temperature control switch is not disconnected.

[0021] Preferably, in the control method, at least one of the third harmonic components of the input and output voltages is obtained using a fast Fourier transform method.

[0022] Preferably, in the control method, the step of using the effective value of the output voltage to determine whether the temperature control switch is disconnected includes:

[0023] It is determined whether the ratio S of the input to output voltage reaches T2 consecutive cycles within the interval between the third threshold and the fourth threshold. If yes, it is determined that the temperature-controlled switch is disconnected; if not, it is determined that the temperature-controlled switch is not disconnected.

[0024] Preferably, in the control method, the first threshold is within a range of 60% to 90% of a current value of the secondary side of the AVR transformer under rated load conditions.

[0025] Preferably, the control method further comprises:

[0026] Before determining whether it is in the step-down mode, first determine whether the AVR transformer is in the running mode. If not, determine that the temperature control switch is not disconnected; if yes, continue to determine whether the AVR transformer is in the step-down mode.

[0027] Preferably, in the control method, the voltage outputted by the secondary side of the transformer is provided to a load, and the load type is a resistive load and / or a nonlinear load; and

[0028] The second threshold is also determined according to the load type.

[0029] A second aspect of the present application provides a fault judgment device for an AVR transformer, wherein the AVR transformer has a first winding and a second winding for receiving an input voltage on a primary side, and a third winding for providing an output voltage on a secondary side, wherein the AVR transformer is provided with a temperature-controlled switch capable of disconnecting the first winding from the primary side in an abnormal state;

[0030] The fault judgment device comprises:

[0031] A sensor module, wherein the sensor module is configured to obtain voltage and current values ​​of the primary side and the secondary side of the AVR transformer respectively;

[0032] A control module, wherein the control module is configured to execute any one of the methods described in the first aspect of the present application according to the voltage and current values ​​output by the sensor module.

[0033] A third aspect of the present application provides an uninterruptible power supply, comprising an AVR transformer and the fault judgment device described in the second method of the present application, wherein the fault judgment device is configured as follows:

[0034] When the temperature control switch is determined to be disconnected, the AVR transformer is disconnected from or bypassed from the circuit of the uninterruptible power supply.

[0035] According to the AVR transformer control method and the device including the same described in various aspects of the present invention, the accuracy and calculation speed of the AVR transformer detecting the disconnection of the temperature control switch in the prior art are significantly improved. In addition, because the logic adopted by the control method enables it to be easily integrated into the control unit of the existing AVR transformer, and the judgment parameter only needs to be provided by the sensor of the existing AVR transformer, the durability of the AVR transformer in the prior art can be improved at a low cost, and it has excellent cost-effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The embodiments of the present invention are further described below with reference to the accompanying drawings, in which:

[0037] Figure 1 The topological circuit diagram corresponding to the primary side and the secondary side of the AVR transformer is shown;

[0038] Figure 2 The corresponding curves of the secondary side output voltage, the primary side input voltage, the voltage difference between the secondary side output voltage and the primary side input voltage, and the secondary side output current are shown when the load side is at rated R load;

[0039] Figure 3The corresponding curves of the secondary side output voltage, the primary side input voltage, the voltage difference between the secondary side output voltage and the primary side input voltage, and the secondary side output current are shown when the load side is the rated RCD load;

[0040] Figure 4 In one embodiment, a measurement result interface of input voltage harmonics is provided when the voltage reduction detection threshold value is 109Vac and the normal mains sine wave is input without load;

[0041] Figure 5 In one embodiment, an interface for measuring input voltage harmonics and input and output voltage waveforms is provided when the voltage drop detection threshold value is 109Vac input, under the condition that the normal mains sine wave is >90% rated R load and the thermostat is not disconnected;

[0042] Figure 6 An embodiment is provided in which, when the voltage drop detection threshold value is 109Vac, the input voltage harmonics and the input and output voltage waveform measurement result interface are under the condition of >90% rated R load of the normal mains sine wave and the thermostat disconnected;

[0043] Figure 7 From left to right, the output voltage harmonic value, input voltage harmonic value and input and output voltage waveforms after the thermostat is disconnected under the condition of sine wave input and RCD load are shown;

[0044] Figure 8 From left to right, the output voltage harmonic value, input voltage harmonic value and input and output voltage waveforms after the thermostat is disconnected under the condition of DST07 high disturbance third harmonic input and RCD load are shown;

[0045] Fig. 9 From left to right, the output voltage harmonic value, input voltage harmonic value and input and output voltage waveforms after the thermostat is disconnected under the condition of DST13 square wave input and R load are shown;

[0046] Fig.10 From left to right, the output voltage harmonic value, input voltage harmonic value and input and output voltage waveforms after the thermostat is disconnected under the condition of DST26 step square wave input and RCD load are given. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0048] The inventor found that when the AVR transformer works in buck mode, the N1 coil on the primary side is disconnected from the circuit, which will cause the output voltage on the secondary side to be distorted, and further cause the effective voltage to deviate from the predetermined range, causing the control logic that originally detects and judges whether the AVR transformer is abnormal to deviate and easily make misjudgments. For this special situation, the inventor conducted a series of tests. Analysis and explanation based on normal AC input: For example, for the buck working mode, when the buck detection threshold value is 109Vac, the input voltage harmonics are compared under normal AC sine wave conditions.

[0049] Figure 4 In one embodiment, an interface of measurement results of input voltage harmonics when a normal mains sine wave is input at a no-load condition and a voltage drop detection threshold of 109 Vac is provided.

[0050] Figure 5 In one embodiment, the measurement result interface of input voltage harmonics and input and output voltage waveforms is provided when the voltage drop detection threshold value is 109Vac, the normal mains sine wave is >90% rated R load and the thermostat is not disconnected. Among them, Figure 5 The right figure shows the input and output voltage waveforms. The four color blocks above the right figure represent the colors of the corresponding curves of the AVR transformer secondary side output voltage, the primary side input voltage, the voltage difference between the secondary side output voltage and the primary side input voltage, and the secondary side output current from left to right.

[0051] Figure 6 An embodiment is given in which the input voltage harmonics and the input and output voltage waveform measurement result interface is provided when the voltage drop detection threshold value is 109Vac input, the normal mains sine wave is >90% rated R load and the thermostat is disconnected. Among them, Figure 6 The right figure shows the input and output voltage waveforms. The four color blocks above the right figure represent the colors of the corresponding curves of the AVR transformer secondary side output voltage, the primary side input voltage, the voltage difference between the secondary side output voltage and the primary side input voltage, and the secondary side output current from left to right.

[0052] It can be seen that: before and after loading, the harmonic difference of the input voltage is very small, and the third harmonic differences are 0.38V and 0.13V respectively; after the temperature control switch is disconnected, the output harmonics intensify and the waveform is distorted. In a specific case, the relative difference from the input harmonics is above 17V (only for illustrative purposes and not a limitation on the method described in the present invention). This solution considers calculating the odd harmonic component values of the input and output voltages through FFT (for example, the harmonic components can include at least one of the following multiple odd harmonic components: the third harmonic component, the fifth harmonic component, and the seventh harmonic component), and using the difference in the values of a certain predetermined odd harmonic component as the judgment condition to detect the failure of the AVR transformer. This is because in a generally symmetric power system, even harmonics can cancel each other out, so the even harmonic components are relatively small, while the odd harmonic content is higher and is more suitable as a judgment variable.

[0053] Based on the above understanding, the inventor proposes an improved control method for an AVR transformer or an uninterruptible power supply including the same to more accurately detect the disconnection of the temperature control switch caused by the failure of the AVR transformer, thereby avoiding damage to the hardware.

[0054] Regarding the current detection method - the voltage effective value judgment method, there are limitations in the buck mode. Since the output voltage is distorted, its output transformer effective value will also decrease. Using the ratio of the output voltage to the input voltage, it is very difficult to judge the operation of the temperature control switch of the transformer. By observing the output voltage waveform, after the temperature control switch is disconnected, the first coil N1 on the primary side of the transformer is disconnected from the primary side, and only the second coil N2 (usually with fewer turns) is connected to the circuit, and its non-linearity often brings distortion of the output voltage. The inventor can find obvious changes in its harmonics by performing Fourier decomposition on the output voltage. For this reason, an innovative method is proposed. When the AVR transformer is operating in the buck mode, by performing Fourier decomposition on the input voltage and the output voltage respectively, for example, the fast Fourier transform (FFT) can be used, and by comparing the differences in the harmonic components (which can be any combination adjusted according to the electrical characteristics of the actual power conversion device of the third, fifth, or other higher-order odd harmonics), it is possible to judge whether the over-temperature protection of the AVR transformer operates.

[0055] When the AVR transformer is operating in the Boost boost mode, it can maintain the existing voltage effective value judgment method. The judgment conditions are that when the output voltage value Vo > K1 or Vo < K2, or when the ratio range of the input voltage Vo / output voltage Vin is K3 < Vin / Vo < K4 for T2 consecutive cycles, it is determined that the temperature control switch is disconnected, an output overvoltage / undervoltage fault or an AVR transformer fault is reported, and three AVR transformer relays are disconnected and / or switched to bypass.

[0056] When operating in step-down mode with an AVR transformer, the effective value determination of voltage and the voltage third harmonic method can be comprehensively used. When the output current is small (<K5), first calculate the effective value to confirm whether a fault can be detected and protected. When the current is large (>K5), then confirm that when the difference between the third harmonic of the output voltage and the third harmonic of the input voltage is >K6 for T1 consecutive cycles, report an output overvoltage fault or an AVR transformer fault, disconnect the three AVR transformer relays and switch to bypass.

[0057] According to the above principle, in a preferred embodiment, the AVR transformer control method includes the following fault judgment process:

[0058] 1) Determine whether the AVR transformer is in the operating mode. If not, it is determined that the temperature control switch is not disconnected; if so, proceed to step 2) to continue determining whether the AVR transformer is in the step-down mode.

[0059] 2) Determine whether the AVR transformer is in the step-down mode. If so, proceed to step 3) to determine whether the output current of the AVR transformer is greater than the first threshold; if not, use the effective value of the output voltage to determine whether the temperature control switch is disconnected, including: determining whether the ratio S of the input voltage to the output voltage is within the interval between the third threshold and the fourth threshold for T2 consecutive cycles. If so, it is determined that the temperature control switch is disconnected; if not, it is determined that the temperature control switch is not disconnected. Among them, the first threshold is preferably within the interval of 60% to 90% of the current value on the secondary side of the AVR transformer under rated load conditions, and more preferably can be within the interval between any two of 70%, 75%, 80%, or 85%.

[0060] 3) If it is determined in step 2) that the AVR transformer is in the step-down mode, continue to determine whether the output current of the AVR transformer is greater than the first threshold. If so, proceed to step 4) to determine whether the temperature control switch is disconnected based on the difference in the harmonic components of its input and output voltages; if not, use the effective value of the output voltage to determine whether the temperature control switch is disconnected, including: determining whether the ratio S of the input voltage to the output voltage is within the interval between the third threshold and the fourth threshold for T2 consecutive cycles. If so, it is determined that the temperature control switch is disconnected; if not, it is determined that the temperature control switch is not disconnected.

[0061] 4) using the FFT fast Fourier transform method in the Fourier transform method to calculate the third harmonic components of the input and output voltages and obtain the difference thereof, and determining whether the temperature-controlled switch is disconnected according to a comparison result of the difference and a second threshold, including: determining whether the difference is greater than the second threshold for T1 consecutive cycles, if so, determining that the temperature-controlled switch is disconnected; if not, determining that the temperature-controlled switch is not disconnected, wherein the second threshold is determined according to the voltage input and output levels of the uninterruptible power supply used by the AVR transformer, or is determined according to the turns ratio of at least two of the first, second and third windings.

[0062] Optionally, in another embodiment, the method further comprises, after determining that the temperature control switch is disconnected, controlling a plurality of relays coupled to the AVR transformer to disconnect and bypassing the AVR transformer from the uninterruptible power supply.

[0063] The cycle values ​​T1 and T2 in the above-mentioned embodiments are positive integers, and their values ​​can be determined according to the empirical values ​​commonly used in abnormality detection in the art, and are not listed here in a limiting sense.

[0064] The method of judging the fault of the AVR transformer by combining the harmonic difference of the input and output voltages after the temperature control switch is disconnected with the voltage effective value difference also needs to consider the influence of the harmonic components of the mains itself during the actual application process. Therefore, the inventors illustrate several typical special waveforms of actual testing, and take the 1.5KVA model as an example to test the influence of the harmonic difference on the scheme under the conditions of R load and RCD load. The RCD load is a nonlinear simulation load composed of resistors (R), capacitors cc), and diodes (D) as the main components. According to the special waveforms in the Chroma AC source programmable AC power supply, the test results of the method for judging the difference between the third harmonics of the input and output voltages combined with the effective value ratio and the third harmonic difference of the input and output voltages are as follows. The actual test of the third harmonic difference is obvious, and it can be judged by calculating the harmonic value. However, the third harmonic is only shown as an example. According to other embodiments of the present invention, all harmonics above the second order can be used. According to the actual input voltage waveform and the load type of the system loop, the circuit inductive and capacitive components and other related configurations, one or more of the harmonics of each order are used as the target value to be determined in the method for judging the difference between the input voltage and the output power industry described in this application.

[0065] In a preferred embodiment, the control method of the present invention is tested for sine wave input. When carrying R load, the small load (<12A) can be detected by the voltage effective value method, and the difference between the output voltage third harmonic and the input in the large load (>12A) is above 17V, where 12A is used as the first threshold and 17V is used as the second threshold; when carrying RCD load, the load <0.8A can be judged by the voltage effective value method, and the difference between the output voltage third harmonic and the input of a slightly larger load is above 9.9V, where 0.8A is used as the first threshold and 9.9V is used as the second threshold; in other embodiments, any value of 70%, 80% or 60-90% of the full load level current can be used as the first threshold to distinguish between large load and small load.

[0066] In a preferred embodiment, the control method of the present invention is tested for the DST07 high disturbance third harmonic special waveform input. When carrying R load, the fault can be judged by the voltage effective value method. When carrying RCD load, the load <0.8A can be judged by the voltage effective value method, and the difference between the output voltage third harmonic and the input of a slightly larger load is above 10.6V, where 0.8A is used as the first threshold and 10.6V is used as the second threshold.

[0067] In a preferred embodiment, the control method of the present invention is tested for the DST13 square wave special waveform input. When the RCD load is used, the fault can be judged by the voltage effective value method; when the R load is used, the load <1.0A can be judged by the voltage effective value method, and the difference between the output voltage third harmonic and the input of a slightly larger load is above 7.9V;

[0068] In a preferred embodiment, the control method of the present invention is tested for the special waveform input of DST26 step square wave. When carrying R load, the fault can be judged by the voltage effective value method; when carrying RCD load, the load <0.7A can be judged by the voltage effective value method, and the difference between the third harmonic of the output voltage and the input of a slightly larger load is more than 10.7V.

[0069] Table 1 shows the logic judgment threshold settings of the voltage effective value method and the input and output voltage third harmonic difference method for each of the above special waveforms in the test.

[0070] Table 1

[0071]

[0072] The test results and waveforms of the above embodiments are as follows:

[0073] For sine wave input, the waveform and harmonic values ​​of R are as follows Figure 5 and Figure 6 As shown, only the case where RCD is loaded is listed here.

[0074] Figure 7From left to right, the output voltage harmonic value, input voltage harmonic value and input and output voltage waveforms after the thermostat is disconnected under RCD load conditions under sinusoidal wave input conditions are given. Figure 7 The rightmost figure shows the input and output voltage waveforms, and the four color blocks above it represent the colors of the corresponding curves of the AVR transformer secondary output voltage, primary input voltage, voltage difference between the secondary output voltage and the primary input voltage, and the secondary output current from left to right. The RCD load is 0.8A.

[0075] For DST07 high disturbance third harmonic special waveform input, R load can be judged by voltage effective value method. Only the RCD load situation is listed here.

[0076] Figure 8 From left to right, the output voltage harmonic value, input voltage harmonic value and input and output voltage waveforms after the thermostat is disconnected under the condition of DST07 high disturbance third harmonic input and RCD load are given. Figure 8 The rightmost figure shows the input and output voltage waveforms, and the four color blocks above it represent the colors of the corresponding curves of the AVR transformer secondary output voltage, primary input voltage, voltage difference between the secondary output voltage and the primary input voltage, and secondary output current from left to right. The RCD load is 0.87A.

[0077] For DST13 square wave special waveform input, RCD load can be determined by voltage effective value method. Only R load is listed here.

[0078] Fig. 9 From left to right, the output voltage harmonic value, input voltage harmonic value and input and output voltage waveforms after the thermostat is disconnected under the DST13 square wave input condition and R load are given. Fig. 9 The rightmost figure shows the input and output voltage waveforms, and the four color blocks above it represent the colors of the corresponding curves of the AVR transformer secondary output voltage, primary input voltage, voltage difference between the secondary output voltage and the primary input voltage, and secondary output current from left to right. R load is 1.0A load.

[0079] For the DST26 step square wave special waveform input, the R load can be determined by the voltage effective value method. Only the RCD load situation is listed here.

[0080] Fig.10 From left to right, the output voltage harmonic value, input voltage harmonic value and input and output voltage waveforms after the thermostat is disconnected under the condition of DST26 step square wave input and RCD load are given. Fig.10The rightmost figure shows the input and output voltage waveforms, and the four color blocks above it represent the colors of the corresponding curves of the AVR transformer secondary output voltage, primary input voltage, voltage difference between the secondary output voltage and the primary input voltage, and secondary output current from left to right. The RCD load is 0.87A.

[0081] It can be seen from the above test results that this new method is not only effective for positive harmonic input, but also for other special input voltage waveforms (such as high-disturbance third harmonic, square wave, step square wave, etc.). At the same time, it is also feasible for different load types (such as resistive load and / or nonlinear load), and the second threshold can be adjusted accordingly according to the load type.

[0082] Another embodiment of the present invention provides a fault judgment device for an AVR transformer, wherein the primary side of the AVR transformer has a first winding and a second winding for receiving an input voltage, and the secondary side thereof has a third winding for providing an output voltage, wherein the AVR transformer is provided with a temperature-controlled switch capable of disconnecting the first winding from the primary side in an abnormal state;

[0083] The fault judgment device comprises:

[0084] A sensor module, wherein the sensor module is configured to obtain voltage and current values ​​of the primary side and the secondary side of the AVR transformer respectively;

[0085] A control module, wherein the control module is configured to execute the AVR transformer control method described in the above embodiment of the present invention according to the voltage and current values ​​output by the sensor module. In a preferred embodiment, the control module is configured to:

[0086] 1) Determine whether the AVR transformer is in the running mode. If not, determine that the temperature control switch is not disconnected; if yes, proceed to step 2) to continue determining whether the AVR transformer is in the step-down mode.

[0087] 2) Determine whether the AVR transformer is in step-down mode. If yes, proceed to step 3) Determine whether the output current of the AVR transformer is greater than a first threshold. If not, use the effective value of the output voltage to determine whether the temperature control switch is disconnected.

[0088] 3) If it is determined in step 2) that the AVR transformer is in the step-down mode, then continue to determine whether the output current of the AVR transformer is greater than the first threshold value. If so, proceed to step 4) to determine whether the temperature-controlled switch is disconnected based on the difference between the harmonic components of its input and output voltages; if not, use the effective value of the output voltage to determine whether the temperature-controlled switch is disconnected.

[0089] 4) using an FFT fast Fourier transform method in a Fourier transform method to calculate the odd harmonic components of the input and output voltages, such as the third harmonic component, and obtain the difference thereof, and determining whether the temperature control switch is disconnected according to a comparison result of the difference and a second threshold value; after determining that the temperature control switch is disconnected, the control module controls a plurality of relays coupled to the AVR transformer to disconnect and bypass the AVR transformer from the uninterruptible power supply.

[0090] Another embodiment of the present invention provides an uninterruptible power supply, which includes the AVR transformer described in the above embodiment and a fault judgment device for the AVR transformer. The structure and working mode of the uninterruptible power supply are well known to ordinary technicians in the field and will not be repeated here.

[0091] The AVR transformer control method and the device including the same according to the various embodiments of the present invention can more accurately determine whether the temperature control switch is disconnected, and the judgment speed is faster. The improved judgment method using the harmonic change of the output voltage before and after the temperature control switch is disconnected is only executed in the step-down mode, and the judgment method of the effective value of the output voltage is still used in other modes. Therefore, such multiple condition limitations make the judgment efficiency higher and the calculation speed faster. The durability of the existing AVR transformer can be improved at a reduced cost, saving costs.

[0092] Although the present invention has been described through preferred embodiments, the present invention is not limited to the embodiments described herein but includes various changes and modifications that may be made without departing from the scope of the present invention.

Claims

1. A control method for an AVR transformer connected in a loop, wherein the AVR transformer has a first winding and a second winding on the primary side for receiving an input voltage, and a third winding on the secondary side for providing an output voltage, wherein the AVR transformer is provided with a temperature-controlled switch capable of disconnecting the first winding from the primary side in an abnormal state; The method comprises: Determining whether the AVR transformer is in a step-down mode, and if not, using the effective value of the output voltage to determine whether the temperature control switch is disconnected; If yes, it is determined whether the temperature-controlled switch is disconnected according to the difference between the harmonic components of the input and output voltages, wherein when the temperature-controlled switch is determined to be disconnected, the AVR transformer is disconnected from the loop or bypassed.

2. The control method according to claim 1, further comprising: After determining that the AVR transformer is in the step-down mode, first determine whether the output current of the AVR transformer is greater than a first threshold value. If so, determine whether the temperature control switch is disconnected based on the difference between the harmonic components of its input and output voltages; if not, determine whether the temperature control switch is disconnected using the effective value of the output voltage.

3. The control method according to claim 1 or 2, wherein: The harmonic component includes at least one of the following odd harmonic components: The third harmonic component, the fifth harmonic component and the seventh harmonic component; as well as Determining whether the temperature-controlled switch is disconnected based on the difference between the harmonic components of the input and output voltages includes: using a Fourier transform method to calculate the harmonic components of the input and output voltages and obtain the difference, and determining whether the temperature-controlled switch is disconnected based on a comparison result of the difference with a second threshold.

4. The control method according to claim 3, wherein the second threshold is determined according to at least one of the following factors: The level of current or voltage of the loop, or the turns ratio of at least two of the first, second and third windings.

5. The control method according to claim 3, wherein determining whether the temperature control switch is disconnected according to the comparison result between the difference and the second threshold value comprises: Determine whether the difference is greater than the second threshold for T1 consecutive cycles, and if so, determine that the temperature control switch is disconnected; If not, it is determined that the temperature control switch is not disconnected.

6. The control method according to claim 3, wherein at least one of the harmonic components of the input and output voltages is obtained by using a fast Fourier transform method.

7. The control method according to claim 1, wherein the using the effective value of the output voltage to determine whether the temperature control switch is disconnected comprises: It is determined whether the ratio S of the input to output voltage reaches T2 consecutive cycles within the interval between the third threshold and the fourth threshold. If yes, it is determined that the temperature-controlled switch is disconnected; if not, it is determined that the temperature-controlled switch is not disconnected. 8 . The control method according to claim 2 , wherein the first threshold is within a range of 60% to 90% of a current value of the secondary side of the AVR transformer under a rated load condition.

9. The control method according to claim 1, further comprising: Before determining whether it is in the step-down mode, first determine whether the AVR transformer is in the running mode, and if not, determine that the temperature control switch is not disconnected; If yes, then continue to determine whether the AVR transformer is in the step-down mode.

10. The control method according to claim 4, wherein the voltage outputted by the secondary side of the transformer is provided to a load, and the load type is a resistive load and / or a nonlinear load; and The second threshold is also determined according to the load type.

11. A fault judgment device for an AVR transformer, wherein the primary side of the AVR transformer has a first winding and a second winding for receiving an input voltage, and the secondary side thereof has a third winding for providing an output voltage, wherein the AVR transformer is provided with a temperature-controlled switch capable of disconnecting the first winding from the primary side in an abnormal state; The fault judgment device comprises: A sensor module, wherein the sensor module is configured to obtain voltage and current values ​​of the primary side and the secondary side of the AVR transformer respectively; A control module, wherein the control module is configured to execute the method according to any one of claims 1 to 10 according to the voltage and current values ​​output by the sensor module.

12. An uninterruptible power supply, comprising an AVR transformer and the fault judgment device according to claim 11, wherein the fault judgment device is configured as follows: When the temperature control switch is determined to be disconnected, the AVR transformer is disconnected from or bypassed from the circuit of the uninterruptible power supply.

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