JP6868927B1 - 3-pulse PWM control method for three-phase inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a 3-pulse PWM control method for a three-phase inverter. SOLUTION: A square wave signal having a fundamental frequency of an output wave of a three-phase inverter and a triangular wave having twice the frequency synchronized with the fundamental wave are used as a carrier, and a signal compared with a reference input signal for controlling the magnitude of the fundamental wave component. By generating an exclusive logical sum signal with the two signals as inputs as a PWM switching signal for one phase, and generating a PWM switching signal having a phase difference of 120 degrees for each of the remaining two phases in the same configuration. It enables 3-pulse PWM control for each phase. [Selection diagram] Fig. 2

Description

The present invention relates to a PWM control method in a three-phase inverter when a switch element with restrictions on high-speed switching is used, or when the fundamental wave frequency is high, and the number of times switching is possible with respect to the fundamental wave output is restricted. It is a technology.

When a low-speed switching element such as GTO is used as the switching element of a three-phase inverter, the switching frequency increases as the fundamental wave output of the inverter increases, so the number of PWM switching pulses is switched as the fundamental wave frequency increases. The method has been used for inverter control of electric railways.

In this case, the three-phase output waveform that can be output is 3-pulse PWM, and it occurs in a special case of 3-pulse because it must be controlled while maintaining the positive / negative waveform and the symmetry between the three phases with a limited number of switchings. PWM control methods that overcome the problems have been studied.

Recently, with the spread of electric vehicles, a three-phase inverter has been used as a drive power source for electric motors. At low speeds, multi-pulse PWM control is used from the viewpoint of reducing torque pulsation and response characteristics, but in the high-speed rotation region, the output of the inverter Since the influence of torque pulsation due to the low-order tuning component of the waveform is reduced, a one-pulse square wave output is used in order to reduce the switching loss as much as possible.

However, since the output voltage of the 1-pulse square wave cannot be controlled, the control system is complicated because the speed control up to the high-speed region is realized by the additional control of the phase.

On the other hand, due to the remarkable development of switching elements in recent years, PWM switching control can be performed with a loss that is unmatched in the past, and there is a balance with the current waveform distortion due to the low-order harmonic component of the 1-pulse square wave. Considering this, it is considered that utilizing 3-pulse PWM control for fundamental wave output control even in the high-speed rotation region and continuously controlling 1-pulse square wave at the maximum output will lead to further improvement in characteristics.

Further, in the field of large capacitance, the control of the fundamental wave component causes a problem in the control characteristics in the 1-pulse square wave unless it is in the high-speed rotation region. The development of control methods is desired.

Furthermore, in the application field where the fundamental wave frequency of the three-phase inverter is relatively high and the low-order harmonic component can be relatively easily reduced by the filter even if the output waveform contains some harmonic components, the magnitude is large. It is desired to develop a PWM control method that reduces the number of switchings that can only be controlled.

Based on the above, the 3-pulse PWM control method for three-phase inverters has been an issue for a long time, but with the development of switching elements and the expansion of application fields of power electronics, the fundamental wave output while suppressing the generation of low-order tuning components. It is expected that a better PWM control method that can control the size of the device will be developed.

Yano, Uchida, "Power Electronics", Maruzen Co., Ltd., pp.144-pp.146, 2000. Japanese Patent Application Laid-Open No. 4-67780 Japanese Patent Application Laid-Open No. 58-182480 Japanese Patent Application Laid-Open No. 5-284751

In (Non-Patent Document 1), among the PWM inverter control technologies, if the switching frequency cannot be set so high with respect to the output fundamental wave, synchronous PWM control is used in which the carrier frequency is selected to be an integral multiple of the fundamental wave frequency. Has been done.

In (Patent Document 1), while the output frequency is controlled from low frequency to high frequency, the stepwise change of the output voltage when the number of pulses of the PWM control waveform is gradually increased from 3 to an integral multiple is described. A control method to eliminate it has been proposed.

In (Patent Document 2) and (Patent Document 3), when generating a three-pulse waveform, a general method of pulse-distributing a signal obtained by comparing a conveyed triangular wave and a reference input to obtain a PWM switching signal is used. A control method has been proposed in which the symmetry of the PWM waveform is suppressed due to a control problem or a variation in the switching characteristics of the element when the phase inverter is operated.

Since all of these patent documents are based on batch control by a conventional 3-pulse PWM control method, there is a problem with each phase control.

If the output pulse width is controlled at an arbitrary timing of the output waveform of the three-phase inverter, the symmetry of the output waveform between the three phases cannot be maintained. Has a basic problem that it can be controlled only at a limited timing.

As a 3-pulse PWM control method for a three-phase inverter, a triangular wave with a frequency of 6 times that is synchronized with the fundamental wave of the output wave is generally used as a carrier common to each phase, and is used as a reference input signal for controlling the magnitude of the fundamental wave component. The compared outputs of the above are applied to a pulse distributor to generate a 3-pulse PWM control signal for all three phases.

For this reason, if there are variations in the three-phase PWM switching control operation when operating the three-phase inverter, the symmetry method of the output waveform will be broken, waveform distortion and DC components will be generated, and if a transformer is connected, etc. Then, since it causes a problem of DC demagnetization and the like, it is necessary to add some measures as seen in (Patent Document 3), and there is a problem that PWM control becomes complicated.

Further, when the load connected to the three-phase inverter is unbalanced, the multi-pulse PWM control method can perform instantaneous value control of the three-phase current, but the three-pulse PWM control cannot be applied.

In the conventional 3-pulse PWM control, the three-phase batch PWM control is used, and the waveform compensation control as in (Patent Document 3) cannot support a large output control.

Therefore, the issue is how to realize 3-pulse PWM control that can significantly control the output waveform for each phase.

In the present invention, a square wave signal of the output frequency and a triangular wave having a frequency twice that is synchronized with the fundamental wave are used as carriers, and two signals of a signal compared with a reference input signal for controlling the magnitude of the fundamental wave component are input. By generating a PWM switching signal for one phase and generating a PWM switching signal having a phase difference of 120 degrees for each of the remaining two phases in the same configuration. Enables 3-pulse PWM control.

FIG. 1 shows a main circuit configuration of a three-phase voltage type inverter targeted by the present invention, and controls a method of performing 3-pulse PWM control for switching elements S1 to S3 on a phase-by-phase basis.

In the method of 3-pulse PWM control of the present invention, in order to control in each phase unit, three sets of carrier triangle waves are compared with three sets of reference inputs of each phase in which the output magnitude is controlled in each phase unit. And determine the switching timing.

The method of 3-pulse PWM control of the present invention is divided into two cases: a) when the size of the triangular wave comparison reference input x is 2/3 or more of the triangular wave amplitude, and b) when it is 2/3 or less of the triangular wave amplitude. ..

Hereinafter, in the description of the 3-pulse PWM control according to the present invention, the former will be referred to as a) A-Type and the latter will be referred to as b) B-Type.

FIG. 2 shows a) the principle of 3-pulse PWM control in A-Type. If each triangular wave for three-phase (a, b, c-phase) control is fa, fb, fc, then fb for triangular wave fa. Is a triangular wave with a delay phase difference of 120 degrees and is twice the fundamental frequency. Therefore, fb is advanced and fc is a delay position for the fundamental waves of each phase of a, b, and c. It becomes a triangular wave with a phase difference of 120 degrees.

Then, the reference input x to be compared with these triangular waves is set to be the same for all three phases as x = xa = xb = xc, and the timing chart when a) A-Type (x> xo) is shown.

By comparing the triangular wave signal fa, which has a frequency twice that of the output frequency of the inverter, with the reference input signal x, a pulse signal qa can be obtained, but this is exclusively the square wave signal ga that synchronizes with the output frequency. By taking the logical sum, the a-phase PWM switching signal pa is obtained.

Next, the b-phase PWM switching signal pb can be similarly generated as a 120-degree phase difference signal with respect to the a-phase PWM switching signal pa.

Further, the c-phase PWM switching signal pc can also be generated as a phase difference signal of 120 degrees with respect to the b-phase PWM switching signal pb in the same manner.

The output voltage waveform at this time becomes a waveform proportional to the difference between these switching signals, and assuming that the a-phase and b-phase signals are the switching signals of the three-phase voltage type inverter, as shown in the figure, positive and negative symmetric 3-pulse PWM. It becomes a control waveform.

The size of the three-pulse PWM waveform can be controlled by two zero-voltage period To in 120 ° conduction period T _D.

The zero voltage period To of the 3-pulse PWM waveform spreads when the reference input x increases, becomes a square wave with a width of 120 degrees when it becomes 1, narrows when x becomes small, and both the center and the center when x = xo (2/3). The pulse width on the side disappears and the voltage becomes zero.

Next, FIG. 3 shows b) the principle of 3-pulse PWM control in B-Type, and a) the same as in the case of A-Type, but the common reference input x compared with the triangular wave fa, fb, fc. B) The timing chart when B-Type (x <xo) is shown.

In the line voltage waveform euv of the 3-pulse PWM control obtained in this case, _{pulses are generated on both sides of the 120-degree section T D} of the three-phase square wave inverter waveform as shown in the figure, and 3 depends on the size of the reference input x. The magnitude of the pulse PWM waveform can be controlled.

b) In the case of B-Type, when the reference input x becomes smaller, the zero voltage period Tx of both side pulses of the 3-pulse PWM waveform becomes smaller, the central pulse width Ty becomes wider, and when it becomes 0, it becomes a square wave with a width of 120 degrees. As x becomes larger, the 3 pulse width becomes narrower, and when x becomes xo (= 2/3), the PWM control pulse width disappears and the output becomes zero voltage.

Here, looking at the line voltage waveforms controlled by a) A-Type and b) B-Type, the waveform of 3-pulse PWM control can be controlled by the reference input, and if the reference input x is made smaller than the case of 1, It can be seen that the output pulse does not appear when X = 2/3, but when it becomes smaller than that, the pulse width widens and becomes a square wave with a width of 120 degrees again.

Then, the sign of a) the waveform of the line output voltage euv in the A-Type control is inverted with respect to the waveform of the line output voltage euv in the B-Type control.

FIG. 4 is a control characteristic showing the rate of change of the line output voltage with respect to the maximum value of the fundamental wave component with respect to the reference input change in the 3-pulse PWM control according to the present invention.

Further, FIG. 5 shows the control characteristics including the sign change of the change rate of the magnitude of the fundamental wave component at a specific time point with respect to the reference input change, and the 3-pulse PWM control can be continuously performed from + 100% to -100%. Is shown.

FIG. 7 shows a switching state diagram of the voltage type inverter at the time of the three-phase PWM waveform in the switching sections of (1) and (2) of the three-pulse PWM control waveform shown in FIG.

The switching states of the three-phase voltage type inverter in the section (1) are S1: on, S2: off, S3: on, and S4, S5, and S6 are opposite to these, and in the section (2), S1: off, S2: Off, S3: On, and S4, S5, and S6 are the opposite.

FIG. 8 shows the switching signals of the six switching elements with respect to the line output voltage waveform of the three-phase voltage type inverter when outputting the three-pulse PWM control waveform.

In the 3-pulse PWM control of the present invention, since the comparison control of the triangular wave and the reference input for each phase is performed, the PWM control of each phase can be performed independently by the reference input, and the above-mentioned 3-pulse PWM control waveform when the reference input is the same. However, PWM control can be performed for each phase by changing the reference input.

So far, it has been described by applying it to a three-phase voltage type inverter, but there are a voltage type inverter and a current type inverter in the three-phase inverter, and the three-pulse PWM control of the present invention can be easily applied to the current type inverter. Can be done.

FIG. 9 shows an example of the main circuit configuration of the three-phase current type inverter, and the three-pulse PWM control method of the present invention can be applied to the six switching elements constituting the current type in the same manner as the voltage type. it can.

FIG. 10 is a three-pulse PWM control waveform generated by the present invention, and FIG. 11 shows the flow path of the three-phase current type inverter in the section (1) and the section (2).

In the current type inverter, it is necessary to secure a constant DC current path in any PWM control section, but it can be confirmed that the current path can be secured in all the PWM control sections.

FIG. 12 shows switching signals given to each of the six switching elements of the current inverter for the 3-pulse PWM control waveform of the present invention.

Unlike the conventional control method, the three-pulse PWM control of the present invention has a feature that each phase can be controlled independently by three sets of conveyed triangular waves and a reference input, and arbitrary three-phase load control is possible.

The 3-pulse PWM control of the present invention can generate two types of 3-pulse PWM control patterns, a) A-Type and b) B-Type, depending on the control range of the PWM control reference input.

In the 3-pulse PWM control of the present invention, the magnitude of the PWM control waveform can be continuously controlled by the comparison reference input for the conveyed triangular wave.

The 3-pulse PWM control of the present invention can be applied not only to a three-phase voltage type inverter but also to a three-phase current type inverter, and the three-pulse PWM control can be applied to a three-phase rectified power supply. A wide range of applications can be expected.

Three-phase voltage type inverter circuit A-Type 3-pulse PWM control method B-Type 3-pulse PWM control method Output control characteristics of 3-pulse PWM control for changes in reference input Positive / negative output control characteristics of 3-pulse PWM control for changes in reference input 3-pulse PWM pattern for three-phase voltage inverter Switch circuit state of voltage type inverter for the operating section of 3-pulse PWM pattern Switching signal of three-phase voltage type inverter for 3-pulse PWM pattern Three-phase current type inverter circuit 3-pulse PWM pattern for three-phase current inverter Switch circuit state of current type inverter for the operating section of 3-pulse PWM pattern Switching signal of three-phase current type inverter for 3-pulse PWM pattern Load current control system for 3-phase voltage inverter with 3-pulse PWM control Load voltage control system for 3-phase current type inverter with 3-pulse PWM control Resonant load current control system for 3-phase voltage inverter with 3-pulse PWM control 3-pulse PWM switching operation waveform in the A-Type region (x = 0.9) region 3-pulse PWM switching operation waveform in the boundary region (X = 2/3) 3-pulse PWM switching operation waveform in B-Type region (x = 0.3) Operating waveform of 3-pulse PWM-controlled three-phase voltage inverter at maximum output (X = 1.0) 3-pulse PWM control operation waveform in the A-Type region (x = 0.9) region 3-pulse PWM control operation waveform in B-Type region (x = 0.1) region Frequency spectrum of operating waveform in B-Type region (x = 0.1) region Operating waveform of current control system under the same current reference (Ir = 100A) Operating waveform of the current control system when the current reference is reduced by only one phase Operating waveform of the current control system when the load impedance is changed by only one phase

FIG. 13 controls a 3-pulse PWM waveform by detecting a three-phase current and generating a triangular wave comparison reference input x for each phase through a PI current regulator so that the magnitude matches the reference value of the three-phase current. The system configuration that controls the magnitude of the three-phase current is shown.

In the 3-pulse PWM control of the present invention, the magnitude of the output waveform can be controlled by controlling the pulse width by changing the reference input as described above.

In the current type inverter, since the load inductance is usually included, a capacitor is connected to the output end, and the magnitude of the voltage between the output terminals appearing at both ends of the capacitor filter is controlled by 3-pulse PWM control.

FIG. 14 shows a three-phase voltage control system by three-pulse PWM control, in which each phase is detected through a PI voltage regulator so that the three-phase load terminal voltage is detected and the magnitude matches the reference value of the three-phase voltage. The magnitude of the three-phase load voltage is controlled by generating the triangular wave comparison reference input x and controlling the three-pulse PWM waveform.

In the 3-pulse PWM control according to the present invention, the current pulse width control of the three-phase current type inverter can be easily applied to the three-phase rectifier circuit section.

As described above, the 3-pulse PWM control method according to the present invention is applied to various fields as a method capable of continuously controlling the magnitude of the PWM waveform in a power converter having a three-phase inverter configuration regardless of voltage type or current type. Can be expected.

Hereinafter, the PWM switching operation waveform and the output control operation waveform of the voltage type inverter will be used as examples for the resonance load current control system shown in FIG. 15 in which the 3-pulse PWM control method according to the present invention is applied to the three-phase voltage type inverter. Shown.

The operating conditions in the following simulation analysis are as follows: DC voltage Ed = 300V of the voltage type inverter, the fundamental wave frequency of the inverter is 1kHz, the frequency of the three sets of conveyed triangular waves is 2kHz, which is twice the fundamental wave frequency, and the resonance load circuit constant. R = 1 ohm, L = 200uH, C = 126uF.

The 3-pulse PWM control of the present invention controls the magnitude of the fundamental wave output by an output waveform control method that suppresses the generation of low-order harmonic components, and is easily three-phase sine by the filter effect of the resonance circuit. In order to confirm that the magnitude of the wave current can be controlled, the LCR resonance circuit shown in the example was used.

In order to confirm the PWM switching operation by the 3-pulse PWM control of the present invention, the A-Type region (x = 0.9), the boundary region (X = 2/3), and the B-Type region (X = 2/3) where the reference input x is large and the B-Type region (X = 0.9) are small. The switching operation waveforms at x = 0.3) are shown in FIGS. 16 to 18.

FIG. 16 showing the operation in the A-Type region (x = 0.9) corresponds to the principle waveform FIG. 2, and FIG. 18 showing the operation in the B-Type region (x = 0.3) corresponds to the principle waveform FIG. It can be seen that the PWM control system is able to generate a switching signal in principle.

FIG. 17 shows a switching operation waveform in the boundary region (X = 2/3), and it can be seen that the pulse width of the output voltage euv is almost eliminated and the output voltage can be controlled to zero.

The voltage euN in FIGS. 16 to 18 shows the phase voltage waveform with respect to the neutral point of the three-phase load, and euR shows the voltage waveform across the resistance load. It can be seen that the waveform is a sinusoidal current.

The output voltage / current waveform by PWM switching control by 3-pulse PWM control of the present invention is operated in the A-Type region (x = 0.9) operation and the B-Type region (x = 0.3) with respect to the square wave output operation. The waveforms are shown in FIGS. 19 to 20.

FIG. 19 shows a simulation result when the reference input is set to 1 as the operation waveform at the maximum output of the A-Type control region, and the same waveform is obtained when the reference input is set to 0.

FIG. 20 shows a line voltage waveform, a phase voltage waveform, and a load current waveform by PWM control in the A-Type region (x = 0.9).

FIG. 21 shows a line voltage waveform, a phase voltage waveform, and a load current waveform by PWM control in the A-Type region (x = 0.9).

FIG. 22 shows the frequency spectrum for each operation waveform during the PWM control operation, and it can be seen that the low-order harmonic component can be sufficiently removed by the 3-pulse PWM control.

The above simulation results show the results of setting the reference input independently to confirm the basic operation, and the load current amplitude can be controlled to match the reference value by giving the current reference value and operating the current control loop.

FIG. 23 is an operation waveform when the reference value Iur of the three-phase current is set to 100A in the output current control system using the three-phase voltage type inverter shown in FIG. 13, and each output current waveform is based on the current control reference. It can be confirmed that the waveform and size of the above can be controlled in the same way.

FIG. 24 shows an operation waveform when the reference value Iur of the three-phase current is set to 50 A and the current reference values Ivr and Iwr of the other phases are set to 100 A. It can be confirmed that it can be controlled.

FIG. 25 shows an operating waveform when the load impedance of only one phase of the three-phase load is increased by 20%, assuming that the reference value of the magnitude of the three-phase current is constant at 100 A, and an unbalanced load is connected. However, it can be confirmed that the three-phase equilibrium current can be controlled to a size that matches the reference value as long as it is within the controllable range.

100 ... Inverter DC power supply 200 ... Three-phase inverter 300 ... Three-phase load circuit 310 ... Three-phase load circuit filter circuit unit 320 ... Three-phase actual load circuit 400 ... PWM control system unit 410 ... Load current detection unit 420 ... Reference value Comparison with detected value Control controller unit 430 ... PWM control signal generator unit

Claims (6)

A square wave signal with a fundamental wave frequency of the output waveform of a three-phase voltage inverter, a triangular wave carrier signal with a frequency twice the fundamental wave frequency, and a reference input signal for controlling the magnitude of the fundamental wave of the output waveform. By taking two signals of the signal obtained by comparing and taking an exclusive logical sum, a PWM switching signal for one phase is generated, and the remaining two phases have the same configuration with respect to the fundamental wave. A three-pulse PWM control method for a three-phase inverter, characterized in that a PWM switching signal having a phase difference of 120 degrees is generated, and the magnitude of the voltage of each phase can be controlled by the magnitude of the reference input signal. In the three-pulse PWM control method according to claim 1, the magnitude of the fundamental wave output in the previous period is obtained by comparing the reference input signal between the magnitudes of 2/3 to 1 times the triangular wave amplitude and performing PWM control. A 3-pulse PWM control method for a three-phase inverter, which is characterized by being able to control from 0 to 100%. In the three-pulse PWM control method according to claim 1, the magnitude of the fundamental wave output in the previous period is increased by comparing the reference input signal between 0 and 2/3 times the amplitude of the triangular wave and performing PWM control. A 3-pulse PWM control method for a three-phase inverter, which is characterized by being able to control from 100% to 0%. In the three-pulse PWM control method according to claims 1 to 3, the reference input signal is obtained for each phase through the current control unit so that the magnitude of the load current matches the reference current, and the PWM switching signal is obtained. A three-pulse PWM control method for a three-phase inverter, characterized in that the magnitude of the load current of each phase of the three-phase voltage inverter is controlled. A PWM switching signal is generated by using the PWM control three-phase line output voltage waveform of the three-phase voltage type inverter generated by the three-pulse PWM control method according to claims 1 to 4 as the three-phase current waveform of the three-phase current type inverter. A 3-pulse PWM control method for a three-phase inverter. In the three-pulse PWM control method according to claim 5, a capacitor is connected to the output terminal, and the previous term reference input signal is obtained for each phase through the voltage control unit so that the magnitude of the terminal voltage matches the reference voltage. A 3-pulse PWM control method for a three-phase inverter, characterized in that the magnitude of the load terminal voltage of the three-phase current inverter is controlled by obtaining a switching signal.

Images