KR101996260B1 - Power converting apparatus and air controller having the same - Google Patents

Abstract

A power converter is disclosed. Embodiments of the present invention can be applied to both a normal inverter using a large capacity electrolytic capacitor or a capacitorless inverter using a low capacity capacitor. Embodiments of the present invention perform a power-based control to smoothly control the power output from the DC link capacitor to the inverter to make the inverter operate stably. In addition, embodiments of the present invention can improve the power factor, control the driving range and harmonics by controlling the inverter output power. In addition, embodiments of the present invention may reduce the harmonics of grid current by driving a motor as a resistor, and may modify the inverter output power by performing power-based control.

Description

Power converter and air conditioner with same {POWER CONVERTING APPARATUS AND AIR CONTROLLER HAVING THE SAME}

The present invention relates to a power converter, and more particularly, to a power converter that improves the power factor and reduces harmonics.

In general, a power converter includes a converter and an inverter connected in parallel between an input AC power supply and a load, for example, a motor. At this time, a DC link capacitor is interposed between the converter and the inverter.

In general, a power converter uses a converter (diode rectifier circuit) to obtain a DC power source from an AC power source, and then uses an inverter to drive a motor. This type of converter does not allow energy regeneration, which requires a braking resistor. In addition, a large capacity electrolytic capacitor should be used as the DC link capacitor to absorb the instantaneous energy regenerated in the inverter. Inverters using electrolytic capacitors are called normal inverters. Electrolytic capacitors can increase the harmonics of the input supply current as well as their lifetime.

A power converter having a circuit for preventing overvoltage due to regenerative voltage is shown in Japanese Laid-Open Patent Publication No. 2005-253282. Such a power converter needs to improve power factor and harmonics, and thus require a separate circuit.

In addition, a DC or AC reactor is further provided to suppress harmonics of the input power current, and as the capacity of the reactor increases, the cost, product volume, and weight increase.

Accordingly, researches on power conversion devices that perform power conversion using inverters using low capacitance capacitors, or capacitorless inverters, which do not use large electrolytic capacitors as DC link capacitors have been actively conducted in recent years. Such an inverter has an advantage in price and volume in comparison with a conventional inverter.

An embodiment of the present invention is to provide a power conversion device to improve the power factor, and to improve the operating range and harmonics by controlling the inverter output power through power-based control.

In one embodiment, a power converter includes a converter for converting an input AC voltage into a DC voltage, a DC link capacitor connected in parallel to the converter, and a DC link voltage of the DC link capacitor according to a control signal as a motor driving voltage. A power conversion device comprising an inverter for converting and supplying to a motor, and a control unit for generating the control signal, the control unit comprising: a speed controller for generating a reference current for controlling the speed of the motor; A power converter configured to generate a reference power using the reference current; And an indirect current controller configured to generate a reference voltage for controlling the current of the motor. Here, the reference power is generated in proportion to the DC link voltage.

The speed controller receives a reference speed and a speed of the motor, and generates a d-axis reference current and a q-axis reference current to control the speed of the motor.

The power converter generates a peak of the reference power using the q-axis reference current, the d-axis reference current, and the rotation frequency of the motor, and uses the peak of the reference power and the DC link voltage to generate the peak power. Create and print

The power converter pulsates the d-axis reference current using the DC link voltage.

The indirect current controller includes a d-axis current controller configured to generate the d-axis reference voltage based on the d-axis reference current and the d-axis current of the motor. The indirect current controller may further include a power controller configured to calculate the q-axis reference voltage using the reference power and the d-axis reference voltage. The indirect current control unit may further include a compensator connected to the d-axis current controller and configured to limit the d-axis current by using the q-axis reference voltage and the d-axis reference voltage.

In accordance with another aspect of the present invention, a power converter includes a converter for converting an input AC voltage into a DC voltage, a DC link capacitor connected in parallel with the converter, and a DC link voltage of the DC link capacitor as a motor driving voltage according to a control signal. A power conversion device comprising an inverter for converting and supplying to a motor, and a control unit generating the control signal, wherein the control unit receives a reference speed and a speed of the motor, and receives a d-axis reference current and a q-axis reference. A speed control unit generating a current to control the speed of the motor; A power converter configured to receive the q-axis reference current and the DC link voltage and output a reference power; And an indirect current controller configured to generate a d-axis reference voltage and a q-axis reference voltage for controlling the current of the motor. Here, the power converter performs power control so that the output power output to the motor becomes the reference power input in the form of an open circuit to the motor through the inverter.

Embodiments of the present invention provide a power conversion apparatus having a control algorithm that can be applied to both a normal inverter using a large capacity electrolytic capacitor or a capacitorless inverter using a low capacitance capacitor.

Embodiments of the present invention perform a power-based control to smoothly control the power output from the DC link capacitor to the inverter to make the inverter operate stably. In addition, embodiments of the present invention can improve the power factor, control the driving range and harmonics by controlling the inverter output power. In addition, embodiments of the present invention may reduce the harmonics of grid current by driving a motor as a resistor, and may modify the inverter output power by performing power-based control.

Embodiments of the present invention can take the form of power as desired by directly outputting the inverter output power in an open loop, reduce the voltage and current of the DC link capacitor, there is no delay in power control. In addition, embodiments of the present invention can be easily tuned by controlling only the d-axis current of the motor, thereby improving the ease of control.

1 is a circuit diagram showing a power conversion apparatus according to embodiments of the present invention;
FIG. 2 is a signal graph of driving a motor by the power converter of FIG. 1; FIG.
3 is a block diagram showing a detailed configuration of the control unit of FIG.
4 is a signal graph according to Power Based Control by the control unit of FIG. 3;
5 shows a detailed configuration of a speed control unit constituting a control unit;
6 is a diagram showing a detailed configuration of a power conversion unit constituting a control unit;
7 shows a detailed configuration of an indirect current control unit constituting a control unit;
8 is a diagram for explaining a power conversion operation by a control unit;
9 is a view for explaining a current control operation by an indirect current control section;
10 shows the difference between the inverter output power and the load power in practice;
11 is a diagram for explaining the field weakening control operation by the control unit; And
12 is a view showing an air conditioner having a power converter according to embodiments of the present invention.

Referring to FIG. 12, an air conditioner is disclosed as an example of an electronic device including a power converter according to embodiments of the present disclosure.

An air conditioner equipped with a power conversion device according to embodiments of the present invention, at least one indoor unit (2) for performing the air conditioning, a compressor for compressing the refrigerant to a high temperature, high pressure, a motor for operating the compressor, and the motor A control device for controlling the driving of the device is provided. In addition, the air conditioner includes an outdoor unit 1 connected to at least one indoor unit and a pipe to drive the indoor unit. The control device comprises a power conversion device according to the invention.

The outdoor unit 1 includes an evaporator 13 for exchanging heat by exchanging a refrigerant compressed by a compressor with air, an expansion valve 14 for expanding the refrigerant radiated from the evaporator at low temperature and low pressure, and a refrigerant having low temperature and low pressure. It further comprises a condenser 15 for exchanging heat with water, and a refrigerant switching valve 17 provided at the outlet of the compressor 12 to guide the refrigerant compressed by the compressor to the evaporator 13 or the condenser 15. do.

Referring to FIG. 12, in the outdoor unit 1, a refrigeration cycle including a compressor 12, an evaporator 13, an expansion valve 14, and a condenser 15 is installed in the case 11, and the case 11 is provided. A plurality of intake fans 16 are installed on the upper surface or the side of the air inlet to exchange heat with the evaporator 13, and the condenser 15 is configured to supply cold or hot water to the indoor units 2. The medium circulation pipe 3 is connected. At the outlet of the compressor 12, a refrigerant switching valve 17 for converting the refrigerant compressed by the compressor 12 into the evaporator direction or the condenser direction according to the operating conditions is provided.

The refrigerant switching valve 17 usually consists of a four-way valve. The outdoor unit 1 as described above is operated by switching to a heater in winter while operating as a cooler in summer. For example, in the summer, the refrigerant is compressed at high temperature and high pressure in the compressor 12, the refrigerant switching valve is guided to the evaporator 13, the heat exchanged with the air in the evaporator 13, heat dissipation, and the low temperature, After making it low pressure, it heat-exchanges with water in the condenser 15, and supplies the heat-exchanged water to the indoor units 2 which use it as a cooling heat source. Meanwhile, in winter, the refrigerant switching valve 17 guides the refrigerant toward the condenser so that a high temperature and high pressure refrigerant exchanges heat with water in the condenser 15 to supply the indoor units 2 using the heat exchanged water as a heating heat source. do.

Referring to FIG. 1, a power conversion apparatus according to embodiments of the present invention may include a converter 20 for converting an input AC voltage V _s of an input AC power supply 10 into a DC voltage, and the converter 20. A DC link capacitor 30 connected in parallel, an inverter 40 converting the DC link voltage V _dc of the DC link capacitor 30 into a motor driving voltage according to a control signal, and supplying the motor link voltage to the motor 50; It is configured to include a control unit 100 for generating the control signal.

In addition, the power converter may further include a reactor (L) 60 for removing harmonic components and compensating for power efficiency of the input AC power supply 10.

The converter 20 is connected to the input AC power source 10 and rectifies the AC from the input AC power source 10 to DC. The converter 20 generally includes a plurality of diodes (four diodes D1 to D4 constitute a bridge circuit in FIG. 1), and the diodes perform full-wave rectification of the AC voltage of the AC power source by the diodes, and convert the DC voltage into DC voltages. do.

The DC link capacitor 30 is connected in parallel to the output terminal of the converter 20, and applies a DC voltage generated at both ends of the capacitor, that is, a DC link voltage V _dc to the input terminal of the inverter 40. The DC link capacitor 30 smoothes the ripple voltage (voltage fluctuation) generated corresponding to the switching frequency while the switching elements S1 to S6 in the inverter 40 switch.

The case of having a small DC link capacitor capable of smoothing only the ripple voltage is called a capacitorless inverter or capacitorless control. Therefore, the DC link voltage Vdc pulsates. As a small capacitor, a so-called film capacitor can be used. It has a capacity on the order of 1/100 of the electrolytic capacitor capacity described later. In the present invention, a description will be given of a capacitorless inverter. However, the power converter may employ a normal inverter described later.

That is, a so-called normal inverter or normal control using an electrolytic capacitor has a large capacity DC link capacitor capable of smoothing the voltage rectified by the converter 20, that is, the voltage varying with the power supply voltage. Use

The inverter 40 has one end connected in parallel to the DC link capacitor 30 and the other end connected to the motor M 50 to switch the output of the DC link capacitor 30 to switch the motor drive voltage, generally. It converts into three-phase alternating current and supplies it to the motor 50.

As shown in FIG. 1, in general, the inverter 40 includes a plurality of switching elements constituting a bridge circuit. The switching element may be, for example, an Insulated Gate Bipolar Transistor (IGBT), a MOSFET, or the like.

When outputting three-phase alternating current to the motor 50, the inverter 40 has six switching elements S1 to S6. The midpoints of the switching elements S1, S3, S5 of the upper arm and the switching elements S2, S4, S6 of the lower arm are connected to the coils of each phase of the motor 50. Reflux diodes, so-called freewheeling diodes, may be connected in reverse parallel to each switching element.

The inverter 40 receives the switching signal and the control signal of the control unit 100 and converts the DC link voltage Vdc into the motor driving voltages Vu, Vv, and Vw. In this case, a pulse width modulation (PWM) scheme is generally used as a modulation scheme.

FIG. 2 is a graph in which a simulation is performed, in which the inductance of the reactor L is 60 mH, the capacitance of the DC link capacitor is 20 uF, and the motor is a resistive load.

Basically, by driving the motor like a resistor, harmonics of the input current i _s can be reduced. However, due to the phenomenon that the charging current to the DC link capacitor 30 and the zero current of the input voltage V _s are maintained near the zero crossing point, the inverter output power, that is, the reference power, must be changed to improve the harmonics.

Hereinafter, a power conversion operation of the power conversion apparatus according to the embodiments of the present invention will be described.

Referring to FIG. 3, the control unit 100 includes a speed controller 110, a power converter 120, and an indirect current controller 130.

The speed controller 110 generates reference currents i ^e _{d , ref} , i ^e _{q, ref} for controlling the speed of the motor 50. Referring to FIG. 5, the speed controller 110 receives a reference speed ω ^* _e and a speed ω _e of the motor 50, and receives a d-axis reference current i ^e _{d and ref} and a q-axis reference. The current i ^e _{q , ref} is generated to control the speed of the motor 50.

The speed controller 110 may include a proportional controller 111 that reduces an error in speed, a low pass filter (LPF) 115, and a maximum torque operating point (MTPA) 113 per unit current. As shown in FIG. 9, the control unit 100, that is, the speed controller 110, uses the reference power P _ref and the d-axis reference current i ^e _{d , ref} to obtain the maximum torque driving point per unit current. (MTPA) is calculated.

The power converter 120 generates the reference power P _ref using the reference currents i ^e _{d , ref} , i ^e _{q , ref} generated by the speed controller 110. At this time, the reference power is generated in proportion to the DC link voltage. Here, the reference power means so-called inverter output power _Piv output from the DC link capacitor to the inverter.

Strictly speaking, as shown in FIG. 10, the inverter output power _Piv and the load power P _L applied to the motor 50 are not exactly the same. Briefly, the load power P _L is a low pass filtered value of the inverter output power P _inv .

If the inverter output power (P _inv ) is expressed by the equation, it is expressed by the following equation (1).

In addition, the load power PL may be expressed as in Equation 2 below.

Where L _d , L _q , ω _e , and φ _m are the d-phase inductance, q-phase inductance, rotor speed, and rotor flux of the motor, respectively.

Assuming the efficiency is 100% in a steady state where the inverter output power P _inv and the load power P _L are DC values, the inverter output power P _inv and the load power P _L are equal. Accordingly, the present invention does not control the d-axis current i _d and the q-axis current i _q , but calculates and controls the inverter output power _Pinv as a reference power.

Referring to FIG. 6, the power converter 120 may determine the q-axis reference current i ^e _{q , ref} , the d-axis reference current i ^e _{d , ref} , and the rotation frequency ω _e of the motor 50. The peak of the reference power (P _{ref , peak} ) is generated.

The power converter 120 generates and outputs the reference power P _ref using the _peaks P _{ref and peak} of the reference power and the DC link voltage V _dc / E. Here, E is a peak value of the DC link voltage and may be a scaling factor.

Using the d-axis current and the q-axis current peak (P _{ref , peak} ) of the reference power can be generated as shown in Equation 3 below.

At this time, it is also possible to compensate for the results of the torque control (torque control) in the peak (P _{ref, peak)} of the reference power.

The power converter 120 generates a reference power proportional to the DC link voltage V _{dc in} order to improve the power factor (PF). The power converter 120 pulses the d-axis reference current i ^e _{d . Ref} using the DC link voltage V _dc . Without considering the flux weakening control, the d-axis reference current (i ^e _{d , ref} ) is also pulsated since the magnitude of power and current is proportional.

7, the indirect current control unit 130 generates a reference voltage (V ^e _{d, ref,} V ^e _{q, ref)} for controlling the current of the motor 50.

The indirect current controller 130 generates d-axis reference voltage (V ^e _{d , ref} ) based on the d-axis reference current (i ^e _{d , ref} ) and the d-axis current (i _d ) of the motor 50. An axial current controller 131. The d-axis current controller 131 may include a proportional integration controller PI. Since the d-axis current controller 131 is a classic controller, detailed description thereof will be omitted.

In addition, indirect current control unit 130, a reference power (P _ref) and the d-axis reference voltage (V ^e _{d, ref),} the power controller 133 for calculating a q-axis reference voltage (V ^e _{q, ref)} using It further includes.

The power converter is such that the output power P _L output to the motor 50 is the reference power P _ref input to the motor 50 through an inverter 40 in the form of an open loop. Perform power control. The indirect current controller 130, that is, the power controller 133, obtains the q-axis reference voltage V ^e _{q , ref} for giving the inverter output power, that is, the reference power P _ref , in the form of an open circuit.

Referring to FIG. 8, the indirect current controller 130 is connected to the d-axis current controller 131 and uses a q-axis reference voltage (V ^e _{q , ref} ) and a d-axis reference voltage (V ^e _{d , ref} ). It may further include a compensator 135 for limiting the d-axis current (i _d ).

The compensator 135 performs an anti-windup function. The compensator 135 controls the d-axis current so that the reactive power does not diverge while the reactive power increases during the voltage limit. Do this.

In the case of a normal inverter using a large-capacity electrolytic capacitor, the field weakening control is implemented in a loop with feedback, but in the case of a capacitorless inverter, an open loop is implemented for fast operation. When performing field weakening control, as shown in FIG. 11, the controllable section can be widened by adding the d-axis current to an appropriate magnitude in the − direction.

As illustrated in FIG. 9, the power converter may control the d-axis current and the q-axis current to a desired point P _equilibrium without using a q-axis controller. That is, if the inverter output power _Pinv and the d-axis current are determined, the q-axis current can be calculated and the operating point can be determined.

A power conversion operation of the power converter will be described with reference to FIGS. 3 and 4. 4 is a graph showing reference power, current, and reference voltage on the assumption that the load is doubled.

As described above, the speed controller 110 calculates and outputs reference power from the feedback speed, and the power converter 120 and the indirect current controller 130 generate and output the reference voltage. At this time, the detected motor output currents V _u , V _v , V _w are fed back.

Referring to FIG. 3, since the power is controlled in the form of an open circuit, the reference power P _ref , that is, the inverter output power _Pinv and the load power P _L , are nearly identical, as shown in FIG. 4. Therefore, it is advantageous when power control is to be performed while arbitrarily changing the reference power. As a result, the ripple of the DC link voltage and current of the DC link capacitor is reduced. In addition, although the current may be somewhat delayed by the power control, there is no delay with respect to the power.

On the other hand, although not shown, in the case of performing current control instead of power control, a transient state may occur with respect to the load variation, and even if the current follows quickly, ripple of the load input power may occur. Unlike the power conversion device according to the present invention, the current control is performed, especially in the case of a capacitorless inverter using a small capacity capacitor, which operates in a transient state according to the change of the DC link voltage and removes the ripple generated in the inverter input power. There is a difficulty.

The power converter according to the present invention can be applied to both a normal inverter using a large capacity electrolytic capacitor and a capacitorless inverter using a low capacity capacitor. Embodiments of the present invention perform a power-based control to smoothly control the power output from the DC link capacitor to the inverter to make the inverter operate stably. In addition, embodiments of the present invention can improve the power factor, control the driving range and harmonics by controlling the inverter output power. In addition, embodiments of the present invention may reduce the harmonics of grid current by driving a motor as a resistor, and may modify the inverter output power by performing power-based control.

10 input AC power 20 converter
30: DC link capacitor 40: inverter
50: motor, load 100: control unit
110: speed control unit 120: power conversion unit
130: indirect current control

Claims (15)

A converter for converting an input AC voltage into a DC voltage,
A direct current link capacitor connected to the converter in parallel;
An inverter converting the DC link voltage of the DC link capacitor into a motor driving voltage and supplying the motor to the motor according to a control signal;
A power conversion device comprising a control unit for generating the control signal,
The control unit,
A speed controller configured to generate a reference current for controlling the speed of the motor;
A power converter configured to generate a reference power using the reference current; And
And an indirect current controller configured to generate a reference voltage for controlling the current of the motor.
The reference power is generated in proportion to the DC link voltage,
The speed control unit,
The speed of the motor is controlled by receiving a reference speed and a speed of the motor and generating a d-axis reference current and a q-axis reference current.
The power converter,
Generating a peak of the reference power by using the q-axis reference current, the d-axis reference current, and a rotation frequency of the motor, and generating and outputting the reference power by using the peak of the reference power and the DC link voltage. A power converter, characterized in that. delete delete According to claim 1,
The power converter,
And pulsating the d-axis reference current using the DC link voltage. According to claim 1,
The indirect current controller,
And a d-axis current controller configured to generate the d-axis reference voltage based on the d-axis reference current and the d-axis current of the motor. The method of claim 5,
The indirect current controller,
And a power controller that calculates the q-axis reference voltage using the reference power and the d-axis reference voltage. The method of claim 6,
The indirect current controller,
And a compensator coupled to the d-axis current controller and configured to limit the d-axis current by using the q-axis reference voltage and the d-axis reference voltage. The method according to any one of claims 1 to 4, wherein
The control unit,
And a maximum torque driving point per unit current using the reference power and the d-axis reference current. A converter for converting an input AC voltage into a DC voltage,
A direct current link capacitor connected to the converter in parallel;
An inverter converting the DC link voltage of the DC link capacitor into a motor driving voltage and supplying the motor to the motor according to a control signal;
A power conversion device comprising a control unit for generating the control signal,
The control unit,
A speed controller configured to receive a reference speed and a speed of the motor and control a speed of the motor by generating a d-axis reference current and a q-axis reference current;
A power converter configured to receive the q-axis reference current and the DC link voltage and output a reference power; And
And an indirect current controller configured to generate a d-axis reference voltage and a q-axis reference voltage for controlling the current of the motor.
Power control is performed such that the output power output to the motor becomes the reference power input to the motor in the form of an open circuit through the inverter,
The power converter,
Generating a peak of the reference power by using the q-axis reference current, the d-axis reference current, and a rotation frequency of the motor, and generating and outputting the reference power by using the peak of the reference power and the DC link voltage. A power converter, characterized in that. The method of claim 9,
The indirect current controller,
And a d-axis current controller configured to generate the d-axis reference voltage based on the d-axis reference current and the d-axis current of the motor. The method of claim 10,
The indirect current controller,
And a power controller that calculates the q-axis reference voltage using the reference power and the d-axis reference voltage. delete The method of claim 11, wherein
The control unit,
And a maximum torque driving point per unit current using the reference power and the d-axis reference current. delete The air conditioner provided with the electric power conversion apparatus in any one of Claims 1, 4-7, 9-11, and 13.

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