Power line loop communication method based on current type rectifier bridge and reactive power variation

Abstract

The present invention provides a power line loop communication method based on a current-type rectifier bridge and reactive power variation. This method is based on a single-phase AC current-type rectifier bridge loop circuit, relying on the reactive power current generated in the circuit with controllable variation as the communication signal. The communication transmitter uses the reactive power current generated in the circuit to conduct different magnitudes of reactive power currents corresponding to binary digital communication code elements in the loop through an algorithm. The modulated reactive power current uses the power line as the transmission medium, and the communication receiver uses the detection of reactive power in the circuit as the demodulation method to demodulate the detected reactive power into received information, thereby realizing power line loop communication.

Description

Technical Field

[0001] The present invention relates to the technical field of power line communication, and in particular to a power line loop communication method based on a current-type rectifier bridge and reactive power variation. Background Art

[0002] The power communication network came into being to ensure the safe and stable operation of the power system. It, together with the power system's security and stability control system and dispatching automation system, is collectively referred to as the three major pillars for the safe and stable operation of the power system. It is even more the foundation for grid dispatching automation, network operation marketization, and management modernization; an important means to ensure the safe, stable, and economic operation of the power grid; and an important infrastructure of the power system.

[0003] With the advancement of power line carrier communication technology, its characteristics of low cost, high stability, strong economic benefits, and good scene adaptability are becoming increasingly prominent. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a power line loop communication method based on a current-type rectifier bridge and reactive power variation. During the communication process, the energy consumption is low, and it can not only be widely and deeply applied in power communication, but also has good application prospects in specific mines and local communication systems.

[0005] To achieve the above object, the present invention provides a power line loop communication method based on a current-type rectifier bridge and reactive power variation, including:

[0006] The current maintained on the DC side of the current-type rectifier bridge is transmitted to the AC side of the rectifier bridge through PWM control, so that the reactive power on the AC side of the rectifier bridge changes;

[0007] Based on binary digital communication code elements, the PWM control signal of the rectifier bridge switching tube is adjusted so that the change in reactive power on the AC side of the rectifier bridge is the same as the change in binary digital communication code elements;

[0008] The binary digital communication code elements are restored at the remote position of the power supply line on the AC side of the rectifier bridge according to the change in reactive power.

[0009] Further, a freewheeling inductor L d is provided on the DC side of the rectifier bridge, which is L connected in series with a discharge resistor R L and a discharge bypass control switch is connected in parallel with the discharge resistor R;

[0010] When starting the communication function, the discharge bypass control switch is turned on; when closing the communication function, by disconnecting the discharge bypass control switch, the current of the freewheeling inductor L d is attenuated and released through the discharge resistor R. L ​

[0011] Further, in each modulation period T of PWM control m , positive pulses centered at T m / 4 with a width of T mp and negative pulses centered at 3T m / 4 with a width of T mn are respectively generated; for the positive pulses, the positive terminal of the DC side of the rectifier bridge switch tube is connected to the live wire of the AC power supply, and the negative terminal of the DC side is connected to the neutral wire of the AC power supply; for the negative pulses, the positive terminal of the DC side of the rectifier bridge switch tube is connected to the neutral wire of the AC power supply, and the negative terminal of the DC side is connected to the live wire of the AC power supply; when there are no positive and negative pulses, the positive and negative terminals of the DC side of the rectifier bridge switch tube are short - circuited to one end of the live wire or the neutral wire of the AC power supply, and the current in the free - wheel inductor L d continues to flow; the difference in the widths of the positive and negative pulses is used to provide a sustaining current for the free - wheel inductor L d .

[0012] Further, during the PWM control process, the instantaneous target current value on the AC side of the rectifier bridge is set as:

[0013]

[0014] where V rms is the effective value of the AC - side power supply voltage, G L (m) is the equivalent reactance in the m - th power - frequency cycle, corresponding to the active - power consumption, and X L (m) is the equivalent susceptance in the m - th power - frequency cycle, corresponding to the reactive power absorbed from the AC side;

[0015] At the moments of T m / 4 and 3T m / 4 in each modulation period, the DC - side current values i d1 (k) and i d2 (k) of the rectifier bridge are respectively obtained, and the k - th modulation period ΔT(k) is calculated:

[0016]

[0017] When ΔT(k)≥0, T mp (k) = T m / 2, T mn (k) = max(T m / 2 - ΔT(k), 0);

[0018] When ΔT(k)<0, T mn (k) = T m / 2, T mp (k) = max(T m / 2+ΔT(k), 0);

[0019] wherein, i s ((k + 0.5)·T m ) represents the target current on the AC side of the rectifier bridge corresponding to the k-th modulation period.

[0020] Furthermore, the current maintained on the DC side of the current-type rectifier bridge is controlled by PWM, and it further includes: adjusting the equivalent reactance G L (m) of the m-th power frequency period by using proportional-integral feedback control to maintain the current in the freewheeling inductor L d as the target current I d .

[0021] Furthermore, adjusting the equivalent reactance G L (m) includes:

[0022] Calculating intermediate parameters:

[0023]

[0024] wherein, I d is the target current set for the inductor L d , T0 is the power frequency period, and i d (m) is the instantaneous current of the inductor L d at the start moment of the m-th period;

[0025] According to proportional-integral control, G L (m) is obtained:

[0026] G L (m) = max(min(G L (m - 1) + (K p + K i )d(m) + (K i - K p )d(m - 1), G Lmax ), G Lmin )

[0027] wherein, K p is the proportional coefficient of the equivalent reactance control, K i is the integral coefficient of the equivalent reactance control, G Lmax is the upper threshold of G L (m), and G Lmin is the lower threshold of G L (m).

[0028] Furthermore, after communication starts, wait until the current in the freewheeling inductor L d charges to the target current I d , and then, when the communication symbol is 0, set the equivalent impedance X within N power frequency periods of the corresponding symbol period time.L (m) is X L0 When the communication symbol is 1, an equivalent impedance X is set within N power frequency cycles corresponding to the symbol period time L (m) is X L1 Thereby changing the magnitude of the reactive power absorbed by this circuit, collecting the change of reactive power at the remote position of the power supply line on the AC side of the rectifier bridge, and restoring the binary digital communication symbol

[0029] The above technical solution of the present invention has the following beneficial technical effects

[0030] (1) Based on the single-phase AC current-type rectifier bridge circuit, the present invention relies on the variable and controllable reactive power current generated in the circuit as the communication signal. The communication transmitting end uses the reactive power current generated in the circuit to conduct different magnitudes of reactive power current corresponding to binary digital communication symbols in the loop through an algorithm. The modulated reactive power current uses the power line as the transmission medium, and the communication receiving end uses detecting the reactive power in the circuit as the demodulation method to demodulate the detected reactive power into received information, thereby realizing power line loop communication

[0031] (2) The carrier for transmitting the signal is reactive power. The present invention controls the reactive power loss, endows it with a communication function, and realizes power line communication using the loop reactive power without increasing the active power consumption, reducing the energy consumption compared with the traditional power line loop communication

[0032] (3) The communication method of the present invention is applicable to the communication between the concentrator and the electric meter. The electric meter end generates a variable and controllable reactive power current as the communication signal, and the concentrator collects the change of reactive power to obtain the communication information

[0033] (4) The communication method of the present invention can not only be widely and deeply applied in power communication, but also has good application prospects in specific mines and local communication systems Brief Description of the Drawings

[0034] Figure 1 is the basic communication principle diagram

[0035] Figure 2 is the modulation circuit model based on the PWM current source type rectifier bridge

[0036] Figure 3 is the inductor L d the current i d in the charging process

[0037] Figure 4 is the Matlab simulation of the PWM current source type rectifier based on reactive power control

[0038] Figure 5The current and power outputs of the PWM current-source rectifier increase by 3 Var of reactive power at 0.8 s;

[0039] Figure 6 A transceiver system for a communication system based on reactive power variation;

[0040] Figure 7 The active power, reactive power, communication input data, and communication output data curves corresponding to the simulation results;

[0041] Figure 8 The AC-side current, DC-side current, and equivalent conductance of the rectifier bridge measured by the control system during the simulation process. Detailed implementation manners

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer and more obvious, the present invention will be further described in detail below in combination with the detailed implementation manners and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0043] As Figure 1 shown, the working principle of a power line loop communication method based on a current-source rectifier bridge and reactive power variation is presented. This method is based on a single-phase AC current-source rectifier bridge loop circuit and relies on the generation of a controllable reactive power current in the circuit as the communication signal. The communication transmitter uses the reactive power current generated in the circuit to conduct different magnitudes of reactive power currents corresponding to binary digital communication code elements in the loop through an algorithm. The modulated reactive power current uses the power line as the transmission medium, and the communication receiver uses the detection of reactive power in the circuit as the demodulation method to demodulate the detected reactive power into received information, thereby realizing power line loop communication.

[0044] As Figure 2 shown, it is a modulation circuit model based on a PWM current-source rectifier bridge. The single-phase AC source end and the line are equivalent to a voltage source V S and a line impedance R S +jωL S . In fact, from the power grid to the distribution transformer, then through the distribution line, branch box, and then to the load end, its equivalent model may be very complex and also includes the incoming impedance of various current transformers, line stray impedance, and the influence of load impedance of other branches. For the corresponding unpredictable impedance situation, especially the impedance situation that may correspond to different frequencies and different characteristics, it cannot be described by fixed and single parameters. Actually, it may be: R S (f)+jX S (f). If there is no self-excited oscillation, there is always R S (f)>0.

[0045] The parallel impedance at the rectifier bridge access terminal is regarded as capacitor C f caused, corresponding impedance 1 / (jωC f ). The actual value of the source-end parallel impedance is not very certain either. For example, in the power line carrier scenario, for each STA module of HPLC, there is a 4.7 nF or 10 nF impedance in parallel with 220V. At the same time, for multiple meters on a certain phase in a meter box, the parallel capacitance C f value will double. There is also a parallel impedance corresponding to the load on 220V, and it may change with frequency and equivalently change with the cycle.

[0046] Adopt a fully controlled rectifier bridge based on MOS transistors. The switching control is as shown in the following table:

[0047] Table 1 Switching states and space current vectors of single-phase PWM current source type

[0048]

[0049] When only one tube of the rectifier bridge conducts, no current path is formed at the source end. However, when S1 and S3 conduct, or S2 and S4 conduct, the 220V power supply will be short-circuited.

[0050] The zero switching state corresponds to two cases, namely: S1 and S2 conduct, S3 and S4 are off; S3 and S4 conduct, S1 and S2 are off.

[0051] The non-zero switching state corresponds to two cases, namely: S1 and S4 conduct, S2 and S3 are off, and at this time the source-end current i w = I d ; S3 and S4 conduct, S1 and S2 are off.

[0052] Therefore, if the fluctuation of the DC-side current I d is ignored, the characteristic modulation current generated by the PWM current source type rectifier is still -I d , 0, I d three values.

[0053] The rectifier bridge will first switch from a non-zero switching state to a zero switching state and then enter another non-zero switching state. Therefore, the fixed zero switching state is selected

[34] so that there is only one tube on-off change each time.

[0054] The rectifier bridge output first uses a freewheeling inductor with an inductance of L d , and then a parallel circuit of a load control switch S d and a resistor R L is connected in series. When the load control switch S d conducts, the corresponding load resistance is R d = 0; when the load control switch S dWhen disconnected, the corresponding load resistance is R d = R L .

[0055] The load circuit can also adopt a current-limiting MOS transistor circuit to limit the conduction current within I dmax range.

[0056] For the above circuit to achieve that when the fully controlled rectifier bridge of the MOS transistor is in a non-zero switching state and connected to a voltage with a peak value of 311V, the current increase does not exceed 10 mA within half of the modulation period. Assuming a modulation frequency of 833.3 Hz and a modulation period of 1.2 ms, then:

[0057]

[0058] The communication process method of the present invention includes:

[0059] (1) The reactive power current generated on the DC side of the rectifier bridge is transmitted to the AC side of the rectifier bridge, causing the reactive power on the AC side of the rectifier bridge to change.

[0060] A freewheeling inductor L is provided on the DC side of the rectifier bridge d in series with the load R L , and a load R L is shunted with a load control switch; when communication is required, the discharge bypass control switch is turned on; when the communication function is turned off, by disconnecting the discharge bypass control switch, the current of the freewheeling inductor L d is attenuated and released through the discharge resistor R L .

[0061] (2) Based on binary digital communication code elements, the PWM control signal of the rectifier bridge MOS transistor is adjusted so that the change in the reactive power on the AC side of the rectifier bridge is the same as the change in the binary digital communication code elements. For example, when the reactive power on the AC side of the rectifier bridge does not change or the change ratio does not exceed the threshold, it corresponds to "0", and when the change ratio exceeds the threshold, it corresponds to "1".

[0062] Further, within each modulation period T m of the PWM control, positive pulses with a center at T m / 4 and a width of T mp and negative pulses with a center at 3T m / 4 and a width of T mn are respectively generated; the positive pulses correspond to connecting the live wire of the AC power supply to the positive terminal of the DC side of the rectifier bridge switch tube and the neutral wire of the AC power supply to the negative terminal of the DC side; the negative pulses correspond to connecting the neutral wire of the AC power supply to the positive terminal of the DC side of the rectifier bridge switch tube and the live wire of the AC power supply to the negative terminal of the DC side; when there are no positive or negative pulses, the positive and negative terminals of the DC side of the rectifier bridge switch tube are short-circuited to one end of the live wire or the neutral wire of the AC power supply, and the freewheeling inductor L dCurrent freewheeling in it; the difference between the positive and negative pulse widths is used to provide sustaining current for the freewheeling inductor L d Provide sustaining current.

[0063] Further, in the PWM control process, the instantaneous target current value on the AC side of the rectifier bridge is set as:

[0064]

[0065] Wherein, V rms Is the effective value of the power supply voltage on the AC side, G L (m) is the equivalent reactance in the m-th power frequency cycle, corresponding to the active power consumption. The larger G L (m) is, the more active power is absorbed. The current i d Of the freewheeling inductor L increases, X d (m) is the equivalent susceptance in the m-th power frequency cycle, corresponding to the reactive power absorbed from the AC side. L (m) is the equivalent susceptance in the m-th power frequency cycle, corresponding to the reactive power absorbed from the AC side.

[0066] At T m / 4 and 3T m / 4 of each modulation period, respectively obtain the rectifier bridge DC side current values i d1 (k) and i d2 (k), and calculate the k-th modulation period ΔT(k):

[0067]

[0068] When ΔT(k) ≥ 0, T mp (k) = T m / 2, T mn (k) = max(T m / 2 - ΔT(k), 0);

[0069] When ΔT(k) < 0, T mn (k) = T m / 2, T mp (k) = max(T m / 2 + ΔT(k), 0);

[0070] Wherein, i s ((k + 0.5)·T m ) represents the unidirectional AC power supply current on the AC side of the rectifier bridge collected in the k-th modulation period.

[0071] (3) The rectifier bridge AC side restores binary digital communication code elements according to the change of reactive power.

[0072] After starting communication, wait for the current in the freewheeling inductor L d To charge to the target current I dAfter that, when the communication symbol is 0, an equivalent reactance X is set within N power frequency cycles corresponding to the symbol period time. L (m) is X L0 When the communication symbol is 1, an equivalent reactance X is set within N power frequency cycles corresponding to the symbol period time. L (m) is X L1 Thereby, the magnitude of the reactive power absorbed by this circuit is changed, and the change in reactive power is collected at the far - end position of the power supply line on the AC side of the rectifier bridge to restore the binary digital communication symbol.

[0073] Furthermore, controlling the current i d includes:

[0074] To obtain a larger modulation current, in each modulation period, centered on T m / 4, a positive pulse with a width of T wp is generated, and centered on 3T m / 4, a negative pulse with a width of T wn is generated. The difference in the widths of the positive and negative pulses is used to provide a sustaining current for the inductor L d so that the average value of the current is Id. When it is necessary to increase id, if the single - phase AC power supply voltage is positive, then T wp >T wn , T wp can be taken up to T m / 2, and when it is necessary to increase the free - wheeling current i d to the maximum, T wn =0; if the single - phase AC power supply voltage is negative, then T wp <T wn , T wn can be taken up to T m / 2, and when it is necessary to increase the free - wheeling current i d to the maximum, T wp =0.

[0075] The energy losses include: the MOS - tube switching losses of the full - controlled rectifier bridge; the resistance losses and magnetic losses in the inductor; the losses of the load Rd. Thus, if the current i d in the inductor L d tends to the set average current value I d as the control target, the control method using the PI control strategy is:

[0076] At the T m / 4 and 3T m / 4 moments of each modulation period, the current values i d1 (k) and i d2 (k) on the DC side are obtained twice.

[0077] Δi(k)=(i d1 (k)+id2 (k)) / 2 - I d

[0078] i p (k) = k p ·Δi(k)

[0079] i i (k) = k i ·Δi(k) + i i (k - 1)

[0080] where k p is the proportional coefficient of equivalent reactance control, and k i is the integral coefficient of equivalent reactance control. When 2|v s (k)| < |v s (k - 1)| (this condition includes |v s (k)| < |v s (k - 1)|), then take T mp (k) = T mn (k) = 0; otherwise, calculate

[0081]

[0082] When v s (t) > 0 and ΔT(k) ≥ 0, T mn (k) = T m / 2, and T mp (k) = max(T m / 2 - ΔT(k), 0);

[0083] When v s (t) > 0 and ΔT(k) < 0, T mp (k) = T m / 2, and T mn (k) = max(T m / 2 + ΔT(k), 0);

[0084] When v s (t) < 0 and ΔT(k) ≥ 0, T mp (k) = T m / 2, and T mn (k) = max(T m / 2 - ΔT(k), 0);

[0085] When v s (t) < 0 and ΔT(k) < 0, T mn (k) = T m / 2, and T mp (k) = max(T m / 2 + ΔT(k), 0);

[0086] Furthermore, to achieve soft start, the following control is required:

[0087] Regarding the inductor L d For the maximum adjustment value of the current in it, if other losses are ignored, the calculation of the average current adjustment rate is as follows:

[0088]

[0089] According to the current simulation parameters, the effective value of the AC-side power supply voltage V rms = 220V, L d = 20H, the calculation result of the above formula is D id = 4.95A·s, and the current change in one cycle is Δ id = 0.099A. Figure 3 is the rising process of the simulation current i d The data is basically consistent. The data difference corresponds to: simulation error, and for pulse width control, there are treatments for switch protection time and non-pulse generation at zero crossing.

[0090] For the above charging, the harmonic and power factor problems of the charging current are not considered. Assume that the equivalent conductance during the charging process is G max , and after M chg cycles, the current in the inductor L d charges to I d , M chg should satisfy:

[0091]

[0092] When I d = 0.2A and T0 = 0.02s, there is M chg > 2.02.

[0093] Calculated according to the energy conservation after charging, the energy of the inductor is:

[0094]

[0095] Thus:

[0096]

[0097] When M chg = 6, G Lmax = 6.887×10 -5 .

[0098] If the charging equivalent conductance G Chg of this device is set as the control target, the output control parameter G Chg (m) is adjusted once per cycle, and it is assumed that the system loss is the conductance GLoss The overall conductance of this device is G L (m) = G Loss +G Chg (m). Maintain the current in the inductor L d Then G Chg (m) tends to 0, and G L (m) tends to G Loss . Corresponding to the current in L d before and after one cycle and then the estimation formula for G Loss is:

[0099]

[0100] where m is the cycle count. Since the inductance L d , power supply voltage V rms have errors in the above formula, feedback control of the PWM modulation output is set according to the conductance parameter. When the system converges, the current tends to the set value Id, so there are and The above formula is approximated as:

[0101]

[0102] If the loss is mainly caused by the DC loop resistance R d , then there is:

[0103]

[0104] From G Loss <G lmax , V rms = 220V, I d = 0.05A, we can get R d <1333Ω.

[0105] From G Loss <G lmax , V rms = 220V, I d = 0.2A, we can get R d <83.33Ω.

[0106] The control based on conductance can achieve soft start and further achieve power factor control.

[0107] The control based on conductance can achieve power factor control through the control of the instantaneous current waveform on the AC side. The control conductance G L (m) is adjusted once per cycle T0; then the target instantaneous value of the AC side current is obtained from the synchronous power frequency voltage :

[0108]

[0109] The part before the symbol corresponds to active power and controls the inductance L d Charge and discharge; X L (m) corresponds to the susceptance of reactive power and can be set as needed. Assume X L (m) is 0. Just for the control of G L (m), proportional-integral regulation is carried out. Calculate the intermediate parameter:

[0110]

[0111] Among them, I d is the target current in the set inductance L d . Further proportional-integral control is carried out to obtain G L (m):

[0112] G L (m) = max(min(G L (m - 1)+(K p +K i )d(m)+(K i -K p )d(m - 1), G Lmax ), G Lmin )

[0113] Among them, take G Lmin =-G Lmax / 10. Among them, K p is the proportional coefficient of equivalent reactance control, K i is the integral coefficient of equivalent reactance control, G Lmax is the upper threshold of G L (m), G Lmin is the lower threshold of G L (m).

[0114] Based on Adjust the PWM pulse width. The specific control method is: at T m / 4 and 3T m / 4 of each modulation period, obtain the current values i d1 (k) and i d2 (k) on the DC side twice. In each pulse width modulation period T m , calculate:

[0115]

[0116] When ΔT′(k)≥0, T mp (k)=T m / 2, T mn(k) = max(T m / 2 - ΔT(k), 0);

[0117] When ΔT′(k) < 0, T mn (k) = T m / 2, T mp (k) = max(T m / 2 + ΔT(k), 0);

[0118] 3), Reactive power control

[0119] Furthermore, a certain amount of reactive power can be output by this rectifier to achieve power factor regulation. The maximum peak current of PWM is about 0.5 * I d , that is, 0.1 A. Thus, the maximum reactive power is According to the set reactive power Q C , the reactance X of the reactive part is obtained L :

[0120]

[0121] Thus, the instantaneous value of the target AC-side current:

[0122]

[0123] Based on i s (t) to adjust the PWM pulse width, the specific control method is: at T m / 4 and 3T m / 4 of each modulation period, the current values i d1 (k) and i d2 (k) of the DC side are obtained twice. In each pulse width modulation period T m , calculate:

[0124]

[0125] When ΔT(k) ≥ 0, T mp (k) = T m / 2, T mn (k) = max(T m / 2 - ΔT(k), 0);

[0126] When ΔT(k) < 0, T mn (k) = T m / 2, T mp (k) = max(T m / 2 + ΔT(k), 0);

[0127] Such as Figure 4 , is the Matlab simulation of the PWM current source rectifier based on reactive power control

[0128] Figure 4 Set the second input of Fun_CurrentMod_addPQ_PWM as reactive power setting, i.e., 3 Var, and set that the regulation of GL is started only after the phase-locked loop is stable at 0.2 s; at 0.8 s, after the current of inductor L d is stable, start the reactive power regulation.

[0129] Such as Figure 5 , it is the current and power output of the PWM current source rectifier increasing 3 Var reactive power at 0.8 s

[0130] Based on the above theory, the present invention adopts a fully controlled rectifier bridge based on MOS transistors. A freewheeling inductor is used at the DC side output of the rectifier bridge, and then a load control switch and a resistor parallel circuit are connected in series. According to the basic characteristics of the PWM current source rectifier, the rectifier bridge can output a certain amount of reactive power to achieve power factor regulation. According to the set reactive power, the reactive part impedance is obtained, and the instantaneous value of the AC side current of the target can be obtained. Based on this instantaneous value of the AC side, the PWM pulse width is adjusted. Its Matlab simulation circuit is as Figure 6 shown, which describes the simulation communication model built based on the above theory. The specific implementation parameters can be built and verified with reference to the specific parameters given in the figure.

[0131] The algorithm for converting the reactive power generated by the freewheeling inductor on the DC side of the rectifier bridge into a controllable reactive power signal takes the pulse width modulation frequency, the reactive power corresponding to the set conversion ratio of the symbol, the measured value of the instantaneous phase of the AC side voltage, and the effective value of the AC side voltage as inputs to obtain the equivalent impedance; at the same time, according to the feedback control logic of the freewheeling inductor current, the equivalent conductance is obtained; according to the equivalent conductance and equivalent impedance, the instantaneous value of the equivalent current on the AC side is calculated; in each modulation period, according to the instantaneous value of the equivalent current on the AC side, it is proportionally converted into a forward current pulse width centered on 1 / 4 of the modulation period and a reverse current pulse width centered on 3 / 4 of the modulation period, which are used as the PWM control signals for each MOS transistor of the fully controlled rectifier bridge; under the control of this signal, the freewheeling inductor on the DC side of the fully controlled rectifier bridge maintains the set current, and the required reactive power current is generated on the AC side. Such as Figure 7 shown, which shows the input and output waveforms of the simulation communication system built based on the above theory.

[0132] Communication data stream is input into the communication system in the above figure at a rate of one bit per 0.1 s. For the corresponding bit 0, the reactive power input control is 0 Var; for the corresponding bit 1, the reactive power input control is 5 Var. In the reactive power detection circuits of the terminal and the branch box, the measurement delay is less than 2 cycles, that is, 0.04 s. The change in reactive power is detected. If there is an increase of 2.5 Var every 0.1 s compared to the previous 0.1 s, then output 1; if there is a decrease of more than 2.5 Var every 0.1 s compared to the previous 0.1 s, then output 0; otherwise, the output data remains unchanged.

[0133] As Figure 7 shown, since C s itself has a reactive power of -3.0 Var, the reactive power outputs of the simulation system are -3 Var and 2 Var with the communication input data 0 and 1. The process AC side current, DC side current, and the equivalent conductance of the rectifier bridge measured by the control system are as Figure 8 shown.

[0134] In summary, the present invention provides a power line loop communication method based on a current - type rectifier bridge and reactive power variation. This method is based on a single - phase AC current - type rectifier bridge loop circuit, relying on the variable and controllable reactive power current generated in the circuit as the communication signal. The communication transmitting end uses the reactive power current generated in the circuit to conduct different magnitudes of reactive power currents corresponding to binary digital communication code elements in the loop through an algorithm. The modulated reactive power current uses the power line as the transmission medium, and the communication receiving end uses the detection of reactive power in the circuit as the demodulation method to demodulate the detected reactive power into received information, thereby realizing power line loop communication.

[0135] It should be understood that the above - mentioned specific embodiments of the present invention are only used for exemplary illustration or explanation of the principle of the present invention, and do not constitute a limitation to the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention shall be included within the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modification examples falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A power line loop communication method based on a current-type rectifier bridge and reactive power variation, characterized in that, Including: The current maintained on the DC side of the current-type rectifier bridge is transmitted to the AC side of the rectifier bridge after PWM control, causing the reactive power on the AC side of the rectifier bridge to change; Based on binary digital communication code elements, the PWM control signal of the rectifier bridge switching tube is adjusted so that the change in reactive power on the AC side of the rectifier bridge is the same as the change in binary digital communication code elements; At the remote position of the power supply line, the binary digital communication code elements are restored according to the change in reactive power on the AC side of the rectifier bridge.

2. The power line loop communication method based on a current-type rectifier bridge and reactive power variation according to claim 1, characterized in that, A freewheeling inductor L is provided on the DC side of the rectifier bridge. d is connected in series with a discharge resistor R L The discharge resistor R L is connected in parallel with a discharge bypass control switch. When the communication function is started, the discharge bypass control switch is turned on; when the communication function is turned off, by turning off the discharge bypass control switch, the current of the freewheeling inductor L d is decayed and released through the discharge resistor R L .

3. The power line loop communication method based on a current-type rectifier bridge and reactive power variation according to claim 1, wherein During each PWM control modulation period T m , positive pulses centered at T m / 4 with a width of T mp and negative pulses centered at 3T m / 4 with a width of T mn are generated respectively; for the positive pulses, the positive terminal of the DC side of the rectifier bridge switch tube is connected to the live wire of the AC power supply, and the negative terminal of the DC side is connected to the neutral wire of the AC power supply; for the negative pulses, the positive terminal of the DC side of the rectifier bridge switch tube is connected to the neutral wire of the AC power supply, and the negative terminal of the DC side is connected to the live wire of the AC power supply; when there are no positive and negative pulses, the positive and negative terminals of the DC side of the rectifier bridge switch tube are short-circuited to one end of the live wire or the neutral wire of the AC power supply, and the current in the freewheeling inductor L d freewheels; the difference between the widths of the positive and negative pulses is used to provide a sustaining current for the freewheeling inductor L d .

4. The power line loop communication method based on a current type rectifier bridge and reactive power variation according to claim 3, characterized in that, During the PWM control process, the instantaneous target current value on the AC side of the rectifier bridge is set as: Among them, V rms is the effective value of the AC-side power supply voltage, and G L (m) is the equivalent reactance in the m-th power frequency cycle, corresponding to the active power consumption. X L (m) is the equivalent susceptance in the m-th power frequency cycle, corresponding to the reactive power absorbed from the AC side; At T m / 4 and 3T m / 4 moments of each modulation period, respectively obtain the DC side current values i d1 (k) and i d2 (k) of the rectifier bridge, and calculate the k-th modulation period ΔT(k): When ΔT(k) ≥ 0, T mp (k) = T m / 2, T mn (k) = max(T m / 2 - ΔT(k), 0); When ΔT(k) < 0, T mn (k) = T m / 2, T mp (k) = max(T m / 2 + ΔT(k), 0); where i s ((k + 0.5)·T m ) represents the target current on the AC side of the rectifier bridge corresponding to the k-th modulation period.

5. The power line loop communication method based on a current-type rectifier bridge and reactive power variation according to claim 4, characterized in that The current maintained on the DC side of the current-type rectifier bridge is controlled by PWM, and further includes: adjusting the equivalent reactance G L (m) of the m-th power frequency cycle by using proportional-integral feedback control to maintain the current in the freewheeling inductor L d as the target current I d . L (m) to maintain the current in the freewheeling inductor L d as the target current I d .

6. The power line loop communication method based on a current-type rectifier bridge and reactive power variation according to claim 5, characterized in that Adjust the equivalent reactance G of the m-th power frequency cycle L (m) includes: Calculate intermediate parameters: Among them, I d is the set inductance L d is the target current in, T0 is the power frequency period, i d (m) is the instantaneous current of the inductance L at the starting moment of the m-th cycle d ; According to proportional-integral control, G L (m): G L (m) = max(min(G L (m - 1)+(K p +K i )d(m)+(K i -K p )d(m - 1), G Lmax ), G Lmin ) Among them, K p is the proportional coefficient of equivalent reactance control, and K i is the integral coefficient of equivalent reactance control. G Lmax is the upper threshold of G L (m), and G Lmin is the lower threshold of G L (m).

7. The power line loop communication method based on a current-type rectifier bridge and reactive power variation according to claim 2, wherein After starting communication, wait for the current in the freewheeling inductor L d to charge up to the target current I d After that, when the communication symbol is 0, set the equivalent impedance X in N power frequency cycles within the corresponding symbol period time L (m) to be X L0 ; when the communication symbol is 1, set the equivalent impedance X in N power frequency cycles within the corresponding symbol period time L (m) to be X L1 ; thereby changing the magnitude of the reactive power absorbed by this circuit, collecting the change of reactive power at the remote position of the power supply line on the AC side of the rectifier bridge, and restoring the binary digital communication symbol.

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