A method for measuring direct current in a rectifier-inverter device

Abstract

The application relates to a direct current measurement algorithm in a rectifier inverter device, and belongs to the field of power electronic converters. The method for measuring direct current in a rectifier inverter device provided by the application collects an alternating current waveform through an alternating current transformer, performs fitting calculation on the direct current by using the current waveform, and obtains the waveform of the direct current. The method does not need to use an additional direct current measurement device, only needs to measure alternating current through a commonly used alternating current transformer, processes and calculates the real-time measured alternating current through an algorithm in software, and the direct current can be calculated, at this time, the calculated direct current is a real-time value and is consistent with the actual direct current in real time.

Description

Technical Field

[0001] This invention relates to an algorithm for measuring DC current in a rectifier-inverter device, belonging to the field of power electronic converters. Background Technology

[0002] Currently, rectifier-inverter devices are widely used in power electronic conversion, such as high-frequency switching power supplies, uninterruptible power supplies, excitation devices, inverters, frequency converters, and ultra-high voltage direct current transmission. In these applications, the control algorithm needs to collect and measure DC current, mainly in two ways: one is to directly measure the DC current using current transformers and Hall sensors, or to synchronously reduce the AC current using a current transformer, then rectify this current through another rectifier bridge, and finally measure the rectified DC current; the other is to indirectly measure the DC current using the mathematical relationship between the effective values ​​of AC and DC currents. Direct current measurement often leads to inaccuracies due to the accuracy and drift issues of the measuring device. Furthermore, direct measurement is often only suitable for measuring smaller DC currents, and is less common for measuring large DC currents. Additionally, measuring large DC currents often involves high hardware costs and is susceptible to environmental interference, resulting in low measurement accuracy. Indirect DC measurement methods use the mathematical relationship between the effective values ​​of AC and DC currents for calculation. Because they use the effective values, the timeliness and accuracy of the measurement are poor, and they can only be applied to situations where the accuracy requirements are not high and the calculation speed requirements are not high, so their application is very limited. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a DC current measurement algorithm for rectifier-inverter devices. This method does not require an additional DC current measuring device; it only requires a commonly used AC current transformer to measure the AC current. The algorithm in the software processes and calculates the real-time measured AC current to obtain the DC current. The calculated DC current is a real-time value and is consistent with the actual DC current in real time.

[0004] To achieve the above objectives, the technical solution provided by this invention is: a method for measuring DC current in a rectifier-inverter device, which is operated according to the following steps:

[0005] (1) Determine the AC current acquisition point: Determine the location of the AC current acquisition point in the rectifier-inverter circuit to be acquired, and use the AC transformer to acquire the real-time waveform of the three-phase ABC current.

[0006] (2) Obtain the three-phase AC currents ia and i b Real-time waveform of IC: During normal operation of the rectifier-inverter circuit, the waveform of the power supply throughout the entire sinusoidal cycle is as follows: The real-time waveforms of the sampled three-phase AC currents ia, ib, and ic are vector values. b The IC is collected in time periods to obtain the three-phase AC current ia and i. b Real-time waveform of IC;

[0007] (3) Calculate the value of the DC current id: At the common point of the common cathode and common anode of the selected rectifier-inverter circuit, determine the DC current id according to Formula 1, i.e. Kirchhoff's laws.

[0008]

[0009] In the formula: This represents the current flowing into phase A of the power supply. This indicates the current flowing out of phase A of the power supply; This represents the current flowing into phase B of the power supply. This indicates the current flowing out of phase B power supply; This represents the current flowing into phase C of the power supply. S1 to S6 represent the current flowing out of the C-phase power supply; S1 to S6 represent the corresponding power devices that are turned on or off. S1 and S4 are mutually exclusive, S3 and S6 are mutually exclusive, and S5 and S2 are mutually exclusive. If one of the mutually exclusive power devices is turned on, the other is turned off. The number 1 represents the power device being turned on, and the number 0 represents the power device being turned off. At any given time, only two power devices are turned on.

[0010] (4) Calculate the waveform of the DC current id: Use the PLC controller to judge the three-phase ABC currents collected by the AC transformer. If the A-phase current ia > 0, then take the waveform of the A-phase current ia > 0 and assign it to parameter a; if the B-phase current i b If the value is greater than 0, then take the phase B current i. b The waveform of the part where >0 is taken is assigned to parameter b; if the C-phase current ic>0, the waveform of the part where the C-phase current ic>0 is taken is assigned to parameter c, the vector superposition of parameters a, b and c is assigned to parameter x, and finally the value of parameter x is passed to the DC current parameter id.

[0011] The rectifier-inverter circuit in step (1) includes at least a 6-pulse rectifier-inverter circuit and a 12-pulse and multi-pulse rectifier-inverter circuit. The AC current sampling point of the 6-pulse rectifier-inverter circuit is located at the AC power supply, and the AC current sampling point of the 12-pulse and multi-pulse rectifier-inverter circuit is located at any one of the AC power supplies of the multiple series-connected rectifier-inverter circuits.

[0012] The normal operation of the rectifier-inverter circuit in step (2) includes the following six scenarios: At this time, the line voltage of two phases of the three-phase ABC current is applied to the load, and the circuit current in the loop is equal.

[0013] In step (4), only two of the three-phase ABC currents have AC current waveforms. For the entire 360° cycle of the A-phase current, the positive current is 120° and the zero current is 60°, and the negative current is 120° and the zero current is 60°. The B-phase and C-phase currents have the same pattern as the A-phase current, but their phases lag by 120°. Therefore, the positive waveforms of the three-phase currents form a complete cycle. When current flows at any time, the AC current waveform is the DC current waveform. It can be seen from the three-phase AC current waveforms that the positive waveforms of the three-phase currents form a complete cycle, and the DC current is actually the positive part of the AC current. The positive current of the three-phase AC current is collected in time periods and then spliced ​​together to form the actual DC current.

[0014] As can be seen from the above technical solution, the method for measuring DC current in a rectifier-inverter device provided by this invention acquires the AC current waveform using an AC current transformer, and then uses the current waveform to fit and calculate the DC current to obtain the DC current waveform. Compared with the prior art, this invention has the following advantages: because the technical solution adopted by this invention does not require hardware circuitry for DC measurement, it can achieve non-destructive and accurate measurement regardless of the current level being measured. It boasts high measurement accuracy and strong anti-interference capability. Since it uses an AC current transformer to acquire the AC current waveform and calculates the DC current through software algorithms, it saves significant costs. This DC current measurement method is a highly efficient and accurate algorithm for measuring DC current in rectifier-inverter devices. Attached Figure Description

[0015] Figure 1 This is a typical structural diagram of the rectifier-inverter device of the present invention;

[0016] Figure 2 This is a diagram illustrating the commutation process of the power devices in the rectifier-inverter circuit of the present invention.

[0017] Figure 3 The measured three-phase symmetrical current waveform on the AC side of the rectifier-inverter device according to the present invention;

[0018] Figure 4 This is a comparison chart of the DC current calculated by the DC current measurement method of the present invention and the DC current measured by actual hardware.

[0019] Figure 5 This is a flowchart of the DC current measurement algorithm of the present invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0021] The DC current measurement algorithm for a rectifier-inverter device provided in the technical solution of the present invention includes at least the following steps:

[0022] A method for measuring DC current in a rectifier-inverter device, comprising the following steps:

[0023] (1) Determine the AC current acquisition point: Determine the location of the AC current acquisition point in the rectifier-inverter circuit to be acquired, and use the AC transformer to acquire the real-time waveform of the three-phase ABC current.

[0024] In this embodiment, as Figure 1 The diagram shows two typical rectifier-inverter circuits. The three-phase AC current on the AC side of the rectifier-inverter device is collected in real time using an AC current transformer. The AC current transformer is installed on the AC side of the rectifier-inverter device. The rectifier-inverter circuit in step (1) includes at least a 6-pulse rectifier-inverter circuit and 12-pulse and multi-pulse rectifier-inverter circuits. The AC current acquisition point of the 6-pulse rectifier-inverter circuit is located at the AC power source, while the AC current acquisition point of the 12-pulse and multi-pulse rectifier-inverter circuit is located at any one of the AC power sources of the multiple series-connected rectifier-inverter circuits. The rectifier-inverter circuit in this embodiment includes 6-pulse, 12-pulse and multi-pulse, multi-level rectification, inversion, and frequency conversion devices, involving AC to DC, DC to AC, and AC to DC to AC conversion devices. The rectifier-inverter device is a reversible device capable of bidirectional energy flow.

[0025] (2) Obtain the three-phase AC current i a i b i c Real-time waveform: When the rectifier-inverter circuit is operating normally, such as Figure 3 As shown, during the entire sinusoidal cycle of the power supply, The sampled three-phase AC current i a i b and i c The real-time waveform of the alternating current is a vector value. For the three-phase alternating current i a i b and i c Data is collected in time intervals to obtain the three-phase alternating current i. a i b and i c Real-time waveform;

[0026] The normal operation of the rectifier-inverter circuit in step (2) includes the following six scenarios: At this time, the line voltage of two phases of the three-phase ABC current is applied to the load, and the circuit current in the loop is equal.

[0027] (3) Calculate the value of the DC current id: At the common point of the common cathode and common anode of the selected rectifier-inverter circuit, determine the DC current id according to Formula 1, i.e. Kirchhoff's laws.

[0028]

[0029] In the formula: This represents the current flowing into phase A of the power supply. This indicates the current flowing out of phase A of the power supply; This represents the current flowing into phase B of the power supply. This indicates the current flowing out of phase B power supply; This represents the current flowing into phase C of the power supply. S1 to S6 represent the current flowing out of the C-phase power supply; S1 to S6 represent the corresponding power devices that are turned on or off. S1 and S4 are mutually exclusive, S3 and S6 are mutually exclusive, and S5 and S2 are mutually exclusive. If one of the mutually exclusive power devices is turned on, the other is turned off. The number 1 represents the power device being turned on, and the number 0 represents the power device being turned off. At any given time, only two power devices are turned on.

[0030] (4) Calculate the waveform of the DC current id: Use the PLC controller to judge the three-phase ABC currents collected by the AC transformer, such as... Figure 5 As shown, if the phase A current ia > 0, then the waveform of the phase A current ia > 0 is taken and assigned to parameter a; if the phase B current i b If the value is greater than 0, then take the phase B current i. b The waveform of the part where >0 is taken is assigned to parameter b; if the C-phase current ic>0, the waveform of the part where the C-phase current ic>0 is taken is assigned to parameter c, the vector superposition of parameters a, b and c is assigned to parameter x, and finally the value of parameter x is passed to the DC current parameter id.

[0031] In step (4), among the three-phase ABC currents, only two phases have AC current waveforms. For the entire 360° cycle of the A-phase current, the positive current is 120° and the zero current is 60°, and the negative current is 120° and the zero current is 60°. The B-phase and C-phase currents have the same pattern as the A-phase current, but their phases lag behind each other by 120°. Therefore, the positive waveforms of the three-phase currents form a complete cycle. When current flows at any time, the AC current waveform is the DC current waveform. It can be seen from the three-phase AC current waveforms that the positive waveforms of the three-phase currents are exactly a complete cycle, and the DC current is actually the positive part of the AC current. The positive current of the three-phase AC current is collected in time periods and then spliced ​​together to form the actual DC current.

[0032] In this embodiment, during the AC current sampling process of the AC current transformer, there may be a linearly reduced transformation ratio k, where k is a constant. The DC current waveform obtained by the calculation algorithm is multiplied by the transformation ratio k to obtain the DC current waveform.

[0033] During the commutation process of power devices, a short-term short-circuit process occurs. This means that the power device to be turned off and the power device to be turned on form a short-term short-circuit current loop. The current in the power device to be turned off gradually decreases, while the current in the power device to be turned on gradually increases, completing the current transfer. Throughout this current transfer process, the current sum of the two power devices must remain equal to ensure the accuracy of the algorithm during commutation. (See attached diagram.) Figure 2 As shown, during the commutation process from the conduction of power devices 6 and 1 to the conduction of power devices 1 and 2, the AC current is transferring from phase B to phase C. Since it is a transfer between currents, the sum of the currents in phases B and C remains unchanged. Therefore, the DC current algorithm provided by this method is still effective during the commutation process.

[0034] As attached Figure 4 As shown, the first two waveforms from top to bottom represent the DC current measured using this DC measurement algorithm in a 12-pulse rectifier-inverter device. The AC current sampling points for the two waveforms are slightly different, located on the AC sides of the two rectifier-inverter bridges of the 12-pulse device. However, the calculated DC current waveforms are completely identical. (See attached image.) Figure 5 The third waveform from top to bottom is the DC current directly measured by the hardware circuit. By comparing it with the DC current measured by the DC measurement algorithm, the waveforms are completely consistent, verifying the effectiveness and accuracy of the algorithm.

Claims

1. A method for measuring DC current in a rectifier-inverter device, characterized in that... Follow these steps: (1) Determine the AC current acquisition point: Determine the location of the AC current acquisition point in the rectifier-inverter circuit to be acquired, and use the AC transformer to acquire the real-time waveform of the three-phase ABC current. (2) Obtaining three-phase alternating current , , Real-time waveform: During the entire sinusoidal cycle of the power supply when the rectifier-inverter circuit is operating normally, , , The sampled three-phase alternating current , and The real-time waveform of the alternating current is a vector value, for three-phase alternating current. , and Data is collected in time intervals to obtain three-phase alternating current. , and Real-time waveform; (3) Calculate the DC current i d The value of i: At the common cathode and common anode common point of the selected rectifier-inverter circuit, the DC current i is determined according to Formula 1, i.e. Kirchhoff's laws. d , Official 1 In the formula: This represents the current flowing into phase A of the power supply. This indicates the current flowing out of phase A of the power supply; This represents the current flowing into phase B of the power supply. This indicates the current flowing out of phase B power supply; This represents the current flowing into phase C of the power supply. This represents the current flowing out of phase C of the power supply; This indicates whether the corresponding power device is turned on or off. and Mutually exclusive and Mutually exclusive and Mutually exclusive: In a mutually exclusive group of electrical devices, if one is turned on, the other is turned off. The number 1 represents the electrical device being turned on, and the number 0 represents the electrical device being turned off. At any given time, only two electrical devices can be turned on. (4) Calculate the DC current i d Waveform: The PLC controller judges the three-phase ABC currents collected by the AC transformer. If the A-phase current... Then take the phase A current. The waveform of a portion is then assigned to parameter a; if the B-phase current... Then take the B-phase current. The waveform of a portion is then assigned to parameter b; if the C-phase current... Then take the C-phase current. The waveform of a portion is obtained and assigned to parameter c. Parameters a, b, and c are vector-superimposed and assigned to parameter x. Finally, the value of parameter x is passed to the DC current parameter i. d .

2. The method for measuring DC current in a rectifier-inverter device according to claim 1, characterized in that: The rectifier-inverter circuit in step (1) includes at least a 6-pulse rectifier-inverter circuit and a 12-pulse and multi-pulse rectifier-inverter circuit. The AC current sampling point of the 6-pulse rectifier-inverter circuit is located at the AC power source, and the AC current sampling point of the 12-pulse and multi-pulse rectifier-inverter circuit is located at any one of the AC power sources of the multiple series-connected rectifier-inverter circuits.

3. The method for measuring DC current in a rectifier-inverter device according to claim 1, characterized in that: In step (2), the rectifier-inverter circuit operates normally under the following six conditions: , , At this time, the line voltage of two phases of the three-phase ABC current is applied to the load, and the circuit current in the loop is equal.

4. The method for measuring DC current in a rectifier-inverter device according to claim 1, characterized in that: In step (4), among the three-phase ABC currents, only two phases have AC current waveforms. For the entire 360° cycle of the A-phase current, the positive current is 120° and the zero current is 60°, the negative current is 120° and the zero current is 60°. The B-phase and C-phase currents have the same pattern as the A-phase current, but their phases lag behind each other by 120°. Therefore, the positive waveforms of the three-phase currents form a complete cycle. When current flows at any time, the AC current waveform is the DC current waveform. From the three-phase AC current waveforms, we can see that the positive waveforms of the three-phase currents form a complete cycle, and the DC current is actually the positive part of the AC current. The positive current of the three-phase AC current is collected in time periods and then spliced ​​together to form the actual DC current.

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