JP3397180B2 - Method of generating sine wave PWM control signal for inverter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a PW for an inverter.
The present invention relates to a method of generating an M control signal.

[0002]

2. Description of the Related Art As a conventional method of generating a sine wave PWM control signal of this kind, there is known a basic operation shown in operation waveform diagrams of FIGS.

FIG. 5 shows a case where a sawtooth wave having a constant crest value and a width equal to its cycle is used as a carrier wave to be compared with the sine wave control signal, and Vc1 in the figure. The sawtooth carrier shown has a signal sequence with a constant peak value, with its period being T. Further, Vs is the sine wave control signal, and the one shown in the figure is a schematic representation of the state between (n-1) T and (n + 2) T of the control signal and its vicinity. Further, the signal PWM · S is an inverter sine wave PWM control signal which forms a pulse train by forming each period of the carrier wave Vc1 with its time width being a period in which the control signal Vs is larger than the carrier wave Vc1.

Next, FIG. 6 shows a case where a triangular wave Vc2 having a constant crest value and a width equal to its cycle T is used as a carrier wave to be compared with the sine wave control signal Vs. Sine wave PWM control signal PWM ・ S
Can be obtained in the same manner as in the case shown in FIG.

[0005]

However, in the conventional sine wave PWM control signal generating method as described above, when the sawtooth carrier Vc1 as shown in FIG. 5 is used, the sine wave obtained as described above is used. Wave PWM control signal PWM
The center time point of each pulse of S, that is, the center phase point thereof does not coincide with the center time point of each corresponding period in the carrier wave Vc1, and therefore the center phase point is unevenly distributed on the left side.

Now, the signal PWM.S as described above is organized into three sets of control signals having a phase difference of 120 degrees, and the three-phase AC voltage is obtained by controlling the three-phase inverter with each of the control signals. Driving the three-phase induction motor causes an increase in vibration and noise of the motor and a decrease in efficiency. As a countermeasure against this, the center of each pulse width of the signal PWM · S and the center of each cycle of the carrier wave Vc1 If you perform a correction operation to match with, the time width (or phase width) of each pulse of the detected signal PWM / S
Of the pulse time width (or phase width) before and after the calculation time (or phase point), and the center time (or center phase point) of each cycle of the carrier wave Vc1. This leads to an increase in required calculation such as distribution of / 2 values.

When the triangular wave Vc2 as shown in FIG. 6 is used as a carrier wave, it is necessary to find the intersections of the signals Vs and Vc2 at two points in order to find the signal PWM.S. As in the case, the required calculation is increased.

Therefore, in any case, the conventional method illustrated in FIGS. 5 and 6 causes an increase in calculation processing time in software and an increase in price in both software and hardware.

In view of the above, the present invention provides a sine wave PWM inverter that solves various problems during operation of the induction motor without the problems of both software and hardware.
The purpose of the present invention is to provide a control signal generating method.

[0010]

In order to achieve the above object, a method of generating a sine wave PWM control signal for an inverter according to the present invention has a frequency equal to the output frequency of the inverter and an amplitude proportional to the output voltage of the inverter. A sine wave control signal having a value and a sawtooth carrier having a constant crest value are compared, and a pulse of an on / off control pulse for a switching element forming the main circuit of the inverter is cycled according to the comparison result. In the method of generating a sine wave PWM control signal of an inverter for determining the width, the width of the sawtooth carrier wave is set to ½ of the carrier wave period, and the pulse width obtained by comparing the sine wave control signal and the carrier wave. PW is performed by distributing and synthesizing before and after the central time point of each cycle of the carrier wave and using a pulse signal having a width twice the pulse width.
M control signal, and further, to prevent a short circuit of the DC main power supply due to simultaneous conduction of the switching elements of the upper and lower arms of each phase of the inverter main circuit bridge configuration, a blocking-conducting conjugate operation of both switching elements. It is assumed that the inter-time difference is less than the pulse width.

[0011]

When the sine wave PWM control signal for the inverter main circuit switching element is obtained by comparing the instantaneous values between the sine wave control signal and the sawtooth carrier wave signal, the waveform width of the carrier wave is set to ½ of its cycle. By doing so, the center time of each cycle of the carrier wave is automatically determined, and further, a logical operation using a sine table or the like or analog voltage comparison of the two signals is performed for the instantaneous value comparison between the two signals, and the result of the comparison is performed. By synthesizing the pulse waveform having the obtained time width as the width before and after the center time of each cycle of the corresponding carrier wave, the pulse width is twice the time width obtained by the instantaneous value comparison. A required sine wave PWM control signal whose center coincides with the center time of each cycle of the carrier wave can be obtained. At the time t that defines the instantaneous value of both signals, the angular velocity is ω with reference to the sine wave control signal.
Then, there is a relationship between the phase angle θ and θ = ωt, and the central time and the time width can be equivalently converted into the central phase point (or the central phase angle) and the phase width in accordance with the relationship.

The present invention obtains the required sine wave PWM control signal in accordance with the above-mentioned logical operation by the CPU, and the time nT of the sawtooth carrier signal having a period of T and a time width of T / 2. In obtaining the sine-wave PWM control signal corresponding to the n-th waveform between time (n + 1) T, the elapsed time from the time nT to the point when the sawtooth carrier signal becomes larger than the sine-wave control signal. t
n and the time tn obtained by subtracting the operation time difference ΔT for preventing simultaneous conduction of the switching elements of the upper and lower arms of the inverter bridge from the time tn, which is 1/2 the pulse width of the required sine wave PWM control signal. Width ton and time nT
Times tun and tdn, which are obtained by dividing the time ton before and after + T / 2 as the central time, are obtained according to the following equation (1), and the respective calculations are performed from the time (n-3 / 2) T. T
The operation is repeatedly performed in the order of tn-ton-tun-tdn every / 2 period, and the logical output level between the times tun and tdn is set to H to form the required sine wave PWM control signal.

[0013]

[Equation 1] Here, λ = Es / Ec, Es is the amplitude of the sine wave control signal, Ec is a half value of the peak value of the sawtooth carrier, and θna
Is the average phase angle between the times nT and (n + 1) T of the sine wave control signal.

[0014]

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

First, FIG. 1 is an operation waveform diagram showing the relative relationship among the sine wave PWM control signal PWM.S, the sine wave control signal Vs and the sawtooth carrier signal Vc obtained according to the present invention. In FIG. 1, the signal Vc forms a sawtooth wave pulse train having a period of T and a time width of T / 2.
The illustrated signal Vs is a period (n-1) T from the (n-1) th pulse to the (n + 1) th pulse of the signal Vc.
It is a partial display of the sine wave control signal in the vicinity of (n + 1) T. Further, taking the period nT to (n + 1) T corresponding to the nth pulse of the signal Vc as an example, the time tn is the time nT.
From the starting point to the time when the signal Vc becomes larger than Vs, and the time ton is obtained by subtracting the operation time difference ΔT for preventing simultaneous conduction of the upper and lower arm switching elements of the inverter main circuit bridge from the time tn. , The signal PWM · S is the central time nT of the period nT to (n + 1) T.
The time ton is distributed before and after + T / 2, and the width is 2 · t
There is no on pulse and such operation is performed at each time ... (n-1)
T-nT- (n + 1) T ···································· is there.

Next, FIG. 2 shows one of the signals Vc in FIG.
It is an enlarged view of the signal Vc and the signal Vs in a / 2 cycle, and shows the principle of calculation of the time tn. In this figure, the magnitude of the signal Vc and the signal Vs is made dimensionless with the amplitude Ec, which is a half value of the crest value of the signal Vc, as a reference value, and both signals are expressed by the following equation (2). ).

[0017]

[Equation 2] Es is the amplitude of the signal Vs. Further, the signal V
½ cycle T / 2 of c and ½ cycle π / of the signal Vs
ω has a relationship of T / 2 << π / ω, and therefore, in the illustrated period 0
The signal Vs in T / 2 can be approximated as a constant value of λ · sin θna by using the average value θna of the phase angle in the period.

Therefore, the time tn is defined as the elapsed time at which Vc = Vs in the period 0 to T / 2 excluding the time T / 2 by the following equation (3), and C is calculated using a sine table.
The PU sequentially performs a logical operation on each number n.

[0019]

[Equation 3] Next, FIGS. 3 and 4 are a time chart and a flow chart of the creation operation of the PWM control signal PWM.S according to the quantities defined by the equation (1), and the quantities of the equation (1). Is obtained by logical operation using a CPU, and the various operations are 1 of the sawtooth carrier signal (carrier signal) Vc.
/ 2 cycles, that is, the signal n is sequentially executed by an interrupt operation on the software every T / 2.

As shown in FIG. 3, for example, at times nT and (n +
1) Various calculations of the signal PWM · S corresponding to the pulse waveform of the n-th signal Vc between T are performed at time (n-3 / 2)
From T, the above-mentioned tn-ton-
The process is performed in the order of tun-tdn, and the n-th pulse waveform of the signal PWM.S is completed by setting the logical output level of the CPU to the H level between the tun and tdn.

In each interrupt section after the time (n-1 / 2) T, various values corresponding to the (n + 1) th pulse waveform of the signal PWM.S centering around the time (n + 3/2) T. The quantity calculation proceeds in parallel in the order of t (n + 1) -to (n + 1) -tu (n + 1) -td (n + 1).

Further, FIG. 4 is a CP of various quantity calculation corresponding to FIG.
Fig. 7 shows a calculation flow in U, wherein the calculation is performed according to whether the interrupt timing is the center position of the cycle of the carrier signal Vc, for example, nT, or the end portion, for example, (n ± 1/2) T. For number n, tn-tu
It is divided into two routes, n and ton-tdn.

[0023]

According to the present invention, a method of generating a sine wave PWM control signal for an inverter by comparing the instantaneous value of a sine wave control signal and a sawtooth carrier signal is provided. As the half cycle of the carrier wave, various calculations relating to the creation of the sine wave PWM control signal are sequentially repeated by the CPU by the interrupt operation for each half cycle of the carrier wave signal, and the logical operation is performed. The center of the required sine wave PWM control signal and each cycle of the carrier wave signal is obtained by performing various operations in the CPU in two routes according to whether the timing is at the center time of the cycle of the carrier wave signal or at the end thereof. The operation of matching the time point or the center phase angle can be easily and surely performed by one CPU without increasing the calculation time in software, increasing the size of hardware and increasing the price. Bets can be, further, to avoid reduction of increase or efficiency of vibration and noise in the induction motor as a load of the inverter to be sinusoidal wave PWM control by sawtooth carrier wave.

[Brief description of drawings]

1 shows a sinusoidal PWM control signal obtained according to the invention.
Operation waveform diagram of PWM · S, sine wave control signal Vs, and sawtooth carrier signal Vc

FIG. 2 is an enlarged view of a sine wave control signal Vs and a signal Vc in a half cycle of a sawtooth carrier signal Vc.

FIG. 3 is a time chart for creating a sine wave PWM control signal PWM · S corresponding to FIG. 1.

FIG. 4 is a flowchart of the operation of creating the sine wave PWM control signal PWM · S corresponding to FIG. 1.

FIG. 5 is an operation waveform diagram corresponding to FIG. 1 and showing a first method example according to a conventional technique.

FIG. 6 is an operation waveform diagram corresponding to FIG. 1 and showing a second method example according to the conventional technique.

[Explanation of symbols]

tn Time at which Vc and Vs are Vc ≧ Vs ΔT Inter-switching operation command time difference ton 1 / n of the n-th waveform pulse time width of the PWM · S
Binary ton Output H level command time for creating nth waveform of PWM / S tdn Output L level command time for creating nth waveform of PWM / S

Claims (2)

(57) [Claims] 1. A sine wave control signal having a frequency equal to the output frequency of an inverter and an amplitude having a value proportional to the output voltage of the inverter is compared with a sawtooth carrier having a constant peak value. In the method of generating a sine-wave PWM control signal of an inverter for determining the pulse width of an on / off control pulse for a switching element that constitutes a main circuit of the inverter for each cycle of a carrier wave, the width of the sawtooth carrier wave is set to A pulse signal having a width that is twice the pulse width, which is 1/2 of the cycle, and the pulse width obtained by comparing the sine wave control signal with the carrier is distributed before and after the center point of each cycle of the carrier. A PWM control signal generating method for an inverter, comprising: 2. The sine wave PWM of the inverter according to claim 1.
In the control signal generating method, the time difference between the conjugate operation of interruption and conduction of both switching elements provided for preventing the short circuit of the DC main power supply due to simultaneous conduction of the switching elements of the upper and lower arms of each phase of the inverter main circuit bridge configuration is described above. A method of generating a sine wave PWM control signal for an inverter, characterized by reducing the pulse width.