Current source type AC meter and its control system

Abstract

The present invention discloses a current source type AC meter and a control system thereof. The current source type AC meter comprises a power supply unit, a main circuit unit and a load unit. The power supply unit comprises a power supply and an input inductor Ldc. The main circuit unit comprises a first branch, a second branch and a third branch connected in parallel to the power supply unit. Each branch is provided with a transistor and a diode. The load unit is connected to the second branch and the third branch. The control system comprises a coil load current proportional-resonance control outer loop, a capacitor voltage model predictive control inner loop and a DC bus current hysteresis control logic. The solution can reduce the volume and cost, realize the adjustable DC bus current, reduce the switching loss and conduction loss, and increase the reliability and use efficiency of the structure.

Description

Technical Field

[0001] The invention relates to the field of power electronics and instrumentation, and in particular to a current source type AC meter and a control system thereof. Background Art

[0002] In the daily operation and maintenance of metering devices, the replacement or removal of electric energy meters and the reading of old meter data are one of the key tasks of the operation and maintenance personnel. According to the work requirements, the data of the old meters need to be checked and signed with the customer on site; however, many old meters have been in use for too long. Now, after a power outage, the LCD screen of the old meter cannot display, resulting in the inability to read the meter or the display error, resulting in data reading error. Only when the old meter is powered on again can it display normally. In view of the problem that the old meter displays abnormally and needs to be powered on again, there are currently two commonly used solutions. One is to take power on site, use a wire clamp to directly connect the old meter in parallel to the energized metering voltage secondary circuit in the metering cabinet, and the old meter will display and complete the data reading normally after powering on. The second is to take power from a single-phase transformer, bring the old meter back to the office, use the transformer to reduce the mains voltage to the rated voltage of the electric energy meter, and power it on to complete the reading of the electric energy meter data. Both methods have certain safety hazards. Taking power on site and connecting the old meter in parallel to the voltage secondary circuit may cause the voltage transformer to overload and affect the subsequent measurement accuracy. At the same time, it also increases the risk of short circuit or grounding of the voltage circuit and the risk of electric shock. Drawing power from a single-phase transformer may cause the energy meter to burn out due to insufficient voltage reduction. In addition, there are many wiring connections and the operation is complicated, which can easily cause electric shock accidents if you are not careful. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a current source type AC meter and a control system thereof, which can reduce volume and cost, realize adjustable DC bus current, reduce switching loss and conduction loss, and increase structural reliability and utilization efficiency.

[0004] To achieve the above-mentioned object, the present invention provides a current source type AC meter, which includes a power supply unit, a main circuit unit and a load unit. The power supply unit includes a power supply and an input inductor Ldc. Two ends of the input inductor Ldc are connected with a diode D5 and a transistor S5. The electrode of the transistor S5 is connected to the output end of the input inductor Ldc, the emitter of the transistor S5 is connected to the positive electrode of the diode D5, and the negative electrode of the diode D5 is connected to the positive electrode of the power supply. The main circuit unit includes a first branch, a second branch and a third branch connected in parallel to the power supply unit. The first branch is provided with a transistor S0 and a diode D0. The electrode of the transistor S0 is connected to the output end of the input inductor Ldc, the emitter of the transistor S0 is connected to the positive electrode of the diode D0, and the negative electrode of the diode D0 is connected to the negative electrode of the power supply. The second branch includes a transistor S1, a transistor S4, a diode D1 and a diode D4. The electrode of the transistor S1 is connected to the output end of the input inductor Ldc. The output end is connected, the emitter of transistor S1 is connected to the positive electrode of diode D1, the negative electrode of diode D1 is connected to the positive electrode of diode D4, the negative electrode of diode D4 is connected to the electrode of transistor S4, and the output stage of transistor S4 is connected to the power supply; the third branch includes transistor S3, transistor S2, diode D3 and diode D2, the electrode of transistor S3 is connected to the output end of input inductor Ldc, the emitter of transistor S3 is connected to the positive electrode of diode D3, the negative electrode of diode D3 is connected to the positive electrode of diode D2, the negative electrode of diode D2 is connected to the electrode of transistor S2, and the output stage of transistor S2 is connected to the power supply; the load part is connected to the second branch and the third branch, the load part includes capacitor C and load L, the positive electrode of capacitor C is connected to the negative electrode of diode D1, the negative electrode of capacitor C is connected to the positive electrode of diode D2, and the load L is connected between the negative electrode of diode D1 and the positive electrode of diode D2.

[0005] As a further configuration of the current source type AC meter, the transistor S 0 With transistor S 4 The switching signal is generated by a hysteresis controller.

[0006] The present invention also discloses a control system for a current source type AC meter, comprising a coil load current proportional-resonance control outer loop, a capacitor voltage model predictive control inner loop, and a DC bus current hysteresis control logic, wherein the frequency domain transfer function expression of the coil load current proportional-resonance control outer loop is:

[0007] In the formula represents the given value of the capacitor voltage, ∆ i Represents the error in the load current, ξ Represents the damping ratio, set to 0.5, ω nrepresents the natural frequency, which is 100π rad / s. k p and k r Expressed as the proportional coefficient and integral coefficient of the controller.

[0008] As a further setting of the system, the frequency domain transfer function of the coil load current proportional-resonance control outer loop is discretized to obtain a differential expression: In the formula, T s To control the cycle.

[0009] As a further setting of this system, the capacitor voltage model predictive control inner loop is designed based on the capacitor voltage state equation, and the state equation is as follows:

[0010] Discretizing the state equation, we get the difference equation expression {u}_{0}(n+1)-{u}_{0}(n)=\frac {{T}_{s}} {C}[{i}_{0}(n)-i(n)]

[0011] In order to achieve u o right , The calculation expression is {i}^{*}_{0}=\frac {C} {{T}_{s}}[{u}^{*}_{0}-{u}_{0}(n)]+i(n)

[0012] Will Compared with the triangle carrier with an amplitude of 1, when >0, When it is greater than the triangular carrier, the transistor S 1 With transistor S 2 turned on, the other transistors turned off; when <0, When the triangular carrier is smaller than the 3 With transistor S 4 is turned on and the other transistors are turned off.

[0013] As a further setting of this system, the DC bus current hysteresis control logic is: When it is less than the triangular carrier: i dc When S is greater than its given value, 5 turned on, the other transistors turned off; when i dc When S is less than its given value, 0is turned on and the other transistors are turned off.

[0014] This current source AC meter and its control system have the following beneficial effects: S0 is turned on to complete the input inductor Ldc freewheeling in the zero vector stage. Compared with the zero vector state of the traditional CSI, since there is only one set of transistors and diodes turned on, the conduction loss and switching loss in the zero vector stage can be reduced; when the DC bus current idc is too large, S5 is turned on to complete the input inductor Ldc freewheeling in the zero vector stage. At this time, the battery no longer charges Ldc, thereby suppressing the increase of the DC bus current. This setting realizes the reduction of conduction loss and switching loss in part of the zero vector stage, as well as the tracking and constant output of the DC bus current to a given value. The control strategy combining the proportional-resonance outer loop and the voltage inner loop model predictive control is adopted to realize high-precision, high-efficiency and high-quality power supply for the meter. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A topological structure block diagram of an embodiment of the present invention;

[0016] Figure 2 is a block diagram of a load current control structure according to an embodiment of the present invention;

[0017] Figure 3 A waveform harmonic analysis structure diagram of a load current according to an embodiment of the present invention;

[0018] Figure 4 is a harmonic analysis structure diagram of a load current according to an embodiment of the present invention;

[0019] Figure 5 A block diagram of the DC bus current hysteresis control in an embodiment of the present invention;

[0020] Figure 6 : is the current waveform of the DC bus in the embodiment of the present invention. DETAILED DESCRIPTION

[0021] The present invention provides an embodiment of a current source type AC meter and a control system thereof, such as Figures 1 to 6As shown, a current source type AC meter includes a power supply unit, a main circuit unit and a load unit, the power supply unit includes a power supply and an input inductor Ldc, the two ends of the input inductor Ldc are connected with a diode D5 and a transistor S5, the electrode of the transistor S5 is connected to the output end of the input inductor Ldc, the emitter of the transistor S5 is connected to the positive electrode of the diode D5, and the negative electrode of the diode D5 is connected to the positive electrode of the power supply, the main circuit unit includes a first branch, a second branch and a third branch connected in parallel to the power supply unit, the first branch is provided with a transistor S0 and a diode D0, the electrode of the transistor S0 is connected to the output end of the input inductor Ldc, the emitter of the transistor S0 is connected to the positive electrode of the diode D0, and the negative electrode of the diode D0 is connected to the negative electrode of the power supply; the second branch includes a transistor S1, a transistor S4, a diode D1 and a diode D4, the electrode of the transistor S1 is connected to the output end of the input inductor Ldc, the emitter of the transistor S5 is connected to the positive electrode of the diode D0, and the negative electrode of the diode D0 is connected to the negative electrode of the power supply; The emitter of transistor S1 is connected to the positive electrode of diode D1, the negative electrode of diode D1 is connected to the positive electrode of diode D4, the negative electrode of diode D4 is connected to the electrode of transistor S4, and the output stage of transistor S4 is connected to the power supply; the third branch includes transistor S3, transistor S2, diode D3 and diode D2, the electrode of transistor S3 is connected to the output end of input inductor Ldc, the emitter of transistor S3 is connected to the positive electrode of diode D3, the negative electrode of diode D3 is connected to the positive electrode of diode D2, the negative electrode of diode D2 is connected to the electrode of transistor S2, and the output stage of transistor S2 is connected to the power supply; the load part is connected to the second branch and the third branch, and the load part includes capacitor C and load L, the positive electrode of capacitor C is connected to the negative electrode of diode D1, the negative electrode of capacitor C is connected to the positive electrode of diode D2, and the load L is connected between the negative electrode of diode D1 and the positive electrode of diode D2.

[0022] As a further configuration of the current source type AC meter, the transistor S 0 With transistor S 4 The switching signal is generated by a hysteresis controller.

[0023] The control system of the current source type AC meter includes a coil load current proportional-resonance control outer loop, a capacitor voltage model predictive control inner loop and a DC bus current hysteresis control logic. The frequency domain transfer function expression of the coil load current proportional-resonance control outer loop is:

[0024] In the formula represents the given value of the capacitor voltage, ∆ i Represents the error in the load current, ξ Represents the damping ratio, set to 0.5, ω n represents the natural frequency, which is 100π rad / s. kp and k r Expressed as the proportional coefficient and integral coefficient of the controller.

[0025] As a further setting of the system, the frequency domain transfer function of the coil load current proportional-resonance control outer loop is discretized to obtain a differential expression: In the formula, T s To control the cycle.

[0026] As a further setting of this system, the capacitor voltage model predictive control inner loop is designed based on the capacitor voltage state equation, and the state equation is as follows:

[0027] Discretizing the state equation, we get the difference equation expression {u}_{0}(n+1)-{u}_{0}(n)=\frac {{T}_{s}} {C}[{i}_{0}(n)-i(n)]

[0028] In order to achieve u o right , The calculation expression is {i}^{*}_{0}=\frac {C} {{T}_{s}}[{u}^{*}_{0}-{u}_{0}(n)]+i(n)

[0029] Will Compared with the triangle carrier with an amplitude of 1, when >0, When it is greater than the triangular carrier, the transistor S 1 With transistor S 2 turned on, the other transistors turned off; when <0, When the triangular carrier is smaller than the 3 With transistor S 4 is turned on and the other transistors are turned off.

[0030] As a further setting of this system, the DC bus current hysteresis control logic is: When it is less than the triangular carrier: i dc When S is greater than its given value, 5 turned on, the other transistors turned off; when i dc When S is less than its given value, 0 is turned on and the other transistors are turned off.

[0031] This current source AC meter and its control system have the following beneficial effects: S0 is turned on to complete the input inductor Ldc freewheeling in the zero vector stage. Compared with the zero vector state of the traditional CSI, since there is only one set of transistors and diodes turned on, the conduction loss and switching loss in the zero vector stage can be reduced; when the DC bus current idc is too large, S5 is turned on to complete the input inductor Ldc freewheeling in the zero vector stage. At this time, the battery no longer charges Ldc, thereby suppressing the increase of the DC bus current. This setting realizes the reduction of conduction loss and switching loss in part of the zero vector stage, as well as the tracking and constant output of the DC bus current to a given value. The control strategy combining the proportional-resonance outer loop and the voltage inner loop model predictive control is adopted to realize high-precision, high-efficiency and high-quality power supply for the meter.

[0032] The above example is only one preferred specific example of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention are all included in the protection scope of the present invention.

Claims

1. A current source type AC meter, characterized in that: The invention comprises a power supply unit, a main circuit unit and a load unit, wherein the power supply unit comprises a power supply and an input inductor Ldc, wherein two ends of the input inductor Ldc are connected with a diode D5 and a transistor S5, wherein an electrode of the transistor S5 is connected to an output end of the input inductor Ldc, an emitter of the transistor S5 is connected to an anode of the diode D5, and a cathode of the diode D5 is connected to an anode of the power supply, wherein the main circuit unit comprises a first branch, a second branch and a third branch connected in parallel to the power supply unit, wherein the first branch is provided with a transistor S0 and a diode D0, wherein an electrode of the transistor S0 is connected to an output end of the input inductor Ldc, an emitter of the transistor S0 is connected to an anode of the diode D0, and a cathode of the diode D0 is connected to an anode of the power supply; wherein the second branch comprises a transistor S1, a transistor S4, a diode D1 and a diode D4, wherein an electrode of the transistor S1 is connected to an output end of the input inductor Ldc, an emitter of the transistor S1 is connected to an anode of the diode D1, a cathode of the diode D1 is connected to an anode of the diode D4, and a cathode of the diode D4 is connected to an electrode of the transistor S4 The output stage of transistor S4 is connected to the power supply; the third branch includes transistor S3, transistor S2, diode D3 and diode D2, the electrode of transistor S3 is connected to the output end of input inductor Ldc, the emitter of transistor S3 is connected to the positive electrode of diode D3, the negative electrode of diode D3 is connected to the positive electrode of diode D2, the negative electrode of diode D2 is connected to the electrode of transistor S2, and the output stage of transistor S2 is connected to the power supply; the load part is connected to the second branch and the third branch, the load part includes capacitor C and load L, the positive electrode of capacitor C is connected to the negative electrode of diode D1, the negative electrode of capacitor C is connected to the positive electrode of diode D2, and the load L is connected between the negative electrode of diode D1 and the positive electrode of diode D2; the switching signals of transistor S0 and transistor S4 are generated by hysteresis controller; it also includes coil load current proportional-resonance control outer loop, capacitor voltage model predictive control inner loop and DC bus current hysteresis control logic, the frequency domain transfer function expression of the coil load current proportional-resonance control outer loop is In the formula represents the given value of the capacitor voltage, Δi represents the error of the load current, ξ represents the damping ratio, which is set to 0.5, ω n represents the natural frequency, which is 100πrad / s, k p With k r It is expressed as the proportional coefficient and integral coefficient of the controller; The frequency domain transfer function of the coil load current proportional-resonance control outer loop is discretized to obtain a differential expression: Where, T s To control the cycle; The capacitor voltage model predictive control inner loop is designed based on the capacitor voltage state equation, and the state equation is as follows: The state equation is discretized to obtain the difference equation expression: In order to achieve u within a control cycle o right The calculation expression is Will Compared with the triangle carrier with an amplitude of 1, when When it is greater than the triangular carrier, transistors S1 and S2 are turned on, and the other transistors are turned off; when When it is less than the triangular carrier, transistors S3 and S4 are turned on, and other transistors are turned off; The DC bus current hysteresis control logic is: When i is less than the triangular carrier: dc When it is greater than its given value, S5 is turned on and other transistors are turned off; when i dc When it is less than a given value, S0 is turned on and other transistors are turned off.

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