JPH02151270A - Pwm-pam control switching method for voltage type inverter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] This invention relates to sine wave PWM control and PWM control in a voltage source inverter device having a chopper circuit that controls a DC intermediate voltage.
This invention relates to a mutual switching method with AM control.

[Conventional technology]

As a conventional control system switching method of this type, various command data for the inverter circuit and chopper circuit are
It is known that two types are prepared, one for WM control and one for PAM control, and the command data for both are selectively switched by a multiplexer that operates according to a control method switching command.

[Problem to be solved by the invention]

However, in the conventional method as described above, the PWM control command and the PAM control command are instantaneously switched by the multiplexer, and the inverter circuit output voltage according to both commands also instantaneously shifts to the new command state value, and accordingly Therefore, the rate of change over time of the inverter circuit output current may become extremely large. Furthermore, in an inverter circuit, the rate of change from the DC intermediate voltage that is the input voltage to the output AC voltage is different between PWM control and PAM control. In order to avoid fluctuations in the voltage, it is necessary to instantaneously switch the DC intermediate voltage, that is, the output voltage of the chopper circuit, to an appropriate value. However, the chopper circuit has a control delay due to its main circuit time constant and the time characteristics of the voltage control system, and its output voltage cannot be controlled to change instantaneously, and its instantaneous fluctuation is unavoidable.

Therefore, when the motor is driven by the inverter circuit, the normal inverter may not function properly due to the occurrence of an overcurrent condition in the inverter circuit or the transmission of excessive shift to the driving load due to the torque fluctuation of the motor. It may become impossible to continue driving.

In view of the above, the present invention provides a voltage source inverter device in which a variable output voltage chopper circuit is a DC intermediate voltage circuit.
The object of the present invention is to provide a smooth switching method that suppresses fluctuations in the output voltage and output current of the inverter device caused by switching between WM and PAM control systems.

[Means to solve the problem]

In order to achieve the above object, the voltage source inverter device of the present invention pwM-pAMilJ? The II mutual switching method includes a DC chopper circuit with a variable output voltage and an inverter circuit that receives the output voltage as input, and generates a sine wave PWM*l? i1.
! : In a voltage source inverter device that uses PAM control in combination, a modulation coefficient that is the ratio of the amplitude of a sine wave control signal with a value proportional to the required output voltage of the inverter device to the amplitude of a triangular wave carrier signal is continuously set. A modulation coefficient generation circuit that changes and outputs the modulation coefficient, and a reciprocal calculation circuit that multiplies the reciprocal of the modulation coefficient by an appropriate constant are provided. PWM control that continuously and widely changes the conduction angle of the switching element in response to changes in the sine wave signal by changing the modulation coefficient according to an appropriate time gradient, and operates at a predetermined combination of conduction angles. A PAM controller state in which the conduction angle is the maximum continuous conduction state for each positive and negative section of the sine wave signal, mutual switching by continuous transition between both control states, and reciprocal calculation of the modulation coefficient. The command signal for the chopper circuit is modulated by the output signal of the circuit to change the conduction rate of the switching element of the chopper circuit and control the output voltage thereof.

[Effect]

-a, sine wave PWM control in an inverter consists of a sine wave control signal that has a frequency equal to the required output frequency of the inverter and whose midpoint value is proportional to the midpoint value of the required output voltage, and a constant peak value that is used as a carrier. and a triangular wave signal, and use a pulse train having various angles emitted during a period in which the sine wave signal is larger than the triangular wave signal as a conduction command signal to the main circuit switching element of the inverter. The amplitude of the output AC voltage is adjusted by changing the amplitude of the sine wave control signal while keeping the amplitude of the triangular wave signal constant, thereby changing the conduction period of the switching element. This is what we do.

PAM control in the inverter involves alternately and repeatedly applying continuous conduction command signals of a maximum angle of 180 degrees to the switching elements for each positive and negative half-wave section of the sine wave control signal, and controlling the DC input voltage of the inverter. This is used to adjust the amplitude of the output AC voltage.

Therefore, the PAM control is performed in a state in which the sine wave control signal in the pwMi 41B is made larger than all waves of the carrier triangular wave signal in its positive and negative half wave sections, that is, the sine wave control for the amplitude of the triangular wave signal. This corresponds to a state where the modulation coefficient, which is the ratio of signal amplitudes, is controlled to be extremely large.

In other words, the PAM control is based on the pwMIJ! using the modulation coefficient as a parameter. It can be obtained as a form of II. Continuous and wide-ranging changes of the modulation coefficients with appropriate time gradients therefore enable a continuous and smooth transition between the PWM and PAM controls.

In addition, the voltage conversion rate between the human-powered DC voltage of the inverter and the absolute value of its output AC voltage half-wave is PWM by intermittent wave synthesis.
It is larger during PAM control using continuous wave extraction than during control. Therefore, in order to avoid fluctuations in the output AC voltage at the time of re-control mutual switching, interlock control is required to reduce the input DC voltage of the inverter corresponding to the PAM control according to an appropriate value corresponding to the voltage conversion rate. Become.

In accordance with the above, the present invention provides a modulation coefficient generation circuit capable of continuously and widely changing and outputting the modulation coefficient, controls conduction of an inverter circuit, and multiplies the reciprocal of the modulation coefficient by an appropriate coefficient. A reciprocal calculation circuit is provided to perform output voltage reduction control of a chopper circuit that supplies the input DC voltage of the inverter, and to achieve smooth mutual transition switching between the PWM and PAM controls.Furthermore, in the PWM control, , by fixing the conduction angle distribution of the switching element by setting the modulation coefficient to an appropriate fixed value, and further adjusting the amplitude of the output AC voltage by controlling the output DC voltage of the chopper circuit, the content in the required output AC voltage is This makes it possible to optimize the harmonic component distribution.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block circuit diagram of an inverter system showing an embodiment of the present invention, and FIGS. 2 and 3 are signal waveform diagrams of the first response section, respectively.

Regarding the main circuit in FIG. 1, 9 is an AC power supply, 10 is a converter circuit consisting of a rectifier and a smoothing capacitor, 11
12 is an inverter circuit consisting of a switching transistor, a commutating diode, a smoothing diode, a capacitor, etc. and outputs a variable DC voltage; 13 is a motor.

Next, regarding the control circuit in FIG. 1, 1 is a reference sine wave control signal S. 3 is a sine wave generator that outputs the signal S
,. Modulation coefficient signal S, for. 4 is a modulation coefficient generator that outputs both signals S. and S.

2 is a carrier generator that outputs a carrier triangular wave signal SL, and 5 receives both signals SSR and SL and compares their magnitude. It is a comparator and the signal S2.
, is larger than St, and this signal S serves as a conduction command for each switching transistor of the inverter circuit 12.

6 is the signal S. The signal S obtained by multiplying the reciprocal of by an appropriate coefficient
7 is a chopper command generator that outputs a reference voltage command signal Sco for the chopper circuit 11; 8 is a voltage command signal S which is modulated by multiplying both the signals S and Sco; The signal S cr becomes a command signal for the required output DC voltage of the chopper circuit 11 corresponding to both the PWM and PAM control states.

Next, in the signal waveform diagram of FIG. 2, diagram (a) shows two types of sine wave control signals S srl and S t modulated by the carrier triangular wave signal S1 and the modulation coefficient signal S1°.
The relative relationship with rz is expressed with respect to the phase angle θ, and Figure (b) shows the pulse train signal S (l) having the conduction pulse width of the angular period in which the signal S1□ is larger than SL. Similarly, Figure (C) shows the pulse train signal S1 when the signal S1□ is larger than 31. Both the signals Sit and StZ are PWM signals for the switching transistor of the inverter circuit 12. This is a conduction command signal, and its conduction angle changes according to the change in the modulation coefficient as shown in the figure.

Next, the signal waveform diagram in FIG.
CO+Sll. + 5llrl scr each shows a change pattern with respect to the inverter output frequency f. Now, as shown in Figure (A), it is assumed that the voltage command signal Sco is increased linearly with respect to the frequency f, and furthermore, in the PWM control region shown, the modulation coefficient signal S. If S is a constant value, then the signal S,. The reciprocal corresponding signal S sr becomes fixed as shown in Figure (C), and therefore the voltage command signal S cr obtained by modulating the signal S C6 by the signal S1 also increases linearly as shown in Figure (D). Therefore, in the PWM control region, the output voltage of the inverter is given as a composite value of voltage pieces having a constant conduction angle distribution regardless of the voltage amplitude, based on the conduction angle designation shown in the second answer diagram, and its content harmonic The wave distribution is constant, and the amplitude of the output voltage changes proportionally to the frequency f according to the characteristics shown in FIG. 3(d).

In addition, in the transition region between the PWM and PAM control regions in FIG. 3, the signal S and Scr are respectively set as shown in FIG. As shown in Figure (d), the input DC voltage of the inverter is reduced. Therefore said signal S,. When P becomes sufficiently large, the control of the inverter 12 becomes
Transitioning from WM'MJ'4B to PAM control, the amplitude of the output voltage of the inverter changes according to the characteristics shown in Figure (d),
Furthermore, by appropriate selection of the characteristics of the signals S, it is possible to avoid fluctuations in the inverter output voltage in the transition region.

C Effects of the Invention] According to the present invention, in an inverter device that switches between sine wave PWMII control and PAM control, the modulation coefficient, which is the ratio of the amplitude of the sine wave control signal to the amplitude of the carrier triangular wave signal, is set appropriately. Smooth mutual transition switching between the PWM and PAM control is possible by changing the inverter input DC voltage continuously and widely according to the time gradient and by controlling the inverter input DC voltage to reduce according to an appropriate value corresponding to the reciprocal of the modulation coefficient. Therefore, if the motor is driven by the inverter, it is possible to prevent torque pulsation or circuit overcurrent caused by switching the control method.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of an inverter system showing an embodiment of the present invention, and FIGS. 2 and 3 are signal waveform diagrams of the first response section, respectively. 1... Sine wave generator, 2... Carrier generator, 3...
... Modulation coefficient generator, 4... Multiplier, 5... Comparator, 6... Divider, 7... Chopper command generator, 8...
... Multiplier, 9 ... AC power supply, 10 ... Converter circuit, 11 ... Chopper circuit, 12 ... Inverter circuit, 13 ... Motor Figure 1

Claims (1)

[Claims] 1) In a voltage source inverter device that has a DC chopper circuit with a variable output voltage and an inverter circuit that receives the output voltage as input, and uses both sine wave PWM control and PAM control, a modulation coefficient generation circuit that continuously changes and outputs a modulation coefficient that is the ratio of the amplitude of a sine wave control signal having a value to the amplitude of a triangular wave carrier signal; and a reciprocal calculation circuit that multiplies the reciprocal of the modulation coefficient by an appropriate constant. and changing the conduction angle of each switching element of the inverter circuit according to an appropriate time gradient of the modulation coefficient, which is specified by the magnitude comparison result of the sine wave signal and the triangular wave signal. A PWM control state in which the conduction angle is changed continuously and widely in response to the change, and the conduction angle is operated at a predetermined combination of conduction angles, and the conduction angle becomes the maximum continuous conduction state for each positive and negative section of the sine wave signal. P
The AM control state and the AM control state are mutually switched by continuous transition between both control states, and the command signal for the chopper circuit is modulated by the output signal of the reciprocal calculation circuit of the modulation coefficient to conduct the switching elements of the chopper circuit. 1. A PWM-PAM control switching method for a voltage source inverter device, characterized in that the output voltage is controlled by changing the ratio.