RU2539347C1 - Control method of independent asynchronous motor - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in control method of independent asynchronous generator with a valve inverter in a rotor circuit, rotor voltage frequency is proportional to a sum of rotor rotation frequencies and a generator stator field, signals for setting of instantaneous values of sine three-phase voltages of a rotor winding, which are offset relative to each other through an angle of 2π/3 are shaped, deviation between the specified and the measured signals of phase voltages is determined, deviation is compared to a threshold level, at the exceedance of which control signals are supplied to control inputs of the corresponding phase of the valve inverter, key elements of the valve inverter are switched, thus reducing deviations between the specified and the measured signals of phase voltages at the output of the valve inverter to the value that is lower than the threshold level.

EFFECT: reduction of frequency deviations and reduction of level of higher harmonics of generator output voltage.

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Description

The invention relates to electrical engineering and can be used for power supply of autonomous objects requiring a stable alternating current network with a variable speed of rotation of the generator shaft.

A known method of controlling a stand-alone asynchronous generator, in which the signal for the deviation of the output voltage of the generator acts on the inverter in the rotor circuit, and the switching frequency of the converter valves in the stator circuit is set constant [1].

In this method, an asynchronous machine starts to operate in a generator mode only when the rotation speed of the primary motor exceeds the synchronous speed of the used asynchronous machine. When the speed is lower than synchronous, the asynchronous machine can only operate in motor mode, consuming energy from a stand-alone inverter. Thus, the range of operating speeds of an autonomous generator constructed by this method has a lower limit.

Closest to the invention in technical essence and the achieved result is a method of controlling an autonomous asynchronous generator with a valve converter in the rotor circuit, which consists in applying a signal to deviate the generator output voltage to the valve converter and maintaining a constant output voltage frequency at a variable rotor speed, in accordance with which the switching frequency of the converter valves is set by the mismatch of the frequencies of the output voltage and the reference generator of forming a constant frequency, the frequency switching inverter gates exceeds system frequency by an amount proportional to the speed of the rotor [2].

The disadvantage of this method is the low quality of the output voltage of the generator with a rapid change in the rotation speed of the generator shaft due to the low speed and low accuracy of the frequency control loop. When the frequency of rotation of the generator shaft changes, the task for the rotor voltage frequency changes, however, due to the lack of a rotor speed sensor, the accuracy of the rotor voltage frequency setting is low, in addition, the measurement of the generator output frequency can be performed with a delay of a part of the output voltage period, which also reduces accuracy of maintaining the required frequency of the generator output voltage. A PWM voltage inverter feeds the rotor winding with rectangular voltage pulses, this leads to an increased level of higher harmonics in the output voltage of the generator.

The aim of the invention is to reduce frequency deviations and reduce the level of higher harmonics of the output voltage of the generator.

In the proposed method of controlling an autonomous asynchronous generator with a valve converter in the rotor circuit, which consists in applying a signal to deviate the generator output voltage to the valve converter and maintaining a constant output voltage frequency at a variable rotor speed, the voltage frequency at the converter output exceeds the generator output voltage frequency by a value proportional to the rotor speed, the signal of the deviation of the output voltage of the generator p they are fed to a proportional-integral controller, the output signal of which is limited when the maximum permissible level is reached and a signal for setting the amplitude of the sinusoidal voltage at the output of the valve converter is formed, the desired frequency of rotation of the magnetic field of the generator stator is set, the rotation frequency of the generator rotor is measured and the sum of these frequencies is calculated proportionally which form a signal for setting the frequency of the sinusoidal voltage at the output of the valve Converter, based on the generated signal amplitude and frequency reference signals, generate signals for setting instantaneous values of sinusoidal three-phase voltages at the output of the valve converter, shifted relative to each other by an angle of 2π / 3, apply these sinusoidal signals to the first inputs of three-phase relay-hysteresis voltage regulators, measure signals for instantaneous values of phase voltages at the output of the valve converter, these signals are fed to the second inputs of the relay-hysteresis voltage regulators, in each relay-hysteresis regulator is determined They deviate the deviation between the set and measured phase voltage signals, compare the deviation with a threshold level, above which control signals are input to the control inputs of the corresponding phases of the valve converter, switch the key elements of the valve converter and reduce the deviation between the set and measured phase voltage signals at the output of the valve converter to a value less than the threshold level.

In the proposed method for controlling an autonomous asynchronous generator, the voltage quality at the generator output is improved, namely, frequency deviations are reduced and the harmonic composition is improved.

Figure 1 shows the functional diagram of the control of an autonomous asynchronous generator; figure 2 shows a diagram of a relay-hysteresis voltage regulator; figure 3 shows the instantaneous values of the phase voltage of the rotor.

A device that implements the proposed method contains a standalone asynchronous generator with a phase rotor 1, connected to a source of mechanical energy of rotation 2, having a variable speed of rotation. An adjustable converter 3 is included in the phase rotor circuit of the autonomous asynchronous generator 1, comprising an autonomous current inverter 4 sequentially connected via a DC circuit, an adjustable rectifier 5, a smoothing reactor 6. The adjustable rectifier 5 operates in the current source mode. Capacitors are connected to the power input of the inverter 4 in parallel with the rotor winding 7. The power input of the adjustable rectifier 5 is connected to the output circuit of an autonomous asynchronous generator. For the initial start-up of an autonomous asynchronous generator, a rechargeable battery 8 is connected parallel to the rectifier. The voltage at the output of the autonomous current inverter 4 is controlled using relay-hysteresis phase voltage regulators 9 having internal nodes for comparing input signals. The first inputs of the relay-hysteresis phase voltage regulators 9 are connected to the phase outputs of the shaper 10, generating signals for setting instantaneous voltage values at the inverter output, the second inputs of the relay-hysteresis phase voltage regulators 9 are connected to the phase outputs of the inverter 4. The amplitude input of the shaper 10 is connected to the output of the unit restrictions 11, the input of which is connected to the output of the proportional-integral voltage regulator 12, and its input is connected to the output of the comparison node 13. Positive input of the node comparison 13 is connected to the output of the output voltage setting unit of the generator 14, the negative input of the comparison unit 13 is connected to the output of the sensor 15 of the output voltage of the generator 1. The frequency input of the driver 10 is connected to the output of the adder 16, the first input of which is connected to the output of the output frequency setting unit 17, the second the input of the adder 16 is connected to the output of the proportional block 18, the input of which is connected to the output of the rotor speed sensor 19 mounted on the same shaft with the generator 1 and the source of mechanical energy 2.

Management autonomous asynchronous generator is as follows. Upon initial start-up, a stand-alone current inverter converts the direct voltage from the battery into a three-phase voltage supplied to the rotor of the stand-alone asynchronous generator. Under the influence of this voltage, a rotating electromagnetic field is formed in the air gap of the autonomous asynchronous generator. As a result of this, the EMF is induced in the stator winding. When the output voltage of the autonomous asynchronous generator 1 appears, the voltage at the output of the adjustable rectifier 5, which now provides power to the autonomous inverter 4 and recharges the battery 8. The adjustable rectifier 5 provides a given value of the input current of the inverter 4. To maintain a sufficient value of the input current of the inverter in the adjustable rectifier 5, an internal closed loop current regulation may be performed. The ripple of the current in the rectified circuit is smoothed by the reactor 6.

The phase sequence in the rotor is selected so that the electromagnetic field in the air gap rotates in the direction opposite to the direction of rotation of the rotor, then the frequency of the output voltage ω ₁ will be determined by the formula:

$${\omega }_{\mathrm{one}}={\omega }_2-{\omega }_p\cdot p_n,\text{(one)}$$

where ω ₂ is the frequency of the voltage at the output of the inverter; ω _p - measured rotor speed of the generator; p _n is the number of pairs of generator poles.

The frequency of the voltage at the output of the inverter 3 is formed in accordance with the formula

$${\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">\omega </figure-callout>}}_2={\omega }_{\mathrm{one}}^{*}+{\omega }_p\cdot p_n,\text{(2)}$$

- задаваемая частота напряжения статора.Where $${\omega }_{\mathrm{one}}^{*}$$

- set frequency of the stator voltage.

The signal from the output of the adder 16 is fed to the frequency input of the shaper 10 job sinusoidal phase voltages. Any change in the frequency of rotation of the generator shaft is accompanied by a change in the frequency of the voltage at the inverter output in accordance with formula (2), as a result, the voltage frequency at the generator output ω _{1 is} maintained at a given level.

Unit 14 generates a task for the output voltage of the generator 1, which is compared in the comparison unit 13 with the measured sensor 15 to the value of the output voltage of the generator 1. The deviation signal is converted by the PI controller into a reference signal for the amplitude of the output voltage of the inverter and fed to the amplitude input of the shaper 10, which generates the reference signal to the sinusoidal phase voltage at the output of the inverter 3, shifted relative to each other by an angle of 2π / 3. These signals for setting the instantaneous values of phase voltages u _2a *, u _2b *, u _2c * are fed to the first inputs of the relay-hysteresis voltage regulators 9 in the form of a sinusoidal signal of the required amplitude U * and frequency ω *, the instantaneous values of phase voltages u _2a , u _2b , u _2c , measured at the output of the inverter 3. In the phase controllers 9 (figure 2) at the outputs of the comparison elements we obtain the difference between the set and the actual voltage values in the phases:

$$\{\begin{array}{c}\Delta u_{2A}=u^{*}{}_{2A}-{\mathrm{<figure-callout\; id="2A"\; label="u"\; filenames="00000007.png"\; state="\{\{state\}\}">u</figure-callout>}}_{2A}\\ \Delta u_{2B}=u^{*}{}_{2B}-{\mathrm{<figure-callout\; id="2B"\; label="u"\; filenames="00000007.png"\; state="\{\{state\}\}">u</figure-callout>}}_{2B},\\ \Delta u_{2C}=u^{*}{}_{2C}-{\mathrm{<figure-callout\; id="2C"\; label="u"\; filenames="00000007.png"\; state="\{\{state\}\}">u</figure-callout>}}_{2C}\end{array}\text{(3)}$$

then the received signals are fed to the inputs of the hysteresis blocks, operating according to the following algorithm:

$$\{\begin{array}{l}e\mathrm{from}l\mathrm{and}\mathrm{<figure-callout\; id="2"\; label="\Delta \; u"\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}{\text{u}}_{}{}_{\text{2}}\le -\Delta \text{,}\text{at the exit}\text{active}\text{state}\text{(0);}\\ \text{if}\mathrm{<figure-callout\; id="2"\; label="\Delta \; u"\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}{\text{u}}_{}{}_{\text{2}}\ge \Delta \text{,}\text{at the exit}\text{active}\text{state}\text{(one),}\end{array}\text{(four)}$$

where Δ is the hysteresis modulus specified from the condition of accuracy of voltage maintenance.

The generated phase voltages at the output of the inverter 3 have two boundary values - upper and lower, differing from the given voltage sine wave by the value Δ (Fig. 3), within which at any time there should be a voltage at the output of the inverter 4. If the deviation is between the given and the measured signals exceed the threshold level, the relay-hysteresis regulator generates a signal g * entering the inverter, and the corresponding keys of the inverter are switched, resulting in a decrease in mismatched The voltage and voltage at the inverter output are included in the permissible deviation zone. If the upper limit of the voltage is violated, the switch is switched in the corresponding arm of the autonomous inverter 4 and a negative current pulse is generated, which discharges the corresponding phase capacitor 7, lowering the voltage on it. In case of violation of the lower voltage boundary, the switch in the other arm of the autonomous inverter 4 is switched and a positive current pulse is generated, which charges the corresponding phase capacitor 7, increasing the voltage on it.

When changing the rotation speed ω _{r of the} shaft of the source of mechanical energy of rotation 2, in the case of changing the amplitude and frequency of the voltage at the output of the autonomous asynchronous generator, a mismatch appears at the input of the voltage regulator, the reference signal for the amplitude of the voltage at the output of the inverter changes, and the signal for setting the voltage frequency changes the output of the autonomous inverter 4, determined by the expression (2). These changes in the reference signals act on the autonomous voltage inverter 4, and deviations of the output voltage of the generator are eliminated by changing the frequency and voltage at the output of the autonomous inverter 4.

In a device that implements the proposed method for controlling an autonomous asynchronous generator, in order to achieve an improved, closest to the sinusoid, voltage and current shape in the rotor winding, which ensures high quality voltage at the output of an autonomous asynchronous generator with a minimum level of harmonics, autonomous current inverter 3 is made with the internal circuit for regulating the instantaneous values of phase voltages, and is controlled by phase relay-hysteresis voltage regulators 9, which carry out switching the inverter keys at the moment of reaching the threshold level by the deviation between the set and measured instantaneous values of the rotor voltage.

Bibliography

1. USSR Copyright Certificate No. 543121. MKP Н02Р 9/14 03/26/73.

2. RF patent No. 2213409. A way to control a stand-alone asynchronous generator. MKP Н02Р 9/00, 9/48, 09/27/2003. Bull. Number 27.

Claims (1)

The method of controlling an autonomous asynchronous generator with a valve converter in the rotor circuit, which consists in applying a signal to deviate the generator output voltage to the valve converter and maintaining a constant output voltage frequency at a variable rotor speed, the voltage frequency at the converter output exceeding the generator output frequency by an amount proportional to the rotor speed, characterized in that, as a function of the signal, the deviations of the output voltage Generator generator generates a signal for setting the amplitude of the sinusoidal voltage at the output of the valve converter, sets the desired frequency of rotation of the magnetic field of the generator stator, measures the frequency of rotation of the generator rotor and calculates the sum of these frequencies, which is proportional to which the signal for setting the frequency of the sinusoidal voltage at the output of the valve converter is generated based on the generated signals amplitude and frequency settings, generate signals for setting instantaneous values of sinusoidal three-phase voltages at the output of the valve converter, shifted relative to each other by an angle of 2π / 3, these sinusoidal signals are fed to the first inputs of the three-phase relay-hysteresis voltage regulators, the signals of the instantaneous values of phase voltages are measured at the output of the valve converter, these signals are fed to the second inputs of the relay-hysteresis voltage regulators , in each relay-hysteresis controller, the deviation between the set and measured phase voltage signals is determined, the deviation is compared with a threshold level, at exceeding which the control signals are applied to the control inputs of the corresponding phases of the valve converter, commutate the key elements of the valve converter and reduce the deviation between the set and measured phase voltage signals at the output of the valve converter to a value lower than the threshold level.

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