CN102064749A - Motor soft startup device capable of giving consideration to reactive power compensation and control method thereof - Google Patents

Abstract

The invention discloses a motor soft start device and its control method taking into account reactive power compensation. The converter includes a three-phase phase-shifting transformer, several rectification modules, inverter modules, and AC reactors. The primary winding of the three-phase phase-shifting transformer is connected to the grid through a grid-side switch, and the secondary winding is connected to the rectification module of the same level. , the rectifier module is connected to the inverter module, and the inverter modules in the same phase are connected in series in sequence to the AC reactor, and the AC reactor is connected to the grid through the motor; the main controller is respectively connected to the primary side of the three-phase phase-shifting transformer and the AC reactor The voltage transformer is connected to the current transformer, and connected to the inverter module through optical fiber. The invention also discloses a control method based on the above device. The invention can realize the soft start of the motor, and can dynamically compensate the reactive power according to the working condition of the motor.

Description

A motor soft start device and control method taking into account reactive power compensation

technical field

The invention relates to the field of motor soft-start research, in particular to a motor soft-start device and a control method taking into account reactive power compensation.

Background technique

In practical applications, if the motor, especially the high-voltage and high-power motor, is directly started, a starting current several times the rated current will be generated. The electrical and mechanical shocks caused by the current will cause the motor to fail to start, and even threaten the equipment. Safety, so the starting device must be used to limit the current during the motor starting process. Existing motor starters include: series reactor step-down starters, variable resistor starters, and electronic thyristor voltage-regulating soft starters. There are some problems in these starting devices. For example, when a series reactor step-down starter is used, the starting inrush current is large, and there is a secondary impact when switching; the variable resistance starter takes up a large area, and the civil construction cost is high. It cannot be put into use again in a short period of time; the electronic thyristor voltage regulation soft start device adopts phase control to adjust the output voltage, which will reduce the power factor of the power grid and bring harmonic pollution. In addition, after the motor is started, the motor is cut into the power frequency grid for operation, and the starting equipment is out of operation. Therefore, in the traditional motor starting technical scheme, the utilization rate of the equipment is very low.

At present, high-voltage and high-power motors are mainly asynchronous motors. The rated power factor of asynchronous motors is about 0.9, and the power factor will be lower during light-load operation. Therefore, reactive power compensation equipment needs to be installed. Currently, reactive power compensation equipment mainly refers to power capacitors. However, the compensation characteristics of power capacitors depend on the power supply voltage level, which cannot realize dynamic compensation according to load changes, and can only be switched in groups through mechanical devices. Reactive over-compensation or under-compensation, so it is difficult to control accurately.

Therefore, it is necessary to provide a motor soft start device and a control method thereof that can realize the shockless start of the motor and dynamically compensate reactive power.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and provide a motor soft start device and its control method taking into account reactive power compensation, through which the motor can be started without impact and reactive power can be dynamically compensated.

The present invention provides a motor soft start device that takes into account reactive power compensation, including a power converter, a transfer switch and a main controller, and the transfer switch includes a power grid side switch, a motor side switch and a grid-connected switch; the power converter includes Three-phase phase-shifting transformer, several rectification modules and inverter modules, AC reactor, the primary winding of the three-phase phase-shifting transformer is connected to the power grid through the grid-side switching switch, and the secondary winding group is divided into N groups of windings; the input of the rectification module The side is connected to the secondary winding of the three-phase phase-shifting transformer of the same level, and the output side is connected to the input side of the inverter module. The side switch is connected to the motor stator, and the motor stator is connected to the grid through the grid-connected switch; the main controller is connected to the grid-side voltage transformer and current transformer installed on the primary side of the three-phase phase-shifting transformer, and connected to the grid-side voltage transformer and current transformer installed on the AC reactance The motor-side current transformer at the output end of the inverter is connected to the voltage transformer, and connected to the inverter module through an optical fiber.

The primary winding of the three-phase phase-shifting transformer is the high-voltage side, and the secondary winding is the low-voltage side and is divided into multiple groups of secondary windings. The output voltage amplitudes of each group of secondary windings are equal, and the phases are sequentially different by a phase shift angle.

The phase shift angle is 60°/N, where N is the number of secondary windings of the three-phase phase shift transformer.

The rectification module includes a three-phase rectification circuit composed of diodes for converting AC voltage into DC voltage.

The inverter module includes a connection contactor, a DC support capacitor, an H-bridge inverter circuit and a module controller. The inverter module is connected to the rectifier module through the connection contactor. The DC support capacitor is used to stabilize the DC voltage, and its two ends are inverter The input side of the variable module, the output of the H-bridge inverter circuit is the output side of the inverter module, the module controller is connected with the connection contactor, the DC support capacitor and the H-bridge inverter circuit, and connected with the main controller through an optical fiber for The instruction of the main controller is received to control the inverter module to work, and the status information of the inverter module is fed back at the same time; the H-bridge inverter circuit is used to convert the DC voltage into an AC voltage.

The H-bridge inverter circuit in the inverter module is composed of full-control power electronic devices such as IGBT or IGCT.

The AC reactor in the power converter is used to absorb high-order components in the output voltage of the device, limit the circulating current that may be caused by control errors when the motor is connected to the grid, and isolate the grid voltage and the output voltage of the commutation chain when compensating reactive power.

The changeover switch operates according to the instruction of the main controller. When starting the motor, the power converter is connected in series with the motor, and when reactive power is compensated, the power converter is connected in parallel with the motor.

The present invention also provides a motor soft-start control method based on the above-mentioned device and taking into account reactive power compensation, which specifically includes the following steps:

(1) First close the grid-side switch connecting the primary side of the three-phase phase-shifting transformer and the power grid, and then close the motor-side switch connecting the reactor and the motor stator side. At this time, a DC voltage is established at both ends of the DC support capacitor, and the power converter It becomes a series relationship with the motor;

(2) The main controller increases the frequency and amplitude of the output voltage proportionally according to the set acceleration curve, and the motor gradually accelerates from standstill under the action of the output voltage;

(3) When the frequency of the output voltage rises to the power frequency and the amplitude rises to the rated voltage of the motor, the main controller collects the grid voltage signal measured by the voltage transformer, and phase-locks the grid voltage to obtain the phase of the grid voltage;

(4) The main controller adjusts the amplitude and phase of the output voltage according to the phase-locked result of the grid voltage, taking the grid voltage as a reference, and controls the input voltage of the motor to be completely consistent with the grid voltage, that is, the frequency, amplitude and phase are uniform. It coincides with the grid voltage, and the synchronization is successful at this time;

(5) After the synchronization is successful, run stably for a period of time, the main controller sends the motor grid-connected command, closes the grid-connected switch at the connection between the motor and the grid, puts the motor into the grid, and disconnects the motor side at the connection between the AC reactor and the motor After that, the motor is fed by the power grid, and the soft start is completed; then judge whether there are other motors to be started in the system, and if so, repeat steps (1) to (5) in turn until all the motors to be started have completed the soft start, and then Enter step (6), otherwise directly enter step (6);

(6) The main controller issues an instruction to disconnect the switch on the grid side, disconnect the connecting contactor in each inverter module, the power converter transforms into an inverter module in the same phase and connects the AC reactor in series, closes the switch on the motor side, and The device is put into the power grid again, and the power converter and the motor are connected in parallel;

(7) The main controller calculates the reactive power to be compensated according to the voltage and current signals on the stator side of the motor measured by the voltage transformer and current transformer, and controls the power converter to output the same amount of reactive power to realize reactive power compensation.

The acceleration curve set in the step (2) is expressed as follows:

$\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, u is the output voltage of the device, f is the frequency of the output voltage, f _N is the rated frequency of the motor, U _N is the rated voltage of the motor, U ₀ is the torque boost voltage, which is 0.01 to 0.05 times the rated voltage of the motor, and the selected U ₀ Different acceleration curves will be obtained. When U ₀ =0, the more commonly used acceleration curves can be obtained:

$\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Compared with the prior art, the present invention has the following beneficial effects:

1. The present invention controls the output voltage through the main controller, and can always control the motor current near the rated value during the motor startup process, which greatly reduces the impact of the motor startup on the power grid and the damage to the motor itself, and realizes the shockless startup of the motor .

2. In the present invention, the main controller can dynamically compensate the reactive power according to the working condition of the motor, which improves the power factor of the power grid and avoids the waste of electric energy caused by reactive power flow.

3. The present invention can continuously start multiple motors in a short time, and can quickly switch between the two functions of motor starting and reactive power compensation, which improves the utilization rate of equipment.

Description of drawings

Fig. 1 is the electrical wiring diagram that device of the present invention starts a motor;

Fig. 2 is the topological structure diagram of the power converter in the device of the present invention;

Fig. 3 is a topological structure diagram of a rectifier module and an inverter module in the device of the present invention;

Fig. 4 (a)-(b) is the rise process diagram of output voltage amplitude and frequency when the device of the present invention starts the motor;

Fig. 5 (a) is the grid voltage when the device of the present invention starts the motor;

Fig. 5 (b1)-(b4) is the process diagram of the output voltage tracking grid voltage when the device of the present invention starts the motor;

Fig. 6 is the electrical wiring diagram of starting three motors of the device of the present invention.

In Figures 1 to 3: 1-power converter; 2-main controller; 3-three-phase phase-shifting transformer; 4-rectifier module; 5-inverter module; 6-AC reactor; 7-grid side switch; 8 -motor side switch; 9-grid switch; 10-connector contactor; 11-DC support capacitor; 12-H bridge inverter circuit; 13-module controller; 14-optical fiber; 15-grid side voltage transformer; 16 - grid side current transformer; 17 - motor side voltage transformer; 18 - motor side current transformer.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example 1

Figures 1 to 3 show a solution for starting a motor and performing reactive power compensation, a motor soft start device that takes reactive power compensation into account, including a power converter 1, a switch and a main controller 2, the switch The switch includes a grid-side switch 7, a motor-side switch 8, and a grid-connected switch 9; the power converter 1 includes a three-phase phase-shifting transformer 3, several rectification modules 4 and inverter modules 5, an AC reactor 6, and three-phase shifting The primary winding of the phase transformer 3 is connected to the grid through the grid-side switch, and the secondary winding is divided into N groups of windings; the input side of the rectifier module 4 is connected to the secondary winding of the three-phase phase-shifting transformer of the same level, and the output side is connected to the inverter The input side of the module 5 is connected, and the inverter modules 5 in the same phase are connected in series to form a commutation chain, which is connected to the AC reactor 6, and the AC reactor 6 is connected to the motor stator after passing through the motor side switch 8, and the motor stator passes through the grid-connected switch 9 Connected to the grid; the main controller 2 is connected to the grid-side voltage transformer 15 and the grid-side current transformer 16 installed on the primary side of the three-phase phase-shifting transformer 3, and is connected to the motor-side current transformer installed at the output end of the AC reactor 6 The transformer 18 is connected to the voltage transformer 17 on the motor side, and connected to the inverter module 5 through the optical fiber 14 .

The primary winding of the three-phase phase-shifting transformer 3 is the high-voltage side, and the secondary winding is the low-voltage side and is divided into multiple groups of secondary windings. The output voltage amplitudes of each group of secondary windings are equal, and the phases are sequentially different by a phase shift angle.

The phase shift angle is 60°/N, and N is the number of groups of the 3 secondary windings of the three-phase phase shift transformer.

The rectification module 4 includes a three-phase rectification circuit composed of diodes for converting AC voltage into DC voltage.

As shown in Figure 3, the inverter module 5 includes a connection contactor 10, a DC support capacitor 11, an H-bridge inverter circuit 12 and a module controller 13, the inverter module 5 is connected to the rectifier module 4 through the connection contactor 10, The DC support capacitor 11 is used for stabilizing the DC voltage, and its two ends are the input side of the inverter module 5, the output of the H-bridge inverter circuit 12 is the output side of the inverter module 5, and the module controller 13 is connected with the contactor 10, the DC The supporting capacitor 11 is connected to the H-bridge inverter circuit 12, and is connected to the main controller 2 through an optical fiber 14, and is used to receive instructions from the main controller 2 to control the inverter module 5 to work, and to feed back the state information of the inverter module 5 at the same time; The H-bridge inverter circuit 12 is used to convert the DC voltage into AC voltage.

The H-bridge inverter circuit 12 in the inverter module 5 is composed of IGBTs.

The AC reactor 6 in the power converter 1 is used to absorb high-order components in the output voltage of the device, limit the circulating current that may be caused by the control error when the motor is connected to the grid, and isolate the grid voltage and the output of the commutation chain when compensating reactive power Voltage.

The changeover switch operates according to the instruction of the main controller 2. When starting the motor, the power converter 1 is connected in series with the motor, and when reactive power is compensated, the power converter 1 is connected in parallel with the motor.

The present invention also provides a motor soft-start control method based on the above-mentioned device and taking into account reactive power compensation, which specifically includes the following steps:

(1) First close the grid-side switch 7 connecting the primary side of the three-phase phase-shifting transformer 3 and the power grid, and then close the motor-side switch 8 connecting the reactor and the motor stator side. At this time, a DC voltage is established at both ends of the DC support capacitor 11, And the power converter 1 and the motor are connected in series;

(2) The main controller 2 increases the frequency and amplitude of the output voltage proportionally according to the set acceleration curve, and the motor gradually accelerates from a standstill under the action of the output voltage; the change process of the voltage amplitude and frequency is shown in Figure 4 As shown in Figure 4(a), according to the acceleration curve 1, the amplitude and frequency of the output voltage rise from zero and maintain a constant amplitude/frequency ratio. Increase the voltage in stages, and rise according to the trajectory shown in acceleration curve 2; t1, t2 and t3 in Figure 4(b) represent three different acceleration times;

(3) When the frequency of the output voltage rises to the power frequency and the amplitude rises to the rated voltage value of the motor, the main controller 2 collects the grid voltage signal measured by the voltage transformer, phase-locks the grid voltage, and obtains the phase of the grid voltage;

(4) The main controller 2 adjusts the amplitude and phase of the output voltage according to the phase-locked result of the grid voltage and with the grid voltage as a reference, and controls the input voltage of the motor to be completely consistent with the grid voltage. The process of voltage synchronization is shown in Figure 5 It shows that after the completion of the motor acceleration, the phase difference between the phase of the output voltage and the phase of the grid voltage is random. The waveform in Figure 5(b1) represents the output voltage of the device after the completion of the motor acceleration. Figure 5(a) shows Grid voltage, under the adjustment of the main controller 2, the voltage waveform changes from Figure 5(b1) to Figure 5(b4), and Figure 5(b4) is exactly the same as Figure 5(a), that is, the frequency of the output voltage , amplitude and phase coincide with the grid voltage, and the synchronization is successful at this time;

(5) After successful synchronization, run stably for a period of time, the main controller 2 sends the motor grid-connected command, closes the grid-connected switch 9 at the connection between the motor and the grid, puts the motor into the grid, and disconnects the AC reactor 6 at the connection with the motor The motor side switch 8, after which the motor is fed by the grid, and the soft start is completed;

(6) The main controller 2 issues an instruction to disconnect the grid-side switch 7, disconnect the connection contactor 10 in each inverter module 5, and the power conversion part transforms into a series connection between the same-phase inverter module 5 and the AC reactor 6, Close the switch 8 on the motor side, put the device into the power grid again, and at this time, the power converter 1 and the motor are connected in parallel;

(7) The main controller 2 calculates the reactive power to be compensated according to the voltage and current signals measured by the voltage transformer and current transformer on the stator side of the motor, and controls the power converter 1 to output an equivalent amount of reactive power to realize reactive power compensation.

The acceleration curve 2 formula of setting in described step (2) is expressed as follows:

$\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="u"\; filenames="HDA0000043392040000021.png,HDA0000043392040000022.png"\; state="\{\{state\}\}">u</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}$

Among them, u is the output voltage of the device, f is the frequency of the output voltage, f _N is the rated frequency of the motor, U _N is the rated voltage of the motor, U ₀ is the torque boost voltage, which is 0.01 times the rated voltage of the motor, when U ₀ =0 , the more commonly used acceleration curve can be obtained, that is, the acceleration curve 1, the formula is as follows:

$\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; f</span>}$

Example 2

Except for the following features, other structures and implementation methods are the same as those in Embodiment 1: as shown in Figure 6, it is a technical solution in which a soft starter device starts three motors M ₁ , M ₂ and M ₃ respectively, and performs reactive power compensation. The soft start device is connected to the power grid through the grid-side switches K _N1 and K _N2 , and connected to the motor to be started through the motor-side switches K _M1 , K _M2 and K _M3 , and the motor is connected to the power grid through the grid-connected switches K ₁ , K ₂ and K ₃ respectively. grid connected.

Assuming that the first motor to be started is M ₁ , the control method for starting M ₁ is exactly the same as that for starting a motor in Embodiment 1, that is, steps (1) to (5) in the control method. That is, after the motor meets the grid-connection conditions, the main controller 2 sends a switching command to close K ₁ first, and then open K _M1 , then the motor M ₁ is connected to the grid, the start-up process of M ₁ is completed, and the output voltage becomes zero. Then determine whether there are other motors to be started in the system, and find that there are still motors _M2 and _M3 that need to be started, so repeat the method steps (1) to (5) in the embodiment, that is, close K _M2 , disconnect _K2 , Motor _M2 and power converter 1 are connected in series, repeat the process of starting motor _M1 , put motor _M2 into the grid, close _K2 , disconnect _KM2 , the starting process of _M2 is completed, and the output voltage becomes zero; repeatedly start the motor In the process of M ₂ , put M ₃ into the power grid, close K ₃ , disconnect K _M3 , the start-up process of M ₃ is completed, and the output voltage becomes zero.

According to the above control method, after the three motors are accelerated and connected to the grid in turn, the motors are powered by the grid and enter the power frequency operation state. The device enters the working mode of reactive power compensation, disconnects the connection contactor K between each rectifier module 4 and inverter module 5, disconnects the grid-side switch K _N1 , closes the grid-side switch K _N2 , and the power converter 1 is switched After the switch K _N2 is connected to the power grid, it forms a parallel relationship with the three load motors and hangs on the high-voltage bus together. The voltage transformer and current transformer installed on both sides of the motor stator side measure the voltage and current signals of the motor stator side, and the measurement results are sent to the main controller 2, and the reactive power absorbed by all motor loads from the grid is calculated in the main controller 2 The sum of the power, the device outputs the same amount of reactive power, thereby improving the power factor at the connection between the motor and the grid.

In this embodiment, the H-bridge inverter circuit 12 in the inverter module 5 is composed of an IGCT.

As mentioned above, the present invention can be better realized. The above-mentioned embodiment is only a preferred embodiment of the present invention, and is not used to limit the scope of the present invention; Covered by the scope of protection required by the claims of the present invention.

Claims (10)

1. a soft starter for motor device of taking into account reactive power compensation is characterized in that, comprises power inverter, diverter switch and master controller, and described diverter switch comprises grid side switch, motor side switch and the switch that is incorporated into the power networks; Described power inverter comprises three-phase phase-shifting transformer, several rectification modules and inversion module, AC reactor, and the former limit winding of three-phase phase-shifting transformer links to each other with electrical network by the grid side diverter switch, and the secondary winding is divided into N group winding; The input side of rectification module links to each other with the three-phase phase-shifting transformer secondary winding of peer, outlet side links to each other with the input side of inversion module, after connecting successively, the inversion module of homophase constitutes change of current chain, link to each other with AC reactor, link to each other with motor stator behind the AC reactor process motor side switch, motor stator links to each other with electrical network through the switch that is incorporated into the power networks; Described master controller links to each other with the grid side voltage transformer summation current transformer that is installed in the former limit of three-phase phase-shifting transformer, links to each other with voltage transformer with the motor side current transformer that is installed in the AC reactor output, links to each other with inversion module through optical fiber.

2. a kind of soft starter for motor device of taking into account reactive power compensation according to claim 1, it is characterized in that, the former limit winding of described three-phase phase-shifting transformer is the high-pressure side, the secondary winding is low-pressure side and is divided into many group secondary windings, every group of secondary winding output voltage amplitude equates that phase place differs a phase shifting angle successively.

3. a kind of soft starter for motor device of taking into account reactive power compensation according to claim 2 is characterized in that phase shifting angle is 60 °/N, and N is the group number of three-phase phase-shifting transformer secondary winding.

4. a kind of soft starter for motor device of taking into account reactive power compensation according to claim 1 is characterized in that, described rectification module comprises the rectified three-phase circuit that diode constitutes, and is used for alternating voltage is converted into direct voltage.

5. a kind of soft starter for motor device of taking into account reactive power compensation according to claim 1, it is characterized in that, described inversion module comprises the connection contactor, direct current supports electric capacity, H bridge inverter circuit and module controller, inversion module is connected with rectification module by connecting contactor, direct current supports electric capacity and is used for stable DC voltage, its two ends are the input side of inversion module, the H bridge inverter circuit is output as the outlet side of inversion module, module controller be connected contactor, direct current supports electric capacity and links to each other with the H bridge inverter circuit, link to each other by optical fiber with master controller, be used to receive the commands for controlling inversion module work of master controller, feed back the state information of inversion module simultaneously; Described H bridge inverter circuit is used for direct voltage is converted into alternating voltage.

6. a kind of soft starter for motor device of taking into account reactive power compensation according to claim 5 is characterized in that the H bridge inverter circuit is made of all-controlling power electronics device in the described inversion module.

7. a kind of soft starter for motor device of taking into account reactive power compensation according to claim 1, it is characterized in that, AC reactor in the described power inverter is used for the high order composition of absorption plant output voltage, the circulation that the restriction departure may cause when motor drops into electrical network, the output voltage of isolation line voltage and change of current chain during compensating reactive power.

8. a kind of soft starter for motor device of taking into account reactive power compensation according to claim 1, it is characterized in that, described diverter switch is according to the instruction action of master controller, and power inverter is connected with motor when starter motor, power inverter and motor parallel when compensating reactive power.

9. a soft starter for motor control method of taking into account reactive power compensation is characterized in that, specifically may further comprise the steps:

(1) the closed earlier grid side switch that connects former limit of three-phase phase-shifting transformer and electrical network, the closed again motor side switch that connects reactor and motor stator side, direct voltage is set up at direct current support this moment electric capacity two ends, and becomes series relationship between power inverter and the motor;

(2) master controller is according to the frequency and the amplitude of the proportional boosted output voltages of setting of acceleration curve, and motor quickens gradually from static beginning under the effect of output voltage;

(3) frequency of output voltage rise to power frequency, when amplitude rises to the motor load voltage value, master controller is gathered the mains voltage signal of voltage measuring transformer, line voltage is carried out phase-locked, obtains the phase place of line voltage;

(4) master controller is according to the phase-locked result of line voltage, with the line voltage is reference, regulates output voltage amplitude and phase place, controls to line voltage the motor input voltage in full accord, just frequency, amplitude and phase place all overlap with line voltage, and this moment is success synchronously;

(5) back stable operation a period of time of success synchronously, master controller sends the motor instruction of being incorporated into the power networks, the switch that is incorporated into the power networks of this motor of closure and electrical network junction, this motor drops into electrical network, disconnect the motor side switch of AC reactor and this motor junction, after this this motor is by the electrical network feed, and soft start is finished; Whether judge then has other motors to be started in the system, be then successively repeating step (1) all finish soft start to (5) until remaining starter motor, enter step (6) then, otherwise directly enter step (6);

(6) master controller sends instruction, disconnect the grid side switch, disconnect the connection contactor in each inversion module, power inverter is changed in quality and is the inversion module of homophase and AC reactor series connection, closed motor side switch, to install and drop into electrical network once more, this moment, power inverter became relation in parallel with motor;

(7) master controller is according to the voltage and current calculated signals reactive power to be compensated of voltage transformer summation current transformer measurement motor stator side, and the reactive power of power controlling converter output equivalent realizes reactive power compensation.

10. the soft starter for motor control method of taking into account reactive power compensation according to claim 9 is characterized in that, the acceleration curve of setting in the described step (2) is expressed as follows:

$u=k\&CenterDot;f+b=\frac{U_N-U_0}{f_N}\&CenterDot;f+U_0$

Wherein u is the device output voltage, and f is the frequency of output voltage, f _NBe motor rated frequency, U _NBe motor rated voltage, U ₀Being torque magnification voltage, is 0.01～0.05 times motor rated voltage, the U of selection ₀Different then the acceleration curve difference that obtains.

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