JP2000050640A - Method for generating sine wave pwm control signal of inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a required sine wave PWM control signal which matches the center time of each period of a carrier by setting the width of a sawtooth carrier at the half period of the carrier and a pulse signal having a width which is as broad as a specific multiple of its pulse width, by composing the pulse width by dividing the pulse width to the front and rear sides of the center time of each period of the carrier as the PWM control signal. SOLUTION: A sawtooth carrier signal Vc forms a sawtooth pulse train with a period set to T and a time width set to T/2. The pulse width of each pulse of the pulse train is set at 2to(n-1), 2ton, 2to(n+1) by performing such operation that a signal PWM.S is changed to a pulse having a width of 2ton by dividing the time ton which is obtained by subtracting the operating time lag for preventing the simultaneous conduction of the upper and lower arm switching elements of the main circuit bridge of an inverter from the time tn, until the single Vc becomes larger than a sine wave control signal Vs from a time nT to the front and rear sides of the center time nT+T/2 of periods nT to (n+1)T for each of time (n-1)T to nT to (n+1)T.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PW in an inverter.
The present invention relates to a method for 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 method as shown in the operation waveform diagrams of FIGS.

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

FIG. 6 shows a case where a triangular wave Vc2 having a constant peak value and a width equal to the period T is used as a carrier to be compared with the sine wave control signal Vs. Sine wave PWM control signal PWM · S
Is obtained in the same manner as in the case shown in FIG.

[0005]

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

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

When a triangular wave Vc2 as shown in FIG. 6 is used as a carrier wave, it is necessary to determine the intersection of the two signals Vs and Vc2 at two places in order to obtain the signal PWM.S, as shown in FIG. As in the case, the number of required calculations increases.

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

In view of the above, the present invention provides a sine-wave PWM for an inverter that solves the various problems during the operation of the induction motor without the above-mentioned problems in both software and hardware.
It is intended to provide a control signal generation 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 is provided, wherein the frequency is equal to the output frequency of the inverter and the amplitude is proportional to the output voltage of the inverter. A comparison is made between a sine wave control signal having a value and a sawtooth carrier wave having a constant peak value, and a pulse of an on / off control pulse for a switching element constituting a main circuit of the inverter is provided for each cycle of the carrier wave according to the comparison result. In the method of generating a sine wave PWM control signal of an inverter for determining a width, a width of the sawtooth carrier is set to の of a period of the carrier, and a pulse width obtained by comparing the sine wave control signal with the carrier is calculated. A pulse signal having a pulse width twice as large as the pulse width is divided and synthesized before and after the center point of each cycle of the carrier wave.
M control signal, and furthermore, a conjugate operation of cut-off and conduction of both switching elements provided to prevent a short circuit of the DC main power supply due to simultaneous conduction of the switching elements of both upper and lower arms of each phase of the inverter main circuit bridge configuration. It is assumed that the inter-time difference is smaller than the pulse width.

[0011]

When a sine wave PWM control signal for the inverter main circuit switching element is obtained by instantaneous value comparison between the sine wave control signal and the sawtooth carrier signal, the waveform width of the carrier is set to 1/2 of the period. By doing so, the center time of each cycle of the carrier wave is automatically determined, and a logical operation using a sine table or the like or an analog voltage comparison of the two signals is performed with respect to an instantaneous value comparison between the two signals, and the result of the comparison is performed. By dividing and synthesizing a pulse waveform having the obtained time width as the width before and after the center time of each corresponding carrier wave cycle, the pulse width is set to twice the time width obtained by the instantaneous value comparison. It is possible to obtain a required sine wave PWM control signal whose center coincides with the center time of each cycle of the carrier wave. At the time t defining the instantaneous value of the two signals, the angular velocity is represented by ω with respect to the sine wave control signal.
Then, the phase angle θ and θ = ωt are in a relationship, and the center time and the time width can be equivalently converted into a center phase point (or a center phase angle) and a phase width, respectively, according to the relationship.

According to the present invention, the required sine-wave PWM control signal is obtained in accordance with the above-described logical operation by the CPU, and the time nT of the sawtooth carrier signal whose period is T and whose time width is T / 2 is obtained. 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 as a starting point until the sawtooth carrier signal becomes larger than the sine wave control signal t
n and a time which is 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 and which is 1/2 of the pulse width of the required sine wave PWM control signal. Width ton and time nT
The time tun and tdn obtained by distributing the time ton before and after + T / 2 as the center time are obtained according to the following equation (1), and the respective operations are calculated from the time (n−3 / 2) T. T
This is repeated in the order of tn-ton-tun-tdn every / 2 period, and the logic output level between the time tun and tdn is set to H to form a 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 wave, θna
Is the average phase angle of the sine wave control signal between times nT and (n + 1) T.

[0014]

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

FIG. 1 is an operation waveform diagram showing a relative relationship among a sine wave PWM control signal PWM.S, a sine wave control signal Vs, and a sawtooth carrier signal Vc obtained according to the present invention. In FIG. 1, the signal Vc forms a saw-tooth wave pulse train whose cycle is T and its time width is T / 2.
The illustrated signal Vs has 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, as an example, a period nT to (n + 1) T corresponding to the n-th pulse of the signal Vc, and a time tn is a time nT
Indicates the elapsed time from when the signal Vc becomes greater than Vs, and the time ton is obtained by subtracting the operation time difference ΔT for preventing simultaneous conduction of the inverter main circuit bridge upper and lower arm switching elements from the time tn. , The signal PWM · S is the center 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.
Each pulse is turned on and such an operation is performed at each time... (n−1).
T-nT- (n + 1) T... To form a pulse train in which each pulse width is... 2.to (n-1) -2.ton-2.to (n + 1). is there.

FIG. 2 shows one of the signals Vc in FIG.
FIG. 3 is an enlarged view of the signal Vc and the signal Vs in a / 2 cycle, showing the principle of calculating the time tn. In this figure, the magnitude of the signal Vc and the signal Vs is made dimensionless using the amplitude Ec which is a half value of the peak value of the signal Vc as a reference value, and the two signals are respectively expressed by the following formula (2) ).

[0017]

(Equation 2) Es is the amplitude of the signal Vs. Further, the signal V
c / 2 cycle T / 2 and the signal Vs 1/2 cycle π /
ω has a relationship of T / 2≪π / ω, and therefore, the
The signal Vs at .about.T / 2 can be approximated as a constant value of .lambda.sin .theta.na using the average value .theta.na of the phase angle in the period.

Therefore, the time tn is defined by the following equation (3) as an elapsed time when Vc = Vs in a period 0 to T / 2 excluding the time T / 2.
The PU performs a logical operation sequentially on each number n.

[0019]

(Equation 3) Next, FIG. 3 and FIG. 4 are a time chart and a flow chart of an operation for generating the PWM control signal PWM · S based on the various quantities defined by the above equation (1), respectively. Is obtained by a logical operation using a CPU, and the various operations are ones of the sawtooth carrier signal (carrier signal) Vc.
The signal n is sequentially performed by an interrupt operation on software every / 2 cycle, that is, every T / 2.

As shown in FIG. 3, for example, time nT and (n +
1) Various calculations of the signal PWM · S corresponding to the n-th pulse waveform of the signal Vc during T are performed at time (n−3 / 2)
From T, the above-mentioned tn-ton-
The operation 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 tun and tdn.

In each interruption section after the time (n-1 / 2) T, various signals corresponding to the (n + 1) th pulse waveform of the signal PWM.S centering on the time (n + 3/2) T are used. The quantity operation proceeds in parallel in the order of t (n + 1) -to (n + 1) -tu (n + 1) -td (n + 1).

FIG. 4 shows a CP of various quantities corresponding to FIG.
7 shows the operation flow in U, wherein the operation 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, for example, (n ± １ ／) T, for example, For the number n, tn-tu
This is performed by dividing into two routes of n and ton-tdn.

[0023]

According to the present invention, there is provided a method for generating a sine wave PWM control signal of an inverter by comparing an instantaneous value between a sine wave control signal and a sawtooth carrier signal. The CPU repeatedly performs various operations relating to the generation of the sine wave PWM control signal as a half of the cycle of the carrier by an interrupt operation for each half cycle of the carrier signal, and performs a logical operation. Depending on whether the timing is at the center of the cycle of the carrier signal or at the end, various operations in the CPU are performed in two routes, so that the center between the required sine wave PWM control signal and each cycle of the carrier signal is obtained. The matching operation of the time point or the center phase angle is easily and reliably performed by one CPU without increasing the calculation time on software or increasing the size and cost on hardware. 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 the drawings]

FIG. 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 signal Vc and a sine wave control signal Vs in a half cycle of the sawtooth carrier signal Vc.

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

FIG. 4 is a flowchart showing a generation operation of a 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 example of a method according to the prior art;

FIG. 6 is an operation waveform diagram corresponding to FIG. 1 and showing a second method example according to the prior art;

[Explanation of symbols]

tn Time when Vc and Vs are Vc ≧ Vs ΔT Operation command time difference between switching elements ton 1/1/3 of the n-th waveform pulse time width of PWM · S
Binary tun Output H level command time for creating the nth waveform of the PWM · S tdn Output L level command time for creating the nth waveform of the PWM · S

Claims (2)

[Claims] A sine wave control signal having a frequency equal to the output frequency of an inverter and having an amplitude proportional to the output voltage of the inverter is compared with a sawtooth carrier having a constant peak value. In a method for generating a sine wave PWM control signal of an inverter for determining a pulse width of an on / off control pulse for a switching element constituting a main circuit of the inverter for each cycle of the carrier, the width of the sawtooth carrier is determined by changing the width of the carrier. A pulse signal having a width twice as long as the pulse width obtained by comparing the sine wave control signal with the carrier wave before and after the center of each cycle of the carrier wave. A method for generating a sine wave PWM control signal for an inverter, comprising: 2. The sine wave PWM of the inverter according to claim 1.
In the control signal generation method, the time difference between the conjugate operation of cut-off and conduction of both switching elements provided to prevent short-circuiting of a DC main power supply due to simultaneous conduction of the switching elements of both upper and lower arms of each phase of the inverter main circuit bridge configuration. A method for generating a sine wave PWM control signal for an inverter, wherein the control signal is reduced from a pulse width.